Antivirals Flashcards
Virus characteristics
non-cellular. Obligate intracellular parasites, require host to replicate. RNA or DNA genome, can be enveloped by lipid membrane, 20-350nm diameter.
Simple life cycle of virus
Enter host cell. RNA/protein synthesis to replicate genome. Further protein synthesis to assemble new inflectional viral particles. Release new viral particles from cell for further infection.
Functions of host cell
The raw materials for viral biomolecule synthesis (amino acids, nucleotides). Machinery for protein synthesis. Protective membrane. Transport around cell.
Properties of antiviral drugs
Cell membrane permeable. Selective against cellular targets. inhibit virus-encoding proteins or viral-spefic functions. Target a critical stage of virus life. Little resistance potential.
HIV structure
gp120 surface glycoprotein, gp41 transmembrane glycoprotein, p17 matrix antigen, p24 capsid antigen enclosing genome, unique reverse transcriptase protease and integrase enzymes.
Pathology of HIV
Qualitative and quantitative decline in CD4+ lymphocytes. Infects CD4 cells = dendritic cells, T-lymphocytes and macrophages. CD4=glycoprotein
Course of HIV infection
primary phase illness = high viraemia, decreasing CD4 count. Asymptomatic phase =(10yrs+) viraemia stays at set point and steady decrease in CD4, AIDS phase = great increase in viraemia, drop in CD4 count.
HIV therapy
HAART. Nucleoside analogue reverse transcriptase inhibitors. Non-nucleoside reverse transcriptase inhibitors, Protease inhibitors. 2NRTI and 1PI or NNRTI. 99% reduction in viraemia in 8 weeks. Can interrupt treatment and can manipulate Rx.
Reactions in HIV cell
Reverse transcriptase = create double stranded DNA copy of single stranded RNA genome. Integrase = ingrate DNA into nucleus. Maturation of new virons to become infectious = proteases.
NRTI mode of action
Selective reverse transcriptase inhibitors. Needs to be phosphorylated by cellular kinases. Act as analogue to endogenous substrate thymidine triphosphate but drug lacks 3’-hydroxyl group preventing phosphodiester bonding. Incoperatd into chain at 5” area. Product is chain terminator so abnormal DNA created.
NRTI problems
Resistance within patients, virus replication recovers as RT mutates. Life long treatment as memory cells act as reservoir for virus. Toxicity: (gamma DNA of mitochondria particular target and cause of ADR ) GI upset, anaemia and other blood disorders, dizziness, insomnia, headache.
NRTI examples
Azidothymidine (AZT/Zidovudine), Deoxycytidine, Adenosine.
NNRTI
Bind to allosteric site on enzyme but various structures within group. Do not compete with NRTI so can use in combo.
Examples of NNRTI
Etravirine, Efavirenz.
Enzymes in HIV
All from Pol gene on genome. reverse transcriptase, protease, integrase.
Proteins in HIV iron maturaion
Gag and Gag-Pol. Cleave when virus buds off . Need protease to cleave.
Protease inhibitors for HIV and example
Competitive inhibition of aspartyl protease. This enzyme is needed to create functioning proteins from poly proteins. Inhibition prevents production of mature viral particles. Needs to be membrane permeable. e.g: Nelfinavir, Saquinavir
Hepatitis C pathology
7 different genotypes with different toxicities. 15% get initial acute infection then clearance. 85% get chronic infection of which 50% get mild hepatitis with normal ALT and 50% get elevated ALT, cirrhosis and increase risk of heptatocellular carcinoma.
Life cycle targets for HCV
Translation and polyprotein processing, need protease and helicase enzymes = NS3 inhibitors. RNA replication with RNA-dependent RNA-polymerase (5B) 5A know enzyme = NS5A/NS5B inhibitors.
NS3 inhibitors types
Protease inhibitors. 1st gen are potent but high resistance, specific to genotype 1 e.g. telaprevir. 2nd gen potent, less resistance, wider genome spectrum e.g. simprevir.
