Carbonic Anhydrase Inhibitors for Treatment of Glaucoma Example: Based on Presentation from: Parnian Eslami, Neeloufar Fakourfar, Mandana Moshtael Desease: Glaucoma Glaucoma- build up of fluid in the aqueous humor of the eye, the fluid presses against the optic nerve Untreated glaucoma can lead to permanent damage of the optic nerve and results in field loss, which can result into blindness These two drugs help decrease the pressure in the eye Add stats on Glaucoma Target: Carbonic Anhydrase CO2 + H2O <-----> HCO3- + H+ • An enzyme that drives the hydration of carbon dioxide and dehydration of Bicarbonate • Examples are found in: • Parietal Cells in Stomach • Pancreatic duct cells • Renal tubules • Red blood cells • CAH2 found in ciliary process, cornea, iris, and retina • Please ADD Connection with Glaucoma and pH Target: Structures of Carbonic Anhydrase 5 Types: α,β,γ,δ,ε - Type αfound in humans - Others found in bacteria and plants - 4 broad subgroups - Cytosolic, mitochondria, secreted and membrane associate - with several isoforms in each (ex: CA2, CA13) Length: ≈ 260 AA MW: 29kDa Inhibitor action Target: Active site Zinc Mechanism of Action: Inhibitor binds to active site, blocking interactions of water bound to zinc and inhibiting enzymatic activity Target: Carbonic Anhydrase II H+ + HCO3- H2CO3 CO2+ H2O Inhibitors mostly sulfanomides Metalloenzyme (has Zn2+ in active site) Binds near the active site and disrupts the interactions of the water bound to the zinc ion, blocking enzyme action Prolonged use can effect the same enzyme present in other tissues and can lead to kidney and liver damage Drugs Acetazolamide Dorzolamide For treatment of: For treatment of: Open angle glaucoma Open angle glaucoma Drug induced edema Ocular hypertension Centrencephalic epilepsies Edema due to conjuctive heart failure Metabolic alkalaemia Periodic paralysis Acetazolamide Dorzolamide Stereoisomer None; 2 polymorphic forms A&B 4; stereoisomer of brand Trusopt MW 222.245 g/mol 324.44 g/mol Formulation 125mg, 250mg tab 500mg SR cap, 500mg/5cc IV Opthalmic solution 2% Nature Potent carbonic anhydrase inhibitor Potent carbonic anhydrase inhibitor Half life 3-9 hours 4 months Marketing status Acetamox, Diamox, Diluran, Trusopt, Dorzolamide/timolol, etc. Cosopt, etc. Acetazolamide rotatable bonds • Rotatable (essential) bonds: 2 • Restricted bonds: 2 • Estimated number of drug conformers: 32=9 • Estimated number gives energy contribution due to conformation entropy loss upon binding or crystallization is: ΔGconf= 0.6 x 1= 0.6 kcal/mol Dorzolamide Rotatable bonds • Rotatable (essential) bonds: 3 • Restricted bonds: 0 • Estimated number of drug conformers: 33 = 27 • Estimated gives energy contribution due to conformation entropy loss upon binding or crystallization is: ΔGconf= 0.6 x 3= 1.8 kcal/mol Ionization • • • • • Acetazolamide Acidic Pka: 6.93 Basic pKa: -3.3 LogS: -2.36 Sw: .002 M Solubility: .980mg/mL @ 30oC - Dorzolamide - Acidic pKa: 8.1 - Basic pKa: 7.14 - LogS: -2.7 Sw: .004 M - Solubility: .699mg/mL Protein Binding Acetazolamide Protein Binding: 98% Dorzolamide Protein Binding: 33% Target binding Acetazolamide Dorzolamide Kd (dissociation constant) 20 nM 0.37 nM pKd (-logkd) 7.7 9.4 ΔGbind (RTlnKd) -10.64 kcal/mol -13.03 kcal/mol Acetazolamide Drug Target Interaction Hydrogen bonding: 2 Length: 1.67, 2.09 Hydrogen bonding off of Threonine Electrostatic Interaction: The high electron density of drug, is making strong interaction with positively charged Zinc. Van der Waals Interaction: Perfect steric Hydrogen bonding continued.. Hydrogen bond donors: 2 Hydrogen bond acceptors: 5 Hydrogen bond formation: 2 Unsatisfied donors and acceptors: 3 Dorzolamide Drug Target Interaction Hydrogen bond: 3 Length: 1.68, 2.13, 2.16 Bonds off of Threonine and Electrostatic Interaction: The high electron Density of drug is making strong Interaction with positively charged Zinc. Van der Waals interaction: Perfect steric fit. Hydrogen bonding continued… Hydrogen bond donors: 2 Hydrogen bond acceptors: 5 Hydrogen bond formation: 3 Unsatisfied donors and acceptors: 3 Phase partitioning Acetazolamide Dorzolamide LogP -0.26 -1 [Oct]/[H2O] 0.513 0.1 Lipophilic or Hydrophilic Hydrophilic Hydrophilic Polar surface area Acetazolamide Dorzolamide Hydrophilic Hydrophilic There are 9 polar atoms with total polar surface area of 115.04 A2 There are 9 polar atoms with total polar surface area of 106.33 A2 Permeable for regular blood stream (<140A2 ) Permeable for regular blood stream (<140A2 ) Not permeable for brain (>75A2) Not permeable for brain (>75A2) Pharmacokinetics Acetazolamide Dorzolamide Oral bioavailability: >90% Bioavailability: little to no systemic absorption Food co-ingestion: neither delays the rate of absorption nor reduces extent of absorption Tmax: 2-4 hours Drug interactions Acetazolamide: Salicylates increase the effect of the inhibitor Any other CAH2 inhibitor concurrent use will result in toxicity Dorzolamide Any other CAH2 inhibitor because of adverse effects Future Acetazolamide is looking to make an eye drop more effective than Dorzolamide 2% Using new formulation High concentration of the drug Surfactant gel preparations of Acetazolamide Acetazolamide loaded into liposomes Addition of cyclodestrins to increase solubility Questions?