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The role of autophagy, a process in which the cell self-digests its own components, was investigated in glioma cell death induced by the hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase-inhibiting drug simvastatin. Induction of autophagy and activation of autophagy-regulating signalling pathways were analyzed by immunoblotting. Flow cytometry/fluorescent microscopy was used to assess autophagy-associated intracellular acidification and apoptotic markers (phosphatidylserine exposure, DNA fragmentation and caspase activation). Cell viability was determined by crystal violet, MTT or LDH release assay. Simvastatin treatment of U251 and C6 glioma cell lines caused the appearance of autophagolysosome-like intracytoplasmic acidic vesicles. The induction of autophagy in U251 cells was confirmed by the upregulation of autophagosome-associated LC3-II and pro-autophagic beclin-1, as well as by the downregulation of the selective autophagic target p62. Simvastatin induced the activation of AMP-activated protein kinase (AMPK) and its target Raptor, while simultaneously downregulating activation of Akt. Mammalian target of rapamycin (mTOR). a major AMPK/Akt downstream target and a major negative autophagy regulator, and its substrate p70 S6 kinase 1 were also inhibited by simvastatin. Mevalonate, the product of HMG-CoA reductase enzymatic activity, AMPK siRNA or pharmacological inactivation of AMPK with compound C suppressed, while the inhibitors of Akt (10-DEBC hydrochloride) and mTOR (rapamycin) mimicked autophagy induction by simvastatin. Inhibition of autophagy with bafilomycin A1, 3-methyladenine and LC3 beta shRNA, as well as AMPK inhibition with compound C or AMPK siRNA, markedly increased apoptotic death of simvastatin-treated U251 cells. These data suggest that inhibition of AMPK-depenclent autophagic response might sensitize glioma cells to statin-induced apoptotic death. (C) 2011 Elsevier Ltd. All rights reserved. Ministry of Science and Technological Development of the Republic of Serbia [41025, 173053]

Anticancer activities of various extracts of the medicinal mushroom, Ganoderma lucidum, have been widely demonstrated and are mainly associated with the presence of different bioactive polysaccharides and triterpenoids. We have evaluated and compared in vitro and in vivo the antitumor effects of two preparations from Ganoderma lucidum: a methanol extract containing total terpenoids (GLme) and a purified methanol extract containing mainly acidic terpenoids (GLpme). Both extracts inhibited tumor growth of B16 mouse melanoma cells inoculated subcutaneously into syngeneic C57BL/6 mice and reduced viability of B16 cells in vitro, whereby GLme exhibited stronger effect. Furthermore, anticancer activity of GLme was demonstrated for the first time against two other rodent tumor cell lines, L929-mouse fibrosarcoma and C6-rat astrocytoma. The mechanism of antitumor activity of GLme comprised inhibition of cell proliferation and induction of caspase-dependent apoptotic cell death mediated by upregulated p53 and inhibited Bcl-2 expression. Moreover, the antitumor effect of the GLme was associated with intensified production of reactive oxygen species, whereas their neutralization by the antioxidant, N-acetyl cysteine, resulted in partial recovery of cell viability. Thus, our results suggest that GLme might be a good candidate for treatment of diverse forms of cancers. Serbian Ministry of Science [143029, 143016]

