Lecture 2 HIV Hep C Flashcards
What is the definition of a virus?
A non-cellular micro-organism that can only replicate within cells
What does it mean by ‘obligate intracellular parasites’?
Has to be inside the cell to replicate
Describe the structure of a virus
protein coat (capsid) surrounding a nucleic acid genome Can be enveloped = surrounded by lipid membrane, may have glycoproteins on the membrane to interact with the host cells non enveloped = only a protein and genome [see slide for image]
Is the genome made from DNA or RNA?
Depends on virus, can be either
Also can be single stranded, duplex, circular or linear
Described the simplified virus life cycle
Cell entry → RNA/protein synthesis → genome replication → protein synthesis → assembly of infectious virus particles → release from the cell (cycles back to cell entry)
What does a virus need from the host cells?
Raw materials for synthesis of biomolecules (proteins) e.g. nucelotides, amino acids
Machinery for synthesis of biomolecules e.g. protein synthesis requires hosts ribosomes as the virus does not have any
Enveloped viruses need membranes
Transport around the cell
Life! - viruses cannot replicate in a dead cell
What are the ideal characteristics of antiviral drugs?
Cell membrane is permeable
No activity against cellular targets - needs specificity
Inhibition of virus encoded protein/virus specific function/process - specificity
Targets critical stage of virus life cycle
No resistance
What is HIV?
Human immunodeficiency virus
Causes acquired immunodeficiency syndrome (AIDS)
RNA retrovirus
Which cells does HIV infect?
CD4+ cells e.g. T-lymphocytes
Macrophages
Dendritic cells
How is HIV defined by WHO?
Progressive qualitative and quantitative decline in CD4+ lymphocytes
How many types of HIV is there and which is more harmful?
HIV 1 = human aids
HIV 2 = also causes immunosuppression but less harmful, mainly in africa
Which area of the world has the highest death rate in 2016 from HIV/AIDS
Sub saharan africa - also the biggest decline in deaths
Which area of the world has the highest newly infected rate in 2016 from HIV/AIDS
Sub Saharan africa - though it is reducing
Explain the trend in the number of people accessing antiretroviral therapy
Increasing in number
20 million treated out of 35 million suffering
What are the 3 stages of the course of the HIV infection?
1) primary phase illness
2) Asymptomatic stage
3) AIDS
What is viraemia?
the presence of viruses in the blood
High = high infection
Explain what happens in the primary illness phase
Influenza like illness - virons distribute throughout the body
Sharp rise in viraemia
Increase in HIV specific cytotoxic level = effective at reducing viraemia
Antibodies produced
[See slide for image]
What is the relevance of the set point?
The lower the set point, the greater the chance of survival of the patient
Explain what happens in the asymptomatic phase
~10+ years
Immune response is controlling the viraemia level well - cytotoxic level stable and high, viraemia stable and low
Antibody level stable
[See slide for image]
Explain what happens in the AIDS phase
Viraemia increases rapidly and CD4 level decreases as well as cytotoxic cells and antibodies
Death around 2 years later
[See slide for image]
What is the structure of a HIV particle?
Enveloped virus
2 copies of RNA
[see slide for image]
What enzyme is responsible for transcribing the viral RNA into double-stranded DNA? What is this process known as?
Reverse transcription
Explain the HIV life cycle
HIV virus binds and fuses with host cells membrane → RNA is converted into DNA via reverse transcriptase → DNA enters the nucleus via intergrase enzyme → DNA is transcribed and translated to form viron → maturation of viron occurs via protease enzyme = now infective
What enzyme is inhibited by NRTI/NNRTI’s?
reverse transcriptase
What 3 classes of drugs are licensed to treat HIV?
Nucleoside analogue reverse transcriptase inhibitors (NRTIs)
Non nucleoside analogue reverse transcriptase inhibitors (NNRTIs)
Protease inhibitors (PI)
What is HAART?
Highly active retroviral therapy
Triple therapy
Usually 2 NRTI’s and NNRTI or PI
How long is HAART treatment given for?
lifetime therapy
reduces viraemia in 8 weeks
Name 4 examples of NNRTIs
Nevirapine
Etravirine
Delavirdine
Efavirenz
How do NNRTIs work?
