gene ther dsouza ggm and weissig v approaches to mitochondrial gene therapy curr gene ther manfredi g, fu j, ojaimi j, sadlock je, kwong jq, guy j and schon ea rescue of a deficiency in atp synthesis by transfer of mtatp, a mitochondrial dnaencoded gene, to the nucleus nat genet jacobs ht structural similarities between a mitochondrially encoded polypeptide and a family of prokaryotic respiratory toxins involved in plasmid maintenance suggest a novel mechanism for the evolutionary maintenance of mitochondrial dna mol evol allen jf the function of genomes in bioenergetic organelles philos trans r soc lond � biol sci weissig v and torchilin vp mitochondriotropic cationic vesicles a strategy towards mitochondrial gene therapy curr pharm biotechnol weissig v and torchilin vp towards mitochondrial gene therapy dqasomes as a strategy j drug targ weissig v, lizano � and torchilin vp selective dna release from g postmessage propecia smiley reply dqasome dna complexes at mitochondrialike membranes drug del dsouza gg, rammohan r, cheng sm, torchilin vp and weissig v dqasome mediated delivery of plasmid dna toward mitochondria in living cells j control rel lasch j, meye a, taubert h, koelsch r, mansaard j and weissig v dequalinium vesicles form stable complexes with plasmid dna which are protected from dnase attack biol chem weissig v, dsouza gg and torchilin vp dqasomedna complexes release dna upon contact with isolated mouse liver mitochondria j control rel weissig v, seibel p, seibel m and torchilin v p binding and release of dna peptide conjugates by cationic mitochondriotropic vesicles dqasomes proc intl symp control rel bioact mater dsouza gg, boddaparti s and weissig v proc intl symp control rel bioact mater xu y and szoka fc, jr mechanism of dna release from cationic liposomedna complexes used in cell transfection biochemistry weiss g postmessage propecia smiley reply mj, wong jr, ha cs, bleday r, salem rr, steele gd, jr and chen lb dequalinium, a topical antimicrobial agent, displays anticarcinoma activity based on selective mitochondrial accumulation proc natl acad sci usa dsouza gg, boddapati s, lightowlers rn and weissig v mitochondriotropic vesicles deliver mitochondrial leader peptide conjugates of circular and linear double stranded dna into mammalian mitochondria proc intl symp control rel bioact mater wheeler vc, prodromou c, pearl lh, williamson r and coutelle � synthesis of a modified gene encoding human ornithine transcarbamylase for expression in mammalian mitochondrial and universal translation systems a novel approach towards correction of a genetic defect gene wheeler vc, aitken m and coutelle � modification of the mouse mitochondrial genome by insertion of an exogenous gene gene bigger bw, tolmachov o, collombet jm, fragkos m, palaszewski i and coutelle � an araccontrolled bacterial ere expression system to g postmessage propecia smiley reply produce dna minicircle vectors for nuclear and mitochondrial gene therapy j biol chem ferreira cg, epping m, kruyt ae and giaccone g apoptosis target of cancer therapy clin cancer res reed jc dysregulation of apoptosis in cancer } clin oncol costantini p, jacotot e, decaudin d and kroemer g mitochondrion as a novel target of anticancer chemotherapy j nat cancer inst weissig v, cheng sm, pabba s, dsouza g, torchilin vp, schubert r and kimpfler a a novel strategy for mitochondriaspecific delivery of apoptosisinducing agents dqasomal incorporated paclitaxel proc intl symp control rel bioact mater cheng sm, pabba s, torchilin vp, fowle w, kimpfler a, schubert r and weissig v towards mitochondriaspecific delivery of apoptosisinducing agents dqasomal incorporated paclitaxel j drug del sci technol modicanapolitano js and aprille jr basis for the selective cytotoxicity of rho damine cancer res modicanapolitano js and aprille jr delocalized lipophilic g postmessage propecia smiley reply cations selectively target the mitochondria of carcinoma cells adv drug del rev modicanapolitano js, koya k, weisberg e, brunelli ��, li y and chen lb selective damage to carcinoma mitochondria by the rhodacyanine mkt cancer res manetta a, emma d, gamboa g, liao s, berman m and disaia p failure to enhance the in vivo killing of human ovarian carcinoma by sequential treatment with dequalinium chloride and tumor necrosis factor gynecol oncol christman je, miller ds, coward p, smith lh and teng nn study of the selective cytotoxic properties of cationic, lipophilic mitochondrialspecific compounds in gynecologic malignancies gynecol oncol eisenhauer ea and vermorken jb the taxoids comparative clinical pharmacology and therapeutic potential drugs seligson al, terry rc, bressi jc, douglass jg, rd and sovak m a new prodrug of paclitaxel synthesis of protaxel anticancer drugs andre n, carre m, brasseur g, pourroy b, kovacic h, briand g postmessage propecia smiley reply � and braguer d paclitaxel targets mitochondria upstream of caspase activation in intact human neuroblastoma cells febs lett fulda s, susin sa, kroemer g and debatin km molecular ordering of apoptosis induced by anticancer drugs in neuroblastoma cells cancer res waterhouse nj, ricci je and green dr and all of a sudden its over mitochondrial outermembrane permeabilization in apoptosis biochimie discher ed and eisenberg a polymer vesicles science this page is intentionally left blank liposomal drug carriers in cancer therapy alberto a gabizon introduction in the last two decades, we have witnessed the development of implantable and injectable drug delivery systems for applications in the treatment of cancer and other diseases these systems have arisen from various needs to provide depot forms of drug administration and more convenient dosing schedules examples are implantable biodegradable wellbutrin medication 2008 jelsoft enterprises ltd rods for slow release of peptides such as lhrh partial agonists g postmessage propecia smiley reply eg goserelin depot, for blockade of gonadal production of androgens or estrogens this is a simple and pharmacologically effective approach developed for an implantable drug delivery system to provide for convenient vehicles of administration for poorly soluble drugs these systems may or may not confer an advantage to the therapeutic index of the drug, but their basic raison detre is to provide a vehicle of injection an example is paclitaxel entrapped in polymerized albumin nanoparticles for iv administration of paclitaxel in cremophorfree form these should be distinguished from simple excipients used as solubilizers eg cremophor in the case of paclitaxel, because, in the former, the drug and vehicle are physically in one single complex at least during the initial phase in circulation to improve the efficacy and reduce the side effects of new and old anticancer drugs examples include formulations of anthracyclines encapsulated in liposomes eg g postmessage propecia smiley reply doxil, myocet, daunoxome or conjugated to polymers the objective here is to change the pharmacokinetics, biodistribution, and the bioavailability profile so as to achieve a positive impact on the drug pharmacodynamics this is the most refined approach to drug delivery and includes intravenous administration of a drug stably associated to a carrier, with or without specificity to a target cancer cell molecule in this review chapter, we will focus on injectable particulate drug delivery systems of anticancer drugs fig , particularly on liposomes, the most widely used drug nanocarrier in cancer the physicochemical properties of liposomes are discussed elsewhere in this book briefly, liposomes are vesicles with an aqueous interior surrounded by one or more concentric bilayers of phospholipids with a diameter ranging from a minimal diameter of nm to several microns however, for injectable clinical applications, practically all liposome formulations are in the submicron ultrafilterable range g postmessage propecia smiley reply nm size and can be considered as nano size particulate systems liposomes are formed spontaneously when amphiphilic lipids such as phospholipids are dispersed in water the ensuing structures are physically stable supramolecular assemblies, and unlike polymerized particles fig cancer therapy and drug delivery systems � schematic drawing illustrating various approaches to smart cancer drug delivery targeting of drugs conjugated to antibodies or ligands directed to tumor cellspecific surface receptors controlled release of drugs entrapped in microspheres or nanospheres by diffusion andor degradation of the particle matrix in extracellular fluid release of drugs entrapped in phospholipids vesicles liposomes by leakage andor endocytosis and liposome breakdown delivery of drugs conjugated to polymers by endocytosis and intracellular drug release these approaches may also be combined, for instance, in the case of liposomes targeted with ligands or antibodies to tumor cells [note relative scales are disproportionate polymer microsphere �� g postmessage propecia smiley reply liposome they are not covalently bound although liposome formation is actually a spontaneous process, the current trend is to classify them into a class of pharmaceutical devices in the nanoscale range engineered by physical andor chemical means, and referred to as nanomedicines nanomedicines are a direct result of the application of nanotechnology to medicine, and encompass in their wide context, molecular and supramolecular devices such as liposomes and other nanoparticulate carriers in fact, liposomes are the first generation of nanosize drug delivery devices approved for the treatment of cancer ie doxil containing doxorubicin and fungal infections ie ambisome containing amphotericin b current liposome formulations represent a basic form of nanomedicine involving a slow drug release system, and often a passive targeting process known as enhanced permeability and retention epr that will be discussed later in this chapter the field of nanomedicines is rapidly evolving and aims g postmessage propecia smiley reply at increased sophistication of nanosize devices interacting with cellular targets at the nanoscale level the challenge of cancer therapy our understanding of the molecular processes underlying the pathologic behavior of cancer cells has progressed enormously in the last decade of particular relevance to cancer targeting is the fact that a number of receptors, mostly growth factor receptors, have been found to be overexpressed in tumor cells, and to play an important role as catalysts of growth receptor profiling of tumors may offer a potential achilles heel for targeting specific ligands or antibodies, with or without delivery of a cytotoxic drug cargo in addition, the pathophysiology of tumor neovasculature and the interaction of tumor with stroma have been recognized as processes that play a major role in tumor development cancer is ultimately a disease caused by somatic gene mutations that result in the transformation of a normal g postmessage propecia smiley reply cell into a malignant tumor cell eventually, the tumor cell phenotype progresses along three major steps increased proliferation rate andor decreased apoptosis, causing an increase of tumor cell mass invasion of surrounding tissues and switch on of angiogenesis this is a critical step that differentiates in situ, noninvasive, tumors with no metastatic potential from invasive tumors with metastatic and lifethreatening potential although there is considerable variability, tumors with angiogenic potential become vascularized when the cell load reaches an order of cells, equivalent to a nodule of � mm diameter metastases, ie abnormal migration of tumor cells from the primary tumor site via blood vessels or lymphatics to distant organs, with formation of secondary tumors this is most commonly the process that causes death of the host due to disruption of the function of vital organs or systems ie brain, lung, liver, kidney, bone marrow, coagulation, g postmessage propecia smiley reply intestinal passage, and others despite formidable advances in clinical imaging, the diagnosis of a tumor massusually requires the presence of a nodule of mm diameter, representing a cluster of cells since the lethal tumor burden is in the order of cells in most cancer patients, this implies that tumors have already gone through of their doubling cell expansion process by the time of clinical diagnosis as a result, significant heterogeneity and phenotypic diversity are already present in most diagnosed cancers, posing a major therapeutic challenge due to the development of metastatic ability and drug resistance nowadays, drugbased therapy of cancer is applied in three possible settings primary treatment, which is also known as