Exploiting the Cryptic αD Pocket of Casein Kinase 2α (CK2α) to Deliver Highly Potent and Selective Type 1 Inhibitors

Casein kinase 2α (CK2α) is an oncology drug target that acts as a positive regulator of many tumorigenic signaling pathways. We previously reported that CK2α has a unique cryptic binding site, the αD pocket, that offers the potential for inhibitors with improved kinase selectivity. The prototype bivalent molecule CAM4066 (6) confirmed that improved selectivity could be achieved while binding in both the ATP-binding site and the αD pocket. A drug discovery project to develop a new series of bivalent CK2α inhibitors with increased cell potency and selectivity identified 61f (APL-5125), a highly potent, ATP-competitive CK2α inhibitor with exquisite kinase selectivity and cellular potency. Compound 61f demonstrates in vivo inhibition of p-AKT S129 in tumors (HCT116) following once-daily oral administration and shows a clear PK–PD relationship with unbound drug exposure. 61f has a superior preclinical profile to existing CK2α inhibitors and is currently under evaluation in patients with advanced solid tumors.