Differential effects of streptozotocin and streptozotocin-induced diabetes mellitus on tumor metastases and growth in mice.

Diabetic mouse serum was found to be toxic to F-10 melanoma cells in vitro. However, when F-10 cells were injected intravenously into streptozotocin-induced diabetic mice there was a significant increase in the number of lung tumors. Contrarily, when streptozotocin was injected after F-10 cells there was a 5-fold decrease in lung metastases. Reversal of the diabetes in these mice by nicotinamide or insulin injection did not increase the lung metastases. Solid tumors (resulting from the subcutaneous injection of F-10 cells) grew at similar rates in both control and diabetic mice. Streptozotocin injected after F-10 cells resulted in a 6 day delay in the appearance of solid tumors. Triglycerides, the toxic factors in vitro, were elevated to similar extents in both tumor-bearing control and diabetic mice. Most of the differences in tumor growth between control and streptozotocin injected mice were attributable to the antitumor activity of streptozotocin, rather than the diabetic state.