2-Aminothiazole Derivatives as Selective Allosteric Modulators of the Protein Kinase CK2. 1. Identification of an Allosteric Binding Site

Abstract

CK2 is a ubiquitous Ser/Thr protein kinase involved in the control of various signaling pathways and is known to be constitutively active. In the present study, we identified aryl 2-aminothiazoles as a novel class of CK2 inhibitors, which displayed a non-ATP-competitive mode of action and stabilized an inactive conformation of CK2 in solution. Enzyme kinetics studies, STD NMR, circular dichroism spectroscopy, and native mass spectrometry experiments demonstrated that the compounds bind in an allosteric pocket outside the ATP-binding site. Our data, combined with molecular docking studies, strongly suggested that this new binding site was located at the interface between the αC helix and the flexible glycine-rich loop. A first hit optimization led to compound 7, exhibiting an IC 50 of 3.4 μM against purified CK2α in combination with a favorable selectivity profile. Thus, we identified a novel class of CK2 inhibitors targeting an allosteric pocket, offering great potential for further optimization into anticancer drugs.

2-Aminothiazole Derivatives as Selective Allosteric Modulators of the Protein Kinase CK2. 2. Structure-Based Optimization and Investigation of Effects Specific to the Allosteric Mode of Action

“…The preliminary Structure-Activity Relationships (SAR) obtained from a small series of analogs of the original hit compound 1 (Figure 1) had suggested that the three aryl ring system as well as the carboxylic acid function are needed for CK2α inhibition. 20 In order to gain further insight into essential key features and to optimize the inhibitory potency, we synthesized a targeted set of derivatives to systematically explore the SAR around the new scaffold. First, we varied the position and number of the essential carboxyl function (compounds 9 and 30, Table 1).…”

“…Figure 1). 20 We also synthesized and tested the pyridinyl derivative 17 in order to explore more polar heterocycles with a ring dipole moment similar to the nitrophenyl compound. However, the measured IC 50 value of 19 µM was unfavorable, suggesting that the polar H-bond acceptor nitrogen in the ring is not complementary to the electrostatic potential of the binding pocket.…”

“…On the other hand, some of the bicyclic aromatic systems were good substitutes for the potentially unstable or toxic 3-bromophenyl moiety, with the naphthalenyl derivative 19 being the most potent (Table 2). More polar bicycles, such as chromene (20) and 2-benzofuran (21), were less active than 19, underlining the preference of a hydrophobic aromatic moiety by this part of the binding pocket. Interestingly, a plain thiophene ring (18, IC 50 = 5 µM) led to an almost twofold increase of potency compared with the original phenyl congener (3, Figure 1).…”

“…Figure 4) with docking simulations both carried out with the isolated CK2α subunit, we selected PDB entry 3FWQ for further docking studies. The docking poses with the ten highest scores were evaluated for plausibility taking into account all previous results 20 : i) the binding pocket is located close to the ATP binding site without or with only marginal overlap; ii) the binding pocket is delimited by residues Val73, Lys74 and Lys77; iii) the observed pose fits to the STD-NMR-based binding epitope mapping as previously determined with 4. The most consistent binding model of 19 in the 3FWQ structure (Chain B) displayed a tight fitting of the naphthalene ring in the hydrophobic pocket, with an additionally fixed orientation due to a double CH-π interaction of Gly177 with the naphthalene cycle ( Figure 5A).…”

Synthesis and Evaluation of Aminothiazole Derivatives as Hedgehog Pathway Inhibitors

“…Acylthiourea and aminothiazole are the bioisosteres in accordance with conceptual cyclization principle. Moreover, aminothiazole is a well‐known pharmacophore with diverse biological properties, for instance, neuroprotection, anti‐inflammation, antibacterial and anticancer . We envision that aminothiazole as linker in our target compounds will enhance their selectivity and affinity with Hh‐related receptors.…”