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.     

Reduction responsive and surface charge switchable polyurethane micelles with acid cleavable crosslinks for intracellular drug delivery

Previously we synthesized redox sensitive polyurethane micelles, core crosslinked by diisocyanates (PU-CCL). To improve the intracellular drug release and tumor cellular toxicity of anticancer drugs loaded into polyurethane micelles, we now describe redox sensitive polyurethane micelles with tunable surface charge switchabilities, crosslinked with pH cleavable Schiff bonds, as anticancer drug carriers. Different amounts of 1,6-diaminohexane were connected onto the pendant carboxyl groups of amphiphilic multi-blocked polyurethane (PU-SS-COOH), resulting in polyurethanes with various ratios of pendant carboxyl and amine groups (denoted as PU-SS-COOH-NH₂-1, PU-SS-COOH-NH₂-2 and PU-SS-COOH-NH₂-3). The surface charge switched as the pH was increased for PU-SS-COOH-NH₂-1, PU-SS-COOH-NH₂-2 and PU-SS-COOH-NH₂-3. Then the PU-SS-COOH-NH₂-3 micelles, dissolved in water, were crosslinked by glutaraldehyde resulting in surface charge switchable and reduction responsive polyurethane micelles with acid cleavable crosslinks (PU-ACCL). The crosslinked polyurethane micelles (PU-ACCL) demonstrated superior particle stability in phosphate buffered saline (PBS, pH = 7.4) solution without reducing agents, whereas the drug release rate was markedly accelerated by the addition of glutathione (GSH). Notably, the drug release from PU-ACCL was further accelerated in acidic fluid as the result of acid induced cleavage of the crosslinks. In vitro cytotoxicity studies demonstrated that doxorubicin (DOX)-loaded PU-ACCL micelles displayed increased cytotoxicity against tumor cells which was comparable to that obtained for DOX loaded into uncrosslinked polyurethane micelles. The reduction responsive and surface charge switchable polyurethane micelles with acid cleavable crosslinks, which have superior extracellular stability and provide rapid intracellular drug release, may hold great potential as a bio-triggered drug delivery system for cancer therapy.

Previously we synthesized redox sensitive polyurethane micelles, core crosslinked by diisocyanates (PU-CCL).     

Molecular design of biodegradable polymeric micelles for temperature-responsive drug release.

We designed thermo-responsive and biodegradable polymeric micelles for an ideal drug delivery system whose target sites are where external stimuli selectively release drugs from the polymeric micelles. The thermo-responsive micelles formed from block copolymers that were composed both of a hydrophobic block and a thermo-responsive block. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) showing a lower critical solution temperature (LCST) around 40 degrees C was synthesized for the thermo-responsive block, while biodegradable poly(D,L-lactide), poly(epsilon-caprolactone), or poly(D,L-lactide-co-epsilon-caprolactone) was used for the hydrophobic block. By changing both the block lengths of the poly(D,L-lactide)-containing block copolymers, physical parameters such as micelle diameter and critical micelle concentration were varied. On the other hand, the choice of the hydrophobic block was revealed to be critical in relation to both on the thermo-responsive release of the incorporated anti-cancer drug, doxorubicin, and the temperature-dependent change of the hydrophobicity of the micelles' inner core. One polymeric micelle composition successfully exhibited rapid and thermo-responsive drug release while possessing a biodegradable character.     

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.     

Investigation of pH-responsive block glycopolymers with different structures for the delivery of doxorubicin

