NK105, a paclitaxel-incorporating micellar nanoparticle formulation, can extend in vivo antitumour activity and reduce the neurotoxicity of paclitaxel

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

In vitro human plasma distribution of nanoparticulate paclitaxel is dependent on the physicochemical properties of poly(ethylene glycol)-block-poly(caprolactone) nanoparticles

In this study, we synthesized and characterized two methoxy poly(ethylene glycol)-block-poly(caprolactone) (MePEG-b-PCL) amphiphilic diblock copolymers, both based on MePEG with a molecular weight of 5000 g/mol (114 repeat units) and PCL block lengths of either 19 or 104 repeat units. Nanoparticles were formed from these copolymers by a nanoprecipitation and dialysis technique. The MePEG(114)-b-PCL(19) copolymer was water soluble and formed micelles that had a hydrodynamic diameter of 40 nm at all copolymer concentrations tested, and displayed a relatively low core microviscosity. The practically water insoluble MePEG(114)-b-PCL(104) copolymer formed nanoparticles with a larger hydrodynamic diameter, which was dependent on copolymer concentration, and possessed a higher core microviscosity than the MePEG(114)-b-PCL(19) micelles, characteristic of nanospheres. The micelles solubilized a maximum of 1.6% w/w of the hydrophobic anticancer agent, paclitaxel (PTX), and released 92% of their drug payload over 7 days, as compared to the nanospheres, which solubilized a maximum of 3% w/w of PTX and released 60% over the same period of time. Both types of nanoparticles were found to be hemocompatible, causing only minimal hemolysis and no changes in plasma coagulation times as compared to control. Upon in vitro incubation in human plasma, PTX solubilized by micelles had a plasma distribution similar to free drug. The majority of PTX was associated with the lipoprotein deficient plasma (LPDP) fraction, which primarily consists of albumin and alpha-1-acid glycoprotein. In contrast, nanospheres were capable of retaining more of the encapsulated drug with significantly less PTX partitioning into the LPDP fraction.

Self-assembled poly(butadiene)-b-poly(ethylene oxide) polymersomes as paclitaxel carriers

In this work, self-assembled poly(butadiene)-b-poly(ethylene oxide) (PB-PEO) polymersomes (polymer vesicles) and worm micelles were evaluated as paclitaxel carriers. Paclitaxel was successfully incorporated into PB-PEO polymersomes and worm micelles. The loading capacity of paclitaxel inside PB-PEO colloids ranged from 6.7% to 13.7% w/w, depending on the morphology of copolymer colloids and the molecular weight of diblock copolymer. Paclitaxel loaded OB4 (PB219-PEO121) polymersome formulations were colloidally stable for 4 months at 4 degrees C and exhibited slow steady release of paclitaxel over a 5 week period at 37 degrees C. Evaluation of the in vitro cytotoxicity of paclitaxel-polymersome formulations showed that the ability of paclitaxel-loaded polymersomes to inhibit proliferation of MCF-7 human breast cancer cells was less compared to paclitaxel alone. By increasing the concentration of paclitaxel in polymersomes from 0.02 to 0.2 mug/mL, paclitaxel-polymersome formulations showed comparable activity in inhibiting the growth of MCF-7 cells. Taken together, these results demonstrate that paclitaxel-polymersomes have desirable restrained release profile and exhibit long-term stability.

Enhanced distribution of NK012, a polymeric micelle-encapsulated SN-38, and sustained release of SN-38 within tumors can beat a hypovascular tumor

Human pancreatic cancer is generally hypovascular in nature and rich in interstitium. These pathological barriers may contribute to the intractable nature of pancreatic cancer by binding the penetration of anticancer agents throughout the tumor tissue. The aim of the present study was to determine whether NK012 is an appropriate formulation for the treatment of hypovascular tumors. Among pancreatic tumor xenografts, PSN1 appeared to have the richest tumor vasculature and the least number of stromal cells and matrix. In contrast, Capan1 had the poorest tumor vasculature and most abundant stromal tissue. Fluorescence microscopy and high-performance liquid chromatography analysis demonstrated that although NK012 accumulated and continued to be distributed for more than 48 h throughout the entire body of both tumors, CPT-11 disappeared almost entirely from both tumors within 6 h. In addition, efficient sustained release of SN-38 was maintained for more than 96 h in both tumors following administration of NK012. Following the administration of CPT-11, SN-38 was no longer detectable after 24 h in the Capan1 tumor or after 48 h in the PSN1 tumor. All tumors were eradicated in the mice treated with NK012 but not in those treated with CPT-11. Because the antitumor activity of SN-38 is time dependent, NK012, which combines enhanced distribution with sustained release of SN-38 within tumors, may be ideal for the treatment of hypovascular tumors, such as pancreatic cancer.

Poly (amino acid) micelle nanocarriers in preclinical and clinical studies

Polymeric micelles are expected to increase the accumulation of drugs in tumor tissues utilizing the EPR effect and to incorporate various kinds of drugs into the inner core by chemical conjugation or physical entrapment with relatively high stability. The size of the micelles can be controlled within the diameter range of 20 to 100 nm, to ensure that the micelles do not pass through normal vessel walls; therefore, a reduced incidence of the side effects of the drugs may be expected due to the decreased volume of distribution. These are several anticancer agent-incorporated micelle carrier systems under clinical evaluation. Phase 1 studies of a CDDP incorporated micelle, Nc-6004, and an sN-38 incorporated micelle, NK012, are now underway. A phase 2 study of a PTX incorporated micelle, NK105, against stomach cancer is also underway.

