Synthesis and in vitro antitumor potency of (cyclohexane-1,2-diamine)platinum(II) complexes with aminotris(methylenephosphonic acid) as bone-seeking ligand

In order to develop platinum complexes with selective activity in primary and secondary bone malignancies and with the aim to optimize antitumor activity, platinum(II) complexes with aminotris(methylenephosphonic acid) as bone-seeking (osteotropic) ligand have been synthesized, characterized and tested in the cisplatin-sensitive ovarian carcinoma cell line CH1. As non-leaving diamine ligands, which are decisive for the cellular processing of DNA adducts, cis-R,S-cyclohexane-1,2-diamine, trans-S,S-cyclohexane-1,2-diamine and trans-R,R-cyclohexane-1,2-diamine have been used, resulting in complexes 1, 2, and 3, respectively. The cytotoxicity of the complexes under investigation decreases in the order 3 > 2 > 1 which is in accord with structure-activity relationships with other (cyclohexane-1,2- diamine)platinum(II) and platinum(IV) complexes: Both trans complexes (2 and 3) display a higher in vitro potency than the corresponding cis isomer (I), with the trans-R,R isomer (3) being the most active in this series. In comparison to the analogous (cyclohexane-1,2-diamine)platinum(II) complexes with bis(phosphonomethyl)aminoacetic acid as osteotropic carrier ligand, the cytotoxicity of 1-3 was found to be 1.5 - 2 fold higher, which is explainable by a different coordination mode of the phosphonic acid ligands (acetato versus phosphonato).