Polymeric Micelle Carrier System Research Articles

Utilization of Polymeric Micelle Magnetic Resonance Imaging (MRI) Contrast Agent for Theranostic System

We applied a polymeric micelle carrier system for the targeting of a magnetic resonance imaging (MRI) contrast agent. Prepared polymeric micelle MRI contrast agent exhibited a long circulation characteristic in blood, and considerable amount of the contrast agent was found to accumulate in colon 26 solid tumor by the EPR effect. The signal intensities of tumor area showed 2-folds increase in T1-weighted images at 24 h after i.v. injection. To observe enhancement of the EPR effect by Cderiv pretreatment on tumor targeting, we used the contrast agent for the evaluation by means of MRI. Cderiv pretreatment significantly enhanced tumor accumulation of the contrast agent. Interestingly, very high signal intensity in tumor region was found at 24 h after the contrast agent injection in Cderiv pretreated mice. The contrast agent visualized a microenvironmental change in tumor. These results indicate that the contrast agent exhibits potential use for tumor diagnostic agent. To combine with a polymeric micelle carrier system for therapeutic agent, the usage of the combination makes a new concept of "theranostic" for a better cancer treatment.

Polymeric Micelles Possessing Polyethyleneglycol as Outer Shell and Their Unique Behaviors in Accelerated Blood Clearance Phenomenon

Polymeric micelles are assemblies of synthetic polymers and have been studied and developed as drug carriers for targeting. Polymeric micelles are composed of the inner core and the outer shell, and typically form from AB-type block copolymers in which two polymer blocks are connected in a tandem form. Polyethyleneglycol (PEG) has been most commonly used as one polymer block composing the outer shell. This review describes the reasons that PEG is used for the outer shell of the polymeric micelle carrier systems. On the other hand, accelerated blood clearance (ABC) phenomenon is a well-known immunological response of PEG-coated liposomes. Since the ABC phenomenon greatly influences targeting functions of carrier systems, elaborative studies on polymeric micelles' ABC phenomenon have been done, and revealed different behaviors of the polymeric micelle systems from those of PEG-coated liposomes. These studies indicate that polymeric micelle systems are highly feasible tools for contrast agent targeting as well as theranostics.

Tumor Environment Changed by Combretastatin Derivative (Cderiv) Pretreatment That Leads to Effective Tumor Targeting, MRI Studies, and Antitumor Activity of Polymeric Micelle Carrier Systems

To evaluate effect of a vascular disrupting agent, a combretastatin derivative (Cderiv), on tumor targeting for polymeric micelle carrier systems, containing either a diagnostic MRI contrast agent or a therapeutic anticancer drug. Cderiv was pre-administered 72h before polymeric micelle MRI contrast agent injection. Accumulation of the MRI contrast agent in colon 26 murine tumor was evaluated with or without pretreatment of Cderiv by ICP and MRI. Significantly higher accumulation of the MRI contrast agent was found in tumor tissues when Cderiv was administered at 72h before MRI contrast agent injection. T(1)-weighted images of the tumor exhibited substantial signal enhancement in tumor area at 24h after the contrast agent injection. In T(1)-weighted images, remarkable T(1)-signal enhancements were observed in part of tumor, not in whole tumor. These results indicate that Cderiv pretreatment considerably enhanced the permeability of the tumor blood vessels. Antitumor activity of adriamycin encapsulated polymeric micelles with the Cderiv pretreatment suppressed tumor growth in 44As3 human gastric scirrhous carcinoma-bearing nude mice. Pretreatment of Cderiv enhanced tumor permeability, resulting in higher accumulation of polymeric micelle carrier systems in solid tumors.

