Metabolic reprogramming of glioblastoma cells by L-asparaginase sensitizes for apoptosis in vitro and in vivo

Abstract

Cancer cells display a variety of global metabolic changes, which aside from the glycolytic pathway largely involve amino acid metabolism. To ensure aggressive growth, tumor cells highly depend on amino acids, most notably due to their pivotal need of protein synthesis. In this study, we assessed the overall hypothesis that depletion of asparagine by E. coli-derived L-asparaginase might be a novel means for the therapy of one of the most recalcitrant neoplasms and for which no efficient treatment currently exists - glioblastoma (WHO grade IV). Our results suggest that certain glioma cell cultures are particularly susceptible to inhibition of proliferation by L-asparaginase, while others display a more resistant phenotype. In sensitive cells, L-asparaginase induces apoptosis with dissipation of mitochondrial membrane potential and activation of effector caspases. L-asparaginase-mediated apoptosis was accompanied by modulation of pro- and anti-apoptotic Bcl-2 family members, including Noxa, Mcl-1 and the deubiquitinase Usp9X. Given the impact of L-asparaginase on these molecules, we found that L-asparaginase potently overcomes resistance to both intrinsic apoptosis induced by the Bcl-2/Bcl-xL inhibitor, ABT263, and extrinsic apoptosis mediated by TRAIL even in glioma cells that are resistant towards L-asparaginase single treatment. RNA interference studies showed that Usp9X, Mcl-1, Noxa and Bax/Bak are involved in ABT263/L-asparaginase-mediated cell death. In vivo, combined treatment with ABT263 and L-asparaginase led to an enhanced reduction of tumor growth when compared to each reagent alone without induction of toxicity. These observations suggest that L-asparaginase might be useful for the treatment of malignant glial neoplasms.

Efficacy of Asparaginase Erwinia chrysanthemi With and Without Temozolomide Against Glioma Cells and Intracranial Mouse Medulloblastoma

“…We reported in 2013 that the anti-leukemia agent E. coli-ASNase enhances chemo-cytotoxicity against brain tumors (20). Additional studies validating the antiglioblastoma activity of ASNase in vitro and in vivo were recently reported (33,34). Our current study shows that activity of Erwinaze against brain tumor cells is comparable to the reported in vitro effects of E. coli-ASNase ( Figure 1A and 4).…”

Targeting intrinsic apoptosis and other forms of cell death by BH3-mimetics in glioblastoma

“…What makes this drug so interesting to be used in combination therapy against glioblastoma is the fact that L-asparaginase elicits its anti-tumor effects without the need to pass the blood brain barrier, which is an inherent concern for the drug treatment of glioblastoma. By its own, L-asparaginase was particularly active in a pediatric glioblastoma cell line, SF188, which is known to express high levels of c-myc [34]. Based on this notion, we were anticipating that L-asparaginase might have high anti-proliferative activity in stem cell-like glioma cells since those cell cultures are particularly dependent on c-myc.…”

“…Based on this notion, we were anticipating that L-asparaginase might have high anti-proliferative activity in stem cell-like glioma cells since those cell cultures are particularly dependent on c-myc. Unfortunately, single treatment with L-asparaginase was rather ineffective against these cells [34]. However, when combined with ABT-263, L-asparaginase showed strong synergism in relevant model systems of glioblastoma, including stem cell-like glioma cells.…”

“…However, when combined with ABT-263, L-asparaginase showed strong synergism in relevant model systems of glioblastoma, including stem cell-like glioma cells. Mechanistically, L-asparaginase regulated the levels of Noxa, Mcl-1 and Usp9X, favoring a pro-apoptotic state [34]. Consistently, inhibition of Noxa by siRNA attenuated the effects of the combination treatment.…”

Bcl-xL inhibition - a novel strategy for glioma therapy

“…In our recently published manuscript, we have taken advantage of this approach by utilizing L-asparaginase, which is an approved drug for acute lymphoblastic leukemia, for the treatment of glio-blastoma. While this idea has been pursued for brain tumors before, we have further refined this strategy by combining L-asparaginase with an orally available inhibitor targeting Bcl-xL [2]. In that regard, we utilized one of the recently designed BH3-mimetics, ABT-263, which aside from Bcl-xL also interferes with Bcl-2 [3].…”