Targeting the ubiquitin-proteasome pathway in breast cancer

A ubiquitin-proteasome system-related signature to predict prognosis, immune infiltration, and therapy efficacy for breast cancer

The ubiquitin-proteasome system (UPS) is an essential regulatory system for maintaining homeostasis, and its dysfunction may cause various diseases. The activity of proteasome and ubiquitin-conjugating enzymes has been found to be greatly increased in breast cancer (BC), indicating that the heterogeneity of UPS may be related to the progression of BC. Gene data was obtained from The Cancer Genome Atlas and Gene Expression Omnibus databases and performed in multiple algorithms to construct a UPS-related signature for BC. Patients in the UPS low-risk group had greater overall and recurrence-free survival probability than those in the UPS high-risk group. This signature was closely associated with functional enrichment. Some high metabolism-related pathways were more active in the UPS high-risk group. The UPS low-risk group had more abundant anti-tumor immune cells, while in the UPS high-risk group, immunosuppressive cells were dominant. More importantly, we found that the UPS low-risk group was more sensitive to immunotherapy, while the UPS high-risk group responded better to radiotherapy. Drug sensitivity analysis identified more effective chemotherapy drugs in different UPS-related risk groups. This UPS-related signature may serve as a novel biomarker and independent prognostic factor for BC. It can effectively predict prognosis, immune infiltration, and therapy efficacy, providing new strategies for individualized treatment.

Chemical Proteomics Reveals that the Anticancer Drug Everolimus Affects the Ubiquitin-Proteasome System

Rapamycin is a natural antifungal, immunosuppressive, and antiproliferative compound that allosterically inhibits mTOR complex 1. The ubiquitin-proteasome system (UPS) responsible for protein turnover is usually not listed among the pathways affected by mTOR signaling. However, some previous studies have indicated the interplay between the UPS and mTOR. It has also been reported that rapamycin and its analogs can allosterically inhibit the proteasome itself. In this work, we studied the molecular effect of rapamycin and its analogs (rapalogs), everolimus and temsirolimus, on the A549 cell line by expression proteomics. The analysis of differentially expressed proteins showed that the cellular response to everolimus treatment is strikingly different from that to rapamycin and temsirolimus. In the cluster analysis, the effect of everolimus was similar to that of bortezomib, a well-established proteasome inhibitor. UPS-related pathways were enriched in the cluster of proteins specifically upregulated upon everolimus and bortezomib treatments, suggesting that both compounds have similar proteasome inhibition effects. In particular, the total amount of ubiquitin was significantly elevated in the samples treated with everolimus and bortezomib, and analysis of the polyubiquitination patterns revealed elevated intensities of the ubiquitin peptide with a GG modification at the K48 residue, consistent with a bottleneck in proteasomal protein degradation. Moreover, the everolimus treatment resulted in both ubiquitin phosphorylation and generation of a significant amount of semitryptic peptides, illustrating the increase in the protease activity. These observations suggest that everolimus affects the UPS in a unique way, and its mechanism of action is different from that of its close chemical analogs, rapamycin and temsirolimus.

Gold Nanoparticles Induced Size Dependent Cytotoxicity on Human Alveolar Adenocarcinoma Cells by Inhibiting the Ubiquitin Proteasome System

Gold nanoparticles (AuNPs) are widely used in biomedicine due to their remarkable therapeutic applications. However, little is known about their cytotoxic effects on the ubiquitin proteasome system (UPS). Herein, the cytotoxicity of different sizes of AuNPs (5, 10, and 80 nm) on the UPS was investigated with a particular focus on deubiquitinating enzymes (DUBs) such as ubiquitin-specific proteases (USP) and ubiquitin carboxyl-terminal hydrolases (UCHL-1) in human alveolar epithelial adenocarcinoma (A549). It was found that all sizes of AuNPs reduced the percentage of viable A549 cells and increased lactate dehydrogenase (LDH) release, measured using the MTT and LDH assays, respectively. Furthermore, the 5 nm AuNPs were found to exhibit greater cytotoxicity than the 10 and 80 nm AuNPs. In addition, apoptosis and necrosis were activated through reactive oxygen species (ROS) generation due to AuNPs exposure. The internalisation of AuNPs in A549 cells increased with increasing particle size (80 > 10 > 5 nm). Interestingly, the expression of USP7, USP8, USP10, and UCHL-1 was significantly (p < 0.001) downregulated upon treatment with 5-30 µg/mL of all the AuNPs sizes compared to control cells. Moreover, the inhibition of these proteins triggered mitochondrial-related apoptosis through the upregulation of poly (ADP-ribose) polymerase (PARP), caspase-3, and caspase-9. Collectively, these results indicate that AuNPs suppress the proliferation of A549 cells and can potentially be used as novel inhibitors of the proteasome.

Exploration of Lung Cancer-Related Genetic Factors via Mendelian Randomization Method Based on Genomic and Transcriptomic Summarized Data

Lung carcinoma is one of the most deadly malignant tumors in mankind. With the rising incidence of lung cancer, searching for the high effective cures become more and more imperative. There has been sufficient research evidence that living habits and situations such as smoking and air pollution are associated with an increased risk of lung cancer. Simultaneously, the influence of individual genetic susceptibility on lung carcinoma morbidity has been confirmed, and a growing body of evidence has been accumulated on the relationship between various risk factors and the risk of different pathological types of lung cancer. Additionally, the analyses from many large-scale cancer registries have shown a degree of familial aggregation of lung cancer. To explore lung cancer-related genetic factors, Genome-Wide Association Studies (GWAS) have been used to identify several lung cancer susceptibility sites and have been widely validated. However, the biological mechanism behind the impact of these site mutations on lung cancer remains unclear. Therefore, this study applied the Summary data-based Mendelian Randomization (SMR) model through the integration of two GWAS datasets and four expression Quantitative Trait Loci (eQTL) datasets to identify susceptibility genes. Using this strategy, we found ten of Single Nucleotide Polymorphisms (SNPs) sites that affect the occurrence and development of lung tumors by regulating the expression of seven genes. Further analysis of the signaling pathway about these genes not only provides important clues to explain the pathogenesis of lung cancer but also has critical significance for the diagnosis and treatment of lung cancer.