The present study identifies xanthones gentiakochianin and gentiacaulein as the active principles responsible for the in vitro antiglioma action of ether and methanolic extracts of the plant Gentiana kochiana. Gentiakochianin and gentiacaulein induced cell cycle arrest in G(2)/M and G(0)/G(1) phases, respectively, in both C6 rat glioma and U251 human glioma cell lines. The more efficient antiproliferative action of gentiakochianin was associated with its ability to induce microtubule stabilization in a cell-free assay. Both the xanthones reduced mitochondrial membrane potential and increased the production of reactive oxygen species in glioma cells, but only the effects of gentiakochianin were pronounced enough to cause caspase activation and subsequent apoptotic cell death. The assessment of structure-activity relationship in a series of structurally related xanthones from G. kochiana and Gentianella austriaca revealed dihydroxylation at positions 7, 8 of the xanthonic nucleus as the key structural feature responsible for the ability of gentiakochianin to induce microtubule-associated G(2)/M cell block and apoptotic cell death in glioma cells. (C) 2008 Elsevier Ltd. All rights reserved. null

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Given the important role of gaseous free radical nitric oxide (NO) in tumor cell biology, we investigated the ability of the anti-cancer drugs 5-Aza-2'-deoxycytidine (ADC) and paclitaxel to modulate NO production in mouse L929 fibrosarcoma cells. Both drugs reduced IFN-gamma-stimulated NO release in cultures of L929 and primary fibroblasts, but not in mouse peritoneal macrophages. The inhibitory effect was due to the reduced expression of inducible NO synthase (iNOS), the enzyme responsible for cytokine-induced intracellular NO synthesis, as both agents markedly suppressed the interferon-ganuna (IFN-gamma)-triggered increase in iNOS concentration in L929 cells. In addition, ADC and paclitaxel prevented the FFN-gamma-triggered activation of p44/p42 mitogen-activated protein (MAP) kinase in L929 fibroblasts, suggesting a possible mechanism for the observed inhibition of iNOS expression. These results might have important implications for the therapeutic effect of ADC and paclitaxel, since their inhibitory action on NO release partly neutralized the NO-dependent toxicity of IFN-gamma on L929 fibrosarcoma cells. (C) 2003 Elsevier B.V All rights reserved. null

Although astrocytes presumably participate in maintaining the immune privilege of the central nervous system (CNS), the mechanisms behind their immunoregulatory properties are still largely undefined. In this study, we describe the development of regulatory T cells upon contact with astrocytes. Rat T cells pre-incubated with astrocytes completely lost the ability to proliferate in response to mitogenic stimuli. The cells were blocked in G0/G1 phase of the cell cycle, expressed less IL-2R, and produced significantly lower amounts of interferon-gamma (IFN-gamma), but not interleukin-2 (IL-2), IL-10, or tumor necrosis factor (TNF). These anergic cells completely prevented mitogen-induced growth of normal T lymphocytes, as well as CNS antigen-driven proliferation of autoreactive T cells. The suppressive activity resided in both CD4(+) and CD8(+) T-cell compartments. Heat-sensitive soluble T-cell factors, not including transforming growth factor-beta (TGF-beta) or IL-10, were solely responsible for the observed suppression, as well as for the transfer of suppressive activity to normal T cells. The administration of astrocyte-induced regulatory T cells markedly alleviated CNS inflammation and clinical symptoms of CNS autoimmunity in rats with experimental allergic encephalomyelitis. Finally, the cells with suppressive properties were readily generated from human lymphocytes after contact with astrocytes. Taken together, these data indicate that astrocyte-induced regulatory T cells might represent an important mechanism for self-limitation of excessive inflammation in the brain. (C) 2004 Wiley-Liss, Inc. null

Taxol is a microtubule-stabilizing agent that has recently been shown effective in the treatment of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. As astrocytes could modulate central nervous system (CNS) autoimmunity through inducible nitric oxide synthase (iNOS)-mediated production of immunoregulatory free radical nitric oxide (NO), we investigated the effect of taxol on NO synthesis in rat astrocytes. Taxol, either alone or in combination with interferon-gamma, induced NO generation in primary astrocytes and astrocytoma C6 cells in a dose- and time-dependent manner. Accordingly, the drug markedly up-regulated the expression of both iNOS mRNA and protein in astrocytes. The observed effect of taxol was mediated through induction of iNOS transcription factors NF-kappaB and IRF-1, and required the activation of p38 MAP kinase and JNK. Finally, NO release by taxol-stimulated astrocytes was blocked with the microtubule-depolymerizing agent colchicine, suggesting the involvement of a microtubule-stabilizing activity of taxol in the observed effect. null

