Metabolic Analysis of Three-Dimensional Cultured Gastrointestinal Cancer Cells Suggests that <sc>l</sc>-Arginine Inhibits Tumor Growth by Affecting the Urea Cycle.

INTRODUCTION

There is evidence for the anticancer effects of l-arginine (arginine); however, the direct effects on cancer cells and mechanism of action are unclear.

METHODS

Various upper gastrointestinal cancer cells (OE19, OE33, MKN1, MKN45, MKN74, and AGS) were divided into arginine-treated and -untreated groups and cultured using two-dimensional and three-dimensional culture systems. Proliferation was evaluated using the MTT assay to identify arginine-sensitive (OE33) and arginine-insensitive (OE19) strains. Furthermore, the effects of arginine were evaluated using a mitochondrial stress test, cell cycle assay, comprehensive metabolic analysis, and tracer study using (13C6) l-arginine.

RESULTS

In OE33 (but not in OE19), the maximal respiratory capacity of mitochondria was lower in the treated group than in the control group. In OE33, S phase cells (determined using BrdU) were significantly reduced. In a comprehensive metabolic analysis of OE33, citrulline/ornithine levels were significantly lower in arginine-treated than in untreated cells. Using OE33, carbamoyl aspartic acid (CAA) levels were significantly lower in arginine-treated than in untreated cells. A tracer study suggested that arginine promotes the urea cycle.

CONCLUSION

Arginine affected urea cycle metabolism, thereby decreasing CAA, which is required for pyrimidine nucleotide synthesis. These findings provide insight into the mechanism underlying the anticancer effects of arginine.