Synergistic interaction between trifluorothymidine and docetaxel is sequence dependent

Area of Science:

• Oncology
• Cell Biology
• Pharmacology

Background:

• Docetaxel is a microtubule inhibitor affecting S and G(2)-M cell cycle phases.
• Trifluorothymidine (TFT) induces DNA damage and G(2)-M arrest.
• TFT (as part of TAS-102) is an oral chemotherapeutic agent for colon and gastric cancers.

Purpose of the Study:

• Determine the optimal administration sequence of TFT and docetaxel.
• Investigate the underlying mechanisms of their combined cytotoxicity.

Main Methods:

• Sulforhodamine B assays and combination index analyses for drug interactions.
• Clonogenic assays for long-term effects.
• Flow cytometry and immunostaining for cell death and mitotic spindle analysis.
• Western blotting for cell cycle signaling pathway analysis.

Main Results:

• Preincubation with docetaxel showed synergistic effects (combination index 0.6-0.8) with TFT.
• Synergistic combinations induced time-dependent cell death (17-36%), polynucleation (22%), and mitotic spindle inhibition.
• TFT followed by docetaxel displayed antagonistic activity with reduced cell death and polynucleation.
• Synergistic combinations led to G(2)-M arrest (25-50%) with Chk2 phosphorylation and cdc25c dephosphorylation.
• Caspase 3 activation was low, suggesting caspase-independent cell death.

Conclusions:

• Docetaxel administered first is crucial for synergistic activity, initiating mitotic failure before TFT damage signaling.
• Antagonism occurs when TFT-induced cell cycle arrest reduces docetaxel susceptibility.
• The findings provide a basis for clinical studies investigating this sequential combination therapy.