KEY POINTS
- The investigators tested six cannabinoids—CP-55,940, cannabigerovarin, cannabidiol, cannabicyclol, cannabielsoin, and cannabichromene—across four glioblastoma cell lines: U251-MG, T98G, SNB75, and LN229, using concentrations generally ranging from 3–30 µM.
- Cannabinoids alone generally did not kill glioblastoma cells at lower concentrations. At 30 µM, cannabidiol induced substantial apoptosis across the tested glioblastoma lines, but the same concentration also induced apoptosis in approximately 98% of human neural progenitor ReNcells, arguing against tumor-selective cytotoxicity at high doses.
- Cannabinoids frequently reduced chemotherapy-induced apoptosis. In U251-MG cells treated with 100 µM carboplatin, only 32.1% of cells remained viable, compared with 64.7% when 30 µM cannabigerovarin was added; protective effects were also observed with bleomycin, etoposide, paclitaxel, and other agents.
- The effect extended beyond short-term viability. 10 µM cannabigerovarin increased colony outgrowth after carboplatin, bleomycin, etoposide, or paclitaxel compared with chemotherapy alone, suggesting that cannabinoid exposure could permit long-term survival rather than merely delaying cell death.
- Cannabinoids also reduced apoptosis after glioblastoma-standard treatments. 30 µM cannabigerovarin, 10 µM cannabidiol, and 20 µM CP-55,940 protected U251-MG cells from apoptosis after 10 or 20 Gy irradiation, while CP-55,940, cannabigerovarin, and cannabielsoin reduced apoptosis after combined 8 Gy plus 100 µM temozolomide.
- Mechanistically, cannabinoid exposure reduced mitochondrial apoptotic priming and increased expression of the pro-survival protein BCL-XL. Cannabigerovarin and cannabidiol also increased p21 signaling and shifted irradiated cells toward G1 arrest; at 24 hours, the G1 population increased by 12.33% with cannabigerovarin (p=0.0007) and 9.41% with cannabidiol (p=0.0311).
- Knockdown of the canonical cannabinoid receptors CB1 and CB2 did not abolish the protective effect, suggesting that alternative cannabinoid receptors or receptor-independent mechanisms may be involved. The study remains entirely preclinical, and whether these effects occur at clinically relevant tumor exposures in patients is unknown.
CLINICAL TAKEAWAY
These data raise a credible preclinical concern that cannabinoids could reduce glioblastoma cell killing by radiation and chemotherapy rather than enhance it. They are not sufficient to recommend changing clinical practice, but concurrent cannabinoid exposure during glioblastoma treatment deserves prospective investigation rather than being assumed to be oncologically neutral.