Stabilization of disulfide linkage in drug-polymer-immunoglobulin conjugate by microenvironmental control

The stability of disulfide linkage in the conjugate composed of the anti-cancer agent adriamycin, poly(ethylene glycol)-poly(aspartic acid) block copolymer, and immunoglobulin G was studied. The disulfide linkage between the block copolymer and immunoglobulin G was found to be resistant to reduction with dithiothreitol (DTT). This extraordinary resistance is considered to be brought about by steric hindrance of the poly(aspartic acid) chain binding adriamycin.     

Novel polymer-DNA hybrid polymeric micelles composed of hydrophobic poly(D,L-lactic-co-glycolic acid) and hydrophilic oligonucleotides.

Biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) was chemically conjugated to oligonucleotide (ODN) to form an amphiphatic structure which is similar to an A-B type block copolymer. A terminal end of PLGA was activated and reacted with primary amine-terminated ODN. The ODN/PLGA conjugates self-assembled in aqueous solution to form a micellar structure by serving PLGA segments as a hydrophobic core and ODN segments as a surrounding hydrophilic corona. Critical micelle concentration was determined by a spectroflurometric method. Atomic force microscopic observation revealed that the micelle size was around 80 nm. These micelles could release ODN in a sustained manner by controlled degradation of hydrophobic PLGA chains. Compared to unconjugated ODN, the ODN/PLGA micelles could be more efficiently transported within cells, presumably by endocytosis. This study proposes a potential delivery method of ODN into cells by forming hybrid ODN/PLGA micelles.     

Hyperbranched double hydrophilic block copolymer micelles of poly(ethylene oxide) and polyglycerol for pH-responsive drug delivery

We report the synthesis of a well-defined hyperbranched double hydrophilic block copolymer of poly(ethylene oxide)-hyperbranched-polyglycerol (PEO-hb-PG) to develop an efficient drug delivery system. In specific, we demonstrate the hyperbranched PEO-hb-PG can form a self-assembled micellar structure on conjugation with the hydrophobic anticancer agent doxorubicin, which is linked to the polymer by pH-sensitive hydrazone bonds, resulting in a pH-responsive controlled release of doxorubicin. Dynamic light scattering, atomic force microscopy, and transmission electron microscopy demonstrated successful formation of the spherical core-shell type micelles with an average size of about 200 nm. Moreover, the pH-responsive release of doxorubicin and in vitro cytotoxicity studies revealed the controlled stimuli-responsive drug delivery system desirable for enhanced efficiency. Benefiting from many desirable features of hyperbranched double hydrophilic block copolymers such as enhanced biocompatibility, increased water solubility, and drug loading efficiency as well as improved clearance of the polymer after drug release, we believe that double hydrophilic block copolymer will provide a versatile platform to develop excellent drug delivery systems for effective treatment of cancer.     

Synthesis of biocompatible,stimuli-responsive,physical gels based on ABA triblock copolymers

ABA triblock copolymers [A = 2-(diisopropylamino)ethyl methacrylate), DPA or 2-(diethylamino)ethyl methacrylate), DEA; B = 2-methacryloyloxyethyl phosphorylcholine, MPC] prepared using atom transfer radical polymerization dissolve in acidic solution but form biocompatible free-standing gels at around neutral pH in moderately concentrated aqueous solution (above approximately 10 w/v % copolymer). Proton NMR studies indicate that physical gelation occurs because the deprotonated outer DPA (or DEA) blocks become hydrophobic, which leads to attractive interactions between the chains: addition of acid leads to immediate dissolution of the micellar gel. Release studies using dipyridamole as a model hydrophobic drug indicate that sustained release profiles can be obtained from these gels under physiologically relevant conditions. More concentrated DPA-MPC-DPA gels give slower release profiles, as expected. At lower pH, fast, triggered release can also be achieved, because gel dissolution occurs under these conditions. Furthermore, the nature of the outer block also plays a role; the more hydrophobic DPA-MPC-DPA triblock gels are formed at lower copolymer concentrations and retain the drug longer than the DEA-MPC-DEA triblock gels.     

Synthesis of bioadhesive lectin-HPMA copolymer-cyclosporin conjugates

An amino group containing cyclosporin A (CsA) derivative has been synthesized and conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer via an aromatic azo bond, which can be specifically cleaved by azoreductase activity in colon to release the drug for the treatment of colon diseases. Lectins, peanut (Arachis hypogea) agglutinin (PNA) and wheat germ agglutinin (WGA), have been conjugated to HPMA copolymer-CsA derivative conjugates (PCsA), respectively, to give bioadhesive conjugates. The PNA and WGA are the targeting proteins that can bind to diseased colon tissue and healthy tissue, respectively. There were on average four P(CsA) copolymer chains attached on one WGA molecule with a drug content of 16.0 wt % and five P(CsA) copolymer chains attached on one PNA molecule with a drug content of 11.5 wt %. The incubation of a P(CsA) copolymer with the rat cecal contents resulted in the cleavage of the azo bond and release of the cyclosporin derivative. The biological evaluation of the conjugates is under way.     

