Bortezomib inhibits docetaxel-induced apoptosis via a p21-dependent mechanism in human prostate cancer cells

Synonymous mutations in the phosphoglycerate kinase 1 gene induce an altered response to protein misfolding in Schizosaccharomyces pombe

Background

Proteostasis refers to the processes that regulate the biogenesis, folding, trafficking, and degradation of proteins. Any alteration in these processes can lead to cell malfunction. Protein synthesis, a key proteostatic process, is highly-regulated at multiple levels to ensure adequate adaptation to environmental and physiological challenges such as different stressors, proteotoxic conditions and aging, among other factors. Because alterations in protein translation can lead to protein misfolding, examining how protein translation is regulated may also help to elucidate in part how proteostasis is controlled. Codon usage bias has been implicated in the fine-tuning of translation rate, as more-frequent codons might be read faster than their less-frequent counterparts. Thus, alterations in codon usage due to synonymous mutations may alter translation kinetics and thereby affect the folding of the nascent polypeptide, without altering its primary structure. To date, it has been difficult to predict the effect of synonymous mutations on protein folding and cellular fitness due to a scarcity of relevant data. Thus, the purpose of this work was to assess the effect of synonymous mutations in discrete regions of the gene that encodes the highly-expressed enzyme 3-phosphoglycerate kinase 1 (pgk1) in the fission yeast Schizosaccharomyces pombe.

Results

By means of systematic replacement of synonymous codons along pgk1, we found slightly-altered protein folding and activity in a region-specific manner. However, alterations in protein aggregation, heat stress as well as changes in proteasome activity occurred independently of the mutated region. Concomitantly, reduced mRNA levels of the chaperones Hsp9 and Hsp16 were observed.

Conclusion

Taken together, these data suggest that codon usage bias of the gene encoding this highly-expressed protein is an important regulator of protein function and proteostasis.

The Effect of Phase Transition Temperature on Therapeutic Efficacy of Liposomal Bortezomib

AIMS

Here, three liposomal formulations of DPPC/DPPG/Chol/DSPE-mPEG2000 (F1), DPPC/DPPG/Chol (F2) and HSPC/DPPG/Chol/DSPE-mPEG2000 (F3) encapsulating BTZ were prepared and characterized in terms of their size, surface charge, drug loading, and release profile. Mannitol was used as a trapping agent to entrap the BTZ inside the liposomal core. The cytotoxicity and anti-tumor activity of formulations were investigated in vitro and in vivo in mice bearing tumor.

BACKGROUND

Bortezomib (BTZ) is an FDA approved proteasome inhibitor for the treatment of mantle cell lymphoma and multiple myeloma. The low solubility of BTZ has been responsible for the several side effects and low therapeutic efficacy of the drug. Encapsulating BTZ in a nano drug delivery system; helps overcome such issues. Among NDDSs, liposomes are promising diagnostic and therapeutic delivery vehicles in cancer treatment.

OBJECTIVE

Evaluating anti-tumor activity of bortezomib liposomal formulations.

METHODS

Data prompted us to design and develop three different liposomal formulations of BTZ based on Tm parameter, which determines liposomal stiffness. DPPC (Tm 41°C) and HSPC (Tm 55°C) lipids were chosen as variables associated with liposome rigidity. In vitro cytotoxicity assay was then carried out for the three designed liposomal formulations on C26 and B16F0, which are the colon and melanoma cancer mouse-cell lines, respectively. NIH 3T3 mouse embryonic fibroblast cell line was also used as a normal cell line. The therapeutic efficacy of these formulations was further assessed in mice tumor models.

RESULT

MBTZ were successfully encapsulated into all the three liposomal formulations with a high entrapment efficacy of 60, 64, and 84% for F1, F2, and F3, respectively. The findings showed that liposomes mean particle diameter ranged from 103.4 to 146.8nm. In vitro cytotoxicity studies showed that liposomal-BTZ formulations had higher IC50 value in comparison to free BTZ. F2-liposomes with DPPC, having lower Tm of 41°C, showed much higher anti-tumor efficacy in mice models of C26 and B16F0 tumors compared to F3-HSPC liposomes with a Tm of 55°C. F2 formulation also enhanced mice survival compared with untreated groups, either in BALB/c or in C57BL/6 mice.

CONCLUSION

Our findings indicated that F2-DPPC-liposomal formulations prepared with Tm close to body temperature seem to be effective in reducing the side effects and increasing the therapeutic efficacy of BTZ and merits further investigation.

Targeting Wnt/EZH2/microRNA-708 signaling pathway inhibits neuroendocrine differentiation in prostate cancer

Prostate cancer (PC) castration resistance has been linked to the differentiation of PC luminal cells into hormone-refractory neuroendocrine (NE) cells. However, the molecular mechanisms controlling the emergence of lethal NE prostate cancer (NEPC) remain unclear. The present study aimed to investigate the mechanisms underlying the transition from prostate adenocarcinoma to NEPC. The microRNA miR-708 was involved in NE differentiation and was downregulated in NEPC cells and tumor specimens. miR-708 targeted Sestrin-3 to inhibit Forkhead Box O1 (FOXO1) phosphorylation, resulting in apoptosis of prostate adenocarcinoma cells and AKT-inactivated NEPC cells, the latter of which was consistent with the progression of tumor xenografts in mice under miR-708 treatment. In silico analysis of PC and NEPC tumor specimens suggested that the polycomb repressive complex subunit Enhancer of zeste homolog 2 (EZH2) was particularly overexpressed in NEPC. Notably, EZH2 bound to the miR-708 promoter and induced its silencing in NEPC. Inhibition of EZH2 prevented NE differentiation of PC cells. EZH2 expression was regulated by both Cyclin Dependent Kinase 1 (CDK1) and Wnt signaling. Silencing transcription factor 4 (TCF4), as a key protein in Wnt signaling, prevented NEPC formation. These results provide a molecular basis for the roles of miR-708 and EZH2 in NE differentiation in PC and highlight a new paradigm in NEPC formation and survival.

