Effective treatments are urgently needed for elderly acute myeloid leukemia (AML) and relapsed or refractory diffuse large B-cell lymphoma (DLBCL) patients as only 10-25% of the population respond to standard therapies and resistance often occurred. Concurrent overexpression of anti-apoptotic BCL-2 gene and proto-oncogene MYC are frequently found in AML and DLBCL and this molecular characteristic is associated with poor prognosis of patients. CDK9 controls non-ribosomal transcription of genes including MYC and MCL-1. Dysregulation in the CDK9 pathway had been reported in AML and DLBCL, making it an attractive target for the combination with BCL-2 inhibitor to achieve more effective therapy.

To test the above hypothesis, in this study, we applied the combination of APG-2575 with a CDK9 inhibitor (alvocidib or dinaciclib) to preclinical tumor models. APG-2575 is a novel, orally bioavailable BH3-mimetic that selectively inhibits BCL-2, but not BCL-xL or MCL-1. After the treatment, synergistic effect of the combination treatment was demonstrated in mice bearing xenograft tumors of human AML or DLBCL. Specifically, in xenograft tumor models derived from human DLBCL cell line U2932, the treatment with APG-2575, alvocidib, or dinaciclib single agent for 22 days exhibited antitumor activity with T/C values of 20-50% (T/C value, average tumor volumes in treatment group vs. the vehicle control group). The combination treatment achieved substantial antitumor activity with T/C value of 5%. All animals in the combination groups showed either partial or complete tumor regression whereas none in the single arms.

Similar synergistic antitumor activity of the combination treatment was consistently observed in the myelodysplastic syndrome SKM-1 and AML OCI-AML-3 xenograft models. Taken together, our data suggest that APG-2575 and CDK9 inhibition combination has a potential therapeutic application in treatment of patients with AML and DLBCL.

Citation Format: Douglas D. Fang, Ran Tao, Qiuqiong Tang, Shoulai Gu, Guoqin Zhai, Jiajun Li, Qixin Wang, Xu Fang, Na Li, Dajun Yang, Yifan Zhai. Synergistic effect of BCL-2 inhibitor APG-2575 and CDK9 inhibitor in acute myeloid leukemia and DLBCL preclinical tumor models [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 3068.