Editorial
For reprint orders, please contact [email protected]
Future
Medicinal Chemistry
Targeting cell death pathways with small molecules: playing with life and death at the cellular level to treat diseases “Modulation of cell death is a potential game changer for the treatment of a large number of diseases.” Targeting cell death A recent review describes seven distinct cell death pathways underpinned by complex cellular cascades (hence the term ‘programmed cell death’) [1] . These multiple pathways paint an intricate picture of how a cell behaves in response to a plethora of stimuli: they speak to the ability of cells to control their number, thereby allowing multicellular organisms to remain healthy. While some of these pathways share common components (e.g., caspases, RIP kinases), others function almost independently (e.g., ferroptosis). Some have been studied for almost 30 years (e.g., apoptosis), while others have only been identified during the last few years (e.g., pyroptosis) and are, as a consequence, much less understood. One important discriminating factor between these various cell death mechanisms is the degree with which they are able to summon an immunological response: apoptosis is characterized by a ‘silent’ removal of dying cells; conversely, necroptosis leads to an inflammatory response. To add to this complexity, it has recently become clear that proteins, originally thought to be in charge of deploying cell death, have other roles, especially in modulating the immune response to cellular stresses [2] . Indeed, it has become increasingly evident that cell death and immune/inflammatory pathways are strongly embedded, rather than a distinct phenomenon [1] . Deregulation of cell death & diseases With such crucial roles in normal physiology, it is not surprising that deregulation of cell death signaling has been linked to many lifethreatening diseases [3] . This inter-relation
10.4155/FMC.14.169 © 2015 Future Science Ltd
is particularly well illustrated by the role of apoptosis in cancer: most – if not all – tumor cells develop the ability to evade apoptotic cell death [4] . This advantage allows them to abnormally survive in spite of conditions that would otherwise result in their death (DNA damage, loss of adhesion to tissue of origin, uncontrolled proliferation). However, much less is understood about the reverse situation, in other words, when excessive apoptosis occurs in healthy tissues. Yet, upregulated cell death has also been implicated in a large number of disease states including stroke, traumatic injury, macular degeneration, hearing loss and neurodegenerative disorders such as Alzheimer’s diseases; essentially, any condition that leads to the death of otherwise healthy cells, and thus causes tissue loss. Our current understanding of necroptosis in diseases suggests that it acts as a failsafe response in cases where apoptosis is blocked (e.g., after infection by pathogens that express their own apoptosis inhibitors) [5,6] . Deregulation of the biological cascade leading to necroptosis is thought to contribute to sustained inflammation, resulting, for example, in diseases such as psoriasis and rheumatoid arthritis. Similar to upregulated apoptosis, excessive cell death through necroptosis has also been linked to ischemia-reperfusion injuries and neurodegenerative diseases. A combination of these two cellular pathways – as well as others – is likely contributing to these diseases. Considering a broad range of diseases are associated with deregulated cell death, it is not surprising that significant effort from private as well as academic drug discovery groups is devoted to developing small
Future Med. Chem. (Epub ahead of print)
Guillaume Lessene ACRF Chemical Biology Division, The Walter & Eliza Hall Institute of Medical Research, 1G Royal Parade Parkville, VIC-3052, Australia and Department of Medical Biology, The University of Melbourne, VIC-3050, Australia and Department of Pharmacology & Therapeutics, The University of Melbourne, VIC-3050, Australia [email protected]
part of
ISSN 1756-8919
