Lec 17 Viral Therapy Flashcards
When should vaccines be given? Acute and Chronic Infections?
Latent infections?
Serotypes?
Respiratory viruses?
Vaccines must be given early in the infection.
Acute infections do not last very long when symptoms arise the virus has already been dealt with by the IS.
Latent infections cannot be cured, they can be ameliorated.
Immune response to 1 serotype can have a negative response if the individual is infected with a different serotype of the same or different virus!
Respiratory viruses cause similar symptoms and are difficult to diagnose accurately!
2 approaches to vaccine development
Blind screening
Targeted Approach
BLIND SCREENING: Shotgun approach. Many chemicals are tested to see if they INHIBIT VIRAL REPLICATION or not in cell cultures .
TARGETED APPROACH: require 3D structure and function of virus proteins. Use RECOMBINANT GENES. Useful for VIRUSES THAT CANNOT REPLICATE IN CELLS
Initial screenings done in live culture, not animals
IN VIVO Evaluation of virus in living tissues
Animal Models
Human clinical trials
Animal models: Tolerance/toxicity, pharmokinetics, resistance development
THEN Human clinical trials
Phase 1: Viral shedding, drug resistance, and tolerability NOT TOXICITY are evaluated, for different amounts of the virus.
Phase2: LARGER # of individuals, safety assessments, repeat of phase 1.
Phase 3: get stats used for drug registration purposes. Advantageous b/c the number of shed virus can be measured
Effect -> Low toxicity -> low effects on animal the human hosts -> very low toxicity -> general use
Pharma companies focus on treating viruses that are more easily diagnosed and treated!
Where and how Antiviral agents block viral steps
Fig 13.1
Drugs that DO NOT GO ENTER THE CELL are the MOST FAVOURABLE (target viral antigens). Against ATTACHMENT, ENTRY and RELEASE steps of viral life.
Others often:
Inhibit viral proteins using the drug. These proteins/enzymes must be VERY DIFFERENT FROM THE HOST PROTEINS so TOXICITY is not involved.
Viral proteins activate the drug eg. Thymidine Kinase from HSV activates Acyclovir, for lower toxicity. Weak b/c the virus can mutate its proteins!
AIDS
4 Long Term Damages
3 Phases
- Acute
- Asymptomatic Phase
- Development of AIDS
AIDS (HIV +ssRNA lentivirus from Retroviridae)
Long incubation period,
shuts IS down,
threat of secondary infections,
cancer
RNAPs cause many mutations in ssRNA, (reverse transcriptase makes DNA from RNA genome). Integrase incorporates DNA into genome
- Acute: A large # of CD4 cells die but levels off. A lot of HIV RNA made, but levels off.
- Asymptomatic Phase: CD4+ cells continue to die over time, CD8 T+ and CD8 Anti HIV response is plateaued.
- Development of AIDS: CD8+ T cells start declining, HIV specific CD8+ cells start dying en masse, more than the non specific CD8+ cells, CD4+ cells start dying a lot too.
A jump in the number of HIV vRNA made and found in blood!
Prevent Virus from ATTACHING and ENTERING cell
eg. HIV and ENFUVIRITDE
HIV binding to HR-1 induces conf. change, HR-1 binds HR-2, tethers the 2 cells together to form a fusion pore with the viral and host membranes.
HR = Heptad Fusion Repeat
The ENFUVIRTIDE drug prevents the membrane fusion. Binds to HR-1 by mimicking HR-2, preventing host membrane fusion!
Prevent virus from UNCOATING
eg. Influenza A only and AMANTADINE
AMANTADINE binds against Influenza A virus
(8 segmented -ssRNA) attaches to Sialic Acid, internalized by ACIDIC conditions in ENDOSOME
Amandatine prevents Ribonucleoprotein from associating w/ Matrix protein, by PREVENTING ENDOSOMAL ACIDIFICATION from BEING DETECTED by the M2 channel in the virion OR changes it conformation so M2 does not work,
Viral protein cannot be uncoated, virus stuck in endosome!
Most antiviral agents inhibit viral GENOME REPLICATION
Nucleoside monophosphate inhibit DNAP
Acyclovir and HSV
Acyclovir Mechanism
Acyclovir SPELLING!!!
NucleoSIDE MONOPHOSPHATES are nucleoTIDE ANALOGUES activated by PHOSPHORYLATION.
The NTP analogues compete w/ dNTPs to terminate DNA elongation. Normally a viral polymerase is inhibited, sometimes host’s one is necessary.
