Paradoxical action of fulvestrant in estradiol-induced regression of tamoxifen-stimulated breast cancer.
BACKGROUND
Long-term tamoxifen treatment of breast cancer can result in tamoxifen-stimulated breast cancer, in which estrogen inhibits tumor growth after tamoxifen withdrawal. We investigated the molecular mechanism(s) of estradiol-induced tumor regression by using an in vivo model of tamoxifen-stimulated human breast cancer.


METHODS
Growth of parental estradiol-stimulated MCF-7E2 and long-term tamoxifen-stimulated MCF-7TAMLT xenografts in athymic mice was measured during treatment with vehicle, estradiol, estradiol plus tamoxifen, tamoxifen alone, estradiol plus fulvestrant, or fulvestrant alone. Apoptosis was detected by the terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay. Protein expression was assessed by western blot analysis. mRNA expression was assessed by real-time reverse transcription-polymerase chain reaction. All statistical tests were two-sided.


RESULTS
MCF-7E2 tumor growth was stimulated by estradiol (cross-sectional area at week 13 = 1.06 cm2, 95% confidence interval [CI] = 0.82 to 1.30 cm2; P<.001) compared with control (0.06 cm2, 95%CI = -0.02 to 0.14 cm2), but tumor growth was inhibited by tamoxifen or fulvestrant. MCF-7TAMLT tumor growth was stimulated by tamoxifen) cross-sectional area at week 10 = 0.60 cm2, 95% CI = 0.50 to 0.70 cm2; P<.001) compared with control (0.02 cm2, 95% CI = 0.00 to 0.04 cm2). For MCF-7TAMLT tumors that were initially 0.35 cm2, estradiol-induced regression to 0.18 cm2 (95% CI = 0.15 to 0.21 cm2; P<.001), and tamoxifen or estradiol plus fulvestrant enhanced tumor growth to 1.00 cm2 (95% CI = 0.88 to 1.22 cm2). Estradiol increased the number of apoptotic cells in tumors by 23% (95% CI = 20% to 26%; P<.001) compared with all other treatments, decreased estrogen receptor alpha(ERalpha) protein expression, increased the expression of Fas mRNA and protein, decreased the expression of HER2/neu mRNA and protein and nuclear factor kappaB (NF-kappaB) protein but did not affect Fas ligand protein expression compared with control. Paradoxically, fulvestrant reversed this effect and stimulated MCF-7TAMLT tumor growth apparently through ERalpha-mediated regulation of Fas, HER2/neu, and NF-kappaB.


CONCLUSIONS
Physiologic levels of estradiol induced regression of tamoxifen-stimulated breast cancer tumors, apparently by inducing the death receptor Fas and suppressing the antiapoptotic/prosurvival factors NF-kappaB and HER2/neu.
Osipo
Clodia
C
Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Gajdos
Csaba
C
Liu
Hong
H
Chen
Bin
B
Jordan
V Craig
VC
D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000009:adverse effects / Q000627:therapeutic use*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000188:drug therapy* / Q000473:pathology; D004958:Estradiol / Q000031:analogs & derivatives* / Q000627:therapeutic use*; D020847:Estrogen Receptor Modulators / Q000009:adverse effects / Q000627:therapeutic use*; D053222:Fas Ligand Protein; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D020287:In Situ Nick-End Labeling; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D016133:Polymerase Chain Reaction; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D013629:Tamoxifen / Q000009:adverse effects*; D016211:Transforming Growth Factor alpha / Q000378:metabolism; D014183:Transplantation, Heterologous
D018931:Antineoplastic Agents, Hormonal; D004958:Estradiol; D020847:Estrogen Receptor Modulators; D053222:Fas Ligand Protein; D000077267:Fulvestrant; D008562:Membrane Glycoproteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D013629:Tamoxifen; D016211:Transforming Growth Factor alpha; C505661:FASLG protein, human; C505658:Fasl protein, mouse