Researchers at Hiroshima University, Japan, recently developed a new sensitive assay to detect drug resistant mutations in patients infected with hepatitis C virus (HCV). The study, published in the journal PLoS One, is entitled “Rapid, Sensitive, and Accurate Evaluation of Drug Resistant Mutant (NS5A-Y93H) Strain Frequency in Genotype 1b HCV by Invader Assay”.

According to the Centers for Disease Control and Prevention (CDC), HCV infection is the most common chronic blood-borne infection in the United States, with approximately 3.2 million people infected. It is known that 60 to 70% of the individuals infected with HCV are asymptomatic or experience only mild clinical illness. HCV is a major cause of chronic liver disease, liver cirrhosis and hepatocellular carcinoma. Most infected subjects might not be aware of their condition, however, they can be a source of transmission to other individuals and are at risk of developing chronic liver disease or other HCV-related conditions several years or even decades after infection.

Daclatasvir (DCV) and asunaprevir (ASV) are two oral drugs that target important HCV proteins, NS5A and NS3, respectively. A dual oral therapy based on these drugs provides patients with HCV genotype 1b infection (the most prevalent genotype in East Asia) a high sustained virological response (SVR) rate (defined by the absence of detectable HCV RNA in blood serum). However, the virus can acquire resistance against these direct acting antiviral agents. The mutation Y93H in NS5A has been reported to promote the development of resistance, and is an important predictor of treatment failure. It is estimated that 8.3 to 19% of all Japanese HCV patients carry the Y93H mutation.

In the study, researchers used the Invader assay, a quantitative assay with high specificity, to develop a system that allows a rapid and accurate detection of drug resistant mutant strains and determine the proportion of patients carrying the Y93H mutation.

The team analyzed 702 Japanese HCV genotype 1b patients and reported that their assay had an overall success rate of 98.9%, allowing the analysis of serum samples even with low HCV titers. The assay had a better lower detection limit than direct sequencing. Researchers found that 23.6% of the patients had a Y93H mutant strain, and that these patients had higher serum levels of HCV RNA, lower alanine transaminase (ALT, a biomarker of liver health) and lower hepatocellular carcinoma risk in comparison to patients without the mutation.

The research team concluded that their assay is a rapid and sensitive method that allows the accurate detection of the NS5A-Y93H mutant strain, and proposes that the assay can provide important pre-treatment information that may influence therapeutic decisions and be a valuable prediction tool for disease progression in patients with HCV genotype 1b.