To understand the influence of the construction of pH-responsive glycopolymer carriers on loading and release behaviors of the drug, three types of block glycopolymers with similar compositions but different constructions, PEG-b-P(DEA-co-GAMA), PEG-b-PDEA-b-PGAMA and PEG-b-PGAMA-b-PDEA, were successfully synthesized via atom transfer radical polymerization (ATRP) method. The compositions and structures of the three glycopolymers were characterized using ¹H NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography), while the morphology and size of aggregates from pH-sensitive block glycopolymers were measured using TEM (transmission electron microscopy) and DLS (dynamic light scattering). The results indicated that the micelles prepared from PEG-b-PGAMA-b-PDEA had a more compact shell structure. The drug-loaded micelles were prepared using the diafiltration method at pH 10, and the loading content and loading efficiency were analyzed using a UV-visible spectrophotometer. DOX-loaded micelles formed by PEG-b-PGAMA-b-PDEA with the more compact shell construction showed the highest loading content and loading efficiency (12.0 wt% and 58.0%) compared with the other two micelles. Moreover, the DOX release tests of these micelles were carried out under two PBS conditions (pH 7.4 and pH 5.5), and the DOX release amount in a certain time was analyzed using a UV-visible spectrophotometer. The results showed that the more compact shell construction of the three layered micelle obstructed the diffusion of a proton into the PDEA core at pH 5.5 and delayed the drug from releasing under both conditions. Moreover the two-layered micelle with a PDEA and PGAMA mixed core showed a relatively high release amount owing to the porous core permitting unimpeded releasing at pH 7.4 and promoted the protonation of PDEA at pH 5.5. Insights gained from this study show that the structure of block copolymers, leading to different constructions of micelles, could adjust the drug loading and release behavior to certain extent, thus it may contribute to improving the design of desirable drug delivery systems.

Synthesized a pH-responsive block glycopolymers micelles, for the DOX loading and release behavior enhancing the design of drug delivery systems.     

PEGylated ethyl cellulose micelles as a nanocarrier for drug delivery

Natural polymers provide a better alternative to synthetic polymers in the domain of drug delivery systems (DDSs) because of their renewability, biocompatibility, and low immunogenicity; therefore, they are being studied for the development of bulk/nanoformulations. Likewise, current methods for engineering natural polymers into micelles are in their infancy, and in-depth studies are required using natural polymers as controlled DDSs. Accordingly, in our present study, a new micellar DDS was synthesized using ethyl cellulose (EC) grafted with polyethylene glycol (PEG); it was characterized, its properties, cell toxicity, and hemocompatibility were evaluated, and its drug release kinetics were demonstrated using doxorubicin (DOX) as a model drug. Briefly, EC was grafted with PEG to form the amphiphilic copolymers EC-PEG1 and EC-PEG2 with varying PEG concentrations, and nano-micelles were prepared with and without the drug (DOX) via a dialysis method; the critical micelle concentrations (CMCs) were recorded to be 0.03 mg mL⁻¹ and 0.00193 mg mL⁻¹ for EC-PEG1 and EC-PEG2, respectively. The physicochemical properties of the respective nano-micelles were evaluated via various characterization techniques. The morphologies of the nano-micelles were analyzed via transmission electron microscopy (TEM), and the average size of the nano-micelles was recorded to be ∼80 nm. In vitro, drug release studies were done for 48 h, where 100% DOX release was recorded at pH 5.5 and 52% DOX release was recorded at pH 7.4 from the micelles. In addition, cytotoxicity studies suggested that DOX-loaded micelles were potent in killing MDA-MB-231 and MCF-7 cancer cells, and the blank micelles were non-toxic toward cancerous and normal cells. A cellular uptake study via fluorescence microscopy indicated the internalization of DOX-loaded micelles by cancer cells, delivering the DOX into the cellular compartments. Based on these studies, we concluded that the developed material should be studied further via in vivo studies to understand its potential as a controlled DDS to treat cancer.

Ethyl cellulose was developed as an amphiphilic polymer by PEGylation and fabricated as nanomicelles for delivery of active molecules. This polymeric system can be used as next generation nano drug delivery system (nanoDDS) for cancer therapy.     

pH-Responsive hyperbranched polypeptides based on Schiff bases as drug carriers for reducing toxicity of chemotherapy

