Effect of the nonionic surfactant poloxamer 338 on the fate and deposition of polystyrene microspheres following intravenous administration

The impact of molecular tumor profiling on the design strategies for targeting myeloid leukemia and EGFR/CD44-positive solid tumors

Nanomedicine has emerged as a novel cancer treatment and diagnostic modality, whose design constantly evolves towards increasing the safety and efficacy of the chemotherapeutic and diagnostic protocols. Molecular diagnostics, which create a great amount of data related to the unique molecular signatures of each tumor subtype, have emerged as an important tool for detailed profiling of tumors. They provide an opportunity to develop targeting agents for early detection and diagnosis, and to select the most effective combinatorial treatment options. Alongside, the design of the nanoscale carriers needs to cope with novel trends of molecular screening. Also, multiple targeting ligands needed for robust and specific interactions with the targeted cell populations have to be introduced, which should result in substantial improvements in safety and efficacy of the cancer treatment. This article will focus on novel design strategies for nanoscale drug delivery systems, based on the unique molecular signatures of myeloid leukemia and EGFR/CD44-positive solid tumors, and the impact of novel discoveries in molecular tumor profiles on future chemotherapeutic protocols.

Toxicological study of doxorubicin-loaded PLGA nanoparticles for the treatment of glioblastoma

Doxorubicin loaded in poloxamer 188-coated PLGA nanoparticles (Dox-NP + P188) was shown to produce a high antitumor effect against the experimental orthotopic 101.8 glioblastoma in rats upon intravenous administration. The objective of the present study was to evaluate the acute and chronic toxicity of this nanoformulation. The parent drug was used as a reference formulation. Acute toxicity of doxorubicin-loaded nanoparticles in mice and rats was similar to that of free doxorubicin. The chronic toxicity study was conducted in Chinchilla rabbits; the treatment regimen consisted of 30 daily intravenous injections using two dosage levels: 0.22 mg/kg/day and 0.15 mg/kg/day. The study included assessment of the body weight, hematological parameters, blood biochemical parameters, urinalysis, and pathomorphological evaluation of the internal organs. The results of the study demonstrated that the hematological, cardiac, and testicular toxicity of doxorubicin could be reduced by binding the drug to PLGA nanoparticles. Coating of PLGA nanoparticles with poloxamer 188 contributed to the reduction of cardiotoxicity. Functional and morphological abnormalities caused by the nanoparticulate doxorubicin were dose-dependent and reversible. Altogether these results provide evidence that the PLGA-based nanoformulation not only might enable the broadening of the spectrum of doxorubicin activity but also an improvement of its safety profile.

Metal Nanomaterial Toxicity Variations Within the Vascular System

Engineered nanomaterials (ENM) are anthropogenic materials with at least one dimension less than 100 nm. Their ubiquitous employment in biomedical and industrial applications in the absence of full toxicological assessments raises significant concerns over their safety on human health. This is a significant concern, especially for metal and metal oxide ENM as they may possess the greatest potential to impair human health. A large body of literature has developed that reflects adverse systemic effects associated with exposure to these materials, but an integrated mechanistic framework for how ENM exposure influences morbidity remains elusive. This may be due in large part to the tremendous diversity of existing ENM and the rate at which novel ENM are produced. In this review, the influence of specific ENM physicochemical characteristics and hemodynamic factors on cardiovascular toxicity is discussed. Additionally, the toxicity of metallic and metal oxide ENM is presented in the context of the cardiovascular system and its discrete anatomical and functional components. Finally, future directions and understudied topics are presented. While it is clear that the nanotechnology boom has increased our interest in ENM toxicity, it is also evident that the field of cardiovascular nanotoxicology remains in its infancy and continued, expansive research is necessary in order to determine the mechanisms via which ENM exposure contributes to cardiovascular morbidity.

