Inhoudsopgave
Les 02: Novel approaches for anti-influenza virus therapy .................................................................. 2
1. Epidemiology of influenza viruses ......................................................................................... 2
1.1 Influenza viruses: many HxNx subtyps.................................................................................. 2
1.2 Medical burden of influenza ................................................................................................. 3
1.3 Antigenic variation of influenza virus .................................................................................... 4
1.4 Influenza pandemics in the 20th century ............................................................................... 4
2. Clinical picture of influenza .................................................................................................. 5
2.1 Disease spectrum of seasonal influenza .............................................................................. 5
2.2 Clinical picture of highly pathogenic avian influenza virus in humans .................................... 5
3. Mode of action and use of the first-generation antivirals – NA inhibitors .................................. 7
3.1 Antiviral therapy for influenza: targets ................................................................................... 7
3.2 Mechanism of the neuraminidase inhibitors ......................................................................... 7
3.3 Clinical use of neuraminidase inhibitors ............................................................................... 8
3.4 Resistance to neuraminidase inhibitors: rare but possible ..................................................... 8
3.5 Binding of the NAI in the catalytic site of NA .......................................................................... 9
3.6 Conclusion: first-generation antiviral drugs ........................................................................ 10
4. Trial design for drug candidates ........................................................................................... 10
4.1 Influenza drug efficacy studies ........................................................................................... 10
5. Inhibitors of virus entry ....................................................................................................... 11
5.1 Drugs in clinical testing or recently approved ...................................................................... 11
5.2 Antiviral targets ................................................................................................................. 11
5.3 Inhibitors of virus entry ...................................................................................................... 11
5.4 HA has two functions in influenza virus entry ...................................................................... 12
5.5 Inhibition of one of the two HA functions ............................................................................ 12
6. Inhibitors of the viral polymerase......................................................................................... 15
6.1 Influenza virus RNA synthesis ............................................................................................ 16
6.2 Inhibitors of influenza virus polymerase – Part 01 ................................................................ 17
6.3 Inhibitors of influenza virus polymerase – Part 02 ................................................................ 18
6.4 Inhibitors of influenza virus polymerase – Part 03 ................................................................ 19
7. Conclusion ........................................................................................................................ 20
1
, Les 02: Novel approaches for anti-influenza virus therapy
1. Epidemiology of influenza viruses
1.1 Influenza viruses: many HxNx subtyps
Influenza A viruses are classified based on two major
surface proteins:
• Hemagglutinin (HA)
- Allows the virus to attach to host cells,
specifically to sialic acid receptors.
- Without HA, the virus cannot enter the cell.
• Neuraminidase (NA)
- Helps newly formed viruses to exit the host
cell.
- It cleaves sialic acid
These proteins determine how the virus enters and exits
host cells. Not all combinations infect humans.
HA/NA variants, define viral subtypes.
Influenza B is one of the three main types of influenza virus
infecting humans. Unlike influenza A, which infects many
animal species, influenza B circulates only in humans.
Seasonal influenza A and B viruses
• Annual epidemics
• High morbidity and mortality in <5 and >65 yrs.
• Vaccine needs annual updating and is only partially effective at >65 yrs.
- In elderly individuals (>65 years), the immune respons is weaker, making
the vaccine les effective, but still offers protection against severe
outcomes like hospitalization or death.
Highly pathogenic avian influenza viruses
• H5N1: 2003 – 2022 ca. 870 cases worldwide
• H7N9: 2013 – 2022 ca. 1600 cases worldwide
• Mortality: 60% (?) for H5N1; 30% for H7N9
• Thus far no human-to-human transmission
2
, 1.2 Medical burden of influenza
The medical burden of influenza refers
to the total impact on population
health, healthcare systems, and
society.
In vulnerable individuals, influenza can
cause pneumonia, cardiac events, and
worsening of chronic diseases.
1.2.1 Current H5N1 threat in cattle - USA
In March 2024, the U.S. confirmed for the first time that highly
pathogenic avian influenza A (H5N1) was infecting diary cattle.
Some human cases have been documented in people exposed to
infected cattle or their environment.
• Sustained human-to-human transmission is currently
considered unlikely
• The presence of H5N1 is dairy herds raises exposure risk for
people working in close contact with cows.
PB2 mutations (= Polymerase Basic Protein 2) → allows the virus to
replicate its RNA inside host cells.
• Certain mutations in the PB2 protein allows the virus to
replicate more efficiently in mammalian hosts.
- This improves viral fitness, possible enabling transmission between mammals, which raises
pandemic potential.
• PB2-E627K: Enhances replication in mammalian cells
1.2.2 Next steps in human adaption
The progression of avian influenza viruses –
towards becoming human-adapted viruses,
potentially leading to a pandemic or even
seasonal flu.
Avian reservoir: PB2 mutation frequently arise
here, but they are not yet sufficient for
mammalian infection.
Spillover & mammalian epidemic: the virus
crosses over to mammals.
• It acquires mammalian-adaptation mutations in the polymerase complex, particularly in PB2.
Potential human pandemic: key HA (hemagglutinin) mutations for efficient human-to-human transmission have
not yet been observed.
Seasonal human influenza: with further adaptation, the virus could become endemic and seasonal in humans.