Polymeric micelles have great potential in drug delivery systems because of their multifunctional adjustability, excellent stability, and biocompatibility. To further increase the drug loading efficiency and controlled release ability, a pH-responsive hyperbranched copolymer methoxy poly(ethylene glycol)-b-polyethyleneimine-poly(Nε-Cbz-l-lysine) (MPEG-PEI-PBLL) was synthesized successfully. MPEG-PEI-NH₂ was synthesized to initiate the ring-opening polymerization of benzyloxycarbonyl substituted lysine N-carboxyanhydride (Z-lys NCA). The introduction of Schiff bases in the polymer make it possible to respond to the variation of pH values, which cleaved at pH 5.0 while stable at pH 7.4. As the polymer was amphiphilic, MPEG-PEI-PBLL could self-assemble into micelles. Owing to the introduction of PEI, which make the copolymer hyperbranched, the pH-responsive micelles could efficiently encapsulate theranostic agents, such as doxorubicin (DOX) for chemotherapy and NIRF dye DiD for in vivo near-infrared (NIR) imaging. The drug delivery system prolonged the drug circulation time in blood and allowed the drug accumulate effectively at the tumor site. Following the guidance, the DOX was applied in chemotherapy to achieve cancer therapeutic efficiency. All the results demonstrate that the polymer micelles have great potential for cancer theranostics.

Polymeric micelles have great potential in drug delivery systems because of their multifunctional adjustability, excellent stability, and biocompatibility.     

Factors affecting acoustically triggered release of drugs from polymeric micelles.

A custom ultrasonic exposure chamber with real-time fluorescence detection was used to measure acoustically-triggered drug release from Pluronic P-105 micelles under continuous wave (CW) or pulsed ultrasound in the frequency range of 20 to 90 kHz. The measurements were based on the decrease in fluorescence intensity when drug was transferred from the micelle core to the aqueous environment. Two fluorescent drugs were used: doxorubicin (DOX) and its paramagnetic analogue, ruboxyl (Rb). Pluronic P-105 at various concentrations in aqueous solutions was used as a micelle-forming polymer. Drug release was most efficient at 20-kHz ultrasound and dropped with increasing ultrasonic frequency despite much higher power densities. These data suggest an important role of transient cavitation in drug release. The release of DOX was higher than that of Rb due to stronger interaction and deeper insertion of Rb into the core of the micelles. Drug release was higher at lower Pluronic concentrations, which presumably resulted from higher local drug concentrations in the core of Pluronic micelles when the number of micelles was low. At constant frequency, drug release increased with increasing power density. At constant power density and for pulse duration longer than 0.1 s, peak release under pulsed ultrasound was the same as stationary release under CW ultrasound. Released drug was quickly re-encapsulated between the pulses of ultrasound, which suggests that upon leaving the sonicated volume, the non-extravasated and non-internalized drug would circulate in the encapsulated form, thus preventing unwanted drug interactions with normal tissues.     

纳米纤维介导的紫杉醇/阿霉素序贯联合治疗SHg-44胶质瘤

背景:纳米纤维技术可同时担载多种药物,避开血脑屏障限制实现脑胶质瘤的序贯联合化疗。目的:用乳液电纺法制备同时担载紫杉醇和阿霉素的聚乙二醇-聚乳酸共聚物纳米纤维并实现两种药物的序贯释放,探讨纳米纤维介导的紫杉醇和阿霉素序贯联合治疗SHg-44胶质瘤的效果及机制。方法:实验分为4组,1640培养液对照组,1%阿霉素组,1%紫杉醇组,5%(阿霉素+紫杉醇)组。采用高效液相色谱法测定紫杉醇和阿霉素的体外释放情况。四甲基偶氮唑盐法检测纳米纤维介导的紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞的增殖抑制率;流式细胞仪检测法检测紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞的凋亡诱导作用。结果与结论:纳米纤维介导的紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞具有明显的生长抑制及促凋亡作用,且作用效果好于单独药物应用。提示聚乙二醇-聚乳酸纳米纤维作为一种药物载体能提高紫杉醇和阿霉素对SHg-44胶质瘤细胞增殖抑制和诱导凋亡作用。     

Acoustic activation of drug delivery from polymeric micelles: effect of pulsed ultrasound.

