Preparation And Antitumor Activity Of Pt Complex-substituted Polyoxometalates

Polyoxometalates?POMs?as a promising chemotherapeutic drug candidate are drawing special attention owing to their remarkable antitumor and antiviral activities.The unique advantage of POMs over current drugs lies in the fact that the molecular structure and physichemical properties of POMs are tunable.However,POMs exhibit lower bioactivity and toxic side effects.Recently,it was found that incorporating organic molecules,organicmetal and small biological molecules into the POMs matrix can enhance the bioactivity and decrease the toxic side effects of POMs.In this study,bivalent and tetravalent organoplatinum-substituted Keggin type POMs were prepared though covalent and metal coordination processes.Organoplatinum ligands can significantly improve the interaction of POMs and DNA,leading to apoptosis.Furthermore,to further enhance anticancer efficacy of tetravalent organoplatinum-substituted Keggin type POMs in vitro and in vivo,we suggest encapsulation of tetravalent organoplatinum-substituted Keggin type POMs with the micelle and polypeptide to form nanoparticles.The passive targeting properties of liposome and active targeting characteristics of the polypeptide could target delivery POMs into the tumor cells and tumor.The in vitro and in vivo antitumor activity and mechanism were studied.The detailed study are as follows:Three kinds of organic-inorganic hybrid compound were designed and synthesized based on Keggin-type POMs,including two organoplatinum???-substituted POMs and an organoplatinum???-substituted POMs.Fourier infrared spectroscopy,nuclear magnetic resonance and electrospray ionization mass spectrometry confirmed the successful preparation of platinum complexes substituted Keggin-type POMs.In vitro antitumor activity and cytotoxicity of Keggin-type POMs,organoplatinum???-substituted Keggin-type POMs and organoplatinum???-substituted Keggin-type POMs were measured by MTT assay.MTT assay results show that the organoplatinum-substituted Keggin-type POMs shows strongest inhibition action on HT29 cells in a time and concentration-dependent manner,while toxicity is very low on normal cells HUVEC.The intracellular localization of POMs-based organic-inorganic compound was studied using confocal microscopy and flow cytometry.Fluorescence techniques and gel electrophoresis were further used to deep study the antitumor mechanism of organoplatinum-substituted Keggin-type POMs.It was confirmed the antitumor mechanism of organoplatinum-substituted Keggin-type POMs involved DNA binding of platinum???-substituted POM and subsequent apoptosis.The organoplatinum???-substituted Keggin-type POMs was then encapsulated with distearoyl phosphatidylethanolamine-polyethylene glycol(DSPE-PEG₂₀₀₀)to form nanoparticles.The physical and chemical properties?such as morphology,size characterization,drug p H sensitive release process,etc.?of nanoparticles were examined.In vivo and in vitro antitumor activity and toxicity of the nanoparticles were assessed.In vitro studies show that the drug-loaded micelles enable p H-sensitive release,greatly enhancing drug accumulation in tumor cells,thereby significantly improving the inhibition effect on tumor cells.In vivo experiments confirmed that the drug-loaded micelles can passively target human colorectal cancer,and thus demonstrate superior antitumor efficacy in treating human colorectal cancer and low side effects,in comparsion with classic cisplatin administered in its conventional form.The organoplatinum???-substituted Keggin-type POMs was encapsulted with a novel tumor cell targeting peptide,cystine-arginine-glycine-asparticacidlysine?Cys-Arg-Gly-Asp-Lys,CRGDK?,to obtain a new drug-loaded nanoparticles Pt?-PW11@CRGDK.The CRGDK peptide surrounding the Pt?-PW11@CRGDK nanoparticles enables nanoparticles to actively target the Neuralpilin-1?Nrp-1?-expressed tumor cells.In vitro studies show that the Pt?-PW11@CRGDK nanoparticles can specifically bind with Nrp-1 receptor and exhibit high inhibition action on Nrp-1-expressed tumor cells.In vivo studies further verify the targeting efficiency and penetrating ability of the nanoparticles in the site of tumor.