MIF regulates MM cell sensitivity to PIs. (A) Relationship between MIF expression from gene-profiling data of purified human MM cells and MM patient disease status, such as sustained response (Response, n = 375) versus Relapse (n = 184). PFS (B) and OS (C) of MM patients with high MIF (MIF^high) and low MIF (MIF^low) expression in MMRF CoMMpass study IA13. (D) Relative MIF messenger RNA expression in plasma cells of healthy donor BMs (HD#1-3) or MM patient BMs (MM#1-3) and MM cell lines by quantitative polymerase chain reaction. Cell viability of CTR-KO or MIF-KO MM cell lines with pulse treatment with Btz (E) or Cfz (F) for 1 hour followed by 48 hours of culture in drug-free medium, or with continuous treatment with melphalan (Mel) (G) or lenalidomide (Len) (H) by MTS Assay, significance was analyzed by one-way analysis of variance with Tukey’s post hoc test at each concentration point. Apoptotic rate of CTR-KO or MIF-KO MM cell lines pulsed with 150 nM Btz (I) or 80 nM Cfz (J) for 1 hour and allowed to recover for 24 hours by Annexin V assay; values were normalized to DMSO-treated MM cells. Histogram (K) and summarized results (L) of apoptosis in KMS-11/Cfz or KMS-11 cells with 1 hour of pulse treatment with DMSO or 200 nM Cfz followed by exposure to drug-free medium for 24 hours. (M) Summary of apoptosis analysis of primary MM cells at 24 hours after pulse treatment with 100 nM Cfz. Expression of MIF in primary MM cells determined by flow cytometry for intercellular staining of MIF (n = 8 for each MIF^high and MIF^low). For panel K, a representative result of 3 independent experiments is shown. The Student t test was used to compare 2 samples. Panels B and C show Kaplan-Meier estimates of PFS and OS with a P value from a log-rank test. *P < .05; **P < .01; ***P < .001. n.s., not significant.