Purpose: In recent years, a number of reports have shown the anticancer activity of plant extracts and phytoalkaloid.
Methods: We have evaluated the cytotoxicity profiles of 157 extracts prepared from dietary or medical plants growing in the Okinawa island, using 10 different cell lines. In vitro cytotoxicity screening indicated the presence of a highly selective cytotoxic compound in the extract of Toddalia asiatica Lam. The known alkaloid (1,3)benzodioxolo(5,6-c)phenanthridine, 12,13-dihydro-2,3-dimethoxy-12-methyl-(dihydronitidine) was identified as an active material from this plant. This alkaloid had highly specific cytotoxicity to human lung adenocarcinoma (A549) cells.
Results: The results of the fluorescence activated cell sorter (FACS) analysis and the measurement of caspase-3 activity showed that dihydronitidine induced specific apoptotic cell death in A549 cells. Gene expression analysis in the apoptotic cells found that dihydronitidine variously regulated the cell cycle related genes (CDK2 and CCNE), and up-regulated the cell death related genes specifically in tumor cells. Thus dihydronitidine manifested its characteristics in the tumor selective cytotoxicity, contrasting with the case of a known anticancer agent camptothecin (CPT). Microscopic observation further revealed the specific accumulation of dihydronitidine within the cytosolic organelle, but not in the nuclei of adenocarcinoma. No accumulation was observed with CPT in all cell lines.
Conclusion: The data suggested that dihydronitidine toxicity targeted a particular intracellular organelle in the tumor cells.