| Chemotherapy is one of the main methods of cancer treatment,but is limited by drug resistance,especially multidrug resistance(MDR).Unfortunately,the mechanism of MDR occurrence is quite complex and overexpression of drug efflux is considered as the significant contributor to MDR in cancer.MRP1 is an important member of ATP-binding cassette(ABC)transporter family,which efflux a number of chemotherapeutic drugs,including doxorubicin,etoposide and vincristine.Except finding the specific inhibitors of MRP1,great effort has been taken on developing nanotechnology-based strategies to inhibit the MRP1-mediated MDR by encapsulating or linking drugs to nanoparticles.In this study,we designed novel micellar vectors for doxorubicin based on amphiphilic copolymers sequentially linking β-cyclodextrin(β-CD),polylacticacid(PLA)or polycaprolactone(PCL)block,and polyethylene glycol(PEG)block to overcome MDR in human acute myeloid leukemia cells(HL60/ADR)The main content and conclusions of this dissertation are described below(1)A series of amphiphilic copolymers compounding with β-CD,PEG,LA or CL were synthesized successfully.The copolymers were named as PELA-CD and PECL-CD.The polymer structure was characterized by 1H-NMR.These amphiphilic copolymers could self-assemble into micelles in aqueous solution and the CMCs were quite small.The blank micelles had spherical shape with uniform size between 100 and 200 nm.(2)A series of DOX-loaded micelles with different amphiphilic copolymers were prepared by a oil/water emulsion-solvent evaporation method.The LC and EE of DOX in micelles were measured and the results showed PELA54-CD and PECL54-CD achieved the highest LC in their series,respectively.This high loading capacity was attributed to the cooperation of β-CD and relatively long PLA or PCL segments,whereβ-CD could interact with DOX to form inclusion compound and PLA or PCL aggregations could encapsulate DOX in the hydrophobic micelle core.The DOX-loaded micelles also had spherical shape with uniform size between 100 and 200 nm.(3)HL60/ADR cells mainly overexpress MRP1 and DOX is the substrate of MRP 1.Assays in HL60/ADR cells showed DOX-loaded micelles could result in significant enhancement in cytotoxicity.Furthermore,PELA-CD and PECL-CD DOX-loaded micelles tended to enhance the cellular accumulation of DOX through promoting uptake or inhibiting efflux,leading to the improved cytotoxicity in HL60/ADR cells.Besides,DOX-loaded micelles could serve as carriers for drug delivery by preventing lysosomal degradation,resulting in higher intracellular accumulation of therapeutic agents(4)In vivo study in the HL60/ADR mouse model demonstrated that these DOX-loaded micelles not only prevented tumor growth efficaciously,but also reduced the toxic side effects of DOX.(5)Several analyses were performed to understand the molecular interactions between polymers themselves and multidrug resistance protein 1(MRP1)at the cellular level.The results showed that PELA-CD and PECL-CD polymers could induce decline on intracellular ATP,MMP and GSH levels.Reverse transcription-polymerase chain reaction(RT-PCR)analysis did not show remarkable correlation of MRP1 gene and polymer treatment in HL60/ADR cells.This result was consistent with western blotting,which indicated little effect of these polymers on the expression of MRP 1 protein.In conclusion,these novel composite micelles can be considered as a promising drug delivery system for tumor therapy to reverse MRP1-mediated MDR. |
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