Anti Viral Agents Flashcards
What is a virus
An infectious obligate intracellular parasite
Dependant on cell machinery of host to replicate
Sizes of viruses
From 10nm to 1 um
What do non-enveloped viruses have as an outside layer?
Protein capsid e.g. adenovirus, picornavirus, calicivirus
What do enveloped viruses have as an outside layer
Lipid envelope derived from host membrane
Can be pleiomorphic e.g. measles virus
OR typical shape like ebola
Central dogma
DNA is converted by transcriptase into RNA which is translated into proteins by ribosomes
Reverse transcriptase
Makes DNA from hosts nucleotides using virus rna
Rna is negative sensed
Complementary strand of mrna
Before translating genome into proteins they copy the negative sense back into the positive sense
Do RNA viruses & Retroviruses use their own machinery to replicate? and how does this affect their mutation rate?
They use their own polymerase to replicate
These lack proof reading, so higher mutation rate
How do RNA viruses compensate for RNA genomes being shorter than DNA genomes
Use complex coding strategies to make more proteins than expected from small RNA genome e.g. overlapping reading frames
Dna viruses
Have genomes up to 100s kb
Have accessory genes which can modify immune response so however these are often lost as there is no immune system in cultured cells
Segemented genomes
Allow reassert ent
Generic virus replication cycle
- Virus contains nuclear capside which contains its genome
- Virus attaches to specific virus receptor cell surface, infecting the cell
- Once inside, capsid falls away, exposing genome to cell machinery
- Genome can be converted into mRNA, or it may be mRNA itself
- This is translated by host cell ribosomes into proteins
- Viral genome can utuilise self polymerase or host cell polymerase to create new proteins
HIV replication cycle
- HIV virion binds to cell surface receptor CD4 with its gp120 spike protein
- Virus is brought closer to cell surface, engages with coreceptor CXCR4 or CCR5
- Virus membrane and host cell membrane fuse and release core of virus particle
- This undergoes reverse transcriptaseof the RNA genome → dsDNA + integrase → spliced into host’s own DNA
- Viral genome is transcribed into mRNA → codes for viral proteins and RNA
- These assemble and bud out of the cell to infect other cells
Influenza replication cycle
- Virus particle spikes latches onto glycoproteins adn glycolipids
- Virus is endocytosed into host cell
- Viral particle fuses envelope with endosomal lipids → releasing genomic segments of negative sense RNA
- These enter nucleus, where RNA dependent RNA polymerase turns them into mRNA → replicates them into new genomes
- mRNA leaves nucleus and picked up by ribosomes → makes new proteins
- New genomes move to cell surface alongside proteins of virus where they bud out of the cell
- For every 1 virus that enters the cell 100-1000 leave the cell
Cytopathic effect
Result of virus lysing the cell
Could be due to accumulation of viral proteins
What do viruses form in cell monolayers
A plaque where virus kills a bunch of cells in the middle
How can you find out how many virus particles are in a particular preparation of virus?
Making dilutions and putting them onto monolayers of cells
After 2/3 days, count number of plaques formed
Syncytia
Some viruses with surface proteins that can fuse at neutral pH often fuse cells together
Syncytia assay is also a method of finding out how may virus particles there are in a certain sample
How can viruses be detected
- Detecting viral genome PCR, RT-PCR
- Detecting viral antigen IFA, ELISA
- Detecting virus particles EM, HA
- Detecting virus cytopathic effect in cultured cells (virus isolation)
Why is RT-PCR used to detect SARS CoV2?
SARS CoV2 only contains RNA
Therapeutic index
Ratio between how much drug you have to use in order to control the virus and the amount that makes a person feel ill from the side effects of the drug
Targets for antiviral drugs
Viral enzymes
Some act as nucleoside analogues to inhibit or interfere with nucleic acid replication
Some drugs target specific viral factors
Acyclovir
Targets herpes virus
Is a nucleoside (guanine) analogue which lacks 3’ hydroxyl group preventing phosphodiester bind formation and
Onl activate in virus infected cells
The thymidine kinase that phosphorylates acyclovir monophosphate only formed by heroes family
Resistance is rare but causes by mutation in thymidine kinase
Remdesivir
Analogue of adenosine causes chain termination of 3 nucleotides downstream as it twists the shape
Made for hep c tested against Ebola but didn’t work
Amantadine/rimantadine
Influenza a target
Blocks M2 channel so protons from endosome can’t enter virus and so virus is locked preventing virus uncoating
Single point mutation in S31N encoding for M2 channel can cause resistance
Most H3N2, H5N1 and H1N1 strains are resistant
Taimflu (oseltamivir)
Influenza
Inhibits neuraminidase enzyme that cleaves sialic acid from the infected cells surface preventing spread of new virus particles
Baloxavir
Influenza
Inhibits PA endonuclease subunit of viral RNA polymerase
Resistance occurs by single point mutation I38T
It decreases viral shedding which can interrupt transmission
Hepatitis c
Relied on interferon treatment with ribavirin which was only effective in 50% of patients
Hepatitis c meds
NS3/4A protease inhibitors (PIs)
Inhibit post-translational processing of viral proteins by inhibiting NS3/4A serine protease
NS5A inhibitors
Inhibit viral rna replication
NS5B nucleoside polymerase inhibitors (NS5B inhibitors) and NS5B non-nucleoside polymerase inhibitors (NNPIs)
Inhibit rna dependant rna polymerase NS5B to inhibit conversion of + to - sense viral RNA
Antivirals against HIV
Inhibiting entry of virus by stopping it from attaching to its receptors and co-receptors
Inhibit fusion of viral and host cell membrane
Targeting reverse transcriptase
Target integrase
Target proteases unique to viruses
Why is there no cure for hiv
HIV is a retrovirus so integrates its genomic material into host cell DNA so there are always reservoir cells in HIV patients even if they take those antivirals against it that carry the viral DNA
Only two people have been cured
How were two people cured of HIV
Both of these had leukemia so got bone marrow transplants → doctors transferred marrow from naturally HIV resistant people who had mutation in CCR5 coreceptor gene (a Delta 32) which means CCR5 not expressed so HIV can’t enter new cells
Zidovudine is a nucleoside analogue used to treat HIV
Biologicals
Passive immunotherapy- antibodies taken from recovered individuals, or produced in the laboratory from immortalised B cells
Dexamethasone
Corticosteroid used for immunosuppressants
Toculizimab
Targets pro-inflammatory cytokine IL-6
Future forantiviral therapy
- New antiviral therapies that target host
- Combinations of drugs with different targets
- Broad acting antivirals
- Delivery systems suitable for target population e.g. oral ones > IV in terms of what patients prefer
- Diagnostics to justify antiviral use
HIV meds
CCR5 co receptor antagonist-inhibits viral entry
Fusion inhibitors-inhibit viral entry
NRTIs or NNRTIs-inhibit HIV reverse transcriptase to inhibit viral dna synthesis
INSTI-inhibit integration of viral dna into host genetic
Protease inhibitors-inhibit cleavage of hiv by proteases
PrEP is an NRTI
Why is neuroaminidase important
Cleaves bond between haemagluttinins on influenza and sialic acid allowing virus to continue infecting more cells,essential for viral release
