Diosgenin and temozolamide: A potential combinatorial chemotherapy to overcome temozolamide resistance in glioblastoma multiforme

Abstract

Introduction: Glioblastoma multiforme (GBM) accounts for the most aggressive form of tumor showing poor prognosis. Prevailing treatment modality includes chemotherapy with temozolomide (TMZ) concomitant with surgical resection and/or irradiation. However, it has been observed that a number of patients are developing resistance to TMZ owing to its high dosage regimen. The aim of this study is to examine the effects of diosgenin (DSG), a natural steroidal saponin obtained from fenugreek, in combination with TMZ in human GBM cells and TMZ resistant GBM cells. Methodology: The potential of combinatorial chemotherapy for overcoming TMZ resistance was evaluated through development of TMZ resistant GBM clones. These clones were generated by treatment of GBM cells with sub-lethal dose of TMZ over several cycles. Cellular effects were studied by viability assay, flow cytometry and wound healing assay on both single and combined drug treated GBM cells and TMZ resistant cells, respectively. The morphological study and cellular uptake in combined or individual drug treated cells was assessed by microscopy and immunofluorescence staining. The time dependant effect of drugs on invasive and migratory potential of GBM cells and TMZ resistant cells was analysed through zymography for matrix metalloproteinases (MMPs) activity and western blot for apoptotic proteins, epithelial and mesenchymal (EMT) markers, MMPs and VEGF expression. Further, the drug induced apoptosis was also assessed through chromatin condensation and DNA laddering assay. Results: Our investigation shows that co-administration of DSG and TMZ resulted in a substantial increase in GBM cell apoptosis and marked inhibition of cell growth in vitro. Anti-angiogenic and anti-invasive potential of DSG and TMZ were assessed through in vitro studies. At molecular level, DSG and TMZ synergistically lower XIAP expression and cleavage of intracellular death substrates such as PARP thereby shifting the balance from survival to apoptosis as indicated by the rise in the sub-G1 cell population. This combination also alters EMT markers, downregulates the expression of Bcl-xL, Bcl-2, Mcl1, MMPs and VEGF and induces expression of Bax, AIF, cytochrome C. Conclusion: The results suggested that DSG in combination with TMZ reduced the dose of TMZ, when administered singly, and also inhibited the migration and invasion of GBM and TMZ resistant cells. It induced apoptosis and altered the expression of EMT markers. These findings reveal a new therapeutic potential for overcoming TMZ resistance in GBM therapy. This novel modality may be a promising tool for GBM treatment.