Biodegradable polymeric micelles composed of doxorubicin conjugated PLGA-PEG block copolymer.

Biodegradable polymeric micelles containing doxorubicin in the core region were prepared from a di-block copolymer composed of doxorubicin-conjugated poly(DL-lactic-co-glycolic acid) (PLGA) and polyethyleneglycol (PEG). The di-block copolymer of PLGA-PEG was first synthesized and the primary amino group of doxorubicin was then conjugated to the terminal hydroxyl group of PLGA, which had been pre-activated using p-nitrophenyl chloroformate. The resulting polymeric micelles in aqueous solution were characterized by measurement of size, drug loading, and critical micelle concentration. The micelles containing chemically-conjugated doxorubicin exhibited a more sustained release profile than PEG-PLGA micelles containing physically-entrapped doxorubicin. The cytotoxic activity of the micelles against HepG2 cells was greater than free doxorubicin, suggesting that the micelles containing conjugated doxorubicin were more effectively taken up cellularly, by an endocytosis mechanism rather than by passive diffusion. Confocal microscopic observation and flow cytometry analysis supported the enhanced cellular uptake of the micelles.     

Doxorubicin-conjugated biodegradable polymeric micelles having acid-cleavable linkages.

Doxorubicin was chemically conjugated to the terminal end of a di-block copolymer composed of poly(L-lactic acid) (PLLA) and methoxy-poly(ethylene glycol) (mPEG) via two acid-cleavable linkages. A hydrazone bond and a cis-acotinyl bond were formed between doxorubicin and the terminal group of PLLA segment in the block copolymer. Doxorubicin-conjugated PLLA-mPEG di-block copolymers self-assembled to form micelles in aqueous solution. The doxorubicin-conjugated micelles were about 89.1 nm in diameter and their critical micelle concentration was 1.3 microg/ml. These values were comparable with those of unconjugated micelles. In an acidic condition, the conjugated doxorubicin in the hydrazone linkage was readily cleaved, releasing doxorubicin in an intact structure. Doxorubicin-conjugated PLLA-mPEG micelles were more potent in cell cytotoxicity than free doxorubicin, suggesting that they were more easily taken up within cells with concomitant rapid release of cleaved doxorubicin into the cytoplasm from acidic endosomes.     

Folate receptor mediated intracellular protein delivery using PLL-PEG-FOL conjugate.

To develop a receptor-mediated intracellular delivery system that can transport therapeutic proteins or other bioactive macromolecules into a specific cell, a di-block copolymer conjugate, poly(L-lysine)-poly(ethylene glycol)-folate (PLL-PEG-FOL), was synthesized. The PLL-PEG-FOL conjugate was physically complexed with fluorescein isothiocyanate conjugated bovine serum albumin (FITC-BSA) in an aqueous phase by ionic interactions. Cellular uptake of PLL-PEG-FOL/FITC-BSA complexes was greatly enhanced against a folate receptor over-expressing cell line (KB cells) compared to a folate receptor deficient cell line (A549 cells). The presence of an excess amount of free folate (1 mM) in the medium inhibited the intracellular delivery of PLL-PEG-FOL/FITC-BSA complexes. This suggests that the enhanced cellular uptake of FITC-BSA by KB cells in a specific manner was attributed to folate receptor-mediated endocytosis of the complexes having folate moieties on the surface. The PLL-PEG-FOL di-block copolymer could be potentially applied for intracellular delivery of a wide range of other biological active agents that have negative charges on the surface.     

Polymeric micelle for tumor pH and folate-mediated targeting.

