7065 Eradication of Metastatic ER-positive Breast, Ovarian, Endometrial and Lung Cancer in Mouse Xenografts and Patient Derived Organoids

Abstract Disclosure: D.J. Shapiro: None. D. Duraki: None. S. Ghosh: None. J. Zhu: None. C. Mao: None. J. Kim: None. M. Jabeen: None. M.W. Boudreau: None. M.P. Mulligan: None. R. Romero: None. Y. Han: None. J. Zhang: None. E.R. Nelson: None. O. Olopade: None. G. Chang: None. P.J. Hergenrother: Advisory Board Member; Self; Systems Oncology. We described the tumor protective estrogen-ER activated anticipatory Unfolded Protein Response (a-UPR) pathway. Here we report a previously undescribed multistep pathway by which very rapid estrogen-ER activation of the a-UPR authorizes and regulates subsequent transcription of the estrogen-ER transcriptome. We repurposed the tumor protective a-UPR through identification and optimization of the small molecule ErSO and its family of agents. ErSO acts non-competitively with estrogen to induce lethal hyperactivation of the a-UPR. In orthotopic mouse xenografts containing wild type or mutant ER, ErSO often induced complete regression without recurrence of large primary breast tumors and of most lung, bone and liver metastases, near complete regression of normally lethal brain metastases and complete destruction of patient derived organoids (PDOs) in Matrigel. Six research teams in four locations have confirmed the remarkable effectiveness of ErSO in ER-positive breast cancer. We next evaluated ErSO in diverse ER containing cancers in which estrogen is not the primary driver of proliferation. ErSO often induced complete regression in multiple orthotopic xenograft models of primary and metastatic ovarian cancer. Using fresh ovarian cancer organoids immediately after removal from patients by paracentesis, ErSO destroyed the organoids from some patients with advanced stage III and stage IV disease. ErSO was effective in a mouse xenograft model of endometrial cancer and, surprisingly, even in ERalpha positive lung cancer. Our ongoing studies demonstrate ErSO induces complete, or near complete regression, of primary and metastatic lung cancer in mice. Studies of ErSO’s mechanism of action using genome-wide CRISPR screens with positive selection, and other techniques, unveil a novel death pathway in which ErSO activation of the a-UPR triggers rapid calcium release into the cell body. The calcium opens the plasma membrane TRPM4 sodium channel, leading to an influx of extracellular sodium. This swells the cells, resulting in osmotic stress that sustains lethal a-UPR activation. A little-studied cytoskeleton regulator we identified, FGD3, plays a pivotal role in whether the cells rupture their membranes, inducing necrotic cell death. Notably, medium from diverse cancer cells killed by ErSO-induced necrosis robustly activates human macrophage and induces their migration - potentially facilitating immunotherapy. These studies describe a pathway from a multiprotein ER-SRC-PLC complex, through the a-UPR, to a novel cell swelling and necrosis pathway, that we are exploiting to target diverse, therapeutically challenging, ER-positive human cancers. Presentation: 6/2/2024