Sequence dependent synergistic cytotoxicity between etoposide and fluoropyrimidines

Area of Science:

• Pharmacology
• Cancer Biology
• Molecular Toxicology

Background:

• Etoposide and fluoropyrimidines (FP) are common chemotherapeutic agents.
• Understanding their combined cytotoxic effects and sequence dependency is crucial for optimizing cancer treatment strategies.

Purpose of the Study:

• To investigate the cytotoxic interactions between etoposide and two fluoropyrimidines (5-fluorouracil and 5-fluoro-2'-deoxyuridine).
• To determine the influence of administration sequence on cytotoxicity and DNA damage in cancer cells.

Main Methods:

• Cytotoxicity assays: soft agar clonogenic assay in L1210 cells and colony growth assay in five human adenocarcinoma cell lines.
• Assessment of DNA single-strand breaks in L1210 cells following drug administration.

Main Results:

• Administering etoposide before fluoropyrimidines resulted in synergistic cytotoxicity across multiple cell lines (L1210, HCT-8, Mia PaCa, MCF-7, T47-D).
• The reverse sequence (FP before etoposide) showed additive or antagonistic cytotoxicity in some cell lines.
• Etoposide followed by 5-fluoro-2'-deoxyuridine increased DNA single-strand breaks more than expected in L1210 cells, unlike the reverse sequence.

Conclusions:

• The sequence of drug administration significantly impacts the cytotoxic outcome of etoposide-fluoropyrimidine combinations.
• Sequence-dependent synergistic cytotoxicity correlates with the extent of DNA single-strand break induction.
• Findings suggest that pre-administration of etoposide may enhance the efficacy of fluoropyrimidine-based chemotherapy.