Effects of Difluoromethylornithine on Growth Inhibition and Apoptosis in Human Cervical Epithelial and Cancerous Cell Lines

Objective. Difluoromethylornithine(DFMO), an irreversible inhibitor of ornithine decarboxylase and an angiogenesis inhibitor, has been used in phase I cervical intraepithelial neoplasia (CIN) trials, producing a 50% regression of CIN 3 lesions. DFMO is currently in phase II trials. In the experiments reported here, DFMO's growth inhibition and apoptosis induction were explored in an in vitro model to elucidate mechanisms of action. Methods. Four immortalized cervical epithelial cell lines, serving as in vitro models of precancerous CIN lesions, and nine cervical carcinoma cell lines were studied. DFMO's growth inhibitory effect was tested in monolayer culture and in semisolid medium, and concentrations required for a 50% growth inhibition (IC50) with a 5-day treatment were determined. Apoptosis induction was analyzed using the terminal deoxynucleotidyl transferase assay of DNA fragmentation. Results. DFMO inhibited growth of immortalized cervical epithelial cell lines and cervical cancer cell lines in monolayer culture and in semisolid medium. The immortalized cervical epithelial cell lines were more sensitive than the cervical cancer cell lines to DFMO's growth inhibitory effect. Concentrations required for 50% growth inhibition after a 5-day treatment ranged from 100 μM to >5 mM for cervical carcinoma cell lines and from 100 μM to 1 mM for immortalized cervical epithelial cell lines. DFMO induced apoptosis in precancerous and cancerous cell lines at a concentration of 5 mM, regardless of the cells' human papillomavirus status. Conclusion. DFMO inhibits the growth of cervical precancerous and cancerous cells in vitro in a dose-dependent and time-dependent manner, partially through inducing apoptosis.