Anti-viral agents Flashcards
How do we know if a particular organism causes a disease?
i. Found in large numbers in diseased, but not healthy, individuals
ii. Can be isolated from diseased person and cultured outside
iii. When re-injected into healthy organism, should cause same disease
iv. Isolate from this new individual, and compare to first strain to check if identical
Koch’s Postulates ^
What are the three types of viral structures? Give examples of each
Non-enveloped - adenovirus
Enveloped -
Lipid envelope from host membrane
either pleiomorphic - measles or typical shape - ebola
Combination of capsid and envelope - herpes
What are the three types of viral structures? Give examples of each
Non-enveloped - adenovirus
Enveloped -
Lipid envelope from host membrane
either pleiomorphic - measles or typical shape - ebola
Combination of capsid and envelope - herpes
What are the four stages of the basic viral life cycle
Attachment of the virus to host cell
Endocytosis of the endosome containing the viral core
Capsid falls away exposing genome
early (regulatory) and late (structural) proteins, making virion
Transcribes mRNA to encode it’s proteins
- Early (functional) proteins
- Late (structural) proteins
New genomes and capsids (virus coat) assemble
Budding or cytolysis
What is the HIV life cycle?
Attachment
(the HIV has gp120 which binds to CD4, then co-receptor CCR5 or CXCR4) & entry by fusion (not endocytosis)
Capsid falls away, exposing genome
Reverse transcription.
RNA -> dsDNA; integrase to enter host DNA
Host makes viral proteins
Budding to release virion
What is the life cycle of influenza?
Attachment
(the Influenza has haemagglutinin spike protein, which binds to virus receptors on cells), entry by endocytosis
Capsid falls away, exposing the 8 segments of –ve sense RNA genome
mRNA made using RNA-dependent RNA polymerase
Viral proteins made using host ribosomes
Cytolytic release of virion using neuraminidase
Which areas of the influenza life cycle are targeted by antivirals?
Blocking the uncoating of the virus with amantadines (blocking the M2 channels)
RNA polymerisation
Neuraminidase inhibitors (preventing the newly budded viruses from cleaving the sialic acid, leaving them attached to the host cell)
What are the 5 methods of viral diagnostics?
Viral enome (PCR) Viral antigen (elisa) Viral particles (electon microscope) Cytopathic effect (isolation and culture) Anti-viral antibodies (serology) useful in seroconverted patients
What is the cytopathic effect?
Cytopathiceffectis usually a resultof the viruslysingthe cell.
This could be dueto shut down ofhost proteinsynthesis oraccumulation ofviral proteins.
If you infect a monolayer of cells with a virus, lysis occurs due to shutdown of host protein synthesis or virus using cytolytic exit
This results in a laboratory sign called the cytopathic effect (death of cells following viral infection)
This can end up forming a plaque and we can do serial dilutions to quantify (plaque assay)
Or could form a syncytium where instead of dying, the cells fuse (HIV)
What do we need to think about when developing antiviral agents?
Cost
administration ease
Safety
Does it deal with all strains?
Why do antiviral agents require a higher specificity than antibodies?
The bacteria being targetted by antibiotics are prokaryotic and have a large number of distinct differences from our eukaryotic cells e.g. 50s ribosomes, cell walls etc.
However viruses use our own machinery for their reproduction - our own ribosomes and vessicles etc. thus we cannot target all of these without damaging our own cells.
What is amantadine/rimantadine?
Antiviral for influenza, cyclin amines
By products of petroleum refinement
Binds to M2 channels prevents the virus from releasing its contents by preventing acidic influx into virus
What do neuramindase inhibitors do? Give some examples.
Relenza, tamiflu adn baloxavir
Designed to look like the substrate sialic acid it inhibits NA which captures sialic acid, cuts it, and releases it to allow the virus to move on to the next cell to infect
NA inhibitors stick into the enzyme more than sialic acid which means newly formed viruses are stuck onto the old cell and cannot move onto the next cell.