Potential Diagnostic and Prognostic Utility of miR-141, miR-181b1, and miR-23b in Breast Cancer

miRNAs, a group of short noncoding RNAs, are key regulators of fundamental cellular processes and signaling pathways. Dysregulation of miRNA expression with known oncogenic or tumor suppressor functions has been associated with neoplastic transformation. Numerous studies have reported dysregulation of miRNA-141, miR-181b1, and miR-23b in a wide range of malignancies, including breast cancer. To the best of our knowledge, no previous study had demonstrated the expression of miR-141-3p, miR-181b1-5p, and miR-23b-3p in different histological grades and molecular subtypes of breast cancer. Here, we identified differential expression of these three miRNAs in breast cancer tissues compared with benign breast fibroadenomas. In addition, high expression levels of miR-141-3p and miR-181b1-5p are strongly associated with aggressive breast carcinomas. We also confirmed the clinical potential of using the three miRNAs individually or combined as diagnostic and prognostic markers in breast cancer. Using bioinformatics analyses, we identified 23 hub genes of these three miRNAs which are involved in key signaling pathways in breast cancer. Furthermore, the KM plotter online database analysis demonstrates the association between elevated expression of miR-141 and miR-181b and shorter overall survival of breast cancer patients. Together, our data suggest an oncogenic role of the studied miRNAs and highlight their molecular roles and potential clinical applications in breast cancer.

Tradeoff between metabolic i-proteasome addiction and immune evasion in triple-negative breast cancer

In vitro studies have suggested proteasome inhibitors could be effective in triple-negative breast cancer (TNBC). We found that bortezomib and carfilzomib induce proteotoxic stress and apoptosis via the unfolded protein response (UPR) in TNBC cell lines, with sensitivity correlated with expression of immuno-(PSMB8/9/10) but not constitutive-(PSMB5/6/7) proteasome subunits. Equally, the transcriptomes of i-proteasome-high human TNBCs are enriched with UPR gene sets, and the genomic copy number landscape reflects positive selection pressure favoring i-proteasome activity, but in the setting of adjuvant treatment, this is actually associated with favorable prognosis. Tumor expression of PSMB8 protein (β5i) is associated with levels of MHC-I, interferon-γ-inducible proteasome activator PA28β, and the densities of stromal antigen-presenting cells and lymphocytes (TILs). Crucially, TILs were protective among TNBCs that maintain high β5i but did not stratify survival amongst β5i-low TNBCs. Moreover, β5i expression was lower in brain metastases than in patient-matched primary breast tumors (n = 34; P = 0.007), suggesting that suppression contributes to immune evasion and metastatic progression. Hence, inhibiting proteasome activity could be counterproductive in the adjuvant treatment setting because it potentiates anti-TNBC immunity.

Network modeling of patients' biomolecular profiles for clinical phenotype/outcome prediction

Methods for phenotype and outcome prediction are largely based on inductive supervised models that use selected biomarkers to make predictions, without explicitly considering the functional relationships between individuals. We introduce a novel network-based approach named Patient-Net (P-Net) in which biomolecular profiles of patients are modeled in a graph-structured space that represents gene expression relationships between patients. Then a kernel-based semi-supervised transductive algorithm is applied to the graph to explore the overall topology of the graph and to predict the phenotype/clinical outcome of patients. Experimental tests involving several publicly available datasets of patients afflicted with pancreatic, breast, colon and colorectal cancer show that our proposed method is competitive with state-of-the-art supervised and semi-supervised predictive systems. Importantly, P-Net also provides interpretable models that can be easily visualized to gain clues about the relationships between patients, and to formulate hypotheses about their stratification.

Quantitative structure-activity relationship and molecular docking studies on human proteasome inhibitors for anticancer activity targeting NF-κB signaling pathway

The abnormal ubiquitin-proteasome is found as an important target in various human diseases, especially in cancer, and recently it has received prevalent attention as a challenging therapeutic target. The current work is designed to derive a predictive two-dimensional quantitative structure-activity relationship model for anticancer human proteasome target of NF-κB signaling pathway. The established 2 D-QSAR is dependent on multiple linear regression approach and validated through leave-One-Out and external test set prediction method. The robust QSAR model showed the r² of 0.83 and q² of 0.80 and pred_r² of 0.77. Three chemical properties, electronegativity count, average potential, and T_2_N_6 were identified as significant descriptors to predict the anticancer activities of the proteasome antagonists. Besides, the predicted top hit compounds were considered to check out the compliance with Rule of five and pharmacokinetic parameters for oral bioavailability in the human body. The molecular docking was accomplished to unravel the molecular mode of action of best-predicted compounds which was compatible with the standard drug. Following this approach, lastly two compounds NP and AP were recognized as the best candidates since these top compounds follow all the standard limit point of entire filters and indicated effective and decent docking score. The outcomes of the study sturdily suggested that the developed model and top hit compound's binding conformation are rational in the exploration of unknown antagonist's anticancer activity. The research would be of great support and is supposed to be of immense significance in the development and designing of drug-like candidates in preliminary drug discovery. Communicated by Ramaswamy H. Sarma.