Povećane energetske potrebe tumorske ćelije zadovoljavaju prevashodno aerobnom glikolizom, ali ukoliko je ona inhibirana ove metabolički plastične ćelije prelaze na oksidativnu fosforilaciju. Veliki nestabilni lizozomi, bogati hidrolitičkim enzimima, omogućavaju tumorima metastaziranje i rezistenciju na lekove, ali je njihovo izlivanje u citoplazmu citotoksično. Cilj ove disertacije je bio da se ispitaju antitumorski efekti kombinovanih tretmana inhibitora glikolize 2-dezoksi-D-glukoze (2DG) sa supresorom oksidativne fosforilacije rotenonom (ROT), ili sa lizozomalnim deterdžentom N-dodecilimidazolom (NDI). Pokazali smo da i 2DG+ROT i 2DG+NDI sinergistički ubijaju B16 melanomske i U251 gliomske ćelije nekrozom, a ne apoptozom, nekroptozom i autofagijom. Kombinovani tretmani su izazvali depleciju ATP, aktivaciju AMPK i produkciju mitohondrijskog superoksida. 2DG+ROT je stimulisao otpuštanje heksokinaze II sa membrane mitohondrija i posledično otvaranje VDAC kanala, što je omogućilo izlazak superoksida i citohroma c u citoplazmu. Citohrom c je aktivirao kaspaze, ali zbog nedostatka ATP nije došlo do fragmentacije DNK i inicijalno aktivirana apoptoza je završena nekrozom. Deplecija ATP je aktivirala AMPK i suprimirala mTORC1, ali je paradoksalno inhibirala autofagiju. Sa druge strane, NDI je indukovao permeabilizaciju membrane lizozoma i izlazak proteolitičkih enzima katepsina, depolarizaciju mitohondrija, oksidativni stres i supresiju oksidativne fosforilacije, što je u kombinaciji sa inhibicijom glikolize izazvanom 2DG, dovelo do potpune deplecije ATP i nekroze tumorskih ćelija. Istovremena inhibicija glikolize i oksidativne fosforilacije, ili inhibicija glikolize i destabilizacija lizozoma, mogle bi se iskoristiti u antitumorskoj terapiji. Tumor cells preferentially use aerobic glycolysis to satisfy increased energy needs, but if glycolysis is inhibited they switch to oxidative phosphorylation. Tumor cells have large unstable lysosomes, rich in hydrolytic enzymes that stimulate metastases and drug resistance, but induce cell death if released into cytoplasm. The aim of this dissertation was to investigate the antitumor effects of combined treatments of glycolysis inhibitor 2-deoxy-D-glucose (2DG) with the oxidative phosphorylation suppressor rotenone (ROT), or with the lysosomal detergent N-dodecylimidazole (NDI). We showed that both, 2DG+ROT and 2DG+NDI, synergistically induced B16 melanoma and U251 glioma cell death by necrosis, and not apoptosis, necroptosis, and autophagy. Combined treatments caused ATP depletion, AMPK activation, and mitochondrial superoxide production. 2DG+ROT induced release of hexokinase II from the mitochondrial membrane and the consequent opening of the VDAC channel, which led to the release of superoxide and cytochrome c into the cytoplasm. Cytochrome c activated caspases, but due to ATP deficiency, there was no DNA fragmentation and the initially activated apoptosis converted to necrosis. ATP depletion activated AMPK and suppressed mTORC1, but paradoxically inhibited autophagy. On the other hand, NDI induced lysosome membrane permeabilization and release of proteolytic enzymes cathepsins, depolarization of mitochondria, oxidative stress and suppression of oxidative phosphorylation, which in combination with inhibition of glycolysis induced by 2DG, led to complete energy depletion and necrosis of tumor cells. Concomitant inhibition of glycolysis and oxidative phosphorylation, or inhibition of glycolysis and destabilization of lysosomes, could be used in antitumor therapy.

