Background: Ovatodiolide (Ova), a major bioactive diterpenoid isolate of Anisomeles indica has drawn considerable attention lately as an effective anticancer agent with several published works demonstrating its tumor-inhibitory activity in various cancer types. Purpose: In this study, we examined the modulatory effect of Ova on the oncogenicity, proliferation, and cancer stem cell-like traits of glioblastoma (GBM) cells, as well as investigated the underlying molecular mechanism for the anticancer activity of Ova in GBM cell lines, U-87MG and GBM8401. Methods: The antiproliferative, apoptotic, and stemness-attenuating effects of Ova were evaluated using the sulforhodamine B (SRB) colorimetric assay, western blot and fluorescent immunocytochemistry. Cell apoptosis was analyzed based on variation in the expression levels of Bcl-2 family of regulator proteins Bax, Bak, Bcl-2 and Bcl-xL. Results: Ova induced the apoptosis of the U-87MG and GBM8401 cells, as well as effectively inhibited the proliferation and motility of the GBM cell lines in a dose- and time-dependent manner. Ova-induced apoptosis correlated with increased Bax/Bcl-2 ratio, while inhibition of tumor cell migration and colony formation was associated with reduced Slug, Vimentin, N[sbnd]Cadherin and β-catenin protein expression and increased E-Cadherin. In addition, exposure to Ova inhibited tumorsphere formation, elicited downregulation of CD44, CD133, Sox2, and Oct4, as well as correlated with dysregulation of the JAK2-STAT3 signaling pathway. Furthermore, we showed for the first time to the best of our knowledge that Ova potentiate the chemotherapeutic effect of Temozolomide. Conclusion: Taken together, our findings demonstrate the anticancer potential of Ova in GBM and its efficacy in the treatment of GBM as monotherapy and in combination with Temozolomide.
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