Indisulam is potent against MM in vitro and in vivo by selectively degrading RBM39. (A) Indisulam induced apoptosis in MM.1S, H929, and LP-1 cells. Apoptosis was detected after 48 hours of indisulam treatment. (B) Indisulam induced H929 cells cell cycle arrest at G2/M phase. Cell cycle was detected after 48 hours of indisulam treatment. (C) Indisulam inhibited H929 cell proliferation in a dose- and time-dependent manner. (D) The cyclin B1-CDK1 complex at the G2/M checkpoint was decreased after indisulam treatment. (E) Image of subcutaneous H929 tumor tissues treated with indisulam. H929 cells were injected into BALB/c nude mice to form subcutaneous tumors. The mice received 9 consecutive daily treatments with either vehicle or 10 mg/kg indisulam via intraperitoneal administration. (F) H929 tumors growth curve in panel E. (G) Bioluminescence images of mice transplanted with luciferase-labeled LP-1 (LP-1-luc) cells treated with vehicle or indisulam. LP-1-luc cells were injected into the tail vein of NOG mice. Five weeks after injection, the mice received 20 consecutive daily treatments of either vehicle or 20 mg/kg indisulam by intraperitoneal administration. Bioluminescence was detected at the indicated time points. (H) Quantification of bioluminescence imaging in vehicle- or indisulam-treated mice in panel G. (I) H929 cells overexpressing RBM39 or RBM39^G268V were treated with 20 μM indisulam for 48 hours followed by western blot analysis to detect the expression of RBM39, p65, and p-p65. (J) Dose-response curve of cell viability assay for H929 cells overexpressed RBM39 or RBM39^G268V mutant. (K) Image of H929 xenografts with RBM39 or RBM39^G268V overexpressing that were treated with indisulam (10 mg/kg) for 9 consecutive days. (L) H929 tumors growth curve in panel K. ∗P < .05, ∗∗P < .01, ∗∗∗P < .001, ∗∗∗∗P < .0001). vec, vector.