Review : Biodegradable Microcapsular Drug Delivery Systems: Manufacturing Methodology, Release Control and Targeting Prospects

An overview of the subject of biodegradable microcapsular drug delivery systems is presented from a polymer chemist's viewpoint. Various polymerization and microencapsulation techniques (including emulsion polymerization, interfacial polycondensation, suspension crosslinking, coacer vation/phase separation and solvent evaporation/extraction) suitable for the preparation of biodegradable microcapsules based on proteins, polysaccharides, polyesters, polyamides, or cyanoacrylates are described. Drug release from biodegradable microcapsules is discussed, and examples are presented to illus trate how the rate of drug release can be controlled by adjusting parameters such as microcapsule size, porosity, and crosslinking. Prospects of site-specific chemotherapy by means of passive and active targeting of microcapsular drug carriers are also analyzed.

Delivery of cancer therapeutics to extracellular and intracellular targets: Determinants, barriers, challenges and opportunities

Advances in molecular medicine have led to identification of worthy cellular and molecular targets located in extracellular and intracellular compartments. Effectiveness of cancer therapeutics is limited in part by inadequate delivery and transport in tumor interstitium. Parts I and II of this report give an overview on the kinetic processes in delivering therapeutics to their intended targets, the transport barriers in tumor microenvironment and extracellular matrix (TME/ECM), and the experimental approaches to overcome such barriers. Part III discusses new concepts and findings concerning nanoparticle-biocorona complex, including the effects of TME/ECM. Part IV outlines the challenges in animal-to-human translation of cancer nanotherapeutics. Part V provides an overview of the background, current status, and the roles of TME/ECM in immune checkpoint inhibition therapy, the newest cancer treatment modality. Part VI outlines the development and use of multiscale computational modeling to capture the unavoidable tumor heterogeneities, the multiple nonlinear kinetic processes including interstitial and transvascular transport and interactions between cancer therapeutics and TME/ECM, in order to predict the in vivo tumor spatiokinetics of a therapeutic based on experimental in vitro biointerfacial interaction data. Part VII provides perspectives on translational research using quantitative systems pharmacology approaches.

Current understanding of synergistic interplay of chitosan nanoparticles and anticancer drugs: merits and challenges

Recent advances have been made in cancer chemotherapy through the development of conjugates for anticancer drugs. Many drugs have problems of poor stability, water insolubility, low selectivity, high toxicity, and side effects. Most of the chitosan nanoparticles showed to be good drug carriers because of their biocompatibility, biodegradability, and it can be readily modified. The anticancer drug with chitosan nanoparticles displays efficient anticancer effects with a decrease in the adverse effects of the original drug due to the predominant distribution into the tumor site and a gradual release of free drug from the conjugate which enhances drug solubility, stability, and efficiency. In this review, we discuss wider applications of numerous modified chitosan nanoparticles against different tumors and also focusing on the administration of anticancer drugs through various routes. We propose the interaction between nanosized drug carrier and tumor tissue to understand the synergistic interplay. Finally, we elaborate merits of drug delivery system at the tumor site, with emphasizing future challenges in cancer chemotherapy.

Biodistribution and in vivo activities of tumor-associated macrophage-targeting nanoparticles incorporated with doxorubicin

Tumor-associated macrophages (TAMs) are increasingly considered a viable target for tumor imaging and therapy. Previously, we reported that innovative surface-functionalization of nanoparticles may help target them to TAMs. In this report, using poly(lactic-co-glycolic) acid (PLGA) nanoparticles incorporated with doxorubicin (DOX) (DOX-NPs), we studied the effect of surface-modification of the nanoparticles with mannose and/or acid-sensitive sheddable polyethylene glycol (PEG) on the biodistribution of DOX and the uptake of DOX by TAMs in tumor-bearing mice. We demonstrated that surface-modification of the DOX-NPs with both mannose and acid-sensitive sheddable PEG significantly increased the accumulation of DOX in tumors, enhanced the uptake of the DOX by TAMs, but decreased the distribution of DOX in mononuclear phagocyte system (MPS), such as liver. We also confirmed that the acid-sensitive sheddable PEGylated, mannose-modified DOX-nanoparticles (DOX-AS-M-NPs) targeted TAMs because depletion of TAMs in tumor-bearing mice significantly decreased the accumulation of DOX in tumor tissues. Furthermore, in a B16-F10 tumor-bearing mouse model, we showed that the DOX-AS-M-NPs were significantly more effective than free DOX in controlling tumor growth but had only minimum effect on the macrophage population in mouse liver and spleen. The AS-M-NPs are promising in targeting cytotoxic or macrophage-modulating agents into tumors to improve tumor therapy.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Effects of particle size and surface modification on cellular uptake and biodistribution of polymeric nanoparticles for drug delivery

