Abstract 631: Role of thymidylate synthase in genomic instability and tumorigenesis.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Thymidylate synthase (TS) is a well-established chemotherapy target frequently overexpressed in cancer. Multiple clinical studies demonstrated that high levels of TS correlate with the disease stage and resistance to fluoropyrimidine chemotherapy. Previous studies from our laboratory reassessed the paradigm of TS as a passive proliferation biomarker by providing evidence towards its tumor-promoting capabilities (Cancer Cell 2004; Oncogene 2007). We demonstrated that ectopic TS overexpression combined with loss of tumor suppressor genes significantly enhances the rate and severity of tumorigenesis; however the underlying mechanism of this process remained unclear. TS fuels DNA replication and repair through dTMP and folate biosynthesis. We hypothesized that TS overexpression could become a strong tumor-promoting force by inducing nucleotide imbalance that results in DNA misincorporation and damage. In this study, we analyze effects of TS overexpression in context of aberrant DNA repair and cell cycle misregulation by using Ink4/Arf−/- genetically engineered mouse model. We show that ectopic TS overexpression markedly enhances tumorigenesis in hTS/Ink4/Arf−/- mice compared to Ink4/Arf−/- control resulting in more aggressive tumors. HPLC analyses of mouse tumor-derived cell lines confirmed significant nucleotide imbalance and increase in dTMP, dTDP and dTTP levels in hTS/Ink4/Arf−/- mice compared to control. Analysis of chromosomal changes by spectral karyotyping demonstrated 4 to 5 fold increase in chromosomal aberrations and aneuploidy in hTS positive tumor cell lines. Chromosomal translocations were only found in hTS/Ink4/Arf−/- subtype, indicative of strand-break damage. We assessed extent of damage by Comet assay and yH2AX phosphorylation in mouse tumor cell lines and found increased DNA fragmentation and high yH2AX signal in hTS/Ink4/Arf−/- cells as opposed to Ink4/Arf−/- control. In summary, these studies demonstrate a novel capacity for TS to promote nucleotide imbalance, increase DNA susceptibility to damage and chromosomal aberrations, suggesting a new model where TS overexpression plays a role in the development of genomic instability and tumorigenesis. Citation Format: Lidia V. Kulemina, Min Chen, Kyungah Maeng, Akbar Nawab, Maria Zajac-Kaye. Role of thymidylate synthase in genomic instability and tumorigenesis. [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 631. doi:10.1158/1538-7445.AM2013-631