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 AnhydraseCO2 + 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

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 AAMW: 29kDa

Target: Structures of Carbonic Anhydrase

Inhibitor actionTarget: 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 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 222.245 g/mol 324.44 g/molFormulation 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 monthsMarketing 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: 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 - Dorzolamide• Acidic Pka: 6.93 - Acidic pKa: 8.1• Basic pKa: -3.3 - Basic pKa: 7.14• LogS: -2.36 Sw: .002 M - LogS: -2.7 Sw: .004 M• Solubility: .980mg/mL @ 30oC - 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

Hydrogen bonding: 2Length: 1.67, 2.09Hydrogen 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: 2Hydrogen bond acceptors: 5Hydrogen bond formation: 2Unsatisfied donors and acceptors: 3

Dorzolamide Drug Target Interaction

Hydrogen bond: 3Length: 1.68, 2.13, 2.16Bonds off of Threonine and Glutamine

Van der Waals interaction: Perfect steric fit.

Electrostatic Interaction: The high electronDensity of drug is making strongInteraction with positively charged Zinc.

Hydrogen bonding continued…

Hydrogen bond donors: 2Hydrogen bond acceptors: 5Hydrogen bond formation: 3Unsatisfied 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

Hydrophilic

There are 9 polar atoms with total polar surface area of 115.04 A2

Permeable for regular blood stream (<140A2 )

Not permeable for brain (>75A2)

Dorzolamide

Hydrophilic

There are 9 polar atoms with total polar surface area of 106.33 A2

Permeable for regular blood stream (<140A2 )

Not permeable for brain (>75A2)

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?