Polymeric micelles as a new drug carrier system and their required considerations for clinical trials

Importance of the field: A polymeric micelle is a macromolecular assembly composed of an inner core and an outer shell, and most typically is formed from block copolymers. In the last two decades, polymeric micelles have been actively studied as a new type of drug carrier system, in particular for drug targeting of anticancer drugs to solid tumors.Areas covered in this review: In this review, polymeric micelle drug carrier systems are discussed with a focus on toxicities of the polymeric micelle carrier systems and on pharmacological activities of the block copolymers. In the first section, the importance of the above-mentioned evaluation of these properties is explained, as this importance does not seem to be well recognized compared with the importance of targeting and enhanced pharmacological activity of drugs, particularly in the basic studies. Then, designs, types and classifications of the polymeric micelle system are briefly summarized and explained, followed by a detailed discussion regarding several examples of polymeric micelle carrier systems.What the reader will gain: Readers will gain a strategy of drug delivery with polymeric carriers as well as recent progress of the polymeric micelle carrier systems in their basic studies and clinical trials.Take home message: The purpose of this review is to achieve tight connections between the basic studies and clinical trials.

Convection-Enhanced Delivery of a Synthetic Retinoid Am80, Loaded into Polymeric Micelles, Prolongs the Survival of Rats Bearing Intracranial Glioblastoma Xenografts

Prognosis for the patients with glioblastoma, the most common malignant brain tumor, remains dismal. A major barrier to progress in treatment of glioblastoma is the relative inaccessibility of tumors to chemotherapeutic agents. Convection-enhanced delivery (CED) is a direct intracranial drug infusion technique to deliver chemotherapeutic agents to the central nervous system, circumventing the blood-brain barrier and reducing systemic side effects. CED can provide wider distribution of infused agents compared to simple diffusion. We have reported that CED of a polymeric micelle carrier system could yield a clinically relevant distribution of encapsulated agents in the rat brain. Our aim was to evaluate the efficacy of CED of polymeric micellar Am80, a synthetic agonist with high affinity to nuclear retinoic acid receptor, in a rat model of glioblastoma xenografts. We also used systemic administration of temozolomide, a DNA-alkylating agent, which has been established as the standard of care for newly diagnosed malignant glioma. U87MG human glioma cells were injected into the cerebral hemisphere of nude rats. Rats bearing U87MG xenografts were treated with CED of micellar Am80 (2.4 mg/m(2)) on day 7 after tumor implantation. Temozolomide (200 mg/m(2)/day) was intraperitoneally administered daily for 5 days, starting on day 7 after tumor implantation. CED of micellar Am80 provided significantly longer survival than the control. The combination of CED of micellar Am80 and systemic administration of temozolomide provided significantly longer survival than single treatment. In conclusion, temozolomide combined with CED of micellar Am80 may be a promising method for the treatment of malignant gliomas.

Incorporation methods for cholic acid chitosan-g-mPEG self-assembly micellar system containing camptothecin

A water-insoluble anticancer agent, camptothecin (CPT) was incorporated to a polymeric micelle carrier system preparing from cholic acid chitosan-grafted poly (ethylene glycol) methyl ether (CS-mPEG-CA). CS-mPEG-CA formed a core–shell micellar structure with a critical micelle concentration (CMC) of 7.08 μg/ml. Incorporation efficiency was investigated by varying physical incorporation method and initial drug loading. Among three incorporation methods (dialysis, emulsion and evaporation methods), an emulsion method showed the highest CPT incorporation efficiency. Increasing the initial CPT loading from 5 to 40%, the incorporation efficiency decreased. In all examined CPT-loaded CS-mPEG-CA micelles, 5% initial drug loading showed the highest drug incorporation efficiency. Release of CPT from the micelles was sustained when increasing the initial CPT loading. This indicates the importance of incorporation method and the initial drug loading to obtain the optimum particle size with high drug loading and sustained drug release. When compared to the unprotected CPT, CPT-loaded CS-mPEG-CA micelles were able to prevent the hydrolysis of the lactone group of the drug. This novel CS-mPEG-CA polymer presents considerable potential interest in the further development of CPT carrier.

Encapsulation of the synthetic retinoids Am80 and LE540 into polymeric micelles and the retinoids' release control

The objective of this study was to encapsulate two synthetic retinoids Am80 and LE540 into polymeric micelles and to control the retinoids' release rate in vitro. Highly efficient encapsulation yields of these retinoids were obtained for micelles forming from PEG-poly(benzyl aspartate) block copolymers in the wide range of the benzyl substitution degree. The in vitro release examination for LE540 indicated very stable encapsulation of this retinoid owing to its strongly hydrophobic nature. On the other hand, Am80 exhibited a rapid release in Dulbecco's phosphate buffer saline. An addition of a hydrophobic alkyl amine in the Am80-encapsulation process successfully led to significant retardation of the Am80 release rate. A mechanism of the retardation was considered an increase of Am80 hydrophobicity due to an ion-pairing with the alkyl amine. This paper is the first report on release control in the polymeric micelle carrier system through the ion-pairing between an encapsulated drug and an additive.

