DNA‐binding properties of novel cis‐ and trans platinum‐based anticancer agents in 2 human ovarian carcinoma cell lines

Abstract

We have investigated the comparative initial DNA binding properties of 7 platinum-based anticancer drugs: 5 cis-oriented compounds, cisplatin, tetraplatin (Ormaplatin), JM118 [cis ammine dichloro (cyclohexylamine) platinum (II)], JM216 [bis-acetato cis ammine dichloro (cyclohexylamine) platinum (IV)] and JM149 [cis ammine dichloro (cyclohexylamine) trans dihydroxo platinum (IV)], and 2 trans-oriented compounds, transplatin and JM335 [trans ammine dichloro (cyclohexylamine) dihydroxo platinum (IV)] in SKOV-3 and CH1 human ovarian carcinoma cells. Unlike transplatin, the trans complex JM335 was comparably cytotoxic to its cis isomer JM149 and cisplatin. No significant correlation was observed between levels of total platinum bound to DNA after exposure to the 7 drugs and cytotoxicity in either cell line. Using a competitive enzyme-linked immunoabsorbent assay, DNA extracted from CM1 cells exposed to the 5 cis platinum drugs was recognized by the monoclonal antibody ICR4 (raised against DNA platinated by cisplatin) in the order JM118 > cisplatin > JM216 > tetraplatin > JM149; a strong positive correlation which just attained statistical significance was observed between recognition by ICR4 and cytotoxicity. In contrast, DNA extracted from CH1 cells exposed to the trans platinum drugs transplatin and JM335 was no more immunoreactive than control DNA. Using alkaline elution, interstrand cross-link levels after exposure to drug did not correlate with cytotoxicity in either cell line. The 5 cis drugs formed interstrand cross-links in both cell lines, whereas transplatin formed very low levels in SKOV-3 and undetectable levels in CH1. JM335 was efficient at forming interstrand cross-links in SKOV-3 but, notably, none were observed in CH1. In contrast, in the CH1 cells, single-strand breaks were observed with JM335 (but not with any other drug). The novel trans complex JM335 was unique, among the platinum drugs studied, in its ability to form both DNA interstrand cross-links and single strand breaks (DNA lesion formation being cell line dependent), a property which may account for its cytotoxicity.