Editorial Lessene molecules that modulate the pathways essential to their regulation. Although these attempts have been met with various degrees of success, they are all underpinned by the substantial challenges facing medicinal chemists. These challenges can be roughly divided in two categories: medicinal chemistry, and biological validation of activity. The BCL-2 family of proteins: targeting the impossible As discussed above, apoptosis was the first programmed cell death pathway to be described and is perhaps the best characterized. The BCL-2 family of proteins are critical regulators of apoptotic cell death [7] . This family is broadly divided into two classes: proteins that promote apoptosis (pro-apoptotic) and those that block it (prosurvival). The latter comprises proteins such as BCL-2 itself (first discovered and after which the whole family is named), MCL-1 and BCL-X L . The proteins that promote cell death can be further divided into two categories: the sensors that detect and initiate the apoptotic cascade, named ‘BH3-only’ proteins (e.g., BIM, BAD and NOXA), and the pro-apoptotic proteins, BAX and BAK, that operate at the mitochondrial membrane. In response to apoptotic stimuli (e.g., extracellular stresses, DNA damage, etc.), BH3-only proteins bind and inactivate the prosurvival proteins. This interaction releases the brake on BAX and BAK leading to their multimerization at the mitochondrial membrane to form pores that allow cytochrome c to be released. This event, often called the ‘point-of-noreturn’ leads to caspase activation and cell demolition. Since upregulation of prosurvival BCL-2 prevents apoptosis functioning properly in cancer cells, strategies aimed at replicating the activity of pro-apoptotic BH3-only proteins with small molecules (the so-called ‘BH3-mimetics’) and thus re-instating cell death in cancer cells, have been actively pursued [8] . In this context, the key challenge for medicinal chemists has been the design and development of small molecules that target the protein–protein interfaces characteristic of the BCL-2-mediated apoptotic cascade [9] : these interfaces are large, shallow and mainly hydrophobic, with seemingly few anchor points to hook a small molecule. Yet, while this concept represented an immense challenge at inception, groundbreaking work by us and others has demonstrated that targeting these protein surfaces is feasible [10] . Compounds with either a broad or narrow spectrum of selectivity have been developed. Recently, published examples of selective compounds include, ABT-199 (BCL-2 selective) [11] and WEHI539 (BCL-X L-selective) [12] , which along with other validated BH3-mimetics represent milestones in drug discovery. The fact that two compounds derived from
10.4155/FMC.14.169
Future Med. Chem. (Epub ahead of print)
ABT-737 (ABT-263 and ABT-199/GDC-199) have reached the clinic and exhibit acceptable oral bioavailability, despite their size and properties, is testament that drug-like chemical space can exist outside the current Lipinski rules. As for many other modern drug discovery programs, these achievements are made possible through convergence of modern drug discovery techniques, such as X-ray crystallography, molecular modeling, structure-based drug design and fragmentbased drug discovery. However, limitations remain, especially in our ability to predict the position of areas of flexibility on the surface of proteins where small molecules may interact. Blocking cell death Comparatively, strategies aimed at blocking cell death have lagged significantly. Early on, caspases presented attractive targets as they were key effectors of downstream apoptosis and had a defined enzymatic pocket with druggable features. Caspase inhibitors have now reached the clinic but their efficacy has failed to match initial expectations; the reasons for which vary: Blocking caspase enzymatic activity at a cellular level is very challenging, due to the exponential nature of the activation signaling cascade (upstream caspases activating downstream caspases); Once caspases are activated, dying cells have already reached the point-of-noreturn. This raises questions about the rationale of rescuing cells that are essentially already dead; developing selectivity within caspase inhibitors is extremely challenging; finally, there is growing evidence that caspases contribute to other biological pathways. Blocking cell death upstream of the mitochondria by inhibiting BAX and/or BAK appears a more convincing strategy since it provides the enormous advantage of keeping cells viable. However, this presents another protein–protein inhibition challenge compounded by the fact that these two proteins act at the mitochondrial membrane. Moreover, it is not clear whether small molecules binding to BAX/BAK will activate or inhibit apoptosis. Only a handful of compounds targeting BAX/BAK have been described, but overall their activity remains weak and their mode of action is questionable [13] . Due to its potential involvement in chronic inflammation and the fact that a specific cellular mechanism controls it, necroptosis has attracted a rapid and growing interest [1] . Small molecule inhibitors of key signaling proteins involved in the regulation of necroptosis have been disclosed: these include the well-known RIP1 inhibitor, necrostatin [14] , RIP3 inhibitors [15] and more recently, small molecules that block MLKL [16,17] , the last known effector in the pathway. MLKL belongs to the intriguing class of pseudo-kinases
