The hepatitis C virus (HCV) is a small, enveloped, positive-sense single-stranded RNA virus of the family Flaviviridae. The hepatitis C virus is the cause of hepatitis C and some cancers such as liver cancer and lymphomas in humans.
NS2-3 protease is an enzyme responsible for proteolytic cleavage between NS2 and NS3, which are non-structural proteins that form part of the HCV virus particle. NS3 protease of hepatitis C virus, on the other hand, is responsible for the cleavage of non-structural protein downstream. Both of these proteases are directly involved in HCV genome replication, that is, during the viral life-cycle that leads to virus multiplication in the host that has been infected by the virus.
Telaprevir (VX-950), marketed under the brand names Incivek and Incivo, is a pharmaceutical drug for the treatment of hepatitis C co-developed by Vertex Pharmaceuticals and Johnson & Johnson. It is a member of a class of antiviral drugs known as protease inhibitors. Specifically, telaprevir inhibits the hepatitis C viral enzyme NS3/4A serine protease. Telaprevir is only indicated for use against hepatitis C genotype 1 viral infections and has not been proven to be safe or effective when used for other genotypes of the virus. The standard therapy of pegylated interferon and ribavirin is less effective than telaprevir in those with genotype 1.
Nonstructural protein 3 (NS3), also known as p-70, is a viral nonstructural protein that is 70 kDa cleavage product of the hepatitis C virus polyprotein. It acts as a serine protease. C-terminal two-thirds of the protein also acts as helicase and nucleoside triphosphatase. First (N-terminal) 180 aminoacids of NS3 has additional role as cofactor domains for NS2 protein.
Nonstructural protein 5A (NS5A) is a zinc-binding and proline-rich hydrophilic phosphoprotein that plays a key role in Hepatitis C virus RNA replication. It appears to be a dimeric form without trans-membrane helices.
Nonstructural protein 2 (NS2) is a viral protein found in the hepatitis C virus. It is also produced by influenza viruses, and is alternatively known as the nuclear export protein (NEP).
Vaniprevir (MK-7009) is a macrocyclic hepatitis C virus (HCV) NS3/4A protease inhibitor, developed by Merck & Co., which is currently in clinical testing.In Japan, it was approved for treating hepatitis C in 2014 under the brand name Vanihep.
Asunaprevir is an experimental drug candidate for the treatment of hepatitis C. It was undergoing development by Bristol-Myers Squibb and has completed Phase III clinical trials in 2013.
Daclatasvir, sold under the brand name Daklinza, is an antiviral medication used in combination with other medications to treat hepatitis C (HCV). The other medications used in combination include sofosbuvir, ribavirin, and interferon, vary depending on the virus type and whether the person has cirrhosis. It is taken by mouth.
Simeprevir, sold under the trade names Olysio among others, is a medication used in combination with other medications for the treatment of hepatitis C. It is specifically used for hepatitis C genotype 1 and 4. Medications it is used with include sofosbuvir or ribavirin and peginterferon-alfa. Cure rates are in 80s to 90s percent. It may be used in those who also have HIV/AIDS. It is taken by mouth once daily for typically 12 weeks.
Nonstructural protein 5B (NS5B) is a viral protein found in the hepatitis C virus (HCV). It is an RNA-dependent RNA polymerase, having the key function of replicating HCV's viral RNA by using the viral positive RNA strand as a template to catalyze the polymerization of ribonucleoside triphosphates (rNTP) during RNA replication. Several crystal structures of NS5B polymerase in several crystalline forms have been determined based on the same consensus sequence BK. The structure can be represented by a right hand shape with fingers, palm, and thumb. The encircled active site, unique to NS5B, is contained within the palm structure of the protein. Recent studies on NS5B protein genotype 1b strain J4's (HC-J4) structure indicate a presence of an active site where possible control of nucleotide binding occurs and initiation of de-novo RNA synthesis. De-novo adds necessary primers for initiation of RNA replication.
