G2/M cycle

Introduction

Glioblastoma (GBM) is recognized as the most common and aggressive primary brain tumor in adults, accounting for about 50% of all gliomas. Despite optimization of treatment approaches that include surgery, radiation, and chemotherapy, the prognosis remains poor, with a median survival ranging from 15 to 20 months, and only 3-5% of patients surviving beyond five years. Traditional chemotherapy with temozolomide (TMZ) shows limited efficacy due to acquired resistance and side effects, making the search for novel therapeutic agents imperative.

3-O-acetyl-11-keto-β-boswellic acid (AKBA)

Background on AKBA

3-O-acetyl-11-keto-β-boswellic acid (AKBA), derived from Boswellia serrata, is known for its anti-inflammatory properties and has potential as an anticancer agent. Prior research has indicated its ability to induce apoptosis in various cancer cell lines, including prostate and colon cancer, but its effects on glioblastoma and the mechanisms involved have not been fully elucidated.

Objectives of the Study

This study investigates the anti-tumor effects of AKBA on human glioblastoma cell lines (U251 and U87-MG), focusing on its impact on cell proliferation, migration, invasion, cell cycle progression, and apoptosis. The mechanisms underlying these effects are explored through flow cytometry, RNA sequencing, and Western blot analysis.

Results

Antiproliferative Effects of AKBA

AKBA significantly inhibited cell proliferation in a time- and dose-dependent manner, with IC50 values identified at 27.62 μM for U251 cells and 31.61 μM for U87-MG cells after 24 hours. AKBA also led to increased lactate dehydrogenase (LDH) release, indicating cytotoxicity. Furthermore, the EdU-DNA synthesis assay confirmed that AKBA obstructed DNA synthesis, emphasizing its potential to inhibit cell proliferation.

Inhibition of Migration and Invasion

Results indicate that AKBA treatment reduced the migration and invasion capabilities of glioblastoma cells as assessed by transwell assays. Additionally, colony formation assays demonstrate that AKBA effectively curtailed the ability of these cells to form colonies in soft agar.

Induction of Apoptosis

Apoptosis assays revealed that AKBA treatment resulted in an increase in early and late apoptotic cells. Mitochondrial membrane potential measurements indicated that AKBA caused depolarization, suggesting a mitochondrial-dependent apoptotic pathway. Evidence of caspase-3/7 activation and increased expression of cleaved-caspase 3 and PARP further supports the conclusion that AKBA promotes apoptosis in glioblastoma cells.

Cell Cycle Arrest at G2/M Phase

Cell cycle assays revealed that AKBA treatment led to a notable arrest at the G2/M phase. Subsequent analyses showed that AKBA regulated key signaling pathways associated with cell cycle checkpoints. Specifically, levels of p-CDK1, cyclin B1, and FOXM1 were found to be markedly decreased, indicating that AKBA disrupts the CDK1/cyclin B1 complex essential for G2/M progression. Conversely, the expression of p21 and GADD45A was upregulated, suggesting they play a role in mediating AKBA's effects.

In Vivo Efficacy

In a xenograft model, oral administration of AKBA significantly suppressed tumor growth in mice implanted with U87-MG cells, with no apparent systemic toxicity, further highlighting its therapeutic potential.

Conclusion

The study concludes that AKBA exerts promising anti-tumor effects against glioblastoma through mechanisms involving the induction of apoptosis and cell cycle arrest at the G2/M phase. The regulation of the p21/FOXM1/cyclin B1 pathway, coupled with suppression of the Aurora B/TOP2A pathway, underscores AKBA's potential as a novel chemotherapeutic agent in glioblastoma treatment.