Pharmacological modulation of autophagy- therapeutic potential and persisting obstacles.pdf

Pharmacological modulation of autophagy:therapeutic potential and persisting obstaclesLorenzo Galluzzi1,2,*,Jos Manuel Bravo-San Pedro2,3,4,5,6,*,Beth Levine7,8,Douglas R.Green9,and Guido Kroemer2,3,4,5,6,10,111Department of Radiation Oncology,Weill Cornell Medical College,New York,New York 10065,USA2Universit Paris Descartes/Paris V,Sorbonne Paris Cit,Paris 75006,France3Universit Pierre et Marie Curie/Paris VI,Paris 75006,France4Equipe 11 labellise Ligue contre le Cancer,Centre de Recherche des Cordeliers,Paris 75006,France5INSERM,U1138,Paris 75006,France6Metabolomics and Cell Biology Platforms,Gustave Roussy Comprehensive Cancer Institute,Villejuif 94805,France7Center for Autophagy Research,University of Texas Southwestern Medical Center,Dallas,Texas 75390,USA8Howard Hughes Medical Institute,Dallas,Texas 75390,USA9St Jude Childrens Research Hospital,Memphis,Tennessee 38105,USA10Karolinska Institute,Department of Womens and Childrens Health,Karolinska University Hospital,Stockholm 17176,Sweden11Ple de Biologie,Hopitl Europen George Pompidou(AP-HP),Paris 75015,FranceAbstractAutophagy is central to the maintenance of organismal homeostasis in both physiological and pathological situations.Accordingly,alterations in autophagy have been linked to clinically relevant conditions as diverse as cancer,neurodegeneration and cardiac disorders.Throughout the past decade,autophagy has attracted considerable attention as a target for the development of novel therapeutics.However,such efforts have not yet generated clinically viable interventions.In this Review,we discuss the therapeutic potential of autophagy modulators,analyse the obstacles that have limited their development and propose strategies that may unlock the full therapeutic potential of autophagy modulation in the clinic.Correspondence to L.G.deadocvodafone.it.*These authors contributed equally to this work.Competing interests statementThe authors declare no competing interests.Publishers noteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.HHS Public AccessAuthor manuscriptNat Rev Drug Discov.Author manuscript;available in PMC 2017 December 04.Published in final edited form as:Nat Rev Drug Discov.2017 July;16(7):487511.doi:10.1038/nrd.2017.22.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor ManuscriptAutophagy is a highly conserved mechanism through which eukaryotic cells deliver dispensable or potentially dangerous cytoplasmic material to lysosomes for degradation1.Thus far,three major routes for the delivery of autophagic substrates to lysosomes have been characterized:microautophagy,chaperone-mediated autophagy(CMA)and macroautophagy.Microautophagy relies on the direct uptake of cytoplasmic material through an invagination of the lysosomal membrane2.CMA involves the lysosomal-associated membrane protein 2(LAMP2)-dependent translocation of autophagic substrates bound to cytosolic chaperones of the heat shock protein family across the lysosomal membrane3.Macroautophagy involves specialized double-membraned vesicles known as autophagosomes,which progressively sequester autophagic cargo and upon closure deliver the cargo to lysosomes by membrane fusion1.The organelle that forms upon the fusion of one autophagosome and one lysosome is generally referred to as an autolysosome1.Macroautophagy is by far the best-characterized form of autophagy.For this reason,the word autophagy is used throughout this article to refer to macroautophagy,unless otherwise specified.Autophagy is fundamental to the preservation of organismal fitness,for multiple reasons.Constitutive autophagic responses efficiently degrade products of normal cellular metabolism that can become cytotoxic upon accumulation,such as damaged mitochondria and redox-active protein aggregates4.Inducible autophagic responses promote the survival of cells that respond to perturbations of intracellular or extracellular homeostasis5.Autophagy is indeed central to adaptation to stress,as demonstrated by the fact that pharmacological or genetic inhibition of autophagy usually precipitates the demise of cells facing infections and nutritional,metabolic,physical and chemical challenges6.Furthermore,autophagy is intimately connected with cell-extrinsic circuitries that operate to maintain homeostasis and support healthy ageing at the whole-body level.For instance,autophagic responses in the liver,skeletal muscle and other tissues underlie the beneficial effects of physical exercise on whole-body glucose metabolism7.Along similar lines,autophagy induction in malignant cells that succumb to some chemotherapies and radiotherapies results in the emission of danger signals and,ultimately,the initiation of a therapeutically relevant anticancer immune response8.Autophagy can also mediate cytotoxic effects,at least in specific pathophysiological settings9,although the term autophagic cell death should be used with extreme