Preparation and characterization of intestinal transporter-targeted polymeric micelles

The intestinal epithelium is the main barrier to the oral delivery of poorly water-soluble drugs. Based on the specific transporters expressed on the apical membrane of the intestinal epithelium, novel polymer micelles targeting to the organic cation transporter 2 (OCTN2) were constructed by combining carnitine conjugated poly(2-ethyl-2-oxazoline)-poly(D,L-lactide) (Car-PEOz-PLA) with monomethoxy poly(ethylene glycol)-poly(D,L-lactide) (mPEG-PLA). The structure of the synthesized Car-PEOz-PLA was confirmed by ¹H NMR, TLC and ammonium reineckate precipitation reaction, and the number-average molecular weight determined by GPC was 7260 g/mol with a low PDI of 1.44. Coumarin 6-loaded carnitine modified polymeric micelles prepared by film hydration method were characterized to have a nano-scaled size of about 31 nm in diameter, uniform spherical morphology, high drug loading content of 0.098%±0.03% and encapsulation efficiency of 92.67%±2.80%. Moreover, the carnitine-modified micelles exhibited the similar in vitro release behavior in SGF and SIF, and evidently enhanced intestinal absorption of poorly water-soluble agent. Therefore, the designed OCTN2-targeted micelles might have a promising potential for oral delivery of poorly water-soluble drugs.     

Preparation and characterization of dual pH-sensitive polymer-doxorubicin conjugate micelles

In the present study, we designed and fabricated pH-sensitive polymeric micelles based on the conjugate of poly(2-ethyl-2-oxazoline)-poly(D,L-lactide) (PEOz-PLA) with doxorubicin (PEOz-PLA-imi-DOX) to efficiently inhibit tumor cell growth. Hence, PEOz-PLA-imi-DOX was successfully synthesized by connecting DOX to the hydrophobic end of pH-sensitive PEOz-PLAvia acid cleavable benzoic imine linker and characterized by ¹H NMR spectrum and thin layer chromatography. The critical micelle concentration of PEOz-PLA-imi-DOX was determined to be (14.84±3.85) mg/L. The conjugate micelles (denoted as PP-DOX-PM) formed by PEOz-PLA-imi-DOX using film-hydration method were characterized to have a nano-scaled size of about 21 nm in diameter, and the drug loading content was 1.67%. PP-DOX-PM showed pH-dependent drug release behavior with gradually accelerated release of DOX with decrease of pH value, illustrating the micelles’ distinguishing feature of endo/lysosomal pH from physiological pH by accelerating drug release. As anticipated, PP-DOX-PM maintained the cytotoxicity of DOX against MDA-MB-231 cells. Collectively, PP-DOX-PM might have great potential for effective suppression of tumor growth.     

去氧胆酸修饰的聚合物胶束的构建及其跨膜转运的研究

口服给药是患者顺应性最好的给药方式,而小肠上皮是口服药物吸收的主要屏障.为了克服小肠上皮屏障口服递送难溶性药物,本研究设计合成了小肠胆酸转运体的底物脱氧胆酸偶联的聚(2-乙基-2-噁唑啉)-聚(D,L-乳酸)(DA-PEOz-PLA),并基于小肠胆酸特殊的转运途径构建了由DA-PEOz-PLA和mPEG-PLA组成的聚...     

Preparation and in vitro characterization of paclitaxel-loaded pH-responsive polymeric micelles based on poly(2-ethyl-2-oxazoline)-vitamin E succinate

To ensure the delivery of antitumor drugs to tumor site and quick release in tumor cells, we designed and prepared pH-sensitive polymeric micelles by combining cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EOz) with vitamin Esuccinate (VES), and then encapsulating paclitaxel (PTX) into the micelles self-assembled by poly(2-ethyl-2-oxazoline)-vitamin E succinate (PEOz-VES). The structure of the synthesized PEOz-VES was confirmed by ¹H NMR spectrum, and the molecular weight measured by GPC was 1212 g/mol. The pK_a of PEOz-VES with a low critical micelle concentration of (5.84±0.02) mg/L was determined to be 6.01. The PTX-loaded PEOz-VES polymeric micelles prepared by film hydration method were characterized to have a nanoscaled size of about 30 nm in diameter, a positive Zeta potential of 4.86 mV and uniform spherical morphology by TEM observation. The drug loading content and encapsulation efficiency were (2.63±0.16)% and (84.1±3.38)%, respectively. The in vitro release behavior of PTX from PEOz-VES micelles in PBS displayed pH-dependent pattern and was gradually accelerated with decrease of pH value, implying that the micelles could distinguish endo/lysosomal pH and tumor extracellular pH from physiological pH by accelerating drug release. Therefore, the designed PEOz-VES micelles might have significant promise for anti-cancer drug delivery.     