Autofagija, razgradnja nepotrebnih/nefunkcionalnih unutarćelijskih komponenti u autolizozomima, kiselim organelama nastalim spajanjem autofagozoma i lizozoma, može biti citoprotektivna i citotoksična. U ovoj tezi ispitivana je uloga glavnog ćelijskog energetskog senzora protein kinaze aktivirane adenozin monofosfatom (AMPK) i mitogenom aktivirane protein (MAP) kinaze p38 u autofagiji i apoptozi ćelija humanog neuroblastoma SH-SY5Y izazvanoj mimetikom Parkinsonove bolesti 6-hidroksidopaminom (6-OHDA). 6-OHDA je indukovao apoptozu zavisnu od oksidativnog stresa i aktivacije kaspaza. Prisustvo autofagnih vezikula, zakišeljavanje citoplazme, autofagozomima asocirana konverzija LC3 proteina i razgradnja supstrata autofagne proteolize p62 ukazali su da 6-OHDA indukuje autofagiju. 6-OHDA je aktivirao AMPK i njegov supstrat Raptor, te inhibirao glavni supresor autofagije mTOR i njegov supstrat S6K, uprkos tome što je stimulisao mTOR aktivator Akt. Konverzija LC3, degradacija p62, zakišeljavanje citoplazme i inhibicija mTOR/S6K izazvani 6-OHDA poništeni su supresijom AMPK. Inhibicija AMPK i autofagije su smanjile, dok su inhibicije mTOR i Akt pojačale oksidativni stres i apoptozu indukovanu 6-OHDA. 6-OHDA je stimulisao MAP kinaze JNK, ERK i p38. Inhibicija JNK i ERK nisu imale uticaja, dok je inhibicija p38 suprimirala proapoptotsko dejstvo 6-OHDA, ali nije delovala na aktivnost AMPK i autofagiju. Sa druge strane, inhibicija AMPK smanjila je aktivaciju p38 u ćelijama tretiranim 6-OHDA. Antioksidans N-acetil cistein je inhibirao aktivaciju AMPK, p38 i autofagiju stimulisanu 6-OHDA. Navedeni rezultati ukazuju da bi oksidativnim stresom indukovana AMPK/mTOR zavisna citotoksična autofagija i AMPK/p38 zavisna apoptoza mogle biti pogodne mete za terapiju Parkinsonove bolesti. Autophagy, the degradation of unused/dysfunctional cellular components in autolysosomes, acidic organelles created by fusion of autophagosomes and lysosomes, can be either cytotoxic or cytoprotective. Here we investigated the role of the main cellular energy sensor, AMP-activated protein kinase (AMPK) and mitogen activated protein (MAP) kinase p38 in autophagy and apoptosis caused by the Parkinsonian mimetic 6-hydroxydopamine (6-OHDA) in human neuroblastoma SH-SY5Y cells. 6-OHDA induced apoptosis dependent on oxidative stress and caspase activation. Presence of autophagic vesicles, cytoplasm acidification, autophagosomeassociated conversion of LC3 protein, degradation of autophagic proteolysis substrate p62, all indicated that 6-OHDA induced autohagy. 6-OHDA activated AMPK and its substrate Raptor, and suppressed main autophagy inhibitor, mTOR and its target S6K, in spite of activating the mTORactivating Akt. LC3 conversion, p62 degradation, cytoplasm acidification and mTOR/S6K inhibition caused by 6-OHDA were all abolished by AMPK suppression. Inhibition of AMPK and autophagy decreased, while inhibition of mTOR and Akt potentiated oxidative stress and apoptosis caused by 6-OHDA. 6-OHDA stimulated MAP kinases JNK, ERK and p38. Inhibition of JNK and ERK did not affect, while p38 inhibition reduced pro-apoptotic effects of 6-OHDA, although it did not influence AMPK activation nor autophagy. Conversely, AMPK inhibition mitigated p38 activation in 6-OHDA treated cells. Antioxidant N-acetyl cysteine suppressed activation of AMPK, p38 and autophagy stimulated by 6-OHDA. These results suggest that oxidative stress-induced, AMPK/mTOR-dependent cytotoxic autophagy and AMPK/p38-dependent apoptosis could be valid therapeutic targets for treating Parkinson’s disease.

