Therapeutic modulation of autophagy which dise.pdf

Cell Death&Differentiation(2019)26:680689https:/doi.org/10.1038/s41418-019-0290-0REVIEW ARTICLETherapeutic modulation of autophagy:which disease comes first?Maria Chiara Maiuri1,2,3,4,5Guido Kroemer2,3,4,5,6,7Received:11 January 2019/Accepted:11 January 2019/Published online:6 February 2019 ADMC Associazione Differenziamento e Morte Cellulare 2019AbstractThe relentless efforts of thousands of researchers have allowed deciphering the molecular machinery that regulates andexecutes autophagy,thus identifying multiple molecular targets to enhance or block the process,rendering autophagy“druggable”.Autophagy inhibition may be useful for preserving the life of cells that otherwise would succumb toexcessive self-digestion.Moreover,autophagy blockade may reduce the fitness of cancer cells or interrupt metaboliccircuitries required for their growth.Autophagy stimulation is probably useful for the prevention or treatment of aging,cancer(when stimulation of immunosurveillance is the therapeutic goal),cardiovascular disease,cystic fibrosis,infection by intracellular pathogens,obesity,and intoxication by heavy metals,just to mention a few examples.Epidemiological evidence suggests broad health-improving effects for lifestyles,micronutrients,and drugs that favorautophagy.In this review,we discuss the role of autophagy in disease pathogenesis while focusing on the question,which disease will become the first clinically approved indication for therapeutic autophagy modulation.FactsAutophagy is one of the best-studied phenomena in cellbiology.Drugs for enhancing or inhibiting general orspecific autophagy are being developed.Acquiredorgeneticallydeterminedalterationsinautophagic flux are involved in multiple pathologiesacross the entire spectrum of human diseases.Autophagy inhibition might be useful for the avoidanceof unwarranted autophagy-dependent cell death.Chronic autophagy stimulation has a positive impact onpreclinical models of aging and multiple distinct age-dependent diseases,including arteriosclerosis,cancer,and neurodegeneration.Acute autophagy stimulationalso has organ-protective effects in models of ischemiaor intoxication.Open questionsOptimal pharmacological agents that modulate autop-hagy at the expense of acceptable side effects must beselected and characterized at the preclinical level.For autophagy induction,it remains to be determinedwhether pharmacological agents are superior to life styleinterventions(quantity and quality of nutrition,physicalexercise)for long-term benefits.The question remains open,which particular disease willbe the first-in-human indication for clinical trials thatexplore pharmacological autophagy modulators.IntroductionThe final fate of cells is death,while that of cytoplasmicorganelles is macroautophagy 1,2.For this reason,manyEdited by G.Melino*Maria Chiara Maiurichiara.maiuricrc.jussieu.fr*Guido KroemerKroemerorange.fr1Equipe 11 labellise par la Ligue contre le Cancer,Centre deRecherche des Cordeliers,75006 Paris,France2Cell Biology and Metabolomics Platforms,Gustave RoussyCancer Campus,94805 Villejuif,France3INSERM U1138,75006 Paris,France4Universit Paris Descartes,Sorbonne Paris Cit,75006 Paris,France5Sorbonne Universit,75006 Paris,France6Ple de Biologie,Hpital Europen Georges Pompidou,AP-HP,75015 Paris,France7Karolinska Institute,Department of Womens and ChildrensHealth,Karolinska University Hospital,17176 Stockholm,Sweden1234567890();,:1234567890();,:scientists that started their carrier on cell death switched thefocus of their work to macroautophagy(hitherto“autop-hagy”).This move from one area of research to another hasalso been motivated by the ambiguous effect of autophagyon cell death.On one hand,autophagy constitutes a formidable processallowing cells to adapt to changing and stressful conditionsbyremovingdamagedsubcellularstructuresandbydigesting macromolecules to small molecules that then caneither be used to fuel bioenergetics or to rebuild neworganelles,thus rejuvenating the cytoplasm 3 and perhapseven the nuclear envelope and nucleoli 4.For this reason,autophagy is viewed as a major anti-aging mechanism that,if stimulated in an adequate fashion at the whole-body level,may enhance health span and longevity 57.Regrettably,autophagy may also enhance the fitness of cancer cells thatattempt to strive in a hostile microenvironment,thusresisting endogenous stressors(absence of trophic support,hypoxia,and attack by the immune system)or therapeuticmeasures(chemotherapy,radiotherapy,or targeted therapy)8,9.Moreover,autophagy may be important for main-taining the pool of cancer stem cells 10.Given the cyto-protectiveactionofautophagy,scientistshavebeenreasoning that autophagy should be stimulated when thegoal is the preservation of normal cellular or organismalfunctions 5,6,but inhibited when the goal is the treatmentof cancer 8,9.On the other hand,deregulated autophagy may partici-pate in the destruction of cells,be it during normaldevelopment(to