Radiosynthesis and Preclinical Evaluation of Ga-NOTA-Folate for PET Imaging of Folate Receptor β Positive Macrophages

Moisio, O.; Palani, S.; Virta, J.; Elo, P.; Liljenback, H.; Tolvanen, T.; Kakela, M.; Miner, M. G.; Atencio Herre, E.; Marjamaki, P.; Ord, T.; Heinaniemi, M.; Kaikkonen-Maatta, M.; Zhang, F.; Srinivasarao, M.; Knuuti, J.; Low, P. S.; Saraste, A.; Li, X.-G.; Roivainen, A.

doi:10.1101/2020.05.18.102483

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bioRxiv · 10.1101/2020.05.18.102483

Radiosynthesis and Preclinical Evaluation of Ga-NOTA-Folate for PET Imaging of Folate Receptor β Positive Macrophages

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Abstract

Folate receptor {beta} (FR-{beta}) is one of the markers expressed on macrophages and a promising target for imaging of inflammation. Here, we report the radiosynthesis and preclinical evaluation of [68Ga]Ga-NOTA-folate (68Ga-FOL). First, we determined the affinity of 68Ga-FOL using human FR-{beta} expressing cells. Then, we studied atherosclerotic mice with 68Ga-FOL and 18F-FDG PET/CT. After sacrifice, the tissues excised were measured with a {gamma}-counter for ex vivo biodistribution. Further, the tracer distribution and co-localization with macrophages in aorta cryosections were studied using autoradiography, hematoxylin-eosin staining and immunostaining with anti-Mac-3 antibody. Specificity of 68Ga-FOL was assessed in a blocking study with excess of folate glucosamine. As a last step, human radiation doses were extrapolated from rat PET data. We were able to produce 68Ga-FOL at high radioactivity concentration, with high molar activity and radiochemical purity. The cell binding studies showed high (5.1 {+/-} 1.1 nM) affinity of 68Ga-FOL to FR-{beta}. The myocardial uptake of 68Ga-FOL (SUV 0.43 {+/-} 0.06) was 20-folds lower compared to 18F-FDG (SUV 10.6 {+/-} 1.8, P = 0.001). The autoradiography and immunohistochemistry of aorta revealed that 68Ga-FOL radioactivity co-localized with Mac-3-positive macrophage-rich atherosclerotic plaques. The plaque-to-healthy vessel wall ratio of 68Ga-FOL (2.44 {+/-} 0.15) was significantly higher than that of 18F-FDG (1.93 {+/-} 0.22, P = 0.005). Blocking studies verified 68Ga-FOL specificity to FR. As estimated from rat data the human effective dose was 0.0105 mSv/MBq. The organ with highest absorbed dose was kidney (0.1420 mSv/MBq). In conclusion, 68Ga-FOL is a promising new FR-{beta}-targeted tracer for imaging macrophage-associated inflammation. TABLE OF CONTENT/ABSTRACT GRAPHIC O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

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Moisio, O., Palani, S., Virta, J., Elo, P., Liljenback, H., Tolvanen, T., Kakela, M., Miner, M. G., Atencio Herre, E., Marjamaki, P., Ord, T., Heinaniemi, M., Kaikkonen-Maatta, M., Zhang, F., Srinivasarao, M., Knuuti, J., Low, P. S., Saraste, A., Li, X.-G., Roivainen, A.. 2020-05-20. Radiosynthesis and Preclinical Evaluation of Ga-NOTA-Folate for PET Imaging of Folate Receptor β Positive Macrophages. https://doi.org/10.1101/2020.05.18.102483

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