Controlled Preparation And Application Of Paclitaxel-loaded Nano-micelles Based On Poly(Lactic Acid)Block Copolymer

As a microtubule-stabilizing agent,paclitaxel promotes polymerization of tubulin and disrupts the dynamics necessary for cell division.It exhibits a significant antineoplastic activity against various solid tumors including ovarian cancer,breast cancer,head and neck carcinomas,and nonsmall-cell lung cancers.There are several kinds of paclitaxel-loading methods,such as liposomes,cyclodextrin inclusion compound,paclitaxel prodrugs,polymeric micro/nanospheres and so on.Among them,amphiphilic polymer micelles have become a hotspot in the field of pharmacy due to their excellent performance as a drug carrier.PEG-PLA is an amphiphilic biodegradable material,it has been approved by the FDA for biomedical applications and widely used as pharmaceutical carriers for drugs.However,there are still many problems in the preparation of drug-loaded micelles by PEG-PLA.For example,when the drug is encapsulated by physical method,the drug loading content is limited by the compatibility between the drug molecule and the hydrophobic segment-PLA,therefore the drug loading content is low and the drug release speed is too fast.When PTX was loaded to PEG-PLA via the ester bond,the burst release of PTX was avoided,however the drug loading content could not be improved significantly.In the case of chemical embedding of drugs by azide-alkyne click reaction,the drug loading content of the micelles can be significantly improved.But,this method is time consuruing and complicated,and the drugs used in the process are more toxic.Besides,the release rate of PTX was too fast to meet the requirement of drug release.In order to improve the effect of PEG-PLA as apaclitaxel drug carrier,this thesis proposed a method of connecting PTX-PDLA-PTX with MPEG-PLLA for preparation of MPEG-SCPLA-PTX drug-loaded micelles via the combination of chemical embedding and stereocomplexing for the first time.This method is simple and the drug loading content is adjustable.It meets the requirements for drug release:1)Amphiphilic block copolymers of MPEG2000-PLLA6000 MPEG5000-PLLA6000 and MPEG5000-PLLA2000 were synthesized by ring-opening polymerization of L-lactide with MPEG as a macroinitiator and CR as a catalyst,the reaction was carried out at 150℃ for 10-15 h.The product was characterized by GPC,1H-NMR and DSC.The DSC analysis characterized the thermodynamic properties such as melting point and melting enthalpy of the copolymers.2)PDLA(Mn 2000Da)was synthesized by polycondensation of D-lactic acid with CR as a catalyst.The obtained PDLA was then reacted with succinic anhydride to prepare dicarboxyl-ended PDLA(DI-PDLA)with DMAP as a catalyst.PTX-PDLA-PTX was finally formed by the reaction of DI-PDLA with 2-hydroxyl group of paclitaxel catalyzed by DCC and DMAP.The results were characterized by1H-NMR,GPC,DSC.The DSC analysis characterized the thermodynamic properties such as melting point and melting enthalpy of the copolymers.The PTX loading content of PTX-PDLA-PTX was 36.36%,and the utilization content of PTX was 98.57%,which was calculated by 1H-NMR and GPC data.3)In order to get the drug-loaded micelles or blank micelles with MPEG as a hydrophilic shell,SC-PLA-PTX or SC-PLA as a hydrophobic core,the MPEG-PLLA blocks were reacted with PTX-PDLA-PTX or DI-PDLA block in solution to form an MPEG-SCPLA-PTX structure.Specifically,the combination of MPEG5000-PLLA6000,MPEG5000-PLLA2000,MPEG2000-PLLA6000 with PTX-PDLA-PTX led to 5-6 micelles,5-2 micelles,2-6 micelles;the combination of MPEG5000-PLLA6000 with DI-PDLA led to 5-6 blank micelles.The melting point of PLA in micells was 40-50℃ higher than that of MPEG-PLLA,which confirmed the formation of SC-PLA.The average particle size of micells is about 100 nm,CMC value ranges 1.0-2.5 × 10-3 g/L.The PTX load content of 2-6 micelles,5-2 micelles,5-6 micelles is 20.1%,11.6%,17.2%,respectively.The results indicated that the loading content of paclitaxel can be controlled by adjusting the length of PDLA and PLLA in the copolymer.The vitro release rate of 2-6 micelles,5-2 micelles,5-6 micelles in simulated human environment is 37.7%,51.5%and 52.0%within 216h,respectively.The micells prepared in this paper can meet the requirement of drug release,due to the gental release.