Autofagija, proces programirane ćelijske razgradnje unutarćelijskog sadržaja, je uključena u regulaciju preživljavanja i smrti ćelija kancera. U ovoj doktorskoj disertaciji je po prvi put ispitivana sposobnost antileukemijskih lekova citarabina i idarubicina da indukuju autofagiju u različitim humanim leukemijskim ćelijskim linijama i mononuklearnim ćelijama periferne krvi (MNPK) pacijenata obolelih od leukemije in vitro. Takođe, ispitivani su unutarćelijski mehanizmi odgovorni za indukciju autofagije, kao i uloga autofagije u citotoksičnosti ovih lekova. Vijabilitet REH, HL-60, K562 leukemijskih ćelijskih linija, MNPK pacijenata obolelih od leukemije i MNPK zdravih kontrola je određivan merenjem aktivnosti kisele fosfataze i mitohondrijalnih dehidrogenaza. Protočna citofluorimetrija je korišćena za detekciju apoptoze i zakišeljavanja citoplazme. Indukcija autofagije je ispitivana fluorescentnom mikroskopijom (detekcija unutarćelijskih kiselih vezikula obojenih akridin oranžom), transmisionom elektronskom mikroskopijom (posmatranje autofagnih vezikula) i imunoblot analizom (konverzija LC3-I u LC3-II, degradacija SQSTM1/p62). Aktivacija signalnih puteva koji učestvuju u regulaciji autofagije je analizirana imunoblot metodom. Uloga autofagije u citotoksičnosti citarabina i idarubicina je ispitivana primenom farmakološke inhibicije bafilomicinom A1, hlorokinom, vortmaninom i amonijum hloridom, kao i genetske inaktivacije ekspresije beklina-1, LC3β i SQSTM1 transfekcijom odgovarajućim malim interferirajućim RNK. Citarabin i idarubicin su izazvali povećanje unutarćelijske kiselosti i pojavu autofagnih vezikula sa delimično razgrađenim ćelijskim sadržajem u leukemijskim ćelijskim linijama. Antileukemijski lekovi su stimulisali razgradnju supstrata autofagije SQSTM1 i povećali konverziju LC3-I u LC3-II formu asociranu autofagozomima u odsustvu ili prisustvu inhibitora proteolize, ukazujući tako na povećanje autofagnog fluksa. Oba leka su smanjila fosforilaciju mTOR kinaze, glavnog negativnog regulatora autofagije i njegovog supstrata p70S6 kinaze, dok je tretman mTOR aktivatorom leucinom sprečio indukciju autofagije. Idarubicin je suprimirao aktivnost mTOR aktivatora... Autophagy, a process of programmed cellular self-digestion, has been implicated in regulation of cancer cell survival and death. The present study investigated for the first time the ability of antileukemic drugs cytarabine and idarubicin to induce autophagy in different human leukemic cell lines and peripheral blood mononuclear cells (PBMC) from leukemia patients in vitro. Intracellular mechanisms responsible for the induction of autophagy, as well as the role of autophagy in cytotoxicity of these drugs were also investigated. Cell viability of REH, HL-60, K562 leukemic cell lines, and PBMC from leukemic patients and healthy controls was determined by measuring the acid phosphatase and mitochondrial succinate dehydrogenase activity. Flow cytometry was used for the detection of apoptosis and intracellular acidification. Autophagy induction was assessed by fluorescent microscopy (detection of acridine orange stained intracellular acidic vesicles), by transmission electron microscopy (observation of autophagic vacuoles), as well as by immunoblot analysis of LC3 conversion and SQSTM1/p62 proteolysis. Activation of autophagy-regulating signaling pathways was analyzed by immunoblotting. Pharmacological inhibition of autophagy with bafilomycin A1, chloroquine, wortmannin, and NH4Cl or RNA interference-mediated knockdown of beclin-1, LC3β and SQSTM1 were used to determine the role of the autophagy in cytotoxicity of antileukemic drugs. Cytarabine and idarubicin induced an increase in intracellular acidification and appearance of autophagic vesicles with partially digested cellular components in leukemic cell lines. Antileukemic drugs stimulated the degradation of autophagic target SQSTM1 and enhanced the conversion of LC3-I to autophagosome-associated LC3-II in the absence or presence of proteolysis inhibitors, thus indicating the increase in autophagic flux...

