CD38 Inhibits Prostate Cancer Metabolism and Proliferation by Reducing Cellular NAD+ Pools

Tumor cells require increased rates of cell metabolism to generate the macromolecules necessary to sustain proliferation. They rely heavily on NAD thorn as a cofactor for multiple metabolic enzymes in anabolic and catabolic reactions. NAD thorn also serves as a substrate for PARPs, sirtuins, and cyclic ADP-ribose synthases. Dysregulation of the cyclic ADP-ribose synthase CD38, the main NAD'ase in cells, is reported in multiple cancer types. This study demonstrates a novel connection between CD38, modulation of NAD thorn, and tumor cell metabolism in prostate cancer. CD38 expression inversely correlates with prostate cancer progression. Expressing CD38 in prostate cancer cells lowered intracellular NAD thorn, resulting in cell-cycle arrest and expression of p21Cip1 (CDKNA1). In parallel, CD38 diminishes glycolytic and mitochondrial metabolism, activates AMP-activated protein kinase (AMPK), and inhibits fatty acid and lipid synthesis. Pharmacologic inhibition of nicotinamide phosphoribosyltransferase (NAMPT) mimicked the metabolic consequences of CD38 expression, demonstrating similarity between CD38 expression and NAMPT inhibition. Modulation of NAD thorn by CD38 also induces significant differential expression of the transcriptome, producing a gene expression signature indicative of a nonproliferative phenotype. Altogether, in the context of prostate cancer, the data establish a novel role for the CD38-NAD thorn axis in the regulation of cell metabolism and development. Implications: This research establishes a mechanistic connection between CD38 and metabolic control. It also provides the foundation for the translation of agents that modulate NAD thorn levels in cancer cells as therapeutics. (C) 2018 AACR.