GPX4 Inhibitors Research Articles

Inhibition of GPX4 enhances CDK4/6 inhibitor and endocrine therapy activity in breast cancer.

CDK4/6 inhibition in combination with endocrine therapy is the standard of care for estrogen receptor (ER+) breast cancer, and although cytostasis is frequently observed, new treatment strategies that enhance efficacy are required. Here, we perform two independent genome-wide CRISPR screens to identify genetic determinants of CDK4/6 and endocrine therapy sensitivity. Genes involved in oxidative stress and ferroptosis modulate sensitivity, with GPX4 as the top sensitiser in both screens. Depletion or inhibition of GPX4 increases sensitivity to palbociclib and giredestrant, and their combination, in ER+ breast cancer models, with GPX4 null xenografts being highly sensitive to palbociclib. GPX4 perturbation additionally sensitises triple negative breast cancer (TNBC) models to palbociclib. Palbociclib and giredestrant induced oxidative stress and disordered lipid metabolism, leading to a ferroptosis-sensitive state. Lipid peroxidation is promoted by a peroxisome AGPAT3-dependent pathway in ER+ breast cancer models, rather than the classical ACSL4 pathway. Our data demonstrate that CDK4/6 and ER inhibition creates vulnerability to ferroptosis induction, that could be exploited through combination with GPX4 inhibitors, to enhance sensitivity to the current therapies in breast cancer.

Lycium barbarum polysaccharide alleviates ferroptosis in Sertoli cells through NRF2/SLC7A11/GPX4 pathway and ameliorates DEHP-induced male reproductive damage in mice

Di-(2-ethylhexyl)phthalate (DEHP) is a common plasticizer that has been shown to significantly negatively affect male reproductive health. On the other hand, Lycium barbarum polysaccharide (LBP) has been shown to improve reproductive function. Therefore, we hypothesized that LBP may ameliorate DEHP-induced male reproductive damage. Herein, we found that LBP could alleviate DEHP-induced testicular damage and sperm abnormalities. Furthermore, histomorphological analysis of mice testis revealed that LBP primarily ameliorated the DEHP-induced male reproductive damage by targeting Sertoli cells. Moreover, the detection of the function-related genes of Sertoli cells confirmed this finding. The serum of mice in the Control, DEHP alone, and DEHP+LBP groups was analyzed using non-targeted metabolomics to further elucidate the mechanism of action of LBP in improving DEHP-induced male reproductive damage. According to the results, the differential metabolites were mainly enriched in the glutamate metabolism pathway, implying that LBP may alleviate the ferroptosis-related DEHP-induced testicular injury. Related ferroptosis markers were also found in mice testis. These findings collectively suggest that LBP may ameliorate DEHP-induced testicular injury via alleviating ferroptosis in Sertoli cells. To clarify the specific mechanism, we constructed a cell model in vitro by treating TM4 cells (the Sertoli cell line) with LBP and MEHP (the in vivo DEHP metabolite). Our findings revealed that LBP can improve the function of DEHP-affected Sertoli cells. Furthermore, the analysis of lipid peroxidation, Fe2+ content, and ferroptosis-related protein expressions demonstrated that LBP could ameliorate MEHP-induced ferroptosis in TM4 cells. To clarify the specific mechanism, glutamate metabolism-related proteins involved in the ferroptosis pathway were detected. According to the results, there were significant changes in the expression of NRF2, SLC7A11 and GPX4 proteins, which are involved in the ferroptosis glutamate metabolism pathway. Furthermore, supplementation of NRF2, SLC7A11, and GPX4 inhibitors (ML385, Erastin, and RSL3, respectively) blocked the therapeutic effect of LBP in alleviating MEHP-induced ferroptosis in TM4 cells, implying that LBP could also ameliorate MEHP-induced ferroptosis via the NRF2/SLC7A11/GPX4 pathway. In summary, these findings show that LBP can alleviate DEHP/MEHP-induced ferroptosis through the NRF2/SLC7A11/GPX4 pathway, ameliorating Sertoli cell dysfunction and improving the DEHP-induced male reproductive damage. Therefore, the clinical administration of LBP could be an effective strategy for preventing DEHP-induced male reproductive injury.

Combined blockade of GPX4 and activated EGFR/HER3 bypass pathways inhibits the development of ALK-inhibitor-induced tolerant persister cells in ALK-fusion-positive lung cancer.

Cancers can develop resistance to treatment with ALK tyrosine kinase inhibitors (ALK-TKIs) via emergence of a subpopulation of drug-tolerant persister (DTP) cells that can survive initial drug treatment long enough to acquire genetic aberrations. DTP cells are thus a potential therapeutic target. We generated alectinib-induced DTP cells from a patient-derived ALK+ non-small-cell lung cancer (NSCLC) cell line and screened 3114 agents in the anticancer compounds library (TargetMol). We identified phospholipid hydroperoxide glutathione peroxidase GPX4 as being involved in promoting the survival of DTP cells. GPX4 was found to be upregulated in DTP cells and to promote cell survival by suppressing reactive oxygen species (ROS) accumulation; GPX4 inhibitors blocked this upregulation and facilitated ROS-mediated cell death. Activated bypass signals involving epidermal growth factor receptor (EGFR)/receptor tyrosine-protein kinase erbB-3 (HER3) were also identified in DTP cells, and co-treatment with EGFR-TKI plus ALK-TKI enhanced ROS levels. Triple combination with an ALK-TKI plus a bypass pathway inhibitor plus a GPX4 inhibitor suppressed cell growth and induced intracellular ROS accumulation more greatly than did treatment with each agent alone. The combined inhibition of ALK plus inhibition of activated bypass signals plus inhibition of GPX4 may be a potent therapeutic strategy for patients with ALK+ NSCLC to prevent the development of resistance to ALK-TKIs and lead to tumor eradication.