Carrier effects on antitumor activity and neurotoxicity of AZ10992, a paclitaxel-carboxymethyl dextran conjugate, in a mouse model

AZ10992 is a novel paclitaxel-carboxymethyl (CM) dextran conjugate via a Gly-Gly-Phe-Gly linker with the molecular weight (MW) of 150 kDa. Our previous studies demonstrated that AZ10992 exerts strong antitumor activity against the human tumor xenografts that are highly refractory to paclitaxel, attributable to passive tumor targeting of released paclitaxel. This study examines the effects of carrier MW, anionic charge and drug-contents on the antitumor effects of AZ10992. To study antitumor effects, colon26 carcinoma-bearing BALB/c female mice received repeated (3 injections administered with 7 d intervals) intravenous administration of non-polymer-bound paclitaxel or paclitaxel-CM dextran conjugates. The results indicated that the conjugate comprising dextran T-110 (MW 110 kDa) with the degree of substitution (DS) value for the CM group of 0.50-0.55 per glucose residue and the drug contents of 5.5-6.5% (w/w) would be appropriate for AZ10992 regarding antitumor activity. Maximal tolerated dose (MTD) of AZ10992 was more than twice of non-polymer-bound paclitaxel. Furthermore, normal BALB/c female mice were treated with repeated (3 injections administered with 2 d intervals) intravenous administration of non-polymer-bound paclitaxel or AZ10992 at 50 mg/kg/d (based on the amount of paclitaxel to CM dextran) to study neurotoxicity. AZ10992 did not induce degeneration of myelin or swelling of Schwann cells in sciatic nerves.

Polymeric micelles for drug targeting

Polymeric micelles are nano-delivery systems formed through self-assembly of amphiphilic block copolymers in an aqueous environment. The nanoscopic dimension, stealth properties induced by the hydrophilic polymeric brush on the micellar surface, capacity for stabilized encapsulation of hydrophobic drugs offered by the hydrophobic and rigid micellar core, and finally a possibility for the chemical manipulation of the core/shell structure have made polymeric micelles one of the most promising carriers for drug targeting. To date, three generations of polymeric micellar delivery systems, i.e. polymeric micelles for passive, active and multifunctional drug targeting, have arisen from research efforts, with each subsequent generation displaying greater specificity for the diseased tissue and/or targeting efficiency. The present manuscript aims to review the research efforts made for the development of each generation and provide an assessment on the overall success of polymeric micellar delivery system in drug targeting. The emphasis is placed on the design and development of ligand modified, stimuli responsive and multifunctional polymeric micelles for drug targeting.

Polymeric micelles in oral chemotherapy

Oral administration of anticancer agents is preferred by patients for its convenience and potential for use in outpatient and palliative setting. In addition, oral administration facilitates a prolonged exposure to the cytotoxic agents. Enhancement of bioavailability of emerging cytotoxic agents is a pre-requisite for successful development of oral modes of cancer treatment. Over the last decade, our studies have focused specifically on the utilization of large (MW>10(5)) and non-degradable polymers in oral chemotherapy. A family of block-graft copolymers of the poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) Pluronic(R) polyethers and poly(acrylic acid) (PAA) bound by carbon-carbon bonds emerged, wherein both polymeric components are generally recognized as safe. Animal studies with Pluronic-PAA copolymers demonstrated that these molecules are excreted when administered orally and do not absorb into the systemic circulation. The Pluronic-PAA copolymers are surface-active and self-assemble, at physiological pH, into intra- and intermolecular micelles with hydrophobic cores of dehydrated PPO and multilayered coronas of hydrophilic PEO and partially ionized PAA segments. These micelles efficiently solubilize hydrophobic drugs such as paclitaxel and steroids and protect molecules such as camptothecins from the hydrolytic reactions. High surface activity of the Pluronic-PAA copolymers in water results in interactions with cell membranes and suppression of the membrane pumps such as P-glycoprotein. The ionizable carboxyls in the micellar corona facilitate mucoadhesion that enhances the residence time of the micelles and solubilized drugs in the gastrointestinal tract. Large payloads of the Pluronic-PAA micelles with weakly basic and water-soluble drugs such as doxorubicin and its analogs, mitomycin C, mitoxantrone, fluorouracil, and cyclophosphamide are achieved through electrostatic interactions with the micellar corona. Mechanical and physical properties of the Pluronic-PAA powders, blends, and micelles allow for formulation procedures where an active is simply dispersed into an aqueous Pluronic-PAA micellar formulation followed by optional lyophilization and processing into a ready dosage form. We review a number of in vivo and in vitro experiments demonstrating that that the oral administration of the cytotoxics formulated with the Pluronic-PAA copolymer micelles results in enhanced drug bioavailability.

Polymeric micelles for the solubilization and delivery of STAT3 inhibitor cucurbitacins in solid tumors

Poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) and newly developed poly(ethylene oxide)-block-poly(alpha-benzyl carboxylate epsilon-caprolactone) (PEO-b-PBCL) micelles were evaluated for the solubilization and delivery of cucurbitacin I and B, poorly water soluble inhibitors of signal transducer and activator of transcription 3 (STAT3). Encapsulation of cucurbitacins in PEO-b-PCL and PEO-b-PBCL by co-solvent evaporation technique resulted in polymeric micelles <90 nm in diameter. The aqueous solubility of both derivatives increased from less than 0.05 mg/mL in the absence of the copolymer to around 0.30-0.44 and 0.65-0.68 mg/mL in the presence of 5000-5000 and 5000-24,000 PEO-b-PCL micelles, respectively. Maximum cucurbitacin solubilization was achieved with PEO-b-PBCL micelles for both derivatives. PEO-b-PCL micelles having longer PCL block were found to be more efficient in sustaining the rate of release for cucurbitacins. The anti-cancer and STAT3 inhibitory activity of polymeric micellar cucurbitacins were comparable with free drugs in B16.F10 melanoma cell line in vitro. Intratumoral injection of 1 mg/kg/day cucurbitacin I resulted in the regression of established B16.F10 mouse melanoma tumors in vivo. In comparison to free cucurbitacin I, PEO-b-PBCL micellar cucurbitacin I was found to provide comparable anti-cancer effects against B16.F10 tumors and limit drug levels in animal serum while maintaining high drug levels in tumor following intratumoral administration. The results indicate the potential of polymeric micelles as suitable vehicles for the delivery of cucurbitacin- I and B.