Folate-conjugated thermoresponsive block copolymers: highly efficient conjugation and solution self-assembly

A combination of controlled radical polymerization and azide-alkyne click chemistry was employed to prepare temperature-responsive block copolymer micelles conjugated with biological ligands with potential for active targeting of cancer tissues. Block copolymers of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization with an azido chain transfer agent (CTA). Pseudo-first-order kinetics and linear molecular weight dependence on conversion were observed for the RAFT polymerizations. CuI-catalyzed coupling with propargyl folate resulted in folic acid residues being efficiently conjugated to the alpha-azido chain ends of the homo and block copolymers. Temperature-induced self-assembly resulted in aggregates capable of controlled release of a model hydrophobic drug. CuI-catalyzed azide-alkyne cycloaddition has proven superior to conventional methods for conjugation of biological ligands to macromolecules, and the general strategy presented herein can potentially be extended to the preparation of folate-functionalized assemblies with other stimuli susceptibility (e.g., pH) for therapeutic and imaging applications.     

Self-assembled micelles of biodegradable triblock copolymers based on poly(ethyl ethylene phosphate) and poly(-caprolactone) as drug carriers

A series of novel amphiphilic triblock copolymers of poly(ethyl ethylene phosphate) and poly(-caprolactone) (PEEP-PCL-PEEP) with various PEEP and PCL block lengths were synthesized and characterized. These triblock copolymers formed micelles composed of a hydrophobic core of poly(-caprolactone) (PCL) and a hydrophilic shell of poly(ethyl ethylene phosphate) (PEEP) in aqueous solution. The micelle morphology was spherical, determined by transmission electron microscopy. It was found that the size and critical micelle concentration values of the micelles depended on both hydrophobic PCL block length and PEEP hydrophilic block length. The in vitro degradation characteristics of the triblock copolymers were investigated in micellar form, showing that these copolymers were completely biodegradable under enzymatic catalysis of Pseudomonas lipase and phosphodiesterase I. These triblock copolymers were used for paclitaxel (PTX) encapsulation to demonstrate the potential in drug delivery. PTX was successfully loaded into the micelles, and the in vitro release profile was found to be correlative to the polymer composition. These biodegradable triblock copolymer micelles are potential as novel carriers for hydrophobic drug delivery.     

Preparation and biological characterization of polymeric micelle drug carriers with intracellular pH-triggered drug release property: tumor permeability, controlled subcellular drug distribution, and enhanced in vivo antitumor efficacy

A novel intracellular pH-sensitive polymeric micelle drug carrier that controls the systemic, local, and subcellular distributions of pharmacologically active drugs has been developed in this study. The micelles were prepared from self-assembling amphiphilic block copolymers, poly(ethylene glycol)-poly(aspartate hydrazone adriamycin), in which the anticancer drug, adriamycin, was conjugated to the hydrophobic segments through acid-sensitive hydrazone linkers. By this polymer design, the micelles can stably preserve drugs under physiological conditions (pH 7.4) and selectively release them by sensing the intracellular pH decrease in endosomes and lysosomes (pH 5-6). In vitro and in vivo studies show that the micelles have the characteristic properties, such as an intracellular pH-triggered drug release capability, tumor-infiltrating permeability, and effective antitumor activity with extremely low toxicity. The acquired experimental data clearly elucidate that the optimization of both the functional and structural features of polymeric micelles provides a promising formulation not only for the development of intracellular environment-sensitive supramolecular devices for cancer therapeutic applications but also for the future treatment of intractable cancers with limited vasculature.     

