[Role of metallothionein in cancer chemotherapy]

Metallothionein (MT) shows a protective effect against toxic actions of some antitumor drugs and gamma-irradiation in animals. Preadministration of bismuth subnitrate, an MT inducing drug, significantly reduced side effects of antitumor drugs without affecting antitumor activity of the drugs. This specific effect of bismuth on the toxicity of antitumor drugs appears to be attributable to its specific induction of MT in normal tissues, but not in tumor tissue. Preinduction of MT synthesis in the lung also prevented mice from carcinogenesis caused by cisplatin and melphalan in the lung. On the other hand, zinc compound induced MT synthesis in the tumor, and significantly suppressed the antitumor activity of some antitumor drugs. Propargylglycine (PPG), an inhibitor of cystathionine pathway, significantly inhibited MT induction by zinc in the tumor inoculated in mice, and, consequently, PPG could diminish cisplatin resistance acquired by an increase in the tumor MT levels.