Poly(N-vinyl-pyrrolidone)-block-poly(D,L-lactide) as polymeric emulsifier for the preparation of biodegradable nanoparticles

Poly(D,L-lactide) (PDLLA) amphiphilic block copolymers were employed as emulsifiers in the preparation of PDLLA nanoparticles by an oil/water emulsion solvent evaporation technique. The surface-active properties of poly(N-vinyl-pyrrolidone)-block-poly(D,L-lactide) (PVP-b-PDLLA) toward the biphasic system were compared to those of polyethylene glycol(PEG)-b-PDLLA of similar composition. PVP-b-PDLLA was found to be a suitable emulsifier for dichloromethane/water emulsions, yielding narrowly distributed nanoparticles (<250 nm) surrounded by a hydrophilic PVP corona. PEG-b-PDLLA, however, was only effective in producing appropriately sized nanoparticles when dichloromethane was replaced with ethyl acetate. Furthermore, the lyoprotectant properties of PVP allowed the freeze-dried nanoparticles to recover their initial size following reconstitution, while PEG-coated nanoparticles could not be redispersed following lyophilization. Two poorly water-soluble drugs, that is, paclitaxel and etoposide, were efficiently loaded into PVP-decorated PDLLA nanoparticles. The entrapment efficiency of etoposide was significantly enhanced by adding MgCl2 to the aqueous phase. It was found that the nanoparticles released the drugs progressively over several days in vitro. The obtained experimental results were corroborated with the theoretical compatibility between a given drug, polymer, and solvent, predicted by total solubility parameters.

Targeted nanoparticle-based drug delivery and diagnosis

Nanotechnology, or systems/device manufacture at sizes generally ranging between 1 and 100 nm, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to advances in medicine, communications, genomics and robotics. One of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e. nanomedicine). This review focuses on the potential of nanomedicine as it relates to the development of nanoparticles for enabling and improving the targeted delivery of therapeutic and diagnostic agents. We highlight the use of nanoparticles for specific intra-compartmental analysis using the examples of delivery to malignant cancers, to the central nervous system, and across the gastrointestinal barriers.

Anti-tumor Effect of All-Trans Retinoic Acid Loaded Polymeric Micelles in Solid Tumor Bearing Mice

PURPOSE

All-trans retinoic acid (ATRA) polymeric micelles were developed for parenteral administration. The distribution characteristics and antitumor activities of ATRA polymeric micelles were evaluated after intravenous administration to mice bearing CT26 solid tumors.

METHODS

ATRA incorporated in poly(ethylene glycol)-poly(benzyl aspartate) block copolymer was prepared by the evaporation method. The levels of [3H]ATRA in blood and tissue including tumor were determined by measuring the radioactivity after injection into mice. The tumor volume and the survival of the mice were determined to assess the anticancer activity.

RESULTS

The delivery of ATRA by polymeric micelles prolonged the blood circulation and enhanced the accumulation of ATRA in the tumor tissue compared with the administration of free ATRA. Tumor growth was significantly delayed and the survival time of mice was prolonged following the treatment by ATRA polymeric micelles demonstrating the improved anticancer activity of ATRA.

CONCLUSION

Polymeric micelles are a promising and effective carrier of ATRA in order to enhance tumor delivery and they have a promising potential application in the treatment of solid tumors.

Solubilization of docetaxel in poly(ethylene oxide)-block-poly(butylene/styrene oxide) micelles

Poly(ethylene oxide)-block-poly(styrene oxide) (PEO-b-PSO) and PEO-b-poly(butylene oxide) (PEO-b-PBO) of different chain lengths were synthesized and characterized for their self-assembling properties in water by dynamic/static light scattering, spectrofluorimetry, and transmission electron microscopy. The resulting polymeric micelles were evaluated for their ability to solubilize and protect the anticancer drug docetaxel (DCTX) from degradation. The drug release kinetics as well as the cytotoxicity of the loaded micelles were assessed in vitro. All polymers formed micelles with a highly viscous core at low critical association concentrations (<10 mg/L). Micelle morphology depended on the nature of the hydrophobic block, with PBO- and PSO-based micelles yielding monodisperse spherical and cylindrical nanosized aggregates, respectively. The maximum solubilization capacity for DCTX ranged from 0.7 to 4.2% and was the highest for PSO micelles exhibiting the longest hydrophobic segment. Despite their high affinity for DCTX, PEO-b-PSO micelles were not able to efficiently protect DCTX against hydrolysis under accelerated stability testing conditions. Only PEO-b-PBO bearing 24 BO units afforded significant protection against degradation. In vitro, DCTX was released slower from the latter micelles, but all formulations possessed a similar cytotoxic effect against PC-3 prostate cancer cells. These data suggest that PEO-b-P(SO/BO) micelles could be used as alternatives to conventional surfactants for the solubilization of taxanes.

