Phenethyl Caffeate Benzoxanthene Lignan is a derivative of Caffeic Acid Phenethyl Ester that induces bystander autophagy in WiDr cells

We recently reported that Phenethyl caffeatebenzoxanthene lignan (PCBL), a semisynthetic compoundderived from Caffeic Acid Phenethyl Ester (CAPE), inducesDNA damage and apoptosis in tumor cells. In thisstudy, we further investigated whether PCBL inducesautophagy in WiDr cells. We also analyzed the pathwaysregulating autophagy and the role of autophagy in PCBLinducedcell death. Our acridine orange staining and LC3 IIexpression results suggest that PCBL induces autophagosomesin WiDr cells. The levels of LC3 II expression weobserved after co-treatment of PCBL with bafilomycin A1and the reductions in p62 expression we observed afterPCBL treatment in WiDr cells demonstrate increasedautophagic flux, a reliable indicator of autophagic induction.The increased Beclin 1 expression in PCBL-treatedcells and the incapacity of PCBL to induce LC3 II in3-methyladenine (3-MA)-treated cells we observed suggeststhat PCBL-induced autophagy is class III PI3-kinasedependent. PCBL did not alter phosphorylation of themTOR substrate p70 S6 kinase, indicating that PCBLinducedautophagy was not mTOR regulated. Twoautophagy related proteins, Atg5 and Atg12, also remaineduninduced during PCBL treatment. The increased caspaseactivity and expression levels of LC3 II and p62 weobserved in response to PCBL treatment in primary gliomacells demonstrates that PCBL-induced apoptosis andautophagy were not cell line specific. Pharmacologicalinhibition of autophagy did not alter the antitumor efficacyof PCBL in WiDr cells. This attests to the bystander natureof PCBL-induced autophagy (in terms of cell death). Intoto, these data suggest that PCBL induces a class IIIkinase dependent, but mTOR independent, bystander modeof autophagy in WiDr cells.