Fig. 3.

NO-metabolism-related anti-cancer strategies. A schematic illustration of NO metabolic pathways in a cancer cell. Red arrows denote the cancer-related up- or down-regulation of proteins that are involved in NO metabolism, leading to a net increase in NO production. Tumor cells can enhance NO production by: upregulating NOS levels; increasing arginine transport; increasing the levels of ASS1 and ASL to enhance arginine availability for NO synthesis; or by decreasing arginine metabolism by inhibiting arginase. Purple arrows denote the cancer-related up- or down-regulation of proteins involved in NO metabolism, leading to a net decrease in NO production. In addition to restricting NO levels, ASS1 inhibition and ARG2 upregulation might also metabolically support cancer by increasing the production of pyrimidines and polyamines, respectively (dashed blue arrows). Anti-cancer NO-related strategies that increase NO levels are denoted in a red box and those that downregulate NO levels are depicted in blue boxes. NO-related anti-cancer strategies include increasing levels of NO with NO donors, or decreasing NO levels via NOS inhibition or with PEGylated arginine-degrading enzymes. ADI, arginine deiminase; ASA, argininosuccinic acid; ASL, argininosuccinate lyase; ASS1, argininosuccinate synthase 1; NO, nitric oxide; NOS, nitric oxide synthase.