EP09.02 THE COMBINATION OF CANNABINOIDS AND RADIOTHERAPY DEMONSTRATES STRONG ANTI-TUMOR EFFECTS ON HUMAN GLIOMA CELLS

Abstract BACKGROUND The lack of comprehensive studies on how cannabinoids function and the limited data on their combination with radiotherapy have restricted their therapeutic application in treating brain tumors. Therefore, this study aimed to demonstrate the anti-tumor effects of cannabinoids, explore their interaction with radiotherapy, and identify the optimal dosing regimen required to achieve an anti-tumor effect when used alongside radiotherapy. This investigation was conducted in vitro using glioblastoma multiforme (GBM) cells. MATERIAL AND METHODS In this study, Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol (CBD)-containing Sativex, and a GBM cell line (U87-MG) were utilized. Throughout all experimental steps, the cells were cultured in Dulbecco’s Modified Eagle Medium (DMEM) with 10% fetal bovine serum, 1% penicillin-streptomycin, and 1% L-glutamine in an incubator set to 37°C with 5% CO₂ and 5% humidity. Before application, Sativex was dissolved in DMSO at a 1: 1 ratio and then diluted in the culture medium to concentrations ranging from 1/3000 to 1/6000 before being applied to the cells. Cell viability under Sativex treatment was assessed using the MTT assay, and absorbance values were measured at 595 nm using a microplate reader (Thermo; Multiscan FC). Results were expressed as percentage viability, with the untreated group serving as the control. Cells in the Radiation-Sativex group underwent exposure to Sativex for 24 hours, followed by irradiation at doses of 2Gy, 4Gy, and 6Gy. All radiotherapy applications in the study were performed using a phantom specifically designed to accommodate the culture plates. All clonogenic assays were conducted using the Puck and Marcus technique and evaluated by counting colonies containing at least 50 cells. After staining, the cell colonies in each well were meticulously counted, and plating efficiency (PE) and clonogenic survival (SF) were calculated using standard formulas. RESULTS Different dilutions of Sativex were tested to assess their effect on cell viability, and the 1/5500 dilution resulted in 50.4% cell viability. The combination of Sativex and radiation significantly enhanced the anti-tumor effect compared to radiation alone. With Sativex treatment, the survival rate decreased from 84.26% to 49.69% at 2Gy, 81.32% to 40.66% at 4Gy, and 65.96% to 36.82% at 6Gy. CONCLUSION This study demonstrated that cannabinoids when used concurrently with radiation, enhanced the anti-tumor efficacy of radiotherapy through a synergistic effect. This combination therapy may offer a promising approach, particularly in treating high-grade gliomas resistant to current treatments. However, these findings need to be supported by in vivo experiments, and the data obtained should be further evaluated in clinical studies to establish a safe and effective therapeutic profile.