antiviral (Dr. Cochrane) Flashcards
What is CC50?
Drug concentration at which reduces cell viability by 50%
How to find selectivity (SI) or therapeutic index (TI)?
CC50/IC50
What does a high TI/SI indicate?
drug is more selective to the virus targeted
what is drug clearance affected by?
i) metabolism in liver
ii) excretion through kidney/gut
Factors to consider when developing antivirals
i) toxicity of drug (try to minimize)
ii) efficacy of drug (better if done in low conc)
iii) drug delivery (how is the drug delivered to site of infection)
iv) drug clearance
v) how quick does drug resistance occur in virus?
Ways to deliver drug to targeted site
i) gut
ii) IV, inhalation, topical
iii) directly to site of infection (reduce toxicity while maximize drug efficacy)
What happens after pattern recognition receptors are activated?
signaling induced through IRF3/7 or NFkB
–> express interferons + proinflammatory cytokines
Pattern recongition receptors found on cell surface
TLR2,4,6
Pattern recongition receptors found on endosome
TLR3,7,8,9
Pattern recongition receptors found in cytoplasm
RIG-1, cGAS
What does TLR2,4 detect?
viral coat proteins
What does TLR7,8 detect?
ssRNA
What does TLR3, MDA5, RIG-1 detect
dsRNA
What does cGAS detect?
DNA
What does TRL9 detect?
hypomethylated CpG DNA
what PRR detects dsRNA?
TLR3, MDA5, RIG-1
what PRR detects DNA?
cGAS
what PRR detect viral coat proteins?
TLR2,4
What PRR detect hypomethylated CpG DNA?
TLR9
What PRR detect ssRNA?
TLR7,8
What happens after interferon interacts with its receptor?
signalling –> increase interferon-stimulated genes (ISG) expression
–> increase the cells’ ability to repsond and block virus replication
Types of interferon present
i) type I
ii) type II
iii)type III
examples of type 1 interferon
interferon alpha, beta
examples of type II interferon
interferon gamma
examples of type III interferon
interferon pheta
where are type I interferons found?
all nucleated cells
Where are type II interferons made?
T helper cells, NK cells, CD8 killer cells after they are activated
Examples where immune system leads to serious clinical outcomes
immune system hyperactivated (too much cytokines)
–> systemic inflammatory response syndrome (SIRS) or ARDS in Covid
–> multi-organ failure, systemic damage
Where is interferon treatment applied to?
hepatitus B, C with interferon alpha
–> more than 24 weeks
possible side effects of interferon treatment
have significant side effect reducing quality of life
Alternative approach to using interferon
activate innate immune system with TLR7/8 agonist (Imiquimod)
–> treat warts (HPV)
drugs that inhibit viral entry
i)Miraviroc
ii)T20
iii)Sunitinib (inhibits AAK1, GAK)
iv) lenacapavir (HIV-1, by binding to capsid)
How does Miraviroc work?
binds to CCR5 coreceptor –> compete with HIV-1 Gp120
How does T20 work?
mimic one of helical bundles
–> prevent six helical bundle from forming
Drugs that inhibit endosome release
i) chloroquine
ii) amantidine
How does chloroquine work?
prevent acidification of endosome needed for many virus
–> absorb protons to prevent pH change
How does amantidine work?
bind to M2 ion channel on influenza A virus
–> block ion flow
Why amantidine no longer recommmended for treatment?
lots of resistant virus formed
Drugs that inhibit viral genome replication
acyclovir
How does acyclovir work?
recognize and phosphorylate thymidine kinase of herpes virus
What viruses do acyclovir work on?
herpes virus
Herpes inhibitors present
i) Acyclovir (phosphorylate thymidine kinase)
ii) other chain terminators (e.g. famciclovir and other drugs with -vir)
iii)Foscarnet
How does Foscarnet work?
block PPi binding site in polymerase
–> prevent PPi being cleaved from deoxynucleotide triphosphate
Concentration of foscarnet needed to inhibit viral polymerase
100 fold lower than cellular DNA polymerase is inhibited
How do drugs inhibit viral reverse transcription in HIV-1?
i) these drugs lack 3’OH in ribose
–> cannot add next base
ii) induce conformational change by binding to other sites on RT
–> affect polymerization site
Why are inhibitors for viral reverse transcription able to incorporate in DNA?
lack 3’ to 5’ exonuclease in reverse transcriptase
other infections where HIV-1 NRTi inhibitors are used on
HBV (lamuvidine, tenofovir)
How does tenofovir work?
also facilitate chain termination even tho it has 3’OH
How does non-nucleoside reverse transcriptase inhibitors (NNRTi) work?
bind to other site
–> induce conformational change in RT that changes polymerase active site
Drugs that inhibits integration of HIV-1
i) dolutegravir
ii) cabotegravir
why does dolutegravir have high barrier to drug resistance?
i) long plasma half-life
ii) slow dissociation rate
what’s special abt cabotegravir?
long half life
–> can be formulated as nanoparticle injection
drugs that inhibit HIV-1 capsid interaction
lenacapavir
How does lenacapavir work?
bind to HIV capsid in a pocket between capsid protein in hexamers
Effect of using lenacapvir in HIV-1 life cycle
i) Viral entry – by interacting with sites that help traffick viral core to nucleus
–> virus stay in cytoplasm
ii) Viral core assembly
–> interfere with capsid-capsid interaction of Gag
–> prevent viral particle assembly + release
How does inhibitors to HIV-1 protease work
bind to catalytic site of HIV-1 protease
–> mimic transition state of substrate during rxn
Describe HIV-1 treatment evolution
i) first used AZT, not effective after couple of months
ii) combine multiple drugs to lower the chance of virus obtaining resistance on all of the drugs
Standard therapy for HCV?
