The current status of new platinum analogs

Nine platinum analogs are currently in clinical development, including three that contain the diaminocyclohexane substituent and five that contain the cyclobutanedicarboxylato leaving group. Many of them have shown activity in at least one cisplatin (CDDP)-resistant cell line, most commonly L1210 murine leukemia. In addition, most were less nephrotoxic than CDDP in preclinical evaluations. While these agents share certain key structural similarities, there are important differences in their toxicity profiles that may be exploitable in future combination therapies. Though neuropathy has been a troubling toxicity with two of the three diaminocyclohexane (DACH) compounds, it differs in that it appears to be less chronic and cumulative with oxaliplatin (I-OHP), which is also associated with much less myelosuppression. Of the cyclobutanedicarboxylato compounds that are structurally related to carboplatin (CBDCA), there are several notable differences. For several compounds, isolated neutropenia has been dose-limiting and thrombocytopenia, which is common with CBDCA, has been uncommon. Like CBDCA, neurotoxicity has not been an issue with this group. Therefore, the potential for dose escalation with a colony stimulating factor (CSF) appears enhanced. Furthermore, promising early clinical leads, such as the substantial response rates in cervix and head and neck cancers with 254-S and in patients with colon cancer using circadian modulation of I-OHP, require careful evaluation. Preclinical synergy data are also cited that suggest other potential clinical leads. The development of a number of these agents has been complicated by unanticipated issues, including unexpected chronic dose-limiting neurotoxicity with ormaplatin (OP), formulation and stability problems with liposomal-neodecanoato-diaminocyclohexane platinum (II) (L-NDDP), and problematic nephrotoxicity with zeniplatin (ZP). However, several of these new compounds are likely to enter broader phase II and III development and should provide important information not only about the utility of the agents themselves but also about the predictive value of some of these preclinical models of CDDP resistance.