Identification of High-Level DNA Amplifications in AML with Complex Karyotype Using Array-CGH.

Complex karyotype acute myeloid leukemia (AML), commonly defined as the presence of three or more chromosome abnormalities without specific fusion transcripts, is seen in approximately 10–15% of all AML cases. In this subset of cases, genomic losses and gains are much more frequent than balanced translocations, indicating other mechanisms of leukemogenesis. One possible mechanism is the activation of oncogenes through high-level DNA amplifications. To detect high-level DNA amplifications and to identify corresponding candidate genes, we applied comparative genomic hybridization to microarrays (array-CGH) in 100 cases of complex karyotype AML and correlated the findings with gene expression profiling (GEP) data. For array-CGH a custom-made 2.8k-microarray was used consisting of 2799 different BAC- or PAC-vectors with an average resolution of approximately 2 Mb. Hybridization experiments were performed in a dye-swap setting; significant aberrations were defined as mean plus/minus three times the standard deviation of a set of balanced clones for each individual experiment. In selected cases correlation with global gene expression studies was performed to further delineate candidate genes.

We identified 50 high-level DNA amplifications in 20 different genomic regions. Amplifications occurring in at least two cases mapped to (candidate genes in the amplicon) 11q23.3-q24.1 (n=10; ETS, FLI1, APLP2); 11q23.3 (n=8;MLL, DDX6, LARG, SC5DL); 21q22 (n=5; ERG, ETS2); 9p24 (n=4; JAK2); 13q12 (n=4; CDX2, FLT3, PAN3); 8q24 (n=3; C8FW, MYC); 12p13 (n=2; FGF6, CCND2); 20q11 (n=2; ID1, BCL2L1); and 11q13 (n=2; STARD10, GARP, RAD30, DLG2). To better characterize the genomic architecture of the amplicons, we applied array-CGH using an 8.0k-microarray with an average resolution of approximately 1 Mb. Using this approach highly complex amplicon structures with several distinct amplicon peaks were identified for e.g. the amplified regions in 8q24, 11q23, and 13q12. In addition, parallel analysis of GEP in a subset of 43 of 100 cases displayed overexpressed candidate genes in the critical amplified regions; for some of the genes an oncogenic role has been implicated e.g. C8FW and MYC in 8q24, ETS1, FLI1 and APLP2 in 11q24.1, as well as FLT3 and CDX2 in 13q12. In conclusion, using high-resolution genome-wide screening tools such as array-CGH, a large number of high-level DNA amplifications were identified in AML with complex karyotype suggesting a more general role for protooncogene activation in this AML subset. This high-resolution technique allows the detection of complex amplicon structures with several distinct amplicon peaks pinpointing to selective candidate genes. In addition, correlation with GEP studies facilitates the delineation of overexpressed candidate genes within the amplified regions.