neoadjuvant or preoperative treatment in this setting, anti tumor drugs are given prior to potentially curative local therapeutic modalities such as surgery or radiotherapy these patients have a primary tumor, but no clinical g postmessage propecia smiley reply evidence of distant metastases concomitant treatments of chemotherapy, or hormonal therapy, with radiotherapy can also be included in this category the goal is to reduce tumor bulk, the risk of tumor seeding, and to facilitate surgery or radiotherapy of the primary tumor adjuvant treatment the aim is to eradicate clinically undetectable residual tumor cells, presumably left over after surgical removal of the primary tumor adjuvant treatment is generally applied in patients with a high risk of micrometastases to some extent, the adjuvant approach likens to a black box because all patients at high risk are treated without knowing for sure who are the patients harboring metastases and who are not also, we have no immediate way of knowing whether the treatment is effective or not only long followup periods will reveal if cancer will recur in a specific patient therefore, the proof of efficacy of adjuvant g postmessage propecia smiley reply treatment is exclusively statistical despite these limitations, it has been demonstrated statistically that adjuvant treatment can cure subclinical, micrometastatic disease in a fraction of patients with breast cancer, colon cancer, and other tumors, who would not be amenable to cure if the disease is to become macroscopic and clinically detectable prior to treatment the evaluation of adjuvant treatment effects is complicated by the poorly understood phenomenon of tumor dormancy in which tumor cells appear to remain as tiny, quiescent avascular clusters for long periods of time small, microscopic, tumor cell clusters may get their nutrients by diffusion from preexisting adjacent vessels of normal tissues therefore, adjuvant therapies specifically directed to tumor vasculature are unlikely to be effective against some micrometastases during the avascular phase treatment of metastatic disease or neoplastic conditions not amenable to surgical or radiotherapeutic eradication in these cases, chemotherapy is potentially curative g postmessage propecia smiley reply only in hematological and lymphoid neoplasms, and in a few cases of solid tumors such as testicular cancer and choriocarcinoma in most instances, including the most common types of cancer namely breast, prostate, lung, and colon, chemotherapy is palliative, ie temporary tumor regression and prolongation of survival can be achieved, but cure is exceptional and most tumors ultimately recur and are lethal let us now examine the currently available cancer drug armamentarium drug therapies of cancer can be divided into three major groups cytotoxic agents as the name implies, these agents are toxic to cells and lack tumor cell specificity they can be divided into three major groups agents that damage the dna template directly or indirectly agents that damage the microtubulebased spindle apparatus agents that inhibit dna synthesis antimetabolites upon structural damage or arrest of the cell cycle, tumor cells undergo apoptosis which is the g postmessage propecia smiley reply main form of cell death treatment with cytotoxic agents is usually referred to as cancer chemotherapy the use of cytotoxic agents remains the mainstay of cancer therapy it is this group of agents that urgently requires a delivery system to improve its tumor specificity, andor reduce its damage to normal tissues in addition to the lack of specificity of chemotherapeutic cytotoxic agents, a number of physiologic factors can seriously limit the efficiency of drug distribution from plasma to tumors and neutralize their effects these include competition for drug uptake of wellperfused tissues such as liver and kidneys, rapid glomerular filtration and urinary excretion of low molecular weight drugs, protein binding with drug inactivation eg cisplatin, and stability problems in biological fluids eg hydrolysis of nitrosoureas, opening of lactone ring of camptothecin analogs hormonal agents they are used mainly against breast and prostate cancers these tumors often g postmessage propecia smiley reply require estrogen or androgen receptor activation for growth stimulation the hormonal therapies currently in use are mostly based on synthetic compounds modeled to block the gonadal or peripheral production of estrogens and androgens ie lhrh partial agonists, aromatase inhibitors or to compete for the tumor cell receptors of these hormones ie antiestrogens, antiandrogens corticosteroids and somatostatin analogs can also be included in the category of hormonal agents noncytotoxic agents modifying biological response these can be classified in at least three distinct groups antibodies blocking growth factors, growth factor receptors and other cell membrane receptors of tumor cells or supporting stroma eg bevacizumab, trastuzumab, cetuximab, rituximab agents blocking signal transduction kinases eg gefitinib, imatinib cytokines with miscellaneous activities eg interferona, interleukin the rationale for the use of liposomal drug carriers in cancer the rationale for the use of liposomes in cancer drug delivery is based on g postmessage propecia smiley reply the following pharmacological principles, which are also applicable to nonliposomal nanoparticulate drug carriers slow drug release drug bioavailability depends on drug release from liposomes entrapment of drug in liposomes will slow down drug release and reduce renal clearance to a variable extent slow release may range from a mere blunting of the peak plasma levels of free drug, to a sustained release of drug mimicking continuous infusion these pharmacokinetic changes may have important pharmacodynamic consequences with regard to toxicity and efficacy of the liposome delivered agents site avoidance of specific tissues the biodistribution pattern of liposomes may lead to a relative reduction of drug concentration in tissues specifically sensitive to the delivered drug this may have implications with regard to the therapeutic window of various cytotoxic drugs, such as the cardiotoxic anthracyclines, provided that anti tumor efficacy is not negatively affected accumulation in tumors prolongation of g postmessage propecia smiley reply the circulation time of liposomes results in significant accumulation in tissues with increased vascular permeability this is often the case of tumors, especially in those areas with active neoangiogene sis tumor localization of longcirculating liposomes, such as pegylated liposomes, sometimes referred to as stealth or stericallystabilized, is a passive targeting effect that enables substantial accumulation of liposomeencapsulated drug in the interstitial fluid at the tumor site, a phenomenon sometimes referred to as enhanced permeability and retention epr effect fig there are a number of differential effects of physiologic factors on clearance and biodistribution of low molecular weight drugs and nanoparticles see also table protein binding low molecular weight drugs may be inactivated andor irreversibly bound by plasma proteins, thus reducing the bioavailability towards fig extravasation and release of liposomal drug cargo in tumor interstitial fluid compartment � schematic drawing illustrating the concept of passive targeting of g postmessage propecia smiley reply liposomes to tumors exploiting the epr effect the dots represent the drug molecules encapsulated in the liposome water phase the various steps implied in the targeting process are numerically designated from to liposomes with longcirculating properties are required to increase the number of passages through the tumor microvasculature increased vascular permeability in tumor tissue enables properly downsized liposomes to extra vasnte and reach the tumor interstitial fluid because of their limited diffusion capacity, liposomes remain in close vicinity to blood vessels drug is gradually released from liposomes accumulating in the interstitial fluid moving swiftly through the tumor cell layers and entering tumor cells the cytotoxic effect leading to tumor cell death is expected to follow the same mechanism known for free drug [note relative scales are disproportional] cellular target molecules cisplatin, a widely used anticancer cytotoxic drug, is one such example in the case of g postmessage propecia smiley reply nanoparticles, plasma proteins can adsorb to their surface a process known as opsonization that results in tagging the particle for recognition and removing it by macrophages in addition, protein binding to the liposome surface may destabilize the bilayer and accelerate the leakage of liposome contents peg coating pegylation of liposomes reduces opsonization and the effects associated with it reticuloendotheliai system res clearance it is unimportant for low molecular weight drugs, but plays a major role in the clearance of nanoparticles reducing the fraction available for distribution to tumor tissue kupffer cell macrophages lining the liver sinusoids remove opsonized liposomes and other nanoparticles from circulation, and represent a major factor in the clearance of particulate carriers table differential effects of physiologic factors on clearance and biodistribution of low molecular weight mw drugs and nanoparticles factor extravascular transport microvascular permeability fenestrations glomerular filtration protein binding res clearance low g postmessage propecia smiley reply mw drugs diffusion not filterable binding and unimportant important inactivation nanoparticles convection critical for non opsonization major tissue filterable and clearance targeting destabilization pathway glomerular filtration unless they become proteinbound, low molecular weight drugs can be filtered out by kidney glomeruli in contrast, liposomes and other nanoparticles are nonfilterable, because their diameter exceeds the glomerular filterable threshold size microvascular permeability enhanced microvascular permeability with fenestrations in capillaries and postcapillary venules is critical for the extravasation of nanoparticles from the blood stream to the interstitial fluid of the target tissues the presence of fenestrations is irrelevant for tissue delivery of small molecules extravascular transport diffusion is the predominant mechanism of transport for small molecules in contrast, convective transport plays a major role in the extravascular movement of nanoparticles, for which diffusion rates are very slow large tumors tend to develop high interstitial pressure that reduces the rate g postmessage propecia smiley reply of convective transport significantly in fact, in an animal model, it has been shown that liposomes accumulate significantly less in larger tumors on a per gram tissue basis in agreement with this, large tumor size predicts poor response to liposomedelivered chemotherapy in ovarian cancer table lists a number of tumor and liposome factors that play important roles in the delivery of liposomal drugs on the tumor side, a rich blood flow and a highly permeable microvascular table parameters affecting delivery of liposomal drugs to tumors tumor factors liposome factors blood flow long circulation time vascular permeability stability drug retention interstitial pressure small vesicle size phagocytic activity saturation of the res bed will increase the probability of liposome deposition, while a high interstitial fluid pressure is likely to reduce the movement of molecules and particles into the tumor compartment on the liposome side, avoiding drug leakage g postmessage propecia smiley reply and prolonging the circulation time will result in more liposomes reaching the tumor vascular bed with an intact drug payload, and a small vesicle size will facilitate extravasation through the endothelium gaps or fenestrations there are also data indicating that saturation of the res will prolong circulation time and indirectly enhance liposome deposition in tumors liposome formulation and pharmacokinetics � stealth liposomes in , gregoriadis et al, published the first research work in which liposomes were used as drug carriers for medical applications this initial study led to growing interest in liposomes, and many laboratories began examining liposome pharmacokinetics and biodistribution in animals, as well as in vitro stability in serum the early liposome work was mostly based on formulations composed of neutral egg lecithin pc, often in combination with negatively or positively charged lipids these liposomes were found to release rapidly a large fraction of their g postmessage propecia smiley reply encapsulated contents in