PURPOSE

To investigate the effects of the particle size and surface coating on the cellular uptake of the polymeric nanoparticles for drug delivery across the physiological drug barrier with emphasis on the gastrointestinal (GI) barrier for oral chemotherapy and the blood-brain barrier (BBB) for imaging and therapy of brain cancer.

METHODS

Various sizes of commercial fluorescent polystyrene nanoparticles (PS NPs) (viz 20 50, 100, 200 and 500 nm) were modified with the d-α-tocopheryl polyethylene glycol 1,000 succinate (vitamin E TPGS or TPGS). The size, surface charge and surface morphology of PS NPs before and after TPGS modification were characterized. The Caco-2 and MDCK cells were employed as an in vitro model of the GI barrier for oral and the BBB for drug delivery into the central nerve system respectively. The distribution of fluorescent NPs after i.v. administration to rats was analyzed by the high performance liquid chromatography (HPLC).

RESULTS

The in vitro investigation showed enhanced cellular uptake efficiency for PS NPs in both of Caco-2 and MDCK cells after TPGS surface coating. In vivo investigation showed that the particle size and surface coating are the two parameters which can dramatically influence the NPs biodistribution after intravenous administration. The TPGS coated NPs of smaller size (< 200 nm) can escape from recognition by the reticuloendothelial system (RES) and thus prolong the half-life of the NPs in the blood system.

CONCLUSIONS

TPGS-coated PS NPs of 100 and 200 nm sizes have potential to deliver the drug across the GI barrier and the BBB.

Effects of surface modification on delivery efficiency of biodegradable nanoparticles across the blood–brain barrier

Aim: The aim of this work was to investigate the effect of surface modification of biodegradable nanoparticles on their cellular uptake, cytotoxicity and biodistribution for the delivery of imaging and therapeutic agents across the blood–brain barrier. Materials & methods: Coumarin-6- and docetaxel-encapsulated poly(D,L-lactide-co-glycolide) nanoparticles were prepared by a modified single emulsion method using polyvinyl alcohol or D-α-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS or TPGS) as emulsifier. The nanoparticles’ surface was further modified with surfactants such as polysorbate-80 (Tween® 80), poloxamer 188 (F68) and poloxamer 407 (F127) to enhance cellular uptake of the NPs. Results: The F68-coated poly(D,L-lactide-co-glycolide) nanoparticles demonstrated the greatest cellular uptake and achieved highest fluorescence concentration in the brain tissues over those with T80 and F127 surface modification. Conclusion: Surface modification is a feasible and efficient strategy for nanoparticles made of biodegradable polymers to deliver diagnostic and therapeutic agents across the blood–brain barrier.

Cationic surface modification of PLG nanoparticles offers sustained gene delivery to pulmonary epithelial cells

Biodegradable polymeric nanoparticles are currently being explored as a nonviral gene delivery system; however, many obstacles impede the translation of these nanomaterials. For example, nanoparticles delivered systemically are inherently prone to adsorbing serum proteins and agglomerating as a result of their large surface/volume ratio. What is desired is a simple procedure to prepare nanoparticles that may be delivered locally and exhibit minimal toxicity while improving entry into cells for effectively delivering DNA. The objective of this study was to optimize the formulation of poly(D,L-lactide-co-glycolide) (PLG) nanoparticles for gene delivery performance to a model of the pulmonary epithelium. Using a simple solvent diffusion technique, the chemistry of the particle surface was varied by using different coating materials that adsorb to the particle surface during formation. A variety of cationic coating materials were studied and compared to more conventional surfactants used for PLG nanoparticle fabrication. Nanoparticles (approximately 200 nm) efficiently encapsulated plasmids encoding for luciferase (80-90%) and slowly released the same for 2 weeks. In A549 alveolar lung epithelial cells, high levels of gene expression appeared at day 5 for certain positively charged PLG particles and gene expression was maintained for at least 2 weeks. In contrast, PEI gene expression ended at day 5. PLG particles were also significantly less cytotoxic than PEI suggesting the use of these vehicles for localized, sustained gene delivery to the pulmonary epithelium.

