The WHIM-like CXCR4(S338X) somatic mutation activates AKT and ERK, and promotes resistance to ibrutinib and other agents used in the treatment of Waldenstrom's Macroglobulinemia

CXCR4(WHIM) somatic mutations are common Waldenstrom's Macroglobulinemia (WM), and are associated with clinical resistance to ibrutinib. We engineered WM cells to express the most common WHIM (Warts, Hypogammaglobulinemia, Infections and Myelokathexis), CXCR(S338X) mutation in WM. Following SDF-1a stimulation, CXCR4(S338X) WM cells exhibited decreased receptor internalization, enhanced and sustained AKT kinase (AKT) and extracellular regulated kinase (ERK) signaling, decreased poly (ADP-ribose) polymerase and caspase 3 cleavage, and decreased Annexin V staining versus CXCR4 wild-type (WT) cells. CXCR4(S338X)-related signaling and survival effects were blocked by the CXCR4 inhibitor AMD3100. SDF-1a-treated CXCR4(S338X) WM cells showed sustained AKT and ERK activation and decreased apoptotic changes versus CXCR4(WT) cells following ibrutinib treatment, findings which were also reversed by AMD3100. AKT or ERK antagonists restored ibrutinib-triggered apoptotic changes in SDF-1a-treated CXCR4(S338X) WM cells demonstrating their role in SDF-1a-mediated ibrutinib resistance. Enhanced bone marrow pAKT staining was also evident in CXCR4(WHIM) versus CXCR4(WT) WM patients, and remained active despite ibrutinib therapy in CXCR4(WHIM) patients. Last, CXCR4(S338X) WM cells showed varying levels of resistance to other WM relevant therapeutics, including bendamustine, fludarabine, bortezomib and idelalisib in the presence of SDF-1a. These studies demonstrate a functional role for CXCR4(WHIM) mutations, and provide a framework for investigation of CXCR4 inhibitors in WM.