Structure-based Discovery of Novel CK2α-Binding Cyclic Peptides with Anti-cancer Activity.

Protein kinase CK2 is considered as an emerging target in cancer therapy, and recent efforts have been made to develop its ATP-competitive inhibitors, but achieving selectivity with respect to related kinases remains challenging because of the highly conserved ATP-binding pocket of kinases. Non-ATP competitive inhibitors might solve this challenge; one such strategy is to identify compounds that target the CK2α/CK2β interface as CK2 holoenzyme antagonists. Here we improved the binding affinity to CK2α and cell-based anti-cancer activity of a CK2β-derived cyclic peptide (Pc) by combining structure-based computational design with experimental evaluation. By analyzing molecular dynamics simulations of Pc bound to CK2α, a series of Pc-derived peptides was rationally designed and synthesized to evaluate their binding affinity to CK2α, as well as anti-proliferative and pro-apoptotic effects against HepG2 cancer cell line. One amino acid substitutions on Pc, I192F, exhibited over 10-fold improvement in the predicted binding affinity to CK2α when compared to Pc, and a cell-permeable version, I192F-Tat, also demonstrated more potent anti-proliferative and pro-apoptotic effects against HepG2 compared to Pc. A second modification of Pc, H193W, also led to more potent cell-based activity, despite having weaker binding affinity (∼5×) to CK2α. The discovery of the I192F and H193W peptides provides new insights for further optimization of CK2 antagonist candidates as anti-cancer leads.