Evaluation of the effect of SMA–pirarubicin micelles on colorectal cancer liver metastases and of hyperbaric oxygen in CBA mice

Tetrahydropyranyladriamycin (THP or pirarubicin) destroys tumors via several mechanisms; one of which involves the production of ROS that requires molecular oxygen for its generation. SMA forms stable self-assembled associated micelles with pirarubicin (SMA–pirarubicin), and confers macromolecular characteristics to pirarubicin. This micellar macromolecular drug is selectively delivered to solid tumors via the EPR effect and its preferential tumor accumulation suppresses the systemic toxicity whilst its prolonged high concentration at the site of tumor enhances its efficacy much higher compared to free pirarubicin. Administration of SMA–pirarubicin micelle under HBO can further enhance the delivery of molecular oxygen that facilitates tumor selective generation of ROS, thus augmenting its antitumor potency. In this study, we evaluated the efficacy of SMA–pirarubicin micelles either as single drug or in combination with HBO in a mouse metastatic colorectal cancer model. At or below the maximum tolerated dose, SMA–pirarubicin remarkably reduced metastatic tumor nodules and it was far more effective than free pirarubicin. The data also suggests a potential benefit of combined therapy of HBO with micellar anthracyclins.     

Polymeric micelles of zinc protoporphyrin for tumor targeted delivery based on EPR effect and singlet oxygen generation

Polymeric micelles of zinc protoporphyrin (ZnPP) with water soluble biocompatible and amphiphilic polymer, polyethylene glycol (PEG) demonstrated unique characteristics to target tumor tissues selectively based on the enhanced permeability and retention (EPR) effect. The micellar macromolecular drug of ZnPP (SMA-ZnPP and PEG-ZnPP) previously showed notable anticancer activity as a consequence of selective tumor targeting ability and its potent HO-1 inhibitory potential, resulting in suppressed biliverdin/bilirubin production in tumors thereby leading to oxystress induced tumor cell killing. Furthermore, recent findings also showed that ZnPP efficiently generated reactive singlet oxygen under illumination of visible light, laser, or xenon light source, which could augment its oxystress induced cell killing abilities. In the present paper, we report the synergistic effects of light induced photosensitizing capabilities and HO-1 inhibitory potentials of these unique micelles when tested in vitro and in vivo on tumor models under localized, mild illumination conditions using a tungsten-xenon light source. The results indicate that these water soluble polymeric micelles of ZnPP portend to be promising candidates for targeted chemotherapy as well as photodynamic therapy against superficial tumors as well as solid tumors located at light penetrable depths.     

Disease-directed design of biodegradable polymers: Reactive oxygen species and pH-responsive micellar nanoparticles for anticancer drug delivery

Herein, we report reactive oxygen species (ROS)- and pH-responsive biodegradable polyethylene glycol (PEG)-block-polycarbonate by installing thioether groups onto the polycarbonate and its self-assembled core/shell structured micelles for anticancer drug delivery. Oxidation of thioethers to sulfoxide and subsequently sulfone induces an increase in hydrophilicity, resulting in more hydrophilic micellar core. This phase-change caused the micelles to swell and enhance cargo release. Carboxylic acid groups have also been installed onto thioether-containing polycarbonate to promote loading of amine-containing anticancer doxorubicin through electrostatic interaction. Urea-functionalized thioether-containing PEG-block-polycarbonates were synthesized to mix with the acid-functionalized PEG-block-polycarbonate for stabilizing micelle structure through hydrogen-bonding interaction. The mixed micelles were 50?nm in diameter and had a 25?wt% loading capacity for doxorubicin. Enhanced drug release from the micelles was triggered by low pH and high content of ROS. Drug-encapsulated micelles accumulated in tumors through leaky tumor vasculature in PC-3 human prostate cancer xenograft mouse model.     

