Background: The red fluorescent dye Sulforhodamine 101 (SR101) has been used in
neuroscience research as a useful tool for staining of astrocytes, since it has been reported as a
marker of astroglia in the neocortex of rodents in vivo. The aim of this work is to label SR101 with
positron emission radionuclides, in order to provide a radiotracer to study its biological behavior.
This is the first attempt to label SR101 by [18F], using a chemical derivatization via a sulfonamidelinker
and a commercially available platform.
Methods: The synthesis of SR101 N-(3-Bromopropyl) sulfonamide and SR101 N-(3-
Fluoropropyl) sulfonamide (2B-SRF101) was carried out. The radiosynthesis of SR101 N-(3-
[18F]Fluoropropyl) sulfonamide ([18F]2B-SRF101) was performed in a TRACERlab® FX-FN.
Different labeling conditions were tested. Three pilot batches were produced and quality control
was performed. Lipophilicity, plasma protein binding and radiochemical stability of [18F]2BSRF101
in final formulation and in plasma were determined.
Results: SR101 N-(3-Bromopropyl) sulfonamide was synthetized as a precursor for radiolabeling
with [18F]. 2B-SRF101 was prepared for analytical purpose. [18F]2B-SRF101 was obtained with
radiochemical purity of (97.0 ± 0.6%). The yield of the whole synthesis was (11.9 ± 1.7 %), nondecay
corrected. [18F]2B-SRF101 was found to be stable in final formulation and in plasma. The
octanol-water partition coefficient was (Log POCT = 1.88 ± 0.14). The product showed a high percentage
of plasma protein binding.
Conclusions: The derivatization of SR101 via sulfonamide-linker and the first radiosynthesis of
F]2B-SRF101 were performed. It was obtained in accordance with quality control specifications.
In vitro stability studies verified that [18F]2B-SRF101 was suitable for preclinical evaluations.