Chair for Pharmaceutical Radiochemistry, Technische Universität München, Garching, Germany
Chair for Pharmaceutical Radiochemistry, Technische Universität München, Garching, Germany.
J Nucl Med. 2019 Jan;60(1):71-78. doi: 10.2967/jnumed.118.212720. Epub 2018 Sep 20.
The prostate-specific membrane antigen (PSMA)-targeted radiotracers Ga/Lu-PSMA-I&T and Tc-PSMA-I&S (for maging and urgery) are currently successfully used for clinical PET imaging, radionuclide therapy, and radioguided surgery of metastatic prostate cancer. To additionally exploit the high sensitivity and spatial resolution of fluorescence imaging for improved surgical guidance, a PSMA-I&T-based hybrid tracer, PSMA-I&F (DOTAGA-k(Sulfo-Cy5)-y-nal-k-Sub-KuE), has been developed and evaluated. The in vitro PSMA-targeting efficiency of PSMA-I&F, the reference PSMA-I&T, and their corresponding Ga-/Ga- and Lu/Lu counterparts was determined in LNCaP cells via competitive binding assays (IC) and dual-tracer radioligand and fluorescence internalization studies. Biodistribution and small-animal PET imaging studies were performed in CB17 SCID and LNCaP xenograft-bearing SHO mice, respectively, and complemented by intraoperative far-red fluorescence imaging using a clinical laparoscope. Additionally, fully automated serial cryosectioning and fluorescence imaging of 1 tumor-bearing animal as well as PSMA immunohistochemistry and fluorescence microscopy of organ cryosections (tumor, kidney, spleen) were also performed. Compared with the parent PSMA-I&T analogs, the PSMA affinities of PSMA-I&F and its Ga-/Lu-complexes remained high and unaffected by dye conjugation (7.9 < IC < 10.5 nM for all ligands). The same was observed for the internalization of Ga- and Lu-PSMA-I&F. In vivo, blood clearance of Ga- and Lu-PSMA-I&F was only slightly delayed by high plasma protein binding (94%-95%), and very low accumulation in nontarget organs was observed already at 1 h after injection. Dynamic PET imaging confirmed PSMA-specific (as demonstrated by coinjection of 2-PMPA) uptake into the LNCaP xenograft (4.5% ± 1.8 percentage injected dose per gram) and the kidneys (106% ± 23 percentage injected dose per gram). Tumor-to-background ratios of 2.1, 5.2, 9.6, and 9.6 for blood, liver, intestines, and muscle, respectively, at 1 h after injection led to excellent imaging contrast in Ga-PSMA-I&F PET and in intraoperative fluorescence imaging. Furthermore, fluorescence imaging of tissue cryosections allowed high-resolution visualization of intraorgan PSMA-I&F distribution in vivo and its correlation with PSMA expression as determined by immunohistochemistry. Thus, with its high PSMA-targeting efficiency and favorable pharmacokinetic profile, Ga/Lu-PSMA-I&F serves as an excellent proof-of-concept compound for the general feasibility of PSMA-I&T-based hybrid imaging. The PSMA-I&T scaffold represents a versatile PSMA-targeted lead structure, allowing relatively straightforward adaptation to the different structural requirements of dedicated nuclear or hybrid imaging agents.
前列腺特异性膜抗原(PSMA)靶向放射性示踪剂 Ga/Lu-PSMA-I&T 和 Tc-PSMA-I&S(用于成像和手术)目前已成功用于转移性前列腺癌的临床 PET 成像、放射性核素治疗和放射性引导手术。为了进一步利用荧光成像的高灵敏度和空间分辨率来改善手术指导,已经开发并评估了一种基于 PSMA-I&T 的杂交示踪剂 PSMA-I&F(DOTAGA-k(Sulfo-Cy5)-y-nal-k-Sub-KuE)。 通过竞争性结合测定(IC)和双示踪放射性配体和荧光内化研究,在 LNCaP 细胞中测定了 PSMA-I&F、参比 PSMA-I&T 及其相应的 Ga-/Ga-和 Lu/Lu 对应物的体外 PSMA 靶向效率。在 CB17 SCID 和 LNCaP 异种移植荷瘤 SHO 小鼠中分别进行了生物分布和小动物 PET 成像研究,并通过临床腹腔镜进行术中远红荧光成像进行补充。此外,还对 1 只荷瘤动物进行了全自动连续冷冻切片和荧光成像,以及对器官冷冻切片(肿瘤、肾脏、脾脏)进行 PSMA 免疫组织化学和荧光显微镜检查。 与母体 PSMA-I&T 类似物相比,PSMA-I&F 及其 Ga-/Lu 复合物的 PSMA 亲和力仍然很高,并且不受染料偶联的影响(所有配体的 IC<7.9-10.5 nM)。Ga-和 Lu-PSMA-I&F 的内化也是如此。体内,Ga-和 Lu-PSMA-I&F 的血液清除率仅因高血浆蛋白结合(94%-95%)而略有延迟,并且在注射后 1 小时已观察到非靶器官的低蓄积。动态 PET 成像证实了 PSMA 的特异性(如通过 2-PMPA 共注射所证明)摄取到 LNCaP 异种移植物(每克 4.5%±1.8%注入剂量)和肾脏(每克 106%±23%注入剂量)。注射后 1 小时时,血液、肝脏、肠和肌肉的肿瘤与背景比分别为 2.1、5.2、9.6 和 9.6,导致 Ga-PSMA-I&F PET 和术中荧光成像的出色成像对比度。此外,组织冷冻切片的荧光成像允许高分辨率可视化体内 PSMA-I&F 分布及其与免疫组织化学确定的 PSMA 表达的相关性。 因此,Ga/Lu-PSMA-I&F 具有高 PSMA 靶向效率和良好的药代动力学特征,是 PSMA-I&T 基杂交成像一般可行性的极好概念验证化合物。PSMA-I&T 支架代表了一种多功能的 PSMA 靶向先导结构,允许相对简单地适应专用核素或杂交成像剂的不同结构要求。