Dexamethasone protected human glioblastoma U87MG cells from temozolomide induced apoptosis by maintaining Bax:Bcl-2 ratio and preventing proteolytic activities.

in Molecular cancer by Arabinda Das, Naren L Banik, Sunil J Patel, Swapan K Ray

TLDR

  • The study looked at how a medicine called dexamethasone (DXM) affects the way another medicine called temozolomide (TMZ) works on human brain tumor cells. The study found that DXM does not help with the way TMZ works on the cells, and in fact, it might make the treatment less effective. The study also found that DXM can cause the cells to die in a different way than TMZ, which might not be as helpful for the treatment. The study suggests that doctors should be careful when giving DXM to patients who are also taking TMZ for brain tumors.

Abstract

Glioblastoma is the deadliest and most prevalent brain tumor. Dexamethasone (DXM) is a commonly used steroid for treating glioblastoma patients for alleviation of vasogenic edema and pain prior to treatment with chemotherapeutic drugs. Temozolomide (TMZ), an alkylating agent, has recently been introduced in clinical trials for treating glioblastoma. Here, we evaluated the modulatory effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells. Freshly grown cells were treated with different doses of DXM or TMZ for 6 h followed by incubation in a drug-free medium for 48 h. Wright staining and ApopTag assay showed no apoptosis in cells treated with 40 microM DXM but considerable amounts of apoptosis in cells treated with 100 microM TMZ. Apoptosis in TMZ treated cells was associated with an increase in intracellular free [Ca2+], as determined by fura-2 assay. Western blot analyses showed alternations in the levels of Bax (pro-apoptotic) and Bcl-2 (anti-apoptotic) proteins resulting in increased Bax:Bcl-2 ratio in TMZ treated cells. Western blot analyses also detected overexpression of calpain and caspase-3, which cleaved 270 kD alpha-spectrin at specific sites for generation of 145 and 120 kD spectrin break down products (SBDPs), respectively. However, 1-h pretreatment of cells with 40 microM DXM dramatically decreased TMZ induced apoptosis, decreasing Bax:Bcl-2 ratio and SBDPs. Our results revealed an antagonistic effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells, implying that treatment of glioblastoma patients with DXM prior to chemotherapy with TMZ might result in an undesirable clinical outcome.

Overview

  • The study evaluates the modulatory effect of dexamethasone (DXM) on temozolomide (TMZ) induced apoptosis in human glioblastoma U87MG cells. The study aims to determine if treatment of glioblastoma patients with DXM prior to chemotherapy with TMZ might result in an undesirable clinical outcome. The methodology used for the experiment includes treating freshly grown cells with different doses of DXM or TMZ for 6 h followed by incubation in a drug-free medium for 48 h. The study uses Wright staining and ApopTag assay to determine apoptosis, fura-2 assay to determine intracellular free [Ca2+], and western blot analyses to determine protein levels and ratios. The primary objective of the study is to determine the antagonistic effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells.

Comparative Analysis & Findings

  • The study compares the outcomes observed under different experimental conditions or interventions, specifically the modulatory effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells. The study identifies that treatment of cells with 40 microM DXM does not induce apoptosis, while treatment with 100 microM TMZ induces significant amounts of apoptosis. The study also finds that apoptosis in TMZ treated cells is associated with an increase in intracellular free [Ca2+], as determined by fura-2 assay. Western blot analyses show that treatment of cells with TMZ results in increased Bax:Bcl-2 ratio and overexpression of calpain and caspase-3, which cleave 270 kD alpha-spectrin at specific sites for generation of 145 and 120 kD spectrin breakdown products (SBDPs), respectively. However, 1-h pretreatment of cells with 40 microM DXM dramatically decreases TMZ induced apoptosis, decreasing Bax:Bcl-2 ratio and SBDPs. The key findings of the study suggest that treatment of glioblastoma patients with DXM prior to chemotherapy with TMZ might result in an undesirable clinical outcome due to the antagonistic effect of DXM on TMZ induced apoptosis.

Implications and Future Directions

  • The study's findings have significant implications for the field of research and clinical practice, as they suggest that treatment of glioblastoma patients with DXM prior to chemotherapy with TMZ might result in an undesirable clinical outcome. The study identifies that 1-h pretreatment of cells with 40 microM DXM dramatically decreases TMZ induced apoptosis, decreasing Bax:Bcl-2 ratio and SBDPs. Future research directions could explore the mechanisms underlying the antagonistic effect of DXM on TMZ induced apoptosis and identify potential therapeutic targets for the treatment of glioblastoma. The study also highlights the importance of considering the timing and dosage of medications when treating glioblastoma patients to optimize treatment outcomes.
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