Investigational luteinizing hormone releasing hormone (LHRH) agonists and other hormonal agents in early stage clinical trials for prostate cancer

INTRODUCTION

The treatment and management of prostate cancer continues to evolve; newer classes of agents and combination therapies are being developed and some are being investigated in early phase clinical trials.

AREAS COVERED

We discuss investigational hormonal agents for the treatment of prostate cancer and focus primarily on luteinizing hormone releasing hormone (LHRH) agonists in early stage trials. We look at agents that target the hormonal axis, including anti-androgens, gonadotropins, estrogenic agents and progestogenic agents and other non-hormonal agents often used in combination with LHRH agonists. We review these candidates in the specific clinical niche in which they might find utility.

EXPERT OPINION

Of all candidate compounds being evaluated in clinical trials, very few will receive FDA approval. Few, if any of the investigational agents discussed here will be used routinely in clinical practice for treating prostate cancer. Recognizing the reasons for the failure of agents to advance to later stage trials is important. Furthermore, a thorough understanding of the mechanisms underlying prostate cancer pathogenesis, including various points in the HGPA and parallel pathways, will help identify potentially actionable targets.

Targeting the androgen receptor (AR) with AR degradation enhancer ASC-J9® led to increase docetaxel sensitivity via suppressing the p21 expression

Chemotherapy with docetaxel remains the effective therapy to suppress castration resistant prostate cancer (CRPC) in some patients. However, most chemotherapy with docetaxel eventually fails with the development of docetaxel resistance after 18-weeks of treatment. Here we found docetaxel treatment might have an adverse effect of increasing the androgen receptor (AR) protein level in the CRPC cells, and combining docetaxel with anti-AR therapy using AR-shRNA or the AR degradation enhancer ASC-J9® may increase docetaxel sensitivity to better suppress the CRPC cell growth. Mechanism dissection found docetaxel might have the adverse effect of increasing the AR protein stability via suppressing the AR ubiquitination due to the increased AR phosphorylation. The consequence of such increased AR protein may then lead to increase p21 expression via transcriptional regulation. Preclinical studies with in vitro cells lines also demonstrated that targeting AR with ASC-J9® led to suppressing the AR-increased p21 expression to improve the docetaxel sensitivity in the CRPC cells that already developed docetaxel resistance. Together, these results suggest that a combined therapy of docetaxel and ASC-J9® is a novel therapy to better suppress CRPC in patients that already developed docetaxel resistance.

A versatile nanoplatform for synergistic combination therapy to treat human esophageal cancer

One of the major goals of precision oncology is to promote combination therapy to improve efficacy and reduce side effects of anti-cancer drugs based on their molecular mechanisms. In this study, we aimed to develop and validate new nanoformulations of docetaxel (DTX) and bortezomib (BTZ) for targeted combination therapy to treat human esophageal cancer. By leveraging our versatile disulfide cross-linked micelles (DCMs) platform, we developed nanoformulations of DTX and BTZ (named DTX-DCMs and BTZ-DCMs). Their physical properties were characterized; their anti-cancer efficacies and mechanisms of action were investigated in a human esophageal cancer cell line in vitro. Furthermore, the in vitro anti-tumor activities of combination therapies (concurrent drug treatment, sequential drug treatment, and treatment using different ratios of the drugs) were examined in comparison with the single drug treatment and free drug strategies. These drug-loaded nanoparticles were spherical in shape and relatively small in size of approximately 20-22 nm. The entrapment efficiencies of DTX and BTZ into nanoparticles were 82.4% and 84.1%, respectively. The drug release rates of DTX-DCMs and BTZ-DCMs were sustained, and greatly increased in the presence of GSH. These nanodrugs were effectively internalized by KYSE30 esophageal cancer cells, and dose-dependently induced cell apoptosis. We further revealed a strong synergistic effect between DTX-DCMs and BTZ-DCMs against KYSE30 esophageal cancer cells. Sequential combination therapy with DTX-DCMs followed by BTZ-DCMs exhibited the best anti-tumor efficacy in vitro. This study demonstrates that DTX and BTZ could be successfully nanoformulated into disulfide cross-linked micelles. The nanoformulations of DTX and BTZ demonstrate an immense potential for synergistic combination therapy to treat human esophageal cancer.

Mitotic catastrophe and cell cycle arrest are alternative cell death pathways executed by bortezomib in rituximab resistant B-cell lymphoma cells

The ubiqutin-proteasome system (UPS) plays a role in rituximab-chemotherapy resistance and bortezomib (BTZ) possesses caspase-dependent (i.e. Bak stabilization) and a less characterized caspase-independent mechanism-of-action(s). Here, we define BTZ-induced caspase-independent cell death pathways. A panel of rituximab-sensitive (RSCL), rituximab-resistant cell lines (RRCL) and primary tumor cells derived from lymphoma patients (N = 13) were exposed to BTZ. Changes in cell viability, cell-cycle, senescence, and mitotic index were quantified. In resting conditions, RRCL exhibits a low-proliferation rate, accumulation of cells in S-phase and senescence. Exposure of RRCL to BTZ reduces cell senescence, induced G2-M phase cell-cycle arrest, and is associated with mitotic catastrophe. BTZ stabilized p21, CDC2, and cyclin B in RRCL and in primary tumor cells. Transient p21 knockdown alleviates BTZ-induced senescence inhibition, G2-M cell cycle blockade, and mitotic catastrophe. Our data suggest that BTZ can induce apoptosis or mitotic catastrophe and that p21 has a pivotal role in BTZ activity against RRCL.

