Antitumor Efficacy of Combination Therapy Consisting of S-1, Leucovorin, and Oxaliplatin against Human Gastric Cancer Xenografts

Abstract

Background/Aim: A phase 3 trial of S-1, leucovorin (LV), and oxaliplatin for treating gastric cancer is now underway. However, the antitumor efficacy of the combination has not yet been examined in an in vivo preclinical study. This study examined the antitumor efficacy of combination therapy consisting of S-1, LV, and oxaliplatin against 4 human gastric cancer xenografts: NUGC-4, St-40, SC-2, and SC-4. Methods: The antitumor efficacy was evaluated using human gastric cancer xenograft-bearing nude mice. S-1 and LV were administered orally once daily on days 1-7 at doses of 6.9 and 10 mg/kg, respectively. Oxaliplatin was administered intravenously at a dose of 8.3 mg/kg on day 1. The tumor volume was measured on day 15, and the relative tumor volume (RTV) was calculated. Results: In all 4 xenograft models, S-1 alone and oxaliplatin alone, but not LV alone, had significant antitumor activities (p < 0.001). Combination therapy consisting of S-1 and LV resulted in a significantly smaller RTV than S-1 alone (p < 0.001). Combination therapy consisting of S-1 and oxaliplatin also resulted in a significantly smaller RTV than either S-1 alone (p < 0.001) or oxaliplatin alone (p < 0.001). Furthermore, combination therapy consisting of S-1, LV, and oxaliplatin resulted in the highest antitumor activity in these models (p < 0.001 vs. S-1 + LV; p < 0.001 or p = 0.003 vs. S-1 + oxaliplatin). Conclusion: Combination therapy consisting of S-1, LV, and oxaliplatin administered according to a 1-week-on/1-week-off schedule may be useful for the treatment of patients with gastric cancer.