Jj. Pink et al., NAD(P)H : quinone oxidoreductase activity is the principal determinant of beta-lapachone cytotoxicity, J BIOL CHEM, 275(8), 2000, pp. 5416-5424
beta-Lapachone activates a novel apoptotic response in a number of cell lin
es. We demonstrate that the enzyme NAD(P)H:quinone oxidoreductase (NQO1) su
bstantially enhances the toxicity of beta-lapachone. NQO1 expression direct
ly correlated with sensitivity to a 4-h pulse of beta-lapachone in a panel
of breast cancer cell lines, and the NQO1 inhibitor, dicoumarol, significan
tly protected NQO1-expressing cells from all aspects of beta-lapachone toxi
city. Stable transfection of the NQO1-deficient cell line, MDA-MB-468, with
an NQO1 expression plasmid increased apoptotic responses and lethality aft
er beta-lapachone exposure. Dicoumarol blocked both the apoptotic responses
and lethality. Biochemical studies suggest that reduction of beta-lapachon
e by NQO1 leads to a futile cycling between the quinone and hydroquinone fo
rms, with a concomitant loss of reduced NAD(P)H. In addition, the activatio
n of a cysteine protease, which has characteristics consistent with the neu
tral calcium-dependent protease, calpain, is observed after beta-lapachone
treatment. This is the first definitive elucidation of an intracellular tar
get for beta-lapachone in tumor cells. NQO1 could be exploited for gene the
rapy, radiotherapy, and/or chemopreventive interventions, since the enzyme
is elevated in a number of tumor types (i.e. breast and lung) and during ne
oplastic transformation.