Automated One-pot Radiosynthesis of [11C]S-adenosyl Methionine

Author(s): Florencia Zoppolo, Williams Porcal, Patricia Oliver, Eduardo Savio*, Henry Engler.

Journal Name: Current Radiopharmaceuticals

Volume 10 , Issue 3 , 2017

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Abstract:

Background: Glycine N-methyltransferase is an enzyme overexpressed in some neoplastic tissues. It catalyses the methylation of glycine using S-adenosyl methionine (SAM or AdoMet) as substrate. SAM is involved in a great variety of biochemical processes, including transmethylation reactions. Thus, [11C]SAM could be used to evaluate transmethylation activity in tumours. The only method reported for [11C]SAM synthesis is an enzymatic process with several limitations. We propose a new chemical method to obtain [11C]SAM, through a one-pot synthesis.

Method: The optimization of [11C]SAM synthesis was carried out in the automated TRACERlab® FX C Pro module. Different labelling conditions were performed varying methylating agent, precursor amount, temperature and reaction time. The compound was purified using a semipreparative HPLC. Radiochemical stability, lipophilicity and plasma protein binding were evaluated.

Results: The optimum labelling conditions were [11C]CH3OTf as the methylating agent, 5 mg of precursor dissolved in formic acid at 60 °C for 1 minute. [11C]SAM was obtained as a diastereomeric mixture. Three batches were produced and quality control was performed according to specifications. [11C]SAM was stable in final formulation and in plasma. Log POCT obtained for [11C]SAM was (-2,01 ± 0,07) (n=4), and its value for plasma protein binding was low.

Conclusion: A new chemical method to produce [11C]SAM was optimized. The radiotracer was obtained as a diastereomeric mixture with a 53:47 [(R,S)-isomer: (S,S)-isomer] ratio. The compound was within the quality control specifications. In vitro stability was verified. This compound is suitable to perform preclinical and clinical evaluations.

Keywords: S-adenosyl methionine, Glycine N-methyltransferase, 11C[SAM], PET radiotracers, radiochemistry, 11C-labelling, automated synthesis.

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Article Details

VOLUME: 10
ISSUE: 3
Year: 2017
Page: [203 - 211]
Pages: 9
DOI: 10.2174/1874471010666170718171441

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