Selective delivery of adriamycin to a solid tumor using a polymeric micelle carrier system

Vital microscopic analysis of polymeric micelle extravasation from tumor vessels: macromolecular delivery according to tumor vascular growth stage

Particles larger than a specific size have been thought to extravasate from tumor vessels but not from normal vessels. Therefore, various nanoparticles incorporating anticancer drugs have been developed to realize selective drug delivery to solid tumors. However, it is not yet clear whether nanoparticles extravasate readily from all tumor vessels including vessels of microtumors. To answer this question, we synthesized new polymeric micelles labeled with fluorescein isothiocyanate (FITC) and injected them into the tail vein of rats with implanted skinfold transparent chambers. We also analyzed, by means of time-lapse vital microscopy with image analysis, extravasation of FITC micelles from tumor vessels at different stages of growth of Yoshida ascites sarcoma LY80. Polymeric micelles readily leaked from vessels at the interface between normal and tumor tissues and those at the interface between tumor tissues and necrotic areas. The micelles showed negligible extravasation, however, from the vascular network of microtumors less than 1 mm in diameter and did not accumulate in the microtumor. Our results suggest that we must develop a novel therapeutic strategy that can deliver sufficient nanomedicine to microtumors.

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.

Encapsulation of a hydrophobic drug into a polymer-micelle core explored with synchrotron SAXS

Synchrotron small-angle X-ray scattering (SAXS) at the SPring-8 40B2 and 45XU beamlines was carried out on aqueous solutions of (PEG-P(Asp(Bzl))): partially benzyl-esterified poly(ethylene glycol)-block-poly(aspartic acid) with LE540 loaded up to 8.3 wt %, where LE540 is a very hydrophobic retinoid antagonist drug. The scattering profiles showed characteristic features for core-shell spherical micelles, confirming that P(Asp(Bzl)) forms a hydrophobic core and PEG forms a hydrophilic shell. Before the addition of LE540, a diffraction peak was observed around q = 4 nm(-1), where q is the magnitude of the scattering vector. This peak can be attributed to ordering between alpha-helices made of P(Asp(Bzl)), the so-called nonspecific hexatic arrangement. The P(Asp(Bzl)) helices disappeared as LE540 was added. This result can be interpreted by assuming a uniform distribution of LE540 in the core. By use of a core-shell spherical micelle model, the SAXS data could be well fitted for all of the samples. The analysis indicated that the core radius increases sigmoidally from 5.9 to 6.9 nm upon addition of LE540 whereas the shell radius stayed at 12.5-12.8 nm. The aggregation number that is the average number of PEG-P(Asp(Bzl))'s consisting of one micelle slightly increased from 145 to 182.

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.

Emerging trends of nanomedicine--an overview

Nanotechnology is an emerging branch of science for designing tools and devices of size 1 to 100 nm with unique function at the cellular, atomic and molecular levels. The concept of using nanotechnology in medical research and clinical practice is known as nanomedicine. Nanoparticles possess some novel properties not seen with the macro molecules and they can be manipulated by attaching therapeutic components to help in diagnosis and treatment. They can also be used to probe cellular movements and molecular changes associated with pathological states. Nanodevices like carbon nanotubes to locate and deliver anticancer drugs at the specific tumour site are under research. Nanotechnology promises construction of artificial cells, enzymes and genes. This will help in the replacement therapy of many disorders which are due to deficiency of enzymes, mutation of genes or any repair in the synthesis of proteins. Currently nanodevices like respirocytes, microbivores and probes encapsulated by biologically localized embedding have a greater application in treatment of anaemia and infections. Thus in the present scenario, nanotechnology is spreading its wings to address the key problems in the field of medicine. Hence this review discusses in detail the applications of nanotechnology in medicine with more emphasis on drug delivery and therapy.

