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Abstract 2639: KB-0742 is active in preclinical MYC high models of TNBC, ovarian, and DLBCL cancers


 MYC is an early-response gene downstream of many receptor complexes, and a component that promotes several pro-growth signal transduction pathways. As a result, MYC expression is highly regulated, but once dysregulated in cancer, MYC promotes tumorigenesis via activation of cell growth, proliferation, and angiogenesis.
 CDK9 is both an upstream and downstream cofactor of MYC. CDK9 promotes MYC expression through its recruitment to super enhancers at the MYC amplicon and acts as a cofactor to drive gene expression programs.
 Previously, we profiled pan-cancer sensitivity to KB-0742, a potent, selective, and orally bioavailable small-molecule inhibitor of CDK9, and identified MYC-amplified cancers as being especially sensitive to KB-0742. To better understand the connection between MYC and KB-0742 sensitivity, 11 different tumor types were evaluated preclinically using immortalized cell lines, patient-derived cell lines (PDCs), patient-derived organoids (PDOs), and patient-derived xenografts (PDXs).
 The 11 indications included head and neck, esophageal, gastric, liver, non-small cell lung cancer (NSCLC), pancreatic, ovarian, triple-negative breast cancer (TNBC), prostate, colon, and lymphoma. For 5 of the indications (head and neck, esophageal, gastric, liver, and colon), little activity was observed in cell lines and in vivo with weak correlations to MYC amplification. TNBC, ovarian cancer, and lymphoma showed good responses to KB-0742 treatment. For TNBC and ovarian, immortalized and patient-derived cell lines indicated lower IC50 values with increased MYC amplification or expression, but the results were not statistically significant. However, in vivo assessments using 15 PDX models showed good correlation of tumor growth inhibition (TGI) and MYC amplification/expression, with some tumor regressions observed in several ovarian models. Two PDO models of TNBC with different treatment histories were also treated with KB-0742 and compared to 4 standard-of-care (SOC) compounds. KB-0742 showed much greater activity in the models, with maximal inhibition rates of 100% and 89%.
 Cell-line screens of blood cancer-derived cell lines showed that lymphocyte-derived cell lines were the most sensitive to KB-0742 as compared to all other cancer types. We tested several PDX models for response to our compound. Treatment with KB-0742 resulted in TGIs of over 50% in several lymphoma models, including a TGI of 56% in 1 model of double-hit diffuse large B-cell lymphoma.
 These data support the continual development of KB-0742, which is currently being tested in a phase 1/2 clinical trial (NCT04718675). The dose-escalation phase is opened to relapsed or refractory solid tumors or non-Hodgkin lymphoma. Once a recommend phase 2 dose is determined, we plan to open dedicated expansion arms enrolling patients with MYC over-expression/amplification within the tumor types supported by these studies.
 Citation Format: Melinda A. Day, Douglas C. Saffran, Tressa Hood, Nikolaus Obholzer, Akanksha Pandey, Charles Y. Lin, Pavan Kumar, Jorge DiMartino. KB-0742 is active in preclinical MYC high models of TNBC, ovarian, and DLBCL cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2639.