The main goal of this proposal is to test the hypotheses that the lipophilicity of a topically applied prodrug significantly influences its topical and systemic activities and that chronic prodrug administration may alter esterase activities in the eye. Timolol, the most widely used topical anti-glaucoma drug, has been chosen as a model drug for prodrug derivatization because of a need to reduce its relatively high incidence of systemic side effects. There are 5 specific aims in this proposed research: (1) Using 5 ester prodrugs of timolol, to demonstrate that prodrug hydrolysis is required for expression of its beta adrenergic blockade activity, the degree of which may be controlled further by its diffusion rate across the cornea, (2) To demonstrate that the rate and duration of timolol release in the eye can be controlled further by using combinations of its prodrugs, (3) To demonstrate that the extent of corneal transport and hydrolysis of timolol prodrugs vary non-linearly with the applied dose due to esterase saturation, (4) Based on these results, to select a timolol prodrug for evaluation of its time course of ocular disposition and systemic absorption following single and multiple doses, and (5) To evaluate the changes in ocular esterase activity and to determine the basis for these changes upon chronic application of a timolol prodrug. An ancillary aim is to confirm that the ocular tissues of rabbits and human subjects differ in the relative proportions of acetyl- and butyrylcholinesterase, resulting in different esterase activities. These experiments will be performed using live rabbits as well as tissues from enucleated human (eye bank) and pigmented rabbit eyes. The methodology includes dihydroalprenolol displacement and inhibition of cAMP production assays to determine beta adrenergic blockage, the pH-stat method to evaluate prodrug hydrolysis, and the use of lucite-block perfusion chambers to evaluate corneal transport of prodrugs in vitro. HPLC will be used to assay for timolol and its prodrugs. The importance of this research is that it demonstrates the generality of the prodrug approach to enhance the therapeutic indices of other topical beta blockers. Furthermore, this research will lead to studies to evaluate the long-term effects of prodrugs on the physiological role of esterases and to investigate the effect of age, disease states, and nutritional status on esterase activity and relative proportions in the eye.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Visual Sciences A Study Section (VISA)
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University of Southern California
Schools of Pharmacy
Los Angeles
United States
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Lee, V H (1996) Ocular epithelial models. Pharm Biotechnol 8:425-36
Kompella, U B; Kim, K J; Lee, V H (1993) Active chloride transport in the pigmented rabbit conjunctiva. Curr Eye Res 12:1041-8
Lee, Y H; Kompella, U B; Lee, V H (1993) Systemic absorption pathways of topically applied beta adrenergic antagonists in the pigmented rabbit. Exp Eye Res 57:341-9
Wang, W; Bundgaard, H; Buur, A et al. (1991) Corneal penetration of 5-fluorouracil and its improvement by prodrug derivatization in the albino rabbit: implication in glaucoma filtration surgery. Curr Eye Res 10:87-97
Chien, D S; Sasaki, H; Bundgaard, H et al. (1991) Role of enzymatic lability in the corneal and conjunctival penetration of timolol ester prodrugs in the pigmented rabbit. Pharm Res 8:728-33
Lee, V H (1990) New directions in the optimization of ocular drug delivery. J Ocul Pharmacol 6:157-64
Diepold, R; Kreuter, J; Himber, J et al. (1989) Comparison of different models for the testing of pilocarpine eyedrops using conventional eyedrops and a novel depot formulation (nanoparticles). Graefes Arch Clin Exp Ophthalmol 227:188-93
Chang, S C; Chien, D S; Bundgaard, H et al. (1988) Relative effectiveness of prodrug and viscous solution approaches in maximizing the ratio of ocular to systemic absorption of topically applied timolol. Exp Eye Res 46:59-69
Chang, S C; Bundgaard, H; Buur, A et al. (1988) Low dose O-butyryl timolol improves the therapeutic index of timolol in the pigmented rabbit. Invest Ophthalmol Vis Sci 29:626-9
Chien, D S; Bundgaard, H; Lee, V H (1988) Influence of corneal epithelial integrity on the penetration of timolol prodrugs. J Ocul Pharmacol 4:137-46

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