Abstract 771: HPRT: A biomarker and potential target for detection and treatment of colorectal cancer
Authors: Townsend Michelle H. , Olsen Eric C. , Weagel Evita G. , Velasquez Edwin J. , Felsted Abigail M. , Burrup Weston , Weber K Scott , Robison Richard , O'Neill Kim L. 
Published: August 2018

Abstract
This study aims to evaluate the expression of the salvage pathway enzymes DCK, APRT, and HPRT in colorectal cancer cells to investigate their potential as biomarkers for diagnosis and treatment. As the third most common cancer diagnosed in the United States, there remains a need to identify biomarkers capable of detecting and characterizing colorectal cancers. Because of their involvement in nucleotide synthesis and their role in cell cycle regulation and proliferation, we hypothesized an increase in these enzymes within malignancy. In order to quantify expression, we utilized two colorectal cancer cell lines (HT29 and SW620) as well as healthy and malignant patient tissue samples. Expression in tissues was evaluated using immunohistochemistry (IHC), and surface presence of the enzymes was assessed via confocal microscopy, flow cytometry, and scanning electron microscopy. Staining of malignant tissue samples using IHC showed upregulation of HPRT in 59% of patients when compared to control tissues derived from healthy patients (p=0.001). Surface analysis was performed utilizing flow cytometry, confocal microscopy, and scanning electron microscopy. Upon flow cytometry evaluation no significant presence of either DCK or APRT was found on the membranes of SW620 and HT29 cells (p=0.234 and 0.93, respectively), while HPRT expression was significantly increased on the surface of both SW620 and HT29 cells (p=0.013). Cell population fluorescence increased 58% and 28% in SW620 and HT29 cells, respectively, compared to controls. Confocal microscopy images showed direct overlap between SW620 cells stained with membrane-specific dye and anti-HPRT antibody, suggesting localization on the membrane. To further confirm the surface presence of HPRT, cells were treated with gold-labelled HPRT antibody and visualized under a scanning electron microscope to determine if surface expression was randomly dispersed across the cell surface. When treated with anti-HPRT antibodies, there was an increase in gold weight percentage on both SW620 (p=8.14x10 -6) and HT29 (p=1.74x10 -4) cells compared to controls, confirming HPRT presence and showing random surface localization patterns. Surface analysis was also conducted on malignant samples of patients with colorectal cancer. Of three samples, one of them exhibited significant HPRT surface localization. This supports the variation found within the tissues, as HPRT overexpression is not found in every patient. One patient did exhibit significant levels of HPRT on the surface of their malignant cells; this indicates HPRT as a potential target in patients that exhibit upregulation of the enzyme. These results suggest a relationship between colorectal cancers and HPRT, and indicate HPRT as a potential target for the detection and treatment of colorectal cancers.
Citation Format: Michelle H. Townsend, Eric C. Olsen, Evita G. Weagel, Edwin J. Velasquez, Abigail M. Felsted, Weston Burrup, K Scott Weber, Richard Robison, Kim L. O'Neill. HPRT: A biomarker and potential target for detection and treatment of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 771.