Intelligent polymeric micelles from functional poly(ethylene glycol)-poly(amino acid) block copolymers

This review describes our recent efforts on the design and preparation of intelligent polymeric micelles from functional poly(ethylene glycol)-poly(amino acid) (PEG-PAA) block copolymers. The polymeric micelles feature a spherical sub-100 nm core-shell structure in which anticancer drugs are loaded avoiding undesirable interactions in vivo. Chemical modification of the core-forming block of PEG-PAA with a hydrazone linkage allows the polymeric micelles to release drugs selectively at acidic pH (4-6). Installation of folic acids on the micelle surface improves cancer cell-specific drug delivery efficiency along with pH-controlled drug release. These intelligent micelles appear to be superior over classical micelles that physically incorporate drugs. Studies showed both controlled drug release and targeted delivery features of the micelles reduced toxicity and improved efficacy significantly. Further developments potentiate combination delivery of multiple drugs using mixed micelles. Therefore clinically relevant performance of the polymeric micelles provides a promising approach for more efficient and patient-friendly cancer therapy.

Polymer micelles with cross-linked polyanion core for delivery of a cationic drug doxorubicin

Polymer micelles with cross-linked ionic cores were prepared by using block ionomer complexes of poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMA) copolymer and divalent metal cations as templates. Doxorubicin (DOX), an anthracycline anticancer drug, was successfully incorporated into the ionic cores of such micelles via electrostatic interactions. A substantial drug loading level (up to 50 w/w%) was achieved and it was strongly dependent on the structure of the cross-linked micelles and pH. The drug-loaded micelles were stable in aqueous dispersions exhibiting no aggregation or precipitation for a prolonged period of time. The DOX-loaded polymer micelles exhibited noticeable pH-sensitive behavior with accelerated release of DOX in acidic environment due to the protonation of carboxylic groups in the cores of the micelles. The attempt to protect the DOX-loaded core with the polycationic substances resulted in the decrease of loading efficacy and had a slight effect on the release characteristics of the micelles. The DOX-loaded polymer micelles exhibited a potent cytotoxicity against human A2780 ovarian carcinoma cells. These results point to a potential of novel polymer micelles with cross-linked ionic cores to be attractive carriers for the delivery of DOX.

Ultrasonic-activated micellar drug delivery for cancer treatment

The use of nanoparticles and ultrasound in medicine continues to evolve. Great strides have been made in the areas of producing micelles, nanoemulsions, and solid nanoparticles that can be used in drug delivery. An effective nanocarrier allows for the delivery of a high concentration of potent medications to targeted tissue while minimizing the side effect of the agent to the rest of the body. Polymeric micelles have been shown to encapsulate therapeutic agents and maintain their structural integrity at lower concentrations. Ultrasound is currently being used in drug delivery as well as diagnostics, and has many advantages that elevate its importance in drug delivery. The technique is noninvasive, thus no surgery is needed; the ultrasonic waves can be easily controlled by advanced electronic technology so that they can be focused on the desired target volume. Additionally, the physics of ultrasound are widely used and well understood; thus ultrasonic application can be tailored towards a particular drug delivery system. In this article, we review the recent progress made in research that utilizes both polymeric micelles and ultrasonic power in drug delivery.

Polymeric micelles from poly(ethylene glycol)-poly(amino acid) block copolymer for drug and gene delivery

Dramatic advances in biological research have revealed the mechanisms underlying many diseases at the molecular level. However, conventional techniques may be inadequate for direct application of this new knowledge to medical treatments. Nanobiotechnology, which integrates biology with the rapidly growing field of nanotechnology, has great potential to overcome many technical problems and lead to the development of effective therapies. The use of nanobiotechnology in drug delivery systems (DDS) is attractive for advanced treatment of conditions such as cancer and genetic diseases. In this review paper for a special issue on biomaterial research in Japan, we discuss the development of DDS based on polymeric micelles mainly in our group for anti-cancer drug and gene delivery, and also address our challenges associated with developing polymeric micelles as super-functionalized nanodevices with intelligent performance.