Inverse targeting of diclofenac sodium to reticuloendothelial system-rich organs by sphere-in-oil-in-water (s/o/w) multiple emulsion containing poloxamer 403

Sphere-in-oil-in-water (s/o/w) multiple emulsions containing diclofenac sodium were prepared by gelatinization of inner aqueous phase. A further modified version (s/o/wp) of s/o/w was formulated by adding 5.0% w/v poloxamer 403 to the external aqueous phase during the second step of emulsification in order to affect the adsorptive coating on the surface (s/o/wp). The inverse targeting of reticuloendothelial system (RES) rich organs was compared with a non reticuloendothelial system after intravenous administration of s/o/w multiple emulsion (treatment I) and poloxamer containing s/o/wp multiple emulsion (treatment II). The amount of diclofenac sodium in the plasma and various organs was measured to elucidate the effect of inverse targeting to RES and targeting to other tissues in terms of the incorporated drug. After i.v. administration, the half life (34.65 vs.16.26 h) and apparent volume of distribution of diclofenac sodium (2815 vs. 1671.5 ml/kg) were significantly higher in treatment II than in treatment I. It is concluded that the amount of drug in RES rich organs (spleen, liver) were significantly lower than the values in non-RES organs such as lungs, inflammatory tissue (synovial fluid) in treatment II than in treatment I.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

Biodegradable microspheres for protein delivery

In a very short time, since their emergence, the field of controlled delivery of proteins has grown immensely. Because of their relatively large size, they have low transdermal bioavailabilities. Oral bioavailability is generally poor since they are poorly absorbed and easily degraded by proteolytic enzymes in the gastrointestinal tract. Ocular and nasal delivery is also unfavorable due to degradation by enzymes present in eye tissues and nasal mucosa. Thus parenteral delivery is currently most demanding and suitable for delivery of such molecules. In systemic delivery of proteins, biodegradable microspheres as parenteral depot formulation occupy an important place because of several aspects like protection of sensitive proteins from degradation, prolonged or modified release, pulsatile release patterns. The main objective in developing controlled release protein injectables is avoidance of regular invasive doses which in turn provide patient compliance, comfort as well as control over blood levels. This review presents the outstanding contributions in field of biodegradable microspheres as protein delivery systems, their methods of preparation, drug release, stability, interaction with immune system and regulatory considerations.

Nanoparticulate systems for brain delivery of drugs

The blood--brain barrier (BBB) represents an insurmountable obstacle for a large number of drugs, including antibiotics, antineoplastic agents, and a variety of central nervous system (CNS)-active drugs, especially neuropeptides. One of the possibilities to overcome this barrier is a drug delivery to the brain using nanoparticles. Drugs that have successfully been transported into the brain using this carrier include the hexapeptide dalargin, the dipeptide kytorphin, loperamide, tubocurarine, the NMDA receptor antagonist MRZ 2/576, and doxorubicin. The nanoparticles may be especially helpful for the treatment of the disseminated and very aggressive brain tumors. Intravenously injected doxorubicin-loaded polysorbate 80-coated nanoparticles were able to lead to a 40% cure in rats with intracranially transplanted glioblastomas 101/8. The mechanism of the nanoparticle-mediated transport of the drugs across the blood-brain barrier at present is not fully elucidated. The most likely mechanism is endocytosis by the endothelial cells lining the brain blood capillaries. Nanoparticle-mediated drug transport to the brain depends on the overcoating of the particles with polysorbates, especially polysorbate 80. Overcoating with these materials seems to lead to the adsorption of apolipoprotein E from blood plasma onto the nanoparticle surface. The particles then seem to mimic low density lipoprotein (LDL) particles and could interact with the LDL receptor leading to their uptake by the endothelial cells. After this the drug may be released in these cells and diffuse into the brain interior or the particles may be transcytosed. Other processes such as tight junction modulation or P-glycoprotein (Pgp) inhibition also may occur. Moreover, these mechanisms may run in parallel or may be cooperative thus enabling a drug delivery to the brain.

