Targeting tumour re-wiring by triple blockade of mTORC1, epidermal growth factor, and oestrogen receptor signalling pathways in endocrine-resistant breast cancer

• Published in: Breast cancer research : BCR Vol. 20; no. 1; pp. 44 - 15
• Main Authors: Ribas, Ricardo, Pancholi, Sunil, Rani, Aradhana, Schuster, Eugene, Guest, Stephanie K, Nikitorowicz-Buniak, Joanna, Simigdala, Nikiana, Thornhill, Allan, Avogadri-Connors, Francesca, Cutler, Jr, Richard E, Lalani, Alshad S, Dowsett, Mitch, Johnston, Stephen R, Martin, Lesley-Ann
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 08.06.2018; BioMed Central; BMC
• Subjects: Analysis; Aromatase; Aromatase Inhibitors - pharmacology; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Breast Neoplasms - pathology; Cell cycle; Cell Proliferation - drug effects; Diagnosis; Dosage and administration; Drug therapy; Endocrine resistance; Endocrine therapy; Epidermal growth factor; Epidermal Growth Factor - antagonists & inhibitors; Epidermal Growth Factor - genetics; Epidermal growth factors; ErbB protein; ErbB-2 protein; ESR1 protein; Estradiol - pharmacology; Estrogen Receptor alpha - genetics; Estrogen receptors; Estrogens - metabolism; Everolimus - pharmacology; Everomilus; Feedback; Female; Fulvestrant; Fulvestrant - pharmacology; Gene expression; Gene Expression Regulation, Neoplastic - drug effects; Gene set enrichment analysis; Humans; Kinases; Ligands; MCF-7 Cells; Mechanistic Target of Rapamycin Complex 1 - antagonists & inhibitors; Mechanistic Target of Rapamycin Complex 1 - genetics; Metastasis; Mutation; Neoplasms, Hormone-Dependent - drug therapy; Neoplasms, Hormone-Dependent - genetics; Neoplasms, Hormone-Dependent - pathology; Neratinib; Oestrogen receptor; Phenols; Phosphorylation; Quinolines - pharmacology; Receptor, ErbB-2 - antagonists & inhibitors; Receptor, ErbB-2 - genetics; Receptor, ErbB-3 - antagonists & inhibitors; Receptor, ErbB-3 - genetics; Ribonucleic acid; RNA; Signal transduction; Signal Transduction - drug effects; Steroid hormones; Tamoxifen; Tamoxifen - pharmacology; Transcription; Tumors; United Kingdom > UK; Endocrine resistance; Everomilus; Breast cancer; Neratinib; Oestrogen receptor
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/s13058-018-0983-1

Endocrine therapies are the mainstay of treatment for oestrogen receptor (ER)-positive (ER ) breast cancer (BC). However, resistance remains problematic largely due to enhanced cross-talk between ER and growth factor pathways, circumventing the need for steroid hormones. Previously, we reported the anti-proliferative effect of everolimus (RAD001-mTORC1 inhibitor) with endocrine therapy in resistance models; however, potential routes of escape from treatment via ERBB2/3 signalling were observed. We hypothesised that combined targeting of three cellular nodes (ER, ERBB, and mTORC1) may provide enhanced long-term clinical utility. A panel of ER BC cell lines adapted to long-term oestrogen deprivation (LTED) and expressing ESR1 or ESR1 , modelling acquired resistance to an aromatase-inhibitor (AI), were treated in vitro with a combination of RAD001 and neratinib (pan-ERBB inhibitor) in the presence or absence of oestradiol (E2), tamoxifen (4-OHT), or fulvestrant (ICI182780). End points included proliferation, cell signalling, cell cycle, and effect on ER-mediated transactivation. An in-vivo model of AI resistance was treated with monotherapies and combinations to assess the efficacy in delaying tumour progression. RNA-seq analysis was performed to identify changes in global gene expression as a result of the indicated therapies. Here, we show RAD001 and neratinib (pan-ERBB inhibitor) caused a concentration-dependent decrease in proliferation, irrespective of the ESR1 mutation status. The combination of either agent with endocrine therapy further reduced proliferation but the maximum effect was observed with a triple combination of RAD001, neratinib, and endocrine therapy. In the absence of oestrogen, RAD001 caused a reduction in ER-mediated transcription in the majority of the cell lines, which associated with a decrease in recruitment of ER to an oestrogen-response element on the TFF1 promoter. Contrastingly, neratinib increased both ER-mediated transactivation and ER recruitment, an effect reduced by the addition of RAD001. In-vivo analysis of an LTED model showed the triple combination of RAD001, neratinib, and fulvestrant was most effective at reducing tumour volume. Gene set enrichment analysis revealed that the addition of neratinib negated the epidermal growth factor (EGF)/EGF receptor feedback loops associated with RAD001. Our data support the combination of therapies targeting ERBB2/3 and mTORC1 signalling, together with fulvestrant, in patients who relapse on endocrine therapy and retain a functional ER.