Se-Methylselenocysteine Ameliorates DEHP-Induced Ferroptosis in Testicular Sertoli Cells via the Nrf2/GPX4 Axis.

Di (2-ethylhexyl) phthalate (DEHP) is an important plasticizer in industrial production, and its toxic effects on testes are widely recognized. Se-methylselenocysteine (SMC) is a major selenium compound found in selenium-rich plants, which possesses unique biological properties such as antioxidants. However, the effect of SMC on DEHP-induced testicular injury and the specific mechanism remains unknown. In this study, 50 mice were randomly divided into 5 groups and were given corn oil (Control), DEHP, low-dose SMC (L-SMC), moderate-dose SMC (M-SMC), or high-dose SMC (H-SMC). The sperm quality of the mice in each group was determined, and HE staining and transmission electron microscopy (TEM) were applied to observe testicular morphology, and testicular tissues were collected for the subsequent molecular biological analyses. The TM4 cell line was applied in vitro for mechanism validation. Our results showed that DEHP could lead to decreased sperm quality and blood-testis barrier damage in mice, which could be alleviated by SMC. Mitochondrial damage accompanied by accumulation of total iron content, MDA, and 4-HNE, as well as downregulation of antioxidants SOD, GSH, and GSH-Px were observed after DEHP treatment, which exhibited a typical ferroptosis feature. In vitro experiments confirmed that SMC promoted upregulation of GPX4 in TM4 cells and was able to alleviate DEHP metabolite MEHP-induced ferroptosis and promote the expression of cell junction key proteins ZO-1, Occludin, and Connexin 43, which could be inhibited by the GPX4 inhibitor RSL3 or the Nrf2 inhibitor ML385. Overall, the above results suggest that SMC ameliorates the DEHP-induced ferroptosis in testicular Sertoli cells, protects the blood-testis barrier, and prevents sperm aberrations via the Nrf2/GPX4 axis.

CBR-470-1 protects against cardiomyocyte death in ischaemia/reperfusion injury by activating the Nrf2–GPX4 cascade

Cardiac ischaemia/reperfusion (I/R) impairs mitochondrial function, resulting in excessive oxidative stress and cardiomyocyte ferroptosis and death. Nuclear factor E2-related factor 2 (Nrf2) is a key regulator of redox homeostasis and has cardioprotective effects against various stresses. Here, we tested whether CBR-470-1, a noncovalent Nrf2 activator, can protect against cardiomyocyte death caused by I/R stress. Compared with vehicle treatment, the administration of CBR-470-1 (2 mg/kg) to mice significantly increased Nrf2 protein levels and ameliorated the infarct size, the I/R-induced decrease in cardiac contractile performance, and the I/R-induced increases in cell apoptosis, ROS levels, and inflammation. Consistently, the beneficial effects of CBR-470-1 on cardiomyocytes were verified in a hypoxia/reoxygenation (H/R) model in vitro, but this cardioprotection was dramatically attenuated by the GPX4 inhibitor RSL3. Mechanistically, CBR-470-1 upregulated Nrf2 expression, which increased the expression levels of antioxidant enzymes (NQO1, SOD1, Prdx1, and Gclc) and antiferroptotic proteins (SLC7A11 and GPX4) and downregulated the protein expression of p53 and Nlrp3, leading to the inhibition of ROS production and inflammation and subsequent cardiomyocyte death (apoptosis, ferroptosis and pyroptosis). In summary, CBR-470-1 prevented I/R-mediated cardiac injury possibly through inhibiting cardiomyocyte apoptosis, ferroptosis and pyroptosis via Nrf2-mediated inhibition of p53 and Nlrp3 and activation of the SLC7A11/GPX4 pathway. Our data also highlight that CBR-470-1 may serve as a valuable agent for treating ischaemic heart disease.

Abstract C018: Targeting KRAS inhibitor resistance by ferroptosis induction in PDAC