Novel pH-sensitive polymeric mixed micelles composed of poly(L-histidine) (polyHis; M(w) 5000)/PEG (M(n) 2000) and poly(L-lactic acid) (PLLA) (M(n) 3000)/PEG (M(n) 2000) block copolymers with or without folate conjugation were prepared by diafiltration. The micelles were investigated for pH-dependent drug release, folate receptor-mediated internalization and cytotoxicity using MCF-7 cells in vitro. The polyHis/PEG micelles showed accelerated adriamycin release as the pH decreased from 8.0. When the cumulative release for 24 h was plotted as a function of pH, the gradual transition in release rate appeared in a pH range from 8.0 to 6.8. In order to tailor the triggering pH of the polymeric micelles to the more acidic extracellular pH of tumors, while improving the micelle stability at pH 7.4, the PLLA/PEG block copolymer was blended with polyHis/PEG to form mixed micelles. Blending shifted the triggering pH to a lower value. Depending on the amount of PLLA/PEG, the mixed micelles were destabilized in the pH range of 7.2-6.6 (triggering pH for adriamycin release). When the mixed micelles were conjugated with folic acid, the in vitro results demonstrated that the micelles were more effective in tumor cell kill due to accelerated drug release and folate receptor-mediated tumor uptake. In addition, after internalization polyHis was found to be effective for cytosolic ADR delivery by virtue of fusogenic activity. This approach is expected to be useful for treatment of solid tumors in vivo.     

Characterization of physical entrapment and chemical conjugation of adriamycin in polymeric micelles and their design for in vivo delivery to a solid tumor

An anticancer drug adriamycin (ADR) was incorporated into polymeric micelles forming from poly(ethylene glycol)-poly(aspartic acid) block copolymer by chemical conjugation and physical entrapment. Structural stability of the polymeric micelles was found to be dependent on both the contents of chemically conjugated and physically entrapped ADR. The polymeric micelle with high contents of the chemically conjugated ADR and the physically entrapped ADR expressed very high in vivo antitumor activity against murine C 26 tumor, while the polymeric micelle with only the chemically conjugated ADR showed negligible in vivo activity. This indicates that the physically entrapped ADR played a major role in antitumor activity in vivo. For the polymeric micelle with the high ADR contents, it was found that a dimer of adriamycin molecules formed and that this dimer was physically entrapped in the inner core of the micelle as well as intact ADR.     

Co-delivery of doxorubicin and shRNA of Beclin1 by folate receptor targeted pullulan-based multifunctional nanomicelles for combinational cancer therapy

Doxorubicin (DOX) is a widely-used effective antitumor agent. However, its clinical application is limited due to its side effects including anti-apoptotic defense of cancer cells caused by DOX-induced autophagy and deleterious effects in normal tissues. Therefore, in this study, a new folate (FA)-decorated amphiphilic bifunctional pullulan-based copolymer (named as FPDP) was developed as an efficient nano-carrier for the co-delivery of DOX and short hairpin RNA of Beclin1, a pivotal autophage-related gene, to enhance the anticancer effect of DOX by the blockade of the Beclin1 protein mediated autophagy process. In FPDP molecules, pullulan was modified with lipophilic desoxycholic acid for the formation of micelles, the introduced low molecular weight (1 kDa) branched polyethylenimine (PEI) was for shBeclin1 delivery, and folate (FA) was employed as the tumor-targeting group. FPDP micelles demonstrated an average diameter of 161.9 nm, good biocompatibility, applicable storage stability, excellent loading capacities for both DOX and shBeclin1 and a sustained drug release profile. In vitro cell culture experiments demonstrated that the uptake amount of FPDP/DOX micelles in folate receptor positive (FR⁺) HeLa cells was more than that in folate receptor negative (FR⁻) HepG2 cells, leading to significantly higher cytotoxicity against FR⁺ HeLa cells. The simultaneous co-delivery of shBeclin1 and DOX to HeLa cells with FPDP micelles led to efficient reduction in the expression level of Beclin1 as well as synergistic cell apoptotic induction. Furthermore, in vivo studies revealed superior antitumor efficacy of tumor-targeted FPDP/DOX/shBeclin1 in comparison with non-FR-targeted PDP micelles and free DOX. These results highlighted that co-delivery of DOX and shRNA of Beclin1 with FPDP micelles has the potential to overcome the limitations of DOX in clinical cancer therapy.

