Cytogenetic Effects of Methylphenidate Pediatric Advisory Committee

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Cytogenetic Effects of Methylphenidate
Pediatric Advisory Committee

• June 30, 2005
• David Jacobson-Kram, Ph.D. DABT
• Office of New Drugs
• Center for Drug Evaluation and Research
• Food and Drug Administration

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The Issue
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Study design

• Examined three endpoints in 12 children diagnosed
  with ADHD. Blood drawn before and after 3 month
  treatment with methylphenidate.
• Sister chromatid exchange
• Chromosomal aberrations
• Micronuclei
• Therapeutic doses were 20 to 54 mg/day

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What are sister chromatid exchanges (SCE)?

• Reciprocal exchanges of chromatid arms visualized
  in metaphase cells that have undergone two rounds
  of DNA replication in the presence of the
  nucleotide analogue bromodeoxyuridine.
• While the mechanism of SCE is poorly understood,
  increases in their frequencies are generally
  indicative of DNA damage.

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What are sister chromatid exchanges (SCE)?
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What are chromosomal aberrations?

• Chromosomal aberrations represent unrepaired or
  misrepaired chromosomal lesions that are visible
  under the light microscope.
• The same processes that give rise to these events
  are associated with chromosomal alterations
  resulting in cancer, e.g. Burkitts lymphoma.

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What are chromosomal aberrations?
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What are micronuclei?

• Micronuclei result from acentric chromosome
  fragments or whole chromosomes left behind in the
  cytoplasm after mitosis
• They are visualized in binucleated cells that
  have been blocked for cytokinesis
• Indicative of chromosome breakage or
  nondisjunction.

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What are micronuclei?
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What is the significance of these cytogenetic
endpoints?

• Chromosome aberration frequency in peripheral
  blood lymphocytes is an independent risk factor
  for cancer.
• If reproducible, data from the El-Zein paper
  suggest that patients taking methylphenidate may
  be at increased risk for cancer.

Chromosomal aberrations and risk of cancer in
humans an epidemiologic perspective. Bonassi et
al. 2004
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What else is known about the mutagenicity/carcinog
enicity of methylphenidate?

• No structural alerts
• Metabolism qualitatively similar in humans and
  animals but quantitative differences exist
• Negative in rat carc study and mouse p53 study
• Positive for liver tumors in mouse 2-year study
• Negative in Ames assay, mouse lymphoma gene
  mutation assay and in vivo micronucleus test
  some positive or equivocal results for in vitro
  chromosomal aberrations and SCE
• Review of pharmacy and medical records of 143,574
  patients found fewer cancer cases than expected
  (Selby et al., Cancer Res. 1989).

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Data summary from El-Zein et al.
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Data summary from El-Zein et al.
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Questions Regarding El-Zein Study

• Lack of placebo controls
• Use of unusual data presentation
• Aberrations/cell instead of damaged cells
• Total SCE in 25 cells
• Presence of 6 subjects with 0 SCE/cell
• Investigators agreed to a site visit to answer
  questions

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Site visit to Univ. of Texas

• Representatives from NIEHS, NICHD, FDA and EPA
  site visited U of T on May 23rd.
• Reviewed
• Patient selection
• Methods
• Raw data
• Slide evaluation

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Observations at site visit

• Investigators cordial, cooperative and responded
  to all inquiries.
• Good concordance between raw data sheets and data
  in publication.
• The slides were evaluated in a blinded fashion
  but the same technician coded, evaluated and
  decoded slides.
• A number of slides were chosen at random and were
  found to have low mitotic indices and poor
  differential staining for SCE.

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Effect of preparation quality on SCE frequencies
Good preparation
Bad preparation
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Ongoing efforts to assess methylphenidate
clastogenic potential organized under BPCA

• El-Zein et al., are seeking funding to perform
  larger (100 informative subjects) study
• NICHD, NIEHS and Duke are collaborating to
  reproduce the El-Zein study
• CDC has developed a protocol for a
  cross-sectional study that incorporates
  cytogenetic endpoints
• NIMH will assess stable chromosomal
  rearrangements as part of an ongoing cross
  sectional study

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Ongoing efforts to assess methylphenidate
clastogenic potential organized under BPCA

• Division of Neuropharm drugs is asking IND
  holders to assess clastogenic potential
• NCTR will perform experimental studies in
  non-human primates and transgenic mice
• Other drugs used to treat ADD and ADHD will also
  be studied
• First results will likely be available in about 1
  year

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