Fluorine‐18 labelling of small interfering RNAs (siRNAs) for PET imaging

Small interfering RNAs (siRNAs), a class of macromolecules constituted by the association of two single‐stranded ribonucleic acids of short sequences, have been labelled with the positron‐emitter fluorine‐18 ( T 1/2 : 109.8 min). The strategy involves (1) prosthetic conjugation of a single‐stranded oligonucleotide with [ 18 F]FPyBrA ( N ‐[3‐(2‐[ 18 F]fluoropyridin‐3‐yloxy)‐propyl]‐2‐bromoacetamide) followed by (2) formation of the target duplex by annealing with the complementary sequence, therefore, permitting parallel and combinatorial preparation of [ 18 F]siRNAs. Pure fluorine‐18‐labelled siRNAs (0.55–1.11 GBq, specific activity: 74–148 GBq/µmol at EOB) could be obtained within 165 min starting from 37.0 GBq of starting [ 18 F]fluoride (1.5–3.0%, non‐decay‐corrected isolated yields).