Immunohistochemical evaluation of glutaminase expression in prostate adenocarcinoma and correlation with clinicopathologic parameters.

Abstract

251 Background: Glutaminolysis plays a significant role in the metabolic reprogramming of cancer cell growth and proliferation. Glutaminase (GLS1), the rate-limiting enzyme of the glutamine pathway, is frequently dysregulated in cancer. High GLS1 expression is reported in colorectal and breast cancers and has been found to correlate with the tumor stage and disease progression. Furthermore, a new orally bioavailable glutaminase inhibitor (CB-839) is in early phase clinical trials in select tumors. The purpose of this study is to investigate the status of GLS1 expression in prostate cancer (PCa) and to correlate expression levels with clinicopathologic parameters. Methods: Radical prostatectomy samples from 154 patients with prostate adenocarcinoma were retrospectively reviewed and used to evaluate GLS1 expression by immunohistochemistry (IHC). The IHC expression score was calculated by multiplying the intensity of the stain by the proportion of cells staining; cases were then segmented into negative, low, or high expression groups. In addition, 41 samples of benign prostate tissue were used as a control. Associations between GLS1 levels and clinicopathologic parameters were analyzed by Pearson’s chi-squared and Log-rank tests. Results: GLS1 expression in the benign controls were negative, low, and high in 59%, 41%, 0% of cases, respectively, compared to 53%, 21.5%, 25.5%, respectively, in PCa (p < 0.003). Most PCa patients were age < 60 (55.8%), white (78.6%), stage T2 (52.9%), node negative (80.5%), Grade Group 3 (44%), and non-smokers (63.6%). There was no difference between GLS1 expression and age, race, Gleason score, stage, node status, and smoking status by univariate analysis. The median biochemical-progression free survival for negative, low, and high expression was 10, 9, and 10 years, respectively (p = 0.7). Conclusions: In our study, PCa samples were more likely to have GLS1 expression compared to benign controls. Although GLS1 expression did not appear to be a prognostic marker, our cohort was enriched for cases with localized disease and low-to-intermediate grade PCa. As a result, future studies are warranted to evaluate the expression levels in high grade and advanced PCa cases to determine a role for prognostic and or therapeutic implication to justify future preclinical studies with CB-839.