Novel Strategies to Improve the Endocrine Therapy of Breast Cancer

Endocrine therapy (ET) constitutes the usual first-line of therapy for patients in the treatment of metastatic hormone receptor-positive breast cancer. Unfortunately, not all patients respond to first-line endocrine treatment due to intrinsic resistance, while others may initially respond but eventually progress with secondary acquired resistance leading to disease progression. Mechanisms of resistance to anti-estrogen therapy include, loss of expression for estrogen or progesterone receptor, upregulation of epidermal receptor growth factor 2, increased receptor tyrosine kinase signaling, leading to activation of various intracellular pathways that are involved in signal transduction such as PI3K/AKT/mammalian target of rapamycin, and others. Growing understanding of the signal cascade of estrogen receptors and the signaling pathways that interact with estrogen receptors has revealed the complex role of these receptors in cell growth and proliferation, and on the mechanism in development of resistance. These insights have led to the development of targeted therapies that may prove to be effective options for the treatment of breast cancer and may overcome hormone therapy resistance. In this review we summarize some of the mechanisms of endocrine resistance, selected clinical trials of ET and targeted therapies, which might interfere with estrogen receptor pathways and might reduce or reverse resistance to traditional, sequential, single-agent ET.

Association of LIM Domain 7 Gene Polymorphisms and Plasma Levels of LIM Domain 7 with Dilated Cardiomyopathy in a Chinese Population

The aim of our study was to investigate the potential association of mRNA expression and plasma levels of the LIM domain 7 (LMO7) gene with the pathogenesis of dilated cardiomyopathy (DCM). Two SNPs of the LMO7 gene were genotyped in 310 patients with DCM and 415 controls. Our results showed that SNP rs7986131 (p = 0.002, OR = 1.38, 95% CI = 1.12-1.71), but not SNP rs4884021, was associated with DCM in the Han Chinese population. Haplotype analysis showed that the haplotype GT was associated with increased DCM susceptibility while AC was a protective haplotype. The Cox multivariate survival analysis indicated that the rs7986131 TT genotype (HR 1.659, 95% CI = 1.122-2.454, p = 0.011) was an independent multivariate predictor for shorter overall survival in patients with DCM. LMO7 mRNA expression and plasma LMO7 levels were significantly decreased in DCM (p < 0.0001). Spearman correlation test revealed that the plasma LMO7 level was negatively associated with left ventricular end-diastolic diameter (r = -0.384, p = 0.01), left ventricular end-diastolic volume (r = -0.375, p = 0.012), and brain natriuretic peptide (r = -0.482, p = 0.001). Our study suggested that the LMO7 gene may play an important role in the pathogenesis of DCM in the Han Chinese population.

Disulfide cross-linked micelles of novel HDAC inhibitor thailandepsin A for the treatment of breast cancer

Histone deacetylase (HDAC) inhibitors are an emerging class of targeted therapy against cancers. Thailandepsin A (TDP-A) is a recently discovered class I HDAC inhibitor with broad anti-proliferative activities. In the present study, we aimed to investigate the potential of TDP-A in the treatment of breast cancer. We demonstrated that TDP-A inhibited cell proliferation and induced apoptosis in breast cancer cells at low nanomolar concentrations. TDP-A activated the intrinsic apoptotic pathway through increase of pro-apoptotic protein Bax, decrease of anti-apoptotic Bcl-2, and cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP). TDP-A also induced cell cycle arrest at the G2/M phase, and promoted the production of reactive oxygen species (ROS). We have successfully encapsulated TDP-A into our recently developed disulfide cross-linked micelles (DCMs), improving its water solubility and targeted delivery. TDP-A loaded DCMs (TDP-A/DCMs) possess the characteristics of high loading capacity (>20%, w/w), optimal and monodisperse particle size (16 ± 4 nm), outstanding stability with redox stimuli-responsive disintegration, sustained drug release, and preferential uptake in breast tumors. In the MDA-MB-231 breast cancer xenograft model, TDP-A/DCMs were more efficacious than the FDA-approved FK228 at well-tolerated doses. Furthermore, TDP-A/DCMs exhibited synergistic anticancer effects when combined with the proteasome inhibitor bortezomib (BTZ) loaded DCMs (BTZ/DCMs). Our results indicate that TDP-A nanoformulation alone or in combination with BTZ nanoformulation are efficacious against breast cancer.

Transcriptome meta-analysis reveals dysregulated pathways in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant cancer arising from the epithelial surface of the nasopharynx that mostly appears in advanced stages of the disease, leading to a poor prognosis. To date, a number of mRNA profiling investigations on NPC have been reported in order to identify suitable biomarkers for early detection. However, the results may be specific to each study with distinct sample types. In this study, an integrative meta-analysis of NPC transcriptome data was performed to determine dysregulated pathways, potentially leading to identification of molecular markers. Ten independent NPC gene expression profiling microarray datasets, including 135 samples from NPC cell lines, primary cell lines, and tissues were assimilated into a meta-analysis and cross-validation to identify a cohort of genes that were significantly dysregulated in NPC. Bioinformatics analyses of these genes revealed the significant pathways and individual players involving in cellular metabolism, cell cycle regulation, DNA repair, as well as ErbB pathway. Altogether, we propose that dysregulation of these molecular pathways in NPC might play a role in the NPC pathogenesis, providing clues, which could eventually translate into diagnostic and therapeutic approaches.