It stops viral polymerase from carrying out it’s endonuclease function.
(It’s an enzyme inhibitor)
What is acyclovir? How does it work?
Nucleoside analogue antiviral - used to treat HSV-1 (treats coldsores)
prevents phosphodiester bond formation in viral genomic replication when it is incorporated
Why is resistance to acyclovir rare?
While possible it is rare because there is a high barrier - when the virus compromises its ability to separate thymidine kinase, it becomes less fit so there is not a good selection pressure.
Why doesn’t acyclovir damage human cells?
It has a degree of specificity.
It is delivered in anunphosphorylatedform (ACV’) and will only interfere with replication once it becomestriphosphorylated.
onlyvirus-infected cells will contain thymidine kinase, the enzyme required to add the first phosphate on toform ACVMPwhich can then go on to become ACVTP (triphosphate) which can then be incorporated into the growing DNA.
Further specificty comes from the fact that ACVTP has ahigher affinity for viral DNA polymerase
What are other antivirals?
Remdesivir - Hep C, ebola, covid
What are some HIV treatments?
HAART - highly active antiretroviral therapy
PrEP - preventative, taking HIV antivirals daily to prevent possible HIV infection during sex with an infected partner.
AZT -
guidelines recommend that everyone with HIV should start treatment immediately, usually with three anti-HIV drugs.
For the combination of three antivirals, these drugs are available combined with the NNRTI efavirenz in a pill called Atripla.
Why is combined therapy important for HIV?
If the person is already HIV infected, they may have a lot of virus in their body already.
Treating with only two drugs could lead to selection of resistance more easily than the standard which is three drugs at once.
What does Methicillin-resistance Staphylococcus aureus acquire to be able to resist beta-lactam antibiotics?
PBP 2a peptidoglycan transpeptidase that can catalyse cell wall biosynthesis in the presence of béta lactams
What aspects of HIV virus drugs target?
Inhibit entry of virus by stopping it attaching to its receptors
Inhibit fusion of the viral membrane with host cell membrane
Targets reverse Transcriptase, enzyme unique to retroviruses
Targets integrase, unique enzyme
Target proteases
What must be considered when making an antibody against influenza?
Targets unique/essential gene or function of virus
Effective against a range of strains
Easy to administer even to very sick patients
Few side effects for compliancy
Why is amantadine no longer useful?
completely useless now as a single point mutation on the binding site ie S31N
little to no cost to the fitness of the virus which means there’s strong selection
every modern flu strand is resistant to amantadine.
What is baloxavir?
Anti-influenza drug that inhibits the Polymerase acidic endonuclease (PA endonuclease) prevents transcription of viral mRNA
mutation is conferred by single point mutations in PA138T
What are the two types of antivirals used to treat HCV? and give some examples of each
Protease inhibitors - telaprevir, boceprevir, asunaprevir, simeprevir, faldaprevir
NSSB polymerase inhibitors - inhibit Hep C protein NSSA which is part of the replication complex
Why is it difficult to cure HIV?
What cures did happen?
HIV integrates its genomic sequence into the DNA of the cell
Reservoir cells in HIV patients even when viral load is controlled
2 patients - bone marrow transplants of cells from people naturally resistant to HIV due to mutations in CCR5 co-receptor gene so HIV could not enter new cells
What is palivizumab?
Passive immunotherapy - antibodies taken from recovered individuals or from immortalised B cells
Against RSV (respiratory syncytial virus)
What is palivizumab?
Passive immunotherapy - antibodies taken from recovered individuals or from immortalised B cells
Against RSV (respiratory syncytial virus)
What is dexamethasone?
Steroid antiviral - targets pro inflammatory
What is toculizimab?
IL6 antibody - targets pro inflammatory
How do nucleoside anaolgues work? Give some examples
as antimetabolites by being similar enough to nucleotides to be incorporated into growing DNA strands; but they act as chain terminators and stop viral DNA polymerase
Acyclovir
Remdesivir
Favipiravir
