Effect CB-R antagonists of cell viability. CEM, HEL-92, and HL60 cells were cultured continuously with either the CB1-R or the CB2-R antagonist (0-50 μM) for 2 days. As the trend in the effects of the individual antagonists were similar in that the CB1-R alone had no effect on viability while the CB2-R was cytotoxic, only the results of the effects on CEM are shown graphically, with the IC₅₀s seen in the cell lines shown in the inset box (A). Cells were also cultured for 2 days with a combination of THC (IC₅₀) and increasing concentrations of either the CB1-R antagonist (B) or the CB2-R antagonist (C). The effect of the CB1-R antagonist on the cytotoxic effect of the CB2-R antagonist (IC₅₀) (D), and the cytotoxic effect of the putative CB2-R agonist PEA (E), were also studied. The effect of PEA in CEM, HEL-92, and HL60 cells at IC₅₀ concentrations on THC-induced cytotoxicity were assessed on day 2 (F). White bars show untreated samples; light gray bars, THC at IC₅₀; dark gray bars, PEA alone; and black bars, the effect of both agents used concomitantly. Each data point represents the means and SDs of at least 3 separate experiments.