Vaidyanathan Ganesan, McDougald Darryl, Grasfeder Linda, Zalutsky Michael R, Chin Bennett
Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Appl Radiat Isot. 2011 Oct;69(10):1401-6. doi: 10.1016/j.apradiso.2011.05.004. Epub 2011 May 19.
Radiolabeled amino acids have been used extensively in oncology both as diagnostic and therapeutic agents. In our pursuit to develop radiopharmaceuticals to target breast cancer, we were interested in determining the uptake of radioiodinated 4-iodophenylalanine, among other labeled amino acids, in breast cancer cells. In this work, we have developed an alternative method for the synthesis of this agent. The novel tin precursor, (S)-tert-butyl 2-(tert-butoxycarbonylamino)-3-(4-(tributylstannyl)phenyl)propanoate (3) was synthesized from the known, corresponding iodo derivative. Initially, the labeled 4-iodophenylalanine was synthesized from the above tin precursor in two steps with radiochemical yields of 91.6 ± 2.7% and 83.7 ± 1.7% (n=5), for the radioiodination (first) and deprotection (second) step, respectively. Subsequently, it was synthesized in a single step with an average radiochemical yield of 94.8 ± 3.4% (n=5). After incubation with MCF-7 breast cancer cells for 60 min, an uptake of up to 49.0 ± 0.7% of the input dose was seen; in comparison, the uptake of [¹⁴C]phenylalanine under the same conditions was 55.9 ± 0.5%. Furthermore, the uptake of both tracers was inhibited to a similar degree in a concentration-dependent manner by both unlabeled phenylalanine and 4-iodophenylalanine. With [¹⁴C]phenylalanine as the tracer, IC₅₀ values of 1.45 and 2.50 mM were obtained for Phe and I-Phe, respectively, and these values for [¹²⁵I]I-Phe inhibition were 1.3 and 1.0 mM. In conclusion, an improved and convenient method for the synthesis of no-carrier-added 4-[(⁎)I]phenylalanine was developed and the radiotracer prepared by this route demonstrated an amino acid transporter-mediated uptake in MCF-7 breast cancer cells in vitro that was comparable to that of [¹⁴C]phenylalanine.
放射性标记的氨基酸在肿瘤学中已被广泛用作诊断和治疗剂。在我们开发用于靶向乳腺癌的放射性药物的过程中，我们有兴趣确定放射性碘化的4-碘苯丙氨酸以及其他标记氨基酸在乳腺癌细胞中的摄取情况。在这项工作中，我们开发了一种合成该试剂的替代方法。新型锡前体（S）-叔丁基2-（叔丁氧羰基氨基）-3-（4-（三丁基锡烷基）苯基）丙酸酯（3）由已知的相应碘代衍生物合成。最初，标记的4-碘苯丙氨酸由上述锡前体分两步合成，放射性碘化（第一步）和脱保护（第二步）步骤的放射性化学产率分别为91.6±2.7%和83.7±1.7%（n = 5）。随后，它以单步合成，平均放射性化学产率为94.8±3.4%（n = 5）。与MCF-7乳腺癌细胞孵育60分钟后，观察到摄取量高达输入剂量的49.0±0.7%；相比之下，在相同条件下[¹⁴C]苯丙氨酸的摄取量为55.9±0.5%。此外，未标记的苯丙氨酸和4-碘苯丙氨酸均以浓度依赖性方式将两种示踪剂的摄取抑制到相似程度。以[¹⁴C]苯丙氨酸作为示踪剂，苯丙氨酸（Phe）和4-碘苯丙氨酸（I-Phe）的IC₅₀值分别为1.45和2.50 mM，而[¹²⁵I]I-Phe抑制的这些值为1.3和1.0 mM。总之，开发了一种改进的、方便的合成无载体添加的4-[(⁎)I]苯丙氨酸的方法，通过该途径制备的放射性示踪剂在体外MCF-7乳腺癌细胞中表现出与[¹⁴C]苯丙氨酸相当的氨基酸转运体介导的摄取。
