title: Genetic Barrier to Direct Acting Antivirals in HCV Sequences Deposited in the European Databank.
abstract: OBJECTIVE
  Development of resistance results from mutations in the viral genome, and the presence of selective drug pressure leads to the emergence of a resistant virus population. The aim of this study was to analyze the impact of genetic variability on the genetic barrier to drug resistance to DAAs.
  
  
  METHODS
  The genetic barrier was quantified based on the number and type of nucleotide mutations required to impart resistance, considering full-length HCV NS3, NS5A and NS5B regions segregated by genotype into subtypes 1a, 1b, 2a, 2b and 3a. This study analyzeds 789 NS3 sequences, 708 sequences and 536 NS5B sequences deposited in the European Hepatitis C Virus Database, in the following resistance-associated positions: NS3: F43/I/L/S/V, Q80K/R, R155K/G, A156G/S/T and D168A/C/E/G/H/N/T/V/Y; NS5A: L/M28A/T/V, Q30E/H/R, L31F/I/M/V, H58D or P58S and Y93C/F/H/N/S; NS5B: S282P/R/T, C316H/N/Y, S368T, Y448C/H, S556G/R, D559R.
  
  
  RESULTS
  Variants that require only one transversion in NS3 were found in 4 positions and include F43S, R80K, R155K/G and A156T. The genetic barrier to resistance shows subtypic differences at position 155 of the NS3 gene where a single transition is necessary in subtype 1a. In the NS5A gene, 5 positions where only one nucleotide change can confer resistance were found, such as L31M which requires one transversion in all subtypes, except in 0.28% of 1b sequences; and R30H, generated by a single transition, which was found in 10.25% of the sequences of genotype 1b. Other subtypic differences were observed at position 58, where resistance is less likely in genotype 1a because a transversion is required to create the variant 58S. For the NS5B inhibitors, the genetic barrier at positions conferring resistance was nearly identical in subtypes 1a and 1b, and single transitions or transversions were necessary in 5 positions to generate a drug-resistant variant of HCV. The positions C316Y and S556D required only one transition in all genotypes, Y448H and S556 G/N/R positions required only one transition for up to 98.8% of the sequences analyzed. A single variant in position 448 in genotype 1a is less likely to become the resistance variant 448H because it requires two transversions. Also, in the position 559D a transversion and a transition were necessary to generate the resistance mutant D559H.
  
  
  CONCLUSIONS
  Results revealed that in 14 out of 16 positions, conversion to a drug-resistant variant of HCV required only one single nucleotide substitutions threatening direct acting antivirals from all three classes.
authors: Graduate Program in Medicine, Hepatology, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Porto Alegre, RS, Brazil.|Medical Infectologist, Hospital Nossa Senhora da Conceição (HNSC), Porto Alegre, RS, Brazil.
authors: Dimas Alexandre
authors: http://orcid.org/0000-0003-4326-0024
authors: DA
authors: Kliemann
authors: Graduate Program in Medicine, Hepatology, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Porto Alegre, RS, Brazil.
authors: Cristiane Valle
authors: CV
authors: Tovo
authors: Graduate Program in Medicine, Hepatology, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Porto Alegre, RS, Brazil.|Department of Basic Health Sciences, Laboratory of Molecular Biology, Graduate Program in Pathology, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Brazil.
authors: Ana Beatriz
authors: AB
authors: Gorini da Veiga
authors: Graduate Program in Medicine, Hepatology, Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA), Porto Alegre, RS, Brazil.|Medical Infectologist, Hospital Nossa Senhora da Conceição (HNSC), Porto Alegre, RS, Brazil.
authors: André Luiz
authors: AL
authors: Machado
authors: School of Biological Sciences, Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America, University of Nebraska, Lincoln, NE, United States of America.
authors: John
authors: J
authors: West
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology*; D003062:Codon / Q000235:genetics; D030541:Databases, Genetic; D024882:Drug Resistance, Viral / Q000235:genetics; D005060:Europe; D005838:Genotype; D016174:Hepacivirus / Q000187:drug effects* / Q000235:genetics*; D009154:Mutation
chemical_list: D000998:Antiviral Agents; D003062:Codon