The purpose of this study is to examine the differences in the induction of cytotoxic effects and
poly(ADP-ribose) polymerase-1 activation in human MCF-7
breast cancer cells by quinonoid derivatives of
naphthalene, including
1,2-naphthalenediol (NCAT), 1,4-naphthalenediol (NHQ),
1,2-naphthoquinone (1,2-NQ), and
1,4-naphthoquinone (1,4-NQ). Results from the cytotoxic response analyses in cells indicated that all
naphthalene quinonoids induced cell death in MCF-7 cells at concentrations ranging from 0.1 to 100microM where NHQ and 1,4-NQ were more efficient than NCAT and 1,2-NQ in the induction of cell death. Results from Western blot analyses confirmed that treatment of cells with NCAT and NHQ resulted in up-regulation of p53
protein expression and a significant shift in bax/bcl2 ratio, suggesting the induction of p53-dependent apoptosis in MCF-7 cells. Additionally, we observed that all
naphthalene quinonoids induced increases in
reactive oxygen species (ROS) formation and
glutathione (GSH) depletion in MCF-7 cells. The induction of ROS formation and GSH depletion in cells by
naphthalene quinonoids decreases in the rank order 1,4-NQ>NHQ>1,2-NQ approximately equal to NCAT. Further investigation indicated that least-squares estimates of the overall rates of elimination (k(e)) of
naphthalene quinonoids in MCF-7 cells decreased in the rank order 1,4-NQ>1,2-NQ>NHQ>NCAT. Values of k(e) were estimated to be between 0.280h(-1)(T(1/2)=151min) and 13.8h(-1)(T(1/2)=3.05min). These results provide evidence that the para-isomeric form of
naphthalene quinonoids tend to induce acute production of ROS and alterations in intracellular redox status in cells, leading to the subsequent cell death. Further, all
naphthalene quinonoids induced decreases in intracellular
NAD(P)H and
NAD(+) in MCF-7 cells at non-cytotoxic concentrations. The reduction of intracellular
NAD(P)H in cells exposed to NCAT and 1,2-NQ was blocked by two types of
poly(ADP-ribose) polymerase (
PARP) inhibitors whereas
PARP inhibitors did not prevent the reduction of
NAD(P)H in cells exposed to NHQ and 1,4-NQ. Further investigation confirmed that increases in the number of
DNA single-strand breaks were detected in MCF-7 cells exposed to NCAT and 1,2-NQ as measured by the single-cell gel electrophoresis (Comet) assay whereas NHQ and 1,4-NQ did not induce increases in the number of single-strand breaks in MCF-7 cells. Overall, results from our investigation suggest that while NHQ and 1,4-NQ are more efficient in the induction of cell death, NCAT and 1,2-NQ are prone to induce depletion of
NAD(P)H and
NAD(+) mediated by PARP-1 activation through formation of
DNA single-strand breaks in human cultured cells.