Abstract 6000: A novel pathway controlling anticancer drug induced immunogenic cell death

Abstract Acting through estrogen receptor alpha (ERα), in orthotopic mouse xenograft models and a PDX, our non-competitive anticancer drug ErSO induces complete or near complete regression of primary and metastatic therapy-resistant ERα-positive breast, ovarian and endometrial tumors. ErSO is also highly effective in ovarian cancer PDOs from patient ascites. Unlike most anticancer agents which inhibit cancer cell proliferation or induce apoptosis, ErSO induces immune-cell-activating necrosis through sustained hyperactivation of the anticipatory unfolded protein response (a-UPR) pathway resulting in ATP depletion and cell swelling followed by membrane rupture. The medium from cancer cells killed by ErSO not only robustly activates mouse and human macrophages, but also dramatically increases monocyte migration. ErSO therefore has the potential to help extend the reach of immunotherapy to many solid tumors that do not express neoantigens. However, unlike apoptosis which has an established signaling pathway, how ErSO induces necrosis was unknown. From a genome-wide CRISPR-Cas9 screen in MCF-7 cells with negative selection against ErSO, we identified FGD3, a guanine exchange factor (GEF) of Rho GTPase Cdc42 as the top target. Consistent with the screen, through subsequent knockout and overexpression of FGD3 in human breast cancer cells, we found that the knockout cells have significant resistance to ErSO while the overexpressing cells exhibit increased sensitivity to killing by ErSO in both 2D cell culture and a 3D organoid model. Our data indicates that this protein is not an upstream regulator of the ErSO-induced necrosis pathway. Instead, it is a regulator of the last stage of necrosis - cell membrane rupture. Thus, we identified an actin reorganization signaling pathway with multiple components that plays a pivotal role in whether the breast cancer cell responds to a-UPR activation and swelling by membrane rupture and necrotic cell death or reorganizes its actin enabling the cancer cell to survive. RNA-seq and other studies indicate that by regulating actin reorganization, this axis is important in ErSO-persister breast cancer cells exhibiting long-term survival in ErSO. This work enables identification of breast cancer patients whose elevated levels of components of this signaling pathway make them most likely to benefit from this novel therapy. Notably, FGD3 knockout cells also show considerable resistance to necrosis or necroptosis induced by other anticancer drugs. Here, we describe a therapy that induces immunogenic cell death in ERα-positive breast, ovarian and endometrial cancer cells. We also show that, as cancer cells respond to agents that induce immunogenic cell death through membrane rupture, an actin regulating pathway plays a critical role in life-death decisions. Citation Format: Junyao Zhu, Santanu Ghosh, Darjan Duraki, Matthew Boudreau, Musarrat Jabeen, Chengjian Mao, Ben H. Park, Georgina Cheng, Erik R. Nelson, Paul J. Hergenrother, David J. Shapiro. A novel pathway controlling anticancer drug induced immunogenic cell death abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6000.