Antiviral chemotherapy Flashcards
1
Q
What is herpesvirus?
A
Large family of DNA viruses
2
Q
What is the size of the herpesvirus genome?
A
100 - 250 kb
3
Q
Who does herpesvirus infect?
A
All mammalian and bird species and also fish and invertebrates
4
Q
How many subfamilies of herpesvirus are there?
A
Eight - 3 alpha, 3 beta and 2 gamma
5
Q
What is the most common herpesvirus?
A
Herpes simplex type 1
6
Q
What does Herpes simplex type 1 most commonly present as?
A
Cold sores
7
Q
Why is HSV1 particularly dangerous in children?
A
Children can touch cold sores and rub eyes which can lead to blindness
8
Q
What is Herpes encephalitis?
A
Infection of HSV1 in the brain (primarily temporal lobes) which can lead to oedema, haemorrhages, necrosis and eventual death
9
Q
What proportion of people are infected with HSV1?
A
67% of people below the age of 50 (3.7 billion people)
10
Q
Where is Herpes simplex type 2 particularly worrying?
A
In the developing world
11
Q
What does Herpes simplex type 2 most commonly present as?
A
Genital herpes
12
Q
What proportion of people are infected with HSV2?
A
11% of the population (417 million people)
13
Q
What is the Varicella Zoster Virus more commonly known as?
A
Chicken pox or Shingles
14
Q
What are the concerns associated with Varicella Zoster Virus?
A
Becoming an increasing problem in the ageing population and can lead to nerve damage and long term pain
15
Q
What is Kaposi’s sarcoma?
A
Oncogenic herpesvirus - anti-proliferative tumour of skin, lymph nodes and viscera
16
Q
Where is Kaposi’s sarcoma particularly concerning?
A
The developing world - it is most common in sub-saharan African and there are currently no treatments
17
Q
What four diseases is KSHV a cause of?
A
- Kaposi’s sarcoma
- Multi-centric Castleman’s disease
- Primary effusion lymphoma
- KSHV inflammatory cytokine syndrome
18
Q
How many lifecycles does herpes simplex virus have?
A
Two distinct life cycles
19
Q
What is the lytic cycle?
A
Virus replicates in epithelial cells, in the host cell nucleus , leading to production of infectious particles (virions) and destruction of host cell
20
Q
What is the latent cycle?
A
Infectious virions travel up the neuronal axon to neuronal ganglion in CNS sits in the epitome of the brain and is not incorporated into the genome. When the immune system is compromised, virus seizes the opportunity to reactivate and produce infectious virions. Cycle begins again.
21
Q
How does the virus maintain a latent state?
A
Virus must evade host immune response and so limit virus gene expression
22
Q
What are the five stages of the lytic cycle?
A
- Virus entry
- Transcription
- Genome replication
- Virus assembly
- Virus envelopment/release
23
Q
What is the biggest challenge in treating the virus?
A
Latency - herpesviruses have evolved strategy to persistently infect the host via lifelong latent infection
24
Q
What are the general principles for the treatment and management of herpesviruses?
A
Have to treat the lytic cycle
25
How is HSV-2 transmitted?
Sexually, only when lesions are present.
26
Is there a cure for HSV-1 and 2?
No, but there are effective antiviral drugs to alleviate symptoms and decrease virus shedding
27
What are the three antivirals used to treat HSV-2?
1. Acyclovir
2. Valacyclovir (pro drug of acyclovir)
3. Famcyclovir (pro drug of penciclovir)
28
What is a prodrug?
Once administered it is metabolised into an active state
29
Which of the three antiviral for herpes have the greatest oral bioavailability?
Valacyclovir (esterified version of acyclovir) and famcyclovir
30
What is the drug classification of acyclovir?
Guanosine analogue
31
What is the mechanism for acyclovir?
Activated by viral thymidine kinase and further phosphorylated by two cellular kinases. It is incorporated into viral and cellular DNA of infected cell and disrupts viral and host polymerases preventing chain elongation and causing cell death.
32
What is the drug regimen for genital herpes (HSV-2)?
Continuous drug regimen for people with recurrent episodes
33
Why is there a need for new antivirals
Acyclovir resistant strains are becoming evident
34
What is a useful alternative to acyclovir?
Helicase - Primase inhibitors
35
What is the purpose of the helicase - primase complex?
