Abstract 4484: Uracil DNA glycosylase expression determines human lung cancer cell sensitivity to pemetrexed.

Abstract

Abstract Uracil misincorporation into DNA is a consequence of pemetrexed inhibition of thymidylate synthetase (TS). The DNA base excision repair (BER) enzyme, uracil DNA glycosylase (UNG) is the major glycosylase responsible for removal of misincorporated uracil. We previously illustrated hypersensitivity to pemetrexed in UNG-/- human colon cancer cells (DLD1) and proposed that cytotoxic uracil accumulation leads to collapsed replication forks, double strand breaks and cell death. Here, we examined the relationship between cellular capability to remove uracil-DNA and pemetrexed sensitivity in human lung cancer cells. Viral siRNA and shRNA knockdown of UNG enhanced pemetrexed sensitivity in A549 and H1975 cells, respectively. We further evaluated induction of UNG as a mechanism of pemetrexed resistance. Exposure of H1299 cells to step-wise increasing concentrations of pemetrexed established drug resistant sublines: H1299PR-1 and H1299PR-2. Significant induction of UNG protein was observed in both sublines. Importantly, co-treatment with the BER inhibitor, methoxyamine (MX), overcame pemetrexed resistance in H1299PR-1/2 underscoring the utility of BER directed therapeutics to offset acquired pemetrexed resistance. Lastly, differential expression of UNG in cell lines and primary lung cancer tissues was associated with pemetrexed sensitivity. Cell lines derived from squamous and small cell carcinoma, known to be clinically resistant to pemetrexed, had the highest levels of UNG expression in a panel of eight lung cancer cell lines. Analysis of cDNA microarrays derived from primary human lung cancer tissues also indicated high UNG expression in pemetrexed-resistant histological subtypes. Thus, we propose that UNG is a major determinant of pemetrexed sensitivity in human lung cancer. Citation Format: Lachelle D. Weeks, Pingfu Fu, Lili Liu, Stanton L. Gerson. Uracil DNA glycosylase expression determines human lung cancer cell sensitivity to pemetrexed. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4484. doi:10.1158/1538-7445.AM2013-4484