Nanoparticulate systems for brain delivery of drugs

The blood--brain barrier (BBB) represents an insurmountable obstacle for a large number of drugs, including antibiotics, antineoplastic agents, and a variety of central nervous system (CNS)-active drugs, especially neuropeptides. One of the possibilities to overcome this barrier is a drug delivery to the brain using nanoparticles. Drugs that have successfully been transported into the brain using this carrier include the hexapeptide dalargin, the dipeptide kytorphin, loperamide, tubocurarine, the NMDA receptor antagonist MRZ 2/576, and doxorubicin. The nanoparticles may be especially helpful for the treatment of the disseminated and very aggressive brain tumors. Intravenously injected doxorubicin-loaded polysorbate 80-coated nanoparticles were able to lead to a 40% cure in rats with intracranially transplanted glioblastomas 101/8. The mechanism of the nanoparticle-mediated transport of the drugs across the blood-brain barrier at present is not fully elucidated. The most likely mechanism is endocytosis by the endothelial cells lining the brain blood capillaries. Nanoparticle-mediated drug transport to the brain depends on the overcoating of the particles with polysorbates, especially polysorbate 80. Overcoating with these materials seems to lead to the adsorption of apolipoprotein E from blood plasma onto the nanoparticle surface. The particles then seem to mimic low density lipoprotein (LDL) particles and could interact with the LDL receptor leading to their uptake by the endothelial cells. After this the drug may be released in these cells and diffuse into the brain interior or the particles may be transcytosed. Other processes such as tight junction modulation or P-glycoprotein (Pgp) inhibition also may occur. Moreover, these mechanisms may run in parallel or may be cooperative thus enabling a drug delivery to the brain.

Effect of adsorption of bovine serum albumin on liposomal membrane characteristics

The effect of adsorption of bovine serum albumin (BSA) on the membrane characteristics of liposomes at pH 7.4 was examined in terms of zeta potential, micropolarity, microfluidity and permeability of liposomal bilayer membranes, where negatively charged L-alpha-dipalmitoylphosphatidylglycerol (DPPG)/L-alpha-dipalmitoylphosphatidylcholine (DPPC), negatively charged dicetylphosphate (DCP)/DPPC and positively charged stearylamine (SA)/DPPC mixed liposomes were used. BSA with negative charges adsorbed on negatively charged DPPG/DPPC mixed liposomes but did not adsorb on negatively charged DCP/DPPC and positively charged SA/DPPC mixed liposomes. Furthermore, the adsorption amount of BSA on the mixed DPPG/DPPC liposomes increased with increasing the mole fraction of DPPG in spite of a possible electrostatic repulsion between BSA and DPPG. Thus, the adsorption of BSA on liposomes was likely to be related to the hydrophobic interaction between BSA and liposomes. The microfluidity of liposomal bilayer membranes near the bilayer center decreased by the adsorption of BSA, while the permeability of liposomal bilayer membranes increased by the adsorption of BSA on liposomes. These results are considered to be due to that the adsorption of BSA brings about a phase separation in liposomes and that a temporary gap is consequently formed in the liposomal bilayer membranes, thereby the permeability of liposomal bilayer membranes increases by the adsorption of BSA.