Responsible for DNA replication so make DNA for the virus
36
Why are they a great target for inhibition?
As a complex they have DNA helicase, RNA polymerase and ssDNA activated by ATPase
37
What is the mechanisms for Helicase primase inhibitors?
Prevent movement of polymerase, causing chain termination
38
Give an example of a helicase - primase inhibitor
BILS179
39
Describe some methods for prevention of HSV-2
Abstinence if symptomatic and use condoms at all other times (still a risk)
40
What is vertical transmission?
Passage of disease-causing agent from mother to baby during the period immediately before and after birth
41
Why is it extremely important to prevent vertical transmission of HSV-2?
HSV-2 is horrendous in newborns - severe neuronal damage and fatality (encephalitis and skin and eye diseases) - can lead to cognitive impairment, oral dysfunction and other complications
42
How is vertical transmission prevented?
Daily dose of acyclovir from 36 weeks onwards and Caesarean section where possible
43
How does Varicella Zoster virus develop?
Causes chickenpox in children, latent infection when reactivated in older people causes shingles
44
Why is shingles more prevalent currently?
Due to ageing populations
45
Why is there significant morbidity associated with shingles?
Major pain complication (post-herpetic neuralgia)
46
What is post herpetic neuralgia?
Nerve damage causes by Herpes Zoster (loss of neurites and fewer nerve endings) - leads to excruciating pain
47
What are the three antivirals used against VZV?
1. Cidofovir derivatives
2. ASP2151 (Helicase - primase inhibitor)
3. Bicyclic pyrimidine nucleoside analogues
48
What is the drug classification of Cidofovir derivatives?
Acyclic nucleoside phosphonate
49
What is the mechanism of Cidofovir derivatives?
Similar to acyclovir - selectively inhibit viral DNA polymerase preventing viral DNA replication and transcription
50
What is the difference between mechanism of Acyclovir and Cidofovir?
Cidofovir is not activated by viral TK because it is a nucleoside phosphonate and only requires 2 phosphorylation steps to become active
51
How does ASP2151 work?
Acts like BILS179 inhibiting Helicase - primase complex, but is just more specific for VZV
52
What is the best drug for shingles and why?
BCNAs because they are really potent (almost 10,000 fold more potent than acyclovir)
53
What is the drug classification for BCNAs?
Nucleoside analogue
54
What is the mechanism of BCNAs?
Similar to acyclovir but no cellular kinase step as it is phosphorylated before it enters the cell making it very specific
55
What is another important element in the treatment of VZV?
Treating the pain as well as the virus
56
What are some methods of pain treatment in VZV?
Opioid analgesics such as morphine and oxycodone (treat acute and persistent pain)
57
How do opioid analgesics work?
Bind to opioid receptors in the brain
58
What are some of the side effects of opioids?
Drowsiness, cognitive slowing and nausea
59
Why are Tricyclic antidepressants sometimes administered with opioids?
Opioid receptors in the brain play a role in depression so they are administered to counter act the side effects and enhance mood and sleep
60
What is "ZOSTAVAX"?
The life attenuated vaccine programme for VZV
61
What is a life attenuated vaccine?
A vaccine containing a modified pathogen that is still able to replicate when injected and produce immunity but mostly do not cause illness
62
What is the purpose of the ZOSTAVAX vaccine programme?
Reduce the incidence and severity of shingles disease in people aged 70 and above and reduce Post-herpetic neuralgia
63
How does ZOSTAVAX work?
Boosts individuals immunity so that the latent virus is less likely to reactivate and produce infectious virions
64
What is unusual about KSHV?
Its latency site isn't the brain its in the B-lymphocytes
65
How does KSHV cause tumours?
Virus is reactivated in the B lymphocytes and enters the lytic cycle; the virus spreads through the blood causing tumours
66
What is the current treatment for KSHV?
There is no current treatment - present therapeutics involve targeting HIV-related immunosuppression and using conventional cancer chemotherapy
67
Which two antivirals hold the most potential for HSHV treatment?
VEGF inhibitors and Kit inhibitors
68
Give an example of a VEGF inhibitor
Bevacizumab
69
Give an example of a Kit inhibitor
Imatinib (Gleevec)
70
Why is VEGF inhibition a good target?
KSHV induces vascular endothelial growth factor (VEGF) pathway
71
Why is Kit inhibition a good target?