Paritaprevir is an acylsulfonamide inhibitor of the NS3-4A serine protease manufactured by Abbott Laboratories that shows promising results as a treatment of hepatitis C. When given in combination with ritonavir and ribavirin for 12 weeks, the rate of sustained virologic response at 24 weeks after treatment has been estimated to be 95% for those with hepatitis C virus genotype 1. Resistance to treatment with paritaprevir is uncommon, because it targets the binding site, but has been seen to arise due to mutations at positions 155 and 168 in NS3.
Ledipasvir/sofosbuvir, sold under the trade name Harvoni among others, is a medication used to treat hepatitis C. It is a fixed-dose combination of ledipasvir and sofosbuvir. Cure rates are 94% to 99% in people infected with hepatitis C virus (HCV) genotype 1. Some evidence also supports use in HCV genotype 3 and 4. It is taken daily by mouth for 8–24 weeks.
Grazoprevir is a drug approved for the treatment of hepatitis C. It was developed by Merck and completed Phase III trials, used in combination with the NS5A replication complex inhibitor elbasvir under the trade name Zepatier, either with or without ribavirin.
Elbasvir/grazoprevir is a fixed-dose combination for the treatment of hepatitis C, containing elbasvir and grazoprevir. It is used to treat chronic hepatitis C virus (HCV) genotypes 1 or 4 infection in both treatment-naïve and treatment-experienced patients.
Nonstructural protein 5A (NS5A) inhibitors are direct acting antiviral agents (DAAs) that target viral proteins, and their development was a culmination of increased understanding of the viral life cycle combined with advances in drug discovery technology. However, their mechanism of action is complex and not fully understood. NS5A inhibitors were the focus of much attention when they emerged as a part of the first curative treatment for hepatitis C virus (HCV) infections in 2014. Favorable characteristics have been introduced through varied structural changes, and structural similarities between NS5A inhibitors that are clinically approved are readily apparent. Despite the recent introduction of numerous new antiviral drugs, resistance is still a concern and these inhibitors are therefore always used in combination with other drugs.
Narlaprevir, is an inhibitor of NS3/4A serine protease, intended for the treatment of chronic hepatitis C caused by genotype 1 virus in combination with other antiviral drugs.
Danoprevir (INN) is an orally available 15-membered macrocyclic peptidomimetic inhibitor of NS3/4A HCV protease. It contains acylsulfonamide, fluoroisoindole and tert-butyl carbamate moieties. Danoprevir is a clinical candidate based on its favorable potency profile against multiple HCV genotypes 1–6 and key mutants (GT1b, IC50 = 0.2–0.4 nM; replicon GT1b, EC50 = 1.6 nM). Danoprevir has been evaluated in an open-label, single arm clinical trial in combination with ritonavir for treating COVID-19 and favourably compared to lopinavir/ritonavir in a second trial.
Glecaprevir/pibrentasvir (G/P), sold under the brand names Mavyret and Maviret, is a fixed-dose combination medication used to treat hepatitis C. It contains glecaprevir and pibrentasvir. It works against all six types of hepatitis C. At twelve weeks following treatment between 81% and 100% of people have no evidence of hepatitis C. It is taken once a day by mouth with food.
Non-structural protein 5B (NS5B) inhibitors are a class of direct-acting antivirals widely used in the treatment of chronic hepatitis C. Depending on site of action and chemical composition, NS5B inhibitors may be categorized into three classes—nucleoside active site inhibitors (NIs), non-nucleoside allosteric inhibitors, and pyrophosphate analogues. Subsequently, all three classes are then subclassified. All inhibit RNA synthesis by NS5B but at different stages/sites resulting in inability of viral RNA replication. Expression of direct-acting NS5B inhibitors does not take place in cells that are not infected by hepatitis C virus, which seems to be beneficial for this class of drugs.
