Multiple myeloma with 1q21 amplification is highly sensitive to MCL-1 targeting

Prosurvival Bcl-2 Family proteins are potent inhibitors of Apoptosis and often overexpressed in lymphoid malignancies. In multiple myeloma (MM), Mcl-1 expression contributes to survival of malignant plasma cells, and overexpression correlates with poor prognosis. In this study, we investigated whether sensitivity to the novel Mcl-1 Inhibitor S63845 could be predicted using cytogenetics, focusing on amplification of 1q21, the chromosomal region that contains the MCL1 locus. In addition, we studied the relation of Mcl-1 Inhibitor sensitivity with other diagnostic characteristics and Bcl-2 Family protein expression. In 31 human myeloma cell lines and in bone marrow aspirates from 47 newly diagnosed MM patients, we measured the effect of S63845 alone, or combined with Bcl-2 Inhibitor ABT-199 (venetoclax), and Bcl-xL Inhibitor A-1155463 or A-1331852 on cell viability. We demonstrated for the first time that MM cells from patients with 1q21 amplification are significantly more sensitive to inhibition of Mcl-1. We suggest that this increased sensitivity results from high relative MCL1 expression resulting from amplification of 1q21. Additionally, and partially independent from 1q21 status, high serum β2 microglobulin level and presence of renal insufficiency correlated with increased sensitivity to Mcl-1 Inhibitor treatment. Combining S63845 with other BH3 mimetics synergistically enhanced Apoptosis compared with single inhibitors, and sensitivity to inhibitor combinations was found in a large proportion of MM insensitive to Mcl-1 inhibition alone. Collectively, our data indicate that amplification of 1q21 identifies an MM subset highly sensitive to Mcl-1 Inhibitor treatment and can be used as a predictive marker to guide selection of therapy.