Sensitization of a human ovarian cancer cell line to temozolomide by simultaneous attenuation of the Bcl-2 antiapoptotic protein and DNA repair by O6-alkylguanine-DNA alkyltransferase

Vincent A. Barvaux, Paul Lorigan, Malcolm Ranson, Amanda M. Gillum, R. Stanley McElhinney, T. Brian H McMurry, Geoffrey P. Margison

Research output: Contribution to journalArticlepeer-review

Abstract

Temozolomide is an alkylating agent that mediates its cytotoxic effects via O6-methylguanine (O6-meG) adducts in DNA. O6-alkylguanine-DNA-alkyltransferase (MGMT) can repair such adducts and therefore constitutes a major resistance mechanism to the drug. MGMT activity can be attenuated in vitro and in vivo by the pseudosubstrate O6-(4-bromothenyl)guanine (PaTrin-2, Patrin, Lomeguatrib), which in clinical trials is in combination with temozolomide. Resistance to cytotoxic agents can also be mediated by the Bcl-2 protein, which inhibits apoptosis and is frequently up-regulated in tumor cells. Attenuation of Bcl-2 expression can be affected by treatment of cells with the antisense oligonucleotide, oblimersen sodium (Genasense), currently in phase III clinical trials in combination with the methylating agent dacarbazine. Using a human ovarian cancer cell line (A2780) that expresses both Bcl-2 and MGMT, we show that cells treated with active dose levels of either oblimersen (but not control reverse sequence or mismatch oligonucleotides) or PaTrin-2 are substantially sensitized to temozolomide. Furthermore, the exposure of oblimersen-pretreated cells to PaTrin-2 leads to an even greater sensitization of these cells to temozolomide. Thus, growth of cells treated only with temozolomide (5 μg/mL) was 91% of control growth, whereas additional exposure to PaTrin-2 alone (10 μmol/L) or oblimersen alone (33 nmol/L) reduced this to 81% and 66%, respectively, and the combination of PaTrin-2 (10 μmol/L) and oblimersen (33 nmol/L reduced growth to 25% of control. These results suggest that targeting both Bcl-2 with oblimersen and MGMT with PaTrin-2 would markedly enhance the antitumor activity of temozolomide and merits testing in clinical trials. Copyright © 2004 American Association for Cancer Research.
Original languageEnglish
Pages (from-to)1215-1220
Number of pages6
JournalMolecular Cancer Therapeutics
Volume3
Issue number10
DOIs
Publication statusPublished - 14 Oct 2004

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