PT  - JOURNAL ARTICLE
AU  - Trivedi, Ram N.
AU  - Almeida, Karen H.
AU  - Fornsaglio, Jamie L.
AU  - Schamus, Sandra
AU  - Sobol, Robert W.
TI  - The Role of Base Excision Repair in the Sensitivity and Resistance to Temozolomide-Mediated Cell Death
AID  - 10.1158/0008-5472.CAN-05-0715
DP  - 2005 Jul 15
TA  - Cancer Research
PG  - 6394--6400
VI  - 65
IP  - 14
4099  - http://cancerres.aacrjournals.org/content/65/14/6394.short
4100  - http://cancerres.aacrjournals.org/content/65/14/6394.full
SO  - Cancer Res2005 Jul 15; 65
AB  - DNA-alkylating agents have a central role in the curative therapy of many human tumors; yet, resistance to these agents limits their effectiveness. The efficacy of the alkylating agent temozolomide has been attributed to the induction of O6-MeG, a DNA lesion repaired by the protein O6-methylguanine-DNA methyltransferase (MGMT). Resistance to temozolomide has been ascribed to elevated levels of MGMT and/or reduced mismatch repair. However, >80% of the DNA lesions induced by temozolomide are N-methylated bases that are recognized by DNA glycosylases and not by MGMT, and so resistance to temozolomide may also be due, in part, to robust base excision repair (BER). We used isogenic cells deficient in the BER enzymes DNA polymerase-β (pol-β) and alkyladenine DNA glycosylase (Aag) to determine the role of BER in the cytotoxic effect of temozolomide. Pol-β–deficient cells were significantly more susceptible to killing by temozolomide than wild-type or Aag-deficient cells, a hypersensitivity likely caused by accumulation of BER intermediates. RNA interference–mediated pol-β suppression was sufficient to increase temozolomide efficacy, whereas a deficiency in pol-ι or pol-λ did not increase temozolomide-mediated cytotoxicity. Overexpression of Aag (the initiating BER enzyme) triggered a further increase in temozolomide-induced cytotoxicity. Enhanced Aag expression, coupled with pol-β knockdown, increased temozolomide efficacy up to 4-fold. Furthermore, loss of pol-β coupled with temozolomide treatment triggered the phosphorylation of H2AX, indicating the activation of the DNA damage response pathway as a result of unrepaired lesions. Thus, the BER pathway is a major contributor to cellular resistance to temozolomide and its efficacy depends on specific BER gene expression and activity. ©2005 American Association for Cancer Research.