Abstract 3066: A novel class of allosteric CDK8/19 inhibitors induces synthetic lethality through concurrent mTOR and c-MYC suppression and activation of p53-mediated G2/M arrest

Abstract Cancer cells exhibit dysregulated signal transduction and cell cycle control pathways that drive unchecked proliferation. Both uncontrolled tumor cell growth and the expansion of immunosuppressive macrophages contribute to tumor progression. Although PI3K and MEK inhibitors can initially suppress tumor growth, resistance frequently develops through compensatory activation of alternative signaling pathways. We have identified a novel class of allosteric tyrosine kinase receptor inhibitors that induce synthetic lethality in acute myeloid leukemia (AML), lung carcinoma, pancreatic carcinoma, and other cancers. These compounds target both tumor cells and proliferating macrophages in vitro and in vivo by concurrently inhibiting c-Myc and mTOR, while activating the stress-activated kinase JNK, leading to p53-mediated G2/M cell cycle arrest. Mechanistically, selective inhibitors containing a uniquely positioned single side chain suppress CDK8/19 activation, resulting in Myc degradation, mTOR inhibition, and phosphorylation of JNK and p38. JNK activation drives sustained ATF-2 and c-Jun signaling, leading to activation of p53, Chk1/Chk2, G2/M arrest, and apoptosis. These compounds markedly suppress tumor growth in vivo by blocking both tumor and macrophage proliferation and exhibit strong synergy with anti-PD-1 and anti-CTLA-4 immunotherapies, resulting in tumor eradication and durable immunological memory. Collectively, these findings define a new class of allosteric CDK8/19 inhibitors with potent, synthetically lethal, and immunologically synergistic anti-tumor activity, revealing a promising therapeutic avenue for overcoming resistance in cancer treatment. Citation Format: Hui Chen, Zihan Xu, Erpei Wang, Jason Rivera, Judith Varner. A novel class of allosteric CDK8/19 inhibitors induces synthetic lethality through concurrent mTOR and c-MYC suppression and activation of p53-mediated G2/M arrest abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3066.