Fabrication Of Polypeptide-Based Nanomedicines And Their Combination Chemo-Photothermal Therapy Studies

Owning to the sophisticated micro-environment and the multi-drug resistence properties of tumor tissues,the combination of several therapies in one anti-tumor system is at the frontiers of biomedical materials and nanomedicine.Human tissues show very weak scattering and absorbing properties towards near infrared（NIR）light,which makes NIR light ideal source to penetrate deeply into human bodies without side effects.Nanomedicine systems with NIR-based photothermal therapy or combined chemo-photothermal therapy have drawn much attention in the field of cancer theranostic.Gold nanorods（AuNR）and gold nanoshells（AuNS）were known to possess excellent NIR photothermal properties,and have been intensively studied as photothermal therapy reagents.However,the above mentioned gold photothermal reagents displayed low biocompatibilities and weak stabilities.Furthermore,their preparation methods were found to be quiet complicated.Those drawbacks strongly hindered the further application of gold nanoparticles in biomedical applications.In this thesis,a series of comb-like polycysteine derivatives with functional side groups was synthesized through UV photo-cleavage reaction and thiol-ene chemistry.Taking the advantage of multivalent Au-S interactions,the self-assembled micelles of comb-like polycysteine derivatives were used as templates to prepare several kinds of polypeptide composite nanoparticles with excellent photothermal conversion properties.（1）The comb-like polycysteine derivatives with different side groups and different grafting ratio were synthesized.The influences of side groups and grafting ratio on polycysteine secondary structures and self-assembly structures were studied.The UV and DTT responsiveness of drug-loaded comb-like polycysteine derivative micelles were evaluated regarding drug release profile and cell toxicity.（2）Utilizing polycysteine-g-polyethylene glycol micelles as templates and reducing reagents,an auto-reduction method was developed to prepare polypeptide micelle/gold composite nanoparticles with strong NIR absorption and photothermal conversion property.The structure of composite nanoparticles was further characterized by XRD,XPS,TEM and SEM etc.,and their NIR triggered drug release were demonstrated.Flow cytometry analysis showed the composite nanoparticles can by internalized by cells quickly;while cell toxicity analysis confirmed the composite nanoparticles had synergistic effect between chemotherapy and photothermal therapy.（3）Lactose moieties with hepatic targeting property were introduced to polycysteine backbone by click chemistry.Then glycol-polypeptide micelles were used as templates to prepare gold composite nanoparticles with excellent phototheraml conversion property.At the same time,two anti-cancer drugs DOX and 6-MP were loaded at the composite nanoparticles’core and surface respectively,and the dual drugs-loaded composite nanoparticles displayed NIR and DTT triggered drugs release profiles.The hepatic targeting property of composite nanoparticles were further confirmed by MTT analysis,flow cytometry analysis and fluorescence microscopy.The composite nanoparticles showed an IC₅₀ of 6.14μg/mL for chemo-photothermal therapy,and IC₅₀0 of 75.69μg/mL for photothermal therapy alone and 8.76μg/mL for single cocktail chemotherapy,which demonstrated the composite nanoparticles had synergistic antitumor effect.（4）Utilizing the host-guest interaction betweenα-cyclodextran and PEG,polypeptide micelles with polycysteine chain located at micelle corona were prepared.The structure of the micelle was proved by XRD and NMR spectroscopy.Gold composite nanoparticles were prepared using micelles as templates,and gold were found to be conjugated at the micelle surfaces as observed by TEM.The combination index between chemotherapy and photothermal therapy was found to be 0.80,which means the composite nanoparticles had synergistic anititumor effect.（5）The self-polymerization of dopamine with PEG-b-PC micelle was utilized to prepare composite nanoparticles with photothermal conversion property.Dopamine self-polymerization was proved to take place at micelle surface;and a core-shell structure with micelle as the core and polydopamine as the shell was formed.By adjusting micelle structure,dopamine concentration and polymerization time,the photothermal conversion efficiency of composite nanoparticles was optimized,and their chemo-photothermal synergistic effect was further evaluated by cell toxicity analysis.