Antiviral Agents / Virotherapy Flashcards
While antiviral ______ are the classical approaches, antiviral _________ is an upcoming field of research and development for the treatment of infectious diseases.
Drugs; Immunotherapy
For which viral infections do we rely on antiviral drugs?
For those that cannot be effectively controlled via public health measures and vaccines.
(T/F) To date, most antiviral drugs are targeted against HIV and herpesvirus due to their clinical significance.
True!
Millions of lives have been saved by the use of antiviral drugs!
What are the three major limitations in antiviral drug development?
1) Requirement for a high degree of SAFETY (must ensure compound does not have deleterious effects on host cell)
2) Requirement for POTENCY (modest viral growth in the presence of inhibitor is NOT good enough; allows for mutants)
3) Some viruses difficult to PROPAGATE IN VITRO in the lab or there may be a LACK of animal models to test safety + potency
What does R and D mean for R&D of antiviral drugs?
R = Research and compound identification (only the beginning of the process of producing a drug)
D = Development, compromises all steps necessary to take an antiviral lead compound through safety testing, scale-up of synthesis, formulation, pharmacokinetic studies, and clinical trials
Takes 5-15 years!
Briefly describe the descending staircase of antiviral drug discovery.
First you have thousands of compounds synthesized or purified from the library.
Then you have preclinical testing where you test potency and toxicity in cells and then animals.
Finally, you have clinical testing where you test toxicity and potency in humans.
In each step, the numbers of promising candidates are decreasing, resulting in a descending staircase.
It takes several years before a final product that is safe and effective is produced!
Clinical trials occur in a series of phases. Match the phases to their definitions.
1) Phase I
2) Phase II
3) Phase III
4) Phase IV
A) focus on EFFECTIVENESS, slightly large groups (<100), still continue to monitor safety
B) once the drug is approved; further evaluation of EFFECTIVENESS and LONG TERM SAFETY, groups of hundreds to thousands
C) SAFETY assessment in small groups (20-80), early evidence of efficacy
D) focus on EFFECTIVENESS, SIDE EFFECTS compared to standard therapy, larger groups (100-thousands) who are randomly assigned to “trail arms”
Phase I: SAFETY assessment in small groups (20-80), early evidence of efficacy
Phase II: focus on EFFECTIVENESS, slightly large groups (<100), still continue to monitor safety
Phase III: focus on EFFECTIVENESS, SIDE EFFECTS compared to standard therapy, larger groups (100-thousands) who are randomly assigned to “trial arms”
Phase IV: once the drug is approved; further evaluation of EFFECTIVENESS and LONG TERM SAFETY, groups of hundreds to thousands
True or False
1) It takes around 10-15 years to discover a drug. We can fast track certain drugs using phase I-II (safety + efficacy in the same phase).
2) Pharmaceutical/biotech companies pay for clinical trials in collaboration with clinical investigators.
3) Phase I and Phase II take around 1 year altogether.
1) True
2) True
3) False; 2-4 years
How are antiviral compounds discovered?
Knowledge of viral life cycle IDENTIFIES TARGET for antiviral drug discovery:
The life cycle of many viruses are known, allowing for identification of several targets for intervention.
Viral genes essential for reproduction can be cloned and expressed in genetically tractable organisms and their products can be purified and analyzed in molecular and anatomical detail - INHIBITORS OF CRITICAL PROCESSES CAN BE IDENITFIED
What are some of the challenges/things to consider after a drug target is identified?
Must determine if compound:
1) will get to the right place at the right concentration (bioavailability)
2) will persist in the body long enough to be effective (pharmacokinetics)
3) will be tolerated or toxic
Differentiate mechanism-based screens with cell-based screens.
Mechanism-based screens: seeks to identify compounds that affect the function of a known viral target such as enzymes, transcriptional activators, cell surface receptors, ion channels. often screening is conducted with purified protein in formats that facilitate automated assays of many samples.
Cell-based screens: elements of the mechanism to be inhibited are engineered into an appropriate cell system. provides information not only about target inhibition, but also cytotoxicity & specificity. the use of multiple reporter molecules may also allow for detection for more than one event at a time.
Briefly describe a mechanism based screen for inhibitors of a viral protease.