interferon + ribavirin
newer treatment for HCV
combination of drugs that target different virus coded proteins (NS3 protease, replicase)
What does the newer treatment for HCV target
NS3 protease, NS5A&B replicase
What is targeted within SARS-Cov2?
i) viral protease
ii) viral replicase
how does viral protease affected by drug?
prevent processing of viral polyprotein precursors needed for viral replication
Drugs that target viral protease of SARS-Cov2
Paxlovid
–> nirmatrelvir + rotonavir
Strategies used to target viral replicase of SARS Cov-2
i) stalling by replacing ATP with RTP – elongation barrier after three nt added – RdRp stalling
ii)induce hypermutation (increase rate of forming defective viral genome)
Drugs used to target viral replicase of SARS-Cov2
remdesivir –> stalling
molnupiravir, favipiravir
–> hypermutation
How does molnupiravir and favipiravir work?
induce hypermutation (increase rate of forming defective viral genome)
How does remdesivir work?
stalling by replacing ATP with RTP – elongation barrier after three nt added – RdRp stalling
How is viral release inhibited by drugs?
i)target neuraminidase by mimicking its substrate
–> unable to cleave sialic acid
–> cannot leave the cell and infect others
ii) lenacapavir by binding to capsid that prevent virus assembly and release
iii) Nilotinib –> prevent assembly plus release of Ebola
Function of viral neuraminidase
cleaves terminal sialic acid from surface glycoprotein
–> prevent re-infection + allow virus to leave and infect others
When can inhibitors for neuraminidase be used?
i) 36 to 48 hrs after onset of illness
ii) can be used before or after exposure of influenza A and B (prevent disease)
Alternate approaches to drug development
i) re-purpose FDA approved drugs
ii) develop compounds that prevent virus to use cellular processes
Examples of drugs being re-purposed
i) Lamuvidine –> HIV-1, HBV
ii) Cyclosporine A
iii) Nilotinib
What virus can ribavarin be used in?
HCV, RSV
What are the proposed mechanisms for ribavirin?
i) Inhibit inosine monophosphate dehydrogenase (IMPDH)
–> reduce GTP available
ii) modulate immune function thru T helper type 1
iii) inhibit RNA 5’ capping –> recognized by immune system
iv) inhibit viral RNA polymerase
v) increase mutation frequency
the effect of inhibiting RNA 5’ capping to virus
less stable RNA, get recognized by immune system
Original function of cyclosporin A
as a calcineurin inhibitor that act on T cells
–> immunosuppressive drug to block t cell proliferation
What does cyclosporin A act on
cycophilin A –> proline cis0trans isomerase
Which viruses do cyclosporin A act on?
HCV, HIV
How does cyclosporin A act on HCV?
dissociate cyclophilin A from replicase
–> stop replication
How does cyclosporin A act on HIV?
destabilize capsid
–> stop nuclear import of viral genome, block viral infection
Where is cyclophilin A found in HCV?
part of replicase complex
Where is cyclophilin A found in HIV?
binds to incoming viral capsid
–> stabilize it to allow import into nucleus
Drug that target viral glycoprotein maturation
castanospermine
How does castanospermine work?
inhibits ER alpha-glucosidase I
–> stop removal of terminal glucose on N-linked glycans
–> disrupt folding of viral proteins
What does castanospermine act on
ER alpha-glucosidase I
Which virus does castanospermine act on?
Dengue virus (all 4 serotypes)
–> no effect on yellow fever, west nile virus
Original purpose of nilotinib
cancer drug through inhibiting ABL of BCR-ABL involved in modulating cell signalling
What is nilotinib re-purposed to?
Ebola virus –> reduce production of viral particles
How does nilotinib help to stop virual growth?
ABL phosphorylation needed on VP40 of Ebola
–> bind to ABL portion will stop viral particles from leaving
What are the targets for drugs that inhibit membrane trafficking
AAK1, GAK
How does inhibitors of AAK1 and GAK have an effect on virus?
affect virus entry and release
–> affect intracellular trafficking of viral particle
What does AAK1 and GAK help virus?
acts as kinase regulators for AP1 and 2
–> essential for HCV infection
Which viruses do inhibitors on AAk1 and GAK work?
HCV, West nile, Zika, dengue, ebola
What happens if inhibitors for membrane trafficking are added post-infeciton?
no effect on viral RNA replication
A host mechanism where durgs can use to manipualte
RNA splicing
Viruses that uses alternative RNA splicing
HIV-1, adenovirus, influenza, papilloma, herpes
Drugs tested to alter RNA processing
digoxin
Original purpose of digoxin
inhibit Na+/K+ ATPase
–> more Ca2+ accumulate
==> stronger contractions
Why is digoixn not a viable treatment
limited therapeutic index
–> need high dosages for it to work
Which virusesis digoxin effective on?
HIV, adenovirus, SARS-Cov2
Strategies to prepare for future pandemic
i) vaccine
ii) virus-directed antiviral
iii) host-directed antivirals
Advantage of using host-directed antivirals
i) resistance not as worried as interaction with host is crucial
ii) broad-spectrum
Problems of using vaccine
short shelf-life may limit ability to store vaccines
How to develop host-directed antivirals
i) generate population of cells with CRISPR with one gene disrupted in each cell
ii) infect cells with virus –> virus kill susceptible cells
iii) harvest surviving cells, isolate DNA
–> identify the killssgRNA sequence
iv) identify antiviral properties of known inhibitors of identified proteins
Issue of using virus-directed antiviral
specificty of antivirals might limit effectiveness of treatment
–> use combination of drugs to slow down buildup of resistance
