Supplementary Figure S1-S6
Supplementary Figure S1 shows tumor burden in the mice before BTZ treatment started (S1A), MM cell growth and apoptosis after co-cultured with BMS or pre-OBs of OB-Runx2-/- or OB-Runx2+/+ mice (S1B-F), and the proportion of PMN-MDSCs and M-MDSCs in the BM of Runx2-/- or OB-Runx2+/+ mice after 4-week treatment with BTZ (S1G-H).Supplementary Figure S2 shows tumor burden in the mice before SRI31277 and BTZ treatment (S2A) and the proportion of PMN-MDSCs and M-MDSCs in the BM of Runx2-/- or OB-Runx2+/+ mice after 4-week treatment with SRI31277 and BTZ (S2B-C).Supplementary Figure S3 shows tumor burden in the mice before 5-Fu and BTZ treatment.Supplementary Figure S4 shows the impact of GEM treatment on BTZ resistance of MM cells in OB-Runx2-/- mice.Supplementary Figure S5 shows the proportion of PMN-MDSCs and M-MDSCs in the BM of Runx2-/- or OB-Runx2+/+ mice after 4-week treatment with 5-Fu and BTZ.Supplementary Figure S6 shows the impact of GEM and BTZ treatment on MDSCs and CD8 T cells.
ARTICLE ABSTRACT
Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM). The proteasome inhibitor bortezomib is one of the most effective first-line chemotherapeutic drugs for multiple myeloma; however, 15% to 20% of high-risk patients do not respond to or become resistant to this drug and the mechanisms of chemoresistance remain unclear. We previously demonstrated that multiple myeloma cells inhibit Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB), and that this OB-Runx2 deficiency induces a cytokine-rich and immunosuppressive microenvironment in the BM. In the current study, we assessed the impact of OB-Runx2 deficiency on the outcome of bortezomib treatment using OB-Runx2+/+ and OB-Runx2−/− mouse models of multiple myeloma. In vitro and in vivo experiments revealed that OB-Runx2 deficiency induces multiple myeloma cell resistance to bortezomib via the upregulation of immunosuppressive myeloid-derived suppressor cells (MDSCs), downregulation of cytotoxic T cells, and activation of TGFβ1 in the BM. In multiple myeloma tumor-bearing OB-Runx2−/− mice, treatment with SRI31277, an antagonist of thrombospondin-1 (TSP-1)–mediated TGFβ1 activation, reversed the BM immunosuppression and significantly reduced tumor burden. Furthermore, treatment with SRI31277 combined with bortezomib alleviated multiple myeloma cell resistance to bortezomib-induced apoptosis caused by OB-Runx2 deficiency in cocultured cells and produced a synergistic effect on tumor burden in OB-Runx2−/− mice. Depletion of MDSCs by 5-fluorouracil or gemcitabine similarly reversed the immunosuppressive effects and bortezomib resistance induced by OB-Runx2 deficiency in tumor-bearing mice, indicating the importance of the immune environment for drug resistance and suggesting new strategies to overcome bortezomib resistance in the treatment of multiple myeloma.
