School of Medicine, Vanderbilt University, Nashville, Tennessee, United States of America.
PLoS One. 2011;6(7):e22182. doi: 10.1371/journal.pone.0022182. Epub 2011 Jul 20.
Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA(2)) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA(2) and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.
尽管采用了广泛的边缘和高剂量照射，但是无法切除的恶性神经胶质瘤（MG）对放射治疗的反应较差，并且普遍致命。我们之前发现胞质型磷脂酶 A2（cPLA（2））是通过血管内皮使癌症对放射治疗敏感的分子靶标。自分泌酶（ATX）和溶血磷脂酸（LPA）受体是 cPLA（2）的下游产物，在 MG 中高度表达。我们使用 ATX 和 LPA 受体抑制剂，α-溴亚甲基膦酸 LPA（BrP-LPA），研究了 ATX 和 LPA 受体作为 MG 肿瘤血管放射增敏的潜在分子靶标。用 5μmol/L BrP-LPA 和 3Gy 照射处理人脐静脉内皮细胞（HUVEC）和小鼠脑微血管细胞 bEND.3 后，克隆存活、小管形成和迁移减少。外源性添加 LPA 显示出放射保护作用，而在 BrP-LPA 存在下则被消除。在使用 bEND.3 和小鼠 GL-261 神经胶质瘤细胞的共培养实验中，用 BrP-LPA 处理可降低两种辐照细胞系中的 Akt 磷酸化，并降低辐照 GL-261 细胞的存活和迁移。用 siRNA 敲低 HUVEC 中的 LPA 受体 LPA1、LPA2 或 LPA3，我们证明敲低 LPA2 但不敲低 LPA1 或 LPA3 导致细胞活力和增殖增加。然而，敲低 LPA1 和 LPA3 但不敲低 LPA2 导致小管形成完全被阻断，这意味着内皮细胞上的 LPA1 和 LPA3 可能是 BrP-LPA 放射增敏作用的靶标。在 GL-261 的异位肿瘤模型中，与单独接受照射的小鼠相比，用 BrP-LPA 和照射治疗的小鼠的肿瘤生长延迟了 6.8 天，这表明抑制 ATX 和 LPA 受体可能显著改善恶性神经胶质瘤对放射治疗的反应。这些发现确定了 ATX 和 LPA 受体作为 MG 放射增敏剂开发的分子靶标。