Synthesis and characterization of biodegradable poly(ethylene glycol)-block-poly(5-benzyloxy-trimethylene carbonate) copolymers for drug delivery

Amphiphilic diblock copolymers with various block compositions were synthesized with monomethoxy-terminated poly(ethylene glycol) (MePEG) as the hydrophilic block and poly(5-benzyloxy-trimethylene carbonate) (PBTMC) as the hydrophobic block. When the copolymerization was conducted using MePEG as a macroinitiator and stannous 2-ethylhexanoate (Sn(Oct)2) as a catalyst, the molecular weight of the second block was uncontrollable, and the method only afforded a mixture of homopolymer and copolymer with a broad molecular weight distribution. By contrast, the use of the triethylaluminum-MePEG initiator yielded block copolymers with controllable molecular weight and a more narrow molecular weight distribution than the copolymers obtained using Sn(Oct)2. GPC and 1H NMR studies confirmed that the macroinitiator was consumed and the copolymer composition was as predicted. Two of the newly synthesized MePEG-b-PBTMC copolymers were evaluated in terms of properties primarily relating to their use in micellar drug delivery. MePEG-b-PBTMC micelles with a narrow monomodal size distribution were prepared using a high-pressure extrusion technique. The MePEG-b-PBTMC copolymers were also confirmed to be biodegradable and noncytotoxic.     

Conjugation of arginine-glycine-aspartic acid peptides to poly(ethylene oxide)-b-poly(epsilon-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.     

Controlling the aggregation of conjugates of streptavidin with smart block copolymers prepared via the RAFT copolymerization technique

Block copolymers containing stimuli-responsive segments provide important new opportunities for controlling the activity and aggregation properties of protein-polymer conjugates. We have prepared a RAFT block copolymer of a biotin-terminated poly(N-isopropylacrylamide) (PNIPAAm)-b-poly(acrylic acid) (PAA). The number-average molecular weight (M(n)) of the (PNIPAAm)-b-(PAA) copolymer was determined to be 17.4 kDa (M(w)/M(n) = 1.09). The PNIPAAm block had an M(n) of 9.5 kDa and the poly(acrylic acid) (PAA) block had an M(n) of 7.9 kDa. We conjugated this block copolymer to streptavidin (SA) via the terminal biotin on the PNIPAAm block. We found that the usual aggregation and phase separation of PNIPAAm-SA conjugates that follow the thermally induced collapse and dehydration of PNIPAAm (the lower critical solution temperature (LCST) of PNIPAAm is 32 degrees C in water) is prevented through the shielding action of the PAA block. In addition, we show that the cloud point and aggregation properties (as measured by loss in light transmission) of the [(PNIPAAm)-b-(PAA)]-SA conjugate also depended on pH. At pH 7.0 and at temperatures above the LCST, the block copolymer alone was found to form particles of ca. 60 nm in diameter, while the bioconjugate exhibited very little aggregation. At pH 5.5 and 20 degrees C, the copolymer alone was found to form large aggregates (ca. 218 nm), presumably driven by hydrogen bonding between the -COOH groups of PAA with other -COOH groups and also with the -CONH- groups of PNIPAAm. In comparison, the conjugate formed much smaller particles (ca. 27 nm) at these conditions. At pH 4.0, however, large particles were formed from the conjugate both above and below the LCST (ca. 700 and 540 nm, respectively). These results demonstrate that the aggregation properties of the block copolymer-SA conjugate are very different from those of the free block copolymer, and that the outer-oriented hydrophilic block of PAA shields the intermolecular aggregation of the block copolymer-SA bioconjugate at pH values where the -COOH groups of PAA are significantly ionized.     

Diethylenetriaminepentaacetic acid-gadolinium (DTPA-Gd)-conjugated polysuccinimide derivatives as magnetic resonance imaging contrast agents

Biocompatible polysuccinimide (PSI) derivatives conjugated with diethylenetriaminepentaacetic acid gadolinium (DTPA-Gd) were prepared as magnetic resonance imaging (MRI) contrast agents. In this study, we synthesized PSI derivatives incorporating methoxy-poly(ethylene glycol) (mPEG) as hydrophilic ligand, hexadecylamine as hydrophobic ligand, and DTPA-Gd as contrast agent. PSI was synthesized by the polycondensation polymerization of aspartic acid. All the synthesized materials were characterized by proton nuclear magnetic resonance (1H NMR). Critical micellization concentrations were determined using fluorescent probes (pyrene). Micelle size and shape were measured by electro-photometer light scattering (ELS) and atomic force microscopy (AFM). The formed micelle size ranged from 100 to 300 nm. The T1-weighted MR images of the phantom prepared with PSI-mPEG-C16-(DTPA-Gd) were obtained in a 3.0 T clinical MR imager, and the conjugates showed a great potential as MRI contrast agents.     