future science group
Targeting cell death pathways with small molecules
(kinase-like proteins) that have lost part or all of their ability to process ATP [18] ; they act more as scaffolding proteins or, like MLKL, as death-effector proteins. Pseudo-kinases in general, and MLKL in particular, represent very compelling drug discovery targets with more classical features. It is likely that proof-of-concept compounds will emerge in the near future that will help validate necroptosis as a bona fide therapeutic target in multiple diseases. The biology challenge: determining on-target activity Beyond the difficulties associated with designing and developing small molecules directed at challenging targets such as the BCL-2 proteins, the field of cell death drug discovery faces another problem: validation of the mode-of-action of compounds that directly impact on cell pathways is difficult. As discussed, signaling pathways regulating cell death, such as the BCL-2 family protein cascade or the RIP1/RIP3/MLKL axis for necroptosis, lie at the focal point of numerous biological pathways that can be activated for any number of reasons. The ability of a small molecule to induce cell death does not mean that it targets the cell death machinery directly. A particularly good example of this conundrum is the activity of the anticancer small molecule, Gleevec, which has been shown to rely on functional BCL-2-driven apoptosis [19] . Thus, cell death induced by Gleevec is apoptotic in nature and BCL-2 family driven, yet it does not interact directly with any of the components of this pathway. In the context of apoptosis, we have previously delineated a number of criteria to guide medicinal chemists during their mechanism of action studies [8] . Still, too many so-called ‘BCL-2 inhibitors’ or ‘BH3-mimetics’ continue to appear in the literature with poorly characterized mode-of-action, if not outright Pan-Assay Interferences Compounds (PAINS) [20] . Validation of compounds inducing apoptosis is a case in point and highlights the fact that carefully chosen reagents and cellular tools are particularly indispensable in this field. Although certain cell lines and binding assays References 1
2
3
Linkermann A, Stockwell BR, Krautwald S, Anders H-J. Regulated cell death and inflammation: an autoamplification loop causes organ failure. Nat. Rev. Immunol. 14(11), 759–767 (2014). White MJ, McArthur K, Metcalf D et al. Caspases render apoptosis immunologically silent by suppressing mtDNAinduced STING-mediated type I IFN production. Cell 159(7), 1549–1562 (2014). Hotchkiss RS, Strasser A, McDunn JE, Swanson PE. Cell death. N. Engl. J. Med. 361(16), 1570–1583 (2009).
future science group
Editorial
are available and have been described in the literature, important tools, such as a good assay to phenotypically discriminate between various forms of cell death, are yet to be developed. Outlook Modulation of cell death is a potential game changer for the treatment of a large number of diseases. Recent discoveries are confirming the link between the immune response and cell death. This editorial has highlighted examples specifically related to apoptosis and necroptosis, but other more recently identified forms of programmed cell death, will further unravel novel therapeutic targets. Academic institutions such as the Walter and Eliza Hall Institute, where seminal discoveries have been made around the BCL-2 family of proteins and now around necroptosis, are particularly well placed to prosecute this essential translational work: from biological discoveries to proof-of-concept small molecules to validate these cell death pathways as therapeutically relevant. Provided that future studies are executed with careful consideration for both the compounds and the assays to validate them, great potential to open new and innovative therapeutic avenues exists. Acknowledgement The author thanks C De Nardo for editorial assistance.
