AG-183, a member of tyrphostin, is an inhibitor of protein tyrosine kinase [1].

Protein tyrosine kinase is an enzyme that catalyzes the transfer of the γ phosphate of ATP to tyrosine residues on protein substrates. Phosphorylation of proteins by kinases is an important mechanism in signal transduction and regulating cellular activity, such as cell division. Tyrosine phosphorylation is a key covalent modification that occurs in multicellular organisms as a result of intercellular communication during embryogenesis and maintenance of adult tissues. Phosphorylation of tyrosine residues modulates enzymatic activity and creates binding sites for the recruitment of downstream signaling proteins [2].

PTK inhibitors could preferentially inhibit the epidermal growth factor (EGF) receptor kinase to block EGF-dependent cell proliferation [1]. In the human epidermoid carcinoma cell line, A431AG-183 inhibited the activity of epidermal growth factor (EGF) receptor kinase with an IC50 value of 800 nM [1].

References:
[1] Gazit A, Yaish P, Gilon C, et al. Tyrphostins I: synthesis and biological activity of protein tyrosine kinase inhibitors[J]. Journal of medicinal chemistry, 1989, 32(10): 2344-2352.
[2] Hubbard S R, Till J H. Protein tyrosine kinase structure and function[J]. Annual review of biochemistry, 2000, 69(1): 373-398.