Enhanced epidermal growth factor receptor signaling in MCF7 breast cancer cells after long-term culture in the presence of the pure antiestrogen ICI 182,780 (Faslodex)
Ra. Mcclelland et al., Enhanced epidermal growth factor receptor signaling in MCF7 breast cancer cells after long-term culture in the presence of the pure antiestrogen ICI 182,780 (Faslodex), ENDOCRINOL, 142(7), 2001, pp. 2776-2788
This paper describes the establishment of an antiestrogen-resistant MCF7 br
east cancer cell subline (FASMCF) by continuous culture of the estrogen-res
ponsive parental line in steroid-depleted, ICI 182,780 (Faslodex; 10(-7) M)
-supplemented medium. After a 3-month period of growth suppression, cells b
egan to proliferate in ICI 182,780 at rates similar to those of untreated w
ild-type cells. Immunocytochemistry showed these cells to have reduced estr
ogen receptor and an absence of progesterone receptor proteins. RT-PCR and
transient transfection studies with estrogen response element-reporter cons
tructs confirmed that ICI 182,780-suppressed estrogen response element-medi
ated signaling. FASMCF cells show increased dependence upon epidermal growt
h factor receptor (EgfR)/mitogen-activated protein kinase (MAPK)-mediated s
ignaling. Thus, EgfR protein and messenger RNA, growth responses to transfo
rming growth factor-a, and extracellular signal-regulated kinase 1/2 MAPK a
ctivation levels are all increased. Unlike wild-type cells, FASMCF cells ar
e highly sensitive to growth inhibition by an EgfR-specific tyrosinekinase
inhibitor (TKI), ZD1839 (Iressa), and an inhibitor of the activation of MEK
1 (MAPKK), PD098059.
Short-term (similar to3 weeks) withdrawal of cells from antiestrogen had no
effect on growth or phenotype, whereas longer withdrawal(> 10 weeks) appea
red to partially reverse the cellular phenotype with increasing estrogen re
ceptor and decreasing FgfR levels.
In subsequent studies FASMCF cells were maintained in TKI, where their grow
th was again suppressed and secondary TKI resistance failed to develop with
in the 3-month period in which initial ICI 182,780 resistance arose. Furthe
rmore, wild-type cells similarly maintained in combination ICI 182,780 and
TKI treatment conditions remained growth arrested (>6 months), with notable
cell loss through both reduced rates of cellular proliferation and increas
ed cell death.