Breast cancer cell proliferation and migration are inhibited by naturally extracted trans-(-)-kusunokinin. However, three additional enantiomers of kusunokinin have yet to be investigated: trans-(+)-kusunokinin, cis-(-)-isomer and cis-(+)-isomer. According to the results of molecular docking studies of kusunokinin isomers on 60 breast cancer-related proteins, trans-(-)-kusunokinin was the most preferable and active component of the trans-racemic mixture. Trans-(-)-kusunokinin targeted proteins involved in cell growth and proliferation, whereas the cis-(+)-isomer targeted proteins involved in metastasis. Trans-(-)-kusunokinin targeted CSF1R specifically, whereas trans-(+)-kusunokinin and both cis-isomers may have bound AKR1B1. Interestingly, the compound's stereoisomeric effect may influence protein selectivity. CSF1R preferred trans-(-)-kusunokinin over trans-(+)-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 trans-(-)-kusunokinin, trans-(+)-kusunokinin and pexidartinib bound CSF1R differently. Pexidartinib had the highest binding affinity, followed by trans-(-)-kusunokinin and trans-(+)-kusunokinin, respectively. The trans-(-)-kusunokinin-CSF1R complex was found to be stable, whereas trans-(+)-kusunokinin was not. Trans-(±)-kusunokinin, a potential racemic compound, could be developed as a selective CSF1R inhibitor when combined.
Keywords: CSF1R inhibitor; kusunokinin isomers; molecular dynamics simulation; stereoselectivity; trans-(−)-kusunokinin; virtual screening.