Histological study on side effects and tumor targeting of a block copolymer micelle on rats

Histological examinations were performed with polymeric micelle-injected rats for evaluations of possible toxicities of polymeric micelle carriers. Weight of major organs as well as body weight of rats was measured after multiple intravenous injections of polymeric micelles forming from poly(ethylene glycol)-b-poly(aspartate) block copolymer. No pathological toxic side effects were observed at two different doses, followed only by activation of the mononuclear phagocyte system (MPS) in the spleen, liver, lung, bone marrow, and lymph node. This finding confirms the absence of--or the very low level of--in vivo toxicity of the polymeric micelle carriers that were reported in previous animal experiments and clinical results. Then, immunohistochemical analyses with a biotinylated polymeric micelle confirmed specific accumulation of the micelle in the MPS. The immunohistochemical analyses also revealed, first, very rapid and specific accumulation of the micelle in the vasculatures of tumor capsule of rat ascites hepatoma AH109A, and second, the micelle's scanty infiltration into tumor parenchyma. This finding suggests a unique tumor-accumulation mechanism that is very different from simple EPR effect-based tumor targeting.

Biodegradable and biocompatible multi-arm star amphiphilic block copolymer as a carrier for hydrophobic drug delivery

Multi-arm star amphiphilic block copolymers (SABCs) with approximately 32 arms were synthesized and characterized for drug delivery applications. A hyperbranched polyester, boltorn H40 (H40), was used as the macroinitiator for the ring-opening polymerization of epsilon-caprolactone (epsilon-CL). The resulting multi-arm H40-poly(epsilon-caprolactone) (H40-PCL-OH) was further reacted with carboxyl terminated methoxy poly(ethylene glycol) (MPEG-COOH) to form H40-PCL-b-MPEG copolymers. The resulting SABCs were characterized by (1)H NMR spectroscopy and gel permeation chromatography (GPC). The critical aggregation concentration (CAC) of H40-PCL-b-MPEG was 3.8 mg/L as determined by fluorescence spectrophotometry. Below the CAC, stable unimolecular micelles were formed with an average diameter of 18 nm as measured by TEM. Above the CAC, unimolecular micelles exhibited agglomeration with an average diameter of 98 nm. The hydrodynamic diameter of these agglomerates was found to be 122 nm, as measured by dynamic light scattering (DLS). The drug loading efficacy of the H40-PCL-b-MPEG micelles was 26 wt%. Drug release study showed an initial burst followed by a sustained release of the entrapped hydrophobic model drug, 5-fluorouracil, over a period of 9-140 h. These results indicate that the H40-PCL-b-MPEG micelles have great potential as hydrophobic drug delivery carriers.

Preparation and in vivo imaging of PEG-poly(L-lysine)-based polymeric micelle MRI contrast agents

A polymeric micelle drug carrier system was applied to the targeting of an MRI (magnetic resonance imaging) contrast agent. A block copolymer, PEG-b-poly(L-lysine), was used for conjugation of gadolinium ions through chelating moieties, DOTA. The DOTA moieties were successfully conjugated to all primary amine groups of the lysine residues. The obtained block copolymer, PEG-b-poly(L-lysine-DOTA), formed a polymeric micelle. The polymeric micelle structure was maintained even after partial gadolinium chelation ( approximately 40%) to the DOTA moieties. The prepared polymeric micelle MRI contrast agent was injected into a mouse tail vein at a dose of 0.05 mmol Gd/kg. The polymeric micelle-based MRI contrast agent exhibited stable blood circulation. A considerable amount (6.1+/-0.3% of ID/g of the polymeric micelle) was found to accumulate at solid tumors 24 h after intravenous injection by means of the EPR effect. An MRI analysis revealed that the signal intensity of the tumor was enhanced 2.0-fold by the use of this contrast agent.

