Abstract 5828: Withaferin A and tumor treating fields synergistically inhibit glioma proliferation

Abstract

Abstract Glioblastoma multiforme (GBM) is the most lethal primary brain cancer (median survival: 15-17 months, 5-year survival: 5-10%). Current interventions consist of equally aggressive surgical resection, radiotherapy, and chemotherapy. However, this cancer is heterogeneous and not easily accessible so standardized, non-specific therapies are often ineffective. Novel, unorthodox approaches against GBM need consideration. Withaferin A is a steroidal lactone that originates from the roots and leaves of the winter cherry plant (Withania somnifera). Within Ayurvedic medicine, Withania somnifera extracts are applied to many disorders including several cancers. Extracts such as AshwaMAX can contain up to 4.3% (w/w) Withaferin A, a biologically active compound from Withania somnifera. Tumor Treating Fields (TTFields) are thought to disrupt mitotic spindle formation and stymie proliferation of actively dividing cancer cells. We report on the anti-cancer properties of both Withaferin A and TTFields. We also examined the hypothesis that combining TTFields with Withaferin A would synergistically inhibit GBM growth. We used GBM cells (U87-MG, GBM2, and GBM39) and breast adenocarcinoma cells (MDA-MB-231) isolated from human primary tumors. Each GBM cell line was modified to express firefly luciferase. Proliferative potential was assessed by bioluminescent imaging (BLI), cell counting via hemocytometer, or through the CellTiter-Blue® viability assay. Intracranial orthotopic U87-MG GBM xenografts were grown in the right frontal lobe of female nude mice (n=5/experiment). TTFields were imposed on cell cultures with the inovitroTM system from Novocure Ltd. Neurosphere cultures (U87-MG, GBM2, and GBM39) were inhibited by AshwaMAX at IC50 of 1.4, 0.19 and 0.22 µM (Withaferin A equivalent), respectively, and by Withaferin A with IC50 of 0.31, 0.28, and 0.25 µM, respectively. Oral gavage, every other day, of AshwaMAX (40mg/kg per dose) significantly reduced BLI signal (n=5 mice/group, p<0.02, four-parameter non-linear regression analysis) in preclinical models. Comsol modeling showed that the inovitroTM device imposed optimal TTFields in the center of the cell culture dishes. TTFields at 4 V/cm significantly inhibited (n=4 measurements per time point, p<0.001, 2-way ANOVA) growth of MDA-MB-231 cancer lines and all three human GBM lines. The effects were due to the TTFields alone and not to the slight temperature rises caused by the TTFields. Combination of Withaferin A (10-100 nM) with TTFields (4 V/cm) significantly inhibited GBM growth, to a degree beyond that of Withaferin A or TTFields alone. Poisson-based analysis of significance for regression indicated that the interaction of the combined treatments on GBM cells was synergistic (p<0.01, n=3 experiments). The findings suggest a novel approach to treat GBM in a manner that is likely better than either treatment (Withaferin A or TTFields) alone and that is synergistic. Citation Format: Edwin Chang, Chirag Patel, Christoph Pohling, Nooshin Beygui, Dong Ho Ha, Sanjiiv S. Gambhir. Withaferin A and tumor treating fields synergistically inhibit glioma proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5828.