Effects of the proteasome inhibitor bortezomib on gene expression profiles of pancreatic cancer cells

Comprehensive Structure-Activity Relationship Studies of Cepafungin Enabled by Biocatalytic C-H Oxidations

The cepafungins are a class of highly potent and selective eukaryotic proteasome inhibitor natural products with potential to treat refractory multiple myeloma and other cancers. The structure-activity relationship of the cepafungins is not fully understood. This Article chronicles the development of a chemoenzymatic approach to cepafungin I. A failed initial route involving derivatization of pipecolic acid prompted us to examine the biosynthetic pathway for the production of 4-hydroxylysine, which culminated in the development of a 9-step synthesis of cepafungin I. An alkyne-tagged analogue enabled chemoproteomic studies of cepafungin and comparison of its effects on global protein expression in human multiple myeloma cells to the clinical drug bortezomib. A preliminary series of analogues elucidated critical determinants of potency in proteasome inhibition. Herein we report the chemoenzymatic syntheses of 13 additional analogues of cepafungin I guided by a proteasome-bound crystal structure, 5 of which are more potent than the natural product. The lead analogue was found to have 7-fold greater proteasome β5 subunit inhibitory activity and has been evaluated against several multiple myeloma and mantle cell lymphoma cell lines in comparison to the clinical drug bortezomib.

Resistance to Gemcitabine in Pancreatic Ductal Adenocarcinoma: A Physiopathologic and Pharmacologic Review

Pancreatic ductal adenocarcinoma (PDAC) is a very aggressive tumor with a poor prognosis and inadequate response to treatment. Many factors contribute to this therapeutic failure: lack of symptoms until the tumor reaches an advanced stage, leading to late diagnosis; early lymphatic and hematic spread; advanced age of patients; important development of a pro-tumoral and hyperfibrotic stroma; high genetic and metabolic heterogeneity; poor vascular supply; a highly acidic matrix; extreme hypoxia; and early development of resistance to the available therapeutic options. In most cases, the disease is silent for a long time, andwhen it does become symptomatic, it is too late for ablative surgery; this is one of the major reasons explaining the short survival associated with the disease. Even when surgery is possible, relapsesare frequent, andthe causes of this devastating picture are the low efficacy ofand early resistance to all known chemotherapeutic treatments. Thus, it is imperative to analyze the roots of this resistance in order to improve the benefits of therapy. PDAC chemoresistance is the final product of different, but to some extent, interconnected factors. Surgery, being the most adequate treatment for pancreatic cancer and the only one that in a few selected cases can achieve longer survival, is only possible in less than 20% of patients. Thus, the treatment burden relies on chemotherapy in mostcases. While the FOLFIRINOX scheme has a slightly longer overall survival, it also produces many more adverse eventsso that gemcitabine is still considered the first choice for treatment, especially in combination with other compounds/agents. This review discusses the multiple causes of gemcitabine resistance in PDAC.

Enhancing Apoptosis and Overcoming Resistance of Gemcitabine in Pancreatic Cancer with Bortezomib: A Role of Death-Associated Protein Kinase-Related Apoptosis-Inducing Protein Kinase 1

Aims and Background

To investigate the role of the apoptosis gene, DAP (death-associated protein) kinase-related apoptosis-inducing protein kinase 1 (DRAK1), which is involved in enhancing cell sensitivity and overcoming cell resistance to gemcitabine in pancreatic cancer cells by the proteasome inhibitor bortezomib.

Methods

Cultured human pancreatic cancer gemcitabine-sensitive cell lines (bxpc-3) and gemcitabine-resistant (panc-1) cell lines were divided into four groups: control, treatment with bortezomib, treatment with gemcitabine, and the two-drug combination. Expression of DRAK1 genes in each group was detected by using reverse transcription-polymerase chain reaction and western blot. Apoptosis in the pancreatic cancer cell lines was measured by flow cytometry.

