Antibody-based therapies targeting CD38 are currently used as single agents as well as in combination regimens for multiple myeloma, a malignant plasma cell disorder. In this study, we aimed to develop anti-CD38 single-domain antibodies (sdAbs) that can be used to trace CD38+ tumour cells and subsequently used for targeted radionuclide therapy. SdAbs are derived from Camelidae heavy-chain antibodies and have emerged as promising theranostic agents due to their favourable pharmacological properties. Four different anti-CD38 sdAbs were produced, and their binding affinities and potential competition with the monoclonal antibody daratumumab were tested using biolayer interferometry. Their binding kinetics and potential cell internalisation were further studied after radiolabelling with the diagnostic radioisotope Indium-111. The resulting radiotracers were evaluated in vivo for their tumour-targeting potential and biodistribution through single-photon emission computed tomography (SPECT/CT) imaging and serial dissections. Finally, therapeutic efficacy of a lead anti-CD38 sdAb, radiolabelled with the therapeutic radioisotope Lutetium-177, was evaluated in a CD38+ MM xenograft model. We retained anti-CD38 sdAb #2F8 as lead based on its excellent affinity and superior stability, the absence of competition with daratumumab and the lack of receptor-mediated internalisation. When intravenously administered to tumour-xenografted mice, radiolabelled sdAb #2F8 revealed specific and sustained tumour retention with low accumulation in other tissues, except kidneys, resulting in high tumour-to-normal tissue ratios. In a therapeutic setting, myeloma-bearing mice received three consecutive intravenous administrations of a high (18.5 MBq) or a low radioactive dose (9.3 MBq) of 177Lu-DTPA-2F8 or an equal volume of vehicle solution. A dose-dependent tumour regression was observed, which translated into a prolonged median survival from 43 days for vehicle-treated mice, to 62 days (p = 0.027) in mice receiving the low and 65 days in mice receiving the high (p = 0.0007) radioactive dose regimen, respectively. These results highlight the theranostic potential of radiolabelled anti-CD38 sdAbs for the monitoring and treatment of multiple myeloma.

中文翻译：

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用于监测和治疗多发性骨髓瘤的非内化 CD38 结合放射性标记单域抗体片段

针对 CD38 的基于抗体的疗法目前用作多发性骨髓瘤（一种恶性浆细胞疾病）的单一药物以及联合治疗方案。在本研究中，我们旨在开发可用于追踪 CD38+ 肿瘤细胞并随后用于靶向放射性核素治疗的抗 CD38 单域抗体 (sdAbs)。SdAbs 来源于骆驼科重链抗体，由于其良好的药理特性，已成为有前途的治疗诊断剂。生产了四种不同的抗 CD38 sdAb，并使用生物层干涉法测试了它们的结合亲和力和与单克隆抗体 daratumumab 的潜在竞争。在用诊断性放射性同位素 Indium-111 进行放射性标记后，进一步研究了它们的结合动力学和潜在的细胞内化。通过单光子发射计算机断层扫描 (SPECT/CT) 成像和连续解剖，在体内评估所得放射性示踪剂的肿瘤靶向潜力和生物分布。最后，在 CD38+ MM 异种移植模型中评估了用治疗性放射性同位素 Lutetium-177 放射性标记的先导抗 CD38 sdAb 的治疗效果。我们保留抗 CD38 sdAb #2F8 作为先导，基于其出色的亲和力和卓越的稳定性、不与达雷妥尤单抗竞争以及缺乏受体介导的内化。当对肿瘤异种移植小鼠进行静脉内给药时，放射性标记的 sdAb #2F8 显示出特异性和持续的肿瘤保留，在除肾脏以外的其他组织中蓄积较少，导致肿瘤与正常组织的比例较高。在治疗环境中，患有骨髓瘤的小鼠接受了 3 次连续静脉内给药的高 (18.5 MBq) 或低放射性剂量 (9.3 MBq) 的 177Lu-DTPA-2F8 或等体积的载体溶液。观察到剂量依赖性肿瘤消退，这转化为载体治疗小鼠的中位生存期从 43 天延长至接受低剂量小鼠的 62 天（p = 0.027）和接受高剂量小鼠的 65 天（p = 0.0007 ) 放射性剂量方案，分别。这些结果突出了放射性标记的抗 CD38 sdAb 用于监测和治疗多发性骨髓瘤的治疗诊断潜力。这转化为延长的中位生存期，从接受载体治疗的小鼠的 43 天，到接受低放射性剂量方案的小鼠的 62 天（p = 0.027）和接受高（p = 0.0007）放射性剂量方案的小鼠的 65 天，分别。这些结果突出了放射性标记的抗 CD38 sdAb 用于监测和治疗多发性骨髓瘤的治疗诊断潜力。这转化为延长的中位生存期，从接受载体治疗的小鼠的 43 天，到接受低放射性剂量方案的小鼠的 62 天（p = 0.027）和接受高（p = 0.0007）放射性剂量方案的小鼠的 65 天，分别。这些结果突出了放射性标记的抗 CD38 sdAb 用于监测和治疗多发性骨髓瘤的治疗诊断潜力。