Synergistic effects of proteasome inhibitor carfilzomib in combination with tyrosine kinase inhibitors in imatinib-sensitive and -resistant chronic myeloid leukemia models

The tyrosine kinase inhibitor (TKI) imatinib has transformed the treatment and outlook of chronic myeloid leukemia (CML); however, the development of drug resistance and the persistence of TKI-resistant stem cells remain obstacles to eradicating the disease. Inhibition of proteasome activity with bortezomib has been shown to effectively induce apoptosis in TKI-resistant cells. In this study, we show that exposure to the next generation proteasome inhibitor carfilzomib is associated with a decrease in ERK signaling and increased expression of Abelson interactor proteins 1 and 2 (ABI-1/2). We also investigate the effect of carfilzomib in models of imatinib-sensitive and -resistant CML and demonstrate a potent reduction in proliferation and induction of apoptosis in a variety of models of imatinib-resistant CML, including primitive CML stem cells. Carfilzomib acts synergistically with the TKIs imatinib and nilotinib, even in imatinib-resistant cell lines. In addition, we found that the presence of immunoproteasome subunits is associated with an increased sensitivity to carfilzomib. The present findings provide a rational basis to examine the potential of carfilzomib in combination with TKIs as a potential therapy for CML, particularly in imatinib-resistant disease.

The simple economics of risk-sharing agreements between the NHS and the pharmaceutical industry

The Janssen-Cilag proposal for a risk-sharing agreement regarding bortezomib received a welcome signal from NICE. The Office of Fair Trading report included risk-sharing agreements as an available tool for the National Health Service. Nonetheless, recent discussions have somewhat neglected the economic fundamentals underlying risk-sharing agreements. We argue here that risk-sharing agreements, although attractive due to the principle of paying by results, also entail risks. Too many patients may be put under treatment even with a low success probability. Prices are likely to be adjusted upward, in anticipation of future risk-sharing agreements between the pharmaceutical company and the third-party payer. An available instrument is a verification cost per patient treated, which allows obtaining the first-best allocation of patients to the new treatment, under the risk sharing agreement. Overall, the welfare effects of risk-sharing agreements are ambiguous, and care must be taken with their use.

Proteasome inhibition and ROS generation by 4-nerolidylcatechol induces melanoma cell death

Induction of apoptotic cell death in response to chemotherapy and other external stimuli has proved extremely difficult in melanoma, leading to tumor progression, metastasis formation and resistance to therapy. A promising approach for cancer chemotherapy is the inhibition of proteasomal activity, as the half-life of the majority of cellular proteins is under proteasomal control and inhibitors have been shown to induce cell death programs in a wide variety of tumor cell types. 4-Nerolidylcatechol (4-NC) is a potent antioxidant whose cytotoxic potential has already been demonstrated in melanoma tumor cell lines. Furthermore, 4-NC was able to induce the accumulation of ubiquitinated proteins, including classic targets of this process such as Mcl-1. As shown for other proteasomal inhibitors in melanoma, the cytotoxic action of 4-NC is time-dependent upon the pro-apoptotic protein Noxa, which is able to bind and neutralize Mcl-1. We demonstrate the role of 4-NC as a potent inducer of ROS and p53. The use of an artificial skin model containing melanoma also provided evidence that 4-NC prevented melanoma proliferation in a 3D model that more closely resembles normal human skin.

Protein quality control disruption by PKC beta II in heart failure: rescue by the selective PKC beta II inhibitor, beta IIV5-3