Abstract KRAS inhibitors (KRASi) have shown promising antitumor activity in PDAC patients; however, intrinsic and acquired resistance will likely preclude durable monotherapy responses in the clinic. Genetic and pharmacologic targeting of the KRAS pathway is associated with transcriptional and metabolic adaptations, including epithelial-to-mesenchymal transition (EMT) and dysregulated iron homeostasis that contribute to resistance. Therapy resistant mesenchymal cancer cells have a high reliance on iron that increases their susceptibility to ferroptosis, an iron-dependent form of cell death characterized by generation of lipid reactive oxygen species (ROS). We hypothesize that KRASi resistance characterized by EMT can be overcome by ferroptosis induction in PDAC. Here, we use in vitro and ex vivo PDAC models and transcriptomic and proteomic profiling to define critical ferroptotic liabilities in KRASi-treated PDAC. First, we evaluated the effect of inhibiting different ferroptosis defense mechanisms (e.g. SLC7A11, GPX4, FSP1) using newly developed ferroptosis inducers (FINs) in a panel of epithelial and mesenchymal PDAC cells. Mesenchymal cells were more sensitive to ferroptosis induction compared to epithelial cells. Since ferroptotic death is regulated by multiple ferroptosis defense pathways, and in general PDAC are relatively resistant to ferroptosis induction, it is unlikely that a single ferroptosis inducer will be successful. Therefore, targeting multiple nodes with FINs in a combinatorial approach may lead to a more pronounced effect. Combination GPX4 and SLC7A11 inhibition and GPX4 and FSP1 inhibition were the most effective combinations compared to respective monotherapies. Next, we evaluated if combination of KRASi and ferroptosis induction is synergistic. Transcriptomic analysis of KRAS-mutant PDAC cell lines sensitive or with a priori resistance to KRASi revealed that EMT-related gene sets were upregulated in KRASi resistant cell lines. Quantitative proteomics revealed that PDAC cells treated long-term with KRASi undergo EMT and likewise long-term KRASi in in vivo PDAC models induces EMT. A KRASi-anchored CRISPR/Cas9 screen showed that sgRNAs targeting GPX4 dropped out in multiple cell lines indicating that ferroptosis induction may be synergistic upon KRAS inhibition. Remarkably, KRASi induced an increase of lipid peroxidation levels in PDAC cells which was rescued with antioxidant ferrostatin-1. We also observed that previously generated KRASi resistant cells were more sensitive to GPX4 inhibition. Combination of GPX4 inhibitor with KRASi led to a synergistic effect on cell viability and a significantly higher level of lipid peroxidation compared to monotherapy. These findings highlight the importance of investigating ferroptosis induction as a novel strategy to overcome therapeutic resistance in KRAS-mutant PDAC. We aim to further evaluate these combinations in vivo to determine the best combinatorial strategies in PDAC to prevent or circumvent KRASi resistance. Citation Format: Aparna Padhye, Qijia Yu, Nicole Sindoni, Huan Zhang, Julien Dilly, Hanrong Feng, Andrew Aguirre, Joseph Mancias. Targeting KRAS inhibitor resistance by ferroptosis induction in PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C018.

Targeting GPX4-mediated ferroptosis protection sensitizes BRCA1-deficient cancer cells to PARP inhibitors

BRCA1 is one of the most frequently-mutated tumor suppressor genes in ovarian and breast cancers. Loss of BRCA1 triggers homologous recombination (HR) repair deficiency, consequently leading to genomic instability and PARP inhibitors (PARPi)-associated synthetic lethality. Although, the roles of BRCA1 in DNA repair and replication have been extensively investigated, its tumor suppressive functions beyond genome safeguard remain poorly understood. Here, we report that BRCA1 promotes ferroptosis susceptibility through catalyzing K6-linked polyubiquitination of GPX4 and subsequently accelerating GPX4 degradation. Depletion of BRCA1 induces ferroptosis resistance in ovarian cancer cells due to elevated GPX4 protein, and silence of GPX4 significantly suppresses the growth of BRCA1-deficient ovarian cancer xenografts. Importantly, we found that PARPi triggers ferroptosis in ovarian cancer cells, inhibition of GPX4 markedly increase PARPi-induced ferroptosis in BRCA1-deficient ovarian cancer cells. Combined treatment of GPX4 inhibitor and PARPi produces synergistic anti-tumor efficacy in BRCA1-deficient ovarian cancer cells, patient derived organoid (PDO) and xenografts. Thus, our study uncovers a novel mechanism via which BRCA1 exerts tumor suppressive function through regulating ferroptosis, and demonstrates the potential of GPX4 as a therapeutic target for BRCA1-mutant cancers.

Hehuan Anshen decoction inhibits ferroptosis to ameliorate p-Chlorophenylalanine-induced insomnia by activating GPX4 pathway

IntroductionInsomnia is a chronic disease affecting a third of the global adult population. Hehuan Anshen Decoction (HHASD), an innovative formula derived from Traditional Chinese medicine, has demonstrated therapeutic efficacy in treating insomnia, however, the potential pharmacological mechanism underlying its anti-insomnia effects remains incompletely elucidated. This study aimed to explore the underlying mechanism of HHASD treatment in mice with insomnia induced by p-Chlorophenylalanine (PCPA). MethodsThe active constituents of HHASD were analysed by means of UPLCHRMS. PCPA mice were administered HHASD orally for 7 days. The anti-insomnia phenotype of HHASD were assessed by behavioral tests, encompassing the open field test and pentobarbital sodium-induced sleep test, alongside the measurement of hypothalamic 5-HT levels. Then, we conducted an in-depth analysis of specific ferroptosis markers, considering biochemistry, genetics and morphology. Additionally, ferroptosis inhibitor RSL3 was used to observe the underlying mechanism of the effects of HHASD. ResultsHHASD could effectively improve the insomnia behaviors induced by PCPA, resulting in increased movement trajectories, decreased sleep latency and prolonged sleep duration. Specifically, HHASD exerted a neuroprotective effect by enhancing the integrity of Nissl bodies in the hypothalamus of the PCPA mice. Mechanistic analysis revealed that HHASD could reverse the hypothalamic ferroptosis phenotype of insomnia mice by restoring the lowered levels of glutathione (GSH), inhibiting iron accumulation and elevated malondialdehyde (MDA), and mitigating mitochondrial cristae damage. Furthermore, HHASD enhanced the expression of SLC7A11 and GPX4 and reduced the ASCL4 in the hypothalamus, while the anti-insomnia effect of HHASD in the PCPA mice was eliminated by the GPX4 inhibitor RLS3. ConclusionHHASD ameliorates insomnia-related behaviors and protects against neuronal damage by suppressing ferroptosis by regulation GPX4 signaling. This study is not only a valuable attempt to explore the potential mechanism of Traditional Chinese formula but also will provide a novel targeted therapy for the treatment strategy of insomnia.

