Russell H. Morgan Department of Radiology and Radiological Science, Baltimore, MD, USA.
Sidney Kimmel Comprehensive Cancer Center, Baltimore, MD, USA.
Eur J Nucl Med Mol Imaging. 2022 Nov;49(13):4369-4381. doi: 10.1007/s00259-022-05933-3. Epub 2022 Aug 15.
We developed a theranostic radiopharmaceutical that engages two key cell surface proteases, fibroblast activation protein alpha (FAP) and prostate-specific membrane antigen (PSMA), each frequently overexpressed within the tumor microenvironment (TME). The latter is also expressed in most prostate tumor epithelium. To engage a broader spectrum of cancers for imaging and therapy, we conjugated small-molecule FAP and PSMA-targeting moieties using an optimized linker to provide Cu-labeled compounds.
We synthesized FP-L1 and FP-L2 using two linker constructs attaching the FAP and PSMA-binding pharmacophores. We determined in vitro inhibition constants (K) for FAP and PSMA. Cell uptake assays and flow cytometry were conducted in human glioma (U87), melanoma (SK-MEL-24), prostate cancer (PSMA + PC3 PIP and PSMA - PC3 flu), and clear cell renal cell carcinoma lines (PSMA + /PSMA - 786-O). Quantitative positron emission tomography/computed tomography (PET/CT) and tissue biodistribution studies were performed using U87, SK-MEL-24, PSMA + PC3 PIP, and PSMA + 786-O experimental xenograft models and the KPC genetically engineered mouse model of pancreatic cancer.
Cu-FP-L1 and Cu-FP-L2 were produced in high radiochemical yields (> 98%) and molar activities (> 19 MBq/nmol). K values were in the nanomolar range for both FAP and PSMA. PET imaging and biodistribution studies revealed high and specific targeting of Cu-FP-L1 and Cu-FP-L2 for FAP and PSMA. Cu-FP-L1 displayed more favorable pharmacokinetics than Cu-FP-L2. In the U87 tumor model at 2 h post-injection, tumor uptake of Cu-FP-L1 (10.83 ± 1.02%ID/g) was comparable to Cu-FAPI-04 (9.53 ± 2.55%ID/g). Cu-FP-L1 demonstrated high retention 5.34 ± 0.29%ID/g at 48 h in U87 tumor. Additionally, Cu-FP-L1 showed high retention in PSMA + PC3 PIP tumor (12.06 ± 0.78%ID/g at 2 h and 10.51 ± 1.82%ID/g at 24 h).
Cu-FP-L1 demonstrated high and specific tumor targeting of FAP and PSMA. This compound should enable imaging of lesions expressing FAP, PSMA, or both on the tumor cell surface or within the TME. FP-L1 can readily be converted into a theranostic for the management of heterogeneous tumors.
我们开发了一种治疗性放射性药物，该药物结合了两种关键的细胞表面蛋白酶，成纤维细胞激活蛋白α（FAP）和前列腺特异性膜抗原（PSMA），这两种蛋白酶在肿瘤微环境（TME）中均过度表达。后者也在大多数前列腺肿瘤上皮中表达。为了对更广泛的癌症进行成像和治疗，我们使用优化的接头将小分子 FAP 和 PSMA 靶向部分缀合，以提供 Cu 标记的化合物。
我们使用连接 FAP 和 PSMA 结合药效团的两种接头构建物合成了 FP-L1 和 FP-L2。我们确定了 FAP 和 PSMA 的体外抑制常数（K）。在人神经胶质瘤（U87）、黑色素瘤（SK-MEL-24）、前列腺癌（PSMA+PC3 PIP 和 PSMA-PC3 flu）和透明细胞肾细胞癌系（PSMA+/PSMA-786-O）中进行了细胞摄取测定和流式细胞术。使用 U87、SK-MEL-24、PSMA+PC3 PIP 和 PSMA+786-O 实验性异种移植模型和 KPC 基因工程胰腺癌小鼠模型进行了定量正电子发射断层扫描/计算机断层扫描（PET/CT）和组织生物分布研究。
Cu-FP-L1 和 Cu-FP-L2 的放射化学产率（>98%）和摩尔活性（>19 MBq/nmol）均较高。对于 FAP 和 PSMA，K 值均在纳摩尔范围内。PET 成像和生物分布研究表明，Cu-FP-L1 和 Cu-FP-L2 对 FAP 和 PSMA 的靶向性高且特异性强。与 Cu-FP-L2 相比，Cu-FP-L1 的药代动力学更有利。在注射后 2 小时的 U87 肿瘤模型中，Cu-FP-L1 的肿瘤摄取量（10.83±1.02%ID/g）与 Cu-FAPI-04（9.53±2.55%ID/g）相当。在 U87 肿瘤中，Cu-FP-L1 在 48 小时时的保留率为 5.34±0.29%ID/g。此外，Cu-FP-L1 在 PSMA+PC3 PIP 肿瘤中的保留率较高（2 小时时为 12.06±0.78%ID/g，24 小时时为 10.51±1.82%ID/g）。
Cu-FP-L1 对 FAP 和 PSMA 的肿瘤靶向性高且特异性强。该化合物应能够对肿瘤细胞表面或肿瘤微环境中表达 FAP、PSMA 或两者的病变进行成像。FP-L1 可以很容易地转化为治疗性药物，用于管理异质性肿瘤。