circulation furthermore, they were quickly removed from the circulation by macrophages of the res reformulation with high phasetransition temperature tm lipids distearoylpc, dipalmitoylpc, sphingomyelin and addition of cholesterol led to improved retention of liposome contents and prolongation of circulation time, especially when the vesicles were properly downsized to nm diameter however, these relatively improved liposome formulations would still accumulate largely in the res and a greater improvement in circulation halflife appeared to be required for cancer targeting surface modifications of liposomes that could reduce the res affinity were investigated based on the erythyrocyte paradigm, whereby a layer of carbohydrate groups prolongs circulation for nearly months a number of glycolipids such as monosialoganglio side gm, phosphatidylinositol, and cerebroside sulfate, were included in the formulations and extended liposome circulation time however, a major advance took place when the hydrophilic polymer polyethyleneglycol peg, which was known g postmessage propecia smiley reply to reduce immunogenicity and prolong circulation time when attached to enzymes and growth factors, was introduced into liposomes in the early s peg, which is inexpensive due to easy synthesis and could be prepared in high purity and large quantities, had distinct advantages over the other gly colipid surface modifiers addition of a conjugate of peg with a lipid anchor, distearoylphosphatidylethanolamine pegdspe to the liposomal formulation was shown to prolong liposome circulation time significantly and formed a pivotal element of the pharmaceutical development of the doxil formulation described thereafter in this chapter due to their ability to avoid res clearance mechanisms, pegcoated liposomes have been coined stealth liposomes in parallel to the development of stable formulations with longer circulation half lives, it was soon realized that a prolonged residence time in circulation was a critical pharmacokinetic factor for liposome deposition in tumors and that there g postmessage propecia smiley reply was a strong correlation between liposome circulation time and tumor uptake a number of studies have addressed the mechanism of liposome accumulation in tumors microscopic observations with colloidal goldlabeled liposomes and morphologic studies with fluorescent liposomes in the skinfold chamber model have demonstrated that liposomes extravasate into the tumor extracellular fluid through gaps in tumor microvessels and are found predominantly in the perivascular area with minimal uptake by tumor cells studies with ascitic tumors demonstrate a steady extravasation process of long circulating liposomes into the ascitic fluid, with gradual release of drug followed by drug diffusion into the ascitic cellular compartment the process underlying the preferential tumor accumulation of liposomes, as well as other macromolecular and particulate carriers, is known as epr enhanced permeability and retention effect this is a passive and nonspecific process resulting from increased microvascular permeability and defective lymphatic drainage in tumors creating g postmessage propecia smiley reply an in situ depot of liposomes in the tumor interstitial fluid circulating liposomes cross the leaky tumor vasculature, moving from plasma into the interstitial fluid of tumor tissue, following convective transport and diffusion processes although convective transport of plasma fluid also occurs in normal tissues, the continuous, nonfenestrated endothelium and basement membrane prevents the extravasation of liposomes epr is a relatively slow process, in which longcirculating liposomes possess a distinct advantage because of the repeated passage through the tumor microvascular bed and their high concentration in plasma during an extended period of time for any intravascular drug carrier device to access the tumor cell compartment and interact with tumor cell receptors, it must first cross the vascular endothelium and diffuse into the interstitial fluid, since with few exceptions, tumor cells and their surface receptors are not directly exposed to the blood stream therefore, the epr effect g postmessage propecia smiley reply is not only important for the tumor accumulation of nontargeted liposomes, but it is also for that of ligandtargeted liposomes this has led us to postulate that the extravasation process is the ratelimiting step of liposome accumulation in tumors experimental data with targeted and nontargeted liposomes have so far lent consistent support to this hypothesis in most instances, delivery of drug to tumor cells depends on the release of drug from liposomes in the interstitial fluid, since liposomes are seldom taken up by tumor cells, unless they are tagged with specific ligands the factors controlling this process and its kinetics are not well understood and may vary among tissues, depending on the liposome formulation in question in the case of remote loaded formulations, eg anthracyclines, a gradual loss of the liposome gradient retaining the drug, in addition to the disruption of the integrity of the g postmessage propecia smiley reply liposome bilayer by phospholipases, may be involved in the release process uptake by tumorinfiltrating macrophages could also contribute to liposomal drug release in any case, once the drug is released from liposomes, it will diffuse freely through the interstitial tumor space and reach deep layers of tumor cells this is an inherent advantage of this delivery system as opposed to covalently bound drugcarrier systems it is also a critical factor for the success of the liposomal drug approach, since most of the liposomes appear to remain in interstitial spaces immediately surrounding the blood vessels, and therefore would not be able to interact with more than one layer of tumor cells the epr effect has been confirmed in a variety of implanted tumor models its validity regarding human tumors, and particularly, cancer metastases, is as yet unclear one concern is that interstitial fluid pressure increases in most g postmessage propecia smiley reply tumors once they grow beyond a certain size threshold, thereby hindering extravascular transport and liposome delivery unfortunately, there is a paucity of imaging studies in cancer patients with radiolabeled liposomes one of the few studies with radiolabeled pegylated liposomes demonstrated significant liposome accumulation based on tumor imaging findings in out of patients tested in another study, in which tumor metastases and normal muscle tissues of breast cancer patients were examined for doxorubicin concentration after injection of pegylated liposomal doxorubicin pld, liposomal drug was found at fold greater concentration in tumor, as compared with muscle another important piece of work in this area is the study of northfelt et al,i that pointed to an enhanced deposition of drug in kaposis sarcoma skin lesions of patients receiving pld, compared with the normal skin of the same patients and to doxorubicin concentration in kaposis sarcoma biopsies of patients g postmessage propecia smiley reply receiving free doxorubicin more imaging and drugcarrier biodistribution studies are needed to determine how important and frequent is the observation of human tumors with selectively enhanced uptake of liposomes these studies would also enable to determine whether there is a correlation between liposome accumulation in tumors and anti tumor response, and a need to select patients for liposomedelivered drug therapy based on positive liposome tumor imaging preclinical observations with liposomal drug carriers in tumor models the drug most frequently tested in liposomal formulations is doxorubicin and related anthracyclines the choice of doxorubicin by many of the early research groups examining the role of liposomes as drug carriers in cancer chemotherapy, stems from its broad spectrum of anti tumor activity on the one hand, and its disturbing cumulative doselimiting cardiac toxicity on the other hand anthracyclines such as doxorubicin and daunorubicin cause acute toxic side effects g postmessage propecia smiley reply including bone marrow depression, alopecia, and stomatitis, and are dose limited by a serious and mostly irreversible characteristic cardiomyopathy the first study describing the encapsulation of anthracyclines into liposomes appeared in work from various research groups followed, supporting the general principle that liposomal formulations reduced the toxicity of anthracyclines in animal models using the stealth technology and an elegant loading mechanism based on an ammonium sulfate gradient, a formulation of pegylated liposomal doxorubicin pld known as doxil in the usa caelyx in europe has been developed the loading mechanism, coined remote active loading, leads to highly efficient accumulation of doxorubicin inside the aqueous phase , doxorubicin moleculesvesicle, where the drug forms a crystallinelike precipitate, contributing to stable drug entrapment by remaining osmotically inert, this loading technology provides substantial stability with negligible drug leakage in circulation, while still enabling satisfactory rates of drug release in tissues and malignant g postmessage propecia smiley reply effusions studies in animal tumor models with doxorubicin encapsulated in pegylated and other longcirculating liposomes, established the following pharmacologic observations increased anti tumor activity of liposomal drug, as compared with optimal doses of free drug in various rodent models of syngeneic and human tumors increased accumulation of liposomal drug in various transplantable mouse and human tumors, compared with free drug delayed peak tumor concentration and slow tissue clearance after injection of liposomal drug the most valuable pharmacokinetic advantage of the stealth liposomal delivery system is the enhancement of tumor exposure to doxorubicin, as a result of the accumulation of stealth liposomes in tumors, as demonstrated in animal models and in some forms of human cancer when the tissue uptake of pld was examined in a couple of syngeneic mouse tumor models, it was found that the tumor drug uptake correlated linearly with dose, while the liver g postmessage propecia smiley reply drug uptake showed a saturation profile in the case of free doxorubicin, liver uptake increased linearly with dose, while tumor uptake increased marginally with dose as a result, the delta of tumor drug concentration in favor of pld was substantially greater at high doses these results suggest a passive process of liposomal uptake into tumor, with nonsaturable kinetics in preclinical therapeutic studies using a variety of rodent tumors and human xenografts in immunodeficient nude mice, pld was more effective than free doxorubicin and other nonpegylated formulations of liposomal doxorubicin in a few instances, the activity of pld preparations was matched but not surpassed by other nonpegylated, longcirculating preparations of liposomal doxorubicin in most of these studies, the improved efficacy of pld was obtained at milligram equivalent doses of the mtd of free doxorubicin, indicating that there was a net therapeutic gain per milligram drug, independent g postmessage propecia smiley reply of toxicity buffering an elegant study addressed this issue directly by examining the activity of escalating doses of pld and doxorubicin against implants of the mouse ll tumor lewis lung carcinoma, and concluded that the activity of mgkg doxil was approximately equivalent to mgkg doxorubicin, ie a fold enhancement in efficacy similar observations were made in the ml model, pointing to a fold advantage for pld, compared with free doxorubicin, ie a dose of mgkg pld was at least as effective as mgkg free doxorubicin there is a large body of preclinical data on other liposome formulations of anticancer agents moving into clinical development, or already approved for clinical use in many cases, it is likely that the added value of these formulations has not been or will not be sufficient to justify further development, despite positive preclinical data liposomal anthracyclines in the clinic the anthracycline g postmessage propecia smiley reply antibiotic doxorubicin has a broad spectrum of antineoplastic action and a correspondingly widespread degree of clinical use in addition to its role in the treatment of breast cancer, doxorubicin is indicated in the treatment of various cancers of the lymphatic and hematopoyetic systems, gastric carcinoma, smallcell cancer of the lung, soft tissue and bone sarcomas, as well as cancer of the uterus, ovary, bladder and thyroid unfortunately, toxicity often limits the therapeutic activity