KS tumours have been shown to express c-kit
72
What is c-kit?
A tyrosine kinase that regulates intracellular processes such as cell growth, division and migration
73
How does Bevacizumab work?
It is a humanised monoclonal antibody that recognises and blocks VEGF A
74
How does Imatinib work?
Specific inhibitor of tyrosine kinase enzymes - it occupies the TK active site leading to a decrease in activity
75
Why is influenza virus so important?
One of only few pathogens with the potential to decimate the human population - future emergence of another highly pathogenic strain that is highly transmissible is inevitable
76
What is the classification of influenza virus?
RNA virus - negative sense
Order: Articulavirales
Family: Orthomyxoviridae
77
How many variants of influenza are there?
Four
78
Which influenza variant has the most potential to case global pandemics?
Influenza virus A
79
How is influenza transmitted?
Through respiratory secretions (breathing, sneezing, coughing) small airborne droplets
80
What are the tissue targets for influenza?
Epithelial cells lining the respiratory tract
81
What are the symptoms for influenza?
Tiredness, sore throat, runny nose, head and muscle ache, fever and cough
82
Describe the disease progression of influenza?
Rapid onset of symptoms (24 hours); symptoms peak day 3 and persist until day 8 or 9
83
What causes the majority of the symptoms?
Massive innate immune response
84
Describe the external morphology of influenza
Pleomorphic particles (80-120 nm), outer membrane with three membrane proteins (NA (trimer), HA and M2 (tetramers) )
85
Describe the internal morphology of influenza
The virus interior includes eight RNA segments comprising of viral genes
86
Briefly describe the viral life cycle of influenza
1. Virus binds sialic acid receptor via HA, internalised by endocytosis
2. Low pH induced membrane fusion via HA
3. Segments released into cytoplasm
4. Segments imported into nucleus
5. RNA synthesis
6. RNA/RNP export (translation)
7. Virus assembly at plasma membrane
8. Release using neuraminidase enzyme
87
Why do we need an influenza antiviral?
Influenza virus is always mutating and new viruses are constantly emerging
88
How do influenza antivirals typically work?
Target stages of the virus life cycle, specifically 3,5 and 8
89
What are the Adamantanes?
Amantadine and Rimantadine - stage 3 blockers
90
Which influenza variant are Adamantanes specific for?
Influenza virus A
91
What are the pros and cons of Adamantanes?
They are cheap and effective but must be administered during early stages of infection (before day 2)
92
What role does M2 channel play in virus life cycle?
Stage 3 - M2 is needed for the RNPs to enter the cell because it forms a transmembrane proton channel causing an influx of H+ ions causing the matrix layer to breakdown, allowing segments to be released into the cytoplasm
93
How do the Adamantanes work?
They prevent M2 ion channel activity by binding to them, either blocking tor closing the pore so the matrix layer remains intact an the virus cannot exit the endosome
94
What is the problem with Adamantanes?
Most human influenza strains are now resistant
95
How is Adamantane resistance conferred?
Virus mutations within the M2 channel itself (valine to isoleucine and serine to asparagine)
96
What is the result of the Adamantane resistance?
They are no longer FDA approved
97
What is xofluza?
Pro drug and stage 5 blocker - inhibition of endonuclease active site
98
What is the role of the endonuclease in stage 5?
cleaves the host cell mRNAs for protein synthesis
99
How does xofluza work?
Binds the PA endonuclease active site and reduces the virus titres by 1000 fold - alleviating symptoms within 2 days
100
Has any resistance to xofluza been detected?
Yes but only in the lab
101
Why is neuraminidase (NA) essential for virus release in stage 8?
NA needs to be able to bind and cleave sialic acid on the old cell so that the virus can be released from the cell and spread and infect new cells
102
What was the principle for the strategy to block stage 8?
Design a molecule that could outcompete NA by binding sialic acid better (early example of structure based design)
103
What are the three antivirals that block stage 8?
Relenza (zanamir) aerosol, Tamiflu (oseltamivir) oral tablet and Repivab (peramivir) IV
104
How do the stage 8 blockers work?
Mimic sialic acid and block the NA active site so it can no longer bind and digest sialic acid so virus cannot be released and the infection is contained
105
How effective are NA inhibitors?
Drugs must be given early on in the infection - could be enough to slow the spread (£500 million stockpiles of tamiflu and relenza exist in the UK)
106
What is the future of influenza antivirals?
