β-Asarone promotes Temozolomide's entry into glioma cells and decreases the expression of P-glycoprotein and MDR1

Glioma is the most common primary brain tumor and has an undesirable prognosis due to the blood-brain barrier (BBB) and drug resistance. A thorough investigation of the changes in intracellular drug concentrations is important to observe therapeutic effects and cell resistance. P-glycoprotein (P-gp) is an essential protein of Multi-drug resistance 1 (MDR1). The over-expression of P-gp and MDR1 is associated with poor prognosis and drug-resistance in glioma. However, β-asarone can pass through the BBB easily and increase the drug concentration in the rat brain. Our aim is to study the effect of β-asarone on promoting the entry of temozolomide (TMZ) into human glioma U251 cells. The cells were divided into three groups: model group, TMZ group (300 μM) and co-administration group (360 μM β-asarone; 300 μM TMZ). We further detected P-gp and MDR1 expression in U251 and rat glioma C6 cells in four groups: model group (U251/C6), TMZ group (U251 300 μM, C6 420 μM), β-asarone group (U251 360 μM, C6 450 μM) and co-administration group (β-asarone 360 μM, TMZ 300 μM for U251; β-asarone 450 μM, TMZ 420 μM for C6). Then, high performance liquid chromatography was used to determine the intracellular and extracellular levels of TMZ. Morphological changes in both cells were observed by the microscope. The Counting Kit-8 assay was used to measure the cell proliferation and toxicity. Cell immunohistochemistry/immunofluorescence, flowcytometry and western blot were synchronously used to examine the expression of P-gp. We also determined the levels of MDR1 mRNA by RT-PCR. The results showed that β-asarone could promote the entry of TMZ into U251 cells through the membrane. The co-administration of β-asarone and TMZ also decreased cell proliferation and the expression of P-gp and MDR1 better than single medication in U251 and C6 cells. All of the data suggest that β-asarone might contribute to treatment by promoting TMZ's entry into glioma cells, thereby contributing to anti-cancer growth and inhibiting P-gp and MDR1 expression.