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Investing.com -- Arcturus Therapeutics Holdings Inc. (NASDAQ:ARCT) stock fell 50% Wednesday after the company released interim Phase 2 data for its cystic fibrosis treatment that failed to show meaningful lung function improvement.
The San Diego-based mRNA medicines company reported that its investigational inhaled therapy ARCT-032 was generally safe and well-tolerated in the second cohort of its ongoing Phase 2 trial. Six adults with Class I cystic fibrosis received daily 10 mg doses over 28 days.
While initial analysis comparing FEV₁ (forced expiratory volume) values from Day 1 to Day 28 did not demonstrate meaningful improvement in lung function, the company highlighted that high-resolution CT scans showed encouraging reductions in mucus burden in four of the six participants.
A post hoc exploratory analysis suggested potential improvements in lung function in four participants, with an average absolute increase of 3.8% and a relative increase of 5.1% in percent predicted FEV₁ when comparing pre-treatment measurements with Day 42 values. However, the company acknowledged these changes fall within the range of natural variability of FEV1 measurements.
One serious adverse event occurred in a participant after the dosing period ended, though the Data Monitoring Committee found no convincing evidence it was related to ARCT-032 and approved the study to continue.
Arcturus is currently enrolling up to six subjects in an expanded third cohort to test a higher 15 mg dose. The company plans to initiate a 12-week safety and preliminary efficacy study in up to 20 cystic fibrosis participants in the first half of 2026.
The sharp stock decline suggests investors were disappointed with the preliminary efficacy data, particularly the lack of clear lung function improvement in the initial analysis, despite the company’s emphasis on encouraging mucus reduction trends.
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