Inhibitor Of Glutathione Synthesis Research Articles

Bag1 protein loss sensitizes mouse embryonic fibroblasts to glutathione depletion.

Bcl2-associated athanogene-1 protein (Bag1) acts as a co-chaperone of heat shock protein 70 and heat shock cognate 70 (HSP70/HSC70) and regulates multiple cellular processes, including cell proliferation, apoptosis, environmental stress response, and drug resistance. Since Bag1 knockout mice exhibited fetal lethality, the in vivo function of Bag1 remains unclear. In this study, we established a mouse line expressing Bag1 gene missing exon 5, which corresponds to an encoding region for the interface of HSP70/HSC70. Despite mice carrying homoalleles of the Bag1 mutant (Bag1Δex5) expressing undetectable levels of Bag1, Bag1Δex5 homozygous mice developed without abnormalities. Bag1Δex5 protein was found to be highly unstable in cells and in vitro. We found that the growth of mouse embryonic fibroblasts (MEFs) derived from Bag1Δex5-homo mice was attenuated by doxorubicin and a glutathione (GSH) synthesis inhibitor, buthionine sulfoximine (BSO). In response to BSO, Bag1Δex5-MEFs exhibited a higher dropping rate of GSH relative to the oxidized glutathione level. In addition, Bag1 might mitigate cellular hydrogen peroxide levels. Taken together, our results demonstrate that the loss of Bag1 did not affect mouse development and that Bag1 is involved in intracellular GSH homeostasis, namely redox homeostasis.

Feasibility study of multimodal imaging for redox status and glucose metabolism in tumor

Understanding the tumor redox status is important for efficient cancer treatment. Here, we noninvasively detected changes in the redox environment of tumors before and after cancer treatment in the same individuals using a novel compact and portable electron paramagnetic resonance imaging (EPRI) device and compared the results with glycolytic information obtained through autoradiography using 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG). Human colon cancer HCT116 xenografts were used in the mice. We used 3-carbamoyl-PROXYL (3CP) as a paramagnetic and redox status probe for the EPRI of tumors. The first EPRI was followed by the intraperitoneal administration of buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, or X-ray irradiation of the tumor. A second EPRI was performed on the following day. Autoradiography was performed after the second EPRI. After imaging, the tumor sections were evaluated by histological analysis and the amount of reducing substances in the tumor was measured. BSO treatment and X-ray irradiation significantly decreased the rate of 3CP reduction in tumors. Redox maps of tumors obtained from EPRI can be compared with tissue sections of approximately the same cross section. BSO treatment reduced glutathione levels in tumors, whereas X-ray irradiation did not alter the levels of any of the reducing substances. Comparison of the redox map with the autoradiography of [18F]FDG revealed that regions with high reducing power in the tumor were active in glucose metabolism; however, this correlation disappeared after X-ray irradiation. These results suggest that the novel compact and portable EPRI device is suitable for multimodal imaging, which can be used to study tumor redox status and therapeutic efficacy in cancer, and for combined analysis with other imaging modalities.

Mechanisms of lipopolysaccharide protection in tumor drug–induced macrophage damage

Malignant tumors contribute significantly to human mortality. Chemotherapy is a commonly used treatment for tumors. However, due to the low selectivity of chemotherapeutic drugs, immune cells can be damaged during antitumor treatment, resulting in toxicity. Lipopolysaccharide (LPS) can stimulate immune cells to respond to foreign substances. Here, we found that 10 ng/mL LPS could induce tolerance to antitumor drugs in macrophages without altering the effect of the drugs on tumor cells. Differentially expressed genes (DEGs) were identified between cells before and after LPS administration using transcriptome sequencing and found to be mainly associated with ATP-binding cassette (ABC)-resistant transporters and glutathione S-transferase (GST). LPS was shown by qRT-PCR and western blotting to promote the expression of ABCC1, GSTT1, and GSTP1 by 38.3 %, 194.8 %, and 27.0 %. Furthermore, three inhibitors (inhibitors of GST, glutathione synthesis, and ABCC1) were used for further investigation, showing that these inhibitors reduced macrophage survival rates by 44.0 %, 52.3 %, and 43.3 %, while the intracellular adriamycin content increased by 28.9 %, 42.9 %, and 51.3 %, respectively. These findings suggest that the protective mechanism of LPS on macrophages is associated with increased GST activity, the consumption of glutathione, and increased expression of ABCC1 protein. Therefore, LPS has a potential role in enhancing immunity.