Myocardial remodeling and heart failure (HF) are common sequelae of many forms of cardiovascular disease and a leading cause of mortality worldwide. Accumulation of damaged cardiac proteins in heart failure has been described. However, how protein quality control (PQC) is regulated and its contribution to HF development are not known. Here, we describe a novel role for activated protein kinase C isoform beta II (PKC beta II) in disrupting PQC. We show that active PKC beta II directly phosphorylated the proteasome and inhibited proteasomal activity in vitro and in cultured neonatal cardiomyocytes. Importantly, inhibition of PKC beta II, using a selective PKC beta II peptide inhibitor (beta IIV5-3), improved proteasomal activity and conferred protection in cultured neonatal cardiomyocytes. We also show that sustained inhibition of PKC beta II increased proteasomal activity, decreased accumulation of damaged and misfolded proteins and increased animal survival in two rat models of HF. Interestingly, beta IIV5-3-mediated protection was blunted by sustained proteasomal inhibition in HF. Finally, increased cardiac PKC beta II activity and accumulation of misfolded proteins associated with decreased proteasomal function were found also in remodeled and failing human hearts, indicating a potential clinical relevance of our findings. Together, our data highlights PKC beta II as a novel inhibitor of proteasomal function. PQC disruption by increased PKC beta II activity in vivo appears to contribute to the pathophysiology of heart failure, suggesting that PKC beta II inhibition may benefit patients with heart failure. (218 words)

Integrating novel agents into multiple myeloma treatment - current status in Switzerland and treatment recommendations

The treatment of multiple myeloma has undergone significant changes in the recent past. The arrival of novel agents, especially thalidomide, bortezomib and lenalidomide, has expanded treatment options and patient outcomes are improving significantly. This article summarises the discussions of an expert meeting which was held to debate current treatment practices for multiple myeloma in Switzerland concerning the role of the novel agents and to provide recommendations for their use in different treatment stages based on currently available clinical data. Novel agent combinations for the treatment of newly diagnosed, as well as relapsed multiple myeloma are examined. In addition, the role of novel agents in patients with cytogenetic abnormalities and renal impairment, as well as the management of the most frequent side effects of the novel agents are discussed. The aim of this article is to assist in treatment decisions in daily clinical practice to achieve the best possible outcome for patients with multiple myeloma.

Hyperammonemic encephalopathy in multiple myeloma

HISTORY AND CLINICAL FINDINGS A 54-year old man had suffered from advanced multiple myeloma for two years. After initially good response the myeloma was refractrory to treatment with dexamethasone, cyclophosphamide, bortezomibe, zoledronate and additionally doxorubicine. The patient then complained of dyspnea without clinical signs of cardiopulmonary disease. INVESTIGATIONS Arterial blood gas analysis showed hyperventilation with respiratory alkalosis and normal alveolo-arterial gradient as the reason for the dyspnea. With a normal MRI of the brain and lumbal puncture, a neurological disease could be excluded. Serum calcium, creatinine and serum viscosity were normal. Eventually, serum ammonia levels were found to be substantially elevated (144 µmol/l) and hyperammonemic encephalopathy was diagnosed. TREATMENT AND COURSE Therapy with bortezomib and high dose dexamethason was repeated, and the patient also received bendamustin. Despite this treatment, he lost consciousness and died after two weeks because of aspiration pneumonia. CONCLUSION The existence of respiratory alkalosis and multiple myeloma should prompt a search for hyperammonemia.

Proteasome inhibitors increase missense mutated dysferlin in patients with muscular dystrophy

No treatment is available for patients affected by the recessively inherited, progressive muscular dystrophies caused by a deficiency in the muscle membrane repair protein dysferlin. A marked reduction in dysferlin in patients harboring missense mutations in at least one of the two pathogenic DYSF alleles encoding dysferlin implies that dysferlin is degraded by the cell's quality control machinery. In vitro evidence suggests that missense mutated dysferlin might be functional if salvaged from degradation by the proteasome. We treated three patients with muscular dystrophy due to a homozygous Arg555Trp mutation in dysferlin with the proteasome inhibitor bortezomib and monitored dysferlin expression in monocytes and in skeletal muscle by repeated percutaneous muscle biopsy. Expression of missense mutated dysferlin in the skeletal muscle and monocytes of the three patients increased markedly, and dysferlin was correctly localized to the sarcolemma of muscle fibers on histological sections. Salvaged missense mutated dysferlin was functional in a membrane resealing assay in patient-derived muscle cells treated with three different proteasome inhibitors. We conclude that interference with the proteasomal system increases expression of missense mutated dysferlin, suggesting that this therapeutic strategy may benefit patients with dysferlinopathies and possibly other genetic diseases.

