Blom Thomas, Meinsma Rutger, Rutgers Marja, Buitenhuis Corine, Dekken-Van den Burg Marieke, van Kuilenburg André B P, Tytgat Godelieve A M
Princess Máxima Center for Pediatric Oncology, Utrecht, The Netherlands.
Gastroenterology & Metabolism, Department of Clinical Chemistry, Amsterdam University Medical Center, Amsterdam, The Netherlands.
EJNMMI Res. 2020 Jul 8;10(1):78. doi: 10.1186/s13550-020-00662-w.
The therapeutic use of [I]meta-iodobenzylguanidine ([I]MIBG) is often accompanied by hematological toxicity, mainly consisting of persistent and severe thrombocytopenia. While MIBG accumulates in neuroblastoma cells via selective uptake by the norepinephrine transporter (NET), the serotonin transporter (SERT) is responsible for cellular uptake of MIBG in platelets. In this study, we have investigated whether pharmacological intervention with selective serotonin reuptake inhibitors (SSRIs) may prevent radiotoxic MIBG uptake in platelets without affecting neuroblastoma tumor uptake.
To determine the transport kinetics of SERT for [I]MIBG, HEK293 cells were transfected with SERT and uptake assays were conducted. Next, a panel of seven SSRIs was tested in vitro for their inhibitory potency on the uptake of [I]MIBG in isolated human platelets and in cultured neuroblastoma cells. We investigated in vivo the efficacy of the four best performing SSRIs on the accumulation of [I]MIBG in nude mice bearing subcutaneous neuroblastoma xenografts. In ex vivo experiments, the diluted plasma of mice treated with SSRIs was added to isolated human platelets to assess the effect on [I]MIBG uptake.
SERT performed as a low-affinity transporter of [I]MIBG in comparison with NET (K = 9.7 μM and 0.49 μM, respectively). Paroxetine was the most potent uptake inhibitor of both serotonin (IC = 0.6 nM) and MIBG (IC = 0.2 nM) in platelets. Citalopram was the most selective SERT inhibitor of [I]MIBG uptake, with high SERT affinity in platelets (IC = 7.8 nM) and low NET affinity in neuroblastoma cells (IC = 11.940 nM). The in vivo tested SSRIs (citalopram, fluvoxamine, sertraline, and paroxetine) had no effect on [I]MIBG uptake levels in neuroblastoma xenografts. In contrast, treatment with desipramine, a NET selective inhibitor, resulted in profoundly decreased xenograft [I]MIBG levels (p < 0.0001). In ex vivo [I]MIBG uptake experiments, 100- and 34-fold diluted murine plasma of mice treated with citalopram added to isolated human platelets led to a decrease in MIBG uptake of 54-76%, respectively.
Our study demonstrates for the first time that SSRIs selectively inhibit MIBG uptake in platelets without affecting MIBG accumulation in an in vivo neuroblastoma model. The concomitant application of citalopram during [I]MIBG therapy seems a promising strategy to prevent thrombocytopenia in neuroblastoma patients.
[I]间碘苄胍（[I]MIBG）的治疗应用常伴有血液学毒性，主要表现为持续性严重血小板减少。虽然MIBG通过去甲肾上腺素转运体（NET）的选择性摄取在神经母细胞瘤细胞中蓄积，但血清素转运体（SERT）负责血小板对MIBG的细胞摄取。在本研究中，我们调查了用选择性5-羟色胺再摄取抑制剂（SSRI）进行药物干预是否可防止放射性毒性的MIBG在血小板中摄取，而不影响神经母细胞瘤肿瘤摄取。
为确定SERT对[I]MIBG的转运动力学，将SERT转染至HEK293细胞并进行摄取试验。接下来，在体外测试了一组7种SSRI对分离的人血小板和培养的神经母细胞瘤细胞中[I]MIBG摄取的抑制效力。我们在体内研究了4种表现最佳的SSRI对携带皮下神经母细胞瘤异种移植瘤的裸鼠中[I]MIBG蓄积的疗效。在体外实验中，将用SSRI处理的小鼠的稀释血浆添加到分离的人血小板中，以评估对[I]MIBG摄取的影响。
与NET相比，SERT作为[I]MIBG的低亲和力转运体（K分别为9.7μM和0.49μM）。帕罗西汀是血小板中5-羟色胺（IC = 0.6 nM）和MIBG（IC = 0.2 nM）最有效的摄取抑制剂。西酞普兰是[I]MIBG摄取最具选择性的SERT抑制剂，在血小板中具有高SERT亲和力（IC = 7.8 nM），在神经母细胞瘤细胞中具有低NET亲和力（IC = 11.940 nM）。体内测试的SSRI（西酞普兰、氟伏沙明、舍曲林和帕罗西汀）对神经母细胞瘤异种移植瘤中[I]MIBG摄取水平无影响。相反，用NET选择性抑制剂地昔帕明治疗导致异种移植瘤[I]MIBG水平显著降低（p < 0.0001）。在体外[I]MIBG摄取实验中，添加到分离的人血小板中的用西酞普兰处理的小鼠的100倍和34倍稀释血浆分别导致MIBG摄取减少54 - 76%。
我们的研究首次证明，在体内神经母细胞瘤模型中，SSRI可选择性抑制血小板中MIBG摄取，而不影响MIBG蓄积。在[I]MIBG治疗期间同时应用西酞普兰似乎是预防神经母细胞瘤患者血小板减少的一种有前景的策略。
