In vivo siRNA distribution and pharmacokinetics assessed by nuclear imaging are modulated according to radiolabelling site.
Garin D., Ahmadi M., Gauchez AS., Bohic S., Boccard S., Cloetens P., Fagret D., Berger F., Briat A., Ghezzi C., Pelletier L.
INTRODUCTION: RNA interference is efficient in in vitro studies, and appears as a therapeutic tool of major clinical interest. Nevertheless, the clinical utilisation of siRNAs is restrained by the poor availability of biodistribution data on this new class of pharmaceutics. This study aimed at defining the biodistribution and pharmacokinetics properties of an siRNA directed to the Casein Kinase-2 beta (CK2β) subunit, a potential target in cancer therapy. METHODS: Four CK2β siRNAs were chemically modified on each extremity of sense or anti-sense strand and radioiodinated. The biodistribution of each entity was analysed in glioblastoma-bearing mice using nuclear imaging and compared to a control GFP siRNA. RESULTS: The labelling process was associated with preservation of interference activity, except when applied to the 5' antisense terminus. Radioactivity was predominantly observed in organs of the excretory system after intravenous administration: liver, kidneys and bladder. Tumor/Contralateral muscle ratio showed significant differences depending on the labelling site. Activity associated with CK2β5's was quite constant over 2 hours, while CK2β3'as activity decreased by 40% in tumor. Finally, synchrotron X-ray analysis showed that CK2β3's is more abundant in tumor than in liver, brain or muscle, and uniformly distributed between intra- and extracellular compartments. CONCLUSIONS: In this study, we highlighted the large influence of siRNAs radiolabelling position on their biodistribution and pharmacokinetic profiles, and proposed a systematic approach for the imaging of all siRNAs of clinical interest.