Observing an antisense drug complex in intact human cells by in-cell NMR

Abstract

Gaining insight into the uptake of drugs into cells, trafficking and their target engagement enhances understanding of the drugs function and efficiency. Here we study an antisense oligonucleotide drug (ASO) delivered into HEK293T and HeLa cells, by Nuclear Magnetic Resonance (NMR). Using a combination of transfection, cryoprotection and dynamic nuclear polarization (DNP), we were able to detect the drug directly in intact frozen cells. Activity of the drug was confirmed by qRT-PCR, measuring downregulation of its target mSTAT3. Applying DNP NMR to frozen cells, we overcome limitations of traditional solution-state in-cell NMR (e.g. size, stability and sensitivity) as well as of visualization techniques, where (e.g. fluorescent) tagging of the ASO decreases its activity. The possibility to study an untagged, active drug, interacting in its natural environment, will increase insights into molecular mechanisms of delivery, intracellular trafficking and target engagement in intact cells.