Workshop on Clinical Outcome Measures and endpoints for efficacy assessment in spinal muscular atrop

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Workshop on Clinical Outcome Measures and
endpoints for efficacy assessment in spinal
muscular atrophy13th October European Medicines
Agency, London

• Scientific consensus on Biomarkers for SMA
• Christina Brahe and F. Danilo Tiziano
• Istituto di Genetica Medica, Università
  Cattolica, Roma

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At present, the only available biomarker for SMA
is dosage of SMN protein or SMN transcripts (mRNA)
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• Dosage of SMN protein
• Quantification of SMN protein is likely the most
  suitable and sensitive biomarker
• Present status
• Only one approach has been reported, a cell
  immunoassay for quantification SMN in blood
  samples
• An ELISA assay would be more appropriate but is
  presently available only for measuring SMN
  protein in cultured cells
• Perspectives
• Efforts to develop a suitable ELISA assay are
  ongoing
• 
  Kolb et al. 2006
  Thi Man et al. 2008

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Dosage of SMN mRNA

• There is a general consensus that dosage of SMN
  mRNA levels in peripheral blood leukocytes may
  be, at present, the most feasible biomarker

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• Rationales
• small amounts of blood (2.5 ml) are sufficient
  for mRNA quantification
• peripheral blood mRNA is stable up to 5 days when
  collected in PAXgene tubes and stored at 4C (or
  room temperature), allowing shipment between
  different Centers
• SMN transcripts are stable over time
• several methods are available to measure SMN mRNA
  levels in blood samples
• Sumner et al. 2006 Brichta et al. 2006
  Simard et al. 2007 Vezain et al. 2007

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The ICC Biomarker Subcommittee has reached a
general consensus on the usefulness of a recently
developed absolute real-time quantification assay
of SMN transcripts in blood samples
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Rationales

• by using this assay, a significant difference
  between SMN-fl transcripts in patients and
  controls and a correlation between SMN mRNA
  levels and clinical severity were shown these
  are prerequisites for the use of SMN dosage as
  biomarker
• the assay does not depend on the use of
  endogenous controls which may be affected by
  exposure to drugs
• the assay allows the quantification of full
  length SMN (SMN-fl) transcripts and SMN
  transcripts lacking exon 7 (SMN-7)
• the assay has been shown to detect variations in
  SMN transcripts in a group of patients undergoing
  pharmacological treatment (preliminary,
  unpublished data)
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  Tiziano et al., submitted

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The present data strongly suggest that SMN mRNA
may serve as a reliable biomarker and should
allow one to distinguish between responders and
non-responders, at the molecular level, in
clinical trials.
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Confirmation that SMN mRNA is a valid biomarker
relies on the demonstration that variations in
SMN transcript levels correlate with a clinical
outcome in pharmacological trials
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In what trials is dosage of SMN mRNA recommended?

• All trials with compounds or molecules that
  affect SMN gene expression or splicing of SMN
  transcripts
• Examples
• Compounds valproic acid, phenylbutyrate,
  hydroxyurea, indoprofen, salbutamol/albuterol,
  etc.
• Molecules antisense oligonucleotides,
  bifunctional RNAs, etc
• Neuroprotective agents?

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Future perspectives

• 1) Test the feasibility of SMN mRNA
  quantification in sources other than blood (oral
  mucosal cells, saliva)
• 2) Development of a robust ELISA assay for
  measurement of SMN protein

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Future perspectives (2)

• 3) Identification of Biomarkers different from
  SMN
• In progress Multi-Center pilot study
  coordinated by SMA Foundation (limited to USA)
• Objective Identification of candidate plasma
  and urine biochemical biomarkers that correlate
  with disease severity, as determined by the
  Modified Hammersmith Functional Motor Scale,
  across a range of SMA type I-III children

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Future perspectives (3)

• 4) Development of a commercial kit for the
  absolute real-time quantification of SMN-fl and
  SMN-7 transcripts to be made available to the
  scientific community and Centers involved in
  clinical trials

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Conclusions

• The study of a biomarker for SMA has become a
  realistic opportunity for monitoring the
  molecular efficacy of drugs during clinical
  trials
• There is a general consensus that, at present,
  dosage of SMN transcripts is the appropriate
  strategy to provide the most reliable data
  however, dosage of SMN protein is highly
  desirable
• Future clinical trials should provide
  confirmation that a SMA biomarker(s) is
  biologically/clinically relevant