Recent Progress in Ferroptosis Inducers for Ca.pdf

1904197(1 of 25)2019 WILEY-VCH Verlag GmbH&Co.KGaA,Weinheimwww.advmat.deProgress rePortRecent Progress in Ferroptosis Inducers for Cancer TherapyChen Liang,Xinglin Zhang,Mengsu Yang,*and Xiaochen Dong*DOI:10.1002/adma.201904197cell death”(RCD).2 Understanding how the RCD processes are modulated by internal and external factors is of great therapeutic interest.3,4Historically,cell death was classified into three categories based on their mor-photypes:1)type I,apoptosis;2)type II,autophagy;and 3)type III,necrosis.1 Among which the caspase-dependent apoptosis has long been considered as the only form of RCD and is adopted for the development of anticancer drugs.5 However,the therapeutic outcomes of those drugs are far from satisfactory due to the intrinsic or acquired apoptosis resistance of cancer cells.For instance,as a self-defense response,drug resistance occurs frequently in cancer cells upon the induction of apoptosis by chemothera-peutics.6,7 Mutations have been observed in many cancer cell types that can evade apoptosis,which result in treatment failure.8 In some cases,the overexpression of apoptosis inhibitors can reduce thera-peutic effectiveness in malignant cells.9,10 Recently,our tradi-tional understanding of cell death process has been challenged by the discovery of several novel cell death processes with unique regulatory pathways.Some of these newly discovered RCDs that share different mechanisms with apoptosis can cir-cumvent its limitations,which open up new opportunities to treat cancer.11Among these non-apoptotic forms of RCDs,ferroptosis has received considerable attention due to its involvement in development,immunity,senescence,and a variety of pathological scenarios.Ferroptosis is defined as an oxidative,iron-dependent form of RCD that is characterized by accumu-lation of reactive oxygen species(ROS)and lipid peroxidation products to lethal levels.12,13 Despite the important role of ferroptosis in sustaining survival of normal cells and tissues,it has been increasingly recognized that some oncogenic path-ways are related to ferroptosis,rendering cancer cells extremely vulnerable to ferroptotic death.14 As one of the most well-studied tumor suppressor genes,p53 inhibits the expression of cystine/glutamate antiporter transcriptionally,thus positively regulates ferroptosis pathway.1517 In addition,mitochon-drial tumor suppressor fumarase has been found necessary for cysteine-deprivation-induced ferroptosis.18 Actually,the investigation of ferroptosis derives from the studies aiming to identify small molecules that are selectively toxic to oncogenic RAS,which accounts for cancer growth,invasion,and metas-tasis.13,1921 Some highly aggressive malignancies have been identified to be vulnerable to ferroptosis intrinsically.22 Due to its non-apoptotic nature,ferroptosis-based cancer therapy Ferroptosis is a newly discovered form of regulated cell death that is the nexus between metabolism,redox biology,and human health.Emerging evidence shows the potential of triggering ferroptosis for cancer therapy,particularly for eradicating aggressive malignancies that are resistant to traditional therapies.Recently,there has been a great deal of effort to design and develop anticancer drugs based on ferroptosis induction.Recent advances of ferroptosis-inducing agents at the intersection of chemistry,materials science,and cancer biology are presented.The basis of ferroptosis is summarized first to highlight the feasibility and characteristics of triggering ferroptosis for cancer therapy.A literature review of ferroptosis inducers(including small molecules and nanomaterials)is then presented to delineate their design,action mechanisms,and anticancer applications.Finally,some considerations for research on ferroptosis inducers are spotlighted,followed by a discussion on the challenges and future development directions of this burgeoning field.C.Liang,Prof.M.YangDepartment of Biomedical SciencesCity University of Hong Kong83 Tat Chee Avenue,Hong Kong 999077,ChinaE-mail:bhmyangcityu.edu.hkX.Zhang,Prof.X.DongKey Laboratory of Flexible Electronics(KLOFE)and Institute of Advanced Materials(IAM)Nanjing Tech University(NanjingTech)Nanjing 210009,ChinaE-mail:Prof.M.YangKey Laboratory of Biochip TechnologyBiotech and Health CentreShenzhen Research Institute of City University of Hong KongShenzhen 518057,ChinaProf.X.DongSchool of Chemistry and Materials ScienceNanjing University of Information Science&TechnologyNanjing 210044,ChinaThe ORCID identification number(s)for the author(s)of this article can be found under https:/doi.org/10.1002/adma.201904197.1.IntroductionDeath is the common fate of all living organisms,so is every cell in our body.Despite a reminiscent of degradation or damage,cell death is an indispensable part of life since it involves in diverse aspects of development and pathophysiolog-ical processes.1 Especially,some of the cell death processes rely on dedicated