There is increasing evidence that
L-ascorbic acid (LAA) is selectively toxic to some types of
cancer cells at pharmacological concentrations, functioning as a
pro-oxidant rather than as an
anti-oxidant. However, the molecular mechanisms by which LAA initiates cellular signaling leading to cell death are still unclear. In an effort to gain insight into these mechanisms, the effects of LAA on eukaryotic transcription nuclear factor
NF-kappaB and
cyclooxygenase-2 (COX-2) expression were investigated. In the present study, LAA suppressed
DNA binding activity of
NF-kappaB, composed of a p65/p50 heterodimer, through inhibition of degradation of inhibitory kappaB-alpha (
IkappaB-alpha) and prevention of nuclear translocation of p65. The inhibitory effect of LAA on
NF-kappaB activity was dependent upon
glutathione levels in HL-60 cells, as well as generation of H2O2 but not
superoxide anion. LAA also downregulated the expression of COX-2, which has a
NF-kappaB binding site on its promoter, through repressing
NF-kappaB DNA binding activity. Moreover, cotreatment of 1 microM
arsenic trioxide (
As2O3) with various concentrations of LAA enhanced an LAA-induced repression of
NF-kappaB activity and COX-2 expression. In conclusion, our data suggest that LAA exerts its anti-
tumor activity through downregulation of
NF-kappaB activity and COX-2 expression, and these inhibitory effects can be enhanced by co-treatment with
As2O3.