caution(BOX 1).Moreover,components of the autophagic apparatus have recently been shown to participate in processes other than the degradation of cytoplasmic material.These processes include:LC3-associated phagocytosis(LAP)10(BOX 2),migration(mainly as a result of focal adhesion turnover)11 and unconventional secretion,which is a mechanism by which cytoplasmic entities(including soluble proteins,organellar material and pathogens)are exported from the cell in a manner that does not depend on the conventional secretory route that operates between the endoplasmic reticulum and the Golgi apparatus12.The detailed description of the molecular machinery that underlies constitutive and inducible autophagic responses is beyond the scope of this Review(BOX 2).However,it should be noted that the biochemical reactions that enable the generation of autophagosomes,the Galluzzi et al.Page 2Nat Rev Drug Discov.Author manuscript;available in PMC 2017 December 04.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor Manuscriptrecognition of autophagic substrates,their sequestration and the delivery of autophagic cargo to lysosomes for degradation involve at least 100 different proteins1.Thus,they provide multiple targets for the activation or inhibition of autophagy(FIG.1).Although alterations in autophagy have been implicated in the aetiology of neurodegeneration,acute neuronal injury,ageing,cardiovascular conditions,hepatic and metabolic disorders,cancer,infectious diseases,inflammatory and autoimmune conditions,and other pathological conditions(as discussed below),no intervention aimed specifically at modulating autophagy is currently available for use in humans(TABLE 1).Indeed,although rapamycin(also known as sirolimus),chloroquine,hydroxychloroquine(HCQ)and other drugs that are approved for some indications stimulate or inhibit autophagy,they were not developed for this purpose.Thus,there is considerable,but still unrealized,potential for translating preclinical findings on autophagy modulation into therapeutic benefit for different patient populations13.Notably,the key role of autophagy in cell biology and its considerable therapeutic potential recently received one of the most important forms of recognition from the scientific community as the Japanese cell biologist Yoshinori Ohsumi was awarded the 2016 Nobel Prize in Physiology or Medicine for his discoveries on the mechanisms of autophagy.Here,we discuss recent progress on the therapeutic potential of pharmacological and nutritional modulators of autophagy,dissect the obstacles that have limited the development of these interventions thus far,and propose strategies by which such hurdles may be circumvented in the near future to obtain clinically relevant interventions for a variety of human disorders.Autophagy as a therapeutic targetWhole-body knockout studies in mice have demonstrated that specific components of the autophagic machinery are required for embryonic development or are critical for animals to survive birth and reach adulthood1416.Three main approaches have been pursued as alternatives to the use of whole-body knockout mice to study the role of autophagy in physiology and disease:the generation of animals with partial autophagic defects at the whole-body level(such as Becn1+/mice);the engineering of tissue-specific or inducible knockout models;and the restoration of autophagic activity in key organs(such as the central nervous system(CNS)in animals with whole-body autophagic defects17.Results obtained with these models have implicated alterations of autophagy or autophagy-associated processes in a wide range of clinically relevant disorders(as discussed below),which supports the possibility that pharmacological modulators(activators or inhibitors)of autophagy may be beneficial for large patient populations.NeurodegenerationThe deletion of autophagy-related 5(Atg5)or Atg7 in the mouse CNS during embryonic development results in the delivery of viable pups that survive birth,but develop progressive motor and behavioural deficits starting at 3 weeks of age18,19.The cortex and cerebellum of these animals exhibit swelling,markers of regulated cell death(RCD)and ubiquitin-containing inclusions18,19,which are pathological hallmarks of various neurodegenerative disorders,including Alzheimer disease(AD),Parkinson disease(PD),Galluzzi et al.Page 3Nat Rev Drug Discov.Author manuscript;available in PMC 2017 December 04.