Visual and fluorometric determination of telomerase activity by using a cationic conjugated polymer and fluorescence resonance energy transfer

The detection of telomerase activity is important in cancer diagnosis and in screening for anti-cancer drugs. This work describes a fluorometric method for the determination of telomerase activity by using a cationic conjugated polymer (CCP). Telomerase substrate primers were labelled with carboxyfluorescein (FAM-TS) which display weak electrostatic interactions with the CCP. Hence, fluorescence resonance energy transfer (FRET) from photoexcited CCP to FAMis weak. However, in the presence of telomerase, telomeric repeats (TTAGGG) x were elongated to the 3'-end of FAM-TS to form multiple G-quadruplexes in the presence of potassium ion (K+). These G-quadruplexes trigger strong electrical interaction between the condensed G-quadruplexes and the CCP, and this results in closer proximity and in more efficient FRET. As a result, strong green fluorescence (peaking at 527 nm) is emitted by FAM. Fluorescence can be visually observed under a UV lamp and be used to quantify the activity of telomerase by using a fluorometer. The assay was applied to the determination of HeLa cells in the 30 to 1000 cells per mL range, with a detection limit as low as 5 cells per mL (at an S/N ratio of 3). The method was applied to the detection of various cancer cell lines in human urine samples. The method is simple, sensitive, selective and accurate.