Results

We found that the effects of growth inhibition and apoptosis of gemcitabine on both pancreatic cancer cell lines were enhanced by bortezomib. Treatment of panc-1 and bxpc-3 cells with bortezomib (100 nM) and gemcitabine (50 μg/ml and 0.05 μg/ml, respectively) induced an increase in the levels of DRAK1 mRNA compared with the control and single-agent treatment. Furthermore, immunblotting analysis in panc-1 but not bxpc-3 cells showed similar changes in the expression of DRAK1 protein produced by combination therapy.

Conclusions

Our results demonstrated that bortezomib enhanced cell sensitivity and overcame cell resistance to gemcitabine in pancreatic cancer cells, which may be attributed to DRAK1 induced by bortezomib and the combination with gemcitabine.

Proteasome Addiction Defined in Ewing Sarcoma Is Effectively Targeted by a Novel Class of 19S Proteasome Inhibitors

Ewing sarcoma is a primitive round cell sarcoma with a peak incidence in adolescence that is driven by a chimeric oncogene created from the fusion of the EWSR1 gene with a member of the ETS family of genes. Patients with metastatic and recurrent disease have dismal outcomes and need better therapeutic options. We screened a library of 309,989 chemical compounds for growth inhibition of Ewing sarcoma cells to provide the basis for the development of novel therapies and to discover vulnerable pathways that might broaden our understanding of the pathobiology of this aggressive sarcoma. This screening campaign identified a class of benzyl-4-piperidone compounds that selectively inhibit the growth of Ewing sarcoma cell lines by inducing apoptosis. These agents disrupt 19S proteasome function through inhibition of the deubiquitinating enzymes USP14 and UCHL5. Functional genomic data from a genome-wide shRNA screen in Ewing sarcoma cells also identified the proteasome as a node of vulnerability in Ewing sarcoma cells, providing orthologous confirmation of the chemical screen findings. Furthermore, shRNA-mediated silencing of USP14 or UCHL5 in Ewing sarcoma cells produced significant growth inhibition. Finally, treatment of a xenograft mouse model of Ewing sarcoma with VLX1570, a benzyl-4-piperidone compound derivative currently in clinical trials for relapsed multiple myeloma, significantly inhibited in vivo tumor growth. Overall, our results offer a preclinical proof of concept for the use of 19S proteasome inhibitors as a novel therapeutic strategy for Ewing sarcoma. Cancer Res; 76(15); 4525-34. ©2016 AACR.

DKK3 blocked translocation of β-catenin/EMT induced by hypoxia and improved gemcitabine therapeutic effect in pancreatic cancer Bxpc-3 cell

The Wnt/β-catenin signalling pathway is activated in pancreatic cancer initiation and progression. Dickkopf-related protein 3 (DKK3) is a member of the human Dickkopf family and an antagonist of Wnt ligand activity. However, the function of DKK3 in this pathway in pancreatic cancer is rarely known. We examined the expression of DKK3 in six human pancreatic cancer cell lines, 75 pancreatic cancer and 75 adjacent non-cancerous tissues. Dickkopf-related protein 3 was frequently silenced and methylation in pancreatic cancer cell lines (3/6). The expression of DKK3 was significantly lower in pancreatic cancer tissues than in adjacent normal pancreas tissues. Further, ectopic expression of DKK3 inhibits nuclear translocation of β-catenin induced by hypoxia in pancreatic cancer Bxpc-3 cell. The forced expression of DKK3 markedly suppressed migration and the stem cell-like phenotype of pancreatic cancer Bxpc-3 cell in hypoxic conditions through reversing epithelial-mesenchymal transition (EMT). The stable expression of DKK3 sensitizes pancreatic cancer Bxpc-3 cell to gemcitabine, delays tumour growth and augments gemcitabine therapeutic effect in pancreatic cancer xenotransplantation model. Thus, we conclude from our finding that DKK3 is a tumour suppressor and improved gemcitabine therapeutic effect through inducing apoptosis and regulating β-catenin/EMT signalling in pancreatic cancer Bxpc-3 cell.

Luteolin and Gemcitabine Protect Against Pancreatic Cancer in an Orthotopic Mouse Model

OBJECTIVE

This study aimed to evaluate the ability of luteolin (Lut), gemcitabine (Gem), and their combination (Lut + Gem) to prevent the growth of pancreatic tumors in vivo.

