Integrated Multi-Omics and Interactome Analysis of CDK8 Inhibition Reveals Erythroid Differentiation Programs and Therapeutic Synergy with BET Blockade in AML.

Acute myeloid leukaemia (AML) is a therapeutically challenging malignancy driven by the self-renewal, quiescence, and therapy resistance of leukaemic stem cells (LSCs). CDK8, a kinase component of the Mediator complex, regulates oncogenic transcription, and the selective CDK8/CDK19 inhibitor RVU120 (Romaciclib) targets AML cells with CD34+/pSTAT5-high LSC-like characteristics; however, the epigenetic and transcriptional consequences of CDK8 blockade and actionable combinatorial strategies remain incompletely defined. Using the TEX cell line, an LSC-enriched surrogate model, we performed time-resolved RNA-seq, whole-proteome and phosphoproteomics mass spectrometry (MS), and CUT&Tag chromatin profiling following treatment with RVU120 and CCT251921. CDK8 protein-protein interactions were mapped by co-immunoprecipitation MS across five AML models, and synergy with Pelabresib (BET inhibitor) or CB6644 (RUVBL1/2 inhibitor) was assessed by high-content screening in three cell lines and three patient-derived xenograft (PDX) models. Both inhibitors suppressed STAT5 phosphorylation, induced loss of the CD34+/CD38- LSC-enriched phenotype, and drove erythromegakaryocytic differentiation. Transcriptomic and proteomic responses were concordant, and CDK8 inhibition triggered widespread enhancer activation with redistribution of RNAP2, BRD3, and NFRKB. CDK8 combined with Pelabresib acted synergistically in MOLM-16 cells and two of three PDX models. These findings identify CDK8 as a transcriptional node of LSC-associated programs and provide a mechanistic rationale for combined CDK8-BET inhibition in molecularly defined AML subsets, which will require validation in functional LSC assays and primary specimens.