of doxorubicin and may preclude adequate dosing other common complications of conventional anthracycline therapy include alopecia and dose limiting myelosuppression most importantly, cardiotoxicity limits the cumulative dose of conventional anthracycline that can be given safely encapsulation of anthracyclines within liposomes significantly alters their pharmacokinetic profiles and promotes selectively high drug concentrations in tumors in animal studies, these pharmacologic effects resulted in maintained or enhanced anthracycline efficacy and safety in a variety of experimental g postmessage propecia smiley reply tumor types improved therapeutic index profiles in clinical trials of liposomal anthracycline therapy for kaposis sarcoma, ovarian cancer, breast cancer, or multiple myeloma have been reported liposomal anthracycline therapy should be preferred when conventional anthracycline therapy is likely to be effective, but the required course of treatment would lead to unacceptable risk of toxicity the relative lack of cardiotoxicity with liposomal anthracycline therapy is an important asset of the liposomal approach there are commercial formulations of liposomal anthracyclines that have been approved for clinical use doxil, myocet, and daunoxome tables and present a comparative list of their tolerated doses and pharmacokinetic parameters, respectively a summary of their main clinical highlights is presented below doxil as indicated before, doxil� known in europe as caelyx� is a doxorubicin formulation in which the drug is encapsulated in pegylated liposomes stealth table comparative single and cumulative tolerated doses of g postmessage propecia smiley reply free and liposomal anthracyclines based on their acutesubacute toxicity and cardiac toxicity respectively doxorubicin doxil myocet daunorubicin daunoxome maximal mgm mgm mgm mgm mgm single does maximal mgm undetermined mgm mgm undetermined cumulative mgm dose maximal mg mg mg mgm mg dose m week m week m week week m week intensity dose neutropenia stomatitis neutropenia neutropenia neutropenia limiting stomatitis skin toxicity stomatitis mucositis toxicities other anthracyclines in clinical use epirubicin is an epimer of doxorubicin widely used in breast cancer with less cardiotoxicity but also less activity on a per mg basis, owing to faster glucuronidation and faster clearance its therapeutic index advantage over doxorubicin, if any, is marginal idarubicin, an analog of daunorubicin, is another clinically approved anthracycline but of less common use mitoxantrone, an antracenedione, is a drug related to anthracyclines with doselimiting neutropenia and with cardiotoxic potential albeit after longer treatment periods g postmessage propecia smiley reply than doxorubicin it is also approved for clinical use but its added value is doubtful since it appears to be somewhat less active than doxorubicin in metastatic breast cancer doxorubicin cumulative dose may be substantially increased with coadministration of dexrazoxane, a cardioprotective agent dose associated with risk of cardiotoxicity table comparative human pharmacokinetics parameters of free and liposomal anthracyclines doxorubicin doxil myocet daunorubicin daunoxome distribution tvi rapid min rapid min hr terminal f nd nd hr clearance mlhr volume of distribution l dose mgm reference swenson gabizon swenson riggs bellott et al effl etalf etal to normalize for body surface, values were corrected for an average body surface area of m median values of studies are shown not reported extrapolated approximation is shown monoexponential elimination of liposomal drug from plasma terminal clearance phase of released drug not detected liposomes, formulated with a hydrogenated high phase transition g postmessage propecia smiley reply temperature pc and cholesterol doxil was granted market clearance in by the us food and drug administration fda for use in the treatment of aidsrelated kaposis sarcoma ks, in patients with disease that has progressed on prior to combination chemotherapy and who are intolerant to such therapy in , it was granted market clearance by the european unions commission for proprietary medicinal products for the same indication in , doxil was granted us market clearance for use in the treatment of recurrent carcinoma of the ovary in patients with disease that is refractory to paclitaxeland platinum based chemotherapy regimens in january , the european commission of the european union has granted centralized marketing authorization to doxil, as monotherapy for metastatic breast cancer in patients who are at increased cardiac risk in addition, phase ii trials have been completed in the us and europe, investigating the safety and efficacy g postmessage propecia smiley reply of doxil in multiple myeloma and in other solid tumors including sarcomas, carcinoma of head and neck, hepatocellular carcinoma, prostate cancer and the rest doxil was already recognized years ago as a liposomal doxorubicin formulation with unique pharmacokinetics and a dramatic change in the clinical toxicity profile clinical pharmacokinetic studies have indicated that doxil prolongs the circulation time of doxorubicin dramatically, in agreement with preclinical studies in , we published the results of a pharmacokinetic study in which patients were given sequentially the same dose in drugequivalents of free doxorubicin and doxil a dramatic reduction in the drug clearance and volume of distribution, resulting in a fold increase in auc with the liposomal formulation, was observed it was also found that nearly all the drug circulating in plasma is in liposomeencapsulated form metabolites in plasma were undetectable or at very low levels however, they were readily detected g postmessage propecia smiley reply in urine hrs or later after injection, indicating that the drug has become bioavailable the following drug distribution picture has emerged from this initial study and from more recent ones drug circulates in plasma for prolonged periods of time ie halflife in the range of hours in liposome encapsulated form despite its prolonged presence in blood, the drug is not bioavailable, as long as it remains in the interior of a circulating liposome most of the injected drug is distributed to tissues in liposome encapsulated form once in tissues, drug leakage and liposome breakdown with or without liposome internalization by cells gradually provides a pool of bioavailable drug metabolites are formed rate of metabolite production is slower than the rate of renal clearance of metabolites as a result, metabolites do not accumulate in plasma but can be detected in urine a small fraction of injected drug g postmessage propecia smiley reply leaks from circulating liposomes and is handled as a free drug with fast plasma clearance and rapid metabolism this drug fraction is the source of small amounts of metabolites that can sometimes be detected in plasma in , a phase i study of doxil in patients with solid tumors provided clear evidence of a major change in the toxicity profile, with mucocutaneous toxicities as the major doselimiting toxicities in contrast, myelosuppression, and alopecia were minor and cardiotoxicity was conspicuously absent the maximal tolerated dose was established as mgm, with mucositis being the doselimiting toxicity it was also found that the optimal dosing interval for retreatment was weeks rather than the standard week schedule of doxorubicin the doseschedule limiting toxicity was a form of skin toxicity known as handfoot syndrome, also referred to as palmarplantar erythrodysesthesia ppe, which appears to be related to the long halflife of g postmessage propecia smiley reply doxil thus, it became wellestablished that the doxil liposome formulation imparts a significant pharmacokineticpharmacodynamic change to the drug doxorubicin, unprecedented in magnitude for any intravenous drug delivery system later on, data gathered from phase ii and iii studies in metastatic breast cancer and recurrent ovarian cancer, brought down the recommended dose of doxil to mgm once in weeks, ie mgm per week this dose reduction was needed mainly to prevent skin toxicity resulting from successive courses of therapy at a dose intensity of mgmweek kaposis sarcoma ks is a multifocal tumor affecting the skin and sometimes the mucosas well known for its extremely high microvascular permeability profuse extravasation of colloidal goldlabeled stealth liposomes in a transgenic mouse model of ks has been shown in aids patients, ks is frequent and has an aggressive course therefore, this condition was chosen for the initial clinical testing of doxil g postmessage propecia smiley reply in phase ii�iii studies indeed, doxil as a single agent therapy demonstrated a significantly greater efficacy and better safety than standard chemotherapy ie combinations of bleomycin and vincristine, with or without doxorubicin and was also effective as second line chemotherapy in pretreated patients as a result of the extreme sensitivity of ks to chemotherapy, a low and relatively subtoxic dose of mgm every weeks is sufficient for effective treatment further to the successful application in ks treatment, there are three important benchmarks in the clinical research development of doxil in solid tumors cardiac function in patients receiving doxil evidence of a major risk reduction of cardiotoxicity, compared with free doxorubicin historical data a retrospective analysis of patients treated with large cumulative doses of doxil did not reveal any significant cardiac toxicity, despite the fact that some of these patients were treated with times as much as g postmessage propecia smiley reply the maximal cumulative dose acceptable for free doxorubicin two additional reports focusing on the cardiac biopsies of doxil treated patients at high cumulative doses confirmed the cardiac safety of doxil phase iii study in recurrent ovarian cancer significant increase in median survival with improved safety profile in the doxil patient group versus the topotecantreated patient group, where topotecan was the former standard therapy in this condition the use of doxil was particularly beneficial in platinumsensitive patients ie patients in whom tumor recurrence occurred more than months after the discontinuation of platinumbased frontline therapy in this subgroup, the median survival of doxiltreated patients was weeks, compared with weeks for topotecantreated patients, a difference of months, equivalent to a increase in survival as a result, doxil has become the standard therapy for recurrent ovarian cancer phase iii study in metastatic breast cancer equivalent anti tumor activity and g postmessage propecia smiley reply reduced cardiotoxicity in this study, it was found that treatment with doxil mgm every weeks dose intensity = mgmweek had equivalent efficacy to free doxorubicin of mgm every weeks dose intensity mgmweek, despite the lower dose intensity of the former in addition, cardiotoxicity, as well as alopecia, were dramatically reduced in doxiltreated patients myelosuppression and nausea were also milder in doxiltreated patients however, as seen in phase i�ii studies, skin toxicity was prominent with doxil and almost absent with doxorubicin treatment myocet myocet liposome encapsulated doxorubicin citrate complex is a nonpegylated formulation of liposomal doxorubicin that has been approved for the treatment of metastatic breast cancer in europe, but not in the united states myocet lipid composition consists of a fluid phase low phase transition temperature pc, as well as cholesterol with doxorubicin entrapped in the water phase a unique feature of this formulation is that g postmessage propecia smiley reply the drug is loaded into liposomes using a vial kit, just prior to administration in the hospital pharmacy the strategy employed is to decrease toxicity in a way that a net gain of therapeutic index is obtained in the pivotal phase i trial of myocet, the maximum tolerated dose was between mgm, given on day or split in consecutive daily doses of each week cycle the major doselimiting toxicity was neutropenia gcsf granulocytecolony stimulating factor administration may increase the maximum tolerated dose, when higher doses of myocet are desired by reducing the incidence of doselimiting neutropenia phase iii studies in metastatic breast cancer, comparing myocet to free doxorubicin, have shown similar anti tumor activity with significantly lesser cardiotoxicity for myocet, however, a study of high dose myocet with gcsf in patients with advanced breast cancer resulted in a disturbingly high incidence of cardiotoxicity , after a median g postmessage propecia smiley reply cumulative dose of mgm range of mgm, suggesting