New folate receptor targeted nano-micelles enhanced the anticancer effect of doxorubicin by shBeclin1 with the blockade of the autophagy process.     

Doxorubicin-loaded poly(ethylene glycol)-poly(beta-benzyl-L-aspartate) copolymer micelles: their pharmaceutical characteristics and biological significance.

Doxorubicin (DOX) was physically loaded into micelles prepared from poly(ethylene glycol)-poly(beta-benzyl-L-aspartate) block copolymer (PEG-PBLA) by an o/w emulsion method with a substantial drug loading level (15 to 20 w/w%). DOX-loaded micelles were narrowly distributed in size with diameters of approximately 50-70 nm. Dimer derivatives of DOX as well as DOX itself were revealed to be entrapped in the micelle, the former seems to improve micelle stability due to its low water solubility and possible interaction with benzyl residues of PBLA segments through pi-pi stacking. Release of DOX compounds from the micelles proceeded in two stages: an initial rapid release was followed by a stage of slow and long-lasting release of DOX. Acceleration of DOX release can be obtained by lowering the surrounding pH from 7.4 to 5.0, suggesting a pH-sensitive release of DOX from the micelles. A remarkable improvement in blood circulation of DOX was achieved by use of PEG-PBLA micelle as a carrier presumably due to the reduced reticuloendothelial system uptake of the micelles through a steric stabilization mechanism. Finally, DOX loaded in the micelle showed a considerably higher antitumor activity compared to free DOX against mouse C26 tumor by i.v. injection, indicating a promising feature for PEG-PBLA micelle as a long-circulating carrier system useful in modulated drug delivery.     

In vitro and in vivo anti-tumor activities of nanoparticles based on doxorubicin-PLGA conjugates.

Doxorubicin was chemically conjugated to a terminal end group of poly(D,L-lactic-co-glycolic acid) [PLGA] by an ester linkage and the doxorubicin-PLGA conjugate was formulated into nanoparticles. A carboxylic acid end group of PLGA was conjugated to a primary hydroxyl group of doxorubicin. The primary amine group of doxorubicin was protected during the conjugation process and then deprotected. The nanoparticles containing the conjugate exhibited sustained doxorubicin release profiles over a 1-month period, whereas those containing unconjugated free doxorubicin showed a rapid doxorubicin release within 5 days. Doxorubicin release patterns could be controlled by conjugating doxorubicin to PLGA having different molecular weights. The conjugated doxorubicin nanoparticles showed increased uptake within a HepG2 cell line, which was quantitated by a flow cytometry and visualized by confocal microscopy. The nanoparticles exhibited slightly lower IC(50) value against the HepG2 cell line compared to that of free doxorubicin. In vivo anti-tumor activity assay also showed that a single injection of the nanoparticles had comparable activity to that of free doxorubicin administered by daily injection. The conjugation approach of doxorubicin to PLGA was potentially useful for the formulation of nanoparticles that requires targeting for cancer cells as well as sustained release at the site.     

Self-assembled siRNA-PLGA conjugate micelles for gene silencing

Biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) was conjugated to the 3′ end of small interfering RNA (siRNA) via a disulfide bond to synthesize siRNA-PLGA hybrid conjugates. siRNA-PLGA conjugates were spontaneously self-assembled to form a spherical core/shell type micellar structure of ~ 20 nm in an aqueous environment, probably by hydrophobic interaction of PLGA blocks in the core surrounded by an siRNA shell layer. When linear polyethylenimine was added to the siRNA-PLGA micelles in aqueous solution, stable siRNA-PLGA/LPEI micelles with a size of ~ 30 nm were produced via ionic complexation between siRNA and LPEI in the outer shell. The cationic siRNA-PLGA/LPEI micelles showed superior intracellular uptake and enhanced gene silencing effect, compared to naked siRNA/LPEI complexes. The hybrid micelle structure based on siRNA and PLGA can be potentially used as an efficient siRNA delivery system for gene silencing.     