Effects of lysozyme and bovine serum albumin on membrane characteristics of dipalmitoylphosphatidylglycerol liposomes

The effects of adsorption of two kinds of proteins on the membrane characteristics of liposomes were examined at pH 7.4 in terms of adsorption amounts of proteins on liposomes, penetrations of proteins into liposomal bilayer membranes, phase transition temperature, microviscosity and permeability of liposomal bilayer membranes, using positively charged lysozyme (LSZ) and negatively charged bovine serum albumin (BSA) as proteins and negatively charged L-alpha-dipalmitoylphosphatidylglycerol (DPPG) liposomes. The saturated adsorption amount of LSZ was 720 g per mol of liposomal DPPG, while that of BSA was 44 g per mol of liposomal DPPG. The penetration of LSZ into DPPG lipid membranes was greater than that of BSA. The microviscosity in the hydrophobic region of liposomal bilayer membranes increased due to adsorption (penetration) of LSZ or BSA, while the permeability of liposomal bilayer membranes increased. The gel-liquid crystalline phase transition temperature of liposomal bilayer membranes was not affected by adsorption of LSZ or BSA, while the DSC peak area (heat of phase transition) decreased with increasing adsorption amount of LSZ or BSA. It is suggested that boundary DPPG makes no contribution to the phase transition and that boundary DPPG and bulk DPPG are in the phase-separated state, thereby increasing the permeability of liposomal bilayer membranes through adsorption of LSZ or BSA. A possible schematic model for the adsorption of LSZ or BSA on DPPG liposomes was proposed.

Biodegradable polymeric nanoparticles as drug delivery devices

This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drug delivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surface modification methods as well as surface characterization are covered from 1990 through mid-2000.

Stabilized plasmid-lipid particles: pharmacokinetics and plasmid delivery to distal tumors following intravenous injection

A previous study has shown that plasmid DNA can be encapsulated in lipid particles (SPLP, "stabilized plasmid lipid particles") of approximately 70 nm diameter composed of 1,2-dioleoyl-3-phosphatidyl-ethanolamine (DOPE), the cationic lipid N,N-dioleoyl-N,N-dimethylammonium chloride (DODAC) and poly(ethylene glycol) conjugated to ceramide (PEG-Cer) using a detergent dialysis process (Wheeler et al. (1999) Gene Therapy 6, 271-281). In this work we evaluated the potential of these SPLPs as systemic gene therapy vectors, determining their pharmacokinetics and the biodistribution of the plasmid and lipid components. It is shown that the blood clearance and the biodistribution of the SPLPs can be modulated by varying the acyl chain length of the ceramide group used as lipid anchor for the PEG polymer. Circulation lifetimes observed for SPLPs with PEG-CerC14 and PEG-CerC20 were t(1/2) = approximately 1 and approximately 10 h, respectively. The SPLPs are stable while circulating in the blood and the encapsulated DNA is fully protected from degradation by serum nucleases. The accelerated clearance of SPLPs with PEG-CerC14 is accompanied by increased accumulation in liver and spleen as compared to PEG-CerC20 SPLPs. Delivery of intact plasmid to liver and spleen was detected. Significant accumulation (approximately 10% of injected dose) of the long circulating SPLPs with PEG-CerC20 in a distal tumor (Lewis lung tumor in the mouse flank) was observed following i.v. application and delivery of intact plasmid to tumor tissue at approximately 6% injected dose/g tissue is demonstrated.

Body distribution in mice of intravenously injected camptothecin solid lipid nanoparticles and targeting effect on brain

The objective of the present study was to investigate the specific drug targeting of anticarcinogenic drugs, such as camptothecin (CA), after intravenous (i.v.) injection by incorporation into solid lipid nanoparticles (SLN). A CA loaded SLN suspension consisted of 0.1% (w/w) camptothecin, 2.0% (w/w) stearic acid, 1.5% (w/w) soybean lecithin and 0.5% (w/w) polyoxyethylene-polyoxypropylene copolymer (Poloxamer 188) was prepared by high pressure homogenization. In vitro drug release was investigated in pH 7.4 phosphate-buffered saline at 37 degrees C. The concentrations of camptothecin in various organs were determined using reversed-phase high-performance liquid chromatography with a fluorescence detector after i.v. administration of CA-SLN and a camptothecin control solution (CA-Sol). The results showed that the CA-SLN had an average diameter 196.8 nm with a Zeta potential of -69.3 mV and in vitro drug release was achieved for up to a week. In tested organs, the AUC/dose and the mean residence times (MRT) of CA-SLN were much higher than those of CA-Sol, especially in brain, heart and reticuloendothelial cells containing organs. The brain AUC ratio of CA-SLN to CA-Sol was the highest among the tested organs. These results indicate that SLN are a promising sustained release and drug targeting system for lipophilic antitumour drugs, and may also allow a reduction in dosage and a decrease in systemic toxicity.

