Abstract LB-328: Preclinical activity of interleukin 21 in mantle cell lymphoma.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Mantle cell lymphoma (MCL) is a distinct subtype of non-Hodgkin lymphoma characterized by overexpression of cyclin D1 (CCND1) in 95% of patients due to the t(11;14)(q13;q32) chromosomal translocation. This incurable lymphoma is highly chemoresistant with short duration response, frequent relapses and eventual death, even with the most aggressive chemotherapeutic regimens. Interleukin 21 (IL21), a member of the IL2 cytokine family, has shown anti-tumor effects in solid tumors, chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL) and it is currently in clinical trials for renal cell carcinoma and metastatic melanoma. Herein, we carried out a comprehensive study to delineate the effects of IL21 on MCL cell lines and primary tumors. Flow-cytometric analysis revealed that all MCL cell lines (Mino, HBL-2, Jeko-1, G-519, IRM-2, SP53, Z138, UPN1 and L-128) as well as primary tumors expressed surface IL21R at variable levels. Treatment of Mino, HBL-2 and SP53 cells with IL21 (100ng/mL) led to a marked time-dependent decrease in cell proliferation and increased cell death. In contrast, Jeko1, IRM2, L128, Z138, UPN1 and G519 cells exhibited resistance to IL21 treatment. Similarly, primary MCL tumors treated with IL21 in vitro exhibited significant cell death in 3 of 5 cases. To decipher the mechanism of IL21-induced apoptosis, responsive and resistant cell lines as well as primary tumors were utilized. Similarly to our previous study in DLBCL, IL21 stimulation resulted in dramatic phosphorylation of STAT1 and STAT3 in IL-21 responsive cell lines (Mino, HBL-2, SP53) and a primary tumor, while minimal phosphorylation of STAT5 was observed only in Mino. However, observed levels of phosphorylated STAT1, 3 and 5 were significantly lower in the resistant cells (Jeko-1) and primary tumor. We have previously demonstrated that IL21-induced cell death in DLBCL is mediated by STAT3-induced upregulation of c-Myc expression. Correspondingly, IL21 led to c-Myc upregulation in IL21-sensitive MCL cell lines and primary tumors. Strikingly, IL21 failed to induce c-Myc in the resistant cell line and primary tumor despite expressing similar level of IL21R. IL21 treatment also resulted in upregulation of the pro-apoptotic protein Bax and downregulation of the anti-apoptotic proteins Bcl-XL and Bcl2, as previously observed in DLBCL. Moreover, knockdown of STAT3, c-Myc or Bax using specific siRNAs in Mino cells resulted in abrogation of the IL21-induced cell death. In contrast to a previous report, knockdown of STAT1 did not prevent IL21-induced Mino cell death. Overall, these observations suggest that in vitro IL21 induces cell death and apoptosis in a subset of MCL cell lines and primary tumors by activating the STAT3-cMyc pathway and not through the STAT1 signaling pathway. Additionally, from our observations, MCL resistance to IL21 may be due to abolition of STAT3-c-Myc activation in response to IL21. Citation Format: Shruti Bhatt, Kristopher A. Sarosiek, Izidore S. Lossos. Preclinical activity of interleukin 21 in mantle cell lymphoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-328. doi:10.1158/1538-7445.AM2013-LB-328