title: Carnosine inhibits carbonic anhydrase IX-mediated extracellular acidosis and suppresses growth of HeLa tumor xenografts.
abstract: BACKGROUND
  Carbonic anhydrase IX (CA IX) is a transmembrane enzyme that is present in many types of solid tumors. Expression of CA IX is driven predominantly by the hypoxia-inducible factor (HIF) pathway and helps to maintain intracellular pH homeostasis under hypoxic conditions, resulting in acidification of the tumor microenvironment. Carnosine (β-alanyl-L-histidine) is an anti-tumorigenic agent that inhibits the proliferation of cancer cells. In this study, we investigated the role of CA IX in carnosine-mediated antitumor activity and whether the underlying mechanism involves transcriptional and translational modulation of HIF-1α and CA IX and/or altered CA IX function.
  
  
  METHODS
  The effect of carnosine was studied using two-dimensional cell monolayers of several cell lines with endogenous CA IX expression as well as Madin Darby canine kidney transfectants, three-dimensional HeLa spheroids, and an in vivo model of HeLa xenografts in nude mice. mRNA and protein expression and protein localization were analyzed by real-time PCR, western blot analysis, and immunofluorescence staining, respectively. Cell viability was measured by a flow cytometric assay. Expression of HIF-1α and CA IX in tumors was assessed by immunohistochemical staining. Real-time measurement of pH was performed using a sensor dish reader. Binding of CA IX to specific antibodies and metabolon partners was investigated by competitive ELISA and proximity ligation assays, respectively.
  
  
  RESULTS
  Carnosine increased the expression levels of HIF-1α and HIF targets and increased the extracellular pH, suggesting an inhibitory effect on CA IX-mediated acidosis. Moreover, carnosine significantly inhibited the growth of three-dimensional spheroids and tumor xenografts compared with untreated controls. Competitive ELISA showed that carnosine disrupted binding between CA IX and antibodies specific for its catalytic domain. This finding was supported by reduced formation of the functional metabolon of CA IX and anion exchanger 2 in the presence of carnosine.
  
  
  CONCLUSIONS
  Our results indicate that interaction of carnosine with CA IX leads to conformational changes of CA IX and impaired formation of its metabolon, which in turn disrupts CA IX function. These findings suggest that carnosine could be a promising anticancer drug through its ability to attenuate the activity of CA IX.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Ditte
authors.forename: Peter
authors.initials: P
authors.lastname: Ditte
authors.forename: Martina
authors.initials: M
authors.lastname: Labudova
authors.forename: Veronika
authors.initials: V
authors.lastname: Simko
authors.forename: Filippo
authors.initials: F
authors.lastname: Iuliano
authors.forename: Miriam
authors.initials: M
authors.lastname: Zatovicova
authors.forename: Lucia
authors.initials: L
authors.lastname: Csaderova
authors.forename: Silvia
authors.initials: S
authors.lastname: Pastorekova
authors.affiliation: Department of Molecular Medicine, Institute of Virology, Slovak Academy of Sciences, Dubravska cesta 9, Bratislava 845 05, Slovak Republic. virupast@savba.sk.
authors.forename: Jaromir
authors.initials: J
authors.lastname: Pastorek
mesh_terms: D000138:Acidosis / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics* / Q000378:metabolism; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000235:genetics* / Q000378:metabolism; D002336:Carnosine / Q000008:administration & dosage*; D004285:Dogs; D006367:HeLa Cells; D064593:Heterografts; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics
chemical_list: D000951:Antigens, Neoplasm; D002336:Carnosine; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases