Cystine transporter SLC7A11/xCT in cancer: ferroptosis, nutrient dependency, and cancer therapy

Ferroptosis, a form of iron-dependent, nonapoptotic cell death that is induced by excessive lipid peroxidation, has been recently identified as a new tumor suppression mechanism. In this issue of Cancer Research, Liu and colleagues demonstrate that the deubiquitinase (DUB) OTUB1 is frequently overexpressed in human cancers, and functions to "dub" (trim) the ferroptosis process in cancer cells and promotes tumor development by stabilizing the cystine transporter, SLC7A11. This study not only reveals a hitherto unappreciated regulatory mechanism of ferroptosis but also identifies potential therapeutic targets for cancer treatment.See related article by Liu et al., p. 1913.

Mind the IQGAP

Moreover, the metabolic alterations in cancer enable cancer cells drug resistance in cancer therapy [3]. Actually, metabolic factors have recently been suggested as one part of the important targets for the development of novel, combinatory drugs to overcome the resistance to chemotherapy, target therapy and immunotherapy [4]. In addition, host metabolic factors, such as metabolites derived from commensal gut microbiota, have also been recognized as modifiers of the cancer microenvironment and been targeted for therapeutic gain in cancer [5; 6].The metabolites derived from amino acid have been recognized as modifiers of the cancer microenvironment and targets for cancer therapeutics. As a non-essential amino acid, glutamine can be synthesized by cells. Glutamine metabolism contributes to the growth and proliferation of mammalian cells as well as tumor cells. Yang XJ et al. summarized the role of glutamine metabolism in ovarian cancer cell proliferation, invasion, and drug resistance. They also discussed the role of glutamine in protein synthesis and in the purine and pyrimidine synthesis as primary nitrogen donor. In addition, they collected the studies that glutamine-addicted tumor cells depend on glutamine for survival. Most interestingly, combining platinum-based chemotherapy with inhibition of glutamine metabolic pathways may be a new strategy for treating ovarian cancer, especially drug resistant ovarian cancer.Branched-chain amino acid metabolism affects systemic metabolism in cancer cells. Branched-chain amino acid transferase (BCAT) is an enzyme that catalyzes the transamination of three branched-chain amino acid to branched-chain keto acids.Nong XZ et al. reviewed the potential roles of BCAT in different cancer development and treatments. They also discussed the BCAT as the target of the proto-oncogene c-Myc. Furthermore, they emphasized that BCAT usually promotes cancer proliferation and invasion by activating the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin pathway as well as Wnt/β-Catenin signal transduction.Cornett K et al. summarized another well-known gene GAPDH involved in glycolysis. Recently, GAPDH is found to have diverse localizations and its role is largely dependent on its cellular location and interaction partners. They discussed the membrane-associated function of GAPDH in stimulating glucose uptake in neuroblastomaand the nuclear complex of GAPDH in DNA repair, which demonstrated its potential role in cancer metabolism, treatment and drug resistance.The perceptions of cancer metabolism are driven by technological and methodological advances in omics. Genome sequencing has been widely used in clinic cancer target therapeutics. Li CX et al. conducted next generation sequencing for a rare case of secondary tumor of the ovary from liver and identified BRCA2 mutation. Therefore, they treated the patient with poly adenosine diphosphate-ribose polymerase inhibitor olaparib after the administration of surgery. The patient has achieved nearly 2-year survival and lives a relatively normal life with good quality.Meanwhile, enormous amount of information is contained in the public cancer genomics database waiting for deep mining to provide clues for cancer therapeutics.To this end, Li K et al. analyzed the data from Genomics of Drug Sensitivity in Cancer (GDSC) database, and found that cuproptosis-related genes are associated with the development, tumor microenvironment, and prognosis of lung adenocarcinoma. They also provided a scoring system based on these cuproptosisrelated genes to predict the efficacy of targeted drugs and immune response. These findings may indicate the potential roles of copper metabolism in cancer biology and provide a new path for the assessment of cancer prognosis and therapeutics.Spatial metabolomics offers an opportunity to demonstrate the drug-resistant tumor profile with metabolic heterogeneity, and poses a data-mining challenge to reveal meaningful insights from high-dimensional spatial information. Zhang ZQ et al.discussed the latest progress, with the focus on currently available bulk, single-cell and spatial metabolomics technologies and their successful applications in cancer drug resistance. They summarized the underlying metabolic mechanisms including the Warburg effect, altered amino acid/lipid/drug metabolism, generation of drugresistant cancer stem cells, and immunosuppressive metabolism. The perspective of how the spatial metabolomics approach (integrating spatial metabolomics) could be further developed to improve the management of drug resistance in cancer patients is expounded.More recently, gut microbiome has demonstrated great influence on the cancer formation, prognosis and treatment via their metabolites. Huang JT et al. discussed the effects and the underlying mechanisms of gut microbiome and microbial-derived metabolites in cancer development and treatment. They reviewed the works of gut microbiome intervention of cancer patients by fecal microbiota transplantation from healthy ones, which can suppress the carcinogenesis, or augment therapeutic effect on the tumor through the related metabolites, suggesting targeting gut microbiome will be a new approach to improve the efficacy of tumor prevention and treatment.Overall, our research topic highlights the ongoing challenges in the field of the amino acid metabolism in cancer cells, the metabolites of microbes in the gut of host, and the methodology of omics in cancer metabolism. These knowledges will ultimately contribute to better understanding the role of metabolism in tumorigenesis and advance the translation of these findings to overcome drug resistance in cancer therapy.

