Construction Of Small-Sized And Reversibly Crosslinked Polytyrosine Micelles For High Loading And Targeted Delivery Of Chemotherapeutics

Polypeptide with excellent biocompatibility,biodegradability and functionalities have been extensively employed for the fabrication of nanocarriers.The polypeptided based nanocarriers currently used in the clinic trials,however,suffer from some drawbackes including inefficient drug encapsulation,relatively big sizes,low tumor cell selectivity,and slow intracellular drug release.In these thesis,small-sized and reversibly crosslinked polypeptide micelles were designed and developed for high loading and targeted delivery of chemotherapeutics including doxorubicin(Dox)and phosphated gemcitabin(PGEM).In Chapter 1,we briefly summarized the current status and challenges of nanomedicine.In chapter 2,cRGD decorated,small-sized,robust and reduction-responsive polytyrosine micelles(cRGD-rPTM)based on poly(ethylene glycol)-b-poly(L-tyrosine)-lipoic acid(PEG-b-PTyr-LA)conjugate were developed for high loading and targeted delivery of Dox.Notably,cRGD-rPTM exhibited efficient loading of Dox,giving cRGD-rPTM-Dox with a drug loading content(DLC)of 18.5 wt.%and small size of 45 nm at a theoretical DLC of 20 wt.%.cRGD-rPTM-Dox displayed reduction-triggered drug release,high specificity and superior antitumor activity toward ?v?3 integrin positive MDA-MB-231 breast cancer cells(IC50?1.5 ?g/mL)to both non-targeted rPTM-Dox and clinical liposomal formulation(LP-Dox).cRGD-rPTM-Dox displayed a prolonged circulation time compared with the non-crosslinked cRGD-PTM-Dox control and significantly better accumulation in MDA-MB-231 breast tumor xenografts than non-targeted rPTM-Dox.In vivo therapeutic experiments revealed that cRGD-rPTM-Dox at 6 mg Dox equiv./kg could effectively suppress growth of MDA-MB-231 human breast tumor without inducing obvious side effects,outperforming both rPTM-Dox and LP-Dox.These reduction-responsive multifunctional polytyrosine micelles appear to be a robust and potentially viable platform for targeted chemotherapy.In chapter 3,A6 peptide decorated,small-sized,and reversibly crosslinked polytyrosine micelles(A6-rPTM)were developed for high loading and CD44-targeted delivery of PGEM.A6,a eight L-amino acid peptide(Ac-kPSSPPEE-NH2),can bind to CD44 resulting in the inhibition of migration,invasion,and metastasis of tumor cells.The results displayed that A6-rPTM achieved a high drug loading of PGEM,with a drug loading content up to 33.6 wt.%,which was significantly higher than most reported nanoparticulate GEM.Moreover,the PGEM-loaded A6-rPTM(A6-rPTM-PGEM)exhibited small size(?50 nm),narrow polydispersities(PDI<0.1),and high stability against extensive dilution and vortex.Flow cytometry and confocal imaging measurement revealed that A6-rPTM-PGEM achieved more effective internalization than non-targeting counterpart(rPTM-PGEM)in CD44 positive cancer cells like A549 lung cancer cells.MTT assay exhibited that A6-rPTM-PGEM could effeciently suppress the proliferation of A549 cells with an IC50 of 28.6,g/mL,which was much lower than that of free PGEM(IC50=137.1 ?g/mL).In sharp contrast with free GEM that is hardly internalized in human equilibrative nucleoside transportor(hENT)knock down A549 cancer cells,A6-rPTM-PGEM exhibited potent antiproliferative effect(IC50=41.5 ?g/mL).Thus,small sized and reversibly crosslinked A6-rPTM-PGEM not only largely improve the antiproliferativer effect toward lung cancer cells,but also extend their application in hENT knock down lung cancer cells,thus hold great potential in chemotherapy of lung cancer.In chapter 4,we summarized the whole thesis and presented the prospectives.