Design And Biological Activities Of Hypotoxic Platinum Complexes Targeting At Osteosarcoma

Osteosarcoma is the most frequent primary cancer of bone with a higher incidence in adolescents and young adults.It exists commonly in metaphysis of distal femur,proximal tibia and proximal humerus.Owing to the special location of osteosarcoma,clinic used anti-tumor drugs such as cisplatin is hard to reach the lesion area of osteosarcoma.Therefore,osteosarcoma patients have to face poor therapeutic effect,high risk of amputation and low 5-year survival rate.Bisphosphonates can be hydrolyzed by esterases in vivo and bisphosphonate acids can be produced.Both kinds of compounds can chelate with Ca2+ in bone mineral and be enriched in bone tissue.Based on the characteristics of bisphosphonates and long-term research on platinum anti-tumor drugs of our group,the research of this thesis is focused on constructing new bone-targeted platinum anti-tumor complexes and investigations on activity and selectivity of them.Moreover,molecular mechanisms are elucidated based on cellular and molecular level.Further,in vitro and in vivo toxicity was determined.The main factors that play important role in the higher selectivity and lower toxicity of targeting platinum drugs are analyzed which will provide crucial theoretical and practical basis of drug design.The research in the thesis is as follows:In the first chapter,we review the population,characteristics,pathogenesis and targeted therapy of osteosarcoma.By combining the defects of platinum anti-tumor agents used clinically and merits of non-traditional platinum anti-tumor agents such as pyriplatin,oxaliplatin and multi-platin,aims of the thesis are proposed based on detailed investigation of bisphosphonate platinum antitumor complexes.In view of merits of pyriplatin and multi-platin,in chapter 2 complexes 1 and 2 were designed and synthesized which are derivatives of pyriplatin.Complex 2 has bisphosphonate targeting group in its structure.The lipophilicity parameter of complexes 1 and 2 are larger than that of cisplatin,indicating that they are more lipophilic than cisplatin.In addition,both complexes can enter U2OS cells efficiently.Moreover,complex 2 is more potent than complex 1 towards U2OS cells at every tested concentration.complex 2 can prompt the phosphatidylserine exposure(Annexin V+)and loss of plasma membrane integrity(PI+)of the cells.A dose dependent increase in the population of late apoptotic tumor cells was observed.Further,complex 2 arrests U20S cells mainly at the G2/M phase.both complexes revealed intercalation and covalent binding with DNA.In comparison with complex 1,the acute toxicity of complex 2 was reduced due to bisphosphonate linking.Chapter 3 is on the basis of chapter 2.Bisphosphonate linked pyriplatin dinuclear platinum complex has shown excellent selectivity towards U2OS cells,but its acute toxicity is high.Oxaliplatin is hte third generation of platinum which can overcome partial defects of cisplatin.Therefore,complexes 3 and 4 were designed and synthesized which are derivatives of oxaliplatin.Complex 4 has bisphosphonate targeting group in its structure.Similar to complexes in chapter 2,complex 4 is more potent than complex 3,but less potent than complex 2 towards U20S cells.The acute toxicity of complex 4 is lower than that of complex 2,indicating that cyclohexanediamine linking helps to reduce the toxicity of complex.A dose dependent increase in the population of early apoptotic tumor cells was observed.Further,complex 4 can induce conformation change of DNA.In combination with results in the previous two chapters,we found that bisphosphonate targeting group can not only increase the selectivity towards U2OS but also reduce the acute toxicity.However,the toxicity reduction is limited.Since complexes 1-4 can interact with DNA,among which complex 2 and complex 4 have lower toxicity due to their weak interaction with DNA.Therefore in the last chapter we design and synthesis complex BPP which is a derivative of pyriplatin.BPP exhibits moderate inhibition against U20S cells through a mechanism involving both DNA binding and a mevalonate pathway.The acute toxicity of BPP to mice is 7-fold lower than that of cisplatin.The relative low systemic toxicity may result from the steric hindrance of the ligand,which blocks BPP approaching the bases of DNA.The results suggest that incorporating bisphosphonates into a platinum complex not only enhances its bone-targeting property but also minimizes its reactivity toward DNA and thereby lowers the systematic toxicity of the complex.The diminished cytotoxicity of BPP could be compensated for by increasing the therapeutic dose with marginal harm.This strategy provides a new possibility for overcoming the ineffectiveness and systemic toxicity of platinum drugs in the treatment of osteosarcoma.In conclusion,in this study,bisphosphonate bone targeting groups can enrich the platinum complexes in bone tissue.This will solve the problem that cisplatin can not reach the location of osteosarcoma.In addition,regulating the distance between bisphosphonate targeting group and the platinum center could also affect the interaction between platinum complexes and DNA.Moreover,one of the complex could also work through a mechanism involving the mevalonate pathway.Further,the toxicity of the complexes was reduced.This study will provide a solid theoretical and experimental basis for the treatment of osteosarcoma in the future.