Synthesis and pharmacological activity of adaprolol enantiomers: a new soft drug for treating glaucoma.

Adaprolol maleate is a new beta-adrenergic antagonist that is being developed to treat glaucoma. The soft drug was designed to minimize systemic activity through facile inactivation to an inactive metabolite. Studies with other potent beta-adrenergic antagonists indicated that tissue specific receptor differences might be more stringent for selected beta-adrenergic blocking activities and suggested that R enantiomers of traditional beta-blockers should be developed for controlling glaucoma. The present studies demonstrate that the potent ocular hypotensive effects of adaprolol are not stereoselective. In contrast, cardiac effects could be detected after intravenous S(+) adaprolol, but not R(-) adaprolol. The studies confirm that adaprolol functions as a potent beta-adrenergic antagonist. The negligible systemic beta-blocking activity detected with opthalmic administration of adaprolol is consistent with soft drug design.

The effect of dihydronicotinate N-substitution on the brain-targeting efficacy of a zidovudine chemical delivery system.

Enhanced brain delivery of zidovudine (AZT) has been demonstrated using a redox-based chemical delivery system (CDS). Optimization of the prototype AZT-CDS (5'-[(1-methyl-1,4-dihydropyridin-3-yl)carbonyl]-3'-azido-3'-deoxy thymidine ) was investigated by manipulation of the N-methyl group present on the dihydronicotinate portion of the molecule and examining the release of AZT in vivo in a rat model. Of the five compounds examined, all produced higher brain levels and lower blood levels of AZT than did AZT itself. In comparing the novel AZT-CDS analogues to the N-methyl benchmark, the N-propyl system proved to be the most efficient of the compounds tested.

Improved delivery through biological membranes. LVI. Pharmacological evaluation of alprenoxime--a new potential antiglaucoma agent.

A new site-specific chemical delivery system (CDS) for alprenolol was designed and investigated as a potential novel antiglaucoma agent. The effect of this compound, alprenoxime (AO), on the intraocular pressure (IOP) of rabbits was evaluated after its uni- and bilateral administration. AO produced significant reduction of the IOP starting at 30 min and lasting for more than 6 hr after its topical administration. Both in rats and in rabbits the i.v. bolus injection of AO (6 mg/kg) led to insignificant transient bradycardia, while no activity was found after oral or topical administration. Alprenolol (ALP) in a similar dose produced a sustained and significant bradycardia for more than 30 min. When the beta-adrenergic blocking activity was assessed against isoprenaline-tachycardia, the same results were obtained, i.e., AO led to a transient brief activity, whereas ALP produced a significant long-lasting beta blockade. These results support the potent ocular hypotensive action and the weak systemic beta-adrenergic blocking and cardiovascular activity of AO: a significant improvement in the therapeutic index. This finding recommends alprenoxime as a potent site-specific antiglaucoma agent with minimal systemic side effects.

Novel 'soft' beta-blockers as potential safe antiglaucoma agents.

A series of novel "soft" beta-blockers was designed and synthesized based on the "inactive metabolite approach". Accordingly, the acidic metabolite of metoprolol was converted into various lipophilic esters. The new compounds were tested for their effect on the intraocular pressure (IOP) of rabbits using the ultra-short acting beta-adrenergic antagonist "Esmolol" as a reference compound. Most of the tested compounds displayed a higher and a more prolonged ocular hypotensive activity than the reference methyl ester. The adamantaneethyl ester 2 emerged as the best potential candidate for ophthalmic use as an antiglaucoma agent. This compound exhibited an effective and long lasting ocular hypotensive activity without local irritation to the eye. At the same time, it showed a very fast rate of hydrolysis in human blood (t1/2 = 7.0 minutes) to the inactive acid metabolite. This makes possible effective separation of the desired ocular activity from unwanted systemic beta-blocking action. Unilateral treatment with 2 produced reduction in the IOP only in the treated eye, consistent with the mechanism proposed.

Improved delivery through biological membranes. 26. Design, synthesis, and pharmacological activity of a novel chemical delivery system for beta-adrenergic blocking agents.

Novel ketoxime analogues of known beta-blockers (propranolol, timolol, carteolol) were synthesized and tested as potential site-specific chemical delivery systems. It was assumed that a hydrolysis-reduction sequence could produce the active beta-blockers in the iris-ciliary body. It was found that some of these bioprecursors are remarkably active in reducing intraocular pressure in rabbits. The ketoxime derivative of propranolol is more effective and much less irritant than its parent beta-blocker. While the ketoximes also displayed activity on isoprenaline-induced tachycardia after iv administration, they were void of activity when given orally. Propranolol was found for a prolonged time and in significant concentrations in the rabbit's eye following topical administration of its ketoxime precursor; however, the inactive ketoximes apparently were not converted to the corresponding beta-blockers in the eye. A correlation was found between the physicochemical properties of the ketoximes and their conversion to the amino alcohol and thus their subsequent activity. The results suggest that at least some of the ketoxime precursors could have a use as antiglaucoma agents without systemic side effects.