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50 Cards in this Set
- Front
- Back
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How is the progression of HIV checked?
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Look for presence of viral RNA using PCR (however, this is not always reliable)
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What happens during primary infection?
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-Rapid dec of CD4+ cell levels
-Large inc in number of viral mRNA |
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What is the progression of HIV?
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-Primary infection
-Latentcy -On set of AIDS symptoms (which leads to a sharp drop in CD4 count) |
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What are the treatments available for HIV?
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-Monotherapy: Only used AZT, but virus rapidly mutates, which nullifies action of drugs, mainly use nucleoside inhibitors
-Multidrug therapies: HAART (highly active antiretroviral therapy), Protease inhibitors + nucleoside inhibitor |
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What are the drug targets of HIV?
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-RT inhibitor
-Protease inhibitor: interfere with processing of vral precursor ptns. Block active sites so that viruses cannot mature -Entry inhibitors: Useful cuz now many viruses are resistant vs integrase and protease inhibitors -Integrase inhibitors |
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What are the 2 kinds of nucleoside inhibitors?
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-Analogue RT inhibitors
-Non-analogue RT inhibitors |
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What do Analogue RT inhibitors do?
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-Imitate nucleoside
-Bind competitively to the active site of nucleotide incorporation event -Prevent synthesis of 2nd strand, chain terminators -Active vs HIV-1 and 2 -They are all like nucleosides, except that they don't have the 3' OH groups, which prevents Nuc attack -Need to be P by cellular kinases -Toxic since they can enter cellular complexes |
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How is the 3' OH group replaced in AZT, d4T and 3TC?
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AZT: has C-N3
d4T: has C=C (C db C) 3TC: S instead of a C in the ring |
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Wht's the problem with analogue RT inhibitors?
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Viruses have developed a mechanism to excise these kinds of nucleosides
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What are non-analogue RT inhibitors?
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-Bind to hydrophobic site on RT (instea of its active site)
-Non-competitive binding -Causes allosteric change that reduces the effectiveness of the active site Problem: only effective vs HIV-1, not HIV-2 |
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What are 2 examples of non-analogue nucleoside RT inhibitors?
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-Efavirenz
-Nevirapine |
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What is acyclovir? Why is it not very effective in HIV treatment?
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-Nucleoside inhibitor (first used against herpes infection)
-Less effective in HIV treatment cuz HIV doesn't provide its own kinase and Acyclovir needs to be P -If someone with HIV is already co-infected with HSV, than acyclovir will be P and will work better |
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Why can't nucleosides be P in medication form?
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-When P, they become negatively charged and unviable
-Cost concerns -Impossible to start off with a triP medication |
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How can nucleoside analogue incorporation into cellular processes be avoided?
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-RT/viral enz are sloppy so they can' really tell the dif btw the analogues and real nucleosides
-RT/viral enz don't have intrinsic proofreading abilities **can still be somewhat toxic to the cell tho, cuz pol delta in the mito does use the analogues |
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How are most drugs now used? Examples?
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In combination
-Combivir: 2TC. AZT -Atripla: 3 drugs (non-nuc analogue inhib + 2 nuc anaogue inhibitors): Efavirez, tenofivir, emtricitabine |
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What do Protease inhibitors do?
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-Competitive inhibitors
-Interfere with the active site so that the pro-peptide can't bind and be cleaved -Works best with other drugs -Viral load will drop, but will be a rebound curve that suggest mutation or resistance by the virus |
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What is PI (Potease Inhibitor) Boosting? Why?
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-Cell enz can degrade PIs
-Protease potency decreases wit tme -Protease inhibitors are usually used with other drugs to keep the [PI] up |
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How does Ritonavir work in PI boosting?
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Ritonavir binds to enz and cytochromes that would otherwise degrade the protease inhibitor (prevents fct of those cell enz)
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Whats the problem with having a large viral population?
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-If have a small virus population: less likely to have relevant pre-existent mutation, so can give patient enough drugs to bloc replication and can keep the virus in check
-Large population: won't be enough drug to block replication, virus develops resistance,get more and more mutations and lots of viral growth |
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How is resistance to 3TC developed?
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2 mutations at methionine 184
-M184I: ATG--> ATA (G pairs with T), get ILE (isoleucine) -few weeks later, M184V: ATG-->GTG (A bp with C) -M184V overpowers M184I, has highe replication capacity -M184V confers resistance vs 3TC |
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What are other mutatons in HIV and what drugs are they now resistant to?
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-K103N: now resistant to non-analogue RT inhibitors (only 3rd generation NNRTIs can be used)
-Q151M: efficiency to RTI (except 3Tc), but low prevalence in clinical settings -M184V confers resistance to 3TC by diminishing its chain-termination action. However, becomes more susceptible to AZT |
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When no drugs are administerd, what kinds of viruses exist in the cell?
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Viruses that don't have resistance to drugs (viruses with resistance to drugs are a minor species)
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What happens when drugs are administerd?
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-Replication effciency decreases cuz most of the viruses don't have resistance.
-The viruses that do have resistance continue to replicate -Get major mutation occuring at first, which fundamentally alters the affects of the drugs -Minor mutations will then occur to try and solve the damage the virus incurred as a result of the major changes |
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What is the mechanism of AZT resistance?
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-AZT monoP can be incorporated into viral DNA, but pyrophosphate can bind and excise it
-ATP acts a s a pypophosphate donor: mutations far from the active site facilitate binding of ATP so that the B/y phosphates can do that -A single incorporation event is not enough to shut down DNA synthesis |
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What are the ways clinicians use to see if the virus is resistant to certain drugs?
