Adapting molecular inversion probe (MIP) technology for allele quantification in childhood leukemia

Abstract

9530 Background: Leukemia accounts for ∼40% of newly diagnosed pediatric malignancies, and relapsed leukemia is the leading cause of death in childhood cancer. Genomic instability events contribute to neoplastic development and have been used to classify and risk stratify non-leukemic adult and pediatric tumors. Analyzing leukemic blasts for gene copy changes with advanced molecular techniques could prove useful in further risk stratifying and developing new treatment strategies for pediatric leukemia. Methods: Molecular Inversion Probes (MIPs) analyze genetic target sequences in parallel with high specificity and sensitivity at the highest genomic resolution, and were originally designed for single nucleotide genotyping. The MIP assay was adapted to analyze both gene copy number and loss of heterozygosity (LOH) events in pediatric leukemia samples (pre-B ALL, T-ALL, AML). DNA was extracted (100 ng) from paired bone marrow (diagnosis) and peripheral blood (remission) samples (n = 40). The MIP assay was run with a customized Affymetrix 20K Cancer Panel (representing oncogenes, tumor suppressor, DNA repair, cell growth, and metabolism genes). Gene copy number changes were identified by comparing probe signal intensity between leukemia samples and normal cell-lines. LOH events were determined by identifying genotype changes between matched leukemic and remission samples. Results: Each sample had unique patterns of multiple gene copy changes and LOH events distributed across all chromosomes. Additionally, samples were found to have overlapping copy number changes and LOH regardless of leukemia type. AML samples had fewer LOH events and could be separated by unsupervised clustering from the other leukemia samples. Conclusions: MIPs represent novel genotyping technology that can be adapted for gene copy analysis of childhood leukemia. Unique and distinguishing signatures of allelic imbalance can be determined between ALL and AML clinical samples using MIP technology. The unexpected overlap of LOH and deleted genes may represent a common molecular mechanism that requires further investigation. No significant financial relationships to disclose.