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Changes of CFTR functional measurements and clinical improvements in cystic fibrosis patients with non p.Gly551Asp gating mutations treated with ivacaftor
1 Myriam Mesbahi and Michal Shteinberg are equally first authors.
Michal Shteinberg
Footnotes
1 Myriam Mesbahi and Michal Shteinberg are equally first authors.
Affiliations
Cystic Fibrosis Center, Carmel Medical Center, Haifa, IsraelRuth and Bruce Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa, Israel
2 Laurence Bassinet and Galit Livinat are equally last authors.
Galit Livnat
Footnotes
2 Laurence Bassinet and Galit Livinat are equally last authors.
Affiliations
Cystic Fibrosis Center, Carmel Medical Center, Haifa, IsraelRuth and Bruce Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa, Israel
Ivacaftor, a CFTR potentiator, has been found to improve CFTR function and clinical outcomes in patients with cystic fibrosis (CF) gating mutations. We investigated the effects of ivacaftor on CFTR functional measurement in CF patients carrying gating mutations other than p.Gly551Asp.
Two siblings aged 13 and 12 carrying the p.Ser549Asn mutation, two sisters (45 and 43 years old) compound heterozygotes for p.Asp1152His and p.Gly1244Glu, a 37 year old man homozygous for the p.Gly1244Glu mutation, and a 7 year old girl with p.Arg352Gln and p.Gly1244Glu mutations commenced treatment with ivacaftor. NPD was performed in all the patients and approached normal for four patients who had also clinical improvement (p.Ser549Asn compound heterozygotes, and p.Asp1152His/p.Gly1244Glu siblings). Beta-adrenergic sweat chloride secretion performed in thep.Asp1152His/p.Gly1244Glu patients improved significantly. The p.Gly1244Glu mutation homozygous patient, who had undergone an ileal resection with ileostomy and enterocutaneous fistula, did not respond clinically to ivacaftor and did not modify his sweat test.
These results highlight the importance of different CFTR activity measurements to explore CFTR modulator efficacy.
The past few years have been marked by the development of novel therapies in Cystic Fibrosis (CF), aimed to modulate Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein function [
]. Ivacaftor, a powerful CFTR potentiator has been approved for clinical use for the p.Gly551Asp mutation and more recently for 8 other mutations associated with defective channel pore gating, including the p.SerS549Asn and the p.Gly1244Glu mutation [
]. Very interestingly, ivacaftor activity does not seem to be specific as this compound has also been shown to increase in vitro CFTR activity for mutations displaying residual activity such as p. Asp1152His [
We report rapid clinical and epithelial functional improvement in patients carrying gating mutations other than p.Gly551Asp followed in France and Israel.
2. Methods
2.1 Sweat gland functional evaluation
Sweat chloride (Cl−) concentrations were determined either by Gibson and Cooke method or coulometry. CFTR function in the sweat gland acinus was assessed based on sweat secretion rate after β-adrenergic activation [
]. Results were compared to diagnosis cutoffs calculated from data obtained in typical CF patients and healthy subjects from Hadassah, Jerusalem and Paris Necker Centers.
3. Results
3.1 Patient characteristics and clinical evolution
Patients' characteristics before initiation of ivacaftor and at follow up are shown inTable 1.
Table 1Main clinical clinical characteristics, sweat measurements and Nasal Potential Difference results of patients at beginning of treatment and at follow-up.
Patient 1
Patient 2
Patient 3
Patient 4
Patient 5
Patient 6
Age/Sex (M, F)
13/M
12/M
37/M
45/F
43/F
7/F
CFTR mutations
p.Trp1282X/p.Ser549Asn
p.Trp1282X/p.Ser549Asn
p.Gly1244Glu/p.Gly1244Glu
p.Asp1152His/p.Gly1244Glu
p.Asp1152His/p.Gly1244Glu
p.Arg352Gln/p.Gly1244Glu
Basal
Treated (3 months)
Basal
Treated (3 months)
Basal
Treated (6 months)
Basal
Treated (3 weeks)
Basal
Treated (3 months)
Basal
Treated (6 months)
Weight (kg)
58.5
61.5
31
32.3
51
56
70
72
75
75
38
40
FEV1 (% of predicted)
89
93
98
104
35
35
105
107
94
98
85%
98%
CFTR function in sweat gland epithelium (sweat test and evaporimetry)
Patient 1 and 2 weresiblings, 13 and 12 years old, compound heterozygotes for p.Trp1282X and p.Ser549Asn CFTR mutations. Both had never grownPseudomonas aeruginosain their sputa. They continued to do well after 3 months of ivacaftor, gaining weight and improving FEV1by4 to 6%.
Patient 3 was a 37 year old man, homozygous for the p.Gly1244Glu mutation. He was pancreatic insufficient with impaired glucose tolerance. He had several episodes of complete Distal Intestinal Occlusion Syndrome, one of which was surgically treated with resection of 20 cm of terminal ileum with a loop ileostomy and a secondary enterocutaneous fistula created. His lung function was severely reduced, with an FEV1of 35–40% predicted. He was chronically infected withPseudomonas aeruginosaand methicillin-resistantStaphylococcus aureus. After initial improvement, he experienced another severe pulmonary exacerbation with a loss of weight and a deterioration of lung function with return to basal status after 6 months of treatment.
