Abstract 4687: DNA polymerase ≤ inhibitors enhance the chemotherapeutic efficacy of Temozolomide by increasing senescence in colon cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL While much is known about the genetic background of colon cancer development, surgical removal still remains the main strategy for its treatment. One of the critical strategies for cancer chemotherapy is blocking a cancer cell's ability to recognize and repair the damaged DNA. The fine balance between DNA damage and repair determines the final therapeutic consequences of these drugs. One such drug that induces DNA damage is Temozolomide (TMZ). However, tumor resistance to TMZ remains a significant problem in the treatment of colon cancer. In addition, the major limitations of the use of high doses of TMZ to maximize therapeutic efficacy in colon cancer is due to serious side effects, which makes TMZ unsuitable for colon cancer treatment. Thus, there is an urgent need for the development of new strategies to increase the therapeutic efficacy of TMZ with minimum or no side-effects. The type of DNA alkylation damage induced by TMZ is primarily repaired by DNA polymerase ≤ (Pol-α)-directed base excision repair (BER) pathway. Thus, Pol-α activity blockade can be a potential mechanism to sensitize colon cancer cells. We used structure-based molecular docking of Pol-α and identified potent small molecular inhibitors (SMI) (NSC-666715; NSC-666719) that specifically interacts with Pol-α. Our initial findings showed that the interaction of NSC-666715 with Pol-α blocks Pol-α-directed BER and enhances the TMZ-induced killing of colon cancer cells both in vitro and in vivo at 10-fold lower concentrations. We also found that the disruption of BER negates its contribution to drug-resistance and bypasses other resistance factors such as mismatch repair (MMR) defects. In the present study, we propose to determine the molecular mechanisms by which NSC-666715 and its potent derivative (NSC-666719) enhance the chemotherapeutic efficacy of TMZ against colon cancer growth. Our central hypothesis is that the blockade of Pol-α activity by NSC-666715 or NSC-666719 will significantly enhance the cytotoxic effects of TMZ-induced DNA damage that is repaired by BER pathway. Results show that NSC-666715 or NSC-666719 in combination with TMZ blocks BER pathway in vitro and increases accumulation of apurinic/apyrimidinic (AP)-site lesions in cells. Results also show that the AP-lesion accumulation is linked with p53/p21 signaling pathway. Results further show that increased cellular senescence in a p53/p21-dependent pathway might be one of the mechanisms by which NSC-666715 or NSC-666719 increases the therapeutic efficacy of TMZ in colon cancer cells. More importantly, the combination of SMI's reduces TMZ concentration, but keeps the biological outcome same, which is shown by the reduced IC50 of TMZ in combination experiments. The proposed mechanistic studies will allow us to establish the “proof-of-principle” by which Pol-α-targeted compounds enhance the efficacy and reduce the dose of TMZ. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4687. doi:1538-7445.AM2012-4687