Current status and updated recommendations for diagnosis and treatment of plasma cell myeloma in Switzerland

The availability of drugs such as thalidomide, bortezomib and lenalidomide changed the landscape in myeloma treatment and has extended the median survival up to 10 years with a substantial improvement in quality of life. This development prompted a Swiss expert panel to re-evaluate the current status and formulate updated clinical recommendations for the diagnosis and treatment of plasma cell myeloma. These recommendations should help clinicians in their decision making to achieve the best outcome based on currently available data.

Preclinical evaluation of proteasome inhibition for the treatment of prostate cancer

Prostatic carcinoma is the most prevalent cancer detected in men. Bortezomib is the first proteasome inhibitor to undergo clinical trials for several forms of cancer. Although we know this class of agent preferentially kills cancer cells, our knowledge of proteasome inhibition mechanisms of induced death is far from complete. We investigated the effects of bortezomib on the LNCaP-Pro5 (Pro5) and PC-3-Pro4 (Pro4) human prostatic adenocarcinoma cells lines. We showed a reduction in proliferation and an increase in DNA fragmentation, caspase 3 activity, and cell surface phosphatidyl serine exposure. The bortezomib-treated tumors from both cell lines were dramatically reduced, and apoptosis was induced. There was also a reduction in proliferation in the treated tumors from both cells lines. We looked at changes in the levels of the proangiogenic factors VEGF, IL-8 and bFGF in vitro and in vivo. Although there was a reduction in the levels of VEGF produced by the Pro5 cell line and tumor due to bortezomib, no similar observations were made for the other angiogenic factors or in the Pro4 cells. We investigated the effects of bortezomib on p53 in the Pro5 cell line. Bortezomib induced strong stabilization of p53. It did not promote phosphorylation on serines 15 and 24 and p53 remained bound to its inhibitor, mdm2. Nonetheless, confocal microscopy revealed that bortezomib stimulated p53 translocation to the nucleus and enhanced p53 DNA binding, accumulation of p53-dependant transcripts, and activation of a p53-responsive reporter gene. Furthermore, stable transfectants of LNCaP-Pro5 expressing the p53 inhibitor, HPV-E6, displayed reduced bortezomib-induced p53 activation and cell death. Our data shows bortezomib to induce antitumor effects in the human Pro4 and Pro5 prostatic adenocarcinoma cell lines by the direct induction of apoptosis. The drug also causes a reduction in cell proliferation and mean vessel density while modulating the secretion of proangiogenic factors. Although we show that proteasome inhibition stimulates p53 activation via a novel mechanism in Pro5 cells, it is also toxic to p53 null cells as is seen in the Pro4 line. ^

The transcription factor nuclear factor kappa B (NFkappaB) maintains TRAIL resistance in human pancreatic cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) is a member of the TNF family of cytokines that induces apoptosis in a variety of tumor cells while sparing normal cells. However, many human cancer cell lines display resistance to TRAIL-induced apoptosis and the mechanisms contributing to resistance remain controversial. Previous studies have demonstrated that the dimeric transcription factor Nuclear Factor kappa B (NFκB) is constitutively active in a majority of human pancreatic cancer cell lines and primary tumors, and although its role in tumor progression remains unclear it has been suggested that NFκB contributes to TRAIL resistance. Based on this, I examined the effects of NFκB inhibitors on TRAIL sensitivity in a panel of nine pancreatic cancer cell lines. I show here that inhibitors of NFκB, including two inhibitors of the proteasome (bortezomib (Velcade™, PS-341) and NPI-0052), a small molecule inhibitor of IKK (PS1145), and a novel synthetic diterpene NIK inhibitor (NPI-1342) reverse TRAIL resistance in pancreatic cancer cell lines. Further analysis revealed that the expression of the anti-apoptosic proteins BclXL and XIAP was significantly decreased following exposure to these inhibitors alone and in combination with TRAIL. Additionally, treatment with NPI0052 and TRAIL significantly reduced tumor burden relative to the control tumors in an L3.6pl orthotopic pancreatic xenograft model. This was associated with a significant decrease in proliferation and an increase in caspase 3 and 8 cleavage. Combination therapy employing PS1145 or NPI-1342 in combination with TRAIL also resulted in a significant reduction in tumor burden compared to either agent alone in a Panc1 orthotopic xenograft model. My studies show that combination therapy with inhibitors of NFκB alone and TRAIL is effective in pre-clinical models of pancreatic cancer and suggests that the approach should be evaluated in patients. ^