Synthesis, characterization, antitumor activity of pluronic mimicking copolymer micelles conjugated with doxorubicin via acid-cleavable linkage

Pluronic mimicking poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer having multiple hydroxyl groups in the PPO middle segment (core-functionalized Pluronic: CF-PLU) was synthesized for conjugation of doxorubicin (DOX). DOX was conjugated on the multiple hydroxyl groups of CF-PLU via an acid-labile hydrazone linkage (CF-PLU-DOX). In aqueous solution, CF-PLU-DOX copolymers self-assembled to form a core/shell-type micelle structure consisting of a hydrophobic DOX-conjugated PPO core and a hydrophilic PEO shell layer. The conjugated DOX from CF-PLU-DOX micelles was released out more rapidly at pH 5 than pH 7.4, indicating that the hydrazone linkage was cleaved under acidic condition. CF-PLU-DOX micelles exhibited greatly enhanced cytotoxicity for MCF-7 human breast cancer cells compared to naked DOX, while CF-PLU copolymer itself showed extremely low cytotoxicity. Flow cytometry analysis revealed that the extent of cellular uptake for CF-PLU-DOX micelles was greater than free DOX. Confocal image analysis also showed that CF-PLU-DOX micelles had a quite different intracellular distribution profile from free DOX. CF-PLU-DOX micelles were mainly distributed in the cytoplasm, endosomal/lysosomal vesicles, and nucleus, while free DOX was localized mainly within the nucleus, suggesting that CF-PLU-DOX micellar formulation might be advantageously used for overcoming the multidrug resistance (MDR) effect, which gradually develops in many tumor cells during repeated drug administration.     

Triply triggered doxorubicin release from supramolecular nanocontainers

The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly(N-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers.     

Solubilization and controlled release of a hydrophobic drug using novel micelle-forming ABC triblock copolymers

Amphiphilic ABC triblock copolymers composed of monomethoxy-capped poly(ethylene glycol) (MPEG), poly(2-(dimethylamino)ethyl methacrylate) (DMA), and poly(2-(diethylamino)ethyl methacrylate) (DEA) have been synthesized by atom transfer radical polymerization (ATRP). These copolymers dissolve molecularly in acidic aqueous media at room temperature due to protonation of the tertiary amine groups on the DMA and DEA residues. On adjusting the pH with base, micellization occurred at pH 8, with the water-insoluble, deprotonated DEA block forming the hydrophobic cores and the MPEG and DMA blocks forming the hydrophilic micellar coronas and inner shells, respectively. This pH-induced micellization has been exploited to develop a solvent-free protocol for drug loading. A model hydrophobic drug, dipyridamole (DIP), which dissolves in acid but is insoluble above pH 5.8, was incorporated into the micelles by increasing the pH of an aqueous drug/copolymer mixture to 9. Both the empty and the drug-loaded micelles were characterized by dynamic light scattering and fluorescence studies. The interaction of both pyrene and DIP with the MPEG-DMA-DEA micelles was studied by fluorescence; both compounds had relatively high partition coefficients into the micelles, 4.5 x 10(5) and 1.5 x 10(4), respectively. Intensity-average micelle diameters ranged from 20 to 90 nm, depending on the polymer composition and concentration. Shorter MPEG blocks (Mn = 2000) produced larger micelles than longer MPEG blocks (Mn = 5000) due to the shift in the hydrophilic-hydrophobic balance of the copolymer. Transmission electron microscopy studies of the drug-loaded micelles indicated spherical morphologies and reasonably uniform particle size distributions, which is in marked contrast to the needlelike morphology observed for pure DIP in the absence of the copolymer. Experiments on controlled release demonstrated that DIP-loaded MPEG-DMA-DEA micelles act as a drug carrier, giving slow release to the surrounding solution over a period of days. Rapid release can be triggered by reducing the pH to reverse the micellization.     

Evaluation of protein-N-(2-hydroxypropyl)methacrylamide copolymer conjugates as targetable drug carriers. 1. Binding, pinocytic uptake and intracellular distribution of transferrin and anti-transferrin receptor antibody conjugates

The transferrin receptor of human skin fibroblasts was studied as an in vitro model target antigen receptor for interaction with protein-polymer conjugates having potential for targeted drug delivery. Pinocytic uptake of 125I-labelled N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugated to monoclonal antibody B3/25 (specific for the transferrin receptor) or transferrin was up to 9-fold greater than uptake of the parent HPMA copolymer. The ability of these conjugates to bind specifically was confirmed by Scatchard analysis. Pinocytic internalisation was dependent on the molecular mass of the conjugate. Intracellular routing following internalisation was evaluated using density-gradient centrifugation. Unmodified HPMA copolymer was transferred via the endosomal compartment into secondary lysosomes, where, being resistant to degradation, it accumulated. Although the majority of endocytosed transferrin is recycled via the endosome, it was shown that any transferrin reaching the lysosomes was rapidly degraded and low-molecular-weight degradation products were released. Monoclonal antibody B3/25 showed a subcellular distribution consistent with prolongation on the cell surface, followed by internalisation and subcellular trafficking, via endosomes, into the lysosomal compartment, with subsequent degradation. Conjugation of protein to HPMA copolymer increased lysosomal accumulation of polymer up to 9-fold, with no detectable degradation of conjugate. The data presented here have implications regarding clinical potential of protein-HPMA copolymer conjugates designed for lysosomotropic drug delivery.     

