title: Three missense mutations of DNA topoisomerase I in highly camptothecin-resistant colon cancer cell sublines.
abstract: Various anticancer drugs, including camptothecins and indolocarbazoles, target DNA topoisomerase I (Top1). We previously described the camptothecin-resistant colon cancer cell line DLDSNR6, which has a Gly365Ser missense mutation in Top1. In the present study, we established highly camptothecin-resistant sublines from DLDSNR6 cells by continuous exposure to higher camptothecin concentrations. The established sublines grew in the presence of 30 µM of camptothecin, but exhibited markedly retarded growth. In addition to Gly365Ser, these sublines harbored a Top1 Gly717Arg mutation and some had also a Top1 Gln421Arg mutation. Top1 activity was reduced to approximately one-eighth in highly resistant cell lines compared with that in parental DLD-1 cells. Resistant clones with 3 Top1 mutations including Gln421RArg exhibited the highest resistance to the indolocarbazole J-107088 in terms of the effect on the cell cycle distribution. The Gln421 mutation was equivalent to a mutation recently found in camptothecin biosynthesizing plants, but it has not previously been found in mammalian cells.
authors.affiliation: Department of Oncology and Hematology, Jikei University School of Medicine, Minato‑Ku, Tokyo 105‑8471, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Arakawa
authors.forename: Koji
authors.initials: K
authors.lastname: Ozaki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Okawa
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yamada
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002166:Camptothecin / Q000494:pharmacology*; D002227:Carbazoles / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004273:DNA, Neoplasm / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005434:Flow Cytometry; D006801:Humans; D020125:Mutation, Missense / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D018528:ATP-Binding Cassette Transporters; D002227:Carbazoles; D004273:DNA, Neoplasm; D012333:RNA, Messenger; D059004:Topoisomerase I Inhibitors; C121395:edotecarin; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D002166:Camptothecin