Purpose: gp96 (grp94) is a key downstream chaperone in the endoplasmic reticulum (ER) to mediate unfolded protein response (UPR) and the pathogenesis of multiple myeloma is closely linked to dysregulated UPR. In this study, we aimed to determine the roles of gp96 in the initiation and progression of multiple myeloma in vivo and in vitro.

Experimental Design: We generated a mouse model with overexpression of XBP1s and conditional deletion of gp96 in B-cell compartment simultaneously to identify the roles of gp96 in the development of multiple myeloma in vivo. Using a short hairpin RNA (shRNA) system, we silenced gp96 in multiple human multiple myeloma cells and examined the effect of gp96 knockdown on multiple myeloma cells by cell proliferation, cell-cycle analysis, apoptosis assay, immunohistochemistry, and human myeloma xenograft model. The anticancer activity of gp96 selective inhibitor, WS13, was evaluated by apoptosis assay and MTT assay.

Results: Genetic deletion of gp96 in XBP1s-Tg mice attenuates multiple myeloma. Silencing of gp96 causes severe compromise in human multiple myeloma cell growth through inhibiting Wnt-LRP-survivin pathway. We also confirmed that knockdown of gp96 decreased human multiple myeloma growth in a murine xenograft model. The targeted gp96 inhibitor induced apoptosis and blocked multiple myeloma cell growth, but did not induce apoptosis in pre-B leukemic cells. We have demonstrated that myeloma growth is dependent on gp96 both genetically and pharmacologically.

Conclusions: gp96 is essential for multiple myeloma cell proliferation and survival, suggesting that gp96 is a novel therapeutic target for multiple myeloma. Clin Cancer Res; 19(22); 6242–51. ©2013 AACR.