Targeting lactate-driven protein lactylation overcomes proteasome inhibitor resistance in multiple myeloma.

Acquired resistance to proteasome inhibitors (PIs) remains a major challenge limiting the long-term efficacy of multiple myeloma (MM) therapy, while the metabolic-epigenetic mechanisms underlying PI resistance remain incompletely defined. Using clinical bone marrow specimens, paired parental and PI-resistant MM cell models, xenografts, and integrated lactylome, CUT&Tag, and RNA-seq profiling, we investigated the role of lactate-associated lactylation in acquired PI resistance. Bone marrow lactate levels, lactate dehydrogenase (LDH) activity, and global protein lactylation were elevated in relapsed/refractory MM and in PI-resistant cell models. Lactylome profiling revealed extensive lactylation remodeling and identified histone H4K12 lactylation (H4K12la) as a prominent resistance-associated epigenetic mark. Integrative prioritization and functional validation identified EP300 as an upstream regulator of H4K12la; EP300 was upregulated in resistant cells, and its depletion reduced H4K12la and partially restored PI sensitivity. Integration of H4K12la CUT&Tag and RNA-seq linked resistance-associated H4K12la remodeling to autophagy/lysosome-related transcriptional programs, with increased H4K12la occupancy at the Cathepsin L (CTSL) promoter accompanied by increased CTSL expression. Pharmacological LDH inhibition with FX-11 reduced H4K12la and CTSL expression. Moreover, combining FX-11 with carfilzomib markedly enhanced antitumor activity in a PI-resistant MM xenograft model without detectable systemic or hematological toxicity during the treatment period. Collectively, these findings define a lactate-EP300-H4K12la-CTSL pathway that contributes to PI resistance and provide a preclinical rationale for combined metabolic and proteasomal inhibition in refractory MM.