The discovery of small interfering RNAs (siRNAs) and their potential to knock down virtually any gene of interest
has ushered in a new era of RNA interference (RNAi). Clinical use of RNAi faces severe limitations due to inefficiency
delivery of siRNA or short hairpin RNA (shRNA). Many molecular imaging techniques have been adopted in
RNAi-related research for evaluation of siRNA/shRNA delivery, biodistribution, pharmacokinetics, and the therapeutic
effect. In this review article, we summarize the current status of in vivo imaging of RNAi. The molecular imaging techniques
that have been employed include bioluminescence/fluorescence imaging, magnetic resonance imaging/
spectroscopy, positron emission tomography, single-photon emission computed tomography, and various combinations
of these techniques. Further development of non-invasive imaging strategies for RNAi, not only focusing on the delivery
of siRNA/shRNA but also the therapeutic efficacy, is critical for future clinical translation. Rigorous validation will
be needed to confirm that biodistribution of the carrier is correlated with that of siRNA/shRNA, since imaging only detects
the label (e.g. radioisotopes) but not the gene or carrier themselves. It is also essential to develop multimodality imaging
approaches for realizing the full potential of therapeutic RNAi, as no single imaging modality may be sufficient to
simultaneously monitor both the gene delivery and silencing effect of RNAi.
Keywords: RNA interference (RNAi), small interfering RNA (siRNA), gene therapy, molecular imaging, magnetic resonance
imaging (MRI), positron emission tomography (PET), near-infrared fluorescence (NIRF), bioluminescence imaging (BLI).
Rights & PermissionsPrintExport