Targeting STK17B kinase activates ferroptosis and suppresses drug resistance in multiple myeloma.

The progression of multiple myeloma (MM), an incurable malignancy of plasma cells, is often associated with the suppression of ferroptosis, a type of cell death driven by iron-dependent lipid peroxidation. The mechanisms underlying this suppression remain largely unknown. Here, we identified serine/threonine kinase 17b (STK17B) kinase as a critical suppressor of ferroptosis in MM. Elevated levels of STK17B are associated with poor overall survival in patients with MM, and STK17B expression is significantly higher in relapsed vs newly diagnosed MM cases. We found that inhibiting STK17B in MM cells increased the labile iron pool, enhanced lipid peroxidation, and sensitized cells to conventional anti-MM therapies. Notably, an orally available, in-house-generated STK17B inhibitor induced ferroptosis and significantly reduced tumor growth in MM xenograft mouse models. Mechanistically, proximity labeling assay combined with the phospho-proteomic analysis identified 2 major regulators of iron uptake and transport as direct targets of STK17B: iron-responsive element binding protein 2 (IREB2), and heat shock protein family B member 1 (HSPB1). We demonstrated that STK17B phosphorylates critical regulatory sites on IREB2 (S157) and HSPB1 (S15), thereby modulating the balance between IREB2 and HSPB1 downstream effectors, proferroptotic transferrin receptor, and antiferroptotic ferritin heavy chain proteins. Furthermore, we demonstrated that STK17B indirectly maintains activating phosphorylation of STAT3, a ferroptosis suppressor and a major driver of MM pathobiology. Our findings uncovered a clinically relevant and targetable STK17B-pIREB2S157/pHSPB1S15 signaling axis that suppresses ferroptosis and contributes to drug resistance in MM.