Ultrasound-Enhanced Delivery of Medications to the Eye

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Ultrasound-Enhanced Delivery of Medications to the Eye Project Summary The objective of this project is the development of a safe and effective means to deliver macromolecular drugs across the wall of the eye for treatment of disease, especially age-related macular degeneration (AMD). AMD is a progressive eye disease affecting as many as 15 million Americans and is the number one cause of vision loss and legal blindness in adults over 65 years of age in the U.S. Several promising macromolecular drugs are now being evaluated for treatment of AMD. Because the outer shell of the eye (the sclera) is relatively impermeable to high molecular weight drugs, intraocular injection is the most widely used means to accomplish delivery to the retina and choroid. Consequently, delivery of macromolecular medications into the eye must be accomplished by intravitreal injections every few weeks, with the occurrence of complications (infection, retinal detachment, increased intraocular pressure) increasing cumulatively. For this reason, non-invasive methods for delivery of macromolecular drugs are of great interest. Ultrasound has in the past been shown to be capable of making tissues more permeable to macromolecules. We propose to investigate the effect of ultrasound of various frequencies, intensities and durations on transscleral transport of fluorescently labeled molecules (dextrans) into the rabbit eye. We will use dextrans of molecular weights of 10-kDa, 70-kDa and 500-kDa, each with a different wavelength fluorescent label. (Molecular weights of drugs now used for treatment of AMD are typically around 150-kDa.) We will conduct two series of experiments, the first involving use of an unfocused 20-kHz ultrasound source and the second utilizing a novel ultrasound device consisting of two 900-kHz confocal annuli. This device provides the advantage of allowing focusing and avoidance of potentially sensitive structures such as the cornea, lens and macula. By driving the two elements at slightly different frequencies, `beats' at a lower frequency corresponding to the frequency difference are generated. We will expose the rabbit eyes to 20-, 60- and 900-kHz ultrasound using this device. A mixture of the fluorescently labeled dextrans will then be injected subconjunctivally outside the globe. Twenty-four hours after treatment, the eyes will be fixed, cryosectioned and examined by confocal microscopy. We will visualize the distribution of the molecules within the sclera, choroid and retina to evaluate transport and characterize any tissue damage that might have occurred microscopically and by apoptosis assays.