SIRT6 depletion/inhibition sensitizes MM cells to genotoxic agents. (A) MM.1S cells inducibly expressing shRNA targeting SIRT6 were grown with or without doxycycline, and then treated with vehicle, doxorubicin (Doxo; 1 μM) or melphalan (mel; 100 μM) for 1 hour prior to the preparation of lysates and analyzed by western blotting. Representative immunoblots (n = 3) for the indicated proteins in MM cells are shown. (B) Survival curves of NCI-H929 cells transfected with scramble or SIRT6-targeting shRNA and then treated with doxorubicin or melphalan for 48 hours. Western blot shows SIRT6-KD 4 days after viral transduction (insert). (C) Survival curves of the NCI-H929 cell line treated with DMSO or OSSL_126167 (200 μM) and increasing concentration of doxorubicin (10-100 nM) or melphalan (0.3-3 μM). (D) MM.1S cells stably expressing shRNA-targeting SIRT6 were transduced with pLOC carrying SIRT6 open reading frame sequence to rescue shRNA phenotype. Next, doxorubicin (10-100 nM) and melphalan (0.3-3 μM) activities were measured. (B-D) All data are shown as the mean values ± SD of triplicates (1 representative experiment performed in triplicate). ns, not significant, **0.009 < P < .001, ****P < .0001 (Student t test). ctr, control.