Abstract 232: Pharmacological and genetic dissection of one carbon pathway provides novel insights into generation, transformation and utilization of one carbon units
Authors: Suri Vipin , Mainolfi Nello , Friedman Adam , Moyer Mikel P. , Ducker Greg , Rabinowitz Joshua D. , Manfredi Mark 
Published: July 2016

Abstract
Tumorigenesis, tumor progression and metastasis require metabolic rewiring to support the need for rapid biomass accumulation, reduction of oxidative stress and epigenetic remodeling. One carbon (1C) metabolism provides essential substrates for such metabolic rewiring and enzymes of 1C pathway are frequently overexpressed in tumors consistent with the increased demands on these biochemical pathways. While 1C pathway modulators such as antifolates are efficacious, the clinical utility of antifolates is limited by their inability to distinguish between the metabolic requirements of proliferating cells vs transformed cancer cells. Precise targeting of 1C metabolism in transformed cells can potentially lead to highly effective and safe anticancer therapies.
The enzymes of 1C metabolism are organized in a spatially distinct set of parallel reactions in the cytosol and the mitochondrion. The core 1C machinery extracts 1C units from donors such as serine onto a folate backbone. The oxidation state of the folate associated 1C unit can then be manipulated according to the needs of the 1C utilization reactions. The quantitative contribution of cytosolic vs mitochondrial pathway, regulation of 1C metabolism and biochemical basis of partitioning of 1C units between different downstream reactions is not fully understood. To understand the role of the mitochondrial and cytosolic pathways in the generation and transformation of 1C units, we generated potent and selective inhibitors of MethyleneTetraHydroFolate Dehydrogenase Type 2 (MTHFD2) and dual inhibitors of Serine HydroxyMethyl Transferase (SHMT) 1 and 2. We also generated knockout cells lacking various enzymes of mitochondrial and cytosolic 1C pathway. The combined pharmacological-genetic approach allowed quantitative dissection of the contribution of cytosolic and mitochondrial pathways. Interestingly, genetic disruption of the mitochondrial pathway dramatically increased sensitivity of cells to inhibition of SHMT1 while deletion of SHMT1 increased the sensitivity to MTHFD2 inhibitors suggesting interdependence and flexibility between the mitochondrial and cytosolic 1C pathway arms. The effects of 1C inhibitors on cell viability could be rescued by other 1C donors as well as 1C pathway products, further informing on the critical products of 1C metabolism and potential escape mechanisms.
Our observations show that cancer cells can utilize multiple routes to generate 1C units and identify the contribution of specific enzymes. Pharmacological inhibition of some of these enzymes strongly affects cell viability and combination of inhibitors of cytosolic and mitochondrial 1C enzymes in the same or different molecules can be particularly effective. In addition, genetic lesions in the mitochondrial or cytosolic 1C arms can also sensitize tumors to inhibitors of specific 1C pathway enzymes.
Citation Format: Vipin Suri, Nello Mainolfi, Adam Friedman, Mikel P. Moyer, Greg Ducker, Joshua D. Rabinowitz, Mark Manfredi. Pharmacological and genetic dissection of one carbon pathway provides novel insights into generation, transformation and utilization of one carbon units. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 232.