Comparison between CoFactor and Leucovorin activity applied in combination with 5-fluorouracil against two human...

The reduced folate leucovorin (LV) has been used for over 30 years as an enhancer of 5-fluorouracil (5-FU) antitumor activity. CoFactor (CoF) is a calcium salt of LV's active metabolite. Thus, administration of CoF can prevent decrease of intratumoral folate, which was recognized as the main reason for resistance of tumors to 5-FU treatment. The aim of this study was to investigate the cytotoxic activity and type of interactions for 5-FU and CoF applied in combination, in comparison to combination of 5-FU and LV, against human colon cancer cell lines LS- 174 and HT-29.

The single agent activity was estimated in concentration range from 0.1 to 300 microM for 5-FU, CoF, and LV. In combined treatment each concentration of 5-FU (0.1, 1 and 10 microM) was matched with each concentration of CoF or LV (1, 10 and 100 microM). In both experiments the sulforodamine B cytotoxic test was used to assess drugs' activity after 72 h of incubation with cells. The type of interactions in combinations was calculated with the isobole method.

5-FU showed similar activity against LS-174 and HT-29 cell lines (IC50=30.8 and 21.6 microM, respectively). While LV affected both cell lines in a slightly proliferative manner, CoF showed cytotoxic effect on both cell lines, being more active against HT-29 cell (IC50=25.7 microM) and less active on LS-174 cells (IC50=72.6 microM). Addition of LV did not change the cytotoxicity of 5-FU, especially against LS-174 cells, and synergism was found only in HT-29 cells when LV was applied in high concentrations (10 and 100 microM). However, the combination of 5-FU with CoF revealed synergistic and additive interactions in LS-174 and HT-29 cells, respectively.

These results should be taken into consideration when planning or analyzing the results of clinical trials using combination of CoF and 5-FU.