A cell state-specific metabolic vulnerability to GPX4-dependent ferroptosis in glioblastoma

Glioma cells hijack developmental programs to control cell state. Here, we uncover a glioma cell state-specific metabolic liability that can be therapeutically targeted. To model cell conditions at brain tumor inception, we generated genetically engineered murine gliomas, with deletion of p53 alone (p53) or with constitutively active Notch signaling (N1IC), a pathway critical in controlling astrocyte differentiation during brain development. N1IC tumors harbored quiescent astrocyte-like transformed cell populations while p53 tumors were predominantly comprised of proliferating progenitor-like cell states. Further, N1IC transformed cells exhibited increased mitochondrial lipid peroxidation, high ROS production and depletion of reduced glutathione. This altered mitochondrial phenotype rendered the astrocyte-like, quiescent populations more sensitive to pharmacologic or genetic inhibition of the lipid hydroperoxidase GPX4 and induction of ferroptosis. Treatment of patient-derived early-passage cell lines and glioma slice cultures generated from surgical samples with a GPX4 inhibitor induced selective depletion of quiescent astrocyte-like glioma cell populations with similar metabolic profiles. Collectively, these findings reveal a specific therapeutic vulnerability to ferroptosis linked to mitochondrial redox imbalance in a subpopulation of quiescent astrocyte-like glioma cells resistant to standard forms of treatment.

GPX4 Inhibition Enhances the Antitumor Effect of PARP Inhibitor on Homologous Recombination Proficient Ovarian Cancer Cells.

Poly (ADP-ribose) polymerase inhibitors (PARPi) are now widely used in BRCA1/2 mutation or homologous recombination (HR) deficiency ovarian cancer but have limited efficacy in HR-proficient patients. GPX4 is a key regulator of ferroptosis and has been proven to be associated with multiple drug sensitivities. As a molecule that regulates the sensitivity of multiple drugs, the relationship between GPX4 and the efficacy of PARPi in HR-proficient ovarian cancer has not been elucidated. In this study, siRNA transfection was used to regulate the expression of GPX4. The effect of GPX4 inhibition on HR-proficient ovarian cancer was determined by CCK-8 assay and flow cytometry. Immunofluorescence and comet assays were used to reflect DNA dam-age. ROS production was measured using DCFH-DA and flow cytometry. The combination index of PARP inhibitors and RSL3 was calculated using CompuSyn software based on Chou-Talalay methodology. GPX4 inhibition confers HR-proficient ovarian cancer cells sensitive to PARPi due to ROS generation and oxidative stress caused by DNA double-strand breakage. The combina-tion of olaparib and niraparib with GPX4 inhibitor RSL3 also showed a synergistic effect. Combining GPX4 inhibition with PARP inhibitors resulted in a notable increase in DNA damage, ultimately causing the death of cancer cells with proficient HR pathways. Our findings may provide new therapeutic options for HR-proficient patients to benefit from PARP inhibitors and improve outcomes.

Efficacy of FERscore in predicting sensitivity to ferroptosis inducers in breast cancer

Recent studies have highlighted the potential of ferroptosis in treating breast cancer. However, the efficacy of ferroptosis induction in the most common subtype, estrogen receptor-positive (ER + ) breast cancer, remains inadequately explored. This study unveils that both short-term and long-term treatment with ER-targeted endocrine agents sensitizes ER+ breast cancer cells to ferroptosis inducers, particularly the GPX4 inhibitor, revealing a non-mutational sensitization mechanism. Based on this finding, we introduce a 55-gene signature score (FERscore) tailored to assess ferroptosis susceptibility in breast cancer. Data from cell lines and primary tumors demonstrate significant lower FERscores in ER+ breast cancer compared to other subtypes; however, FERscores dramatically increase in endocrine-resistant ER+ tumor cells and residual tumors post-endocrine therapy. Furthermore, FERscore correlates positively with mesenchymal traits, stemness, immune cell infiltration, and cancer-associated fibroblasts enrichment, while inversely correlating with estrogen responsiveness and DNA repair capacity. Additionally, the FERscore proves effective in predicting therapeutic responses to anti-ER, anti-HER2, poly (ADP-ribose) polymerase inhibitor, and anti-angiogenesis therapies in breast cancer. In summary, ferroptosis induction emerges as a promising avenue in breast cancer therapy. The FERscore offers an innovative tool for identifying patients who may benefit from ferroptosis-inducing therapies, especially those responsive to GPX4 inhibitors.