ACYCLOVIR mechanism: VIRAL THYMIDINE KINASE PHOSPHORYLATES acyclovir to mono/di then tri phosphate, which competes w/ GUANINE and PREVENTS CHAIN GROWTH. Outcompetes dGTP…
HSV-1 mutants that are resistant to this are made…
Most antiviral agents inhibit viral GENOME REPLICATION
ZIDOVUDINE and HIV Reverse Transcriptase Target
What is the state of inhibitory Zidovudine?
The thymidine analogues are more potent if
Great target b/c Reverse Transcriptase is very different from host machinery.
All HIV analogues lack 3’OH to resemble dNTPs, which are the [s] for reverse transcriptase.
ZIDOVUDINE is phosphorylated by the HOST KINASE to
ZIDOVUDINE-Monophosphate, which is NOT SELECTIVE for a nucleotide and ACCUMULATES IN ALL CELLS.
ZIDOVUDINE-Monophosphate-Thymidine Kinase INHIBITS REVERSE TRANSCTIPTASE by mimicking dTMP (deoxy Thymidine monophosphate)
The NTP ANALOGUES are TOXIC to ALL CELLS… Low white and red blood cells to use the hosts own
The thymidine analogues are more potent if
- the cellular kinase is unregulated in infected cells
- Infected LYMPHOYTES have UPREGULATED THYMIDINE KINASE wrt dormant lymphoctyes.
Inhibition of ASSEMBLY and MATURATION
The Protease has what foreign aa linkage?
RITONAVIR and HIV Protease
Kill viral (HIV) protease, PREVENT viral MATURATION and POTENCY! They are VERY SPECIFIC
The Protease has a foreign PHENYLALANINE-PROLINE link
RITONAVIR blocks HIV protease from maturing the viral particles.
DIFFICULT b/c the RNAP makes MANY MUTATIONS in the ssRNA, which code for the protease, causing resistance.
Inhibition of VIRAL RELEASE
ZANMAVIR and its Short mechanism
NA-Sialic Acid BLOCK RELEASE of Influenza A and B, like viral attachment. PREVENT SIALIC ACID CLEAVAGE, which would burst cell open and visions escape.
ZANAMIVIR: SIALIC ACID ANALOGUE that occupies and PREVENTS BOND CLEAVAGE, so viral particles are not released.
Principles of Antiviral Therapy
Phases of Therapy Treatment
Phase 1: CD4 memory cells, prevent new infection
Phase 2: vRNA to dendrites, macrophages, CD4 killed
Main objective of Antiviral Therapy is to SUPPRESS VIRION SYNTHESIS.
- Specifity of Situation is important
- Acute viral infections are often cleared by the time symptoms appear in immunoCOMPETENT people
- PREVENT the REACTIVATION of LATENT viruses in immunoCOMPROMISED people!
Phase 1:
(a) vRNA is killed because INFECTED CD4 MEMORY CELLS are DEAD and
(b) prevent new cells from being infected
Phase 2:
vRNA bound to DENDRITES, MACROPHAGES and CD4 cells are KILLED
The more vRNA in blood, the faster the CD4 cells die.
HIV Suppression and HIV Reservoirs
HIV Suppression is incomplete… if plasma HIV is not less than 50 copies / ml blood the infection can become resistant! This is the adequate level in blood.
HIV RESERVOIRS are cells used by the virus that re-emerge after the treatment, INSIDE
IMMUNOLOGICALLY PRIVILEGED SITES like CNS and GONADS, where drugs are not as effective.
Antiviral Drug Resistance
**Continue on from here (slide 30)
RNA viruses are more error prone and mutations cannot be detected. This way the IS and antiviral drug can’t target it.
Mutation rates in DNA virus «_space;RNA Viruses b/c DNAPs correct mistakes, by 1 million times that of the host cell.
HUGE concern for RESILIENT viruses like HIV and HSV. HSV however can be treated effectively by acyclovir due to lower mutation rate.
IMPROPER DOSAGE can be DEVASTATING because exposure to 1 drugs selects for visions that are resistant to it,no choice but to proceed with a different treatment like COMBINATION CHEMOTHERAPY
probability a virus is resistant to several drugs is very low. Combination also work synergistically. Disadvantage: more toxicity and costs!
Hepatitis C
SOVALDI and VELPATASIR
Keith Richards: incredibly powerful IS, does not need treatment!
Extremely expensive