Development of a mouse model expressing a bifunctional glutathione-synthesizing enzyme to study glutathione limitation in vivo

Glutathione (GSH) is a highly abundant tripeptide thiol that performs diverse protective and biosynthetic functions in cells. While changes in GSH availability are associated with inborn errors of metabolism, cancer and neurodegenerative disorders, studying the limiting role of GSH in physiology and disease has been challenging due to its tight regulation. To address this, we generated cell and mouse models that express a bifunctional glutathione-synthesizing enzyme from Streptococcus thermophilus (GshF), which possesses both glutamate-cysteine ligase and glutathione synthase activities. GshF expression allows efficient production of GSH in the cytosol and mitochondria and prevents cell death in response to GSH depletion, but not ferroptosis induction, indicating that GSH is not a limiting factor under lipid peroxidation. CRISPR screens using engineered enzymes further revealed genes required for cell proliferation under cellular and mitochondrial GSH depletion. Among these, we identified the glutamate-cysteine ligase modifier subunit, Gclm, as a requirement for cellular sensitivity to buthionine sulfoximne, a glutathione synthesis inhibitor. Finally, GshF expression in mice is embryonically lethal but sustains postnatal viability when restricted to adulthood. Overall, our work identifies a conditional mouse model to investigate the limiting role of GSH in physiology and disease.

Thiol starvation triggers melanoma state switching in an ATF4 and NRF2-dependent manner

The cystine/glutamate antiporter xCT is an important source of cysteine for cancer cells. Once taken up, cystine is reduced to cysteine and serves as a building block for the synthesis of glutathione, which efficiently protects cells from oxidative damage and prevents ferroptosis. As melanomas are particularly exposed to several sources of oxidative stress, we investigated the biological role of cysteine and glutathione supply by xCT in melanoma. xCT activity was abolished by genetic depletion in the Tyr::CreER; BrafCA; Ptenlox/+ melanoma model and by acute cystine withdrawal in melanoma cell lines. Both interventions profoundly impacted melanoma glutathione levels, but they were surprisingly well tolerated by murine melanomas in vivo and by most human melanoma cell lines in vitro. RNA sequencing of human melanoma cells revealed a strong adaptive upregulation of NRF2 and ATF4 pathways, which orchestrated the compensatory upregulation of genes involved in antioxidant defence and de novo cysteine biosynthesis. In addition, the joint activation of ATF4 and NRF2 triggered a phenotypic switch characterized by a reduction of differentiation genes and induction of pro-invasive features, which was also observed after erastin treatment or the inhibition of glutathione synthesis. NRF2 alone was capable of inducing the phenotypic switch in a transient manner. Together, our data show that cystine or glutathione levels regulate the phenotypic plasticity of melanoma cells by elevating ATF4 and NRF2.

Low-Molecular Thiols as a Factor Improving the Sensitivity of Escherichia coli Mutants with Impaired ADP–Heptose Synthesis to Antibiotics

—Low molecular-weight thiols as glutathione and cysteine are an important part of the cell’s redox regulation system. Previously, we have shown that inactivation of ADP-heptose synthesis in Escherichiacoli with a gmhA deletion induces the oxidative stress. It is accompanied by rearrangement of thiol homeostasis and increased sensitivity to antibiotics. In our study, we found that restriction of cysteine metabolism (∆cysB and ∆cysE) and inhibition of glutathione synthesis (∆gshAB) lead to a decrease in the sensitivity of the ∆gmhA mutant to antibiotics but not to its expected increase. At the same time, blocking of the export of cysteine (∆eamA) or increasing import (Ptet-tcyP) into cells of the oxidized form of cysteine–cystine leads to an even greater increase in the sensitivity of gmhA-deleted cells to antibiotics. In addition, there is no correlation between the cytotoxic effect of antibiotics and the level of reactive oxygen species (ROS), the total pool of thiols, or the viability of the initial cell population. However, a correlation between the sensitivity to antibiotics and the level of oxidized glutathione in cells was found in our study. Apparently, a decrease in the content of low-molecular-weight thiols saves NADPH equivalents and limits the processes of protein redox modification. This leads to increasing of resistance of the ∆gmhA strain to antibiotics. An increase in low-molecular-weight thiols levels requires a greater expenditure of cell resources, leads to an increase in oxidized glutathione and induces to greater increase in sensitivity of the ∆gmhA strain to antibiotics.

The Role of Glutathione and Sulfhydryl Groups in Cadmium Uptake by Cultures of the Rainbow Trout RTG-2 Cell Line.