METHODS

The antitumor effect of intraperitoneally administered Lut, Gem, and Lut + Gem was evaluated using an orthotopic mouse model for 6 weeks. Tumor growth after injection of human pancreatic cancer cells was assessed by measuring pancreatic tumor mass. The mechanism of action of antitumor effect was assessed by immunohistochemistry and Western blot procedures.

RESULTS

Luteolin + Gem significantly lowered (P = 0.048) the pancreatic tumor mass compared with control. Luteolin, Gem, and Lut + Gem significantly reduced the proliferating cell nuclear antigen expression (25%, 37%, and 37%, respectively). Luteolin + Gem treatment led to a significant reduction in the expressions of K-ras (46%, P = 0.0006), GSK-3β (34%, P = 0.014), P(Tyr216)GSK-3β (16%, P = 0.033), P(Ser311)NF-κB p65 (27%, P = 0.036), and bcl-2/bax ratio (68%, P = 0.006) while significantly increasing the expressions of cytochrome c (44%, P = 0.035) and caspase 3 (417%, P = 0.003).

CONCLUSIONS

Luteolin + Gem promoted apoptotic cell death in pancreatic tumor cells in vivo through inhibition of the K-ras/GSK-3β/NF-κB signaling pathway, leading to a reduction in the Bcl-2/Bax ratio, release of cytochrome c, and activation of caspase 3.

FOXM1 and its oncogenic signaling in pancreatic cancer pathogenesis

Pancreatic cancer is a devastating disease with an overall 5-year survival rate less than 5%. Multiple signaling pathways are implicated in the pathogenesis of pancreatic cancer, such as Wnt/β-catenin, Notch, Hedgehog, hypoxia-inducible factor, signal transducer and activator of transcription, specificity proteins/Krüppel-like factors, and Forkhead box (FOX). Recently, increasing evidence has demonstrated that the transcription factor FOXM1 plays important roles in the initiation, progression, and metastasis of a variety of human tumors, including pancreatic cancer. In this review, we focus on the current understanding of the molecular pathogenesis of pancreatic cancer with a special focus on the function and regulation of FOXM1 and rationale for FOXM1 as a novel molecular target for pancreatic cancer prevention and treatment.

Phase I trial of induction histone deacetylase and proteasome inhibition followed by surgery in non-small-cell lung cancer

INTRODUCTION

Despite complete surgical resection survival in early-stage non-small-cell lung cancer (NSCLC) remains poor. On the basis of prior preclinical evaluations, we hypothesized that combined induction proteasome and histone deacetylase inhibitor therapy, followed by tumor resection, is feasible.

METHODS

A phase I clinical trial using a two-staged multiple-agent design of bortezomib and vorinostat as induction therapy followed by consolidative surgery in patients with NSCLC was performed. Standard toxicity and maximum tolerated dose were examined. Pre- and post-treatment tumor gene-expression arrays were performed and analyzed. Pre- and post-treatment fluorodeoxyglucose-positron emission tomography imaging was used to assess tumor metabolism. Finally, serum 20S proteasome levels were analyzed with enzyme-linked immunosorbent assay, and selected intratumoral proteins were assessed by immunohistochemistry.

RESULTS

Of the 34-four patients providing written consent to participate in the trial, 21 were enrolled. One patient withdrew early because of disease progression. The maximum tolerated dose was bortezomib 1.3 mg/m and vorinostat 300 mg twice daily. There were grade III dose-limiting toxicities of fatigue and hypophosphatemia, which were self-limited. There was no mortality. Thirty percent of patients (6 of 20) had more than 60% histologic necrosis of their tumor after treatment, with two having 90% or more tumor necrosis. Tumor metabolism, 20S proteasome activity, and specific protein expression did not demonstrate consistent results. Gene-expression arrays comparing pre- and post-therapy NSCLC specimens revealed robust intratumoral changes in specific genes.