Long non-coding RNA PVT1, as an important carcinogenic lncRNA, is highly expressed in many malignant tumors and suggests a poorer prognosis. It can promote the occurrence and development of cancers by affecting cell proliferation, migration, invasion and apoptosis. This article reviews the progress of lncRNA PVT1 on cancer therapy, in order to facilitate the in-depth study of lncRNA PVT1 acting as a promising target for therapy in cancers. We extracted all relevant studies of lncRNA PVT1 on the treatment of cancers by searching electronic databases Pubmed, Embase, Web of Science from inception to November 30, 2017. Accumulating vigorous evidence has shown that lncRNA PVT1 performs a significant carcinogenic activity in various cancers, for instance, negatively modulating miRNA as a ceRNA or a molecular sponge to exert tumor-promoting effect. Based on the critical role of lncRNA PVT1 in the pathogenesis of cancers, numerous studies have already demonstrated that lncRNA PVT1 might serve as a potential therapeutic target for various cancers, such as non-small cell lung cancer, hepatocellular carcinoma, gastric cancer, breast cancer, glioma, etc. Numerous studies have indicated that lncRNA PVT1 will most likely become a novel target for cancer therapy with the deepening systematic research.

Introduction: For patients with advanced ovarian cancer there are no effective therapies. The need for alternative treatments with high specificity but with low systemic toxicity can be achieved by targeting key molecular markers associated with cancer cells. Here, we show an innovative proof-of-principle approach for efficient killing of proliferating ovarian cancer cells by inactivating a protein associated with cell proliferation namely, the nuclear Ki-67 protein (pKi-67), using nanotechnology-based photodynamic therapy (PDT). pKi-67 is highly expressed in all proliferating cells and antibodies against this protein are widely used as prognostic tools in tumor diagnosis. Materials and Methods: Anti pKi-67 antibodies were first conjugated to fluorescein isothiocyanate (FITC) and then encapsulated inside liposomes. The liposomes encapsulating antibodies were characterized by dynamic light scattering and transmission electron microscopy. We then evaluated the efficacy of Ki-67 targeting using two in vitro ovarian cancer models - monolayer cultures as well as 3D cultures established in our lab. Cell viability after irradiation with laserlight at 488 nm was assessed using MTT viability assay for monolayer cultures while a Live/Dead assay kit was used for analyzing 3D cultures. Results: After incubation of OVCAR-5 ovarian cancer cells with the liposomal constructs, we used confocal microscopy to image localization of the antibodies to the nucleoli of the cells. Irradiation of these cells with a 488 nm laser led to a significant loss of viability. The efficacy of this approach was further demonstrated in a 3D culture model of OVCAR-5 cells. Incubation of 3D cultures with the liposomal constructs followed by light irradiation led to destruction of their acinar structures over 72 h following treatment. Using two different anti pKi-67 antibodies, where one targets the “active” form of pKi-67 while the other binds to the “inactive” form of the protein; we show that cell killing is specific after inactivation of the “active” Ki-67 protein. Further, the specificity of this approach for pKi-67 positive cells is demonstrated in confluent human lung fibroblasts (MRC-5) where minimal cell death was observed. This is in agreement with the flow cytometry results which show that only small populations of confluent MRC-5 cells express pKi-67. Conclusions: Taken together, our findings suggest that pKi-67 is an attractive therapeutic target in cancer and this approach holds promise as an effective alternative cancer therapy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C83.

