4D Molecular Therapeutics has reported interim safety and clinical activity results from the Phase I/II clinical trial, where its intravitreal 4D-125 demonstrated functional improvements in patients suffering from advanced X-linked retinitis pigmentosa (XLRP).

4D-125 is a directed and advanced R100-based product candidate of the company.

The ongoing Phase I/II dose-escalation and dose-expansion trial is analysing intravitreal 4D-125 to treat XLRP.

As of 1 September, eight subjects with clinically advanced XLRP due to RPGR gene mutation were recruited.

Findings showed that 4D-125 was well-tolerated in all eight subjects, including five participants receiving the highest dose.

No dose-limiting toxicities or serious adverse events were reported in the trial.

No chronic inflammation was noted, and transient, grade 1+ anterior chamber and/or vitreous cells were seen in two subjects at assessment timepoint defined by the single protocol.

Interim results also showed that two subjects experienced anatomical retina preservation in the treated eye versus the untreated control eye of the same patient.

Anatomical retina preservation was assessed by ellipsoid zone Area progression, which is a measure of intact photoreceptors.

Furthermore, two subjects had functional improvements as assessed by a rise in the mean retinal sensitivity and number of loci gaining ≥ 7dB sensitivity in the treated eye as against the control eye which is not treated.

The company plans to progress to enrolment in the dose-expansion cohort to include subjects with less advanced disease.

4D Molecular Therapeutics co-founder and CEO David Kirn said: “These are the first clinical data reported with a product invented from our Therapeutic Vector Evolution platform at 4DMT, and these interim data demonstrate clinical proof-of-concept for safety, tolerability and clinical activity.

“These data support our belief that 4D-125 is well tolerated and has the potential to both slow the progressive loss of photoreceptors in patients with XLRP after a single intravitreal injection and to improve visual function.”