Mechanisms involved in the cytotoxic action of Brazilian propolis and caffeic acid against HEp‐2 cells and modulation of P‐glycoprotein activity

Objectives The effects of propolis and phenolic compounds (caffeic acid – Caf; dihydrocinnamic acid – Cin; p‐coumaric acid – Cou) in the same quantity found in our propolis sample were investigated on human laryngeal epidermoid carcinoma (HEp‐2) cells. Methods Cell viability, apoptosis/necrosis and cell cycle arrest, P53 and CASPASE‐3 gene expression, generation of reactive oxygen species (ROS) and the ability of propolis to induce doxorubicin (DOX) efflux using a P‐glycoprotein (P‐gp) inhibitor (verapamil) were assayed. Key findings Propolis exerted a cytotoxic effect on HEp‐2 cells, whereas isolated compounds had no effect on cell viability. Higher concentrations were tested and Caf induced late apoptosis or necrosis in HEp‐2 cells, while propolis induced apoptosis, both probably due to ROS generation. P53 expression was downregulated by propolis but not by Caf. CASPASE‐3 expression was correlated with induction of both early and late apoptosis, with both propolis and Caf alone upregulating its expression. Propolis induced cell cycle arrest at G2/M phase and Caf at S phase. Propolis but not Caf may act as a P‐gp inhibitor by modulating P‐gp activity and inhibiting DOX efflux. Conclusions Propolis exerted cytotoxic effects on HEp‐2 cells, and the mechanisms are discussed, showing its potential as an antitumour drug.