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The EGFR is a Mr 170,000 transmembrane glycoprotein with an external binding domain and an intracellular tyrosine kinase domain. Gefitinib (ZD-1839, Iressa) is an Epidermal Growth Factor Receptor-selective Tyrosine Kinase Inhibitor.

In vitro: Gefitinib inhibited colony formation in soft agar in a dose dependent manner in all cancer cell lines. However, treatment with higher doses resulted in a 2–4-fold increases in apoptosis. Dose-dependent supra-additive increase in growth inhibition was observed when cancer cells were treated with totoxic drugs and Gefitinib. The combined treatment markedly enhanced apoptotic cell death induced by single agent treatment [1].

In vivo: Gefitinib treatment of nude mice bearing established human GEO colon cancer xenografts revealed a reversible dose-dependent inhibition of tumor growth because GEO tumors resumed the growth rate of controls at the end of the treatment [1].

Clinical trial: Administration of a 250-mg dose of gefitinib as a dispersion preparation by drink or nasogastric tube achieved a systemic exposure to gefitinib that was consistent with that achieved when gefitinib was administered as a whole tablet. No evidence of tolerability problems associated with the routes of administration studied was observed in these healthy volunteers [2].

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