Companies: Gilead Sciences Merck
Non-A, Non-B hepatitis (NANBH) is a transmissible disease (or family of diseases) that is believed to be virally induced. Epdemiologic evidence suggests that there may be 3 types of NANBH: the water-borne epidemic type; the blood or needle associated type; and the sporadically occurring community acquired type. The number of causative agents is unknown. However, Hepatitis C virus (HCV) has been identified as the primary (if not only) cause of blood-borne NANBH. HCV infection is one of the most significant health problems affecting humans.
An estimated 170 million people worldwide and more than 4 miilon Americans (1.3%) are infected with HCV. In about 80% of caes, the virus leads to a chronic form of hepatitis, a condition that is incurable in many patients. Without therapeutic intervention, it can lead to morbidity through either cirrhosis and hepatic failure of hepatocellular carcinoma. HCV infection is the most common cause of liver transplantation.
Structure
HCV, the etiologic agent of non-A, non-B hepatitis, was identified in 1989 (Choo, Science 1989) and belongs to the flavivirus (Flaviviridae) family, as a separate genus Hepacivirus. The viral geneomic sequence of HCV is known (WO 89/04669, WO 90/11089). In particular, HCV has a 9.5 kb positive-sense single-stranded ssRNA genome that encodes a large polypeptide protein of 3010 amino acids. Its genome consists of a long (9.6 kb) single stranded RNA of positive polarity composed of 5′ and 5′ untranslated regions and one long open reading frame encoding the HCV structural proteins (Core, E1, E2), p7 and the nonstructural proteins (NS2, NS3, NS4A, NS4B, NS5A and NS5B). Among the structural proteins, E1 and E2 play an important role in cell entry.
HCV isolates from around the world exhibit significant genetic heterogeneity. Currently there are 6 distinct, but related genotypes of HCV based on phylogenetic analyses. Their genomes differ by 31-33% on the nucleotide level. In addition, numerous subtypes have been described showing a difference of 20-25 % at the nucleotide level, with genotype 5 being currently the only genotype featuring only one subtype. Genetic heterogeneity has been attributed to the lack of proofreading activity of the RNA dependent RNA polymerase. This leads to a high mutation rate, allowing HCV to collect mutations that are not detrmental for its life cycle and that in some cases permit escape from host immune responses (Gottwein & Buckh, Chapter 2 “Cutting the Gordian Knot-Development and Biological Relevance of Hepatitis C Virus Cell Culture Systems”).
Transmission/Prevention
Like HBV, HCV is a chronic disease. HCV is transmitted by blood and blood products just as with HBV. Sharing needles or other drug injection equipment has been shown to lead to transmission. HCV can also be transmitted through sexual contact, although the exact mechanism of transmission is not known. There is no vaccine for HCV as of this date.
Detection
HCV appears in the blood of infectd individuals at very low rates relative to other infectious viruses, which makes the virus very difficult to detect.
Symptoms
Most people with HCV infection do not have symptoms and lead normal lives. People with chronic HCV infection often progress to cirrhosis and liver cancer.
Pathology
HCV infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8+ T cells that probably contribute significantly to viral persistence. Incubation time and severity is intermediate to that of HAV and HBV.
Treatment
Presently, there is no vaccine available for prevention of HCV infection due to high degree in strain variation. Determination of the HCV genotype is of great clinical relevance. Current therapeutic options are very limited, especially for genotype 1. For genotypes 2 & 3, pegylated interferon in combination with ribavirin, can lead to a sustained virological response in up to 80% of patients (Ashfaq, Gen. Vac. & Ther. 2011, 9(7)).
–Interferon + ribavirin: The current standard of care (SOC) approved by the FDA is a weekly injection of pegylated interferon-? (PEG-IFN ?) combined with oral administration of ribavirin (RBV) twice-daily (BID). Although this combination therapy results in over 54% sustained viral response (SVR) which is the absence of serum HCV RNA up to 6 months after therapy, the response and rate of SVR can vary significantly dependent on HCV genotypes. Also, current therapies are often poorly tolerated because of a plethora of treatment associated adverse effects, including fatigue, influenza-like symptoms, gastrointestinal distrubances, neuropsychiatric symptoms, anemai, and hematologic abnormalites (Tong, Biomed & Biotechnol, 2012, 13(1): 56-82).
–IVIG:
Hoang (US 15/090.025, published as 15/090025) discloses IVIG purified from Fraction III was effective in treating HPV.
—-Interferon + IVIG: Malaguarnera (Biodrug 2004, 18(1) 63-70) disclses a research student that shows IVIg acts synergistically with IFN-alpha at acheiving a better resonse to IFN treatment in patients with chronic HCV associated with autoimmunity.
–RNA polymerase inhibitors: Sofosbuvir (brand name Sovaldi) is a drug used for HCV infection, with a high cure rate. It inhibits the RNA polymerase that HCV uses to replicate its RNA. It is developed by Gilead Sciences and was approved by the FDA in combination with rebavarin for oral dual therapy of HCV genotypes 2 and 3. Given that the treatment if interferon free, less adverse side effects are expected.
Ledipasvir-Sofosbuvir sold under the trademark Harvoni by Gilead Sciences has been shown to be very effective against HCV genotype 1. It was approved by the FDA on October 10, 2014. Sofosbuvir is a nucleotide analog inhibitor of HCV virus NS5B polymerase-the key enzyme mediating HCV RNA replication whereas Ledipasvir is a potent inhibitor of HCV NS5a, a viral phosphorotein that plays an important role in viral replication, assembly and secretion. The tripohsphate form of sofosbuvir (GS-461203) mimics the natural cellular uridine nuecleotide and is incorporated by the HCV RNA polymerase into the elongating strain, resulting in chain termination.
–Protease Inhibitors: Grazoprevir + elbasviris being developed by Merk for the treatment of HCV. Grazprevir is a second geenration protease inhibitors that words by interfering with teh HCV proteins NS3/4A. Elbasvir interfers with the HCV protein NS5A.
Models for HCV/Research
The assessment of antiviral drugs for chronic hepatitis C patients has been hampered by the lack of a robust cell culture system. The HCV replicon, which focuses on the viral replication deficient in production of infectious viral particles, is basically composed of an antibiotic gene for selection and HCV genomic RNA for autonomous replication in the intracellular compartments around ER. In vitro cell culture system for infectious HCV of genotype 2a, which is highly sensitive to interferon therapy has been developed. However, development of a robust cell culture system for the HCV 1a and 1b genotypes which are the most prevalent genotypes in the world and resistant to interferon therapy, has not yet been successful (Moriishi, Advanced Drug Delivery Rev. 59 (2007) 12-13-1221). Although efforts are ongoing to develop a vaccine, the unusually rapid genetic drift of HCV makes this a daunting task (Njoroge, Accounts of Chem. Res. 41(1) (2008), 50-59).