Patient 4 and 5 were 2 sisters, pancreatic sufficient, with a history of recurring infectious bronchitis from childhood and fertility problems. They were compound heterozygotes for p.Asp1152His/p.Gly1244Glu. The eldest (patient 4), suffered from chronic pancreatitis. The youngest sister (patient 5), had chronic sputum production andPseudomonas aeruginosasputum colonization. She had very mild respiratory symptoms, normal lung function, but middle lobe bronchiectasis. After treatment with ivacaftor (3 weeks and 3 months respectively), both patients reported total resolution of CF related symptoms as early as after2 weeks of treatment. FEV1improved moderately by 2 to 4% respectively. CT scan mucus plugging and bronchial thickening scores improved in both. Patient 5 eradicatedP.aeruginosa(follow up of 10 months).
Patient 6, p.Arg352Gln/p.Gly1244Glu compound heterozygote, was 7 years old at initiation of ivacaftor treatment. She was pancreatic sufficient and reported recurrent mild cough symptoms withS.aureusandStenotrophomonas maltophiliasputum colonization and had normal lung function. All her respiratory symptoms resolved after 6 months of ivacaftor and FEV1improved by 13%.
3.2 CFTR function
Patients sweat chloride and NPD were assessed at baseline, and 3 weeks to 6 months after ivacaftor commencement. All patients apart from patient 3 experienced significant decrease in sweat Cl−measurements which reached normal values in patients 4, 5 and 6. For NPD, results of the nostril with the largest Cl−free Isoproterenol response are shown inTable 1.
NPD was significantly modified in all patients, as assessed by a significant improvement in total Cl−secretion (e.g.; the sum of the response to low Cl−solution and to isoproterenol decreased to more negative values in patient 1, 4 and 6) or decreased Na+transport (e.g.; the response to amiloride decreased in patient 3, 5 and 6) (Fig. 1 Supplementary). For this latter criteria, however, because of the absence of normalization of the values, we cannot exclude a simple variation over time. This impact on different ion transport was reflected by different classifications of the 2 diagnosis scores (as for patient 2 and 6).
Patients 4 and 5 carried the same genotype (p.Asp1152His/p.Gly1244Glu) but interestingly did not show the same NPD characteristics. For Patient 4, pre ivacaftor NPD showed residual CFTR function with subnormal sodium (Na+) transport(Δ Amiloride at 8 mV for a diagnosis cut-off <18.5 mV for healthy subjects) and a partial defect in Cl−secretion (Δ Cl−free Isoproterenol at −6 mV for a diagnosis cut-off <−7 mV for healthy subjects). After ivacaftor treatment, respiratory epithelium Cl−secretion reached the normal level to −12.5 mV. For Patient 5, initial NPD displayed an excessive Na+transport, as previously reported in CF, and a normal Cl−secretion (Δ Cl−free Isoproterenol at −21 mV). Post treatment NPD showed a normalization of Na+transport (Δ Amiloride decreased from 35 mV to 6 mV) while Cl−secretion remained within normal values (Δ Cl−free Isoproterenol at −14 mV).
As a whole, there was a significant correlation between the change in NPD score and the change in FEV1(Spearman correlation test; p=0.03) (Fig. 1). This was also true for sweat test improvement and FEV1change (Spearman correlation test; p=0.04). The same trend was also observed between sweat test and NPD changes, although this did not reach the significant level (Fig. Supplementary 2).
Fig. 1Regression graph between absolute change in FEV1 (% predicted) and change in NPD score (e(Δ Cl−free Isoproterenol/Δ Amiloride)).
β-adrenergic CFTR related sweat secretion was assessed in the French center for patient 4 and 5. For patient 4, althoughsweat test (ST) was intermediate at 34 mmol/l, β-adrenergic CFTR related sweat secretion was absent, demonstrating a defective function of CFTR in the sweat gland acinus. This was partially restored after 3 weeks of treatment. (ratio beta-adrenergic to carbachol increased from 0 to 0.4). For Patient 5, sweat Cl−concentration, initially in the CF range, normalized (93 to 16 mmol/l Cl−), as did β-adrenergic sweat rate (ratio beta-adrenergic to carbachol from 0 to 0.7) (Fig. 3 Supplementary).
4. Discussion
Pharmacologic modulation of mutant CFTR protein function currently holds great promise for a major advance in the treatment of CF. These case reports highlight that functional CFTR measurements were consistent with clinical response in patients carrying the p.ser549Asp and p.Gly1244Glu mutation similar to published results.
This last point is illustrated by case of patient 3, homozygous for the p.Gly1244Glu mutation, previously shown to respond to ivacaftor both in vitro [
]. The patient stated good compliance to treatment but there was no response to ivacaftor. An explanation for this, might be impaired absorption of ivacaftor in the terminal ileum, possibly due to ileal resection, enterocutaneous fistula and ileostomy (9). The correlation of NPD and pulmonary function was an interesting observation and may be followed up in a larger study.
The residual CFTR activity shown by a residual total Cl−secretion in NPD caused by thep.Asp1152His mutationexplains the different clinical presentations in patient 4 and 5c. This conductance isassociated with ENaC dependant hyperactivity in patient 5. In both siblings, Na+and Cl−transport improved to normal values, as early as 3 weeks after commencementtreatment.
The CFTR dependant sweat rate revealed absent CFTR dependant sweat acinus activity, even if the sweat Cl−was intermediate as in patient 4.Interestingly, the value significantly changed after ivacaftor although it did not reach normal level. To the best of our knowledge, this is the first report that β-adrenergic sweat secretion can be modified by CFTR functional modulation.
5. Conclusion
These case reports show that changes in CFTR functional measurements correlate with the clinical response in patients with non p.Gly551Asp. However, the differences between the various surrogate measures illustrate that tissues may respond differently to the CFTR modulators, according to bioavailability of the drug or different physiopathology.
Acknowledgments
Thisresearch was funded by Association proteine ABCF2-2012-6.
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