Maria: you can see in this website and message board several informations about PTC 124:
APRIL
23 - (NATURE, 2007) PTC124 targets genetic disorders caused by nonsense mutations
Ellen M. Welch, Elisabeth R. Barton, Jin Zhuo, Yuki Tomizawa, Westley J. Friesen, Panayiota Trifillis, Sergey Paushkin, Meenal Patel, Christopher R. Trotta, Seongwoo Hwang, Richard G. Wilde, Gary Karp, James Takasugi, Guangming Chen, Stephen Jones, Hongyu Ren, Young-Choon Moon, Donald Corson, Anthony A. Turpoff, Jeffrey A. Campbell, M. Morgan Conn, Atiyya Khan, Neil G. Almstead, Jean Hedrick, Anna Mollin, Nicole Risher, Marla Weetall, Shirley Yeh, Arthur A. Branstrom, Joseph M. Colacino, John Babiak, William D. Ju, Samit Hirawat, Valerie J. Northcutt, Langdon L. Miller, Phyllis Spatrick, Feng He, Masataka Kawana, Huisheng Feng, Allan Jacobson, Stuart W. Peltz & H. Lee Sweeney - USA
Nonsense mutations promote premature translational termination and cause anywhere from 5–70% of the individual cases of most inherited diseases. Studies on nonsense-mediated cystic fibrosis have indicated that boosting specific protein synthesis from ,1% to as little as 5% of normal levels may greatly reduce the severity or eliminate the principal manifestations of disease. To address the need for a drug capable of suppressing premature termination, we identified PTC124—a new chemical entity that selectively induces ribosomal readthrough of premature but not normal termination codons. PTC124 activity, optimized using nonsense-containing reporters, promoted dystrophin production in primary muscle cells from humans and mdx mice expressing dystrophin nonsense alleles, and rescued striated muscle function in mdx mice within 2–8 weeks of drug exposure. PTC124 was well tolerated in animals at plasma exposures substantially in excess of those required for nonsense suppression. The selectivity of PTC124 for premature termination codons, its well characterized activity profile, oral bioavailability and pharmacological properties indicate that this drug may have broad clinical potential for the treatment of a large group of genetic disorders with limited or no therapeutic options.
(NATURE, 2007) Comments: Ignore the nonsense
Anton Schmitz & Michael Famulok - Germany
A small molecule forces the protein-translation machinery to overlook the signals that would otherwise result in its premature termination. Genuine stop signs are, however, read and obeyed.
Several inherited diseases are caused by mutations in single nucleotides within genes. These mutations can transform the products of messenger RNA codons, the sets of three nucleotides that determine which amino acid is incorporated into the growing protein chain. When such 'nonsense' mutations are transcribed into a 'stop' codon, the cellular machinery that translates mRNA into protein misinterprets the codon as a signal to terminate protein synthesis. These false stop codons are known as premature termination codons (PTCs) and result in the formation of truncated proteins that cannot function properly and may even damage the cell, eventually leading to disease. Depending on the disorder, nonsense mutations account for 5–70% of cases of genetic disorders, including cystic fibrosis, muscular dystrophy and several types of cancer. In a paper published on Nature's website today, Welch et al. report that a small organic molecule known as PTC124 can force the translation machinery to ignore PTCs, without preventing it from reading the real stop signals.
It has been known for the past 10 years that the antibiotic gentamycin can prompt ribosomes — the core component of the cellular protein-synthesis machinery — to read through PTCs, thereby generating full-length proteins. Nevertheless, the clinical benefit of gentamycin is limited, because to be effective it has to be used at very high concentrations, which are associated with severe side effects. There is now hope that PTC124, which, like gentamycin, ignores PTCs but lacks its adverse side effects, could be more beneficial in the clinic. Indeed, interim results of phase II clinical trials indicate that patients with PTC-induced forms of cystic fibrosis and Duchenne muscular dystrophy might benefit from treatment with PTC124 — a promising result that has been commented on for some time.
Welch et al. describe an astonishing feature of PTC124 — its selectivity for PTCs. Why is this so striking? All organisms with membrane-bound cell nuclei (eukaryotes) have evolved mechanisms to protect themselves from the harmful products of nonsense mutations. There are two lines of defence. The first relies on the fast and efficient degradation of the truncated proteins after the translation of PTC-containing mRNAs. The second acts before these proteins are synthesized. This quality-control mechanism, known as nonsense-mediated mRNA decay (NMD), detects and degrades PTC-containing mRNAs. But how is a PTC distinguished from a normal termination codon? The answer came from the discovery that, in all organisms, NMD requires ongoing protein translation.