NS5A
NS5A: Not enzyme but acts in RNA replication, viral assembly, interaction with RNA and cellular factors/proteins. Target is in domain 1 of protein.
NS5A inhibitors
e.g. daclatasvir. VERY POTENT even at picomolar levels. 1st gen risk resistance high. 2nd gen have broader genome spectrum.
NS5B inhibitors
Inhibit RNA polymerase. e.g. sofosbuvir.
NICE guideline for genotype 1
12 weeks. Sofosbuvir (NS5Bi) and NS5Ai Velapatasvir. get clearance of virus.
Alpha herpes simplex viruses and pathology
1,2,3. HSV1 = oral and ocular (cold-sores).
HSV2 = genital.
HSV3 = chickenpox & shingles/Varicella Zoster
Beta herpes simplex viruses
5,6,7
Gamma herpes simplex viruses and pathology
4,8. ONCOGENIC. HSV4 = Epstein-Barr virus, B cell tumours. HSV8 = Kaposi’s sarcoma herpes virus
Varicella Zoster
HSV3
Life cycle of HSV
Latent = viral capside is in epithelial cells, travels to CNS ganglion up afferent axon. Quinescent stage, transcriptionally silent, no immune response. Lytic = stimulus re-activates silent virus. Virons release and move back down axon and symptoms seen at original infection site.
HSV1 and HSV2 treatment
Acyclovir, Valacyclovir (acyclovir derivative), Famcyclovir
Acyclovir Action
OTC, little effect on genital herpes. Pro-drug requires vial kinase to form monophosphate form and cellular kinase to form di and tri-phosphate forms. The triphosphate form interferes with DNA polymerase action and can be incorporated into the chain in the place of guanosine. Inactivates DNA polymerase. Chain termination = cell death.
Use of acyclovir
HIV patients use as prophylaxis. Prevent vertical transmission to newborns in pregnant and infected mothers. Resistant strains emerging!
Alternative to acyclovir due to emergence of resistant strains.
Helicase-Primase Complex Inhibitors e.g. Amenamivir and Pritelivir. Bind to complex and prevent movement of enzymes along DNA strand so no complete DNA synthesis. Enzymes in complex: DNA Helicase, RNA polymerase and ssDNA-stimulated ATPase. Shown to reduce virus shredding in clinical trials. Few side effects
Enzymes in Helicase-Primase Complex
DNA helicase, RNA polymerase, ssDNA-stimulated ATPase.
HSV3 symptoms and pathogenesis
Shingles and chickenpox. re-activation of virus = shingles and post-herpetic neuralgia. Neuronal loss causes abnormal signalling to CNS which translates into pain.
HSV3 treatment. Effects of acyclovir and 2 other options
Acyclovir (or derivative) = reduce new lesion formation, aid healing, shorten virus shredding, limit neurones damage and reduce pain severity and duration. Cidofovir derivative and Bicyclic pyrimidine nucleoside analogues.
Cidofovir derivatives
Selectively inhibits viral DNA polymerase so
no viral DNA replication and transcription. Is an acyclic nucleoside phosphonate, needs to be phosphorylated twice which cellular kinases can do so not viral specific.
Bicyclic pyrimidine nucleoside analogues
Activity similar but much more potent than acyclovir. Need to be phosphorylated 3 times so require viral enzymes (thymidine kinase). 2 forms created 5’-monphosphate and 5-diphosphate with the latter having great efficacy.
Kaposi’s sarcoma associated herpes pathology
Endothelial cell vascular cancer. Very aggressive in immunocompromised patients. Life cycle = latent phase inside B lymphocytes. reactivation & lytic phase to infectious virus. Infect spindle cells of endothelial origin and cause viral mediated malignant transformation.
Treatment of Kaposi’s sarcoma associated herpes
Different thymidine kinase in virus to other HSV so acyclovir can not be activated. HARRT can be used or novel agents e.g. vascular endothelial growth factor inhibitors, Kit inhibitors.
