HER2 overexpressing metastatic breast cancer

Opinion statement More than 40,000 women in the United States die each year from metastatic breast cancer. Elucidation of HER2 and its role in malignant transformation has helped define a subset of aggressive breast cancer that may be relatively resistant to non-anthracycline-based therapies and hormonal agents, but responds to targeted molecular therapy. Trastuzumab, an antibody against HER2, has proven effective as single agent therapy in women with HER2 overexpressed metastatic breast cancer. Moreover, in combination with chemotherapy, trastuzumab has been shown to delay disease progression and improve overall survival for women with HER2-positive advanced breast cancer. The combination of chemotherapy and trastuzumab is emerging as a standard of care in women with HER2 overexpressed metastatic breast cancer. Several combination regimens using trastuzumab with taxanes, vinca alkaloids, or platinum compounds have demonstrated efficacy in first- and second-line treatment settings. However, the development of anthracycline-based combinations has been limited by concerns of related cardiotoxicity. Newer multi-agent regimens are in development. The optimal combination, duration, and sequence of trastuzumab therapy remain unknown in patients with HER2-positive metastatic disease. The role of continuing treatment after disease progression is also unclear. Evidence from some retrospective analyses suggest HER2-positive tumors are relatively resistant to tamoxifen and perhaps more responsive to aromatase inhibitors, although such data are inconclusive. HER2 status should not be used routinely for clinical decision making regarding hormonal therapy options. Several ongoing trials are attempting to address these and other issues related to HER2 testing to select the most appropriate candidates for these emerging therapies. While many questions remain, the treatment of HER2 overexpressing metastatic breast cancer is rapidly evolving, and represents a new approach to treatment in oncology.     

Simultaneous targeting of estrogen receptor and HER2 in breast cancer

Approximately 50% of HER2-positive breast cancers express estrogen receptor (ER) and these tumors are characterized by short-lived responses to hormonal agents. Preclinical models have shown that dual targeting of ER and HER2 could reverse and delay the development of drug resistance. Two studies (TAnDEM & EGF3008) have recently been published addressing the combined use of an aromatase inhibitor (AI) and an anti-HER2-targeted agent. Both studies showed that the combined approach is associated with improvement in response rate and progression-free survival compared with an AI alone with an acceptable toxicity profile. These results would indeed extend the treatment options for patients with ER/HER2-positive metastatic breast cancer. In this article, we discuss how the improved understanding of the complex cross-talk between ER and HER2 has resulted in better clinical outcomes. We analyze clinical evidence regarding the combined use of AIs and anti-HER2-targeted agents. We also touch on possible mechanisms of resistance and ways to improve research in this field.     

Interleukin 1 alpha blocks estradiol-stimulated growth and down-regulates the estrogen receptor in MCF-7 breast cancer cells in vitro

We studied the effect of interleukin 1 alpha (IL-1 alpha) on estradiol stimulation of cell growth and estrogen receptor (ER) content in MCF-7 human breast cancer cells in vitro to determine if IL-1 alpha altered cellular estradiol responsiveness. We found that IL-1 alpha blocked estradiol-stimulated growth of these cells in a dose-dependent manner (complete antagonism at 1000 units/ml: day 7 mean growth = vehicle, 47.7 micrograms DNA; estradiol 10(-10) M, 95.1; IL-1 alpha/estradiol, 44.6) and at all concentrations of estradiol from 10(-8) to 10(-11) M. IL-1 alpha in combination with trans-hydroxytamoxifen further inhibited estradiol-stimulated growth (vehicle = 44.8 micrograms DNA, estradiol = 108.3, estradiol/trans-hydroxytamoxifen = 47.8, IL-1 alpha/estradiol/trans-hydroxytamoxifen = 3.0, P less than 0.01). Inhibition with trans-hydroxytamoxifen was IL-1 alpha dose dependent (maximum = 97% at 1000 units/ml, P less than 0.01) and estradiol dose dependent (reversible with 10(-8) M estradiol, maximum inhibition at 10(-10) M estradiol). Concomitantly, IL-1 alpha down-regulated ER concentration by 38.0-43.7% (P less than 0.01) as measured by immunoreactivity or Scatchard analysis, respectively. This occurred as early as 3 h without a change in the Kd (vehicle = 0.23 nM, IL-1 alpha = 0.24 nM), persisted for at least 48 h, was dose dependent (maximum, 43.7% at 1000 units/ml, P less than 0.01), and was blocked by cycloheximide. IL-1 alpha, however, did not block estradiol stimulation of progesterone receptor content (vehicle = 221.9, IL-1 alpha = 238.9 fmol/mg protein) and did not block estradiol down-regulation of ER content. Furthermore, IL-1 alpha alone did not alter levels of ER mRNA and did not alter estradiol down-regulation of ER mRNA. These findings indicate that while IL-1 alpha antagonizes estradiol stimulation of growth and reduces ER content, its mechanism may involve other non-estrogen-regulated pathways.     

