Comparative Efficacy of CK2 Inhibitors CX-4945 and SGC-CK2-2 on CK2 Signaling

The pleiotropic kinase CK2 plays a crucial role in numerous cellular processes and is frequently deregulated in human diseases. Specifically, elevated CK2 expression and/or activity have been observed in human cancers, thus rendering its inhibition a promising pharmacological strategy for treating malignancies. The most widely used CK2 inhibitor, CX-4945 (Silmitarsetib), was developed by Cylene Pharmaceuticals in 2010. It has been tested in clinical trials for various cancers and, more recently, as a potential therapy for COVID-19 patients. However, it has been demonstrated that CX-4945's specificity is limited, as CX-4945 also inhibits other kinases beyond CK2. A recently developed derivative of CX-4945, SGC-CK2-2, has demonstrated enhanced specificity compared with CX-4945, albeit with reduced potency. In this study, we conducted a detailed analysis of the effects of SGC-CK2-2 in two cancer cell lines, comparing its efficacy with CX-4945 in inhibiting CK2 signaling and in cell death induction. The findings of this study demonstrate the differential sensitivity of CK2 phospho-substrates to these inhibitors, thus indicating that complete inhibition of a single phosphosite, such as S129 Akt, is insufficient to fully suppress CK2 signaling. Furthermore, the results suggest that partial CK2 inhibition with the suppression of the most sensitive phosphosites does not significantly impact cell viability, while a near-complete suppression of CK2 signaling affects cell viability and leads to cell death induction.