PHARMACEUTICAL CHEMISTRY II (PHCM672) Lecture 1, Antifungal Drugs (Antimycotics) Dr. Mohammad Abdel-Halim

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1 PHARMACEUTICAL CHEMISTRY II (PHCM672) Lecture 1, Antifungal Drugs (Antimycotics) Dr. Mohammad Abdel-Halim

2 Chemotherapeutic agents Pharmaceutical Chemistry I Antibacterial drugs Pharmaceutical Chemistry II 1) Antifungal Drugs 2) Antihelmintics and ectoparasiticinfections 3) Antimalarial Agents 4) Antimycobacterial Agents 5) Antiprotozoal Drugs 6) Antiviral Drugs 7) Anticancer Drugs Pharmaceutical Chemistry III Drugs affecting CVS, antihistaminics and NSAIDs Pharmaceutical Chemistry IV Drugs affecting CNS, hormones and related drugs, and vitamins

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4 Fungi and fungal infections Fungal kingdom: yeasts, molds, rusts, and mushrooms (~ 1 million species, ~ 300 pathogenic for men) Most fungal infections (mycoses) are caused by yeasts and molds Most fungi live on dead organic matter (in the soil, on leaves or wood) A few can cause infections through wounds or inhalation Only few can only live on mammalian hosts (e.g. Candida albicans is a part of a normal flora of the GI tract and vagina)

5 Human fungal diseases (mycoses) are classified by the location on or in the body where the infection occurs: Cutaneous mycoses: include dermatophytoses caused by dermatophytes also can be by Candida albicans, infection is limited to the epidermis, (Most common) Subcutaneous when the infection penetrates significantly beneath the skin, Systemic : The deep-seated, systemic mycoses, when the infection is deep within the body or disseminated to internal organs (Less common). Systemic Infections can be due to : 1) True pathogenic fungi capable of infecting healthy individuals, 2) Opportunistic fungi OPPORTUNISTIC MYCOSES in individuals who have predisposing conditions such as immunodeficiency or debilitating diseases (for example, AIDS) and use of immunosupressive drugs for organ transplants and cancer chemotherapy. 5

6 Examples of infectins by fungi 6

7 Dermatophytic infections (Tinea, ringworm) athlete s foot face, arms and shoulders scalp groin area onychomycosis toe and finger nails Fungi use keratin as a source of nutrition. This ability allows them to infect keratinized tissues and structures, such as skin, hair, and nails. 7

8 Candida albicans Major cause of oral (thrush) and vaginal yeast infections Occur when the normal population of flora disturbed by treatment of a bacterial infection with an antibiotic Infections of the skin and nails possible In persons with healthy immune system only superficial infectiones of the skin and mucosa In persons with impaired immune system deep-seated systemic infections possible (death threatening), OPPORTUNISTIC Cryptococcus neoformans OPPORTUNISTIC Found in bird droppings (pigeons) Inhalation of the dust contaminated with spores can cause a minor lung infection often mistaken for a cold For immunocompromised persons spreading via the circulatory system possible including CNS infections (fatal without treatment) 8

9 Blastomyces dermatidus Causes Blastomycosis Dimophic : Grow in one form in soil at room temparature and in a different form in the human host at 37 o C after inhalation The resulting lung infections often mild and self-limiting, severe systemic infections possible) Aspergillus species Cause Aspergillosis: OPPORTUNISTIC Aspergillus species (A. fumigatus, A. niger, A. flavus) Dangerous to persons with supressed Immune system, high mortality rate for systemic aspergillosis : Aspergillus species infection through inhalation, wounds, and implanted devices (e.g. catheters) 9

10 Antifungal Chemotherapy Number of antifungal drugs are limited compared to antibacterial agents Both fungi and mammals are eukaryotes (bacteria are prokaryotes) small biochemical difference difficult search for selective agents Two major differences between fungal and mammalian cells : Fungal cells have cell walls (mammalian cells do not) fungal cell wall a potentially good target for selective drugs. However, inhibitors of the fungal cell wall biosynthesis became available only recently Fungal cell membranes contain ergosterol mamalian cell mambranes contain cholesterol vs. HO H H Ergosterol HO H H Cholesterol 10

