AG 99 is primarily used in research settings to study cellular signaling pathways, particularly those involving tyrosine kinase activity. It acts as an inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, making it valuable for investigating cancer biology and potential therapeutic strategies. By blocking EGFR signaling, AG 99 helps researchers understand the role of this pathway in tumor growth and progression. It is also utilized in experiments exploring cellular differentiation, proliferation, and apoptosis. Additionally, AG 99 serves as a tool compound in drug discovery efforts aimed at developing targeted therapies for cancers driven by EGFR mutations or overexpression. Its application extends to studying the effects of EGFR inhibition in various cell lines and animal models, providing insights into resistance mechanisms and combination treatment approaches.