Abstract 4157: A role for miR-137 in enhancing efficacy of delphinidin in human glioblastoma.

Glioblastoma is the most lethal brain cancer in humans. Heterogeneity of cells in glioblastoma makes it extremely hard to control this tumor with a single therapeutic agent. Combination of therapeutic agents with diverse anti-cancer mechanisms must be used to manage this malignancy. Failures of conventional therapies and systemic toxicity have forced the search for newer agents, which may inhibit glioblastoma with less or no toxicity. Recently, microRNAs (miRs) are emerging as important regulators of different cellular processes such as proliferation, differentiation, and apoptosis in different cancers. Recent studies also suggest that the tumor suppressor miR-137 (TS miR-137) can induce differentiation and cell cycle arrest in human glioblastoma stem cells. In colorectal cancer, miR-137 is frequently silenced due to promoter hypermethylation. Use of 5-aza-2′-deoxycytidine (AzaC), an inhibitor of DNA methylation, may increase expression of miR-137 in glioblastoma with significant inhibition of proliferation of tumor cells. Delphinidin (DPN), which belongs to a class of natural chemicals from colored fruits, has been shown to inhibit cell growth and induce apoptosis in many different cancers. We hypothesized that combination therapy with miR-137 overexpression and DPN treatment in presence of AzaC could be an effective therapeutic strategy to control growth of glioblastoma. We used MTT assay to examine the doses (10 to 50 μM) of DPN for inhibition of cell proliferation in three glioblastoma cell lines (U87MG, T98G, and LN18). All cell lines demonstrated 50% inhibition of proliferation at 50 μM DPN. We performed Annexin V staining and flow cytometric analysis after treatment with AzaC, transfection of precursor miR-137 mimic, and treatment with DPN alone and in combination in all three glioblastoma cell lines. Overexpression of only miR-137 could induce apoptosis, which was dramatically increased when the cells were subjected to combination therapy with DPN in presence of AzaC. Then, we examined efficacy of combination of AzaC, miR-137, and DPN for inhibition of angiogenic network formation and invasion properties in all three glioblastoma cell lines. Co-culture of human microvascular endothelial (HMVE) cells with control U87MG, T98G, or LN18 cells prompted HMVE cells for capillary-like network formation, which was completely inhibited during co-culture of HMVE cells and glioblastoma cells treated with combination therapy. Following combination therapy, we observed suppression of expression of angiogenic factors (VEGF and b-FGF), growth factor receptor (EGFR), and invasive factors (MMP-2 and MMP-9) and also inhibition of Akt and NF-κB survival pathways in all three glioblastoma cell lines. So, combination of the methylation inhibitor AzaC, overexpression of the TS miR-137, and the relatively new flavonoid DPN could be a promising therapeutic strategy for inhibiting growth of different human glioblastoma cells. Citation Format: Mrinmay Chakrabarti, Naren L. Banik, Swapan K. Ray. A role for miR-137 in enhancing efficacy of delphinidin in human glioblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4157. doi:10.1158/1538-7445.AM2013-4157