1772

Osteosarcoma (OS) is a solid tumour of the bone, characterized by a high frequency of cytogenetic aberrations and gene amplification. Chromosomal instability (CIN) provides genetic diversity for OS tumour progression, but both the mechanisms that lead to CIN and the biological basis of the conferred selective advantage of genomic aberrations in this tumour are poorly understood. Complex cytogenetic aberrations and gene amplifications are known to arise as a consequence of the instability generated by the breakage-fusion-bridge (BFB) cycle. Moreover fragile sites (FS) have been shown to facilitate BFB-dependent breakage events in other systems. Thus, the first objective of this study was to characterise BFB events in OS and to develop high-resolution maps of recurrently amplified genomic regions in the vicinity of FS. The second objective was to investigate the role of epigenetic DNA modification within genomic intervals recurrently amplified and/or rearranged in OS. An analysis of OS cell lines and patient samples detected inverted duplications within the amplicon subunits and an elevated frequency of anaphase bridges and dicentrics are indicative of the BFB cycle being active in OS. The genomic location of cytogenetic breakpoints in OS indicated that locations at 1p, 6p, 8q, 17p and 19 were recurrently rearranged. For most locations there were FS in locations adjacent to areas subject to rearrangement/amplification. To investigate the role of epigenetic modifications in these genomic regions the cell line U2-OS was treated to the demethylating agent a5-aza-2’-deoxycytidine and expression microarrays were used to identify differentially expressed genes. Distinct clusters of both tumour-specific and osteoblast related gene expression was identified at 1p36, 6p21, 8q24 and 19p13. Taken together, these studies suggest that a small number of discrete genomic locations are subject to methylation modification in OS, and that these regions contain clusters of genes associated with oncogenesis and chromosomal rearrangement.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]