that the myocet margin of cardiotoxicity gain over doxorubicin is limited as described above, the maximum tolerated doses of doxil and myocet differ as a result of their different formulations consequently, a more intense dose schedule is recommended for myocet mgm every weeks than for doxil mgm every weeks the pharmacokinetics of myocet points to a small change in clearance and volume of distribution, when compared with free doxorubicin, suggesting that, in contrast to doxil, myocet liposomes are cleared rapidly from circulation and their drug content also leaks substantially daunoxome daunoxome� daunorubicin citrate liposome injection, is approved for use in patients with advanced hivassociated kaposis sarcoma at a recommended dose of mgm every weeks daunoxome lipid composition consists of a solid phase high phase transition temperature pc, as well as cholesterol with daunorubicin encapsulated in the water g postmessage propecia smiley reply phase the maximum tolerated dose of daunoxome was evaluated in a phase i trial of patients with solid tumors, using daunoxome doses that were escalated in steps from to mgm doselimiting neutropenia occurred in all patients who received mgm the maximum tolerated dose of daunoxome was established as mgm in patients with solid tumors every three weeks a more recent study with daunoxome in breast cancer patients confirmed this dose level as mtd two studies in patients with acute leukemia administered high dose daunoxome in day courses, up to a total dose of mgm mucositis was the doselimiting toxicity in these high dose daunoxome studies in one of the studies, of patients experienced fatal cardiotoxicity in a phase i study of children with relapsed or resistant solid tumors, the trial was prema turedly discontinued due to evidence of cumulative cardiotoxicity, including two deaths after courses of g postmessage propecia smiley reply daunoxome treatment in summary, neutropenia typically limits the maximum dose of daunoxome in solid tumor patients, and mucositis limits the maximum dose that can be given in a single cycle to leukemia patients cardiotoxicity was reported in some patients, and appears especially problematic in children the pharmacokinetics of daunoxome points to a major retardation of clearance and a small volume of distribution, when compared with free daunorubicin the distribution halflife of daunoxome h is nearly times shorter than that of doxil, suggesting that the former is cleared faster by the res, in agreement with the differences observed between pegylated and nonpegylated liposomes in preclinical studies however, in contrast to myocet, the daunoxome pharmacokinetics data do not point at any significant drug leakage in circulation clinical development of other liposomeentrapped cytotoxic agents dosefinding safety studies have been performed with several other liposomal anthracyclines, including a cardiolipinbased g postmessage propecia smiley reply liposome formulation of doxorubicin, doxorubicin entrapped in negatively charged phosphatidylglyc erol liposomes, liposomal annamycin, a pegylated form of liposomal doxorubicin manufactured only in taiwan pegdistearoylpccholesterol, and an immunoliposomeencapsulated form of doxorubicin mcc, targeted with an antibody reacting with human gastric cancer some of these formulations have not progressed any further to phase ii�iii studies for those formulations still under investigation, further clinical trials are needed to establish their efficacy the most advanced compounds currently being developed in liposomes belong to two families of cytotoxic drugs camptothecin analogs with topoiso merase i inhibitory properties and vinca alkaloids both are cell cycle phase specific cytotoxic drugs their antitumor activity tends to increase with liposome encapsulation, as we extend time of exposure by exploiting the liposomal slow release features an additional advantage for camptothecin analogs is the fact that their activity is better maintained in the lactone configuration which g postmessage propecia smiley reply is stable in an acid environment, as is the case of liposomes with remote drugloading techniques based on proton gradients at this time, none of these compounds have yet been approved by a regulatory agency after going through phase iii studies it should be noted that the development of liposomal formulations of cytotoxic agents has often failed for different reasons the formulation of a liposomal anticancer agent is a complex process with at least three distinct variables that may affect the outcome and the risk of failure the choice of the liposome carrier, the choice of the drug, and the method of drug encapsulation one example is the formulation of cisplatin in pegylated liposomes known as spi these liposomes have longcirculating characteristics, retain the drug in plasma exceedingly well, reduce drug toxicity, and produce a high and longlasting accumulation of drug in implanted tumors however, the g postmessage propecia smiley reply antitumor activity is reduced by comparison to free drug in preclinical studies in clinical studies, spi was inactive and showed no doselimiting toxicities, even at doses greater than fold the mtd of free cisplatin it appeared that cisplatin release from these liposomes was minimal in in vitro as well as in vivo systems, as indicated by the low occurrence of dna adducts resulting in a major reduction of bioavailability as a result, the development of spi was discontinued at the phase i clinical level the future of liposomal nanocarriers although progress in the understanding of cancer biology at the molecular level will undoubtedly lead to more new drugs with exquisite selectivity, some of these agents may need an efficient system for in vivo delivery to yield optimal results in addition, the use of broadspectrum cytotoxic drugs will remain as a major tool in cancer therapy g postmessage propecia smiley reply for decades to come, and, for cytotoxic drugs, various delivery systems may have a beneficial effect on the therapeutic index as already shown liposomes remain one of the most attractive platforms for systemic drug delivery, and an increased sophistication of these systems would be expected the most immediate improvement is the coupling of a ligand to the surface of the liposome that will target the vesicles to a specific cellsurface receptor, followed in most cases by internalization and intracellular delivery of the liposome drug cargo examples in this direction are the targeting of doxil to her expressing or folatereceptor, expressing cancer cells using a specific antiher single chain fv respectively or a folate conjugate anchored to the liposome surface another example is the tumor vascular targeting by endotheliumspecific peptides associated to liposomes a major advantage of targeted liposomal nanocarriers over liganddrug bioconjugates is the deliveryamplifying effect g postmessage propecia smiley reply of the former, which may be able to provide to the target cell, a ratio of drug molecules per single ligandreceptor interaction other future avenues that can be exploited using the liposome platform and have a definite preclinical basis include association with a reporter, ie an imaging or tracing element, that will provide the possibility of tracking the fate of the liposome in vivo or even the occurrence of a pharmacological effect such as apoptosis codelivery of synergistic agents the liposome platform offers the possibility of codelivery in space and time of two drugs with different pharmacokinetics and biodistribution patterns, thus enabling the optimal exploitation of synergistic properties association with a bioresponsive element, ie a temperaturesensitive or ph sensitive component that could destabilize the liposome and drive a burst release of drug the fact that liposome technology has matured into an acceptable pharmaceutical technology, and the g postmessage propecia smiley reply promising contributions of liposomes to sophisticated drug delivery methods, augur that liposome carriers are to remain in cancer therapy for the foreseeable future references cockshott id clinical pharmacokinetics of goserelin clin pharmacokinet ibrahim nk, desai n, legha s, et al phase i and pharmacokinetic study of abi , a cremophorfree, proteinstabilized, nanoparticle formulation of paclitaxel clin cancer res duncan r the dawning era of polymer therapeutics nat rev drug discov moghimi sm, hunter ac and murray jc nanomedicine current status and future prospects faseb } hanahan d and weinberg ra the hallmarks of cancer cell van den bossche � and van de wiele � receptor imaging in oncology by means of nuclear medicine current status clin oncol kastan mb molecular biology of cancer the cell cycle, in cancer principles & practice of oncology, th ed, devita jr vt, hellman s and rosenberg sa eds, lippincottraven philadelphia, g postmessage propecia smiley reply pp gabizon a pegylated liposomal doxorubicin metamorphosis of an old drug into a new form of chemotherapy cancer invest jain rk delivery of molecular medicine to solid tumors lessons from in vivo imaging of gene expression and function ] control rel papahadjopoulos d, allen t, gabizon a, et al sterically stabilized liposomes improvements in pharmacokinetics and anti tumor therapeutic efficacy proc natl acad sci usa gabizon a and martin f polyethyleneglycolcoated pegylated liposomal doxorubicin rationale for use in solid tumors drugs suppl swabb ea, wei j and gullino pm diffusion and convection in normal and neoplastic tissues cancer res harrington kj, rowlinsonbusza g, syrigos kn, et al influence of tumor size on uptake of llllndtpalabelled pegylated liposomes in a human tumor xenograft model br j cancer safra t, groshen s, jeffers s, et al treatment of patients with ovarian carcinoma with pegylated liposomal doxorubicin analysis of g postmessage propecia smiley reply toxicities and predictors of outcome cancer gabizon a, tzemach d, ��� l, et al dose dependency of pharmacokinetics and therapeutic efficacy of pegylated liposomal doxorubicin doxil in murine models drug targ gregoriadis g and ryman be liposomes as carriers of enzymes or drugs a new approach to the treatment of storage diseases biochem } p allen tm and chonn a large unilamellar liposomes with low uptake into the reticuloendothelial system febs lett gabizon a and papahadjopoulos d liposome formulations with prolonged circulation time in blood and enhanced uptake by tumors proc natl acad sci usa gabizon a, shiota r and papahadjopoulos d pharmacokinetics and tissue distribution of doxorubicin encapsulated in stable liposomes with long circulation times j natl cancer inst woodle mc and lasic dd sterically stabilized liposomes biochim biophys acta klibanov al, maruyama k, torchilin vp, et al amphipathic polyethyleneglycols effectively prolong the circulation time g postmessage propecia smiley reply of liposomes febs lett allen tm, hansen c, martin f, et al liposomes containing synthetic lipid derivatives of poly ethylene glycol show prolonged circulation halflives in vivo biochim biophys acta lasic dd and martin fj eds stealth liposomes crc press boca raton huang sk, lee kd, hong k, et al microscopic localization of sterically stabilized liposomes in colon carcinomabearing mice cancer res yuan f, leunig m, huang sk, et al microvascular permeability and interstitial penetration of sterically stabilized stealth liposomes in a human tumor xenograft cancer res gabizon aa selective tumor localization and improved therapeutic index of anthracyclines encapsulated in longcirculating liposomes cancer res bally mb, masin d, nayar r, et al transfer of liposomal drug carriers from the blood to the peritoneal cavity of normal and ascitic tumorbearing mice cancer chemother pharmacol maeda h enhanced permeability and retention epr effect in tumor vasculature the g postmessage propecia smiley reply key role of tumorselective macromolecular drug targeting adv enzyme regul goren d, horowitz at, zalipsky s, et al targeting of stealth liposomes to erbb her receptor in vitro and in vivo studies br } cancer gabizon a, shmeeda h, horowitz at, et al tumor cell targeting of liposome entrapped drugs with phospholipidanchored folic acidpeg conjugates adv drug del rev stohrer m, boucher y, stangassinger m, et al oncotic pressure in solid tumors is elevated cancer res harrington kj, mohammadtaghi s, uster ps, et al effective targeting of solid tumors in patients with locally advanced cancers by radiolabeled pegylated liposomes clin cancer res symon z, peyser a, tzemach d, et al selective delivery of doxorubicin to patients with breast carcinoma metastases by stealth liposomes cancer northfelt dw, martin fj, working p, et al doxorubicin