BTKCys481Ser drives ibrutinib resistance via ERK1/2, and protects BTKWild-Type MYD88 mutated cells by a paracrine mechanism

Jiaji G. Chen, Xia Liu, Manit Munshi, Lian Xu, Nicholas Tsakmaklis, Maria G. Demos, Amanda Kofides, Maria Luisa Guerrera, Gloria G. Chan, Christopher J. Patterson, Kirsten E. Meid, Joshua Gustine, Toni Dubeau, Patricia Severns, Jorge J. Castillo, Zachary R. Hunter, Jinhua Wang, Sara J. Buhrlage, Nathanael S. Gray, Steven P. Treon and Guang Yang

Blood 2018 doi: https://doi.org/10.1182/blood-2017-10-811752

Acquired ibrutinib resistance due to BTKCys481 mutations occurs in B-cell malignancies, including those with MYD88 mutations. BTKCys481 mutations are usually sub-clonal, and their relevance to clinical progression remains unclear. Moreover, the signaling pathways that promote ibrutinib resistance remain to be clarified. We therefore engineered BTKCys481Ser and BTKWT expressing MYD88 mutated WM and ABC DLBCL cells, and observed re-activation of BTK–PLCγ2–ERK1/2 signaling in the presence of ibrutinib in only the former. Use of ERK1/2 inhibitors triggered apoptosis in BTKCys481Ser expressing cells, and showed synergistic cytotoxicity with ibrutinib. ERK1/2 re-activation in ibrutinib treated BTKCys481Ser cells was accompanied by release of many pro-survival and inflammatory cytokines, including IL-6 and IL-10 that were also blocked by ERK1/2 inhibition. To clarify if cytokine release by ibrutinib treated BTKCys481Ser cells could protect BTKWT MYD88 mutated malignant cells, we used a TranswellTM co-culture system, and showed that non-transduced BTKWT MYD88 mutated WM or ABC DLBCL cells were rescued from ibrutinib induced killing when co-cultured with BTKCys481Ser but not their BTKWT expressing counterparts. Use of IL-6 and/or IL-10 blocking antibodies abolished the protective effect conferred on non-transduced BTKWT by co-culture with BTKCys481Ser expressing WM or ABC DLBCL cell counterparts. Rebound of IL-6 and IL-10 serum levels also accompanied disease progression in WM patients with acquired BTKCys481 mutations. Our findings show that the BTKCys481Ser mutation drives ibrutinib resistance in MYD88 mutated WM and ABC DLBCL cells through re-activation of ERK1/2 activation, and can confer a protective effect on BTKWT cells through a paracrine mechanism.