Ketal containing amphiphilic block copolymer micelles as pH-sensitive drug carriers

pH-Responsive linkages have been widely exploited in the development of polymeric drug delivery systems, which trigger drug release selectively at tumor tissues or endosomes and lysosomes of cells. Herein we report new pH-sensitive amphiphilic poly(ketal adipate)-co-poly(ethylene glycol) block copolymers (PKA-PEG), which have acid-cleavable ketal linkages in their hydrophobic backbone. PKA-PEG copolymers self-assemble to form stable micelles with a mean diameter of ~175 nm, which can encapsulate a payload of anticancer drugs and rapidly dissociate to release drug payload at the acid environment. The micelles are biocompatible and exhibit abilities to disrupt endosomes to enhance the cytosol drug delivery. Taken together, we anticipate that the pH-sensitive PKA-PEG micelles have great potential as anticancer drug carriers.     

聚（2-乙基-2-噁唑啉）-聚乳酸胶束的血液相容性和细胞相容性研究

合成的二嵌段共聚物聚（2-乙基-2-噁唑啉）-聚乳酸（PEOz-PLA）可自组装形成胶束,其在药物输送领域的应用与口俱增。然而,其与血液和细胞之间的相互作用迄今未知。本研究拟对PEOz-PLA胶束的血液相容性和细胞相容性进行评价,为PEOz-PLA胶束的潜在应用提供数据支持。通过溶血、凝血时间、血小板激活以及与白蛋白的相互作用评价了PEOz-PLA胶束的血液相容性。结果表明,PEOz-PLA胶束的血液相容性良好。SRB的实验结果表明,PEOz-PLA胶束与KBv细胞孵育后并未出现明显的细胞毒性,显示出良好的细胞相容性。总之,PEOz-PLA胶束是血液和细胞相容的药物载体,可用于静脉给药。     

多西他赛pH敏感嵌段共聚物胶束的制备

本文在合成pH敏感两亲性嵌段共聚物聚(2-乙基-2-噁唑啉)-聚乳酸(PEOz-PDLLA)的基础上，采用薄膜分散法制备多西他赛pH敏感嵌段共聚物胶束，利用芘荧光探针技术测定胶束的临界胶束浓度(CMC)；通过高效液相色谱测定胶束的载药量及包封率；分别利用透射电镜、动态光散射法和zeta电位分析仪对胶束的形态、粒径和表面电位进行了表征；采用透析法考察了载药聚合物胶束的体外释放行为。结果表明，胶束的临界胶束浓度值为1.0×10^-3 g·L^-1；载药量可达15.0%，包封率为91.1%；胶束的粒度分布很窄，平均粒径为28.7nm；胶束粒子为圆球形且分散良好，其表面zeta电位值为(1.19±0.12)mV；在pH 7.4释放介质中，多西他赛胶束具有缓释作用；而在pH 5.0条件下，胶束释药明显加快，体现出PEOz-PDLLA胶束释药行为的pH敏感性。综合上述研究可见，PEOz-PDLLA嵌段共聚物胶束作为疏水性抗肿瘤药物的给药系统具有很好的应用前景。     

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.     

