Inhibition of FAO in AML co-cultured with BM adipocytes: mechanisms of survival and chemosensitization to cytarabine.

Adipocytes are the prevalent stromal cell type in adult bone marrow (BM), and leukemia cells continuously adapt to deficiency of nutrients acquiring chemoresistant profiles in the BM microenvironment. We have previously shown that fatty acid metabolism is a key energy pathway for survival of acute myeloid leukemia (AML) cells in the adipocyte-abundant BM microenvironment. The novel fatty acid β-oxidation (FAO) inhibitor avocatin B, an odd-numbered carbon lipid derived from the avocado fruit, induced apoptosis and growth inhibition in mono-cultured AML cells. In AML cells co-cultured with BM adipocytes, FAO inhibition with avocatin B caused adaptive stimulation of free fatty acid (FFA) uptake through upregulation of FABP4 mRNA, enhanced glucose uptake and switch to glycolysis. These changes reflect the compensatory response to a shortage of FFA supply to the mitochondria, and facilitate the protection of AML cells from avocatin B-induced apoptosis in the presence of BM adipocytes. However, the combination treatment of avocatin B and conventional anti-AML therapeutic agent cytarabine (AraC) increased reactive oxygen species and demonstrated highly synergistic effects on AML cells under BM adipocyte co-culture condition. These findings highlight the potential for combination regimens of AraC and FAO inhibitors that target bone marrow-resident chemoresistant AML cells.