Inhibition of the mammalian target of rapamycin (mTOR) by rapamycin increases chemosensitivity of CaSki cells to paclitaxel

Eur J Cancer. 2006 May;42(7):934-47. doi: 10.1016/j.ejca.2005.12.018. Epub 2006 Mar 15.

Abstract

Paclitaxel, a potent anti-neoplastic agent, has been found to be effective against several tumours, including cervical cancer. However, the exact mechanism underlying the cytotoxic effects of pacitaxel, especially in the survival-signalling pathway, is poorly understood. The aim of this study was to investigate the molecular pathway of the cytotoxic effect of paclitaxel in human cervical cancer cell lines. Four human cervical cancer cell lines were treated for 24 h with various concentration of paclitaxel, and the sensitivity was analysed by an MTT assay. The cell cycle progression and sub-G1 population were analysed by flow cytometry. Apoptosis was further measured by DNA fragmentation and microscope examination. The protein expression was determined by Western blot analysis. Our results showed that HeLa cells demonstrated the highest sensitivity to paclitaxel, whereas CaSki cells showed the lowest. In cervical cancer cells, paclitaxel induced apoptosis through an intrinsic pathway with prior G2/M arrest. In addition, we showed that paclitaxel downregulated the phosphorylation of Akt in both HeLa and CaSki cells. Interestingly, in CaSki cells, which were more suggestive of a resistant phenotype, paclitaxel induced the activation of mTOR as a downstream target of Akt. Pre-treatment with rapamycin inhibited activation of mTOR signalling and significantly enhanced the sensitivity of CaSki cells to paclitaxel by increasing apoptotic cell death. This effect was mediated, at least partly, through caspase activation. Overall, paclitaxel exerts its anti-tumour effects on cervical cancer cells by inducing apoptosis through intrinsic pathway, and rapamycin targeted to mTOR can sensitise paclitaxel-resistant cervical cancer cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Blotting, Western
  • Cell Communication
  • Cell Cycle / drug effects
  • Cell Line, Tumor
  • DNA, Neoplasm / analysis
  • Dose-Response Relationship, Drug
  • Down-Regulation
  • Drug Screening Assays, Antitumor
  • Female
  • HeLa Cells
  • Humans
  • Paclitaxel / pharmacology*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Protein Kinases / drug effects*
  • Sirolimus / administration & dosage
  • Sirolimus / pharmacology*
  • TOR Serine-Threonine Kinases
  • Uterine Cervical Neoplasms / drug therapy*
  • Uterine Cervical Neoplasms / pathology

Substances

  • Antineoplastic Agents
  • DNA, Neoplasm
  • Protein Kinases
  • Phosphatidylinositol 3-Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Paclitaxel
  • Sirolimus