Tolerability and efficacy of a rAAV-mediated glaucoma gene therapy in brown norway rats

Abstract

Purpose : Glaucoma is a leading cause of blindness affecting 2.9 million people in the US and is characterized by progressive optic nerve degeneration owing to imbalances between aqueous inflow and drainage. Prostaglandin analogs are effective at reducing IOP but are critically undermined by poor patient compliance. Herein, we set out to evaluate the effectiveness of a single use recombinant adeno-associated (rAAV)-mediated gene therapy treatment aimed at permanently lowering IOP through over-expression of prostaglandin F2a synthase (PTGS2) and receptor (PTGFR).

Methods : Brown norway rats (N=30) underwent baseline electroretinography (ERG), confocal scanning laser ophthalmoscopy (cSLO), optical coherence tomography (OCT), and tonometry. Rats were randomized following baseline characterization; each received a unilateral intracameral injection of rAAV packaging PTGS2 and PTGFR and a tetracycline inducible OFF-switch at either low (3.9x10⁹ vector genomes(vg)/ml), medium (3.9x10¹⁰ vg/ml), or high (3.9x10¹¹ vg/ml) dose. Tonometry was repeated at 1, 3, 6, 9, 12, and 13 months post injection and imaging/ERG repeated at 12 months to assess tolerability and efficacy. Gene expression was switched OFF at 12-months by administration of 5% tetracycline diet ad libitum. Eyes were harvested for histology at 12 and 18 months.

Results : Tonometry showed a dose-dependent reduction in IOP of -12.6% (low, NS), -21.87% (medium, P=0.0036) and -43.2% (high, P<0.0001) maintained until 12-months. Decreased IOP correlated to increased anterior chamber depth in low (+5.2%, P=0.0125), medium (+8.1%, P=0.0447) and high (+24.3%, P=<0.0001) dose treatment (Unpaired T-test) at 12-months. No difference in reflectivity/autofluorescence (cSLO), corneal/retinal thickness (OCT), or ERG were observed in any treatment group. Slit lamp examination showed increased cell (12%), flare (36%), iris exfoliation (88%) and hyphema (20%) in the high dose treatment group. Placement on 5% tetracycline diet increased IOP in high (+22.5%) and medium (+21.5%) dose eyes, representing a partial or complete reversion to normal tension, respectively.

Conclusions : This study demonstrated dose-dependent reduction in IOP following a single injection of vector and excellent tolerability in low and medium dose treatment groups. Critically, IOP reduction could be reversed through oral administration of tetracycline; a critical safety feature for future clinical translation.

This is a 2021 ARVO Annual Meeting abstract.