molecular machinery,making them eligible to be regulated pharmacologically or genetically,known as“regulated Adv.Mater.2019,1904197 2019 WILEY-VCH Verlag GmbH&Co.KGaA,Weinheim1904197(2 of 25)is expected to bypass the drawbacks of traditional therapeutics mediated by apoptosis pathways.Recently,ferroptosis has also been proved to be involved in cancer immunotherapy,where T cells and interferon-gamma(IFN-)sensitize tumor cells to ferroptosis.23 All of these highlight the promising role of ferroptosis induction in cancer treatment.Various ferroptosis inducers have been identified or devel-oped,most of which are small molecules targeting ferroptosis pathways,including clinically approved drugs and molecules in research stage.Notably,nanotechnology offers new possibili-ties in triggering ferroptosis for cancer treatment.Because of the unique physicochemical properties,nanomaterials can not only make up for the deficiencies of traditional pharmaceuticals(e.g.,low targeting efficiency,poor water solubility,severe side effects,etc.),but also introduce new features(e.g.,magnetic property,photothermal effect,electrochemical property,etc.).24 Additionally,many previously reported nanoplatforms,especially those referring to Fenton chemistry to generate ROS,are likely to be involved in the ferroptotic mechanisms,which are worth reevaluation from a new perspective.Given the great potential of ferroptosis in cancer therapy and the rapid development of ferroptosis inducers in recent years,it is necessary to summarize the latest work and track the progress in this field.Meanwhile,the complexity of biological system and the challenge of clinical translation pose both challenges and opportunities for further development of ferroptosis-based cancer therapies.This progress report focuses on recent advances of ferroptosis inducers at the intersection of chemistry,materials science,and cancer biology.In this report,we firstly introduce the basis of ferroptosis involved in cancer therapy,including regulatory mechanisms and biological char-acteristics.Next,we elaborate on ferroptosis inducers(including small molecules and nanomaterials),with an emphasis on their structural design,action mechanisms,and anticancer applica-tions.Finally,we discuss future research directions on how to tackle the challenges in developing ferroptosis inducers into clinical therapeutics.2.Basis of Ferroptosis2.1.Regulatory Mechanisms of FerroptosisRecent studies have enabled us to understand the basic principles and regulatory mechanisms of ferroptosis-based cancer therapy more clearly.Here we briefly summarize the mechanisms and key regulators involved in ferroptosis from the perspectives of iron,ROS(particularly lipid peroxides),and amino acids metabolism with an emphasis on the feasibility of triggering ferroptosis for cancer therapy(Figure 1).For more comprehensive and detailed discussion on the mechanisms of ferroptosis,we direct readers to several recent reviews.25292.1.1.Iron MetabolismAs an important factor for the formation of ROS via enzy-matic or non-enzymatic reactions,iron plays an essential role in sensitizing cells to ferroptosis.Normally,the intracellular Chen Liang is conducting her Ph.D.studies under the supervision of Prof.Mengsu Yang in the Department of Biomedical Sciences,City University of Hong Kong.Her research aim is to develop nanomedicines for biomed-ical applications.Her current research interests include multifunctional nanomate-rials,drug delivery,hyper-thermia therapy,and developing nanomedicines applied to cancer diagnosis and therapy.Mengsu Yang obtained his Ph.D.from University of Toronto,Canada and received postdoctoral training in the Scripps Research Institute in the USA.He is currently the Head of Department of Biomedical Sciences,and Yeung Kin-Man chair pro-fessor of Biomedical Sciences in City University of Hong Kong.The research interest of Yangs group focuses on the development of biochip technology and nanotechnology for molecular diagnostics and therapeutic applications.Xiaochen Dong obtained his Ph.D.degree from Zhejiang University in China in 2007.He then joined the School of Materials Science and Engineering in Nanyang Technological University as a postdoctor.In 2012,he joined the Institute of Advanced Materials,NanjingTech University as a full professor.His current research mainly focuses on biophotonics and bioelectronics.iron maintains a delicate balance by iron transport systems.Extracellular iron can be imported by circulating glycoprotein transferrin(TF)and its carrier protein transferrin receptor(TFR).Imported iron is stored and transported in the form of the ironprotein complex(mainly ferritin).Intracellular iron can be exported by ferroportin(FPN),the only known iron exporter that controls iron efflux in mammal.30 Either increased iron uptake or reduced iron export can sensitize cancer cells to oxidative damage and ferroptosis.20 As a key Adv.Mater.2019,1904197 2019 WILEY-VCH Verlag GmbH&Co.KGaA,Weinheim1904197(3 of 