Department of Radiation-Applied Biology Research, Quantum Beam Science Research Directorate, National Institutes for Quantum Science and Technology, Takasaki 370-1292, Japan.
Department of Radiation-Applied Biology Research, Quantum Beam Science Research Directorate, National Institutes for Quantum Science and Technology, Takasaki 370-1292, Japan.
Nucl Med Biol. 2022 Sep-Oct;112-113:44-51. doi: 10.1016/j.nucmedbio.2022.06.005. Epub 2022 Jun 30.
Meta-[At]astato-benzylguanidine ([At]MABG) accumulates in pheochromocytoma via norepinephrine transporter (NET) and leads to a strong antitumor effect, but it also distributed in normal tissues non-specifically. Meta-[I]iodo-benzylguanidine ([I]MIBG), an iodine-labeled analog of [At]MABG, is known to be transported by not only NET but also organic cation transporter (OCT). The involvement of OCT in [At]MABG uptake is still largely unknown. We investigated the involvement of OCT in the non-NET-driven uptake of [At]MABG both in vitro and in vivo.
[I]MIBG and [At]MABG uptake was investigated in PC-12 (rat pheochromocytoma cell line), NIH/3T3 (mouse fibroblasts cell line), ACHN (human renal cancer cell line), and BxPC-3 (human pancreatic cancer cell line). Herein, we used desipramine and dl-norepinephrine to inhibit NET, and we used steroids (hydrocortisone and prednisolone) to inhibit OCT3. The [At]MABG uptake in OCT3-knockdown cells established with OCT3-selective siRNA was also investigated. We investigated the biodistribution of [At]MABG in PC-12 tumor-bearing mice after a preloading of phosphate-buffered saline (PBS) or hydrocortisone solution.
The uptake of both [I]MIBG and [At]MABG was significantly inhibited by desipramine in PC-12 cells but not the other cell lines. The expression of OCT3 was relatively higher than those of the other OCT subtypes in ACHN and BxPC-3 cells. The expression of OCTs was not observed in NIH/3T3 cells. The uptake of both [I]MIBG and [At]MABG in ACHN and BxPC-3 cells was significantly inhibited by the steroid treatments. The [At]MABG uptake was also reduced in OCT3-knockdown cells (p < 0.001). The radioactivity of [At]MABG was significantly reduced in normal tissues by the preloading of hydrocortisone. In contrast, there was an increasing trend of [At]MABG uptake in the PC-12 tumors. The tumor-to-normal tissue ratio was significantly increased by the preloading of hydrocortisone compared to that of PBS.
Our results suggest that OCT3 is involved in non-NET-driven [At]MABG uptake. The preloading of hydrocortisone selectively reduced [At]MABG accumulation in normal organs in vivo. OCT3 inhibition may therefore be beneficial for a reduction of the radiation risk in healthy organs in the treatment of malignant pheochromocytomas.
金属-[At]替胍苯甲基替胍([At]MABG) 通过去甲肾上腺素转运体 (NET) 在嗜铬细胞瘤中积累，导致强烈的抗肿瘤作用，但它也在正常组织中非特异性分布。碘代-[I]苄基胍([I]MIBG) 是 [At]MABG 的碘标记类似物，已知不仅由 NET 而且由有机阳离子转运体 (OCT) 转运。OCT 参与 [At]MABG 摄取的程度在很大程度上仍不清楚。我们研究了 OCT 在体外和体内非 NET 驱动的 [At]MABG 摄取中的作用。
在 PC-12（大鼠嗜铬细胞瘤细胞系）、NIH/3T3（小鼠成纤维细胞系）、ACHN（人肾癌细胞系）和 BxPC-3（人胰腺癌细胞系）中研究了 [I]MIBG 和 [At]MABG 的摄取。在此，我们使用去甲丙咪嗪和 dl-去甲肾上腺素抑制 NET，并用类固醇（氢化可的松和泼尼松龙）抑制 OCT3。还使用 OCT3 选择性 siRNA 建立的 OCT3 敲低细胞研究了 [At]MABG 的摄取。在 PC-12 肿瘤荷瘤小鼠中，在预加载磷酸盐缓冲盐水 (PBS) 或氢化可的松溶液后，研究了 [At]MABG 的生物分布。
去甲丙咪嗪显著抑制 PC-12 细胞中 [I]MIBG 和 [At]MABG 的摄取，但其他细胞系则不然。OCT3 的表达在 ACHN 和 BxPC-3 细胞中相对高于其他 OCT 亚型。在 NIH/3T3 细胞中未观察到 OCTs 的表达。类固醇处理显著抑制 ACHN 和 BxPC-3 细胞中 [I]MIBG 和 [At]MABG 的摄取。OCT3 敲低细胞的 [At]MABG 摄取也减少（p<0.001）。在正常组织中预加载氢化可的松会显著降低 [At]MABG 的放射性。相比之下，PC-12 肿瘤中的 [At]MABG 摄取呈上升趋势。与 PBS 相比，氢化可的松预加载可使肿瘤与正常组织的比值显著增加。
我们的结果表明，OCT3 参与非 NET 驱动的 [At]MABG 摄取。在体预加载氢化可的松可选择性减少正常器官中 [At]MABG 的积累。因此，OCT3 抑制可能有助于降低恶性嗜铬细胞瘤治疗中健康器官的辐射风险。