Financial & competing interests disclosure This work was supported by Project Grants (67289, 59331, 25138), and an Independent Research Institutes Infrastructure Support Scheme Grant (361646) from the Australian National Health and Medical Research Council; a de Burgh fellowship from The Walter and Eliza Hall Institute; the Australian Cancer Research Fund and a Victorian State Government Operational Infrastructure Support Grant. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript. 4
Juin P, Geneste O, Gautier F, Depil S, Campone M. Decoding and unlocking the BCL-2 dependency of cancer cells. Nat. Rev. Cancer 13(7), 455–465 (2013).
5
Kaczmarek A, Vandenabeele P, Krysko DV. Necroptosis: the release of damage-associated molecular patterns and its physiological relevance. Immunity 38(2), 209–223 (2013).
6
Murphy JM, Silke J. Ars Moriendi; the art of dying well new insights into the molecular pathways of necroptotic cell death. EMBO Rep. 15(2), 155–164 (2014).
7
Czabotar PE, Lessene G, Strasser A, Adams JM. Control of apoptosis by the BCL-2 protein family: implications for
10.4155/FMC.14.169
Editorial Lessene physiology and therapy. Nat. Rev. Mol. Cell Biol. 15(1), 49–63 (2013). 8
Kaiser WJ, Sridharan H, Huang C et al. Toll-like receptor 3-mediated necrosis via TRIF, RIP3, and MLKL. J. Biol. Chem. 288(43), 31268–31279 (2013).
16
Sun L, Wang H, Wang Z et al. Mixed lineage kinase domain-like protein mediates necrosis signaling downstream of RIP3 kinase. Cell 148(1–2), 213–227 (2012).
17
Hildebrand JM, Tanzer MC, Lucet IS et al. Activation of the pseudokinase MLKL unleashes the four-helix bundle domain to induce membrane localization and necroptotic cell death. Proc. Natl Acad. Sci. USA 111(42), 15072–15077 (2014).
9
Arkin MR, Tang Y, Wells JA. Small-molecule inhibitors of protein-protein interactions: progressing toward the reality. Chem. Biol. 21(9), 1102–1114 (2014).
10
Roy MJ, Vom A, Czabotar PE, Lessene G. Cell death and the mitochondria: therapeutic targeting of the BCL-2 familydriven pathway. Br. J. Pharmacol. 171, 1973–1987 (2014).
11
Souers AJ, Leverson JD, Boghaert ER et al. ABT-199, a potent and selective BCL-2 inhibitor, achieves antitumor activity while sparing platelets. Nat. Med. 19, 202–208 (2013).
18
12
Lessene G, Czabotar PE, Sleebs BE et al. Structure-guided design of a selective BCL-XL inhibitor. Nat. Chem. Biol. 9(6), 390–397 (2013).
Lucet IS, Babon JJ, Murphy JM. Techniques to examine nucleotide binding by pseudokinases. Biochem. Soc. Trans. 41(4), 975–980 (2013).
19
13
Gavathiotis E, Reyna DE, Bellairs JA, Leshchiner ES, Walensky LD. Direct and selective small-molecule activation of proapoptotic BAX. Nat. Chem. Biol. 8(7), 639–645 (2012).
Kuroda J, Puthalakath H, Cragg MS et al. Bim and Bad mediate imatinib-induced killing of Bcr/Abl+ leukemic cells, and resistance due to their loss is overcome by a BH3 mimetic. Proc. Natl Acad. Sci. USA 103(40), 14907–14912 (2006).
20
Baell JB. Observations on screening-based research and some concerning trends in the literature. Future Med. Chem. 2(10), 1529–1546 (2010).
14
10.4155/FMC.14.169
Lessene G, Czabotar PE, Colman PM. BCL-2 family antagonists for cancer therapy. Nat. Rev. Drug Discov. 7(12), 989–1000 (2008).
15
Degterev A, Hitomi J, Germscheid M et al. Identification of RIP1 kinase as a specific cellular target of necrostatins. Nat. Chem. Biol. 4(5), 313–321 (2008).