The aim of this study is to investigate the role of cellular sulfhydryl and glutathione (GSH) status in cellular cadmium (Cd) accumulation using cultures of the rainbow trout cell line RTG-2. In a first set of experiments, the time course of Cd accumulation in RTG-2 cells exposed to a non-cytotoxic CdCl2 concentration (25 μM) was determined, as were the associated changes in the cellular sulfhydryl status. The cellular levels of total GSH, oxidized glutathione (GSSG), and cysteine were determined with fluorometric high-performance liquid chromatography (HPLC), and the intracellular Cd concentrations were determined with inductively coupled plasma mass spectrometry (ICP-MS). The Cd uptake during the first 24 h of exposure was linear before it approached a plateau at 48 h. The metal accumulation did not cause an alteration in cellular GSH, GSSG, or cysteine levels. In a second set of experiments, we examined whether the cellular sulfhydryl status modulates Cd accumulation. To this end, the following approaches were used: (a) untreated RTG-2 cells as controls, and (b) RTG-2 cells that were either depleted of GSH through pre-exposure to 1 mM L-buthionine-SR-sulfoximine (BSO), an inhibitor of glutathione synthesis, or the cellular sulfhydryl groups were blocked through treatment with 2.5 μM N-ethylmaleimide (NEM). Compared to the control cells, the cells depleted of intracellular GSH showed a 25% reduction in Cd accumulation. Likewise, the Cd accumulation was reduced by 25% in the RTG-2 cells with blocked sulfhydryl groups. However, the 25% decrease in cellular Cd accumulation in the sulfhydryl-manipulated cells was statistically not significantly different from the Cd accumulation in the control cells. The findings of this study suggest that the intracellular sulfhydryl and GSH status, in contrast to their importance for Cd toxicodynamics, is of limited importance for the toxicokinetics of Cd in fish cells.

Treatment with aripiprazole and N-acetylcysteine affects anaerobic cysteine metabolism in the hippocampus and reverses schizophrenia-like behavior in the neurodevelopmental rat model of schizophrenia.

Preclinical and clinical studies have shown that the antipsychotic drug aripiprazole and the antioxidant N-acetylcysteine have unique biological properties. The aim of the study was to investigate, in a rat model of schizophrenia, the effects of chronic administration of these drugs on schizophrenia-like behaviors and anaerobic cysteine metabolism in the hippocampus (HIP). The schizophrenia-type changes were induced in Sprague-Dawley rats by repeated administration of the glutathione synthesis inhibitor l-butionine-(S,R)-sulfoximine in combination with the dopamine reuptake inhibitor GBR 12909 in the early postnatal period. Adult model rats were chronically treated with aripiprazole (0.3 mg·kg-1 , i.p.) or N-acetylcysteine (30 mg·kg-1 , orally), and their effects on schizophrenia-like behaviors were assessed using the social interaction test and novel object recognition test. In the HIP, the level of anaerobic cysteine metabolites, H2 S, and bound sulfane sulfur were determined by a fluorescence method, while the expression of H2 S-synthetizing enzymes: cystathionine β-synthase (CBS) and mercaptopyruvate sulfurtransferase (MST) by western blot. Long-term treatment with aripiprazole or N-acetylcysteine reversed social and cognitive deficits and reduced the exploratory behaviors. In the HIP of 16-day-old model pups, H2 S levels and MST protein expression were significantly decreased. In adult model rats, H2 S levels remained unchanged, bound sulfane sulfur significantly increased, and the expression of CBS and MST slightly decreased. The studied drugs significantly reduced the level of bound sulfane sulfur and the expression of tested enzymes. The reduction in bound sulfane sulfur level coincided with the attenuation of exploratory behavior, suggesting that modulation of anaerobic cysteine metabolism in the HIP may have therapeutic potential in schizophrenia.

An in situ self‐assembled peptide derivative for inhibition of glutathione synthesis and selective enhancement of tumor radiotherapy

AbstractBackgroundInhibition of glutathione (GSH) synthesis in cancer cells considerably improves the efficacy of reactive oxygen species (ROS)‐related tumor therapy. Self‐assembled peptide derivatives can facilitate the efficient delivery and accumulation of small molecular drugs in cancer cells.MethodsSelf‐assembling modules were covalently linked to the GSH‐biosynthesis inhibitor l‐buthionine sulfoximine (BSO) by solid‐phase synthesis to form the self‐assembling peptide derivative Nap‐DFDFpY‐GG‐BSO (Nano‐BSO@ in situ). Subsequently, its enzyme‐instructed self‐assembly in vitro and on cell surfaces were confirmed, and its intracellular GSH depletion and radiotherapy‐sensitizing effects were determined.ResultsNano‐BSO@ in situ successfully self‐assembles into a hydrogel with a nanofibrous microstructure upon incubation with alkaline phosphatase (ALP) at a critical concentration of 9.84 μM. Furthermore, it selectively self‐assembles in situ on HeLa cells with high ALP expression. At a concentration of 50 μM, Nano‐BSO@ in situ decreases intracellular GSH levels by 80%, ∼2.3 times more than free BSO. Meanwhile, pretreatment of HeLa cells with 50 μM Nano‐BSO@ in situ for 24 h results in a radiotherapy sensitization enhancement ratio to γ‐rays of 2.09.ConclusionsA novel in situ self‐assembling peptide derivative for GSH depletion and selective enhancement of tumor radiotherapy was constructed. The excellent GSH‐depletion ability and remarkable radiotherapy‐enhancement performance indicate that Nano‐BSO@ in situ is a promising selective sensitizer for ROS‐related treatment of tumor cells with high ALP expression.

