A Pilot Study for the Evaluation of Minocycline as a Microglia Inhibitor in the Treatment of Diabetic Macular Edema

Diabetic retinopathy (DR) is one of the leading causes of blindness in the United States. A frequent manifestation of diabetic retinopathy is diabetic macular edema (DME) for which the only proven treatment is laser photocoagulation. In the retina, microglia are capable of migrating through the retina to sites of inflammation to associate closely with neurons and the vasculature, and are key cellular players in the mediation of processes of chronic inflammation implicated in DME. For these reasons, microglia represent a promising cellular target for forms of therapy that limit the deleterious inflammatory changes found in DR. The objective of this study is to investigate the safety and efficacy of minocycline as a microglia inhibitor in patients with DME.

Study Population: Eligibility criteria include previous treatment with standard-of-care focal laser photocoagulation, or macular edema not amenable to focal laser treatment; retinal thickness in the central subfield > 250 microns as measured by optical coherence tomography (OCT); and visual acuity between 20/32 and 20/200 in the study eye.

Design: Five participants will be initially enrolled in this open-label pilot study. However, up to an additional three participants may be enrolled to account for participants who withdraw from the study prior to receipt of six months of study treatment. Participants will take an oral dose of 100 mg of minocycline twice daily for 24 months. During each visit, participants will have their visual acuity measured and will undergo OCT testing to measure retinal thickness. Beginning at the Month 6 visit, participants will be eligible for focal laser therapy unless they show marked improvement in retinal thickness and/or visual acuity or if they are not amenable to focal laser treatment. Participants who do not meet the criteria for improvement will also be eligible for anti-vascular endothelial growth factor (VEGF) treatments such as bevacizumab (Avastin®) or ranibizumab (Lucentis®). Additionally, beginning at the Month 4 visit, participants will be assessed for worsening disease defined as loss of ≥ 15 Early Treatment Diabetic Retinopathy Study (ETDRS) letters of vision compared to baseline or a ≥ 50% increase in total retinal thickness as measured by OCT. Participants deemed to have worsening disease will also be eligible for focal laser and/or anti-VEGF treatments.

Outcome Measures: The primary outcome is the change in best-corrected visual acuity (BCVA) in the study eye at 6 months compared to baseline. Secondary outcomes include the change in retinal thickness as measured by OCT at 6, 12, 18 and 24 months compared to baseline, change in BCVA at 12, 18 and 24 months compared to baseline, as well as changes in fluid leakage in the macula as demonstrated by fluorescein angiography at 6, 12, 18 and 24 months compared to baseline. Safety outcomes include the number and severity of systemic and ocular toxicities, and adverse events.