Acquired Resistance to Endocrine Treatments Is Associated with Tumor-Specific Molecular Changes in Patient-Derived Luminal Breast Cancer Xenografts

Abstract

Purpose: Patients with luminal breast cancer (LBC) often become endocrine resistant over time. We investigated the molecular changes associated with acquired hormonoresistances in patient-derived xenografts of LBC. Experimental Design: Two LBC xenografts (HBCx22 and HBCx34) were treated with different endocrine treatments (ET) to obtain xenografts with acquired resistances to tamoxifen (TamR) and ovariectomy (OvaR). PI3K pathway activation was analyzed by Western blot analysis and IHC and responses to ET combined to everolimus were investigated in vivo. Gene expression analyses were performed by RT-PCR and Affymetrix arrays. Results: HBCx22 TamR xenograft was cross-resistant to several hormonotherapies, whereas HBCx22 OvaR and HBCx34 TamR exhibited a treatment-specific resistance profile. PI3K pathway was similarly activated in parental and resistant xenografts but the addition of everolimus did not restore the response to tamoxifen in TamR xenografts. In contrast, the combination of fulvestrant and everolimus induced tumor regression in vivo in HBCx34 TamR, where we found a cross-talk between the estrogen receptor (ER) and PI3K pathways. Expression of several ER-controlled genes and ER coregulators was significantly changed in both TamR and OvaR tumors, indicating impaired ER transcriptional activity. Expression changes associated with hormonoresistance were both tumor and treatment specific and were enriched for genes involved in cell growth, cell death, and cell survival. Conclusions: PDX models of LBC with acquired resistance to endocrine therapies show a great diversity of resistance phenotype, associated with specific deregulations of ER-mediated gene transcription. These models offer a tool for developing anticancer therapies and to investigate the dynamics of resistance emerging during pharmacologic interventions. Clin Cancer Res; 20(16); 4314–25. ©2014 AACR.

Impaired PRC2 activity promotes transcriptional instability and favors breast tumorigenesis

“…We thus sought to assess the impact of modulating proliferation on the levels of EZH2 and H3K27me3 in the context of human breast cancers. We analyzed EZH2 and H3K27me3 levels by IHC in two previously characterized patient-derived xenografts (PDXs) of estrogen-positive breast cancer (Cottu et al 2014). The engrafted mice were treated with various combinations of endocrine therapies and the mTOR inhibitor everolimus, the impact of which on tumor proliferation was evaluated by Ki67 staining (Cottu et al 2014).…”

“…The engrafted mice were treated with various combinations of endocrine therapies and the mTOR inhibitor everolimus, the impact of which on tumor proliferation was evaluated by Ki67 staining (Cottu et al 2014). As previously reported (Supplemental Table S1; Cottu et al 2014), some drug combinations led to a near complete inhibition of cell proliferation (e.g., everolimus + fulvestrant), while other treatments only reduced proliferation (e.g., everolimus alone or everolimus + tamoxifen) or failed to impair proliferation (e.g., ovariectomy). Quantification of EZH2 signal revealed that it was highly correlated to Ki67 ( Fig.…”

“…IHC analysis on PDXs was performed on tissue microarrays obtained from treated xenografts as described in Cottu et al (2014). Samples were dewaxed, and antigen retrieval was performed for 20 min in pH 6 citrate buffer.…”

AKT Antagonist AZD5363 Influences Estrogen Receptor Function in Endocrine-Resistant Breast Cancer and Synergizes with Fulvestrant (ICI182780) In Vivo

“…In vivo efficacy studies were performed in 8-to 12-week-old female Swiss nude mice implanted with the PDX HBCx22OvaR, as previously described (22), in accordance with the French Ethical Committee. First, a pharmacodynamic study was performed for 4 days to assess biomarker changes with samples removed 2 and 4 hours after treatment.…”

Down-regulation of Forkhead box protein A1 (FOXA1) leads to cancer stem cell-like properties in tamoxifen-resistant breast cancer cells through induction of interleukin-6

“…Finally, we analyzed the gene expression profiles of tamoxifen-resistant breast tumors established from primary ER␣-positive breast tumors in an in vivo tamoxifen treatment model (26). Among five replicates, the three tamoxifen-resistant breast tumors (m27, m58, and m69) showed slightly increased expression of IL6 and decreased expression of FOXA1 and ER␣ as compared with control ER␣-positive tumors (Fig.…”