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Combination studies of antifolates with 5-fluorouracil in colon cancer cell lines
C L van der Wilt1, C M Kuiper, G J Peters
1Department of Medical Oncology, University Hospital Vrije Universiteit, Amsterdam, The Netherlands.
Abstract:
The combined cytotoxic effects of the thymidylate synthase (TS) inhibitors 5-fluorouracil (5FU) and different antifolates were studied in seven colon cancer cell lines. Growth inhibition of the antifolates, Nolatrexed, Raltitrexed, GW1843U89, or MTA in combination with 5FU, was determined and multiple drug effect analysis showed that the drugs acted mostly additively. The only synergistic interaction was found for 5FU and Nolatrexed in the LS174T cell line. Also Raltitrexed and 5FU were slightly synergistic in WiDr/F cells grown at low folate levels, but for the other cell lines grown at high folate levels this combination was more antagonistic. GW1843U89 and 5FU were mainly additive, while 5FU and MTA showed antagonism in WiDr and additivity in LS174T. The effect of the drugs at their target was evaluated by in situ TS inhibition. We observed lower TS activity in all cells when two drugs were used instead of one. Statistical analysis revealed that none of the values of the combinations was higher or lower than could be expected from the product of the effect of single drugs. We concluded that the effects on TS inhibition were additive for all 5FU/antifolate combinations in all cell lines. DNA strand break formation, as a result of TS inhibition, was measured by means of a fluorometric analysis of DNA unwinding. Raltitrexed-induced DNA damage was significantly increased by 5FU in WiDr cells [single agent: 67% double stranded (ds) DNA, combination: 39% ds DNA, P<0.0001]. In LS174T a trend for antagonistic effects was observed for combinations of MTA, GW1843U89, or Raltitrexed and 5FU. The combinations showed additive effects in WiDr/F cells. The overall conclusion of the three assays in each of the cell lines indicated that 5FU and antifolate combinations were predominantly additive in colon cancer cells.
Insights
Combining 5-fluorouracil (5FU) with antifolates showed mostly additive cytotoxic effects in colon cancer cells. The combination
Area of Science:
- Oncology
- Pharmacology
- Molecular Biology
Background:
- Thymidylate synthase (TS) inhibitors like 5-fluorouracil (5FU) are crucial in colon cancer therapy.
- Antifolates are also used in cancer treatment, and their combination with 5FU may enhance efficacy.
- Understanding drug interactions is vital for optimizing cancer treatment strategies.
Purpose of the Study:
- To investigate the combined cytotoxic effects of 5-fluorouracil (5FU) and various antifolates in colon cancer cell lines.
- To analyze the drug interactions, including synergy and antagonism, at the cellular and molecular levels.
- To evaluate the impact of these combinations on thymidylate synthase (TS) inhibition and DNA damage.
Main Methods:
- Cultured seven colon cancer cell lines.
- Determined growth inhibition using antifolates (Nolatrexed, Raltitrexed, GW1843U89, MTA) in combination with 5FU.
- Analyzed drug interactions using multiple drug effect analysis.
- Assessed in situ TS inhibition and DNA strand break formation via fluorometric analysis of DNA unwinding.
Main Results:
- Most 5FU/antifolate combinations exhibited additive cytotoxic effects across colon cancer cell lines.
- Synergistic interaction was observed only for 5FU and Nolatrexed in the LS174T cell line.
- Raltitrexed combined with 5FU showed slight synergy in low-folate conditions but antagonism in high-folate conditions.
- TS inhibition was additive for all combinations, while DNA damage varied, with a significant increase noted for Raltitrexed and 5FU in WiDr cells.
Conclusions:
- 5-fluorouracil (5FU) and antifolate combinations demonstrate predominantly additive cytotoxic effects in colon cancer cells.
- While some specific synergistic or antagonistic interactions were noted, the overall trend suggests additive effects on TS inhibition and variable effects on DNA damage.
- These findings underscore the complex nature of drug interactions in cancer chemotherapy and the need for cell-specific evaluation.
