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CHEMOTHERAPY, ANTIBIOTICS, AND GENE THERAPY

Ethonafide-Induced Cytotoxicity Is Mediated by Topoisomerase II Inhibition in Prostate Cancer Cells

Department of Pharmacology (A.P., R.T.D.), College of Medicine (T.H.L., R.T.D.), Arizona Cancer Center (A.P., T.H.L., R.T.D.), The University of Arizona, Tucson, Arizona

Ethonafide is an anthracene-containing derivative of amonafide that belongs to the azonafide series of anticancer agents. The lack of cross-resistance in multidrug-resistant cancer cell lines and the absence of a quinone and hydroquinone moiety make ethonafide a potentially less cardiotoxic replacement for existing anthracene-containing anticancer agents. For this study, we investigated the anticancer activity and mechanism of ethonafide in human prostate cancer cell lines. Ethonafide was cytotoxic against three human prostate cancer cell lines at nanomolar concentrations. Ethonafide was found to be better tolerated and more effective at inhibiting tumor growth compared with mitoxantrone in a human xenograft tumor regression mouse model. Mechanistically, we found that ethonafide inhibited topoisomerase II activity by stabilizing the enzyme-DNA complex, involving both topoisomerase II and -. In addition, ethonafide induced a potent G₂ cell cycle arrest in the DU 145 human prostate cancer cell line. By creating stable cell lines with decreased expression of topoisomerase II or -, we found that a decrease in topoisomerase II protein expression renders the cell line resistant to ethonafide. The decrease in sensitivity to ethonafide was associated with a decrease in DNA damage and an increase in DNA repair as measured by the neutral comet assay. These data demonstrate that ethonafide is a topoisomerase II poison and that it is topoisomerase II-specific in the DU 145 human prostate cancer cell line.

Address correspondence to: Dr. Robert T. Dorr, Arizona Cancer Center, 1515 N. Campbell Ave., Tucson, AZ 85724. E-mail: bdorr{at}azcc.arizona.edu