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The compound chloropromazine interferes with clatherin, thus impairing HCV endocytosis [ 63 ]. Arbidol, used as an anti-influenza drug, impairs clatherin mediated endocytosis of HCV [ 64 ]. The fusion of virus membrane to host cell is followed by viral replication inside the cell. The indole derivative arbidol also inhibits HCV membrane fusion [ 65 ].
Silymarin is a mixture of several flavonolignans and flavonoid taxifolines and inhibits fusion as done by arbidol [ 66 ]. Other fusion inhibitors include feroquine and aclorocquin, etc. The HCV replication cycle presents another important target for antiviral therapy. Finally, inhibitors targeting NS5A have also been developed.
Simultaneous with viral proteins, several host cellular components were also used as targets while developing drugs against them. Both these proteases are essential for HCV replication and have been pursued as drug targets.
These drugs were put under three different categories on the ground of their properties and action [ 71 ]. The DAAs in category I include linear peptidomimetics that bind proteases enzymes through covalent bonds. For example, telaprevir and boceprevir, the drugs of class I bind to the active-site Ser Serine forming a covalent enzyme - inhibitor adduct.
This not only shows antiviral activity but also uses strong forces to bind the target site. These are linear peptidomimetics or macrocyclic inhibitors and do not bind with their target by covalent bonds. It has been reported that these drugs do not target all HCV genotypes. On the basis of molecular masses, their predominant forms are p56 and p58, respectively [ 74 ].
S-adenosyl-methionine and betaine improve early virological response in chronic hepatitis C patients with previous nonresponse. Buy Softcover. Mean EDSS scores and the cumulative number of relapses have been compared between the two patient groups using the t -test with Welch correction. Controversy has attended the failure to reimburse zanamivir therapy in some countries, and the initial advice from the new National Institute for Clinical Excellence NICE in the UK that it should not be generally prescribed. The mRNA levels of most of the genes are increased 2—fold through IFN stimulation, but some genes are induced even more strongly . Antiviral drugs are particularly useful in these cases.
The phosphorylation in NS5A replicase is reported to be mediated by different kinases [ 75 , 76 ]. Several studies have demonstrated the candidate NS5B inhibitors which are nucleoside and nucleotide inhibitors NIs in nature and bind at active site of the enzyme. The non-nucleoside inhibitors NNIs bind at allosteric sites to bring conformational changes and inhibit polymerase activity [ 67 , 68 , 71 ].
These proteins have been pursued as drug targets. Moreover, there are some non-enzymatic proteins which also make a suitable intervention point. Although the exact function of NS4B is not very clear, it has been found as a good drug target [ 77 ]. Apart from viral proteins, some host cell factors also emerged as promising targets for antiviral therapy. Among host factors contributing to the viral replication cycle, we describe here two main factors that have been studied in detail, which are cyclophilins and miR Some CYPA antagonists have been developed.
Naturally, targeting miRNA by antagonist disrupts HCV replication in vitro and in vivo [ 86 , 87 ] and therefore becomes an effective target of therapy. The experimental studies indicated that antiviral molecules act at different steps of HCV lifecycle. Also many cellular factors act as candidate targets.
This shows a limited effect of DGAT1 inhibitors on the cellular functions [ 92 ]. An increase in viral load decreases SVR rate. HCV has a total of seven genotypes with more than 50 subtypes and several quasispecies. Genotypes play very important roles in deciding the host response to anti- viral treatment. Although, it is not fully established, it is believed that DAAs have better effect on non-responder genotypes like genotype Interferons are involved in host natural immune response against various pathogens including HCV [ 99 ].
This upregulates IFN-stimulated genes ISGs with expression of several types of antiviral effector protein [ - ].
It may be illustrated more specifically in reference to individual HCV viral proteins. This effect of E2 was detected prominently in patients infected with HCV-1 isolate. HCV genotype-2 and -3 could not show the same effect [ ]. This cleavage disrupts not only innate immune response but also IFN-induction pathway, ultimately resulting in down regulation of the transcription of IFN-alpha inducible genes [ , ].
There is high frequency of CC genotypes [ ] in comparison to European and African. IL28B polymorphism is the best predictor of treatment response, better even than viral load, liver fibrosis, glucose level etc. Patients with hepatic steatosis usually do not respond well to HCV infection treatment. Similarly, steatosis affects negatively in patients infected with other genotypes.
It causes relapse after discontinuation of treatment in patients with genotype This all indicates that pathogenesis of steatosis differs in different genotypes and influences the treatment. In addition to all above factors influencing the treatment response, other conditions like age, insulin resistance, and metabolic syndrome etc. The therapy of HCV infection is basically aimed to eradicate the virus and prevent the ensuing disease complications.
The value of SVR indicated not only eradication of virion from circulation but also correlates with symptoms [ - ]. In recent trials of boceprevir and telaprevir in patients with cirrhosis it was noted that SVR was low in comparison to that in non-cirrhotic patients. HCV is a highly variable virus with a large viral population and numerous quasispecies turnover in an infected individual.
Its life cycle remains confined to the cytoplasm in cell with little possibility of its genome integration with host genome. These viral variants have different amino acid composition on target sites and so, are less susceptible to drug action [ ]. Drug exposure inhibits replication of the dominant drug-sensitive viral population to the level of appearance of resistant variants. In vivo , viral resistance is influenced by three major factors including the genetic barrier to resistance, in vivo fitness of the viral variant population and drug exposure.
In view of these alterations, the drug resistant variants may cause a serious challenge to infection and therefore, this problem needs a solution by more extensive investigations. The addition of new drugs including DAAs, cyclophilins and miravirsen, etc. These drugs target and inhibit viral proteases and cell receptor proteins as well as enzymes facilitating viral entry into the cell and viral replication and assembly inside the cell. A check on viral entry as well as their cell to cell transmission or further replication by the use of these drugs achieves the aim of treatment.
Basic viral load and viral genotypes were found to show a significant effect on therapeutic outcome. Similarly, some disease conditions or cellular genomic polymorphism like IL28B polymorphism also have an impact on drug therapy. The development of drug resistant HCV variants during viral propagation still remains a serious challenge and needs to be resolved by different combination or development of new drugs.
Studies are in progress looking towards new aspects of drug therapy against HCV infection. All authors have made equal contributions in the performance of study, compilation of data and preparation of the manuscript.
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