Signaling mechanisms of bortezomib in TRAF3-deficient mouse B lymphoma and human multiple myeloma cells

Bortezomib, a clinical drug for multiple myeloma (MM) and mantle cell lymphoma, exhibits complex mechanisms of action, which vary depending on the cancer type and the critical genetic alterations of each cancer. Here we investigated the signaling mechanisms of bortezomib in mouse B lymphoma and human MM cells deficient in a new tumor suppressor gene, TRAF3. We found that bortezomib consistently induced up-regulation of the cell cycle inhibitor p21(WAF1) and the pro-apoptotic protein Noxa as well as cleavage of the anti-apoptotic protein Mcl-1. Interestingly, bortezomib induced the activation of NF-κB1 and the accumulation of the oncoprotein c-Myc, but inhibited the activation of NF-κB2. Furthermore, we demonstrated that oridonin (an inhibitor of NF-κB1 and NF-κB2) or AD 198 (a drug targeting c-Myc) drastically potentiated the anti-cancer effects of bortezomib in TRAF3-deficient malignant B cells. Taken together, our findings increase the understanding of the mechanisms of action of bortezomib, which would aid the design of novel bortezomib-based combination therapies. Our results also provide a rationale for clinical evaluation of the combinations of bortezomib and oridonin (or other inhibitors of NF-κB1/2) or AD 198 (or other drugs targeting c-Myc) in the treatment of lymphoma and MM, especially in patients containing TRAF3 deletions or relevant mutations.

Pancreatic Cancer Combination Therapy Using a BH3 Mimetic and a Synthetic Tetracycline

Improved treatments for pancreatic cancer remain a clinical imperative. Sabutoclax, a small-molecule BH3 mimetic, inhibits the function of antiapoptotic Bcl-2 proteins. Minocycline, a synthetic tetracycline, displays antitumor activity. Here, we offer evidence of the combinatorial antitumor potency of these agents in several preclinical models of pancreatic cancer. Sabutoclax induced growth arrest and apoptosis in pancreatic cancer cells and synergized with minocycline to yield a robust mitochondria-mediated caspase-dependent cytotoxicity. This combinatorial property relied upon loss of phosphorylated Stat3 insofar as reintroduction of activated Stat3-rescued cells from toxicity. Tumor growth was inhibited potently in both immune-deficient and immune-competent models with evidence of extended survival. Overall, our results showed that the combination of sabutoclax and minocycline was highly cytotoxic to pancreatic cancer cells and safely efficacious in vivo.

Efficacy of therapy with bortezomib in solid tumors: a review based on 32 clinical trials

The ubiquitin-proteasome system is a major pathway for protein degradation, so that proteasome is now considered as an important target for drug discovery. Bortezomib, the first US FDA-approved proteasome inhibitor now used as a front-line treatment for multiple myeloma. To better understand the effects of bortezomib in cancer treatment, we carried out a review based on 32 published clinical trials to determine whether bortezomib will benefit patients with solid tumors. Information of complete response, partial response, stable disease and objective response rate was collected to assess clinical outcomes. A lack of therapeutic effects was observed when bortezomib was used as a single agent. Meanwhile, when bortezomib treatment was combined with other agents, bortezomib offered no statistically significant response versus these agents alone. High-quality studies are required to better understand the clinically effects of bortezomib and the development of a new generation of proteasome inhibitors is absolutely necessary.

Increased acid ceramidase expression depends on upregulation of androgen-dependent deubiquitinases, USP2, in a human prostate cancer cell line, LNCaP

Acid ceramidase (ACDase) metabolizes ceramide to sphingosine, leading to sphingosine 1-phosphate production. Reportedly, ACDase has been upregulated in prostate cancer. However, its regulatory mechanism remains unclear. LNCaP (androgen-sensitive prostate cancer cell line) but not PC3 and DU-145, (androgen-unresponsive cell lines) exhibited the highest ACDase protein. Among three cell lines, ASAH1 mRNA level was not correlated with ACDase protein expression, and the 5'-promoter activity did not show androgen dependency, suggesting the post-transcriptional regulation of ACDase in LNCaP cells. Based on these results, LNCaP was analysed further. Casodex, androgen receptor antagonist, and charcoal-stripped FCS (CS-FCS) decreased ACDase protein and activity, whereas dihydrotestosterone in CS-FCS culture increased ACDase protein and enzyme activity. MG132, a proteasome inhibitor, prevented the decrease of ACDase protein when cultured in CS-FCS, suggesting the involvement of ubiquitin/proteasome system. Reportedly, USP2, a deubiquitinase, plays an important role in LNCaP cells. USP2 siRNA decreased ACDase protein, whereas USP2 overexpression increased ACDase protein of LNCaP cells. However, SKP2, an ubiquitin E3 ligase known to be active in prostate cancer, did not affect androgen-dependent ACDase expression in LNCaP cells. Thus, ACDase regulation by androgen in androgen-sensitive LNCaP cells is mainly due to its prolonged protein half-life by androgen-stimulated USP2 expression.

Structural characterization of functionalized gold nanoparticles for drug delivery in cancer therapy: a NMR based approach

Structure of Bortezomib loaded, surface functionalized Au nanoparticles.

The effects of phenoxodiol on the cell cycle of prostate cancer cell lines

Background

Prostate cancer is associated with a poor survival rate. The ability of cancer cells to evade apoptosis and exhibit limitless replication potential allows for progression of cancer from a benign to a metastatic phenotype. The aim of this study was to investigate in vitro the effect of the isoflavone phenoxodiol on the expression of cell cycle genes.

Methods

Three prostate cancer cell lines-LNCaP, DU145, and PC3 were cultured in vitro, and then treated with phenoxodiol (10 μM and 30 μM) for 24 and 48 h. The expression of cell cycle genes p21^WAF1, c-Myc, Cyclin-D1, and Ki-67 was investigated by Real Time PCR.

