Cytotoxic and apoptosis–inducing activity of ramentaceone – a naphthoquinone from Drosera sp

Naphthoquinones represent a group of compounds, which exhibit various biological activities including anticancer properties. The objective of this research was to evaluate the cytotoxic activity of ramentaceone (7-methyljugone) isolated from Drosera sp. and determine whether cell death induced by this compound is mediated through the induction of apoptosis. Ramentaceone exhibited high cytotoxic activity against various human tumor cell lines, with the highest activity observed against leukemic lines HL-60 and U937 (IC₅₀ 1.5µg/mL).The mode of cell death induced by ramentaceone was evaluated using the HL-60 cell line. Typical morphological features of cells undergoing apoptosis were examined, such as cell shrinkage, nuclear condensation and DNA fragmentation. The treatment of HL-60 cells with ramentaceone induced an increase in the sub-diploid DNA content. A loss in membrane phospholipids asymmetry determined by the externalization of phosphatidylserine as well as a loss in mitochondrial membrane potential (Δψm) were observed upon the treatment of cells with ramentaceone. Naphthoquinones are known redox cycling agents, therefore the generation of reactive oxygen species by ramentaceone was evaluated in HL-60 cells. To determine whether the induction of cell death by ramentaceone is mediated through the generation of ROS, cells were pretreated with a free radical scavenger N-acetylcysteine (NAC). NAC reversed the toxicity of ramentaceone as well as prevented the induction of DNA fragmentation in ramentaceone-treated cells pointing out to the involvement of ROS generation in the mechanism of cell death induced by ramentaceone.

Acknowledgements: Funding from Grant No. BW/B051–5-00620–6, The Foundation for the Development of Gdansk University and The Integrated Regional Operational Programme (IROP).