Abstract GS1-09: Inhibition of GPX4 induces preferential death of p53-mutant triple-negative breast cancer cells
Authors: Tahaney William M , Qian Jing , Powell Reid , Moyer Cassandra L , Ma Yanxia , Nguyen Nghi , Hill Jamal , Stephan Clifford , Mazumdar Abhijit , Davies Peter JA , Brown Powel H 
Published: March 2022

Abstract
Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype characterized by lack of ER, PR, and Her2. Up to 85% of TNBCs have a p53 mutation as their oncogenic driver. TP53 is a tumor suppressor known as the “guardian of the genome” for its roles in regulating growth and death after genomic insult. Due to this high frequency of p53 mutations in TNBCs, targeting p53 mutants in a clinical setting is highly attractive. However, there are currently no FDA-approved drugs that can directly target p53 mutant TNBCs. We propose pathways exist that, when inhibited, will induce the specific death of p53-mutant breast cancer cells, but not p53-wild type breast cells. To investigate this hypothesis, we performed high-throughput drug screening to identify drugs that induce death in p53-mutant TNBCs. We then characterized the identified drugs for mechanism of death induction and in vivo drug effect. Methods: In vitro and in silico drug screens were conducted with small-molecule libraries of drugs with known protein targets, and screens were integrated and common drugs identified. P53-wild type and mutant cells were treated with identified drugs and stained with DAPI and DRAQ7 to identify growth-suppressive and death-inductive effects. One of these drugs, the GPX4 inhibitor ML-162, was selected for further study. Mechanism of death induction by ML-162 was determined with AnnexinV/PI, caspase cleavage, and ferroptosis assays. To confirm these results, GPX4 was knocked out and replicated the effect of ML-162. To determine the reliance of this phenotype on p53 mutational status, a series of inducible p53-mutant cell lines were created in ER+ and TNBC cell lines and then treated with small molecule inhibitors. ML-162 in vivo effect was demonstrated by treating p53-mutant TNBC xenografts in nude mice. Results: Integration of in vitro and in silico screens identified 6 common drugs, representing cell cycle inhibitors, cell division inhibitors, a proteasome inhibitor, and a peroxidase inhibitor. Identified drugs were demonstrated to reduce growth or induce death of p53-mutant TNBC cell lines. The GPX4 inhibitor ML-162 was further characterized, and found to induce death through ferroptosis, and not apoptosis or necroptosis. GPX4 knockout in p53-mutant TNBC cell lines induced ferroptosis and can be blocked with an anti-ferroptosis drug. Inducible p53-mutations in ER+ and TNBC cell lines were treated with ML-162. P53 mutations in TNBC, and not ER+, cell lines showed increased sensitivity to ML-162. To demonstrate in vivo effect of ML-162, TNBC cell line xenografts were grown in nude mice and treated with ML-162. This treatment significantly reduced tumor volume and also induced lipid peroxidation, a hallmark of ferroptosis. Conclusion: Our high-throughput screening demonstrated several of the identified drugs suppress growth or induce death preferentially in p53-mutant breast cancers. One of these drugs, ML-162, induces death of p53-mutant triple-negative breast cancer cells through induction of ferroptosis, both in vitro and in vivo. These studies provide the basic science foundation to further develop ferroptosis inducers for the targeted treatment of p53-mutant breast cancers. This work was funded by the John Charles Cain Endowment.
Citation Format: William M Tahaney, Jing Qian, Reid Powell, Cassandra L Moyer, Yanxia Ma, Nghi Nguyen, Jamal Hill, Clifford Stephan, Abhijit Mazumdar, Peter JA Davies, Powel H Brown. Inhibition of GPX4 induces preferential death of p53-mutant triple-negative breast cancer cells [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS1-09.