[Drug discovery research in in-vivo antitumor-active azolato-bridged dinuclear Pt(II) complexes]

Cis-diamminedichloridoplatinum(II) (cisplatin), which was first introduced as a clinical anticancer agent in the 1970s, is still among the most-utilized agents in current cancer chemotherapy. The discovery of cisplatin antitumor activity has catalyzed drug discovery research on antitumor platinum coordination compounds with improved efficacy. Some of new compounds show fewer side effects or expanded clinical applications. Apart from some clinical inconveniences, such as side effects, the high therapeutic efficacy of platinum-based agents implies that further modifications may lead to more effective anticancer platinum drugs which are effective against cancers that are typically resistant to chemotherapy, such as pancreatic cancer, and platinum-refractory cancer. Most of the cisplatin analogs cause cross-resistance to cisplatin, probably because of the similar biological consequences. It is suggested that platinum complexes which interact with DNA; the most probable target molecule, through a mechanism different from that of cisplatin can provide unique anticancer spectra required for next-generation anticancer drugs. Therefore, we synthesized a series of azolato-bridged dinuclear Pt(II) complexes with a general formula, [{cis-Pt(NH(3))(2)}(2)(µ-OH)(µ-azolato)](2+), which can form 1,2-intrastrand crosslinks with a minimal DNA distortion, whereas clinical platinum-based drugs provide 1,2-intrastrand crosslink with severe DNA distortion. Indeed, they exhibit much higher in vitro cytotoxicity than cisplatin, and we have recently found one of the dinuclear Pt(II) complexes exhibits markedly high in vivo antitumor efficacy against pancreatic cancer. Here, I update our drug-discovery research on the series of azolato-bridged dinuclear Pt(II) complexes that may be more effective and safer than current anticancer chemotherapeutic agents.