Evaluation of an 18F-labeled oligonucleotide probe targeting p21(WAF1) transcriptional changes in human tumor cells.

The ability to image gene expression using 18F-labeled antisense oligonucleotides (asODNs) directed to specific mRNA transcripts during, or immediately following, radio- or chemotherapy would be a valuable clinical tool to monitor the early tumor response to treatment. Imaging of upregulated p21 mRNA postirradiation using 18F-labeled asODNs could offer insights into early tumor responses by detecting signs of accelerated cellular senescence. Thus, the aim of this work was to evaluate the uptake and distribution of a (radio)-fluorinated asODN in vitro in HCT116 p21(+/+) human colon carcinoma cells, asODN and a random sequence oligonucleotide (rsODN) were conjugated with a (radio)fluorine prosthetic group. Irradiated HCT116 cells were treated with naked or liposome-transfected ODNs. Cell fractionation, confocal microscopy, immunofluorescence, and Western blot studies were performed to observe uptake, distribution, and antisense activity of the probes. [F]asODN demonstrated similar antisense binding ability as the unlabeled asODN to p21 mRNA. Liposomal-transfected 18F-labeled asODNs and rsODNs exhibited a three-to fivefold increase in uptake at 2.5 h compared to the naked [18F]ODNs. Distribution of transfected [18F]asODN in the cytoplasm and endosomes increased over time whereas no change in intracellular distribution was observed with transfected [18F]rsODN or naked ODNs. Antisense activity was not compromised with the addition of a fluorine moiety on asODN. The cellular accumulation and distribution of the (radio)fluorinated ODNs was not altered by the addition of the prosthetic group. Radiolabeled ODNs were able to penetrate the cell with preferential uptake observed with the liposome-transfected probes. Increased distribution of [18F]asODN in the cytoplasm suggests the probe is available for targeting its transcript mRNA. This warrants further investigations into the potential of [18F]asODN to image accelerated senescence postirradiation.