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== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
Protein kinase CK2, a member of the eukaryotic protein kinase superfamily, is associated with cancer and other human pathologies and thus an attractive drug target. The indeno[1,2-b]indole scaffold is a novel lead structure to develop ATP-competitive CK2 inhibitors. Some indeno[1,2-b]indole-based CK2 inhibitors additionally obstruct ABCG2, an ABC half transporter overexpressed in breast cancer and co-responsible for drug efflux and resistance. Comprehensive derivatization studies revealed substitutions of the indeno[1,2-b]indole framework that boost either the CK2 or the ABCG2 selectivity or even support the dual inhibition potential. The best indeno[1,2-b]indole-based CK2 inhibitor described yet (IC50 = 25 nM) is 5-isopropyl-4-(3-methylbut-2-enyl-oxy)-5,6,7,8-tetrahydroindeno[1,2-b]indole-9,10 -dione (4p). Herein, we demonstrate the membrane permeability of 4p and describe co-crystal structures of 4p with CK2alpha and CK2alpha', the paralogs of human CK2 catalytic subunit. As expected, 4p occupies the narrow, hydrophobic ATP site of CK2alpha/CK2alpha', but surprisingly with a unique orientation: its hydrophobic substituents point towards the solvent while its two oxo groups are hydro-gen-bonded to a hidden water molecule. An equivalent water molecule was found in many CK2alpha structures, but never as a critical mediator of ligand binding. This unexpected binding mode is independent of the interdomain hinge/helix alphaD region conformation and of the salt content in the crystallization medium.
CK2alpha and CK2alpha' are the two isoforms of the catalytic subunit of human protein kinase CK2, an important target for cancer therapy. They have similar, albeit not identical functional and structural properties, and were occasionally reported to be inhibited with distinct efficacies by certain ATP-competitive ligands. Here, we present THN27, an indeno[1,2-b]indole derivative, as a further inhibitor with basal isoform selectivity. The selectivity disappears when measured using CK2alpha/CK2alpha' complexes with CK2beta, the regulatory CK2 subunit. Co-crystal structures of THN27 with CK2alpha and CK2alpha' reveal that subtle differences in the conformational variability of the interdomain hinge region are correlated with the observed effect. In the case of CK2alpha', a crystallographically problematic protein so far, this comparative structural analysis required the development of an experimental strategy that finally enables atomic resolution structure determinations with ab initio phasing of potentially any ATP-competitive CK2 inhibitor and possibly many non-ATP-competitive ligands as well bound to CK2alpha'.


Unexpected Binding Mode of a Potent Indeno[1,2-b]indole-Type Inhibitor of Protein Kinase CK2 Revealed by Complex Structures with the Catalytic Subunit CK2alpha and Its Paralog CK2alpha'.,Hochscherf J, Lindenblatt D, Witulski B, Birus R, Aichele D, Marminon C, Bouaziz Z, Le Borgne M, Jose J, Niefind K Pharmaceuticals (Basel). 2017 Dec 13;10(4). pii: ph10040098. doi:, 10.3390/ph10040098. PMID:29236079<ref>PMID:29236079</ref>
Diacritic Binding of an Indenoindole Inhibitor by CK2alpha Paralogs Explored by a Reliable Path to Atomic Resolution CK2alpha' Structures.,Lindenblatt D, Nickelsen A, Applegate VM, Hochscherf J, Witulski B, Bouaziz Z, Marminon C, Bretner M, Le Borgne M, Jose J, Niefind K ACS Omega. 2019 Mar 19;4(3):5471-5478. doi: 10.1021/acsomega.8b03415. eCollection, 2019 Mar 31. PMID:31559376<ref>PMID:31559376</ref>


From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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