encapsulated in liposomes containing surfacebound polyethylene glycol pharmacokinetics, tumor localization, and safety in g postmessage propecia smiley reply patients with aidsrelated kaposis sarcoma j clin pharmacol young rc, ozols rf and myers ce the anthracycline antineoplastic drugs n engl j med forssen ea and tokes za in vitro and in vivo studies with adriamycin liposomes biochem biophys res commun lasic dd, frederik pm, stuart mca, et al gelation of liposome interior a novel method for drug encapsulation febs lett haran g, cohen lk, bar y, et al transmembrane ammonium sulfate gradients in liposomes produce efficient and stable entrapment of amphipathic weak bases bioehim biophys acta lasic dd, ceh b, stuart mc, et al transmembrane gradient driven phase transitions within vesicles lessons for drug delivery bioehim biophys acta gabizon aa liposome circulation time and tumor targeting implications for cancer chemotherapy adv drug del rev gabizon a, shmeeda h and barenholz y pharmacokinetics of pegylated liposomal doxorubicin review of animal and human studies clin pharmacokinetics gabizon g postmessage propecia smiley reply a, chemla m, tzemach d, et al liposome longevity and stability in circulation effects on the in vivo delivery to tumors and therapeutic efficacy of encapsulated anthracyclines} drug targ colbern gt, hiller aj, musterer rs, et al significant increase in antitumor potency of doxorubicin hci by its encapsulation in pegylated liposomes j lipos res hortobagyi gn anthracyclines in the treatment of cancer an overview drugs suppl allen tm and martin f advantages of liposomal delivery systems for anthracyclines semin oncol suppl vail dm, amantea ma, colbern gt, et al pegylated liposomal anthracycline formulations proof of principle using preclinical animal models and pharmacokinetics semin oncol suppl krown se, northfelt dw, osoba d, et al use of liposomal anthracyclines in kaposis sarcoma semin oncol suppl markman m, gordon an, mcguire wp, et al liposomal anthracycline treatment for ovarian cancer semin oncol suppl robert nj, vogel cl, henderson g postmessage propecia smiley reply �, et al the role of the liposomal anthracyclines and other systemic therapies in the management of advanced breast cancer semin oncol suppl hussein ma and anderson �� role of liposomal anthracyclines in the treatment of multiple myeloma semin oncol suppl ewer ms, martin fj, henderson �, et al cardiac safety of liposomal anthracyclines semin oncol suppl � gabizon a, catane r, uziely b, et al prolonged circulation time and enhanced accumulation in malignant exudates of doxorubicin encapsulated in poly ethyleneglycol coated liposomes cancer res uziely b, jeffers s, isacson r, et al liposomal doxorubicin antitumor activity and unique toxicities during two complementary phase i studies j clin oncol alberts ds, muggia fm, carmichael j, et al efficacy and safety of liposomal anthracyclines in phase iii clinical trials semin oncol suppl huang sk, martin fj, jay g, et al extravasation and transcytosis of liposomes in kaposis g postmessage propecia smiley reply sarcomalike dermal lesions of transgenic mice bearing the hiv tat gene am } pathol safra t, muggia m, jeffers s, et al pegylated liposomal doxorubicin reduced clinical cardiotoxicity in patients reaching or exceeding mgm cumulative doses of doxil ann oncol berry g, billingham m, alderman e, et al the use of cardiac biopsy to demonstrate reduced cardiotoxicity in aids kaposis sarcoma patients treated with pegylated liposomal doxorubicin ann oncol gabizon aa, lyass o, berry gj, et al cardiac safety of pegylated liposomal doxorubicin doxil�caelyx� demonstrated by endomyocardial biopsy in patients with advanced malignancies cancer invest gordon an, tonda m, sun s, et al longterm survival advantage for women treated with pegylated liposomal doxorubicin compared with topotecan in a phase randomized study of recurrent and refractory epithelial ovarian cancer gynecologic oncol obrien me, wigler n, inbar m, et al reduced cardiotoxicity and comparable efficacy in a phase g postmessage propecia smiley reply iii trial of pegylated liposomal doxorubicin hc caelyxdoxil versus conventional doxorubicin for firstline treatment of metastatic breast cancer ann oncol cowens jw, creaven pj, greco wr, et al initial clinical phase i trial of tlc d doxorubicin encapsulated in liposomes cancer res shapiro cl, ervin t, welles l, et al phase ii trial of highdose liposome encapsulated doxorubicin with granulocyte colonystimulating factor in metastatic breast cancer tlc d study group } clin oncol harris l, batist g, belt r, et al liposomeencapsulated doxorubicin compared with conventional doxorubicin in a randomized multicenter trial as firstline therapy of metastatic breast carcinoma cancer batist g, ramakrishnan g, rao cs, et al reduced cardiotoxicity and preserved antitumor efficacy of liposomeencapsulated doxorubicin and cyclophosphamide compared with conventional doxorubicin and cyclophosphamide in a randomized, multi center trial of metastatic breast cancer ] clin oncol casper es, schwartz gk, sugarman a, et g postmessage propecia smiley reply al phase i trial of doseintense liposome encapsulated doxorubicin in patients with advanced sarcoma j clin oncol conley ba, egorin mj, whitacre my, et al phase i and pharmacokinetic trial of liposomeencapsulated doxorubicin cancer chemother pharmacol gill ps, espina bm, muggia f, et al phase iii clinical and pharmacokinetic evaluation of liposomal daunorubicin } clin oncol guaglianone p, chan k, delaflorweiss e, et al phase i and pharmacologic study of liposomal daunorubicin daunoxome invest new drugs obyrne kj, thomas al, sharma ra, et al a phase i doseescalating study of daunoxome, liposomal daunorubicin, in metastatic breast cancer br } cancer cortes j, obrien s, estey e, et al phase i study of liposomal daunorubicin in patients with acute leukemia invest new drugs fassas a, buffels r, anagnostopoulos a, et al safety and early efficacy assessment of liposomal daunorubicin daunoxome in adults with refractory or relapsed acute g postmessage propecia smiley reply myeloblasts leukaemia a phase i�ii study br j haematol lowis s, lewis i, elsworth a, et al cardiac toxicity may limit the usefulness of liposomal daunorubicin daunoxome results of a phase i study in children with relapsed or resistant tumours � a ukccsgsfop study proc am soc clin oncol abstract rahman a, treat j, roh jk, et al a phase i clinical trial and pharmacokinetic evaluation of liposomeencapsulated doxorubicin clin oncol gabizon a, peretz t, sulkes a, et al systemic administration of doxorubicin containing liposomes in cancer patients a phase i study eur j cancer clin oncol booser dj, perezsoler r, cossum p, et al phase i study of liposomal annamycin cancer chemother pharmacol hong rl and tseng yl phase i and pharmacokinetic study of a stable, polyethyleneglycolated liposomal doxorubicin in patients with solid tumors the relation between pharmacokinetic property and toxicity cancer matsumura y, gotoh g postmessage propecia smiley reply m, muro k, et al phase i and pharmacokinetic study of mcc, a doxorubicin dxr encapsulated in peg immunoliposome, in patients with metastatic stomach cancer ann oncol kehrer df, bos am, verweij j, et al phase i and pharmacologic study of liposomal lurtotecan, nx urinary excretion predicts hematologic toxicity j clin oncol colbern gt, dykes dj, engbers c, et al encapsulation of the topoisomerase i inhibitor glc in pegylated stealth liposomes pharmacokinetics and antitumor activity in ht colon tumor xenografts clin cancer res gelmon ka,tolcher a, diab ar, et al phase i study of liposomal vincristine j clin oncol bandak s, goren d, horowitz at, et al pharmacological studies of cisplatin encapsulated in longcirculating liposomes in mouse tumor models anticancer drugs veal gj, griffin mj, price e, et al a phase i study in pediatric patients, to evaluate the safety and pharmacokinetics of spi, g postmessage propecia smiley reply a liposome encapsulated formulation of cisplatin br } cancer harrington kj, lewanski cr, northcote ad, et al phase i�ii study of pegylated liposomal cisplatin spi in patient with inoperable head and neck cancer ann oncol meerum terwogt jm, groenewegen g, pluim d,etal phase i and pharmacokinetic study of spi, a liposomal encapsulated dosage form of cisplatin cancer chemother pharmacol park jw, hong k, kirpotin db, et al antiher immunoliposomes enhanced efficacy attributable to targeted delivery clin cancer res pastorino f, brignole c, marimpietri d, et al vascular damage and antiangiogenic effects of tumor vesseltargeted liposomal chemotherapy cancer res swenson ce, bolcsak le, batist g, et al pharmacokinetics of doxorubicin administered iv as myocet tlc d liposomeencapsulated doxorubicin citrate compared with conventional doxorubicin when given in combination with cyclophosphamide in patients with metastatic breast cancer anticancer drugs riggs ce clinical pharmacology of daunorubicin in patients with g postmessage propecia smiley reply acute leukemia semin oncol suppl ll bellott r, auvrignon a, leblanc t, et al pharmacokinetics of liposomal daunorubicin daunoxome during a phase i�ii study in children with relapsed acute lymphoblastic leukemia cancer chemother pharmacol nanoparticulate drug delivery to the reticuloendothelial system and to associated disorders mukul kumar basu and sanchaita lala introduction physicochemical methods for sitespecific delivery of drugs in the form of polymeric and colloidal particulate carriers eg liposomes, micelles and nanoparticles, have been of great interest to researchers recently nanoparticles, particularly polymeric nanoparticles, have been investigated since the late s as an alternative to liposomes which suffered from inherent problems such as low encapsulation, rapid leakage, poor stability and production difficulties nanoparticles are particles ranging from nm to nm in diameter and are the collective names for nanospheres and nanocapsules nanospheres are solid particles which can be used as drug carriers, where the active g postmessage propecia smiley reply principles can be dispersed in the polymeric matrix or adsorbed on their surfaces or both nanocapsules have a polymeric shell with an inner liquid core and the active substances can be incorporated within the core or loaded on the surface by physical adsorption or by chemical bonding nanoparticles can be administered by a variety of routes, depending upon the desired therapeutic outcome and can even be used for vaccine administration and diagnostic imaging drug release from nanoparticles is a very important factor for developing successful formulations for achieving this, various targeted and controlled release drug delivery systems have been developed controlled release is one of the basic modes of drug delivery with the objective of releasing a drug into a patients body at a predetermined rate, or at specific times, or with specific release profiles release profiles of the drugs from nanoparticles depend on the g postmessage propecia smiley reply nature of the delivery systems such systems often use synthetic polymers as the carriers for the drug these particulate carrier systems can release the drug by a polymer degradation or chemical cleavage of the drug from the polymer, b swelling of the polymers and releasing the drug entrapped within them, c osmotic pressure effects creating pores and releasing the drugs, which can get dispersed within the polymeric network of the nanoparticles, and d simple diffusion methods they represent an interesting carrier system for the specific enrichment in macrophage containing organs like the liver and spleen thus, injectable nanoparticle carriers have important potential application in sitespecific drug delivery reticuloendothelial system and associated disorders the reticuloendothelial system res represents a group of cells having the ability to take up and sequester inert particles and vital dyes this includes macrophages and macrophage precursors, specialized endothelial cells lining the sinusoids g postmessage propecia smiley reply of the liver, spleen and bone marrow, and the reticular cells of the lymphatic tissue macrophages and of the bone marrow fibroblasts thus, the reticuloendothelial system or the mononuclear phagocyte system encompasses a range of cells capable of phagocytosis ie macrophages and monocytes they are either freely circulating within the blood or fixed to various connective tissues examples of the sites of fixed cells include pulmonary alveoli, liver sinusoids, skin, spleen and joints the res primarily functions to a remove the senescent cells from circulation and b provide phagocytic cells for both inflammatory