Department of Radiotherapy, Martin-Luther-University Halle-Wittenberg, Dryanderstr, 4, 06110 Halle, Germany.
Radiat Oncol. 2011 Sep 9;6:111. doi: 10.1186/1748-717X-6-111.
Betulinic acid (BA) is a novel antineoplastic agent under evaluation for tumor therapy. Because of the selective cytotoxic effects of BA in tumor cells (including gliomas), the combination of this agent with conservative therapies (such as radiotherapy and chemotherapy) may be useful. Previously, the combination of BA with irradiation under hypoxic conditions had never been studied.
In this study, the effects of 3 to 30 μM BA on cytotoxicity, migration, the protein expression of PARP, survivin and HIF-1α, as well as radiosensitivity under normoxic and hypoxic conditions were analyzed in the human malignant glioma cell lines U251MG and U343MG. Cytotoxicity and radiosensitivity were analyzed with clonogenic survival assays, migration was analyzed with Boyden chamber assays (or scratch assays) and protein expression was examined with Western blot analyses.
Under normoxic conditions, a half maximal inhibitory concentration (IC50) of 23 μM was observed in U251MG cells and 24 μM was observed in U343MG cells. Under hypoxic conditions, 10 μM or 15 μM of BA showed a significantly increased cytotoxicity in U251MG cells (p = 0.004 and p = 0.01, respectively) and U343MG cells (p < 0.05 and p = 0.01, respectively). The combination of BA with radiotherapy resulted in an additive effect in the U343MG cell line under normoxic and hypoxic conditions. Weak radiation enhancement was observed in U251MG cell line after treatment with BA under normoxic conditions. Furthermore, under hypoxic conditions, the incubation with BA resulted in increased radiation enhancement. The enhancement factor, at an irradiation dose of 15 Gy after treatment with 10 or 15 μM BA, was 2.20 (p = 0.02) and 4.50 (p = 0.03), respectively. Incubation with BA led to decreased cell migration, cleavage of PARP and decreased expression levels of survivin in both cell lines. Additionally, BA treatment resulted in a reduction of HIF-1α protein under hypoxic conditions.
Our results suggest that BA is capable of improving the effects of tumor therapy in human malignant glioma cells, particularly under hypoxic conditions. Further investigations are necessary to characterize its potential as a radiosensitizer.
白桦脂酸（BA）是一种新型抗肿瘤药物，正在评估用于肿瘤治疗。由于 BA 在肿瘤细胞（包括神经胶质瘤）中具有选择性细胞毒性作用，因此将该药物与保守疗法（如放疗和化疗）联合使用可能是有用的。以前，从未研究过 BA 与缺氧条件下的辐射联合使用。
在这项研究中，分析了 3 至 30μM 的 BA 在人恶性神经胶质瘤细胞系 U251MG 和 U343MG 中对细胞毒性、迁移、PARP、存活素和 HIF-1α 的蛋白表达以及在常氧和缺氧条件下的放射敏感性的影响。细胞毒性和放射敏感性通过集落形成生存分析进行分析，迁移通过 Boyden 室分析（或划痕分析）进行分析，蛋白表达通过 Western blot 分析进行分析。
在常氧条件下，U251MG 细胞的半数最大抑制浓度（IC50）为 23μM，U343MG 细胞的 IC50 为 24μM。在缺氧条件下，10μM 或 15μM 的 BA 可显著增加 U251MG 细胞（p=0.004 和 p=0.01）和 U343MG 细胞（p<0.05 和 p=0.01）的细胞毒性。BA 与放疗联合使用在 U343MG 细胞系中在常氧和缺氧条件下产生相加作用。在常氧条件下用 BA 处理后，U251MG 细胞系中观察到弱的辐射增强作用。此外，在缺氧条件下，用 BA 孵育可导致辐射增强。在用 10μM 或 15μM 的 BA 处理后，在照射剂量为 15Gy 时，增强因子分别为 2.20（p=0.02）和 4.50（p=0.03）。BA 孵育可降低两种细胞系的细胞迁移、PARP 裂解和存活素表达水平。此外，BA 处理可降低缺氧条件下的 HIF-1α 蛋白水平。
我们的结果表明，BA 能够提高人恶性神经胶质瘤细胞的肿瘤治疗效果，特别是在缺氧条件下。需要进一步的研究来表征其作为放射增敏剂的潜力。
