Irofulven (6-hydroxymethylacylfulvene, MGI-114, NSC 683863) is a semisynthetic derivative of illudin S, a natural product obtained from the Omphalotus mushroom. Irofulven has demonstrated potent activity against a broad range of solid tumors in both cellular and xenograft models and has shown promising activity in clinical trials. To guide the clinical use of irofulven, the present study used the MTT viability assay to examine the cytotoxic effects obtained by combining irofulven with two other anticancer agents: cisplatin and 5-fluorouracil (5-FU). The study was carried out with HT-29 and HCT-116 colorectal and A2780 ovarian carcinoma cells as well as with their irofulven- (HT-29/IF2, HCT-116/IF27) or cisplatin-resistant (A2780/CP70) variants. The combinations showed strong sequence specificity. Simultaneous exposure to cisplatin and irofulven was at least additive for four cell lines including the cisplatin-resistant A2780/CP70 ovarian cells which exhibit a multifactorial resistance phenotype. Cisplatin followed by irofulven was additive for parental HCT-116 and A2780 cells whereas irofulven followed by cisplatin was antagonistic in all cellular models. Simultaneous exposure to 5-FU and irofulven was at least additive for all six cell lines. 5-FU followed by irofulven was additive for the parental HT-29 and A2780 cells and synergistic for the irofulven-resistant HCT-116 cell line. Irofulven followed by 5-FU was synergistic for the two ovarian cell lines and additive for the two parental colon cell lines. These studies demonstrate that simultaneous exposure to irofulven and cisplatin is at least additive for most cell lines whereas simultaneous exposure to irofulven and 5-FU is additive to synergistic for all the cell lines tested, including the irofulven- and cisplatin-resistant variants. The enhanced cytotoxicity of irofulven in combination with cisplatin and 5-FU support the clinical application of these regimens.

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