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

Background: Anti-metabolites are less-myelosuppressive than DNA-damaging anticancer drugs and may be useful against brain tumors. Materials and Methods: We evaluated the asparagine/glutamine-deaminating agent Erwinaze with/without temozolomide against brain tumor cells and mouse medulloblastomas. Results. Erwinaze treatment of cell lines and neurospheres led to dose-dependent reductions of cells (reversible by L-glutamine), with half maximal inhibitory concentrations (IC₅₀s) of 0.12->10 IU/ml. Erwinaze at <1 IU/ml reduced temozolomide IC₅₀s by 3.6- to 13-fold (300-1,200 μM to 40-330 μM). Seven-week-old SMO/SMO mice treated with Erwinaze (regardless of temozolomide treatment) had better survival 11 weeks post-therapy, compared to those not treated with Erwinaze (81.25% vs. 46.15, p=0.08). Temozolomide-treated mice developed 10% weight loss, impairing survival. All 16 mice treated with temozolomide (regardless of Erwinaze treatment) succumbed by 40-weeks of age, whereas 5/8 animals treated with Erwinaze alone and 2/6 controls survived (p=0.035). Conclusion: Erwinaze enhances cytotoxicity of temozolomide in vitro, and improves survival in SMO/SMO mice, likely by reducing cerebrospinal fluid glutamine. Temozolomide-associated toxicity prevented demonstration of any potential combinatorial advantage with Erwinaze in vivo.

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