Aim: This study aimed to characterize the cellular basis of the platinum cytotoxicity of two novel platinum
complexes, 3Pt and 1Pt, in comparison with that of cisplatin. 3Pt comprises anionic phosphate moieties, while 1Pt
comprises neutral aromatic ligands.
Methods: We compared the cytotoxic potency of 3Pt and 1Pt with that of cisplatin in osteosarcoma cell lines and an
orthotopic mouse model.
Results: The cytotoxic potency of 3Pt was markedly higher than that of cisplatin in all cell lines. Both novel platinum
complexes showed a complete lack of cross resistance in cisplatin-resistant cells. Caffeine enhanced the cytotoxic
potency of these novel platinum complexes, as observed for cisplatin. Apoptosis after drug administration was observed by DNA ladder
formation and an annexin V/PI assay. DNA double-strand breaks were confirmed by phosphorylation of histone H2AX. In vivo, the
antitumor activity of 3Pt and 1Pt was superior and similar, respectively, to that of cisplatin. Both novel platinum complexes exerted
strong antitumor effects on osteosarcoma in vitro and in vivo.
Conclusions: 3Pt may be an effective drug for the treatment of bone cancer because the PO3 moiety has a high affinity to bone, as
exhibited by bisphosphonates, and is expected to decrease the incidence of side effects at extraskeletal sites and overcome drug
resistance. Cationic 1Pt may also be an effective antitumor drug because of its unique chemical structure and properties. Further
investigations to detail the antitumor effects of these ionic Pt complexes on osteosarcoma are warranted.