Targeting human acute myeloid leukemia cells using human recombinant arginase I (Co) - PEG5000 [HuArgl (Co) - PEG5000] - induced arginine depletion. (c2013)

Abstract

Acute myeloid leukemia (AML) is the most common leukemia in adults. With current chemotherapy protocols, patients have poor prognosis and more than 10,000 patients die yearly of AML. Therefore new treatment to improve survival rate are needed. In this study, we attempt to target AML cells using a pegylated recombinant human Arginase I cobalt [HuArgI (Co)-PEG5000]. HuArgI (Co)-PEG5000 was tested on ten human AML cell lines. All were sensitive to arginine depletion. Human peripheral blood mononuclear cells (PBMCs) and CD34 + bone marrow progenitor blasts (BMPBs) were not sensitive to HuArgI (Co)-PEG5000-mediated arginine depletion demonstrating that arginine deprivation selectively targets AML cells while sparing normal hematopoietic cells. Exogenous L-citrulline addition at low concentrations (1.14 to 114 μM) did not rescue cells from HuArgI (Co)-PEG5000 induced cytotoxicity. However only at the concentrations of 1.14 and 11.4 mM, the addition of exogenous L-citrulline reversed the sensitivity of five AML cell lines to HuArgI (Co)- PEG5000-induced arginine depletion. Furthermore, the sensitivity of AML cells to HuArgI (Co)-PEG5000-induced arginine depletion in the presence or absence of L-citrulline was reliant on the expression levels of argininosuccinate synthetase-1 (ASS1). The cell lines that did not express ASS1 were not rescued by L-citrulline. Addition of the autophagy inhibitor chloroquine increased the sensitivity of AML cell lines to HuArgI (Co)-PEG5000-mediated arginine depletion indicating that autophagy is activated and plays a protective role in AML cells. Staining for annexin V/PI and active caspases showed an increase in cells stained positively with both annexin V and PI and the absence of caspase activation indicating that HuArgI (Co)-PEG5000-mediated arginine depletion in AML cells induces caspaseindependent, nonapoptotic cell death. In this study, we have demonstrated that AML cells lines are sensitive to arginine depletion and thus are auxotrophic for arginine and can be selectively treated by HuArgI (Co)- PEG5000 hence proving that L-Arginine deprivation is a potential selective and potent selective treatment for AML.