Arginine is depleted in mice receiving ADI-PEG 20, and this leads to reduced AML burden. (A) Plasma arginine was reduced in mice receiving ADI-PEG 20 either alone or in combination with cytarabine (data from 95 mice are shown). (B) Plasma citrulline levels were increased in mice receiving ADI-PEG 20 (data from 95 mice are shown). (C-H) The effects of ADI-PEG 20, cytarabine, and combination therapy on bone marrow AML percentage is shown. (C-E) ADI-PEG 20 alone reduced the percentage of AML in 3 experiments (AML samples 2, 3, and 5). (C-F) Cytarabine alone reduced the percentage of AML in 4 experiments (AML samples 2, 3, 4, and 5). (G-H) Neither drug alone was effective for AML samples 1 and 6, but the combination was effective in both. *P < .05.