Abstract
Abstract Background: MicroRNAs (miRNAs) have potential prognostic and therapeutic value in human malignancies, including colorectal cancer (CRC). Many human tumor tissues are available as formalin-fixed paraffin-embedded (FFPE) specimens, which are an excellent source for biomarker discovery. However, the stability of miRNAs and the reliability of measurements of miRNA expression in archival samples stored for long periods of time (> 20 years) are not known. Therefore, we evaluated the stability and expression levels of miRNAs in FFPE CRC specimens and compared their expression levels to those in CRC cell lines. Methods: A panel of seven miRNAs (RNU6B, miR-20a, miR-21, miR-106a, miR-181b, miR-203, and miR-324-5p) in 219 CRC archival tissue samples, stored for 6 to 28 years (1982 through 2004) in a dark, cool place, and 11 CRC cell lines (LoVo, HCT116, HCT116 (p53-/-), RKO, LS174T, CaCo-2, Colo205, SW480, WiDr, HCT-15, and DLD-1) were evaluated by the use of TaqMan® microRNA assays and by quantitative real-time polymerase chain reactions. In CRCs, these miRNAs, excluding RNU6B (an endogenous reference molecule), are candidate prognostic or predictive biomarkers. All assay reagents used were from Applied Biosystems Inc., (Carlsbad, CA). From each block, tissue sections, 10-microns thick, were used for extraction of miRNAs. miRNA expression was measured as threshold cycle (Ct) values. Triplicate reactions were averaged for each miRNA, and the raw Ct values were determined. The Kruskal-Wallis one-way analysis of variance was employed to analyze the miRNA expression difference among archived samples from different years. Correlation coefficient analysis was performed to compare the expression levels of miRNA in archival tissues and cell lines. Results: In both CRC archival tissues and cell lines, the median Ct values of all miRNAs ranged from 19 to 32. All seven miRNAs were stable in CRC tissues stored for up to 28 years; their expression levels were similar across all ages of blocks. (Kruskall-Wallis P values for all 7 miRNAs ranged from 0.627 to 1.000.) There was good correlation between the levels of expression of all seven miRNAs in FFPE tissues and in the CRC cell lines (correlation coefficient R2 range, 0.784 to 0.937). Conclusions: Since miRNAs are stable in archival CRC samples stored for over 20 years, FFPE samples can be used to evaluate miRNAs as biomarkers. These studies were supported by grants 2U54-CA118948-03, R01-CA98932, and R03-CA139629 from the NCI/NIH. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1167. doi:10.1158/1538-7445.AM2011-1167
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