Improving Penetration in Tumors With Nanoassemblies of Phospholipids and Doxorubicin

BACKGROUND

Drug delivery and penetration into neoplastic cells distant from tumor vessels is critical for the effectiveness of solid tumor chemotherapy. We hypothesized that 10- to 20-nm nanoassemblies of phospholipids containing doxorubicin would improve the drug's penetration, accumulation, and antitumor activity.

METHODS

Doxorubicin was incorporated into polyethylene glycol-phosphatidylethanolamine (PEG-PE) block copolymer micelles by a self-assembly procedure to form nanoassemblies of doxorubicin and PEG-PE. In vitro cytotoxicity of micelle-encapsulated doxorubicin (M-Dox) against A549 human non-small-cell lung carcinoma cells was examined using the methylthiazoletetrazolium assay, and confocal microscopy, total internal reflection fluorescence microscopy, and flow cytometry were used to examine intracellular distribution and the cellular uptake mechanism. C57Bl/6 mice (n = 10-40 per group) bearing subcutaneous or pulmonary Lewis lung carcinoma (LLC) tumors were treated with M-Dox or free doxorubicin, and tumor growth, doxorubicin pharmacokinetics, and mortality were compared. Toxicity was analyzed in tumor-free mice. All statistical tests were two-sided.

RESULTS

Encapsulation of doxorubicin in PEG-PE micelles increased its internalization by A549 cells into lysosomes and enhanced cytotoxicity. Drug-encapsulated doxorubicin was more effective in inhibiting tumor growth in the subcutaneous LLC tumor model (mean tumor volumes in mice treated with 5 mg/kg M-Dox = 1126 mm3 and in control mice = 3693 mm3, difference = 2567 mm3, 95% confidence interval [CI] = 2190 to 2943 mm3, P<.001) than free doxorubicin (mean tumor volumes in doxorubicin-treated mice = 3021 mm3 and in control mice = 3693 mm3, difference = 672 mm3, 95% CI = 296 to 1049 mm3, P = .0332, Wilcoxon signed rank test). M-Dox treatment prolonged survival in both mouse models and reduced metastases in the pulmonary model; it also reduced toxicity.

CONCLUSIONS

We have developed a novel PEG-PE-based nanocarrier of doxorubicin that increased cytotoxicity in vitro and enhanced antitumor activity in vivo with low systemic toxicity. This drug packaging technology may provide a new strategy for design of cancer therapies.

A phase I and pharmacokinetic study of NK105, a paclitaxel-incorporating micellar nanoparticle formulation

This phase I study was designed to examine the maximum tolerated dose (MTD), the dose-limiting toxicities (DLTs), the recommended dose (RD) for phase II, and the pharmacokinetics of NK105, a new polymeric micelle carrier system for paclitaxel (PTX). NK105 was administered as a 1-h intravenous infusion every 3 weeks, without antiallergic premedication. The starting dose was 10 mg m⁻², and the dose was escalated according to the accelerated titration method. Nineteen patients were recruited. The tumour types treated included pancreatic (n=11), bile duct (n=5), gastric (n=2), and colonic (n=1) cancers. Neutropenia was the most common haematological toxicity. A grade 3 fever developed in one patient given 180 mg m⁻². No other grades 3 or 4 nonhaematological toxicities, including neuropathy, was observed during the entire study period. DLTs occurred in two patients given 180 mg m⁻² (grade 4 neutropenia lasting for more than 5 days). Thus, this dose was designated as the MTD. Grade 2 hypersensitivity reactions developed in only one patient given 180 mg m⁻². A partial response was observed in one patient with pancreatic cancer. The maximum concentration (C_max) and area under the concentration (AUC) of NK105 were dose dependent. The plasma AUC of NK105 at 150 mg m⁻² was approximately 15-fold higher than that of the conventional PTX formulation. NK105 was well tolerated, and the RD for the phase II study was determined to be 150 mg m⁻² every 3 weeks. The results of this phase I study warrant further clinical evaluation.

Triggered destabilisation of polymeric micelles and vesicles by changing polymers polarity: an attractive tool for drug delivery

Polymeric micelles and vesicles have emerged as versatile drug carriers during the past decades. Furthermore, stimuli-responsive systems are developed whose properties change after applying certain external triggers. Therefore, a triggered release of drugs from stimuli-sensitive micelles and vesicles has become an interesting challenge in the pharmaceutical field. Polymeric micelles or vesicles are mainly composed of amphiphilic block copolymers that are held together in water due to strong hydrophobic interactions between the insoluble hydrophobic blocks, thus forming a core-shell or bilayer morphology. Consequently, destabilisation of these assemblies is induced by increasing the polarity of the hydrophobic blocks. Preferably, this process should be the consequence of an external trigger, or take place in a certain time frame or at a specific location. A variety of mechanisms has recently been described to accomplish this transition, which will be reviewed in this paper. These mechanisms include the destabilisation of polymeric micelles and vesicles by temperature, pH, chemical or enzymatic hydrolysis of side chains, oxidation/reduction processes, and light.

Shape effects of filaments versus spherical particles in flow and drug delivery

Interaction of spherical particles with cells and within animals has been studied extensively, but the effects of shape have received little attention. Here we use highly stable, polymer micelle assemblies known as filomicelles to compare the transport and trafficking of flexible filaments with spheres of similar chemistry. In rodents, filomicelles persisted in the circulation up to one week after intravenous injection. This is about ten times longer than their spherical counterparts and is more persistent than any known synthetic nanoparticle. Under fluid flow conditions, spheres and short filomicelles are taken up by cells more readily than longer filaments because the latter are extended by the flow. Preliminary results further demonstrate that filomicelles can effectively deliver the anticancer drug paclitaxel and shrink human-derived tumours in mice. Although these findings show that long-circulating vehicles need not be nanospheres, they also lend insight into possible shape effects of natural filamentous viruses.

