Effects of sodium ascorbate (vitamin C) and 2-methyl-1,4-naphthoquinone (vitamin K₃) treatment on human tumor cell growth in vitro. I. Synergism of combined vitamin C and K₃ action

The effects of sodium ascorbate (vitamin C) and 2-methyl-1,4-naphthoquinone (vitamin K₃) administered separately or in combination on the in vitro cultured human neoplastic cell lines MCF-7 (breast carcinoma), KB (oral epidermoid carcinoma), and AN₃-CA (endometrial adenocarcinoma) have been examined. When given separately, vitamin C or K₃ had a growth inhibiting action only at high concentrations (5.10³ μmol/1 and 10⁵ nmol/1, respectively). Combined administration of both vitamins demonstrated a synergistic inhibition of cell growth at 10 to 50 times lower concentrations. At this level separately given vitamins are not toxic. The sensitivity to this treatment was somewhat different in the three cell lines, being slightly higher for KB line. This tumor cell growth inhibitory effect was completely suppressed by the addition of catalase to the culture medium containing vitamins C and K₃, suggesting an excessive production of hydrogen peroxide as being implied in mechanisms responsible for the above-mentioned effects.