Inhibits reverse transcriptase by binding to the allosteric site
Does not stop thymidine binding unlike NRTIs
Name 3 examples of NRTIs
Azidothymidine (AZT)
2’,3’-dideoxyinosine (ddl) - analogue of adenosine
Dideoxycytidine (ddC) - analogue of deoxycytidine
How do NRTIs work?
analogue of thymidine - 100 fold more affinity for reverse transcriptase than cellular polymerases (so not that specific) = chain termination
Can you treat with NNRTIs and NRTIs at the same time?
Yes as they both target reverse transcriptase but in different ways
Reduces chance of resistance
Explain the process of HIV maturation
Budding of the cell occurs which shows electron dense material on the outside of the cell
The virus is released and Gag and Gag-Pol is cleaved by the protease enzyme into individual proteins = electron dense material now in the middle
[see slide for image]
Name 2 examples of protease inhibitors
Saquinavir
Nelfinavir
How does the protease inhibitor class work?
Competes with the peptide the protease enzyme normally cleves
Protease inhibitors are membrane permeable to be able to target the virus
Protease is unique to virus = specific
What are 3 pros to HAART therapy?
Manipulate treatment to avoid resistance
Treatment interruptions - stopping the medication for a period of time when the patients develops resistance so that the resistant virus have to compete with all the other viruses and the number reduces
Highly effective at reducing viral load and disease progression
What are 5 cons to HAART therapy?
Cost Compliance - effects lifestyle Side effects Drug-drug interactions Post therapy reversion - removing the patient off the drug = viral load increases
How many people does WHO estimate to be infected with Hep C?
73 million
Which is more prevalent, HIV or Hep C?
Hep C - 6 million new infections per year
What are the consequences of Hep C virus?
Chronic liver disease i.e. Fibrosis, cirrhosis and hepatocellular carcinoma
What is the most common genome group of Hep C?
1
Very variable and can mutate easily
What is the most problematic genome group of Hep C in the UK?
3
What percentage of people with Hep C go on to have the chronic infection
85%
What does the NS3 gene code for?
NS = non functional
protease and helicases
Therefore cleaving and separating strands of DNA
What does the NS5B gene code for?
NS = non functional
RNA dependent RNA polymerase - makes RNA copies of the RNA genome
Differs from HIV polymerase as makes RNA not DNA
What does the NS5A gene code for?
NS = non functional
Not sure as no enzymatic activity but still used as a drug target
Explain the Hep C replication cycle
Virus binds and enters cell via endocytosis → uncoating → translation and polyprotein processing/RNA replication → virus budding into intracellular vessicles → transported outside of the cell to fuse to the membrane and release
NOTE: no maturation is required, the virus is already infective
Give 2 examples of 1st generation NS3 proteases
Telaprevir
Boceprevir
Give an example of a 2nd generation NS3 proteases
Simeprevir
What are the characteristics of 1st generation NS3 proteases?
Potent
Prone to resistance
Specific to genotype 1
What are the characteristics of 2nd generation NS3 proteases?
Potent
Effective against first generation resistance
Effective against some other genotypes but not GT3
Name 2 examples of 1st generation NS5A inhibitors
Daclatasvir
Ledipasvir
How do NS5A inhibitors work?
predicted to target specifically domain I protein of NS5A which has roles in: Virus RNA replication (with domain 2) Virus assembly (with domain 3) Binding to viral RNA (all domains) Binding multiple cellular factors
How potent are NS5A inhibitors?
HIGHLY! very low dose of drug needed
Name an example of 2nd generation NS5A inhibitor
velpatasvir
Pan genotypic
Name an example of a NS5B inhibitor and how it works
Sofosbuvir
RNA polymerase production is inhibited
What is the guideline treatment for Hep C genotypes 1-12 via NICE recommendations?
Sofosbuvir (NS5B) + Velapatasvir (NS5A)
What is the guideline treatment for Hep C genotypes 1-12 via FDA recommendations?
Sofosbuvir (NS5B) + Velapatasvir (NS5A) + Voxilaprevir (NS3)
What is around the total cost of Hep C treatment for 12 weeks?
£40000
