Mechanisms of cell death induced by arginase and asparaginase in precursor B-cell lymphoblasts

Lucy E Métayer,G A Amos Burke,Saskia Carlebur,Guy C Brown,Richard D Brown

doi:10.1007/s10495-018-1506-3

Abstract

Arginase has therapeutic potential as a cytotoxic agent in some cancers, but this is unclear for precursor B acute lymphoblastic leukaemia (pre-B ALL), the commonest form of childhood leukaemia. We compared arginase cytotoxicity with asparaginase, currently used in pre-B ALL treatment, and characterised the forms of cell death induced in a pre-B ALL cell line 697. Arginase and asparaginase both efficiently killed 697 cells and mature B lymphoma cell line Ramos, but neither enzyme killed normal lymphocytes. Arginase depleted cellular arginine, and arginase-treated media induced cell death, blocked by addition of arginine or arginine-precursor citrulline. Asparaginase depleted both asparagine and glutamine, and asparaginase-treated media induced cell death, blocked by asparagine, but not glutamine. Both enzymes induced caspase cleavage and activation, chromatin condensation and phosphatidylserine exposure, indicating apoptosis. Both arginase- and asparaginase-induced death were blocked by caspase inhibitors, but with different sensitivities. BCL-2 overexpression inhibited arginase- and asparaginase-induced cell death, but did not prevent arginase-induced cytostasis, indicating a different mechanism of growth arrest. An autophagy inhibitor, chloroquine, had no effect on the cell death induced by arginase, but doubled the cell death induced by asparaginase. In conclusion, arginase causes death of lymphoblasts by arginine-depletion induced apoptosis, via mechanism distinct from asparaginase. Therapeutic implications for childhood ALL include: arginase might be used as treatment (but antagonised by dietary arginine and citrulline), chloroquine may enhance efficacy of asparaginase treatment, and partial resistance to arginase and asparaginase may develop by BCL-2 expression. Arginase or asparaginase might potentially be used to treat Burkitt lymphoma.

Highlights

Despite the increasingly good outcome in childhood leukaemia, relapsed and refractory ALL still represent the major causes of death from childhood cancer
We compared the mechanism of cell death induced by arginase and asparaginase in pre-B lymphoblasts. We find that both enzymes induce cell death by apoptosis, but the cell death induced by arginase and asparaginase differs in sensitivity to amino acids, caspase inhibitors, PKCactivator phorbol myristate, and autophagy inhibitor chloroquine
The ability of arginase and asparaginase to induce cell death was investigated in three different cell lines derived from B cell malignancies

Summary

Introduction

Despite the increasingly good outcome in childhood leukaemia, relapsed and refractory ALL still represent the major causes of death from childhood cancer. Asparaginase is integral to treatment of leukaemia worldwide, demonstrating the feasibility of clinical treatments by enzymatic amino acid depletion. The arginine dependency of tumours was recognised in the 1970s and is currently being studied in various cancers mainly using the Mycoplasma enzyme arginine deiminase ADI [2,3,4,5,6]. The clinical usefulness of arginase was felt to be limited due to its short in vivo half-life, high K M and optimal pH around 9 [7, 8]. Pegylation allows successful in vivo use, including studies with T-cell leukaemia [9, 10] and AML [11]

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Conclusion