Key Laboratory of Protein and Peptide Pharmaceuticals, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People's Republic of China.
University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
Bioconjug Chem. 2020 May 20;31(5):1510-1521. doi: 10.1021/acs.bioconjchem.0c00170. Epub 2020 May 7.
In this study, we reported a Tc-labeled integrin α-targeted peptide as the molecular imaging probe for tumor imaging by single-photon emission computed tomography (SPECT). We found that replacing Cys-Cys cyclized RWY peptide (sequence: cCRWYDENAC) with lactam-bridged cyclic cKiE peptide (sequence: cKRWYDENAisoE) did not sacrifice the integrin α-binding affinity and specificity of cKiE radiotracer. To further improve the radiotracer's tumor targeting capability, the dimerized cKiE peptide (termed cKiE2) was designed, and the corresponding radiotracer Tc-cKiE2 was evaluated for tumor uptake and in vivo pharmacokinetics properties in tumor models. We found that cKiE2 showed higher binding affinity to integrin α than did monomeric RWY or cKiE peptide. The biodistribution results showed that the tumor uptake of Tc-cKiE2 was twice higher than that of Tc-RWY (3.20 ± 0.12 vs 1.26 ± 0.06 %ID/g, < 0.001) at 0.5 h postinjection. The tumor to nontargeting tissue ratios were also enhanced in most normal organs. Specificity of Tc-cKiE2 for integrin α was demonstrated by competitive blocking of tumor uptake with excess cold peptide (3.20 ± 0.24 to 1.38 ± 0.23 %ID/g, < 0.001). The integrin α-positive tumors were clearly visualized by Tc-cKiE2/SPECT with low background except with a relatively high kidney uptake. The tumor uptake of Tc-cKiE2 correlates well with the tumor integrin α expression levels in a linear fashion (R = 0.9623). We also compared Tc-cKiE2 with an integrin αβ-targeted radiotracer Tc-3PRGD in the orthotopic hepatocellular carcinoma tumor models. We found that the orthotopic tumor was clearly visualized with Tc-cKiE2. Tc-3PRGD imaging did not show tumor contours in situ as clearly as Tc-cKiE2. The tumor-to-liver ratios of Tc-cKiE2 and Tc-3PRGD were 2.20 ± 0.17 and 0.85 ± 0.20. In conclusion, Tc-cKiE2 is an improved SPECT radiotracer for imaging integrin α-positive tumors and has great potential for further clinical application.
在这项研究中，我们报告了一种 Tc 标记的整合素 α 靶向肽作为单光子发射计算机断层扫描（SPECT）肿瘤成像的分子成像探针。我们发现，用酰胺桥接的环化 cKiE 肽（序列：cKRWYDENAisoE）取代半胱氨酸-半胱氨酸环化 RWY 肽（序列：cCRWYDENAC）不会牺牲 cKiE 放射性示踪剂与整合素 α 的结合亲和力和特异性。为了进一步提高放射性示踪剂的肿瘤靶向能力，设计了二聚化的 cKiE 肽（称为 cKiE2），并评估了相应的放射性示踪剂 Tc-cKiE2 在肿瘤模型中的肿瘤摄取和体内药代动力学特性。我们发现 cKiE2 与整合素 α 的结合亲和力高于单体 RWY 或 cKiE 肽。生物分布结果表明，Tc-cKiE2 在 0.5 h 时的肿瘤摄取比 Tc-RWY 高两倍（3.20 ± 0.12%ID/g 比 1.26 ± 0.06%ID/g，<0.001）。大多数正常器官中的肿瘤与非靶向组织的比值也得到了增强。用过量冷肽竞争阻断肿瘤摄取证明了 Tc-cKiE2 对整合素 α 的特异性（3.20 ± 0.24%ID/g 比 1.38 ± 0.23%ID/g，<0.001）。Tc-cKiE2/SPECT 除了肾脏摄取相对较高外，还能清晰地显示整合素 α 阳性肿瘤，背景低。Tc-cKiE2 的肿瘤摄取与肿瘤整合素 α 表达水平呈线性相关（R = 0.9623）。我们还比较了 Tc-cKiE2 与原位肝癌肿瘤模型中的整合素 αβ 靶向放射性示踪剂 Tc-3PRGD。我们发现 Tc-cKiE2 可以清晰地显示原位肿瘤。Tc-3PRGD 成像没有像 Tc-cKiE2 那样清晰地显示肿瘤轮廓。Tc-cKiE2 和 Tc-3PRGD 的肿瘤与肝脏比值分别为 2.20 ± 0.17 和 0.85 ± 0.20。总之，Tc-cKiE2 是一种改良的 SPECT 放射性示踪剂，用于成像整合素 α 阳性肿瘤，具有很大的临床应用潜力。
