$0.00
$2.28
bear $0.00
base $1.19
bull $2.28
margin of safety $0.50
market price* $3.89
Sionna Therapeutics is a clinical-stage drug developer in Waltham, Massachusetts, working on cystic fibrosis (CF). Its science targets NBD1, a part of the CFTR protein that the company believes existing medicines, including Vertex's standard-of-care Trikafta, do not fully correct. It has no approved products and no revenue. In 2024 it licensed AbbVie's CF compounds, including galicaftor (SION-2222), for $5.0 million in cash plus $8.6 million of its own stock. AbbVie is owed up to $130.0 million in commercial and sales-based milestones plus royalties, but only if a product reaches the market. What changed in 2026: On August 10, 2026 the company reported that its lead program, SION-719 added on top of Trikafta, failed its Phase 2a trial (PreciSION CF). In 15 adults the placebo-adjusted change in sweat chloride was -1.0 mmol/L (p=0.7), and the company stopped developing SION-719 as an add-on. A post hoc analysis that excluded drug-level outliers showed up to -8.6 mmol/L, but a post hoc result is not evidence of a working drug. On the same day it reported that a Phase 1 trial of SION-451 combined with SION-2222 or SION-109 in 120 healthy volunteers met its safety and drug-level goals. Two participants stopped because of elevated liver tests and flu-like symptoms. On September 14, 2026 Sionna cut about 46% of its workforce, expecting about $6.4 million of restructuring charges. It now plans an open-label, 28-day Phase 2a trial of SION-451 + SION-2222 (AscenSION CF) in which adults with CF who have two copies of the F508del mutation switch from Trikafta to the combination. The trial is due to start in the first quarter of 2027. Management says its cash lasts into the second half of 2029. How we value it: Value comes only from cash flows we can tie to something that exists today. Sionna has no product, no partner paying it, and no contract that would produce revenue, so we credit the drug pipeline at zero in every case. This is not a judgement that the science will fail. A positive CF result would be worth a great deal, but nothing in the filings lets us count that value before it happens. What shareholders own today is $268.3 million of cash, cash equivalents and marketable securities (June 30, 2026), about $5.92 per share on about 45.3 million diluted shares. They own it net of the spending management has planned. The company has no borrowings. Its lease and other operating liabilities are paid out of the spending below, and the cost of closing or winding down operations is charged separately in each case. The cost of running the company: In 2025 the company's operating cash spending plus stock-based pay was about $78.2 million, or $1.96 per share. That figure is net of $13.3 million of interest earned on its cash. In 2024 the figure was $55.3 million, so spending grew about 41% in 2025. In the first half of 2026 the cost was $56.8 million. We treat stock-based pay as a real cost because it dilutes shareholders. Before interest income and including stock-based pay, spending had been running at roughly $124 million a year. We assume it drops to about $84 million a year of cash plus about $16 million of stock-based pay. The specific reasons for the drop are the September 2026 job cuts and the end of the PreciSION CF trial, and the figure matches management's stated runway into the second half of 2029. Bear case, $0.00 per share: The company follows its plan and spends through the second half of 2029. It runs the AscenSION CF trial and pivots again if that fails, as it did after the August 2026 failure, and no product reaches the market. By then about $20 million of cash would be left, and nearly all of it would go to wind-down costs (about $14 million) and dilution from stock-based pay. The shares are worth essentially nothing, though without debt they cannot be worth less than zero. Base case, $1.19 per share: Spending continues through the AscenSION CF readout, which we estimate around the end of 2027, and about six more months of evaluating options, ending around mid-2028. That reflects how the company handled its first failed trial: it changed course and kept spending rather than stopping. About $108 million of cash would remain, or about $94 million after roughly $14 million of wind-down or transition costs. Discounted at 6% and after stock-based pay, that is about $54 million, or $1.19 per share. Bull case, $2.28 per share: Spending stops at the AscenSION CF readout, which we estimate around the end of 2027. About $138 million would remain after closing costs of about $10 million, worth about $103 million today after discounting and stock-based pay, or $2.28 per share. Even this case gives no credit for a successful drug, because none is approved or contracted. What would make this wrong: Good AscenSION CF data followed by a partnership or sale would be worth far more than any of these cases. Spending faster than planned, or new trials beyond the stated runway, would push the result toward the bear case. The post hoc PreciSION CF analysis comes from a company press release, not an audited filing, and we gave it no weight.