Fate of micelles and quantum dots in cells

Micelles and quantum dots have been used as experimental drug delivery systems and imaging tools both in vitro and in vivo. Investigations of their fate at the subcellular level require different surface-core modifications. Among the most common modifications are those with fluorescent probes, dense-core metals or radionucleids. Cellular fate of several fluorescent probes incorporated into poly(caprolactone)-b-copolymer micelles (PCL-b-PEO) was followed by confocal microscopy, and colloidal gold incorporated in poly 4-vinyl pyridine-PEO micelles were developed to explore micelle fate by electron microscopy. More recently, we have examined quantum dots (QDs) as the next-generation-labels for cells and nanoparticulate drug carriers amenable both to confocal and electron microscopic analyses. Effects of QDs at the cellular and subcellular levels and their integrity were studied. Results from different studies suggest that size, charge and surface manipulations of QDs may play a role in their subcellular distribution. Examples of pharmacological agents incorporated into block copolymer micelles, administered or attached to QD surfaces show how the final biological outcome (e.g. cell death, proliferation or differentiation) depends on physical properties of these nanoparticles.

In vivo fate of unimers and micelles of a poly(ethylene glycol)-block-poly(caprolactone) copolymer in mice following intravenous administration

Methoxy poly(ethylene glycol)-b-poly(caprolactone) (MePEG-b-PCL) copolymers with varying PEG block lengths and a constant PCL block length were synthesized by cationic ring-opening polymerization and used to form nano-sized micelles. Due to their small size and superior in vitro stability, the MePEG(5000)-b-PCL(5000) micelles were selected for further in vitro characterization and an in vivo evaluation of their fate and stability following intravenous (i.v.) administration. Specifically, (3)H-labelled MePEG(5000)-b-PCL(5000) micelles were i.v. administered to Balb/C mice at copolymer doses of 250, 2 and 0.2 mg/kg in order to examine the distribution kinetics of (1) copolymer assembled as thermodynamically stable micelles, (2) copolymer assembled as thermodynamically unstable micelles and (3) copolymer unimers, respectively. Overall, it was found that when the copolymer is assembled as thermodynamically stable micelles the material is effectively restricted to the plasma compartment. Interestingly, the copolymer was found to have a relatively long circulation half-life even when administered at a dose that would likely fall to concentrations below the CMC following distribution. Analysis of plasma samples from this group revealed that even 24 h post-administration a significant portion of the copolymer remained assembled as intact micelles. In this way, this study demonstrates that the hydrophobic and semi-crystalline nature of the PCL core imparts a high degree of kinetic stability to this micelle system.

Improvement of cancer-targeting therapy, using nanocarriers for intractable solid tumors by inhibition of TGF-beta signaling

Transforming growth factor (TGF)-beta plays a pivotal role in regulation of progression of cancer through effects on tumor microenvironment as well as on cancer cells. TGF-beta inhibitors have recently been shown to prevent the growth and metastasis of certain cancers. However, there may be adverse effects caused by TGF-beta signaling inhibition, including the induction of cancers by the repression of TGF-beta-mediated growth inhibition. Here, we present an application of a short-acting, small-molecule TGF-beta type I receptor (TbetaR-I) inhibitor at a low dose in treating several experimental intractable solid tumors, including pancreatic adenocarcinoma and diffuse-type gastric cancer, characterized by hypovascularity and thick fibrosis in tumor microenvironments. Low-dose TbetaR-I inhibitor altered neither TGF-beta signaling in cancer cells nor the amount of fibrotic components. However, it decreased pericyte coverage of the endothelium without reducing endothelial area specifically in tumor neovasculature and promoted accumulation of macromolecules, including anticancer nanocarriers, in the tumors. Compared with the absence of TbetaR-I inhibitor, anticancer nanocarriers exhibited potent growth-inhibitory effects on these cancers in the presence of TbetaR-I inhibitor. The use of TbetaR-I inhibitor combined with nanocarriers may thus be of significant clinical and practical importance in treating intractable solid cancers.

Self-assembled poly(butadiene)-b-poly(ethylene oxide) polymersomes as paclitaxel carriers

In this work, self-assembled poly(butadiene)-b-poly(ethylene oxide) (PB-PEO) polymersomes (polymer vesicles) and worm micelles were evaluated as paclitaxel carriers. Paclitaxel was successfully incorporated into PB-PEO polymersomes and worm micelles. The loading capacity of paclitaxel inside PB-PEO colloids ranged from 6.7% to 13.7% w/w, depending on the morphology of copolymer colloids and the molecular weight of diblock copolymer. Paclitaxel loaded OB4 (PB219-PEO121) polymersome formulations were colloidally stable for 4 months at 4 degrees C and exhibited slow steady release of paclitaxel over a 5 week period at 37 degrees C. Evaluation of the in vitro cytotoxicity of paclitaxel-polymersome formulations showed that the ability of paclitaxel-loaded polymersomes to inhibit proliferation of MCF-7 human breast cancer cells was less compared to paclitaxel alone. By increasing the concentration of paclitaxel in polymersomes from 0.02 to 0.2 mug/mL, paclitaxel-polymersome formulations showed comparable activity in inhibiting the growth of MCF-7 cells. Taken together, these results demonstrate that paclitaxel-polymersomes have desirable restrained release profile and exhibit long-term stability.

