Functional tests for assessment of residual CFTR channel activity and personalized selection of efficacious CFTR-modulators for cystic fibrosis patients with ‘mild’ and ‘severe’ genetic variants

Intestinal current measurement (ICM) and forskolin-induced swelling (FIS) assay in human intestinal organoids from rectal biopsies of cystic fibrosis (CF) patients are the new functional tests for assessment of CFTR channel activity that are widely used in the leading laboratories worldwide for scientific and clinical studies.

The aim of the study was to assess the use of the new functional tests in adult CF patients with identified N1303K and R334W CFTR gene variants.

Methods. Rectal suction biopsies were obtained from the two CF patients aged 36 and 27 years with N1303K/3821delT and R334W/F508del CFTR mutations, respectively. Results of the ICM and FIS assay in intestinal organoids were compared to the clinical data.

Results. ICM has demonstrated that R334W is a ‘mild’ genetic variant with high residual CFTR channel activity. At the same time, N1303K is a ‘severe’ genetic variant and leads to a severe loss of CFTR channel function. These findings correlate with the clinical data. CFTR modulators compensate for the reduced activity of the R334W CFTR variant, as shown by the FIS assay. But there was a limited response of the forskolin-stimulated organoids to VX-770 potentiator and VX-809 corrector in the cells with N1303K genetic variant.

Conclusion. ICM and FIS assay in human intestinal organoids are reliable methods for quantification of CFTR channel activity. They can also predict the efficacy of the targeted therapy in CF patients in vivo.

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