Human exosomes as natural carriers of protein kinase CK2 inhibitors and degraders in targeted anticancer therapy

• Applicant: Professor Dr. Stefan Knapp
• Subject Area: Pharmacy ; Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564760996

The constitutively active kinase CK2 is overexpression in various cancers, particularly prostate, breast, lung cancers and in hematological cancers. Its high activity in cancer cells has been associated with suppression of the programmed cell death, suggesting a protective role of this kinase promoting cell survival. Inhibition of CK2 by chemical inhibitors has been shown to induce apoptosis in cells, indicating CK2 as a promissing target for new therapies. Among ATP-competitive inhibitors, small molecules that form halogen bonds with the kinase hinge region, such as TBBt and similar compounds have been a focus in our research group. However, a challenge with these inhibitors is their low selectivity due to high sequence conservation within the kinase ATP binding pocket. To address this, allosteric inhibitors of CK2 have been developed. We have recently obtained a highly selective chemical probe, SGC-CK2-1, which surprisingly did not reveal growth inhibition screening a comprehensive panel of cancer cell lines. A promising strategy for developing more selective CK2 inhibitors is to target binding pockets outside of the conserved ATP binding site. We and others have developed CK2α inhibitors with nanomolar binding constants, demonstrating improved selectivity compared to TBBi and TBBt derivatives. Allosteric inhibitors targeting a unique pocket adjacent to the ATP binding site show enhanced antiproliferative activity, suggesting that CK2 inhibitors for oncology should also target CK2’s scaffolding functions. In this project, we plan to develop 2 series of CK2 inhibitors: one targeting the orthosteric site and another combining ortho-steric inhibitors with compounds targeting the αD-out allosteric pocket. Additionally, we will explore degraders (PROTACs) that will investigate the consequences of inhibiting all CK2 function through selective degradation. To enable PROTACs development, we have established cell-based assays that track degradation pathways and sensors like HiBIT-based assays to monitor protein degradation. A click chemistry library of commonly used E3 ligands and linker moieties allows rapid development of PROTACs using alkine derivatives of established inhibitors. These PROTACs can be directly screened in cells using HiBIT sensor cell lines. Our research hypothesis posits that encapsulating CK2 inhibitors and PROTACs in extracellular vesicles can improve their bioavailability and anti-cancer properties. The project will focus on optimizing conditions for synthesizing novel CK2 inhibitors and evaluating their anti-cancer potential in breast, prostate, colon cancer, and leukemic cell lines. We will also investigate the effects of exosomes produced by HEK293T cells on patient-derived cells and organoids that mimic the cancer microenvironment. The main goal is to establish the best targeting and delivery strategies for CK2 chemical modulators to create translational studies of CK2 inhibitors in oncology.

• DFG Programme: Research Grants
• International Connection: Poland
• Cooperation Partner: Dr. Particja Joanna Winska