Low free drug concentration prevents inhibition of F508del CFTR functional expression by the potentiator VX‐770 (ivacaftor)

Abstract

BACKGROUND AND PURPOSEThe most common cystic fibrosis (CF) mutation F508del inhibits the gating and surface expression of CFTR, a plasma membrane anion channel. Optimal pharmacotherapies will probably require both a 'potentiator' to increase channel open probability and a 'corrector' that improves folding and trafficking of the mutant protein and its stability at the cell surface. Interaction between CF drugs has been reported but remains poorly understood. EXPERIMENTAL APPROACHCF bronchial epithelial cells were exposed to the corrector VX-809 (lumacaftor) and potentiator VX-770 (ivacaftor) individually or in combination. Functional expression of CFTR was assayed as the forskolin-stimulated short-circuit current (I sc ) across airway epithelial monolayers expressing F508del CFTR. KEY RESULTSThe potentiated I sc response during forskolin stimulation was increased sixfold after pretreatment with VX-809 alone and reached 11% that measured across non-CF monolayers. VX-770 (100 nM) and genistein (50 μM) caused similar levels of potentiation, which were not additive and were abolished by the CFTR inhibitor CFTR inh -172. The unbound fraction of VX-770 in plasma was 0.13 ± 0.04%, which together with previous measurements in patients given 250 mg p.o. twice daily, suggests a peak free plasma concentration of 1.5-8.5 nM. Chronic exposure to high VX-770 concentrations (>1 μM) inhibited functional correction by VX-809 but not in the presence of physiological protein levels (20-40 mg·mL À1 ). Chronic exposure to a low concentration of VX-770 (100 nM) together with VX-809 (1 μM) also did not reduce the forskolin-stimulated I sc , relative to cells chronically exposed to VX-809 alone, provided it was assayed acutely using the same, clinically relevant concentration of potentiator. CONCLUSIONS AND IMPLICATIONSChronic exposure to clinically relevant concentrations of VX-770 did not reduce F508del CFTR function. Therapeutic benefit of VX-770 + VX-809 (Orkambi) is probably limited by the efficacy of VX-809 rather than by inhibition by VX-770. Abbreviations

Development of HPLC and LC–MS/MS methods for the analysis of ivacaftor, its major metabolites and lumacaftor in plasma and sputum of cystic fibrosis patients treated with ORKAMBI or KALYDECO

“…Such inhibitory interactions are especially concerning given that LUMA only partially restores (11–15%) F508del-CFTR surface expression [13, 22, 23]. Various independent research groups have reported that IVA downregulates the restored F508del-CFTR whether it was modulated by LUMA or the investigational corrector VX-661 [14, 22, 23]. Matthes et al claimed that the inhibitory effects of IVA against the corrector function of LUMA only occurs at relatively high IVA concentrations (5–10μM, used in all of the reported cell culture studies) and that this inhibitory effect is unlikely to occur at the low (1.5–8.5 nM) free IVA concentrations achievable in vivo [14].…”

“…The annual cost per patient for both drugs is high ($259,000–$311,000 USD), and presently their manufacturer Vertex has a market monopoly as these are the only drugs on the market available for their indication [12]. The clinical efficacy of ORKAMBI versus the cost of therapy has been brought into question due to potential antagonistic drug-drug interactions between IVA and LUMA that potentially limit the clinical efficacy of ORKAMBI [13, 14]. Additional factors that may limit ORKAMBI’s clinical efficacy come from its less than ideal pharmacokinetic properties [15, 16].…”

“…LUMA on the other hand is not extensively metabolized and is largely excreted unchanged in the faeces [16]. Both IVA and LUMA are very hydrophobic molecules and are ~99% bound to plasma proteins, which significantly limits the free (active) drug concentration [2, 14]. Presently, very little information is available concerning the steady-state plasma concentrations of IVA, M1, M6 and LUMA achievable in patients under the current recommended dosage regimen no methods for therapeutic drug monitoring have been reported so far.…”

Synergistic Potentiation of Cystic Fibrosis Transmembrane Conductance Regulator Gating by Two Chemically Distinct Potentiators, Ivacaftor (VX-770) and 5-Nitro-2-(3-Phenylpropylamino) Benzoate

“…Veit et al, 2014), a compound designed to correct the trafficking defects of the most common pathogenic mutation ΔF508 (Van Goor et al, 2011). Although this negative impact of VX-770 on the action of VX-809 may not be as severe when the VX-770 concentration is in the nanomolar range (Matthes et al, 2016), new CFTR potentiators with few drug-drug interactions seem warranted.…”

Efficacy of lumacaftor-ivacaftor for the treatment of cystic fibrosis patients homozygous for the F508del-CFTR mutation

“…Matthes et al [67] suggested that the inhibitory effects of the lumacaftor-ivacaftor combination therapy is due to high concentrations of free ivacaftor present in plasma, and that improving CFTR function would require lowering potentiator concentration and using more efficacious correctors. It was recently discovered that some other potentiators did not appear to markedly inhibit the correction of F508del [64, 68].…”