The only cellular entity that can read the genetic code, and so decipher stop codons, is the ribosome. In mammals, PTC recognition occurs during an initial 'pioneer' round of translation in which — unlike 'productive' translation, which results in protein synthesis — a ribosome scans only newly synthesized mRNAs for the presence of PTCs. NMD is closely linked to mRNA splicing — a process in which non-coding sequences of a gene (introns), which have been transcribed into the precursor mRNA, are removed. After re-joining of the coding sequences (exons), the splicing machinery labels the joining sites by attaching a set of proteins known collectively as the exon-junction complex. As a rule, the ribosome identifies a termination codon as premature if it is more than 55 bases upstream of an exon-junction complex.
Although NMD's role in mRNA quality control has been known for many years, recent observations indicate that this might not be its main function. On inactivation of the NMD machinery, about 10% of the transcriptome — the set of all mRNAs in a cell — of yeast and human cells are differentially expressed, indicating that NMD is involved in the regulation of gene expression. Examples of NMD-regulated molecules include several proteins that are involved in amino-acid synthesis, as well as pseudo-genes that do not encode a protein but are the source of non-coding RNAs such as small nucleolar RNAs.
Therefore, drug-induced readthrough of PTCs could enhance protein expression in two ways. First, by directly suppressing premature termination during the productive translation of mRNA, it could increase the efficiency of translation (Fig. 1a). Second, by suppressing PTC recognition during pioneer translation, it could prevent NMD, thereby increasing the number of mRNA sequences that are available for productive translation (Fig. 1b). Although both possibilities lead to a favourable increase in protein translation, the second is associated with a risk of an increased amount of mutated proteins and mRNAs, which are normally absent because of mRNA degradation by NMD.
Welch et al. found that, fortunately, PTC124 seems to selectively target productively translating ribosomes, and does not interfere with those that are engaged in NMD. In this way, PTC124 differs from gentamycin, which induces upregulation of several mRNAs that are known to be NMD substrates.
As well as being a prerequisite for its therapeutic efficacy, the specificity of PTC124 could be a starting point for a better understanding of the differences between the productive and the pioneer modes of translation. Although other distinct agents (besides ribosomes) are required for these two types of translation, we don't have detailed structural and functional information about them. The identification of the molecular target of PTC124 should help to fill this gap. Thus, in addition to being a promising drug, PTC124 may also become a research tool for elucidating the underlying mechanisms of the termination of protein translation
26 - (J. Clin. Pharmacol,2007; 47:430-444) Safety, Tolerability, and Pharmacokinetics of PTC124, a Nonaminoglycoside Nonsense Mutation Suppressor, Following Single- and Multiple-Dose Administration to Healthy Male and Female Adult Volunteers
Samit Hirawat, Ellen M. Welch, Gary L. Elfring, Valerie J. Northcutt, Sergey Paushkin, MD, Seongwoo Hwang, Eileen M. Leonard, Neil G. Almstead, William Ju, MD, Stuart W. Peltz, and Langdon L. Miller - USA
Nonsense (premature stop codon) mutations are causative in 5% to 15% of patients with monogenetic inherited disorders. PTC124, a 284-Dalton 1,2,4-oxadiazole, promotes ribosomal readthrough of premature stop codons in mRNA and offers therapeutic potential for multiple genetic diseases. The authors conducted 2 phase I studies of PTC124 in 62 healthy adult volunteers. The initial, single-dose study evaluated doses of 3 to 200 mg/kg and assessed fed-fasting status on pharmacokinetics following a dose of 50 mg/kg. The subsequent multiple-dose study evaluated doses from 10 to 50 mg/kg/dose twice per day (bid) for up to 14 days. PTC124 administered orally as a liquid suspension was palatable and well tolerated through single doses of 100 mg/kg. At 150 and 200 mg/kg, PTC124 induced mild headache, dizziness, and gastrointestinal events. With repeated doses through 50 mg/kg/dose bid, reversible transaminase elevations <2 times the upper limit of normal were sometimes observed. Immunoblot analyses of peripheral blood mononuclear cell extracts revealed no protein elongation due to nonspecific ribosomal readthrough of normal stop codons. PTC124 plasma concentrations exceeding the 2- to 10-µg/mL values associated with activity in preclinical genetic disease models were safely achieved. No sex-related differences in pharmacokinetics were seen. No drug accumulation with repeated dosing was apparent. Diurnal variation was observed, with greater PTC124 exposures after evening doses. PTC124 excretion in the urine was <2%. PTC124 pharmacokinetics were described by a 1-compartment model. Collectively, the data support initiation of phase II studies of PTC124 in patients with nonsense mutation–mediated cystic fibrosis and Duchenne muscular dystrophy.
In other websites more informations:
www.parentprojectmd.org/site/PageServer?pagename=ptc_06_review
