Evaluation of a Connexin-based Peptide for the Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness and visual impairment in US adults. The current standard of care for DR is intravitreal (IVT) injection of anti-vascular endothelial growth factor (VEGF) therapeutics to inhibit vascular permeability and neovascularization. However, anti-VEGF drugs have limited efficacy in a substantial percentage of DR patients. The invasiveness of IVT injections also correlates with poor compliance as well as serious side effects. As such, there is an unmet medical need for an innovative noninvasive treatment that effectively mitigates DR pathogenesis and progression. In this research application, we propose to evaluate the therapeutic potential of a peptide-containing eye drop formulation (iNexin™) to mitigate DR pathophysiology by preserving blood-retina barrier (BRB) integrity. The BRB, which is formed by tight junctions of retinal vascular endothelial cells and retinal pigment epithelial cells, breaks down early in DR pathogenesis and causes vascular permeability and leakage as well as inflammation, leading to loss of retinal homeostasis and neurodegeneration. Diabetes-associated factors also disrupt gap junction intercellular communications to further exacerbate DR. Therefore, protecting intercellular junctions represents a significant therapeutic opportunity to treat DR. Connexin43 (Cx43) is a transmembrane protein component of intercellular junctions that is instrumental to barrier function integrity, cell-cell communication, and apoptosis. FirstString Research Inc. has developed a therapeutic peptide mimetic of Cx43, alpha-Connexin Carboxy-Terminal (aCT1), that stabilizes intercellular junctions while tempering hemichannel activity to preserve barrier function, reduce injury spread, and decrease inflammation. iNexin is a stable non-steroidal, preservative-free aCT1 eye drop formulation validated in a comprehensive set of safety and efficacy studies. From these studies, we hypothesize that iNexin treatment will stabilize intercellular junctions comprising the BRB to ameliorate DR pathophysiology, preserving retinal health and function. To test this hypothesis, we propose to demonstrate proof-of-concept efficacy of iNexin to mitigate diabetic retinopathy (Aim 1), and to confirm aCT1 biodistribution in the diabetic eye following eye drop administration (Aim 2). Using a translationally relevant streptozotocin-induced type 1 diabetic rat model, we propose to evaluate the impact of iNexin on DR using two distinct treatment paradigms. The first initiates iNexin administration concurrent with the onset of hyperglycemia; the second initiates treatment at the clinical manifestation of retinal vascular abnormalities. We will also confirm aCT1 biodistribution in the diabetic eye following topical ocular administration and aCT1’s localization to retinal epithelial and endothelial cells. Successful completion of these activities will provide proof-of-concept efficacy for aCT1’s mechanism of action translating to therapeutic effectiveness in the treatment of DR, while also supporting project advancement into efficacy and safety studies in large (non-rodent) animal models of DR. Translation into the clinic will mean significantly improved outcomes for the rt8M diabetic adults in the US alone.