CONCLUSIONS

Induction bortezomib and vorinostat therapy followed by surgery in patients with operable NSCLC is feasible. Correlative gene-expression studies suggest new targets and cell-signaling pathways that may be important in modulating this combined therapy.

Everolimus combined with cisplatin has a potential role in treatment of urothelial bladder cancer

Cisplatin (CDDP)-based chemotherapy is a commonly treatment for advanced urothelial carcinoma. However, episodes of cisplatin resistance have been referenced. Recently it has been reported that everolimus (RAD001) could have an important role to play in bladder-cancer treatment and that mTOR inhibitors may restore chemosensitivity in resistant tumours. The aim of this study was to assess RAD001 in vitro ability to enhance CDDP cytotoxicity in three human bladder-cancer cell lines. Over the course of 72h, the cells were exposed to different concentrations of CDDP and RAD001, isolated or combined. Treatment with CDDP statistically (P<0.05) decreased cell proliferation in cell lines in a dose-dependent manner. The anti-proliferative activity of CDDP used in combination with RAD001 was statistically significant (P<0.05) in the cell lines at all concentrations tested. RAD001 had a therapeutic effect when used in combination with CDDP and could therefore be a useful anti-cancer drug combination for patients with bladder cancer.

Bufalin enhances the antitumor effect of gemcitabine in pancreatic cancer

Bufalin, an active component of the Chinese medicine chan'su, has been reported to have an inhibitory effect on the growth of various types of cancer cells. In the present study, we investigated whether gemcitabine combined with bufalin enhanced the antitumor efficacy in pancreatic cancer. Three pancreatic cancer cell lines (Bxpc-3, Mia PaCa-2 and Panc-1) were treated with gemcitabine and/or bufalin in vitro. The combination treatment demonstrated greater inhibition of cellular growth and apoptosis. The activity of apoptosis signal-regulating kinase 1 (ASK1)/JNK was upregulated in gemcitabine-induced apoptosis when combined with bufalin. We also observed that tumor growth was significantly inhibited by the combination therapy in a tumor-bearing mouse model, and upregulation of ASK1 activity was validated by immunohistochemical staining. These results suggest that bufalin may be a potential chemotherapeutic agent for pancreatic cancer, which could enhance the antitumor efficacy of gemcitabine when used in combination, possibly through the activation of ASK1/JNK.

Rad knockdown induces mitochondrial apoptosis in bortezomib resistant leukemia and lymphoma cells

To understand the molecular mechanism(s) underlying bortezomib resistance, we sought to identify potential target genes that were differentially expressed in bortezomib-resistant leukemia cells versus parental controls. Microarray analysis revealed that the mRNA levels of Rad (Ras associated with diabetes) were higher in the bortezomib-resistant Jurkat (Jurkat-R) cells than in the parental control cells. The importance of Rad for bortezomib resistance was supported by three observations. First, Rad knockdown overcame bortezomib resistance and induced mitochondrial apoptosis via Noxa/Bcl-2 modulation. Second, Rad decreased cell death in response to bortezomib. Third, leukemia and lymphoma cell lines (K-562, Raji, IM-9 and Jurkat-R) with elevated Rad expression levels showed higher degrees of bortezomib resistance versus those (Sup-B15, JVM-2, U266 and Jurkat) with low Rad expression levels (r=0.48, P=0.0004). Thus, Rad over expression could be a molecular target to improve bortezomib sensitivity in human leukemia and lymphoma.

