Development of small cyclic peptides targeting the CK2α/β interface

CK2 is a ubiquitous protein kinase, with key roles in the regulation of cell growth and proliferation. In particular, CK2 acts as an anti-apoptotic protein and is found to be overexpressed in multiple cancer types. To this end, the inhibition of CK2 is of great interest with regard to the development of novel anti-cancer therapeutics. ATP-site inhibition of CK2 is possible; however, this typically results in poor selectivity due to the highly conserved nature of the catalytic site amongst kinases. An alternative methodology for the modulation of CK2 activity is to inhibit the formation of the holoenzyme complex. This is possible, with the most notable example being CAM7117. However, CAM7117 contains unnatural amino acids, residues not directly involved in the binding to CK2, and its size limits further optimisations. In this work, an iterative cycle of enzymatic assays, X-ray crystallography, molecular modelling and cellular assays were used to develop a functionalisable chemical probe for the CK2α/β PPI. The lead peptide, P8C9, successfully binds to CK2α at the protein-protein interaction site, is easily synthesisable and functionalisable, highly stable in serum and small enough to accommodate further optimisation. Furthermore, its cell-permeable analogues, TAT-P8C9 and R3-P8C9, successfully inhibit cell proliferation. TAT-P8C9 and R3-P8C9 can serve as true chemical probes to further understand the intracellular pathways involving CK2, as well as aiding the development of novel CK2 PPI inhibitors for therapeutic use.