Precisely removing microvessels by photo-mediated ultrasound therapy

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Abstract/Project Summary Wet age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the developed world. Anti- vascular endothelial growth factor (VEGF) therapy is currently the gold standard for wet AMD treatment. However, some patients have poor response to this therapy, or develop resistance over long-term use. A recent study demonstrated persistent fluid in 53% and 71% of patients treated monthly with ranibizumab and bevacizumab, respectively. The other study shows that 20% of patients still become legally blind after 5 years of repeat anti-VEGF therapy. Therefore, development of an alternative therapy for AMD patients especially poor-responders to anti-VEGF therapy is strongly desired by ophthalmology clinic. The ultimate goal of this research is to study the capability of a new, noninvasive therapeutic technique for safely and efficiently eliminating choroidal neovascularization (CNV) that causes vision loss in patients with wet AMD. This technique termed photo-mediated ultrasound therapy (PUT) is agent free with high precision and high selectivity in removing microvessels. PUT employs cavitation produced by concurrently applied short duration laser pulses and ultrasound bursts. Importantly, PUT does not induce cavitation through laser vaporization; instead, the cavitation is produced via photospallation, or tissue cleavage due to transient thermoelastic stress. Therefore, the laser intensity required for PUT is much lower than conventional retinal laser, significantly reducing the risk of unwanted damage to the retina. The objectives of the proposed research are 1) to further understand and optimize PUT removal of microvessels, and 2) to evaluate the safety and efficacy of image-guided PUT in inducing regression of CNV in a well-developed animal model. The central hypothesis is that, by combining with an advanced eye imaging system, PUT can specifically remove microvessels created by CNV without damaging surrounding tissues. Two Specific Aims will be developed to test this hypothesis. Aim 1): Via the experiments on a well-developed in vitro model and mathematical modeling, determine to what extent PUT-produced cavitation induces vasoconstriction of a blood vessel. The role of laser and ultrasound during PUT will be evaluated experimentally in an in vitro whole blood model by quantifying cavitation bubble formation. Aim 2): Via the studies on a rabbit model, evaluate the efficacy and safety of imaging-guided PUT for removing single pathological microvessels in the choroid in vivo. To optimize the technology in anticipation of future studies on personalized treatment of patients, an imaging system with optical coherence tomography (OCT) and photoacoustic (PA) functions will be integrated for real-time feedback and guidance. Fundus photography, fluorescein angiography, indocyanine green angiography, OCT, electroretinography, histopathology, electron microscopy, and immunohistochemistry will be performed up to 1 month following treatment to determine the efficacy and safety of PUT on treating CNV regression.