Zoppolo Florencia, Porcal Williams, Oliver Patricia, Savio Eduardo, Engler Henry
Uruguayan Centre of Molecular Imaging (CUDIM), Montevideo, Uruguay.
Facultad de Quimica, Universidad de la Republica (UdelaR), Montevideo, Uruguay.
Curr Radiopharm. 2017 Nov 10;10(3):203-211. doi: 10.2174/1874471010666170718171441.
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.
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.
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.
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.
甘氨酸N-甲基转移酶是一种在某些肿瘤组织中过表达的酶。它以S-腺苷甲硫氨酸（SAM或AdoMet）为底物催化甘氨酸的甲基化。SAM参与多种生化过程，包括转甲基反应。因此，[11C]SAM可用于评估肿瘤中的转甲基活性。报道的[11C]SAM合成的唯一方法是一种存在若干局限性的酶促过程。我们提出一种通过一锅法合成获得[11C]SAM的新化学方法。
在自动TRACERlab® FX C Pro模块中进行[11C]SAM合成的优化。通过改变甲基化剂、前体用量、温度和反应时间进行不同的标记条件实验。使用半制备型高效液相色谱法对化合物进行纯化。评估放射化学稳定性、亲脂性和血浆蛋白结合情况。
最佳标记条件是以[11C]CH3OTf作为甲基化剂，5 mg前体溶解于甲酸中，在60℃下反应1分钟。[11C]SAM以非对映异构体混合物的形式获得。制备了三批产品，并根据规格进行了质量控制。[11C]SAM在最终制剂和血浆中稳定。[11C]SAM的log POCT值为（-2.01±0.07）（n = 4），其血浆蛋白结合值较低。
优化了一种制备[11C]SAM的新化学方法。获得的放射性示踪剂为非对映异构体混合物，（R,S）-异构体与（S,S）-异构体的比例为53:47。该化合物符合质量控制规格。验证了其体外稳定性。该化合物适用于进行临床前和临床评估。
