Sionna Therapeutics has continued raising capital, closing a $182m Series C financing round to help advance additional cystic fibrosis candidates into clinical trials.
The round, which was upsized and oversubscribed according to the US company, will see Sionna forge ahead with the clinical development of assets designed to stabilise the first nucleotide-binding domain (NBD1) in patients with cystic fibrosis.
The round, which follows a $111m Series B round in 2022, secures the company’s cash runway through 2026.
Sionna’s lead asset is SION-638 – an NBD1 stabiliser currently in Phase I trials. The first subject was dosed in January 2024, with the company stating that target exposure was achieved at all doses.
Sionna said it will now advance two NBD1 stabilisers from its second series – SION-451 and SION-719. The two candidates are slated to join SION-638 in clinical trials in 2024, according to a 6 March press release.
Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene lead to cystic fibrosis. The gene codes for a transmembrane channel that produces mucus, which is usually thin and slippery in healthy individuals but thick and sticky in cystic fibrosis patients. One of the most common CFTR mutations—F508del—leads to NBD1 unfolding, which negatively affects CFTR function. Sionna says that its NBD1 stabilisers are designed to restore the function of the CFTR gene.
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Alongside its trio of NBD1 stabilisers, Sionna is investigating complementary mechanisms in the disease. The company’s CFTR intracellular loop 4 (ICL4) inhibitor SION-109 entered a Phase I trial in January 2024.
The cystic fibrosis market is largely dominated by the Boston, Massachusetts-based Vertex Pharmaceuticals. Sionna stands to benefit from that expertise, with Vertex’s former vice president of clinical development for cystic fibrosis Charlotte McKee joining the company as chief medical officer, in 2022.
Vertex’s Trifakta or Kaftrio (elexacaftor / tezacaftor / ivacaftor) drove much of the company’s revenue growth for 2023. The combo therapy, which is indicated for cystic fibrosis patients who have at least one F508del mutation, was originally US Food and Drug Administration-approved in 2019 and has since been granted label expansions. Trifakta saw sales of $8.9bn in 2023, up 16% from 2022.
Vertex also has Symdeko (tezacaftor / ivacaftor), Orkambi (lumacaftor/ivacaftor), and Kalydeco (ivacaftor) as other FDA-approved therapies in the cystic fibrosis space.
The company is also planning fast-track regulatory submissions for another triple therapy, involving vanzacaftor, by mid-2024 following positive Phase III results.
Sionna’s CEO Mike Cloonan said: “This capital raise provides financial flexibility positioning us to execute our clinical development plan with funding through 2026 and multiple value-creating clinical readouts.”