52 Ferroptosis Suppressor Protein 1 is a Potent and Targetable Inhibitor of Ferroptosis in Chromophobe Renal Cell

Abstract Background There are currently no proven therapies for metastatic or unresectable Chromophobe renal cell carcinoma (ChRCC). Ferroptosis is an iron-dependent form of cell death characterized by the peroxidation of membrane polyunsaturated fatty acids, leading to membrane damage and cell death. Glutathione, a potent cellular antioxidant, counters lipid peroxidation to prevent ferroptosis. Both reduced and oxidized glutathione are markedly elevated in ChRCC (PNAS, 2018). We have previously discovered that ChRCC is hypersensitive to ferroptotic cell death induced by the pharmacologic disruption of glutathione homeostasis via the cysteine transporter SLC7A11 or glutathione peroxidase (GPX4) inhibition (PNAS, 2022). Ferroptosis suppressor protein (FSP1) is a glutathione-independent suppressor of ferroptosis. FSP1’s role in ChRCC is unexplored. Methods Transcriptional data from DepMap (484 cell lines) and Cancer Therapeutics Response Portal (CTRP) (860 cell lines) were used to study genetic or pharmacologic inhibition of GPX4 and SLC7A11. Statistical analysis was performed in PRISM 10 using Mann-Whitney U and ANOVA tests. Statistical significance was defined as p < 0.05. Results DepMap data revealed that FSP1 is the top upregulated gene in cells resistant to RNAi inhibition of GPX4 (Achilles, DEMETER2) (Panel A). In CTRP data, FSP1 was the top upregulated gene in cells resistant to the GPX4 inhibitor RSL3 and the 19th most upregulated gene in cells resistant to the SCL7A11 inhibitor, Erastin (Panel B). In The Cancer Genomic Atlas (TCGA) KICH (ChRCC) dataset, FSP1 was 2-fold higher in ChRCC compared to normal kidney (mean RSEM = 818.9 vs 445.9, p-value <0.0001) (Panel C). In vitro studies of two ChRCC cell lines, UOK276 and RCJ-T2, revealed that while siRNA-mediated inhibition of GPX4 or FSP1 individually did not induce substantial cell death, their combination was synergistic and resulted in almost complete cell death (UOK276 mean viability 8% of siCTRL, p<0.0001; RCJ-T2 mean viability 13% of siCTRL, p<0.0001). Cell viability was completely rescued by the ferroptosis inhibitor ferrostatin-1 but not by the necroptosis inhibitor necrostatin-1 or the apoptosis inhibitor Z-Vad-FMK (Panel D). siRNA-mediated GPX4 knockdown combined with FSP1 pharmacologic inhibition (icFSP1 or FSEN1) induced extensive cell death (mean viability of siGPX4 + icFSP1 group = 21% of siCTRL + DMSO group, p<0.0001; mean viability of siGPX4 + FSEN1 group = 29% of siCTRL + DMSO group, p<0.0001) (Panel E). Combining RSL3 with FSEN1, or IKE with icFSP1, also demonstrated synergy, with the ChRCC cell lines showing increased overall sensitivity to these drug combinations compared to 786-0 cells (ccRCC-derived) and HeLa cells (Panel F). Snapshots from these experiments taken at [IKE] = 177nM and/or [icFSP1] = 20 mM for UOK276, and [RSL3] = 39.4 nM and/or [FSEN1] = 20 mM for RCJ-T2, show almost complete cell death when pharmacologic inhibitors of glutathione-dependent and -independent ferroptosis suppressors are combined, but no substantial cell death when each is used individually (7% and 10% viability in combination group compared to DMSO group for UOK276 and RCJ-T2 respectively, p<0.0001) (Panel G). Conclusions We show that in vitro genetic or pharmacologic inhibition of FSP1, a glutathione-independent inhibitor of ferroptosis, leads to ferroptosis in ChRCC-derived cells when combined with genetic or pharmacologic inhibition of the glutathione-dependent suppressors of ferroptosis GPX4 or SLC7A11.

In vivo vulnerabilities to GPX4 and HDAC inhibitors in drug-persistent versus drug-resistant BRAFV600E lung adenocarcinoma

The current targeted therapy for BRAFV600E-mutant lung cancer consists of a dual blockade of RAF/MEK kinases often combining dabrafenib/trametinib (D/T). This regimen extends survival when compared to single-agent treatments, but disease progression is unavoidable. By using whole-genome CRISPR screening and RNA sequencing, we characterize the vulnerabilities of both persister and D/T-resistant cellular models. Oxidative stress together with concomitant induction of antioxidant responses is boosted by D/T treatment. However, the nature of the oxidative damage, the choice of redox detoxification systems, and the resulting therapeutic vulnerabilities display stage-specific differences. Persister cells suffer from lipid peroxidation and are sensitive to ferroptosis upon GPX4 inhibition invivo. Biomarkers of lipid peroxidation are detected in clinical samples following D/T treatment. Acquired alterations leading to mitogen-activated protein kinase (MAPK) reactivation enhance cystine transport to boost GPX4-independent antioxidant responses. Similarly to BRAFV600E-mutant melanoma, histone deacetylase (HDAC) inhibitors decrease D/T-resistant cell viability and extend therapeutic response invivo.

Coenzyme A protects against ferroptosis via CoAlation of thioredoxin reductase 2.