Polymeric micelles of zinc protoporphyrin for tumor targeted delivery based on EPR effect and singlet oxygen generation

Polymeric micelles of zinc protoporphyrin (ZnPP) with water soluble biocompatible and amphiphilic polymer, polyethylene glycol (PEG) demonstrated unique characteristics to target tumor tissues selectively based on the enhanced permeability and retention (EPR) effect. The micellar macromolecular drug of ZnPP (SMA–ZnPP and PEG–ZnPP) previously showed notable anticancer activity as a consequence of selective tumor targeting ability and its potent HO-1 inhibitory potential, resulting in suppressed biliverdin/bilirubin production in tumors thereby leading to oxystress induced tumor cell killing. Furthermore, recent findings also showed that ZnPP efficiently generated reactive singlet oxygen under illumination of visible light, laser, or xenon light source, which could augment its oxystress induced cell killing abilities. In the present paper, we report the synergistic effects of light induced photosensitizing capabilities and HO-1 inhibitory potentials of these unique micelles when tested in vitro and in vivo on tumor models under localized, mild illumination conditions using a tungsten–xenon light source. The results indicate that these water soluble polymeric micelles of ZnPP portend to be promising candidates for targeted chemotherapy as well as photodynamic therapy against superficial tumors as well as solid tumors located at light penetrable depths.     

Difunctional Pluronic copolymer micelles for paclitaxel delivery: synergistic effect of folate-mediated targeting and Pluronic-mediated overcoming multidrug resistance in tumor cell lines

A significant obstacle for successful chemotherapy with paclitaxel (PTX) is multidrug resistance (MDR) in tumor cells. Micelles and mixed micelles were prepared from Pluronic block copolymer P105 or L101 as PTX delivery systems for overcoming MDR. Both micelle systems were covalently modified with the targeting agent folic acid to recognize and bind a variety of tumor cells via their surface-overexpressed folate receptor. There was an increased level of uptake of folate-conjugated micellar PTX (i.e. FOL-P105/PTX, FOL-PL/PTX) compared to plain micellar PTX (i.e. P105/PTX, PL/PTX) in human breast cancer MDR cell sublines, MCF-7/ADR, and the uptake of folate-conjugated micellar PTX could be inhibited by free folic acid, which suggested that the level of uptake could be mediated by the folate receptor. The cytotoxicity of folate-conjugated micellar PTX in the MDR cell culture model was much higher compared with plain micellar PTX or free PTX, and the plain micellar PTX also has higher cytotoxicity than free PTX. Overall, the MDR cells are more susceptible to the cytotoxic effects of Pluronic micellar PTX than their parental cells. The introduction of folic acid into P105 or PL mixed micelles enhanced the cell-killing effect by active internalization. Increased internalization explained the improved cytotoxicity of the FOL-micellar PTX to tumor cells. We suggest that the combined mechanisms of folate-mediated active internalization and Pluronic-mediated overcoming MDR be beneficial in treatment of MDR solid tumors by targeting delivery of micellar PTX into the tumor cells where folate receptor is frequently overexpressed, reducing accumulation of micellar PTX in other tissues or organs and further reducing side effects and toxicities of the drug.     

Analytical Studies on Photochemical Behavior of Phototoxic Substances; Effect of Detergent Additives on Singlet Oxygen Generation

