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 CO 2 + H 2 O HCO 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

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 Target: Structures of Carbonic Anhydrase

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 + + HCO 3 -  H 2 CO 3  CO 2 + H 2 O  Inhibitors mostly sulfanomides  Metalloenzyme (has Zn 2+ 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  For treatment of:  Open angle glaucoma  Drug induced edema  Centrencephalic epilepsies  Edema due to conjuctive heart failure  Metabolic alkalaemia  Periodic paralysis Dorzolamide  For treatment of:  Open angle glaucoma  Ocular hypertension

Stereoisomer None; 2 polymorphic forms A&B 4; stereoisomer of brand Trusopt MW g/mol g/mol Formulation 125mg, 250mg tab 500mg SR cap, 500mg/5cc IV Opthalmic solution 2% Nature Potent carbonic anhydrase inhibitor Half life 3-9 hours4 months Marketing status Acetamox, Diamox, Diluran, etc. Trusopt, Dorzolamide/timolol, Cosopt, etc. Acetazolamide Dorzolamide

Acetazolamide rotatable bonds Rotatable (essential) bonds: 2 Restricted bonds: 2 Estimated number of drug conformers: 3 2 =9 Estimated number gives energy contribution due to conformation entropy loss upon binding or crystallization is: ΔG conf = 0.6 x 1= 0.6 kcal/mol

Dorzolamide Rotatable bonds Rotatable (essential) bonds: 3 Restricted bonds: 0 Estimated number of drug conformers: 3 3 = 27 Estimated gives energy contribution due to conformation entropy loss upon binding or crystallization is: ΔG conf = 0.6 x 3= 1.8 kcal/mol

Ionization Acetazolamide - Dorzolamide Acidic Pka: Acidic pKa: 8.1 Basic pKa: Basic pKa: 7.14 LogS:  Sw:.002 M- LogS: -2.7  Sw:.004 M 30 o C- Solubility:.699mg/mL

Protein Binding  Acetazolamide  Protein Binding: 98%  Dorzolamide  Protein Binding: 33%

Target binding AcetazolamideDorzolamide Kd (dissociation constant) 20 nM0.37 nM pKd (-logkd) ΔG bind (RTlnKd) kcal/mol kcal/mol

Hydrogen bonding: 2 Length: 1.67, 2.09 Hydrogen bonding off of Threonine Acetazolamide Drug Target Interaction Van der Waals Interaction: Perfect steric Electrostatic Interaction: The high electron density of drug, is making strong interaction with positively charged Zinc.

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 Glutamine Van der Waals interaction: Perfect steric fit. Electrostatic Interaction: The high electron Density of drug is making strong Interaction with positively charged Zinc.

Hydrogen bonding continued… Hydrogen bond donors: 2 Hydrogen bond acceptors: 5 Hydrogen bond formation: 3 Unsatisfied donors and acceptors: 3

Phase partitioning AcetazolamideDorzolamide LogP [Oct]/[H2O] Lipophilic or Hydrophilic Hydrophilic

Polar surface area Acetazolamide  Hydrophilic  There are 9 polar atoms with total polar surface area of A 2  Permeable for regular blood stream (<140A 2 )  Not permeable for brain (>75A 2 ) Dorzolamide  Hydrophilic  There are 9 polar atoms with total polar surface area of A 2  Permeable for regular blood stream (<140A 2 )  Not permeable for brain (>75A 2 )

Pharmacokinetics Acetazolamide  Oral bioavailability: >90%  Food co-ingestion: neither delays the rate of absorption nor reduces extent of absorption  Tmax: 2-4 hours Dorzolamide  Bioavailability: little to no systemic absorption

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?