Sensitization of human breast cancer cells to gemcitabine by the protein kinase C modulator bryostatin 1

Cancer Chemother Pharmacol. 2003 Sep;52(3):235-46. doi: 10.1007/s00280-003-0628-6. Epub 2003 Jun 14.


Purpose: Protein kinase C (PKC) plays an important role in cell proliferation, differentiation, and apoptosis. The interaction between the PKC modulator bryostatin 1 (BRYO), and gemcitabine in human breast cancer MCF-7 and MDA-MB-231 cells and in the non-transformed MCF-10A human breast epithelial cells was investigated.

Methods: Immunoblotting was used to determine the expression of PKC isoenzymes and proteins involved in the cell cycle and apoptosis. MTT, ELISA and flow cytometry assays were used to determine cell survival.

Results: Treatment of cells with BRYO 200 n M resulted in a significant downregulation of cytoplasmic PKC in all three cell lines. However, the expression of membranous PKC was differentially affected in these cells. BRYO (1-200 n M) had no significant effects on cell viability in any of the cell lines. Nevertheless, BRYO significantly enhanced the antiproliferative and apoptotic effects of gemcitabine in the MCF-7 and MDA-MB-231 cells, but not in the MCF-10A cells. This was associated with significant reduction in the bcl-2/bax ratio. There was a significant upregulation of p53, p21(waf1), and p27 in MCF7 and MCF-10A cells treated with the combination of gemcitabine and BRYO compared to gemcitabine-treated cells.

Conclusions: The potentiation of the effect of gemcitabine by BRYO was demonstrated in MCF-7 and MDA-MB-231 cells and was associated with a specific pattern of PKC modulation. Further investigation of the role of specific isoforms of PKC in the downstream molecular events of gemcitabine-induced cytotoxicity is warranted.

MeSH terms

  • Antineoplastic Agents / therapeutic use*
  • Apoptosis / drug effects
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / enzymology
  • Bryostatins
  • Cell Survival / drug effects
  • Cytosol / enzymology
  • Deoxycytidine / analogs & derivatives*
  • Deoxycytidine / therapeutic use*
  • Drug Synergism
  • Enzyme Inhibitors / therapeutic use*
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Flow Cytometry
  • Humans
  • Isoenzymes
  • Lactones / therapeutic use*
  • Macrolides
  • Protein Kinase C / drug effects*
  • Tumor Cells, Cultured / drug effects*
  • Tumor Cells, Cultured / enzymology


  • Antineoplastic Agents
  • Bryostatins
  • Enzyme Inhibitors
  • Isoenzymes
  • Lactones
  • Macrolides
  • Deoxycytidine
  • bryostatin 1
  • gemcitabine
  • Protein Kinase C