Pancreatic tumor sensitivity to plasma L-asparagine starvation.

OBJECTIVES: In this study, our aim was to test whether asparagine synthetase (ASNS) deficiency in pancreatic malignant cells can lead to sensitivity to asparagine starvation. We also investigated, in tumor-bearing mice, the efficacy of L-asparaginase entrapped in red blood cells (RBCs), a safe formulation, to induce asparagine depletion. METHODS: First, ASNS expression was evaluated by immunohistochemistry in sporadic pancreatic ductal adenocarcinoma. Then, 4 pancreatic carcinoma cell lines were examined by Western blot, immunocytochemistry, and cytotoxicity assay to L-asparaginase and in asparagine-free or reduced-asparagine media. Finally, mice bearing the most in vitro sensitive cell line received RBC-entrapped L-asparaginase to investigate the anticancer efficacy of serum asparagine depletion in vivo. RESULTS: Approximately 52% of pancreatic adenocarcinomas expressed no or low ASNS. The highest in vitro cytotoxicity to L-asparaginase or to reduced asparagine medium was observed with SW1990 line when ASNS expression was the lowest. In vivo sensitivity was confirmed for this cell line. CONCLUSIONS: Plasma asparagine depletion by RBC-entrapped L-asparaginase in selected patients having no low or no ASNS may be a promising therapeutic approach for pancreatic cancer.