| Platinum-based drugs have been widely used in clinics for chemotherapy,but small molecular platinum drugs have poor pharmacokinetic properties,severe side effects,and susceptibility to drug resistance,limiting their clinical applications.Platinum-based nanodrugs can effectively prolong the circulation time of platinum drugs,enhance tumor accumulation,and reduce toxic side effects,but only achieve limited therapeutic efficacy.The problems are that traditional Pt nanodrugs can not efficiently release drugs at the tumor site,and cancer cells have high heterogeneity and multidrug resistance,resulting in the inefficient killing of cancer cells.To solve these problems,we design and construct platinum nanocomplexes with well-defined structures and controlled release profiles;we evaluate the in vitro and in vivo antitumor activities of the pH-responsive nanocarrier,the high throughput screened cell-selective killing nanocarrier,and the Pt drugs and immunotherapeutic molecule codelivery nano carrier.The main findings and contributions of this dissertation include:1.A series of pH-responsive cisplatin nanocapsules were synthesized to address the problem of poor efficacy of platinum nanodrugs due to low intratumor release rate:In chapter 2 of this paper,a series of PEG-G4/amides-Pt nanocapsules(～20 nm)with a high drug loading capacity,pH responsiveness,and controlled release were constructed.Those nanocapsules used the poly(ethylene glycol)-dendritic polylysine block copolymers(PEG-G4,the fourth generation)as the core,amidized the dendritic polylysine with specific anhydrides,and then complexed with CDDP.Due to the β-carboxylic acid amide bonds,those nanocapsules had pH responsive properties.When under the acidic tumor microenvironment,the nanovesicles tended to break,realizing the controlled release of platinum.Nanocapsules exhibited strengthening stability in the blood and enhanced blood circulation.The structure of dendrimers,the morphology,and the size of nanocapsules were characterized in detail by nuclear magnetic resonance,dynamic light scattering,and transmission electron microscopy.The pH responsiveness of the nanocapsules was investigated by PBS dialysis,demonstrating that they can respond to acidic tumor microenvironment and quickly release cisplatin.Meanwhile,the PEG-G4/MSA-Pt nanocapsules with the best pH-responsive release were screened,and their cellular endocytosis,cytotoxicity,and pharmacokinetic behaviors were further investigated.At the same time,an exerted effective anti-tumor activity in the mouse lung cancer(A549)tumor model and PDX model of patient-derived hepatocellular carcinoma could be seen with the tumor inhibition rate of 80%and 90%.respectively.2.To address the problem of low efficacy of platinum nanodrugs due to cellular resistance,a high-throughput screening method for the cell-selective killing of platinum nanodrugs is proposed to achieve precision chemotherapy:In chapter 3 of this paper,a high-throughput screening platform based on dendrimers as carriers was proposed to achieve precision chemotherapy.Based on chapter 2,a fifthgeneration poly(ethylene glycol)-dendritic polylysine block copolymers(PEG-G5)was used as the core,grafting different kinds of amino acids with acid anhydride by two-by-two pairing,and loading 1,2-diaminocyclohexane-platinum(Ⅱ)(DACHPt,oxaliplatin prodrug).A platinum nanodrug library containing about 200 nanoparticles with different internal structures(PEG-G5/Xi-Pt,X represents amino acid unit and i represents the anhydride unit)was constructed.Subsequently,high-throughput screening was performed on different tumor cell lines through cytotoxicity experiments to obtain platinum nanoparticles with different high selective toxicity to different cells;At the same time,we explored the relationship between the cytotoxicity of nanoparticles and cell uptake,and verified the feasibility of highthroughput screening through cytotoxicity experiments in the mouse HCT-8/L oxaliplatin resistant model.It was shown that the PEG-G5/K17-Pt nanoparticles with specific killing of HCT-8/L resistant cells screened by cytotoxicity assay could achieve 84.8%tumor inhibition rate in mice,which provides a new solution to achieve precise chemotherapy.3.In order to address the problem of low therapeutic efficacy of single administration,a dual synergistic tumor-specific polymeric nanoparticle(NC-NP)was prepared:In chapter 4 of this paper,poly(ethylene glycol)-b-polylysine(PEGPLL/NCTD)nanocarriers amidized with norcantharidin(NCTD)were constructed and loaded with DACHPt to form NC-NP nanodrugs.Since NCTD could act as both a pH-responsive acidic anhydride and an immunomodulator,in addition to the pHresponsive release of platinum drugs and NCTD,this nanodrug could alleviate chemotherapy-induced cell cycle arrest and enhance the chemosensitivity of DACHPt by inhibiting protein phosphatase 2A(PP2A)activity;Meanwhile,by downregulating PD-L1 expression,PD-1 and PD-L1 interactions were disrupted and DACHPtinduced immunogenic cell death-induced immunotherapy were enhanced.The experimental results showed that the number of killer T cells(CD8+)in situ breast tumor tissues increased 1.4-fold and the number of immunosuppressive regulatory T cells(Tregs)decreased 37%after NC-NP treatment compared with the succinic anhydride capped control group(SA-NP).It indicates that NC-NP has excellent effects in enhancing anti-tumor lymphocyte infiltration and reducing immunosuppressive lymphocyte infiltration in tumors;And more effective antitumor immunotherapy performance could be achieved in an aggressive mouse breast cancer(4T1)tumor model with 81%tumor inhibition rate,which was much higher than that of the SA-NP administration group(29%),providing a promising example of chemical immunotherapy for cancer treatment. |
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