A FLUOROGENIC MOLECULE is covalently linked to the N-terminus of the substrate (peptide) of the protease and the C-terminus is linked to a bead.
When the protease cleaves the peptide, the fluorogenic N-terminus is released into the soluble fraction which is separated from the insoluble beads containing C-terminus fragment.
Protease activity is assayed by the appearance of soluble fluorescent peptide.
Fluorescence activity if enzyme is NOT inhibited, while there will no fluorescence activity when enzyme is inhibited.
Briefly describe a cell based screen for inhibitors of a viral protease.
Tetracycline-resistant bacteria have tetracycline efflux protein on the membrane with a HIV protease site added.
When there is expression of a (HIV) protease, there is inactivation of the tetracycline efflux protein.
Inactivation causes the bacteria to be tetracycline sensitive! It leads to no bacterial growth on tetracycline-containing media.
A functional inhibitor should result in antibiotic resistant bacteria as the protease site would not be cleaved!
(T/F) Cell based screens can be done in eukaryotic cells. However, bacterial cells are faster and cheaper!
True!
Advances in protein separation techniques, _____ _______ and bioinformatics allow to determine the total protein repertoire aka ________ of virus samples.
We are now able to determine protein interactions of _____ proteins with _____ proteins, identifying critical nodes or _________ ____.
Mass spectrometry; proteome
viral; host; INTERACTION HUBS
*an example of this is the systematic survey of the interaction between cellular and viral proteins of HIV I. these interactions provide clues of potential targets for drugs!
(T/F) After administration, the drug must reach the correct site in the body and must remain at an effective concentration to allow for the inhibition of viral reproduction.
True!
How can we modify compounds to improve absorption? Give an example.
Add side chains!
ACYCLOVIR is not effectively taken up after oral ingestion. But the derivative VALACYCLOVIR has 5x oral bioavailability through the addition of a side group, which allows increased passage of drug from the intestines into the bloodstream..
Match the following drugs to their definitions:
1) Acyclovir (Zovirax)
2) AZT (Retrovir)
3) Amantadine (Symmetrel)
4) Tamiflu
A) Targets INFLUENZA A virus M2 protein which forms a tetramer that creates a transmembrane ion channel to transport protons. By binding to the outside of the tetramer, it blocks the entry of protons.
B) Specific non-toxic drug - effective against HERPES virus. Nucleoside analog related to guanosine. Mediates chain termination of DNA synthesis.
C) Blocks the function of Neuraminidase, an INFLUENZA enzyme that cleaves sialic acid group from glycoproteins to release virion from host cell.
D) First drug licensed for the treatment of AIDS. Analog of thymidine. Mediates chain termination of DNA synthesis.
Acyclovir: Specific non-toxic drug - effective against HERPES virus. Nucleoside analog related to guanosine. Mediates chain termination of DNA synthesis.
AZT: First drug licensed for the treatment of AIDS. Analog of thymidine. Mediates chain termination of DNA synthesis.
Amantadine: Targets INFLUENZA A virus M2 protein which forms a tetramer that creates a transmembrane ion channel to transport protons. By binding to the outside of the tetramer, it blocks the entry of protons.
Tamiflu: Blocks the function of Neuraminidase, an INFLUENZA enzyme that cleaves sialic acid group from glycoproteins to release virion from host cell.
Two major success stories of antiviral drug development: ______ and _________.
HIV; Hepatitis C
*Steps in the reproduction of HIV and HCV are targeted by antiviral drugs.
What is immunotherapy?
Therapeutic strategies to stimulate or restore the ability of the patient’s immune system to fight disease (mimick immune system). These therapies normally employ biological products, known as BIOLOGICAL RESPONSE MODIFIERS.
What are the different kinds of immunotherapies?
Cytokines (interferon-α) and antibodies (super-antibodies) which are PASSIVE immunotherapy.
Lymphocytes (T cells) which are ACTIVE immunotherapy.
(T/F) When cells get infected with pathogens, they will secrete signalling molecules called CYTOKINES to neighbouring cells to notify them of infection, and also to train and boost the immune system.
True!
The cytokine, interferon-α, was the first approved therapy for _________ virus and _______ virus.
The effects on _______ infection are potent, while on ________ are modest.
Hepatitis B; Hepatitis C