Results

Here we report that phenoxodiol induces cell cycle arrest in the G1/S phase of the cell cycle, with the resultant arrest due to the upregulation of p21^WAF1 in all the cell lines in response to treatment, indicating that activation of p21^WAF1 and subsequent cell arrest was occurring via a p53 independent manner, with induction of cytotoxicity independent of caspase activation. We found that c-Myc and Cyclin-D1 expression was not consistently altered across all cell lines but Ki-67 signalling expression was decreased in line with the cell cycle arrest.

Conclusions

Phenoxodiol demonstrates an ability in prostate cancer cells to induce significant cytotoxicity in cells by interacting with p21^WAF1 and inducing cell cycle arrest irrespective of p53 status or caspase pathway interactions. These data indicate that phenoxodiol would be effective as a potential future treatment modality for both hormone sensitive and hormone refractory prostate cancer.

MLN2238, a proteasome inhibitor, induces caspase-dependent cell death, cell cycle arrest, and potentiates the cytotoxic activity of chemotherapy agents in rituximab-chemotherapy-sensitive or rituximab-chemotherapy-resistant B-cell lymphoma preclinical models

To further develop therapeutic strategies targeting the proteasome system, we studied the antitumor activity and mechanisms of action of MLN2238, a reversible proteasome inhibitor, in preclinical lymphoma models. Experiments were conducted in rituximab-chemotherapy-sensitive cell lines, rituximab-chemotherapy-resistant cell lines (RRCL), and primary B-cell lymphoma cells. Cells were exposed to MLN2238 or caspase-dependent inhibitors, and differences in cell viability, alterations in apoptotic protein levels, effects on cell cycle, and the possibility of synergy when combined with chemotherapeutic agents were evaluated. MLN2238 showed more potent dose-dependent and time-dependent cytotoxicity and inhibition of cell proliferation in lymphoma cells than bortezomib. Our data suggest that MLN2238 can induce caspase-independent cell death in RRCL. MLN2238 (and to a much lesser degree bortezomib) reduced RRCL S phase and induced cell cycle arrest in the G2/M phase. Exposure of rituximab-chemotherapy-sensitive cell lines and RRCL to MLN2238 potentiated the cytotoxic effects of gemcitabine, doxorubicin, and paclitaxel and overcame resistance to chemotherapy in RRCL. MLN2238 is a potent proteasome inhibitor active in rituximab-chemotherapy-sensitive and rituximab-chemotherapy-resistant cell models and potentiates the antitumor activity of chemotherapy agents and has the potential of becoming an effective therapeutic agent in the treatment of therapy-resistant B-cell lymphoma.

Gold nanoparticle delivery-enhanced proteasome inhibitor effect in adenocarcinoma cells

BACKGROUND

Proteasome inhibition is a current therapeutic strategy used in the treatment of multiple myeloma. Drugs controlling proteasome activity are ideally suited for unidirectional manipulation of cellular pathways such as apoptosis. The first proteasome inhibitor approved in clinics was bortezomib. This drug is currently used in combination with other anticancer agents.

OBJECTIVES

In this study, the enhancement of bortezomib activity was evaluated using gold nanoparticles coated with poly(ethylene glycol). The uptake mechanism of the gold nanoparticles in pancreatic cell lines, S2-013 and hTERT-HPNE, was assessed by laser scanning confocal microscopy (LSCM).

RESULTS

Pancreatic cancer cells internalized the nanoparticles together with the drug in few minutes through the formation of endocytic vesicles. This rapid uptake leads to an increase in the concentration and diffusion of bortezomib in the cytoplasm yielding an increased toxicity on the cells when compared to the drug alone.

CONCLUSION

Gold nanoparticles can be used as effective delivery systems to increasing the permeation and retention of drugs in cancer cells.

The novel proteasome inhibitor carfilzomib induces cell cycle arrest, apoptosis and potentiates the anti-tumour activity of chemotherapy in rituximab-resistant lymphoma

Targeting the proteasome system with bortezomib (BTZ) results in anti-tumour activity and potentiates the effects of chemotherapy/biological agents in multiple myeloma and B-cell lymphoma. Carfilzomib (CFZ) is a more selective proteasome inhibitor that is structurally distinct from BTZ. In an attempt to characterize its biological activity, we evaluated CFZ in several lymphoma pre-clinical models. Rituximab-sensitive cell lines (RSCL), rituximab-resistant cell lines (RRCL), and primary tumour cells derived from B-cell lymphoma patients were exposed to CFZ or BTZ. Cell viability and changes in cell cycle were determined. Western blots were performed to detect PARP-cleavage and/or changes in Bcl-2 (BCL2) family members. CFZ was 10 times more active than BTZ and exhibited dose- and time-dependent cytotoxicity. CFZ exposure induced apoptosis by upregulation of Bak (BAK1) and subsequent PARP cleavage in RSCL and RRCL; it was also partially caspase-dependent. CFZ induced G2/M phase cell cycle arrest in RSCL. CFZ demonstrated the ability to overcome resistance to chemotherapy in RRCL and potentiated the anti-tumour activity of chemotherapy agents. Our data suggest that CFZ is able to overcome resistance to chemotherapeutic agents, upregulate pro-apoptotic proteins to promote apoptosis, and induce G2/M cell cycle arrest in lymphoma cells. Our pre-clinical data supports future clinical evaluation of CFZ in B-cell lymphoma.

