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 August, E. M. Articles by Prusoff, W. H. Search for Related Content PubMed PubMed Citation Articles by August, E. M. Articles by Prusoff, W. H.

Inhibition of Poly(adenosine Diphosphate-Ribose) Polymerase by Thymidine and Thymidine Analogues in L1210 Cells and Its Relationship to the Potentiation of the Antitumor Activity of 1,3-Bis(2-chloroethyl)-1-nitrosourea but not of 3'-[3-(2-Chloroethyl)-3-nitrosoureido]-3'-deoxythymidine¹

Department of Pharmacology and Comprehensive Cancer Center, Yale University School of Medicine, New Haven, Connecticut 06510

The coadministration of thymidine (dThd) with either 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or 3'-[3-(2-chloroethyl)-3-nitrosoureido]-3'-deoxythymidine (3'-CTNU) to L1210-bearing mice significantly enhanced the antitumor activity of both nitrosoureas (T-S. Lin and W. H. Prusoff, Cancer Res., 47: 394–397, 1987, and T-S. Lin, P. H. Fischer, J. C. Marsh, and W. H. Prusoff, Cancer Res., 42: 1624–1629, 1982). As a possible mechanism for this observed enhancement, we have investigated the role of dThd as an inhibitor of poly(ADP-ribose) polymerase (ADPRP), an enzyme which is activated in response to DNA damage. Exposure of L1210 cells in culture to 50 µM BCNU resulted in a > 10-fold increase in ADPRP activity within 3–4 h. The polymerase activity increased with increasing BCNU concentration after a 4-h exposure, reaching apparent saturation at 50 µM BCNU. However, this activation was abolished by 2 mM dThd. Median inhibition of the ADPRP activity elicited by 30 and 75 µM BCNU occurred at 38 and 135 µM dThd, respectively. When BCNU was replaced by 3'-CTNU, no activation of ADPRP was observed, even at or above concentrations of 3'-CTNU previously shown to cause DNA damage. 3'-Amino-3'-deoxythymidine, the principal hydrolysis product of 3'-CTNU, was found to be an inhibitor of BCNU-stimulated ADPRP activity with potency similar to dThd. Furthermore, intact 3'-CTNU was found to inhibit BCNU-stimulated ADPRP activity. Although 3'-CTNU should be capable of activating ADPRP by causing DNA damage, our results suggest that no net activation is observed due to inhibition by the various thymidine species present. Thus, inhibition of ADPRP by dThd following DNA damage by BCNU is consistent with the potentiation of antitumor activity previously reported. However, the observed potentiation of 3'-CTNU activity by dThd does not appear to result from such a mechanism.

¹ Supported by Grants CH-115G from the American Cancer Society, and CA-08341 and CA-05262 from the National Cancer Institute, NIH, USPHS.

² Present address: Laboratory of Biological Chemistry, National Cancer Institute, Building 37, Room 5E10, National Institutes of Health, Bethesda, MD 20892. To whom requests for reprints should be addressed.

Received 9/ 6/90. Accepted 1/ 8/91.