title: Gefitinib enhances the antitumor activity and oral bioavailability of irinotecan in mice.
abstract: As a single agent the ERBB1 inhibitor, gefitinib (Iressa; ZD1839) showed minimal activity against a panel of 10 pediatric tumor xenografts that do not express the ERBB1 receptor. However, combined with irinotecan (CPT-11), significantly greater than additive activity was observed in four of eight models (P < 0.05), and the combination showed enhanced activity against three additional tumor lines. Breast cancer resistance protein (ABCG2), a transporter that confers resistance to SN-38 (the active metabolite of irinotecan), was readily detected in six of nine xenograft models examined by immunohistochemistry. In vitro gefitinib potently reversed resistance to SN-38 only in a cell line that overexpressed functional ABCG2. However, overexpression of ABCG2 did not decrease accumulation nor increase the rate of efflux of [(14)C]gefitinib. On the basis of these results and the distribution of Abcg2 in mouse tissues, we assessed the ability of gefitinib to modulate irinotecan pharmacokinetics. Oral gefitinib coadministration resulted in no change in clearance of intravenously administered irinotecan. However, gefitinib treatment dramatically increased the oral bioavailability of irinotecan after simultaneous oral administration. It is concluded that gefitinib may modulate SN-38 activity at the cellular level to reverse tumor resistance mediated by ABCG2 through inhibiting drug efflux and may be used potentially in humans to modulate the oral bioavailability of a poorly absorbed camptothecin such as irinotecan.
authors.affiliation: Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
authors.forename: Clinton F
authors.initials: CF
authors.lastname: Stewart
authors.forename: Markos
authors.initials: M
authors.lastname: Leggas
authors.forename: John D
authors.initials: JD
authors.lastname: Schuetz
authors.forename: John C
authors.initials: JC
authors.lastname: Panetta
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Cheshire
authors.forename: Jennifer
authors.initials: J
authors.lastname: Peterson
authors.forename: Najat
authors.initials: N
authors.lastname: Daw
authors.forename: Jesse J
authors.initials: JJ
authors.lastname: Jenkins
authors.forename: Richard
authors.initials: R
authors.lastname: Gilbertson
authors.forename: Glen S
authors.initials: GS
authors.lastname: Germain
authors.forename: Franklin C
authors.initials: FC
authors.lastname: Harwood
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Houghton
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D000284:Administration, Oral; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000493:pharmacokinetics / Q000494:pharmacology*; D001682:Biological Availability; D001859:Bone Neoplasms / Q000188:drug therapy / Q000378:metabolism; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004357:Drug Synergism; D066246:ErbB Receptors / Q000096:biosynthesis; D005260:Female; D000077156:Gefitinib; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D008813:Mice, Inbred ICR; D016513:Mice, SCID; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D012516:Osteosarcoma / Q000188:drug therapy / Q000378:metabolism; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D009363:Neoplasm Proteins; D011799:Quinazolines; D000077146:Irinotecan; D066246:ErbB Receptors; D000077156:Gefitinib; D002166:Camptothecin