The effects of proteasome inhibition in chronic lymphocytic leukemia and prostate cancer

The use of proteasome inhibitors in cancer has received much attention with the recent FDA approval of bortezomib (Velcade/PS-341). However, in the chronic lymphocytic leukemia (CLL) clinical trial, bortezomib was not as effective as it was in vitro. Accordingly, results in prostate cancer were not remarkable, although regression of lymphadenopathy was observed. This response was also seen in CLL. ^ The proteasome degrades ∼80% of intracellular proteins. Although specific pathways affected by proteasome inhibitors are known, there are still unidentified mechanisms by which they induce apoptosis. The efficacy and mechanism of action of the reversible proteasome inhibitor bortezomib were compared to the novel irreversible inhibitor NPI-0052 in this study, and their mechanisms of action in CLL and prostate cancer were examined. ^ NPI-0052 inhibited proteasome activity and induced apoptosis with more rapid kinetics than bortezomib in CLL. Inhibition of proteasome activity with NPI-0052 was also more durable. Interestingly, bortezomib is cleared from the serum within 15min, which is insufficient time for bortezomib to effectively inhibit the proteasome. However, only 5min exposure was needed for NPI-0052 to produce maximal proteasome inhibition. The data suggest that bortezomib's slow kinetics and reversible nature limit its potential in vivo and the use of NPI-0052 should be considered. ^ In examining the mechanism(s) by which bortezomib and NPI-0052 induce apoptosis in CLL, both were found to elicit the ER stress pathway. A stromal cell co-culture system prevented apoptosis induced by both proteasome inhibitors, suggesting that if such factors in vivo were responsible for reducing bortezomib's efficacy, NPI-0052 would not prove useful either. Finally, Lyn, a Src family kinase (SFK), was decreased in response to bortezomib and NPI-0052 and correlated with apoptosis induction in CLL and prostate cancer. Both proteasome inhibitors specifically targeted Lyn rather than SFKs in general. ^ SFKs are overexpressed in cancer and involved in cell signaling, survival, and metastasis. In prostate cancer cells, both proteasome inhibition and Lyn-silencing significantly inhibited migration. Preliminary evidence also suggested that Lyn downregulation decreases invasion potential. Together, these data suggest that proteasome inhibitors are potential candidates for anti-metastasic therapy and further investigation is warranted for the use of Lyn-targeted therapy to treat metastases. ^

The effects of proteasome inhibition on angiogenesis and autophagy in human prostate cancer cells

