Ataluren for the treatment of nonsense-mutation cystic fibrosis: a randomised, double-blind, placebo-controlled phase 3 trial

Abstract

Background Ataluren was developed to restore functional protein production in genetic disorders caused by nonsense mutations, which are the cause of cystic fibrosis (CF) in 10% of patients.. Methods This randomized, double-blind, placebo-controlled study enrolled 238 patients ≥6 years with nmCF to receive oral ataluren 10 mg/kg in the morning, 10 mg/kg mid-day, and 20 mg/kg in the evening or matching placebo for 48 weeks. The primary endpoint was relative change in % predicted forced expiratory volume in one second (FEV1) at Week 48; the secondary endpoint was the rate of pulmonary exacerbations. This study is registered with ClinicalTrials.gov, number NCT00803205. Findings There was no statistically significant difference in relative change from baseline in % predicted FEV1between ataluren and placebo at Week 48(-2•5% vs -5•5%, p=0.1235). The rate of pulmonary exacerbations was not statistically different between treatment arms (rate ratio 0.77 (95% CI 0.57, 1.05), p=0.0992). However, post hoc analysis of the subgroup of patients not using chronic inhaled tobramycin showed a 5.7% difference in relative change from baseline in % predicted FEV1 between ataluren and placebo at Week 48 (-0.7% vs -6.4%, nominal p=0•008, adjusted for multiplicity p = 0•024) and 40% fewer exacerbations in ataluren-treated patients (OR 0.60 (95% CI 0•42, 0•86), nominal p=0•006, adjusted for multiplicity p = 0•018). Interpretation While there was no statistically significant improvement in lung function or exacerbation rate in the ITT population of cystic fibrosis patients with nonsense mutations treated with ataluren, treatment might be beneficial for nmCF patients not receiving chronic inhaled tobramycin.

Ataluren stimulates ribosomal selection of near-cognate tRNAs to promote nonsense suppression

“…However, in cells manifesting substantial ataluren-mediated readthrough of the PTC-containing NanoLuc mRNA, addition of tobramycin showed strong, dose-dependent reduction of ataluren's readthrough activity (Fig. 4), consistent with previous work showing that aminoglycosides reduce the ability of ataluren to promote readthrough but nonaminoglycoside antibiotics have no effect (12). Quantitation of this effect indicated that tobramycin inhibition of ataluren's activity had an IC 50 of 20 μM (Fig.…”

“…1 and SI Appendix, Fig. S3) (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)23); (ii) the effects on luciferase activity could not be independently replicated by others (24) or by us (SI Appendix , Fig. S3C); (iii) ataluren's putative luciferase inhibitory activity depends on a specific enzyme substrate (25); and (iv) most of the hypothetical inhibitory molecule, PTC124-AMP (22), is rapidly converted to the active readthrough molecule PTC124 (ataluren) under conditions of in vitro translation (SI Appendix, Fig.…”

“…Multiple experimental approaches with cell lines, patient cells, animal models, and genetic disorder patients have demonstrated that the drug ataluren can restore expression to genes and mRNAs otherwise inactive because of the presence of premature nonsense codons (1,(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)23). Collectively, such experiments have strongly suggested that ataluren promotes nonsense suppression, i.e., the insertion of near-cognate tRNAs at PTCs, but direct evidence for this activity has been lacking.…”

“…To date, ataluren has been shown to restore function to more than 20 different disease-specific or reporter nonsense alleles in systems ranging in complexity from in vitro translation to cell culture to mouse models and human patients (1,(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). In the latter, Translarna clinical trials have demonstrated restoration of full-length functional protein in Duchenne muscular dystrophy and cystic fibrosis nonsense mutation patients (10,11,13,15,16).…”

Disease-modifying drug therapy in cystic fibrosis

“…No statistically significant difference was seen in the ataluren treatment group when compared to the placebo group in a large phase 3 trial, although significant benefits were seen in patients not receiving inhaled aminoglycoside antibiotics; these drugs also act on the ribosome, making competitive inhibition highly likely as the explanation (15). A second phase 3 trial is currently underway in patients 6 years and older not receiving these drugs (NCT02139306) .Read through agents also have therapeutic potential for a range of other inherited diseases caused by stop mutations; conditional approval has recently been granted for certain types of Duchenne muscular dystrophy.…”