Disposition of drugs in block copolymer micelle delivery systems: from discovery to recovery

Since their discovery in the early 1980s, polymeric micelles have been the subject of several studies as delivery systems that can potentially improve the therapeutic performance and modify the toxicity profile of encapsulated drugs by changing their pharmacokinetic characteristics. The efforts in this area have led in recent years to the advancement of several polymeric micellar formulations to clinical trials, some of which have shown promise in changing the biodistribution of the incorporated drug after intravenous administration as a means of tumour-targeted drug delivery. Recently, the possible benefit of polymeric micellar delivery in enhancing the absorption and bioavailability of incorporated drugs from alternative routes of drug administration has attracted interest. This article provides an overview of the effect of polymeric micellar delivery on absorption, distribution, metabolism and excretion of incorporated therapeutic agents. It also aims to assess the current information on the performance of polymeric micellar delivery systems in modifying the pharmacokinetics/pharmacodynamics of the incorporated drugs in clinical trials, and to re-examine the important structural factors required for successful design of polymeric micellar delivery systems capable of inducing favourable changes in the pharmacokinetics of the encapsulated drug.

Long circulating PEGylated poly(D,L-lactide-co-glycolide) nanoparticulate delivery of Docetaxel to solid tumors

PURPOSE

The aim of this study was to investigate the ability of PEGylated poly(D,L-lactide-co-glycolide) nanoparticles (NPs) to deliver Docetaxel (DTX) (an anticancer agent) to solid tumors.

METHODS

PLGA-mPEG diblock copolymers were synthesized by ring opening polymerization reaction and characterized by (1)H NMR, FT-IR and gel permeation chromatography. NPs, with a smooth spherical shape and near 100 nm size were prepared using the emulsion solvent evaporation technique and characterized. The drug release rate was investigated in acidic and physiological media (phosphate buffer saline, pH 5.0 and 7.4). The therapeutic efficacy and biocompatibility of NP formulations were evaluated for in vitro cytotoxicity by MTT assay using MCF-7 and C26 cell lines. The pharmacokinetic and biodistribution studies were performed on C26 tumor bearing mice. The antitumor efficacy of DTX NP formulations on C26 tumor bearing mice was investigated.

RESULTS

DTX-loaded PEGylated NPs increased the drug's biological half-life while providing substantial accumulation at the solid tumors. PEGylated NPs appear to be a promising alternate carrier for DTX having greater efficacy in inhibiting tumor growth.

Therapeutic efficacy of a polymeric micellar doxorubicin infused by convection-enhanced delivery against intracranial 9L brain tumor models

Convection-enhanced delivery (CED) with various drug carrier systems has recently emerged as a novel chemotherapeutic method to overcome the problems of current chemotherapies against brain tumors. Polymeric micelle systems have exhibited dramatically higher in vivo antitumor activity in systemic administration. This study investigated the effectiveness of CED with polymeric micellar doxorubicin (DOX) in a 9L syngeneic rat model. Distribution, toxicity, and efficacy of free, liposomal, and micellar DOX infused by CED were evaluated. Micellar DOX achieved much wider distribution in brain tumor tissue and surrounding normal brain tissue than free DOX. Tissue toxicity increased at higher doses, but rats treated with micellar DOX showed no abnormal neurological symptoms at any dose tested (0.1-1.0 mg/ml). Micellar DOX infused by CED resulted in prolonged median survival (36 days) compared with free DOX (19.6 days; p = 0.0173) and liposomal DOX (16.6 days; p = 0.0007) at the same dose (0.2 mg/ml). This study indicates the potential of CED with the polymeric micelle drug carrier system for the treatment of brain tumors.

