Characterization and metabolic synthetic lethal testing in a new model of SDH-loss familial pheochromocytoma and paraganglioma

// John Smestad 1, 2, * , Oksana Hamidi 3, * , Lin Wang 4 , Molly Nelson Holte 2 , Fatimah Al Khazal 2 , Luke Erber 5 , Yue Chen 5 and L. James Maher III 2 1 Mayo Clinic Medical Scientist Training Program, Mayo Clinic College of Medicine and Science, Rochester, MN, USA 2 Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN, USA 3 Division of Endocrinology, Diabetes, and Nutrition, Mayo Clinic, Rochester, MN, USA 4 Department of Pediatric and Adolescent Medicine, Mayo Clinic College of Medicine and Science, Rochester, MN, USA 5 Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota at Twin Cities, Minneapolis, MN, USA * These authors contributed equally to this work and are co-first authors Correspondence to: L. James Maher III, email: maher@mayo.edu Keywords: transcriptomics; epigenomics; proteomics; synthetic lethality; lactate dehydrogenase Received: September 30, 2017      Accepted: November 20, 2017      Published: December 22, 2017 ABSTRACT Succinate dehydrogenase (SDH)-loss pheochromocytoma and paraganglioma (PPGL) are tumors driven by metabolic derangement. SDH loss leads to accumulation of intracellular succinate, which competitively inhibits dioxygenase enzymes, causing activation of pseudohypoxic signaling and hypermethylation of histones and DNA. The mechanisms by which these alterations lead to tumorigenesis are unclear, however. In an effort to fundamentally understand how SDH loss reprograms cell biology, we developed an immortalized mouse embryonic fibroblast cell line with conditional disruption of Sdhc and characterize the kinetics of Sdhc gene rearrangement, SDHC protein loss, succinate accumulation, and the resultant hypoproliferative phenotype. We further perform global transcriptomic, epigenomic, and proteomic characterization of changes resulting from SDHC loss, identifying specific perturbations at each biological level. We compare the observed patterns of epigenomic derangement to another previously-described immortalized mouse chromaffin cell model of SDHB loss, and compare both models to human SDH-loss tumors. Finally, we perform analysis of SDHC synthetic lethality with lactate dehydrogenase A (LDHA) and pyruvate carboxylase (PCX), which are important for regeneration of NAD+ and aspartate biosynthesis, respectively. Our data show that SDH-loss cells are selectively vulnerable to LDH genetic knock-down or chemical inhibition, suggesting that LDH inhibition may be an effective therapeutic strategy for SDH-loss PPGL.