Synergistic Antitumor Activity of Vitamins C and K3 on Human Bladder Cancer Cell Lines

Abstract

Exponentially growing cultures of human bladder tumor cells (RT4 and T24) were treated with Vitamin C (VC) alone, Vitamin K3 (VK3) alone, or with a VC:VK3 combination continuously for 5 days or treated with vitamins for 1 h, washed with PBS and then incubated in culture medium for 5 days. Co-administration of the vitamins enhanced the antitumor activity 12- to 24-fold for the RT-4 cells and 6- to 41-fold for the T24 cells. Flow cytometry of RT4 cells ex- posed to the vitamins revealed a growth arrested population and a population undergoing cell death. Growth arrested cells were blocked near the G0/G1-S-phase interface, while cell death was due to autoschizis. Catalase treatment abro- gated both cell cycle arrest and cell death which implicated hydrogen peroxide (H2O2) in these processes. The H2O2 production resulted in a moderate increase in lipid peroxidation and depletion of cell thiol levels. Analysis of cellular ATP levels revealed a transient increase in ATP production for VC and the VC:VK3 combination, but decreased ATP levels following VK3 treatment. Lipid peroxidation, thiol depletion and ATP modulation occurred at a 17-fold lower concentration in the vitamin combination than with either vitamin alone. These results suggested that the increased cy- totoxicity of the vitamin combination was due to redox cycling and increased oxidative stress.