Article published by the Endocrine Society Article published by the Endocrine Society

The estrogen receptor alpha (ERα) plays a critical role in the pathogenesis and clinical behavior of breast cancer. To obtain further insights into the molecular basis of estrogen-dependent forms of this malignancy, we used real-time quantitative reverse transcription (RT)-PCR to compare the mRNA expression of 560 selected genes in ERα-positive and ERα-negative breast tumors. Fifty-one (9.1%) of the 560 genes were significantly upregulated in ERα-positive breast tumors compared with ERα-negative breast tumors. In addition to well-known ERα-induced genes (PGR, TFF1/PS2, BCL2, ERBB4, CCND1, etc.) and genes recently identified by cDNA microarray-based approaches (GATA3, TFF3, MYB, STC2, HPN/HEPSIN, FOXA1, XBP1, SLC39A6/LIV-1, etc.), an appreciable number of novel genes were identified, many of, which were weakly expressed. This validates the use of large-scale real-time RT-PCR as a method complementary to cDNA microarrays for molecular tumor profiling. Most of the new genes identified here encoded secreted proteins (SEMA3B and CLU), growth factors (BDNF, FGF2 and EGF), growth factor receptors (IL6ST, PTPRT, RET, VEGFR1 and FGFR2) or metabolic enzymes (CYP2B6, CA12, ACADSB, NAT1, LRBA, SLC7A2 and SULT2B1). Importantly, we also identified a large number of genes encoding proteins with either pro-apoptotic (PUMA, NOXA and TATP73) or anti-apoptotic properties (BCL2, DNTP73 and TRAILR3). Surprisingly, only a small proportion of the 51 genes identified in breast tumor biopsy specimens were confirmed to be ERα-regulated and/or E2-regulated in vitro (cultured cell lines). Therefore, this study identified a limited number of genes and signaling pathways, which better delineate the role of ERα in breast cancer. Some of the genes identified here could be useful for diagnosis or for predicting endocrine responsiveness, and could form the basis for novel therapeutic strategies.

Aberrant activation of the PI3K/Akt/mTOR pathway is found in many types of cancer and thus plays a major role in breast cancer cell proliferation and anti-cancer drug resistance. The mechanisms involved in the activation of this pathway include: constitutively activated receptor tyrosine kinases (IGF/IGFR, ErbB, FGF/FGFR systems) leading to constitutive activation of PI3K; loss of PTEN function; PI3K mutations; aberrant activation of Akt, eIF4E, 4E-BP1 and p70S6K. These alterations trigger a cascade of biological events, from cell growth and proliferation to survival and migration, which contribute to tumor progression. Therefore, the PI3K/Akt/mTOR pathway is considered an attractive target for the development of novel anti-cancer molecules, and several specific tyrosine kinase inhibitors and signal transduction inhibitors specifically targeting the kinases involved in this pathway have been developed. Many of these inhibitors currently under clinical evaluation represent a promising approach for the treatment of breast cancer patients. This review provides an overview of the most recent patents, of pre-clinical and clinical studies of inhibitors targeting the different members and/or activators of the PI3K/Akt/mTOR pathway, used alone or in combination with other targeted agents for the treatment of breast cancer.

The Krüppel-like zinc finger protein ZNF217 is a candidate oncogene in breast cancer. In this study, we showed that high levels of expression of ZNF217 mRNA are associated with poor prognosis and the development of metastases in breast cancer. Overexpression of ZNF217 in breast cancer cells stimulated migration and invasion in vitro and promoted the development of spontaneous lung or node metastases in mice in vivo. ZNF217 also promoted epithelial–mesenchymal transition (EMT) in human mammary epithelial cells, and the TGF-β–activated Smad signaling pathway was identified as a major driver of ZNF217-induced EMT. In addition, a TGF-β autocrine loop sustained activation of the TGF-β pathway in ZNF217-overexpressing mammary epithelial cells, most likely because of ZNF217-mediated direct upregulation of TGFB2 or TGFB3. Inhibition of the TGF-β pathway led to the reversal of ZNF217-mediated EMT. Together, our findings indicate that ZNF217 mRNA expression may represent a novel prognostic biomarker in breast cancer. Therapeutic targeting of ZNF217 of the TGF-β signaling pathway may benefit the subset of patients whose tumors express high levels of ZNF217. Cancer Res; 72(14); 3593–606. ©2012 AACR.

Endocrine therapy resistance is one of the main challenges in the treatment of estrogen receptor positive (ER+) breast cancer patients. This study showed that two ER+ human breast carcinoma cell lines derived from MCF‐7 (MVLN cells) that have acquired under OH‐Tamoxifen selection two distinct phenotypes of endocrine resistance both displayed constitutive activation of the PI3K/Akt and MAPK pathways. Aberrant expression and activation of the ErbB system (phospho‐EGFR, phospho‐ErbB2, phospho‐ErbB3, over‐expression of ErbB4 and over‐expression of several ErbB ligands) were also observed in the two resistant cell lines, suggesting the existence of an autocrine loop leading to constitutive activation of MAPK and PI3K/Akt survival pathways. The recent clinical use of specific signal transduction inhibitors is one of the most promising therapeutic approaches in breast cancers. The MEK inhibitor PD98059 and the PI3K inhibitor LY294002 were both able to enhance the cytostatic effect of OH‐Tamoxifen or fulvestrant on MVLN sensitive cells. In the two resistant cell lines, inhibition of the MAPK or the PI3K/Akt pathways associated with endocrine therapy was sufficient to reverse OH‐Tamoxifen or fulvestrant resistance. Investigating the effect of a combination of both inhibitors on the reversion of OH‐Tamoxifen and fulvestrant resistance in the two resistant cell lines suggested that, in clinical practice, a strategy combining the two inhibitors would be the best approach to target the different endocrine resistance phenotypes possibly present in a tumor. In conclusion, the combination of MAPK and PI3K inhibitors represents a promising strategy to overcome endocrine therapy resistance in ER+ breast cancer patients.