The effect of zinc on mouse melanoma growth in vitro and in vivo

The effect of Zn2+ on mouse melanoma growth in vitro and in vivo was studied. Under in vitro conditions the proliferation of a Cloudman mouse melanoma cell line was inhibited by zinc ions at 10(-4) M, as measured by 3H-thymidine incorporation and optical density of NaOH cell digests. However, in vivo it was not possible to suppress both B16 and Cloudman S91 melanoma growth in mice by the administration of zinc ions. There were no significant differences in tumor growth after subcutaneous inoculation between mice constantly receiving 0.1% zinc acetate or 0.05% zinc sulphate in their drinking water and control groups, nor was it possible to decrease the number of lung metastases by zinc treatment after intravenous inoculation of tumor cells. The increased dietary supply of Zn failed to influence the survival time of mice in both melanoma types studied. Preincubation in vitro of cell suspensions in 10(-3) M zinc acetate prior to injection inhibited melanoma development in vivo. This implies that the in vivo zinc levels did not reach the necessary cytotoxic concentration.