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COMPLETE LOSS OF SUCCINATE DEHYDROGENASE B (SDHB) IN PEDIATRIC GASTROINTESTINAL STROMAL TUMORS (GIST)

COMPLETE LOSS OF SUCCINATE DEHYDROGENASE B (SDHB) IN PEDIATRIC GASTROINTESTINAL STROMAL TUMORS (GIST). Katherine A. Janeway, MD November 7, 2009 Connective Tissue Oncology Society. Pediatric GIST. Definition: GIST diagnosed at age 18 years or less

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COMPLETE LOSS OF SUCCINATE DEHYDROGENASE B (SDHB) IN PEDIATRIC GASTROINTESTINAL STROMAL TUMORS (GIST)

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  1. COMPLETE LOSS OF SUCCINATE DEHYDROGENASE B (SDHB) IN PEDIATRIC GASTROINTESTINAL STROMAL TUMORS (GIST) Katherine A. Janeway, MD November 7, 2009 Connective Tissue Oncology Society

  2. Pediatric GIST • Definition: GIST diagnosed at age 18 years or less • 85% “wildtype”, lacking mutations in KIT or PDGFRA • KIT is expressed and activated • Underlying oncogenic event is not known • Less sensitive to tyrosine kinase inhibition than KIT or PDGFRA mutant tumors • Better understanding of biology is needed • A proportion of pediatric patients with GIST have additional tumors (syndromic GIST)

  3. Syndromic GIST • Carney Triad • GIST, pulmonary chondroma, paraganglioma • Not inherited • Carney-Stratakis syndrome • GIST and paraganglioma • Autosomal dominant • Incomplete penetrance

  4. Succinate Dehydrogenase and paraganglioma • Familial paraganglioma • 10% of paragangliomas • Caused by germline mutations in SDHB, SDHC, SDHD • Germline SDHB mutations can be associated with pheochromocytoma and renal cell carcinoma • Classic tumor suppressor • Mutations missense in conserved AAs or nonsense • Tumors have loss of the normal allele • Sporadic paraganglioma • 10% of patients with germline mutations in SDH Amar L JCO 23(34): 8812, 2005

  5. Succinate Dehydrogenase Gottlieb and Tomlinson, Nature Reviews Cancer, 2005

  6. SDH Mutations in Carney-Stratakis Syndrome • 11 patients from 9 families with Carney-Stratakis Diad • Age 9 to 37 at GIST diagnosis • Germline mutation or deletion of SDHB, SDHC or SDHD McWhinney, et al NEJM, 2007

  7. Pediatric wildtype GIST and SDH • Objective: To determine whether pediatric wildtype GISTs express SDHB • Western blot with whole cell lysates from 3 KIT mutant GISTs and 8 pediatric wildtype GISTs • Stain with antibodies for SDHB, Kit, PKCθ and actin

  8. Pediatric wildtype GIST and SDH • Objectives: • Determine whether loss of SDHB restricted to pediatric wildtype GIST • Evaluated additional GIST subtypes for SDHB loss • Larger number of KIT mutant GISTs evaluated for SDHB loss • Immunohistochemistry of SDHA and SDHB • 6 pediatric wildtype cases • 5 NF-1 associated cases • 15 KIT mutant cases • Exon 11: 9 • Exon 13: 2 • Exon 9: 2 VHL mutant pheo SDH mutant pheo

  9. Pediatric wildtype GIST and SDH

  10. Pediatric wildtype GIST and SDH • Objective: To determine whether SDH / complex II functions normally in pediatric wildtype GIST

  11. Pediatric wildtype GIST and SDH • Normal Complex III and IV activity in pediatric GIST KIT mutant Pediatric KIT wildtype

  12. SDH mutation analysis • Objective: To determine if loss of SDHB expression and SDH function is due to mutations in SDHB, SDHC or SDHD • Genomic DNA sequencing of 14 pediatric wildtype GISTs and 2 pediatric KIT mutant GISTs • SDHB • 6bp intronic deletion in several cases BUT cDNA sequencing normal • SDHC: No mutations • SDHD: No mutations

  13. SNP analysis for SDH deletions • Objective: To determine if loss of SDHB expression and SDH function is due to deletions in SDHB, SDHC or SDHD • Affymetrix 250 K SNP (Sty) array • 13 pediatric wildtype GISTs • 4 KIT mutant GISTs • Normal control samples Ch 1p Ch 11 Ch 1q NO DELETION NO DELETION

  14. qRTPCR for expression of SDH subunits • Objective: To determine if there might be epigenetic causes for loss of SDHB expression and SDH function • qRTPCR of SDHB, SDHC, SDHD • No significant difference in expression of SDHA, SDHB, and SDHD in pediatric wildtype vs. KIT mutant GISTs SDHC p = 0.06 (with P3) p = 0.004 (without P3)

  15. Conclusions • Pediatric wildtype GISTs lack SDHB expression and complex II activity • In contrast to KIT-mutant GISTs • Loss of SDHB expression and complex II activity is not due to mutations or deletions of SDHB, SDHC or SDHD • Loss of SDHB expression and complex II activity may be due to epigenetic events (methylation) causing decreased SDHC expression • Work is ongoing

  16. Acknowledgements • Brigham and Women’s Hospital • Jonathan Fletcher • Vania Nose • Hopital Robert Debre, Paris • Pierre Rustin • University of Texas Health Science Center • Patricia Dahia • Broad Institute • Jordi Barretina • Dana Farber Cancer Institute • Angela Lai

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