title: Inhibition of carbonic anhydrase IX (CA9) sensitizes renal cell carcinoma to ionizing radiation.
abstract: While normal kidneys are relatively sensitive to ionizing radiation (IR), renal cell carcinoma (RCC) is considered radioresistant. Carbonic anhydrase IX (CA9), an enzyme that maintains intracellular pH by carbon dioxide dissolution, is upregulated in the majority of RCC, but not in normal kidneys. Since regulation of intracellular pH may enhance radiation effects, we hypothesized that inhibition of CA9 may radiosensitize RCC. Clonogenic survival assay of human clear cell RCC 786-O and murine RCC RAG cells in the presence of a pharmacological CA9 inhibitor or with shRNA-mediated knockdown of CA9 was performed to investigate the response to IR in vitro (single dose or fractionated) and in vivo. Extracellular pH changes were measured in vitro. Treatment with AEBS [4-(2-aminoethyl)benzene sulfonamide], a sulfonamide, was used as a pharmacological inhibitor of the enzymatic activity of CA9. Nude mice bearing subcutaneous xenografts of 786-O cells stably expressing CA9 shRNA or scrambled control were irradiated (6 Gy). Tumor growth was followed longitudinally in the 786-O-bearing mice receiving AEBS (50-200 µg/ml drinking water) or control (vehicle only) which were irradiated (6 Gy) and compared with mice receiving either IR or AEBS alone. In vitro inhibition of CA9 activity or expression significantly sensitized RCC cells to the effects of IR (p<0.05), an effect even more significant when hypofractionated IR was applied. In vivo irradiated xenografts from RCC cells transfected with CA9 shRNA were significantly smaller compared to irradiated xenografts from the scrambled shRNA controls (p<0.05). RCC xenografts from mice treated with AEBS in combination with IR grew significantly slower than all controls (p<0.05). Inhibition of CA9 expression or activity resulted in radiation sensitization of RCC in a preclinical mouse model.
authors.affiliation: Department of Surgery, Division of Urology, McMaster University, Hamilton, ON, Canada.
authors.forename: Wilhelmina C M
authors.initials: WC
authors.lastname: Duivenvoorden
authors.affiliation: Department of Surgery, Division of Urology, McMaster University, Hamilton, ON, Canada.
authors.forename: Sarah N
authors.initials: SN
authors.lastname: Hopmans
authors.affiliation: Department of Medical Physics, McMaster University, Hamilton, ON, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gallino
authors.affiliation: Department of Medical Physics, McMaster University, Hamilton, ON, Canada.
authors.forename: Thomas
authors.initials: T
authors.lastname: Farrell
authors.affiliation: Juravinski Cancer Centre, Hamilton, ON, Canada.
authors.forename: Carrie
authors.initials: C
authors.lastname: Gerdes
authors.affiliation: Department of Medical Physics, McMaster University, Hamilton, ON, Canada.
authors.forename: Diana
authors.initials: D
authors.lastname: Glennie
authors.affiliation: Juravinski Cancer Centre, Hamilton, ON, Canada.
authors.forename: Himu
authors.initials: H
authors.lastname: Lukka
authors.affiliation: Department of Surgery, Division of Urology, McMaster University, Hamilton, ON, Canada.
authors.forename: Jehonathan H
authors.initials: JH
authors.lastname: Pinthus
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D002292:Carcinoma, Renal Cell / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D034741:RNA, Small Interfering / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D011839:Radiation, Ionizing; D013449:Sulfonamides / Q000008:administration & dosage; D023041:Xenograft Model Antitumor Assays; D000096926:Benzenesulfonamides
chemical_list: D000951:Antigens, Neoplasm; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D034741:RNA, Small Interfering; D013449:Sulfonamides; C097944:4-(2-aminoethyl)benzenesulfonamide; D000096926:Benzenesulfonamides; C089226:CA9 protein, human