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CHEM335 (GN) > 7 - Medicinal Chemistry of Antifungal Therapies > Flashcards

7 - Medicinal Chemistry of Antifungal Therapies Flashcards

1
Q

How many species of fungi are there, and how many are medically important?

A

80,000 species of fungi; 400 are medically important.

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2
Q

What beneficial roles do fungi play?

A

Fungi are involved in:
* Breaking down and recycling organic matter
* Production of food and spirits (e.g., cheese, bread, beer)
* Antibiotic production (e.g., penicillin)
* Immunosuppressive drugs (e.g., cyclosporine)

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3
Q

What are the two forms of fungi?

A

Yeast form (unicellular) and Mold form (multicellular).

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4
Q

What is the leading cause of mortality in immunocompromised patients?

A

Fungal infections.

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5
Q

What is the common fungal infection in immunocompetent patients?

A

Candida albicans (Thrush) and skin and nail fungal infections.

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6
Q

Name a true yeast.

A

Cryptococcus neoformans.

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7
Q

Name a yeast-like fungus.

A

Candida albicans.

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8
Q

Identify two dimorphic fungi.

A

Histoplasma capsulatum and Blastomyces dermatitidis.

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9
Q

What class of antifungal drug is Amphotericin B?

A

Polyene.

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10
Q

What is the mode of action of Amphotericin B?

A

Amphotericin B binds to ergosterol, generating a pore in the membrane and inducing oxidative burst.

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11
Q

What are the acute toxicities associated with Amphotericin B?

A

Nausea, vomiting, fever, and hypoxia.

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12
Q

What chronic effect is associated with Amphotericin B?

A

Nephrotoxicity.

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13
Q

What class of antifungal drug is Fluconazole?

A

Azole.

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14
Q

What is Fluconazole used for?

A

Less severe fungal infections and prophylactically in immunocompromised patients.

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15
Q

How does Fluconazole exert its effects?

A

Fluconazole targets the heme protein and co-catalysed cytochrome P450 dependent demethylation of lanosterol

Inhibition of demethylation enzymes results in depletion of ergosterol
- altering structure and membrane function of fungus

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16
Q

What is a significant side effect of Fluconazole?

A

MYELOTOXICITY (bone marrow suppression).
- hugely detrimental in already immunosuppressed patients

(White blood cell count does return to normal within 48 hours of discontinuation though)

Other problems include:
Fluconazole is fungistatic
- suppressing rather than curing infection

Emergence of resistance

17
Q

What is Flucytosine?

A

A pyrimidine analogue.

18
Q

How does Flucytosine exert its antifungal effects?

A

By interfering with DNA and RNA synthesis.

19
Q

What serious side effect is associated with Flucytosine?

A

Hepatotoxicity.

20
Q

What is the first line treatment for C. neoformans?

A

A 2-week course of Amphotericin B and 5-flucytosine followed by a long-term course of Fluconazole.

21
Q

What is a major problem with the co-administration of Flucytosine and Amphotericin B?

A

Increased risk of hepatotoxicity due to nephrotoxicity.

22
Q

What is the significance of Benzimidazoles in antifungal therapy?

A

They represent proof of concept for new treatments with reduced toxicity and improved efficacy.

23
Q

What process do microtubules undergo that is affected by Benzimidazoles?

A

Treadmilling (polymerisation and depolymerisation).

24
Q

How does Mebendazole, a derivative of Benzimidazole, affect cellular mitosis?

A

By blocking the dimerisation interaction between α and β-tubulin, inhibiting microtubule polymerisation.

25
Q

Fluconazole is primarily fungistatic, meaning it _______.

A

suppresses rather than cures the infection.

26
Q

What causes the side effects of Amphotericin-B?

A

These side effects are due to human ergosterol and fungal
ergosterol being structurally analogous enough that amphotericin B
also binds to human membranes and this causes toxic effects,
especially in the case of nephrotoxicity, predominately due to
changes distal tubule permeability, which causes wasting of Na+,
K+, and Mg2+, this results in reduced glomerular filtration

27
Q

What are the side effects associated with Fluconazole?

A

Toxicity - myelotoxicity - bone marrow suppression, meaning that
leukocytes, which are cells that are involved in the body’s immune
response, aren’t synthesised.
* Hugely detrimental in patients with already suppressed immune
systems, allowing for further infections.
* Importantly, white blood cell counts do begin to return to normal
within 48 hours of discontinuation of treatment.
* Emergence of resistance.

28
Q

How is resistance to Flucytosine acquired?

A
29
Q

What is the MOA of benzimidazole?

A
30
Q

What is the MOA of Benzimidazole derivative Mebendazole?

A
31
Q

How are Benzimidazoles metabolised?

A

CHEM335 (GN) (4 decks)

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