Impact of Discontinuing Dornase Alfa in People With CF on Highly Effective CFTR Modulator Therapy-A SIMPLIFY Sub-Study

Despite the increasingly common use of cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies in treating cystic fibrosis (CF), it is still largely unknown whether or not other chronic therapies can be safely stopped. This SIMPLIFY sub-study is being done to test whether or not it is safe to stop taking dornase alfa (Dnase) in those people that are also taking elexacaftor/tezacaftor/ivacaftor (ETI).

ETI is a combination CFTR modulator therapy that was approved by the Food and Drug Administration for people with CF who have at least one F508del mutation. The three drugs that make up ETI work together to allow many more chloride ions to move into and out of the cells, improving the balance of salt and water in the lungs. These changes result in better clearance of mucus from the lungs and improvements in lung function.

Dornase alfa (Dnase) also improves clearance of mucus from the lungs to support lung function and has been available to people with CF for many years. Dnase is considered to be relatively burdensome and it is not known whether Dnase can improve or maintain lung function above what is already gained through ETI use.

The goal of this SIMPLIFY sub-study is to get information about whether or not it is safe to stop Dnase by testing if there is a change in lung function in participants with cystic fibrosis (CF) who are assigned to stop taking Dnase as compared to those who are assigned to keep taking Dnase while continuing to take ETI.

This is a sub study of master protocol SIMPLIFY-IP-19, NCT04378153.

The sub study investigating the impact of discontinuing and continuing hypertonic saline is registered under NCT06350461.

This SIMPLIFY sub-study (Dornase Alfa (Dnase) Trial) is designed to evaluate the effects of discontinuing Dnase in people with cystic fibrosis (CF) age 12 and older currently taking the highly effective modulator elexacaftor/tezacaftor/ivacaftor (ETI). This is an open label two-arm randomized non-inferiority trial consisting of a 2-week screening period, randomization to continue or discontinue dornase alfa, followed by a 6-week study period. Participants at trial entry will be randomized 1:1 to either continue or discontinue their Dnase therapy.

Clinical outcomes (forced expiratory volume in 1 second \[FEV1\], antibiotic use, pulmonary exacerbations, and patient reported outcomes), safety (adverse events) and patient reported outcomes to evaluate respiratory symptoms and the participant's perception of how stopping Dnase would impact their daily life will be evaluated in all subjects. Additionally, a subset of participants at selected study sites will participate in Multiple Breath Washout (MBW) to evaluate changes in lung clearance index (LCI).

Eligibility Criteria:
Inclusion Criteria:

* Diagnosis of CF.
* Age ≥ 12 years at the Screening Visit.
* Forced expiratory volume in 1 second (FEV1) ≥ 70 % predicted at the Screening Visit if \< 18 years old, and ≥ 60 % predicted at Screening Visit if ≥ 18 years old.
* Clinically stable with no significant changes in health status within the 7 days prior to and including the Screening Visit.
* Current treatment with elexacaftor/tezacaftor/ivacaftor (ETI) for at least the 90 days prior to and including the Screening Visit and willing to continue daily use for the duration of the study.
* Currently taking dornase alfa for at least the 90 days prior to and including the Screening Visit and willing to continue daily use for the 2-week screening period.

Exclusion Criteria:

* Active smoking or vaping.
* Use of an investigational drug within 28 days prior to and including the Screening Visit.
* Changes to chronic therapy (e.g., ibuprofen, azithromycin, inhaled tobramycin, aztreonam lysine) within 28 days prior to and including the Screening Visit. This includes new airway clearance routines.
* Acute use of antibiotics (oral, inhaled or IV) or acute use of systemic corticosteroids for respiratory tract symptoms within 7 days prior to and including the Screening Visit.
* Chronic use of systemic corticosteroids at a dose equivalent to ≥ 10mg per day of prednisone within 28 days prior to and including the Screening Visit.
* Antibiotic treatment for nontuberculous mycobacteria (NTM) within 28 days prior to and including the Screening Visit.