Currently, DNA topoisomerases have been recognized as
potential chemotherapeutic targets; etoposide, camptothecin
and several naphthoquinonoid natural products with anticancer
activities e.g. shikonin, lapachol, b-lapachone etc.
function to topoisomerases, albeit with wide variety of mechanisms
controlled by their respective chemical structures.
Again, all these compounds are reported as inducers of apoptosis
in human cancer cells.40) A recent study on the mode of
action of rhinacanthin drugs demonstrated that synthetic rhinacanthins-N
and -Q relaxed supercoiled DNA possibly
through the inhibition of topoisomerase II.14) Moreover, natural
naphthoquinonoid b-lapachone having the chemical
structure related with rhinacanthone which was also isolated
from R. nasutus KURZ., is revealed to induce apoptosis
through p53 independent pathway, cell cycle arrest at S
phase, and activation of caspase-3.28) Based on this knowledge,
it would be interesting to examine the apoptosis-inducing
activity of three rhinacanthin drugs, a main of naphthoquinone
esters isolated from the roots of R. nasutus KURZ., in
human cancer cells, since precise mechanisms of these naphthoquinone
drugs remain unclear