The proteasome degrades approximately 80% of intracellular proteins to maintain homeostasis. Proteasome inhibition is a validated therapeutic strategy, and currently, proteasome inhibitor bortezomib is FDA approved for the treatment of MM and MCL. Specific pathways affected by proteasome inhibition have been identified, but mechanisms of the anti-tumor effects of proteasome inhibition are not fully characterized and cancer cells display marked heterogeneity in terms of their sensitivity to proteasome inhibitor induced cell death. ^ The antitumor effects of proteasome inhibition involve suppression of tumor angiogenesis and vascular endothelial growth factor (VEGF) expression, but the mechanisms involved have not been clarified. In this dissertation I investigated the mechanisms underlying the effects of two proteasome inhibitors, bortezomib and NPI-0052, on VEGF expression in human prostate cancer cells. I found that proteasome inhibitors selectively downregulated hypoxia inducible factor 1alpha (HIF-1α) protein and its transcriptional activity to inhibit VEGF expression. Mechanistic studies demonstrated that proteasome inhibitors mediate the induction of the unfolded protein response (UPR) and that downregulation of HIF-1α is caused by eukaryotic translation initiation factor 2α (eIF2α) phosphorylation and translation repression. Importantly, I showed that proteasome inhibitors activated the UPR in some cells but not in others. My observation may have implications for the design of combination regimens that are based on exploiting proteasome inhibitor-induced ER stress.^ Although proteasome inhibitors have shown modest activity on prostate cancer, there is general consensus that no single agent is likely to have significant activity in prostate cancer. In the second part of this dissertation I attempted to exploit the effects of proteasome inhibition on the UPR to design a combination therapy that would enhance cancer cell death. Autophagy is a lysosome dependent degradation pathway that functions to eliminate long-lived protein and subcellular structures. Targeting autophagy has been shown to inhibit tumors in preclinical studies. I found that inhibition of autophagy with chloroquine or 3-methyladenine enhanced proteasome inhibitor induced cell death and the effects were associated with increased intracellular stress as marked by aggresome formation. Multiple cancers appear to be resistant to proteasome inhibition treatment alone. The implications of synergy for the combined inhibition of autophagy and the proteasome would likely apply to other cancers aside from prostate cancer. ^

Caspase 8: Mediating the effects of a novel proteasome inhibitor, NPI-0052

Targeting the proteasome with the sole FDA approved proteasome inhibitor (PI), bortezomib, has been fruitful in specific cancers. Its success has generated an interest in next-generation PIs that might have a therapeutic advantage in cancers, such as leukemia, where bortezomib monotherapy was less effective. This study focuses on a novel, clinically relevant PI, NPI-0052. Experiments show that NPI-0052 targets chymotrypsin- and caspase-like activities more potently than the trypsin-like activity in leukemia cells. NPI-0052 induced apoptosis, as determined by caspase-3 activation and DNA fragmentation. Using caspase inhibitors and caspase-8 (I9.2) or FADD (I2.1) deficient cells revealed that caspase-8 was essential for NPI-0052-induced apoptosis. NPI-0052 killed cells via a caspase-8-tBid-mitochondrial pathway, relying on caspase-8, whereas bortezomib relies on several caspases. NPI-0052 increased reactive oxygen species (ROS) levels, which contributed towards cytotoxicity since an antioxidant conferred protection. To improve the clinical efficacy of PIs, NPI-0052 was combined with epigenetic anti-cancer agents, histone deacetylase inhibitors (HDACi). NPI-0052 with MS-275 or vorinostat (FDA approved HDACi), synergistically induced apoptosis more effectively than an HDACi/bortezomib regimen in Jurkat cells. Caspase-8 and ROS contributed towards NPI-0052/HDACi cytotoxicity and caspase-8 mediated superoxide production by NPI-0052 or NPI-0052/HDACi. The proximal targets of these agents: proteasome activity and histone acetylation were examined to determine if they contributed towards synergistic effects. HDACi targeted proteasomal β subunits and corresponding catalytic activities responsible for degrading proteins. Immunoblotting showed increases in histone-H3 expression and its acetylation with NPI-0052 or NPI-0052/HDACi in Jurkat and primary cells. Importantly, the hyper-acetylation by NPI-0052 was not detected with bortezomib, suggesting that this effect may be unique to NPI-0052. An antioxidant attenuated histone-H3 expression and acetylation induced by NPI-0052 alone or with HDACi. Furthermore, the hyper-acetylation by NPI-0052 relied on caspase-8. These novel results show that a PI is eliciting classical epigenetic alterations, demonstrated by hyper-acetylation of histone-H3. This alteration was oxidant and caspase-8 dependent. Overall, results reveal that caspase-8 mediates many effects induced by NPI-0052. Data show overlapping activities by NPI-0052 and HDACi which are contributing, along with caspase-8 activation and oxidative stress, to cytotoxic interactions in leukemia cells, reinforcing the potential clinical utility of combining these two compounds. ^

