A new S-alkylated cysteine-derivatized tumor targeting agent, 2,2′-(12-(2-((2-acetamido-2-carboxyethyl)thio)acetamido)-11,13-dioxo-1,4,7,10-tetraazacyclotridecane-4,7-diyl)diacetic acid was developed for positron emission tomography (PET) imaging. N-Acetyl cysteine (NAC) was conjugated to ATRIDAT as a specific targeting agent toward L-type and ASC amino acid transporter systems in the oncogenic cells. NAC was attached via S-alkylation to prevent its incorporation at undesired recognition sites affecting the signal-to-noise ratio. NAC-ATRIDAT was subjected to gallium-68 complexation with >75% radiolabeling yield. The radiocomplex was purified through the tc18 cartridge to obtain 99.89% radiochemical yield. IC-50 of the NAC-ATRIDAT conjugate was 0.8 mM in A549 cells as evaluated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide assay. Binding affinity experiments on A549 cells showed noteworthy binding with K_D in the nanomolar range. A time course study showed a K_m value of 0.19 μM and V_max value of 0.49 pmol/μg protein/min showing reasonable tumor kinetics. Efflux studies showed that the synthesized radioligand is transported majorly by LAT followed by the ASC system. Clearance was found to be renal with 7.67 ± 1.48% ID/g uptake at 30 min which substantially declined to 0.52 ± 0.% ID/g at 4 h. A significant uptake of 10.06 ± 1.056% ID/g was observed at the tumor site in mice at 1 h. μPET images revealed a high contrast with a tumor-to-kidney ratio of 4.8 and a tumor-to-liver ratio of 35.85 at 1 h after injection. These preclinical in vitro and in vivo evaluation supports its potential on the way of becoming a successful ⁶⁸Ga-radiolabeled amino acid-based PET imaging agent.

中文翻译：

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新型S-烷基化半胱氨酸衍生物与C取代的大环电子共轭正电子发射断层扫描的放射性标记和临床前评价。

一种新的S-烷基化半胱氨酸衍生的肿瘤靶向剂2,2'-（12-（2-（（（2-acetamido-2-羧乙基）硫代）乙酰氨基）-11,13-dioxo-1,4,7，开发了10-四氮杂环十三烷-4,7-二基）二乙酸用于正电子发射断层扫描（PET）成像。ñ-乙酰半胱氨酸（NAC）与ATRIDAT偶联，作为对致癌细胞中L型和ASC氨基酸转运系统的特异性靶向剂。NAC通过S-烷基化连接，以防止其掺入不希望的识别位点，从而影响信噪比。将NAC-ATRIDAT进行镓68络合，放射标记收率> 75％。通过tc18柱纯化放射性复合物，从而获得99.89％的放射化学产率。通过3-（4,5-二甲基噻唑-2-基）-2,5-二苯基四唑鎓溴化物测定评估，NAC-ATRIDAT缀合物的IC-50在A549细胞中为0.8 mM。在A549细胞上的结合亲和力实验表明，在纳摩尔范围内，与K _D的结合非常明显。时程研究显示K _m值为0.19μM，V _max 值为0.49 pmol /μg蛋白质/分钟，显示出合理的肿瘤动力学。外排研究表明，合成的放射性配体主要由LAT转运，然后由ASC系统转运。发现清除率为肾脏，在30分钟时摄取7.67±1.48％ID / g，在4 h时显着下降至0.52±0.％ID / g。在1小时时，在小鼠的肿瘤部位观察到10.06±1.056％ID / g的显着摄取。μPET图像显示出高对比度，注射后1小时的肿瘤与肾脏的比率为4.8，肿瘤与肝脏的比率为35.85。这些临床前的体外和体内评估支持了其成为成功的⁶⁸ Ga-放射性标记的氨基酸基PET显像剂的潜力。