The Cystine-xCT transporter-Glutathione (GSH)-GPX4 axis is the canonical pathway to protect against ferroptosis. While not required for ferroptosis-inducing compounds (FINs) targeting GPX4, FINs targeting the xCT transporter require mitochondria and its lipid peroxidation to trigger ferroptosis. However, the mechanism underlying the difference between these FINs is still unknown. Given that cysteine is also required for coenzyme A (CoA) biosynthesis, here we show that CoA supplementation specifically prevents ferroptosis induced by xCT inhibitors but not GPX4 inhibitors. We find that, auranofin, a thioredoxin reductase inhibitor, abolishes the protective effect of CoA. We also find that CoA availability determines the enzymatic activity of thioredoxin reductase, but not thioredoxin. Importantly, the mitochondrial thioredoxin system, but not the cytosolic thioredoxin system, determines CoA-mediated ferroptosis inhibition. Our data show that the CoA regulates the in vitro enzymatic activity of mitochondrial thioredoxin reductase (TXNRD2) by covalently modifying the thiol group of cysteine (CoAlation) on Cys-483. Replacing Cys-483 with alanine on TXNRD2 abolishes its in vitro enzymatic activity and ability to protect cells from ferroptosis. Targeting xCT to limit cysteine import and, therefore, CoA biosynthesis reduced CoAlation on TXNRD2, an effect that was rescued by CoA supplementation. Furthermore, the fibroblasts from patients with disrupted CoA metabolism demonstrate increased mitochondrial lipid peroxidation. In organotypic brain slice cultures, inhibition of CoA biosynthesis leads to an oxidized thioredoxin system, mitochondrial lipid peroxidation, and loss in cell viability, which were all rescued by ferrostatin-1. These findings identify CoA-mediated post-translation modification to regulate the thioredoxin system as an alternative ferroptosis protection pathway with potential clinical relevance for patients with disrupted CoA metabolism.

Targeting PAX8 sensitizes ovarian cancer cells to ferroptosis by inhibiting glutathione synthesis.

Ovarian cancer is a malignant tumor originating from the ovary, characterized by its high mortality rate and propensity for recurrence. In some patients, especially those with recurrent cancer, conventional treatments such as surgical resection or standard chemotherapy yield suboptimal results. Consequently, there is an urgent need for novel anti-cancer therapeutic strategies. Ferroptosis is a distinct form of cell death separate from apoptosis. Ferroptosis inducers have demonstrated promising potential in the treatment of ovarian cancer, with evidence indicating their ability to enhance ovarian cancer cell sensitivity to cisplatin. However, resistance of cancer cells to ferroptosis still remains an inevitable challenge. Here, we analyzed genome-scale CRISPR-Cas9 loss-of function screens and identified PAX8 as a ferroptosis resistance protein in ovarian cancer. We identified PAX8 as a susceptibility gene in GPX4-dependent ovarian cancer. Depletion of PAX8 rendered GPX4-dependent ovarian cancer cells significantly more sensitive to GPX4 inhibitors. Additionally, we found that PAX8 inhibited ferroptosis in ovarian cancer cells. Combined treatment with a PAX8 inhibitor and RSL3 suppressed ovarian cancer cell growth, induced ferroptosis, and was validated in a xenograft mouse model. Further exploration of the molecular mechanisms underlying PAX8 inhibition of ferroptosis mutations revealed upregulation of glutamate-cysteine ligase catalytic subunit (GCLC) expression. GCLC mediated the ferroptosis resistance induced by PAX8 in ovarian cancer. In conclusion, our study underscores the pivotal role of PAX8 as a therapeutic target in GPX4-dependent ovarian cancer. The combination of PAX8 inhibitors such as losartan and captopril with ferroptosis inducers represents a promising new approach for ovarian cancer therapy.

Evaluating the efficacy of vatiquinone in preclinical models of mitochondrial disease.

Genetic mitochondrial diseases are a major challenge in modern medicine, impacting around 1:4,000 individuals. Leigh syndrome is the most common pediatric presentation of mitochondrial disease. There are currently no effective clinical treatments for mitochondrial disease. In humans, patients are often treated with antioxidants, vitamins, and strategies targeting energetics. The vitamin-E related compound vatiquinone (EPI-743, α-tocotrienol quinone) has been the subject of at least 19 clinical trials in the US since 2012, but the effects of vatiquinone on an animal model of mitochondrial disease have not yet been reported. Here, assessed the impact of vatiquinone on disease progression and in two animal models of mitochondrial disease. The efficacy of vatiquinone in vitro was assessed using human fibroblasts treated with the general mitochondrial oxidative stress inducer paraquat, the GPX4 inhibitor RSL3, or the glutathione synthase inhibitor BSO in combination with excess iron. The therapeutic potential of vatiquinone in vivo was assessed using tamoxifen-induced mouse model for GPX4 deficiency and the Ndufs4 knockout mouse model of Leigh syndrome. In both models, animals were treated daily with vatiquinone or vehicle and relevant disease endpoints were assessed. Vatiquinone robustly prevented death in cultured cells induced by RSL3 or BSO/iron, but had no effect on paraquat induced cell death. Vatiquinone had no impact on disease onset, progression, or survival in either the tamoxifen-inducible GPX4 deficient model or the Ndufs4(-/-) mouse model, though the drug may have reduced seizure risk. Vatiquinone provided no benefit to survival in two mouse models of disease, but may prevent seizures in the Ndufs4(-/-) model. Our findings are consistent with recent press statements regarding clinical trial results and have implications for drug trial design and reporting in patients with rare diseases.

