KI-ARv-03 is a potent and selective ATP-competitive CDK9 inhibitor with an IC50 of 0.15 μM (in the presence of 45 μM ATP), demonstrating over 130-fold selectivity for CDK9 over other CDKs (including CDK1-7). It reduces AR-driven transcription and proliferation in prostate cancer cells and is applicable for research on leukemia, pancreatic cancer, alveolar rhabdomyosarcoma (ARMS), and castration-resistant prostate cancer (CRPC). Additionally, KI-ARv-03 serves as a ligand for target protein for PROTAC and is used in the synthesis of PROTAC KI-CDK9d-32[1][2].

CDK9:0.15 μM

KI-ARv-03 binds to the ATP pocket of CDK9, creating essential interactions with the hinge residues Glu107, His108, and the DFG motif's Asp109. At a concentration of 5 μM over 18 hours, it selectively suppresses AR-V7 transcript in VCaP-16 and 22Rv1 cells, resulting in KLK3 downregulation only in VCaP-16 cells without affecting AR-FL. KI-ARv-03 exhibits dose-dependent antiproliferative activity (GR₅₀ = 1.52 μM in MV-4-11; GR₅₀ = 3.26 μM in 22Rv1) and induces stronger apoptosis in MV-4-11 AML cells, indicating an increased sensitivity to CDK9 inhibition in hematologic malignancies. At 0-40 μM for 1 hour, it acts directly on CDK9 but not on AR species, suggesting it affects AR levels by diminishing CDK9 enzymatic activity. Within a range of 0.5-10 μM for 1-48 hours, it dose-dependently reduces RNA Pol II (pSer2/pSer7) levels in 22Rv1 cells, and time-dependently lowers AR-FL, AR-V7, and AR (pSer81) levels, aligning with its role in CDK9-mediated transcriptional regulation at the AR locus. At 5 μM for 6-24 hours, KI-ARv-03 triggers AR protein depletion through the proteasome pathway, a mechanism confirmed by rescue from degradation via MG132, linking CDK9 inhibition with AR protein stability. Lastly, KI-ARv-03 inhibits the proliferation of MOLT-4, PSN-1, and RH-4 cells in a dose-dependent manner, with IC₅₀ values ranging from 279.2 nM to 9.99 μM.