Purpose Monitoring of reactive oxygen species (ROS) generation from photoirradiated compounds would be effective for the prediction of the phototoxic potential. The aim of this investigation was to clarify the possible role of biomimetic vehicle systems on the photochemical properties of phototoxic compounds, focusing on the singlet oxygen generation. Materials and Methods Nine phototoxic and one non-phototoxic compounds (200 μM), dissolved in Tween 20, sodium laurate, or sodium dodecyl sulfate (SDS) micellar solution, were exposed to UVA/B light (250 W/m²), and singlet oxygen generation was monitored by RNO bleaching methodology. Photochemical properties of photosensitizers were also evaluated by UV measurement, and the interaction of photosensitizers with surfactant micelles was assessed by Z-potential and NMR spectroscopic analyses. Results All phototoxic compounds tended to generate singlet oxygen under light exposure in the all micellar solutions tested. There appeared to be some differences in photoreactivity of both cationic and anionic photosensitizers among the micelles tested, whereas ROS data on anthracene, dissolved in three micellar solutions, were found to be quite similar. Photosensitizers exhibited no significant changes in UV spectral patterns among the dissolving micellar solutions. Addition of cationic photosensitizer at the final concentration of 100 μM into 100 mM SDS solution resulted in the 20 mV increase of zeta potential and transition of NMR spectral pattern, which would reflect the electrostatic interaction with anionic micelles. Conclusion Based on the data obtained, the photoreactivity of photosensitizing molecules, especially cationic and anionic photosensitizers, strongly depends on the physicochemical properties of the microenvironment.     

Ultrasound-enhanced tumor targeting of polymeric micellar drug carriers

Cancer chemotherapy is often complicated by toxic side effects of anticancer drugs. We are developing a new modality of tumor chemotherapy aimed at circumventing side effects of treatment via drug targeting to tumors. The technique is based on drug encapsulation in polymeric micelles followed by a controlled drug release at a target site triggered by ultrasonic irradiation. The encouraging in vitro results of previous years warranted animal experiments for verification of the in vivo feasibility of the proposed technique. We report here on the effect of ultrasound on a biodistribution of a micellar drug carrier (fluorescently labeled Pluronic micelles) in ovarian cancer-bearing nu/nu mice. The degree of carrier accumulation in the cells of various organs was characterized by flow cytometry. Polymeric micelles were formed in either pure Pluronic P-105 solutions (unstabilized micelles) or 1:1 (weight) mixtures of Pluronic P-105 with PEG-diacylphospholipid (stabilized micelles). Intraperitoneal (ip) and intravenous (iv) injections were compared. The data showed that a 30 s ultrasonic irradiation by 1 or 3 MHz ultrasound applied locally to the tumor significantly enhanced accumulation of Pluronic in the tumor cells, which was observed for both ip and iv injections and for unstabilized and stabilized micelles. The data indicated targeting of Pluronic micelles to the tumors; the degree of targeting was enhanced by a local tumor sonication.     

Investigation on design of stable etoposide-loaded PEG-PCL micelles: effect of molecular weight of PEG-PCL diblock copolymer on the in vitro and in vivo performance of micelles

In the present study, six different molecular weight diblock copolymer of methoxy poly (ethylene glycol)-b-poly (ε-caprolactone) (MPEG-PCL) were synthesized and characterized and was used for fabrication of etoposide-loaded micelles by nanoprecipitation technique. The particle size and percentage drug entrapment of prepared micelles were found to be dependent on the molecular weight of PCL block and drug to polymer ratio. The maximum drug loading of 5.32% was found in micellar formulation MPEG5000-PCL10000, while MPEG2000-PCL2000 exhibited 2.73% of maximum drug loading. A variation in the fixed aqueous layer thickness and PEG surface density of micellar formulations was attributed to difference in MPEG molecular weight and interaction of PEG and PCL block of copolymer. The MPEG2000-PCL2000 micelles demonstrated poor in vitro stability among other micellar formulations, due to its interaction with bovine serum albumin and immediate release of drug from micelles. Furthermore, plain etoposide and MPEG2000-PCL2000 micelles exhibited greater extent of hemolysis, due to presence of surfactants and faster release of drug from micelles, respectively. The biodistribution studies carried out on Ehrlich ascites tumor-bearing Balb/C mice confirmed higher accumulation of etoposide-loaded micellar formulation at tumor site compared to plain etoposide due to enhanced permeability and retention effect.     