The effect of a continuous wave (CW) and pulsed 20-kHz ultrasound on the Doxorubicin (DOX) uptake by HL-60 cells from the phosphate buffered saline solution (PBS) and Pluronic micellar solutions was studied. Both CW and pulsed ultrasound enhanced DOX uptake from PBS and Pluronic micelles. The main factor that effected drug uptake was ultrasound power density; however, with increasing power, the enhanced drug uptake was accompanied by the extensive cell sonolysis. For PBS, no significant effect of duration of the ultrasound pulse or inter-pulse interval on the drug uptake was observed. For Pluronic micelles, the uptake increased with increasing pulse duration in the range 0.1-2 s, overall sonication time being the same. For 2-s pulses, the uptake was close to that under CW ultrasound. There was no significant effect of the duration of the inter-pulse interval on the drug uptake from Pluronic micelles. The data on the effect of pulse duration on drug uptake suggest that the characteristic times of drug release from micelles and drug uptake by the cells are comparable. The results point to two independent mechanisms controlling acoustic activation of drug uptake from Pluronic micelles. Both mechanisms work in concert. The first one is related to the acoustically-triggered drug release from micelles that results in higher concentration of the free drug in the incubation medium. The second mechanism is based on the perturbation of cell membranes that results in the increased uptake of the micellar-encapsulated drug. The intracellular uptake of Pluronic micelles was confirmed by fluorescence microscopy.     

DOX sensitized upconversion metal–organic frameworks for the pH responsive release and real-time detection of doxorubicin hydrochloride

Drug resistance is a major obstacle in cancer treatment, and designing a material that monitors real-time drug release remains a top priority. In this study, metal–organic frameworks doped with lanthanum and thulium were synthesized and then coated with aminated silica to form La/Tm-MOF@d-SiO₂ as a drug carrier. Doxorubicin hydrochloride (DOX) was selected as a drug model, and the drug loading and release were investigated. It was found that the release of DOX under acidic conditions reached an optimal level, indicating the pH-responsiveness of La/Tm-MOF@d-SiO₂. Under acidic conditions (pH = 5.8), upconversion fluorescence was generated after loading DOX on La/Tm-MOF@d-SiO₂. At pH = 5.8, the longer the drug released, the stronger the upconversion fluorescence. It was found that the upconversion fluorescence intensity is directly proportional to the amount of drug released; thus, the real-time monitoring of DOX release in tumor cells can be performed based on the upconversion fluorescence.

Drug resistance is a major obstacle in cancer treatment, and designing a material that monitors real-time drug release remains a top priority.     

纳米纤维介导的紫杉醇/阿霉素序贯联合治疗SHg-44胶质瘤

背景：纳米纤维技术可同时担载多种药物,避开血脑屏障限制实现脑胶质瘤的序贯联合化疗。目的：用乳液电纺法制备同时担载紫杉醇和阿霉素的聚乙二醇-聚乳酸共聚物纳米纤维并实现两种药物的序贯释放,探讨纳米纤维介导的紫杉醇和阿霉素序贯联合治疗SHg-44胶质瘤的效果及机制。方法：实验分为4组,1640培养液对照组,1%阿霉素组,1%紫杉醇组,5%（阿霉素＋紫杉醇）组。采用高效液相色谱法测定紫杉醇和阿霉素的体外释放情况。四甲基偶氮唑盐法检测纳米纤维介导的紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞的增殖抑制率;流式细胞仪检测法检测紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞的凋亡诱导作用。结果与结论：纳米纤维介导的紫杉醇和阿霉素序贯治疗对SHg-44胶质瘤细胞具有明显的生长抑制及促凋亡作用,且作用效果好于单独药物应用。提示聚乙二醇-聚乳酸纳米纤维作为一种药物载体能提高紫杉醇和阿霉素对SHg-44胶质瘤细胞增殖抑制和诱导凋亡作用。     

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.     

Drug delivery in pluronic micelles: effect of high-frequency ultrasound on drug release from micelles and intracellular uptake.

