In vitro selected RNA aptamer recognizing glutathione induces ROS-mediated apoptosis in the human breast cancer cell line MCF 7

Glutathione (GSH) is an abundant natural tripeptide with antioxidant properties. Under different conditions, it can play protective as well as pathogenic roles. The redox state of the cell has an important role in the induction of apoptosis. Elevated level of glutathione in cancer cells provides resistance to a number of chemotherapeutic drugs. Inhibition of glutathione synthesis sensitizes the cells for apoptosis and enhances the activity of chemotherapeutic drugs. We have selected GSH-binding RNA aptamers by employing in vitro selection protocol SE LEX. The K_d value of these aptamers with respect to GSH were determined by surface plasmon resonance (SP R) analysis and isocratic affinity chromatography. Two aptamers GSHapt 8.17 (class-III) and GSHapt 5.39 (class-IV) had K_d values of 4.18 and 4.89 × 10^-8 M, respectively and GSHapt class-I had a K_d value of 1.2 × 10^-6 M. CD spectra suggested conformational change in aptamers upon GSH binding. Cultured breast cancer cells (MCF7) responded to expression of GSH aptamers by accumulating ROS and undergoing morphological transition, nuclear condensation and DNA fragmentation, with concurrent depletion of cellular GSH and activation of caspase 3 eventually leading to apoptosis. DTT and caspase-3 inhibitor partially rescued aptamer induced apoptosis. These aptamers exhibit high specificity to GSH over non specific competitor. The same aptamers did not induce apoptosis in 293T cells. The kinetic properties and pro-apoptotic effects suggest that glutathione-binding RNA aptamer could be developed into an effective anti-cancer chemotherapeutic agent.