Targeting the ubiquitin+proteasome system in solid tumors

The ubiquitin+proteasome system (UPS) is a highly complex network that maintains protein homeostasis and cell viability through the selective turnover of targeted substrates. The proteasome serves as the catalytic core of the UPS to recognize and execute the coordinated and efficient removal of ubiquitinated proteins. Pharmacologic inhibitors that exploit the pivotal role of the proteasome in cellular metabolism promote tumor cytotoxicity and have yielded durable clinical responses that dramatically improve patient survival. Success of the proteasome inhibitor (PI) bortezomib in the treatment of the hematologic malignancy multiple myeloma (MM) has emerged as the standard-of-care and catapulted the UPS into a position of prominence as a model system in cancer biology and drug development. However, expansion of PIs in the treatment of the more complex solid tumors has been less successful. While clinical evaluation of second-generation PIs progresses, other potential sites of therapeutic intervention within the UPS continue to emerge, such as the non-proteolytic activities associated with the proteasome and the rapidly expanding number of Ub-binding proteins. Molecular-genetic approaches to further unravel the complexity of the UPS will advance its utilization as a platform for the development of novel, mechanism-based anticancer strategies.

Bortezomib-enhanced radiosensitization through the suppression of radiation-induced nuclear factor-κB activity in human oral cancer cells

Oral cancer cells have a significantly augmented nuclear factor-κB (NF-κB) activity and the inhibition of this activity suppresses tumor growth. Bortezomib is a proteasome inhibitor and a drug used for molecular-targeted therapy (targets NF-κB). In this study, we investigated whether bortezomib would be effective as an inhibitor of proliferation and a radiosensitizer for the treatment of oral cancer. We demonstrate that bortezomib inhibits NF-κB activity and cell proliferation. The combined treatment with bortezomib and radiation (RT) suppressed NF-κB activity and cell growth in vitro and in vivo compared with RT treatment alone. To investigate the mechanisms by which bortezomib suppresses tumor growth, the expression of signaling molecules downstream of NF-κB were examined by ELISA. The combined treatment significantly inhibited the radiation-induced production of angiogenic factors and decreased the number of blood vessels in the tumor tissues. Although the expression of anti-apoptotic proteins was upregulated by RT, bortezomib downregulated the RT-induced expression of these proteins. Moreover, the expression of cleaved poly(ADP-ribose) polymerase in vitro and in vivo was enhanced by bortezomib, indicating that bortezomib inhibits tumor growth by inducing apoptosis. This study clearly demonstrates that bortezomib significantly inhibits tumor growth and that the combined treatment with bortezomib and RT results in a significant inhibition of tumor growth. The mechanisms underlying the inhibition of tumor growth by bortezomib include the suppression of angiogenesis and the induction of apoptosis. A novel molecular targeting therapy including bortezomib may be effective in the treatment of oral cancer by suppressing NF-κB activity.

Combined inhibition of cellular pathways as a future therapeutic option in fatal anaplastic thyroid cancer

Conventional treatment by surgery, radioiodine, and thyroxin-suppressive therapy often fails to cure anaplastic thyroid cancer (ATC). Therefore several attempts have been made to evaluate new therapy options by use of "small molecule inhibitors". ATC was shown to respond to monotherapeutic proteasome and Aurora kinase inhibition in vitro as well as in xenotransplanted tumor cells. Aim of this study was to evaluate the effect of combined treatment targeting the ubiquitin-proteasome system by bortezomib and Aurora kinases by use of MLN8054. Three ATC cell lines (Hth74, C643, and Kat4.1) were used. The antiproliferative effect of combined treatment with bortezomib and MLN8054 was assessed by MTT-assay and cell cycle analysis (FACS). Proapoptotic effects were evaluated by measurement of Caspase-3 activity, and effects on VEGF secretion were analyzed by ELISA. Compared to mono-application combined treatment with bortezomib and MLN8054 resulted in a further decrease of cell density, whereas antagonizing effects were found regarding cell cycle progression. Caspase-3 activity was increased up to 2.7- and 14-fold by mono-application of MLN8054 and bortezomib, respectively. When the two drugs were used in combination, a further enhancement of Caspase-3 activity was achieved, depending on the cell line. VEGF secretion was decreased following bortezomib treatment and remained unchanged by MLN8054. Only in C643 cells, the bortezomib-induced down-regulation was enhanced when MLN8054 was applied simultaneously. In conclusion, our data demonstrate that targeting the proteasome and Aurora kinases simultaneously results in additional antitumoral effects in vitro, especially regarding cell growth and induction of apoptosis. The efficacy of this therapeutic approach remains to be revised by in vivo and clinical application.

The association of statins and taxanes: an efficient combination trigger of cancer cell apoptosis

Background:

Cancer cell killing might be achieved by the combined use of available drugs. Statins are major anti-hypercholesterolemia drugs, which also trigger apoptosis of many cancer cell types, while docetaxel is a potent microtubule-stabilising agent.

Methods:

Here, we looked at the combined effects of lovastatin and docetaxel in cancer cells.

Results:

Whole transcriptome microarrays in HGT-1 gastric cancer cells demonstrated that lovastatin strongly suppressed expression of genes involved in cell division, while docetaxel had very little transcriptional effects. Both drugs triggered apoptosis, and their combination was more than additive. A marked rise in the cell-cycle inhibitor p21, together with reduction of aurora kinases A and B, cyclins B1 and D1 proteins was induced by lovastatin alone or in combination with docetaxel. The drug treatments induced the proteolytic cleavage of procaspase-3, a drop of the anti-apoptotic Mcl-1 protein, Poly-ADP-Ribose Polymerase and Bax. Strikingly, docetaxel-resistant HGT-1 cell derivatives overexpressing the MDR-1 gene were much more sensitive to lovastatin than docetaxel-sensitive cells.

Conclusion:

These results suggest that the association of lovastatin and docetaxel, or lovastatin alone, shows promise as plausible anticancer strategies, either as a direct therapeutic approach or following acquired P-glycoprotein-dependent resistance.