The effect of high-frequency ultrasound on doxorubicin (DOX) release from Pluronic micelles and intracellular DOX uptake was studied for promyelocytic leukemia HL-60 cells, ovarian carcinoma drug-sensitive and multidrug-resistant (MDR) cells (A2780 and A2780/ADR, respectively), and breast cancer MCF-7 cells. Cavitation events initiated by high-frequency ultrasound were recorded by radical trapping. The onset of transient cavitation and DOX release from micelles were observed at much higher power densities than at low-frequency ultrasound (20-100 kHz). Even a short (15-30 s) exposure to high-frequency ultrasound significantly enhanced the intracellular DOX uptake from PBS, RPMI 1640, and Pluronic micelles. The mechanisms of the observed effects are discussed.     

Polycaprolactone-b-poly(ethylene oxide) copolymer micelles as a delivery vehicle for dihydrotestosterone.

Block copolymer micelles formed from copolymers of poly(caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) were investigated as a drug delivery vehicle for dihydrotestosterone (DHT). The physical parameters of the PCL-b-PEO micelle-incorporated DHT were measured, including the loading capacity of the micelles for DHT, the apparent partition coefficient of DHT between the micelles and the external medium and the kinetics of the release of DHT from the micelle solution. The MTT survival assay was used to assess the in vitro biocompatibility of PCL-b-PEO micelles in HeLa cell cultures. The biological activity of the micelle-incorporated DHT was evaluated in HeLa cells which had been co-transfected with the expression vectors for the androgen receptor and the MMTV-LUC reporter gene. The PCL-b-PEO micelles were found to have a high loading capacity for DHT and the release profile of the drug from the micelle solution was found to be a slow steady release which continued over a 1-month period. The biological activity of the micelle-incorporated DHT was found to be fully retained.     

ATRP-based synthesis of a pH-sensitive amphiphilic block polymer and its self-assembled micelles with hollow mesoporous silica as DOX carriers for controlled drug release

The atom transfer radical polymerization (ATRP)-based synthesis of a pH-sensitive fluorescent polymer (PSDMA-b-POEGMA) was successfully prepared using 3,6-dibromo-isobutyramide acridine (DIA), an initiator with a fluorescent chromophore, to initiate a lipophilic monomer 2-styryl-1,3-dioxan-5-yl methacrylate (SDMA) and a hydrophilic monomer oligo(ethylene glycol) methyl ether (OEGMA), which contained a cinnamic aldehyde acetal structure. With the addition of hollow mesoporous silicon (HMS@C18), the pH-sensitive core–shell nanoparticles (HMS@C18@PSDMA-b-POEGMA) were developed via a self-assembly process as carriers for the anticancer drug doxorubicin (DOX) for drug loading and controlled release. The nanocomposites showed a higher drug loading capacity which was much higher than that observed using common micelles. At the same time, the polymer coated on the surface of the nanoparticles contains the fluorescent segment of an initiator, which can be used for fluorescence contrast of the cells. The nanocomposite carrier selectively inhibits human melanoma cell A375 relative to human normal fibroblasts GM. The in vitro results suggested that a smart pH sensitive nanoparticles drug delivery system was successfully prepared for potential applications in cancer diagnosis and therapy.

A pH-sensitive core–shell nanoparticle (HMS@C18@PSDMA-b-POEGMA) was developed via a self-assembly process as the carrier of anticancer drug doxorubicin (DOX) for drug loading and controlled release.     

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.     

PEG-oligocholic acid telodendrimer micelles for the targeted delivery of doxorubicin to B-cell lymphoma