The 26S proteasome complex: an attractive target for cancer therapy

The 26S proteasome complex engages in an ATP-dependent proteolytic degradation of a variety of oncoproteins, transcription factors, cell cycle specific cyclins, cyclin-dependent kinase inhibitors, ornithine decarboxylase, and other key regulatory cellular proteins. Thus, the proteasome regulates either directly or indirectly many important cellular processes. Altered regulation of these cellular events is linked to the development of cancer. Therefore, the proteasome has become an attractive target for the treatment of numerous cancers. Several proteasome inhibitors that target the proteolytic active sites of the 26S proteasome complex have been developed and tested for anti-tumor activities. These proteasome inhibitors have displayed impressive anti-tumor functions by inducing apoptosis in different tumor types. Further, the proteasome inhibitors have been shown to induce cell cycle arrest, and inhibit angiogenesis, cell-cell adhesion, cell migration, immune and inflammatory responses, and DNA repair response. A number of proteasome inhibitors are now in clinical trials to treat multiple myeloma and solid tumors. Many other proteasome inhibitors with different efficiencies are being developed and tested for anti-tumor activities. Several proteasome inhibitors currently in clinical trials have shown significantly improved anti-tumor activities when combined with other drugs such as histone deacetylase (HDAC) inhibitors, Akt (protein kinase B) inhibitors, DNA damaging agents, Hsp90 (heat shock protein 90) inhibitors, and lenalidomide. The proteasome inhibitor bortezomib is now in the clinic to treat multiple myeloma and mantle cell lymphoma. Here, we discuss the 26S proteasome complex in carcinogenesis and different proteasome inhibitors with their potential therapeutic applications in treatment of numerous cancers.

In vivo and in vitro effects of RAD001 on bladder cancer

OBJECTIVE

To evaluate the influence of Everolimus (RAD001) on chemically induced urothelial lesions in mice and its influence on in vitro human bladder cancer cell lines.

METHODS

ICR male mice were given N-butyl-N-(4-hydroxybutyl) nitrosamine in drinking water for a period of 12 weeks. Subsequently, RAD001 was administered via oral gavage, for 6 weeks. At the end of the experiment, all the animals were sacrificed and tumor development was determined by means of histopathologic evaluation; mammalian target of rapamycin (mTOR) expressivity was evaluated by immunohistochemistry. Three human bladder cancer cell lines (T24, HT1376, and 5637) were treated using a range of RAD001 concentrations. MTT assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and flow cytometry were used to assess cell proliferation, apoptosis index, and cell cycle analysis, respectively. Immunoblotting analysis of 3 cell line extracts using mTOR and Akt antibodies was performed in order to study the expression of Akt and mTOR proteins and their phosphorylated forms.

RESULTS

The incidence of urothelial lesions in animals treated with RAD001 was similar to those animals not treated. RAD001 did not block T24 and HT1376 cell proliferation or induce apoptosis. A reduction in cell proliferation rate and therefore G0/G1 phase arrest, as well as a statistically significant induction of apoptosis (P = 0.001), was only observed in the 5637 cell line.

CONCLUSION

RAD001 seems not to have a significant effect on chemically induced murine bladder tumors. The effect of RAD001 on tumor proliferation and apoptosis was achieved only in superficial derived bladder cancer cell line, no effect was observed in invasive cell lines.

Identification of HSP90 as a new GABARAPL1 (GEC1)-interacting protein

GABARAPL1 belongs to the small family of GABARAP proteins (including GABARAP, GABARAPL1 and GABARAPL2/GATE-16), one of the two subfamilies of the yeast Atg8 orthologue. GABARAPL1 is involved in the intracellular transport of receptors, via an interaction with tubulin and GABA(A) or kappa opioid receptors, and also participates in autophagy and cell proliferation. In the present study, we identify the HSP90 protein as a novel interaction partner for GABARAPL1 using GST pull-down, mass spectrometry and coimmunoprecipitation experiments. GABARAPL1 and HSP90 partially colocalize in MCF-7 breast cancer cells overexpressed Dsred-GABARAPL1 and in rat brain. Moreover, treatment of MCF-7 cells overexpressed FLAG-GABARAPL1-6HIS with the HSP90 inhibitor 17-AAG promotes the GABARAPL1 degradation, a process that is blocked by proteasome inhibitors such as MG132, bortezomib and lactacystin. Accordingly, we demonstrate that HSP90 interacts and protects GABARAPL1 from its degradation by the proteasome.

