Identification of Ion Channels in Meningioma Cell Lines as Possible Targets for Combination Therapy

Abstract

Meningiomas (MN) are one of the most common types of brain tumors and are categorized by the World Health Organization (WHO) in three grades according to the severity, with grade III MNs being the most aggressive; patients diagnosed with the latter do not have a positive prognosis. Increased malignancy correlates with genetic heterogeneity, which is partly responsible for the difficulty of finding a chemical treatment. As of now, surgical resection is the best option for treatment of high grade MNs, however, failure to excise all cancerous tissue can lead to recurrence with increased aggressivity. The current chemotherapeutic treatment with the best efficacy is hydroxyurea (HU) although it has modest effect and is very toxic to the system. Therefore, there is a need to find alternative drug targets for potential treatment; for instance, voltage-gated calcium channels (VGCC) have garnered attention as potential target alternatives given their expression pattern in often abnormal and they can further enhance cancer malignancy and help with neoplastic growth. In fact, high voltage (HVA) and low-voltage (LVA) VGCC over-expression in cancer cells has positive effects on tumor cell proliferation, cell survival, apoptosis resistance and cancer invasiveness/metastasis. The use of antagonists targeting either channel types has proven successful in helping halt cancer cell proliferation. Research has shown that combination therapy of HU and a non-specific calcium channel antagonist (diltiazem) or a HVA antagonist (verapamil) has greater effect on decreasing tumor size and cell number compared to a monotherapy of either drug. LVA antagonists have recently been used to treat cancers such as glioblastoma with some efficacy. Here, we hypothesize that low-voltage gated calcium channels are also present in MN and that their targeting can be used to decrease MN cell viability or survival. We used immunocytochemistry, electrophysiology and cell biology assays to test our hypothesis. We first assessed whether ion channels and specifically VGCCs are present two MN cell lines (IOM-Lee and CH-157MN). We identified the presence of various VGCCs and a calcium-activated potassium channel (CNMA1). Moreover, 48-hr treatment with HVA (nimodipine, NIMO) or LVA (mibefradil, MIB) antagonists was effective in reducing MN cell viability, whereas a non-specific K channel blocker (TEA) had no effect on cell survival. Remarkably, co-incubation of MN cells with HU+MIB at clinically relevant doses resulted in significant synergy of the HU effect whereas HU+NIMO did not. We conclude the presence of VGCC is necessary for meningioma cell survival; when used at clinically relevant doses, monotherapy with HVA or LVA antagonist was sufficient to reduce MN survival, however, combination therapy with HU+MIB was the only treatment that induced a synergistic effect of the antineoplastic drug, suggesting a possible divergence in function between these channels in MN cells . Our data contributes to our understanding of the potential clinical use of MIB as a prospective drug for combination therapy approaches to treat meningiomas.