3
Les 02: Novel approaches for anti-influenza virus therapy .................................................................. 2
1. Epidemiology of influenza viruses ......................................................................................... 2
1.1 Influenza viruses: many HxNx subtyps.................................................................................. 2
1.2 Medical burden of influenza ................................................................................................. 3
1.3 Antigenic variation of influenza virus .................................................................................... 4
1.4 Influenza pandemics in the 20th century ............................................................................... 4
2. Clinical picture of influenza .................................................................................................. 5
2.1 Disease spectrum of seasonal influenza .............................................................................. 5
2.2 Clinical picture of highly pathogenic avian influenza virus in humans .................................... 5
3. Mode of action and use of the first-generation antivirals – NA inhibitors .................................. 7
3.1 Antiviral therapy for influenza: targets ................................................................................... 7
3.2 Mechanism of the neuraminidase inhibitors ......................................................................... 7
3.3 Clinical use of neuraminidase inhibitors ............................................................................... 8
3.4 Resistance to neuraminidase inhibitors: rare but possible ..................................................... 8
3.5 Binding of the NAI in the catalytic site of NA .......................................................................... 9
3.6 Conclusion: first-generation antiviral drugs ........................................................................ 10
4. Trial design for drug candidates ........................................................................................... 10
4.1 Influenza drug efficacy studies ........................................................................................... 10
5. Inhibitors of virus entry ....................................................................................................... 11
5.1 Drugs in clinical testing or recently approved ...................................................................... 11
5.2 Antiviral targets ................................................................................................................. 11
5.3 Inhibitors of virus entry ...................................................................................................... 11
5.4 HA has two functions in influenza virus entry ...................................................................... 12
5.5 Inhibition of one of the two HA functions ............................................................................ 12
6. Inhibitors of the viral polymerase......................................................................................... 15
6.1 Influenza virus RNA synthesis ............................................................................................ 16
6.2 Inhibitors of influenza virus polymerase – Part 01 ................................................................ 17
6.3 Inhibitors of influenza virus polymerase – Part 02 ................................................................ 18
6.4 Inhibitors of influenza virus polymerase – Part 03 ................................................................ 19
7. Conclusion ........................................................................................................................ 20
1
, Les 02: Novel approaches for anti-influenza virus therapy
1. Epidemiology of influenza viruses
1.1 Influenza viruses: many HxNx subtyps
Influenza A viruses are classified based on two major
surface proteins:
• Hemagglutinin (HA)
- Allows the virus to attach to host cells,
specifically to sialic acid receptors.
- Without HA, the virus cannot enter the cell.
• Neuraminidase (NA)
- Helps newly formed viruses to exit the host
cell.
- It cleaves sialic acid
These proteins determine how the virus enters and exits
host cells. Not all combinations infect humans.
HA/NA variants, define viral subtypes.
Influenza B is one of the three main types of influenza virus
infecting humans. Unlike influenza A, which infects many
animal species, influenza B circulates only in humans.
Seasonal influenza A and B viruses
• Annual epidemics
• High morbidity and mortality in <5 and >65 yrs.
• Vaccine needs annual updating and is only partially effective at >65 yrs.
- In elderly individuals (>65 years), the immune respons is weaker, making
the vaccine les effective, but still offers protection against severe
outcomes like hospitalization or death.
Highly pathogenic avian influenza viruses
• H5N1: 2003 – 2022 ca. 870 cases worldwide
• H7N9: 2013 – 2022 ca. 1600 cases worldwide
• Mortality: 60% (?) for H5N1; 30% for H7N9
• Thus far no human-to-human transmission
2
, 1.2 Medical burden of influenza
The medical burden of influenza refers
to the total impact on population
health, healthcare systems, and
society.
In vulnerable individuals, influenza can
cause pneumonia, cardiac events, and
worsening of chronic diseases.
1.2.1 Current H5N1 threat in cattle - USA
In March 2024, the U.S. confirmed for the first time that highly
pathogenic avian influenza A (H5N1) was infecting diary cattle.
Some human cases have been documented in people exposed to
infected cattle or their environment.
• Sustained human-to-human transmission is currently
considered unlikely
• The presence of H5N1 is dairy herds raises exposure risk for
people working in close contact with cows.
PB2 mutations (= Polymerase Basic Protein 2) → allows the virus to
replicate its RNA inside host cells.
• Certain mutations in the PB2 protein allows the virus to
replicate more efficiently in mammalian hosts.
- This improves viral fitness, possible enabling transmission between mammals, which raises
pandemic potential.
• PB2-E627K: Enhances replication in mammalian cells
1.2.2 Next steps in human adaption
The progression of avian influenza viruses –
towards becoming human-adapted viruses,
potentially leading to a pandemic or even
seasonal flu.
Avian reservoir: PB2 mutation frequently arise
here, but they are not yet sufficient for
mammalian infection.
Spillover & mammalian epidemic: the virus
crosses over to mammals.
• It acquires mammalian-adaptation mutations in the polymerase complex, particularly in PB2.
Potential human pandemic: key HA (hemagglutinin) mutations for efficient human-to-human transmission have
not yet been observed.
Seasonal human influenza: with further adaptation, the virus could become endemic and seasonal in humans.
3