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor Manuscriptdementia with Lewy bodies(DLB),Huntington disease(HD),amyotrophic lateral sclerosis(ALS)and Lafora disease20.Autophagy robustly protects neurons from RCD by preventing the accumulation of cytotoxic protein aggregates and by preserving metabolic homeostasis21.In line with this idea,markers of impaired autophagy such as activation of mechanistic target of rapamycin(mTOR),autophagosome accumulation and limited degradation of sequestosome 1(SQSTM1;also known as p62)have been detected in samples from patients with multiple forms of neurodegeneration22.Moreover,many of the genes that are mutated in familiar variants of PD including parkin RBR E3 ubiquitin protein ligase(PARK2),Parkinsonism-associated deglycase(PARK7),PTEN-induced putative kinase 1(PINK1)and leucine-rich repeat kinase 2(LRRK2)are involved in mitophagy or aggrephagy23,24.Furthermore,AD-associated variants of presenilin 1(PSEN1)block autophagy as a result of impaired lysosomal acidification25;mutations in SQSTM1,optineurin(OPTN,which encodes another autophagic adaptor)and TANK-binding kinase 1(TBK1,which encodes a regulator of both p62 and OPTN)are common among individuals with familial and sporadic ALS2628;and both laforin glucan phosphatase(EPM2A)and NHL repeat-containing E3 ubiquitin protein ligase 1(NHLRC1),which are mutated in individuals with Lafora disease,also seem to promote autophagy29.Finally,mutations in WD repeat domain 45(WDR45)which encodes an ATG9 interactor of the WD repeat domain phosphoinositide-interacting(WIPI)family have been shown to be involved in the pathogenesis of static encephalopathy of childhood with neurodegeneration in adulthood,which is a rare neurological disorder30.Interventions that promote autophagy or autophagy-associated processes have been shown to mediate beneficial effects in animal models of neurodegeneration.Alzheimer diseaseAdministration of the mTOR inhibitor rapamycin which potently activates autophagy ameliorates cognitive deficits and alleviates the accumulation of-amyloid in mice expressing mutant myloid-precursor protein(APP)31 as well as in 3xTg-AD mice(which bear three distinct genetic alterations that are associated with AD in humans)32.Along similar lines,resveratrol,which is a natural polyphenol that promotes autophagy by operating as a caloric restriction mimetic(CRM),decreased-amyloid overload in mice expressing a chimeric variant of mutant APP and AD-associated human PSEN1.This effect was ascribed to the AMP-activated protein kinase(AMPK)-dependent inhibition of mTOR complex 1(mTORC1)33(BOX 2).Of note,behavioural alterations that develop in mice engineered to express one or several APP mutations that are linked to AD in humans could also be ameliorated by the concomitant deletion of genes that encode endogenous inhibitors of lysosomal proteases,such as cystatin B(Cstb)or cystatin C(Cst3)34,35.ParkinsonismThe intracerebral injection of a lentiviral vector encoding ATG7 or BECN1 decreases neuronal inclusions in synuclein-(SNCA)-expressing mice(a model of PD and DLB),and this has been associated with reduced neurodegeneration22,36.Along similar lines,the intracerebral administration of an adenoviral vector encoding BECN1 or transcription factor EB(TFEB)which is a master transcriptional regulator of autophagy and lysosomal functions to rats expressing SNCA in the brain limited the accumulation Galluzzi et al.Page 4Nat Rev Drug Discov.Author manuscript;available in PMC 2017 December 04.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor Manuscriptof SNCA aggregates within dopaminergic neurons and prevented behavioural impairment37.Comparable results have been obtained by activating autophagy with systemic or intracerebral administration of rapamycin,trehalose or valproate in several mouse models of PD and DLB,including SNCA-expressing mice22,mice expressing mutant Park2(REF.38),Park2/mice expressing human microtubule-associated protein tau(MAPT)39 as well as mice or rats that develop parkinsonism upon administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)4042,6-hydroxydopamine(6-OHDA)43,44 or lactacystin45.Rapamycin also alleviated neurotoxicity in Drosophila melanogaster with mutations in parkin(park;the fly orthologue of human PARK2)or Pink1(REF.46)as well as in flies treated with the dopaminergic toxin paraquat47.Of note,defects in late-stage autophagy leading to PD-like and DLB-like disorders in mice have also been ascribed to loss of type I interferon signalling48.Accordingly,intracerebral interferon 1(Ifnb1)delivery by a lentiviral vector boosted autophagy and limited the loss of dopaminergic neurons in rats expressing human SNCA in the brain48.These findings identify cytokine signalling as a potential target for the treatment of PD and DLB through the induction of autophagy.Interestingly,defects in CMA may also be implicated in the development of PD and DLB,as was demonstrated recently in rats49.Whether boosting CMA ameliorates the manifestations of disease in animal models of parkinsonism remains to be elucidated.Huntington diseaseIn flies and mice expressing HD-associated variants of human huntingtin,rapamycin(and other mTOR inhibitors,including temsirolimus and everolimus)alone or combined with lithium exerts considerable neuroprotective effects,as has been determined histologically and in behavioural tests50,51.However,the adenovirus-mediated intracerebral delivery of either of two mTORC1 activators namely,RASD family member 2(RASD2;also known as RHES)and RAS homo