Phospho-Sulindac (OXT-328) Inhibits Dry Eye Disease in Rabbits: A Dose-, Formulation- and Structure-Dependent Effect

Inflammation of the ocular surface is central to dry eye disease (DED). The anti-inflammatory agent phospho-sulindac (PS) at a high dose was efficacious against DED in a rabbit model. We assessed the dose, formulation and structure dependence of PS's effect. In rabbits with concanavalin A-induced DED we evaluated a range of PS concentrations (0.05%-1.6%) and dosing frequencies, assessed the duration of its effect with PS in 2 solution formulations and one emulsion formulation, and compared the efficacy of PS to that of sulindac, and of the structurally similar phospho-ibuprofen amide. We determined tear breakup time (TBUT) (tear stability), Schirmer's tear test (tear production), and by esthesiometry corneal sensitivity (symptoms). We also determined the biodistribution in the eye of topically applied PS. PS in a solution formulation, given as eye drops q.i.d. was efficacious starting at a dose of 0.1%. The effect was apparent after 2 days of treatment and lasted at least 8 days after the last dose. Both signs (evidenced by TBUT and Schirmer's test) and symptoms (measured by corneal sensitivity) improved significantly. The best formulation was the solution formulation; a cyclodextrin-based formulation was also successful but the emulsion formulation was not. PS and its metabolites were essentially restricted to the anterior chamber of the eye. Sulindac and phospho-ibuprofen amide had no efficacy on DED. PS is efficacious against DED. Its effect, encompassing signs, and symptoms, are dose, formulation, and structure dependent. PS has therapeutic promise and merits further development.