(430) Ivacaftor treatment decreases the prevalence of insoluble mucus flakes in young patients with CF

Background: Analysis of the biochemical and biophysical properties of bronchoalveolar lavage fluid (BALF) of pediatric patients with CF has previously identified several markers of early disease compared to age-matched disease control patients. These markers include mucin and DNA concentration, and the presence and abundance of insoluble, viscoelastic mucus flakes. The advent of highly effective modulator therapy (HEMT) in young patients raises the prospect of reducing marker concentration/abundance in BALF and reversing patterns of CF disease progression. Accordingly, we hypothesized that mucin and DNA concentration and flake abundance would decrease in patients post-HEMT treatment initiation.

Methods: A total of 10 patients that underwent annual surveillance bronchoscopy and BAL as part of the AREST-CF Synergy initiative were studied prior to (mean age 2.9 y/o) and after (mean age 4.3 y/o) initiation of ivacaftor. A total of 9 control BALF samples from untreated patients with CF (mean age 3.4 y/o) were also studied. Mucin concentration was determined via light scattering and refractometry. DNA concentration was determined via PicoGreen assay. BALF and flakes biophysics were determined via particle-tracking microrheology (PTMR) using 1µm diameter, fluorescent polystyrene spheres. All methods are described in Esther et al. 2019 [1].

Results: The relative proportion of viscoelastic signal associated with insoluble mucus flakes was lower in HEMT-treated subjects (49%) compared to untreated subjects (80%) (p< 0.01), however, this was also true for those same subjects before treatment (54%) (p< 0.05). This contributed to an apparent, though not statistically significant decrease in overall BALF complex viscosity (η*) between post-treatment (mean η* = 0.018 Pa·s) and control (mean η* = 0.052 Pa·s) subjects (p=0.11) as well as pre-treatment subjects (η* = 0.020 Pa·s, p=0.052). No biochemical differences achieved significance, possibly due to the small sample sizes of each cohort.

Conclusions: PTMR analysis detected a reduced viscoelastic signal in BALF from patients pre- and post-HEMT treatment compared to controls. This reduction in total signal contributed to an apparent reduction in the average viscosity of the BALF from pre- and post-treatment subjects relative to controls. Analysis of these samples is not yet complete, as 4 pre- and post-treatment subjects and 5 controls await processing. Though not yet finalized, these results demonstrate that HEMT therapy may reduce flake burden and overall viscoelasticity of airway mucus in young patients with CF.

Acknowledgements: We are grateful to the Cystic Fibrosis Foundation for their support of this work (HILL19G0 and HILL20Y2-OUT.

References: [1] Esther CR, Muhlebach MS, Ehre C, Hill DB, Wolfgang MC, Kesimer M, Ramsey KA, Markovetz MR, Garbarine IC, Forest MG, Seim I, Zorn B, Morrison CB, Delion MF, Thelin WR, Villalon D, Sabater JR, Turkovic L, Ranganathan S, Stick SM, Boucher RC. Mucus accumulation in the lungs precedes structural changes and infection in children with cystic fibrosis. Sci. Transl. Med. 2019; 11: eaav3488.