U ovoj doktorskoj disertaciji ispitivan je uticaj inhibicije intracelularnog energetskog senzora protein kinaze aktivirane adenozin-monofosfatom (AMPK) na indukciju apoptoze i autofagije u tumorskim ćelija. Farmakološki inhibitor AMPK dorzomorfin indukovao je G2/M blokadu ćelijskog ciklusa, praćen apoptozom koju karakteriše aktivacija kaspaza, eksternalizacija fosfatidilserina i fragmentacija DNK u U251 humanim i C6 pacovskim ćelijama glioma, dok na vijabilitet primarnih pacovskih astrocita i ćelija mišjeg melanoma B16 nije imao uticaja. Mehanizam indukcije apoptoze dorzomorfinom bio je posredovan stimulacijom produkcije reaktivnih vrsta kiseonika i inhibicijom ekspresije antiapoptotskog Bcl-2 proteina. Dorzomorfin je inhibirao fosforilaciju i enzimatsku aktivnost AMPK, što je za posledicu imalo smanjenje fosforilacije njenog supstrata acetil-CoA karboksilaze. Aktivatori AMPK metformin i AICAR delimično su neutralisali blokadu ćelijskog ciklusa, oksidativni stres i apoptozu indukovanu dorzomorfinom. Mala interferirajuća RNK (siRNK) koja sprečava ekspresiju humanog AMPK enzima je poput dorzomorfina zaustavila proliferaciju ćelija u G2/M fazi ćelijskog ciklusa, ali nije izazvala oksidativni stres i apoptozu u U251 ćelijama. Dakle, inhibicija AMPK je neophodna, ali ne i dovoljna za indukciju apotpoze dorzomorfinom u ćelijama glioma. U ovoj studiji takođe je pokazano da dorzomorfin indukuje autofagiju u ćelijama kancera. Indukcija autofagije u U251 ćelijama detektovana je fluorescentnim bojenjem unutarćelijskih kiselih vezikula akridin oranžom, indukcijom beklina-1, degradacijom p62 proteina i konverzijom LC3-I u formu asociranu sa autofagozomima LC3-II u odsustvu i prisustvu proteolitičkih inhibitora... In this doctoral dissertation the effect of intracellular energy sensor AMP-activated protein kinase (AMPK) inhibition on induction of apoptosis and autophagy in tumor cells was investigated. Pharmacological AMPK inhibitor dorsomorphin caused G2/M cell cycle block, accompanied by apoptotic cell death characterized by caspase activation, phosphatidylserine exposure and DNA fragmentation in U251 human and C6 rat glioma cells, while it had no effect on viability of primary rat astrocytes and B16 mouse melanoma cells. The mechanisms underlying the pro-apoptotic action of dorsomorphin involved induction of oxidative stress and down-regulation of antiapoptotic molecule Bcl-2. Dorsomorphin diminished AMPK phosphorylation and enzymatic activity, resulting in reduced phosphorylation of its target acetyl CoA carboxylase. AMPK activators metformin and AICAR partly prevented the cell cycle block, oxidative stress and apoptosis induced by dorsomorphin. The small interfering RNA (siRNA) targeting of human AMPK mimicked dorsomorphin-induced G2/M cell cycle arrest, but failed to induce oxidative stress and apoptosis in U251 glioma cells. Therefore, AMPK inhibition is required, but not sufficient for dorsomorphin-mediated apoptotic death of glioma cells. In this study, it was also reported that dorsomorphin can induce autophagy in cancer cells. The induction of autophagy in U251 human glioma cell line was demonstrated by acridine orange staining of intracellular acidic vesicles, Beclin 1 induction, p62 decrease and conversion of LC3-I to autophagosome-associated LC3-II in the absence and presence of proteolysis inhibitors. The presence of autophagosome like vesicles was confirmed by transmission electron microscopy. Dorsomorphin-mediated inhibition of AMPK and Raptor in U251 cells was associated with paradoxical decrease in phosphorylation of AMPK/Raptor-repressed mTOR, a major negative regulator of autophagy, and its downstream target p70S6K...

