Bone-targeting melphalan prodrug with tumor-microenvironment sensitivity： Synthesis, in vitro and in vivo evaluation

Bone tumor is a refractory neoplastic growth of tissue in bone. According to the unique environment and phys-chemical characteristics of bone tissues, the chemotherapeutic agents are unlikely to prolong the survival of patients and often associated with systemic side effects. The bone targeting drug delivery via systemic administration may provide both better treatment efficacy and less frequent administration. In this study, we describe the synthesis, in vitro and in vivo evaluation of novel melphalan-bisphosphonate hybrids, with a tumor microenvironment sensitive linkage, which could be enzymatic activation under tumor microenvironment conditions. We have also evaluated the in vitro targeting efficiency of these prodrugs via the affinity of hydroxyapatite （HA） and cellular proliferation. The in vivo distribution suggested the bisphosphonate conjugated prodrugs with high bone selectivity.