Doxorubicin (DOX) is one of most common anti-cancer chemotherapeutic drugs, but its clinical use is associated with dose-limiting cardiotoxicity. We have recently developed a series of PEG-oligocholic acid based telodendrimers, which can efficiently encapsulate hydrophobic drugs and self-assemble to form stable micelles in aqueous condition. In the present study, two representative telodendrimers (PEG^5k-CA₈ and PEG^2k-CA₄) have been applied to prepare DOX micellar formulations for the targeted delivery of DOX to lymphoma. PEG^2k-CA₄ micelles, compared to PEG^5k-CA₈ micelles, were found to have higher DOX loading capacity (14.8% vs. 8.2%, w/w), superior stability in physiological condition, and more sustained release profile. Both of these DOX-loaded micelles can be efficiently internalized and release the drug in Raji lymphoma cells. DOX-loaded micelles were found to exhibit similar in vitro cytotoxic activities against both T- and B-lymphoma cells as the free DOX. The maximum tolerated dose (MTD) of DOX-loaded PEG^2k-CA₄ micelles in mice was approximately 15 mg/kg, which was 1.5-fold higher of the MTD of free DOX. Pharmacokinetics and biodistribution studies demonstrated that both DOX-loaded micelles were able to prolong the blood retention time, preferentially accumulate and penetrate in B-cell lymphomas via the enhanced permeability and retention (EPR) effect. Finally, DOX-PEG^2k-CA₄ micelles achieved enhanced anti-cancer efficacy and prolonged survival in Raji lymphoma bearing mice, compared to free DOX and PEGylated liposomal DOX (Doxil®) at the equivalent dose. In addition, the analysis of creatine kinase (CK) and lactate dehydrogenase (LDH) serum enzymes level indicated that DOX micellar formulations significantly reduced the cardiotoxicity associated with free DOX.     

Properties of HPMA copolymer-doxorubicin conjugates with pH-controlled activation: effect of polymer chain modification.

Various conjugates of anticancer drug doxorubicin (DOX) covalently attached via hydrolytically degradable hydrazone bond to water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer drug carriers were synthesized. Three types of precursors containing either positively or negatively charged groups or a hydrophobic substituent were employed. In vitro incubation of the conjugates in buffers showed relative stability at pH 7.4 (modelling blood) and a fast DOX release at pH 5 (modelling intracellular environment). The presence of carboxylic groups in the copolymer structure resulted in an increase in the DOX release rate of 15-20% while no effect of the introduction of positively charged groups was observed if compared with the unmodified conjugate. Self-assembling of the oleoyl groups-containing conjugate led into formation of polymeric micelles with high apparent molecular weight (M(w)=170,000) in aqueous solution and resulted in a decrease in the DOX release rate of approximately 20%. The cytostatic activity of the conjugates tested on several cancer cell lines was comparable with that of free DOX.HCl, depending on the sensitivity of a particular cell line to DOX. All the conjugates showed a much higher antitumour activity in vivo than the free drug tested in mice bearing EL4 T-cell lymphoma and treated using the therapeutic regime of drug administration. The highest activity (100% long-term survivors) exhibited polymer-DOX conjugate containing negatively charged GFLG sequences.     

Polymeric micellar pH-sensitive drug delivery system for doxorubicin.

A novel polymeric micellar pH-sensitive system for delivery of doxorubicin (DOX) is described. Polymeric micelles were prepared by self-assembly of amphiphilic diblock copolymers in aqueous solutions. The copolymers consist of a biocompatible hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block containing covalently bound anthracycline antibiotic DOX. The starting block copolymers poly(ethylene oxide)-block-poly(allyl glycidyl ether) (PEO-PAGE) with a very narrow molecular weight distribution (Mw/Mn ca. 1.05) were prepared by anionic ring opening polymerization using sodium salt of poly(ethylene oxide) monomethyl ether as macroinitiator and allyl glycidyl ether as functional monomer. The copolymers were covalently modified via reactive double bonds by the addition of methyl sulfanylacetate. The resulting ester subsequently reacted with hydrazine hydrate yielding polymer hydrazide. The hydrazide was coupled with DOX yielding pH-sensitive hydrazone bonds between the drug and carrier. The resulting conjugate containing ca. 3 wt.% DOX forms micelles with Rh(a)=104 nm in phosphate-buffered saline. After incubation in buffers at 37 degrees C DOX was released faster at pH 5.0 (close to pH in endosomes; 43% DOX released within 24 h) than at pH 7.4 (pH of blood plasma; 16% DOX released within 24 h). Cleavage of hydrazone bonds between DOX and carrier continues even after plateau in the DOX release from micelles incubated in aqueous solutions is reached.