Estrogen-dependent, tamoxifen-resistant tumorigenic growth of MCF-7 cells transfected with HER2/neu.
Since the poor prognosis associated with HER2 amplified breast cancers might be explained by a mechanistic association between p185HER2 overexpression and therapeutic resistance, we assessed the chemo-endocrine sensitivity of estrogen receptor (ER) containing MCF-7 breast cancer cells transfected with full-length HER2 cDNA. Of the 36 isolated MCF/HER2 subclones, 7 were found to overexpress p185HER2 surface receptor at levels 3 to 45-fold greater than parental or control transfected cells (MCF/neo). The overexpressing transfectants possessed increased inositol-1,4,5-triphosphate-3'-kinase activity comparable to enzyme activity in the endogenously HER2 amplified breast cancer cell lines SK-Br-3 and BT-474. The anti-p185HER2 monoclonal antibody and receptor-specific partial agonist, muMAb4D5 (4D5), known to inhibit growth of SK-Br-3 and BT-474 cells, produced no significant growth inhibitory effect on any of the transfectants including the 45-fold overexpressing MCF/HER2-18 cells which were studied in greater detail. MCF/HER2-18 cells contained at least partially functioning exogenous receptor since 4D5 (3 micrograms/ml) specifically stimulated phosphorylation of p185HER2 and its co-precipitating ptyr56 substrate within 5 min, and this was followed at 1 h by a transient induction of c-myc but not c-fos mRNA. ER content and the in vitro sensitivity of MCF/HER2-18 cells to 5-fluorouracil and adriamycin were identical to those of control transfectants and parental cells. However, these highly overexpressing transfectants had acquired low level (2 to 4-fold) resistance to cisplatin and were no longer sensitive to the antiestrogen tamoxifen (TAM). To compare the hormone-dependent tumorigenicity of the HER2 transfectants, MCF/HER2-18 and control cells (MCF, MCF/neo-3) were implanted into ovariectomized athymic nude mice. No tumors were produced in the absence of estradiol (E2) administration. In E2 supplemented mice, MCF/HER2-18 tumors grew most rapidly. When E2 treatment was stopped and daily TAM injections were initiated, MCF-7 and MCF/neo-3 tumor growth ceased immediately, while MCF/HER2-18 tumors continued to show an accelerated growth rate lasting weeks. This pattern of hormone-dependent, TAM-resistant growth exhibited by the MCF/HER2-18 tumors in nude mice supports the possibility that p185HER2 overexpression in human breast cancers may be linked to therapeutic resistance.
Benz
C C
CC
Cancer Research Institute, University of California, San Francisco 94143.
Scott
G K
GK
Sarup
J C
JC
Johnson
R M
RM
Tripathy
D
D
Coronado
E
E
Shepard
H M
HM
Osborne
C K
CK
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D004351:Drug Resistance; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D010770:Phosphotransferases / Q000187:drug effects / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor); D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D004967:Estrogens; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011518:Proto-Oncogene Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen; C051038:Inositol 1,4,5-trisphosphate 3-kinase