Inhibition of Acyl-CoA Synthetase Long Chain (ACSL) Isozymes Decreases Multiple Myeloma Cell Proliferation, Mitochondrial Function and Affects Key Survival Pathways

Multiple myeloma (MM) is an incurable cancer of plasma cells that will cause ~12,590 deaths in the USA in 2023. Dysregulation of fatty acid (FA) metabolism is associated with MM development and progression but the underlying mechanisms remains unknown. The acyl-CoA synthetase long-chain family members (ACSLs) convert free long-chain fatty acids into fatty acyl-CoA esters, and play a key role in catabolic and anabolic fatty acid metabolism. Cancer Dependency Map data suggested that ACSL4 and ACSL3 are among the top 25% Hallmark Fatty Acid Metabolism genes that support MM fitness. Here, we show inhibition of the ACSLs in human myeloma cell lines using the pharmacological inhibitor Triascin C (TriC) caused apoptosis, and decreased proliferation in a dose- and time-dependent manner. As KRAS mutants are the most common mutation among MM patients, we used MM.1S cells to study the mechanisms of TriC toxicity. RNA-seq of MM.1S cells treated with 1.00 μM TriC for 24 hours had gene expression profiles significantly enriched in apoptosis, ferroptosis, and ER stress compared to vehicle treated cells. Proteomics of MM.1S cells treated with either 1.00 μM or 2.00 μM TriC for 48 hours revealed that mitochondrial dysfunction and oxidative phosphorylation were significantly enriched pathways of interest relative to vehicle treated cells. Indeed, metabolic flux analysis showed MM.1S cells treated with TriC after 24 hours had decreased mitochondrial ATP production rate. Flow cytometric analyses revealed concomitant decreases in number and mitochondrial membrane potential, and increases in mitochondrial superoxide. Implications: Overall, our data support the hypothesis that suppression of ACSL in human MM cells inhibited their growth and viability, potentially indicating that ACSL proteins may be promising therapeutic targets in treating myeloma progression. To understand the transcriptional changes associated with triacsin C inhibition of the ACSL family, we treated the human multiple myeloma cell line, MM.1S cells that constitutively express GFP and luciferase (MM.1S GFP(+), Luc(+) ) with either vehicle (dimethyl sulfoxide, DMSO) or 1.00 μM triacsin C for 24 hours. We then performed gene expression profiling analysis using paired-end RNA seqencing for three biological replicates per treatment condition.