Cellular uptake of modified oligonucleotides enhanced by porphyrins studied by time-resolved microspectrofluorimetry and fluorescence imaging techniques

A critical analysis of methods used to investigate the cellular uptake and subcellular localization of RNA therapeutics

RNA therapeutics are a promising strategy to treat genetic diseases caused by the overexpression or aberrant splicing of a specific protein. The field has seen major strides in the clinical efficacy of this class of molecules, largely due to chemical modifications and delivery strategies that improve nuclease resistance and enhance cell penetration. However, a major obstacle in the development of RNA therapeutics continues to be the imprecise, difficult, and often problematic nature of most methods used to measure cell penetration. Here, we review these methods and clearly distinguish between those that measure total cellular uptake of RNA therapeutics, which includes both productive and non-productive uptake, and those that measure cytosolic/nuclear penetration, which represents only productive uptake. We critically analyze the benefits and drawbacks of each method. Finally, we use key examples to illustrate how, despite rigorous experimentation and proper controls, our understanding of the mechanism of gymnotic uptake of RNA therapeutics remains limited by the methods commonly used to analyze RNA delivery.

Study of Cellular Uptake of Modified Oligonucleotides by Using Time-Resolved Microspectrofluorimetry and Florescence Imaging

Fluorescence microimaging and homodyne phase-resolved confocal microspectrofluorimetry were used to monitor the transport of antisense oligonucleotide into cancer MCF7 cells and the subsequent intracellular distribution. Phosphorothioate analog of 15-mer oligoadenylate (dA15) labeled by ATTO 425 was complexed with 5,10,15,20-tetrakis (1-methyl-4-pyridyl) porphyrin (H2TMPyP4) as an uptake-mediating agent. Fluorescence lifetime data within a broad spectral range have revealed properties of both components inside the cell. H2TMPyP4 lifetime inside the cell is not influenced in this malignant cell line, while the lifetime of modified oligonucleotide was found to be slightly shortened.