Folate-conjugated methoxy poly(ethylene glycol)/poly(epsilon-caprolactone) amphiphilic block copolymeric micelles for tumor-targeted drug delivery.

Amphiphilic block copolymers composed of methoxy poly(ethylene glycol) (MPEG) and poly(epsilon-caprolactone) (PCL) were synthesized and then conjugated with folic acid to produce a folate-receptor-targeted drug carrier for tumor-specific drug delivery. Folate-conjugated MPEG/PCL micelles containing the anticancer drug paclitaxel were prepared by micelle formation in aqueous medium. The size of the folate-conjugated MPEG/PCL micelles formed was about 50-130 nm, depending on the molecular weight of block copolymers, and was maintained at less than 150 nm even after loading with paclitaxel. The in vitro release profile of the paclitaxel from the MPEG/PCL micelles exhibited no initial burst release and showed sustained release. Paclitaxel-loaded folate-conjugated MPEG/PCL micelles (PFOL50) exhibited much higher cytotoxicity for cancer cells, such as MCF-7 and HeLa cells, than MPEG/PCL micelles without the folate group (PMEP50). Confocal image analysis revealed that fluorescent paclitaxel-loaded PFOL50 micelles were endocytosed into MCF-7 cells through the interaction with overexpressed folate receptors on the surface of the cancer cells.     

Micellar carriers based on block copolymers of poly(epsilon-caprolactone) and poly(ethylene glycol) for doxorubicin delivery.

Diblock copolymers of poly(epsilon-caprolactone) (PCL) and monomethoxy poly(ethylene glycol) (MPEG) with various compositions were synthesized. The amphiphilic block copolymers self-assembled into nanoscopic micelles and their hydrophobic cores encapsulated doxorubicin (DOX) in aqueous solutions. The micelle diameter increased from 22.9 to 104.9 nm with the increasing PCL block length (2.5-24.7 kDa) in the copolymer composition. Hemolytic studies showed that free DOX caused 11% hemolysis at 200 microg ml(-1), while no hemolysis was detected with DOX-loaded micelles at the same drug concentration. An in vitro study at 37 degrees C demonstrated that DOX-release from micelles at pH 5.0 was much faster than that at pH 7.4. Confocal laser scanning microscopy (CLSM) demonstrated that DOX-loaded micelles accumulated mostly in cytoplasm instead of cell nuclei, in contrast to free DOX. Consistent with the in vitro release and CLSM results, a cytotoxicity study demonstrated that DOX-loaded micelles exhibited time-delayed cytotoxicity in human MCF-7 breast cancer cells.     

High intensity focused ultrasound-responsive release behavior of PLA-b-PEG copolymer micelles

Poly(lactic acid) (PLA) was synthesized by solution polycondensation of L-lactic acid and further reacted with dihydroxyl poly(ethylene glycol) (PEG) to obtain the amphiphilic block copolymer PLA-b-PEG. The biodegradable PLA-b-PEG copolymer can self-assemble into spherical micelles in aqueous solution. Nile Red, as a payload model, was used to examine the release behavior of the micelles. The hydrophobic Nile Red can be adsolubilized into the hydrophobic inner core of PLA-b-PEG micelles. With the introduction of Nile Red, the size of micelles increased. Moreover, high intensity focused ultrasound (HIFU), as a non-contact and remote control approach, was introduced to control the release behavior of PLA-b-PEG micelles containing Nile Red. The release behavior of Nile Red was monitored by fluorescence emission spectra. The results showed that HIFU can trigger the release of the encapsulated Nile Red from PLA-b-PEG micelles. By adjusting the HIFU time, intensity and location, the release behavior of Nile Red from micelles can be tuned. Base on the results, an irreversible release mechanism under HIFU was proposed. The irreversible release of Nile Red from the PLA-b-PEG micelle was attributed to a chemically breaking process of micelle structure due to the degradation of the PLA-b-PEG chain that resulted from the transient cavitation in the HIFU focal spot.     

