title: Ring-expanded ("fat") nucleoside and nucleotide analogues exhibit potent in vitro activity against flaviviridae NTPases/helicases, including those of the West Nile virus, hepatitis C virus, and Japanese encephalitis virus.
abstract: A series of ring-expanded ("fat") heterocycles, nucleoside and nucleotide analogues (RENs) containing the imidazo[4,5-e][1,3]diazepine ring system (9, 14, 15, 18, 24-26, 28, 31, and 33) and imidazo[4,5-e][1,2,4]triazepine ring systems (30b, 30c, 32, and 34), have been synthesized as potential inhibitors of NTPases/helicases of Flaviviridae, including the West Nile virus (WNV), hepatitis C virus (HCV), and Japanese encephalitis virus (JEV). An amino-terminal truncated form of human enzyme Suv3(delta1-159) was also included in the study so as to assess the selectivity of RENs against the viral enzymes. The analogues of RENs included structural variations at position 1 of the heterocyclic base and contained changes in both the type of sugar moieties (ribo, 2'-deoxyribo, and acyclic sugars) and the mode of attachment (alpha versus beta anomeric configuration) of those sugars to the heterocyclic base. The target RENs were biochemically screened separately against the helicase and ATPase activities of the viral NTPases/helicases. A number of RENs inhibited the viral helicase activity with IC50 values that ranged in micromolar concentrations and exhibited differential selectivity between the viral enzymes. In view of the observed tight complex between some nucleosides and RNA and/or DNA substrates of a helicase, the mechanism of action of RENs might involve their interaction with the appropriate substrate through binding to the major or minor groove of the double helix. The REN-5'-triphosphates, on the other hand, did not influence the above unwinding reaction, but instead exerted the inhibitory effect on the ATPase activity of the enzymes. The activity was found to be highly dependent upon the low concentration levels of the substrate ATP. At concentrations >500 microM of RENs and the ATP concentrations >10 times the Km value of the enzyme, a significant activation of NTPase activity was observed. This activating effect underwent further dramatic enhancement (>1000%) by further increases in ATP concentration in the reaction mixture. A tentative mechanistic model has been proposed to explain the observed results, which includes an additional allosteric binding site on the viral NTPases/helicases that can be occupied by nucleoside/nucleotide-type molecules such as RENs.
authors.affiliation: Laboratory for Drug Design and Synthesis, Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Huan-Ming
authors.initials: HM
authors.lastname: Chen
authors.forename: Verena
authors.initials: V
authors.lastname: Koch
authors.forename: Herbert
authors.initials: H
authors.lastname: Schmitz
authors.forename: Ching-Len
authors.initials: CL
authors.lastname: Liao
authors.forename: Maria
authors.initials: M
authors.lastname: Bretner
authors.forename: Vishweshwar S
authors.initials: VS
authors.lastname: Bhadti
authors.forename: Ali I
authors.initials: AI
authors.lastname: Fattom
authors.forename: Robert B
authors.initials: RB
authors.lastname: Naso
authors.forename: Ramachandra S
authors.initials: RS
authors.lastname: Hosmane
authors.forename: Peter
authors.initials: P
authors.lastname: Borowski
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D001381:Azepines / Q000737:chemistry / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D004664:Encephalitis Virus, Japanese / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology*; D018067:Flaviviridae / Q000201:enzymology*; D016174:Hepacivirus / Q000201:enzymology; D006801:Humans; D020128:Inhibitory Concentration 50; D009705:Nucleosides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D009711:Nucleotides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D020815:Polyproteins / Q000737:chemistry; D017361:Viral Nonstructural Proteins / Q000037:antagonists & inhibitors; D014902:West Nile virus / Q000201:enzymology
chemical_list: D001381:Azepines; D004791:Enzyme Inhibitors; D009705:Nucleosides; D009711:Nucleotides; D020815:Polyproteins; D017361:Viral Nonstructural Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; D004265:DNA Helicases