Reversal of the estrogen receptor negative phenotype in breast cancer and restoration of antiestrogen response.
OBJECTIVE
In breast cancer, the presence of estrogen receptor alpha (ER) denotes a better prognosis and response to antiestrogen therapy. Lack of ERalpha correlates with overexpression of epidermal growth factor receptor or c-erbB-2. We have shown that hyperactivation of mitogen-activated protein kinase (MAPK) directly represses ERalpha expression in a reversible manner. In this study, we determine if inhibition of MAPK in established ERalpha(-) breast cancer cell lines and tumors results in reexpression of ERalpha, and further, if reexpression of ERalpha in these ERalpha(-) tumors and cell lines could restore antiestrogen responses.


METHODS
Established ERalpha(-) breast cancer cell lines, ERalpha(-) breast tumors, and tumor cell cultures obtained from ERalpha(-) tumors were used in this study. Inhibition of hyperactive MAPK was accomplished via the MAPK/ERK kinase 1/2 inhibitor U0126 or via upstream inhibition with Iressa or Herceptin. Western blotting or reverse transcription-PCR for ERalpha was used to assess the reexpression of ERalpha in cells treated with U0126. Growth assays with WST-1 were done to assess restoration of antiestrogen sensitivity in these cells.


RESULTS
Inhibition of MAPK activity in ERalpha(-) breast cancer cell lines results in reexpression of ERalpha; upstream inhibition via targeting epidermal growth factor receptor or c-erbB-2 is equally effective. Importantly, this reexpressed ERalpha can now mediate an antiestrogen response in a subset of these ERalpha(-) breast cancer cell lines. Treatment of ERalpha(-) tumor specimens with MAPK inhibitors results in restoration of ERalpha mRNA, and similarly in epithelial cultures from ERalpha(-) tumors, MAPK inhibition restores both ERalpha protein and antiestrogen response.


CONCLUSIONS
These data show both the possibility of restoring ERalpha expression and antiestrogen responses in ERalpha(-) breast cancer and suggest that there exist ERalpha(-) breast cancer patients who would benefit from a combined MAPK inhibition/hormonal therapy.
Department of Internal Medicine, Division of Hematology/Oncology, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0640, USA.
Jill
J
Bayliss
Amy
A
Hilger
Prakash
P
Vishnu
Kathleen
K
Diehl
Dorraya
D
El-Ashry
D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D002070:Butadienes / Q000494:pharmacology; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010641:Phenotype; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology
D002070:Butadienes; D066246:ErbB Receptors; D004958:Estradiol; D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D000077267:Fulvestrant; D020928:Mitogen-Activated Protein Kinases; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen; C113580:U 0126