Effects of γ-crystallin aggregation inhibitors Closantel and Gambogic Acid on cataract progression in the OPJ mouse

Abstract

Purpose : We recently identified six small molecules from a Microsource Discovery library (N=2650) with ability to block thermal aggregation of human recombinant γ-crystallins (Islam et al JBC 2022). These were selected based on a screen that included both an oxidation step with H₂O₂ and a thermal stress. Results showed that Closantel (Drug C, an antihelmintic drug) and Gambogic Acid (Drug G, from Gambogia tree) most potently inhibited thermal aggregation of oxidized hγD, deamidated hγS, and bovine γ-crystallins. These inhibitors had either no or only partial activity at high concentrations against hγD mutants W43R, R58H and R14C. In contrast, both drugs C and G quite effectively inhibited thermal aggregation of OPJ mouse mutant hγS F9S at 50-100uM concentration, leading us to choose this strain for in vivo testing.

Methods : Mice were started on drug or vehicle administration after weaning at 21 days of age, Testing groups included diet control (CON), powdered diet with Drug C (n = 52 lens), or topical application of vehicle with 5%DMSO, Drug C (0.5%), Drug G (0.25%) in vehicle/DMSO for 50-60 days (n=14), 85-91 days (n=80), and 100-110 days (n=6 lens). Mice were sacrificed and lenses were photographed using dark field microscopy. Surface area of opacity was determined digitally and expressed in decile from 1-100. Quantitative pixel analysis in nucleus and cortex was also carried using Image J software.

Results : Control lenses were mostly cataract free at 50-60days and exhibited 70-90% cataract at 80-90 days. Neither Drug C in the diet not C or G topically suppressed cataract. At 50-60 days, 70% of control lenses had no opacity while 70% of topically treated lenses with Drug G had cataract. However, while total cataract area was identical in Drug C vs CON, nuclear cataract severity was lowered by Drug C vs CON (29% vs 40.2%, p<0.01). Topical Drug C shifted cataract frequency to lower cataract grades vs CON (p<0.01). When opacity was ranked as continuing variable (Fitness plot) at day 85-91, opacity was 5-16% lower in the Drug C vs. CON (p=0.01)

Conclusions : While neither Drugs C nor G can block the progression of cataract in the OPJ mice, Drug C applied to the diet or topically was associated with small but significantly reduced lens opacification in the OPJ mouse.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.