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 (Cmax) 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.

Phase I study of NK105, a paclitaxel-incorporating micellar nanoparticle, in patients with advanced cancer

2018 Background: NK105 is a new polymeric micelle carrier system for paclitaxel (PTX). A preclinical study revealed that the plasma AUC and tumor AUC of NK105 were 90-fold higher and 25-fold higher, respectively, than those of free-PTX, i.e., the conventional PTX formulation. NK105 had higher in vivo antitumor activity and lower neurotoxicity than free-PTX. This phase I study was designed to examine the MTD, DLTs, recommended dose (RD) for phase II, and the pharmacokinetics of NK105. Methods: NK105 was administered as a 1-hour intravenous infusion every 3 weeks, without antiallergic premedication. The starting dose was 10 mg PTX equivalent/m2, and the dose was escalated according to the accelerated titration method. Results: To date, 17 patients (pts) have received the following doses: 10 mg/m2 (n=1); 20 mg/m2 (n=1); 40 mg/m2 (n=1); 80 mg/m2 (n=1); 110 mg/m2 (n=3); 150 mg/m2 (n=5); and 180 mg/m2 (n=5). The tumor types treated included pancreatic (n=9), bile duct (n=5), gastric (n=2), and colonic (n=1) cancers. Neutropenia was the most common hematological toxicity. Grade 3 fever developed in 1 pt given 180 mg/m2. No other grade 3 or 4 non-hematological toxicity, including neuropathy, was observed. DLTs occurred in pts given 180 mg/m2 (grade 4 neutropenia lasting for more than 5 days). This dose was designated as the MTD. Allergic reactions developed in only one pt at 180 mg/m2, who was sensitive to other drugs such as antibiotics anti-inflammatory. A partial response was observed in one pt with pancreatic cancer and pts with colonic and gastric cancer had stable disease. The Cmax and AUC of NK105 were dose dependent. The plasma AUC of NK105 at 180 mg/m2 was approximately 30-fold higher than that of the conventional formulation of PTX. Conclusions: Accrual is ongoing at the 150 mg/m2 dose level to determine the RD. DLT was Grade 4 neutropenia. NK105 produces prolonged high levels of PTX in plasma. A 1-hour infusion of NK105 every 3 weeks was feasible, well tolerated, and effective in patients with pancreatic cancer. Even after the long term usage, only grade 1 or 2 neuropathy was observed. NK105 will be evaluated in Phase II studies of patients with advanced pancreatic and gastric cancers. No significant financial relationships to disclose.

Intelligent thermoresponsive polymeric micelles for targeted drug delivery

Nano-order sized supramolecular assemblies called polymeric micelles possess two-separated phase structure; a hydrated hydrophilic outer shell provides their highly structural stabilities in aqueous media and a hydrophobic inner core acts as a drug loading container. First anticancer polymeric micelle carrier systems showed a selective accumulation at solid tumor tissues and a subsequent in vivo anticancer activity. Recently, stimuli-responsive polymeric micelles have been designed as the next generation of micelle systems for application in selective drug release at target sites by physical and/or chemical signals. We suggested a concept using thermoresponsive polymeric micelle drug carriers in conjunction with local heating systems for multi-targeting therapeutic systems to achieve effective cancer chemotherapy with fewer side effects. The present review article mainly focuses on strategy and molecular design of thermoresponsive polymeric micelles and discusses their potential for an intelligent targeted drug carrier system with some examples containing anti-cancer drugs.