U ovoj doktorskoj disertaciji ispitivan je uticaj inhibicije intracelularnog energetskog senzora protein kinaze aktivirane adenozin-monofosfatom (AMPK) na indukciju apoptoze i autofagije u tumorskim ćelija. Farmakološki inhibitor AMPK dorzomorfin indukovao je G2/M blokadu ćelijskog ciklusa, praćen apoptozom koju karakteriše aktivacija kaspaza, eksternalizacija fosfatidilserina i fragmentacija DNK u U251 humanim i C6 pacovskim ćelijama glioma, dok na vijabilitet primarnih pacovskih astrocita i ćelija mišjeg melanoma B16 nije imao uticaja. Mehanizam indukcije apoptoze dorzomorfinom bio je posredovan stimulacijom produkcije reaktivnih vrsta kiseonika i inhibicijom ekspresije antiapoptotskog Bcl-2 proteina. Dorzomorfin je inhibirao fosforilaciju i enzimatsku aktivnost AMPK, što je za posledicu imalo smanjenje fosforilacije njenog supstrata acetil-CoA karboksilaze. Aktivatori AMPK metformin i AICAR delimično su neutralisali blokadu ćelijskog ciklusa, oksidativni stres i apoptozu indukovanu dorzomorfinom. Mala interferirajuća RNK (siRNK) koja sprečava ekspresiju humanog AMPK enzima je poput dorzomorfina zaustavila proliferaciju ćelija u G2/M fazi ćelijskog ciklusa, ali nije izazvala oksidativni stres i apoptozu u U251 ćelijama. Dakle, inhibicija AMPK je neophodna, ali ne i dovoljna za indukciju apotpoze dorzomorfinom u ćelijama glioma. U ovoj studiji takođe je pokazano da dorzomorfin indukuje autofagiju u ćelijama kancera. Indukcija autofagije u U251 ćelijama detektovana je fluorescentnim bojenjem unutarćelijskih kiselih vezikula akridin oranžom, indukcijom beklina-1, degradacijom p62 proteina i konverzijom LC3-I u formu asociranu sa autofagozomima LC3-II u odsustvu i prisustvu proteolitičkih inhibitora. Prisustvo autofagozomima sličnih vezikula potvrđeno je transmisionom elektronskom mikroskopijom. Inhibicija AMPK i Raptora indukovana dorzomorfinom u U251 ćelijama bila je paradoksalno asocirana sa smanjenjem fosforilacije AMPK/Raptorom inhibiranog glavnog represora autofagije mTOR i njegovog supstrata p70S6K. Fosforilacija mTOR aktivatora Akt i PI3K-aktivirane Src kinaze bile su takođe inhibirane u ćelijama tretiranim dorzomorfinom. Poništavanje ekspresije AMPK sa siRNA nije redukovalo aktivnost Akt/mTOR/p70S6K signalnog puta, a AMPK aktivatori metformin i AICAR nisu uspeli da blokiraju autofagiju indukovanu dorzomorfinom. Inhibitori autofagije bafilomicin i hlorokin značajno su povećali citotoksičnost dorzomorfina prema U251 ćelijama, što je pokazano povećanjem oslobađanja laktat dehidrogenaze, fragmentacije DNK i aktivacije kaspaze-3. Sličan efekat dorzomorfin je imao i prema ćelijama pacovskog glioma C6, mišjeg fibrosarkoma L929 i mišjeg melanoma B16. Pošto je ranije pokazano da dorzomorfin suprimira AMPK-zavisnu autofagiju u različitim ćelijskim tipovima, rezultati ove studije sugerišu da efekat dorzomorfina na autofagiju zavisi od doze, konteksta i/ili vrste ćelija. Imajući u vidu da dorzomorfin indukuje autofagiju u ćelijama kancera nezavisno od inhibicije AMPK, inhibicijom Akt/mTOR signalnog puta, rezultati ove studije ukazuju na neophodnost opreza pri interpretaciji rezultata eksperimenata u kojima se dorzomorfin koristi kao inhibitor AMPK, ali takođe sugerišu da bi dorzomorfin, sam ili u kombinaciji sa inhibitorima autofagije, mogao