Future Med. Chem. (Epub ahead of print)
future science group
For reprint orders, please contact [email protected]
Future
Medicinal Chemistry
Targeting cell death pathways with small molecules: playing with life and death at the cellular level to treat diseases “Modulation of cell death is a potential game changer for the treatment of a large number of diseases.” Targeting cell death A recent review describes seven distinct cell death pathways underpinned by complex cellular cascades (hence the term ‘programmed cell death’) [1] . These multiple pathways paint an intricate picture of how a cell behaves in response to a plethora of stimuli: they speak to the ability of cells to control their number, thereby allowing multicellular organisms to remain healthy. While some of these pathways share common components (e.g., caspases, RIP kinases), others function almost independently (e.g., ferroptosis). Some have been studied for almost 30 years (e.g., apoptosis), while others have only been identified during the last few years (e.g., pyroptosis) and are, as a consequence, much less understood. One important discriminating factor between these various cell death mechanisms is the degree with which they are able to summon an immunological response: apoptosis is characterized by a ‘silent’ removal of dying cells; conversely, necroptosis leads to an inflammatory response. To add to this complexity, it has recently become clear that proteins, originally thought to be in charge of deploying cell death, have other roles, especially in modulating the immune response to cellular stresses [2] . Indeed, it has become increasingly evident that cell death and immune/inflammatory pathways are strongly embedded, rather than a distinct phenomenon [1] . Deregulation of cell death & diseases With such crucial roles in normal physiology, it is not surprising that deregulation of cell death signaling has been linked to many lifethreatening diseases [3] . This inter-relation
10.4155/FMC.14.169 © 2015 Future Science Ltd
is particularly well illustrated by the role of apoptosis in cancer: most – if not all – tumor cells develop the ability to evade apoptotic cell death [4] . This advantage allows them to abnormally survive in spite of conditions that would otherwise result in their death (DNA damage, loss of adhesion to tissue of origin, uncontrolled proliferation). However, much less is understood about the reverse situation, in other words, when excessive apoptosis occurs in healthy tissues. Yet, upregulated cell death has also been implicated in a large number of disease states including stroke, traumatic injury, macular degeneration, hearing loss and neurodegenerative disorders such as Alzheimer’s diseases; essentially, any condition that leads to the death of otherwise healthy cells, and thus causes tissue loss. Our current understanding of necroptosis in diseases suggests that it acts as a failsafe response in cases where apoptosis is blocked (e.g., after infection by pathogens that express their own apoptosis inhibitors) [5,6] . Deregulation of the biological cascade leading to necroptosis is thought to contribute to sustained inflammation, resulting, for example, in diseases such as psoriasis and rheumatoid arthritis. Similar to upregulated apoptosis, excessive cell death through necroptosis has also been linked to ischemia-reperfusion injuries and neurodegenerative diseases. A combination of these two cellular pathways – as well as others – is likely contributing to these diseases. Considering a broad range of diseases are associated with deregulated cell death, it is not surprising that significant effort from private as well as academic drug discovery groups is devoted to developing small
Future Med. Chem. (Epub ahead of print)
Guillaume Lessene ACRF Chemical Biology Division, The Walter & Eliza Hall Institute of Medical Research, 1G Royal Parade Parkville, VIC-3052, Australia and Department of Medical Biology, The University of Melbourne, VIC-3050, Australia and Department of Pharmacology & Therapeutics, The University of Melbourne, VIC-3050, Australia [email protected]
part of
ISSN 1756-8919
