Sionna secures $182M series C to more than double its clinical-stage cystic fibrosis contenders

Sionna Therapeutics has closed a $182 million series C, enough to last through 2026 and more than double the number of cystic fibrosis treatments in clinical development.  

The midstage raise announced Wednesday is just the latest evidence that biotechs are biding their time before testing Wall Street. Sionna CEO Mike Cloonan told Fierce Biotech this will be the company’s last private financing but declined to put a timescale on when the company could go public.

“We want as much clinical data as possible and we want that to put ourselves in the best position as to when we would IPO,” Cloonan said.

Sionna is the latest example of the benefits of biotechs maintaining a tight therapeutic focus, be it on a single asset or disease area. The sole priority of the company—for now, at least—is developing cystic fibrosis treatments, with a lead candidate set to report interim phase 1 data in the next few months. 

Sionna’s candidate is one of three NBD1 inhibitors in development with the other two set to enter the clinic before the end of the year. The plan, according to Cloonan, is for Sionna to select the best performer to take into a phase 2 trial once data on all three have been accrued.  

While this NBD1 work may be Sionna’s main course, the side dishes are just as important. The first, SION‑109, is an ICL4 inhibitor that began a phase 1 trial earlier this year. The second potential add-on med, SION-676, is targeting TMD1 and is slated for the clinic in 2025. Similar to the NBD1 programs, those two will be assessed based on phase 1 data with the more compelling candidate taken into a proof-of-concept trial as a combo with the lead NBD1 asset. The new financing allows Sionna to afford all of these clinical assessments before a phase 2 trial. 

“Right now, it's looking like [SION-109] could be the best combination asset just based on what we know today,” Cloonan said. 

Sionna unveiled in April 2022 after closing a $111 million series B, hiring Charlotte McKee, M.D., Vertex’s former vice president of clinical development for cystic fibrosis work, as its chief medical officer. It’s a market largely dominated by Vertex, but there’s room for new entrants, with one recent estimate projecting that the global cystic fibrosis market could top $37 billion by 2030. The clear market potential plus Sionna’s multiple candidates has made it a prized option among investors, Cloonan believes. 

“If we were a single shot on goal in this big market, that's more risk for an investor,” he said. “But because we have this portfolio of options … it really was attractive to the investors in terms of how they think about the risk of return.”