The effect of bispecific monoclonal antibody recognizing both hepatoma-specific membrane glycoprotein and anthracycline drugs on the metastatic growth of hepatoma AH66

A monoclonal mouse antibody (MoHG) was produced using in vitro cultured AH66R tumor cells treated with cholesteryl hemisuccinate as an immunogen. The antibody identified a 90 kd membrane glycoprotein (HG-90) which is expressed on in vitro cultured hepatoma cell lines AH66 and AH66R. A monoclonal antibody was prepared to the anthracycline drug daunomycin, and it also reacted with adriamycin. A fusion was made of the hybridoma HG-90 with the hybridoma which recognized daunomycin/adriamycin. This bispecific hybridoma A8C recognized both determinants. We studied the therapeutic effect of the A8C bispecific antibody with adriamycin treatment and compared it to the effect of the bispecific antibody to which adriamycin had been conjugated via an albumin (Alb) bridge. The therapy model used was the tumor AH66R in Donryu rats. Tumor bearing rats had their subcutaneous tumors resected on day 10, a time when distant metastases were present. After the surgical resection of the tumor the rats were injected intravenously for two cycles with the bispecific antibodies, followed by the administration of adriamycin (ADR) or MoHG.Alb.ADR conjugates. A slight therapeutic effect occurred with either MoHG or ADR alone but treatment with the bispecific antibody followed by the administration of ADR or with the MoHG.Alb.ADR conjugates significantly prolonged survival, with 60% of the treated animals being "tumor free" when sacrificed on day 80. Lower serum concentrations of alphafetoprotein were observed with the bispecific antibody and drug treatment. This suggests that the bispecific antibody/drug treatment is potentially more beneficial in the suppression of distant metastases than the MoHG.Alb.ADR conjugate. This may be due to an increase in the local drug concentration of unmodified adriamycin.     

Specific and nonspecific macromolecule-drug conjugates for the improvement of cancer chemotherapy

Antineoplastic drugs such as daunomycin, adriamycin, methotrexate, 5-fluorouridine, cytosine arabinoside, and platinate were bound to antibodies directly or via a polymeric bridge. The drug antibody conjugates retained most of their drug and antibody activities when tested in vitro. Daunomycin–antibody conjugates were shown to penetrate tumor cells in the conjugated form. In animals, daunomycin–antibody conjugates were at least as effective chemotherapeutically as the corresponding free drugs and considerably less toxic. In some tumor systems, the daunomycin–antibody conjugates represented an improvement over the free drug. This improvement was restricted in some tumors to a particular injection route of the tumor and the treatment.     

New hydrazone derivatives of adriamycin and their immunoconjugates--a correlation between acid stability and cytotoxicity

New N-substituted hydrazine linkers were synthesized and their hydrazone derivatives of adriamycin were prepared. These functionalized adriamycin derivatives were conjugated with a monoclonal antibody, 5E9. The release rate of adriamycin from the hydrazones and from some of the conjugates was studied, and their relationship to the IC50's of the conjugate against 5E9-positive Daudi cells was investigated.     

Polymeric micelles with water-insoluble drug as hydrophobic moiety for drug delivery

The hydrophobic block of polymeric micelles formed by amphiphilic copolymers has no direct therapeutical effect, and the metabolites of these hydrophobic segments might lead to some unexpected side effects. Here the hydrophobic core of polymeric micelles is replaced by highly water-insoluble drugs themselves, forming a new micellar drug delivery system. By grafting hydrophobic drugs of paclitaxel (PTX) onto the surface of hydrophilic hyperbranched poly(ether-ester) (HPEE), we constructed an amphiphilic copolymer (HPEE-PTX). HPEE-PTX could self-assemble into micellar nanoparticles in aqueous solution with tunable drug contents from 4.1 to 10.7%. Moreover, the hydrolysis of HPEE-PTX in serum resulted in the cumulative release of PTX. In vivo evaluation indicated that the dosage toleration of PTX in mice had been improved greatly and HPEE-PTX micellar nanoparticles could be used as an efficient prodrug with satisfactory therapeutical effect. We believe that most of the lipophilic drugs could improve their characters through this strategy.