Oral N-acetylcysteine improves cone function in retinitis pigmentosa patients in phase I trial

Abstract

BACKGROUNDIn retinitis pigmentosa (RP), rod photoreceptors degenerate from 1 of many mutations, after which cones are compromised by oxidative stress. N-acetylcysteine (NAC) reduces oxidative damage and increases cone function/survival in RP models. We tested the safety, tolerability, and visual function effects of oral NAC in RP patients.METHODSSubjects (n = 10 per cohort) received 600 mg (cohort 1), 1200 mg (cohort 2), or 1800 mg (cohort 3) NAC bid for 12 weeks and then tid for 12 weeks. Best-corrected visual acuity (BCVA), macular sensitivity, ellipsoid zone (EZ) width, and aqueous NAC were measured. Linear mixed-effects models were used to estimate the rates of changes during the treatment period.RESULTSThere were 9 drug-related gastrointestinal adverse events that resolved spontaneously or with dose reduction (maximum tolerated dose 1800 mg bid). During the 24-week treatment period, mean BCVA significantly improved at 0.4 (95% CI: 0.2-0.6, P < 0.001), 0.5 (95% CI: 0.3-0.7, P < 0.001), and 0.2 (95% CI: 0.02-0.4, P = 0.03) letters/month in cohorts 1, 2, and 3, respectively. There was no significant improvement in mean sensitivity over time in cohorts 1 and 2, but there was in cohort 3 (0.15 dB/month, 95% CI: 0.04-0.26). There was no significant change in mean EZ width in any cohort.CONCLUSIONOral NAC is safe and well tolerated in patients with moderately advanced RP and may improve suboptimally functioning macular cones. A randomized, placebo-controlled trial is needed to determine if oral NAC can provide long-term stabilization and/or improvement in visual function in patients with RP.TRIAL REGISTRATIONNCT03063021.FUNDINGMr. and Mrs. Robert Wallace, Mr. and Mrs. Jonathan Wallace, Rami and Eitan Armon, Marc Sumerlin, Cassandra Hanley, and Nacuity Pharmaceuticals, Inc.

Keywords: Drug therapy; Neuroscience; Ophthalmology.

Conflict of interest statement

Conflict of interest: Johns Hopkins University has a licensing agreement concerning N-acetylcysteine amide with a company, Nacuity Pharmaceuticals, Inc. (Nacuity), under which the University is entitled to royalty distributions and has equity in Nacuity. GMW is also an employee of Nacuity.

Figures

Figure 1. Patient enrollment and disposition.

Patients who had previously been diagnosed to have retinitis pigmentosa (RP) at the Wilmer Eye Institute or were referred or self-referred with that diagnosis were screened. There were 9 screen failures defined as a patient who signed the consent form, completed at least 1 study assessment or procedure, and was found ineligible or chose not to participate. Five patients were ineligible because their fixation was compromised to the point that they could not perform macular sensitivity testing, 1 patient had poorly controlled blood pressure, and 3 patients decided not to participate after the screening visit. *One patient in cohort 2 had only one eligible eye because he had previously had a central retinal vein occlusion in his other eye. **One patient in cohort 3 who lived a long distance away decided to exit the study after the week 12 visit because a family member was diagnosed with a terminal illness that required constant attention and precluded the patient making monthly trips for study visits.

Figure 2. Adverse events.

There were 11 adverse events that were judged likely related to study medication and 9 were related to the gastrointestinal tract. Eight of the adverse events were transient and resolved spontaneously without change in study medication dosage and 3 resolved after dosing was reduced from 3 times a day (tid) to twice a day (bid).

Figure 3. N-acetylcysteine (NAC) levels in aqueous humor.

The dose of NAC was 600 mg twice a day for 12 weeks and then 600 mg 3 times a day for the subsequent 12 weeks in cohort 1 (A), 1200 mg twice a day for 12 weeks and then 1200 mg 3 times a day for the subsequent 12 weeks in cohort 2 (B), and 1800 mg twice a day for 12 weeks and then 1800 mg 3 times a day for the subsequent 12 weeks in cohort 3 (C). At each visit during the treatment period, an aqueous sample was obtained and NAC concentration was measured by LC-MS. The colored circles corresponding to patient identifiers show aqueous NAC levels in study eyes at each visit. Bars show the mean for each time point. The number of eyes (n) for each time point is shown along the x axis. Aqueous NAC was below the limit of quantification (20 ng/mL) for all subjects (except for the cohort 3 subject who exited at week 12 for whom no samples were available) at weeks 28, 32, and 36.

Figure 4. Change in best-corrected visual acuity (BCVA) during NAC treatment.

A trained visual acuity examiner measured BCVA on a standardized chart at 4 meters in letter score using a validated protocol established in the Early Treatment Diabetic Retinopathy Study (ETDRS). The BCVA at each study visit is shown for each eligible right (OD) and left (OS) eye in cohorts 1 (A), 2 (B), and 3 (C). In each plot, each colored line reflects the BCVA values of 1 eye over time. At each visit, the number of eyes with BCVA values (n) is shown along the x axis. The black line is the estimated trend of change over the 24-week treatment period in that cohort as estimated by linear mixed-effects model. There was a statistically significant improvement in mean BCVA over time during the 24-week treatment period in each cohort: 0.40 letters/month (95% CI: 0.20–0.59, P < 0.001) in cohort 1, 0.49 letters/month (95% CI: 0.29–0.69, P < 0.001) in cohort 2, and 0.22 letters/month (95% CI: 0.02–0.43, P = 0.03) in cohort 3. Box plots of the mean change in BCVA between baseline and week 24 showed a significant improvement in mean BCVA of 2.33 (95% CI: 1.17–3.48) letters (P < 0.001) in cohort 1, and 3.28 (95% CI: 0.93–5.64) letters (P = 0.006) in cohort 2 by linear mixed-effects model (D). In cohort 3, the improvement of 1.83 letters (95% CI: –0.45 to 4.11, P = 0.12) was not statistically significant. In each box plot, the box upper and lower borders correspond to the 25th to 75th percentile, the solid line in the middle of the box is the median, and the dotted line is the mean of the data.

