An alternative route for β-hydroxybutyrate metabolism supports cytosolic acetyl-CoA synthesis in cancer cells.

Cancer cells are exposed to diverse metabolites in the tumour microenvironment that are used to support the synthesis of nucleotides, amino acids and lipids needed for rapid cell proliferation. In some tumours, ketone bodies such as β-hydroxybutyrate (β-OHB), which are elevated in circulation under fasting conditions or low glycemic diets, can serve as an alternative fuel that is metabolized in the mitochondria to provide acetyl-CoA for the tricarboxylic acid (TCA) cycle. Here we identify a non-canonical route for β-OHB metabolism that bypasses the TCA cycle to generate cytosolic acetyl-CoA. We show that in cancer cells that can metabolize ketones, β-OHB-derived acetoacetate in the mitochondria can be shunted into the cytosol, where acetoacetyl-CoA synthetase (AACS) and thiolase convert it into cytosolic acetyl-CoA. This alternative metabolic routing allows β-OHB to avoid oxidation in the mitochondria and to be used as a major source of cytosolic acetyl-CoA, even when other key cytosolic acetyl-CoA precursors such as glucose are available in excess. Finally, we demonstrate that ketone body metabolism, including this alternative AACS-dependent route, can support the growth of mouse KrasG12D; Trp53-/- pancreatic tumours grown orthotopically in the pancreas of male mice, as well as the growth of mouse B16 melanoma tumours in male mice fed a calorie-restricted diet. Together, these data reveal how cancer cells use β-OHB as a major source of cytosolic acetyl-CoA to support cell proliferation and tumour growth.