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.
Temozolomide is an alkylating agent that mediates its cytotoxic effects via O(6)-methylguanine (O(6)-meG) adducts in DNA. O(6)-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 O(6)-(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 microg/mL) was 91% of control growth, whereas additional exposure to PaTrin-2 alone (10 micromol/L) or oblimersen alone (33 nmol/L) reduced this to 81% and 66%, respectively, and the combination of PaTrin-2 (10 micromol/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.
Paterson Institute for Cancer Research, Wilmslow Road, Manchester M204BX, UK.
Vincent A
VA
Barvaux
Paul
P
Lorigan
Malcolm
M
Ranson
Amanda M
AM
Gillum
R Stanley
RS
McElhinney
T Brian H
TB
McMurry
Geoffrey P
GP
Margison
D000970:Antineoplastic Agents / Q000494:pharmacology; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis; D045744:Cell Line, Tumor; D004260:DNA Repair; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000494:pharmacology*; D009841:Oligonucleotides / Q000737:chemistry; D010051:Ovarian Neoplasms / Q000188:drug therapy; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D000077204:Temozolomide; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D013997:Time Factors; D015854:Up-Regulation
D000970:Antineoplastic Agents; D018906:Antineoplastic Agents, Alkylating; D009841:Oligonucleotides; D019253:Proto-Oncogene Proteins c-bcl-2; D013778:Tetrazolium Salts; D013844:Thiazoles; D013873:Thionucleotides; D003606:Dacarbazine; C408162:oblimersen; D019853:O(6)-Methylguanine-DNA Methyltransferase; C022616:thiazolyl blue; D000077204:Temozolomide