Effects of receptor tyrosine kinase inhibitor A47 on estrogen and growth factor-dependent breast cancer cell proliferation and apoptosis in vitro.
OBJECTIVE
We propose that a growth factor receptor tyrosine kinase (RTK) inhibitor, such as tyrphostin A47, could serve as an adjunct to estrogen replacement therapy (ERT) for postmenopausal breast cancer survivors. Tyrphostins have been shown to block estrogen (E2)-induced proliferation in the human breast cancer MCF-7 cell line. Therefore, the effects of A47 on signal transduction, cell cycle progression, and apoptosis in E2-mediated breast cancer cell growth in vitro were investigated.


METHODS
Cell growth was determined by MTT proliferation assay, cell cycle analysis assessed by flow cytometry, and RTK activation by Western blot. Apoptosis assays included nuclear staining, TdT-mediated dUTP-X nick end labeling, and caspase 3 activation.


RESULTS
We find A47 selectively inhibits epidermal growth factor (EGF) and basic fibroblast growth factor but not insulin growth factor-1 proliferation. Although A47 inhibits EGF-induced phosphorylation of the EGF receptor in A431 cells, it does not consistently block MAP kinase phosphorylation.


CONCLUSIONS
Taken together, A47 blocks E2/EGF-induced activation of EGFR and therefore interferes with the proximal EGFR signaling pathway. A47 also arrests the cells at the G1-S transition of the cell cycle and induces cell death by apoptosis. Thus, a growth factor RTK may be useful in blocking hormone-dependent tumor growth in an elevated E2 environment.
Turbov
Jane M
JM
Evanston Northwestern Healthcare Research Institute, Evanston, Illinois 60201, USA. jturbov@enh.org
Twaddle
George M
GM
Yang
Xiaohe
X
Liu
Naxin M
NM
Murthy
Satya
S
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000517:prevention & control; D002453:Cell Cycle / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000187:drug effects*; D015914:Estrogen Replacement Therapy; D004967:Estrogens; D005260:Female; D005346:Fibroblast Growth Factors / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D009364:Neoplasm Recurrence, Local / Q000517:prevention & control; D009376:Neoplasms, Hormone-Dependent / Q000517:prevention & control; D017698:Postmenopause; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects*; D017741:Survivors; D014407:Tumor Cells, Cultured / Q000187:drug effects; D020032:Tyrphostins / Q000494:pharmacology*
D000970:Antineoplastic Agents; D004967:Estrogens; D020032:Tyrphostins; C060152:tyrphostin 47; D005346:Fibroblast Growth Factors; D004815:Epidermal Growth Factor; D011505:Protein-Tyrosine Kinases