Lecture 3: HCV Flashcards
The virus overview
→ enveloped, +RNA, 8 genotypes,subtypes, high variability
→ acute and chronic
→ untreated chronic can lead to cirrhosis
→ fully curable
Genome
only 1 ORF leading to polyproteine
→ processing of polyprotein via proteases
→ E1/E2 in ER lumen, others in membrane or cytosol
→ glycoproteins and NS5A highly variable region
Relevant drug targets in HCV
time line
Immunomodulation
→ Interferon alpha and Ribavirin
Polymerase inhibitors
→ NS5B
Protease inhibitors
→ NS3,4A
Phosphoprotein inhibitors
→ NS5A
Interferon, then Interferon+Ribavirin or peg-Interferon+Ribavirin
Peg-IFN-Ribavirin+DAAs
→ NS3,4A inhibitor Boceprevir, Telaprevir
DAAs without Interferon
→ NS5B inhibitor Sofosbuvir
Interferon therapy
→ induces IFN-stimulated genes as part of immune response via JAK/STAT pathway
→ species specific, 3 forms
→ poor response even after extended treatment
How is it possible to enhance treatment response of interferon therapy
Polyethylenglycol (PEG) that increases serum halftime 10x
What´s another antiviral that can be used to enhance treatment response for HCV
SVR dependent on what ?
Ribavirin
→ nucleoside analogue
→ 1. incorporation into growing viral RNA leading to increased mutation rate
→ 2. Depletion of GTP via competitive inhibition of IMPDH, an essential step of guanin nucleotides
dependent on genotype of HCV
Cyclophilin A (CypA) → antiviral drug
peptidyl prolyl isomerase (PPIase)
→ proline only trans conformation, isomeration only with enzyme (PPIase)
→ Cyclophillin required for HCV replication, CypA and CypB stimulate RNA synthesis by NS5B, CypA interacts with NS5A, knock down would lead to blockage of replication
→ cyclic peptide cyclosporin (CsA) has antiviral activity
→ CypA/CsA complex → blockage
NS3,4A Protease
→ mechanism
→ drug mechanism
→ drugs
→ combination with
→ target for direct acting antiviral
mechanism
→ hydrophic protein with NTD serine protease and CTD helicase that are modulated by cofactor NS4A
→ cleaves mitochondrial antiviral signaling protein MAVS and TRIF as part of innate immune system
Inhibitors
→ blocks cleavage of HCV polyprotein and facilitates strong Interferon response
→ after cleavage, product peptide acts as inhibitor of HCV N3/NS4A protease
→ non covalent inhibitors of enzyme usefull called peptidomimetics
→ bind to active site
drug: Ciluprevir (toxic), Simeprevir, Faldaprevir (not good), Boceprevir, Telaprevir, Voxilaprevir, Gelcaprevir
→ combination with PEGylated Interferon and Ribavirin
NS5A
→ characteristics
→ drugs in use
→ characteristics
→ hydrophilic phosphoprotein
→ hyper or hypophosphorylated
→ RNA replication and particle assembly
→ counteracts innate immunity
→ anchored to ER via NTD
→ Dom 1: Zn-binding domain
→ Dom 2: RNA replication essential
→ deletion of Dom 3 or CTD decreases particle assembly
Drugs
→ symetry
→ biphenyl core, imidazole moiety, proline moiety, capping group of animo acid derivates
→ e.g. Daclatasvir, Lepipasvir, Pibrentasvir, Velpatasvir
NS5B
→ characteristics
→ target for …
→ single chain RNA dependent RNA polymerase
→ Deprotonation of 3-OH group, stabilization of transition state and release of pyrophophate
→ tail anchored membrane via CT helix
→ right-hand structure
target for
→ nucleoside inhibitors
→ phosphorylated nucleosides inhibit
delivery of nucleotides due to charge
→ rarely resitance
→ Sofosbuvir
→ non nucleoside inhibitors
→ allosteric binding site
→ more often resistent
→ Desabuvir
Advantages and disadvantages of different drugs
NS3,4 Protease
→ Voxilaprevir
→ high resistence barrier, restricted gt specificity
NS5A Complex Inhibitors
→ Daclatasvir
→ low resietence barrier, pan-genotypic
NS5B Polymerase Inhibitors
→ NI Sofosbuvir
→ high resistence barrier, pan-genotypic
→ NNI Dasabuvir
→ low resistence barrier, restricted gt specifiy
Combination therapy targets different steps in life cycle