Enhanced antitumor efficacy of gemcitabine by evodiamine on pancreatic cancer via regulating PI3K/Akt pathway

Evodiamine has therapeutic potential against cancers. This study was designed to investigate whether combination therapy with gemcitabine and evodiamine enhanced antitumor efficacy in pancreatic cancer. In vitro application of the combination therapy triggered significantly higher frequency of pancreatic cancer cells apoptosis, inhibited the activities of PI3K, Akt, PKA, mTOR and PTEN, and decreased the activation of NF-κB and expression of NF-κB-regulated products. In vivo application of the combination therapy induced significant enhancement of tumor cell apoptosis, reductions in tumor volume, and inhibited activation of mTOR and PTEN. In conclusion, evodiamine can augment the therapeutic effect of gemcitabine in pancreatic cancer through direct or indirect negative regulation of the PI3K/Akt pathway.

p21(WAF1/CIP1) upregulation through the stress granule-associated protein CUGBP1 confers resistance to bortezomib-mediated apoptosis

Background

p21^WAF1/CIP1 is a well known cyclin-dependent kinase inhibitor induced by various stress stimuli. Depending on the stress applied, p21 upregulation can either promote apoptosis or prevent against apoptotic injury. The stress-mediated induction of p21 involves not only its transcriptional activation but also its posttranscriptional regulation, mainly through stabilization of p21 mRNA levels. We have previously reported that the proteasome inhibitor MG132 induces the stabilization of p21 mRNA, which correlates with the formation of cytoplasmic RNA stress granules. The mechanism underlying p21 mRNA stabilization, however, remains unknown.

Methodology/Principal Findings

We identified the stress granules component CUGBP1 as a factor required for p21 mRNA stabilization following treatment with bortezomib ( =  PS-341/Velcade). This peptide boronate inhibitor of the 26S proteasome is very efficient for the treatment of myelomas and other hematological tumors. However, solid tumors are sometimes refractory to bortezomib treatment. We found that depleting CUGBP1 in cancer cells prevents bortezomib-mediated p21 upregulation. FISH experiments combined to mRNA stability assays show that this effect is largely due to a mistargeting of p21 mRNA in stress granules leading to its degradation. Altering the expression of p21 itself, either by depleting CUGBP1 or p21, promotes bortezomib-mediated apoptosis.

Conclusions/Significance

We propose that one key mechanism by which apoptosis is inhibited upon treatment with chemotherapeutic drugs might involve upregulation of the p21 protein through CUGBP1.

Distinct regulatory mechanisms of eukaryotic transcriptional activation by SAGA and TFIID

A growing number of human diseases are linked to abnormal gene expression which is largely controlled at the level of transcriptional initiation. The gene-specific activator promotes the initiation of transcription through its interaction with one or more components of the transcriptional initiation machinery, hence leading to stimulated transcriptional initiation or activation. However, all activator proteins do not target the same component(s) of the transcriptional initiation machinery. Rather, they can have different target specificities, and thus, can lead to distinct mechanisms of transcriptional activation. Two such distinct mechanisms of transcriptional activation in yeast are mediated by the SAGA (Spt-Ada-Gcn5-Acetyltransferase) and TFIID (Transcription factor IID) complexes, and are termed as "SAGA-dependent" and "TFIID-dependent" transcriptional activation, respectively. SAGA is the target of the activator in case of SAGA-dependent transcriptional activation, while the targeting of TFIID by the activator leads to TFIID-dependent transcriptional activation. Both the SAGA and TFIID complexes are highly conserved from yeast to human, and play crucial roles in gene activation among eukaryotes. The regulatory mechanisms of eukaryotic transcriptional activation by SAGA and TFIID are discussed here. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!

The chemotherapeutic agent bortezomib induces the formation of stress granules

BACKGROUND

Cytoplasmic stress granules (SGs) are specialized storage sites of untranslated mRNAs whose formation occurs under different stress conditions and is often associated with cell survival. SGs-inducing stresses include radiations, hypoxia, viral infections, and chemical inhibitors of specific translation initiation factors. The FDA-approved drug bortezomib (Velcade(R)) is a peptide boronate inhibitor of the 26S proteasome that is very efficient for the treatment of myelomas and other hematological tumors. Solid tumors are largely refractory to bortezomib. In the present study, we investigated the formation of SGs following bortezomib treatment.

