Abstract 2858: Thymidine kinase 1 variability in primary and metastatic human breast cell lines and its correlation to metastatic potential
Authors: Bitter Eliza E. , Townsend Michelle H. , Bennion Kelsey A. , Mejia Juan , Shrestha Gajendra , Hirschi Kelsey , Arroyo Juan , O'Neill Kim 
Published: August 2019

Abstract
The purpose of this study is to determine the role of Thymidine Kinase 1 (TK1) in the cellular invasion of breast cancer cells in vitro. TK1 is a cytosolic DNA salvage pathway enzyme responsible for the conversion of thymidine to thymidine monophosphate; it is known to increase during G1/S phase of the cell cycle and is significantly elevated in the serum of multiple cancer patients including breast, lung, and colon. As such, TK1 has been implicated as a useful biomarker for cancer prognosis and patient monitoring. In addition to TK1 upregulation in cancer serum, recent findings have shown that TK1 also localizes to the surface of ALL, AML, and colon cancer cells in patients. However, minimal studies have determined how the surface localization of TK1 is an indicator of metastatic potential. In addition, the function and timing of TK1 expression on the cellular surface has not been determined. When comparing the TK1 expression in metastatic cancer cell lines we found that there was a trend of overall elevation in metastatic cell lines (n = 39) when compared to primary cell lines (n = 31). This expression was extremely irregular between cell lines and TK1 showed significant variability between samples. We tested several breast cancer cell lines (primary: HCC 1806, HCC 1937, and JIMT-1; metastatic: T47D, BT 549, and MDA-MB-231) for their TK1 surface localization, more specifically the difference between metastatic cells and primary cells. We found significant TK1 expression in all cell lines tested with the highest expression in HCC 1806 primary breast cancer cells (90.36%; p = .0001) and the lowest expression in MDA-MB-231 metastatic breast cancer cells (47.2%; p = .01). We hypothesized that the expression of TK1 on the surface of cancer cells was dependent on the proliferative state of the cells and would be highest in the S phase of the cell cycle. To evaluate this hypothesis, cell cycle analysis was performed utilizing a PI stain to determine DNA content within the cells. Preliminary analysis of this data indicates that surface localized TK1 may not be dependent on the cell cycle but may be dependent on the proliferative capacity of individual patient’s tumors. Currently under investigation is the direct effect of surface TK1 on invasion potential. To accomplish this, TK1-/-cells are actively being produced and their invasion potential against TK1WT cells will be compared to determine whether TK1 surface localization is influential in the metastatic ability of cancer cells. We plan to test the correlation between TK1 expression for a potential indicator of tumor aggressiveness and invasion potential.
Citation Format: Eliza E. Bitter, Michelle H. Townsend, Kelsey A. Bennion, Juan Mejia, Gajendra Shrestha, Kelsey Hirschi, Juan Arroyo, Kim O'Neill. Thymidine kinase 1 variability in primary and metastatic human breast cell lines and its correlation to metastatic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2858.