Micellar Delivery of Flutamide Via Milk Protein Nanovehicles Enhances its Anti-Tumor Efficacy in Androgen-Dependent Prostate Cancer Rat Model

Purpose

This article describes the preparation, physicochemical characterization and in vivo assessment of parenteral colloidal formulation of flutamide (FLT) based on biocompatible casein (CAS) self-assembled micelles in order to control drug release, enhance its antitumor efficacy and reduce its hepatotoxicity.

Methods

Spray-drying technique was successfully utilized to obtain solidified redispersible drug-loaded micelles.

Results

Spherical core-shell micelles were obtained with a particle size below 100 nm and a negative zeta potential above ?30 mV exhibiting a sustained drug release up to 5 days. After intravenous administration into prostate cancer bearing rats for 28 days, FLT-loaded CAS micelles showed a higher antitumor efficacy as revealed by significantly higher reduction in PSA serum level (65.95%) compared to free FLT (55.43%). Moreover, micellar FLT demonstrated a marked decrease in relative weights of both prostate tumor and seminal vesicle (34.62 and 24.59%) compared to free FLT (11.86 and 17.74%), respectively. These antitumor responses were associated with notable reduction of cell proliferation, intratumoral angiogenesis and marked increase of tumor apoptosis. A significantly lower risk of hepatotoxicity was observed by micellar FLT as evidenced by lower alanine aminotransferase (ALT) serum level compared to free FLT.

Conclusions

Overall this approach suggested that CAS micelles might be an ideal candidate for intravenous delivery of hydrophobic anticancer drugs.     

Targeted Delivery of Doxorubicin via CD147-Mediated ROS/pH Dual-Sensitive Nanomicelles for the Efficient Therapy of Hepatocellular Carcinoma

Low accumulation in tumor sites and slow intracellular drug release remain as the obstacles for nanoparticles to achieve effective delivery of chemotherapeutic drugs. In this study, multifunctional micelles were designed to deliver doxorubicin (Dox) to tumor sites to provide more efficient therapy against hepatic carcinoma. The micelles were based on pH-responsive carboxymethyl chitosan (CMCh) modified with a reactive oxygen species (ROS)-responsive segment phenylboronic acid pinacol ester (BAPE) and an active targeted ligand CD147 monoclonal antibody. The Dox-loaded micelles provided rapid and complete drug release in pH 5.3 incubation conditions with 1 mM H₂O₂. In addition, an in vitro cell uptake study revealed that CD147 modification significantly enhanced cellular internalization due to the high affinity to CD147 receptors, which are overexpressed on tumor cells. An in vivo study revealed that CD147-modified micellar formulations exhibited high accumulation in tumor sites and markedly enhanced antiproliferation effects with fewer side effects than other formulations. In conclusion, this CD147 receptor targeted delivery system with ROS/pH dual sensitivity provides a promising strategy for the treatment of hepatic carcinoma.     

Stabilized micelles as delivery vehicles for paclitaxel

Paclitaxel is an antineoplastic drug used against a variety of tumors, but its low aqueous solubility and active removal caused by P-glycoprotein in the intestinal cells hinder its oral administration. In our study, new type of stabilized Pluronic micelles were developed and evaluated as carriers for paclitaxel delivery via oral or intravenous route. The pre-stabilized micelles were loaded with paclitaxel by simple solvent/evaporation technique achieving high encapsulation efficiency of approximately 70%. Gastrointestinal transit of the developed micelles was evaluated by oral administration of rhodamine-labeled micelles in rats. Our results showed prolonged gastrointestinal residence of the marker encapsulated into micelles, compared to a solution containing free marker. Further, the oral administration of micelles in mice showed high area under curve of micellar paclitaxel (similar to the area of i.v. Taxol(?)), longer mean residence time (9-times longer than i.v. Taxol(?)) and high distribution volume (2-fold higher than i.v. Taxol(?)) indicating an efficient oral absorption of paclitaxel delivered by micelles. Intravenous administration of micelles also showed a significant improvement of pharmacokinetic parameters of micellar paclitaxel vs. Taxol(?), in particular higher area under curve (1.2-fold), 5-times longer mean residence time and lower clearance, indicating longer systemic circulation of the micelles.     

