Myeloma mesenchymal stem cells' bioenergetics afford a novel selective therapeutic target

Bone-marrow mesenchymal stem cells (BM-MSCs) rely on glycolysis, yet their trafficked mitochondria benefit recipient cells' bioenergetics in regenerative and cancerous settings, most relevant to BM-resident multiple myeloma (MM) cells. Fission/fusion dynamics regulate mitochondria function. Proteomics demonstrates excessive mitochondrial processes in BM-MSCs from MM patients compared to normal donors (ND). Thus, we aimed to characterize BM-MSCs (ND, MM) mitochondrial fitness, bioenergetics and dynamics with a focus on therapeutics. MM-MSCs displayed compromised mitochondria evidenced by decreased mitochondrial membrane potential (ΔΨm) and elevated proton leak. This was accompanied by stimulation of stress-coping mechanisms: spare respiratory capacity (SRC), mitochondrial fusion and UPR^mt. Interfering with BM-MSCs mitochondrial dynamics equilibrium demonstrated their significance to bioenergetics and fitness according to the source. While ND-MSCs depended on fission, reducing MM-MSCs fusion attenuated glycolysis, OXPHOS and mtROS. Interestingly, optimization of mtROS levels is central to ΔΨm preservation in MM-MSCs only. MM-MSCs also demonstrated STAT3 activation, which regulates their OXPHOS and SRC. Targeting MM-MSC' SRC with Venetoclax diminished their pro-MM support and sensitized co-cultured MM cells to Bortezomib. Overall, MM-MSCs distinct mitochondrial bioenergetics are integral to their robustness. Repurposing Venetoclax as anti-SRC treatment in combination with conventional anti-MM drugs presents a potential selective way to target MM-MSCs conferred drug resistance.