Abstract 923: Ibrutinib inhibits malignant cell adhesion and migration and reduces tumor burden in lymph node and bone marrow in a murine model of mantle cell dissemination and progression.

Abstract

Abstract Introduction: Ibrutnib is a potent and selective Btk inhibitor that covalently modifies Cys481 in Btk and inhibits B cell antigen receptor (BCR) signaling. Ibrutinib is currently in a Phase II study in patients with relapsed or refractory mantle cell lymphoma (MCL). In MCL patients following 1-2 weeks of ibrutinib treatment, we observed a transient increase of MCL cells in peripheral blood which was associated with a rapid reduction of tumor burden in MCL patients suggesting mobilization of malignant cells from tissues to the periphery (Wanga; Changb). At the same time, levels of plasma chemokines CCL4, CCL22, CXCL13 were significantly decreased by 40-60% (p<0.05) (Changb). As Btk is an essential element in BCR- and chemokine-mediated adhesion and migration in B lymphocytes, we determined effects of Btk inhibition by ibrutinib in MCL primary cells co-cultured with stromal cells, and studied its effects in vivo on MCL homing in immunocompetent C57Bl/6 mice and lymphadenopathy in a disseminated human xenograft model of MCL in SCID mice. Results and Conclusions: Ibrutinib inhibited phosphorylation of Btk, PLCγ, Erk and JNK in MCL cell lines (Mino, Jeko, HBL2) and primary MCL cells stimulated by co-culture with stromal cells or anti-IgM. Furthermore, ibrutinib inhibited BCR- and chemokine (CXCL12, CXCL13)-induced adhesion and migration of MCL cells lines, and the migration of MCL underneath bone marrow-derived stromal cells in co-culture (pseudoemperipoleisis). In addition, ibrutinib significantly inhibited the production of chemokines CCL3, CCL4, CCL22, TARC and CXCL13 by 50-70% (p<0.01) in human MCL co-culture or following BCR activation in MCL cell lines or primary MCL cells. Gene expression studies of both MCL cells and patients treated with ibrutinib for either 24 hrs or 8 days resulted in over 80% inhibition of NF-κB, IL-6, CCL3, CCL4 gene expression. In vivo, ibrutinib treatment at 12 mg/kg inhibited homing of MCL cells into lymphoid tissues of C57Bl/6 mice by 70%. Ibrutinib at 3 and 12 mg/kg significantly and dose-dependently suppressed tumor burden in the mandibular/cervical lymph nodes, mesenteric lymph nodes/Peyer Patches and bone marrow by over 90% in a prevention model of MCL lymphadenopathy in SCID mice. In a treatment setting of the same model where tumor injected mice were treated with vehicle for 6 weeks prior to receiving 12 mg/kg of ibrutinib for 3 weeks, a 90% and 68% reduction of tumor cells in the lymph nodes and bone marrow, respectively, was observed. These results collectively demonstrate Btk inhibition mediated by ibrutinib, suppresses adhesion and migration of malignant MCL cells in vitro and reduces tumor burden in lymph nodes and bone marrow in vivo. aWang L et al., ASH 2011. bChang BY et al., ASH 2011. Citation Format: Betty Y. Chang, Michelle Francesco, Susanne Steggerda, Stella Chang, Padmaja Magadala, Lucy Jawed, Patricia Thiemann, Joseph J. Buggy. Ibrutinib inhibits malignant cell adhesion and migration and reduces tumor burden in lymph node and bone marrow in a murine model of mantle cell dissemination and progression. [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 923. doi:10.1158/1538-7445.AM2013-923