US-based clinical-stage ophthalmology company Acucela, a subsidiary of Kubota Pharmaceutical, has begun enrolment for its Phase IIa study of emixustat hydrochloride (emixustat) to treat Stargardt disease.

Vitamin A is recycled in the eye through a process known as the visual cycle.

Emixustat controls the visual cycle by preventing a key enzyme of this pathway, retinal pigment epithelium protein 65 (RPE65).

A slowed visual cycle limits availability of vitamin A derivatives to formation of toxic vitamin A byproducts such as A2E and related compounds.

"This is an important therapeutic development for patients with Stargardt Disease."

The Phase IIa study will be conducted as a multicentre, randomised, masked trial intended to determine pharmacodynamics and the safety and tolerability of emixustat in subjects diagnosed with macular atrophy secondary to Stargardt disease.

The study will enrol about 30 patients across four to six clinical sites in the US who will be randomly assigned to one of three treatment arms in a 1:1:1 ratio.

The subjects will receive an oral administration of dosages of emixustat in 2.5mg, 5mg, and 10mg on a once-daily basis in the evening for one month.

University Hospital in Basel Switzerland and Stargardt Disease Natural History Study (PROGSTAR) study director Dr Hendrik Scholl said: “This is an important therapeutic development for patients with Stargardt Disease.

“Emixustat addresses a well-understood mechanism that leads to toxic accumulation of material underneath the retina linked to visual loss in Stargardt disease and therefore is a promising compound for this debilitating disease.”