Treatment with the NO donor JS-K reduces lung metastases and improves survival by acting directly on the primary tumor. (A and B) WT mice were treated with either the NO donor JS-K or the non–NO-releasing analogue JS-43-126. (A) On day 22, mice were euthanized and the primary tumor was dissected and measured. (B) Lungs from these treated mice were collected on the same day and fixed in Bouin’s solution. The number of lung metastases was counted under a dissecting microscope. The pooled results from two experiments each consisting of 10 mice/treatment group are shown. *, P < 0.05; **, P < 0.002 for the indicated comparisons. The error bars indicate the standard error of the means for each treatment group. (C) For studies of tumor progression, some mice were treated with JS-K only on days 4, 6, 8, and 10 (JSK early). All mice received surgical removal of the tumor-bearing kidney on day 11 followed treatment with IL-2/α-CD40 or saline (VC) beginning on day 12 for 2 wk. Some mice were treated with JS-K on days 13, 15, 18, 20, and 22 (JSK late). Survival analysis was plotted according to the Kaplan-Meier method. The results are from one experiment in which each treatment group contained at least eight mice.