Triple-negative breast cancer: new perspectives for targeted therapies

Breast cancer is a heterogeneous disease, encompassing a large number of entities showing different morphological features and having clinical behaviors. It has became apparent that this diversity may be justified by distinct patterns of genetic, epigenetic, and transcriptomic aberrations. The identification of gene-expression microarray-based characteristics has led to the identification of at least five breast cancer subgroups: luminal A, luminal B, normal breast-like, human epidermal growth factor receptor 2, and basal-like. Triple-negative breast cancer is a complex disease diagnosed by immunohistochemistry, and it is characterized by malignant cells not expressing estrogen receptors or progesterone receptors at all, and human epidermal growth factor receptor 2. Along with this knowledge, recent data show that triple-negative breast cancer has specific molecular features that could be possible targets for new biological targeted drugs. The aim of this article is to explore the use of new drugs in this particular setting, which is still associated with poor prognosis and high risk of distant recurrence and death.

The ubiquitin–proteasome system in HIV replication: potential targets for antiretroviral therapy

Since the discovery of HIV approximately 20 years ago, more than 60 million individuals have been infected, and AIDS still remains one of the most devastating diseases humankind has ever faced. Unfortunately, there is little hope that an effective vaccine will be developed in the near future. Current antiretroviral treatment is based on drugs that either target the viral enzymes (protease and reverse transcriptase) or the attachment and entry of the virus. Although the introduction of highly active antiretroviral therapy in the mid-1990s has led to a profound reduction in HIV-related morbidity and mortality, the complete eradication of the virus from infected individuals has never been achieved. In addition, these antiviral drugs can induce serious adverse effects, particularly when administered in combination over prolonged treatment periods. A further drawback to these treatments is that with the high mutation rate of HIV, drug-resistant mutants are evolving, particularly when antiretroviral treatment only suppresses virus replication to marginal levels in latently infected cells making up the virus reservoirs in vivo. Cellular genes have much lower mutation rates, and drug-mediated modulation of specific cellular pathways represents an attractive antiviral strategy. Recent findings showing that proteasome inhibitors interfere with budding, maturation and infectivity of HIV have triggered intensive investigation of the hitherto unappreciated function of the ubiquitin-proteasome system in HIV replication. It was also observed that, like several other retroviruses, HIV-1 virions contain a small amount of mono-ubiquitinylated Gag proteins. Currently, two E3-type ubiquitin ligases, in addition to one E3-like protein, have been identified as regulators of HIV budding. These ligases might represent interesting targets for therapeutic intervention.

CIP2A is a target of bortezomib in human triple negative breast cancer cells

Introduction

Triple negative breast cancer (TNBC) is very aggressive and currently has no specific therapeutic targets, such as hormone receptors or human epidermal growth factor receptor type 2 (HER2); therefore, prognosis is poor. Bortezomib, a proteasome inhibitor, may exert efficacy in TNBC through its multiple cellular effects. Here, we tested the efficacy of bortezomib and examined the drug mechanism in breast cancer cells.

Methods

Five breast cancer cell lines: TNBC HCC-1937, MDA-MB-231, and MDA-MB-468; HER2-overexpressing MDA-MB-453; and estrogen receptor positive MCF-7 were used for in vitro studies. Apoptosis was examined by both flow cytometry and Western Blot. Signal transduction pathways in cells were assessed by Western Blot. Gene silencing was done by small interfering RNA (siRNA). In vivo efficacy of bortezomib was tested in nude mice with breast cancer xenografts. Immunohistochemical study was performed on tumor tissues from patients with TNBC.

Results

Bortezomib induced significant apoptosis, which was independent of its proteasome inhibition, in the three TNBC cell lines, but not in MDA-MB-453 or MCF-7 cells. Furthermore, cancerous inhibitor of protein phosphatase 2A (CIP2A), a cellular inhibitor of protein phosphatase 2A (PP2A), mediated the apoptotic effect of bortezomib. We showed that bortezomib inhibited CIP2A in association with p-Akt downregulation in a dose- and time-dependent manner in all sensitive TNBC cells, whereas no alterations in CIP2A expression and p-Akt were noted in bortezomib-resistant cells. Overexpression of CIP2A upregulated p-Akt and protected MDA-MB-231 and MDA-MB-468 cells from bortezomib-induced apoptosis, whereas silencing CIP2A by siRNA overcame the resistance to bortezomib-induced apoptosis in MCF-7 cells. In addition, bortezomib downregulated CIP2A mRNA but did not affect the degradation of CIP2A protein. Furthermore, bortezomib exerted in vivo antitumor activity in HCC-1937 xenografted tumors, but not in MCF-7 tumors. Bortezomib downregulated CIP2A expression in the HCC-1937 tumors but not in the MCF-7 tumors. Importantly, CIP2A expression is readily detectable in tumor samples from TNBC patients.

Conclusions

CIP2A is a major determinant mediating bortezomib-induced apoptosis in TNBC cells. CIP2A may thus be a potential therapeutic target in TNBC.

Reduced association of anti-apoptotic protein Mcl-1 with E3 ligase Mule increases the stability of Mcl-1 in breast cancer cells

Background:

Mechanisms that increase resistance to apoptosis help promote cellular transformation. Cancer cells have deregulated apoptotic pathways, where increased expression and stability of anti-apoptotic proteins Mcl-1 and Bcl-2 increases resistance to apoptosis. Pathways that increase the stability of proteins in cancer cells remain poorly understood.

Methods:

Using human mammary epithelial and established breast cancer cell lines, we assessed the mechanisms that increase the stability of anti-apoptotic proteins in breast cancer cells by caspase assay, western blot, small-inhibitory RNA treatment and immunoprecipitation.

