Abstract A40: MicroRNA expression patterns as potential biomarkers of responsiveness to the MEK1/2 inhibitor, AZD6244, in colorectal cancer cell lines

Abstract

Abstract Background: miRNAs are small, ∼22 oligonucleotides which typically act as negative regulators of gene expression. Recent data have demonstrated that aberrant expression of miRNAs may play a key role in the development of certain cancers and may also be involved in resistance to anticancer therapies. In this study, we tested whether miRNA expression patterns in AZD6244-sensitive (S) or -resistant (R) CRC cell lines could be used as potential biomarkers of responsiveness to this agent. Methods: Responsiveness to AZD6244 (ARRY-142886) was assessed by exposing 24 CRC cell lines to increasing concentrations of the drug and measuring proliferation using the sulforhodamine B method. Sensitivity and resistance to AZD6244 was defined as: S, IC50<0.8 M; and R, IC50 ≥0.8 µM. Baseline total RNA was isolated from 4 S and 3 R cell lines for miRNA and mRNA profiling on Dharmacon miRNA microarray and Affymetrix HG-U133 Plus 2.0 microarray platforms, respectively. For miRNA microarray data pre-processing, 342 miRNA probes with relative intensity of p≤0.01 in at least 2 of the 8 experiments were kept for further data analysis. For mRNA microarray analysis, probe sets representing the same gene were collapsed based on maximum values and the expression levels were converted to a rank-based matrix. Significance Analysis of Microarray (SAM) was used to determine the differentially expressed miRNAs in cell lines S or R to AZD6244. Results: Out of 24 CRC cell lines analyzed, 7 S and 17 R lines were identified. Six miRNAs were over-expressed in the R cell lines with at least four-fold change vs. S and with a false-discovery rate (FDR)<0.01. TargetScan listed 1181 genes potentially regulated by these six miRNAs. miRNA-target and Affymetrix gene expression profiles were compared and 171 genes that correlated inversely with miRNA expression at FDR<5% were identified. To assess the pathways enriched by these target genes, we queried this gene list against the KEGG database. Interestingly, expression of genes involved in the MAPK signaling pathway were down regulated in the AZD6244 R cell lines, which correlated with overrepresentation of the miRNAs associated with these genes. Conclusions: In this study, we determined that AZD6244 S and R CRC cell lines exhibit differential expression patterns of miRNAs, which may have potential utility as a predictive biomarker for sensitivity to this drug. Furthermore, we found that overexpression of specific miRNAs in AZD6244 R cell lines correlates with down regulation of genes involved in the MAPK pathway, which may confer resistance to AZD6244. Suppression of these candidate miRNAs may induce sensitivity to AZD6244 in resistant CRC cell lines and therefore may have clinical application in the targeted therapy of patients with advanced CRC. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A40.