Integrin beta1 upregulation in MCF-7 breast cancer cells by angiotensin II.

AIMS: Integrins are a major family of cell adhesion molecules whose function is perturbed in tumour invasion and metastasis. Angiotensin II (A II) is well-known in the systemic control of water and electrolyte homeostasis and haemodynamics, but recent evidence points to an additional local renin-angiotensin system (RAS) with possible long-term trophic effects including carcinogenesis. METHODS: The effect of angiotensin II on MCF-7 human breast cancer cell line integrin expression was evaluated with immunocytochemistry (ICC) and immunoprecipitation (IP). RESULTS: The experiments demonstrated a 1.40 +/- 0.14-fold increase in beta, integrin expression on MCF-7 cells following treatment with A II. CONCLUSIONS: These findings report the first evidence of an association between integrins and the RAS in human breast cancer cells and suggest a novel research avenue for future anti-metastatic strategies, through the manipulation of cell adhesion mechanics, in the management of invasive human breast cancer.     

The liver receptor homolog-1 regulates estrogen receptor expression in breast cancer cells

Estrogen receptor-?? (ER) is expressed in the great majority of breast cancers, and the inhibition of ER action is a key part of breast cancer treatment. The inhibition of ER action is achieved using anti-estrogens, primarily tamoxifen, and with aromatase inhibitors that inhibit estrogen biosynthesis, thereby preventing ER activation. However, resistance to these therapies is common. With the aim of identifying new molecular targets for breast cancer therapy, we have identified the liver receptor homolog-1 (LRH-1) as an estrogen-regulated gene. RNA interference and over-expression studies were used to investigate the role of the LRH-1 in regulating breast cancer growth and to identify the targets of an LRH-1 action. Promoter recruitment was determined using reporter gene and chromatin immunoprecipitation (ChIP) assays. We show that LRH-1 regulates breast cancer cell growth by regulating the ER expression. Reporter gene and in vitro DNA-binding assays identified an LRH-1-binding site in the ER gene promoter, and ChIP assays have demonstrated in vivo binding at this site. We also provide evidence for new LRH-1 variants in breast cancer cells arising from the use of alternative promoters. Previous studies have shown that LRH-1 functions in estrogen biosynthesis by regulating aromatase expression. Our findings extend this by highlighting LRH-1 as a key regulator of the estrogen response in breast cancer cells through the regulation of ER expression. Hence, inhibition of LRH-1 could provide a powerful new approach for the treatment of endocrine-resistant breast cancer.     

Peroxisome proliferator-activated receptor gamma agonists induce proteasome-dependent degradation of cyclin D1 and estrogen receptor alpha in MCF-7 breast cancer cells

Treatment of MCF-7 cells with the peroxisome proliferator-activated receptor (PPAR) gamma agonists ciglitazone or 15-deoxy-Delta 12,14-prostaglandin J2 resulted in a concentration- and time-dependent decrease of cyclin D1 and estrogen receptor (ER) alpha proteins, and this was accompanied by decreased cell proliferation and G(1)-G(0)-->S-phase progression. Down-regulation of cyclin D1 and ER alpha by PPARgamma agonists was inhibited in cells cotreated with the proteasome inhibitors MG132 and PSII, but not in cells cotreated with the protease inhibitors calpain II and calpeptin. Moreover, after treatment of MCF-7 cells with 15-deoxy-Delta 12,14-prostaglandin J2 and immunoprecipitation with cyclin D1 or ER alpha antibodies, there was enhanced formation of ubiquitinated cyclin D1 and ER alpha bands. Thus, PPARgamma-induced inhibition of breast cancer cell growth is due, in part, to proteasome-dependent degradation of cyclin D1 (and ER alpha), and this pathway may be important for other cancer cell lines.     

