C3 Antifungal Treatment Flashcards
Why are there only 3 classes licencesed for systemic anti fungal
Limited range of targets specific for fungi cell wall or some parts of membrane
Give an example of why systemic illness has risen
Increased chemotherapy and the 80s aids epidemic led to rise in oral candida
Aspergillus in. 90s
Since the aids epidemic, what emerging fungi has overtaken candida
Aspergillus fumigatus (invasive aspergillosis)
What are the 3 major diseases and how many people killed with them yearly
Cryptococcal meningitis/crypto - 1 mill
Systemic candidiasis - 400k
Aspergillosis- 700k
If you have aids with aspergillosis what is death rate - much higher for Immunocompromised
And what suppressive condition is associated with candida or cryptococcus death
86%
Candida- neutropenia
Cryptococcus - transplantation
What percentage of people with these systemic infections will die - v serious
Half of them
Give 2 targets of drugs which can’t be used for systemic infections / not licenced for systemic use
Microtubule synthesis
Dna/rna synthesis (flucytosine - for budding yeast)
What drugs can be used for dermatophytoses/skin infections like tinea pedis that target microtubules
Griseofulvin
Give the timeline of introduced 3 classes
Amphotericin B (polyenes) first late 50s
Azoles in 80s aids epidemic (flu con Azoles and itraconazoles first class)
Then early 2000s echinocandins
Has there been any new class since 2000s
Non
What is ampB polyene target
Ergosterol in pm needed to regulate fluidity so if disrupted causes cell stress
What shape do polyenes have which first suggested it acted as a pore to let Leakage out
Amphipathic molecule could help form a pore within pm
Has a hydrocarbon hydrophobic chain
And a polyhydroxyl hydrophilic chain
What do recent biochemical studies suggest instead
It acts as a sterol sponge sitting on top of membrane and absorbs sterol to cause fluidity
What shape does mode of action suggest how it’s more affinity to ergosterol thwn cholesterol in host
Cylindrical shape ergosterol vs sigmoidal cholesterol
What is the 2 main advantage and of polyenes
Broad spectrum use (aspergillus, candida and cryptocccus)
Also very limited resistance has been shown
What are the 2 main disadvantages of it
Only IV injection through drip = not accessible to developing countries
Also lack of specificity causes toxicity eg neohrotoxicity
Infusion related injections also have problems which suggest oral admin is beneficial. Explain
Hypomagneisum and other adverse effects like nephrotoxicity
Which 2 formulations alternative to natural Micelle form of ampb have been studied for oral admin not systemic
Liposomal ampb (inserted in liposome)
Cochleate insertioj
What are cochleates
Phospholipid-cation structures forming spiral lipid bilayers where ampb is inserted
When injecting mice with candida what did these formulas show
100% survival with cochleTe, 90% with l-amb and 70% natural ampb
Which one is now licensed
Liposomal (cochleate did not move from preclinical)
Ambisome is licenced for severe mycoses
What is still an issue with ambisome
Iv injection and still some nephrotxicity but less toxic
Which modified ampB cannot bind cholesterol had been in clinical trials but synthetic access isn’t good enough to licence
C2’ hydroxyl deletion
What are the 4 triazoles and what they work on
Fluconazole - ca,cu NOT AF
Itraconizole- same but works on dermatophytes too
Latest voriconazole (all 4)
Posaconazole - extended sp
What is their structure
5 side aromatic rings with 3N 2C (3N why they’re called triazoles)
What change to fluconazole makes voriconazole work on aspergillus
Extra methyl group
What is the target of triazoles
Also target ergosterol but they target it’s synthesis
Which enzyme in biosynthesis pathway do they bind AS of
Erg11/cyp51 lanosterol demethylase
What does it contain in active site that the N binds to and blocks
Iron ion in the iron protoporphyrin structure (heme like) in active site
What happens instead
Get a precursor forming which is then converted by upstream erg3 enzyme to a sterol precursor causing fluidity disregulatiom
In shat forms is it taken
Iv or orally
Is it fungistatic or fungicidal like ampB
Fungistatic (making it more likely resistance)
Other than being taken iv or oral and broad spectrum, what is another advantage over ampB
Not toxic
B-road spectrum voriconazole
Fluco taken as prophylactics
Give an example where they are taken as prophylactics for immunosuppressive patients and how this can have adverse effects via drug-drug interactions
Patients taking calcineurin drug immunosuppressant eg transplant patients
Calcineurin metabolism due to cyp450 being targeted
Stay immunosuppressant for longer than wanted
What are azoles used for in agriculture which can impact more on resistance
Crop sprayed with azoles so more resistant exposed strains can infect humans
Why would being fungistatic cause resistance during infection too
Adaptation mutations can occur
Other than resistance and adverse drug-drug what are the disadvantages
Hard to maintain plasma levels
Birth defect issues have been reported
Which water based prodrug of isavuconazole now licenced and why is it better
Isavuconazovium sulfate
Prolonged elimination half life to maintain plasma levels
What is the strucrure of echinocandins
Lipopeptides
Hexa peptide core with lipid side chain
What does it work for and give examples
Micafungin, caspofungin
Asp (licensed 2001) and candidiasis (2003 licensed)
