Key Points• Glutamine removal and knockdown of the glutamine transporter SLC1A5 have antileukemic activity in AML.• The glutaminase activity of L-asparaginase inhibits mTORC1 and protein synthesis and induces a strong autophagy in AML.Cancer cells require nutrients and energy to adapt to increased biosynthetic activity, and protein synthesis inhibition downstream of mammalian target of rapamycin complex 1 (mTORC1) has shown promise as a possible therapy for acute myeloid leukemia (AML). Glutamine contributes to leucine import into cells, which controls the amino acid/Rag/mTORC1 signaling pathway. We show in our current study that glutamine removal inhibits mTORC1 and induces apoptosis in AML cells. The knockdown of the SLC1A5 high-affinity transporter for glutamine induces apoptosis and inhibits tumor formation in a mouse AML xenotransplantation model. L-asparaginase (L-ase) is an anticancer agent also harboring glutaminase activity. We show that L-ases from both Escherichia coli and Erwinia chrysanthemi profoundly inhibit mTORC1 and protein synthesis and that this inhibition correlates with their glutaminase activity levels and produces a strong apoptotic response in primary AML cells. We further show that L-ases upregulate glutamine synthase (GS) expression in leukemic cells and that a GS knockdown enhances L-ase-induced apoptosis in some AML cells. Finally, we observe a strong autophagic process upon L-ase treatment. These results suggest that L-ase anticancer activity and glutamine uptake inhibition are promising new therapeutic strategies for AML. (Blood. 2013;122(20):3521-3532)

Previous experimental studies have highlighted that citrulline (CIT) could be a promising pharmaconutrient. However, its pharmacokinetic characteristics and tolerance to loading have not been studied to date. The objective was to characterise the plasma kinetics of CIT in a multiple-dosing study design and to assess the effect of CIT intake on the concentrations of other plasma amino acids (AA). The effects of CIT loading on anabolic hormones were also determined. Eight fasting healthy males underwent four separate oral loading tests (2, 5, 10 or 15 g CIT) in random order. Blood was drawn ten times over an 8 h period for measurement of plasma AA, insulin and growth hormone (Gh). Urine samples were collected before CIT administration and over the next 24 h. None of the subjects experienced side effects whatever the CIT dose. Concerning AA, only CIT, ornithine (ORN) and arginine (ARG) plasma concentrations were affected (maximum concentration 146 (SEM 8) to 303 (SEM 11) mmol/l (ARG) and 81 (SEM 4) to 179 (SEM 10) mmol/l (ORN); time to reach maximum concentration 1·17 (SEM 0·26) to 2·29 (SEM 0·20) h (ARG) and 1·38 (SEM 0·25) to 1·79 (SEM 0·11) h (ORN) according to CIT dose). Even at high doses, urinary excretion of CIT remained low (,5 %). Plasma insulin and Gh were not affected by CIT administration. Short-term CIT administration is safe and well-tolerated. CIT is a potent precursor of ARG. However, at the highest doses, CIT accumulated in plasma while plasma ARG levels increased less than expected. This may be due to saturation of the renal conversion of CIT into ARG.Pharmacokinetics: Arginine: Ornithine: Insulin: Growth hormone Citrulline (CIT) is an amino acid whose name is derived from Citrullus vulgaris (commonly known as watermelon) from which it was first isolated in the 1930 s (for a recent review, see Curis et al.( 1) ). Until recently, CIT had not attracted much interest in the scientific community because (i) it is a non-proteic amino acid and (ii) it was considered only as an intermediate of the urea cycle (2) . In the early 1980 s, Windmueller & Spaeth (3) demonstrated that the small intestine releases large amounts of CIT which is mainly taken up by the kidney (of note, CIT is not taken up by the liver) and, in turn, arginine (ARG) was released in amounts equivalent to about 75 % of the CIT taken up. Then, Castillo et al. (4,5) were the first to characterise the CIT and ARG in vivo kinetics at the whole-body level in healthy subjects. These findings allowed the suggestion of an ARG -CIT -ARG inter-organ cycle which can be seen (6) as a mechanism for protecting dietary ARG from excessive liver degradation (because CIT is not taken up by the liver (7) ) and thus maintaining protein homeostasis. Concurrently, it was also demonstrated that CIT was the endproduct of the NO synthase reaction (8) .The role of the intestine as a key regulator of CIT production was further emphasised in situations where intestinal function is altered (i.e. short-bowel syndrome, coeliac disease, radiation-induced intestinal ...