Artepillin C is the main compound present in propolis from Baccharis 
dracunculifolia, whose antitumor activity has been the focus of many studies. 
Herein, we shall investigate the Artepillin C mechanisms of action against cells 
derived from the oropharyngeal carcinoma (HEp-2). Cytotoxicity tests revealed 
that the concentrations of Artepillin C required to reduce cell viability by 50% 
(CC50) are dependent on the incubation time, decreasing from 40.7 × 10-5 mol/L 
to 15.7 × 10-5 mol/L and 9.05 × 10-5 mol/L considering 12, 24 and 48 h, 
respectively. Hydrophobic interactions on neutral species of Artepillin C induce 
aggregation over the HEp-2 plasma membrane, given the acid conditions of the 
cellular culture. Indeed, Langmuir monolayers mimicking cellular membranes of 
tumor cells revealed Artepillin C affinity to interact with 
1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) containing 20 mol% of 
1,2-dipalmitoyl-sn-glychero-3-phosphoserine (DPPS), leading aggregation on giant 
unilamellar vesicles (GUVs) at pH 3.2. Moreover, leakage experiments on GUVs 
have shown that the presence of DPPS enhances the efflux of the fluorescent 
probe signaling the membrane permeabilization, which is the origin of the 
necrotic pathway triggered in HEp-2 cells, as observed by flow cytometry assays.