Inducible gene-knockout studies in mice have suggested that this IRE1CXBP1s pathway may support insulin secretion by pancreatic cells (45, 46) and homeostasis of hepatocytes (47). tumor growth in vivo, we disrupted the XBP1 gene by CRISPR/Cas9 in KMS-11 (R)-(-)-Mandelic acid cells. Similar to the IRE1 KO clones, two impartial XBP1 KO clones failed to grow appreciably upon s.c. injection into C.B-17 SCID mice, while parental IRE1 WT cells formed tumors as expected (Fig. 2and and and 0.05 compared with IRE1 knockdown alone) (Fig. 2and 0.01 compared with IRE1 knockdown alone) (Fig. 2and and and and and 0.01, *** 0.001. Harrington et al. (35) recognized kinome-selective inhibitors of IRE1 kinase, including compounds 16 and 18 (Fig. 3and and and and and and and and and = 15 per group): vehicle, Dox in the drinking water (0.5 mg/kg), or compound 18 (30 mg/kg) intraperitoneally (IP) twice per day (BID). Tumor growth was monitored over 24 d. Individual tumor data are shown in = 14 per group) treated as in with either vehicle, Dox in the drinking water, or compound 18 IP once per day and monitored for tumor growth over 11 d. Individual tumor data are shown in = 3) or compound 18 (30 mg/kg IP, BID, = 5) for 2 wk, and analyzed for tumor burden. One control mouse died during anesthesia and one treated mouse was killed due to excess weight loss. Luminescence images of representative mice are depicted around the left. The tumor burden of each mouse is shown as percent tumor growth on day 14 (at the end of 8 wk) compared with day 0 of treatment (Tx, at the end of 6 wk). ** 0.01, *** 0.001. We then turned to a more stringent orthometastatic model of MM, in which luciferase and mCherry double-labeled RPMI-8226 TNF-alpha cells, injected into the tail vein of NSG mice, develop common malignant disease with bone marrow involvement over a period of 6 wk (and and and and and and and = 3) were similarly tested and are depicted for comparison ( 0.05, *** 0.001. We next turned to investigate whether pharmacologic IRE1 kinase inhibition disrupts normal function of other cell types. Inducible gene-knockout studies in mice have suggested that this IRE1CXBP1s pathway may support insulin secretion by (R)-(-)-Mandelic acid pancreatic cells (45, 46) and homeostasis of hepatocytes (47). Therefore, we first verified the ability of compound 18 to inhibit XBP1s induction in human pancreatic islet 3D microtissues, which contain all of the endocrine cell types (R)-(-)-Mandelic acid and can retain viability and function in culture for up to 4 wk (48). At 2.4 M, 18 suppressed Tg-induced XBP1s production to baseline levels (Fig. 6and and and and = 5 per treatment) were then (and and = 5 per treatment). Microtissues were incubated for 7 d with serial dilutions of compound 18 or vehicle control (DMSO) and then viability analyzed by CellTiter-Glo or insulin secretion analyzed after glucose challenge (16.7 mM) for 1 h by ELISA. Human Hepatocyte Experiments. Normal primary human hepatocytes (Millipore Sigma) were cultured on collagen-coated 96-well plates and assays were performed in serum-free hepatocyte incubation media. Hepatocytes were treated with Tm (5 g/mL) for 8 h in the presence of compound 18 or (R)-(-)-Mandelic acid vehicle control (DMSO) at the indicated concentration and analyzed for XBP1s levels by RT-qPCR or cultured for 48 h in the presence of vehicle (DMSO) or 18 at the indicated concentrations and analyzed for viability by CellTiter-Glo. s.c. Xenograft Growth and Efficacy Studies. All procedures were approved by and conformed to the guidelines and principles set by the Institutional Animal Care and Use Committee of Genentech and were carried out in an Association for the Assessment and Accreditation of Laboratory Animal Care-accredited facility. For tumor growth studies, 10 106 KMS-11 parental, IRE1 KO or XBP1 KO clones, or IRE1.