Potential Stereoselective Binding of -(±)-Kusunokinin and -(±)-Kusunokinin Isomers to CSF1R.

Breast cancer cell proliferation and migration are inhibited by naturally extracted -(-)-kusunokinin. However, three additional enantiomers of kusunokinin have yet to be investigated: -(+)-kusunokinin, -(-)-isomer and -(+)-isomer. According to the results of molecular docking studies of kusunokinin isomers on 60 breast cancer-related proteins, -(-)-kusunokinin was the most preferable and active component of the -racemic mixture. -(-)-kusunokinin targeted proteins involved in cell growth and proliferation, whereas the -(+)-isomer targeted proteins involved in metastasis. -(-)-kusunokinin targeted CSF1R specifically, whereas -(+)-kusunokinin and both -isomers may have bound AKR1B1. Interestingly, the compound's stereoisomeric effect may influence protein selectivity. CSF1R preferred -(-)-kusunokinin over -(+)-kusunokinin because the binding pocket required a ligand planar arrangement to form a π-π interaction with a selective Trp550. Because of its large binding pocket, EGFR exhibited no stereoselectivity. MD simulation revealed that -(-)-kusunokinin, -(+)-kusunokinin and pexidartinib bound CSF1R differently. Pexidartinib had the highest binding affinity, followed by -(-)-kusunokinin and -(+)-kusunokinin, respectively. The -(-)-kusunokinin-CSF1R complex was found to be stable, whereas -(+)-kusunokinin was not. -(±)-kusunokinin, a potential racemic compound, could be developed as a selective CSF1R inhibitor when combined.