l-asparaginase and 6-diazo-5-oxo-l-norleucine synergistically inhibit the growth of glioblastoma cells

Purpose: Glioblastoma is an aggressive central nervous system tumor with a 5-year survival rate of < 10%. The standard therapy for glioblastoma is maximal safe resection, followed by radiation therapy and chemotherapy with temozolomide. New approaches to treatment of glioblastoma, such as targeting metabolism, have been studied. The object of this study is to evaluate whether asparagine could be a new target for treatment of glioblastoma. Methods: We investigated a potential treatment for glioblastoma that targets the amino acid metabolism. U251, U87, and SF767 glioblastoma cells were treated with l-asparaginase and/or 6-diazo-5-oxo-l-norleucine (DON). l-asparaginase hydrolyzes asparagine into aspartate and depletes asparagine. l-asparaginase has been used for the treatment of acute lymphoblastic leukemia. DON is a glutamine analog that inhibits several glutamine-utilizing enzymes, including asparagine synthetase. Results: Cell viability was measured after 72 h of treatment. MTS assay showed that l-asparaginase suppressed the proliferation of U251, U87, and SF767 cells in a dose-dependent manner. DON also inhibited the proliferation of these cell lines in a dose-dependent manner. Combined treatment with these drugs had a synergistic antiproliferative effect in these cell lines. Exogenous asparagine rescued the effect of inhibition of proliferation by l-asparaginase and DON. The expression of asparagine synthetase mRNA was increased in cells treated with a combination of l-asparaginase and DON. This combined treatment also induced greater apoptosis and autophagy than did single-drug treatment. Conclusion: The results suggest that the combination of l-asparaginase and DON could be a new therapeutic option for patients with glioblastoma.