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PLK1 Silencing Achieved in Bladder Cancer Cells Via Exosomes Containing PLK1 siRNA

The use of small interfering RNAs (siRNAs) in gene therapy is limited by the lack of safe and efficient delivery vectors. Exosomes are nanovesicles that naturally carry RNA and have the ability to induce transcriptional and translational changes in target cells, thus their use as delivery vectors for siRNA is promising. Polo-like kinase-1 (PLK1) gene is a regulator of mitotic progression and is overexpressed in bladder cancer. Studies show that PLK1 depletion leads to cell cycle arrest and apoptosis in bladder cancer cells. The objective of the current work was to use exosomes as a vector to deliver PLK1 siRNA to bladder cancer cells lines. The work is described in the April 2016 issue of The Journal of Urology. The title of the article is “MP34-16 PLK1 Silencing in Bladder Cancer by siRNA Delivered with Exosomes.” Exosomes were isolated by ultracentrifugation from human embryonic kidney (HEK) cell conditioned media and labeled with PKH-26 membrane dye. Exosomes were then co-cultured with bladder cancer cells as well as normal bladder epithelial cells and imaged on Amnis ImageStreamX to assess for differential uptake. PLK1 siRNA and negative control siRNA were loaded into HEK exosomes using electroporation. An invasive bladder cancer cell line (UMUC3) was co-cultured with electroporated exosomes. Total RNA was isolated 24 and 48 hours following the addition of exosomes and real-time PCR was performed. Bladder cancer cells lines internalize an increased percentage of HEK exosomes when compared to normal bladder epithelial cells. Exosomes electroporated with PLK1 siRNA achieved successful knockdown of PLK1 RNA when compared to the negative control at both 24 and 48 hour timepoints. The higher rate of HEK exosome uptake by cancer cells has implications for using exosomes as a gene delivery vector in the intravesical therapy setting. The exosomes would be preferentially taken up by bladder cancer cells and exert less effect on normal epithelium. HEK exosomes were effectively used as a delivery vector to transport PLK1 siRNA to bladder cancer cells resulting in selective gene silencing of PLK1. The authors colclude that the use of exosomes as a delivery vector is attractive as they enter cells easily and have the potential to be non-immunogenic if isolated from an individual patient.

[Journal of Urology abstract]