Design of gene therapy trials in CF patients

Insights into the variability of nasal potential difference, a biomarker of CFTR activity

BACKGROUND

Nasal potential difference (NPD) is used to evaluate CFTR function in vivo. We aimed to evaluate the intrasubject and intersubject variability of NPD measurements.

METHODS

We reviewed NPD tracings of 116 patients with CF enrolled in the placebo arm of a multicenter study. Patients carried at least one nonsense mutation and underwent repeated NPD tests every 16 weeks. NPD parameters included basal potential difference (basal PD), inhibition of sodium absorption by amiloride (Δ Amiloride), chloride (Cl^-) transport in response to a Cl^--free solution (Δ Low Cl^-), isoproterenol (Δ Isoproterenol), the sum of Δ Low Cl^- and Δ Isoproterenol (Δ Low Cl^--Isoproterenol) and ATP (Δ ATP).

RESULTS

Basal PD and Δ Amiloride displayed the highest variabilities, mainly stemming from intercenter and intrasubject effect. Δ Low Cl^-, Δ Isoproterenol and Δ Low Cl^--Isoproterenol demonstrated a large intrasubject variability but a smaller intersubject variability. The intrasubject measurement variability for Δ Low Cl^--Isoproterenol, was within ± 7.2 mV with 95% probability. It was greater in patients reporting ongoing pulmonary exacerbations.

CONCLUSIONS

The large intercenter variability of basal PD and Δ Amiloride highlights the operator-dependent aspect of these measurements. A difference greater than 7.2 mV in Δ Low Cl^--Isoproterenol in a given patient on CFTR modulator can be attributed, with 95% probability, to a treatment effect rather than to the variability inherent in the measurement.

The search for a common structural moiety among selected pharmacological correctors of the mutant CFTR chloride channel

BACKGROUND

The F508del mutation impairs the trafficking of CFTR from endoplasmic reticulum to plasma membrane and is responsible of a severe form of cystic fibrosis. Trafficking can be improved by small organic molecules called 'correctors'.

MATERIALS & METHODS

By different synthetic ways, we prepared 4-chloroanisole and 2-(4-chloroanisol-2-yl)aminothiazole derivatives. Such compounds were ineffective as correctors but we could find a sign of activity in an intermediate. In the meantime, we found a common pharmacophoric moiety present in four known correctors.

RESULTS

Following this structural indication, we synthesized a small set of new molecules endowed with a significant, even if not great, F508del-CFTR rescue activity.

CONCLUSION

The cited structural feature seems interesting in the search of new correctors. To corroborate this observation, later on we found a new pyrazine derivative (Novartis) endowed with a potent activity as corrector and having the cited common design.