Micelles and nanoparticles for ultrasonic drug and gene delivery

Drug delivery research employing micelles and nanoparticles has expanded in recent years. Of particular interest is the use of these nanovehicles that deliver high concentrations of cytotoxic drugs to diseased tissues selectively, thus reducing the agent's side effects on the rest of the body. Ultrasound, traditionally used in diagnostic medicine, is finding a place in drug delivery in connection with these nanoparticles. In addition to their non-invasive nature and the fact that they can be focused on targeted tissues, acoustic waves have been credited with releasing pharmacological agents from nanocarriers, as well as rendering cell membranes more permeable. In this article, we summarize new technologies that combine the use of nanoparticles with acoustic power both in drug and gene delivery. Ultrasonic drug delivery from micelles usually employs polyether block copolymers and has been found effective in vivo for treating tumors. Ultrasound releases drug from micelles, most probably via shear stress and shock waves from the collapse of cavitation bubbles. Liquid emulsions and solid nanoparticles are used with ultrasound to deliver genes in vitro and in vivo. The small packaging allows nanoparticles to extravasate into tumor tissues. Ultrasonic drug and gene delivery from nanocarriers has tremendous potential because of the wide variety of drugs and genes that could be delivered to targeted tissues by fairly non-invasive means.

What are determining factors for stable drug incorporation into polymeric micelle carriers? Consideration on physical and chemical characters of the micelle inner core

Partially benzyl-esterified poly(ethylene glycol)-b-poly(aspartic acid) (PEG-P(Asp(Bzl))) having different hydrophobic inner-core structure were synthesized and analyzed. We obtained two types of the block copolymers for formation of polymeric micelle drug carriers; one had an amide-bond ratio of 1:3 (alpha/beta) in the poly(aspartic acid) residues through alkaline hydrolysis, and the other one had 100% of the alpha-amide through acid hydrolysis. Subsequently, we prepared partially benzyl-esterified block copolymers with an esterification degree of 40 to 100% in the aspartic acid residue. Regarding camptothecin (CPT) incorporation into polymeric micelles, we evaluated effects that block copolymers' inner hydrophobic block structures have on CPT behavior. Regarding CPT-incorporation stability, PEG-P(alpha,beta-Asp(Bzl) block copolymers with the alpha and beta-amides were found to exhibit higher CPT-incorporation stability. Using fluorescent probes, we evaluated the properties of inner-core blocks such as hydrophobicity and mobility/rigidity, and the findings implied that stable CPT incorporation could be obtained by an adequate balance between the micelle inner core's hydrophobicity and the micelle inner core's rigidity or between the micelle inner core's hydrophobicity and steric configuration of the hydrophobic block chain.

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.

Optimization of (1,2-diamino-cyclohexane)platinum(II)-loaded polymeric micelles directed to improved tumor targeting and enhanced antitumor activity

Polymeric micelles are promising nanocarriers, which might enhance the efficacy of antitumor drugs. Herein, polymeric micelles incorporating dichloro(1,2-diamino-cyclohexane)platinum(II) (DACHPt), the oxaliplatin parent complex, were prepared through the polymer-metal complex formation of DACHPt with poly(ethylene glycol)-b-poly(glutamic acid) [PEG-b-P(Glu)] block copolymer having different lengths of the poly(glutamic acid) block [p(Glu): 20, 40, and 70 U]. The resulting micelles were studied with the aim of optimizing the system's biological performance. DACHPt-loaded micelles (DACHPt/m) were approximately 40 nm in diameter and had a narrow size distribution. In vivo biodistribution and antitumor activity experiments (CDF1 mice bearing the murine colon adenocarcinoma C-26 inoculated subcutaneously) showed 20-fold greater accumulation of DACHPt/m at the tumor site than free oxaliplatin to achieve substantially higher antitumor efficacy. Moreover, the micelles prepared from PEG-b-P(Glu) with 20 U of P(Glu) exhibited the lowest non-specific accumulation in the liver and spleen to critically reduce non-specific accumulation, resulting in higher specificity to solid tumors. The antitumor effect of DACHPt/m was also evaluated on multiple metastases generated from intraperitoneally injected bioluminescent HeLa (HeLa-Luc) cells. The in vivo bioluminescent data indicated that DACHPt/m decreased the signal 10-to 50-fold compared to the control indicating a very strong antitumor activity. These results suggest that DACHPt/m could be an outstanding drug delivery system for oxaliplatin in the treatment of solid tumors.

