Participation of BTK in MYD88 signaling in malignant cells expressing the L265P mutation in Waldenstrom’s macroglobulinemia, and effect on tumor cells with BTK-inhibitor PCI-32765 in combination with MYD88 pathway inhibitors.

8106 Background: Bruton’s tyrosine kinase (BTK) promotes B-cell receptor signaling along with B-cell expansion and survival through NF-κB and MAPK. MYD88 L265P is a widely expressed somatic mutation in tumor cells from WM patients. MYD88 L265P promotes enhanced tumor cell survival through IRAK 1/4 mediated NF-κB and MAPK signaling. We therefore sought to clarify the role of BTK signaling in MYD88 L265P expressing WM cells, and the impact of BTK and MYD88/IRAK inhibition on WM cell signaling and survival. Methods: Western blot analysis was performed using total and phospho-specific BTK antibodies in MYD88 L265P expressing primary WM patient cells, BCWM.1 and MCWL-1 WM cell lines following MYD88 knockdown by lentiviral transduction, and/or use of MYD88 or IRAK signal inhibitors. Cells were also treated with the BTK inhibitor PCI-32765, in the presence or absence of MYD88 homodimerization or IRAK1/4 inhibitors. Annexin V / PI staining was used to assess cell survival, and synergism assessed with CalcuSyn sof...