Benzodiazepine Compounds as Inhibitors of the Src Protein Tyrosine Kinase: Screening of a Combinatorial Library of 1,4-Benzodiazepines

We screened 1680 spatially separated compounds of a diverse combinatorial library of 1,4-benzodiazepines for their ability to inhibit the kinase activity of protein tyrosine kinases Src, Yes, Abl, Lck, Csk, and fibroblast growth factor receptor. This screening yielded novel ligands for the protein tyrosine kinase Src. In the 1,4-benzodiazepine-2-one scaffold, the preferred substituent at position R1 was 4-hydroxyphenylmethyl or a 3-indolemethyl derived from a tyrosine or tyrptophan used in building the benzodiazepine, while the substituent at R2, introduced by alkylating agents, was preferably aromatic in nature. The preferred ring structure introduced on the bicyclic ring of the scaffold by acid chlorides was a p-hydroxy phenyl group. The lead compound, designated as N-l-Yaa, has a l-4-hydroxyphenylmethyl ring at R1 and a biphenylmethyl substituent at R2. The compound has an IC50 of 73 μM against Src, 2- to 6-fold lower than against other protein tyrosine kinases and >10-fold lower than against other nucleotide-utilizing enzymes. The mechanism of binding of N-l-Yaa to Src is mixed against the peptidic substrate with a Ki of 35 μM and noncompetitive against ATP-Mg with a Ki of 17 μM. Multiple inhibition analysis of the lead compound in the presence of other competitive inhibitors demonstrated that the binding of the lead compound is nonexclusive to the other competitive inhibitor. The inhibitor was found to be nontoxic to the AFB-13-human fibroblasts cells and inhibited the colony formation of HT-29 colon adenocarcinoma cells that are dependent on Src activity.