3,4-Diaryl-isoxazoles and -imidazoles as Potent Dual Inhibitors of p38α Mitogen Activated Protein Kinase and Casein Kinase 1δ

Abstract

In this study, we report on the discovery of isoxazole 1 as a potent dual inhibitor of p38alpha (IC(50) = 0.45 microM) and CK1delta (IC(50) = 0.23 microM). Because only a few effective small molecule inhibitors of CK1 have been described so far, we aimed to develop this structural class toward specific agents. Molecular modeling studies comparing p38alpha/CK1delta suggested an optimization strategy leading to design, synthesis, biological characterization, and SAR of highly potent compounds including 9 (IC(50) p38alpha = 0.006 microM; IC(50) CK1delta = 1.6 microM), 13 (IC(50) p38alpha = 2.52 microM; IC(50) CK1delta = 0.033 microM), 17 (IC(50) p38alpha = 0.019 microM; IC(50) CK1delta = 0.004 microM; IC(50) CK1epsilon = 0.073 microM), and 18 (CKP138) (IC(50) p38alpha = 0.041 microM; IC(50) CK1delta = 0.005 microM; IC(50) CK1epsilon = 0.447 microM) possessing differentiated specificity. Selected compounds were profiled over 76 kinases and evaluation of their cellular efficacy showed 18 (CKP138) to be a highly potent and dual-specific inhibitor of CK1delta and p38alpha.

Impaired CK1 Delta Activity Attenuates SV40-Induced Cellular Transformation In Vitro and Mouse Mammary Carcinogenesis In Vivo

“…The kinase activity in kinase peak fractions was also analyzed in the presence of CK1 specific inhibitors IC261 [43] or compound 17, which inhibits specifically CK1δ in the lower nanomolar range [44]. Phosphorylated proteins were separated by SDS-PAGE and the protein bands were visualized on dried Coomassie stained gels by autoradiography.…”

The CK1 Family: Contribution to Cellular Stress Response and Its Role in Carcinogenesis

“…A conserved glycine-rich loop (P-loop, bridging strands β1 and β2) forms the ceiling of the ATP active site and contributes to coordination of the γ-phosphate moiety of ATP (30). Contributing to structure-based inhibitor design, another loop (L-78) in close proximity to the hinge region has been demonstrated to trigger CK1 inhibitor selectivity (31). Within the C-terminal region, a specific phosphate moiety binding motif (W1) has been identified affording recognition of phosphorylated protein substrates and is further believed to be involved in CK1 regulatory interactions (9, 24, 25).…”

“…Moreover, loops L-9D and L-EF may be of importance in substrate recognition (Figure 1C) (24–27). The ATP active site itself mainly consists of a deep hydrophobic pocket (HPI, selectivity pocket) lined by the gatekeeper (Met-82 in CK1δ) and a second spacious hydrophobic region (HRII) adjacent to the hinge region as well as sugar and phosphate binding domains (Figure 1D) (31). …”

“…Furthermore, several roscovitine-derivatives, among them (R)-DRF053, have been shown to inhibit both CK1 and CDK family members (360). In 2009, imidazole- (compounds 17 and 18) and isoxazole-derivatives have been found to be highly potent inhibitors for CK1δ and ε (31). Furthermore, a 2-phenylamino-6-cyano-1 H -benzimidazole derivate (compound 1h) was identified as CK1γ-specific inhibitor with excellent selectivity, cellular potency, and acceptable pharmacokinetic properties (368).…”

Pharmacophore Design of p38α MAP Kinase Inhibitors with Either 2,4,5-Trisubstituted or 1,2,4,5-Tetrasubstituted Imidazole Scaffold

“…[25] 2009 Molecular modeling studies, design, synthesis and biological characterization of isoxazole as a potent dual inhibitor of p38 and CK1 delta. [26] 2008 Evaluation of imidazole derivatives containing a 4-fluorophenyl group, a pyrimidine ring, and a CN-or CONH2-substituted benzyl moiety as p38 inhibitors. [27] 2008 Rational design, synthesis, and SAR studies of a novel class of p38 inhibitors based on a benzothiazole ring system.…”