Emerging Therapies For Dmd
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Emerging Therapies For Dmd

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    Emerging Therapies For Dmd Emerging Therapies For Dmd Presentation Transcript

    • Sriharsha Gowtham
      • Connects actin to sacrolemmal plasma membrane
      • Likely a shock absorber as muscle contracts
              • (Finkel)
      • Mutations produce stop codons UAA, UAG or UGA in mRNA (Welch et al.)
      • Instability of transcript or truncation of protein can occur (Mendell and Dietz)
      • ptcbio.com
      • Can cause 5%-70% of cases of most inherited diseases (Welch et al.)
      • Cause 5-13% of DMD cases (Nelson et al.)
      • Degradation of truncated proteins
      • The nonsense-mediated mRNA decay pathway of the ribosome. This determines the decay rate of altered transcript during pre mRNA modification and extension of truncated protein
      • NMD pathway acts with the ribosome during “pioneering round of translation” as opposed to “productive translation”
      • Ribosome uses the exon-junction complex to determine the location of the nonsense mutation
              • (Schmitz and Famulok)
      • To suppress the ribosome’s ability to read nonsense codons (Welch et al.)
      • Results in only one change in amino acid
      • Should help for other diseases with premature stop codons such as cystic fibrosis (Finkel)
      • ptcbio.com
      • Two high through-put screens for a total of 800,000 low molecular weight compounds
      • 1 st used human embryonic kidney cells(HEK293) transfected with defective luciferase reporter gene
      • 2 nd used in vitro assay of luciferase mRNA and rabbit reticulocyte lysate
      • Non-toxic compounds that rescued the luciferase expression were isolated.
      • (Welch et. al Supp. info.)
      .
      • PTC124 (C15H9FN2O3) isolated.
      • no structural similarity to aminoglycosides(potentially toxic compounds shown to have worked before)
      • Active at low concentrations- non-toxic
              • (Welch et al)
            • Welch et al.
      • PTC124 treated in cells of human DMD patients and mdx mice (contained premature UAA codon in Exon 23 of dystrophin gene) .
      • Antibody for dystrophin protein used
      • Read through of nonsense codon successful
      • 40-60% of normal dystrophin: myosin in humans, 35% in mdx samples
              • (Welch et al.)
      • PTC124 dosing in mdx mice: oral, intraperitoneal or both for 2-8 weeks
      • All three dosings improved strength
      • Protection from contraction-induced injury increased
      • Serum creatine kinase decreased
      • Full length dystrophin detected in western blots
      • Membrane localization determined with immunohistological assays.
              • (Welch et al)
      • Microarray analysis of HEK293 cells treated with PTC124 or gentamicin showed few transcripts changed in expression vs control
      • Do normal stop codons differ from nonsense mutations?
      • Luciferase transcript with nonsense mutation and treated with PTC124 showed full length protein and no read through.
              • (Welch et al)
      • Reads through the mutation but not correct stop codon.
      • Possibly due to the secondary structure of mRNA near triplet codon (Finkel, Nelson et al.)
      • Or it prevents nonsense-mediated decay. (Nelson et al.)
      • Welch et al. claims that PTC124 induces read through of nonsense codons.
      • Auld et al claims that PTC124 stabilizes the protein with nonsense codon.
      • Many aspects of the experiment differed including the concentrations of PTC124 used by Auld et al.
      • Since PTC124 shows differing efficacy with differing nonsense codons, it is likely inducing read through.
      • The molecular target of PTC124 is unknown
              • Nelson et al.
      • After it was clear that no normal stop codon read through occurred in humans (Phase 1), a study regarding cystic fibrosis was conducted (Phase 2).
      • Nonsense codon was successfully suppressed
      • A study on DMD patients was conducted (Phase 3) showing dose dependent improvement.
      • Drug is being considered for Hemophilia A and B
              • Finkel
      • Finkel RS. Read-Through Strategies for Suppression of Nonsense Mutations in Duchenne/ Becker Muscular Dystrophy: Aminoglycosides and Ataluren (PTC124). Journal of Child Neurology. 25(9) 1158-1164
      • Mendell JT and Dietz HC . When the Message Goes Awry: Disease-Producing Mutations that Influence mRNA Content and Performance. Cell, Vol. 107, 411–414, November 16, 2001
      • Nelson SF, Crosbie RH, et al. Emerging genetic therapies to treat Duchenne muscular dystrophy. Curr Opin Neurol. 2009 October ; 22(5): 532–538.
      • Schmitz A and Famulok M. Chemical Biology: Ignore the Nonsense. Nature  447, 42-43 (3 May 2007)
      • Welch EM, Barton ER, Zhuo J, et al. PTC124 targets genetic disorders caused by nonsense mutations. Nature 2007;447:87–91
      • http://www.ptcbio.com/3.1.1_genetic_disorders.aspx