Pulmonary
metastasis is the most significant prognostic determinant for
osteosarcoma, but methods for its prediction and treatment have not been established. Using
oligonucleotide microarrays, we compared the global gene expression of biopsy samples between seven
osteosarcoma patients who developed pulmonary
metastasis within 4 years after
neoadjuvant chemotherapy and curative resection, and 12 patients who did not relapse. We identified
argininosuccinate synthetase (ASS) as a gene differentially expressed with the highest statistical significance (Welch's t test, P = 2.2 x 10(-5)). Immunohistochemical analysis of an independent cohort of 62
osteosarcoma cases confirmed that reduced expression of ASS
protein was significantly correlated with the development of pulmonary
metastasis after surgery (log-rank test, P < 0.05). Cox regression analysis revealed that ASS was the sole significant predictive factor (P = 0.039; hazard ratio, 0.319; 95% confidence interval, 0.108-0.945). ASS is one of the
enzymes required for the production of a nonessential
amino acid,
arginine. We showed that
osteosarcoma cells lacking ASS expression were auxotrophic for
arginine and underwent G(0)-G(1) arrest in
arginine-free medium, suggesting that an
arginine deprivation
therapy could be effective in patients with
osteosarcoma. Recently, phase I and II clinical trials in patients with
melanoma and
hepatocellular carcinoma have shown the safety and efficacy of plasma
arginine depletion by stabilized
arginine deiminase. Our data indicate that in patients with
osteosarcoma, reduced expression of ASS is not only a novel predictive
biomarker for the development of
metastasis, but also a potential target for pharmacologic intervention.