Elsevier

The Lancet

Volume 372, Issue 9640, 30 August–5 September 2008, Pages 719-727
The Lancet

Articles
Effectiveness of PTC124 treatment of cystic fibrosis caused by nonsense mutations: a prospective phase II trial

https://doi.org/10.1016/S0140-6736(08)61168-XGet rights and content

Summary

Background

In about 10% of patients worldwide and more than 50% of patients in Israel, cystic fibrosis results from nonsense mutations (premature stop codons) in the messenger RNA (mRNA) for the cystic fibrosis transmembrane conductance regulator (CFTR). PTC124 is an orally bioavailable small molecule that is designed to induce ribosomes to selectively read through premature stop codons during mRNA translation, to produce functional CFTR.

Methods

This phase II prospective trial recruited adults with cystic fibrosis who had at least one nonsense mutation in the CFTR gene. Patients were assessed in two 28-day cycles. During the first cycle, patients received PTC124 at 16 mg/kg per day in three doses every day for 14 days, followed by 14 days without treatment; in the second cycle, patients received 40 mg/kg of PTC124 in three doses every day for 14 days, followed by 14 days without treatment. The primary outcome had three components: change in CFTR-mediated total chloride transport; proportion of patients who responded to treatment; and normalisation of chloride transport, as assessed by transepithelial nasal potential difference (PD) at baseline, at the end of each 14-day treatment course, and after 14 days without treatment. The trial was registered with who.int/ictrp, and with clinicaltrials.gov, number NCT00237380.

Findings

Transepithelial nasal PD was evaluated in 23 patients in the first cycle and in 21 patients in the second cycle. Mean total chloride transport increased in the first treatment phase, with a change of −7·1 (SD 7·0) mV (p<0·0001), and in the second, with a change of −3·7 (SD 7·3) mV (p=0·032). We recorded a response in total chloride transport (defined as a change in nasal PD of −5 mV or more) in 16 of the 23 patients in the first cycle's treatment phase (p<0·0001) and in eight of the 21 patients in the second cycle (p<0·0001). Total chloride transport entered the normal range for 13 of 23 patients in the first cycle's treatment phase (p=0·0003) and for nine of 21 in the second cycle (p=0·02). Two patients given PTC124 had constipation without intestinal obstruction, and four had mild dysuria. No drug-related serious adverse events were recorded.

Interpretation

In patients with cystic fibrosis who have a premature stop codon in the CFTR gene, oral administration of PTC124 to suppress nonsense mutations reduces the epithelial electrophysiological abnormalities caused by CFTR dysfunction.

Funding

PTC Therapeutics, Cystic Fibrosis Foundation Therapeutics.

Introduction

Cystic fibrosis results from mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR), an apical cell-surface epithelial chloride channel that promotes chloride efflux and secondarily inhibits constitutive sodium influx via the epithelial sodium channel (ENaC).1 Dysfunction of this regulator leads to epithelial mucous dehydration and viscous secretions, which often cause chronic neutrophilic inflammation and occlusion of respiratory airways. Obstruction of pancreatic ducts, the biliary tract, and the vas deferens can occur. Patients typically develop progressive respiratory dysfunction and persistent pulmonary infections and often have pancreatic insufficiency, diminished bodyweight, chronic hepatobiliary inflammation, and male infertility. Respiratory failure is the most common cause of death. No means for correcting the genetic defect has been available; current medical treatments are palliative.

A nonsense mutation is a single point alteration in DNA that results in the inappropriate presence of a UAA, UAG, or UGA stop codon in the protein-coding region of the corresponding messenger RNA (mRNA) transcript. Such a stop codon causes premature cessation of translation, with protein truncation leading to loss of function and consequent disease. Nonsense mutations are responsible for about 10% of cystic fibrosis cases worldwide.2 However, in Israel, nonsense mutations are the cause of cystic fibrosis in most patients.3 Because people with such mutations produce little functional CFTR, these patients usually have a phenotype of severe cystic fibrosis.4

Certain aminoglycoside antibiotics (eg, gentamicin) can induce ribosomes to read through a premature stop codon in mRNA, resulting in incorporation of an amino acid and continuation of translation to produce a complete protein.5 We have previously shown that topical application of gentamicin drops to the nasal mucosa can cause a local increase in CFTR-mediated chloride transport as assessed by nasal transepithelial potential difference (PD) in patients who have sufficient CFTR transcripts that contain a nonsense mutation.6, 7 However, the inconvenience of parenteral administration and the potential for serious toxic effects preclude long-term systemic use of gentamicin for supression of nonsense mutations.

