Anticancer effects of phytocannabinoids used with chemotherapy in leukaemia cells can be improved by altering the sequence of their administration

Phytocannabinoids possess anticancer activity when used alone, and a number have also been shown to combine favourably with each other in vitro in leukaemia cells to generate improved activity. We have investigated the effect of pairing cannabinoids and assessed their anticancer activity in cell line models. Those most effective were then used with the common anti-leukaemia drugs cytarabine and vincristine, and the effects of this combination therapy on cell death studied in vitro. Results show a number of cannabinoids could be paired together to generate an effect superior to that achieved if the components were used individually. For example, in HL60 cells, the IC50 values at 48 h for cannabidiol (CBD) and tetrahydrocannabinol (THC) when used alone were 8 and 13 µM, respectively; however, if used together, it was 4 µM. Median-effect analysis confirmed the benefit of using cannabinoids in pairs, with calculated combination indices being