Targeting cancer metabolism by simultaneously disrupting parallel nutrient access pathways.

RESEARCH ARTICLE The Journal of Clinical Investigation Targeting cancer metabolism by simultaneously disrupting parallel nutrient access pathways Seong M. Kim, 1 Saurabh G. Roy, 1 Bin Chen, 2 Tiffany M. Nguyen, 1 Ryan J. McMonigle, 1 Alison N. McCracken, 1 Yanling Zhang, 3 Satoshi Kofuji, 4 Jue Hou, 5 Elizabeth Selwan, 1 Brendan T. Finicle, 1 Tricia T. Nguyen, 1 Archna Ravi, 1 Manuel U. Ramirez, 1 Tim Wiher, 1 Garret G. Guenther, 1 Mari Kono, 6 Atsuo T. Sasaki, 4 Lois S. Weisman, 3 Eric O. Potma, 5 Bruce J. Tromberg, 5 Robert A. Edwards, 7 Stephen Hanessian, 2,8 and Aimee L. Edinger 1 Department of Developmental and Cell Biology, University of California Irvine (UCI), Irvine, California, USA. 2 Department of Chemistry, Universite de Montreal, Montreal, Quebec, Canada. 3 Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA. 4 Departments of Internal Medicine, Neurosurgery, and Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA. Department of Biomedical Engineering, UCI, Irvine, California, USA. 6 National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Bethesda, Maryland, USA. 7 Department of Pathology, University of California Irvine School of Medicine, Irvine, California, USA. 8 Department of Pharmaceutical Sciences, UCI, Irvine, California, USA. Oncogenic mutations drive anabolic metabolism, creating a dependency on nutrient influx through transporters, receptors, and macropinocytosis. While sphingolipids suppress tumor growth by downregulating nutrient transporters, macropinocytosis and autophagy still provide cancer cells with fuel. Therapeutics that simultaneously disrupt these parallel nutrient access pathways have potential as powerful starvation agents. Here, we describe a water-soluble, orally bioavailable synthetic sphingolipid, SH-BC-893, that triggers nutrient transporter internalization and also blocks lysosome-dependent nutrient generation pathways. SH-BC-893 activated protein phosphatase 2A (PP2A), leading to mislocalization of the lipid kinase PIKfyve. The concomitant mislocalization of the PIKfyve product PI(3,5)P2 triggered cytosolic vacuolation and blocked lysosomal fusion reactions essential for LDL, autophagosome, and macropinosome degradation. By simultaneously limiting access to both extracellular and intracellular nutrients, SH-BC-893 selectively killed cells expressing an activated form of the anabolic oncogene Ras in vitro and in vivo. However, slower-growing, autochthonous PTEN-deficient prostate tumors that did not exhibit a classic Warburg phenotype were equally sensitive. Remarkably, normal proliferative tissues were unaffected by doses of SH-BC-893 that profoundly inhibited tumor growth. These studies demonstrate that simultaneously blocking parallel nutrient access pathways with sphingolipid-based drugs is broadly effective and cancer selective, suggesting a potential strategy for overcoming the resistance conferred by tumor heterogeneity. Introduction To meet the anabolic demands of cell division, oncogenic muta- tions drive glucose and glutamine transporter gene expression (1–4). The LDL receptor is similarly upregulated in cancer cells to provide exogenous cholesterol and fatty acids that fuel cell growth (5, 6). Oncogenic signaling pathways also promote nutrient uptake posttranscriptionally by preventing the lysosomal degradation of these nutrient transport proteins (7). Tumors with activated Ras acquire additional extracellular nutrients via macropinocytosis, an endocytic process that produces amino acids when engulfed pro- teins are degraded in the lysosome (8, 9). Cancer cells are “addict- ed” to these nutrient influx pathways, because oncogenic muta- tions create a continuous, high demand for fuel and limit metabolic flexibility. A classic example of how this addiction can be exploited therapeutically is the use of L-asparaginase to kill acute lympho- blastic leukemia cells that cannot synthesize sufficient quantities of the nonessential amino acid asparagine to meet their metabolic demand (10). Preclinical studies show that a subset of human can- cers likewise requires imported LDL, arginine, serine, or glycine Conflict of interest: The authors have declared that no conflict of interest exists. Submitted: February 18, 2016; Accepted: August 16, 2016. Reference information: J Clin Invest. 2016;126(11):4088–4102. doi:10.1172/JCI87148. jci.org Volume 126 Number 11 November 2016 for growth and survival (5, 11–13). These studies demonstrate that limiting nutrient uptake can selectively eliminate transformed cells and also highlight that the specific nutrient addictions of different cancer classes diverge depending on the molecular defects present. An increasingly sophisticated understanding of how individu- al oncogenes and tumor suppressors alter flux through key meta- bolic pathways and the expanding ability to catalog the mutations present in tumors will facilitate the use of targeted metabolic therapies. However, tumor heterogeneity limits the effectiveness of these agents. Preexisting tumor cells that rely on a distinct set of anabolic enzymes would be enriched during treatment with small-molecule metabolic inhibitors, thereby contributing to the development of resistance (14, 15). Selective pressures may also promote rewiring of metabolic pathways in tumor cells that are crippled but not killed by targeted metabolic therapies, akin to what has been observed with cytostatic agents targeting oncogen- ic signal transduction pathways (16). One means to circumvent these hurdles would be to target the apex of the anabolic pyramid, that of nutrient uptake. No matter which biosynthetic pathways are essential in a given tumor cell, exogenous nutrients will be required to build biomass. If access to multiple nutrients could be restricted simultaneously, many different tumor classes would be sensitive and potential resistance pathways suppressed.