: Fatty acid synthase (FAS) inhibition initiates selective apoptosis of cancer cells both in vivo and in vitro, which may involve malonyl-CoA metabolism. These findings led to exploration of malonyl-CoA decarboxylase (MCD) as a potential novel target for cancer treatment. MCD regulates the levels of cellular malonyl-CoA through the decarboxylation of malonyl-CoA to acetyl-CoA. Malonyl-CoA is both a substrate for FAS and an inhibitor of fatty acid oxidation acting as a metabolic switch between anabolic fatty acid synthesis and catabolic fatty acid oxidation. We now report that treatment of human breast cancer (MCF7) cells with MCD small interference RNA (siRNA) reduces MCD expression and activity, reduces ATP levels, and is cytotoxic to MCF7 cells, but not to human fibroblasts. In addition, we synthesized a small molecule inhibitor of MCD, 5-{(Morpholine-4-carbonyl)-[4-(2,2,2-trifluoro-1-hydroxy-1- trifluoromethyl-ethyl)-phenyl]-amino}-pentanoic acid methyl ester (MPA). Similar to MCD siRNA, MPA inhibits MCD activity in MCF7 cells, increases cellular malonyl-CoA levels and is cytotoxic to a number of human breast cancer cell lines in vitro. Taken together, these data indicate that MCD-induced cytotoxicity is likely mediated through malonyl-CoA metabolism. These findings support the hypothesis that MCD is a potential therapeutic target for cancer therapy.