Editorial Lessene molecules that modulate the pathways essential to their regulation. Although these attempts have been met with various degrees of success, they are all underpinned by the substantial challenges facing medicinal chemists. These challenges can be roughly divided in two categories: medicinal chemistry, and biological validation of activity. The BCL-2 family of proteins: targeting the impossible As discussed above, apoptosis was the first programmed cell death pathway to be described and is perhaps the best characterized. The BCL-2 family of proteins are critical regulators of apoptotic cell death [7] . This family is broadly divided into two classes: proteins that promote apoptosis (pro-apoptotic) and those that block it (prosurvival). The latter comprises proteins such as BCL-2 itself (first discovered and after which the whole family is named), MCL-1 and BCL-X L . The proteins that promote cell death can be further divided into two categories: the sensors that detect and initiate the apoptotic cascade, named ‘BH3-only’ proteins (e.g., BIM, BAD and NOXA), and the pro-apoptotic proteins, BAX and BAK, that operate at the mitochondrial membrane. In response to apoptotic stimuli (e.g., extracellular stresses, DNA damage, etc.), BH3-only proteins bind and inactivate the prosurvival proteins. This interaction releases the brake on BAX and BAK leading to their multimerization at the mitochondrial membrane to form pores that allow cytochrome c to be released. This event, often called the ‘point-of-noreturn’ leads to caspase activation and cell demolition. Since upregulation of prosurvival BCL-2 prevents apoptosis functioning properly in cancer cells, strategies aimed at replicating the activity of pro-apoptotic BH3-only proteins with small molecules (the so-called ‘BH3-mimetics’) and thus re-instating cell death in cancer cells, have been actively pursued [8] . In this context, the key challenge for medicinal chemists has been the design and development of small molecules that target the protein–protein interfaces characteristic of the BCL-2-mediated apoptotic cascade [9] : these interfaces are large, shallow and mainly hydrophobic, with seemingly few anchor points to hook a small molecule. Yet, while this concept represented an immense challenge at inception, groundbreaking work by us and others has demonstrated that targeting these protein surfaces is feasible [10] . Compounds with either a broad or narrow spectrum of selectivity have been developed. Recently, published examples of selective compounds include, ABT-199 (BCL-2 selective) [11] and WEHI539 (BCL-X L-selective) [12] , which along with other validated BH3-mimetics represent milestones in drug discovery. The fact that two compounds derived from
10.4155/FMC.14.169
Future Med. Chem. (Epub ahead of print)
ABT-737 (ABT-263 and ABT-199/GDC-199) have reached the clinic and exhibit acceptable oral bioavailability, despite their size and properties, is testament that drug-like chemical space can exist outside the current Lipinski rules. As for many other modern drug discovery programs, these achievements are made possible through convergence of modern drug discovery techniques, such as X-ray crystallography, molecular modeling, structure-based drug design and fragmentbased drug discovery. However, limitations remain, especially in our ability to predict the position of areas of flexibility on the surface of proteins where small molecules may interact. Blocking cell death Comparatively, strategies aimed at blocking cell death have lagged significantly. Early on, caspases presented attractive targets as they were key effectors of downstream apoptosis and had a defined enzymatic pocket with druggable features. Caspase inhibitors have now reached the clinic but their efficacy has failed to match initial expectations; the reasons for which vary: Blocking caspase enzymatic activity at a cellular level is very challenging, due to the exponential nature of the activation signaling cascade (upstream caspases activating downstream caspases); Once caspases are activated, dying cells have already reached the point-of-noreturn. This raises questions about the rationale of rescuing cells that are essentially already dead; developing selectivity within caspase inhibitors is extremely challenging; finally, there is growing evidence that caspases contribute to other biological pathways. Blocking cell death upstream of the mitochondria by inhibiting BAX and/or BAK appears a more convincing strategy since it provides the enormous advantage of keeping cells viable. However, this presents another protein–protein inhibition challenge compounded by the fact that these two proteins act at the mitochondrial membrane. Moreover, it is not clear whether small molecules binding to BAX/BAK will activate or inhibit apoptosis. Only a handful of compounds targeting BAX/BAK have been described, but overall their activity remains weak and their mode of action is questionable [13] . Due to its potential involvement in chronic inflammation and the fact that a specific cellular mechanism controls it, necroptosis has attracted a rapid and growing interest [1] . Small molecule inhibitors of key signaling proteins involved in the regulation of necroptosis have been disclosed: these include the well-known RIP1 inhibitor, necrostatin [14] , RIP3 inhibitors [15] and more recently, small molecules that block MLKL [16,17] , the last known effector in the pathway. MLKL belongs to the intriguing class of pseudo-kinases
