The clinical efficacy of
cisplatin-based
chemotherapy for
ovarian cancer is frequently compromised by drug resistance or dose-limiting renal and neurologic toxicities.
CI-973 (NK-121), a 2-methyl-1,4-butanediamine analogue of
carboplatin, has shown little nephro- and neuro-toxicity in pre-clinical model systems and in phase-I trials. Its in vitro spectrum of activity against
ovarian cancer cell lines has not been previously characterized. The in vitro activities of
CI-973,
cisplatin,
carboplatin and
tetraplatin were compared in several
platinum-sensitive and -resistant human ovarian
carcinoma cell lines. Cytotoxicity was assessed by inhibition of clonogenic survival in soft
agar with continuous
drug exposure. On a molar basis,
cisplatin and
tetraplatin were the most potent analogues, while
carboplatin was consistently less potent.
Cisplatin,
carboplatin and
CI-973 elicited a very similar response pattern by Spearman rank correlation, distinct from that seen with
tetraplatin. The magnitude of resistance to
CI-973 was comparable to
cisplatin in 5 cell lines but was substantially lower in the highly
cisplatin-resistant 2780-CP70 and OVCAR-10 cell lines. These results suggest that
CI-973 and
tetraplatin may have potential utility in some cases of
cisplatin-resistant
ovarian cancer. In addition, our data are consistent with the existence of at least 2
platinum-resistance phenotypes--one with moderate levels of resistance to
cisplatin,
carboplatin and
CI-973 but highly resistant to
tetraplatin, the other highly resistant to
cisplatin and
carboplatin but only partially cross-resistant with
tetraplatin and
CI-973. The recognition of different resistance phenotypes may facilitate the study of cellular resistance mechanisms to
cisplatin and newer
platinum analogues.