biti potencijalni kandidat za terapiju tumora. In this doctoral dissertation the effect of intracellular energy sensor AMP-activated protein kinase (AMPK) inhibition on induction of apoptosis and autophagy in tumor cells was investigated. Pharmacological AMPK inhibitor dorsomorphin caused G2/M cell cycle block, accompanied by apoptotic cell death characterized by caspase activation, phosphatidylserine exposure and DNA fragmentation in U251 human and C6 rat glioma cells, while it had no effect on viability of primary rat astrocytes and B16 mouse melanoma cells. The mechanisms underlying the pro-apoptotic action of dorsomorphin involved induction of oxidative stress and down-regulation of antiapoptotic molecule Bcl-2. Dorsomorphin diminished AMPK phosphorylation and enzymatic activity, resulting in reduced phosphorylation of its target acetyl CoA carboxylase. AMPK activators metformin and AICAR partly prevented the cell cycle block, oxidative stress and apoptosis induced by dorsomorphin. The small interfering RNA (siRNA) targeting of human AMPK mimicked dorsomorphin-induced G2/M cell cycle arrest, but failed to induce oxidative stress and apoptosis in U251 glioma cells. Therefore, AMPK inhibition is required, but not sufficient for dorsomorphin-mediated apoptotic death of glioma cells. In this study, it was also reported that dorsomorphin can induce autophagy in cancer cells. The induction of autophagy in U251 human glioma cell line was demonstrated by acridine orange staining of intracellular acidic vesicles, Beclin 1 induction, p62 decrease and conversion of LC3-I to autophagosome-associated LC3-II in the absence and presence of proteolysis inhibitors. The presence of autophagosome like vesicles was confirmed by transmission electron microscopy. Dorsomorphin-mediated inhibition of AMPK and Raptor in U251 cells was associated with paradoxical decrease in phosphorylation of AMPK/Raptor-repressed mTOR, a major negative regulator of autophagy, and its downstream target p70S6K. The phosphorylation of mTOR activator Akt and PI3K-activating kinase Src was also impaired in dorsomorphin-treated cells. The siRNA-mediated AMPK silencing did not reduce the activity of the Akt/mTOR/p70S6K pathway and AMPK activators metformin and AICAR failed to block dorsomorphin-induced autophagy. Autophagy inhibitors bafilomycin and chloroquine significantly increased the cytotoxicity of dorsomorphin towards U251 cells, as confirmed by the increase in lactate dehydrogenase release, DNA fragmentation and caspase-3 activation. Similar effects of dorsomorphin were also observed in C6 rat glioma, L929 mouse fibrosarcoma and B16 mouse melanoma cell lines. Since dorsomorphin has previously been reported to suppress AMPK dependent autophagy in different cell types, results in this study suggest that the effects of dorsomorphin on autophagy might be dose-, cell type- and/or context-dependent. By demonstrating the ability of dorsomorphin to induce autophagic response in cancer cells via AMPK inhibition-independent downregulation of Akt/mTOR pathway, results warrant caution when using dorsomorphin to inhibit AMPK-dependent cellular responses, but also suggest that dorsomorphin, alone or in combination with autophagy inhibitors, could be potential candidate for anticancer therapy.