Sinnes Jean-Philippe, Bauder-Wüst Ulrike, Schäfer Martin, Moon Euy Sung, Kopka Klaus, Rösch Frank
Johannes Gutenberg-University Mainz, Department of Chemistry/ TRIGA, Fritz-Strassmann-Weg 2, 55128, Mainz, Germany.
German Cancer Research Center (DKFZ), Division of Radiopharmaceutical Chemistry, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.
EJNMMI Radiopharm Chem. 2020 Nov 26;5(1):28. doi: 10.1186/s41181-020-00107-8.
The AAZTA chelator and in particular its bifunctional derivative AAZTA was recently investigated to demonstrate unique capabilities to complex diagnostic and therapeutic trivalent radiometals under mild conditions. This study presents a comparison of Ga, Sc and Lu-labeled AAZTA-PSMA-617 with DOTA-PSMA-617 analogues. We evaluated the radiolabeling characteristics, in vitro stability of the radiolabeled compounds and evaluated their binding affinity and internalization behavior on LNCaP tumor cells in direct comparison to the radiolabeled DOTA-conjugated PSMA-617 analogs.
AAZTA was synthesized in a five-step synthesis and coupled to the PSMA-617 backbone on solid phase. Radiochemical evaluation of AAZTA-PSMA-617 with Ga, Sc and Lu achieved quantitative radiolabeling of > 99% after less than 5 min at room temperature. Stabilities against human serum, PBS buffer and EDTA and DTPA solutions were analyzed. While there was a small degradation of the Ga complex over 2 h in human serum, PBS and EDTA/DTPA, the Sc and Lu complexes were stable at 2 h and remained stable over 8 h and 1 day. For all three compounds, i.e. [Ga]Ga-AAZTA-PSMA-617, [Sc]Sc-AAZTA-PSMA-617 and [Lu]Lu-AAZTA-PSMA-617, in vitro studies on PSMA-positive LNCaP cells were performed in direct comparison to radiolabeled DOTA-PSMA-617 yielding the corresponding inhibition constants (K). K values were in the range of 8-31 nM values which correspond with those of [Ga]Ga-DOTA-PSMA-617, [Sc]Sc-DOTA-PSMA-617 and [Lu]Lu-DOTA-PSMA-617, i.e. 5-7 nM, respectively. Internalization studies demonstrated cellular membrane to internalization ratios for the radiolabeled Ga, Sc and Lu-AAZTA5-PSMA-617 tracers (13-20%IA/10 cells) in the same range as the ones of the three radiolabeled DOTA-PSMA-617 tracers (17-20%IA/10 cells) in the same assay.
The AAZTA-PSMA-617 structure proved fast and quantitative radiolabeling with all three radiometal complexes at room temperature, excellent stability with Sc, very high stability with Lu and medium stability with Ga in human serum, PBS and EDTA/DTPA solutions. All three AAZTA-PSMA-617 tracers showed binding affinities and internalization ratios in LNCaP cells comparable with that of radiolabeled DOTA-PSMA-617 analogues. Therefore, the exchange of the chelator DOTA with AAZTA within the PSMA-617 binding motif has no negative influence on in vitro LNCaP cell binding characteristics. In combination with the faster and milder radiolabeling features, AAZTA-PSMA-617 thus demonstrates promising potential for in vivo application for theranostics of prostate cancer.
最近对AAZTA螯合剂，尤其是其二功能衍生物AAZTA进行了研究，以证明其在温和条件下络合诊断和治疗用三价放射性金属的独特能力。本研究对镓、钪和镥标记的AAZTA-PSMA-617与DOTA-PSMA-617类似物进行了比较。我们评估了放射性标记特性、放射性标记化合物的体外稳定性，并与放射性标记的DOTA共轭PSMA-617类似物直接比较，评估了它们对LNCaP肿瘤细胞的结合亲和力和内化行为。
AAZTA通过五步合成法合成，并在固相上与PSMA-617主链偶联。用镓、钪和镥对AAZTA-PSMA-617进行放射化学评估，在室温下不到5分钟后实现了>99%的定量放射性标记。分析了其对人血清、磷酸盐缓冲液（PBS）以及乙二胺四乙酸（EDTA）和二乙烯三胺五乙酸（DTPA）溶液的稳定性。虽然镓络合物在人血清、PBS和EDTA/DTPA中2小时内有少量降解，但钪和镥络合物在2小时时稳定，并在8小时和1天内保持稳定。对于所有三种化合物，即[镓]Ga-AAZTA-PSMA-617、[钪]Sc-AAZTA-PSMA-617和[镥]Lu-AAZTA-PSMA-617，在PSMA阳性的LNCaP细胞上进行了体外研究，并与放射性标记的DOTA-PSMA-617进行了直接比较，得出相应的抑制常数（K）。K值在8-31 nM范围内，与[镓]Ga-DOTA-PSMA-617、[钪]Sc-DOTA-PSMA-617和[镥]Lu-DOTA-PSMA-617的K值相当，分别为5-7 nM。内化研究表明，放射性标记的镓、钪和镥-AAZTA5-PSMA-617示踪剂的细胞膜到内化比率（13-20%IA/10个细胞）与同一项试验中三种放射性标记的DOTA-PSMA-示踪剂的比率（17-20%IA/10个细胞）处于同一范围。
AAZTA-PSMA-617结构在室温下用所有三种放射性金属络合物均可实现快速定量放射性标记，在人血清、PBS和EDTA/DTPA溶液中，与钪具有优异的稳定性，与镥具有非常高的稳定性，与镓具有中等稳定性。所有三种AAZTA-PSMA-617示踪剂在LNCaP细胞中的结合亲和力和内化比率与放射性标记的DOTA-PSMA-617类似物相当。因此，在PSMA-617结合基序内用AAZTA替换螯合剂DOTA对体外LNCaP细胞结合特性没有负面影响。结合更快、更温和的放射性标记特性，AAZTA-PSMA-617因此显示出在前列腺癌诊疗一体化体内应用中的潜在前景。
