Design of CK2β-mimicking peptides as tools to study the CK2α/CK2β interaction in cancer cells.

The ubiquitously expressed Ser/Thr kinase CK2 is a key regulator in a variety of key processes in normal and malignant cells. Due to its distinctive anti-apoptotic and tumor-driving properties, elevated levels of CK2 have frequently been found in tumors of different origin. In recent years, development of CK2 inhibitors has largely been focused on ATP-competitive compounds; however, targeting the CK2α/CK2β interface has emerged as a further concept that might avoid selectivity issues. In order to address the CK2 subunit interaction site, we have synthesized halogenated CK2β-mimicking cyclic peptides modified with the cell-penetrating peptide sC18 to mediate cellular uptake. We investigated the binding of the resulting chimeric peptides to recombinant human CK2α using a recently developed fluorescence anisotropy assay. The iodinated peptide sC18-I-Pc was identified as a potent CK2α ligand (Ki = 0.622 µM). It was internalized in cells to a high extent and exhibited significant cytotoxicity towards cancerous HeLa cells (IC50 = 37 µM) in contrast to non-cancerous HEK-293 cells. The attractive features and functionalities of sC18-I-Pc offer the opportunity for further improvement.