Influence of the surfactant concentration on the body distribution of nanoparticles

The rapid reticuloendothelial system (RES) uptake of nanoparticles after i.v. injection, especially by the liver, can be reduced and the body distribution can be altered by coating them with non-ionic surfactants. In the present work 2-14C-poly(methyl methacrylate) nanoparticles were coated with poloxamine 908 and polysorbate 80, and the influence of different surfactant concentrations on the body distribution was investigated. These surfactants were chosen because earlier studies showed that poloxamine 908 was very effective in decreasing the liver uptake and keeping the nanoparticles in circulation, whereas polysorbate 80 was the most effective surfactant to direct the particles to organs that do not belong to the RES. Above nanoparticles were injected i.v. to rats and the animals were sacrificed after 30 min. Below a surfactant concentration of 0.1% the nanoparticle preparations behaved like uncoated particles. At a 0.1% concentration a very sudden and significant change in the body distribution occurred with poloxamine 908. The liver concentration decreased from about 75% of the dose to 13% and stayed at this level at higher surfactant concentrations. This decrease was combined with a similar sudden complementary increase in blood and other organ and tissue concentrations. With polysorbate 80 the decrease in liver concentration and increase in the blood and the other organ levels was gradual and became important only above 0.5% surfactant concentration. The results indicate that the type of interaction and the strength of the adsorptive binding to the nanoparticles are different with different surfactants. This in turn leads to different body distribution patterns after i.v. injection of surfactant coated nanoparticles.

Polymeric micelles as carriers of diagnostic agents

This review deals with diagnostic applications of polymeric micelles composed of amphiphilic block-copolymers. In aqueous solutions these polymers spontaneously form particles with diameter 20-100 nm. A variety of diagnostic moieties can be incorporated covalently or non-covalently into the particulates with high loads. Resulting particles can be used as particulate agents for diagnostic imaging using three major imaging modalities: gamma-scintigraphy, magnetic resonance imaging and computed tomography. The use of polyethyleneoxide-diacyllipid micelles loaded with chelated (111)In/Gd(3+) as well as iodine-containing amphiphilic copolymer in percutaneous lymphography and blood pool/liver imaging are discussed as specific examples.

Polymer-coated long-circulating microparticulate pharmaceuticals

The field of long-circulating microparticulate drug carriers is reviewed. The protective effect of certain polymers including poly(ethylene glycol) on nanoparticulate carriers (liposomes, nanoparticles, micelles) is considered in terms of statistical behaviour of macromolecules in solution. Using liposomes as an example, the mechanism is discussed assuming that surface-grafted chains of flexible and hydrophilic polymers form dense 'conformational clouds' preventing other macromolecules from interaction with the surface even at low concentrations of the protecting polymer. The scale of the protective effect is interpreted as the balance between the energy of the hydrophobic anchor interaction with the liposome membrane core or with the particle surface and the energy of the polymer chain free motion in solution. The possibility of using protecting polymers other than poly(ethylene glycol) is analysed, and examples of such polymers are given, based on polymer-coated liposome biodistribution data. General requirements for protecting polymers are formulated. Sterically protected nanoparticles and micelles are considered, and differences in steric protection of liposomes and particles are discussed. The problem of the preparation of drug carriers combining longevity and targetability is analysed. The biological consequences of steric protection of drug carriers with surface-grafted polymers are discussed, and possible clinical applications for long-circulating pharmaceutical carriers are considered.

