Aim: Most colorectal cancers develop from adenomas via the so-called adenoma-carcinoma sequence. In individuals with a high risk of developing colorectal cancer, more effective inhibition of this sequence by means of chemoprevention is urgently needed. Research on the biological background of colorectal adenoma formation is warranted in order to reveal possible targets for chemoprevention. Therefore, our aim was to analyze differences in pathway activity between normal colorectal mucosa and adenomas in a combined set of publicly available microarray data. Design:All available microarray expression data from normal mucosa and adenomas were obtained from Gene Expression Omnibus. Quality check was performed using Principal Component Analysis. After standardization and minimizing expression differences due to multiple study selection, we performed Gene Set Enrichment Analysis (GSEA) in order to assess which pathways are deregulated in colorectal adenomas. As a proof of concept we investigated the functionality of one of the identified deregulated pathways, and inhibited the Rb pathway in colon adenoma cell lines VACO-235 and VACO-330, using the cyclin-dependent kinase inhibitor roscovitine (CYC202) which is currently in phase I/II trials. Results: Data from four out of five available studies met predefined quality criteria, resulting in expression data from 26 normal mucosa and 47 adenoma samples. In the top 100 of individual genes up- or downregulated in adenomas, we identified several genes known to be involved in colon carcinogenesis. By using GSEA, 10, 11 and 16 gene sets according to KEGG, GenMAPP and Biocarta data bases respectively, specifically distinguished adenomas from normal mucosa. Pathways known to be involved in colon carcinogenesis such as cell cycle (P = .002) and Wnt signaling (P = .007) were strongly enriched. In addition, we found deregulation of novel pathways among which the Rb pathway (P = .002), folate biosynthesis (P = .019), Src pathway (P = .004) and hedgehog signaling (P = .037). The Rb pathway inhibitor roscovitine decreased phosphorylated and total Rb protein levels as expected. Along with decreased Rb expression, treatment with roscovitine (0-100 µM) resulted in a marked dose-dependent induction of apoptosis in adenoma cell lines VACO-235 and VACO-330 (mean degree of apoptosis after 100 µM roscovitine up to 61 and 55%, respectively). Conclusions:By combining sets of microarray data, we found enrichment in adenomas of known key biological pathways, underscoring the integrity of our approach. Furthermore, we elucidated novel, interesting and less well-studied pathways. These pathways could be explored and targeted for chemoprevention. The possible relevance of targeting those pathways was illustrated by the fact that roscovitine, an inhibitor of the identified Rb pathway, effectively induced apoptosis in adenoma cell lines. Supported by grant 2005-3361 of the Dutch Cancer Society.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2872.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO