Structural modification of naturally-occurring phenolics as a strategy for developing cytotoxic molecules towards cancer cells

Natural products belonging to different chemical classes have been established as a promising source of novel anticancer drugs. Several low molecular weight compounds from the classes of monoterpenes, phenylpropanoids and flavonoids were shown to possess anticancer activities in previous studies. In this work, over 20 semisynthetic derivatives of molecules belonging to these classes, namely thymol, eugenol and 6-hydroxyflavanone were synthesized and tested for their cytotoxicity against two human cancer cell lines, namely gastric adenocarcinoma (AGS cells) and human lung carcinoma (A549 cells). An initial screening based on viability assessment was performed in order to identify the most cytotoxic compounds at 100 μM. The results evidenced that two 6-hydroxyflavanone derivatives were the most cytotoxic among the compounds tested, being selected for further studies. Noteworthy, in a general way some of the derivatives synthesized displayed enhanced toxicity when compared with their natural counterparts. Moreover, LDH assay showed that the loss of cell viability was not accompanied by a loss of membrane integrity, thus ruling out a necrotic process. Morphological studies with AGS cells demonstrated chromatin condensation compatible with apoptosis, confirmed by the activation of caspase 3/7. Furthermore, a viability assay on non-cancer human embryonic lung fibroblast cell line (MRC-5) confirmed these two derivatives possess selective anticancer activity.