Covalent Bruton's tyrosine kinase-inhibitors (cBTK-i) are highly active in MYD88-mutated (MYD88Mut) Waldenstrom's macroglobulinaemia and suppress nuclear factor kappa-light-chain-enhancer of activated B cells and extracellular signal-regulated kinases-1/2 (ERK1/2)-related signalling. BTKCys481 mutations are associated with cBTK-i acquired resistance and are accompanied by reactivation of ERK1/2 that promotes inflammatory cytokine secretion and paracrine-mediated resistance of BTK wild-type (BTKWT) tumour cells. Pirtobrutinib is a non-covalent BTK-inhibitor that binds at non-BTKCys481 sites. We show that pirtobrutinib blocked p-ERK1/2, ERK1/2-driven inflammatory cytokines, and overcame paracrine-mediated resistance in MYD88Mut lymphoma cells expressing mutated BTKCys481. Our results provide important mechanistic insights for the activity of pirtobrutinib in MYD88Mut lymphomas carrying BTKCys481 mutations.
Keywords: MYD88; ABC DLBCL; BTK; ERK1/2; Waldenstrom's macroglobulinaemia; ibrutinib; pirtobrutinib.
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