Figure 1. CBD enhances the inhibitory effects of Δ⁹-THC on glioblastoma cell growth.

To test for positive and negative interactions a 2 × 2 factorial design using specific µM concentrations of drug were used as described in the methods. Cell proliferation was measured using the MTT assay. A) SF126 and B) U251 cells were treated for three days with vehicle/no drug, Δ⁹-THC, CBD, or a combination of Δ⁹-THC and CBD. Concentrations of Δ⁹-THC and CBD that produce only minimal effects on cell proliferation were also tested in 2 × 2 factorial design in C) SF126 and D) U251 cells. % control was calculated as the MTT product absorbance in the treated cells/control cells × 100. Data are the mean of at least 3 independent experiments; bars, ± SE. Data was analyzed using a two-way ANOVA (GraphPad Prism, San Diego, CA). (*) indicates statistically significant interaction (p<0.01). Inset on D) Representative light microscope image of the effects of the combination treatment on U251 cells (40X).