Abstract B005: Metabolic liabilities in high L-2HG kidney cancer

Abstract Renal cell carcinoma (RCC) is among the top 10 cancers in the USA. Despite several approved therapies, patients with the advanced disease rarely have durable responses and therefore, face a poor prognosis (median survival 2-3 years). This underscores the need for new strategies. Alterations in metabolism are well-established in cancers including RCC. The oncometabolite, L-2-hydroxyglutarate (L-2HG) is elevated in the most common form of RCC (clear cell histology) and promotes tumor progression. However, L-2HG’s roles in RCC progression and its mediated therapeutic vulnerability are yet to be explored. RCC cell lines lack the L-2HG dehydrogenase enzyme (L2HGDH) which results in their high L-2HG level. RNA-seq of control (high L-2GH) and an L2HGDH reconstituted (low L-2HG) RCC cell line reveals that L-2HG suppresses the expression of serine biosynthesis genes, PHGDH and PSAT1. In agreement, high L-2HG renal tumors demonstrate lower levels of serine biosynthesis enzymes compared to their matched normal kidneys. Mechanistic studies reveal L-2HG-mediated remodeling of both the epigenome and epitranscriptome suppress serine biosynthesis genes. Consistently, 13C-metabolomics labeling studies demonstrate that raised L-2HG suppresses de novo serine biosynthesis. Moreover, LC-MS analysis of the metabolites isolated from the kidneys of L2hgdh KO and wild-type (WT) mice revealed lower serine levels in L2hgdh KO kidneys. In accordance with these data, found that high L-2HG RCC cells require exogenous serine for in vitro proliferation and in vivo tumor growth. Likewise, the pharmacologic blockade of serine uptake decreases the proliferation of high L-2HG RCC cells. Furthermore, this serine liability can be rescued upon lowering cellular L-2HG levels. Untargeted metabolomics analyses demonstrate that exogenous serine is required to maintain cellular pools of glutathione (GSH+GSSG) in high L-2HG RCC. This is particularly relevant as glutathione is among the most highly enriched metabolites in RCC compared to normal kidneys. Our metabolomics data also suggest that serine might be essential for the transsulfuration process of glutathione biosynthesis in RCC that lacks the xCT system required to uptake cysteine for transsulfuration. In vivo, we find that intratumoral levels of glutathione are reduced in mice fed a chow diet lacking serine compared to regular chow diet-fed mice. Pharmacologic inhibition of glutathione synthesis ablates the growth of high L-2HG RCC cells even in the presence of serine, suggesting the importance of redox homeostasis for RCC proliferation. The data indicate that the L-2HG elevation in RCC reconfigures tumor metabolism, resulting in serine liability. Collectively, our data unmask a metabolic vulnerability that can be harnessed for precision-based approaches to kidney cancer. Citation Format: Anirban Kundu, Garrett J. Brinkley, Hyeyoung Nam, Suman Karki, Devin Absher, William J. Placzek, Jason Locasale, Dinesh Rakheja, Victor Darley-Usmarc, Jason Tennessen, Sunil Sudarshan. Metabolic liabilities in high L-2HG kidney cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr B005.

Glutathione is involved in selenium detoxification and suppresses the selenate-induced SULTR1;1 gene expression in plants

Selenium (Se) as a sulfur (S) analog is beneficial to plants. However, excessive Se is toxic. Glutathione (GSH) can protect plant cells from metal toxicity. In this study, we investigated the role of GSH in resistance to Se toxicity and in regulating sulfate/selenate transporter gene expression. We also examined the effects of Se and S treatments on GSH production and growth of Arabidopsis thaliana (a non-Se-accumulator) and broccoli (Brassica oleracea var. italica, a secondary-Se-accumulator). By treating the Arabidopsis wild-type and the glutathione-deficient mutant pad2–1 plants with and without selenate, reduced glutathione, or GSH synthesis inhibitor L-buthionine sulfoximine, we demonstrated that GSH is involved in Se detoxification. The pad2–1 mutant exhibited lower selenate tolerance, and GSH supply alleviated the toxicity. However, selenate treatment reduced GSH levels in a dose-dependent manner, which was further augmented in low sulfur (S) conditions as shown in broccoli plants. Interestingly, the selenate-induced SULTR1;1 gene expression was negatively associated with GSH levels in plants. The pad2–1 mutant showed a much higher AtSULTR1;1 expression than WT under excess Se supply, and GSH supply partially inhibited its expression. Moreover, selenate conferred higher toxicity than selenite under a low S supply in broccoli plants. In contrast, S alleviated selenate toxicity, which was associated with GSH levels. These findings demonstrate the critical role of GSH in resistance to Se toxicity and provide insights into processes related to Se toxicity resistance in plants, which enhances our understanding of metal tolerance for Se biofortification in crops.

