Ramachandran Cheppail, Khatib Ziad, Petkarou Athena, Fort John, Fonseca Hugo B, Melnick Steven J, Escalon Enrique
Research Institute, Miami Children's Hospital, FL 33155, USA.
J Neurooncol. 2004 Mar-Apr;67(1-2):19-28. doi: 10.1023/b:neon.0000021738.77612.1b.
Tamoxifen, a non-steroidal anti-estrogen widely used against breast cancer, is also useful for treatment of other malignancies, due to its sensitizing effect on other chemotherapeutic agents and radiation. We have investigated the advantages of combining tamoxifen with one of the commonly used cancer chemotherapeutic drug, etoposide (VP-16) in brain tumor cell lines. While tamoxifen (10 microM) increased etoposide cytotoxicity 8.3-fold in the human glioma cell line (HTB-14), it increased etoposide cytotoxicity 47.5- and 40-fold in two primary cell lines established from pediatric medulloblastoma patients (MCH-BT-31 and MCH-BT-39), respectively. Similarly, in the pediatric ependymoma cell lines (MCH-BT-30 and MCH-BT-52), tamoxifen enhanced etoposide cytotoxicity 6- and 2.68-fold, respectively. CalcuSyn analysis of cytotoxicity data showed that tamoxifen and etoposide combinations were synergistic with combination index values ranging from 0.243 to 0.369 at IC50 level among different pediatric brain tumor cell lines. Tamoxifen is also cytotoxic at higher concentrations (> 20 microM) in brain tumor cells. To understand the mechanism underlying the tamoxifen modulation of etoposide cytotoxicity, we analyzed expression of P-glycoprotein (P-gp), insulin-like growth factor-I receptor (IGF-IR), IGF-I, IGF-II and estrogen receptor as well as protein kinase C (PKC) activity. While P-gp, IGF-IR and IGF-I were not affected, enhanced inhibition of PKC, and IGF-II were observed in brain tumor cells treated with tamoxifen and etoposide combination as compared to cells treated with either drug alone. Tamoxifen at 10 microM when combined with etoposide at 0-100 microM concentrations reduced PKC activity 77% compared to only 58% without tamoxifen. IGF-II expression decreased to 48.6% of the untreated control in the combination treatment as compared to 31.2% for etoposide alone and 26.2% for tamoxifen alone treatments. These results suggest that inhibitory effect of tamoxifen on brain tumor cells manifest through different mechanisms involving inhibition of targets such as PKC and IGF-II.
他莫昔芬是一种广泛用于治疗乳腺癌的非甾体类抗雌激素药物，由于其对其他化疗药物和放疗具有增敏作用，因此也可用于治疗其他恶性肿瘤。我们研究了他莫昔芬与常用癌症化疗药物之一依托泊苷（VP-16）联合应用于脑肿瘤细胞系的优势。在人胶质瘤细胞系（HTB-14）中，他莫昔芬（10微摩尔）使依托泊苷的细胞毒性增加了8.3倍，而在从儿童髓母细胞瘤患者建立的两个原代细胞系（MCH-BT-31和MCH-BT-39）中，他莫昔芬分别使依托泊苷的细胞毒性增加了47.5倍和40倍。同样，在儿童室管膜瘤细胞系（MCH-BT-30和MCH-BT-52）中，他莫昔芬分别使依托泊苷的细胞毒性增强了6倍和2.68倍。对细胞毒性数据的CalcuSyn分析表明，在不同的儿童脑肿瘤细胞系中，他莫昔芬与依托泊苷的联合用药具有协同作用，在IC50水平下联合指数值范围为0.243至0.369。他莫昔芬在较高浓度（>20微摩尔）时对脑肿瘤细胞也具有细胞毒性。为了了解他莫昔芬调节依托泊苷细胞毒性的潜在机制，我们分析了P-糖蛋白（P-gp）、胰岛素样生长因子-I受体（IGF-IR）、IGF-I、IGF-II和雌激素受体的表达以及蛋白激酶C（PKC）的活性。虽然P-gp、IGF-IR和IGF-I不受影响，但与单独使用任何一种药物处理的细胞相比，在用他莫昔芬和依托泊苷联合处理的脑肿瘤细胞中观察到PKC和IGF-II的抑制作用增强。当10微摩尔的他莫昔芬与0至100微摩尔浓度的依托泊苷联合使用时，与不使用他莫昔芬相比，PKC活性降低了77%，而单独使用依托泊苷时降低了58%。联合处理时IGF-II的表达降至未处理对照的48.6%，而单独使用依托泊苷时为31.2%，单独使用他莫昔芬时为26.2%。这些结果表明，他莫昔芬对脑肿瘤细胞的抑制作用通过涉及抑制PKC和IGF-II等靶点的不同机制表现出来。
