The growth-inhibitory effect of 4-hydroperoxycyclophosphamide against human non-small cell lung carcinoma is enhanced by low-dose difluoromethylornithine

Summary Surgically unresectable buman non-small cell lung carcinoma (NSCC) is highly resistant to present chemotherpy and radiation therapy regimens. Cyclophosphamide, a potent alkylating agent, has shown some efficacy, especially in combination chemotherapy. Difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase (ODC) which produces minimal toxicity in animals and humans, has shown antiproliferative effect against human SCC in culture but a much smaller effect (cytostatic) against NSCC. We therefore investigated 4-hydroperoxycyclophosphamide (4HC) and DFMO alone and in combination against a human NSCC line (NCI-H157). Cells were treated with DFMO at graded concentrations of 0 to 800 M from day 0 to day 7. On day 3, cells were exposed for 1 h to 4HC at graded concentrations of 0 to 80 M, washed, and refed with media containing DFMO at initial concentrations. On day 7, cells were counted by hemacytometer. Cells treated with DFMO or 4HC alone exhibited dose-dependent growth inhibition. Growth inhibition by 4HC was enhanced through combination with DFMO. On day 7, 50 M (5×10^-5 M) DFMO effected a 37% inhibition, 8 M 4HC 47% inhibition, and the combination of 50 M DFMO and 8 M 4HC yielded an elevated 71% inhibition. The growth inhibitory effect and potentiating effect of DFMO were reversible upon addition of putrescine (PU) to the culture medium. The combination of DFMO and 4HC, two agents with different toxicity spectra, may represent an effective chemotherapeutic regimen for the treatment of lung cancer.Abbreviations DFMO difluoromethylornithine - FBS fetal bovine serum - 4HC 4-hydroperoxycyclophosphamide - NSCC non-small celllung carcinoma - ODC ornithine decarboxylase - PBS phosphate-buffered saline - PU putrescine - RPMI 1640 Roswell Park Memorial Institute 1640 medium - SCC small cell lung carcinoma The studies were supported in part by grants RO1 CA-43280 and VO1 CA-37606 from the National Institutes of Health. Gordon D. Luk is a recipient of a Faculty Research Award from the American Cancer Society