title: ClC-3 expression enhances etoposide resistance by increasing acidification of the late endocytic compartment.
abstract: Resistance to anticancer drugs and consequent failure of chemotherapy is a complex problem severely limiting therapeutic options in metastatic cancer. Many studies have shown a role for drug efflux pumps of the ATP-binding cassette transporters family in the development of drug resistance. ClC-3, a member of the CLC family of chloride channels and transporters, is expressed in intracellular compartments of neuronal cells and involved in vesicular acidification. It has previously been suggested that acidification of intracellular organelles can promote drug resistance by increasing drug sequestration. Therefore, we hypothesized a role for ClC-3 in drug resistance. Here, we show that ClC-3 is expressed in neuroendocrine tumor cell lines, such as BON, LCC-18, and QGP-1, and localized in intracellular vesicles co-labeled with the late endosomal/lysosomal marker LAMP-1. ClC-3 overexpression increased the acidity of intracellular vesicles, as assessed by acridine orange staining, and enhanced resistance to the chemotherapeutic drug etoposide by almost doubling the IC(50) in either BON or HEK293 cell lines. Prevention of organellar acidification, by inhibition of the vacuolar H(+)-ATPase, reduced etoposide resistance. No expression of common multidrug resistance transporters, such as P-glycoprotein or multidrug-related protein-1, was detected in either the BON parental cell line or the derivative clone overexpressing ClC-3. The probable mechanism of enhanced etoposide resistance can be attributed to the increase of vesicular acidification as consequence of ClC-3 overexpression. This study therefore provides first evidence for a role of intracellular CLC proteins in the modulation of cancer drug resistance.
authors.affiliation: Medical Research Council Clinical Sciences Centre, Imperial College Faculty of Medicine, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.
authors.forename: Karsten H
authors.initials: KH
authors.lastname: Weylandt
authors.forename: Maxim
authors.initials: M
authors.lastname: Nebrig
authors.forename: Nils
authors.initials: N
authors.lastname: Jansen-Rosseck
authors.forename: Joanna S
authors.initials: JS
authors.lastname: Amey
authors.forename: David
authors.initials: D
authors.lastname: Carmena
authors.forename: Bertram
authors.initials: B
authors.lastname: Wiedenmann
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Higgins
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sardini
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000165:Acridine Orange; D000970:Antineoplastic Agents / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects; D018118:Chloride Channels / Q000378:metabolism*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D011992:Endosomes / Q000187:drug effects* / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D019450:Genes, MDR / Q000502:physiology; D006801:Humans; D007124:Immunoenzyme Techniques; D007668:Kidney / Q000187:drug effects; D009124:Muscle Proteins / Q000494:pharmacology; D017599:Neuroectodermal Tumors / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D018118:Chloride Channels; C115376:ClC-3 channel; D009124:Muscle Proteins; D005047:Etoposide; D000165:Acridine Orange