Results:

While breast cancer cells were resistant to de novo inhibition of protein synthesis, a rapid proteosome-mediated degradation of Mcl-1 and Bcl-2 induced apoptosis in mammary epithelial cells. Although Mule, an E3 ligase that targets Mcl-1 for degradation was expressed in mammary epithelial and breast cancer cell lines, rapid increase of polyubiquitinated Mcl-1 and Bcl-2 was detected only in mammary epithelial cells. Only transient formation of the Mule–Mcl-1 complex was detected in breast cancer cells. Downregulation of pERK1/2 in breast cancer cells reduced Mcl-1 levels and increased Mcl-1/Mule complex.

Conclusion:

Our findings suggest that reduced Mule/Mcl-1 complex has a significant role in increasing the stability of Mcl-1 in breast cancer cells and increased resistance to apoptosis.

Regulation of the Nrf2-Keap1 antioxidant response by the ubiquitin proteasome system: an insight into cullin-ring ubiquitin ligases

Nrf2 is a transcription factor that has emerged as the cell's main defense mechanism against many harmful environmental toxicants and carcinogens. Nrf2 is negatively regulated by Keap1, a substrate adaptor protein for the Cullin3 (Cul3)-containing E3-ligase complex, which targets Nrf2 for ubiquitination and degradation by the ubiquitin proteasome system (UPS). Recent evidence suggests that constitutive activation of Nrf2, due to mutations in Keap1 or Nrf2, is prominent in many cancer types and contributes to chemoresistance. Regulation of Nrf2 by the Cul3-Keap1-E3 ligase provides strong evidence that tight regulation of Cullin-ring ligases (CRLs) is imperative to maintain cellular homeostasis. There are seven known Cullin proteins that form various CRL complexes. They are regulated by neddylation/deneddylation, ubiquitination/deubiquitination, CAND1-assisted complex assembly/disassembly, and subunit dimerization. In this review, we will discuss the regulation of each CRL using the Cul3-Keap1-E3 ligase complex as the primary focus. The substrates of CRLs are involved in many signaling pathways. Therefore, deregulation of CRLs affects several cellular processes, including cell cycle arrest, DNA repair, cell proliferation, senescence, and death, which may lead to many human diseases, including cancer. This makes CRLs a promising target for novel cancer drug therapies.

Combined effects of lapatinib and bortezomib in human epidermal receptor 2 (HER2)-overexpressing breast cancer cells and activity of bortezomib against lapatinib-resistant breast cancer cells

Lapatinib and bortezomib are highly active against breast cancer cells. Breast cancer patients who initially respond to lapatinib may eventually manifest acquired resistance to this treatment. Thus, the identification of novel agents that may prevent or delay the development of acquired resistance to lapatinib is critical. In the current study, we show that the combination of lapatinib and bortezomib results in a synergistic growth inhibition in human epidermal receptor 2 (HER2)-overexpressing breast cancer cells and that the combination enhances apoptosis of SK-BR-3 cells. Importantly, we found that the combination of lapatinib plus bortezomib more effectively blocked activation of the HER2 pathway in SK-BR-3 cells, compared with monotherapy. In addition, we established a model of acquired resistance to lapatinib by chronically challenging SK-BR-3 breast cancer cells with increasing concentrations of lapatinib. Here, we showed that bortezomib notably induced apoptosis of lapatinib-resistant SK-BR-3 pools and further inhibited HER2 signaling in the resistant cells. Taken together, the current data indicate a synergistic interaction between lapatinib and bortezomib in HER2-overexpressing breast cancer cells and provide the rationale for the clinical evaluation of these two noncross-resistant targeted therapies. The combination of lapatinib and bortezomib may be a potentially novel approach to prevent or delay the onset of acquired resistance to lapatinib in HER2-overxpressing/estrogen receptor (ER)-negative breast cancers.

BU-32: a novel proteasome inhibitor for breast cancer

Introduction

Proteasome inhibition provides an attractive approach to cancer therapy and may have application in the treatment of breast cancer. However, results of recent clinical trials to evaluate the effect of the proteasome inhibitor Bortezomib (Velcade^®, also called PS-341) in metastatic breast cancer patients have shown limited activity when used as a single agent. This underscores the need to find new and more efficacious proteasome inhibitors. In this study, we evaluate the efficacy of the novel proteasome inhibitor BU-32 (NSC D750499-S) using in vitro and in vivo breast cancer models.

Methods

We have recently synthesized a novel proteasome inhibitor (BU-32) and tested its growth inhibitory effects in different breast cancer cells including MCF-7, MDA-MB-231, and SKBR3 by in vitro cytotoxicity and proteasomal inhibition assays. The apoptotic potential of BU32 was tested using flow cytometry and analyzing cell cycle regulatory proteins. In vivo tumor xenograft studies for solid tumor as well as tumor metastasis were conducted using MDA-MB-231-GFP cells.

Results

We report for the first time that BU-32 exhibits strong cytotoxicity in a panel of cell lines: MDA-MB-231 (IC₅₀ = 5.8 nM), SKBR3 (IC₅₀ = 5.7 nM) and MCF-7 cells (IC₅₀ = 5.8 nM). It downregulates a wide array of angiogenic marker genes and upregulates apoptotic markers, including Bid and Bax. Incubation of MDA-MB-231 cells with BU-32 results in the accumulation of cell cycle inhibitor proteins p21 and p27 and stabilization of the tumor suppressor protein p53. Studies in in vivo solid tumor and metastasis models show significant effect with a 0.06 mg/kg dose of BU-32 and marked reduction in tumor burden in the skeleton.

Conclusions

We have shown that BU-32 is effective in cultured breast cancer cells and in breast cancer xenografts. The results suggest its potential benefit in breast cancer treatment.

