Silencing peroxiredoxin-2 sensitizes human colorectal cancer cells to ionizing radiation and oxaliplatin.

Colorectal cancer (CRC) remains one of the leading causes of cancer-related death worldwide. Antioxidant enzymes decrease the generation of ionizing radiation (IR)-induced free radicals and therefore are associate to radioresistance. The main goal of this work is to study the involvement of peroxiredoxin-2 (Prx2) in the radio and chemoradiotherapy response in CRC cells in vitro and in vivo. We found that Prx2 oxidation state is associated to differential response to ionizing radiation in CRC cell lines. HCT116 radioresistant CRC cell line have lower ROS levels and a higher monomer/dimer Prx2 ratio, compared to halfway resistant Caco-2 and T84, and radiosensitive LoVo cell line. Constitutive and transient Prx2 silencing in CRC cells increase ROS levels, and most importantly, enhance in vitro radiation sensitivity. In addition, we showed that administration of IR plus oxaliplatin in down regulated Prx2 HCT116 cells has higher citotoxic effect than in control cells. Finally, radiosensitizing effect of Prx2 depletion was confirmed in vivo. These results suggest that Prx2 is an important component in tumoral radiation response, and their inhibition could improve radio and chemoradiotherapy protocols in patients with CRC.

Magnetic nanoparticle and magnetic field assisted siRNA delivery in vitro.

This chapter describes how to design and conduct experiments to deliver siRNA to adherent cell cultures in vitro by magnetic force-assisted transfection using self-assembled complexes of small interfering RNA (siRNA) and cationic lipids or polymers that are associated with magnetic nanoparticles (MNPs). These magnetic complexes are targeted to the cell surface by the application of a gradient magnetic field. A further development of the magnetic drug-targeting concept is combining it with an ultrasound-triggered delivery using magnetic microbubbles as a carrier for gene or drug delivery. For this purpose, selected MNPs, phospholipids, and siRNAs are assembled in the presence of perfluorocarbon gas into flexible formulations of magnetic lipospheres (microbubbles). Methods are described how to accomplish the synthesis of magnetic nanoparticles for magnetofection and how to test the association of siRNA with the magnetic components of the transfection vector. A simple method is described to evaluate magnetic responsiveness of the magnetic siRNA transfection complexes and estimate the complex loading with magnetic nanoparticles. Procedures are provided for the preparation of magnetic lipoplexes and polyplexes of siRNA as well as magnetic microbubbles for magnetofection and downregulation of the target gene expression analysis with account for the toxicity determined using an MTT-based respiration activity test. A modification of the magnetic transfection triplexes with INF-7, fusogenic peptide, is described resulting in reporter gene silencing improvement in HeLa, Caco-2, and ARPE-19 cells. The methods described can also be useful for screening vector compositions and novel magnetic nanoparticle preparations for optimized siRNA transfection by magnetofection in any cell type.