Unit Four Flashcards
Therapeutics, Vaccines, Cancer (27 cards)
What are antiviral therapeutics for?
Antiviral drugs/immunotherapies
used to treat an ongoing infection and in some cases cure a disease
What is a vaccine for?
Used to precent an individual from ever getting a disease.
What are the hurdles associated with developing antiviral drugs?
- Difficult to find targets that will inhibit viral replication without adversely affecting the host cell
- Certain medically relevant human viruses may not be easily grown in vitro or may not have appropriate animal models for testing drug efficacy
- Antiviral drugs must be highly potent and able to completely stop virus replication.
- Acute viral infections are so brief that by the time the patient has been diagnosed and treatment initiated it is too late to be effective (FLU)
What is selective toxicity?
drugs that are effective in inhibiting the viral replication cycle without damaging the host
What are 2 antivirial drug susceptibility assays?
(a) plaque reduction assays: cells are infected with a virus and then incubated in the presence of the antiviral drug. Plaques are counted after staining
(b) PCR viral load assays: animals infected with a virus and then treatment with antiviral drug initiated then blood samples from animals are taken each day post infection measured by PCR.
What happens when antiviral drugs aren’t potent enough?
Less potent antiviral drugs will eliminate some of the viral population but also select for drug resistant mutants. With potent antiviral drug, virus cannot replicate and is eliminated.
How do you find and develop antiviral drugs?
- Identify the target: either a broad or focused target approach.
- Develop the screen that will be used to assess potential antiviral drugs. (cell based or mechanism based)
- Obtain or construct the compound library
- Identify “hits” from the screening process and evaluate these compounds in secondary screens and through biophysical and biochemical analysis.
What can a compound library be?
(a) previously prepared small molecule libraries originally designed for other applications that are available for purchase
(b) bioprospecting natural sources for new/novel compound
(c) rational drug design, utilizing knowledge about the target or earlier drugs plus computer models to generate “re-told” compounds
What are characteristics of a good drug?
- high efficacy
- high potency
- selective toxicity
- excellent pharmacokinetics including drug stability and bioavailability
What makes up drug resistance?
viruses produce large numbers of progeny
error prone viral polymerases
selective pressure (antiviral drug)
How can drug resistance occur in herpes simplex virus 1?
HSV1 has a vTK that is broad substrate specificity therefore HSV1 will use acyclovir analog that will terminate the replication process. However it just requires one mutation in the dna polymerase gene and there is resistance. Due to it being a persistent infection there will be resistance.
How can drug resistance occur in the flu virus?
Influenza A virus has an M2 protein that is an ion channel that is required for uncoating. Therefore the drug amantadine was used to bind in between the channels thus blocking it and uncoating.
But the flu virus has an error prone rna polymerase and a single mutation in the M2 protein is sufficient to cause resistance as well. There apparently was long term treatment of chickens in China for the bird flu causing a selective pressure.
But we have a vaccine for the flu lol.
How can drug resistance occur in hepatitis C virus?
HCV Rna is directly translated on the surface of ER to produce a single viral polypeptide.
NS3 is critical for processing of the viral proteins necessary for genome replication. NS5A/NS5B are critical for genome replication.
Have drugs that directly bind to the viral protease active site thereby inhibiting enzyme activity. Has drugs directly bind to the viral protein so that dimerization and protein interaction with viral RdRp is inhibited. Nucleotide prodrug analogs that mimics uridine triphosphate but when incorporated into RNA by RdRp causes chain termination.
It’s a persistent infection and error prone RdRp.
How can drug resistance occur in HIV?
Carries a unique RT. Key features of infectious cycle established relatively quickly and several unique virus targets identified.
Azidothymidine (AZT) nucleoside analog but does not have a viral TK.
Side effects, poor selective toxicity, high drug concentration and high number of doses.
At high AZP-Tp concentrations drug substrate will be used by host cell polymerases -> poor selective toxicity.
What is nucleotide excision?
specific set of mutations in HIV RT that enhances the bidirectionality of the enzyme
wild type HIV RT favors polymerization reaction and when it binds to and incorpartes AZT-TP into growing DNA chain termination induced.
Mutations in HIV RT allow enzyme to reverse reaction and excise AZT using ATP as substrate
What are NNRTI’s?
They bind in RT polymerase pocket, which directly inhibits RT activity.
What PREP?
Pre-exposure prophylaxis against HIV: a combination therapy consisting of two NRTIs (one a cytosine analog and the other an adenosine analog) that is taken daily
What are three types of antiviral therapeutics?
siRNAs
small molecules
immunotherapy
How are antibodies used to treat viral disease?
Antibodies against a specific virus will bind to viral proteins on the surface of the virus capsid or envelope, which blocks one of the early steps in the infectious cycle (Typically Attachment)
Antibodies that inhibit attachment are said to “neutralize” a viral infection and are thus termed neutralizing antibodies
What types of antibodies are there?
Polyclonal antibodies = a diverse population of antibodies that bind to a variety of different epitopes on an antigen
Monoclonal antibodies = a single antibody population that binds to a single, unique epitope on an antigen
You need neutralizing antibodies (antibodies that bind to specific regions on a viral protein and in so doing lead to inhibition of the virus infectious cycle.
How are the antibodies (Abs) used in immunotherapy generated?
Antigen could be infectious virus, killed virus or a viral protein. Repeated administration to increase Ab response.
Obtain blood from immunize animal or could also obtain blood for humans who have recovered from that specific viral infection.
How do you know if the sample contains neutralizing antibodies?
Isolate antibodies from blood, which will contain polyclonal antibodies against the virus or viral protein.
Virus Neutralization Assay
what are The Limitations of Polyclonal Sera?
easy to produce but… limited supply so new “batches” must be made using new animals and new blood samples
and
immune responses in individual animals and/or human varies so each “batch” of polyclonal sera produced will likely vary
problem: inconsistency in composition of drug product
How are the antibodies used in immunotherapy generated?
the development of monoclonal antibodies in 1975 eliminated production consistency issues
MAb production generates immortal cell lines that continuously secrete 1 specific antibody that reacts with 1 specific antigen epitope
major limitation of early therapeutic mMabs high immunogenicity, which allowed no repeat dosing.
