ABCMdb

PMID: 18722008

Kerem E, Hirawat S, Armoni S, Yaakov Y, Shoseyov D, Cohen M, Nissim-Rafinia M, Blau H, Rivlin J, Aviram M, Elfring GL, Northcutt VJ, Miller LL, Kerem B, Wilschanski M
Effectiveness of PTC124 treatment of cystic fibrosis caused by nonsense mutations: a prospective phase II trial.
Lancet. 2008 Aug 30;372(9640):719-27. Epub 2008 Aug 20., [PubMed]

Sentences

No. Mutations Sentence Comment

38 ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Asn1303Lys ABCC7 p.Asn1303Lys ABCC7 p.Gly542* ABCC7 p.Gly542* ABCC7 p.Gly542* ABCC7 p.Gly542* ABCC7 p.Gly542* ABCC7 p.Gly542* §Based on normative data for age, sex, and height.15 Table 1: Baseline characteristics Allele 1 Allele 2 Stop codon Total Treatment response* Change to normal range†; G542X ΔF508 UGA 3 3 (100%) 3 (100%) G542X W1282X UGA/UGA 1 0 1 (100%) G542X N1303K UGA 1 1 (100%) 1 (100%) W1282X ΔF508 UGA 13 10 (77%) 9 (69%) W1282X W1282X UGA/UGA 3 1 (33%) 1 (33%) W1282X 3849+10kB C→T‡ UGA/UAA 1 1 (100%) 1 (100%) 3849+10kB C→T‡ ΔF508 UAA 1 1 (100%) 1 (100%) Data are n or n (%). Login to comment 86 ABCC7 p.Trp1282* ABCC7 p.Gly542* The predominant premature stop mutations in these 23 patients were W1282X and G542X (table 2). Login to comment 94 ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Gly542* ABCC7 p.Gly542* Table 3 also shows that the proportion of patients who had normal chloride transport (predefined as nasal PD at least as electrically negative as -5 mV) increased during PTC124 treatment (first cycle p=0·0003, second cycle p=0·020).14 Results showed that participants who had all three genotypes for premature stop mutations (G542X, W1282X, and 3849+10 kB C→T), including patients who had a nonsense mutation in a single CFTR allele or in both CFTR alleles, had a total chloride transport response or normalisation during at least one cycle of PTC124 treatment (table 2). Login to comment 103 ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Trp1282* In the 13 patients who had a W1282X mutation as the only type of nonsense mutation (homozygous W1282X or W1282X/ΔF508), the amount of W1282X transcript was associated with the most electrically negative value for total chloride transport after either treatment phase (r=0·57, R²=0·32, p=0·046). Login to comment 104 ABCC7 p.Gly542* In the two patients whose only nonsense mutation was G542X, total chloride transport became more electrically negative than -5 mV (ie, within the normal range) although in both patients the proportion of CFTR mRNA that contained a nonsense mutation was less than 10% of wild-type CFTR mRNA. Login to comment 141 ABCC7 p.Trp1282* ABCC7 p.Trp1282* ABCC7 p.Gly542* ABCC7 p.Gly542* We did not include cystic fibrosis patients who did not have a CFTR nonsense mutation (eg, ΔF508 homozygous) on the basis that safety data for PTC124 in these patients were not sufficient at the beginning of the G542X only W1282X only 3849+10KB 3849+10KB+W1282X G542x+W1282X r=0·57 R2 =0·32 p=0·046 0 -20·0 -17·5 -15·0 -12·5 -10·0 -7·5 -5·0 -2·5 0·0 10 20 30 40 50 Proportion of CFTR mRNA with a nonsense mutation relative to wild-type mRNA (%) Typical range for patients with cystic fibrosis* Normal range* Nonsense mutation NasalPD(mV) Figure 4: Correlation of most normal nasal potential difference (PD) during treatment in either cycle with proportion of CFTR mRNA that contained a nonsense mutation relative to wild-type MRNA CFTR=cystic fibrosis transmembrane conductance regulator. mRNA=messenger RNA. Login to comment 153 ABCC7 p.Trp1282* These results accord with in vitro data that show that PTC124 does not modify mRNA transcription or stability.8 Preclinical work has previously shown that it is possible to alter translational fidelity at the site of a premature stop codon without modifying the surveillance mechanism that is responsible for degrading mutatedmRNAthroughtheprocessofnonsense-mediated decay.31,32 Our pharmacological strategy was based on the assumption that sufficient mRNA containing a nonsense mutation must be present to provide a template for protein production during drug-induced ribosomal read-through.7,33 We tested this presumption in the largest subset of patients in our study with a single CFTR genotype-W1282X. Login to comment 156 ABCC7 p.Gly542* In two patients who had only the G542X mutation, total chloride transport changed to within the normal range although the proportion of their CFTR mRNA that contained a nonsense mutation was less than 10% of 65 60 55 50 45 40 35 30 25 20 15 10 5 0 60 50 55 45 40 35 30 25 20 15 10 5 0 80 85 90 95 100 75 70 65 80 85 90 95 100 75 70 65 60 50 55 45 p=0·037 p=0·350 p=0·027 p=0·212 p=0·448 p=0·015p<0·0001 p=0·625 40 35 30 25 20 15 10 5 0 0 1000 Bodyweight Time (days) Treatment phase 1* Treatment phase 2* Treatment phase 1* Treatment phase 2* Weight(kg) AbsoluteneutrophilcountpermLProportionofpredictednormalvalue(%) Proportionofpredictednormalvalue(%) 0 14 28 42 Time (days) 0 14 28 42 FEV1 FVC Absolute neutrophil count 2000 3000 4000 5000 6000 7000 Figure 5: Mean clinical measurements at baseline and end of each treatment phase FEV1=forced expiratory volume in 1 second. FVC=forced vital capacity. Login to comment 163 ABCC7 p.Trp1282* ABCC7 p.Gly542* In this regard, preclinical work with PTC124 shows that ribosomal read-through of UGA-G (the sequence of G542X) is more efficient than that for UGA-A (the sequence of W1282X).8 Treatment with PTC124 was associated with small increases in FEV₁, FVC, and bodyweight in most patients, and with a reduction in neutrophil counts. Login to comment