Docetaxel enhances the cytotoxicity of tetrahydropyranyladriamycin in a sequence-dependent manner.

BACKGROUND: Taxanes and anthracyclines are active against breast cancer. In this study we investigated the combined antitumor activity of these drugs, with particular regard to sequence-dependency. MATERIALS AND METHODS: The combined antitumor activity of docetaxel and tetrahydropyranyladriamycin (THP) against two human breast cancer xenografts was assessed using an in vitro histoculture drug-response assay. The sequence-dependency of the combined cytotoxicity was evaluated by isobologram. RESULTS: A synergistic antitumor activity of combined docetaxel + THP was exhibited against the R-27 xenograft when docetaxel was given first or simultaneously with THP. However, this synergism was diminished when THP was used before docetaxel. While an additive effect of combined docetaxel + THP was observed against MX-1 xenograft when docetaxel was given first or simultaneously with THP, this effect was not marked using the THP/docetaxel sequence. CONCLUSION: Docetaxel increased the antitumor activity of THP, but only when administered before or simultaneously with THP.