This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Dorr, R. T. Articles by Gerner, E. W. Search for Related Content PubMed PubMed Citation Articles by Dorr, R. T. Articles by Gerner, E. W.

Modulation of Etoposide Cytotoxicity and DNA Strand Scission in L1210 and 8226 Cells by Polyamines¹

Arizona Cancer Center, Departments of Medicine and Pharmacology/Toxicology [R. T. D., J. D. L.], and Radiation Oncology [E. W. G.], The University of Arizona, Health Sciences Center, Tucson Arizona 85724

The anticancer agent etoposide (VP-16) produces DNA strand scission in intact tumor cells or isolated nuclei. This activity may be mediated by topoisomerase II, an enzyme capable of producing double strand breaks in mammalian cells. Two established tumor cell lines were examined to see whether polyamines, which alter DNA conformation and topoisomerase II activities, affected the cytotoxicity, strand scission, and antitumor efficacy of VP-16. L1210 murine leukemia and 8226 human myeloma cells were treated with -difluoromethylornithine (DFMO) to reduce intracellular polyamine levels via inhibition of ornithine decarboxylase. The polyamines putrescine and spermidine were markedly reduced by a 48-h incubation with 50 µM DFMO. This DFMO concentration did not inhibit colony formation in either cell line, but did reduce the growth rate of both cultures. In contrast, VP-16 produced a dose-dependent inhibition of colony formation. This was especially marked in the 8226 cell line. This correlated with DNA single strand breaks (SSBs) detected by the alkaline elution technique. When cells previously treated with DFMO were exposed to VP-16, a synergistic inhibition of colony formation (determined by isobologram analysis) was observed. However, VP-16-induced SSBs were only marginally increased by the DFMO pretreatment. When putrescine was combined concurrently with VP-16, both the in vitro cytotoxic effects and the number of DNA SSBs in L1210 cells were significantly reduced. These results demonstrate that putrescine inhibits VP-16-induced SSBs and commensurate cytotoxic effects, while DFMO, which depletes intracellular putrescine and partially reduces intracellular spermidine, acts to produce synergistic cytotoxic effects when combined with VP-16.

¹ Supported in part by Grants CA 23074, CA 30052, and CA 18273, from the Department of Health and Human Services, National Cancer Institute, Bethesda, MD.

Received 12/ 2/85. Revised 4/10/86. Accepted 4/25/86.