Rational Design And Mechanistic Study Of Anticancer Platinum (?) Prodrugs For Overcoming Cisplatin Resistance

Cancer is a malignant disease that seriously threatens human life and health,chemotherapy is still the main clinical treatment for cancer.Platinum-based drugs such as cisplatin is one of the most widely used and effective chemotherapy drugs,and it is widely used in the treatment of lung cancer,cervical cancer,ovarian cancer and other many tumors.It is estimated that at least 50%of cancer patients are treated with platinum anticancer drugs.However,there are still many urgent problems in the clinical use of Pt-based drugs,such as drug resistance and side effects.Therefore,it is particularly urgent to develop new platinum complexes that can overcome drug resistance and reduce side effects.As new generation of Pt-based antitumor prodrugs,tetravalent platinum(Pt^?)complexes have attracted extensive attention from researchers at home and abroad in recent years.Pt^? complexes have octahedral coordination structure,which not only enhance the inertia of the complexes,reducing theirs toxic and side effects during transportation in vivo,but also provide convenience for functional modification of the complexes.When Pt^? complexes enter cancer cells,the active divalent platinum units(Pt^II)and the axial ligands will be released due to highly hypoxic and reductive environment in cancer cells.Pt^IIspecies bind to DNA,causing damage and the axial ligands exert their biological activity,ultimately synergistically killing cancer cells.The rise of Pt^? prodrugs provides a new idea for reducing side effects of traditional Pt-based drugs,achieving oral treatment and conquering cisplatin resistance.Drug resistance is a major obstacle to limit the clinical effect of Pt-based drugs.Therefore,defeating platinum resistance has been a hot topic in the research of pharmaceutical chemists.The resistance mechanisms of platinum drugs are very complicated,involving multiple signaling pathways in tumor cells.Taking cisplatin resistance as an example,it includes enhanced DNA damage repair,apoptosis escape and metabolic reprogramming etc.In this paper,the Pt^? complex was used as a matrix,and the bioactive organic small molecules interfering with the key signaling pathways of cisplatin resistance mechanisms were modified in its axial ligands,so as to obtain multiple multi-functional Pt^? prodrugs,which are expected to effectively overcome cisplatin resistance.Cisplatin binding to nuclear DNA will cause damage to single strand,if the repair fails,it will further cause double strand breaks(DSBs),and homologous recombination(HR)is an effective way to repair DNA DSBs.BRCA1/2 are two key HR genes or proteins,so BRCA-deficient tumors have a loss of HR capacity,which makes them more sensitive to platinum drugs,while BRCA-proficient tumors often have innate resistance to platinum chemotherapy.Based on this,we designed two Pt^?-artesunate conjugates,Pt-ART-? and Pt-ART-?,which exhibited significantly higher cytotoxicity than cisplatin in BRCA-proficient ovarian and breast cancer cells by more than 10 times,while showing lower toxicity to normal kidney cells.Mechanism studies have shown that Pt-ART-? and Pt-ART-? can effectively enter tumor cells,release Pt^II units,and cause severe damage to nuclear DNA.The released ART downregulated the expression of HR key executor protein RAD51,inhibited the formation of RAD51 foci,and eventually promoted the significant apoptosis response.In addition to DNA damage repair,escape of apoptosis is also an important cause of cisplatin resistance.By inhibiting DNA repair alone,tumor cells can also resist the killing of cisplatin by activating antiapoptotic pathways.Therefore,simultaneous intervention of these two pathways seems to be more effective in overcoming cisplatin resistance.Accordingly,we designed two thiophene derivatives modified Pt^?complexes 1 and 2,in which complex 2 not only inhibited the expression of antiapoptotic protein Mcl-1,thus promoting cell apoptosis,but also hindered HR-mediated DNA DSBs repair.This is the first report of platinum complexes that interfere with both DNA repair and apoptosis.Complex 2 showed high cytotoxicity against cisplatin-resistant no-small-cell lung and ovarian cancer cells,the IC₅₀ values were 32and 61-fold less than that of cisplatin,and the resistance factor were significantly lower than that of cisplatin.Metabolic reprogramming is an important feature of malignant tumors.Tumors changes their own metabolic patterns to adapt to the needs of rapid growth and metastasis.Recently,researchers have found that cisplatin resistance is also closely related to abnormal tumor metabolism,so interfering with tumor metabolism is a potential direction to overcome cisplatin resistance.So,we designed two Pt^?-epalrestat complexes,Pt-E-? and Pt-E-?,they can effectively restrain the activity of aldose reductase(AKR1B1),intervene of polyol pathway and lipid metabolic pathways(e.g.PGF2a,lipid peroxidation,etc.),eventually induce a variety of modes of cell death,including apoptosis,necrosis and ferroptosis.Pt-E-? and Pt-E-? have high cytotoxicity against many tumor cells,especially cisplatin-resistant A549/DDP cells,and the IC₅₀value of Pt-E-? is reduced to 1/70 of that of cisplatin.In all,overcoming cisplatin resistance is a major target for drug design in this paper,in view of the different aspects of cisplatin resistance mechanisms,we adopted Pt^?prodrug strategy and synthesized a series of prodrugs of cisplatin,the axial ligands of which are small-molecules intervening specific cisplatin resistance pathway including homologous recombination,apoptosis,metabolic reprogramming.The cytotoxicity data shows they all are able to effectively overcome cisplatin resistance.Then we further studied theirs action mechanisms and structure-activity relationship to provide theoretical basis and useful inspiration for the development of novel platinum drugs to overcome platinum resistance.