(not cryptocccus)
What is it’s target
B1,3 glucan synthetase which it blocks
Causing cellular stress
Is the mechanism known for blocking action
No but likely competitive inhibition
How was it found
Random screening in the 70s
When was it approved
Early 2000s
Why is it the safest class in terms of toxicity
Targeting cell wall so specific
Is there resistance and what is the issue with the drug for broad action
Yes , some emerging strains with resistance bc used often but very limited resistance is found
(also doesn’t work for crypto and emerging species like fusarium)
Why could aspergillus eventually develop resistance to it
Only fungistatic against it
What type of admin is it
Iv- not available in all areas
What is primary and secondary resistance and example of intrinsic
Primary is intrinsic, naturally resistant even without drug exposure
Eg candida krusei and glabrata to azoles - commonly isolated from aids patients
Secondary is acquired resistance eg from too much azoles
Which 2 efflux pumps important in overexpression mediated resistance to drugs like candida strains (efflux is a mechanism of resistance)
Cdr1/2 abc transporters (use atp)
Mdr1 efflux pump (uses membrane potential not atp)
How is overexpression achieved through tf
Gof transcription factors mutations
mrr1 for mdr1 efflux pump
Or tac1 for cdr1/2
Where are these resistant strains of candida being seen growing whcih is the serious issue
AIDS or immunocompromosied
Why would treatment with azoles induce these changes
Causes a fitness advantage and the mutation is selected for in tac1 or mrr1.
Selection for these Gof mutations
How does c glabrata show resistance intrinsically through efflux pimps to azoles
Has a tf which a xenobiotic binding domain - binds azoles (pdr1/3) which when bound to drug will recruit machinery for txn of the efflux pumps like cdr1
Eg rna polymerase
Gof mutations in c glabrata means xbd can do this even better so drug never accumulated
Give example of how a less common drug influx alteration mechanisms can cause resistance eg to azoles
Tac1 (Gof in some candida) mediated overexpression of pdr16 for phospholipid synthesis (phosphoinositol transfer protein)
Mediates a different composition of plasma membrane affecting drug uptake and also shown to influence drug efflux cdr1 potentially optimising its activity
Point mutations in which enzyme have been reported to affect affinity of azoles to work - (3rd mech of resistance is alterations to target)
Erg11/cyp51
Which specific mutation affects accessibility of the as of erg11 to azoles and which other point mutations found too
Phe105-leu
Others include in the heme binding domain which would affect N binding
Which other enzyme in this pathway can be affected by resistance mutations
Erg3 where mutations affect its ability to convert precursor 14- methylfecosterol to an unusual sterol causing permeability
14 methylfecosterol supports continuous growth / no altered fluidity
Why would these alterations be common in aids/Immunocompromised patients
Given fluconazole as prophylactics and they are fungistatic
Why would gene amplification eg through trisomy for chr5 affect resistance in candida strains
It’s where tac1 for cdr1 efflux pumpvlocsted
And also where erg11 is located (less competitive inhibition if more of it)
Give the reason echinocandins resistance can occur intrinsically in some candida isolates and give evidence
Mutations within the fks1 glucan synthetase in 2 hotspots which reduces drug sensitivity to fks1
Injection Into mice with fks1 mutants were not sensitive to drugs
Which combination treatment used for cryptococcal meningitis and why - advancement in treatment
Flucytosine and ampB
Both too toxic to be given separately
How does flucytosine work
Converged to 5fluorouracil which causes rna miscoding and also stops dna synthesis
Which improvement to echinocandins is in development
Scy-078
It is oral based fks1 inhibitor instead of iv
What sort of vaccines been used for candidiasis in model animals
B-mannan polysach and sap2 vaccines
Which hsp could be targeted in future somehow (currently being studied with combo of azole use eg fluconazole) and why
Hsp90- reports that it can abrogate erg3 mediated Candida albicans resistance to azoles and also changes azoles from fungistatic to fungicidal if disrupted for af and ca
Why is it still hard to find drugs for it
Not specific enough for it to not target our hsp - toxic effects when you inhibit host hsp90-
Need the development or fungal-selective hsp90 inhibitors instead
Why could gpi biosynthesis pathways be targets in future
Found defects/downreg in gpi biosynthesis can disrupt cell wall composition in fungi, disrupt their morphology or even cause cell death (in Af)
gpi proteins like als 1 and 5 are potent adhesins important for cell binding and subsequent invasion
Eg af and ca.
Give example of very rare polyene resistance issues
Altered pm membrane content such as reduced ergosterol content
Which ampB is in development currently with better specificity to fungal sterols so less toxic
AmpB methyl urea
What is currently being done / developed for improvement to cyp450 interference with azoles
Tetrazoles
What small molecule screened to be an inhibitor of fungal gpi biosynthesis requiring protein gwt1 when administered in sub lethal concentrations can elevate immune responses to CA due to increased b1,3 glucan exposure - promising for future drugs
Gepinacin
