Lecture 12 - Antivirals Flashcards
What are steps involved in pre-clinical development of antiviral drugs?
Identifying medical need, setting objectives, chemical/molecular library synthesized, animal testing, formulation/scale-up feasibility/chronic safety in animals, submit IND
What are steps involved in clinical trials?
Phase 1: <100 health individuals to test safety (toleration)
Phase 2: 100-1000 to test safety and efficacy
Phase 3: 100,000s to test safety, effectiveness and dosing
Phase 4: Testing long term effectiveness comparing to standard treatment (drug is already approved)
What are prodrugs? Why would prodrugs be preferred? What kind of antiviral is typically a prodrug?
Prodrugs are inactive precursors which modified into active forms inside infected cells. Prodrugs are preferred when the active drug is perhaps too hydrophilic to get across PM efficiently. NRTI’s are typically prodrugs, they lack the phosphate group that nucleotides have and get phosphorylated inside infected cell by kinases (viral and cellular).
Which virus does acyclovir work against? What mechanism does it target and how? What is the structure of acyclovir, what substrate does it mimic, and how does it become activated?
HSV. Viral replication by being recognized by the viral pol and being integrated into growing strand, this molecule disrupts polymerization of the growing strand - chain termination. Acyclovir is a nucleoside (guanosine) analog that is missing the ribose and therefore does not have a 3’ OH to add the next nucleotide to in a growing strand. It becomes activated by a viral thymidine kinase and 2 cellular kinases -> ACV-TP, ATP mediated integration into DNA.
How can HSV become resistant to acyclovir?
Tk-minus HSV - No more or low levels of viral TK, acyclovir cannot become activated or isn’t in high enough levels
Mutated viral pol doesn’t incorporate ACV anymore
Mutant Tk doesn’t phosphorylate ACV anymore
Which virus does AZT work against? What mechanism does it target and how? What is the structure of AZT, what substrate does it mimic, and how does it become activated?
HIV. AZT is an NRTI that targets viral RT, becomes incorporated into growing DNA strand, however because the 3’ OH on ribose is replaced with azido group, strand cannot polymerize beyond this nucleoside analog (thymidine), leading to chain termination. Becomes activated by 3 cellular kinases.
How do ACV and AZT insure that cellular DNA pol is not effected?
ACV is phosphorylated by a viral TK, also DNA pol does not bind to ACV as effectively as the viral pol. AZT is activated via cellular TK’s, it is specific to viral RT and the drug acts in the cytoplasm where there is no host DNA pol.
How does HIV become resistant to AZT?
Viral RT gains function whereby it can excise the AZT in an ATP-mediated pyrophosphorylation to unblock the RT.
What are NNRTI’s? Examples? How do they work?
Non-nucleoside reverse transcriptase inhibitors. Nevirapine, dapivirine. Bind to another site on RT, doesn’t compete directly with nucleotides - allosteric non-competitive inhibitor. Binding in hydrophobic pocket causes RT conformational change in active site which renders it unable to polymerize dsDNA.
How does HIV become resistant to NNRTI’s?
Mutation in RT doesn’t allow NNRTI’s to bind. RT is very error prone, NNRTI’s will select for resistant virus.
What Maraviroc and Enfuvertide? How do they work? How would HIV gain resistance to these drugs?
Maraviroc is an entry inhibitor for HIV, it binds to CCR5 on Th cells, preventing gp120 from binding. Enfuvertide is a fusion inhibitor, it works by binding and stabilizing the hydrophobic N-HR on gp41 during the intermediate stage, preventing it from further collapsing into six-helix bundle and fuse with PM. Maraviroc - CXCR5 becomes primary co-receptor for HIV vs CCR5. Enfuvertide - gp41 does not bind to the anti-viral anymore.
What is an example of a HIV protease inhibitor? What does it mimic? What does it inhibit?
Ro31-8959. Peptidomimetic that mimics the binding site of HIV protease that cleaves gag and pol into final proteins (MA, CA, NC, RT, PR, IN).
When are antivirals most effective? When, during the viral life cycle, are they not as effective? What type of drugs are best used then instead of antivirals?
During the replication phase, usually before symptoms occur, as the viral load is highest then. When symptoms appear, the virus is usually done replicating and immune modulators are best used thenafter. Antibiotics/antifungals are also used then because of secondary infections.
List the ways that mAb’s work to fight a virus.
mAbs bind to a particular epitope on the antigen
to which they were raised, and (i) block its
function, (ii) target it for phagocytosis and, (iii) if it
is displayed on infected cells, target those cells for
antibody-dependent cell cytotoxicity (ATCC) by
NK cells.
What are amantidine/rimamantidine? How do they work? What is the difference between the two? How can influenza gain resistance to them?
M2 channel inhibitors. They work by binding the Ser31 in the open M2 channel, thereby blocking protons from flowing through into the virus and M1 disruption and inhibiting viral uncoating and fusion with the endolysosome. Rimantidine contains a methyl group and stops it from crossing blood-brain barrier - less side effects. If the Ser31 is mutated or the channel is mutated elsewhere such that it does not bind these drugs anymore, influenza can become resistant.