Enhanced anticancer effect of conjugated linoleic acid by conjugation with Pluronic F127 on MCF-7 breast cancer cells

This study is designed to evaluate whether conjugated linoleic acid-coupled Pluronic F127 (Plu-CLA) enhances anticancer efficacy in MCF-7 breast cancer cells when compared to conjugated linoleic acid (CLA) itself. CLA was simply coupled to Pluronic F127 through ester linkage between carboxyl group of CLA and hydroxyl one of Pluronic at melting state without solvent or catalyst. Plu-CLA significantly enhanced apoptosis with increasing concentration compared with CLA itself. Moreover, it was found that p53, p21, and Bax were up-regulated, whereas Bcl-2 and procaspase 9 were down-regulated with increasing concentration of Plu-CLA. These results were attributed to the sensitization activity of Pluronic F127.

MMPs-specific PEGylated peptide-DOX conjugate micelles that can contain free doxorubicin

The goal of this study was to develop anti-cancer drug conjugates with increased anti-tumor effect and reduced toxicity. In this regard, we utilized the physiological characteristics of tumors such as angiogenesis, the expression of matrix metalloproteinases (MMPs) and the enhanced permeability and retention (EPR) effect, and designed MMPs-specific PEGylated peptide-DOX conjugate micelles containing doxorubicin. These conjugates were prepared by using two peptides, GPLGV and GPLGVRG (P5D and P7D, respectively), and doxorubicin was loaded into micelles formed by each conjugate. P5D and P7D were specifically cleaved by active MMP-2 and all conjugates showed significantly better cell viability than doxorubicin at equivalent concentrations. In vivo, animals treated with PEGylated peptide-DOX conjugate micelles showed approximately 50% of the tumor growth of the control, and doxorubicin-loaded conjugates micelles inhibited tumor growth up to about 72% compared with the control, which matched the effect of doxorubicin. Doxorubicin-loaded PEGylated peptide-DOX conjugate micelles exhibited longer half-lives and maintained higher concentrations of doxorubicin in plasma than PEGylated peptide-DOX conjugate micelles alone. Doxorubicin-loaded PEGylated peptide-DOX conjugate micelles might offer a cancer therapy with an activity that is similar to that of the parent drug but with reduced toxicity.

N-Phthaloylchitosan-g-mPEG design for all-trans retinoic acid-loaded polymeric micelles

The amphiphilic grafted copolymer N-phthaloylchitosan-grafted poly(ethylene glycol) methyl ether (PLC-g-mPEG) was synthesized using chitosan with four different degrees of deacetylations (DD) (80, 85, 90 and 95%). All-trans retinoic acid (ATRA) was incorporated into PLC-g-mPEG by dialysis method in an attempt to optimize carriers for ATRA delivery. Morphological investigation by transmission electron microscopy (TEM) showed that the particles had round and uniform shapes. The particle sizes of ATRA incorporated into micelles were about 80-160 nm depending on the initial drug-loaded and %DD of chitosan. Physicochemical properties of ATRA-loaded polymeric micelles were also investigated. It was found that %DD of chitosan, which corresponded to the N-phthaloyl groups in the inner core of the micelles, was a key factor in controlling the incorporation efficiency, stability of the drug-loaded micelles and drug release behavior. As the %DD increased, the incorporation efficiency and ATRA-loaded micelles stability increased. The sustained release profiles were also obtained at high %DD (90 and 95%). When compared to the unprotected ATRA, ATRA loaded in PLC-g-mPEG micelles was efficiently protected from photodegradation. This result suggested that loading of ATRA in micelles improved the chemical stability of ATRA.