High-performance liquid chromatography analysis of curcumin in rat plasma: application to pharmacokinetics of polymeric micellar formulation of curcumin

A simple, rapid and reliable high-performance liquid chromatographic (HPLC) method was developed and validated for the determination of curcumin in rat plasma. Plasma was precipitated with acetonitrile after addition of the internal standard (IS), 4-hydroxybenzophenone. Separation was achieved on a Waters muBondapak C(18) column (3.9 x 300 mm, 5 microm) using acetonitrile (55%) and citric buffer, pH 3.0 (45%) as the mobile phase (flow rate = 1.0 mL/min). The UV detection wavelength was 300 and 428 nm for IS and curcumin, respectively. The extraction efficiencies were 97.08, 95.69 and 94.90% for 50, 200 and 1000 ng/mL of curcumin in rat plasma, respectively. The calibration curve was linear over the range 0.02-1 microg/mL with a correlation coefficient of r(2) > 0.999. The intra- and inter-day coefficients of variation were less than 13%, and mean intra- and inter-day errors were less than +/-6% at 50, 200 and 1000 ng/mL of curcumin. This assay was successfully applied to the pharmacokinetic studies of both solubilized curcumin and its polymeric micellar formulation in rats. It was found that polymeric micelles increased the half-life of curcumin 162-fold that of solubilized curcumin and increased the volume of distribution (Vd(ss)) by 70-fold.

Novel SN-38-incorporating polymeric micelles, NK012, eradicate vascular endothelial growth factor-secreting bulky tumors

7-Ethyl-10-hydroxy-camptothecin (SN-38), a biological active metabolite of irinotecan hydrochloride (CPT-11), has potent antitumor activity but has not been used clinically because it is a water-insoluble drug. For delivery by i.v. injection, we have successfully developed NK012, a SN-38-releasing nanodevice. The purpose of this study is to investigate the pharmacologic character of NK012 as an anticancer agent, especially in a vascular endothelial growth factor (VEGF)-secreting tumor model. The particle size of NK012 was approximately 20 nm with a narrow size distribution. NK012 exhibited a much higher cytotoxic effect against lung and colon cancer cell lines as compared with CPT-11. NK012 showed significantly potent antitumor activity against a human colorectal cancer HT-29 xenograft as compared with CPT-11. Enhanced and prolonged distribution of free SN-38 in the tumor was observed after the injection of NK012. NK012 also had significant antitumor activity against bulky SBC-3/Neo (1,533.1 +/- 1,204.7 mm(3)) and SBC-3/VEGF tumors (1,620.7 +/- 834.0 mm(3)) compared with CPT-11. Furthermore, NK012 eradicated bulky SBC-3/VEGF tumors in all mice but did not eradicate SBC-3/Neo tumors. In the drug distribution analysis, an increased accumulation of SN-38 in SBC-3/VEGF tumors was observed as compared with that in SBC-3/Neo tumors. NK012 markedly enhanced the antitumor activity of SN-38, especially in highly VEGF-secreting tumors, and could be a promising SN-38-based formulation.

Paclitaxel nanoparticle inhibits growth of ovarian cancer xenografts and enhances lymphatic targeting

OBJECTIVES

Ovarian cancer has the highest mortality of all the gynecologic cancers. The antitumor agent paclitaxel has been proved to be efficient in the treatment of ovarian cancer. Our study is to develop a polymeric drug delivery system for paclitaxel and determine whether paclitaxel nanoparticle can inhibit growth of ovarian carcinoma xenografts in Fisher344 (F344) rats by intraperitoneal administration. The mechanism of paclitaxel nanoparticles in rats bearing ovarian cancer has been investigated in this study.

METHODS

Synthesize paclitaxel loading nanoparticle (PLA) by ultrasonic emulsification; MTT analysis identified cytotoxic activity of paclitaxel nanoparticle in vitro; rat ovarian carcinoma cells were injected into the peritoneal cavity of F344 rats. The antitumor effect of paclitaxel nanoparticle in vivo has been evaluated by measuring tumor weight and ascite volume. At the end of the procedure rats were sacrificed; tumors were excised and processed for PCNA staining, tissue terminal deoxynucleotide transferase-mediated dUTP nick and labeling assay and RT-PCR to evaluate the proliferative and apoptotic changes and cancer transfer-related gene expression induced by PLA. Paclitaxel concentration in plasma, pelvic lymph nodes, liver, and heart were determined by high-performance liquid chromatography.

RESULTS

Paclitaxel nanoparticle and PTX (Cremophor) showed equivalent cytotoxic activity in vitro. In rats implanted carcinoma cells, paclitaxel nanoparticles significantly reduced tumor weight and ascites volume, and induced apoptosis of tumor cells. PLA also inhibited cell proliferation and matrix metalloproteinase 9 mRNA expression. The paclitaxel concentration of pelvic lymph nodes in PLA treated animals was 20-fold higher than that of free PTX treated animals at 48 h after intraperitoneal administration.

CONCLUSION

The intraperitoneal administration of paclitaxel nanoparticle can significantly inhibit the progression of ovarian carcinoma in peritoneal cavity of female F344 rat. The paclitaxel nanoparticle is safe and lymphatic targeting.

A polymeric micelle MRI contrast agent with changeable relaxivity

Polymeric micelles were formed from cationic polymers (polyallylamine or protamine) and anionic block copolymers (poly(ethylene glycol)-b-poly(aspartic acid) derivative) that bound Gd ions providing high contrasts in Magnetic Resonance Imaging (MRI) by shortening the T(1) longitudinal relaxation time of protons of water. The Gd-binding block copolymer alone showed high relaxivity (T(1)-shortening ability) values from 10 to 11 mol(-1) s(-1), while the polymeric micelles exhibited low relaxivity values from 2.1 to 3.6 mol(-1) s(-1). These findings point to the feasibility of a novel MRI contrast agent that selectively provides high contrasts at solid tumor sites owing to a dissociation of the micelle structures, while selective delivery to the tumor sites is achieved in the polymeric micelle form.

