Mediator kinase inhibition exposes a transcriptional vulnerability and primes AML for venetoclax sensitivity

Acute myeloid leukemia (AML) is a heterogeneous and aggressive hematologic malignancy associated with poor survival despite recent therapeutic advances. To identify novel anti-leukemic agents, we performed a high-throughput viability screen of 10,000 small molecules across 56 genetically diverse primary AML samples. Compounds with similar activity profiles were grouped into Compound Correlation Clusters (CCCs), leading to the identification of CCC163, which includes AML874, as a potent and selective hit. Integrated pharmacological and CRISPR-Cas9 approaches identified the Mediator complex as the molecular target of AML874. We demonstrate that AML874 acts as a selective CDK8/CDK19 inhibitor, disrupting Mediator-dependent transcription. FLT3-mutated AML showed increased sensitivity to AML874, suggesting a subtype-specific vulnerability. Notably, CDK8 inhibition synergized with venetoclax in AML cell lines and patient-derived xenograft models, resulting in enhanced anti-leukemic activity in vivo. Together, these findings identify AML874 as a promising therapeutic candidate and highlight CDK8/CDK19 inhibition as a potential strategy in AML.