Tumor-targeted induction of oxystress for cancer therapy

Reactive oxygen species (ROS), such as superoxide anion radicals (O.-2) and hydrogen peroxide (H2O2) are potentially harmful by-products of normal cellular metabolism that directly affect cellular functions. ROS is generated by all aerobic organisms and it seems to be indispensable for signal transduction pathways that regulate cell growth and reduction-oxidation (redox) status. However, overproduction of these highly reactive oxygen metabolites can initiate lethal chain reactions, which involve oxidation and damage to structures that are crucial for cellular integrity and survival. In fact, many antitumor agents, such as vinblastine, cisplatin, mitomycin C, doxorubicin, camptothecin, inostamycin, neocarzinostatin and many others exhibit antitumor activity via ROS-dependent activation of apoptotic cell death, suggesting potential use of ROS as an antitumor principle. Thus, a unique anticancer strategy named "oxidation therapy" has been developed by inducing cytotoxic oxystress for cancer treatment. This goal could be achieved mainly by two methods, namely, (i) inducing the generation of ROS directly to solid tumors and (ii) inhibiting the antioxidative enzyme (defense) system of tumor cells. Since 1950s, many strategies have been employed based on the first method, namely, administration of ROS per se (e.g. H2O2) or ROS generating enzyme to tumor bearing animals. However no successful and practical results were obtained probably because of the lack of tumor selective ROS delivery and hence resulting in subsequent induction of severe side effects. To overcome these obstacles, we developed polyethylene glycol (PEG) conjugated O.-2 or H2O2-generating enzymes, xanthine oxidase (XO) and D-amino acid oxidase (DAO) (PEG-DAO) respectively. More recently, a pegylated (PEG) zinc protoporphyrin (PEG-ZnPP) and a highly water soluble micellar formulation of ZnPP based on amphiphilic styrene maleic acid (SMA) copolymer, SMA-ZnPP, are prepared, which are potent inhibitors of heme oxygenase-1 (HO-1). HO-1 is a major antioxidative enzyme of tumors, that is different in mechanism of catalase or superoxide dismutase (SOD). Consequently, both PEG-enzymes and PEG-ZnPP exhibited superior in vivo pharmacokinetics than their parental molecules, particularly in tumor delivery by taking advantage of the EPR effect of macromolecular nature, and thus showed remarkable antitumor effects suggesting the potentials of this anticancer therapeutic for clinical application. Furthermore, it has been well known that many antioxidative enzymes such as catalase, SOD are down-regulated in most solid tumors in vivo. On the contrary, HO-1 is highly upregulated and it plays a very important role of antioxidation, because HO-1 generates biliverdin, which being converted to bilirubin exhibits a very potent antioxidative effect, and hence antiapoptosis in tumors. Thus this oxidation therapy, by inhibiting this HO-1 dependent antioxidant (bilirubin) formation by ZnPP, and by enhancing ROS generation, is expected to offer a powerful therapeutic modality for future anticancer therapy.     