Dihydroartemisinin Disrupts Zinc Homeostasis in Plasmodium falciparum To Potentiate Its Antimalarial Action via Pyknosis.

Artemisinins have been used as first-line drugs worldwide to treat malaria caused by Plasmodium falciparum; however, its underlying mechanism is still unclear. This study aimed to identify the factors inducing growth inhibition via pyknosis, a state of intraerythrocytic developmental arrest, when exposing the parasite to dihydroartemisinin (DHA). Changes in the expression of genome-wide transcripts were assessed in the parasites treated with antimalarials, revealing the specific downregulation of zinc-associated proteins by DHA. The quantification of zinc levels in DHA-treated parasite indicated abnormal zinc depletion. Notably, the zinc-depleted condition in the parasite produced by a zinc chelator induced the generation of a pyknotic form and the suppression of its proliferation. The evaluation of the antimalarial activity of DHA or a glutathione-synthesis inhibitor in the zinc-depleted state showed that the disruption of zinc and glutathione homeostasis synergistically potentiated the growth inhibition of P. falciparum through pyknosis. These findings could help further understand the antimalarial actions of artemisinins for advancing malaria therapy.

Artemisia argyi H.Lév. & Vaniot essential oil induces ferroptosis in pancreatic cancer cells via up-regulation of TFR1 and depletion of γ-glutamyl cycle

Artemisia argyi H.Lév. & Vaniot, a traditional Chinese medicine with a history spanning over two millennia, has been extensively used in folk medicine to treat dysmenorrhea, uterine bleeding and inflammation. Recent studies have demonstrated that the essential oil extracted from Artemisia argyi H.Lév. & Vaniot, known as AAEO, exhibits significant anti-tumor properties against liver and lung cancers. There is a scarcity of research on the potential impact of AAEO on pancreatic cancer (PC) cells. In this study, UPLC-MS/MS-based metabolomics method was established to evaluate the effect of AAEO on the proliferation of PC cells. The differential compounds included 5-oxoproline, glutamate, γ-glutamylcysteine, glutathione, arachidonic acid, adrenal acid and linoleic acid were detected by metabolomics, enriching in the γ-glutamyl cycle and polyunsaturated fatty acid metabolism, which were closely related to ferroptosis. Meanwhile, AAEO dramatically increased the levels of intracellular iron ion via up-regulation of TFR1, augmented reactive oxygen species and malondialdehyde in a dose-dependent manner by down-regulation of γ-glutamyl cycle through decreasing expressions of SLC7A11. Additionally, β-caryophyllene oxide, one of the main components of AAEO, could covalently bind to Cys in SW1990 cells to form a conjugate Cpo-Cys, resulting in the inhibition of glutathione synthesis. Importantly, the ferroptosis inhibitor deferoxamine significantly blocked the inhibitory effect of AAEO on SW1990 cells. Meanwhile, β-caryophyllene oxide, dihydro-β-ionone and α-bisabolol had strong binding force with GPX4, SLC7A11 and TFR1, respectively. These findings showed that AAEO induced ferroptosis via regulation of γ-glutamyl cycle by SLC7A11 and iron disorders by TFR1. Our study discovered AAEO as a potential therapeutic approach to induce ferroptosis to prevent or treat PC.

Abstract 4774: Adaptation to chronic oxidative stress promotes metabolic rewiring to maintain redox balance in HER2+ breast tumors