TAT peptide-based micelle system for potential active targeting of anti-cancer agents to acidic solid tumors.

A novel drug targeting system for acidic solid tumors has been developed based on ultra pH-sensitive polymer and cell penetrating TAT. The delivery system consisted of two components: 1) A polymeric micelle that has a hydrophobic core made of poly(l-lactic acid) (PLLA) and a hydrophilic shell consisting of polyethylene glycol (PEG) conjugated to TAT (TAT micelle), 2) an ultra pH-sensitive diblock copolymer of poly(methacryloyl sulfadimethoxine) (PSD) and PEG (PSD-b-PEG). The anionic PSD is complexed with cationic TAT of the micelles to achieve the final carrier, which could systemically shield the micelles and expose them at slightly acidic tumor pH. TAT micelles had particle sizes between 20 and 45 nm and their critical micelle concentrations were 3.5 mg/l to 5.5 mg/l. The TAT micelles, upon mixing with pH-sensitive PSD-b-PEG, showed a slight increase in particle size between pH 8.0 and 6.8 (60-90 nm), indicating complexation. As the pH was decreased (pH 6.6 to 6.0) two populations were observed, one that of normal TAT micelles (45 nm) and the other of aggregated hydrophobic PSD-b-PEG. Zeta potential measurements showed similar trend substantiating the shielding/deshielding process. Flow cytometry and confocal microscopy showed significantly higher uptake of TAT micelles at pH 6.6 compared to pH 7.4 indicating shielding at normal pH and deshielding at tumor pH. The confocal microscopy indicated that the TAT not only translocates into the cells but is also seen on the surface of the nucleus. These results strongly indicate that the above micelles would be able to target any hydrophobic drug near the nucleus.     

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.     

Doxorubicin loaded pH-sensitive polymeric micelles for reversal of resistant MCF-7 tumor.

In order to overcome multidrug resistance in solid tumors, doxorubicin (DOX) loaded pH-sensitive micelles of which surface was decorated with folate (PHSM/f) were evaluated both in vitro and in vivo experiments. PHSM/f were fabricated from a mixture of two block copolymers of poly(L-histidine) (M(n): 5K)-b-PEG (M(n): 2K)-folate (polyHis/PEG-folate) (75 wt.%) and poly(L-lactic acid) (M(n): 3K)-b-PEG (M(n): 2K)-folate (PLLA/PEG-folate) (25 wt.%). The PHSM/f showed more than 90% cytotoxicity of DOX resistant MCF-7 (MCF-7/DOX(R)) when cultured with PHSM/f at a concentration of 10 microg/ml DOX. The result was interpreted by a sequential event of active internalization of PHSM/f via folate-receptor mediated endocytosis and ionization of His residues which result in micelle destabilization and probably disturbance of endosomal membranes. This potential mechanism may endow the drug carriers to bypass Pgp efflux pump and sequestration of DOX in acidic intracellular compartments, yielding high cytotyoxicity. Experimental evaluation of tumor regression was carried out in a small animal model bearing s.c. MCF-7 or MCF-7/DOX(R) xenografts. The tumor (MCF-7/DOX) volumes of mice treated with PHSM/f were significantly less than control groups treated with free DOX or similar micelles but without folate (PHSM). In the MCF-7/DOX(R) xenograft model, the accumulated DOX level of PHSM/f in solid tumors was 20 times higher than free DOX group, and 3 times higher than PHSM group. The results demonstrate that PHSM/f is a viable means for treating drug resistant tumors.     

Controlled and targeted tumor chemotherapy by micellar-encapsulated drug and ultrasound.

