Abstract 857: Development of a Bruton's tyrosine kinase (Btk) inhibitor - ONO-WG-307, a potential treatment for B-cell malignancies
Authors: Ryohei Kozaki, Toshio Yoshizawa, Tomoko Yasuhiro, Jean-François Mirjolet, Joseph Birkett, Masami Narita, Kazuhito Kawabata
Journal: Cancer Research (2012)

Abstract Purpose: Signals from B cell receptors (BCR) play a central role in signal transduction pathways regulating survival, activation, proliferation, and differentiation of B-lineage lymphoid cells. BCR signaling is implicated in the survival of malignant B cells and recent studies indicate that targeting Btk, an essential component of the BCR pathway, may be effective in the treatment of B-cell lymphoma. ONO-WG-307 is a highly potent and selective Btk inhibitor with an IC50 in the sub-nmol/L range. We evaluated the inhibitory effect of ONO-WG-307 alone and in combination with the chimeric type I anti-CD20 antibody rituximab, using in vitro tumor growth assays and mouse xenograft models. Methods: Two types of tumor cell lines (follicular lymphoma (FL) and activated B-cell-like (ABC) sub-type of diffuse large B cell lymphoma (DLBCL)) wereplated on to micro-titration plates (at doses up to 200 umol/L for ONO-WG-307 and 100 ug/mL for rituximab) for in vitro cytotoxic assays. The same cells were also implanted subcutaneously (SC) into female SCID mice to explore ONO-WG-307 anti-tumor activity in vivo (orally at doses up to 50 mg/kg, bid for ONO-WG-307 and intraperitoneally at doses up to 10 mg/kg, q7d). The IC50 of the in vitro cytotoxic activity was determined using a MTS assay 72 and 96 hours after incubation. Anti-tumor activity was defined as the ratio of the median tumor volume of treatment groups versus control group. The determination of combination index (CI) was calculated by the median-effect method. The CI was used to express synergism (&amp;lt;1), additivity (=1) or antagonism (&amp;gt;1). Results: In the MTS assay, ABC-DLBCL cells were much more sensitive to ONO-WG-307 given as single agent compared with FL cell lines, however, the activity of rituximab single agent had no impact on ABC-DLBCL cell lines in contrast to its inhibitory activity against FL cell lines. When ONO-WG-307 was combined with rituximab, a moderate antagonism was observed in vitro on FL cell lines. In an ABC-DLBCL xenograft model, treatment with single agent ONO-WG-307 resulted in a dose-dependent inhibition of tumor growth and also showed moderate anti-tumor activity in a FL xenograft model. Conclusion: ONO-WG-307 is a highly potent and selective oral Btk inhibitor with evidence of efficacy in both the ABC-DLBCL and the FL cell lines and in xenograft models. These preliminary results suggest that ONO-WG-307 may be an effective therapy in the treatment of B-cell malignancies. To determine whether combination of ONO-WG-307 and rituximab is more efficacious, additional in vivo combination work is underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 857. doi:1538-7445.AM2012-857