Solid Biosciences LLC completed the initial close of a $50 million series C financing that it said will help move its experimental gene therapy for Duchenne muscular dystrophy (DMD) into the clinic in the second half of this year. RA Capital Management and Bain Capital Life Sciences led the oversubscribed round, which follows a $42.5 million series B that first closed in 2015.

The adeno-associated virus (AAV)-based candidate, called SGT-001, gained U.S. and European orphan status in October last year.

RTW Investments, Foresite Capital, Cormorant Asset Management LLC, Leerink Partners affiliates and an unnamed health care fund joined the round alongside existing investors Perceptive Advisors, Janus Capital Management and Biogen Inc.

Solid's chairman and co-founder, Andrey Zarur, dismissed the notion that the company is angling for a near-term IPO – something one might reasonably assume from the roster of investors in the series C. Rather, he said, the backing the company has now "gives you the optionality to weather any kind of market conditions, the optionality to go public when you can or should, but doesn't put you in a position where you have to go public."

By using an AAV-based approach, Solid's SGT-001 takes a different tack in addressing DMD than Sarepta Therapeutics Inc.'s exon-skipping drug, eteplirsen, branded Exondys 51. Zarur said that exon-skipping risks leading to the creation of an unknown version of dystrophin.

Solid's approach, he said, is to use an AAV vector to introduce an artificial gene it calls microdystrophin into the muscle cells of DMD patients. So long as an individual doesn't have antibodies against its AAV vector, "every one of the children in our trial would get the same exact protein that we know is expressed in high amounts and that we know is highly functional," he said.

Preclinical data on Solid's approach presented at an American Society of Gene & Cell Therapy event in May 2016 demonstrated that AAV microdystrophin gene therapy "significantly improved skeletal and cardiac muscle function, reduced muscle loss and improved muscle force in preclinical models," according to the company. It also showed that a single administration of the AAV microdystrophin resulted in long-term dystrophin expression throughout the entire body, it said.

In addition to accelerating its work on SGT-001, the Cambridge, Mass.-based company also wanted to take advantage of the opportunity to accelerate investments in a manufacturing platform for the candidate and to advance other programs in its pipeline. The other programs include early stage candidates intended to fight fibrosis and reduce chronic inflammation.

"Even if we are able to treat very young children, there's already going to be a level of deterioration that these kids will have," Zarur said. "Even if our gene therapy is as successful as anyone can dream it will be, we will need other adjuvant therapies to deal with some of the secondary effects of the disease."

Solid joins a growing roster of companies working to meet the needs of DMD patients. In the gene therapy space, it's joined by Boston-based Exonics Therapeutics Inc., which is using CRISPR/Cas9 gene editing technology in hopes of correcting genetic mutations that cause DMD and other neuromuscular diseases. Seattle-based DMD Therapeutics Inc. is taking another approach, advancing a small-molecule candidate, DMD-813, to reduce muscle damage and inflammation. PTC Therapeutics Inc.'s Translarna (ataluren) remains unapproved in the U.S., despite its acceptance in Europe. And Summit Therapeutics plc is completing a phase II trial of its lead drug candidate, SMT C1100 (ezutromid). That trial is expected to read out by the third quarter of this year. (See BioWorld Today, March 1, 2017.)