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Genotyping: look for specific pre-existing mutations that would give resistance to drugs. Sequence important parts of the genome: N-fingers, palm and thumb of RT
-Phenotypic approach: isolate, propagate and then see which drugs work and which ones have a diminished potency. This is costly and time consuming thoigh. |
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What is Entecavir (ETV)?
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-Guanosine analogue that has a 3' OH gp
-Can be inhibitory for HIV-1 if patient co-infected wiht HBV -RT incorporates ETV mono-P, but M184V dec this efficiency |
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What are 3 possible mechanisms of ETV action?
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1) De facto chain termination: Immediated polymerization stop
2) Delayed chain termination: Polymerization stopped a few nt later. RT cannot excise ETV in this case. Most common mechanism. 3) Base-pair confounder: Inhibition of complementary strand production |
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What are 2 mechanism of viral drug resistance?
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1) Discrimination: Mutations in the RT enz discriminate against the inhibitor in favour of the natural nt. All these mutations clustered around the nt binding site and can sense difference btw actual nucleoside and the analogue
2) Excision: Nucleotides like AZT get incorporated, but then the virus excises them out. This is because ATP binds and attacks it, making its excision possible |
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What are TAMs?
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Thymidine analogue-ass't mutations
-They're mutations that select for the excision of AZT. -Can also work against other NRTIs as well -They increase binding of ATP (pyroP donor) |
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What's the relationship btw TAM and M184V?
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-Antagonistic
-TAM inc excision of AZT, while M184V stops the excision |
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What kind of mechanism of resistance does the virus use vs 3TC?
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Discrimination (cuz of M184V)
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What are compensatory mutations?
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-Happen after original mutation
-selection of resistance often comes at a cost of viral fitness -Further mutations can be selected to compensate for this loss of fitness -Compensatory mutations do not directly cause resistance, but rather make an already resistant virus more fit |
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What do clinicians want to avoid?
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1)Cross resistance: K65R confers resistance to 3TC, ddl, ddC
2) Multiple drug resistance: Q151 (shows up infrequently) but confers resistance to literally all available NRTIs |
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What are clinical benefts of viral resistance?
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-Hypersensitivity: M184V and AZT
-Resensitization: Virus becomes susceptible to a drug it was formely resistant to |
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What happens when there are mutations outside of the active site of RT?
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-Can affect older drugs (AZT)
-they amplify excision path because they're ass't with TAMs -Not really a problem for newer drugs |
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What are new drugs targetting?
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Novel ptns that haven't been targetted yet (i.e. not RT)
-Fusion inhibitors, entry inhibitors, HIV integrase strand transfer inhibitors |
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What is Maraviroc?
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Entry inhibitor
-Interferes with coreceptor CCR5 -a concern that HIV might not only use CCR5, but also CXCR4 as a receptor -If we apply drug pressure, we may actually select for viruses that recruit CXCR4 as a coreceptor instead, as a method of drug resistance. This kind of resistance doesn’t spontaneously arise, but rather, it already exists and it is then selected for by drug pressure |
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How do we know that Entacivir uses delayed chain termination a lot?
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-A lot of resistance, selectivity of inhibitor over the natural nt (ETV) at n+4 (rather then n+1)
-Delayed-chain termination rly protects ETV cuz the primer, once it has ETV incorporated, repels the active site of the polymerase and enz slides away -Last nt can’t be excised and ETV is protected from excision -TAMs mutations don’t work against ETC |
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What is the standard treatment against Hepc?
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Interferon and Ribavirin
(Doesn't really work against genotype 1) |
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What are NS5b and NS3?
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NS5b: Polymerase (RNA-dep-RNA-pol)
NS3: Protease, but hard to target -Both these ptns present in HIV, but in modified forms |
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What is STAT-C?
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specifically targeted antiviral therapy for HCV (equivalent to HAART)
-Less toxic, more potent, genotype specific, shorter therapy duration |
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What is the Hep C protease?
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NS3/4a serine protease
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What protease inhibitor is currently bing devloped?
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Telaprevir
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What is the dual fct of protease inhibitors?
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1) Block the viral Protease
2) Viral protease can interfere with signalling of IFN response path, so if you block protease, can indirectly increase innate immunity vs Hep C |
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What is the combination therapy being used?
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Telaprevir + IFN + Ribavirin
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Why shouldn't this combination therap be used for ppl with genotype 1 Hep C?
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They're already resistant to IFN and Ribavirin so it ends up being like monotherapy.
They develop resistance to this drug too and end up getting more mutations in their virus |
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What's the differene btw HCV transcriptional intiation and elongation?
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Initiation: Is more fragile and distributive, Pol frequently diss't. Can get inhibition with non-nucleoside inhibitors (NNI) at this stage
Elongation: More stable/robust, inhibition with NI and PPi's (NNI don't work here) |
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How do the NNI's work?
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RNA binds the complex, but inhibitor slips into the pocket, prevents conformational change that traps ssRNA, loop stays in open conformation and can't form elongation complex
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What are the differences btw HIV and Hep C non-nucleoside inhibitors?
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HIV
- NNRTIs can only bind at one site on RT. -NNRTIs can binds at any stage of revere transcription Hep C -NNIs can bind at 4 different spots on the polymerase -NNIs can only work at the initiation step of transcription |
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Why is it harder to use nucleoside analogues in Hep C then in HIV?
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HIV: use dNTPs of polymerase
Hep C: use ribonucleotides, which are not P. Need the 3' OH gp to be P |
