Tyrphostin AG 538 is a chalcone compound, an IGF-1 receptor kinase inhibitor (IC₅0 : for 400 nM) that is potent, cell-permeable, reversible, and competitive.

IGF-1:400 nM, NS3-DNA complex:3.6 μM

Experimentally it is indeed found that AG 538 does not compete with ATP but competes with the IGF-1R substrate. Both AG 538 and I-OMe AG 538 inhibit IGR-1R autophosphorylation in intact cells in a dose-dependent manner. Both compounds inhibit the activation of the downstream targets PKB and Erk2.[1]

Typical assays used to discover and analyze small molecules that inhibit the hepatitis C virus (HCV) NS3 helicase yield few hits and are often confounded by compound interference. FP-based assay was chosen to screen Sigma's Library of Pharmacologically Active Compounds (LOPAC) for compounds that inhibit NS3-DNA complex formation. Four LOPAC compounds inhibited the FP-based assay: aurintricarboxylic acid (ATA) (IC50=1.4 μM), suramin sodium salt (IC50=3.6 μM), NF 023 hydrate (IC50=6.2 μM) and tyrphostin AG 538 (IC50=3.6 μM).[2]