Breast cancer migration and invasion depend on proteasome degradation of regulator of G-protein signaling 4

Aberrant signaling through G-protein coupled receptors promotes metastasis, the major cause of breast cancer death. We identified regulator of G-protein signaling 4 (RGS4) as a novel suppressor of breast cancer migration and invasion, important steps of metastatic cascades. By blocking signals initiated through G(i)-coupled receptors, such as protease-activated receptor 1 and CXC chemokine receptor 4, RGS4 disrupted Rac1-dependent lamellipodia formation, a key step involved in cancer migration and invasion. RGS4 has GTPase-activating protein (GAP) activity, which inhibits G-protein coupled receptor signaling by deactivating G-proteins. An RGS4 GAP-deficient mutant failed to inhibit migration and invasion of breast cancer cells in both in vitro assays and a mouse xenograft model. Interestingly, both established breast cancer cell lines and human breast cancer specimens showed that the highest levels of RGS4 protein were expressed in normal breast epithelia and that RGS4 down-regulation by proteasome degradation is an index of breast cancer invasiveness. Proteasome blockade increased endogenous RGS4 protein to levels that markedly inhibit breast cancer cell migration and invasion, which was reversed by an RGS4-targeted short hairpin RNA. Our findings point to the existence of a mechanism for posttranslational regulation of RGS4 function, which may have important implications for the acquisition of a metastatic phenotype by breast cancer cells. Preventing degradation of RGS4 protein should attenuate aberrant signal inputs from multiple G(i)-coupled receptors, thereby retarding the spread of breast cancer cells and making them targets for surgery, radiation, and immune treatment.

The silent estrogen receptor--can we make it speak?

One of the most common cancers in women world wide, breast cancer is classically an endocrine-dependent cancer. It has been known for over a century that development, progression and metastasis of breast cancer are strongly influenced by hormonal factors. Indeed about two-thirds of breast cancers express the estrogen receptor α (ERα) protein, a key predictor of prognosis and response to endocrine therapy. These cancers are frequently amenable to therapies that target estrogen signaling pathways, including selective estrogen receptor modulators like tamoxifen, selective estrogen receptor downregulators like fulvestrant; and agents that reduce estrogen ligand like aromatase inhibitors and ovarian suppression through luteinizing hormone-releasing hormone (LHRH) agonists. It is likely that these approaches, especially adjuvant tamoxifen, have contributed to the reduction in breast cancer mortality that has been observed in recent years. However, data from clinical studies have suggested that only about 60% of ERα-positive breast cancers respond to hormonal therapy. Further, those tumors that lack expression of ERα and the estrogen-regulated progesterone receptor (PgR) are unresponsive to hormone therapy. Thus the problem of acquired or de novo endocrine resistance is a substantial one. Recent molecular and biological advances have contributed to our understanding about potential underlying mechanisms. Here we will focus especially on silencing the expression of ERα as one such endocrine-resistance mechanism and how it might be exploited clinically.

Gene expression meta-analysis identifies metastatic pathways and transcription factors in breast cancer

Background

Metastasis is believed to progress in several steps including different pathways but the determination and understanding of these mechanisms is still fragmentary. Microarray analysis of gene expression patterns in breast tumors has been used to predict outcome in recent studies. Besides classification of outcome, these global expression patterns may reflect biological mechanisms involved in metastasis of breast cancer. Our purpose has been to investigate pathways and transcription factors involved in metastasis by use of gene expression data sets.

Methods

We have analyzed 8 publicly available gene expression data sets. A global approach, "gene set enrichment analysis" as well as an approach focusing on a subset of significantly differently regulated genes, GenMAPP, has been applied to rank pathway gene sets according to differential regulation in metastasizing tumors compared to non-metastasizing tumors. Meta-analysis has been used to determine overrepresentation of pathways and transcription factors targets, concordant deregulated in metastasizing breast tumors, in several data sets.

Results

The major findings are up-regulation of cell cycle pathways and a metabolic shift towards glucose metabolism reflected in several pathways in metastasizing tumors. Growth factor pathways seem to play dual roles; EGF and PDGF pathways are decreased, while VEGF and sex-hormone pathways are increased in tumors that metastasize. Furthermore, migration, proteasome, immune system, angiogenesis, DNA repair and several signal transduction pathways are associated to metastasis. Finally several transcription factors e.g. E2F, NFY, and YY1 are identified as being involved in metastasis.

Conclusion

By pathway meta-analysis many biological mechanisms beyond major characteristics such as proliferation are identified. Transcription factor analysis identifies a number of key factors that support central pathways. Several previously proposed treatment targets are identified and several new pathways that may constitute new targets are identified.

A phase I and pharmacologic study of the combination of bortezomib and pegylated liposomal doxorubicin in patients with refractory solid tumors

PURPOSE

Pre-clinical studies combining the proteasome inhibitor bortezomib with anthracyclines have shown enhanced anti-tumor activity. We conducted a phase I trial of bortezomib and pegylated liposomal doxorubicin (PLD) in patients with refractory solid tumors.

METHODS

Patients received bortezomib, 0.9-1.5 mg/m(2), on days 1, 4, 8, and 11 of every 21-day cycle, along with PLD, 30 mg/m(2), on day 4. The goals were to determine the dose limiting toxicity (DLT) and maximum tolerated dose (MTD), and to investigate pharmacokinetic and pharmacodynamic interactions of the combination.