and immune responses there are several res associated disorders involving both macrophages and monocytes these diseases could be of two types � infectious and noninfectious among the infectious diseases, pulmonary tuberculosis, typhoid fever, leishmaniasis, trypanosomiasis and acquired immune deficiency syndrome aids are worth mentioning among the noninfectious type, ulcerative colitis, collagen disease, hodgkins g postmessage propecia smiley reply disease and gauchers disease are equally common uptake of nanoparticles by the reticuloendothelial system sites of uptake the sequestering of nanoparticles and these are a opsonophagocytosis and mechanism of uptake two major mechanisms are involved in other colloidal particles by macrophages, b opsonicindependent recognition a opsonophagocytosis opsonophagocytosis and opsonorecognition of particles by macrophage receptors are greatly enhanced when the particle surface is coated with certain protein ligands such ligands are known as opsonins and the process of their adsorption on the particle surface is termed opsonization opsonins act as a ligand on the particle surface and facilitate their recognition and initial attachment by the phagocyte receptors taking liposomes as a model system, the major classes of opsonins have been found to include various subclasses of immunoglobulins eg igm, iggl and igg in humans, certain components of the complement system eg cb, icb, clq, fibronectin, lipopolysaccharide g postmessage propecia smiley reply binding protein and pen traxins eg creactive proteins and serum amyloid pcomponents more recently, it was shown that both thrombospondin and von willebrand factor can also act as opsonins and trigger phagocytosis of sulfa tiderich or coated particles their it has been observed that nanoparticles, like other colloidal drug delivery systems eg liposomes, niosomes, microparticles etc, on intravenous injections, are rapidly sequestered and retained by the organs comprising of the reticuloendothelial systems res, mainly the liver, spleen and the bone marrow thus, targeting of the nanoparticles to the res is much simpler than to any other organ in the liver, the particles are mainly retained by the scavenging periportal and midzonal kupffer cells, while the hepatocytes and liver endothelial cells may play a secondary role under special pathophysiological conditions or for special physicochemical characteristics of particles in the spleen, the marginal zone and red pulp macrophages g postmessage propecia smiley reply are the major scavengers, while peritoneal macrophages and dendritic cells have a minor contribution in the case of bone marrow, the sequestering mechanism is rather complex and appears to be species specific briefly, it encompasses two routes, a transcellular route, mediated through the diaphragmed fenestrate of the endothelial walls, and an intercellular route, involving the formation of bristlecoated pits containing matter on the internal surface of the endothelium the particles that reach the bone marrow parenchyma are engulfed by stromal or hematopoietic macrophages in guineapig, the venous endothelium has similar phagocytic properties to the sinusoidal endothelium, while in some other species such as rabbit and marmoset, certain macrophage subpopulations named perisinal phagocytes, which penetrate the endothelium sending cytoplasmic processes into the lumen, are also involved modes of interaction have been reviewed in detail some opsonic entities such as the tetrapeptide tuftsin, unlike other opsonins, bind to g postmessage propecia smiley reply the phagocytic cell rather than to the particle and enhance the phagocytic ingestion two or threefold of these, igg along with complement cb and albumin are seen to play the most important roles these opsonins, bound to the particle surface, form a bridge between the particles and the macrophages, facilitating phagocytosis of the particles the fc receptor plays an important role in the clearance of iggopsonized particles the complement system provides the first line of defense against foreign microbes and particles, ensuring their cytolytic andor phagocytic clearance as in the case of liposomes, activation of the complement pathway may occur if the opsonic components cb and icb are deposited on nanoparticles this may be antibodymediated, or nanoparticles may also activate complement through non antibody mediated mechanism via the classical and alterative pathways however, it is known that noncovalent linkage of cb and icb to a g postmessage propecia smiley reply particle surface cannot promote phagocytosis by macrophages rather, the covalent bond between the reactive glutamyl residue of the c thiol ester and the constituents of the particles surface is the central mechanism of opsonization and the mediator of phagocytic recognition in addition, the covalently attached cb or icb must be accessible to their corresponding receptors on phagocytic cell surface moreover, the complement receptors must be in a functional state kupffer cells in humans and rats have been found to contain receptors for cb cr and icb cr and cr, and may play an important role in the macrophage clearance of nanoparticles in humans, cr receptors are also found in monocytes and erythrocytes, while it is found on platelets in rats hence, these cells also play an important role in the clearance of immune complexes via the cbcr interaction in humans, the erythrocytebound immune complexes are transferred g postmessage propecia smiley reply to macrophages during their passage through the liver and the spleen due to the multitude of erythrocytes, this may be a major contributor to the complementmediated clearance process in the case of liposomes, it has been demonstrated that the vesicleblood protein interaction is largely determined by the fluidity and hydrophobicity of the vesicles, as well as by the vesicle size cholesterol free and cholesterol poor vesicles are rapidly captured by macrophages, mostly of the liver the uptake is enhanced in the presence of serum in contrast to hepatic phagocytes, bone marrow cells preferentially capture cholesterolrich rather than cholesterolpoor vesicles primed with serum on the other hand, serum stimulates the uptake of all cholesterolcontaining vesicles by both splenic phagocytes and peritoneal macrophages, but its effect is significantly greater on the uptake of cholesterolrich rather than cholesterol poor vesicles in addition, serum suppressed the uptake of vesicles prepared g postmessage propecia smiley reply from saturated phospholipids by liver phagocytes, but enhanced their uptake by spleen and bonemarrow macrophages thus, vesicle uptake by the liver, spleen, bone marrow and peritoneal macrophages is determined by tissuespecific opsonins again, this is determined by the membrane fluidity and hydrophobicity which plays an important role in attracting the right opsonins which determine phagocytic activity from the above observations, it has been suggested that a balance between the opsonins and dysopsonins ie naturally occurring substances that inhibit phagocytic ingestion, usually by altering the surface properties of the phagocyte or particle or both, thereby interfering with opsonization or altering the metabolic activity of the phagocyte may regulate the uptake of vesicles by phagocytes moreover, large vesicles above nm are more readily cleared by liver macrophages probably by complement activation, while smaller ones nm localize in the spleen and bone marrow macrophages although, calcium at physiological g postmessage propecia smiley reply levels is a prerequisite for the process of phagocytosis, it has been demonstrated that elevation of serum calcium levels above normal can inhibit, while a decrease below normal can facilitate the opsonophagocytosis of particles by kupffer cells b opsoniniridependerit recognition nonopsonic blood proteins could also play an important role in particle clearance nonopsonic proteins, after adsorption onto particle surfaces, could experience conformational changes such changes are likely to expose chemical groups that could either be recognized directly by certain receptors on the phagocytic cell surface, or could act as ligands for the subsequent recognition by the blood opsonins the molecules involved include mannosebinding protein ���, a ctype lectin with specificity for mannose, and nacetyl glucosamine, also known to activate complement through the activation of clr cls complex, and by opsonization through macrophage clq receptor scavenger receptors sr on macrophage plasma membranes and endothelial cells can recognize g postmessage propecia smiley reply modified lipoproteins, polyanionic macromolecules, bacterial polysaccharides, silica and possibly anionic liposomes fcyrli and fcyrl are regarded as putative receptors for lowdensity lipoproteins functioning, independent of igg cd is a physiologically important receptor for lipopolysaccharide, which is also a ligand for srai it is strongly expressed on monocytes and granulocytes, but on kupffer cells, it is only expressed in chronic and acute liver diseases a putative stearylamine receptor on kupffer cells may also play a minor role in the clearance of neutral and anionic vesicles cooperation between different macrophage receptors, eg fibronectin or immunoglobulins with complement or ayfi with cd may increase the efficiency of particle phagocytosis and the clearance from blood alternatively, macrophages as well as hepatocytes and liver endothelial cells may phagocytoseendocytose liposomes via direct recognition of phospholipid headgroups phospholipid recognition may be mediated by a number of plasma membrane receptors such as lectin receptors, g postmessage propecia smiley reply cd, various classes of scavenger receptors eg classes �, � and d, fcyri and fcriib the recognition is specific for unsaturated phospholipids and fails for saturated phospholipids factors influencing uptake extrapolating the above discussion on liposomes to nanoparticles, it may be emphasized that some of the factors which affect their uptake by the cells of the res include particle size, surface charge and surface hydrophobicityhydrophilicity cholesterolfree nanoparticles of diameter above nm, incorporated with unsaturated phospholipid headgroups, are expected to be preferentially sequestered by liver macrophages and endothelial cells, while priming nanoparticles that are smaller than nm diameter, containing phospholipid and probably cholesterol, with serum, may enhance their uptake by the spleen and bone marrow macrophages the hepatic phagocytosis may be facilitated by subnormal blood calcium concentration although the above hypotheses have not yet been experimentally proven entirely, it has been demonstrated many times in our g postmessage propecia smiley reply laboratory that poly dllactide pla and polydllactide coglycolide plga nanoparticles of approximately nm in diameter, containing a high percentage ww of unsaturated phospholipids phosphatidyl ethanolamine or phosphatidyl choline, are highly effective in reducing the spleen and liver parasite loads in the hamster models of experimental visceral leishmaniasis this lends credence to the above view in general, it appears that surface hydrophobic nanoparticles of size greater than nm in diameter have a greater chance of being sequestered by macrophages of the liver and spleen however, it has been reported that very small nanoparticles nm diameter, consisting of polydllactide pla � polyethyleneglycol peg copolymeric micelles, can pass through the sinusoidal fenestrations in the liver and gain access to the liver parenchymal cells moreover, the effect of surface charge on phagocytosis and the biodistribution of albumin nanoparticles have been reported by roser et aln it has been noticed that g postmessage propecia smiley reply albumin nanoparticles, with a zeta potential close to zero, showed a reduced in vitro phagocytic uptake by primary mouse peritoneal macrophages and a human hematopoietic cell line u, in comparison to charged particles, especially particles with a positive zeta potential however, this difference has not been reflected in their in vivo blood circulation times and organ distributions in rats moreover, the influence of surface characteristics which include surface charge density and zeta potential, along with size and surface hydrophobicity, has already been noticed on plasma protein adsorption patterns on colloidal drug carriers after intravenous administration, thus influencing their in vivo organ distribution role of surface modifications on uptake various surface modifications of nanoparticles have been shown to facilitate their uptake by different components of the