The mechanism of antitumor action of a synthetic nitroflavone derivative,
2'-nitroflavone, was evaluated in vitro in HeLa human cervix
adenocarcinoma cells. We showed that the nitroflavone derivative slowed down the cell cycle at the S phase and increase the population of cells at the G2/M phase after 24h of incubation. The treatment with
2'-nitroflavone also induced an apoptotic response, characterized by an increase of the sub-G1 fraction of cells, by cells with
chromatin condensation and membrane blebbing, by a typical ladder of DNA fragmentation and by detection of apoptotic cells stained with
Annexin V. The observed apoptosis was regulated by
caspase-8 and -9, both contributing to the activation of the effector
caspase-3. In addition, inhibitors of
caspase-8 or -9 partially protected HeLa cells from 2'-nitroflavone-induced cell death. We also found that
2'-nitroflavone did not affect the total amount of Bax and Bcl-2
proteins, although a translocation of Bax from cytosol to mitochondria was evident after 6h of exposure. Furthermore,
2'-nitroflavone decreased the expression of the anti-apoptotic
Bcl-XL protein, induced the release of
cytochrome C to cytosol and increased the levels of Fas and Fas-L. Our results indicated that both
death receptor and mitochondria-dependent pathways are involved in the apoptotic cell death triggered by
2'-nitroflavone and suggest that this derivative could be a potentially useful agent for the treatment of certain
malignancies.