The results of a comprehensive in vivo study of a novel tumor-targeting modality are reported. The technique utilized in this study is based on the encapsulation of the chemotherapeutic agent within polymeric micelles in combination with a local ultrasonic irradiation of the tumor. A doxorubicin (DOX) biodistribution, a yield of the internal tumors and a growth rate of the subcutaneous (s.c.) tumors was compared for molecularly dissolved and micellar-encapsulated DOX. This was done with and without tumor sonication, using an ovarian carcinoma tumor model in nu/nu mice. Pure and mixed Pluronic P-105, PEG2000-diacylphospholipid, and poly(ethylene glycol)-co-poly(beta-benzyl-L-aspartate) micelles were used as drug carriers. DOX intracellular uptake was characterized by flow cytometry. A local ultrasonic irradiation of the tumor resulted in a substantially increased drug accumulation in the tumor cells. The effect of the ultrasound was dependent on the time between ultrasound application and drug injection. Ultrasound did not enhance micelle extravasation; the ultrasonic enhancement of drug internalization by the tumor cells required a preliminary passive drug accumulation in the tumor interstitium. Due to the ultrasound-enhanced drug intracellular uptake and cell killing, the yield of intraperitoneal (i.p.) ovarian carcinoma tumors decreased from 70% for DOX dissolved in PBS (positive control) to 36% for the same concentration of DOX encapsulated in Pluronic micelles combined with a 30-s sonication of the abdominal region of a mouse (3 mg/kg DOX, i.p. injection 1 day after inoculation, n>or=10). For s.c. tumors, micellar delivery combined with localized ultrasonic tumor irradiation resulted in a substantial decrease of the tumor growth rates compared to a positive control (3 mg/kg DOX, i.v. injections, n=7, p<0.05). Possible mechanisms of the ultrasound bioeffects on in vivo drug targeting are discussed.     

Effect of PEG conformation and particle size on the cellular uptake efficiency of nanoparticles with the HepG2 cells.

Core-shell nanoparticles were prepared from di-block copolymer of methoxy poly(ethylene glycol)-polycaprolactone (MePEG-PCL) and tri-block copolymer of polycaprolactone-poly(ethylene glycol)-polycaprolactone (PCL-PEG-PCL). The MePEG-PCL copolymers form nanoparticles with PEG "brush" on their surfaces and PCL-PEG-PCL copolymers form nanoparticles with a "mushroom-like" structure on their surfaces in aqueous solution. The morphology and size of nanoparticles were measured by field emission scanning electron microscopy (FESEM) and laser light scattering (LLS). All the nanoparticles are in spherical shape and the sizes are less than 200 nm. The sizes of the nanoparticles increases with increasing PCL segment length. The drug-loading content results showed that the optimal feeding ratio of paclitaxel to copolymer is dependent upon the copolymer composition and 5% is a suitable feeding ratio. The in vitro release behavior exhibits a sustained release manner and is affected by copolymer composition. Experimental results showed that cells would prefer to attach to more hydrophobic polymers. Comparing between MePEG-PCL and PCL-PEG-PCL of similar hydrophobicity, more HepG2 cells have attached to the MePEG-PCL copolymer films because a denser PEG layer was formed on the surfaces of PCL-PEG-PCL copolymers. In vitro cellular uptake experimental results indicated that HepG2 cells prefer smaller nanoparticles with the same PEG configuration on their surfaces. The cytotoxicity of paclitaxel-loaded nanoparticles seemed to increase with increasing drug loading of nanoparticles against HepG2 cells.     

DPD simulations on morphologies and structures of blank PLGA-b-PEG-b-PLGA polymeric micelles and docetaxel-loaded PLGA-b-PEG-b-PLGA polymeric micelles