NK105, a paclitaxel-incorporating micellar nanoparticle, is a more potent radiosensitising agent compared to free paclitaxel

NK105 is a micellar nanoparticle formulation designed to enhance the delivery of paclitaxel (PTX) to solid tumours. It has been reported to exert antitumour activity in vivo and to have reduced neurotoxicity as compared to that of free PTX. The purpose of this study was to investigate the radiosensitising effect of NK105 in comparison with that of PTX. Lewis lung carcinoma (LLC)-bearing mice were administered a single intravenous (i.v.) injection of PTX or NK105; 24 h after the drug administration, a proportion of the mice received radiation to the tumour site or lung fields. Then, the antitumour activity and lung toxicity were evaluated. In one subset of mice, the tumours were excised and specimens were prepared for analysis of the cell cycle distribution by flow cytometry. Combined NK105 treatment with radiation yielded significant superior antitumour activity as compared to combined PTX treatment with radiation (P=0.0277). On the other hand, a histopathological study of lung sections revealed no significant difference in histopathological changes between mice treated with PTX and radiation and those treated with NK105 and radiation. Flow-cytometric analysis showed that NK105-treated LLC tumour cells showed more severe arrest at the G2/M phase as compared to PTX-treated tumour cells. The superior radiosensitising activity of NK105 was thus considered to be attributable to the more severe cell cycle arrest at the G2/M phase induced by NK105 as compared to that induced by free PTX. The present study results suggest that further clinical trials are warranted to determine the efficacy and feasibility of combined NK105 therapy with radiation.

Current state, achievements, and future prospects of polymeric micelles as nanocarriers for drug and gene delivery

Polymeric micelles, self-assemblies of block copolymers, are promising nanocarrier systems for drug and gene delivery. Until now, several micellar formulations of antitumor drugs have been intensively studied in preclinical and clinical trials, and their utility has been demonstrated. Even compared with long-circulating liposomes, polymeric micelles might have several advantages, such as controlled drug release, tissue-penetrating ability and reduced toxicity such as hand-foot syndrome and hypersensitivity reaction. Importantly, critical features of the polymeric micelles as drug carriers, including particle size, stability, and loading capacity and release kinetics of drugs, can be modulated by the structures and physicochemical properties of the constituent block copolymers. Also, nano-engineering of block copolymers might allow the preparation of polymeric micelles with integrated smart functions, such as specific-tissue targetability, as well as chemical or physical stimuli-sensitivity. Thus, polymeric micelles are nanotechnology-based carrier systems that might exert the activity of potent bioactive compounds in a site-directed manner, ensuring their effectiveness and safety in the clinical use.

The pinpoint promise of nanoparticle-based drug delivery and molecular diagnosis

Nanotechnology, or systems/device manufacture at the molecular level, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to the promise of revolutionary advances across medicine, communications, genomics and robotics. Without doubt one of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e., nanomedicine). This review focuses on the potential of nanomedicine as it specifically relates to (1) the development of nanoparticles for enabling and improving the targeted delivery of therapeutic agents; (2) developing novel and more effective diagnostic and screening techniques to extend the limits of molecular diagnostics providing point-of-care diagnosis and more personalized medicine.

Assessment of the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles under biological conditions: a fluorogenic-based approach

The integrity of block copolymer micelles is important for their effectiveness and successful delivery of the incorporated drugs. Here we evaluate the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles in media of varying chemical complexity and in cells by using fluorogenic micelles. Fluorogenic dye fluorescein-5-carbonyl azide diacetate was covalently attached to the micelle-core-forming part of the block copolymer, poly(caprolactone). The fluorescence was not detectable unless the poly(caprolactone)21-b-poly(ethylene oxide)45 micelles were destroyed and the fluorogenic dye was activated by deesterification. The fluorescence of the activated dye from destroyed micelles was easily detectable in various media and in cells. Micelles were stable in simple media such as phosphate-buffered saline but disassembled to varying extents with increasing chemical complexity of the media and addition of serum. The integrity of the internalized micelles within the cells showed a time-dependent decrease but remained largely preserved (80%) after 20 h of incubation with cells. A proof of principle was also demonstrated in vivo in mice. The fluorogenic approach to micelle integrity assessment presented herein should lend itself to other block copolymer micelles and assessments of their integrity in complex biological systems in vitro and in vivo.

Long Circulating Poly(Ethylene Glycol)-Decorated Lipid Nanocapsules Deliver Docetaxel to Solid Tumors

PURPOSE

The purpose of this study was to evaluate the ability of poly(ethylene glycol)-coated lipid nanocapsules (LN) to deliver the highly potent hydrophobic anticancer drug docetaxel to solid tumors.

METHODS

Docetaxel-loaded nanocapsules (80-120 nm) were produced by a solvent-free phase inversion process and were coated with polyethylene glycol distearoylphosphatidylethanolamine conjugate by a postinsertion step. In vivo studies were conducted in mice bearing subcutaneously implanted C26 colon adenocarcinoma to assess the pharmacokinetics and biodistribution of both the drug and LN.

RESULTS

Incorporation of docetaxel into the LN dramatically increased the drug's biological half-life while providing substantial accumulation at the tumoral site. The pharmacokinetics and biodistribution pattern were found to depend on the specific surface area and shell composition of the nanocapsules.

CONCLUSION

This study demonstrates that docetaxel physically entrapped into a lipid colloidal drug carrier can be efficiently targeted to neoplastic tissues.

