Abstract
Nicotinamide, an antipellagratic vitamin, significantly suppressed urethane-induced malformations in mice. In the present study, effects of nicotinamide were examined on the growth of transplanted murine breast adenocarcinoma C3H/HeJ #8, which originated spontaneously in this strain, and urethane-induced lung tumorigenesis in JCL : JCR mice. Nicotinamide also showed potent antitumorigenic effects, when it was given with diet immediately after urethane treatment (1 mg/g, s.c.) or the tumor transplantation (s.c.). The level of inhibition was proportional to the dose of nicotinamide in diet, that is 48.5 and 72% for tumor weights (2.5 and 5.0% in diet), and 20.7, 54.6 and 65.2% for lung tumor (1.0, 2.5 and 5.0%), respectively. Furthermore antiteratogenic and antitumorigenic effects of nicotinamide were also significant even when it was given 2-4 or 10-20 days after urethane treatment, and 14 days after tumor transplantation. Nicotinamide seems to act directly on the organs, fetus, placenta and tumor tissues as nicotinamide itself or NAD^+, but not as nicotinic acid, since only nicotinamide and small amount of NAD^+ were detected chromatographically. The mechanism of the suppressing effects of nicotinamide on the teratogenesis and tumorigenesis has been discussed.
