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Abstract Approximately 90% of Breast Cancer (BrCa) related deaths are caused by metastasis and bone is the first and most frequent site of breast cancer metastatic expansion, which can lead to severe pain, immobility, fractures, and nerve damage, as well as the development of metastases in other organs, hence; a poor quality of life in patients. Currently, treatment options for these bone metastases (BoM) are limited because most patients with BoM shows reduced ER dependency which leads to resistance to standard endocrine or hormonal therapies for estrogen receptor-positive (ER+) BrCa. The long-term goal of the proposed research is to develop a strategy where metastatic cancer cells in bone can be dependent on ER signaling again thereby restoring their sensitivity to endocrine therapies. We observed a transient loss of ER expression in concert with enhanced activity of the transcriptional coactivators YAP/TAZ - the downstream effectors of the Hippo pathway (responsible for regulating cell proliferation and death) during bone colonization by BrCa cells. We hypothesize that the interaction between cancer cells and osteoblasts in the bone microenvironment leads to the activation of calcium signaling in cancer cells, resulting in the de-phosphorylation and nuclear localization of YAP/TAZ which subsequently suppresses the transcription of the estrogen receptor gene (ESR). Our research strategy is as presented below. First, we will employ a combination of 2D/3D co-culture models of BoM along with a mechanical loading system and determine the molecular mechanism driving the dynamical activation of YAP/TAZ in BrCa BoM. Using a unique ex vivo BM model called Bone In Culture Array (BICA) which replicates the in-vivo conditions, we will determine if verteporfin, a YAP/TAZ antagonist, can synergize and possibly enhance the effects of Fulvestrant, an ER antagonist in current use for certain types of BrCa in preventing BoM outgrowths and treating established BoM in mice. This research could ultimately lead to a favorable combination strategy to treat endocrine-resistant BoM in BrCa patients and prolong their survival. Citation Format: Anindita Das, Cheyenne Ernst. Re-sensitizing the Refractory Breast Cancer Bone Metastasis to Endocrine Therapies abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-02.
Das et al. (2024) studied this question.