RESULTS

A total of 37 patients with four median prior therapies were treated. Frequent grade 1-2 toxicities included fatigue, nausea, thrombocytopenia, anemia, neutropenia, constipation, myalgias, and peripheral neuropathy. DLTs included grade 3 nausea and vomiting in 1 of 6 patients receiving bortezomib at 1.2 mg/m(2), and grade 3 nausea, vomiting, and diarrhea in 1 of 6 patients receiving bortezomib at 1.5 mg/m(2). Grade 3 toxicities in later cycles included hand-foot syndrome, thrombocytopenia, anemia, neutropenia, nausea, diarrhea, and abdominal pain. Because of frequent dose-delays, dose-reductions, and gastrointestinal toxicity at the 1.4 and 1.5 mg/m(2) levels, bortezomib at 1.3 mg/m(2) and PLD at 30 mg/m(2) are recommended for further testing. Among 19 patients with breast cancer, four had evidence of a clinical benefit. Pharmacokinetic and pharmacodynamic studies did not show any significant interactions between the two drugs.

CONCLUSIONS

A regimen of bortezomib, 1.3 mg/m(2) on days 1, 4, 8, and 11 with PLD, 30 mg/m(2), on day 4 of a 21-day cycle, was safe in this study, and merits further investigation.

Next generation molecular targeted agents for breast cancer: focus on EGFR and VEGFR pathways

Here we reviewed the recent progress of molecular targeting drugs, including trastuzumab, lapatinib, erlotinib and bevacituzumab. Fortunately, Her-2 positive cases of metastatic or relapsed cases, those with the worse prognosis, are responsive to trastuzumab-based chemotherapy. Lapatinib will likely be effective against trastuzumab-resistant cases and brain metastases. Furthermore, the introduction of bevacituzumab will improve VEGF-VEGFR- associated tumor growth.

Proteasome-regulated ERBB2 and estrogen receptor pathways in breast cancer

A major challenge to broadening oncology applications for inhibitors of the ubiquitin-proteasome system (UPS) is the identification of UPS-dependent cancer pathways predictive of tumors responsive to peptidomimetic inhibitors of its 20S core protease activity. To inform clinical studies evaluating UPS inhibitors as breast cancer therapeutics, seven phenotypically diverse human breast cancer cell line models were characterized for their cellular and molecular responses to the clinically approved 20S inhibitor bortezomib (PS341; Velcade), focusing on those overexpressing estrogen receptor (ER) or ERBB2/HER2, because these oncogenic receptor pathways are constitutively activated in approximately 80% of all breast cancers. All models demonstrated dose-dependent bortezomib reduction in intracellular 20S activity correlating with cell growth inhibition, and bortezomib IC(50) values (concentrations producing 50% growth inhibition) varied directly with pretreatment 20S activities (r = 0.74; *, p < 0.05), suggesting that basal 20S activity may serve as a clinical predictor of tumor responsiveness to UPS inhibition. Reduction in 20S activity (> 60%) was associated with early (24 h) intracellular relocalization of ER (nucleus to cytoplasm) and ERBB2 (plasma membrane to perinuclear lysosomes), buildup of ubiquitinated and Hsp70-associated receptor, degradation and loss of ER and ERBB2 function, and induction of cellular apoptosis. These models were also used to screen a pharmacologic panel of pathway-targeted anticancer agents [4-hydroxy-3-methoxy-5-(benzothiazolylthiomethyl)benzylidenecyanoacetamide (AG825), 6-(4-bromo-2-chloro-phenylamino)-7-fluoro-3-methyl-3H-benzoimidazole-5-carboxylic acid (2-hydroxy-ethoxy)-amide (AZD6244/ARRY142886), 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride (LY294002), 17-N-allylamino-17-demethoxy geldanamycin (17AAG), and (2E)-N-hydroxy-3-[4-[[(2-hydroxyethyl)[2-(1H-indol-3-yl)ethyl]amino]methyl]phenyl]-2-propenamide (LAQ824)] for those capable of sensitizing to bortezomib. In keeping with the observation that 20S reduction has little effect on mitogen-activated protein kinase kinase 1/2 (MEK1/2) signaling in either ER-positive or ERBB2-positive models, only the MEK-1/2 inhibitor AZD6244 consistently improved the antitumor activity of bortezomib.

Genetic and expression aberrations of E3 ubiquitin ligases in human breast cancer

Recent studies revealed that E3 ubiquitin ligases play important roles in breast carcinogenesis. Clinical research studies have found that (epi)-genetic (deletion, amplification, mutation, and promoter methylation) and expression aberration of E3s are frequent in human breast cancer. Furthermore, many studies have suggested that many E3s are either oncogenes or tumor suppressor genes in breast cancer. In this review, we provide a comprehensive summary of E3s, which have genetic and/or expression aberration in breast cancer. Most cancer-related E3s regulate the cell cycle, p53, transcription, DNA repair, cell signaling, or apoptosis. An understanding of the oncogenic potential of the E3s may facilitate identifying and developing individual E3s as diagnosis markers and drug targets in breast cancer.

Targeting the ubiquitin-proteasome pathway in breast cancer therapy

The ubiquitin-proteasome pathway (UPP) is the major eukaryotic mechanism for regulated intracellular proteolysis. Targeting this pathway with proteasome inhibitors has been validated as a rational strategy against hematologic malignancies, but for most solid tumor populations, including breast cancer, such agents have not shown encouraging activity. However, there is an increasing body of evidence showing that UPP dysregulation plays an important role in mammary tumorigenesis. Moreover, modulation of ubiquitin-proteasome function is emerging as a rational strategy to enhance chemosensitivity and overcome chemoresistance. Taken together, these facts suggest that we are only beginning to appreciate the relevance of this pathway for the current and future therapy of patients with breast cancer. This review provides an overview of the biology of the UPP, its role in the malignant process, the current state of knowledge regarding clinical heat shock protein and proteasome inhibition, and some likely future directions that may enhance our ability to exploit this pathway therapeutically.