11 Drugs Classification of Antifungal 1- Inhibitors of Cell Membrane and its Function A-Drugs affecting cell membrane function Polyenes(Nystatin- Amphotericin B) B-Inhibitors of ergosterolsynthesis 1-Azoles - Imidazoles(Clotrimazole, Miconazole, Ketoconazole) - Triazoles(Itraconazole, Posaconazole, Fluconazole, Voriconazole) 2- Allylamines(Terbanafine& Tolnaftate) 3- Morpholines 2- Inhibitors of Cell Wall Synthesis Echinocandins (Caspofungin) 3-Inhibitors of DNA/RNA Functions/ mitosis inhibitors Flucytosin- Griseofulvin

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13 Inhibitors of Cell Membrane A-Drugs affecting cell membrane function Polyene antiboitics(nystatin- Amphotericin B) Natural products (Antibiotics) isolated from cultures of Streptomyces species 13

14 1) Amphotericin B hydrophilic region Macrocyclic lactones including conjugated double bonds (polyenes), OH-groups, a carboxyl group, and an aminosugar mycosamine hydrophobic region two distinct regions: hydrophobic and hydrophilic Named after the amphoteric behaviour (carboxy group + amino group) Breakthrough in systemic antifungal therapy (1956) mycosamine Relatively of low toxicity to human cells permitting IV administration 14

15 1) Amphotericin B Drug of choice for many systemic life-threatening fungal infections Can not cross the blood-brain barier: inthratecal administration (into the spinal cord) for treatment of CNS infections Insoluble in water, formulated as a complex with deoxycholic acid Nephrotoxic New formulations such as liposomal encapsulation decreased toxicity (blood vessels at the site of infection are more permeable for the lipid formulations than those of normal tissue selective delivery of the drug to the site of infection, see the next slide. 15

16 1) Amphotericin B A. Amphotericin B intercalated between the phospholipids of a spherical liposome (AmBisome ). B. Outcomes of antifungal therapy in cancer patients treated with conventional amphotericin B and liposomal amphotericin B. 16

17 O 2) Nystatin (Mycostatin ) OH OH OH HO O OH OH OH OH O OH O Discovered in the New York State Health Lab (1951) O O First clinically used polyene antifungal used topically in creams ointments and oral suspension Used for vaginal (vaginal tablets) and cutaneous candidiasis (topically) No systemic application (too toxic due to high affinity to membrane bound cholesterol in human cells) No absorption from the GI tract oral application to treat fungal infections of the mouth and GI tract e.g GI candidiasis HO NH 2 OH 17

18 Polyenes mechanism of action: insertion into cell membranes tunneling, loss of essential cell constituents (e.g. K + ) cell death Polyenes binds to hydrophobic region of ergosterol forming a hydrophilic channel The number of conjugated double bonds (nystatin and amphotericin 7) correlates directly with antifungal activity, and inversely with toxicity to mamallian cells amphotericin B: the highest activity and the lowest toxicity 18

19 Inhibitors of Cell Membrane B- Inhibitors of ergosterol synthesis 1- Azoles Imidazoles (Clotrimazole, Miconazole, Ketoconazole) Triazoles (Itraconazole, Posaconazole, Fluconazole, Voriconazole) 2- Allylamines (Terbanafine, Tolnaftate) 3- Morpholines will Not to be discussed 19

20 Ergosterol Biosynthesis Inhibitors Three enzymes can be inhibited in this pathway squalene squalene epoxidase (1) allylamines O Squalene epoxidase Inhibitors 1. Allylamines Lanosterol 14αdemethylase Inhibitors 2. Azoles HO (3) Morpholines 14 lanosterol 14 -demethylase 14-reductase α (2) azoles HO CH 3 14α-CH lanosterol 14 -Reductase Inhibitors 3. Morpholines HO HO Ergosterol 20