Abstract Breast cancer is the most commonly diagnosed malignancy in women worldwide. Breast tumors possess a high degree of intra- and inter-tumoral heterogeneity, enabling the emergence of aggressive, therapy-resistant tumors. One contributor to breast tumor heterogeneity is reactive oxygen species (ROS), which are unstable oxygen-containing molecules that modify proteins, lipids, and DNA. Our lab has developed unique models of HER2+ breast cancer that evolved in vivo under conditions of low (ROSLOW) and high (ROSHIGH) chronic oxidative stress to acquire more aggressive properties. As such, we became interested in understanding the underlying mechanisms by which breast cancer cells capitalize on sustained oxidative stress to acquire more aggressive properties. We show that, relative to their parental and ROSLOW counterparts, ROSHIGH-evolved tumors are better able to maintain redox balance by coping with ROS-induced damage in vivo and following H2O2 treatment in vitro. Moreover, ROSHIGH-evolved breast cancer cells lose their aggressive phenotype in vitro, implying a necessary microenvironmental contribution. RNAseq analysis of parental and aggressive breast cancers further identified glycolytic and hypoxic transcriptional signatures that were preferentially induced in breast cancers that adapted to chronic oxidative stress. Therefore, we hypothesized that breast cancer cells conditioned to cope with chronic oxidative stress may re-wire their glucose metabolism to support ROS buffering, which may be facilitated by a hypoxic tumor microenvironment. Notably, ROSHIGH-evolved tumors are insensitive to inhibition of glycolysis using 2-deoxyglucose (2-DG); however, we show that they are specifically sensitized to inhibition of glutathione synthesis, and this sensitivity is exacerbated when treated in combination with 2-DG. As well, we show through glucose tracing that ROSHIGH-evolved tumors exhibit increased incorporation of glucose-derived carbons into glutathione. This data confirms that breast tumor adaptation to chronic oxidative stress promotes metabolic re-wiring to support ROS scavenging. To begin interrogating the role hypoxia plays in this phenotype, we assessed cell proliferation and levels of hypoxia-responsive genes following hypoxia exposure in our breast cancer models in vitro. Relative to their parental counterparts, breast cancer cells that adapted to chronic oxidative stress exhibit enhanced proliferation in hypoxia and are better able to upregulate hypoxia-responsive genes, even in response to modest changes in oxygen levels. Overall, our study shows that tumor adaptation under chronic oxidative stress promotes metabolic rewiring which may be facilitated by a hypoxic microenvironment. Citation Format: Caitlynn Nicole Mirabelli, Rachel La Selva, Matthew Annis, Ouafa Najyb, Steven Hébert, Claudia Kleinman, Julie St-Pierre, Peter Siegel, Josie Ursini-Siegel. Adaptation to chronic oxidative stress promotes metabolic rewiring to maintain redox balance in HER2+ breast tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4774.

Activity of cAMP-Dependent Protein Kinase is Reduced in Protein-Energy Malnourished Rats

Glucagon decreases glutathione synthesis in hepatocytes from well-nourished rats. However, in hepatocytes from malnourished rats, glucagon does not inhibit glutathione synthesis, suggesting a desensitization of cAMP-mediated signal transduction. We investigated the mechanism for this desensitization of cAMP-mediated responsiveness in malnourished rats by comparing the signal transduction pathways in rats fed very low protein diets (0.5 g protein/100 g diet) with those of rats fed diets adequate in protein (15 g protein/100 g diet) for 2 wk. Glucagon receptor and forskolin-stimulated cAMP production were greater in hepatocytes from malnourished rats. Stimulation of adenylyl cyclase with forskolin, guanine nucleotides or manganese in hepatic membranes was also enhanced after malnutrition. Moreover, quantity of the stimulatory guanine nucleotide regulatory protein was 70–80% greater in hepatocytes from malnourished rats but the inhibitory guanine nucleotide regulatory protein was not different. These results suggested that desensitization of cAMP-mediated signal transduction after malnutrition occurred at a site distal to cAMP production. Maximal activity of cAMP-dependent protein kinase was 60% lower in liver homogenates from malnourished rats compared with controls. This difference in activity was confined to the cytosolic compartment, with no difference in activity observed in the particulate fraction. Lower activity of cAMP-dependent protein kinase in the cytosol of malnourished rats was associated with a 43% reduction in the quantity of regulatory subunit type I, with no difference in the regulatory subunit type II. These data indicate that desensitization of cAMP signal transduction in rat liver after malnutrition is due to a decrease in the quantity and activity of cAMP-dependent protein kinase.

Metabolomics analysis reveals cytotoxic effects of ouabain towards psoriatic keratinocytes via impairment of glutathione metabolism

Ouabain is a cardiac glycoside long studied for treating heart diseases, but the attempts to evaluate its anti-psoriatic activity have not been reported. We aimed to explore the effects of ouabain on proliferation and metabolism towards psoriatic keratinocytes. In human HaCaT keratinocytes, ouabain potently decreased viability, promoted apoptosis and caused G2/M cycle arrest. Metabolomics analysis indicated that ouabain markedly impaired glutathione metabolism. The solute carrier family 7 member 11 (SLC7A11) is an amino acid transporter highly specific to cysteine, which is critical for glutathione synthesis. Ouabain downregulated SLC7A11, reduced cysteine uptake and subsequently inhibited glutathione synthesis, probably through inhibiting Akt/mTOR/beclin axis that regulate protein activity of SLC7A11. The impaired glutathione synthesis and oxidative stress caused by ouabain may contribute to its cytotoxicity towards psoriatic keratinocytes. Our results provide experimental evidence supporting further study of ouabain as a potential anti-psoriatic agent.

Low Antioxidant Glutathione Levels Lead to Longer Telomeres: A Sex-Specific Link to Longevity?

