Difluoro analogue of UCS15A triggers activation of exogenously expressed c-Src in HCT 116 human colorectal carcinoma cells

UCS15A, an antibiotic produced by Streptomyces sp., has been reported to specifically disrupt SH3 domain-mediated interactions in eukaryotic cells. Interestingly, in the case of the non-receptor tyrosine kinase Src, UCS15A was effective in suppressing the SH3 domain-mediated intermolecular rather than intramolecular interactions, and thus prevented Src interactions with certain downstream effectors without affecting Src kinase activity. Here the synthesis of a novel difluoro analogue of UCS15A is described. The effects of this compound (8) on Src activity were tested in HCT 116 colorectal carcinoma cells engineered for inducible expression of c-Src. The presence of compound (8) resulted in the increased activity of the induced c-Src implicating that (8) acts as a c-Src activator in vivo. These observations are supported by computer modelling studies which suggest that the aldehyde group of (8) may covalently bind to a lysine residue in the SH2-kinase linker region situated in the proximity of the SH3 domain, which could promote a conformational change resulting in increased Src activity.