title: Carbonic anhydrase inhibitors: X-ray and molecular modeling study for the interaction of a fluorescent antitumor sulfonamide with isozyme II and IX.
abstract: The X-ray crystal structure of the fluorescent antitumor sulfonamide carbonic anhydrase (CA, EC, 4.2.1.1) inhibitor (4-sulfamoylphenylethyl)thioureido fluorescein (1) in complex with the cytosolic isoform hCA II is reported, together with a modeling study of the adduct of 1 with the tumor-associated isoform hCA IX. Its binding to hCA II is similar to that of other benzesulfonamides, with the ionized sulfonamide coordinated to the Zn2+ ion within the enzyme active site, and also participating in a network of hydrogen bonds with residues Thr199 and Glu106. The scaffold of 1 did not establish polar interactions within the enzyme active site but made hydrophobic contacts (<4.5 A) with Gln92, Val121, Phe131, Val135, Leu198, Thr199, Thr200, and Pro202. The substituted 3-carboxy-amino-phenyl functionality was at van der Waals distance from Phe131, Gly132, and Val135. The bulky tricyclic fluorescein moiety was located at the rim of the active site, on the protein surface, and strongly interacted with the alpha-helix formed by residues Asp130-Val135. All these interactions were preserved in the hCA IX-1 adduct, but the carbonyl moiety of the fluorescein tail of 1 participates in a strong hydrogen bond with the guanidine moiety of Arg130, an amino acid characteristic of the hCA IX active site. This may account for the roughly 2 times higher affinity of 1 for hCA IX over hCA II and may explain why in vivo the compound specifically accumulates only in hypoxic tumors overexpressing CA IX and not in the normal tissues. The compound is in clinical studies as an imaging tool for acute hypoxic tumors.
authors.affiliation: Istituto di Biostrutture e Bioimmagini-CNR, via Mezzocannone 16, 80134 Naples, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Alterio
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Vitale
authors.forename: Simona Maria
authors.initials: SM
authors.lastname: Monti
authors.forename: Carlo
authors.initials: C
authors.lastname: Pedone
authors.forename: Andrea
authors.initials: A
authors.lastname: Scozzafava
authors.forename: Alessandro
authors.initials: A
authors.lastname: Cecchi
authors.forename: Giuseppina
authors.initials: G
authors.lastname: De Simone
authors.forename: Claudiu T
authors.initials: CT
authors.lastname: Supuran
mesh_terms: D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm / Q000737:chemistry* / Q000187:drug effects; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology; D001665:Binding Sites; D024402:Carbonic Anhydrase II / Q000037:antagonists & inhibitors / Q000737:chemistry*; D000071231:Carbonic Anhydrase IX; D002257:Carbonic Anhydrase Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000187:drug effects; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005452:Fluoresceins / Q000737:chemistry* / Q000494:pharmacology; D005453:Fluorescence; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence; D013449:Sulfonamides / Q000737:chemistry* / Q000494:pharmacology; D013890:Thiourea / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
chemical_list: C521765:(4-sulfamoylphenylethyl)thioureido fluorescein; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D002257:Carbonic Anhydrase Inhibitors; D005452:Fluoresceins; D007527:Isoenzymes; D013449:Sulfonamides; D024402:Carbonic Anhydrase II; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D013890:Thiourea