Telomeres are repetitive DNA sequences at the end of chromosomes that protect them from degradation. They have been the focus of intense research because short telomeres would predict accelerated ageing and reduced longevity in vertebrates. Oxidative stress is considered a physiological driver of the telomere shortening and, consequently, short lifespan. Among molecules fighting against oxidative stress, glutathione is involved in many antioxidant pathways. Literature supports that oxidative stress may trigger a compensatory "hormetic" response increasing glutathione levels and telomere length. Here, we tested the link between total glutathione concentration and telomere length in captive birds (zebra finches; Taeniopygia guttata). Total glutathione levels were experimentally decreased during birds' growth using a specific inhibitor of glutathione synthesis (buthionine sulfoximine; BSO). We monitored the birds' reproductive performance in an outdoor aviary during the first month of life, and their longevity for almost 9 years. Among control individuals, erythrocyte glutathione levels during development positively predicted erythrocyte telomere length in adulthood. However, BSO-treated females, but not males, showed longer telomeres than control females in adulthood. This counterintuitive finding suggests that females mounted a compensatory response. Such compensation agrees with precedent findings in the same population where the BSO treatment increased growth and adult body mass in females but not males. BSO did not influence longevity or reproductive output in any sex. However, early glutathione levels and adult telomere length interactively predicted longevity only among control females. Those females with "naturally" low (non-manipulated) glutathione levels at the nestling age but capable of producing longer telomeres in adulthood seem to live longer. The results suggest that the capability to mount a hormetic response triggered by low early glutathione levels can improve fitness via telomere length. Overall, the results may indicate a sex-specific link between glutathione and telomere values. Telomerase activity and sexual steroids (estrogens) are good candidates to explain the sex-biased mechanism underlying the early-life impact of oxidative stress on adult telomere length.

Effects of Glutaminase Inhibition on Venetoclax, Ibrutinib, and AZD-5991 Resistance in Chronic Lymphocytic Leukemia Cell Lines

Introduction: Bruton tyrosine kinase and BCL-2 inhibitors are widely used in CLL, but resistance problem is highly relevant. One of the resistance mechanisms may be metabolic rewiring followed by activation of oxidative phosphorylation. Glutamine plays a major role in cancer metabolism, and glutamine limitation rather than glucose contributes to lower oxygen uptake and mediates apoptosis of cancer cells. It was shown that glutamine metabolism changes contribute to venetoclax (Chen Z. et al, Blood, 2021; Guièze R. et al. Cancer Cell, 2019) and ibrutinib (Galicia-Vázquez G. et al. Frontiers in Oncology, 2018) resistance. We investigated in vitro effects of glutaminase-1 (GLS-1) enzyme inhibition and its potential synergistic effects with venetoclax, ibrutinib, and MCL-1 inhibitor AZD-5991 on resistant cell lines. CB-839 (telaglenastat) is a potent, reversible, and selective GLS-1 inhibitor with 24 nM IC50 for recombinant human mitochondrial glutaminase C. The compound was tested in the clinic for hematological malignancies and solid tumors. Methods: We have tested CB-839 alone or in combination with venetoclax, ibrutinib, and AZD-5991 on resistant HG-3 and MEC-1 CLL cell lines. Cells were incubated with 0.01 to 100 μM of CB-839 for 72 hours. The inhibition of glutamine, glutamate, and glutathione induced by CB-839 alone was measured using a luminescence assay. DCFDA/ H2DCFDA and MitoSOX Red stainings were utilized to evaluate cellular reactive oxygen species (Total ROS) and mitochondrial superoxide (MitoSOX) accumulation, respectively. Intracellular nucleotides including ATP level were measured using high-pressure liquid chromatography. For drug combinations, MTS assay and Annexin V/Propidium Iodide staining were used to assess cell proliferation and apoptosis, respectively. The combination index (CI) for synergy was calculated using Compusyn software. Results: HG3 and MEC1 cell lines were resistant to venetoclax, ibrutinib, and AZD-5991 single agents. The IC50 values for HG3 are 8.1 μM, 1.3 μM, 9.9 μM, and for MEC1 are 2.9 μM, 1.2 μM, and 1.9 μM for venetoclax, ibrutinib, and AZD-5991, respectively. In these cell lines, CB-839 caused a dose-dependent decrease in GLS-1 activity, measured as intracellular glutamate concentration, and inhibited glutathione synthesis (Figure 1A). CB-839 treated cells showed increased MitoSOX, but not Total ROS accumulation. However, as the endpoint effect, the decrease of cell proliferation rather than apoptosis was detected. CB-839 treatment caused a mild decrease in ATP pool in both cell lines. According to MTS assay, venetoclax demonstrated only the particular synergism with CB-839 (CI <1.0 at all effective doses (ED50, ED75, ED90, ED95) for MEC-1, and at ED50, ED75 for HG-3 cell line). In addition, CB-839 increased pro-apoptotic effect of venetoclax in both cell lines. Notably, that CB-839 did not improve any ibrutinib-mediated effects on cell proliferation and apoptosis in CLL cell lines. The most distinct synergism was observed in CB-839 and AZD-5991 combination group (CI <1.0 at all ED for MEC-1 and HG-3 cell lines) with 5- and 19.8-fold shifts in IC50 (Figure 1B). To extend these results, we are performing these combinations in primary CLL cells that are sensitive or resistant to targeted agents such as ibrutinib or venetoclax. Conclusions: Combinations of CB-839 with other agents targeting multiple mechanisms have the potential to overcome metabolic adaptation. Our findings suggest that CB-839 has limited efficacy in overcoming ibrutinib CLL resistance. However, the synergism with apoptosis inducers such as venetoclax and AZD-5991 require further investigations. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Intracellular glutathione levels affect the outcomes of verteporfin-mediated photodynamic therapy in esophageal cancer cells

