Early Beginnings – Difficulties Treating Common Fungal Infections Antifungal Drugs Newer Therapies Assigned Reading/References/Homework
About 1408 Million Years Ago, fungi and animals phyla split We are more closely related to fungi then plants! This will prove difficult for one to treat mycotic infections due to the similarities between the eukaryotic fungus and the eukaryotic host (us! )
Symptoms: Delirium, failure of organs, death! Caused by: Inhalation of fungal spores from genus Aspergillus Treated with: nystatin, ketoconazole, fluconazole, capsofungin
Many of the common fungal infections described affect the general population. There is a vaster majority of fungi that cause serious harm to people that are immunocompromised!!
Amphotericin B Fluconazole Capsofungin Terbinafine Keep in mind: We need to target differences between our cell and the fungal cell. Antibiotics will not work because of both cells are eukaryotic and the medication could kill off the good gut flora that competes with the fungus for nutrients. Treatments usually include many combinations of different antifungals.
Known as a polyene macrolide 38 – Membered Ring Isolated 1955, market 1958 Amphiphilic! Anyone want to guess the Mech Of Action?!?!
Mech of Action! Associates with the membrane and causes leakage of Na, K, and Ca across membrane. But how does it differentiate between fungal cells and human cells??
Instead of cholesterol in the cell membrane, fungal cells have ergosterol. The heptaene portion of the ring interacts strongly with ergosterol instead of cholesterol. Cholesterol Ergosterol vs
Bistriazole Azole => Conjugated five-membered ring with at least 1 N and other non carbon atoms (could be N) Belongs to a larger class of well known antifungals – imidazoles (Clotrimazole, Miconazole) Fluconazole is newer though! Imidazoles synthesized to treat both superficial AND systematic infections. FluconazoleClotrimazoleMiconazole
Mech of Action: Specifically inhibits the cytochrome P450 fungal enzyme C- 14(alpha) demethylase. This enzyme is require in the 20 step pathway [thank goodness we didn’t have to memorize this] from lanosterol (intermediate in cholesterol synthesis) to ergosterol. Fluconazole binds to the Fe center of the enzyme (one of the nitrogens coordinates to the Fe).
Semisynthetic cyclic lipid-bearing polypeptide Belongs to class of antifungals: echinocandins – derived from the cyclic polypeptide. Large MW, low oral bioavailability => administered intravenously. Market 2001
Mech of Action: Potent inhibitor of the fungal enzyme 1,3-(beta)-D glucan synthase. This enzyme catalyzes glucan polymerization (glucan is just a polymeric sugar molecule), which is essential in the synthesis of a fungi’s cell wall. Human cells do not possess a cell wall, so the drug is effective.
Belongs to class of antifungals – the allylamines. Treats mainly superficial infections. Discovered by accident in 1974 - antifungal potential related directly to the tertiary allylamine and the 1-substituted naphthalene ring. Eventually developed terbinafine. Terbinafine Butenafine (Lotrimin)
Mech of Action: All allylamines work similarly. They inhibit ergosterol synthesis by inhibiting squalene epoxidase (oh snap!), the enzyme that catalyzes the epoxide formation between the 2 and 3 carbon of squalene. From this 2,3- oxidosqualene intermediate, we produce lanosterol and eventually ergosterol. ***** Terbinafine
Molecules and Medicine. EJ Corey. John Wiley and Sons: 2007 Recent Advances in the Chemistry of Anti-Infective Agents. Editors PH Bentley and R. Ponsford. Royal Society of Chemistry: 1993. http://www.doctorfungus.org. DoctorFungus Corporation http://www.doctorfungus.org http://faculty.swosu.edu/scott.long/phcl/antifung.htm. Long, Scott, Southwestern Oklahoma State University http://faculty.swosu.edu/scott.long/phcl/antifung.htm
Mathew, Bijoy P.; Nath, Mahendra. Recent approaches to antifungal therapy for invasive mycoses. ChemMedChem (2009), 4(3), 310-323.
1) Why is it so difficult to treat fungal infections? 2) The target of which biomolecule’s synthesis is the subject of many antifungal drugs? 3) What are the main families of antifungal agents? Name a member of each family. 4) What is the most commonly employed antifungal agent to treat invasive fungal infections? Describe its mechanism of action. What is the major side effect of this agent? 5) What enzyme is the biological target of the azole antifungal agents? What is the most common mechanism of fungal resistance to these agents? 6) The echinocandin caspofungin was approved by the FDA in 2001 for salvage therapy in cases of resistant invasive aspergillosis. What is the most likely target of these drugs? 7) Another class of antifungal agents is the allylamines, including terbinafine. Draw the structure of terbinafine and define the allylamine moiety. What is the biological target of allylamines?