Abstract A009: Effect of melatonin on the tumor growth and angiogenesis of breast cancer

Abstract

Abstract Background: Breast cancer has a high mortality rate, mainly due to tumor progression and metastatic spread. Once tumor lesion exceeds a few millimeters in diameter, hypoxia triggers a cascade of events to allow neovascularization. The major contributors to angiogenesis are the vascular endothelial growth factor (VEGF) and its receptors, which promote cell proliferation, migration, permeability and survival. Thus, controlling tumor-associated angiogenesis is a promising tactic in limiting cancer development. The melatonin administration, a hormone naturally produced and secreted in the pineal gland, appears to play an important oncostatic role in cancer and have been currently proposed different mechanisms of action. In this study we evaluated the benefits of melatonin treatment on tumor growth and angiogenesis in breast cancer. Methods: MDA-MB-231 breast cancer cell line was cultured and cell viability was measured by MTT assay after incubation with different concentrations of melatonin (5 mM, 10 mM, 20 mM). We performed an in vivo study implanting cells in athymic nude mice. Mice were treated with 1mg of melatonin (n = 5) or vehicle (n = 8) daily, starting in the same day as tumor implantation and continued for 21 days. Tumors were measured with a digital caliper on day 7, 14 and 21 and the animals underwent SPECT scanning with Tc-99m tagged VEGF-c to detect in vivo angiogenesis (expression of VEGFR2/3). In addition, the markers of angiogenesis (VEGFR2, VEGFR3 and von Willebrand Factor (vWF)) and cell proliferation (Ki-67) were evaluated by immunohistochemistry in mammary tumor tissues. Results: Melatonin treatment in vitro was able to significantly decrease cell viability, after 4 hours of exposure, maintaining its efficacy at higher doses after 24 hours exposure (p<0.05). The animals treated with melatonin showed reduced tumor size compared to control animals after 21 days of treatment (p<0.05). The mean tumor volume of control and treated animals were 282.00 ± 88.53 mm3 and 144.90 ± 38.38 mm3, respectively. The mean of tumor volume in control animals increased significantly from day 14 (118.90 ± 40.17 mm3) to day 21 (282.00 ± 88.53 mm3) (p<0.05), which was not observed in the treated group. Furthermore, there was tumor regression in an animal treated with melatonin (Day 7 = 27.38 mm3; Day 14 = 8.79 mm3; Day 21 = 4.8 mm3), similar pattern was not seen in any of the control. Animals treated with melatonin showed lower activity of Tc-99-VEGF-C in the tumors compared to that of the animals that were treated with vehicle. The intensity of radioactivity in the control animals was 183.55 ± 20.92%, while the intensity of radioactivity in animals treated with melatonin was 150.46 ± 17.06%. Although there was difference in the radioactivity in the tumors between the two group, statistically significant difference was not achieved (p>0.05). However, decrease of VEGFR2 in melatonin treated mice was confirmed by immunohistochemistry (p<0.05). In addition, there was a decrease of micro-vessel density (vWF) and cell proliferation (Ki-67) in melatonin treated tumors (p<0.05). Conclusion: Taken together, our results showed that melatonin inhibits tumor growth, cell proliferation and blocks tumor angiogenesis in breast cancer, directing the development of a clinical study to determine its therapeutic potential for breast cancer. Citation Format: Bruna Victorasso Jardim-Perassi, Ali S. Arbab, Lívia Carvalho Ferreira, Thaiz Ferraz Borin, Nadimpalli Ravi S. Varma, Adarsh Shankar, Asm Iskander, Meser M. Ali, Debora Aparecida Pires de Campos Zuccari. Effect of melatonin on the tumor growth and angiogenesis of breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A009.