Abstract 1623: The nucleotide metabolizing enzyme dUTPase confers resistance to thymidylate synthase inhibition in non-small cell lung cancer cells

Abstract

Abstract Chemotherapeutic agents which target the enzyme thymidylate synthase (TS) have demonstrated efficacy and seen wide-spread clinical implementation in a variety of tumor types for many decades. However, despite significant research efforts to date, little is known about the molecular pathways that regulate clinical response and resistance to TS-inhibiting agents including the fluoropyrimidines. Lung cancer is the major cause of cancer-related deaths worldwide and non-small cell lung cancer (NSCLC) is the most frequent sub-type. Several chemotherapeutic agents that target TS are currently employed in NSCLC treatment including capecitabine, S-1 and pemetrexed. Increased expression of TS is associated with resistance to TS-directed agents in a variety of tumor types including NSCLC. In this study, we analyzed the response of 4 NSCLC cell lines to TS-inhibition. All NSCLC cell lines analyzed demonstrated marked resistance to fluoropyrimidine treatment in the MTS growth inhibition assay despite the presence of TS-inhibited ternary complex. Subsequent analysis revealed that TS gene promoter activity, mRNA and protein expression is induced in NSCLC cell lines exposed to clinically relevant concentrations of 5-FU, FUdR and pemetrexed providing a rational explanation for the resistant phenotype. However, depletion of TS by RNA interference (RNAi) had no sensitizing effects to treatment with the specific TS inhibitor FUdR, suggesting that the induction of TS is not the major determinant of resistance. Conversely, depletion of the nucleotide metabolizing enzyme dUTPase by RNAi completely reversed resistance to FUdR in the MTS assay and potently inhibited colony formation in all 4 NSCLC cell lines analyzed. dUTPase depletion in combination with FUdR treatment was associated with increases in cytotoxic dUTP pools, DNA damage and apoptotic cell death. The results of this study indicate that depletion of dUTPase can rapidly sensitize NSCLC cells to otherwise non-lethal doses of a TS inhibitor. The clinical utility of a dUTPase inhibitor may have the potential to significantly increase antitumor activity in NSCLC patients treated with TS-directed agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1623.