Lanza-Jacoby Susan, Dicker Adam P, Miller Sheldon, Rosato Francis E, Flynn John T, Lavorgna Stephanie N, Burd Randy
Department of Surgery, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Mol Cancer Ther. 2004 Apr;3(4):417-24. doi: 10.4161/cbt.3.4.803.
Cyclooxygenase (COX)-2-derived prostaglandins (PGs) are thought to contribute to tumor growth and resistance to radiation therapy. COX-2 protein expression is increased in many tumors including those of the breast. COX-2-derived PGs have been shown to protect cells from radiation damage. This study evaluated the role of COX-2-derived PG in radiation treatment by using the NMF11.2 mammary tumor cell line originally obtained from HER-2/neu mice that overexpress HER-2/neu. We determined whether the effects of the COX-2 inhibitor SC236 on cell growth, radiation-induced PGE2 production and COX expression, cell cycle redistribution, and vascular endothelial growth factor (VEGF) were acting through COX-2-dependent mechanisms. The NMF11.2 cells expressed both COX-1 and COX-2 protein and mRNA. The radiation treatment alone led to a dose-dependent increase in the levels of COX-2 mRNA and COX-2 protein, which was associated with an increase in the production of PGE2 and prostacyclin (PGI2). Treating NMF11.2 cells with high concentrations (20 microM) of SC236 for 48 h reduced the radiation-induced increase in COX-2 activity and also decreased cell growth. SC236 (20 microM) increased the accumulation of the cells in the radiosensitive G2-M phase of the cell cycle. However, a low concentration (5 microM) of SC236 was adequate to reduce COX-2 activity. The lower concentration of SC236 (5 microM) also decreased cell growth after a longer incubation period (96 h) and, in combination with a 2 or 5 Gy dose, led to an accumulation of cells in G2-M phase. Restoring PG to control values in cells treated with 5 microM SC236 prevented the growth inhibition and G2-M cell cycle arrest. Radiation treatment of NMF11.2 cells also increased VEGF protein expression and VEGF secretion in a dose-dependent manner, which was blocked in those cells pretreated with 20 microM SC236 but not in those pretreated with 5 microM SC236. These findings indicate that the COX-2 inhibitor SC236 reduced cell growth and arrested cells in the G2-M phase of the cell cycle by mechanisms that are both dependent and independent of PG production while its effects on VEGF appear to be independent of COX-2.
环氧化酶（COX）-2衍生的前列腺素（PGs）被认为与肿瘤生长及放疗抵抗有关。COX-2蛋白表达在包括乳腺癌在内的许多肿瘤中均有增加。已证实COX-2衍生的PGs可保护细胞免受辐射损伤。本研究利用最初从过表达HER-2/neu的HER-2/neu小鼠获得的NMF11.2乳腺肿瘤细胞系，评估了COX-2衍生的PG在放射治疗中的作用。我们确定了COX-2抑制剂SC236对细胞生长、辐射诱导的PGE2产生及COX表达、细胞周期再分布和血管内皮生长因子（VEGF）的影响是否通过COX-2依赖性机制起作用。NMF11.2细胞同时表达COX-1和COX-2蛋白及mRNA。单独进行放射治疗导致COX-2 mRNA和COX-2蛋白水平呈剂量依赖性增加，这与PGE2和前列环素（PGI2）产生增加相关。用高浓度（20μM）的SC236处理NMF11.2细胞48小时可降低辐射诱导的COX-2活性增加，同时也降低细胞生长。SC236（20μM）使细胞在细胞周期的放射敏感G2-M期积累增加。然而，低浓度（5μM）的SC236就足以降低COX-2活性。较低浓度的SC236（5μM）在较长孵育期（96小时）后也降低细胞生长，并与2或5 Gy剂量联合使用时，导致细胞在G2-M期积累。在用5μM SC236处理的细胞中将PG恢复至对照值可防止生长抑制和G2-M细胞周期停滞。对NMF11.2细胞进行放射治疗还以剂量依赖性方式增加VEGF蛋白表达和VEGF分泌，这在预先用20μM SC236处理的细胞中被阻断，但在预先用5μM SC236处理的细胞中未被阻断。这些发现表明，COX-2抑制剂SC236通过依赖和不依赖PG产生的机制降低细胞生长并使细胞停滞在细胞周期的G2-M期，而其对VEGF的影响似乎独立于COX-2。