Mechanisms Underlying the Heterogeneous Sensitivities of Cancer Cells to Proteasome Inhibitors

The mechanisms underlying cellular response to proteasome inhibitors have not been clearly elucidated in solid tumor models. Evidence suggests that the ability of a cell to manage the amount of proteotoxic stress following proteasome inhibition dictates survival. In this study using the FDA-approved proteasome inhibitor bortezomib (Velcade®) in solid tumor cells, we demonstrated that perhaps the most critical response to proteasome inhibition is repression of global protein synthesis by phosphorylation of the eukaryotic initiation factor 2-α subunit (eIF2α). In a panel of 10 distinct human pancreatic cancer cells, we showed marked heterogeneity in the ability of cancer cells to induce eIF2α phosphorylation upon stress (eIF2α-P); lack of inducible eIF2α-P led to excessive accumulation of aggregated proteins, reactive oxygen species, and ultimately cell death. In addition, we examined complementary cytoprotective mechanisms involving the activation of the heat shock response (HSR), and found that induction of heat shock protein 70 kDa (Hsp72) protected against proteasome inhibitor-induced cell death in human bladder cancer cells. Finally, investigation of a novel histone deacetylase 6 (HDAC6)-selective inhibitor suggested that the cytoprotective role of the cytoplasmic histone deacetylase 6 (HDAC6) in response to proteasome inhibition may have been previously overestimated.

Alterazione della proteostasi a livello del reticolo endoplasmatico: un potenziale target terapeutico nel carcinoma prostatico

