OT-551

To investigate the safety and preliminary efficacy of OT-551, a disubstituted hydroxylamine with antioxidant properties, for the treatment of geographic atrophy (GA), the advanced atrophic form of age-related macular degeneration (AMD).

The study was a single-center, open-label phase II trial, enrolling 10 participants with bilateral GA. Topical 0.45% OT-551 was administered in one randomly assigned eye three times daily for 2 years. Safety measures were assessed by complete ophthalmic examination, fundus photography, and review of symptoms. The primary efficacy outcome measure was the change in best corrected visual acuity at 24 months. Secondary efficacy measures included changes in area of GA, contrast sensitivity, microperimetry measurements, and total drusen area from baseline.

Study drug was well tolerated and was associated with few adverse events. The mean change in BCVA at 2 years was +0.2 ± 13.3 letters in the study eyes and -11.3 ± 7.6 letters in fellow eyes (P = 0.0259). However, no statistically significant differences were found between the study and fellow eyes for all other secondary outcome measures.

OT-551 was well tolerated by study participants and was not associated with any serious adverse effects. Efficacy measurements in this small study indicate a possible effect in maintaining visual acuity. However, the absence of significant effects on other outcomes measures in this study suggests that OT-551, in the current concentration and mode of delivery, may have limited or no benefit as a treatment for GA (ClinicalTrials.gov number, NCT00306488).

OT-551 (1-hydroxy-4-cyclopropanecarbonyloxy-2,2,6,6-tetramethylpiperidine hydrochloride), is a novel small molecule with antioxidant and anti-inflammatory effects. Protective efficacy of OT-551 and its metabolite TEMPOL-H (TP-H) against light-induced degeneration of retinal pigment epithelium (RPE) was tested. Albino rats were intraperitoneally injected with OT-551, TP-H, or water approximately 30 min prior to a 6 h exposure to 2700 lux white fluorescent light. Retinal protection was evaluated histologically by counting the RPE cell nuclei and measuring the extent of RPE damage on the retinal sections as RPE damage index (%). Following light exposure, the number of RPE cell nuclei was significantly reduced in light-exposed eyes from water-treated animals, while the number was not significantly different between light-exposed and unexposed eyes from the animals treated with 100 mg/kg TP-H or with any dose of OT-551 in the inferior hemisphere, and with 100 mg/kg OT-551 in the superior hemisphere. RPE damage index was significantly lower in the animals treated with any dose of OT-551 compared to water-treated animals both in the inferior and superior hemispheres. Systemic administration of OT-551 and TP-H provides RPE cell protection against acute light damage, and the protection by OT-551 was greater than by TP-H.