Cytoprotective and genotoxic effects of vitamins K1 and B1 on irinotecan in vitro.

Cultured human lymphocytes were treated with vitamins K and B, potential anticancer agents, either alone or in combination with irinotecan, a semisynthetic analogue of camptothecin. The frequency of sister chromatid exchanges (SCEs) was measured as an indicator of genotoxicity and the proliferation rate index (PRI) and mitotic index (MI) was measured as indicators of cytostatic effect. Vitamin K alone did not induce SCEs at the concentrations tested and combined with irinotecan does not increase SCE rates induced by irinotecan alone. Vitamin B significantly increased SCEs and, in combination with irinotecan, increased rates further (p < 0.05). Vitamin K decreased PRI and MI in combination with irinotecan, there were further increases in MI. At a low concentration, vitamin B reduced the levels of SCE and increased PRI induced by irinotecan. The use of these vitamins in combination with antitumor agents might reduce clinical side effects of the antineoplastics.