Amlodipine synergizes with temozolomide against glioma stem cells by modulating MGMT expression through downregulation of the AKT/GSK3β/β-catenin axis.

Temozolomide (TMZ) is the primary chemotherapeutic agent used for the treatment of glioblastoma. However, the high chemoresistance observed in glioblastoma remains a significant clinical challenge, which is associated with the repair of DNA alkylation sites by O6-methylguanine-DNA methyltransferase (MGMT). Exploring new strategies to enhance the tumoricidal activity of TMZ against chemoresistant glioma stem cells (GSCs), is crucial for improving patient outcomes. As a classical calcium channel blocker (CCB) against hypertension, amlodipine has been reported to have definite antitumor and chemo-sensitizing effects. However, it remains unclear whether it exhibits anti-glioblastoma activity or synergizes with TMZ in targeting GSCs. The present study revealed that amlodipine inhibited the GSC viability and induced apoptosis, cell cycle arrest in vitro. Furthermore, amlodipine significantly reduced tumor volume and prolonged median survival of tumor-bearing mice in vivo. Additionally, amlodipine enhanced the cytotoxicity of TMZ against GSCs by downregulating MGMT expression through the suppression of the Akt/GSK3β/β-catenin axis. Overexpression of MGMT reversed the synergistic effects of amlodipine with TMZ. Pharmacological inhibition of GSK-3β with CHIR-99021 or overexpression of β-catenin reversed amlodipine-induced downregulation of β-catenin and MGMT, reduction of cell viability and enhancement of TMZ cytotoxicity against GSCs. The intracranial xenograft model also showed that the synergy between amlodipine and TMZ could be achieved by downregulating β-catenin and MGMT, which prolonged the survival time of tumor-bearing mice. These results indicate that amlodipine has novel potential for repurposing as a synergetic chemotherapy against GSCs, aiming to disrupt the progression of therapy-resistant glioblastoma.