Esmaeil Shalaby, A.A.; (2010) Molecular analysis of chordomas and identification of therapeutic targets. Doctoral thesis , UCL (University College London).

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Abstract

Chordoma is a rare malignant bone tumour, showing notochordal differentiation, which occurs in the axial skeleton. Brachyury, a molecule involved in notochordal development, is a highly specific and sensitive marker for chordoma. It is hypothesised that brachyury or genes involved in its activation are implicated in the pathogenesis of chordoma. As there is currently no effective drug therapy for chordoma the aim of this study was to identify genetic events involved in chordoma pathogenesis with a view to identifying potential therapeutic targets. One hundred chordomas (50 skull-based, 50 non-skull based) were studied. Immunohistochemistry showed that the PI3K/AKT/TSC/mTOR pathway was activated in 65% of chordomas, thereby providing a rationale for testing mTOR inhibitors for the treatment of selected cases. DNA sequencing revealed no mutations in PI3KCA or RAS homologue enriched in brain (Rheb) in 23 tumours. Immunohistochemistry and Western blotting showed activation of the fibroblastic growth factor receptor (FGFR)/RAS/RAF/MEK/ERK/ETS2/brachyury pathway in more than 90% of cases, but no mutations were found in the genes analysed (FGFRs, KRAS, BRAF and brachyury) in 23 tumours. Three percent of cases revealed brachyury amplification but nearly half of the cases showed chromosomal abnormalities involving the brachyury locus. Knockdown of brachyury was achieved in the U-CH1 chordoma cell line using shRNA and resulted in premature cell senescence. These findings demonstrate that brachyury plays an important role in chordoma pathology. FISH analysis showed EGFR copy number gain in 45% of chordomas, including 6% with amplification and 39% with high level polysomy. The EGFR inhibitor, tyrphostin (AG1478) significantly inhibited growth of the chordoma cell line, and Western blotting showed this was associated with reduced phosphorylation of EGFR in a dose dependent manner. This study provides evidence for the first time that selected chordomas may be susceptible to treatment with EGFR inhibitors.

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