Oral Tonabersat Connexin-43 Modulator for Diabetic Macular Edema with Good Vision (DRCR Retina Network Protocol AN).

OBJECTIVE

Evaluate oral tonabersat, a connexin-43 hemichannel modulator, on central subfield thickness (CST) in eyes with center-involved diabetic macular edema (CI-DME) and good vision.

DESIGN

Phase II randomized, double-masked clinical trial.

PARTICIPANTS

One hundred twenty-nine adults with CI-DME and visual acuity (VA) 20/32 or better, from 24 US sites.

INTERVENTION: Participants randomly assigned 1:1- to 80-mg tonabersat (N = 64, [71 eyes]) or placebo (N = 65, [73 eyes]) for 6 months.

MAIN OUTCOME MEASURES: Change in OCT CST.

RESULTS

Overall, 37% of participants were female, with a mean age of 63 years. In tonabersat and placebo groups, respectively, the baseline mean CST was 359 and 362 μm; the mean (standard deviation [SD]) change in CST from baseline to 6 months was -15 (55) μm and +5 (51) μm; (adjusted mean difference: -16 [95% confidence interval (CI), -34 to 2], P = 0.08). A post hoc analysis limiting anti-VEGF effect showed adjusted mean difference: -21 [95% CI, -38 to -3], P = 0.02. Among participants with thinner eyes at baseline (CST <75 μm above threshold; tonabersat [n = 45] vs. placebo [n = 43]), adjusted mean difference was -2 μm (95% CI, -26 to 22). For thicker eyes (CST ≥75 μm above threshold; tonabersat [n = 20] vs. placebo [n = 24]), mean difference was -51 μm (95% CI, -83 to -19). The mean (SD) change in best-corrected VA from baseline to 6 months was: tonabersat 0.0 (5.7) letters versus placebo -0.4 (5.7) letters (adjusted mean difference: 0.82 [95% CI, -1.56 to 3.21], adjusted P = 0.39). Dizziness was more common with tonabersat (27% vs. 8%), headaches more common with placebo (17% vs. 6%), and drowsiness rates were 11% in both groups.

CONCLUSIONS

There was no statistically significant improvement in CST at 6 months in the tonabersat versus placebo groups. However, a post hoc analysis limiting anti-VEGF impact demonstrated significant benefit in the tonabersat group. Aside from increased dizziness, consistent tonabersat safety concerns were not identified. Given findings consistent with a potentially favorable biologic effect of tonabersat, further research into the role of the inflammasome in DME is warranted.

FINANCIAL DISCLOSURES: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.