Photodynamic therapy (PDT) induces cancer cell death by generating reactive oxygen species (ROS). In this process, photosensitizers accumulate in cancer cells irradiated by laser light of a specific wavelength, leading to ROS generation. Verteporfin (VP), a second-generation photosensitizer, is used in PDT for age-related macular degeneration. However, the antitumor effects of VP-PDT remain poorly defined. This study investigated the antitumor effects of VP-PDT on esophageal cancer (EC) cell lines in vitro. Two types of EC cell lines, the KYSE30 cell line, derived from highly differentiated esophageal carcinoma, and the KYSE170 cell line, derived from moderately differentiated carcinoma, were used in this study. VP-PDT exerted effective anticancer effects in both cell lines. Our results revealed that the low-density lipoprotein receptor, albumin receptor, and heme carrier protein-1 in VP uptake were not involved in VP uptake. However, cells rich in intracellular glutathione were resistant to VP-PDT. Our study outcomes suggest that lowering intracellular glutathione via a glutathione synthesis inhibitor or sulfasalazine can increase the effectiveness of VP-PDT-mediated anticancer effects.

Abstract 214: Styrylbenzoic acid derivative DC10 potentiates radiotherapy by inhibiting glutathione synthesis, leading to increased oxidative stress and cancer cell death

Abstract Metastatic tumors with moderate radiosensitivity account for most cancer-related deaths, highlighting the limitations of current radiotherapy regimens. The xCT-inhibitor sulfasalazine (SAS) sensitizes cancer cells by blocking xCT-mediated cystine uptake, and thereby glutathione (GSH) synthesis protecting against radiation-induced oxidative stress. However, SAS has limited clinical potential as a radiosensitizer due to side effects and low bio-availability. Using SAS as a starting point, we previously developed synthetic xCT-inhibitors through scaffold hopping &amp; structure optimization aided by structure-activity relationship analysis (SAR). Notably, the compound DC10 exhibited potent inhibition of GSH synthesis. In this study, we validated DC10 as a radiosensitizer in the xCT-expressing cancer cell lines A172, A375 &amp; MCF7 in vitro &amp; in mice harboring melanoma xenografts. After DC10 treatment, we measured 14C-cystine uptake in the cancer cell lines using liquid scintillation counting, and intracellular levels of GSH &amp; reactive oxygen species (ROS) using luminescence assays. We performed immunoblotting for γH2AX &amp; ATM to assess DNA damage after treatment with DC10 and radiotherapy. We then assessed the effect of adding DC10 to radiation upon cancer cell colony formation. Blood samples from mice treated with DC10 underwent biochemical analysis to assess toxicity. Finally, mice with A375 melanomas in the flank, received DC10 and radiotherapy in combination, as monotherapies or no treatment. Notably, DC10 reduced cystine uptake and GSH synthesis &amp; increased ROS levels in a dose-dependent manner. Furthermore, DC10 interacted synergistically with radiation to increase DNA damage &amp; reduce colony formation. Mice receiving DC10 were clinically unaffected, whereas blood samples analyses to assess bone marrow suppression, liver or kidney toxicity revealed no significant differences between mice &amp; untreated controls. Importantly, DC10 potentiated the anti-tumor efficacy of radiation in mice with melanoma xenografts. We conclude that DC10 acts as a radiosensitizer, is well tolerated, &amp; mediates its effect by inhibiting cystine uptake, leading to GSH depletion and increased oxidative stress. Thus, our findings demonstrate the feasibility of using synthetic xCT-inhibitors to overcome radioresistance. The expression of xCT in multiple tumor types further implies it represents a target generic to cancer rather than confined to tumor subtypes. Hence, this therapeutic concept could be applicable to a wide range of radioresistant malignancies. Citation Format: Shahin Sarowar, Davide Cirillo, Pablo Jativa, Mette H. Nilsen, Sarah-Muheha A. Otragane, Jan I. Heggdal, Frode Selheim, Valentín Ceña, Hans-René Bjørsvik, Per Øyvind Enger. Styrylbenzoic acid derivative DC10 potentiates radiotherapy by inhibiting glutathione synthesis, leading to increased oxidative stress and cancer cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 214.