Block-copolymer of polyethylene glycol and polylysine as a carrier of organic iodine: design of long-circulating particulate contrast medium for X-ray computed tomography

In order to obtain small, polymer-stabilized particulate carriers for organic iodine to serve as a contrast agent for X-ray computed tomography (CT) an attempt was made to design a carrier based on polymeric micelles. Here we describe the synthesis of an iodine-containing amphiphilic block-copolymer which can micellize in aqueous solutions. The two blocks of the copolymer consisted of methoxypoly(ethyleneglycol) and poly[epsilon,N-(triiodobenzoyl)-L-lysine]. Upon dispersion in water, the block copolymer formed particles with average diameter 80 nm and iodine content up to 44.7%. The particles start to dissociate to the individual polymeric chains in the concentration range of 0.05-0.5 microM in water at 23 degrees C. Upon intravenous injection at 250 mg of iodine/kg (570 mg of the agent/kg) in rabbits the medium demonstrated exceptional 24 hr half-life in the blood substantiating corona/core structure of the particles with PEG chains protecting the iodine-containing core. The possible use of these particulates as contrast medium for X-ray computed tomography is discussed.

Circulation time and body distribution of 14C-labeled amino-modified polystyrene nanoparticles in mice

Commercially available amino-modified polystyrene particles of size range 100-1,000 nm were radioactively labeled with [14C]-formaldehyde. A study of the circulation time and body distribution of these particles was carried out in mice. The animals were sacrificed at 1-30 min after intravenous administration of the particles. The blood and organ (liver, spleen, lung) profiles of particles were determined by measuring their radioactivity by means of liquid scintillation counting. In general, larger particles were eliminated from blood faster than smaller particles. The blood elimination half-life ranged from 1.36 to 4.92 min. The particles were mainly taken up by the liver with larger particles being taken up faster than the smaller particles. At 30 min after injection, 60% of the administered 100 nm particles were present in the liver, whereas 85% of the 100 nm particles were found in the liver. Accumulation in the spleen was 1-3% of the total number administered in the entire size range. At 1 min after injection, less than 3% of the total dose administered was present in the lungs and this value decreased rapidly to less than 1% at 2 min. The only exception occurred for 100 nm, where 2.35% was present in the lungs at 2 min after injection.

The controlled intravenous delivery of drugs using PEG-coated sterically stabilized nanospheres

Injectable blood persistent particulate carriers have important therapeutic application in site-specific drug delivery or medical imaging. However, injected particles are generally eliminated by the reticuloendothelial system within minutes after administration and accumulate in the liver and spleen. To obtain a coating that might prevent opsonization and subsequent recognition by the macrophages, sterically stabilized nanospheres were developed using amphiphilic diblock or multiblock copolymers. The nanospheres are composed of a hydrophilic polyethylene glycol coating and a biodegradable core in which various drugs were encapsulated. Hydrophobic drugs, such as lidocaine, were entrapped up to 45 wt% and the release kinetics were governed by the polymer physico-chemical characteristics. Plasma protein adsorption was drastically reduced on PEG-coated particles compared to non-coated ones. Relative protein amounts were time-dependent. The nanospheres exhibited increased blood circulation times and reduced liver accumulation, depending on the coating polyethylene glycol molecular weight and surface density. They could be freeze-dried and redispersed in aqueous solutions and possess good shelf stability. It may be possible to tailor "optimal" polymers for given therapeutic applications.

Poloxamer-coated three-ply-walled microcapsules for controlled delivery of diclofenac sodium

The three-ply-walled-based system for controlled delivery of diclofenac was developed. The preparation of three-ply-walled microcapsules is essentially based on the technique of multiple-emulsion formation polymer at the interface followed by rigidization of the wall on evaporation of solvent. The protective colloids with surface-active properties were selected for the present study, viz. acacia gelatin, polyvinyl alcohol and sodium alginate. Ethyl cellulose was taken as hydrophobic polymer. The acacia/ethylcellulose/acacia-based three-ply-walled microcapsule system was selected for further studies. The three-ply-walled microcapsule were subsequently coated with poloxamer 188. The non-ionic hydrophilic surfactant coating retards uptake into the reticuloendothelial system. The coated and uncoated microcapsules were characterized for in vitro and in vivo performance. The microcapsules were noted to provide sustained release of the contained diclofenac. The plasma level observed indicated that poloxamer coating results in prolonged release of the drug. Organ distribution demonstrated a different distribution pattern when compared with uncoated microcapsules.