Experimental gene therapy ST-920 on FDA’s fast track

Sangamo Therapeutics poised for a Phase 3 clinical trial with Fabry patients

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Fabry disease gene therapy | Fabry Disease News | illustration of DNA strand

ST-920 (isaralgagene civaparvovec), an experimental gene therapy for Fabry disease that’s currently headed toward Phase 3 clinical testing, has been granted fast track designation by the U.S. Food and Drug Administration (FDA).

The FDA gives fast track designation to experimental treatments that have the potential to fill an unmet need in the treatment of serious health conditions. The designation gives the therapy’s developer, Sangamo Therapeutics, access to more frequent communications with the FDA throughout the drug development process.

“We are thrilled with the FDA’s decision to grant fast track designation for ST-920,” Nathalie Dubois-Stringfellow, PhD, senior vice president, chief development officer at Sangamo, said in a press release.

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Dubois-Stringfellow added that this designation “underscores the potential for ST-920 to address a serious unmet need and serve as a meaningful therapeutic option for patients with Fabry disease.”

Fabry disease is caused by mutations in the gene that provides instructions for making the enzyme alpha-GalA. Without a working version of this enzyme, fatty molecules such as globotriaosylceramide (Gb3) build up to toxic levels in the body’s cells, ultimately causing tissue damage and disease symptoms.

ST-920 is designed to deliver a healthy copy of the gene encoding alpha-GalA to cells in the liver, allowing liver cells to produce a functional version of this enzyme that can be pumped to the rest of the body to help clear toxic Gb3 buildup.

The gene therapy previously was granted orphan drug designation by the FDA, which is given to incentivize the development of treatments for rare diseases. According to Sangamo, ST-920, which is given in a single administration, may eliminate the need for enzyme replacement therapy infusions and does not require pre-treatment with steroids or other immunomodulating agents to suppress immune responses.

Sangamo is currently sponsoring a Phase 1/2 clinical trial called STAAR (NCT04046224) that is testing multiple doses of ST-920 in adults with Fabry disease. According to the company, 20 patients have been dosed in the study so far. The trial is still recruiting participants at sites in the U.S., Canada, Australia, Italy, Germany, Taiwan, and the U.K.

Positive interim data

Interim data from the first 13 patients showed that, at six months after ST-920 treatment, average Gb3 levels decreased by 78%, while markers of kidney injury decreased by 77%. Patients also reported clinically meaningful and statistically significant improvements in measures of life quality, according to Sangamo.

The proposed Phase 3 trial dose of 50 trillion vector genomes/kg of body weight produced rapid, sustained increases in alpha-Gal A activity in the blood across all participants. No serious treatment-related adverse events had been seen by the cut-off date of Oct 20, 2022.

Buoyed by the positive data from STAAR, Sangamo now is preparing to launch a Phase 3 trial to further test the potential gene therapy for Fabry disease.

“We … look forward to our expected meeting with the FDA on Phase 3 trial design in the summer,” Dubois-Stringfellow said.