title: The HER tyrosine kinase inhibitor CI1033 enhances cytotoxicity of 7-ethyl-10-hydroxycamptothecin and topotecan by inhibiting breast cancer resistance protein-mediated drug efflux.
abstract: Because the activities of HER family members are elevated and/or aberrant in a variety of human neoplasms, these cell surface receptors are receiving increasing attention as potential therapeutic targets. In the present study, we examined the effect of combining the HER family tyrosine kinase inhibitor CI1033 (PD 183805) with the topoisomerase (topo) I poison 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan, in a number of different cell lines. Colony-forming assays revealed that the antiproliferative effects of simultaneous treatment with CI1033 and SN-38 were synergistic in T98G glioblastoma cells and HCT8 colorectal carcinoma cells, whereas sequential treatments were additive at best. In additional studies examining the mechanistic basis for these findings in T98G cells, immunoblotting revealed that the inhibitory effects of CI1033 on epidermal growth factor receptor autophosphorylation were unaffected by SN-38. Likewise, CI1033 had no effect on topo I polypeptide levels, localization, or activity. Nonetheless, CI1033 markedly enhanced the number of covalent topo I-DNA complexes stabilized by SN-38 or the related agent topotecan (TPT). Analysis of intracellular SN-38 levels by high-performance liquid chromatography and intracellular TPT levels by flow microfluorometry revealed that CI1033 increased the steady-state accumulation of SN-38 and TPT by 9.4 +/- 1.9- and 1.8 +/- 0.2-fold, respectively. Further evaluation revealed that the initial rate of TPT uptake was unaffected by CI1033, whereas the rate of efflux was markedly diminished. Additional studies demonstrated that T98G and HCT8 cells express the breast cancer resistance protein (BCRP), a recently cloned ATP binding cassette transporter. Moreover, CI1033 enhanced the uptake and cytotoxicity of SN-38 and TPT in cells transfected with BCRP but not empty vector. Conversely, CI1033 accumulation was diminished in cells expressing BCRP, suggesting that CI1033 is a substrate for this efflux pump. These results indicate that CI1033 can modulate the accumulation and subsequent cytotoxicity of two widely used topo I poisons in cells that have no history of previous exposure to these agents.
authors.affiliation: Division of Medical Oncology, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: C
authors.initials: C
authors.lastname: Erlichman
authors.forename: S A
authors.initials: SA
authors.lastname: Boerner
authors.forename: C G
authors.initials: CG
authors.lastname: Hallgren
authors.forename: R
authors.initials: R
authors.lastname: Spieker
authors.forename: X Y
authors.initials: XY
authors.lastname: Wang
authors.forename: C D
authors.initials: CD
authors.lastname: James
authors.forename: G L
authors.initials: GL
authors.lastname: Scheffer
authors.forename: M
authors.initials: M
authors.lastname: Maliepaard
authors.forename: D D
authors.initials: DD
authors.lastname: Ross
authors.forename: K C
authors.initials: KC
authors.lastname: Bible
authors.forename: S H
authors.initials: SH
authors.lastname: Kaufmann
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000970:Antineoplastic Agents / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002166:Camptothecin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D000077146:Irinotecan; D009025:Morpholines / Q000494:pharmacology*; D009363:Neoplasm Proteins; D014411:Neoplastic Stem Cells / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011993:Recombinant Fusion Proteins / Q000235:genetics; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000378:metabolism / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D009025:Morpholines; D009363:Neoplasm Proteins; D011993:Recombinant Fusion Proteins; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D019772:Topotecan; C420268:Canertinib; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D002166:Camptothecin