Advances in polymeric micelles for drug delivery and tumor targeting

A plethora of formulation techniques have been reported in the literature for targeting drugs to specific sites. Polymeric micelles (PMs) can be targeted to tumor sites by passive as well as active mechanisms. Some inherent properties of PMs, including size in the nanorange, stability in plasma, longevity in vivo, and pathological characteristics of tumor allow PMs to be targeted to the tumor site by a passive mechanism called the enhanced permeability and retention effect. PMs formed from an amphiphilic block copolymer are suitable for encapsulation of poorly water-soluble, hydrophobic anticancer drugs. Other characteristics of PMs such as separate functionality at the outer shell are useful for targeting the anticancer drug to tumor by active mechanisms. PMs can be conjugated with many ligands such as antibody fragments, epidermal growth factors, α₂-glycoprotein, transferrin, and folate to target micelles to cancer cells. Application of heat or ultrasound are the alternative methods to enhance drug accumulation in tumoral cells. Targeting using micelles can also be directed toward tumor angiogenesis, which is a potentially promising target for anticancer drugs. PMs have been used for the delivery of many anticancer agents in preclinical and clinical studies. This review summarizes recently available information regarding targeting of anticancer drugs to the tumor site using PMs.From the Clinical EditorThis review summarizes recent developments related to targeted anticancer drug delivery to tumor sites using polymeric micelles via active and passive mechanisms. Polymeric micelles can be conjugated with diverse ligands such as antibodies fragments, epidermal growth factors, α2-glycoprotein, transferrin, folate to target micelles to cancer cells.     

Amphiphilic polysaccharide-hydrophobicized graft polymeric micelles for drug delivery nanosystems

Self-assembled amphiphilic graft copolymers in aqueous solution to form polymeric micelles, have received growing scientific attention over the years. Among the polymeric micelles, hydrophobicized polysaccharides have currently become one of the hottest researches in the field of drug delivery nanosystems. It is attributable to such appealing properties as small particle size and narrow size distribution, distinctive core-shell structure, high solubilization capacity and structural stability, tumor passive localization by enhanced permeability and retention (EPR) effect, active targeting ability via tailored targeting promoiety, long-circulation property and facile preparation. The polymeric micelles self-assembled by hydrophobicized polysaccharides can be employed as targeted drug delivery nanosystem by including thermo- or pH-sensitive components or by attaching specific targeted moieties to the outer hydrophilic surface. Beside encapsulation of water-insoluble drugs, hydrophobicized polysaccharide polymeric micelles can complex with charged proteins or peptide drugs through electrostatic force or hydrogen bond, and serve as an effective non-viral vector for gene delivery. In the latter case, polymeric micelles can not only markedly protect these macromolecules from degradation by protease or ribozymes, but also increase the gene transfection efficiency. This review will highlight the state of the art self-assembled mechanism, characterization, preparation methods and surface modification of hydrophobicized polysaccharide polymeric micelles and their recent rapid applications as drug delivery nanosystems.     

聚合物胶束作为药物载体及其在肿瘤靶向方面的研究进展

聚合物胶束具有粒径小、稳定性高、滞留时间长、良好的生物相容性等特点,这些优良性质使得聚合物胶束作为药物载体具有许多独特的优势。近年来,涌现了许多围绕聚合物胶束设计肿瘤靶向给药系统的报道,包括利用肿瘤的病理学性质,设计被动靶向给药系统和对聚合物胶束进行表面修饰,设计主动靶向给药系统。本文主要综述了聚合物胶束作为肿瘤靶向药物载体的研究进展。     

Environmental-sensitive micelles based on poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymer for application in drug delivery

Anticancer drug doxorubicin (DOX) was physically loaded into the micelles prepared from poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymers (PEOz-PLLA). PEOz-PLLA consists of hydrophilic segment PEOz and hydrophobic segment PLLA showed pH-sensitivity in the aqueous solution. The DOX-loaded micelle exhibited a narrow size distribution with a mean diameter around 170 nm. The micellar structure can preserve hydrophobic drug DOX under the physiological condition (pH 7.4) and selectively release DOX by sensing the intracellular pH change in late endosomes and secondary lysosomes (pH 4-5). At 37 degrees C, the cumulated released rate of DOX from micelles was about 65% at pH 5.0 in the initial 24 h. Additionally, polymeric micelles had low cytotoxicity in human normal fibroblast HFW cells for 72 h by using MTT assay. Moreover, DOX-loaded micelles could slowly and efficiency decrease cell viability of non-small-cell lung carcinoma CL3 cells. Taken together, PEOz-b-PLLA diblock polymeric micelles may act as useful drug carriers for cancer therapy.     

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

The anticancer drug, adriamycin (ADR), was incorporated by physical entrapment into polymeric micelles for selective delivery to a murine solid tumor colon adenocarcinoma 26 (C 26). In vivo antitumor activity of ADR was greatly enhanced by this incorporation into polymeric micelles. Using one polymeric micelle delivery system, the tumor completely disappeared at two doses, while free ADR exhibited a fair inhibition effect on tumor growth only at the maximum tolerated dose. Biodistribution analysis revealed that the physically entrapped micellar ADR accumulated at tumor sites in a highly selective manner. These results indicate that these polymeric micelles are a promising system for delivering hydrophobic anticancer drugs selectively to solid tumor sites using a passive targeting mechanism.     