Abstract PS12-04: Inhibition of GPX4 enhances CDK4/6 inhibitor activity in breast cancer

Abstract Background: Cyclin D-dependent kinases 4 and 6 (CDK4/6) inhibitors (CDK4/6i) including palbociclib, ribociclib and abemaciclib in combination with endocrine therapy are the standard of care for patients with estrogen receptor-positive (ER+). Despite the success of these treatments, cytostasis is frequently observed, and novel strategies that enhance efficacy are required to eradicate residual cancer in the clinic. Methods: In the search of an effective drug combinations to enhance the efficacy of CDK4/6 inhibitors in breast cancer, we performed a whole genome CRISPR-Cas9 suppressor screen in MCF-7, an ER+ model. We also carried out transcriptomics, proteomics, and functional molecular biology analysis of breast cancer models treated with palbociclib to identify resistant mechanisms. Results: The whole genome CRISPR-Cas9 screen revealed that multiple genes involved in oxidative stress and ferroptosis modulated palbociclib sensitivity, being GPX4 the top sensitizing hit. GPX4 is a key glutathione peroxidase that protects again ferroptosis by catalysing the reduction of phospholipid and cholesterol hydroperoxides. CRISPR-depletion or drug inhibition of GPX4 increased sensitivity to palbociclib in ER+ breast cancer models, and in addition sensitised triple negative breast cancer models to palbociclib. Moreover, GPX4 null xenografts were highly sensitive to palbociclib in vivo. Transcriptomics and proteomics analysis showed that palbociclib upregulate pathways involved in oxidative stress and lipid metabolism promoting a redox-lipid imbalance. Palbociclib induced lipid peroxidation leading to a ferroptosis vulnerable state with GPX4 preventing cell death. Polyunsaturated fatty acids (PUFAs) are highly susceptible of lipid peroxidation, and pathways that regulate their abundance in membrane phospholipids were explored. Interestedly, in ER+ breast cancer models, lipid peroxidation relied on a peroxisome AGPAT3-dependent pathway rather than the classical ACSL4 pathway. Conclusion: Our studies demonstrate that quiescence induced by palbociclib results in a ferroptosis-vulnerable state that could be exploited through combination with GPX4 inhibitors to enhance sensitivity to CDK4/6 inhibition in breast cancer. Citation Format: Maria Teresa Herrera Abreu, Uzma Khalid, Jian Ning, Rosalind Cutts, Gemma Wilson, Christopher Lord, Amanda Swain, Nicholas Turner. Inhibition of GPX4 enhances CDK4/6 inhibitor activity in breast cancer [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 PS12-04.

Role of ferroptosis in Porphyromonas gingivalis-induced impairment of epithelial junction

ABSTRACT Objectives This study aims to clarify the effect of ferroptosis by P. gingivalis on periodontal epithelium impairment and potential mechanisms. Materials and methods The expression of epithelial junction proteins (CDH1, OCLN, ZO-1), FTL and GPX4 in healthy and periodontitis tissues was analyzed using bioinformatics analysis and validated in vivo. An in vitro model was constructed to evaluate ferroptosis by mitochondria morphology, content of iron and GSH, and level of lipid peroxidation, FTL, GPX4 and SLC7A11. The iron concentration was changed with iron chelator DFO and iron supplementation FAC. The epithelial impairment was assessed by protein expression. To investigate the mechanism, si-MYB (a negative transcription factor of SLC7A11) and GPX4 inhibitor RSL3 were employed. Results CDH1, OCLN, ZO-1 and GPX4 expression was decreased, while FTL expression was elevated in periodontitis tissues. Infected cells showed ferroptosis change of the mitochondria with higher level of lipid peroxidation, iron, FTL and lower level of GPX4, GSH, SLC7A11. FAC augmented ferroptosis and weakened epithelial junction, while DFO exhibited a counteractive effect. Silencing MYB rescued SLC7A11, GPX4 and epithelial junction proteins, which was hindered by RSL3. Conclusions Our study demonstrated that P. gingivalis weakened the oral epithelial barrier by causing ferroptosis via inhibiting SLC7A11/GSH/GPX4 axis.

Abstract 4662: High-throughput screening identifies potential combinatorial therapies to overcome lenvatinib resistance in liver cancer