Clinical value of the wild-type estrogen receptor beta expression in breast cancer

To estimate the clinical value of estrogen receptor (ER) beta expression in breast cancer we used an immunohistochemical method to detect the wild-type ERbeta in 88 primary breast cancers. We used a highly specific polyclonal antibody to the carboxyl terminus of wild-type ERbeta. This antibody reacted with neither other variant forms of ERbeta nor any part of ERalpha. Slides were evaluated on a scale representing the estimated proportion and intensity of positive-staining tumor cells. Positive staining could be seen in 52 (59.1%) of 88 breast cancers; 36 (40.9%) were negative. Although there was no correlation between ERbeta staining and age, node status, tumor size, histological grade, or progesterone receptor (PgR)-enzyme immunoassay (EIA) status, we did observe a significant correlation with ERalpha-EIA (Fisher's exact probability test: P=0.0169). Moreover, ERbeta positive cases showed a better prognosis than negative cases in disease-free survival rate (Logrank test: P=0.0662, Breslow-Gehan-Wilcoxson test: P=0.0318). Our data demonstrated the possibility that wild-type ERbeta protein expression could be used as a good prognostic indicator for breast cancer.     

Polyamine profiles and growth properties of ornithine decarboxylase overexpressing MCF-7 breast cancer cells in culture

Summary To determine the direct influence of the polyamine (PA) pathway on breast cancer phenotype, we employed a transfection approach to induce overexpression of the PA biosynthetic enzyme ornithine decarboxylase (ODC) in the hormone-responsive MCF-7 breast cancer cell line. Using a modified calcium phosphate method and an ODC cDNA coding for a truncated and more stable enzyme, we were able to achieve a moderate to marked degree of ODC overexpression (up to 150-fold) in a transient transfection system. ODC-overexpressing MCF-7 cells exhibited a selective increase in cellular putrescine content, while the levels of spermidine and spermine remained unaffected. Under defined culture conditions, overexpression of ODC resulted in a consistent but modest increase in [³H]thymidine incorporation into DNA which was similar in the presence and absence of 17--estradiol, TGF-, and IGF-I. In the presence of serum, the effect of ODC overexpression on basal [³H]-thymidine incorporation into DNA was inconsistent, possibly as a result of subtle differences in culture conditions. Overall, our results support the hypothesis that activation of the PA biosynthetic pathway may confer a growth advantage to breast cancer cells.     

Differences in protein kinase C and estrogen receptor alpha, beta expression and signaling correlate with apoptotic sensitivity of MCF-7 breast cancer cell variants

Widespread use of MCF-7 human breast cancer cells as a model system for breast cancer has lead to variations in these cells between different laboratories. Although several reports have addressed these differences in terms of proliferation and estrogenic response, differences in sensitivity to apoptosis have just begun to be described. Based on the possible differences in apoptotic sensitivity that may arise due to the existence of MCF-7 cell variants, we determined the relative sensitivity of MCF-7 cell variants from three established laboratories (designated M, L and N) to known inducers of apoptosis. Consistent with our previous studies we demonstrate that differences exist among these variants in regards to tumor necrosis factor alpha (TNF)-induced cell death and inhibition of proliferation in a dose-dependent manner. To establish if the difference in apoptotic susceptibility was specific to TNF, the three MCF-7 cell variants were tested for their response to other known inducers of apoptosis: okadaic acid, staurosporine and 4-hydroxy-tamoxifen. Viability and DNA fragmentation analysis revealed a similar pattern of resistance to apoptosis by all agents in the MCF-7 M variant. The MCF-7 L variant was resistant to okadaic acid and 4-hydroxy-tamoxifen but not staurosporine. In contrast, MCF-7 N cells were sensitive to induction of apoptosis by all agents. The role of both protein kinase C (PKC) and estrogen signaling in the regulation of cell survival prompted investigation of these pathways as a mechanism for differential sensitivity of MCF-7 cell variants to apoptosis. While both estrogen receptor alpha (ERalpha) and ERbeta were expressed in MCF-7 M and N cells, the absence of ERbeta in MCF-7 L cells correlated with decreased estrogen responsiveness of the L variant. Variations in estrogenic responsiveness and PKC isoform expression may account for the enhanced susceptibility of both the L and N variants to staurosporine.