Multi-functional near-infrared fluorescent polymer dot–siRNA for gene expression regulation

Regulation of gene expression in eukaryotic cells is critical for cell survival, proliferation, and cell fate determination. Misregulation of gene expression can have substantial, negative consequences that result in disease or tissue dysfunction that can be targeted for therapeutic intervention. Several strategies to inhibit gene expression at the level of mRNA transcription and translation have been developed, such as anti-sense inhibition and CRISPR-Cas9 gene editing. However, these strategies have some limitations in terms of specificity, toxicity, and ease of use. We have designed a nanomaterials-based tool to inhibit gene expression in eukaryotic cells with a potential application in basic and biomedical research. At the heart of our rational design approach is a polymer dots (Pdots)-based nanoplatform that can provide a means to deliver gene-specific small interfering (siRNA) into cells while at the same time providing a visualization mechanism to determine which cells have taken up the siRNA. The Pdots that we designed and synthesized had an average size 64.25 ± 0.60 nm and a zeta potential that was +37.40 ± 8.28 mV. The Pdot-1 nmole Gapdh siRNA showed an average size of 82.27 ± 9.83 nm, with the zeta potential values determined to be -52.00 ± 6.05 mV in the HEPES buffer. Both Pdots and Pdot-siRNA displayed two emission peaks in the visible (588 nm) and near-infrared (NIR) emission range (775 nm). We treated primary cultures of mouse brain-derived microvascular cells with Pdot-Gapdh siRNA and observed uniform cellular uptake of the nanomaterial in the cells and reduced intensity of Gapdh immunolabeling. Our results highlight the potential application of Pdot-siRNA for gene expression targeting with simultaneous visual monitoring of Pdot-siRNA delivery. The simple design offers a flexible and novel strategy to inhibit a wide range of mRNA targets with minimal toxicity, high efficiency, and focused cell visualization.