Abstract 2570: IMO-8400, a selective antagonist of TLRs 7, 8 and 9, inhibits MYD88 L265P mutation-driven signaling and cell survival: A potential novel approach for treatment of B-cell lymphomas harboring MYD88 L265P mutation
Authors: Bhagat Lakshmi , Wang Daqing , Jiang Weiwen , Agrawal Sudhir 
Published: May 2015

Abstract
In studies of B-cell lymphoma, Staudt and colleagues have identified oncogenic mutations in the signaling pathways associated with the B-cell receptor (BCR) and, more recently, the MYD88 L265P mutation (Ngo et al, Nature 2011, 470:115). MYD88 is a key adaptor protein in the Toll-like Receptor (TLR) signaling pathway. It has been shown that the MYD88 L265P mutation leads to the over activation of the TLRs 7 and 9 signaling pathway, whereas blocking of this pathway decreased cell survival, providing a rationale for targeting TLRs 7 and 9 signaling as a therapeutic approach (Lim et al, AACR 2013, #2332). The MYD88 L265P mutation is reported to be present in over 90% of Waldenström's macroglobulinemia (WM) patients, 29% of patients with activated B-cell-like (ABC) diffuse large B cell lymphoma (DLBCL), and in other B-cell lymphomas. We evaluated IMO-8400, an antagonist for TLRs 7, 8 and 9, in preclinical studies employing three cell lines with the MYD88 L265P mutation (OCI-Ly3, OCI-Ly10 and TMD8), primary bone marrow cells from a WM patient with the mutation, and a control GCB-DLBCL cell line SU-DHL-6 with wild-type MYD88. The presence of MYD88 L265P mutation was confirmed by allele-specific PCR and Sanger sequencing. All cell lines expressed TLRs 7 and 9. Treatment of mutation-positive cell lines with IMO-8400 resulted in dose- and duration-dependent decreases in multiple parameters of cell activation, including cell survival (EC50: 0.95 μM and ∼5 μM, with and without use of lipid, respectively), phosphorylation of BTK, IRAK1, IRAK4, NF-κB, STAT3 and p38 (assayed by Western blot), and secretion of cytokines including IL-10, MIG and IL-2R. Gene array analysis indicated that IMO-8400 inhibited the expression of several genes in the NF-κB and JAK/STAT pathways, including NFKB1, TNFSF10, STAT3 and IL2RA. IMO-8400 also inhibited cell survival and cytokine secretion in cells from the WM patient. In a murine model of disseminated OCI-LY10, IMO-8400 as a single treatment agent showed potent anti-tumor activity in vivo, with dose-dependent increase in animal survival. Treatment was well-tolerated at all dose levels. In a subcutaneous tumor model, growth of even well-established tumor nodules (approximately 500 mm3) was significantly inhibited by IMO-8400 treatment, and this effect correlated with decreased IκBα phosphorylation and IL-10 expression (gene and protein) in tumor cells as well as decreased human IL-10 in the serum of the mice. In contrast, IMO-8400 treatment had no effects on control SU-DHL-6 cells in vitro or in vivo. Our studies show that IMO-8400 inhibits oncogenic MYD88 L265P-mediated cell survival and provides a novel approach for treatment of patients with this mutation. A Phase 1/2 trial of IMO-8400 in patients with WM is now open for enrollment.
Citation Format: Lakshmi Bhagat, Daqing Wang, Weiwen Jiang, Sudhir Agrawal. IMO-8400, a selective antagonist of TLRs 7, 8 and 9, inhibits MYD88 L265P mutation-driven signaling and cell survival: A potential novel approach for treatment of B-cell lymphomas harboring MYD88 L265P mutation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2570. doi:10.1158/1538-7445.AM2014-2570