21 1- Azoles: Imidazoles and Triazoles Tha largest class of antimycotics (> 20 drugs in the market for both superficial and systemic mycoses) Broad spectrum of activity, oral bioavailability of some analogs Azoles Can be OR 21

22 1- Azoles: Imidazoles and Triazoles Mechanism of action: Inhibition of CYP450 14α-demethylase lack of ergosterol needed for the intact membrane accumulation of lanosterol in the fungal cell membrane permeability change and dysfunction of membrane-embedded proteins cell death The 14α-demethylase is CYP450 enzyme, it has heme co factor. R N X Imidazole or triazole N N N Fe N N 14α-demethylase Cholesterol synthesis in human cells (also employing 14α-demethylase) is much less affected due to the reduced strengh of inhibition for the human enzyme e,g,ketoconazole has 1000 fold higher affinty to bind the fungal enzyme The basic imidazole/triazole nitrogen of the drug forms a bond to the heme iron preventing the enzyme from oxidizing its normal substrate 22

23 Selected Imidazole Antimycotics 1) Clotrimazole (Canesten ) The simplest prototype structure pka 6.1 Practically insoluble in water, soluble in dilute mineral acids Used only topically for the treatment of many tinea infections and candidiasis (vaginal candidiasis). Available as a solution in polyethylene glycol, lotion, cream, and powder. basic N N Cl Clotrimazole is not considered suitable for the teatment of systemic infections. 23

24 2) Miconazole (Daktarin ) Bis(dichlorobenzyl)-ether pka 6.9 Sparingly soluble in water Used also as mononitrate salt For the treatment of both superficial and systemic infections Injectable form of the free base solubilized with polyethylene glycol treatment of severe systemic infections Cream, lotion, powder, and spray for the treatment of tinea and cutaneous infections dichlorobenzyl Cl Cl O ether Cl dichlorobenzyl Cl N N 24

25 3) Ketoconazole (Nizoral ) Ketal The first orally active antifungal azole Ketal N-deacetylation logp 2.88 more hydrophilic than clotrimazole (5.76) and miconazole (6.42) Slightly soluble in water pka 6.5, bioavailability only at low stomach ph < 4, antacids and H 2 -histamine antagonists which decrease stomach acidity reduce absorption Metabolism Extensively metabolised to inactive metabolites (one step: N- deacetylation) 25

26 3) Ketoconazole (Nizoral ) Indicated for a broad spectrum of systemic infections Not effective against Aspergillus or Cryptococcus Also used orally to treat severe cutaneous dermatophytic infections not responsive to topical therapy Topically: creams and shampoos against cutaneous candidiasis, tinea infections Side effects 1- Hepatotoxic 2- Inhibition of the synthesis of cholesterol and other steroid hormones anti-androgenic effects (loss of libido, gynecomastia) - today s clinical use limited to topical applications - replaced by itraconazole: a systemic agent with less sideeffects and an expanded antifungal spectrum (next slide) 26

27 Selected Triazole Antimycotics Itraconazole (Sporanox,1984) Structurally related to ketoconazole 1,2,4-triazole 1,2,4-triazol-3-one 1 ω-1 Hydroxylation (Active) More effective and better tolerated, orally active, broad-spectrum antifungal agent than ketoconazole (but much more expensive) 27

28 1) Itraconazole (Sporanox,1984) Advatages over ketoconazole i. Not hepatotoxic, no anti-androgenic effects ii. Effective against Aspergillus infections iii. Longer half-life (20-30 h) than ketoconazole (6-9 h), active hydroxy-metabolite (ω-1 hydroxylation) Like ketoconazole : oral absorption requires acidic conditions (see ketoconazole), food doubles oral bioavailability No penetration into CNS and CSF (cerebrospinal fluid) not used to treat meningitis and fungal CNS infections Both Ketoconazole and itraconazole are powerful CYP3A4 inhibitors so, we have to decrease the conc. of coadministrated drugs which are CYP3A4 substrates, such as the hypnotic triazolam, the immuno suppresant cyclosporin.

