Discovery of Non-peptide Small Molecule Allosteric Modulators of the Src-family Kinase, Hck

The eight mammalian Src-family tyrosine kinases are dynamic, multi-domain structures, which adopt distinct “open” and “closed” conformations. In the closed conformation, the regulatory SH3 and SH2 domains pack against the back of the kinase domain, providing allosteric control of kinase activity. Small molecule ligands that engage the regulatory SH3-SH2 region have the potential to modulate Src-family kinase activity for therapeutic advantage. Here we describe an HTS-compatible fluorescence polarization assay to identify small molecules that interact with the unique-SH3-SH2-linker (U32L) region of Hck, a Src-family member expressed exclusively in cells of myeloid lineage. Hck has significant potential as a drug target in acute myeloid leukemia, an aggressive form of cancer with substantial unmet clinical need. The assay combines recombinant Hck U32L protein with a fluorescent probe peptide that binds to the SH3 domain in U32L, resulting in an increased FP signal. Library compounds that interact with the U32L protein and interfere with probe binding reduce the FP signal, scoring as hits. Automated 384-well high-throughput screening of 60,000 compounds yielded Z'-factor coefficients > 0.7 across nearly 200 assay plates, and identified a series of hit compounds with a shared pyrimidine diamine substructure. Surface plasmon resonance assays confirmed direct binding of hit compounds to the Hck U32L target protein as well as near-full-length Hck. Binding was not observed with the individual SH3 and SH2 domains, demonstrating that these compounds recognize a specific three-dimensional conformation of the regulatory regions. This conclusion is supported by computational docking studies, which predict ligand contacts with a pocket formed by the juxtaposition of the SH3 domain, the SH3-SH2 domain connector, and the SH2-kinase linker. Each of the four validated hits stimulated recombinant, near-full-length Hck activity in vitro, providing evidence for allosteric effects on the kinase domain. These results provide a path to discovery and development of chemical scaffolds to target the regulatory regions of Hck and other Src family kinases as a new approach to pharmacological kinase control.

Escitalopram for the management of major depressive disorder: a review of its efficacy, safety, and patient acceptability

Escitalopram (escitalopram oxalate; Cipralex(®), Lexapro(®)) is a selective serotonin reuptake inhibitor (SSRI) used for the treatment of major depressive disorder (MDD) and anxiety disorder. This drug exerts a highly selective, potent, and dose-dependent inhibitory effect on the human serotonin transport. By inhibiting the reuptake of serotonin into presynaptic nerve endings, this drug enhances the activity of serotonin in the central nervous system. Escitalopram also has allosteric activity. Moreover, the possibility of interacting with other drugs is considered low. This review covers randomized, controlled studies that enrolled adult patients with MDD to evaluate the efficacy of escitalopram based on the Montgomery-Asberg Depression Rating Scale and the Hamilton Depression Rating Scale. The results showed that escitalopram was superior to placebo, and nearly equal or superior to other SSRIs (eg, citalopram, paroxetine, fluoxetine, sertraline) and serotonin-noradrenaline reuptake inhibitors (eg, duloxetine, sustained-release venlafaxine). In addition, with long-term administration, escitalopram has shown a preventive effect on MDD relapse and recurrence. Escitalopram also showed favorable tolerability, and associated adverse events were generally mild and temporary. Discontinuation symptoms were milder with escitalopram than with paroxetine. In view of the patient acceptability of escitalopram, based on both a meta-analysis and a pooled analysis, this drug was more favorable than other new antidepressants. The findings indicate that escitalopram achieved high continuity in antidepressant drug therapy.