Centro de Radiofarmácia, Instituto de Pesquisas Energéticas e Nucleares, São Paulo, Brazil.
Clinics (Sao Paulo). 2011;66(2):327-36. doi: 10.1590/s1807-59322011000200024.
Cancer has been investigated using various pre-targeting techniques or models focusing on radiobombesin analogues; however, both are not offered together. In this study, nano-bombesin labeling by a pre-targeting system was undertaken to develop an alternative approach for prostate tumor treatment.
A two-step pre-targeting system utilizing a combination of streptavidin (SA), biotinylated morpholino (B-MORF), biotinylated BBN (B-BBN) with two different spacers (b-Ala and PEG), and a radiolabeled cMORF was evaluated in vitro and in vivo.
Final conjugation conditions consisted of a 1:1:2 ratio of SA:B-MORF:B-BBN, followed by addition of 99mTc-cMORF to compensate for free MORF. In vitro binding experiments with prostate cancer cells (PC-3) revealed that total binding was time-dependent for the Ala spacer but not for the PEG spacer. The highest accumulation (5.06 ± 1.98 %) was achieved with 1 hour of incubation, decreasing as time progressed. Specific binding fell to 1.05 ± 0.35 %. The pre-targeting biodistribution in healthy Swiss mice was measured at different time points, with the best responses observed for 7-h and 15-h incubations. The effector, 99mTc-MAG3-cMORF, was administered 2 h later. Strong kidney excretion was always documented. The greatest tumor uptake was 2.58 ± 0.59 %ID/g at 7 h for B-bAla-BBN, with a region of interest (ROI) value of 3.9 % during imaging. The tumor/blood ratio was low due to the slow blood clearance; however, the tumor/muscle ratio was 5.95.
The pre-targeting approach with a peptide was a viable concept. Further evaluation with modified sequences of MORF, including less cytosine, and additional test intervals could be worthwhile.
已经使用各种前靶向技术或模型研究了癌症，这些模型主要针对放射性 bombesin 类似物；但是，这些技术都没有将两者结合在一起。在这项研究中，通过前靶向系统对纳米 bombesin 进行标记，以开发一种治疗前列腺肿瘤的替代方法。
利用链霉亲和素（SA）、生物素化吗啉代寡核苷酸（B-MORF）、带有两个不同间隔物（b-Ala 和 PEG）的生物素化 BBN（B-BBN）以及放射性标记的 cMORF 的两步前靶向系统在体外和体内进行了评估。
最终的缀合条件包括 SA:B-MORF:B-BBN 的比例为 1:1:2，然后加入 99mTc-cMORF 以补偿游离的 MORF。与前列腺癌细胞（PC-3）进行的体外结合实验表明，Ala 间隔物的总结合是时间依赖性的，但 PEG 间隔物则不是。孵育 1 小时后获得了最高的累积量（5.06 ± 1.98％），随着时间的推移而减少。特异性结合下降至 1.05 ± 0.35％。在健康的瑞士小鼠中测量了前靶向生物分布，在 7 小时和 15 小时孵育时观察到最佳反应。在 2 小时后给予效应物 99mTc-MAG3-cMORF。始终记录到强烈的肾脏排泄。在 7 小时时，B-bAla-BBN 的最大肿瘤摄取量为 2.58 ± 0.59％ID/g，成像时 ROI 值为 3.9％。由于血液清除缓慢，肿瘤/血液比很低，但是肿瘤/肌肉比为 5.95。
使用肽的前靶向方法是一种可行的概念。对包括更少胞嘧啶的 MORF 的修饰序列和额外的测试间隔进行进一步评估可能是值得的。
