PT - JOURNAL ARTICLE AU - Liu, Zhibo AU - Lin, Kuo-Shyan AU - Yapp, Donald AU - Perrin, David TI - Dual mode fluorescent PET tracers: Efficient modular synthesis, facile <sup>18</sup>F-radiolabelling, in vivo PET imaging and ex vivo fluorescence DP - 2014 May 01 TA - Journal of Nuclear Medicine PG - 1161--1161 VI - 55 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/55/supplement_1/1161.short 4100 - http://jnm.snmjournals.org/content/55/supplement_1/1161.full SO - J Nucl Med2014 May 01; 55 AB - 1161 Objectives A fluorescent PET probe that empowers seamless switching between PET and fluorescence imaging is highly desirable. Here we disclose a radiosynthetic strategy that amalgamates a dimeric peptide, a fluorophore, and an organotrifluoroborate prosthetic that affords 1-step aqueous 18F-labelling for the first time. This construct successfully provides fluorescent imaging for binding affinity assay, is labeled at high specific activity, and specifically targets the tumour in PET/optical imaging. Methods Rhodamine-BisRGD-BF3 (cpd 3) was simply synthesized in two steps using a copper-catalyzed click reaction from trisalkyne-BF3 (cpd 1). In terms of kit development, cpd 3 was aliquoted in quantities of 50 nmol for on-demand one-step labeling. The 18F-labeling was performed by 18F-19F isotope exchange. The tracer was obtained without HPLC purification. PET imaging and biodistribution were performed using anesthetized mice bearing U87M glioblastoma tumors. Results The synthesis of the cpd 3 from cpd 1 was achieved in reasonable chemical yield (~36%). 18F-labeled 3 (&gt;200 mCi) was achieved in good radiochemical yield (25%, n=3) with &gt;99% radiochemical purity. The specific activity was measured to be &gt;111 GBq/µmol by a standard curve. &lt;1% decomposition was detected after plasma incubation for two hours. Observed bone uptake was negligible. Very high tumour uptake (&gt;7.5% ID/g) detected at early time points slowly diminished to 5.6% ID/g at 120 mins post injection. Following PET scanning, fluorescent imaging was explored to visualize the tumour uptake at both high and low specific activities. Conclusions Here we successfully develop a new synthetic strategy for the facile and modular construction of dual-mode fluorescent/PET tracers. Given the broad applicability of click conjugations, synthon 1 is amenable to grafting various of peptides, as well as a broad range of fluorophores.