EGFR/HER2 inhibitor AEE788 increases ER-mediated transcription in HER2/ER-positive breast cancer cells but functions synergistically with endocrine therapy.
BACKGROUND
Cross-talk between receptor tyrosine kinases and the oestrogen receptor (ER) is implicated in resistance to endocrine therapy. We investigated whether AEE788 (a combined inhibitor of EGFR, HER2 and VEGFR) plus tamoxifen or letrozole enhanced the individual anti-tumour effects of these agents.


METHODS
Breast cancer cell lines modelling endocrine-resistant and -sensitive disease were engineered to express aromatase (A) and examined using proliferation, western blotting and ER-alpha transcription assays.


RESULTS
AEE788 enhanced the anti-proliferative effect of tamoxifen and letrozole in ER(+) cell lines (MCF-7 2A, ZR75.1 A3 and BT474 A3). This associated with an elevated G1 arrest and nuclear accumulation of p27. It is noteworthy that AEE788 alone or in combination with endocrine therapy increased the expression of progesterone receptor (PGR) and TFF1 in BT474 A3 cells. This may indicate a mechanism of resistance to AEE788 in ER(+)/HER2(+) breast cancers. In a ZR75.1 A3 xenograft, AEE788 alone or in combination with tamoxifen provided no further benefit compared with letrozole. However, letrozole plus AEE788 produced a significantly greater inhibition of tumour growth compared with letrozole alone.


CONCLUSIONS
These data suggest that AEE788 plus letrozole in breast cancer overexpressing HER2 may provide superior anti-tumour activity, compared with single agents.
Evans
A H
AH
Breakthrough Breast Cancer Centre, Institute of Cancer Research, London, UK.
Pancholi
S
S
Farmer
I
I
Thornhill
A
A
Evans
D B
DB
Johnston
S R
SR
Dowsett
M
M
Martin
L-A
LA
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001141:Aromatase / Q000235:genetics / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D019610:Cytoprotection / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D005260:Female; D006801:Humans; D000077289:Letrozole; D051379:Mice; D008819:Mice, Nude; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy; D009570:Nitriles / Q000008:administration & dosage*; D011687:Purines / Q000008:administration & dosage / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011960:Receptors, Estrogen / Q000378:metabolism*; D013629:Tamoxifen / Q000008:administration & dosage*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014230:Triazoles / Q000008:administration & dosage*; D023041:Xenograft Model Antitumor Assays
D001141:Aromatase; D066246:ErbB Receptors; D000077289:Letrozole; D009570:Nitriles; D011687:Purines; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D013629:Tamoxifen; D014230:Triazoles; C508053:ERBB2 protein, human; C489254:AEE 788
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