Abstract Liver cancer has seen an increase in mortality rate over recent decades due to limited targeted therapies and growth in specific etiologies. Lenvatinib, a multi-TKI inhibitor, is used as a first-line therapy for liver cancer patients who cannot receive immunotherapy, which is a component of the current standard of care. Unfortunately, lenvatinib efficacy is short. Understanding why liver cancers become resistant and identifying interventions to restore sensitivity can help prolong the clinical efficacy of lenvatinib. A panel of 20 liver cancer lines was screened to identify four lenvatinib-sensitive lines. These lines were subsequently conditioned to grow under increasing lenvatinib concentrations to generate lenvatinib-resistant (LR) models. One such model, Hep3B LR, exhibited a stable resistance to lenvatinib for up to 12 weeks in culture. Hep3B LR showed cross-resistance to selective inhibitors of FGFR4 and FGFR1 but not of MAPK14 and PDGFR, suggesting that the resistance phenotype may result from FGFR dysfunction. Unlike parental Hep3B, Hep3B LR exhibited a 3.4X increase in migration. Western blot detected an increase in pAKT, a survival marker. Additionally, proteins associated with cancer drug resistance were higher in Hep3B LR cells: Notch receptors and ligands, pStat3, and Axl. To identify means of overcoming lenvatinib resistance in Hep3B LR, a Cell-Titer Glo high-throughput assay was developed to measure the growth inhibition of candidate drugs in the presence and absence of lenvatinib. Preliminary results from the first 24 drugs screened reproduced known drug sensitivities associated with lenvatinib resistance (i.e., MEK/ERK, EGFR, GPX4 inhibition) but also identified novel sensitivities to inhibition of PKMYT1 or γ-secretase, the latter a cleavage enzyme involved in Notch signaling activation. Validation of these candidate hits using a grid-based titration of both drugs showed additive growth inhibition of lenvatinib in combination with ERK, EGFR, or GPX4 inhibitors but not with PKMYT1 or γ-secretase inhibitors in resistant cells. Interestingly, EGFRi and lenvatinib were substantially synergistic in parental cells, suggesting that an upfront combination of these inhibitors could potentially be used before the emergence of lenvatinib resistance in liver cancer. We have established a lenvatinib-resistant liver cancer cell model and validated a drug screening assay to identify potential combinatorial therapies to overcome lenvatinib resistance in liver cancer. Citation Format: Kevin Chau, Martina S. McDermott, KeWei Gong, Dennis J. Slamon. High-throughput screening identifies potential combinatorial therapies to overcome lenvatinib resistance in liver cancer [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(6_Suppl):Abstract nr 4662.

Abstract 4459: Metabolic liabilities of iron-dependent ferroptosis mediated through NRF2/GPX4 axis in osteosarcoma

Abstract Osteosarcoma is an aggressive bone malignancy that predominantly affects adolescents and young adults. Despite recent advancements in treatments, the challenges of recurrence and chemoresistance persist. Ferroptosis is a form of regulated cell death driven by iron-dependent lipid peroxidation, and emerging evidence suggests significant roles for NRF2 and GPX4 in iron metabolism, regulating tumor cell functions. In osteosarcoma, however, the molecular mechanisms of the NRF2/GPX4 axis and its therapeutic potential remain unknown. In this study, we first determined GPX4 and xCT expression levels and cellular responses to RSL3, a GPX4 inhibitor, and Erastin, an xCT inhibitor in osteosarcoma cells. A total of seven osteosarcoma cell lines, consisting of five human cell lines (HOS, 143B, Saos-2, MG-63, U2OS) and two canine cell lines (COS31 and DOUG), were used. Our results revealed that the IC50 values ranged from 0.02 uM to 1.01 uM in cells treated with RSL3 and from 0.35 uM to 1.41 uM in cells treated with Erastin, respectively. These values were proportional to GPX4 and xCT levels across the cell lines. Then, U2OS, as the most sensitive, and Saos-2, the least sensitive based on their IC50 values, were selected to examine the iron regulatory machinery. In U2OS cells, RSL3 treatment significantly decreased NRF2 and GPX4, while increasing ferroportin-1 and ferritin. GPX4 knockdown also led to comparable changes in NRF2, ferroportin-1, and ferritin expression. NRF2 appears to mediate iron metabolism, ferroportin-1 acts as an iron exporter, and ferritin stores intracellular iron. Therefore, our findings suggest that GPX4-mediated ferroptosis is regulated by iron metabolic pathways, potentially to prevent ferroptotic cell death. We also found that Ferrostatin-1, a lipid peroxidation inhibitor showed no changes in ferroportin-1, ferritin, and NRF2. In Saos-2, RSL3 induced a remarkable reduction in GPX4 expression, akin to U2OS. However, no significant change was found in NRF2, ferroportin-1, and ferritin. Instead, Ferrostatin-1 restored the decreased GPX4 and increased NRF2, ferroportin-1, and ferritin levels. In addition, Z-VAD (a pan-caspase inhibitor), Necrosatin-1s (a RIPK1 inhibitor), and Ferrostatin-1 were capable of preventing Saos-2, COS31, and DOUG cells from RSL3-induced cell death at lethal doses. Such protection was undetected in U2OS. These data suggest that metabolic pathways controlling intracellular iron are crucial for NRF2/GPX4-mediated ferroptosis in osteosarcoma cells. Furthermore, we generated RNA-seq and LC-MS/MS data to identify novel molecular targets governing the metabolic pathways of ferroptosis in osteosarcoma. Our ongoing work includes downstream molecular and functional assays following gene modifications in osteosarcoma cells (overexpression and knockout) and assessing metabolic vulnerabilities by targeting iron-mediated ferroptosis in xenografts. Citation Format: Md Abdullah, Donghee Lee, Rong Li, Jong Hyuk Kim. Metabolic liabilities of iron-dependent ferroptosis mediated through NRF2/GPX4 axis in osteosarcoma [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(6_Suppl):Abstract nr 4459.