Semi-high throughput method of measuring proteasome inhibition in vitro and in cultured cells

The ubiquitin proteasome-proteolytic pathway has emerged as one of the most significant pathways in modulating protein homeostasis under both normal and disease states. The use of proteasome inhibitors (PI) has played a pivotal role in understanding protein turn over. The main objective of this work was to develop a comprehensive, fast, and reliable, yet simple in vitro assay that would allow for the identification and characterization of a wide range of PIs. The assays consist of a 96-well plate high throughput (HTP) method to assess proteasome activity in Hs578T breast cancer cell extracts, purified 20S proteasome, using a fluorogenic substrate, Suc-leu-leu-val-tyr-7-AMC, specific to the chymotrypsin-like enzymatic activity of the proteasome. We showed that the chymotrypsin-like activity of the proteasome was inhibited in the two in vitro systems, albeit to different degrees. The assay system also includes two cell-based assays consisting of a vector expressing a fusion protein of green fluorescent protein (gfp) and Mouse Ornithine Decarboxylase (MODC) in Zs578T (parental Hs578T carrying the vector that expresses the fusion protein). In the cell-based assay analyses (qualitatively by microscopy and quantitatively by flow cytometry), treatment of Zs578T with PIs prevented the degradation of MODC, accumulated gfp, indicative of increased proteasome inhibition. Because no single assay represents a definitive proof of proteasome inhibitory activity, combined, these assays should serve as a comprehensive benchmark for the identification and partial characterization of novel inhibitors. In summary, the four-step assay protocol can easily be adapted into a high throughput format to rapidly screen unknown inhibitors.

NF-kappaB activation enhances cell death by antimitotic drugs in human prostate cancer cells

Background

NF-κB is a transcription factor that promotes inhibition of apoptosis and resistance to chemotherapy. It is commonly believed that inhibition of NF-κB activity can increase sensitivity of cancer cells to chemotherapy. However, there is evidence that NF-κB activation can sensitize cells to apoptosis and that inhibition of NF-κB results in resistance to chemotherapy. In prostate cancer, it is not clear in the different cell types (androgen-dependent and castration-resistant) if activation or inhibition of NF-κB is required for stimulation of apoptosis by chemotherapy.

Results

Our data indicate that the response of prostate cancer (PC) cells to the antimitotic drugs docetaxel (Doc) and 2-methoxyestradiol (2ME2) is dependent on the levels of NF-κB activity. In androgen-dependent LNCaP cells, Doc and 2ME2 treatment increased the low basal NF-κB activity, as determined by Western blot analysis of phospho-IκBα/p65, NF-κB promoter reporter assays, and p65 localization. Treatment of LNCaP cells with parthenolide, a pharmacologic inhibitor of NF-κB, or introduction of dominant-negative IκBα, or an shRNA specific for p65, a component of the NF-κB heterodimer, blocked apoptosis induced by Doc and 2ME2. In castration-resistant DU145 and PC3 cells, Doc and 2ME2 had little effect on the high basal NF-κB activity and addition of parthenolide did not enhance cell death. However, the combination of Doc or 2ME2 with betulinic acid (BA), a triterpenoid that activates NF-κB, stimulated apoptosis in LNCaP and non-apoptotic cell death in DU145 and PC3 cells. Increased sensitivity to cell death mediated by the Doc or 2ME2 + BA combination is likely due to increased NF-κB activity.

Conclusions

Our data suggest that the combination of antimitotic drugs with NF-κB inhibitors will have antagonistic effects in a common type of PC cell typical of LNCaP. However, combination strategies utilizing antimitotic drugs with BA, an activator of NF-κB, will universally enhance cell death in PC cells, notably in the aggressive, castration-resistant variety that does not respond to conventional therapies.

Bim-targeted cancer therapy: a link between drug action and underlying molecular changes

In the past few years, the pro-apoptotic molecule Bim has attracted increasing attention as a plausible target for tumor therapy. A variety of normal and pathological systems regulated by Bim, dependent on cell type, apoptotic stimulation, and chemotherapeutic agents, have been documented. Bim promotes anoikis of many tumor cells, such as lung cancer, breast cancer, osteosarcoma, and melanoma. Various chemotherapeutic agents use Bim as a mediating executioner of cell death. Hence, Bim suppression supports metastasis and chemoresistance. Imatinib, gefitinib, bortezomib, and Bim protein itself are spotlighted as current and future Bim-targeting therapeutic agents. The potential benefits of Bim-targeted therapies are selectivity of treatment for tumor cells and reduction in tumor-associated phenomena such as chemoresistance and metastasis. Thus, Bim-targeting therapies may provide more effective and unique tumor management modalities in future. This review article discusses all these issues.

A dose-finding and pharmacodynamic study of bortezomib in combination with weekly paclitaxel in patients with advanced solid tumors

PURPOSE

A phase I study to determine the maximum tolerated dose (MTD) of bortezomib (B) when combined with weekly paclitaxel in patients with advanced solid tumors.

PATIENTS AND METHODS

Eligible patients received escalating doses of intravenous (IV) bortezomib (0.6-2 mg/m(2)) on days 2 and 9 and IV paclitaxel at 100 mg/m(2) on days 1 and 8 of a 21-day cycle. Dose escalation was based on two end-points: not exceeding 80% 20S-proteasome inhibition (20-S PI) and the development of dose-limiting toxicity defined as grade 3 or greater non-hematologic or grade 4 hematologic toxicities.

RESULTS

Forty-five patients with advanced solid tumors and a median of 3 prior chemotherapy regimens (range 0-9), received 318 doses (median 5, range 1-34) of bortezomib and paclitaxel. Dose-related inhibition of 20-S PI was observed with a maximum inhibition of 70-80% at the MTD of 1.8 mg/m(2) of bortezomib. At the MTD (N = 9) the following toxicities were observed: grade 4 neutropenia without fever (n = 2) and cerebrovascular ischemia (n = 1); grade 3 neutropenia (n = 3), diarrhea (n = 2), nausea (n = 1), and fatigue (n = 1); grade 2 fatigue (n = 5), diarrhea (n = 4), and dyspnea (n = 2). There was one partial response in a patient with an eccrine porocarcinoma. Stabilization of disease was observed in 7 (16%) patients, 3 of whom had advanced pancreatic cancer.

