Resistance-Associated Variants in the NS5A Region of HCV and Methods for the Detection
NS5A is a phosphoprotein encoded by the nonstructural region of the HCV genome, in which nucleotide mutations occur frequently. The domain-1 of NS5A forms a dimer and acts as an RNA-binding groove for HCV replication. NS5A inhibitors such as daclatasvir i
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Resistance-Associated Variants in the NS5A Region of HCV and Methods for the Detection Satoshi Mochida
Abstract
NS5A is a phosphoprotein encoded by the nonstructural region of the HCV genome, in which nucleotide mutations occur frequently. The domain-1 of NS5A forms a dimer and acts as an RNA-binding groove for HCV replication. NS5A inhibitors such as daclatasvir inhibit the function of NS5A by binding to the groove. Thus, the antiviral effects of NS5A inhibitors may be attenuated when nucleotide mutations that are responsible for amino acid mutations on the surface of the groove appear. Genotype-1b HCV clones with amino acid mutations in the NS5A region that provoke resistance to NS5A inhibitors are present even in patients without previous antiviral therapies with direct-acting antivirals (DAAs). HCV clones with NS5A-Y93H mutations exist in about 15 % of treatment-naïve patients in Japan, and baseline profiles of HCV, such as NS5A-R30Q/H/L and NS5A-L31/M/V mutations as well as the NS5A-Y93H mutation, have been shown to be crucial for the outcome of antiviral therapies, including NS5A inhibitors. Resistance-associated variants (RAVs) in the NS5A regions can be identified using cycling-prove real-time PCR, an invader assay, and/or direct sequencing. The significance of NS5A-RAVs is currently under investigation in relation to host factors such as IFNL3-related gene polymorphisms and the response to antiviral therapies with interferon as well as DAAs. Keywords
HCV • NS5A • Daclatasvir • Cycling probe
S. Mochida, MD, PhD (*) Department of Gastroenterology & Hepatology, Saitama Medical University, Saitama, Japan e-mail: [email protected] © Springer Science+Business Media Singapore 2017 K. Chayama (ed.), Hepatitis C Virus Treatment, DOI 10.1007/978-981-10-2416-0_4
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Characteristics of HCV-NS5A and the Action Sites of NS5A Inhibitors
NS5A is a 447-amino acid phosphoprotein of 56 and 58 kDa, corresponding to basally phosphorylated (p56) and hyper-phosphorylated (p58) forms, respectively [1]. NS5A mainly consists of three domains. An amphipathic α-helix membrane anchor (aa5–aa25) exists in the N-terminal site of the domain-1 (aa28–aa213) and is responsible for the association of NS5A with the ER membrane [2]. Consequently, domain-1 of NS5A forms a dimer on the surface of the ER membrane and acts as an RNA-binding groove [3], which is crucial for RNA replication through the alteration of NS5B polymerase activity [4]. NS5A is also required for the assembly of viral particles through the action of domain-3 [5] and interacts with a variety of host cellular proteins [6]. HCV replicon-based high-throughput screens (HTS) have yielded several directacting antivirals (DAAs) that act as NS5A inhibitors. In Japan, daclatasvir, an NS5A inhibitor, was approved in July 2014, and the use of this agent in combination with asunaprevir, a second-generation NS3/4S protease inhibitor, has been approved for antiviral therapy in compensated patients with genotype-1b HCV infection since September 2014. Sub
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