September 1, 2005 - Cancer Drug Target Chk1 may also be source of Drug ResistanceNew findings suggest balancing Chk1 activity will produce less toxic cancer drugsLA JOLLA, CA. A study published by The Burnham Institute in the September edition of Molecular Cell reports that a cell-cycle checkpoint protein, known to be activated by an important class of anticancer drugs, may play crucial roles in both the hampering of therapeutic actions and aiding cancer cells to "recover" and start dividing again after treatment with these drugs. The study is expected to help academic researchers and biotechnology and pharmaceutical companies design drugs that combat cancer using this checkpoint protein, but with fewer side effects.Robert Abraham, Ph.D., former director of The Burnham Institute's Cancer Center and now vice president for oncology research at Wyeth Pharmaceuticals, together with his colleagues, found that the Chk1 protein responds with cell-survival activity to stressful conditions induced by hypoxia and certain anticancer drugs. Furthermore these same conditions target Chk1 for eventual destruction. Ironically, stimulation of Chk1 triggers certain repair responses that fight cancer while the simultaneous degradation of Chk1 can allow cancer cells to escape drug-induced death and resume progressive tumor growth.The study suggests the Chk1 protein is critical for ensuring the repair of mutations and other errors in DNA replication before they can alter the function of a cell. If not repaired, these errors can kill the cell when it attempts to divide and proliferate. In cancer cells, Chk1 is responds as a natural defense to the therapeutic damage done by radiation and chemotherapy and attempts to effect repair to DNA damage caused by the cancer therapy, thus makes the drug therapy less effective.The researchers also found that the chemotherapy agent campthothecin (CPT), a clinically important anticancer agent, reduced the activity of the Chk1 protein. "These findings lend strong support to the idea that inactivation of Chk1 contributes to the antitumor activity of CPT by allowing cells bearing damaged DNA to progress through the cell cycle, leading to an unsuccessful and often lethal attempt to undergo cell division," said Abraham who is also a member of the Editorial Board of Cancer Biology and Therapy. "Combination therapy, which pairs a chemotherapy agent with an inhibitor of Chk1, may therefore be an effective strategy to increase the efficacy of certain anticancer drugs, and may well overcome clinical resistance to these drugs."By studying the effects of radiation and other stresses on the pathway that normally regulate Chk1, the researchers discovered that the same pathway that activates Chk1 via phosphorylation by its regulatory enzyme, ATR, also marks Chk1 for eventual destruction."We expect this process prevents activated Chk1 from accumulating in normal cells and prevents abnormal cell proliferation," said Abraham. "ATR activates, but also destabilizes Chk1, which creates a homeostatic mechanism that balances the genome protective function of Chk1 with the process of cell proliferation. This is a new look at drug therapy. Textbook descriptions of ATR and Chk1 don't describe this dual role.""The findings also provide further insight into Chk1 activation and tumor sensitivity," Abraham added. "Cancer cells rely heavily on Chk1 for survival and proliferation under stressful environmental conditions. Instead of halting abnormal growth of cancer cells, drug therapy could in effect induce Chk1 natural activity to prevent cell death in cancer cells."Collaborators on this publication include You-wei Zhang, Diane M. Otterness, and Gary Chiang from Dr. Abraham's laboratory at The Burnham Institute; and Weilin Xie, and Franklin Mercurio of Celgene Corporation; and Yun-Cai Liu of La Jolla Institute for Allergy and Immunology.This work was supported by grants from Johnson & Johnson, the National Institutes of Health, the Department of Defense Breast Cancer Research Program, a postdoctoral training grant from the Susan G. Komen Breast Cancer Foundation, and a Kirschstein-NRSA fellowship.The Burnham Institute, founded in 1976, is an independent not-for-profit biomedical research institution dedicated to advancing the frontiers of scientific knowledge and providing the foundation for tomorrow's medical therapies. The Institute is home to three major centers: the Cancer Center, the Del E. Webb Neuroscience and Aging, and the Infectious and Inflammatory Disease Center. Since 1981, the Institute's Cancer Center has been a member of the National Cancer Institute's prestigious Cancer Centers program. Discoveries by Burnham scientists have contributed to the development of new drugs for Alzheimer's disease, heart disease and several forms of cancer. Today the Burnham Institute employs over 700, including more than 550 scientists. The majority of the Institute's funding derives from federal sources, but private philanthropic support is essential to continuing bold and innovative research. For additional information about the Institute and ways to support the research efforts of the Institute, visit www.burnham.org.

Pancreatic cancer is an aggressive, drug-resistant disease; its first-line chemotherapeutic, gemcitabine, is only marginally effective. Intracellular depletion of glutathione, a major free-radical scavenger, has been associated with growth arrest and reduced drug resistance (chemosensitization) of cancer cells. In search of a new therapeutic approach for pancreatic cancer, we sought to determine whether specific inhibition of the plasma membrane x(c) (-) cystine transporter could lead to reduced uptake of cysteine, a key precursor of glutathione, and subsequent glutathione depletion. Sulfasalazine (approximately 0.2 mmol/L), an anti-inflammatory drug with potent x(c) (-)-inhibitory properties, markedly reduced l¹⁴C]-cystine uptake, glutathione levels, and growth and viability of human MIA PaCa-2 and PANC-1 pancreatic cancer cells in vitro. These effects were shown to result primarily from inhibition of cystine uptake mediated by the x(c) (-) cystine transporter and not from inhibition of nuclear factor kappaB activation, another property of sulfasalazine. The efficacy of gemcitabine could be markedly enhanced by combination therapy with sulfasalazine both in vitro and in immunodeficient mice carrying xenografts of the same cell lines. No major side effects were observed in vivo.The results of the present study suggest that the x(c) (-) transporter plays a major role in pancreatic cancer by sustaining or enhancing glutathione biosynthesis, and as such, represents a potential therapeutic target. Sulfasalazine, a relatively nontoxic drug approved by the U.S. Food and Drug Administration, may, in combination with gemcitabine, lead to more effective therapy of refractory pancreatic cancer.

