A Pathway for Necrotic Cell Death - Unlike other death pathways, protein mediators of drug-induced necrotic cell death were poorly defined. Necrosis activates immune cells, inducing immunogenic cell death. Therefore, understanding necrosis provides new avenues for enhancing drug development and cancer immunotherapy. Our anticancer drugs BHPI and ErSO act via estrogen receptor α (ERα) to induce lethal necrosis-inducing hyperactivation of the anticipatory Unfolded Protein Response (a-UPR). In orthotopic xenografts and a PDX, ErSO eradicates primary and metastatic therapy-resistant ERα+ breast cancer, induces near complete regression of lethal breast cancer in brain, and of endometrial cancer and ovarian cancer, and kills most ovarian cancer cells in patient malignant ascites. From CRISPR screens against BHPI and ErSO, we identified the Ca2+ activated, plasma membrane Na+ channel TRPM4 as the executioner protein that BHPI and ErSO use to induce necrosis and the likely membrane flexibility modulator FGD3. BHPI and ErSO-induced elevated Ca2+ opens the TRPM4 channel, eliciting a rapid influx of external Na+, Cl- and accompanying water. This swells the cells, causing osmotic stress, which hyperactivates the UPR, leading to ATP depletion, FGD3 enhanced membrane rupture and necrotic cell death. TRPM4 knockout abolished ATP depletion, sustained UPR hyperactivation, cell swelling and death. Notably, TRPM4 knockout also inhibited necrosis induced by unrelated anticancer therapies, the mitochondrial targeting oncolytic peptide, LTX-315, the Ca2+ channel targeting agent, Englerin A and Ca2+ electroporation (CaEP). Aim 1. Identify and functionally characterize known and additional shared components of the TRPM4 pathway. We will combine data from completed CRISPR screens, new screens using LTX-315, Englerin A, and CaEP and RNA-seq data from our recently developed ErSO resistant cell lines. Aim 2. Using cell and tumor studies, test the hypothesis that diverse necrosis-inducing anticancer therapies, in which Ca2+ levels are increased by transient a-UPR activation or other mechanisms, share a common pathway that converges on the UPR-TRPM4-FGD3 pathway. To extend UPR activation therapies to ERα- cancers, test the idea that the clinically promising, mechanistically obscure, necrosis-inducing therapy, Ca2+ electroporation, works in part through the UPR-TRPM4-FGD3 necrosis pathway. Aim 3. Using syngeneic mouse models establish whether necrosis-inducing agents extend the reach of immunotherapy to rapidly lethal breast cancer that has metastasized to brain and does not express neoantigens. Aim 4. Mechanisms of resistance to necrosis inducing cancer drugs are largely unexplored. Using our Myc down-regulated reversibly quiescent cells, we will identify ErSO resistance mechanisms and test whether loss of Myc in the quiescent cells is due to a-UPR mediated ATP depletion activating AMPK, thereby inhibiting protein synthesis via eEF2. These studies will establish a new pathway of immunogenic anticancer therapy-induced necrotic cell death through the UPR.
