Abstract：
BACKGROUND: Targeted radionuclide therapy is established as a highly effective strategy for the treatment of metastatic tumors; however, the co-development of suitable imaging companions to therapy remains significant challenge. Theranostic isotopes of terbium (149Tb, 152Tb, 155Tb, 161Tb) have the potential to provide chemically identical radionuclidic pairs, which collectively encompass all modes of nuclear decay relevant to nuclear medicine. Herein, we report the first radiochemistry and preclinical studies involving 155Tb- and 161Tb-labeled crown-αMSH, a small peptide-based bioconjugate suitable for targeting melanoma.
METHODS: 155Tb was produced via proton induced spallation of Ta targets using the isotope separation and acceleration facility at TRIUMF with isotope separation on-line (ISAC/ISOL). The radiolabeling characteristics of crown-αMSH with 155Tb and/or 161Tb were evaluated by concentration-dependence radiolabeling studies, and radio-HPLC stability studies. LogD7.4 measurements were obtained for [161Tb]Tb-crown-αMSH. Competitive binding assays were undertaken to determine the inhibition constant for [natTb]Tb-crown-αMSH in B16-F10 cells. Pre-clinical biodistribution and SPECT/CT imaging studies of 155Tb and 161Tb labeled crown-αMSH were undertaken in male C57Bl/6 J mice bearing B16-F10 melanoma tumors to evaluate tumor specific uptake and imaging potential for each radionuclide.
RESULTS: Quantitative radiolabeling of crown-αMSH with [155Tb]Tb3+ and [161Tb]Tb3+ was demonstrated under mild conditions (RT, 10 min) and low chelator concentrations; achieving high molar activities (23-29 MBq/nmol). Radio-HPLC studies showed [161Tb]Tb-crown-αMSH maintains excellent radiochemical purity in human serum, while gradual metabolic degradation is observed in mouse serum. Competitive binding assays showed the high affinity of [natTb]Tb-crown-αMSH toward MC1R. Two different methods for preparation of the [155Tb]Tb-crown-αMSH radiotracer were investigated and the impacts on the biodistribution profile in tumor bearing mice is compared. Preclinical in vivo studies of 155Tb- and 161Tb- labeled crown-αMSH were performed in parallel, in mice bearing B16-F10 tumors; where the biodistribution results showed similar tumor specific uptake (6.06-7.44 %IA/g at 2 h pi) and very low uptake in nontarget organs. These results were further corroborated through a series of single-photon emission computed tomography (SPECT) studies, with [155Tb]Tb-crown-αMSH and [161Tb]Tb-crown-αMSH showing comparable uptake profiles and excellent image contrast.
CONCLUSIONS: Collectively, our studies highlight the promising characteristics of [155Tb]Tb-crown-αMSH and [161Tb]Tb-crown-αMSH as theranostic pair for nuclear imaging (155Tb) and radionuclide therapy (161Tb).
METHODS: 155Tb was produced via proton induced spallation of Ta targets using the isotope separation and acceleration facility at TRIUMF with isotope separation on-line (ISAC/ISOL). The radiolabeling characteristics of crown-αMSH with 155Tb and/or 161Tb were evaluated by concentration-dependence radiolabeling studies, and radio-HPLC stability studies. LogD7.4 measurements were obtained for [161Tb]Tb-crown-αMSH. Competitive binding assays were undertaken to determine the inhibition constant for [natTb]Tb-crown-αMSH in B16-F10 cells. Pre-clinical biodistribution and SPECT/CT imaging studies of 155Tb and 161Tb labeled crown-αMSH were undertaken in male C57Bl/6 J mice bearing B16-F10 melanoma tumors to evaluate tumor specific uptake and imaging potential for each radionuclide.
RESULTS: Quantitative radiolabeling of crown-αMSH with [155Tb]Tb3+ and [161Tb]Tb3+ was demonstrated under mild conditions (RT, 10 min) and low chelator concentrations; achieving high molar activities (23-29 MBq/nmol). Radio-HPLC studies showed [161Tb]Tb-crown-αMSH maintains excellent radiochemical purity in human serum, while gradual metabolic degradation is observed in mouse serum. Competitive binding assays showed the high affinity of [natTb]Tb-crown-αMSH toward MC1R. Two different methods for preparation of the [155Tb]Tb-crown-αMSH radiotracer were investigated and the impacts on the biodistribution profile in tumor bearing mice is compared. Preclinical in vivo studies of 155Tb- and 161Tb- labeled crown-αMSH were performed in parallel, in mice bearing B16-F10 tumors; where the biodistribution results showed similar tumor specific uptake (6.06-7.44 %IA/g at 2 h pi) and very low uptake in nontarget organs. These results were further corroborated through a series of single-photon emission computed tomography (SPECT) studies, with [155Tb]Tb-crown-αMSH and [161Tb]Tb-crown-αMSH showing comparable uptake profiles and excellent image contrast.
CONCLUSIONS: Collectively, our studies highlight the promising characteristics of [155Tb]Tb-crown-αMSH and [161Tb]Tb-crown-αMSH as theranostic pair for nuclear imaging (155Tb) and radionuclide therapy (161Tb).