Conjugation of Arginine-Glycine-Aspartic Acid Peptides to Poly(ethylene oxide)-b-poly(ε-caprolactone) Micelles for Enhanced Intracellular Drug Delivery to Metastatic Tumor Cells

An arginine-glycine-aspartic acid (RGD) containing model peptide was conjugated to the surface of poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) micelles as a ligand that can recognize adhesion molecules overexpressed on the surface of metastatic cancer cells, that is, integrins, and that can enhance the micellar delivery of encapsulated hydrophobic drug into a tumor cell. Toward this goal, PEO-b-PCL copolymers bearing acetal groups on the PEO end were synthesized, characterized, and assembled to polymeric micelles. The acetal group on the surface of the PEO-b-PCL micelles was converted to reactive aldehyde under acidic condition at room temperature. An RGD-containing linear peptide, GRGDS, was conjugated on the surface of the aldehyde-decorated PEO-b-PCL micelles by incubation at room temperature. A hydrophobic fluorescent probe, that is, DiI, was physically loaded in prepared polymeric micelles to imitate hydrophobic drugs loaded in micellar carrier. The cellular uptake of DiI loaded GRGDS-modified micelles by melanoma B16-F10 cells was investigated at 4 and 37 degrees C by fluorescent spectroscopy and confocal microscopy techniques and was compared to the uptake of DiI loaded valine-PEO-b-PCL micelles (as the irrelevant ligand decorated micelles) and free DiI. GRGDS conjugation to polymeric micelles significantly facilitated the cellular uptake of encapsulated hydrophobic DiI most probably by intergrin-mediated cell attachment and endocytosis. The results indicate that acetal-terminated PEO-b-PCL micelles are amenable for introducing targeting moieties on the surface of polymeric micelles and that RGD-peptide conjugated PEO-b-PCL micelles are promising ligand-targeted carriers for enhanced drug delivery to metastatic tumor cells.

A Novel Contrast Medium Detects Increased Permeability of Rat Injured Carotid Arteries in Magnetic Resonance T2 Mapping Imaging

AIM

Aim of this study was to directly detect increased permeability of vascular lesions by magnetic resonance imaging.

METHODS

A novel contrast medium with a mean hydrodynamic diameter of 100 nm was prepared from monodispersed iron colloids incorporated into micelles of block copolymers composed of polyethylene glycol and polyamino acid. T2 mapping was applied to differentiate the minimal shortening of T2 relaxation time in balloon-injured rat carotid arteries.

RESULTS

The novel contrast medium accumulated in deendothelialized arteries. T2 relaxation times of injured and uninjured arteries were 50.6 +/- 9.5 ms and 26.9 +/- 2.4 ms, respectively (the mean +/- SD, p< 0.01, n=5). The novel contrast medium, but not commercially available contrast media, shortened the T2 relaxation time of the injured artery to 35.5 +/- 9.7 ms (p< 0.01, n=4).

CONCLUSION

A novel iron contrast medium enhanced the lesions with increased permeability. The contrast medium in combination with T2 mapping may be useful to detect unstable atherosclerotic plaques.

Micellar nanocarriers: pharmaceutical perspectives

Micelles, self-assembling nanosized colloidal particles with a hydrophobic core and hydrophilic shell are currently successfully used as pharmaceutical carriers for water-insoluble drugs and demonstrate a series of attractive properties as drug carriers. Among the micelle-forming compounds, amphiphilic copolymers, i.e., polymers consisting of hydrophobic block and hydrophilic block, are gaining an increasing attention. Polymeric micelles possess high stability both in vitro and in vivo and good biocompatibility, and can solubilize a broad variety of poorly soluble pharmaceuticals many of these drug-loaded micelles are currently at different stages of preclinical and clinical trials. Among polymeric micelles, a special group is formed by lipid-core micelles, i.e., micelles formed by conjugates of soluble copolymers with lipids (such as polyethylene glycol-phosphatidyl ethanolamine conjugate, PEG-PE). Polymeric micelles, including lipid-core micelles, carrying various reporter (contrast) groups may become the imaging agents of choice in different imaging modalities. All these micelles can also be used as targeted drug delivery systems. The targeting can be achieved via the enhanced permeability and retention (EPR) effect (into the areas with the compromised vasculature), by making micelles of stimuli-responsive amphiphilic block-copolymers, or by attaching specific targeting ligand molecules to the micelle surface. Immunomicelles prepared by coupling monoclonal antibody molecules to p-nitrophenylcarbonyl groups on the water-exposed termini of the micelle corona-forming blocks demonstrate high binding specificity and targetability. This review will discuss some recent trends in using micelles as pharmaceutical carriers.

