Inhibition of MYD88 signaling induced cytotoxicity and inhibited cell growth in cells expressing MYD88 L265P mutation. Data represent the mean of triplicate experiments plus or minus standard deviation. (A-B) Inhibition of MYD88 by the MYD88 inhibitor induced cytotoxicity and inhibition of cell growth on BCWM1 and MWCL1 cell lines developed from patients with WM, characterized with MYD88^mut. The data are compared with the control peptide (peptide crtl) provided by the manufacturer. Time points varied from 12 to 48 hours, and concentrations from 10 to 50 µM. (A) Cytotoxicity. (B) Inhibition of cell growth proliferation (*P < .05, significant difference with the control). (C-F) Inhibition of MYD88 induced apoptosis in MYD88 mutated cell lines, BCWM1, MWCL1, and OCI-Ly3, and to a lesser extent in MYD88^wild cell lines, MEC-1, RL, and MM.1S. (C) The percentage of cells undergoing apoptosis was studied using annexin V–positive and propidium iodide–negative staining and flow cytometry at 12 and 24 hours, and at 25 µM (BCWM1, MM.1S, MEC-1, and RL) and 50 µM (MWCL1 and OCI-Ly3) of MYD88 inhibitor. (D) Study of mitochondrial membrane potential at 12 hours with 25 µM and 50 µM of MYD88 inhibitor, respectively. (E) Study of caspase 3 activity (caspase cleavage) in presence of the pan-caspase inhibitor Z-VAD-fmk (50 µM) at 12 hours with 25 µM and 50 µM of MYD88 inhibitor, respectively. (F) Study of caspase 8 and 9 cleavage in all 3 cell lines that are MYD88 mutated, BCWM1, MWCL1, and OCI-Ly3, at 12 hours with 25 µM and 50 µM of MYD88 inhibitor, respectively. (G) Inhibition of MYD88 signaling downregulates phosphorylation of STAT3 and IRAK4 in BCWM1 and MWCL1 cell lines. Cell lines were treated for 12 hours at 25 µM and 50 µM of MYD88 inhibitor, respectively.