res colloidal gold nanoparticles, after opsonization with autologous plasma, are found to accumulate in kupffer cells, the predominant opsonizing factor being g postmessage propecia smiley reply fibronectin monocrystalline iron oxide nanoparticles mion were found to be readily captured by macrophages, and opsonization by the serum component c, vitronectin and fibronectin resulted in a sixfold increase polylactide nanoparticles are sequestered by monocytes by passive adsorption and energyrequiring receptormediated endocytosis and the uptake are enhanced by opsonization with lipoproteins body distribution of fully biodegradable [c]poly lactic acid nanoparticles coated with albumin, after parenteral administration to rats, was examined by bazile et al as deduced from wholebody autoradiography and quantitative distribution experiments, the clabelled polymer is rapidly captured by the liver, bone marrow, lymph nodes, spleen and peritoneal macrophages nanoparticle degradation was addressed following c excretion the elimination of c was quick on the first day ie of administered dose, but slowed down subsequently the block copolymers of poloxamine and poloxamer series play an important role in the surface modification of nanoparticles of these, g postmessage propecia smiley reply poloxamine is a polyoxyethylene ���polyoxypropylene pop block copolymer, which adsorbs on nanoparticles via the relatively hydrophobic pop segments, while the mobile ��� chains extend outward, suppressing aggregation and providing stability poloxamer is a block copolymer of ���pop and a nonionic surfactant polystyrene microspheres coated with the block copolymers of poloxamer and poloxamine series were observed to adsorb igg, complement c, transferrin and fibronectin in serum, as well as fibrinogen in plasma poloxamine activates the mononuclear phagocyte system so that the coated particles are sequestered by liver poly organophosphazene nanoparticles coated with poloxamine were mainly captured by the rat liver, while poly organo phosphazene nanoparticles coated with a novel poly organophosphazenepoly ethyleneox ide copolymer with a mw peo chain were reported to be significantly targeted at the bone marrow it has been observed that the sequestration of surfaceengineered polystyrene nanospheres by the liver and spleen could be g postmessage propecia smiley reply greatly augmented by the modification of poloxamer and poloxamine , by introducing a terminal protonated amine group to each peo chain also, the phagocytic uptake of poloxamer and poloxamine coated polystyrene particles by mouse peritoneal macrophages was found to decrease with increasing adsorbed layer thickness, ie longer hydrophilic polymer chains of the coating agent, and consequently, a greater steric stabilization effect surface engineered sterically stabilized nanospheres were synthesized and found to have enhanced drainage into lymphatics, as well as enhanced uptake by macrophages of the regional lymph nodes lymph node localization of biodegradable polylactide coglycolide nanospheres could be enhanced by coating them with poloxamer and poloxamine correlation was observed between the length of the stabilizing ��� chains of the block copolymers polyoxyethylene ��� polyoxypropylene pop in the poloxamerpoloxamine and nanosphere drainage and the passage across tissuelymph interface in dermal lymphatic capillaries in the ratfootpads the longer the g postmessage propecia smiley reply ��� chains, the faster the particle drainage in order for effective opsonization of the nanospheres to occur in the lymphatics, the ��� chains of the block copolymers should be of ethylene oxide units if the dimensions of the stabilizing ��� chains of the poloxamines and poloxamers exceed the range of the van der waals forces of attraction, opsonization fails to occur and the surface modified nanospheres escape sequestration by the macrophages of the regional lymph nodes, and are rapidly drained into the systemic circulation, where they persist for prolonged periods it has also been reported that polystyrene and polylactidecoglycolide nanoparticles show enhanced localization in the lymph nodes when their surfaces are coated with polylactide pla polyethyleneglycol peg or by producing coprecipitate nanospheres of plga and pla peg, depending on surface characteristics pegcoated magnetite nanospheres have also been utilized to target diagnostic agents to regional lymph g postmessage propecia smiley reply nodes it has been reported that small colloidal nanoparticles nm in diameter can be targeted specifically to the sinusoidal endothelial cells of the rabbit bone marrow, following intravenous administration, by coating their surface with the block copolymer poloxamer , a nonionic surfactant influence of surfactant concentration on the body distribution of the nanoparticles was studied by araujo et al they noticed that the rapid res uptake of the nanoparticles after intravenous injection, especially by the liver, can be reduced and the body distribution can be altered by coating them with nonionic surfactants, eg poloxamine and polysorbate evaluation of the likely mechanisms that contribute to the prolonged circulation times of sterically protected nanoparticles has already been made recent evidence showed that sterically stabilized particles are prone to opsonization, particularly by the opsonic components of the complement systems active targeting of nanoparticles by receptor mediated endocytosis active targeting of g postmessage propecia smiley reply nanoparticles to the organs of reticuloendothelial system could be done by attaching appropriate ligands for the well identified receptors on the target cells belonging to this system taking advantage of the presence of man nosyl fucosyl receptors on the macrophage surface, mannose bearing polymeric delivery systems have been designed and used with appropriate antileishmanial drug for sitespecific delivery in the hamster model of experimental leishmaniasis these modified polymeric vesicles have been developed by coupling the amino group of phosphatidyl ethanolamine pe, an essential compound of polymeric vesicles plga with amino group of paminophenyl ad mannoside, in the presence of glutaraldehyde as a bridging agent fig the results demonstrate that because of receptor mediated endocytosis, nanoparticle entrapment of antileishmanial compound enhanced its effectiveness, an effect that seemed to be much greater when mannose bearing polymeric vesicles are used similarly, nanoparticles coated with the polymer mannan as ligand g postmessage propecia smiley reply have been demonstrated to have a enhanced uptake than uncoated nanoparticles by mannosereceptor positive mouse nh, nh mannose �� pevesicle paminophenyl a d mannoside chochchchcho glutaraldehyde n = ch�ch�ch�ch�ch = nmannose mannosegrafted polymeric vesicles a nh nh�f ab pevesicle cho ch� ch chcho glutaraldehyde n = chchch�� ch �ch = n� f ab antibody coated polymeric vesicles b fig formation of mannosegrafted polymeric vesicles a and antibodycoated mannosegrafted polymeric vesicles b macrophage cell line je, by the process of receptor mediated endocytosis alternatively, the possibility of grafting a monoclonal antibody raised against a parasitespecific antigen onto the polymeric vesicle surface cannot be ignored for active targeting of an antileishmanial compound besides the grafting of the synthetic mannoside or the coating with the polymer mannan, similar results could be obtained when indigenous glycosides, eg bacopasaponin � and arjunglucoside i, both isolated from the indian medicinal plants, g postmessage propecia smiley reply ������ monniera and terminalia bel lerica respectively, having glucose at the terminal end of glycosidic chain fig , are incorporated in pla nanoparticles and are subjected to test for antileishmanial property, using both free and nanoparticleincorporated forms, much better therapeutic efficacy could be noticed with the polymeric vesicles incorporated with either of the two glycosides compared with the glycosideunincorporated control vesicles the unique presence of a glucose residue at the terminal end of the glycosidic chain, equipped the compounds to be selftargeting molecules that can be directed towards the glucose receptors present on the macrophage surface for facilitating a receptor mediated drug delivery to the target cells perhaps these are the bacopasaponin � mw fig structures of some glycosides isolated from indigenous sources h corchorusin d mw oh �� hh,c amarogenlin mw very first reports for the targeted delivery of antileishmanial compounds in experimental leishmaniasis, a g postmessage propecia smiley reply resassociated disorder, using polymeric vesicles as drug carriers application in chemotherapy among the major res associated disorders, pulmonary tuberculosis is identified as a killer disease because its death toll every year is enormously high with a view to develop appropriate delivery systems to test the efficacy of frontline anti tubercular drugs in vivo, experimental tuberculosis was induced in murine models and nanoparticleencapsulated antitubercular drugs were administered orally to them at every th day when examined, no tubercle bacilli could be detected in the tissues after such oral doses of treatment thus, nanoparticle encapsulated antitubercular drugs turned out to be a potential oral drug delivery system against murine tuberculosis alternatively, subcutaneous nanoparticle based antitubercular chemotherapy was also tried injectable plg nanoparticles were found to hold promise for increasing drug bioavailability and reducing dosing frequency for a better management of tuberculosis however, nebulization via the respiratory route of g postmessage propecia smiley reply nanoparticlebased antitubercular drugs were reported to form a sound basis for improving drug bioavailability and reducing the dosing frequency for better chemotherapeutic control of pulmonary tuberculosis the next major res associated disorder is leishmaniasis, which causes substantial human morbidity and mortality in many parts of the world in an attempt to probe the disease, several new drugs as well as new delivery systems were put forward with a view to increase the drug efficacy and to reduce the drug toxicity using nanoparticlebound pentamidine in a leishmania majormouse model, ultra structural changes in parasites were noticed by fusai et al in the parasites inside the kupffer cells, transmission electron microscopy showed a swollen mitochondrion with a loss of cristae, destruction or fragmentation of the kinetoplast, loss of ribosomes and the destruction of parasite structures except for the subpellic ular microtubules the therapeutic efficacy of several indigenous g postmessage propecia smiley reply antileishmanial agents eg bacopasaponin c, isolated from the indian medicinal plant bacopa mon niera, quercetin, isolated from fagopyrum esculentum and harmine, isolated from peganum harmala, were not only studied but compared after incorporating them in different vesicular delivery systems against experimental leishmaniasis in hamster models at equivalent quercetin concentration, the nanocapsulated quercetin was found to be the most potent in reducing the parasite burden in the spleen as well as in reducing hepatotoxicity and renal toxicity, compared with free drug or drug in other vesicular forms similarly, bacopasaponin c, at an equivalent dose of mgkg body weight and harmine, at an equivalent dose of mgkg body weight, were found to be very active in all the vesicular forms, but the best efficacy in the lowering of spleen parasite load was found with the nanocapsulated form thus, in each case, the nanoparticleloaded antileishmanial agent was found to g postmessage propecia smiley reply be most efficient in the lowering of spleen parasite load and the efficacy was found to vary in the following order nanoparticles niosomes liposomes microspheres free drug and the hepatotoxicity, as well as the renal toxicity was found to follow in the reverse order as shown above in vitro antileishmanial activity of amphotericin � loaded in poly epsiloncaprolactone nanospheres was also noted, but the nanospheres did not show any improvement of amphotericin � activity against the resistant strain attempt was made to deliver piperine to treat experimental visceral leishmaniasis in mice model using oil in water emulsions known as lipid nanospheres ln or fat emulsions a single dose of mgkg of lipid nanospheres of piperine was found to significantly reduce the liver and splenic parasite burden therapeutic evaluation of free and nanocapsule encapsulated atovaquone was made in the treatment of murine visceral leishmaniasis by cauchetier et al?