29 2) Posaconazole Novel itraconazole analog designed after its active ω-1 hydroxyl metabolite : tetrahydrofuran hase II glucoronide conjugation Red parts in the structure indicate the differences from itraconazole Used to treat invasive infections by Candida, and Aspergillus species in immunosupressed patients Metabolized mainly by phase II glucoronide conjugation (not by CYP450) fewer drug interactions (adavantage over keoconazole and itraconzole 29

30 3) Fluconazole (Diflucan,1984) Two triazol rings + hydroxy group water soluble (logp 0.31) as a free base suitable for both oral and iv administration Excellent oral bioavailability (90%) not affected by the presence of food or ph Long half-life h For the treatment of candidiasis and cryptococcosis Penetrates into CNS and CSF drug of choice for the treatment of cryptococcal meningitis Topically against vaginal candidiasis Little hepatic metabolism, excreted unchanged in the urine 30

31 4) Voriconazole (VFEND ) F Fluconazole analog: additional methyl group, one triazol replaced by fluorinated pyrimidine Broader spectrum of activity N N N F H 2 C F H C C N OH CH 3 N Unlike fluconazole, active against Aspergillus and more potent against Candida (new standard in the treatment of invasive Aspergillosis) Good oral absorption and penetration of blood-brain barrier Metabolism Unlike fluconazole, extensive CYP450 biotransformation drug interactions methyl hydroxylation, N-oxidation) 31

32 triazoles Imidazole Triazoles are superior to imidazoles 32

33 Squalene Epoxidase Inhibitors Effective only against dermatophytes to treat skin and nail infections Inhibition of squalene epoxidation - an early stage of ergosterol synthesis 1) decrease in total sterol content of the fungal cell membrane leads to disfunction of proteins involved in nutrition transport 2) concentration of toxic squalene Cholesterol synthesis in humans unaffected because the drugs are selective for the fungal squalene epoxidase at applied concentrations

34 Squalene Epoxidase Inhibitors 1) Tolnaftate (Tinactin ) 2) Terbinafine HCl (Lamisil ) S N O CH3 CH3 Allyl amine Thiocarbamate Topical treatment of ringworm, jock itch and athlete s foot Old over the counter drug Employed topically (t. pedis, t. cruris, t. corporis) and orally against onychomycosis (ringworm of the nails)

35 Inhibitors of Cell Wall Echinocandins (Caspofungin) 35

36 Echinocandins Echinocandins: penicillins of antifungal drugs Expected to be nontoxic for humans as human cells do not have cell walls Caspofungin Semi-synthetic cyclic peptide with long lipophilic side chain Mode of action Inhibitor of 1,3-β-glucan synthase Used in treating life-threatening systemic infections Effective against Candida species resistant to other drugs Effective against azole-resistant Aspergillus Not effective against Cryptococcus neoformans No oral bioavailability; IV administration Limited hepatic metabolism no drug interactions 36

37 Caspofungin O long lipophilic side chain H 2 N HO HN HO NH HN HN O OH CH 3 CH 3 CH 3 O N O O O O N OH cyclic peptide H 2 N OH N H HO NH OH OH 37

38 Intact cell wall After treatment with caspofungin 38

39 Inhibitors of DNA/RNA Functions/ Mitosis inhibitors Flucytosine - Griseofulvin 39

40 Flucytosine Prodrug Inetrferes with DNA/RNA 5-FU enters the pathways of RNA/DNA-Synthesis antimetabolite cell death Human cells do not contain cytosine deaminase Orally active Can be converted to 5-FU by intestinal flora human toxicity Narrow spectrum of activity: indicated to treat severe systemic infections of andida and Cryptococcus species 40

41 Antifungal antibiotic from Penicillium griseofulvum Spiro structure (two rings having only one common atom) Used orally to treat fingernail and toenail infections (topical use ineffective) Griseofulvin (Grisactin ) Gets incorporated in newly synthesized keratin Does not affect infected keratin long-term therapy (several months) until the new nail grows Mode of action: The drug binds to tubulin, interfering with microtubule function, thus inhibiting mitosis (fungistatic) 41

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43 Thank You 43