Sequence dependent exposure of mammary carcinoma cells to Taxotere and the MEK1/2 inhibitor U0126 causes enhanced cell killing in vitro

Cancer Biol Ther. Nov-Dec 2003;2(6):670-6.


Taxol (paclitaxel) and Taxotere (docetaxel) are considered as two of the most important anti-cancer chemotherapy drugs. The cytotoxic action of these drugs has been linked to their ability to inhibit microtubule depolymerization, causing growth arrest and subsequent cell death. Studies by a number of laboratories have also linked suppression of mitogen activated protein kinase (MAPK) signaling to enhanced Taxol toxicity. The present study examined the interactions of the semi-synthetic taxane Taxotere with MEK1/2 inhibitors in epithelial tumor cells. Concurrent treatment of MDA-MB-231 mammary and DU145 prostate carcinoma cells with Taxotere and MEK1/2 inhibitor resulted in protection from the anti-proliferative effects of Taxotere in MTT assays. In contrast, in MCF-7 mammary cells, concurrent Taxotere and MEK1/2 inhibitor treatment weakly enhanced the anti-proliferative effects of the taxane. Sequential treatment of MDA-MB-231 and MCF-7 cells with Taxotere followed by MEK1/2 inhibitor also enhanced the anti-proliferative effects of the taxane in MTT assays. However, no enhancement was observed in DU145 or PC-3 cells. Colony formation assays, including isobologram analyses, provided a more definitive demonstration that MCF-7 and MDA-MB-231 cells were sensitized to the toxic effects of Taxotere by U0126. Similar data were observed using Laulimalide, which binds to tubulin at a different site to Taxotere. The enhancement in Taxotere anti-proliferative effects by U0126 correlated with increased cell killing, 48-72h after treatment of cells that was blocked by inhibition of caspase 9, but not caspase 8, function. This observation was associated with prolonged suppression of ERK1/2 and AKT activity, without alteration in either p38 or JNK1/2 activity. Collectively these findings demonstrate that sequential administration of Taxotere followed by MEK1/2 inhibition can lead to increased cell death and loss of reproductive capacity in some, but not all, human tumor cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents, Phytogenic / administration & dosage
  • Apoptosis / drug effects*
  • Breast Neoplasms / metabolism*
  • Butadienes / administration & dosage*
  • Carcinoma / metabolism
  • Cell Line, Tumor
  • Docetaxel
  • Drug Administration Schedule
  • Drug Therapy, Combination
  • Enzyme Inhibitors / administration & dosage
  • Female
  • Humans
  • MAP Kinase Signaling System / drug effects*
  • Mitogen-Activated Protein Kinases / antagonists & inhibitors*
  • Nitriles / administration & dosage*
  • Taxoids / administration & dosage*


  • Antineoplastic Agents, Phytogenic
  • Butadienes
  • Enzyme Inhibitors
  • Nitriles
  • Taxoids
  • U 0126
  • Docetaxel
  • Mitogen-Activated Protein Kinases