Self-Assembly Of Peptide For Cancer Therapy

At present,pancreatic cancer remains one of the leading causes of death.Pancreatic cancer treatment is still facing challenges.Surgery,chemotherapy and radiotherapy are common strategies used in clinic,but are precluded by their shortcomings and limitations.Nanodrug delivery systems have long been considered as particularly the promising strategies for cancer therapy owing to their great potential for enhanced selectivity,improved biocompatibility and pharmacokinetic characteristics,and intensive antitumor efficacy.Moreover,mounting nano-chemotherapeutic agents have been exploited for pancreatic cancer treatment.However,few of them received satisfying therapeutic outcomes due to the presence of heterogeneity between tumor cells and complex interstitial barriers which limits their ability to target and penetrate tumors.Peptides and peptide derivatives,owing to their favorable biocompatibility,chemical versatility,and biological recognition abilities,have been widely utilized in biomedical field,such as bioimaging and drug delivery.Enzyme-instructed self-assembly(EISA)has become an ideal strategy for tumor targeting by combining enzymatic catalysis with the self-assembly of polypeptide.To date,a large number of enzymes have been validated to be overexpressed in tumors,which allows enzymes to act as an effective trigger for initiating the self-assembly of polypeptide-based drug carriers,thus enabling drug aggregation in tumors.In this study,a polypeptide camptothecin(CPT)delivery system response to fibroblast activating protein alpha(FAPα)and esterase(CES)was designed for the treatment of pancreatic cancer.The peptide prodrug Asp-Thr-Lys-Thr-Gly-Pro-Ala-Lys(SA-CPT)-Phe-Phe-Nap(1-CPT-Nap)contains Gly-Pro-Ala sequences that can be specifically recognized by FAPα.The peptide bond between Pro-Ala was broken under the hydrolysis of FAPα and then generated Ala-Lys(SA-CPT)-Phe-Phe-Nap(2-CPT-Nap).Subsequently,2-CPT-Nap self-assembled into nanofibers in situ and remained on the surface of pancreatic cancer cells.After uptake by cells,CPT was released under the hydrolysis of CES to achieve specific chemotherapy on pancreatic cancer cells.In the second chapter of this thesis,the synthesis of peptide prodrug 1-CPT-Nap and its control compounds 2-CPT-Nap and 2-Nap by solid-phase synthesis and liquid-phase synthesis were introduced.The accurate synthesis of peptides was proved by high performance liquid chromatography(HPLC),mass spectrometry(LC-MS)and nuclear magnetic resonance(NMR).In the third chapter of this thesis,the self-assembly properties of peptide prodrug 1-CPT-Nap and its control compounds 2-CPT-Nap(FAPα cleavage product)and 2-Nap(FAPα and CES co-cleavage product)were studied.The self-assembly process and secondary structure were characterized by critical micelle concentration,transmission electron microscopy and circular dichroism spectroscopy.The response of 1-CPT-Nap to FAPα and CES was proved by enzyme cleavage reaction.Finally,the therapeutic effect of 1-CPT-Nap on pancreatic cancer was verified by MTT assay,and the sustained-release effect of 1-CPT-Nap was further verified by changing the incubation time.The results of in vitro experiments showed that the anticancer effect of 1-CPT-Nap was better than that of the free drug CPT and had a good sustained release effect.In this thesis,the targeted release of CPT was achieved by designing and synthesizing a polypeptide drug-loading system based on the response of FAPα and CES,and its anti-cancer effect was verified.We expect that this thesis will help to broaden the application of polypeptide delivery systems in the biomedical field and provide new ideas for the therapy of pancreatic cancer.