Ascorbic acid-enhanced antiproliferative effect of flavonoids on squamous cell carcinoma in vitro.

We examined the effects of flavone and two polyhydroxylated plant flavonoids (quercetin and fisetin), either singly or in combination with ascorbic acid, on the growth of a human squamous cell carcinoma cell line (HTB 43) in vitro. Fisetin and quercetin significantly impaired cell growth in the presence of ascorbic acid. Exposure of cells to ascorbic acid (2 micrograms/ml) and 2 micrograms/ml of either fisetin or quercetin resulted in 61 and 45% inhibition of cell growth, respectively, in 72 h, while treatment with ascorbic acid alone had no effect on cellular proliferation. Flavone and ascorbic acid, either as single agents or in combination, exhibited no significant inhibition at any of the concentrations tested. The enhancement of the antiproliferative effect of the above flavonoids by ascorbic acid may be due to its ability to protect these compounds against oxidative degradation.