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Genomic instability is a major feature of neoplastic development in colorectal carcinoma and other cancers. Specific genomic instability events, such as deletions in chromosomes and other alterations in gene copy number, have potential utility as biologically relevant prognostic biomarkers. For example, genomic deletions on chromosome arm 18q are an indicator of colorectal carcinoma behavior and potentially useful as a prognostic indicator. Adapting a novel genomic technology called molecular inversion probes which can determine gene copy alterations, such as genomic deletions, we designed a set of probes to interrogate several hundred individual exons of >200 cancer genes with an overall distribution covering all chromosome arms. In addition, >100 probes were designed in close proximity of microsatellite markers on chromosome arm 18q. We analyzed a set of colorectal carcinoma cell lines and primary colorectal tumor samples for gene copy alterations and deletion mutations in exons. Based on clustering analysis, we distinguished the different categories of genomic instability among the colorectal cancer cell lines. Our analysis of primary tumors uncovered several distinct categories of colorectal carcinoma, each with specific patterns of 18q deletions and deletion mutations in specific genes. This finding has potential clinical ramifications given the application of 18q loss of heterozygosity events as a potential indicator for adjuvant treatment in stage II colorectal carcinoma. (Cancer Res 2006; 66(16): 7910-9)

Supplementary Data 1 from Molecular Inversion Probe Analysis of Gene Copy Alterations Reveals Distinct Categories of Colorectal Carcinoma

Genomic instability is a major feature of neoplastic development in colorectal carcinoma and other cancers. Specific genomic instability events, such as deletions in chromosomes and other alterations in gene copy number, have potential utility as biologically relevant prognostic biomarkers. For example, genomic deletions on chromosome arm 18q are an indicator of colorectal carcinoma behavior and potentially useful as a prognostic indicator. Adapting a novel genomic technology called molecular inversion probes which can determine gene copy alterations, such as genomic deletions, we designed a set of probes to interrogate several hundred individual exons of >200 cancer genes with an overall distribution covering all chromosome arms. In addition, >100 probes were designed in close proximity of microsatellite markers on chromosome arm 18q. We analyzed a set of colorectal carcinoma cell lines and primary colorectal tumor samples for gene copy alterations and deletion mutations in exons. Based on clustering analysis, we distinguished the different categories of genomic instability among the colorectal cancer cell lines. Our analysis of primary tumors uncovered several distinct categories of colorectal carcinoma, each with specific patterns of 18q deletions and deletion mutations in specific genes. This finding has potential clinical ramifications given the application of 18q loss of heterozygosity events as a potential indicator for adjuvant treatment in stage II colorectal carcinoma. (Cancer Res 2006; 66(16): 7910-9)

The DNA mismatch repair (MMR) pathway corrects specific types of DNA replication errors that affect microsatellites and thus is critical for maintaining genomic integrity. The genes of the MMR pathway are highly conserved across different organisms. Likewise, defective MMR function universally results in microsatellite instability (MSI) which is a hallmark of certain types of cancer associated with the Mendelian disorder hereditary nonpolyposis colorectal cancer. (Lynch syndrome). To identify previously unrecognized deleted genes or loci that can lead to MSI, we developed a functional genomics screen utilizing a plasmid containing a microsatellite sequence that is a host spot for MSI mutations and the comprehensive homozygous diploid deletion mutant resource for Saccharomyces cerevisiae. This pool represents a collection of non-essential homozygous yeast diploid (2N) mutants in which there are deletions for over four thousand yeast open reading frames (ORFs). From this screen, we identified a deletion mutant strain of the PAU24 gene that leads to MSI. In a series of validation experiments, we determined that this PAU24 mutant strain had an increased MSI-specific mutation rate in comparison to the original background wildtype strain, other deletion mutants and comparable to a MMR mutant involving the MLH1 gene. Likewise, in yeast strains with a deletion of PAU24, we identified specific de novo indel mutations that occurred within the targeted microsatellite used for this screen.

10005 Background: Genomic instability is a major feature of neoplastic development in colorectal carcinoma and other cancers. Specific genomic instability events such as genomic deletions have potential utility as biologically relevant prognostic biomarkers. Loss of heterozygosity (LOH) on chromosome arm 18q is an indicator of colorectal carcinoma behavior and potentially, prognosis. For stage II and III colorectal cancer, a number of retrospective studies have shown strong correlations between deletions in 18q and reduced survival. However, other studies have failed to identify this correlation. This discrepancy is likely the result of different sets of genetic markers and their widely disparate locations along chromosome arm 18q, often separated by megabases. New technologies are needed to overcome these issues. Methods: Using a novel genomic technology called molecular inversion probes (MIPs), we analyzed genomic deletions at exon-level resolution in primary colorectal carcinoma. Unlike microsatellite genetic markers, MIPs are not dependent on having informative alleles to discern a LOH event. This enables querying microsatellite genetic markers used in any clinical study. We designed a set of probes to interrogate several hundred individual exons of over two hundred cancer genes with an overall distribution covering all chromosome arms. Also represented were a series of over 100 probes along chromosome arm 18q representing genetic markers used in clinical studies. An analysis was carried out on primary tumor samples from patients with stage II and III disease. Results: We discovered several distinct categories of colorectal carcinomas based upon their profile of 18q genomic deletions and other allelic imbalances. Colorectal carcinoma extent of invasion showed an association with cluster designation which suggests that the multiple genomic instability events influence the invasive behavior of colorectal carcinoma. Conclusions: Colorectal cancer has distinct patterns of 18q genomic deletions, representing a potential molecular classifier. This finding has potential clinical ramifications given the application of 18q LOH events as an indicator for adjuvant treatment in stage II colorectal carcinoma. No significant financial relationships to disclose.