Targets in other aspects of the influenza virus life cycle are being pursued
107
What is ribavirin?
Probably the most promiscuous antiviral - there are many forms across many countries
108
What is the drug classification of ribavirin?
Guanosine analogue with incomplete purine ring
109
How is ribavirin administered?
Aerosol or oral tablet - it is a pro drug that is modified in vivo by kinases
110
What is ribavirin active against?
RNA and (few) DNA viruses (unusual)
111
What is ribavirin frequently used to treat?
a. Hepatitis C virus (FDA approved)
b. Respiratory syncytial virus (FDA approved)
c. Lassa fever virus (Non FDA approved)- used as a last resort
d. CCHFV (Non FDA approved) – used as a last resort
112
What is ribavirin occasionally used to treat (activity shown in limited human trials)?
a. Influenza virus
b. West Nile virus
c. Dengue virus
d. Measles virus
e. Hantavirus
f. Rabies virus
g. SARS coronavirus
113
What is ribavirin never used to treat (activity shown in animal models) ?
a. Smallpox virus
b. Polio virus
c. LCMV
114
Give an example of when ribavirin has be used as a last resort
Treatment of rabies virus - there are only three documented cases of survival without vaccine and ribavirin was used
115
Which two viruses is ribavirin FDA approved for?
Hepatitis C and HRSV (Human Respiratory Syncytial virus)
116
What is the genetic makeup for Hepatitis C?
Positive sense RNA
117
What is the genetic makeup for HRSV?
Negative sense RNA
118
What is the general life cycle for Hepatitis C?
Over 50% develop CHRONIC life-long disease (infected can live for 20 years showing no symptoms)
119
What is the general life cycle for HRSV?
Transient and individual will show symptoms 3 to 5 days after infection it is short lived - LYTIC
120
What is the cell tropism for Hepatitis C?
Hepatotrophic (liver)
121
What is the cell tropism for HRSV?
Respiratory pathogen (any cells along the respiratory tract)
122
How is Hepatitis C transmitted?
Via the blood (needle sharing, use of blood product or sexual contact)
123
Describe Hepatitis C treatment using ribavirin
Combination therapy vastly more effective than monotherapy (ribavirin and interferon) but treatment is long with flu symptoms the whole time (24-48 weeks) and still only 50% chance of success - looking for new antivirals
124
Describe HRSV treatment using ribavirin
Aerosol so it gets to lungs and patients isolated due to toxicity - mild benefits at best
125
What are the mechanisms of ribavirin?
Despite being old the mechanisms remain unclear...
1. inhibition of IMPDH by ribavirin 5' monophosphate
2. Error catastrophe
3. Inhibition of RNA polymerisation by the RdRp
126
What is IMPDH required for?
Maintain GTP levels required for cellular RNA and DNA synthesis (converts IMP to XMP
127
How does Ribavirin inhibit IMPDH?
Competitively inhibits IMPDH so IMP can't be converted to XMP, so GTP levels aren't maintained and virus can't replicate
128
How does virus genome replication occur?
Genome replication is carried out by a viral polymerase RdRp
129
What is the issue with RNA virus replication by RdRp for the virus?
It is error prone - increased error rate is lethal to viruses
130
What does ribavirin do to the error rate?
4-10 fold increase in RdRp errors
131
How does ribavirin increase the RdRp error rate?
Ribavirin base pairs with C and U bases rather than G and A pairing with them - enhanced errors in the base sequence leads to error catastrophe
132
How does ribavirin inhibit RdRp action?
Ribavirin fits in the polymerase active site (catalytic site), and mimics an rNTP . It occupies a slightly different position, with different contacts. Performs different function and compromises polymerase activity. This leads to 5 times reduced genome synthesis and reduced virus production
133
What are the drawbacks of ribavirin treatment?
Efficacy as monotherapy is not great
General cytotoxicity (Haemolytic anaemia)
Can affect developing foetus
134
Why is ribavirin actually used?
Often used as a last resort for many viruses that still don't have treatment and viruses with a fatal outcome
135
What is the future for ribavirin treatment?
As we understand more about ribavirin there is more potential to improve mechanism to make it more effective
136
What is viramidine?
A derivative of ribavirin (more efficient structural biology) - a more active prodrug with lower toxicity and better tissue specificity