紫杉醇Pluronic P105聚合物胶束的制备、表征与逆转肿瘤多药耐药性的体外研究

药物递送系统是克服肿瘤多药耐药性(MDR)的一种新策略。本文以聚合物胶束系统和难溶性药物紫杉醇(PTX)为研究对象，旨在制备一种新型的PTX给药系统，既能增溶难溶性药物，又具有克服肿瘤MDR的能力。以Pluronic P105为载体，采用固体分散-水化法制备PTX聚合物胶束，并以星点设计-效应面优化法进行处方优化。对其粒径、体外释放等性质进行表征后，以人耐药卵巢癌细胞SKOV-3/PTX为细胞模型，体外评价PTX聚合物胶束的细胞摄取及其逆转肿瘤细胞耐药性的作用。结果显示，聚合物胶束制剂的载药量约为1.1%、药物浓度约为700 μg·mL^-1、平均粒径约为24 nm。胶束制剂与普通制剂(Taxol)在6 h内的累积释放分别为45.4%和95.2%，前者具有较强的缓释作用；胶束制剂与Taxol对SKOV-3/PTX的IC₅₀值分别为1.14和5.11 μg·mL^-1，二者的耐药逆转指数(RRI)分别为9.65和2.15。胶束制剂可促进耐药细胞对P-糖蛋白(P-gp)底物(PTX或Rhodamine-123)的摄取。结果表明，Pluronic P105可有效增溶难溶性药物PTX，并形成具有较强缓释作用的纳米级聚合物胶束制剂，该制剂可显著提高PTX对人卵巢癌耐药细胞的细胞毒性，能逆转其耐药性。     

Enhanced uptake and cytotoxity of folate-conjugated mitoxantrone-loaded micelles via receptor up-regulation by dexamethasone

Folate conjugated amphiphilic polymeric micelles have attracted much attention for active targeted delivery of drugs in folate receptor α (FR-α) positive tumors. However, the efficacy improvement of targeted delivery folate-based nanovehicles was limited by the abundance of FR-α on the surface of tumor cells. Recently, it was found that FR-α expression of Hela cells could be up-regulated by modulators such as dexamethasone, which open a new avenue to enhance the efficiency of targeted delivery from the biological view. In this study, folate-conjugated or plain lipid-core micelles loaded with fluorescent coumarin 6 or mitoxantrone (MTN) were prepared by self-assembly. In addition, FOLR1 mRNA and cell surface FR-α levels were evaluated in Hela cells with dexamethasone treatment. The endocytosis of folate-conjugated or plain micelles loaded with coumarin 6 was examined with confocal microscopy and flow cytometry, which displayed that folate-conjugated micelles can be internalized more efficiently in dexamethasone-treated Hela cells than in normal Hela cells. Moreover, the antitumor activity of folate-conjugated micellar MTN was also improved through up-regulation of FR-α. Therefore, FR-α up-regulation using modulators has great potential to improve the therapeutic efficacy of folate-conjugated nanovehicles in some FR-α positive tumors via receptor-mediated endocytosis.     

Intestinal absorption of drugs. The influence of mixed micelles on on the disappearance kinetics of drugs from the small intestine of the rat.

The solubilization of the hydrophilic drugs paracetamol and theophylline, and the lipophilic drugs dantrolene, griseofulvin and ketoconazole has been determined in mixed micellar aqueous dispersions composed of 10 mM taurocholate + 5 mM oleic acid. The solubilization of dantrolene and paracetamol has also been determined in aqueous (mixed) micellar dispersions of 1 g L-1 lysophosphatidyl-choline (LPC), or taurocholate/LPC. The influence of these (mixed) micelles on the absorption of the model drugs from solution was studied in the rat chronically isolated internal loop. Absorption kinetics of the drugs were evaluated on the basis of the disappearance rate of the drug dissolved in the perfusion medium in this loop. Absorption experiments with taurocholate/oleic acid in the perfusate resulted in a reduction of the disappearance rate for the lipophilic drugs and the hydrophilic drug theophylline. This could partly be ascribed to the decreased fraction of drug free in solution as a result of its micellar solubilization for dantrolene, griseofulvin and ketoconazole, but the decrease in the disappearance rate of theophylline was unexpected. Taurocholate/oleic acid, LPC and taurocholate/LPC micelles had no effect on the disappearance of paracetamol. The disappearance rate of dantrolene in the presence of LPC alone was not altered, in spite of the decreased fraction of the drug free in solution owing to its micellar solubilization. In contrast, taurocholate/LPC micelles caused a reduction in the rate of disappearance of dantrolene, as expected according to the phase-separation model. In-vitro, taurocholate and taurocholate/LPC reduced the molecular cohesion of porcine intestinal mucus, whereas LPC alone did not exhibit an effect on the gel structure of mucus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of Doxorubicin in Rats Undergoing Ultrasonic Drug Delivery

