Rescue of multiple class II CFTR mutations by elexacaftor+tezacaftor+ivacaftor mediated in part by the dual activities of elexacaftor as both corrector and potentiator

Abstract

Positive results in preclinical studies of the triple combination of elexacaftor, tezacaftor and ivacaftor, performed in airway epithelial cell cultures obtained from patients harboring F508del-CFTR, translated to impressive clinical outcomes for subjects carrying this mutation in clinical trials and approval of TRIKAFTATM. Encouraged by this correlation, we were prompted to evaluate the effect of the elexacaftor, tezacaftor and ivacaftor triple combination on primary nasal epithelial cultures obtained from individuals with rare Class II cystic fibrosis causing mutations; G85E, M1101K and N1303K for which TRIKAFTATM is not approved. Cultures from individuals homozygous for M1101K responded better than cultures harboring G85E and N1303K after treatment with the triple combination with respect to improvement in regulated channel function and protein processing. A similar genotype specific effect of the triple combination was observed when the different mutations were expressed in HEK-293 cells, supporting the hypothesis that these modulators may act directly on the mutant proteins. Detailed studies in nasal cultures and HEK-293 cells showed that the corrector: elexacaftor, exhibited dual activity as both corrector and potentiator and suggested that the potentiator activity contributes to its pharmacological activity. These preclinical studies using nasal epithelial cultures identified mutation genotypes for which elexacaftor, tezacaftor and ivacaftor may produce clinical responses that are comparable to, or inferior to those observed for F508del-CFTR.

Personalized Medicine Based on Nasal Epithelial Cells: Comparative Studies with Rectal Biopsies and Intestinal Organoids

“…This finding highlights that both cellular models can be used to predict the clinical benefit of a single drug or combination of drugs for a certain individual, despite the fact that CFTR function in pHNEs was measured by an Ussing chamber, whereas in intestinal organoids, it was indirectly measured by organoid swelling. Several groups already use either of these two models to predict responses to CFTR modulator drugs [ 16 , 17 , 18 , 20 , 39 , 40 , 46 , 47 , 48 , 49 ], but here, we show that the establishment of a responder or non-responder was the same in both models ( Figure 3 ), using both types of samples from the same individual. The only exception was the individual with the D614G/F508del genotype who was considered a non-responder through pHNE analysis but appeared as a responder from intestinal organoid data.…”

Partial Rescue of F508del-CFTR Stability and Trafficking Defects by Double Corrector Treatment

“…Another possible reason is that VX-445 also acts as a potentiator, as suggested by others [ 20 ]. To address this possibility, we tested VX-445 (5 µM) acutely on CFBE41o- cells expressing F508del-CFTR that were previously kept for 24 h at 32 °C as a rescue maneuver.…”

“…Indeed, in our experiments on bronchial epithelial cells, the fraction of F508del-CFTR activity that can be activated by cAMP, without the potentiator, was increased by the pretreatment with the combination of VX-445 plus VX-809. It has been proposed that VX-445 also has a potentiator activity [ 20 ]. However, when we tested VX-445 in a potentiator assay (acute application of VX-445 after rescue of F508del-CFTR at low temperature), we found only a partial activity, equivalent to 30% of VX-770.…”

Nasal Epithelial Cell-Based Models for Individualized Study in Cystic Fibrosis

“…Three corrector compounds are currently FDA approved for use: lumacaftor (combined with ivacaftor as Orkambi©), tezacaftor (combined with ivacaftor as Symdeko©), and elexacaftor (combined with tezacaftor and ivacaftor as Trikafta TM ) [ 14 , 15 , 16 , 18 , 64 ]. All three were developed to target F508del CFTR , but have been shown effective in other groups as well [ 95 ]. Elexacaftor, tezacaftor, and ivacaftor (ETI) therapy has specifically produced robust clinical responses in a large proportion of the CF population, including F508del homozygotes, heterozygotes, and select rare variants identified through heterologous screening assays [ 14 , 15 , 64 ].…”

“…The processes by which the current correctors improve protein folding and trafficking to the cell surface are not clearly delineated and are likely much more dependent on the intracellular and tissue level milieu, therefore increasing the importance of high fidelity model systems that accurately recapitulate in vivo conditions [ 102 ]. The use of HNE models to meet this need has been instrumental in evaluating the therapeutic potential of small-molecule modulators, as well as in helping to understand the mechanism of action of these molecules and enable the identification of susceptible mutations [ 65 , 95 , 96 , 97 , 103 ]. Nasal cell testing, along with other model systems, has demonstrated the action of elexacaftor as a type 3 corrector compound with efficacy in numerous CFTR variants beyond F508del such as G85E and M1101K CFTR [ 96 ].…”