Personalized CFTR Modulator Therapy for G85E and N1303K Homozygous Patients with Cystic Fibrosis

Abstract

CFTR modulator therapy with elexacaftor/tezacaftor/ivacaftor (ETI) has been approved for people with CF and at least one F508del allele in Europe. In the US, the ETI label has been expanded to 177 rare CFTR mutations responsive in Fischer rat thyroid cells, including G85E, but not N1303K. However, knowledge on the effect of ETI on G85E or N1303K CFTR function remains limited. In vitro effects of ETI were measured in primary human nasal epithelial cultures (pHNECs) of a G85E homozygous patient and an N1303K homozygous patient. Effects of ETI therapy in vivo in these patients were assessed using clinical outcomes, including multiple breath washout and lung MRI, and the CFTR biomarkers sweat chloride concentration (SCC), nasal potential difference (NPD) and intestinal current measurement (ICM), before and after initiation of ETI. ETI increased CFTR-mediated chloride transport in G85E/G85E and N1303K/N1303K pHNECs. In the G85E/G85E and the N1303K/N1303K patient, we observed an improvement in lung function, SCC, and CFTR function in the respiratory and rectal epithelium after initiation of ETI. The approach of combining preclinical in vitro testing with subsequent in vivo verification can facilitate access to CFTR modulator therapy and enhance precision medicine for patients carrying rare CFTR mutations.

Keywords: CFTR; CFTR modulator; G85E; N1303K; cystic fibrosis; human nasal epithelial cells; intestinal current measurement; nasal potential difference.

Figure 1

Treatment with elexacaftor/tezacaftor/ivacaftor (ETI) rescues cystic fibrosis transmembrane conductance regulator (CFTR) function in nasal epithelial cultures from the G85E/G85E and the N1303K/N1303K patient. (A–D) Representative tracings of short-circuit transepithelial current (I_SC) measurements in cultures from a healthy donor (A), a CF patient homozygous for F508del (B), the CF patient homozygous for G85E (C) and the CF patient homozygous for N1303K (D). CF cultures were incubated with elexacaftor/tezacaftor or dimethyl sulfoxide (DMSO) for 24 h. (E–J) Quantification of the basal I_SC (E), amiloride-sensitive I_SC (∆Amiloride) (F), amiloride-insensitive I_SC (G), and effects of cAMP activation (∆Forskolin/IBMX) (H), ivacaftor (∆Ivacaftor) (I) and CFTR inhibitor-172 (∆CFTRinh-172) (J) on I_SC in the G85E/G85E patient. Quantification of the basal I_SC (K), amiloride-sensitive I_SC (∆Amiloride) (L), amiloride-insensitive I_SC (M), and effects of cAMP activation (∆Forskolin/IBMX) (N), ivacaftor (∆Ivacaftor) (O) and CFTR inhibitor-172 (∆CFTRinh-172) (P) on I_SC in the N1303K/N1303K patient. n = 4–6 filters per individual per group, data are presented as mean ± SD. The black tracings and bars represent the vehicle control treated with DMSO and the blue tracings and bars represent the cultures treated with ETI. * p < 0.05, ** p < 0.01 ETI versus DMSO.

Figure 2

Elexacaftor/tezacaftor/ivacaftor (ETI) therapy improves mutant cystic fibrosis transmembrane conductance regulator (CFTR) function in both the G85E/G85E and the N1303K/N1303K patient. (A–F) Paired measurements of the CFTR biomarkers sweat chloride concentration (A), nasal potential difference (NPD) (B–D), and intestinal current measurement (ICM) (E–F) in a G85E/G85E (black) and an N1303K/N1303K (red) patient at baseline and 3 months (G85E/G85E) or 2 weeks (N1303K/N1303K) after initiation of ETI therapy. (A) Sweat chloride concentration. (B–D) NPD basal potential (B), NPD amiloride response (C), and NPD total chloride response (zero chloride plus isoproterenol (iso) solutions). (E,F) ICM cAMP response (E) and ICM total chloride response obtained by cAMP-dependent stimulation and cholinergic (calcium-dependent) co-activation (F). ICM studies were performed in the presence of amiloride and indomethacin. The dotted line represents median values for F508del/F508del patients treated with tezacaftor/ivacaftor (n = 41) and the dashed line represents median values for F508del/F508del patients treated with elexacaftor/tezacaftor/ivacaftor (n = 44) [11].

Figure 3

Elexacaftor/tezacaftor/ivacaftor (ETI) therapy improves clinical outcomes in the G85E/G85E patient. (A–D) Repeated measurements of FEV1% predicted (A), lung clearance index (LCI_2.5) (B), BMI (C) and total immunoglobulin E (IgE) from 200 days before and 600 days after initiation of ETI. (E) Representative MRI image at baseline and after initiation of ETI. Structural airway abnormalities (wall thickening and/or bronchiectasis) are indicated by arrows and mucus plugging by white arrowheads. Perfusion abnormalities are indicated by black arrowheads.

Figure 4

Elexacaftor/tezacaftor/ivacaftor (ETI) therapy improves clinical outcomes in the N1303K/N1303K patient. (A–D) Repeated measurements of FEV1% predicted (A), lung clearance index (LCI_2.5) (B), BMI (C), aspartate transaminase (AST, GOT) and alanine transaminase (ALT, GPT) (D) from 200 days before and 200 days after initiation of ETI.