25)factor for lipid peroxidation and ferroptosis induction,intra-cellular labile iron(redox-active Fe2+)level can be elevated by TF-mediated iron uptake or autophagic/lysosomal degradation of ferritin(ferritinophagy).12 Nuclear receptor coactivator 4(NCOA4)is a ferritinophagy-specific cargo receptor mediating the transportation of ferritin to autophagosome and undergo ferritinophagy.31 Knockdown of NCOA4 decreases the fer-roptotic sensitivity in human fibrosarcoma cell(HT-1080)and human pancreas carcinoma cells(PANC1).32 Iron-responsive element binding protein 2(IREB2)encodes the master regu-lator of iron metabolism.Silencing of IREB2 significantly attenuates erastin-induced ferroptosis.13 In addition,the RASRAFMEK pathway was found to play a decisive role in ferroptosis sensitivity in some cancer cell lines.33 One expla-nation is that oncogenic RAS increases cellular iron content by upregulating TFR and downregulating ferritin.20 To sup-port the fast proliferation,cancer cells have a higher demand for iron than their nonmalignant counterparts.Downregu-lated FPN and upregulated TFR1 have been observed in many cancer cell lines.34,35 The strong iron dependency(known as iron addiction)makes cancer cells more vulnerable to iron overload and ROS accumulation than noncancerous cells,enabling tumor microenvironment(TME)-targeted,ferroptosis-mediated cancer therapy.28Adv.Mater.2019,1904197Figure 1.The occurrence and regulatory mechanisms of ferroptosis.As an intracellular crossroad of iron metabolism,labile iron pool(LIP)can be supplied with iron from either transferrin receptor(TFR)mediated endocytosis or ferritin degradation(ferritinophagy).The increased LIP provides labile iron ions for Fenton-like reaction,thus sensitizing cells to ferroptosis.Cysteine(Cys)and reduced glutathione(GSH)metabolism constitute the principal line in ferroptosis pathways.The uptake of cystine(Cys2)by system Xc represents the most upstream event of ferroptosis cascade under oxidative extracellular conditions.Under reducing conditions,cysteine can be directly imported via the alanine/serine/cysteine transporter(system ASC).GSH is an important intracellular antioxidant,which is generated from glutamate(Glu),cysteine,and glycine(Gly)in two steps under the catalysis of cytosolic enzymes glutamate-cysteine ligase(GCL)and glutathione synthetase(GSS),respectively.The intracellular cysteine level can be sustained by the transulfurylation pathway,converting methionine(Met)into cysteine.Phosphatidylethanolamines(PEs)containing arachidonoyl(AA)or adrenoyl(AdA)moieties(PE-AA/PE-AdA)are the predominant substrates that undergo oxidation and involve in ferroptosis.The fatty acid translo-case(FAT)and fatty acid transport protein(FATP)are responsible for the uptake of AA/AdA.With the help of enzyme acyl-CoA synthetase long-chain family member 4(ACSL4)and lysophosphatidylcholine acyltransferase 3(LPCAT3),free PUFAs can be esterified and incorporated into membrane phospholipids.Iron-catalyzed enzymatic(ALOXs)and non-enzymatic(Fenton chemistry)processes are involved in the generation of phospholipid hydroperoxides(PE-AA-OOH/PE-AdA-OOH).The mevalonate pathway involved in ferroptosis can generate biomolecules with potential anti-ferroptotic activity.As a central regulator of ferroptosis,Glutathione peroxidase 4(GPX4)combats with lipid peroxidation by transforming toxic PE-AA-OOH/PE-AdA-OOH into nontoxic phospholipid alcohols(PE-AA-OH/PE-AdA-OH).During this process,GSH acts as the electron donor.Oxidized GSH(GSSG)can be reduced to GSH by glutathione-disulfide reductase(GSR)using reduced nicotinamide adenine dinucleotide phosphate(NADPH).Some representative ferroptosis inducers are shown in the figure(red boxes).Abbreviations:ALOXs,arachidonate lipoxygenases;BSO,buthionine sulfoxi-mine;CoQ10,coenzyme Q10;Gln,glutamine;HMGCR,3-hydroxy-3-methylglutaryl-CoA reductase;IREB2,iron-responsive element binding protein 2;NCOA4,Nuclear receptor coactivator 4;NADP+,nicotinamide adenine dinucleotide phosphate;TF,transferrin receptor.2019 WILEY-VCH Verlag GmbH&Co.KGaA,Weinheim1904197(4 of 25)2.1.2.Amino Acid and Glutathione MetabolismNutrients such as sugar,fats,and amino acids cannot diffuse into the cell directly.They must be transported across cell membrane with the help of specific transporters.System Xc is one of such transporters,a disulfide-linked heterodimer con-sists of the regulatory subunit solute carrier family 3 member 2(SLC3A2)and the catalytic subunit solute carrier family 7 member 11(SLC7A11).System Xc facilitates the exchange of cystine and glutamate across plasma membrane.Once imported into the cell,cystine is reduced to cysteine.Another cysteine source is cystathionine,which is derived from reverse transulfurylation of methionine(Met)or imported via system Xc.Under oxidative extracellular conditions,the exchange of cystine/cystathionine with glutamate is the most upstream event of ferroptosis.While under reducing extracellular condi-tions,cysteine can be directly imported by