get rid of superfluous cells,especially inmodel organisms)11 or in response to environmentalstress 12,13.Although nowadays the first idea(autop-hagy improving cellular fitness)largely dominates over thesecond one(autophagy as a cell death mechanism),thereare indeed instances in mammalian pathophysiology inwhich excessive autophagy may destroy neurons(forinstance in neonatal ischemia)14,15 or cardiomyocytes(in hypoxiaischemia)16,17.In this context,suppres-sion of autophagy may protect specific cell types againstdeath,calling for the development of cytoprotectiveautophagy inhibitors.In view of the disease-modulatory potential of autop-hagy,scientists working in academia,biotechnology,orpharmaceutical industry are developing pharmacologicalautophagy inhibitors and inducers 18,19.This effort isencouraged by the increasingly accepted notion that thedisease-preventive or therapeutic effects of some widelyused drugs and food components can be explained byautophagy stimulation,as exemplified for aspirin 20,resveratrol 21,and spermidine 22,23.In theory,thereare multiple molecularly defined targets to suppress autop-hagy(each of the essential autophage gene ATG-encodedproteins)and to enhance autophagy(by targeting each ofthe numerous endogenous inhibitors of autophagy).Pro-minent pharmacological targets for autophagy inhibitioninclude proteases(such as the ATG4 isoenzymes requiredfor the proteolytic maturation of LC3 family proteins),lipidkinases(in particular,phosphatidylinositol 3-kinase cataly-tic subunit type 3,PIK3C3,which acts within the Beclin 1,BECN1,complex)and protein kinases(especially,Unc-51-like autophagy activating kinase 1,ULK1)19,24.Drug-gable targets to enhance autophagic flux include a series ofnegative regulators of autophagy such as multidomainproteins of the BCL-2 family(which can be targeted by so-called BH-3 mimetics and perhaps other agents that disrupttheir inhibitory interaction with the Beclin 1/PIK3C3complex)2528,the acetyltransferase E1A binding pro-tein P300(EP300,which is already known as the target ofaspirin and spermidine)20,29,the mammalian target ofrapamycin complex 1(MTORC1,which is inhibited byrapamycin and rapalogs),as well as kinases acting upstreamof MTORC1 such as the members of the phosphatidylino-sitol-4,5-bisphosphate 3-kinase(PI3K)and protein kinase B(PKB)families 19,30.However,this list is not exhaustiveand other potential targets for autophagy modulation mustbe considered.In this article,we will provide an opinionated overviewon the diseases that might be treated by autophagy-modulatory drugs,while polemically centering our focuson the following question.Which will be the first disease(s)to be treated with new drugs designed to enhance or reduceautophagy?Prime indications for autophagy inhibitionAs mentioned above in the Introduction,there are twopossible indications for inhibiting autophagy:(i)autophagy-dependent cell death and(ii)cancer(Fig.1a).Autophagy-dependent cell deathCell death is often preceded by signs of autophagy,anobservation that led to the common belief that autophagywould constitute a major cell death modality(“type-2 celldeath”)31,32.However,when autophagy is inhibited byspecific(i.e.,genetic)methods,it turned out that,in mostcases,autophagy is not necessary for lethality but ratheracts as a cytoprotective mechanisms,hence increasing theresistance of cells to fatal stimuli and avoiding or post-poning their death 33,34.There are several notableexceptions to this rule.In model organisms,abolition ofautophagy can affect the developmental death of some celltypes,contrasting though with the observation that com-plete invalidation of conventional autophagy does notcause any developmental perturbations in mice 11.Therapeutic modulation of autophagy:which disease comes first?681Moreover,in human or mouse cell cultures responding tospecific stimuli,cell death may be favored by autophagy(as a process)or by the expression of ATG proteins,meaning that autophagy inhibition or depletion/deletion ofATG gene products increases the resistance of the cells topotentially lethal insults 12,16.Thus,in mouse models,genetic inhibition of autophagy may reduce motorneuronloss in amyotrophic lateral sclerosis 35,as well as cere-bral damage after neonatal asphyxiation 14.Moreover,cardiac glycosides(CGs)can inhibit“autosis”,a peculiarautophagy-dependent cell death modality characterized bycytoplasmic vacuolization and separation of the nuclearenvelope from the nucleus 36.The precise molecularmechanisms through which autosis is inhibited by CGremains elusive,although it can be recapitulated by geneticinterventions on the Na+,K+-ATPase,the molecular targetof CG 16.Notwithstanding this limitation,it is temptingto speculate that the well-known cardioprotective effects ofCG are not only due to a positive inotropic action but mayalso involve cytoprotection through the suppression ofexcessive autophagy.Indeed,administration of CG canprevent ischemic lesions to the myocardium in mice 16.Nonetheless,during