摘要：
背景：靶向放射性核素治疗被确立为治疗转移性肿瘤的高效策略；然而，共同开发合适的影像学辅助治疗仍然是重大挑战。Theranostic同位素（149Tb，152Tb,155Tb,161Tb）具有提供化学上相同的放射性核素对的潜力，它们共同涵盖了与核医学相关的所有核衰变模式。在这里，我们报告了涉及155Tb和161Tb标记的冠-αMSH的第一个放射化学和临床前研究，一种适用于黑色素瘤靶向的基于小肽的生物缀合物。
方法：155Tb是使用TRIUMF的同位素分离和加速设备通过质子诱导的Ta靶散裂产生的，该设备具有同位素在线分离（ISAC/ISOL）。通过浓度依赖性放射性标记研究评估了具有155Tb和/或161Tb的冠-αMSH的放射性标记特征，和放射性HPLC稳定性研究。对于[161Tb]Tb-冠-αMSH获得LogD7.4测量值。进行竞争性结合测定以确定B16-F10细胞中[natTb]Tb-crown-αMSH的抑制常数。在带有B16-F10黑色素瘤肿瘤的雄性C57Bl/6J小鼠中进行了155Tb和161Tb标记的冠-αMSH的临床前生物分布和SPECT/CT成像研究，以评估每种放射性核素的肿瘤特异性摄取和成像潜力。
结果：在温和条件下用[155Tb]Tb3和[161Tb]Tb3对冠-αMSH进行定量放射性标记（RT，10分钟）和低螯合剂浓度；实现高摩尔活性（23-29MBq/nmol）。放射性HPLC研究表明[161Tb]Tb-crown-αMSH在人血清中保持优异的放射化学纯度，而在小鼠血清中观察到逐渐的代谢降解。竞争性结合测定显示[natTb]Tb-crown-αMSH对MC1R的高亲和力。研究了制备[155Tb]Tb-crown-αMSH放射性示踪剂的两种不同方法，并比较了对荷瘤小鼠生物分布特征的影响。平行进行155Tb和161Tb标记的冠-αMSH的临床前体内研究，在携带B16-F10肿瘤的小鼠中；其中生物分布结果显示相似的肿瘤特异性摄取（在2hpi时为6.06-7.44％IA/g），并且在非靶器官中的摄取非常低。这些结果通过一系列单光子发射计算机断层扫描（SPECT）研究得到了进一步证实，[155Tb]Tb-冠-αMSH和[161Tb]Tb-冠-αMSH显示出可比的摄取曲线和出色的图像对比度。
结论：总的来说，我们的研究强调了[155Tb]Tb-crown-αMSH和[161Tb]Tb-crown-αMSH作为核成像（155Tb）和放射性核素治疗（161Tb）的治疗对的有希望的特征。
方法：155Tb是使用TRIUMF的同位素分离和加速设备通过质子诱导的Ta靶散裂产生的，该设备具有同位素在线分离（ISAC/ISOL）。通过浓度依赖性放射性标记研究评估了具有155Tb和/或161Tb的冠-αMSH的放射性标记特征，和放射性HPLC稳定性研究。对于[161Tb]Tb-冠-αMSH获得LogD7.4测量值。进行竞争性结合测定以确定B16-F10细胞中[natTb]Tb-crown-αMSH的抑制常数。在带有B16-F10黑色素瘤肿瘤的雄性C57Bl/6J小鼠中进行了155Tb和161Tb标记的冠-αMSH的临床前生物分布和SPECT/CT成像研究，以评估每种放射性核素的肿瘤特异性摄取和成像潜力。
结果：在温和条件下用[155Tb]Tb3和[161Tb]Tb3对冠-αMSH进行定量放射性标记（RT，10分钟）和低螯合剂浓度；实现高摩尔活性（23-29MBq/nmol）。放射性HPLC研究表明[161Tb]Tb-crown-αMSH在人血清中保持优异的放射化学纯度，而在小鼠血清中观察到逐渐的代谢降解。竞争性结合测定显示[natTb]Tb-crown-αMSH对MC1R的高亲和力。研究了制备[155Tb]Tb-crown-αMSH放射性示踪剂的两种不同方法，并比较了对荷瘤小鼠生物分布特征的影响。平行进行155Tb和161Tb标记的冠-αMSH的临床前体内研究，在携带B16-F10肿瘤的小鼠中；其中生物分布结果显示相似的肿瘤特异性摄取（在2hpi时为6.06-7.44％IA/g），并且在非靶器官中的摄取非常低。这些结果通过一系列单光子发射计算机断层扫描（SPECT）研究得到了进一步证实，[155Tb]Tb-冠-αMSH和[161Tb]Tb-冠-αMSH显示出可比的摄取曲线和出色的图像对比度。
结论：总的来说，我们的研究强调了[155Tb]Tb-crown-αMSH和[161Tb]Tb-crown-αMSH作为核成像（155Tb）和放射性核素治疗（161Tb）的治疗对的有希望的特征。