Synthesis and evaluation of biotin-conjugated pH-responsive polymeric micelles as drug carriers

pH-Responsive polymeric micelles have been investigated as drug carriers for chemotherapy. Ligand-mediated polymeric micelles, which can penetrate the target tumors due to their high binding affinity to a specific receptor on the surface of tumors, were developed to achieve targeted drug delivery. In this study, biotin-conjugated methoxypoly(ethylene glycol)-grafted-poly(β-amino ester) was prepared for active and pH-sensitive tumor targeting. These polymers were modified by cholesteryl chloroformate to improve the hydrophobicity of the micelle core. The structure of the biotin-conjugated polymer was confirmed by (1)H NMR spectroscopy, and the existence of biotin at the surface of the polymeric micelles was evaluated by an 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay at different pHs. The micelle properties were determined by dynamic light scattering and the result showed that the mean size of the polymeric micelles was approximately 20 nm. For cancer therapy, doxorubicin (DOX) was loaded into the polymeric micelles with a high loading efficiency. From the in vitro cellular uptake results, the biotin-conjugated polymeric micelles can effectively release doxorubicin at acidic tumor cells compared to the micelles without biotin. Overall, biotin-conjugated pH-responsive polymeric micelles have great potential to be used as drug carriers.     

Improved intestinal absorption of paclitaxel by mixed micelles self-assembled from vitamin E succinate-based amphiphilic polymers and their transcellular transport mechanism and intracellular trafficking routes

To ensure that antitumor drugs can be effectively transported across intestinal barrier and then quickly released in tumor cells, mixed polymeric micelles (Mix-PMs) were designed and fabricated by combining poly(2-ethyl-2-oxazoline)-vitamin E succinate (PEOz-VES) with TPGS1000 for enhancing intestinal absorption of paclitaxel. PEOz-VES exhibited an extremely low critical micelle concentration and negligible cytotoxicity. The Mix-PMs were characterized to have about 20?nm in diameter, uniform spherical morphology, high drug-loading content and sustained drug release profile with a retained pH-sensitivity. The results of the transport through Caco-2 cell monolayers and intestinal absorption revealed that Mix-PMs displayed higher transcellular transport efficiency compared with PEOz-VES micelles and Taxol^®. The possible mechanism of transcellular transport for Mix-PMs was elucidated to be mainly through clathrin- and caveolae/lipid rafts-mediated transcytosis. Confocal laser scanning micrographs revealed that late endosomes, lysosomes, endoplasmic reticulum, Golgi apparatus, and mitochondria were all involved in intracellular trafficking of Mix-PMs. The proteins involved in transcytosis of Mix-PMs and finally excreted were unraveled for the first time by the analysis of proteins in the basolateral media according to the proteomics method. Consequently, the fabricated mixed polymeric micelles may have great potential in enhancing intestinal absorption and accelerating drug release in tumor cells.     

Polymeric micelles to deliver photosensitizers for photodynamic therapy

Polymeric micelles are emerging as attractive drug delivery systems. Hydrophobic drugs including photosensitizers for photodynamic therapy can be covalently bound or physically entrapped in the core of the micelles and thus be systemically delivered to, for example, tumors using passive or active targeting strategies. Polymers used for photosensitizer encapsulation include pluronics, poly(ethylene glycol) (PEG)-lipid conjugates, and pH-sensitive poly(N-isopropylacrylamide) based micelles or polyion complex (PIC) micelles. This paper reviews the results obtained so far, including drug loading, biodistribution studies, and therapeutic efficiency. The pH-sensitive micelles appear to be promising candidates for photosensitizer delivery.     

