Preliminary results from a phase 2 trial confirm that the investigational drug RG7916 targets the underlying genetic cause of type 2 and type 3 spinal muscular atrophy (SMA), PTC Therapeutics has announced.

RG7916 is an oral drug that modulates the splicing of the SMN2 gene to increase production of the gene’s survival motor neuron (SMN) protein. The protein is instrumental in maintaining specialized nerve cells called motor neurons, which control muscle movement. The drug is developed by Roche and produced by a joint effort from PTC Therapeutics, Roche, and the SMA Foundation.

Findings from the ongoing SUNFISH trial (NCT02908685) were revealed at the Cure SMA Meeting in Orlando, in a presentation titled “ Clinical Studies of RG7916 in Patients with Spinal Muscular Atrophy: Study Update. “

The trial is composed of two parts. The first part, which runs for 12 weeks, is designed to identify the drug’s optimal dose and evaluate its safety, as well as what the drug does to the body and what the body does to the drug. About 36 patients with type 2 and type 3 SMA are enrolled, and the results for those receiving the drug are compared to those taking a placebo. Part 2 will evaluate the RG7916 optimal dose’s safety and efficacy in about 150 patients with type 2 and type 3 SMA (pediatric patients and adults), compared to a placebo. This part of the study will be followed by an open-label extension study.

So far, results from Part 1 of the study have shown that patients treated with RG7916 have increased expression of the functional copy of the SMN2 gene by 400 percent compared to the study’s start. These results show that RG7916 is able to promote the splicing of the gene in patients. To date, there have been no reports of adverse side effects leading to treatment discontinuation.

“The increase in SMN2 full length transcript in SMA patients is promising and confirms that RG7916 targets the underlying cause of the disease,” Stuart W. Peltz, PhD and PTC Therapeutics’ CEO, said in a press release issued by the company. “The low levels of SMN protein in SMA patients affect multiple tissues throughout the body, including muscles, bones and nerves. We believe that the ease of administration of an oral therapy and its broad tissue distribution give RG7916 the potential to address the complete spectrum of functional deficits observed in SMA patients. We look forward to advancing RG7916 into pivotal clinical trials in the second half of the year.”