Polymer Design and Incorporation Methods for Polymeric Micelle Carrier System Containing Water-insoluble Anti-cancer Agent Camptothecin

A water-insoluble anti-cancer agent, camptothecin (CPT) was incorporated to a polymeric micelle carrier system forming from poly(ethylene glycol)–poly(aspartate) block copolymers. Incorporation efficiency and stability were analyzed in correlation with chemical structures of the inner core-forming hydrophobic blocks as well as with incorporation methods. Among three incorporation methods (dialysis, emulsion and evaporation methods), an evaporation method brought about much higher CPT yields with less aggregation than the other two methods. By the evaporation method, CPT was incorporated to polymeric micelles in considerably high yields and with high stability using block copolymers possessing high contents of benzyl and methylnaphtyl ester groups as hydrophobic moieties. This indicates importance of molecular design of the hydrophobic block chain to obtain targeting using polymeric micelle carriers as well as importance of the drug incorporation method.

Polymeric micelle drug carrier systems: PEG-PAsp(Dox) and second generation of micellar drugs.

Polymeric micelles are one of the most refined and promising modalities of macromolecular drug delivery systems , and show unique disposition characteristics in the body suitable for the drug targeting (e.g., prolonged blood circulation and significant tumor accumulation as described in earlier chapter) . Like the other promising modalities (i.e., watersoluble polymers and long-circulating liposomes), the polymeric micelle carrier systems might possess several advantages such as (1) the applicability to a variety of therapeutic agents (e.g., hydrophobic compounds, metal complexes and charged macromolecules such as polypeptides and nucleic acids), (2) unnecessariness of chemical structure

Process design for efficient and controlled drug incorporation into polymeric micelle carrier systems

For the efficient and well-controlled incorporation of the anti cancer drug adriamycin (ADR) into the inner core of a thermo-responsive polymeric micelle carrier system, we have analyzed and optimized the incorporation procedure in this paper. A dialysis method was used for preparing the micelle solution and ADR incorporation simultaneously. Quantities of ADR and triethylamine (TEA) were varied and the effects of their quantities were analyzed. Solvent composition at the starting time of dialysis was also varied. The initial dialysis condition, solvent with 40% water, brought about the largest amount and yield of ADR incorporation. With the initial 40% water content, it was considered that the block polymers formed a micelle-like association with a swollen hydrophobic core. This swollen core may be suitable for a large amount of ADR incorporation, since this core, swollen by an organic solvent–water mixture, is expected to show a liquid-state character to allow ADR molecules entry into the cores. By starting the dialysis procedure at this 40% water content, this swollen core suitable for the ADR incorporation is considered to be maintained for a much longer period than a case starting with a polymer–ADR solution in a solvent with a water content of less than 40%, and, therefore, ADR is expected to be incorporated efficiently. Preparation temperature of 20–25°C was found to provide the most effective ADR incorporation in this thermo-responsive polymeric micelle system. These results indicate that the efficient incorporation of ADR can be achieved in consideration of the dynamic micelle formation and drug incorporation processes.

Development of the polymer micelle carrier system for doxorubicin

We show the result of pre-clinical study of NK911, a polymeric micelle carrier system for doxorubicin (DOX). The NK911 micelle carrier consists of polyethyleneglycol and conjugated doxorubicin-polyaspartic acid. It has high hydrophobic inner core, and therefore can entrap the sufficient amount of DOX. NK911 has a small particle size of about 40 nm in diameter that accumulates in tumor tissue by EPR effect showing much stronger activity than the free DOX. We plan to perform a clinical trial at National Cancer Center Hospital, Japan from 2001.

Roles of adriamycin and adriamycin dimer in antitumor activity of the polymeric micelle carrier system

Adriamycin (ADR) dimer was prepared and its antitumor activity was evaluated with mouse colon adenocarcinoma 26 (C 26). As compared with original ADR, the dimer did not show significant antitumor activity, either in vitro or in vivo. Furthermore, polymeric micelles containing varied ratios of the dimer to the original ADR were prepared. Polymeric micelles with a higher dimer/ADR ratio (9.7) showed significant antitumor activity, but the effective dose shifted higher. Effective doses were found to largely depend on the concentration of the original ADR, rather than that of the dimer at the tumor sites. Therefore, it was presumed that the original ADR played a major role in antitumor activity, and the dimer played a supplementary role to contribute selective delivery of ADR to the tumor sites.