Bifunctional bisphosphonate derivatives and platinum complexes with high affinity for bone hydroxyapatite.

A series of ethylenediamine/1,3-propanediamine derivatives containing bifunctional bisphosphonate substituents and their corresponding dichloroplatinum(II) complexes have been synthesized and characterized by elemental analysis, H NMR, C NMR, P NMR, and HRMS spectra. Based on WST-8 assay with CCK-8, in general, the newly synthesized dichloroplatinum complexes 1-6 showed higher in vitro antitumor activity than platinum-free compounds L1-L6 against three tumor cell lines (especially osteosarcoma MG-63). According to hydroxyapatite binding experiment, complexes 2, 3, and 6 showed much higher affinity (K'=3.7, 4.0, and 3.0, respectively) for bone hydroxyapatite than cisplatin (K'<0.1), comparable to zoledronate (K'=2.8). It can be found that representative complex 2 with high cytotoxicity and in vitro antiproliferative activity against osteosarcoma cell line, as well as promising hydroxyapatite binding ability has been screened as a potential bone-targeting antitumor agent for subsequent in vivo study. In addition, flow cytometry experiment was applied to investigate the mode of action of representative complex 2.