Dissipative particle dynamics (DPD) simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PLGA-b-PEG-b-PLGA) polymeric micelles and the docetaxel (Dtx)-loaded PLGA-b-PEG-b-PLGA polymeric micelles. We focused on the influences of PLGA-b-PEG-b-PLGA copolymer concentration, composition, Dtx drug content and the shear rate on morphologies and structures of the micelles. Our simulations show that the PLGA-b-PEG-b-PLGA copolymers in the aqueous solutions could aggregate and form blank micelles while Dtx drug and PLGA-b-PEG-b-PLGA could aggregate and form drug-loaded micelles. Under different PLGA-b-PEG-b-PLGA concentrations and drug content, the blank and drug-loaded micelles are observed as spherical, onionlike, columnar, and lamellar structures. The onionlike structures are comprised of the PEG hydrophilic core, the PLGA hydrophobic middle layer, and the PEG hydrophilic shell. As the structure of micelles varies from a spherical core–shell structure to a core–middle layer–shell onionlike structure, the distribution of the Dtx drugs diffuses from the core to the PLGA middle layer of the aggregate. In addition, the drug release process of the Dtx-loaded micelles under shear flow is also simulated. And the results show that the spherical micelles turn into a columnar structure under a shear rate from 0.2 to 3.4. When the shear rate increases to 3.5, the Dtx drugs released gradually increase until all are released with time evolution. These findings illustrate the dependence of the structural morphologies on the detailed molecular parameters of PLGA-b-PEG-b-PLGA and Dtx.

Dissipative particle dynamics simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) polymeric micelles and the docetaxel-loaded polymeric micelles.     

Polymeric drugs based on conjugates of synthetic and natural macromolecules. II. Anti-cancer activity of antibody or (Fab')(2)-targeted conjugates and combined therapy with immunomodulators.

We provide data on in vivo targeting of the Thy 1.2 (CDw90) cell surface receptor expressed on neoplastic T cells, mouse EL4 T cell lymphoma. The targeting antibody and the anticancer drug, doxorubicin (DOX) were conjugated to a water-soluble copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA) acting as a carrier responsible for controlled intracellular release of the conjugated drug. The in vivo therapeutic efficacy of HPMA copolymer-bound DOX targeted with anti-EL4 antibody, polyclonal anti-thymocyte globulin (ATG), monoclonal anti-Thy 1.2 antibody or its F(ab')(2) fragment was compared with the efficacy of DOX conjugated to HPMA copolymer containing nonspecific IgG or bovine serum albumin (BSA). Anti-EL4 antibody-targeted conjugate caused a significant retardation of tumor growth and an extension of the life span of treated mice. The effect was comparable with that of HPMA copolymer-bound DOX targeted with ATG, anti-Thy 1.2 antibody or its F(ab')(2) fragment. However, considerable antitumor effect was seen also in conjugates targeted instead of specific antibodies with syngeneic nonspecific IgG or BSA. Patients with advanced cancer are often immunocompromised due to dysfunction of their immune system induced by cancer and cytotoxic drugs. A significant decrease of unwanted side-effects of targeted drugs against a number of vital organs was already documented. In this study we have compared immunotoxic effects of free DOX with those of its antibody-targeted form on NK cells and cytolytic T lymphocytes (CTLs) isolated from C57BL/10 mice bearing EL4 T cell lymphoma. In the same model we have tested the combination therapy with immunomodulators (beta-glucan or AM-2) injected together with targeted daunomycin. We have observed a significant protective effect of targeted DOX against NK cells and CTLs. Moreover, the data revealed that combination therapy considerably enhances antitumor efficacy of the targeted anticancer drug.     

Micelle-like nanoparticles of star-branched PEO-PLA copolymers as chemotherapeutic carrier.

Four-armed (star-branched) block copolymers of l-PLA and PEO were synthesized using ring opening polymerization with different LA/EO ratio. Micellar aggregates were prepared from these block copolymers and characterized. Some surface segregation of PEG was found : the extent depends on the state of the material (whether it is in film or particle form), as well as on molecular geometry. The degradation behavior of star-shaped copolymer was studied over a three week period and compared to its linear counterpart. Anti-cancer drugs 5-FU and paclitaxel were loaded into the micellar nanoparticles. The drug release profile showed that the release of paclitaxel from these polymers could be controlled over 2 weeks. The kinetics of drug release for star-branched, tri- and di-block copolymers were compared. The micelles from star-shaped branch showed more complete release of drug than the diblock copolymers; also, the lower hydrodynamic radius of star-shaped polymers may result in better clearance of the carrier polymer from the body.