Radiosynthesis and preclinical evaluation of [68Ga]Ga-NOTA-folate for PET imaging of folate receptor β-positive macrophages

Sci Rep. 2020 Aug 12;10(1):13593. doi: 10.1038/s41598-020-70394-3.

Abstract

Folate receptor β (FR-β), a marker expressed on macrophages, is a promising target for imaging of inflammation. Here, we report the radiosynthesis and preclinical evaluation of [68Ga]Ga-NOTA-folate (68Ga-FOL). After determining the affinity of 68Ga-FOL using cells expressing FR-β, we studied atherosclerotic mice with 68Ga-FOL and 18F-FDG PET/CT. In addition, we studied tracer distribution and co-localization with macrophages in aorta cryosections using autoradiography, histology, and immunostaining. The specificity of 68Ga-FOL was assessed in a blocking study with folate glucosamine. As a final step, human radiation doses were extrapolated from rat PET data. We were able to produce 68Ga-FOL with high radiochemical purity and moderate molar activity. Cell binding studies revealed that 68Ga-FOL had 5.1 nM affinity for FR-β. Myocardial uptake of 68Ga-FOL was 20-fold lower than that of 18F-FDG. Autoradiography and immunohistochemistry of the 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 was significantly higher than that of 18F-FDG. Blocking studies verified that 68Ga-FOL was specific for FR. Based on estimations from rat data, the human effective dose was 0.0105 mSv/MBq. Together, these findings show that 68Ga-FOL represents a promising new FR-β-targeted tracer for imaging macrophage-associated inflammation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CHO Cells
  • Cricetinae
  • Cricetulus
  • Fluorodeoxyglucose F18 / chemistry
  • Fluorodeoxyglucose F18 / pharmacokinetics
  • Folate Receptor 2 / metabolism*
  • Folic Acid / chemistry*
  • Gallium Radioisotopes / chemistry
  • Gallium Radioisotopes / pharmacokinetics
  • Heterocyclic Compounds, 1-Ring / chemistry*
  • Humans
  • Macrophages / metabolism*
  • Mice
  • Plaque, Atherosclerotic / metabolism
  • Positron Emission Tomography Computed Tomography / methods
  • Positron-Emission Tomography / methods*
  • Radiopharmaceuticals / chemistry*
  • Radiopharmaceuticals / pharmacokinetics
  • Rats
  • Tissue Distribution

Substances

  • Folate Receptor 2
  • Gallium Radioisotopes
  • Heterocyclic Compounds, 1-Ring
  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18
  • 1,4,7-triazacyclononane-N,N',N''-triacetic acid
  • Folic Acid
  • Gallium-68