Compound 56, 4-[(3-Bromophenyl)amino]-6,7-diethoxyquinazoline, is a potent and specific inhibitor of the tyrosine kinase of the epidermal growth factor receptor (EGFR) showing an IC₅₀ of 0.006 nM. It competitively binds at the adenosine-triphosphate (ATP) site of EGFR. Compound 56 is capable of inhibiting the phosphorylation of EGF-dependent EGFR, suppressing the proliferation and clonogenicity of a wide panel of EGFR-overexpressing human cancer lines, and blocking EGF-mediated mitogenesis and oncogenic transformation in fibroblasts overexpressing EGFR. Besides inhibiting EGFR tyrosine kinase, It also inhibits the tyrosine kinase of human epidermal growth factor receptor 2 (HER2/neu) but with a less potency.

Reference

Bridges AJ, Zhou H, Cody DR, Rewcastle GW, McMichael A, Showalter HD, Fry DW, Kraker AJ, and Denny WA. Tyrosine kinase inhibitors. 8. An unusually steep structure-activity relationship for analogues of 4-(3-bromoanilino)-6,7-dimethoxyquinazoline (PD 153035), a potent inhibitor of the epidermal growth factor receptor.J Med Chem 1966; 39 (1): 267-276

Monique Bos, Jhn Mendelsohn, Young-Mee Kim, Joan Albanell, David W. Fry, and Jose Baelga. PD153035, a tyrosine kinase inhibitor, prevents epidermal growth factor receptor activation and inhibits growth of cancer cells in a receptor number-dependent manner. Clin Cancer Res 1997;3:2099-2106