CONCLUSION

Sequential paclitaxel and bortezomib in previously treated patients with advanced solid tumors resulted in acceptable toxicity and no evidence of interaction. The recommended phase II dose of bortezomib in combination with weekly paclitaxel was 1.8 mg/m(2).

The proteasome inhibitor Bortezomib aggravates renal ischemia-reperfusion injury

Bortezomib is a well-established treatment option for patients with multiple myeloma (MM). It is a selective and reversible inhibitor of the proteasome that is responsible for the degradation of many regulatory proteins that are involved in apoptosis, cell-cycle regulation, or transcription. Because patients with MM are prone to develop acute renal failure, we evaluated the influence of Bortezomib on renal ischemia-reperfusion injury (IRI). Mice were subjected to renal IRI by having the renal pedicles clamped for 30 min followed by reperfusion for 3, 24, and 48 h. Mice were either pretreated with 0.5 mg/kg body wt Bortezomib or vehicle intravenously 12 h before induction of IRI. Serum creatinine and tubular necrosis were significantly increased in Bortezomib compared with vehicle-treated mice. The inflammatory response was found to be significantly decreased in Bortezomib-treated mice as reflected by a decreased infiltration of CD4+ T cells and a significantly decreased Th1 cytokine expression in the kidneys. In contrast, apoptosis was significantly increased in kidneys of Bortezomib-treated mice compared with vehicle-treated controls. Increased numbers of TUNEL-positive cells/mm2 and increased mRNA expression of proapoptotic factors were detected in kidneys of Bortezomib-treated mice. Of note, p21, a cell senescence marker, was also significantly increased in kidneys of Bortezomib-treated mice. In summary, we provide evidence that Bortezomib worsens the outcome of renal IRI by leading to increased apoptosis of tubular cells despite decreased infiltrating T cells and proinflammatory mediators.

Mechanisms of proteasome inhibitor action and resistance in cancer

Proteasome inhibitors (PIs), such as bortezomib, carfilzomib or NPI-0052, have excellent clinical activity in patients with multiple myeloma and mantle cell lymphoma, and they are currently being evaluated in combination with other agents in patients with solid tumors. Although they exert broad effects on cancer cells, their ability to (1) stabilize pro-apoptotic members of the BCL-2 family, (2) inhibit the two major pathways leading to NFkappaB activation, and (3) cause the build-up of misfolded proteins appear to be particularly important. In addition, PIs may disrupt tumor-stromal interactions that drive NFkappaB activation and angiogenesis and in such a way sensitize cancer cells to other agents. Still, drug resistance ultimately emerges in all tumors that initially respond to PIs. This review provides an overview of the current thinking about how PIs may kill cancer cells exemplified for pancreatic cancer and the possible mechanisms involved in resistance to PIs.

Proteasome inhibitors induce apoptosis of prostate cancer cells by inducing nuclear translocation of IkappaBalpha

Proteasome inhibitors are known to suppress the proteasome-mediated degradation of IkappaBalpha in stimulated cells. This results in the cytoplasmic retention of NFkappaB and its reduced nuclear transcriptional activity. In this study, we show that in the metastatic prostate cancer cells, the proteasome inhibitors exhibit a novel, previously unrecognized effect: they increase the cellular levels of IkappaBalpha, which then translocates to the nucleus, associates with the nuclear p65 NFkappaB, thus inhibiting the constitutive NFkappaB DNA binding activity and inducing apoptosis. The proteasome inhibition-induced nuclear translocation of IkappaBalpha is dependent on de novo protein synthesis, occurs also in other cell types, and does not require IkappaBalpha phosphorylation on Ser-32. Since NFkappaB activity is constitutively increased in many human cancers as well as in inflammatory disorders, the proteasome inhibition-induced nuclear translocation of IkappaBalpha could thus provide a new therapeutic strategy aimed at the specific inhibition of NFkappaB activity by the nuclear IkappaBalpha.

Proteasome inhibitors in cancer therapy: lessons from the first decade

The ubiquitin-proteasome pathway is involved in intracellular protein turnover, and its function is crucial to cellular homeostasis. First synthesized as probes of proteolytic processes, proteasome inhibitors began to be thought of as potential drug candidates when they were found to induce programmed cell death preferentially in transformed cells. They made their first leap into the clinic to be tested as therapeutic agents 10 years ago, and since then, great strides have been made in defining their mechanisms of action, their clinical efficacy and toxicity, and some of their limitations in the form of resistance pathways. Validation of the ubiquitin-proteasome pathway as a target for cancer therapy has come in the form of approvals of the first such inhibitor, bortezomib, for relapsed/refractory multiple myeloma and mantle cell lymphoma, for which this agent has become a standard of care. Lessons learned from this first-in-class agent are now being applied to the development of a new generation of proteasome inhibitors that hold the promise of efficacy in bortezomib-resistant disease and possibly in a broader spectrum of diseases. This saga provides a salient example of the promise of translational medicine and a paradigm by which other agents may be successfully brought from the bench to the bedside.

Antiproliferative and survival properties of PMA in MCF-7 breast cancer cell

Although PKCs are assumed to be the main targets of phorbol esters (PMA), additional PMA effectors, such as chimaerins (a family of RacGTPase activating proteins) and RasGRP (exchange factor for Ras/Rap1), can counteract or strengthen the PKC pathways. In this study, we evaluated the proliferative behavior of PMA-treated MCF-7 breast cancer cell and found that: PMA induced growth arrest and inhibited cell death; PMA activated ERKs, which, in turn, induced p21; and inhibitors of ERK (PD98059) and PKC (GF109203X) prevented p21 induction and abolished the PMA survival effect. We conclude that PMA inhibits MCF-7 cell growth and simultaneously stimulates cell survival; both responses are linked to ERK-dependent and p53-independent p21 induction.

