Investigating the Therapeutic Potential of L-asparaginase in Myeloid Leukemia

Acute myeloid leukemia (AML) is a malignant disease of the bone marrow that results in the proliferation and accumulation of dysfunctional myeloid cells and the disruption of the normal hematopoietic process. The high rate of relapse and diversity of the disease at the genetic and epigenetic level make AML a difficult disease to treat. Given the relatively poor long term outcome of patients, alternative therapeutic strategies need to be investigated either by repositioning existing drugs or identifying new targets. L-asparaginase, a component of standard acute lymphocytic leukemia (ALL) treatment, is an enzyme that degrades extracellular asparagine and glutamine. Interestingly, a growing body of evidence has demonstrated cancer metabolism is a distinctive trait that can be targeted by reducing nutrient availability. Therefore it is plausible that cancer metabolism will be affected by L-asparaginase treatment, in addition to the well-established protein synthesis inhibition mechanism. The findings from this study indicate that L-asparaginase elicits classical responses of amino acid deprivation in myeloid cells at both transcriptional and translational levels. In addition, pathway analysis using data from microarray and Multidimensional Protein Identification Technology (MudPIT) show metabolic pathways are indeed affected by treatment. Based on these results, I investigated the metabolic effects of L-asparaginase in myeloid cells further by observing changes to the cellular processes involving asparagine and/or glutamine participation. The results show that L-asparaginase exerts cytotoxic effects on the majority of AML cells tested and that glutamine removal, not asparagine, is responsible for these effects. The anticancer activity of L-asparaginase is pleiotropic in nature and its effects can be seen to affect multiple cellular processes. Intracellular levels of asparagine, glutamine, fumarate, and succinate decreased as a result of L-asparaginase treatment; this was accompanied by development of oxidative stress and inhibition of mitochondrial respiration in the myeloid cells. Data from experiments using 13C-labeled nutrients demonstrated that AML cells utilize glutamine to a significantly higher degree than asparagine, supporting the notion that targeting metabolism by glutamine depletion in AML is a viable option. This study reveals novel therapeutic opportunities in AML, and L-asparaginase has the potential as a metabolic drug to be repositioned for AML therapy.Ph.D