future science group
Targeting cell death pathways with small molecules
(kinase-like proteins) that have lost part or all of their ability to process ATP [18] ; they act more as scaffolding proteins or, like MLKL, as death-effector proteins. Pseudo-kinases in general, and MLKL in particular, represent very compelling drug discovery targets with more classical features. It is likely that proof-of-concept compounds will emerge in the near future that will help validate necroptosis as a bona fide therapeutic target in multiple diseases. The biology challenge: determining on-target activity Beyond the difficulties associated with designing and developing small molecules directed at challenging targets such as the BCL-2 proteins, the field of cell death drug discovery faces another problem: validation of the mode-of-action of compounds that directly impact on cell pathways is difficult. As discussed, signaling pathways regulating cell death, such as the BCL-2 family protein cascade or the RIP1/RIP3/MLKL axis for necroptosis, lie at the focal point of numerous biological pathways that can be activated for any number of reasons. The ability of a small molecule to induce cell death does not mean that it targets the cell death machinery directly. A particularly good example of this conundrum is the activity of the anticancer small molecule, Gleevec, which has been shown to rely on functional BCL-2-driven apoptosis [19] . Thus, cell death induced by Gleevec is apoptotic in nature and BCL-2 family driven, yet it does not interact directly with any of the components of this pathway. In the context of apoptosis, we have previously delineated a number of criteria to guide medicinal chemists during their mechanism of action studies [8] . Still, too many so-called ‘BCL-2 inhibitors’ or ‘BH3-mimetics’ continue to appear in the literature with poorly characterized mode-of-action, if not outright Pan-Assay Interferences Compounds (PAINS) [20] . Validation of compounds inducing apoptosis is a case in point and highlights the fact that carefully chosen reagents and cellular tools are particularly indispensable in this field. Although certain cell lines and binding assays References 1
2
3
Linkermann A, Stockwell BR, Krautwald S, Anders H-J. Regulated cell death and inflammation: an autoamplification loop causes organ failure. Nat. Rev. Immunol. 14(11), 759–767 (2014). White MJ, McArthur K, Metcalf D et al. Caspases render apoptosis immunologically silent by suppressing mtDNAinduced STING-mediated type I IFN production. Cell 159(7), 1549–1562 (2014). Hotchkiss RS, Strasser A, McDunn JE, Swanson PE. Cell death. N. Engl. J. Med. 361(16), 1570–1583 (2009).
future science group
Editorial
are available and have been described in the literature, important tools, such as a good assay to phenotypically discriminate between various forms of cell death, are yet to be developed. Outlook Modulation of cell death is a potential game changer for the treatment of a large number of diseases. Recent discoveries are confirming the link between the immune response and cell death. This editorial has highlighted examples specifically related to apoptosis and necroptosis, but other more recently identified forms of programmed cell death, will further unravel novel therapeutic targets. Academic institutions such as the Walter and Eliza Hall Institute, where seminal discoveries have been made around the BCL-2 family of proteins and now around necroptosis, are particularly well placed to prosecute this essential translational work: from biological discoveries to proof-of-concept small molecules to validate these cell death pathways as therapeutically relevant. Provided that future studies are executed with careful consideration for both the compounds and the assays to validate them, great potential to open new and innovative therapeutic avenues exists. Acknowledgement The author thanks C De Nardo for editorial assistance.