The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. Cancer Res; 77(2); 434-47. ©2016 AACR.

BackgroundmiR-200b has been reported to be a tumor suppressor and a promising therapeutic target in cancer. miR-200b has been associated with epithelial-mesenchymal transition and chemo-resistance in cancer. The aim of this study is to investigate the expression of miR-200b, its prognostic roles and its potential targets in breast cancer.MethodsqRT-PCR was used to detect miR-200b expression in breast cancer tissues and cell lines. In situ hybridization of miR-200b on tissue microarray including 134 breast cancer samples was used to evaluate its prognostic role. Novel targets of miR-200b in breast cancer were predicted and confirmed by luciferase reporter assay and western bloting. Immunohistochemical staining was used for protein detection. The biological effects of miR-200b in breast cancer cells were further confirmed by ectopic expression of its mimics followed by MTT assay and invasion test.ResultsmiR-200b was downregulated in breast cancer tissues and cell lines and its low-expression correlated with poor outcome in breast cancer patients. Members of RAB family, RAB21, RAB23, RAB18 and RAB3B were predicted to be the targets of miR-200b. The luciferase reporter assay was performed to certificate this prediction. The expressions of RAB21, RAB23, RAB18 and RAB3B were suppressed by transfection of miR-200b in breast cancer cells. Over-expression of miR-200b or knock-down of RAB21, RAB23, RAB18 and RAB3B inhibited breast cancer cell proliferation and invasion in vitro.ConclusionsOur study provides evidence that miR-200b is a prognostic factor in breast cancer targeting multiple members of RAB family. MiR-200b could be a potential therapeutic target in breast cancer.

<div>Abstract<p>The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. <i>Cancer Res; 77(2); 434–47. ©2016 AACR</i>.</p></div>

<div>Abstract<p>The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. <i>Cancer Res; 77(2); 434–47. ©2016 AACR</i>.</p></div>

Emerging Role of Semaphorins as Major Regulatory Signals and Potential Therapeutic Targets in Cancer

O1-027 - Minichromosome Maintenance Protein 7 Plays Essential Roles in Cancer Cell Growth and is a Potential Therapeutic Target in Human Cancer

The majority of new drug approvals for cancer are based on existing therapeutic targets. One approach to the identification of novel targets is to perform high-throughput RNA interference (RNAi) cellular viability screens. We describe a novel approach combining RNAi screening in multiple cell lines with gene expression and genomic profiling to identify novel cancer targets. We performed parallel RNAi screens in multiple cancer cell lines to identify genes that are essential for viability in some cell lines but not others, suggesting that these genes constitute key drivers of cellular survival in specific cancer cells. This approach was verified by the identification of PIK3CA, silencing of which was selectively lethal to the MCF7 cell line, which harbours an activating oncogenic PIK3CA mutation. We combined our functional RNAi approach with gene expression and genomic analysis, allowing the identification of several novel kinases, including WEE1, that are essential for viability only in cell lines that have an elevated level of expression of this kinase. Furthermore, we identified a subset of breast tumours that highly express WEE1 suggesting that WEE1 could be a novel therapeutic target in breast cancer. In conclusion, this strategy represents a novel and effective strategy for the identification of functionally important therapeutic targets in cancer.