Clinical impact of succinate-dehydrogenase B protein expression in clear cell renal cell carcinoma.

Abstract

e16511 Background: Succinate-deficiency renal tumors are considered a new entity since WHO 2016 classification. These tumors are mostly characterized by germline mutations in succinate-dehydrogenase gene and a good prognosis. However, previous works suggested that lack of expression of succinate dehydrogenase is related to a worse prognosis in clear cell renal cell carcinoma (ccRCC) histology. In this study, we characterized the protein expression of succinate dehydrogenase B (SDHB) and its relation to survival in a cohort of ccRCC patients. Methods: Paraffin samples from one hundred and nine ccRCC patients were analyzed by mass-spectrometry proteomics. Samples were divided into SDHB-low and high according to the median expression of SDHB protein. Kaplan-Meier and Cox regression were used for survival analyses. Differential biological processes and metabolic pathways according to protein expression in SDHB-low and high tumors were characterized using probabilistic graphical models and flux balance analysis. The obtained results were validated using two ccRCC cell lines, one SDHB-low and one SDHB-high, and one normal renal cell line. Cells were treated with a glycolytic inhibitor and viability studies were performed. Results: One hundred and nine ccRCC patients from La Paz University Hospital were included in this study, 40 (37%) female; 46 (42%) stage Ib, 6 (6%) stage II, 57 (52%) stage III; 9 (8%) grade 1, 39 (36%) grade 2, 17 (16%) grade 3, 7 (6%) grade 4, and 37 (34%) unknown. We found that low levels of SDHB protein were related to worse disease-free survival and overall survival. However, when this population is classified according to Keynote-564 criteria, not all low-SDHB tumors are classified as eligible for pembrolizumab despite their worse prognosis. Moreover, SDHB-low tumors had a higher expression of proteins related to glycolysis, indicative of an elevated Warburg effect, whereas SDHB-high tumors presented higher mitochondrial metabolism and adhesion. This elevated Warburg effect suggested the utility of glycolytic inhibitors for the treatment of SDHB-low tumors. We have tested this hypothesis in vitro. We treated three cell lines (a SDHB-low ccRCC cell line, a SDHB-high ccRCC cell line and a normal renal cell line) with a glycolytic inhibitor, which provoked a significant decrease in the SDHB-low ccRCC cell line viability when compared with the other two. Conclusions: Levels of SDHB protein seem to be a good prognostic biomarker in ccRCC. In addition, in those SDHB-low tumors that are not classified as eligible for pembrolizumab treatment an adjuvant treatment should be considered, with glycolytic inhibitors being an option.