Abstract 2058: BCL-2 selective inhibitor APG-2575 synergizes with BTK inhibitor in preclinical xenograft models of follicular lymphoma and diffuse large B-cell lymphoma

Follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL) are among the most prevalent B-lymphocyte neoplasms with Bruton’s tyrosine kinase (BTK) often found abnormally activated in these patients. BTK inhibitor ibrutinib has showed proven efficacy in both indications, but its clinical application is limited to gradually acquired resistance. Recent studies reported that ibrutinib-resistant cells exhibited higher BCL-2 expression and therefore increase their sensitivity to BCL-2 inhibitors. In this study, using a BCL-2 selective inhibitor APG-2575, we asked whether its combination with ibrutinib enhanced antitumor activity in FL and DLBCL in preclinical studies. Indeed, the combination treatment with APG-2575 and ibrutinib synergistically enhanced antitumor activity in DOHH2 cell-derived FL xenograft models. Similarly, enhanced activity was achieved in DLBCL xenograft models derived from OCI-LY1 cells. Interestingly, in OCI-LY1 xenografts, the combination treatment achieved a 100 % response rate, which include partially (PR) and complete tumor regression (CR), with ~80 % of CR and ~20 % of PR recorded. Durable response was continuously observed till the end of the study after dose suspension. Pharmacokinetic studies revealed that there were no significant changes in drug concentrations between single agents and the combination treatment, suggesting there was no drug-drug interaction between these two agents. On-target pharmacodynamic (PD) modulations of BTK and apoptosis pathways were observed in corresponding tumor tissues co-treated with ibrutinib and APG-2575. An increase in the levels of cleaved PARP-1 protein was observed under the combination treatment suggesting enhanced induction of apoptosis occurred, which may be the biological event contributing to the synergistic effect of the combination treatment. In summary, our study suggests that APG-2575 may be applied to the combination therapy with ibrutinib in the treatment of FL and DLBCL. Citation Format: Douglas D. Fang, Guoqin Zhai, Shoulai Gu, Ran Tao, Qiuqiong Tang, Ping Min, Qixin Wang, Dongmei Yang, Jiaxing Gu, Yinfeng Li, Dingxiong Chen, Jiajun Li, Guangfeng Wang, Dajun Yang, Yifan Zhai. BCL-2 selective inhibitor APG-2575 synergizes with BTK inhibitor in preclinical xenograft models of follicular lymphoma and diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2058.