Nel sesso maschile il carcinoma della prostata (CaP) è la neoplasia più frequente ed è tra le prime cause di morte per tumore. Ad oggi, sono disponibili diverse strategie terapeutiche per il trattamento del CaP, ma, come comprovato dall’ancora alta mortalità, spesso queste sono inefficaci, a causa soprattutto dello sviluppo di fenomeni di resistenza da parte delle cellule tumorali. La ricerca si sta quindi focalizzando sulla caratterizzazione di tali meccanismi di resistenza e, allo stesso tempo, sull’individuazione di combinazioni terapeutiche che siano più efficaci e capaci di superare queste resistenze. Le cellule tumorali sono fortemente dipendenti dai meccanismi connessi con l’omeostasi proteica (proteostasi), in quanto sono sottoposte a numerosi stress ambientali (ipossia, carenza di nutrienti, esposizione a chemioterapici, ecc.) e ad un’aumentata attività trascrizionale, entrambi fattori che causano un accumulo intracellulare di proteine anomale e/o mal ripiegate, le quali possono risultare dannose per la cellula e vanno quindi riparate o eliminate efficientemente. La cellula ha sviluppato diversi sistemi di controllo di qualità delle proteine, tra cui gli chaperon molecolari, il sistema di degradazione associato al reticolo endoplasmatico (ERAD), il sistema di risposta alle proteine non ripiegate (UPR) e i sistemi di degradazione come il proteasoma e l’autofagia. Uno dei possibili bersagli in cellule tumorali secretorie, come quelle del CaP, è rappresentato dal reticolo endoplasmatico (RE), organello intracellulare deputato alla sintesi, al ripiegamento e alle modificazioni post-traduzionali delle proteine di membrana e secrete. Alterazioni della protestasi a livello del RE inducono l’UPR, che svolge una duplice funzione nella cellula: primariamente funge da meccanismo omeostatico e di sopravvivenza, ma, quando l’omeostasi non è più ripristinabile e lo stimolo di attivazione dell’UPR cronicizza, può attivare vie di segnalazione che conducono alla morte cellulare programmata. La bivalenza, tipica dell’UPR, lo rende un bersaglio particolarmente interessante per promuovere la morte delle cellule tumorali: si può, infatti, sfruttare da una parte l’inibizione di componenti dell’UPR per abrogare i meccanismi adattativi e di sopravvivenza e dall’altra si può favorire il sovraccarico dell’UPR con conseguente induzione della via pro-apoptotica. Le catechine del tè verde sono composti polifenolici estratti dalle foglie di Camellia sinesis che possiedono comprovati effetti antitumorali: inibiscono la proliferazione, inducono la morte di cellule neoplastiche e riducono l’angiogenesi, l’invasione e la metastatizzazione di diversi tipi tumorali, tra cui il CaP. Diversi studi hanno osservato come il RE sia uno dei bersagli molecolari delle catechine del tè verde. In particolare, recenti studi del nostro gruppo di ricerca hanno messo in evidenza come il Polyphenon E (estratto standardizzato di catechine del tè verde) sia in grado, in modelli animali di CaP, di causare un’alterazione strutturale del RE e del Golgi, un deficit del processamento delle proteine secretorie e la conseguente induzione di uno stato di stress del RE, il quale causa a sua volta l’attivazione delle vie di segnalazione dell’UPR. Nel presente studio su due diverse linee cellulari di CaP (LNCaP e DU145) e in un nostro precedente studio su altre due linee cellulari (PNT1a e PC3) è stato confermato che il Polyphenon E è capace di indurre lo stress del RE e di determinare l’attivazione delle vie di segnalazione dell’UPR, le quali possono fungere da meccanismo di sopravvivenza, ma anche contribuire a favorire la morte cellulare indotta dalle catechine del tè verde (come nel caso delle PC3). Considerati questi effetti delle catechine del tè verde in qualità di induttori dell’UPR, abbiamo ipotizzato che la combinazione di questi polifenoli bioattivi e degli inibitori del proteasoma, anch’essi noti attivatori dell’UPR, potesse comportare un aggravamento dell’UPR stesso tale da innescare meccanismi molecolari di morte cellulare programmata. Abbiamo quindi studiato l’effetto di tale combinazione in cellule PC3 trattate con epigallocatechina-3-gallato (EGCG, la principale tra le catechine del tè verde) e due diversi inibitori del proteasoma, il bortezomib (BZM) e l’MG132. I risultati hanno dimostrato, diversamente da quanto ipotizzato, che l’EGCG quando associato agli inibitori del proteasoma non produce effetti sinergici, ma che anzi, quando viene addizionato al BZM, causa una risposta simil-antagonistica: si osserva infatti una riduzione della citotossicità e dell’effetto inibitorio sul proteasoma (accumulo di proteine poliubiquitinate) indotti dal BZM, inoltre anche l’induzione dell’UPR (aumento di GRP78, p-eIF2α, CHOP) risulta ridotta nelle cellule trattate con la combinazione di EGCG e BZM rispetto alle cellule trattate col solo BZM. Gli stessi effetti non si osservano invece nelle cellule PC3 trattate con l’EGCG in associazione con l’MG132, dove non si registra alcuna variazione dei parametri di vitalità cellulare e dei marcatori di inibizione del proteasoma e di UPR (rispetto a quelli osservati nel singolo trattamento con MG132). Essendo l’autofagia un meccanismo compensativo che si attiva in seguito all’inibizione del proteasoma o allo stress del RE, abbiamo valutato che ruolo potesse avere tale meccanismo nella risposta simil-antagonistica osservata in seguito al co-trattamento con EGCG e BZM. I nostri risultati hanno evidenziato, in cellule trattate con BZM, l’attivazione di un flusso autofagico che si intensifica quando viene addizionato l’EGCG. Tramite l’inibizione dell’autofagia mediante co-somministrazione di clorochina, è stato possibile stabilire che l’autofagia indotta dall’EGCG favorisce la sopravvivenza delle cellule sottoposte al trattamento combinato tramite la riduzione dell’UPR. Queste evidenze ci portano a concludere che per il trattamento del CaP è sconsigliabile associare le catechine del tè verde con il BZM e che in futuri studi di combinazione di questi polifenoli con composti antitumorali sarà importante valutare il ruolo dell’autofagia come possibile meccanismo di resistenza.