Identification of genes/
proteins that are differentially expressed in HER2 (erbB-2) oncogene-dependent
breast carcinomas is essential in elucidating the mechanistic basis of their increased metastastic potential and resistance to several anti-
cancer therapies. We here applied human
cytokine antibody arrays with the goal of identifying a unique HER2-induced '
cytokine signature' in
breast cancer. Human
Cytokine Array III (RayBiotech, Inc.), which simultaneously detects 42
cytokines and
growth factors on one membrane, was used to determine the profile of
cytokines in
conditioned media obtained from MCF-7/Her2-18 cells, a MCF-7-derived clone engineered to stably express the full-length human HER2
cDNA controlled by a SV40 viral promoter, and from the MCF-7/neo control sub-line. We identified two inflammatory and pro-angiogenic
CXC chemokines with at least a 10-fold increased expression in HER2-overexpressing MCF-7/Her2-18 transfectants when compared to matched control MCF-7/neo cells: CXCL8 (IL-8;
Interleukin-8) and CXCL1 and (GRO; Growth-related oncogene). HER2-induced differential overexpression of
IL-8 and GRO was validated by ELISA and further confirmed by switching off the HER2 signalling. Treatment with the
tyrosine kinase inhibitor gefitinib (
Iressa) returned the expression levels of
IL-8 and GRO back to the baseline observed in MCF-7
breast cancer cells, which express physiological levels of HER2. To evaluate the diagnostic utility of these findings,
cytokine-specific antibody arrays were incubated with sera retrospectively collected from metastatic
breast cancer patients. This approach revealed a high similarity between the '
cytokine signature' observed in serum samples and that obtained in
media conditioned by
breast cancer-derived cell lines. Thus,
IL-8 and GRO circulating levels were significantly higher in HER2-positive
breast cancer patients compared with HER2-negative patients. These findings reveal for the first time that: a) Enhanced synthesis and secretion of members of the IL-8/GRO
chemokine family, which have recently been linked to oestrogen receptor (ER) inaction, increased cell invasion and angiogenesis, may represent a new pathway involved in the metastatic progression and endocrine resistance of HER2-overexpressing
breast carcinomas, and b) Circulating levels of IL-8 and GRO
cytokines may represent novel
biomarkers monitoring
breast cancer responses to endocrine treatments and/or HER2-targeted
therapies.