Role Of L-SPD And Dopamine Receptor Molecule And Discovery And Transformation Of KDR Inhibitors

(-)-Stepholidine (l-SPD), an active ingredient of the Chinese herb Stephania, is the first compound found to have a dual function as a dopamine receptor D1 (D1R) agonist and D2R antagonist. The preliminary dynamical behaviors of D1R and D2R and their interaction modes with l-SPD were investigated in our previous study. Recently, the pharmacological effect of l-SPD on D3R was elucidated as an antagonist. This new discovery in combination with the explosion of structural biology in GPCR superfamily prompted us to perform a more comprehensive investigation on the special pharmacological profiles of l-SPD on dopamine receptors. In this study, the integration of homology modeling, automated molecular docking, and MD simulations were used to probe the agonistic and antagonistic mechanism of l-SPD on D1R, D2R and D3R. Our analyses showed that hydrogen bonding of the hydroxyl group on the D ring of l-SPD with side chain of N6.55 which, in combination with hydrophobic stacking between 13.40, F6.44 and W6.48, is the key feature to mediate the agonist effect of l-SPD on D1R, whereas the absence of hydrophobic stacking between 13.40, F6.44 and W6.48 in D2R and D3R excludes receptor activation. Finally, the agonistic and antagonistic mechanisms of l-SPD and an activation model of D1R were proposed based on these findings. The present study could guide future experimental works on these receptors and has the significance to the design of functionally selective drugs targeting dopamine receptors.Vascular endothelial growth factor receptor 2 or KDR is a member of the VEGFR family of receptor tyrosine kinases that characteristically consists of an extracellular ligand-binding domain connected through a transmembrane segment to an intracellular tyrosine kinase domain.When activated through binding with VEGF, KDR phosphorylates tyrosine residues of downstream signaling proteins and initiates a signal transduction cascade leading to various cellular responses among which excessive and abnormal angiogenesis has been associated with various diseases, including diabetes retinopathy, age-related macular degeneration, rheumatoid arthritis, and solid tumor. Thus, it is considered that inhibiting the kinase activity of KDR is a promising strategy for the treatment of cancer and several other disorders.We describe herein the discovery of KDR inhibitors using privileged structure and kinase focused drug-likeness rule-based compound library pre-filtration and structure-based virtual screening. Our virtual screening compaign resulted in 5 hits with inhibitory activity greater than 50% against KDR at a concentration of 10 μM. Among them, compound FW-04 showed moderate IC50 of 8.1 μM and promising lead-likeness. We investigated the binding pose of FW-04 in KDR in order to guide furture structure-based optimization. Serendipitously, we found that 5 of our 30 purchased compounds also showed good inhibitory activity against the non-receptor tyrosine kinase Src. And compound FW-06 showed an IC50 of 1.2 μM against Src and excellent lead-likeness. We also describe the discovery of KDR inhibitors that feature a novel diarylurea-diaminopyrimidine (DAU-DAP) scaffold by structure-guided hybridization. Optimization of the scaffold by structure-based drug design yielded a compound 6e with an interesting IC50 of 0.1 uM against KDR.