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.

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.

Shell cross-linked stearic acid grafted chitosan oligosaccharide self-aggregated micelles for controlled release of paclitaxel

Stearic acid grafted chitosan oligosaccharide (CSO-SA) with different degree of amino substitution (SD) was synthesized by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated coupling reaction. The critical micelle concentration (CMC) of CSO-SA with different SD was about 0.06, 0.04, 0.01 mg/ml, respectively. With the increase of micelle concentration, the micelle size decreased, and the zeta potential increased. On the other hand, with the increase of SD of CSO-SA, the micelle size and zeta potential decreased due to the increased hydrophobic interaction of SA and the reduced free amino groups. To increase the stability of the micelle in vivo and controll drug release, the shells of micelles were cross-linked by glutaraldehyde. By controlling the molar ratio of CSO-SA to glutaraldehyde, the cross-linking of intra-micelle could be reached, and the nanoparticle with smaller size than that of its initial micelle was obtained. Paclitaxel was then used as model drug to incorporate into the micelles, and the surfaces of the micelles were further cross-linked by glutaraldehyde to form drug loaded and shell cross-linked nanoparticles. The effects of drug loading, SD of CSO-SA and cross-link degree on the size, zeta potential, drug entrapment efficiency and in vitro drug release behavior of micelles and its cross-linked nanoparticles were investigated. The higher drug entrapment efficiencies (above 94%) were observed in all case. The charged amounts of drug did not affect the drug release behavior. The drug release rate decreased with the increase of SD of CSO-SA and cross-link degree.

Toward the Emergence of Nanoneurosurgery: Part III—Nanomedicine: Targeted Nanotherapy, Nanosurgery, and Progress Toward the Realization of Nanoneurosurgery

The notion of nanotechnology has evolved since its inception as a fantastic conceptual idea to its current position as a mainstream research initiative with broad applications among all divisions of science. In the first part of this series, we reviewed the structures and principles that comprise the main body of knowledge of nanoscience and nanotechnology. In the second part, we discussed applications of nanotechnology to the emerging field of nanomedicine, with specific attention on medical diagnostics and imaging. This article further explores the applications of nanotechnology to nanomedicine. Specific attention is given to developments in therapeutic modalities, including advanced drug delivery systems and targeted nanotherapy, which will form the basis for the treatment arm of mature nanomedicine. A variety of modalities are discussed, including polymeric nanoparticles, micelles, liposomes, dendrimers, fullerenes, hydrogels, nanoshells, and smart surfaces. Applications of nanotechnology to nanosurgery and nanoneurosurgery are presented. Femtosecond laser systems, nanoneedles, and nanotweezers are presented as technologies that are operational at the nanoscale level and have the potential to revolutionize the practice of neurosurgery in a profound and momentous way.

Preparation of camptothecin-loaded polymeric micelles and evaluation of their incorporation and circulation stability

To improve its aqueous solubility and stability in biological fluid, CPT was physically loaded in polymeric micelles. Polymeric micelles were composed of various poly(ethylene glycol)-poly(aspartate ester) block copolymers (PEG-P(Asp(R))). The incorporation and circulation stability of CPT micelles were evaluated by measuring the CPT in micelle using gel-permeation chromatography and by CPT concentration measurement after intravenous injection using HPLC, respectively, in terms of chemical structure of block copolymers. The stability of CPT-loaded micelles in vivo depended on the amount of benzyl esters, and length of PEG in the polymers to a greater degree than it did in vitro. A stable formulation of CPT-loaded micelles was obtained using PEG-P(Asp) with PEG of 5,000 (MW), 27 Asp units, and 57-75% benzyl esterification of Asp residue. This CPT-loaded micelles showed about a 17-fold lower blood clearance value than unstable micelles. The CPT-loaded micelles are potentially delivered to tumor sites owing to an extended circulation in the blood stream.

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.