Figure 5. Change in mean macular sensitivity during NAC treatment.

Macular sensitivity was measured at 68 loci in the central 20° using the Macular Integrity Assessment Instrument (MAIA) at each study visit, and the mean sensitivity (MS) for the 68 loci is shown. The average of the 2 pretreatment tests was used as the baseline MS value and along with subsequent values are plotted for each eligible eye in cohort 1 (A), cohort 2 (B), and cohort 3 (C) (each colored line is for 1 eye). The black line shows the estimated trend of MS change during the treatment period using the linear mixed-effects model. There was no statistically significant improvement in MS during the 24-week treatment period in cohort 1 (rate of change = 0.05 dB/month, 95% CI: –0.07 to 0.17, P = 0.38) or cohort 2 (rate of change = 0.04 dB/month, 95% CI: –0.08 to 0.16 dB/month, P = 0.48), but in cohort 3, there was a statistically significant improvement in MS of 0.15 dB/month (95% CI: 0.04–0.26; P = 0.008). (D) Box plots of the mean change in MS between baseline and week 24 showed no significant improvement in cohort 1 (change = 0.17 dB, 95% CI: –0.62 to 0.96, P = 0.67) by linear mixed-effects model, but there were statistically significant improvements in mean MS between baseline and week 24 in cohort 2 (change = 0.33 dB, 95% CI: 0.02–0.64, P = 0.04) and cohort 3 (change = 0.85 dB, 95% CI: 0.29–1.42, P = 0.003). In each box plot, the box upper and lower borders correspond to the 25th to 75th percentile, the solid line in the middle of the box is the median, and the dotted line is the mean of the data.

Figure 6. Heatmaps and fundus images from microperimetry testing during treatment and posttreatment observation in a patient from cohort 1 and a patient from cohort 2.

The heatmaps generated by the Macular Integrity Assessment Instrument software (A–D and I–L) and fundus images showing the sensitivity value at each retinal location (E–H and M–P) obtained pretreatment, during treatment at weeks 12 and 24, and after treatment at week 36 are shown for 1 eye for a cohort 1 patient (1-09) and 1 eye for a cohort 2 patient (2-05). Two pretreatment tests were obtained and the one with the highest mean sensitivity is shown. In heatmaps, the arrows point to regions where the retinal sensitivity improved after the onset of treatment. A change from an arrow to an arrowhead indicates improvement had occurred, and any subsequent decline is noted by a change from arrowhead to arrow. The loci circled in yellow on the pretreatment fundus images (E and M) show loci at which sensitivity increased equal to or more than 6 dB after the onset of treatment. On subsequent fundus images, green circles indicate that sensitivity at that location was increased equal to or more than 6 dB from pretreatment and a change back to yellow indicates a decline below the 6 dB threshold. In both of these eyes, there was a large improvement in sensitivity during treatment that was mostly sustained in A–H and partially sustained in I–P 3 months after treatment ended.

Figure 7. Heatmaps and fundus images from microperimetry testing during treatment and posttreatment observation in 2 patients from cohort 3.

The heatmaps generated by the Macular Integrity Assessment Instrument software (A–D and I–L) and fundus images showing the sensitivity value at each retinal location (E–H and M–P) obtained pretreatment, during treatment at weeks 12 and 24, and after treatment at week 36 are shown for 1 eye of patients 3-06 and 3-08 in cohort 3. Two pretreatment tests were obtained and the one with the highest mean sensitivity is shown. In heatmaps, the arrows point to regions where the retinal sensitivity improved after the onset of treatment. A change from an arrow to an arrowhead indicates improvement had occurred, and any subsequent decline is noted by a change from arrowhead to arrow. The loci circled in yellow on the pretreatment fundus images (E and M) show loci at which sensitivity increased equal to or more than 6 dB after the onset of treatment. On subsequent fundus images, green circles indicate that sensitivity at that location was increased equal to or more than 6 dB from pretreatment and a change back to yellow indicates a decline below the 6 dB threshold. In the right eye of patient 3-06, there was a large improvement in macular sensitivity during treatment that regressed after treatment. In the right eye of patient 3-08, there was a large improvement in macular sensitivity that was partially sustained 3 months after stopping treatment.

Figure 8. Change from baseline in ellipsoid zone (EZ) width.

Spectral domain–optical coherence tomography (SD-OCT) scans through the fovea are shown for a patient with moderately severe loss of EZ width (A, margins marked by blue lines) and severe loss of EZ width (B). The longitudinal EZ width measurements at baseline and weeks 12, 24, and 36 are shown as a colored line for each eye for cohorts 1 (C), 2 (D), or 3 (E). The black line is the average trend of EZ width over the treatment period as estimated by a linear mixed-effects model in each cohort. The number (n) of eyes with EZ measurements for each time point is shown along the x axis.