Development of a Radioiodinated Triazolopyrimidine Probe for Nuclear Medical Imaging of Fatty Acid Binding Protein 4
作者:Kantaro Nishigori、Takashi Temma、Satoru Onoe、Sotaro Sampei、Ikuo Kimura、Masahiro Ono、Hideo Saji
DOI:10.1371/journal.pone.0094668
日期:——
Fatty acid binding protein 4 (FABP4) is the most well-characterized FABP isoform. FABP4 regulates inflammatory pathways in adipocytes and macrophages and is involved in both inflammatory diseases and tumor formation. FABP4 expression was recently reported for glioblastoma, where it may participate in disease malignancy. While FABP4 is a potential molecular imaging target, with the exception of a tritium labeled probe there are no reports of other nuclear imaging probes that target this protein. Here we designed and synthesized a nuclear imaging probe, [123I]TAP1, and evaluated its potential as a FABP4 targeting probe in in vitro and in vivo assays. We focused on the unique structure of a triazolopyrimidine scaffold that lacks a carboxylic acid to design the TAP1 probe that can undergo facilitated delivery across cell membranes. The affinity of synthesized TAP1 was measured using FABP4 and 8-anilino-1-naphthalene sulfonic acid. [125I]TAP1 was synthesized by iododestannylation of a precursor, followed by affinity and selectivity measurements using immobilized FABPs. Biodistributions in normal and C6 glioblastoma-bearing mice were evaluated, and excised tumors were subjected to autoradiography and immunohistochemistry. TAP1 and [125I]TAP1 showed high affinity for FABP4 (Ki = 44.5±9.8 nM, Kd = 69.1±12.3 nM). The FABP4 binding affinity of [125I]TAP1 was 11.5- and 35.5-fold higher than for FABP3 and FABP5, respectively. In an in vivo study [125I]TAP1 displayed high stability against deiodination and degradation, and moderate radioactivity accumulation in C6 tumors (1.37±0.24% dose/g 3 hr after injection). The radioactivity distribution profile in tumors partially corresponded to the FABP4 positive area and was also affected by perfusion. The results indicate that [125I]TAP1 could detect FABP4 in vitro and partly in vivo. As such, [125I]TAP1 is a promising lead compound for further refinement for use in in vivo FABP4 imaging.
脂肪酸结合蛋白4(FABP4)是最为熟知的FABP亚型。FABP4在脂肪细胞和巨噬细胞中调节炎症途径,并参与炎症性疾病和肿瘤形成。最近有研究报道FABP4在胶质母细胞瘤中的表达,可能与疾病恶性程度相关。虽然FABP4是一个潜在的分子影像靶点,但除了一个氚标记探针外,目前尚无针对该蛋白的其他核成像探针的报道。在本研究中,我们设计并合成了一种核成像探针[123I]TAP1,并评估其作为FABP4靶向探针在体外和体内实验中的潜力。我们专注于缺乏羧酸基的1,2,4-三唑并嘧啶骨架的独特结构,以设计TAP1探针,该探针能促进透过细胞膜的传递。合成的TAP1的亲和力使用FABP4和8-苯氨基-1-纳夫thalene磺酸进行测量。[125I]TAP1通过前体的碘去锡化合成,随后使用固定化FABP进行亲和力和选择性测定。在正常小鼠和C6胶质母细胞瘤携带小鼠中评估了其生物分布,切除的肿瘤经过自显影和免疫组织化学分析。TAP1和[125I]TAP1对FABP4表现出高亲和力(Ki = 44.5±9.8 nM,Kd = 69.1±12.3 nM)。[125I]TAP1对FABP4的结合亲和力分别是对FABP3和FABP5的11.5倍和35.5倍。在体内研究中,[125I]TAP1对去碘化和降解表现出高稳定性,并且在C6肿瘤中显示出中等的放射性积累(注射后3小时剂量/g为1.37±0.24%)。肿瘤中的放射性分布曲线部分对应于FABP4阳性区域,并受到灌注的影响。结果表明,[125I]TAP1能够在体外及部分在体内检测FABP4。因此,[125I]TAP1是用于进一步改进以实现体内FABP4成像的有前景的候选化合物。