Characterization of the cytotoxic properties of the benzimidazole fungicides, benomyl and carbendazim, in human tumour cell lines and primary cultures of patient tumour cells.

The benzimidazoles, benomyl and carbendazim, are fungicides suggested to target microtubules. Benomyl is metabolized to carbendazim, which has already been explored as an anticancer drug in phase 1 clinical trials. We further characterized the cytotoxic properties of benomyl and carbendazim in 12 human cell lines and in primary cultures of patient tumour cells with the overall aims of elucidating mechanisms of action and anticancer activity spectrum. Cytotoxicity was assessed in the short-term fluorometric microculture cytotoxicity assay and was correlated with the activity of other anticancer drugs and gene expression assessed by cDNA microarray analysis. Benomyl was generally more potent than its metabolite, carbendazim. Both showed high drug activity correlations with several established and experimental anticancer drugs, but modest association with established mechanisms of drug resistance. Furthermore, these benzimidazoles showed high correlations with genes considered relevant for the activity of several mechanistically different standard and experimental anticancer drugs, indicating multiple and broad mechanisms of action. In patient tumour samples, benomyl tended to be more active in haematological compared with solid tumour malignancies, whereas the opposite was observed for carbendazim. In conclusion, benomyl and carbendazim show interesting and diverse cytotoxic mechanisms of action and seem suitable as lead compounds for the development of new anticancer drugs.