Open Angle Glaucoma

Razuprotafib (AKB-9778) in Primary Open Angle Glaucoma

Unmet medical need:

POAG is a leading cause of blindness affecting approximately 64.3 million people worldwide in 2013 with an expected increase to 76.0 million in 2020 and 118.0 million by 2040. POAG is characterized by optic nerve and neuroretina anomalies and progressive visual field defects. Elevated intraocular pressure, or IOP, is the primary modifiable risk factor and reducing IOP is the only clinical approach shown to slow or prevent vision loss. Despite the availability of effective IOP lowering drugs, many patients require multiple agents to control IOP that together often fail to achieve target IOP. The conventional outflow pathway, consisting of the trabecular meshwork and a specialized vessel called Schlemm’s canal, controls IOP and has been identified as the site of increased resistance to aqueous humor outflow in POAG. Importantly, most current POAG therapies do not target conventional outflow, and reduce IOP by either decreasing the formation of aqueous humor or facilitating non-conventional outflow pathways. The failure of most current therapies to modify conventional outflow has been hypothesized to contribute to continued deterioration of conventional outflow and progressive increases in IOP over time. We believe that developing agents that target conventional outflow pathology directly will likely have improved therapeutic potential alone or in combination with approved glaucoma agents and may prevent progression of POAG that often occurs despite current therapy. 

Emerging role of the Tie2 Pathway in the maintenance of conventional outflow:

Recently, two independent groups have shown that Tie2 is expressed and activated in Schlemm’s canal endothelial cells during development and in the mature vessel. Disruption of the Tie2 pathway in mice by conditional knockout early in postnatal development results in failure of the formation of Schlemm’s canal, associated with increased IOP and with retinal and optic nerve pathology resembling human congenital glaucoma. Tie2 pathway disruption later in postnatal development results in degeneration of Schlemm’s canal with development of increased IOP and retinal and optic pathology reminiscent of POAG. Tie2 is most highly expressed in mature Schlemm’s canal inner wall endothelium and disruption of the Tie2 pathway results in increased cell death, or apoptosis, and reduced formation of giant vacuoles consistent with compromised conventional outflow. Supporting these preclinical findings, Tie2 loss of function variants were identified in 10 of 189 unrelated primary congenital glaucoma families, and SNPs in the Ang-1 promoter region were significantly associated with the risk of POAG. We believe that these preclinical findings along with human genetic evidence provides a sound scientific premise that activation of the Tie2 pathway in Schlemm’s canal could provide a novel conventional outflow-targeted POAG therapy.

Role of VE-PTP in Signaling Pathways and Relevance to Glaucoma

Aerpio has developed first-in-class, potent and selective small molecule inhibitors of the catalytic domain of VE-PTP. In vascular endothelial cells, AKB-9778, Aerpio’s lead VE-PTP inhibitor, activates Tie2 and triggers signaling pathways downstream of Tie2 that have been implicated in modulation of conventional outflow facility. These include endothelial nitric oxide synthase, or eNOS, activation and Rho pathway inhibition via Rac1.

Figure 1. VE-PTP inhibition as a novel conventional outflow targeted approach for glaucoma treatment.

Activation of Tie2, with AKB-9778, affects pathways commonly associated with reduction of intraocular pressure. Rhopressa and Vyzulta are recently approved glaucoma drugs which block the Rho pathway and stimulate the eNOS pathway, respectively. Inhibition of VE-PTP should provide both benefits, blocking Rho and stimulating eNOS.

We have completed a Phase 1b study to evaluate the potential of topical AKB-9778 to lower IOP. The top-line results were reported in January 2020 and presented at Glaucoma 360 conference in February 2020.