(A and B) Relative quantification of BCL6 (B cell marker), BLIMP, XBP1s, and CHOP (PC markers) in H929 cells (A) and primary CD138⁺ MM cells (B) from 3 different patient samples incubated for 5 days either in the absence of stroma (Ctrl) or cocultured with WT or Smo-KO stromal cells. Expression in untreated liquid conditions was set at 1. (A and B) Data represent the mean ± SEM. *P ≤ 0.05 and **P ≤ 0.01, by repeated-measures 1-way ANOVA to determine statistical significance between treatment groups; P values were corrected for multiple comparisons using Dunnett’s test. (C) Flow cytometric analysis of CD138 in H929 or primary CD138⁺ MM cells cocultured for 5 days with WT or Smo-KO stromal cells. Data are representative of 3 independent experiments. (D) BTZ sensitivity of H929 (CFU recovery) or primary CD138⁺ MM cells (cell number recovery) from 3 different patient samples. MM cells were treated with BTZ (2.5 nM) for 48 hours after coculture with WT or Smo-KO stromal cells for 5 days. CFU or cellular recovery was normalized to each condition in the absence of BTZ. Data represent the mean ± SEM. *P ≤ 0.05 and **P ≤ 0.01, by 2-tailed Student’s t test. (E) Cartoon depicting the experimental design of subcutaneous xenografts. Each mouse carried 2 tumors consisting of H929 Luc⁺ cells and either WT or Smo-KO stroma. (F) Bioluminescent images of xenografts upon treatment with IRX (n = 10), BTZ (n = 9), or a combination of both (n = 10) for 4 weeks. (G) Fold change in bioluminescence (photons/second) from day 0 of treatment. Results are the average of 9 to 10 xenografts per treatment group. *P ≤ 0.05 and **P ≤ 0.01, by unpaired, 2-tailed Student’s t test.