Abstract B25: KRAS mutation status is associated with enhanced dependency on purine biosynthesis and related pathways in non small cell lung cancer cells
Authors: Moran Diarmuid M. , Trusk Patricia B. , Pry Karen , Paz Keren , Sidransky David , Bacus Sarah S. 
Published: May 2015

Abstract
KRAS gene mutation is linked to poor prognosis and resistance to oncology therapeutics in Non Small Cell Lung Cancer (NSCLC). We have explored the possibility of exploiting inherent differences in KRAS mutant cell metabolism to enhance the efficacy of treatment. We have identified a greater dependency on purine biosynthesis and related pathways in KRAS mutant compared to KRAS wild type NSCLC cell lines. Purine synthesis requires factors generated from other metabolic reactions including ribose-5-phosphate from the pentose phosphate pathway, THF cofactors from folate metabolism and glycine / amide nitrogen groups from glutamine and aspartate metabolism. In this study, microarray gene expression and biological pathway analysis identified higher expression of purine synthesis and accessory pathways such as folate metabolism, 5-aminoimidazole ribonucleotide biosynthesis and glycine synthesis pathways in KRAS mutant NSCLC cells compared to wildtype counterparts. KRAS knockdown and overexpression studies demonstrated the ability of KRAS to regulate expression of genes that comprise purine synthesis and folate metabolism pathways. Moreover, pathway analysis and knockdown studies suggest a role for MYC, an oncogene previously recognized to be associated with KRAS mutant tumors, in the regulation of these pathways in KRAS mutant NSCLC cells. Proliferation studies demonstrated higher responsiveness to antifolates such as methotrexate and pemetrexed in KRAS mutant NSCLC cells, both of which may interfere indirectly with purine biosynthesis. In vivo analysis of NSCLC tumorgraft models in nude mice also identified an association between KRAS mutant tumor status and response to pemetrexed. The expression of a KRAS driven folate/purine synthesis gene, Methylenetetrahydrofolate Dehydrogenase 2 (MTHFD2), was also correlated with antifolate activity suggesting its use as a possible biomarker of response to antifolates. We propose that KRAS mutation drives increased purine synthesis activity and as a result an elevated dependency on the factors needed to feed this biosynthetic pathway such as those generated by folate metabolism. Thus, antifolates can indirectly inhibit purine synthesis through the depletion of folate cofactors which may account for the stronger response to these agents in KRAS mutant cells. We are currently expanding this study to examine alternative inhibitors of purine synthesis as possible therapeutics in KRAS mutant NSCLC and other cancers. Collectively, our findings highlight that a better understanding of the molecular mechanisms underlying the dependency of cancer cells on specific metabolic pathways may result in more effective metabolic targeting and new approaches in treating specific cancers.
Citation Format: Diarmuid M. Moran, Patricia B. Trusk, Karen Pry, Keren Paz, David Sidransky, Sarah S. Bacus. KRAS mutation status is associated with enhanced dependency on purine biosynthesis and related pathways in non small cell lung cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B25. doi: 10.1158/1557-3125.RASONC14-B25