NNMT and breast cancer: We found that Nnmt KO ameliorated the alteration in the urea cycle and uracil biogenesis (Fig. 5b, e): the amounts of arginine, citrulline, ornithine, and uracil did not significantly differ between the sham group and the 4T1 breast cancer-bearing group in the absence of Nnmt. These were consistent with gene expression profiles whereby Nnmt KO suppressed the upregulation of Asl and Arg1 in the 4T1 breast cancer-bearing condition.