Four human
breast carcinoma xenografts, MCF-7, Br-10,
T-61 and MX-1, were transplanted into female nude mice with or without pretreatment with
estradiol and
progesterone.
Hormone receptors including cytosol and nuclear
estrogen receptor (ERc and ERn) and
progesterone receptor (PgR) were assessed by the
dextran-coated
charcoal method and exchange assay;
epidermal growth factor receptor (EGFR) was measured by the 125I-EGF binding assay. MCF-7 and
T-61 were ERc-, ERn- and PgR- positive, but Br-10 was positive only for ERc; MX-1 was negative for these
hormone receptors, but was the only xenograft showing EGFR. The growth of MCF-7 and Br-10 was enhanced by exogenous
estradiol and
progesterone, whereas the growth of
T-61 was markedly inhibited by exogenous
estradiol; the growth of MX-1 was not influenced by these sex
steroids. Recombinant human
epidermal growth factor (rhEGF) inhibited the growth of EGFR-positive MX-1 dose-dependently, whereas no changes were observed in the growth of EGFR-negative MCF-7, Br-10 and
T-61 after treatment with rhEGF. This paradoxical inhibition of rhEGF on EGFR-positive MX-1 might be due to down-regulation of EGFR, as shown in the ER-positive xenograft
T-61, whose growth was inhibited by
estradiol.