Objective:Bone marrow derived mesenchymal stem cells(MSCs)in bone marrow microenvironment was found to be involved in the chemoresistance of myeloma cells. In this study,we investigate the role of IL-1β or TNF-α-treated bone marrow MSCs in chemosensitivity of myeloma cell line H929 to doxycycline(DOX)in vitro,and find some possible mechanisms. Methods:CCK8 assay was employed to measure the proliferative rate of H929 cells in the presence of DOX at different concentration,either alone or co-culture with bone marrow MSCs pretreated with IL-1β or TNF-α or not. The apoptotic ratio of H929 cells treated with DOX in the presence of IL-1β or TNF-α-treated bone marrow MSCs or not was determine by flow cytometry(FCM). FCM was also used with real time fluorescence quantitative polymerase chain reaction(RT-qPCR)to measure vascular cell adhesion molecule type one(VCAM-1)on MSCs. The p-Erk1/2 expression level in H929 was measured by Western blot. Results:DOX inhibited the proliferation and induced apoptosis of H929 in a time and dose-dependent manner. IL-1β or TNF-α-pretreated bone marrow MSCs reduced the cytotoxic effects of DOX in H929 cells. Expression level of p-Erk1/2 was down-regulated in H929 cells in the presence of DOX treatment,and this down-regulating effect of DOX was most pronounced when H929 cells were co-cultured with IL-1β or TNF-α-pretreated bone marrow MSCs. In addition,we found that VCAM-1 expression of bone marrow MSCs was up-regulated by IL-1β or TNF-α treatment. Conclusion:DOX was shown to have cytotoxicity to myeloma cells line H929 in a time and dose-dependent manner in vitro. IL-1β or TNF-α could abrogate the cytotoxic effects of DOX in H929 cells indirectly via bone marrow MSCs. Erk pathway in H929 cells and VCAM-1 expression on MSCs may be involved in this myeloma-protective effects by IL-1β or TNF-α.