Vascular endothelial growth factor inhibitors
e.g. bevacizumab - monoclonal antibody which prevents action of VEGF-A which is involved in angiogenesis and inflammation of carcinogenic cells. NOT LICENSED still trialling.
Kit inhibitors
e.g. Imatinib. c-Kit is a tyrosine kinase receptor involved in regulation of cell growth, division and migration in response to stem cell factor. Kit inhibition by binding to active site and decreasing activity, decrease cell activity NOT LICENSED still trialling.
Antiviral which is a guanosine analogue with incomplete purine ring
Ribavirin.
Clinical aspects of ribavirin
Oral tablet or aerosol. Pro-drug needs phosphorylation three times to give ribavirin-triphosphate. Acts on RNA and some DNA viruses.
Comparison of FDA approved use of Ribavirin
Hepatitis C = +ve sense RNA genome. Infects liver. chronic lifecycle with latent phase. Rx is ribavirin with pegylated interferon. Human Respiratory Syncytial Virus = -ve sense RNA genome needing transcription, infects resp system. short lifecycle.
Examples of other non-licensed uses of Ribavirin.
Lassa fever virus, Crimean–Congo hemorrhagic fever virus, Rabies virus (ketamine induced coma to stop spread +ribavirin, 3 documented cases post exposure no vaccine), Influenza virus, Dengue virus
Mechanisms of Ribavirin action and clues to them
Inhibition of Inosine Mono-Phosphate Dehydrogenase IMPDH) / Error catastrophe by nucleotide misincoperation by RdRp / Inhibition of RdRp. From evidence of broad spec of antiviral activity and resistant strains are emerging.
Details of Inosine monophosphate dehydrogenase inhibition
IMPDH is needed to maintain GTP levels by converting inosine MP to xanthosine MP. GTP needed for RNA and DNA synthesis. Ribavirin MP will competitively inhibit IMPDH so no GTP for RNA synthesis. Reduction in GTP levels only see at low 20uM of AVx but only minor effect on viral particle growth at this conc. Defo another mode of action for greater effect at higher concs.
Error catastrophe details
replication with RNA dependent RNA polymerase very error prone to allow for adaptability. Limit to amount of mutations and too many e.g. with mutagen = lethal as no viable viruses made = error catastrophe.
Details on Ribavirin causing error catastrophe
Ribavirin incorporated in RNA strand in guanine and adenine and able to base pair with cytosine or thymine. Replication lacks fidelity. 50:50 change correct base pairing. Increase Ribavirin conc increase number of mutations/genome and lower infectious viral particles.
Details on RdRp inhibition action of Ribavirin
Slow down replication cycle by competitively inhibiting RNA dependent RNA polymerase. Analogous structure to endogenous substrate rNTP.
Disadvantages to Ribavirin
Monotherapy efficacy poor.
Avoid in pregnant woman
Cytotoxic and haemolytic aneamia.
Long half life in RBC.
Future Ribavirin derivative
Viramidine. Prodrug of Ribavirin. Better targeting. IN Phase 3 trials.
Influenza A virus
Infects humans other mammals and birds. 8 RNA segments, encoding 10 proteins, including M2ÁM2 protein. Severe disease causative. Most common human pathogen
Influenza B virus
Infect humans only. 8 RNA segments, coding for 10 proteins including M2/BM2 protein. Can cause severe disease.
Influenza C virus
Infect humans and pigs. 7 RNA segments coding for 10 proteins including M2/CM2 protein. Can cause severe disease.
Public health info on Influenza viruses
Most cause mild disease (seasonal flu, low pathogenicity) but some strains have high pathogenicity e.g. avian influenza. Spread via virus particles shredding and released in resp secretions e.g. breathing/sneeze/contact with infected surfaces. Increase in severity of symptoms as virus infects further down resp tract. Antigenic drift and shift mean constantly new strains = new vaccines
Structure of Influenza virus
Get outer membrane from previous host cell. Membrane proteins: NA (tetramer), HA (trimer) and M2 (tetramer). Matrix protein layer beneath membrane. Phleomorphic. RNA is -ve sense and in segments/split up.