Ultrasound (US) increases efficacy of drugs delivered from micelles, but the pharmacokinetics have not been studied previously. In this study, US was used to deliver doxorubicin (Dox) sequestered in micelles in an in vivo rat model with bilateral leg tumors. One of two frequencies with identical mechanical index and intensity was delivered for 15 min to one tumor immediately after systemic injection of micellar Dox. Pharmacokinetics in myocardium, liver, skeletal muscle, and tumors were measured for 1 week. When applied in combination with micellar Dox, the ultrasoincated tumor had higher Dox concentrations at 30 min, compared to bilateral noninsonated controls. Initially, concentrations were highest in heart and liver, but within 24 h they decreased significantly. From 24 h to 7 days, concentrations remained highest in tumors, regardless of whether they received US or not. Comparison of insonated and noninsonated tumors showed 50% more Dox in the insonated tumor at 30 min posttreatment. Four weekly treatment produced additional Dox accumulation in the myocardium but not in liver, skeletal leg muscle, or tumors compared to single treatment. Controls showed that neither US nor the empty carrier impacted tumor growth. This study shows that US causes more release of drug at the targeted tumor. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3122–3131, 2010     

Cisplatin-loaded polymer-metal complex micelle with time-modulated decaying property as a novel drug delivery system

Purpose. The pharmacological activity and pharmacokinetics of cisplatin (CDDP)-loaded polymeric micelles were examined to reveal their usefulness as a novel tumor-directed drug carrier system of CDDP. Methods. In biodistribution assay, free CDDP or CDDP-loaded micelles were administered intravenously to Lewis lung carcinoma-bearing mice. Antitumor activity and nephrotoxicity were respectively evaluated by the measurement of tumor size and plasma blood urea nitrogen (BUN) after single bolus i.v. administration of each drug. Results. The time profile of the plasma Pt level after the injection of the micelles exhibited a time-modulated disappearance as observed in saline in vitro. The micelles exhibited 5.2- and 4.6-fold higher AUC of Pt in the plasma and tumor, respectively, with minimal change in the kidney, in comparison with free CDDP, suggesting that prolonged circulation of Pt in circulation and specific accumulation in the tumor were achieved utilizing the micellar drug carrier system. Administration of the micelles at the dose exhibiting antitumor activity similar to free CDDP did not increase the plasma BUN, whereas free CDDP induced its remarkable increase. Conclusion. CDDP-loaded micelles restrained nephrotoxicity, which is the dose-limiting factor of CDDP, while exhibiting tumor-specific accumulation. Thus, CDDP-loaded micelles are expected to be a novel formulation of CDDP for clinical use.     

Toward a full understanding of the EPR effect in primary and metastatic tumors as well as issues related to its heterogeneity

The enhanced permeability and retention (EPR) effect of solid tumors as seen with nanomedicines and macromolecular drugs is well known. However, many researchers appear to lack a full understanding of this effect. The effect varies depending on a patient's pathological and physiological characteristics and clinical condition. When a patient's systolic blood pressure is low side of about 90 mm Hg instead of 120–130 mm Hg, the hydrodynamic force pushing blood from the luminal side of a vessel into tumor tissue becomes significantly low, which results in a low EPR. Also, a vascular embolism in a tumor may impede blood flow and the EPR. Here, I describe the background of the EPR effect, heterogeneity of this effect, physiological and pathological factors affecting the effect, the EPR effect in metastatic tumors, artifacts of the EPR effect with micellar and liposomal drugs, problems of macromolecular drug stability and drug release, and access to target sites.