The histone deacetylase inhibitor, PXD101, potentiates bortezomib-induced anti-multiple myeloma effect by induction of oxidative stress and DNA damage

Clinical trials have shown the high anti-myeloma activity of the proteasome inhibitor bortezomib. The present study examined the activity of bortezomib combined with PXD101, a histone deacetylase inhibitor, against multiple myeloma (MM) and osteoclastogenesis. Treatment of myeloma cell lines with combinations of bortezomib and PXD101 led to synergistic inhibition of proliferation and induction of cell death. The combination significantly decreased the viability of primary human CD138(+) myeloma cells but not of bone marrow mononuclear cells. Further studies showed a dose-dependent activation of caspases-3, -8 and -9 and nuclear fragmentation in myeloma cells. Bortezomib/PXD101 treatment markedly triggered reactive oxygen species (ROS) generation that was accompanied by p53, H2A.X and p38-mitogen-activated protein kinase phosphorylation. ROS generation could be blocked by the free radical scavenger N-acetyl-L-cysteine. The combination of bortezomib and PXD101 also resulted in synergistic inhibition of osteoclast formation. In conclusion, bortezomib and PXD101 have different molecular targets. The combination induces cell death in myeloma cells via ROS-mediated DNA damage and also inhibits osteoclastogenesis. Therefore, this study provides the rationale for the clinical evaluation of bortezomib combined with PXD101 in patients with MM.

BCL-2 family regulation by the 20S proteasome inhibitor bortezomib

Bortezomib (Velcade, PS341) was licensed in 2003 as a first-in-class 20S proteasome inhibitor indicated for treatment of multiple myeloma, and is currently being evaluated clinically in a range of solid tumours. The mechanisms underlying its cancer cell toxicity are complex. A growing body of evidence suggests proteasome inhibition-dependent regulation of the BCL-2 family is a critical requirement. In particular, the stabilization of BH3-only proteins BIK, NOXA and BIM, appear to be essential for effecting BAX- and BAK-dependent cell death. These mechanisms are reviewed and the implications for favourable novel drug interactions are highlighted.

Phase I/II study of bortezomib plus docetaxel in patients with advanced androgen-independent prostate cancer

PURPOSE

To determine the dose-limiting toxicities and maximum tolerated dose, and evaluate the antitumor activity of bortezomib/docetaxel combination therapy in androgen-independent prostate cancer.

EXPERIMENTAL DESIGN

Two bortezomib doses (1.3 and 1.6 mg/m(2)/dose) in combination with four docetaxel doses (25-40 mg/m(2)/dose) were evaluated. Both drugs were administered weekly for 2 out of 3 weeks. Antitumor activity was evaluated using prostate-specific antigen (PSA) levels and Response Evaluation Criteria in Solid Tumors guidelines.

RESULTS

Eighty-three patients received at least one dose of study drug. No dose-limiting toxicities were observed despite escalation to the highest dose level. PSA response (>or=50% decline in PSA levels from the baseline) occurred in 19 (28%) of 67 evaluable patients and was maintained for >or=4 weeks in 14 patients (21%). According to Response Evaluation Criteria in Solid Tumors guidelines, 11% achieved a partial response, and an additional 67% had stable disease. The degree of proteasome inhibition was similar to that reported with single-agent bortezomib. Treatment was well tolerated; fatigue was the most common drug-related adverse event, whereas diarrhea was the most common drug-related grade 3/4 adverse event. No clinically significant febrile neutropenia or neuropathy occurred.

CONCLUSIONS

The maximum tolerated dose of this 21-day regimen has not been reached. The highest dose level (1.6 mg/m(2) bortezomib plus 40 mg/m(2) docetaxel) was feasible and tolerable; bortezomib plus docetaxel showed antitumor activity. Activity and tolerability results were consistent with previous studies of bortezomib alone or in combination with docetaxel. Further investigations are warranted to determine activity and optimize bortezomib/docetaxel therapy in androgen-independent prostate cancers.

Gefitinib reverses TRAIL resistance in human bladder cancer cell lines via inhibition of AKT-mediated X-linked inhibitor of apoptosis protein expression

In a previous study, we found that the small-molecule epidermal growth factor receptor (EGFR) inhibitor gefitinib (ZD1839, Iressa) blocked cell proliferation at biologically relevant concentrations in approximately one third (6 of 17) of human bladder cancer cell lines examined. Here, we studied the effects of gefitinib on apoptosis in a representative subset of the same panel of cells. The drug had modest effects on DNA fragmentation as a single agent at concentrations that produced strong growth inhibition (< or =1 micromol/L) and also failed to promote apoptosis induced by conventional chemotherapeutic agents (gemcitabine and paclitaxel). However, gefitinib did interact with recombinant human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to induce high levels of apoptosis in gefitinib-responsive but not gefitinib-unresponsive lines. The molecular mechanisms involved down-regulation of active AKT and X-linked inhibitor of apoptosis protein (XIAP) expression and were mimicked by chemical inhibitors of the phosphatidylinositol 3-kinase/AKT pathway but not of the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase/ERK pathway. Furthermore, direct small interfering RNA-mediated knockdown of AKT resulted in down-regulation of XIAP and TRAIL sensitization, and knockdown of XIAP itself was sufficient to reverse TRAIL resistance. Together, our results show that EGFR pathway activation limits TRAIL-induced apoptosis via an AKT- and XIAP-dependent mechanism in EGFR-dependent human bladder cancer cells, providing the conceptual framework for a further evaluation of the combination in relevant preclinical in vivo models.