Abstract 2536: Unique HPRT1 upregulation in malignant tissue: Potential use as diagnostic biomarker

The aim of this study is to examine the gene expression of the purine salvage pathway enzyme Hypoxanthine Guanine Phosphribosyltransferase (HPRT) in malignant and normal tissue to determine potential upregulation. Due to the critical role HPRT plays in the cell cycle, it was hypothesized that in a rapidly proliferating malignant tissue there may be differential gene expression. In breast, colon, lung, and prostate cancer the 5-year survival rates decrease by nearly 72% when diagnosed in stage 3 or 4 as opposed to an early stage diagnosis. We focused our investigation on evaluating if HPRT could serve as an early stage diagnostic agent for the four most commonly diagnosed cancers (lung, colorectal, breast, and prostate cancer) which together make up 42.5% of all cancer diagnoses. Initially, we evaluated differences in HPRT expression levels via RNA-sequencing data in 3,147 tumor and 316 normal samples from The Cancer Genome Atlas (TCGA). Samples from 1119 breast invasive carcinoma (p-value= 1.66x10-42), 483 colon adenocarcinoma (p-value= 9x10-18), 541 lung adenocarcinoma (p-value=3.16x10-32), 502 lung squamous carcinoma (p-value= 1.49x10-59), and 502 prostate adenocarcinoma (p-value= 1.53x10-4) patients were compared to healthy individuals and showed significant HPRT over-expression shifts in malignant tumors. To continue this investigation we obtained histological tissue from 52 breast cancer patients, 54 lung cancer patients, 100 colorectal cancer patients, and 56 prostate cancer patients with a varying level of cancer stage and tumor type. Healthy tissue, margins of carcinoma, and pre-cancerous tissues were also stained to determine stage dependence of HPRT expression. Briefly, tissues were treated with a monoclonal anti-HPRT antibody along with a GAPDH positive control and an isotope control. Tissues were incubated with an HRP-polymer conjugated anti-HPRT antibody and followed by a diaminobenzidine (DAB) substrate which, when oxidized, results in antigen labelling. Tissues were imaged and analyzed using ImageJ software, which converted images to a grayscale. From there, we set a parameter for tissues with “HPRT high” expression, and “HPRT low” expression. Overall, we found 33-55% of malignant tissues to have a significant upregulation of HPRT (Lung-33%, Breast-55%, Colon-33%, Prostate-47%). These findings were consistent with our examination of HPRT expression in TCGA and our findings also indicated that the protein over-expression is not dependent on stage. These findings indicate that HPRT may potentially be a valuable biomarker in detecting early cases of malignancy in all of the four major cancers. Citation Format: Michelle H. Passey, Abigail M. Felsted, Zachary E. Ence, Stephen R. Piccolo, Kim L. O9Neill, Richard A. Robison. Unique HPRT1 upregulation in malignant tissue: Potential use as diagnostic biomarker [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 2536.