RESULTS

We show that bortezomib efficiently induces the formation of SGs in cancer cells. This process involves the phosphorylation of translation initiation factor eIF2alpha by heme-regulated inhibitor kinase (HRI). Depletion of HRI prevents bortezomib-induced formation of SGs and promotes apoptosis.

CONCLUSIONS

This is the first study describing the formation of SGs by a chemotherapeutic compound. We speculate that the activation of HRI and the formation of SGs might constitute a mechanism by which cancer cells resist bortezomib-mediated apoptosis.

Proteasome inhibition enhances antitumour effects of gemcitabine in experimental pancreatic cancer

BACKGROUND

The clinical benefit of gemcitabine, the standard systemic therapy of pancreatic cancer (PaCa), remains modest as a result of high chemoresistance. The proteasome inhibitor bortezomib has antitumour activity against PaCa in vitro and in vivo. We examined the antitumour activity of combination PaCa therapy with bortezomib and gemcitabine.

METHODS

Cell proliferation assays were performed using WST-1 reagent. Protein expression was determined by Western blotting. Efficacy of bortezomib and/or gemcitabine was tested in vivo in a survival study.

RESULTS

Bortezomib at 10 microM caused 29% and 72% inhibition in AsPC-1 PaCa cell proliferation at 48 and 96 h incubation, respectively. Bortezomib was even more active against PaCa cell lines Panc-1 and MiaPaCa, with 80% inhibition of proliferation at 48 h. The combination of bortezomib and gemcitabine inhibited AsPC-1 proliferation more effectively compared with each single agent alone. Poly(ADP-ribose) polymerase (PARP) cleavage, an apoptotic indicator, reached 6.6-, 2- and 8.5-fold over controls for bortezomib, gemcitabine and the combination. The median survival was 31 (controls and bortezomib), 40 (gemcitabine) and 48 days (combination), respectively (P < 0.002).

CONCLUSIONS

Bortezomib and gemcitabine demonstrate additive antitumour activity in vitro and in an experimental PaCa model, indicating the potential for clinical PaCa benefits of additional multiagent therapies that will be based upon the bortezomib and gemcitabine combination.

Regulation of stathmin phosphorylation in mouse liver progenitor-29 cells during proteasome inhibition

Proteasome inhibitors are potential therapeutic agents in the treatment of hepatocarcinoma and other liver diseases. The analysis of alternative protein phosphorylation states might contribute to elucidate the underlying mechanisms of proteasome inhibitor-induced apoptosis. We have investigated the response of mouse liver progenitor-29 (MLP-29) cells to MG132 using a combination of phosphoprotein affinity chromatography, DIGE, and nano LC-MS/MS. Thirteen unique deregulated phosphoproteins involved in chaperone activity, stress response, mRNA processing and cell cycle control were unambiguously identified. Alterations in NDRG1 and stathmin suggest new mechanisms associated to proteasome inhibitor-induced apoptosis in MLP-29 cells. Particularly, a transient modification of the phosphorylation state of Ser(16), Ser(25) and Ser(38), which are involved in the regulation of stathmin activity, was detected in three distinct isoforms upon proteasome inhibition. The parallel deregulation of calcium/calmodulin-activated protein kinase II, extracellular regulated kinase-1/2 and cyclin-dependent kinase-2, might explain the modified phosphorylation pattern of stathmin. Interestingly, stathmin phosphorylation profile was also modified in response to epoxomicin treatment, a more specific proteasome inhibitor. In summary, we report here data supporting that regulation of NDRG1 and stathmin by phosphorylation at specific Ser/Thr residues may participate in the cellular response induced by proteasome inhibitors.