Financial & competing interests disclosure This work was supported by Project Grants (67289, 59331, 25138), and an Independent Research Institutes Infrastructure Support Scheme Grant (361646) from the Australian National Health and Medical Research Council; a de Burgh fellowship from The Walter and Eliza Hall Institute; the Australian Cancer Research Fund and a Victorian State Government Operational Infrastructure Support Grant. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript. 4
Juin P, Geneste O, Gautier F, Depil S, Campone M. Decoding and unlocking the BCL-2 dependency of cancer cells. Nat. Rev. Cancer 13(7), 455–465 (2013).
5
Kaczmarek A, Vandenabeele P, Krysko DV. Necroptosis: the release of damage-associated molecular patterns and its physiological relevance. Immunity 38(2), 209–223 (2013).
6
Murphy JM, Silke J. Ars Moriendi; the art of dying well new insights into the molecular pathways of necroptotic cell death. EMBO Rep. 15(2), 155–164 (2014).
7
Czabotar PE, Lessene G, Strasser A, Adams JM. Control of apoptosis by the BCL-2 protein family: implications for
10.4155/FMC.14.169
Editorial Lessene physiology and therapy. Nat. Rev. Mol. Cell Biol. 15(1), 49–63 (2013). 8
Kaiser WJ, Sridharan H, Huang C et al. Toll-like receptor 3-mediated necrosis via TRIF, RIP3, and MLKL. J. Biol. Chem. 288(43), 31268–31279 (2013).
16
Sun L, Wang H, Wang Z et al. Mixed lineage kinase domain-like protein mediates necrosis signaling downstream of RIP3 kinase. Cell 148(1–2), 213–227 (2012).
17
Hildebrand JM, Tanzer MC, Lucet IS et al. Activation of the pseudokinase MLKL unleashes the four-helix bundle domain to induce membrane localization and necroptotic cell death. Proc. Natl Acad. Sci. USA 111(42), 15072–15077 (2014).
9
Arkin MR, Tang Y, Wells JA. Small-molecule inhibitors of protein-protein interactions: progressing toward the reality. Chem. Biol. 21(9), 1102–1114 (2014).
10
Roy MJ, Vom A, Czabotar PE, Lessene G. Cell death and the mitochondria: therapeutic targeting of the BCL-2 familydriven pathway. Br. J. Pharmacol. 171, 1973–1987 (2014).
11
Souers AJ, Leverson JD, Boghaert ER et al. ABT-199, a potent and selective BCL-2 inhibitor, achieves antitumor activity while sparing platelets. Nat. Med. 19, 202–208 (2013).
18
12
Lessene G, Czabotar PE, Sleebs BE et al. Structure-guided design of a selective BCL-XL inhibitor. Nat. Chem. Biol. 9(6), 390–397 (2013).
Lucet IS, Babon JJ, Murphy JM. Techniques to examine nucleotide binding by pseudokinases. Biochem. Soc. Trans. 41(4), 975–980 (2013).
19
13
Gavathiotis E, Reyna DE, Bellairs JA, Leshchiner ES, Walensky LD. Direct and selective small-molecule activation of proapoptotic BAX. Nat. Chem. Biol. 8(7), 639–645 (2012).
Kuroda J, Puthalakath H, Cragg MS et al. Bim and Bad mediate imatinib-induced killing of Bcr/Abl+ leukemic cells, and resistance due to their loss is overcome by a BH3 mimetic. Proc. Natl Acad. Sci. USA 103(40), 14907–14912 (2006).
20
Baell JB. Observations on screening-based research and some concerning trends in the literature. Future Med. Chem. 2(10), 1529–1546 (2010).
14
10.4155/FMC.14.169
Lessene G, Czabotar PE, Colman PM. BCL-2 family antagonists for cancer therapy. Nat. Rev. Drug Discov. 7(12), 989–1000 (2008).
15
Degterev A, Hitomi J, Germscheid M et al. Identification of RIP1 kinase as a specific cellular target of necrostatins. Nat. Chem. Biol. 4(5), 313–321 (2008).
Future Med. Chem. (Epub ahead of print)
future science group
