Direct S-Poly(T) Plus assay in quantification of microRNAs without RNA extraction and its implications in colorectal cancer biomarker studies

BACKGROUND: Advances in microRNAs (miRNAs) biomarkers have generated disease markers with potential clinical values. However, none of these published results have been applied in clinic until today. The main reason could be the lack of simple but robust miRNA measurements. METHODS: We built up a simple but ultrasensitive RT-qPCR protocol, Direct S-Poly(T) Plus assay, for detecting miRNAs without RNA purification. In this study, the method was optimized and compared with other RNA purification-based miRNA assays, and the sensitivity was tested. Using Direct S-Poly(T) Plus method, seven potential miRNA biomarkers of colorectal cancer were validated. RESULTS: It is possible to detect approximately 100 miRNAs with minimal plasma inputs (20 μl) and time (~ 140 min) with this approach. The sensitivity of this method was 2.7–343-fold higher than that of the stem-loop method, and comparable with S-Poly(T) plus method. 7 validated miRNA biomarkers of colorectal cancer by Direct S-Poly(T) plus assay could discriminate colorectal cancer stage I from healthy individuals, and promised satisfactory discrimination with the area under receiver operating characteristic (ROC) curve ranging from 0.79 to 0.94 (p value < 0.001). CONCLUSIONS: This simple and robust protocol may have strong impact on the development of specific miRNAs as biomarkers in clinic.