br Experimental br Declaration of interest br
Declaration of interest
Material and methods
Results and discussion
Conclusion By screening the NMR Oxaliplatin library an initial hit was found for an inhibitor of the PPI between the α-β subunits of CK2 with an IC50 of 900 μM. This compound was modified and elaborated through several vectors. Through five iterations, 63 compounds were synthesised and tested against CK2. Through the first three iterations (elaborating at each of the vectors highlighted in Fig. 2), it was found that a series of biaryl compounds were the best inhibitors of the PPI with the lead compound at that stage (2) giving an IC50 of 150 μM. Realising this trend additional biaryl compounds were screened against CK2 to give the lead compound, CAM187 (7). These compounds affect their binding by the biaryl part of the molecule filling the PPI pocket on the protein and the pendent ammonium group forming an H-bond with an Asp37 above the pocket. CAM187 is the first small molecule fragment to inhibit the α-β interface of CK2 without also binding in the ATP site. Due to its fragment-like properties, CAM187 leaves room for further development. These developments could lead to drug-like molecules with high potency and selectivity against CK2 as well as deeper understanding between the structure activity relationship.
Acknowledgments We would like to thank the X-ray crystallographic facility and the Biophysics facility at the Department of Biochemistry for support and access to equipment. We thank Diamond Light Source for access to beamlines. Instant JChem was used for structure database management and searching, Instant JChem 18.104.22.168, 2016, ChemAxon (http://www.chemaxon.com). This work was funded by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no [279337/DOS] (to DRS) and the Wellcome Trust Strategic (090340/Z/09/Z) and Pathfinder (107714/Z/15/Z) Awards (to DRS and MH). In addition, the Spring group research was supported by grants from the Engineering and Physical Sciences Research Council, Biotechnology and Biological Sciences Research Council, Medical Research Council and the Royal Society. JI would like to thank Trinity College, University of Cambridge for funding.
Introduction DNA-targeted anti-cancer chemotherapeutics are fundamental components of the most effective chemotherapeutics in clinic. The effect of such DNA-targeted agent like cisplatin has been demonstrated to function via initiating DNA damage to induce cell death , , which can be survived by repairing DNA lesions, potentially leading to innate or acquired drug resistance , , . Thus, a practical approach to reduce the resistance caused by DNA-targeted agents is to combine them with inhibitors , particularly those to inhibit multiple DNA repair pathways to increase the sensitivity of cancer cells to platinum-based chemotherapies . Protein kinase CK2, consisted of two catalytic subunits (α and α′) and two regulatory β subunits, is widely overexpressed in human tumors , . As a key regulator of various cellular events, CK2 could generally regulate diverse pathways in various chemotherapeutics-induced resistance , , , . More importantly, CK2 could be dimed as a key director in DNA repair of both single-strand break (SSB) and double-strand break (DSB) , , . Among the basic components of DNA damage repair pathways, the key proteins XRCC1 and MDC1 are two of the best characterized substrates of the CK2-dependent SSB and DSB repair, respectively. As required for the rapid and slight SSB repair, XRCC1 could be phosphorylated by CK2 at S/T residues in amino acid sequence 403–538 , , . It is well known that SSB-mediated ataxia telangiectasia mutated kinase (ATM) activation is followed by a G1 cell cycle delay that allows more time for repair and thus prevents DNA replication and DSB accrual . Moreover, ATM activation is critical to distinguish SSBs from DSBs. Whereas, the strengthened resistance was associated with a slow and heavy repair of DSB, which was the most damaging form of DNA lesions . As a key mediator of DSB repair, MDC1, activated by CK2 at N-terminal S-D-T-D motifs, can co-localize with aprataxin FHA domain and then bind to γ-H2AX , , , . Thus, DNA damage repair pathways could be destructed by the inhibitors of CK2. Despite several ATP-competitive CK2 inhibitors have been discovered so far, only one of them, CX-4945, as an orally bioavailable selective inhibitor, entered phase II clinical trials to act as a potential anti-cancer drug . Based on that, the approach of combing cisplatin with CX-4945 in a molecule may have the potential superiority to reverse cisplatin-induced resistance.