A dual-signaling electrochemical ratiometric strategy combining "signal-off" and "signal-on" approaches for detection of MicroRNAs

A dual-signaling electrochemical ratio metric strategy was developed for detection microRNA-18a based on the duplex-specific nuclease-assisted target recycling and electrochemical atom transfer radical polymerization signal amplification. In the presence of target microRNA, RNA/DNA duplexes are formed, which become the substrate of the duplex-specific nuclease-assisted target recycling. Hence only the DNA strand is cleaved by duplex-specific nuclease enzyme, resulting in the throw away of methylene blue (MB) from the electrode (signal off) accompanied by releasing of target microRNA, which can be recycled in the next hybridization. The remaining piece of capture DNAs on the electrode surface hybridize with the Azide labeled-signal DNAs. "Click reactions" were carried out between 3-Butynyl-2-bromoisobutyrate and Azide to initiate the electrochemical atom transfer radical polymerization reaction. This process could bring a great number of ferrocenylmethyl methacrylate (FMMA) on the surface of electrode (signal on). The I_FMMA/I_MB value was proportionate to the microRNA-18a concentration and measured by square wave voltammetry. The promising potential of the proposed biosensor in clinical analyses was exhibited by its remarkable features such as strong performance, high specificity, agreeable storage stability, and notable selectivity in real sample evaluation with no pretreatment or amplification. Finally, our biosensing method offers such an application to be used for the early clinical diagnosis of Pancreatic Cancer.

[Tumor escape mechanism involving Fas and Fas-L molecules in human colorectal tumors]

OBJECTIVES

The interaction between Fas and its ligand (Fas-L) leads to Fas-positive cell apoptosis. Our objective was to study a new mechanism of tumor escape involving these molecules, the so-called "counterattack".

METHODS

We used flow cytometry to analyze Fas expression and apoptosis sensitivity in different human colorectal tumor cell lines. The presence of Fas-L mRNA was analyzed by RT-PCR. We studied apoptosis rate in peripheral blood lymphocytes and lymph node lymphocytes from patients with colorectal cancer by flow cytometric cell cycle analysis after in vitro culture with or without tumor cells.

RESULTS

We found differences in Fas expression and sensitivity to Fas-induced apoptosis between different colorectal tumor cell lines. Interferon-gamma was also found to affect Fas expression and apoptosis sensitivity induced by an anti-Fas antibody. Actinomycin-D decreased Fas expression and apoptosis sensitivity in certain cell lines. Our data confirmed the tumor cell "counterattack" hypothesis by showing their capacity to induce apoptosis in lymphocytes from patients with colorectal cancer.

CONCLUSION

Fas expression and apoptosis sensitivity in colorectal tumor cell lines can be modulated by actinomycin-D or interferon-gamma. These data may suggest new therapeutic options based on increased Fas expression in tumor cells induced by interferon-gamma, or on apoptosis induction in tumor cells with a local intratumoral treatment with actinomycin-D.