Life cycle of influenza virus (ALL DETAIL).
HA/hemagglutinin protein helps virus bind to sialic acid receptor which are abundant on ciliated URT cells. Endocytosis. Acidic pH in cell conformationally changes HA so endosome membrane breaks. To break matrix protein layer M2 acts as H+ channel H+ ions in which leads to matrix breaking and 8 RNA segments released into cytoplasm. RNA imported to nucleus. RNA and protein synthesis inside host nucleus. New proteins and RNA assembled at plasma membrane. NA proteins prevents reinfection on new viral particle release. NA has long stalk which cleaves sialic acid from previous infected cell so cant have HA interaction again.
Antigenic drift
1 mistake in genome replication creates many new viral genomes
Antigenic shift
2 different viruses infect simultaneously so new viral particles created have RNA from both.
Adamantanes examples
Rimantadine, amantadine.
Mode of action of amandatanes
Structural analogue for M2 protein. Block H+ flow matrix remains intact and virus can not replicate.
Clinical aspects of Adamantanes
Influenza A only at low concs, higher concs have broader spec. Needs to be given in early stages of disease. Oral or aerosol. DO NOT TREAT INFLUENZA B
Resistance of Adamantanes
M2 mutations from antigenic drift. Prevent drug binding. VERY COMMON. Mostly S31N mutation single amino acid change. Serine to asparagine
Proteins of influenza virus
HA = hemagglutinin, sialic acid receptor interaction. M2 = matrix degradation as H+ channel. NA = Neuraminidase needed for release
Relenza
zanamivir) & Oseltamivir (tamiflu
Prevent the release of new virons and spread of virus. Inhibit neuraminidase by mimicking sialic acid. NA can not bind to receptor as drug interact with receptor at site 2 Glu119. Needs to be given in early stages of infection. Have higher affinity for NA than native sialic acid. Used against influenza A and B.
Other influenza treatment targets
NA and sailic acid interaction. This occurs at 5 different sites. A drug which binds to Salic acid better than NA would prevent interaction.
Stats on NRTI
Reduce vertical mother-to-child transmission by more 20%.
Paper on HAART effectiveness
Efficacy of treatment in Nigeria. 98 patients put on strict NNRT and NRTI treatment regime. At 18 months saw significant increase in CD4 lymphocyte count. Treatment also decreased plasma viral load.
Paper on ADR of HAART treatment
66 out of 339 HIV patients on a HAART regime in the Cameroon had an ADR with the most common being peripheral neuropathy. Other side effects in clouded GI upset, headaches, anaemia, dizziness with anaemia being the major cause of ADR associated hospital admission. However, symptomatic treatment helped prevent the need to alter the HAART regime.
Need for new Hep C treatment
Use of current regime of pegylated interferon and ribavirin can cause serious ADR which can be irreversible, therefore NS3, NS5A and B inhibitors could help improve quality of life in Hep C patients.
New treatment regimes for HepC
Randomised phase 3 clinical trials -> ASTRAL-1, -2, -3 and -4) show Sofosbuvir (NS5B inhibitor) and Velpatasivr (NS5A inhibitor) treatment of Hep C patients to give high sustained virological response (better viraemia).
Future HIV therapy targets
CCR5 - the entry portal for HIV. Disrupt function, prevent virus infecting cells.
Resistance to NA targeted influenza treatments
As Zanamavir is similar to natural ligand resistance potential is less. However, mutations in how the conformational changes occur on drug binding to NA or reducing the affinity of the receptor to the drug have led to mutations of NA inhibitors.
Why can’t bicyclic nucleotide analogues be used in HSV1 and 2
They are not recognised by HSV1 and 2 viral kinases so aren’t phosphorylated into active form.
Case reports of biopharmaceutical agents in HSV8/KSAH
Case report of male with well-suppressed HIV but recurrent Kaposi’s sarcoma treated with Imatinib (kit inhibitor) led to all sarcoma lesions resolving within 9 months.
