A therapeutic target for hormone-independent estrogen receptor-positive breast cancers.
BACKGROUND
The action of the steroid hormone estradiol (E2) is mediated via interaction with a specific receptor (ER) that initiates a series of events downstream, leading to the modulation of hormone-responsive genes and cell proliferation. Antihormones also bind, but do not confer the active configuration to ER, thereby, blocking the transmission of E2-ER-initiated signals for cell proliferation. Although these compounds qualify for successful therapy of ER-positive [ER (+)] breast cancer patients, only a fraction of patients responds to antihormone treatment. In this study, the functional status of ER is determined to identify alternative targets for therapy of antihormone-resistant ER (+) breast cancers.


METHODS
The interaction of ER with a specific DNA sequence, designated as E2 response element (ERE), was targeted to assess the functional state of ER. ER-ERE complex formation was measured by electrophoretic mobility shift assay (EMSA) and by a newly developed technique, based on the preferential binding of DNA-protein complex to a nitrocellulose membrane (NMBA) that measures both total and functional fraction of ER.


RESULTS
The NMBA assay identified functional variants of ER among ER (+) breast cancer cell lines and breast tumor biopsy specimens. ER of (21PT) cells did not bind E2 and these cells were tamoxifen (TAM) resistant. However 21PT cells were sensitive to a calmodulin (CaM) antagonist, W7, that blocked ERE-ER complex formation.


CONCLUSIONS
ER variants of the 21PT type were detected among breast cancer biopsy specimens, emphasizing the significance of an alternative therapeutic target for TAM-resistant ER (+) human breast cancers with compounds such as W7.
Biswas
D K
DK
Division of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA. biswas@mbcrr.harvard.edu
Cruz
A
A
Pettit
N
N
Mutter
G L
GL
Pardee
A B
AB
D000328:Adult; D000368:Aged; D001671:Biochemistry / Q000379:methods; D001706:Biopsy; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D003101:Collodion / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006728:Hormones / Q000494:pharmacology; D006801:Humans; D008875:Middle Aged; D011960:Receptors, Estrogen / Q000032:analysis / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000032:analysis / Q000378:metabolism; D020218:Response Elements / Q000187:drug effects*; D013449:Sulfonamides / Q000494:pharmacology; D013629:Tamoxifen / Q000494:pharmacology; D016896:Treatment Outcome; D014407:Tumor Cells, Cultured
D002147:Calmodulin; D004791:Enzyme Inhibitors; D006728:Hormones; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D013449:Sulfonamides; D013629:Tamoxifen; D004958:Estradiol; C017967:W 7; D003101:Collodion