In vivo and ex vivo effects of STF-083010. (A) STF-083010 blocks bortezomib-induced XBP1 activity in vivo. Transgenic XBP1-luc mice were injected intraperitoneally with drug vehicle (16% chremophor), 1 mg/kg bortezomib, or 1 mg/kg bortezomib and 60 mg/kg STF-083010, and bioluminescence was measured after 24 hours. Graph represents the average change in the number of photons per animal 24 hours after treatment. Error bars represent SEM of at least 4 animals. (B) Images of representative animals before and after treatment. (C) In vitro cytotoxicity of STF-083010. RPMI 8226, MM.1S, and MM.1R MM cells were treated with 0, 30, or 60μM of STF-083010, and viable cell number was measured daily by the trypan blue exclusion method. (D) Antitumor activity of STF-083010 in vivo. RPMI 8226 MM cells were established as subcutaneous tumor xenografts in NOD/SCID/IL2Rγ null mice. When tumors reached an average volume of 150 mm³, 2 groups of 5 mice each were treated with 30 mg/kg STF-083010 or drug vehicle once weekly for 2 weeks. (E) STF-083010 is preferentially cytotoxic against human MM cells. MM cells were obtained by CD138⁺ selection from bone marrow samples from MM patients; lymphocytes were obtained by Ficoll density-gradient centrifugation of peripheral blood samples from control patients, followed by staining with anti-CD3, anti-CD19, and anti-CD56 monoclonal antibodies to differentiate between T, B, and NK cells. Cells were cultured with the indicated concentrations of STF-083010 for 24 hours, and cell viability was measured by flow cytometric analysis of annexin V/propidium iodide (MM) or 7-amino-actinomycin D (peripheral blood lymphocytes)-stained samples.