Increased expression of P-glycoprotein is associated with doxorubicin chemoresistance in the metastatic 4T1 breast cancer model

Am J Pathol. 2011 Feb;178(2):838-52. doi: 10.1016/j.ajpath.2010.10.029.


Development of drug resistance is one of the major causes of breast cancer treatment failure. The goal of this study was to understand the chemoresistance mechanism using the highly metastatic 4T1 breast cancer model, which emulates stage IV breast cancer in humans. The metastatic 4T1 breast cancer cell line treated with either doxorubicin or 5-FU showed a concentration-dependent reduced cell proliferation, with induced G2-phase growth arrest (doxorubicin) or G1-phase growth arrest (5-FU). Doxorubicin treatment partially suppressed the multiorgan metastasis of 4T1 breast cancer cells in the lung, heart, liver, and bone, compared with either 5-FU or cyclophosphamide. We isolated and characterized 4T1 breast cancer cells from doxorubicin-resistant metastatic tumors (cell line 4T1-R). Multiorgan metastasis of drug-resistant 4T1 breast tumors was totally resistant to doxorubicin treatment. Our results indicate that doxorubicin is localized exclusively in the cytoplasm of resistant 4T1 breast cancer cells and that it cannot reach the nucleus because of increased nuclear expression of P-glycoprotein. Pretreatment of doxorubicin-resistant 4T1-R breast cancer cells with verapamil, a general inhibitor of P-glycoprotein, increased nuclear translocation of doxorubicin and cellular cytotoxicity. Thus, impaired nuclear translocation of doxorubicin due to increased expression of P-glycoprotein is associated with doxorubicin resistance of highly metastatic 4T1 breast cancer.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • Animals
  • Biological Transport / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Separation
  • Cell Survival / drug effects
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Doxorubicin / pharmacology
  • Doxorubicin / therapeutic use*
  • Drug Resistance, Neoplasm* / drug effects
  • Female
  • Flow Cytometry
  • Fluorouracil / pharmacology
  • G2 Phase / drug effects
  • Humans
  • Immunohistochemistry
  • Mammary Neoplasms, Experimental / drug therapy*
  • Mammary Neoplasms, Experimental / pathology*
  • Mice
  • Mice, Inbred BALB C
  • Mitosis / drug effects
  • Neoplasm Metastasis
  • Survival Analysis
  • Verapamil / pharmacology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Doxorubicin
  • Verapamil
  • Fluorouracil