Nifuroxazide inhibits the viability of MM cells containing constitutive STAT3 phosphorylation. (A) MM cells containing STAT3 phosphorylation (U266 and INA6), MM cells without STAT3 phosphorylation (RPMI 8226 and H929), and peripheral blood mononuclear cells (PBMCs) from healthy donors were treated with the indicated concentrations of nifuroxazide for 48 hours. Cell viability was measured using an ATP-dependent bioluminescence assay. (B) Bone marrow aspirates from MM patient samples were treated with the indicated concentrations of nifuroxazide for 72 hours. Cell viability was measured using an ATP-dependent bioluminescence assay. (C) U266 cells cultured in the presence or absence of BMSCs were treated with the indicated concentration of nifuroxazide for 6 hours, and then examined by Western blot analysis with the indicated antibodies. (D) U266 cells were cultured in the presence or absence of BMSCs for 48 hours with the indicated concentrations of nifuroxazide. ³H thymidine incorporation was measured during the final 8 hours of incubation to measure DNA synthesis.