recent years CGs have been largelyreplaced by other drugs,mainly due to safety concerns.Hence,it remains to be seen whether their recently dis-covered capacity to inhibit autosis will favor their reintro-duction into the clinics.CancerMalignant cells can be considered as abnormally fit cells thathaveescapedfromcell-autonomoustumor-suppressivemechanisms,as well as from immunosurveillance.Althoughthe inhibition of autophagy can stimulate oncogenesis,espe-cially at the initial steps 3739,it has been observed inseveral instances that autophagy inhibition reduces the growthof advanced cancers 9,40.Thus,inducible knockout of Atg7specifically within cancer cells(as opposed to stromal cells)reduces the growth of lung and pancreas cancers induced byoncogenic KRAS and inactivation of the tumor-suppressorTP53 41,42.There are multiple reports showing that inhi-bition of autophagy using chloroquine or hydroxychloroquinemay sensitize tumors to chemotherapy either in vitro orin vivo 43,44.However,chloroquine and its derivativescannot be considered as specific autophagy inhibitors(theyactually mediate autophagy-independent cytotoxicity due totheir lysosome-disrupting effects),shedding doubts on thequestion whether these anticancer effects are truly mediatedby autophagy suppression 45,46.Beyond the cancer cells themselves,autophagy in othercell types may also contribute to tumor progression.Thus,knockout of ATG genes in endothelial cells can retardtumor angiogenesis 47,whereas inhibition of autophagyin cancer-associated fibroblasts interrupts trophic supportto malignant cells 48.One recent report shows that aninducible total-body knockout of Atg7 triggers majorchanges in metabolism including an increase in the hepaticrelease of arginase 1(ARG1),causing a reduction inextracellularargininelevelsandconsequentgrowthreduction of arginine auxotroph cancers 49.This suggeststhat a global(rather than cancer cell-specific)inhibition ofautophagy may be used for the treatment of neoplasia.Thatsaid,the inducible deletion of Atg7 from the mouse gen-omecausesageneraltissue-degenerativephenotypeaffecting all organs and causing death due to brain dys-function within approximately 6 weeks 41.It remains tobe determined whether temporary,partial,or intermittentinhibition of autophagy obtained by pharmacologicalagents can avoid the manifestation of such an acceleratedaging phenotype,yet conserve antitumor efficacy in vivo(Fig.1b).Prime indications for autophagy inductionAutophagy induction can be most easily obtained byreduced caloric intake and exercise,yet can also beFig.1 Indications for autophagy inhibition.a Hypothetical desirableand side effects of autophagy inhibition are shown in green and red,respectively.b For reducing unacceptable side effects,it may benecessary to administer autophagy inhibitors at a reduced dose and inshort-term or intermittent schedules682M.C.Maiuri,G.Kroemerstimulated by“caloric restriction mimetics(CRMs)”andother pharmacological agents 19,50.There are a numberofpathologicalconditionsthatfavorablyrespondtoautophagy enhancement(Fig.2).AgingIn model organisms like yeast,nematodes,and fruit flies,there is overwhelming evidence that any kind of beha-vioral,nutritional,pharmacological,and genetic manip-ulation capable of extending longevity induces an increasein autophagic flux and actually requires autophagy to beefficient 51,52.Similarly,in mice,it is sufficient tooverexpress ATG5 as a transgene 53 or to introduce again-of-function mutant of BECN1(encoding a BECN1proteinthatdoesnotinteractanymorewiththeautophagy-inhibitory protein BCL-2)54 to induce anincrease in health span and lifespan.Treatment of micewith autophagy inducers including rapamycin(an inhi-bitor of MTORC1)or spermidine(an inhibitor of EP300)has a positive impact on life expectancy as well 22,55.Epidemiological observations in humans confirm thathigh nutritional spermidine uptake reduces mortality fromcancer,cardiovascular disease,and other causes 56,57.Hence,spermidine might be used as a safe food supple-ment to reduce aging and to postpone the manifestationsof age-related diseases.At this stage,however,it remainsto be seen whether this type of intervention would besufficiently lucrative for pharmaceutical companies tostimulate prospective clinical trials in this area.Moreover,aging is not yet considered as a disease,meaningthat neither the Federal Drug Administration(FDA)northe European Medical Agency(EMA)would authorizethis kind of clinical trial to be launched,unless it woulddeal with the prevention or treatment of a particularpathology.Anticancer immunosurveillanceWe have given large room to the hypothesis that autophagyshould be inhibited for the treatment of cancer(see above).However,there are also arguments in favor of the contrary,i.e.,autophagy stimulation for cancer treatment.Thisdebateshould we inhibit or enhance autophagy for cancertreatment?is fueled by rather distinct visions of tumorpathogenesis.Indeed,most cell biologists have beenadhering to