Discovery of pteridine-based inhibitors for the human CDC42 binding protein kinase gamma (MRCKγ)

Full text: The human CDC42 binding protein kinase gamma (MRCKγ), a serine/threonine kinase remains mostly unexplored in comparison to its related isoforms MRCKα and MRCKβ. The α and β MRCKs are involved in the regulation of actomyosin cytoskeleton, in tumorigenesis (invasiveness and metastasis) and in developmental processes (morphogenetic signaling and tissue remodeling). Meanwhile, evidence suggests that MRCKγ can modulate the maturation of dendritic spines in cortical neurons in culture and can be related to glioblastoma, in agreement with its higher expression in the peripheral nervous system. To allow better understanding of the biology of MRCKγ, and in search for selective compounds, here we report the docking studies, synthesis, selectivity profile and preliminary cellular data of pteridine scaffolds as a novel class of potent MRCKγ inhibitors. Our analysis of the Published Kinase Inhibitor Set (PKIS2) revealed a pteridine core molecule, SD208, as a potent and slight selective MRCKs inhibitor with score S(35) of 0.013, and greater affinity for MRCKγ. Supported by in-silico docking studies, a series of derivative compounds were designed and synthesized, initially ranked based on thermal stability in a differential scanning fluorimetry (DSF) assay and later by FRET-based enzymatic assay. Our chemical series was used to compose a SAR (structure-activity) analyses. The original hit SD208 still represents the most potent molecule among the series, with IC50 in nanomolar range in the enzymatic assay. Our derivative SV42 is also selective, cell-permeable and, together with SD208, show inhibition effects on cellular invasion in A172 glioblastoma cells. We are currently following up with co-crystallization attempts to guide better inhibitor design, and intend to use Sirius Beamlines for collection of the X-ray diffraction data. Also, Cryo-EM is being considered for structural determination of the full-length MRCKγ. Access to Sirius beamlines will represent a great opportunity to accelerate this and other projects from our lab with structural-activity base for inhibitors development. (author)