PTC124 (3-[5-(2-fluorophenyl)-[1,2,4]oxadiazol-3-yl]-benzoic acid) is a 284-Dalton, orally bioavailable, non-aminoglycoside compound that was specifically developed to induce ribosomes to read through premature stop codons, but not normal stop codons.8 When tested in a mouse model of stop-mutation-mediated cystic fibrosis, PTC124 generated production of full-length, functional CFTR.9 Phase I studies in healthy volunteers established the initial safety profile for PTC124,10 and defined dosing regimens to achieve target trough plasma concentrations (of 2 to 10 μg/mL) that are known to be active in preclinical models.8, 9

We aimed to use nasal PD to assess whether PTC124 could overcome the effects of a nonsense mutation by restoring the functional activity of CFTR and increasing total chloride transport. We also aimed to assess other nasal PD measures of ion-channel activity, the cellular levels of CFTR mRNA with a nonsense mutation, disease-related clinical parameters, safety of this treatment, compliance with treatment, and PTC124 pharmacokinetics.

Section snippets

Participants

Patients were referred by four participating cystic fibrosis clinics in Israel for treatment at a single centre. All patients were aged 18 years or older, and had cystic fibrosis as established by a typical clinical presentation, an abnormal sweat test (sweat chloride >40 mEq/L by pilocarpine iontophoresis), abnormal chloride transport (nasal transepithelial PD more electrically positive than −5 mV during nasal perfusion with chloride-free amiloride and isoproterenol),11, 12, 13, 14 and the

Results

23 patients who had never been given PTC124 were enrolled, and completed the treatment phase of the first cycle. One patient had an exacerbation of a pre-existing Mycobacterium abscessus infection in the first cycle, and thus did not participate in the second cycle. Another patient had rhinitis, which precluded baseline testing of nasal PD before the second cycle; therefore we had paired assessments of nasal PD in cycle 2 for 21 patients. For FEV1 and FVC, 22 patients had paired assessments in

Discussion

The trial exemplifies the concept of personalised medicine:18 integrating selection of patients with a specific genetic defect, use of a treatment designed to overcome that defect in gene expression, and direct assessment of protein function within disease-affected tissues. We used genotyping to identify patients in whom cystic fibrosis was caused by a CFTR nonsense mutation. We administered PTC124 to induce ribosomes to selectively bypass premature stop codon mutations in mRNA. We used nasal

References (35)

  • L Linde et al.

    Nonsense-mediated mRNA decay affects nonsense transcript levels and governs response of cystic fibrosis patients to gentamicin

    J Clin Invest

    (2007)
  • EM Welch et al.

    PTC124 targets genetic disorders caused by nonsense mutations

    Nature

    (2007)
  • M Du et al.

    PTC124 is an orally bioavailable compound that promotes suppression of the human CFTR-G542X nonsense allele in a CF mouse model

    Proc Natl Acad Sci

    (2008)
  • S Hirawat et al.

    Safety, tolerability, and pharmacokinetics of PTC124, a non-aminoglycoside, nonsense mutation suppressor, following single- and multiple-dose administration to healthy male and female adult volunteers

    J Clin Pharmacol

    (2007)
  • JP Clancy et al.

    Evidence that systemic gentamicin suppresses premature stop mutations in patients with cystic fibrosis

    Am J Respir Crit Care Med

    (2001)
  • MR Knowles et al.

    In vivo nasal potential difference: techniques and protocols for assessing efficacy of gene transfer in cystic fibrosis

    Hum Gene Ther

    (1995)
  • TA Standaert et al.

    Standardized procedure for measurement of nasal potential difference: an outcome measure in multicenter cystic fibrosis clinical trials

    Pediatr Pulmonol

    (2004)
  • Cited by (0)

    View full text