** Shares of Arcturus Therapeutics ARCT.O fall 61.8% to $8.84 premarket

** Co says an initial analysis comparing lung function from day 1 and day 28 after treatment with its experimental cystic fibrosis therapy did not show improvement in a mid-stage study

** However, measurements at day 42 suggests improvements in lung function

** Encouraged by early signals of reduction in mucus plugging - ARCT

** Experimental inhaled mRNA therapy ARCT-032 generally safe and well tolerated - co

** Intend to initiate a 12-week safety and preliminary efficacy study in up to 20 CF participants in H1 2026

** CF is an inherited genetic disorder that causes thick, sticky mucus to build up in the body's organs, primarily affecting the lungs and pancreas

** Up to last close, stock had risen 36.5% YTD

(Reporting by Puyaan Singh)

((Puyaan.Singh@thomsonreuters.com;))