Effect of Argininosuccinate Synthetase Deficiency on Energy Metabolism of Epithelial Ovarian Cancer
Ovarian cancer (OvCa) is the fifth leading cause of cancer related deaths among women with a 5-year survival rate of ~47%. It accounts for nearly 22,000 new diagnosis and ~14,000 deaths each year in the United States. OvCa is a complex set of diseases with diverse classes and histotypes, of which Epithelial ovarian cancer (EOC) is the most common. The serous, clear cell (CCCO), endometrioid (EC) and mucinous (MUC) are sub-histotypes of EOC. Recent molecular studies have correlated reduced expression of argininosuccinate synthetase (ASS1) in 18-87%, 65-85% and 17-67% of CCCO, EC and MUC, respectively and their increased therapeutic resistance to platinum based chemotherapy. ASS1 is a key enzyme of the urea cycle and a rate limiting enzyme for arginine synthesis expressed in most normal tissues. It was hypothesized that ASS1 deficiency in EOC can impair urea cycle by inhibiting production of argininosuccinate, a precursor for arginine synthesis and can force cancer cells to rely on extracellular arginine and rewire energy metabolism to support cancer cell survival and proliferation. To test this hypothesis, an LC-MS/MS based quantitative assay was developed to measure alterations in the urea cycle, glycolysis and tricarboxylic acid cycle (TCA) in EOC and small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) cell lines. The absence of intracellular argininosuccinate and low concentration of arginine confirmed ASS1-deficient COV434 (SCCOHT) and JHOC5 (clear cell carcinoma of ovary-EOC) OvCa cell lines. We observed active oxidative phosphorylation and low glycolysis in ASS1- cell lines which may have attributed to arginine auxotrophy. Overall, this study identified deregulation of urea and energy metabolism in EOC cell lines, which will act as a step towards the development of alternative and effective therapies for OvCa
