Abstract 5675: Metastatic organ-specific changes in ERα and XPO1 signaling and metabolic adaptations dictate the therapy responses in endocrine resistant breast cancers
Authors: Zuo Qianying , Cotul Eylem Kulkoyluoglu , Santaliz-Casiano Ashlie , Imir Ozan Berk , Tunc Elif , Mao Chengjian , Shapiro David J. , Park Ben Ho , Landesman Yosef , Madak-Erdogan Zeynep 
Published: September 2020

Abstract
Introduction: Approximately 70% of human breast cancers express estrogen receptor alpha (ERα), providing a potential for targeted endocrine therapy for patients. Unfortunately, 30-40% of ER+ patients still experience recurrence and metastasis with a 5-year relative overall survival rate of just 24%. The tumor microenvironment (TME) plays a key role in the behavior of cancer cells and their response to endocrine therapies. However, there is a critical need for relevant 3D models of different metastatic sites to use for studying the molecular mechanisms driving resistance in these tumor phenotypes.
Methods: We established 3D cell culture systems in novel hydrogels derived from decellularized bone, lung and liver tissues - the major sites of metastasis of ER+ tumors, and compared with standard Matrigel culture. Endocrine responsive (MCF7 and T47D) and resistant (MCF7 and T47D cells with ESR1 Y537S or D538G mutations) breast cancer cell lines were treated with fulvestrant (FUL), tamoxifen (TAM) and palbociclib (PAL). Tumorigenicity was assessed using in vitro cell viability and colony formation assays and in vivo breast cancer cell line xenografts in athymic mice. ERα cistromes and transcriptomes were assessed using ChIP-Seq and RNA-Seq analysis. Metabolic changes were assessed using whole metabolite profiling by GC-MS, a Seahorse XF analyzer, and flux analysis with labeled glucose and glutamine.
Results: We observed metastatic site-specific responses to each drug. For example, TAM blocked colony formation in Matrigel and lung hydrogel but increased colony formation in bone and liver hydrogels. FUL acted as an agonist and increased colony number and size in all three-tissue matrices, but not in Matrigel. PAL increased colony size and number in Matrigel and liver hydrogel but not in bone or lung hydrogel. Genome-wide ERα recruitment to chromatin was reduced in liver hydrogels, consistent with decreased clinical response to endocrine agents in patients with liver metastasis. We found that treatment with individual drugs activated novel metabolic pathways to increase survival in different metastatic sites. Using RNA-Seq analysis, we identified increased expression of nuclear export pathway components (XPO1, KPNA2, etc.) in various metastatic sites. Combining an FDA-approved XPO1 small molecule inhibitor, Selinexor (SEL) with the current therapies used for advanced breast cancers (FUL, TAM or PAL) decreased metabolic adaptations in response to individual drug treatments and prevented colony formation in hydrogels and tumor growth in xenograft models.
Conclusions: Further developing and characterizing 3D metastatic site models will enable us to elucidate the underlying mechanisms of metastasis and resistance, and target these mechanisms with novel drug combinations in already metastasized patients. Targeting metastatic-site specific adaptations to regenerate new vulnerabilities in endocrine-resistant breast tumors is novel. Given the need for better strategies for improving therapy response of metastatic ER+ tumors, our findings show uncovering the role ERα-XPO1 crosstalk plays in metastatic breast cancer could lead to new combined therapies that reduce mortality.
Citation Format: Qianying Zuo, Eylem Kulkoyluoglu Cotul, Ashlie Santaliz-Casiano, Ozan Berk Imir, Elif Tunc, Chengjian Mao, David J. Shapiro, Ben Ho Park, Yosef Landesman, Zeynep Madak-Erdogan. Metastatic organ-specific changes in ERα and XPO1 signaling and metabolic adaptations dictate the therapy responses in endocrine resistant breast cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5675.