Electron transport chain and mTOR inhibition synergistically decrease CD40 signaling and counteract venetoclax resistance in chronic lymphocytic leukemia

CD40 signaling upregulates BCL-XL and MCL-1 expression in the chronic lymphocytic leukemia (CLL) lymph node microenvironment (TME), affording resistance to the BCL-2 inhibitor venetoclax (VEN). VEN resistance in the therapeutic setting and after long-term laboratory selection has been linked to metabolic alterations, but the underlying mechanism(s) are unknown. We aimed here to discover how CD40 stimulation as a model for TME-mediated metabolic changes, affects VEN sensitivity/resistance. CD40 stimulation increased oxidative phosphorylation (OXPHOS) and glycolysis, but only OXPHOS inhibition countered VEN resistance. Furthermore, blocking mitochondrial import of pyruvate, glutamine or fatty acids affected CLL metabolism, but did not prevent CD40-mediated VEN resistance. In contrast, inhibition of the electron transport chain (ETC) at complex I, III and V attenuated CLL activation and ATP production, and downregulated MCL-1 and BCL-XL, correlating with reduced CD40 surface expression. Moreover, ETC inhibition equaled mTOR1/2 but not mTOR1 inhibition alone for VEN resistance, and all three pathways were linked to control of general protein translation. In line with this, ETC plus mTOR inhibition synergistically counteracted VEN resistance. These findings link oxidative CLL metabolism to CD40 expression and cellular signaling, and may hold clinical potential.