Simultaneous, But Not Consecutive, Combination With Folinate Salts Potentiates 5-fluorouracil Antitumor Activity In Vitro and In Vivo

The combination of folinate salts to 5-fluoruracil (5-FU)-based schedules is an established clinical routine in the landscape of the colorectal cancer treatment. The aim of this study was to investigate the pharmacological differences between the sequential administration of folinate salts (1 h before, as in clinical routine) followed by 5-FU and the simultaneous administration of both drugs. Proliferation and apoptotic assays were performed on human colon cancer cells exposed to 5-FU, calcium (CaLV) or disodium (NaLV) levofolinate or their simultaneous and sequential combination for 24 and 72h. <em>TYMS</em> and <em>SLC19A1</em> gene expression was performed with real time PCR. <em>In vivo</em> experiments were performed in xenografted nude mice, treated with 5-FU escalating doses and CaLV or NaLV alone or in simultaneous and sequential combination. The simultaneous combination of folinate salts and 5-FU was synergistic (NaLV) or additive (CaLV) in a 24h treatment in both cell lines. In contrast, the sequential combination of both folinate salts and 5-FU was antagonistic at 24 and 72h. The simultaneous combination of 5-FU and NaLV or CaLV inhibited <em>TYMS</em> gene expression at 24h, whereas the sequential combination reduced <em>SLC19A1</em> gene expression. <em>In vivo</em> experiments confirmed the enhanced antitumor activity of the 5-FU+NaLV simultaneous combination with a good toxicity profile, whereas the sequential combination with CaLV failed to potentiate 5-FU activity. In conclusion, only the simultaneous, but not the consecutive, <em>in vitro</em> and <em>in vivo</em> combination of 5-FU and both folinate salt formulations potentiated the antiproliferative effects of the drugs.