HCV

Question 1

Name a few facts about HCV infections

Answer 1

• acute (mostly asymptomatic, 25% can clear infection) and chronic infections (can lead to cirrhosis after 25+ years)
• ~58 million chronically infected worldwide
• ~1.5 million new infections annually
• ~290,000 deaths in 2019
• leading cause for liver transplantation
• parental & vertical transmission

Question 2

HCV - the virus

Answer 2

• enveloped
• (+)-ssRNA
• 8 major genotypes

Question 3

HCV genome

Answer 3

• 9.6kb
• not capped
• translation is IRES-dependent
• IRES is part if 5‘-NTR -> 5‘-NTR is important

Question 4

Name the (historical) HCV treatment options

Answer 4

• IFN
• IFN + Ribavirin
• Peg-IFN + Ribavirin
• Peg-IFN + Ribavirin + DAA
• DAA without IFN (ex. Sofosbuvir)

Question 5

Describe the interferon (IFN) therapy

Answer 5

• IFN-α activates IFN-stimulated genes via JAK/STAT pathway -> innate immune response
• approved 1991
• 20% clearance after 48 weeks
• side effects

pegylation increases serum half life from 8h to 80h

Question 6

Describe the Ribavirin therapy

Answer 6

• nucleoside analogue

2 possible mechanisms:
- (d)GTP depletion via competitive inhibition of Inosine-5‘-monophosphate dehydrogenase (IMPDH) -> inhibition of guanine synthesis

• incorporation into growing virus RNA -> error catastrophe

Question 7

Describe Cyclophilin inhibitors (here cyclosporin)

Answer 7

• is a peptidyl-prolyl isomerase (cis/trans proline change)
• cyclosporin has broad antiviral activity
• cyclophilin plays role in HCV replication -> cyclophilin inhibition stops replication

Question 8

What are the targets of DAAs in HCV treatment

Answer 8

• NS3/4A protease (-previr)
• NS5A protease (-asvir)
• NS5B polymerase (-buvir)

Question 9

The NS3/4A protease

Answer 9

NS4A is protease (N-terminal), NS3 is helicase (C-terminal)

• cleaves mitochondrial antiviral signaling protein and TRIF which are part of innate immune system
• inhibition has two results:
  
  1. blocks cleavage of HCV polyprotein
  2. facilitates a strong IFN response

used in combination with PEG-IFN and Ribavirin

Question 10

The NS5A protease

Answer 10

• large hydrophilic phosphoprotein
• essential for RNA replication and particle assembly
• 3 domains (Dom1 - Zn2+ binding; Dom2 - RNA replication)
• possibly involved in cancerogenesis
• counteracts innate immunity (reduces IFN-γ)

Question 11

NS5A inhibitors

Answer 11

• symmetry is important
• biphenyl core
• core connected to imidazole moiety than proline capped off with AA derivative

Question 12

The NS5B polymerase

Answer 12

• single-chain RdRp
• tail-anchored protein
• active side is closed during initiation and open during elongation
• allosteric GTP-binding pocket

Question 13

NS5B inhibitors

Answer 13

1. nucleoside inhibitors (NI) -> sofosbuvir is only approved NI
   - intracellular delivery is difficult due to phosphate group
   - could target host polymerase
   - pan-genotypic
   - rare mutations
2. non-nucleoside inhibitors (NNI) -> dasabuvir only approved NNI (combination therapy)
   - bind to allosteric sites (2 in thumb, 2 in palm)
   - genotype specific
   - mutations typical