Polymeric micelles for drug delivery

Polymeric micelles have been the subject of many studies in the field of drug delivery for the past two decades. The interest has specifically been focused on the potential application of polymeric micelles in three major areas in drug delivery: drug solubilisation, controlled drug release and drug targeting. In this context, polymeric micelles consisting of poly(ethylene oxide)-b-poly(propylene oxide), poly(ethylene oxide)-b-poly(ester)s and poly(ethylene oxide)-b-poly(amino acid)s have shown a great promise and are in the front line of development for various applications. The purpose of this manuscript is to provide an update on the current status of polymeric micelles for each application and highlight important parameters that may lead to the development of successful polymeric micellar systems for individual delivery requirements.

Peripheral neuropathy: A persisting challenge in paclitaxel-based regimes

Cumulative peripheral neuropathy (PNP) still remains a limitation to optimal treatment with paclitaxel (PAC), especially in more dose-dense schedules. This primary sensory PNP may affect the majority of patients after administration of certain cumulative dosages of PAC, while the exact mechanisms of PAC-induced PNP are not known. While a number of preclinical models revealed its vehicle Cremophor EL (CrEL) to be mainly responsible for ganglionopathy, axonopathy and demyelination, clinical data also supports a strong and independent effect of PAC itself, which is most likely based on disturbances in the microtubules in perikaryons, axons and glia cells. Indeed, clinical trials of CrEL-free formulations of PAC still report grade III neurotoxicity as dose-limiting. As treatment options of PAC-induced PNP are rare the use of specific scoring systems for screening purposes is strongly encouraged. In this report we review and discuss the pathogenesis, incidence, risk factors, diagnosis, pharmacodynamics and treatment options for PAC-induced PNP.

Drug targeting with nano-sized carrier systems

This paper discusses the present status of, and future perspectives on, drug targeting through the bloodstream by describing the drug targeting concept, its methodologies, types of drug carriers, and recent clinical examples. This explanation and discussion is made from the viewpoint of possible correlations with studies on artificial organs, implants, and biomaterials. Two targeting methodologies (active and passive targeting), two targeting strategies (the magic bullet and the enhanced permeability and retention effect), and five types of drug carriers are explained. In addition, the clinical status of the five carrier systems is discussed.

Cisplatin-incorporating polymeric micelles (NC-6004) can reduce nephrotoxicity and neurotoxicity of cisplatin in rats

In spite of the clinical usefulness of cisplatin (CDDP), there are many occasions in which it is difficult to continue the administration of CDDP due to its nephrotoxicity and neurotoxicity. We examined the incorporation of CDDP into polymeric micelles to see if this allowed the resolution of these disadvantages. Cisplatin was incorporated into polymeric micelles through the polymer-metal complex formation between polyethylene glycol poly(glutamic acid) block copolymers and CDDP (NC-6004). The pharmacokinetics, pharmacodynamics, and toxicity studies of CDDP and NC-6004 were conducted in rats or mice. The particle size of NC-6004 was approximately 30 nm, with a narrow size distribution. In rats, the area under the curve and total body clearance values for NC-6004 were 65-fold and one-nineteenth the values for CDDP (P<0.001 and 0.01, respectively). In MKN-45-implanted mice, NC-6004 tended to show antitumour activity, which was comparable to or greater than that of CDDP. Histopathological and biochemical studies revealed that NC-6004 significantly inhibited the nephrotoxicity of CDDP. On the other hand, blood biochemistry revealed transient hepatotoxicity on day 7 after the administration of NC-6004. Furthermore, rats given CDDP showed a significant delay (P<0.05) in sensory nerve conduction velocity in their hind paws as compared with rats given NC-6004. Electron microscopy in rats given CDDP indicated the degeneration of the sciatic nerve, but these findings were not seen in rats given NC-6004. These results were presumably attributable to the significantly reduced accumulation of platinum in nerve tissue when NC-6004 was administered (P<0.05). NC-6004 preserved the antitumour activity of CDDP and reduced its nephrotoxicity and neurotoxicity, which would therefore seem to suggest that NC-6004 could allow the long-term administration of CDDP where caution against hepatic dysfunction must be exercised.

Methoxy Poly(ethylene glycol)-block-Poly(δ-valerolactone) Copolymer Micelles for Formulation of Hydrophobic Drugs

Six amphiphilic diblock copolymers based on methoxy poly(ethylene glycol) (MePEG) and poly(delta-valerolactone) (PVL) with varying hydrophilic and hydrophobic block lengths were synthesized via a metal-free cationic polymerization method. MePEG-b-PVL copolymers were synthesized using MePEG with Mn = 2000 or Mn = 5000 as the macroinitiator. 1H NMR and GPC analyses confirmed the synthesis of diblock copolymers with relatively narrow molecular weight distributions (Mn/Mw = 1.05-1.14). DSC analysis revealed that the melting temperatures (Tm) of the copolymers (47-58 degrees C) approach the Tm of MePEG as the PVL content is decreased. MePEG-b-PVL copolymer aggregates loaded with the hydrophobic anti-cancer drug paclitaxel were found to have effective mean diameters ranging from 31 to 970 nm depending on the composition of the copolymers. A MePEG-b-PVL copolymer of a specific composition was found to form drug-loaded micelles of 31 nm in diameter with a narrow size distribution and improve the apparent aqueous solubility of paclitaxel by more than 9000-fold. The biological activity of paclitaxel formulated in the MePEG-b-PVL micelles was confirmed in human MCF-7 breast and A2780 ovarian cancer cells. Furthermore, the biocompatibility of the copolymers was established in CHO-K1 fibroblast cells using a cell viability assay. The in vitro hydrolytic and enzymatic degradation of the micelles was also evaluated over a period of one month. The present study indicates that the MePEG-b-PVL copolymers are suitable biomaterials for hydrophobic drug formulation and delivery.