title: Intrinsic thermodynamics of inhibitor binding to human carbonic anhydrase IX.
abstract: BACKGROUND
  Human carbonic anhydrase 9th isoform (CA IX) is an important marker of numerous cancers and is increasingly interesting as a potential anticancer drug target. Various synthetic aromatic sulfonamide-bearing compounds are being designed as potent inhibitors of CA IX. However, sulfonamide compound binding to CA IX is linked to several reactions, the deprotonation of the sulfonamide amino group and the protonation of the CA active site Zn(II)-bound hydroxide. These linked reactions significantly affect the affinities and other thermodynamic parameters such as enthalpies and entropies of binding.
  
  
  METHODS
  The observed and intrinsic affinities of compound binding to CA IX were determined by the fluorescent thermal shift assay. The enthalpies and entropies of binding were determined by the isothermal titration calorimetry.
  
  
  RESULTS
  The pKa of CA IX was determined to be 6.8 and the enthalpy of CA IX-Zn(II)-bound hydroxide protonation was -24 kJ/mol. These values enabled the analysis of intrinsic thermodynamics of a library of compounds binding to CA IX. The most strongly binding compounds exhibited the intrinsic affinity of 0.01 nM and the observed affinity of 2 nM.
  
  
  CONCLUSIONS
  The intrinsic thermodynamic parameters of compound binding to CA IX helped to draw the compound structure to thermodynamics relationship.
  
  
  CONCLUSIONS
  It is important to distinguish the intrinsic from observed parameters of any disease target protein interaction with its inhibitors as drug candidates when drawing detailed compound structure to thermodynamics correlations.
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania.
authors.forename: Vaida
authors.initials: V
authors.lastname: Linkuvienė
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania.
authors.forename: Jurgita
authors.initials: J
authors.lastname: Matulienė
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania.
authors.forename: Vaida
authors.initials: V
authors.lastname: Juozapaitienė
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania.
authors.forename: Vilma
authors.initials: V
authors.lastname: Michailovienė
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania.
authors.forename: Jelena
authors.initials: J
authors.lastname: Jachno
authors.affiliation: Department of Biothermodynamics and Drug Design, Institute of Biotechnology, Vilnius University, Graičiūno 8, Vilnius LT-02241, Lithuania. Electronic address: daumantas.matulis@bti.vu.lt.
authors.forename: Daumantas
authors.initials: D
authors.lastname: Matulis
mesh_terms: D000951:Antigens, Neoplasm / Q000737:chemistry* / Q000378:metabolism; D000071231:Carbonic Anhydrase IX; D002257:Carbonic Anhydrase Inhibitors / Q000737:chemistry* / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D013816:Thermodynamics
chemical_list: D000951:Antigens, Neoplasm; D002257:Carbonic Anhydrase Inhibitors; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases
keywords: Benzenesulfonamide inhibitors; Carbonic anhydrase; Drug design; Fluorescent thermal shift assay; Intrinsic thermodynamics of protein-ligand binding; Isothermal titration calorimetry