Construction and characterization of intestinal oligopeptide transporter PepT1-targeted polymeric micelles for enhanced intestinal absorption of poorly water-soluble agents

To overcome the main barrier of intestinal epithelium for the oral absorption of poorly water-soluble drugs and further improve their oral absorption, Gly-Sar, the substrate of the oligopeptide transporter PepT1 widely distributed in the small intestine,conjugated poly(ethylene glycol)-block-poly(D,L-lactide) (Gly-Sar-PEG-b-PLA) was designed and synthesized, and PepT1-targetedpolymeric micelles were prepared and characterized. The structure of the synthesized Gly-Sar-PEG-b-PLA was confirmed by use of TLC and ¹H-NMR. The average molecular weight measured by GPC was 5954 g/mol with PDI of 1.34. The DiI-loaded polymeric micelles from Gly-Sar-PEG-b-PLA with drug loading content of 0.076% were characterized to exhibit 40.36 nm in diameter with PDI of 0.294, and well-defined spherical shape observed by TEM. Furthermore, the PepT1-targeted polymeric micelles profoundly enhanced intestinal absorption of poorly water-soluble drug. Therefore, the designed PepT1-targeted polymeric micelles might have a promising potential for oral delivery of water-insoluble drugs.     

Antitumor activity of adriamycin-incorporated polymeric micelles of poly(gamma-benzyl L-glutamate)/poly(ethylene oxide)

The multiblock copolymer composed of poly(gamma-benzyl L-glutamate) (PBLG) and poly(ethylene oxide) (PEO) was synthesized to prepare polymeric micelles as an anticancer drug carrier. Adriamycin (ADR) used as an anticancer drug was incorporated into the polymeric micelles prepared by the multiblock copolymer. The higher the drug feeding ratio, the higher the drug loading contents and the lower the drug loading efficiency. The increased drug feeding ratio resulted in increased particle sizes. At all of the formulations, particle sizes were less than 150 nm. The particles were observed as spherical shapes. ADR release from ADR-loaded polymeric micelles in vitro was decreased with an increased drug loading contents. In in vitro antitumor activity test using CT 26 tumor cells, polymeric micelles showed almost similar cytotoxicity when compared to ADR itself while polymeric micelles themselves did not affect cytotoxicity. In in vivo antitumor activity test using mice tumor xenograft model, the polymeric micelles showed improved survivability of mice with minimized weight changes and excellent tumor growth suppression efficacy. Polymeric micelles of the multiblock copolymer suggested to be a good candidate for anticancer drug delivery carrier.     

Reduction-responsive PEtOz-SS-PCL micelle with tailored size to overcome blood–brain barrier and enhance doxorubicin antiglioma effect

A series of novel reduction-responsive micelles with tailored size were designed and prepared to release doxorubicin (DOX) for treating glioma, which were developed based on amphiphilic block copolymer poly (2-ethyl-2-oxazoline)-b-poly (ε-caprolactone) (PEtOz-SS-PCL) and the micelle size could be regulated by designing the polymer structure. The DOX-loaded PEtOz-SS-PCL micelles had small size and rapid drug release in reductive intracellular environments. Biodistribution and in vivo imaging studies in C6 glioma mice tumor model showed that DOX loaded PEtOz-SS-PCL43 micelles with the smallest size had superior accumulation and fast drug release in tumor sites. In vivo antitumor activity demonstrated that DOX-loaded PEtOz-SS-PCL43 micelles improved antitumor efficacy in contrast to PEtOz-SS-PCL micelles with larger size toward the orthotopic C6-Luci cells-bearing mice. This study shows great potential in tailoring the micelle size and introducing the responsive bonds or compartment for intracellular drug delivery and release in glioma treatment by designing the architecture of the polymer.     

Mechanisms of drug release in pH-sensitive micelles for tumour targeted drug delivery system: A review

During the past decades, chemotherapy has been regarded as the most effective method for tumor therapy, but still faces significant challenges, such as poor tumor selectivity and multidrug resistance. The development of targeted drug delivery systems brings certain dramatic advantages for reducing the side effects and improving the therapeutic efficacy. Coupling a specific stimuli-triggered drug release mechanism with these delivery systems is one of the most prevalent approaches for targeted therapy. Among these approaches, pH-sensitive micelles are regarded as the most general strategy with advantages of increasing solubility of water-insoluble drugs, pH-sensitive release, high drug loading, etc.This review will focus on the potential of pH-sensitive micelles in tumor therapy, analyze four types of drug-loaded micelles and mechanisms of drug release and give an exhaustive collection of recent investigations. Sufficient understanding of these mechanisms will help us to design more efficient pH-sensitive drug delivery system to address the challenges encountered in targeted drug delivery systems for tumor therapy.