Department of Nuclear Medicine, University of Würzburg, D-97080 Würzburg, Germany.
Nucl Med Biol. 2011 May;38(4):451-60. doi: 10.1016/j.nucmedbio.2010.12.002. Epub 2011 Mar 3.
Malignant gliomas represent a major therapeutic challenge because no efficient treatment is currently available. p-[(131)I]iodo-L-phenylalanine ([(131)I]IPA) is a glioma avid radiopharmaceutical that demonstrated antiproliferative and tumoricidal effects in gliomas. The present study validated the therapeutic efficiency of [(131)I]IPA combined with external beam radiotherapy in experimental gliomas.
Glioma cells derived from the primary human A1207, T5135, Tx3868 and M059K glioblastoma cell lines or rat F98 glioma cell line were treated with various doses of [(131)I]IPA, external photon irradiation (RT) or combined [(131)I]IPA/RT treatment. Responsiveness of glioma cells to the different therapy modalities was investigated at 24, 48 and 72 h after treatments by trypan blue, WST-1 assay, propidium iodide and bisbenzimide staining as well as by clonogenic assay. In addition, the therapy-induced DNA damage and repair were evaluated using phosphorylated histone H2AX (γ-H2AX). In vivo, the effectiveness of the combination treatment was validated in human Tx3868 and A1207 glioblastoma xenografts in CD1 nu/nu mice and RNU rats.
In vitro, the combination treatment resulted in a greater than additive increase in cytotoxic effect in glioma cell lines. Cell survival rate following a treatment with 1.0 μCi (37 kBq) of [(131)I]IPA amounted to 70%±15% and 60%±10% after 48 and 72 h, respectively, and decreased under 20% after additional RT with 5 Gy. At higher RT doses, cell survival rate decreased below 5%. As a measure of DNA double-strand break, nuclear γ-H2AX foci were determined as a function of time. Within 24 h, the number of γ-H2AX foci per cell was significantly greater after combined modality compared with the individual treatments. In vivo, when combined with RT, the radionuclide therapy with [(131)I]IPA resulted in an extended tumor growth delay, a reduction of the initial tumor volume and an enhanced radiosensitivity in Tx3868 and A1207 glioblastoma xenografts in CD1 nu/nu mice and RNU rats. On day 90 after monotherapy with [(131)I]IPA (20 MBq) or RT (20 Gy), 35%-50% of the treated rats were still alive. In comparison, up to 70%-80% survival rates were registered after combined [(131)I]IPA/RT treatment on day 100 for all animal models.
These preclinical data convincingly demonstrated that [(131)I]IPA plus external beam photon radiotherapy is a safe and highly effective treatment for experimental gliomas, which may merit a clinical trial to ascertain its potential as a therapeutic approach in patients. As only a low [(131)I]IPA activity and a low RT dose were applied, further optimization strategies should be pursued experimentally, including application of higher radiation doses and conventional fractionated regimens or use of methods aiming to increase target doses and maximize dose effects.
恶性胶质瘤是一种治疗极具挑战性的疾病，目前尚无有效的治疗方法。放射性碘标记的 L-苯丙氨酸([(131)I]IPA)是一种对胶质瘤具有高亲和性的放射性药物，在胶质瘤中显示出抗增殖和杀肿瘤作用。本研究旨在验证[(131)I]IPA联合外照射放疗在实验性胶质瘤中的治疗效果。
用不同剂量的[(131)I]IPA、外光子照射（RT）或联合[(131)I]IPA/RT 处理源自人 A1207、T5135、Tx3868 和 M059K 胶质母细胞瘤细胞系或大鼠 F98 胶质瘤细胞系的胶质瘤细胞。用台盼蓝、WST-1 测定法、碘化丙啶和双苯并咪唑染色以及集落形成测定法在治疗后 24、48 和 72 小时检测胶质瘤细胞对不同治疗方式的反应。此外，用磷酸化组蛋白 H2AX（γ-H2AX）评估治疗诱导的 DNA 损伤和修复。在体内，在 CD1 nu/nu 小鼠和 RNU 大鼠中用 Tx3868 和 A1207 胶质母细胞瘤异种移植模型验证联合治疗的有效性。
在体外，联合治疗导致胶质瘤细胞系的细胞毒性作用明显增加。用 1.0 μCi（37 kBq）的[(131)I]IPA 处理后，细胞存活率在 48 小时和 72 小时时分别达到 70%±15%和 60%±10%，而在接受 5 Gy 的额外 RT 后则降低至 20%以下。在更高的 RT 剂量下，细胞存活率降至 5%以下。作为 DNA 双链断裂的测量，随着时间的推移确定了核γ-H2AX 焦点的数量。在 24 小时内，与单独治疗相比，联合治疗后每个细胞的γ-H2AX 焦点数量明显增加。在体内，当与 RT 联合使用时，[(131)I]IPA 的放射性核素治疗导致 Tx3868 和 A1207 胶质母细胞瘤异种移植在 CD1 nu/nu 小鼠和 RNU 大鼠中的肿瘤生长延迟、初始肿瘤体积减小和放射敏感性增强。在单独用[(131)I]IPA（20 MBq）或 RT（20 Gy）治疗 90 天后，35%-50%的治疗大鼠仍然存活。相比之下，在所有动物模型中，联合[(131)I]IPA/RT 治疗 100 天后，存活率高达 70%-80%。
这些临床前数据令人信服地证明，[(131)I]IPA 联合外照射光子放疗是治疗实验性胶质瘤的一种安全有效的方法，这可能值得进行临床试验以确定其在患者中的治疗潜力。由于仅应用了低剂量的[(131)I]IPA 和低剂量的 RT，因此应在实验中进一步优化策略，包括应用更高的辐射剂量和常规分割方案，或采用旨在增加靶剂量和最大化剂量效果的方法。