Potentiation of the effect of gemcitabine by emodin in pancreatic cancer is associated with survivin inhibition

Pancreatic cancer is one human malignancy which has chemoresistant behavior to gemcitabine treatment. In this study, we revealed that emodin, an active component from Chinese medicinal herbs, could enhance pancreatic cancer cells apoptosis induced by gemcitabine. Survivin, a member of the inhibitor of apoptosis gene family, is involved in control of cell division and inhibition of apoptosis and described as a beta-catenin/Tcf/Lef target gene. Western blot and PCR analysis showed that emodin suppressed survivin expression in a dose- and time-dependent manner. We further demonstrated survivin expression could be up-regulated by gemcitabine. Surprisingly, survivin expression induced by gemcitabine could be inhibited in combination with emodin treatment. Moreover, cells treated with gemcitabine and emodin showed a preferential peri-plasmamembrane position of beta-catenin, blocking the translocation of beta-catenin to nucleus induced by gemcitabine. In addition to these in vitro results, we also found that emodin potentiates the antitumor effects of gemcitabine in vivo by down-regulating the expression of survivin and beta-catenin. Taken together, these results suggest that emodin potentiates gemcitabine antitumor activity through suppression of survivin gene in pancreatic cancer.

Monoclonal antibodies in the treatment of pancreatic cancer

Human pancreatic cancer is a malignant disease with almost equal incidence and mortality. Effective diagnostic and therapeutic strategies are still urgently needed to improve its survival rate. With advances in structural and functional genomics, recent work has focused on targeted molecular therapy using monoclonal antibodies. This review summarizes the target molecules on the tumor cell surface and normal tissue stroma, which are related to pancreatic cancer oncogenesis, tumor growth or resistance to chemotherapy, as well as molecules involved in regulating inflammation and host immunoresponses. Targeted molecules include cell-surface receptors, such as the EGF receptor, HER2, death receptor 5 and IGF-1 receptor. Effects of monoclonal antibodies against these target molecules alone or in combination with chemotherapy, small-molecule signal transduction inhibitors, or radiation therapy are also discussed. Also discussed are the use of toxin or radioisotope conjugates, and information relating to the use of these targeting agents in pancreatic cancer clinical trials. Although targeted molecular therapy with monoclonal antibodies has made some progress in pancreatic cancer treatment, especially in preclinical studies, its clinical application to improve the survival rate of pancreatic cancer patients requires further investigation.

Expression of apoptosis-related Bcl-2-family and P53 in human adenocarcinoma of the pancreas

AIM: To investigate the relationships between P53 and Bcl-2 family (Bcl-2, Bax, Bcl-xL, Bcl-xS) expression and apoptosis in human pancreatic carcinoma (PC).

METHODS: The immunohistochemical method was used to detect the expression of P53 protein in a total of 35 patients with PC. The patients were divided into two groups, group 1 with immunonegative P53 (18 cases) and group 2 with immunopositive (17 cases). The expressions of P53, Bcl-2, Bax, Bcl-xL, and Bcl-xS in both groups were detected by Western blot. The apoptosis index (AI) of group 1 was determined by terminal deoxynucleotidyltransferase-mediated UTP end-labeling (TUNEL).

RESULTS: Bcl-2 was remarkably up-regulated in group 2 but down-regulated in group 1 (P = 0.047). Expressions of both Bax and Bcl-xL proteins were up-regulated in those two groups (P = 0.274, 0.334). Bcl-xS was remarkably down-regulated in group 2 but up-regulated in group1 (P = 0.01). The AI of both groups were 12.1 ± 2.47 and 9.1 ± 1.48, respectively (P = 0.023), no correlations were found between AI and expression of Bcl-2 family members, but marked correlations were noted between AI and the Bcl-2/bax ratios (P < 0.01).

CONCLUSION: Bcl-2 family is a group of anti-apoptotic proteins, and Bcl-xS is a pro-apoptotic protein. Both of them are dependent on the regulation of P53 which modulates apoptosis mainly through modifying Bcl-2/Bax ratios.

Diverse regulatory mechanisms of eukaryotic transcriptional activation by the proteasome complex

The life of any protein within a cell begins with transcriptional activation, and ends with proteolytic degradation. Intriguingly, the 26S proteasome complex, a non-lysosomal protein degradation machine comprising the 20S proteolytic core and 19S regulatory particles, has been implicated in intimate regulation of eukaryotic transcriptional activation through diverse mechanisms in a proteolysis-dependent as well as independent manner. Here, we discuss the intricate mechanisms of such proteasomal regulation of eukaryotic gene activation via multiple pathways.