Differential effects of omega-3 and omega-6 Fatty acids on gene expression in breast cancer cells

Essential fatty acids have long been identified as possible oncogenic factors. Existing reports suggest omega-6 (omega-6) essential fatty acids (EFA) as pro-oncogenic and omega-3 (omega-3) EFA as anti-oncogenic factors. The omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), inhibit the growth of human breast cancer cells while the omega-6 fatty acids induces growth of these cells in animal models and cell lines. In order to explore likely mechanisms for the modulation of breast cancer cell growth by omega-3 and omega-6 fatty acids, we examined the effects of arachidonic acid (AA), linoleic acid (LA), EPA and DHA on human breast cancer cell lines using cDNA microarrays and quantitative polymerase chain reaction. MDA-MB-231, MDA-MB-435s, MCF-7 and HCC2218 cell lines were treated with the selected fatty acids for 6 and 24 h. Microarray analysis of gene expression profiles in the breast cancer cells treated with both classes of fatty acids discerned essential differences among the two classes at the earlier time point. The differential effects of omega-3 and omega-6 fatty acids on the breast cancer cells were lessened at the late time point. Data mining and statistical analyses identified genes that were differentially expressed between breast cancer cells treated with omega-3 and omega-6 fatty acids. Ontological investigations have associated those genes to a broad spectrum of biological functions, including cellular nutrition, cell division, cell proliferation, metastasis and transcription factors etc., and thus presented an important pool of biomarkers for the differential effect of omega-3 and omega-6EFAs.

Differential cellular and molecular effects of bortezomib, a proteasome inhibitor, in human breast cancer cells

The cellular and molecular effects of the proteasome inhibitor bortezomib on breast cancer cells are as yet poorly characterized. Here, in a panel of six breast cancer cell lines, bortezomib reduced viability in a concentration-dependent, time-dependent, and cell line-dependent manner. Proteasome activity was relatively high in two of the three more resistant cell lines. No relationship was observed between bortezomib effects on cell viability and expression/phosphorylation of HER-2, epidermal growth factor receptor (EGFR), AKT, or extracellular signal-regulated kinase 1/2 (ERK1/2). Molecular effects of bortezomib were further studied in SK-BR-3 and BT-474 cells because they share expression of EGFR and overexpression of HER-2 while, in contrast, SK-BR-3 cells were 200-fold more sensitive to this agent. Proteasome activity was inhibited to a similar extent in the two cell lines, and known proteasome substrates accumulated similarly. In SK-BR-3 cells, a marked inhibition of EGFR, HER-2, and AKT phosphorylation was observed at a clinically relevant concentration of bortezomib. In contrast, phosphorylation of Raf/mitogen-activated protein kinase kinase 1/2 (MEK 1/2)/ERK1/2 increased by bortezomib. In BT-474 cells, the effects were much less pronounced. Treatment of SK-BR-3 cells with bortezomib combined with pharmacologic inhibitors of EGFR, phosphatidylinositol 3'-kinase, or MEK resulted in modest or no enhancement of the effects on cell viability. Collectively, these results show that bortezomib has differential cellular and molecular effects in human breast cancer cells. The bortezomib-observed effects on signaling transduction molecules might be relevant to help to design mechanistic-based combination treatments.

Increased proteasome activity, ubiquitin-conjugating enzymes, and eEF1A translation factor detected in breast cancer tissue

The ubiquitin (Ub)/proteasome pathway facilitates the degradation of damaged proteins and regulators of growth and stress response. The activation of this pathway in various cancers and malignancies has been described, and several genetic determinants of breast cancer, including BRCA1 and BRCA2, are linked to protein degradation. To investigate the involvement of the Ub/proteasome system in breast cancer, we examined a collection of 25 patient-matched breast cancer and normal adjacent tissues and detected activation of numerous components of the Ub/proteasome pathway. The activity of the proteasome, and levels of proteasome subunits and various targeting factors, were increased in >90% of primary breast cancer tissue specimens. In contrast, no activation was observed in benign solid tumors, indicating that the response is specific to abnormal growth in neoplastic cells. Additionally, the accumulation of high levels of certain Ub-conjugating enzymes (UbcH1, UbcH2, and UbcH5), was specific to breast cancer, as no change in abundance was detected in primary colon cancer tissue extracts. Surprisingly, the Ub/proteasome system was not activated in a well-characterized cell culture-based breast cancer model system. Collectively, these findings suggest that the analysis of primary breast cancer tissue samples will be indispensable for the biochemical characterization of neoplastic growth and for the development of therapeutics.

Targeting beta-transducin repeat-containing protein E3 ubiquitin ligase augments the effects of antitumor drugs on breast cancer cells

beta-Transducin repeat-containing proteins (beta-TrCP) serve as substrate recognition component of E3 ubiquitin ligases that control stability of important regulators of cell cycle and signal transduction. beta-TrCP function is essential for the induction of nuclear factor kappaB transcriptional activities, which play a key role in proliferation and survival of cancer cells and are often constitutively up-regulated in human breast cancers. Here we show that inhibition of beta-TrCP either by RNAi approach or by forced expression of a dominant-negative beta-TrCP mutant suppresses growth and survival of human breast cancer cells. In addition, inhibition of beta-TrCP augments the antiproliferative effects of anticancer drugs such as doxorubicin, tamoxifen, and paclitaxel on human mammary tumor cells. These data provide the proof of principle that targeting beta-TrCP might be beneficial for anticancer therapies.