PHAR 502 | Exam 3 Review

Lamivudine

• Cytidine analogue

• Reverse transcriptase inhibitor

• HBV DNA polymerase has reversible transcriptase activity — so this drug can be used!

Entecavir

• Guanosine nucleoside analogue

• Converted intracellularly to 5’-triphosphate form

• Inhibits three distinct phases of HBV DNA polymerase

  • HBV DNA polymerase priming

  • Reverse transcription

  • Synthesis of the positive-stranded HBV DNA

Adefovir and Tenofovir

• Adenosine analogues

• DNA polymerase Reverse transcriptase inhibitors

• Originally developed for the treatment of HIV

• Tenofovir more potent

• Fumarate salt

• Prodrugs w/ two pivaloyloxymethyl or diisoproxil groups

  • Oral bioavailability

  • Monophosphate rate-limiting step in situ activation

  • Circumvent resistance

  • Activated by cellular adenylate kinase (adds second phosphate

  • Leads to a 91% lower serum concentration of tenofovir

  • Reduced off-target exposure to the drug

  • Lower adverse effects

Tenofovir alafenamide

• Greater antiviral activity

• 6.5x higher intracellular concentration of tenofovir diphosphate in liver cells

Hepatitis C Virus

Positive-sense, single-stranded RNA virus — Hepacivirus

• Transmission - blood

• No vaccine

Most infected patients (~80%) progress to chronic infection

HCV exists as seven closely related genotypes

Treatment goal: Sustained virologic response (SVR)

• Absence of detectable levels of plasma HCV RNA 12 weeks after the completion of therapy

HCV Structure

• Translated to a single polyprotein and cleaved by cellular and viral proteases

  • Three structural proteins (core, E1, and E2)

  • Seven non-structural (p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B)

Ribavirin

• Used with INFs

  • Mode of action not clear - several proposed

  • Teratogenic

• INFs and Ribavirin active against all HCV genotypes

  • SVR ~50%

Serine Protease Inhibitors

Boceprevir and Telaprevir inhibit HCV NS3/4A serine protease

• This protease is required for self-cleavage of polyprotein during viral replication.

Second Generation HCV Serine Inhibitors

• Simeprevir

• Modification of the first-generation for less functional groups sticking out and improved binding to the site!!

Third Generation HCV Serine Inhibitors

• Glecaprevir, Voxilaprevir

• Developed to be cross-genotype active

• Activity against key Gt1 resistance mutations (A156, R155, and D168)

• These compounds were developed to enable single-table regimens with other HCV Direct Acting Antivirals

Which third generation HCV Protease Inhibitors are active in ALL genotypes (1-6)?

• Glecaprevir in Mavyret

• Voxilaprevir in Vosevi

What genotypes is Grazoprevir active in?

• Genotypes 1 and 4

What is the HCV NS5B Polymerase responsible for?

• Replicating the viral RNA genome, required for HCV replication

• Based on identification of nucleoside analogues that function as alternate substrate inhibitors

Sofosbuvir

• HCV NS5B Polymerase Inhibitor

  • Uridine nucleotide analogue — alternative substrate inhibitor

  • Uses ProTide technology (Phosphoramidate Uracil)

  • Regimens provide a high cure rate

  • Enables INF free regimens

  • Price contreversey ($1000/pill, 12 weeks treatment)

What form is sofosbuvir converted to by liver first pass metabolism?

• Monophosphate

• Delivers the desired uridine monophosphate to hepatocytes

• Conversion to monophosphate to uridine nucleoside slow — lower potency

• Phosphoramidate moiety chrial

  • >10-fold difference in activity between two isomers

  • Active diastereomer obtained by selective crystallization

• Active metabolite = triphosphate made by nucleoside kinases in liver

What does NS5A do in HCV replication?

• Critical in viral replication and assembly

  • No known enzymatic activity

  • Function mediated through interaction with other viral and cellular proteins

  • No homologues in prokaryotes or eukaryotes

• HCV NS5A-targeting molecules are potent antivirals

  • Active in pM range

NS5A Inhibitor Structure

Dimer or dimer-like

• Possible improved interactions with the dimeric form of the NS5A protein

Names end in -asvir

Two peptidomimetic caps with an aromatic linker in the middle

• Carbamate methyl ester caps

• Aromatic linker with an N-containing heterocycle

Ledipasvir

• NS5A

• Genotypes 1, 4, 5, or 6

• Optimized for both antiviral potency and pharmacokinetic parameters

  • HCV NS5A EC50 = 31 pM with a half-life of up to 45 h

  • Low barrier to resistance

Velpatasvir

• NS5A

• In combination with sofusbuvir

• Active against genotypes 1-6

Pibrentasvir

• NS5A

• In combination with Glecaprevir

• Genotypes 1-6

Elbasvir

• NS5A

• In combination wiith Grazoprevir

• Genotypes 1 and 4

Epclusa

• Sofosbuvir (NS5B Polymerase inhibitor) and Valpatasvir (NS5A inhibitor)

• CAN BE USED IN ALL GENOTYPES

Mavyret

• Co-formulation of HCV protease inhibitor glecaprevir and HCV NS5A inhibitor pibrentasvir

• CAN BE USED IN ALL GENOTYPES

Vosevi

Sobusbuvir (NS5B polymerase inhibitor)

Velpatasvir (NS5A inhibitor)

Voxilaprevir (NS3/4A protease inhibitor)

CAN BE USED IN ALL GENOTYPES

Harvoni

Sofosbuvir (NS5B Polymerase Inhibitor)

Ledispavir (NS5A Inhibitor)

CAN ONLY BE USED IN GENOTYPES 1, 4, 5 and 6!!!

Zepatier

Grazoprevir (NS3/4A protease inhibitor)

Elbasvir (NS5A inhibitor)

Genotypes 1 and 4!!!