Gene expression analysis of B-lymphoma cells resistant and sensitive to bortezomib

Review of preclinical data on hyperthermia treatment in lymphomas and its potential for clinical application

INTRODUCTION

Hyperthermia (HT) at temperatures between 39 °C and 44 °C is utilized as an adjunctive cancer therapy, serving as potent radio- and chemosensitizer. Its effectiveness in treating solid malignancies has been well established. This raises the question of whether HT can also benefit patients with nonsolid tumors, such as lymphomas.

OBJECTIVE

To provide an overview of the current literature on research involving the use of HT in the treatment of lymphomas.

MATERIAL AND METHODS

This systematic literature review was conducted following the PRISMA guidelines. For this purpose, a MeSH-term-defined literature search on MEDLINE (Pubmed) and Embase (Ovid) was conducted from June 25 to June 28, 2024. Included were in vitro studies on lymphoma cell lines and preclinical studies on animal models with lymphoma that were both treated with HT as monotherapy or HT in combination with another treatment, and studies on patients with lymphoma. Excluded were studies that used thermal ablation and hyperthermic perfusions.

RESULTS

Thirty-nine studies were included, predominantly in vitro studies (n = 32) or studies on animal models (n = 5). The in vitro studies utilized HT either as monotherapy (n = 6), with substances that enhance HT efficacy (n = 18) or as a sensitizer for other treatments (n = 8). Additionally, two clinical case reports on the treatment of lymphoma patients were included.

CONCLUSIONS

In vitro results suggest that HT can have anticancer effects on lymphoma cells and may enhance existing treatments. These findings are supported by in vivo studies and case reports. However, additional clinical data are needed before translation into the clinic can be implemented.

Hsp90 is a potential risk factor for ovarian cancer prognosis: an evidence of a Chinese clinical center

BACKGROUND

The potential treatment effects of heat shock protein 90 (Hsp90) inhibitors in ovarian cancer (OC) are controversial. This research aims to investigate the relationship between the level of Hsp90 in peripheral blood and the prognosis of OC patients, as well as the clinicopathological indicators.

MATERIALS AND METHODS

We retrospectively collected the clinicopathological indicators of OC patients who were admitted to the Department of Obstetrics and Gynecology of the First Affiliated Hospital of Anhui Medical University from 2017 to 2022. Hsp90 level in patient blood was detected by enzyme-linked immunosorbent assay, and the correlation between Hsp90 level and OC prognosis was systematically investigated. Kaplan-Meier method was used to draw the survival curve, and the average survival time and survival rate were calculated. The log-rank test and Cox model were used for univariate survival analysis, and the Cox proportional hazards model was applied for multivariate survival analysis. Based on the TCGA dataset of OC obtained by cBioPortal, Pearson's correlation coefficients between Hsp90 level values and other mRNA expression values were calculated to further conduct bioinformatics analysis. GSEA and GSVA analysis were also conducted for gene functional enrichment. The expression of Hsp90 in OC tissues were evaluated and compared by Immunohistochemical staining.

RESULTS

According to the established screening criteria, 106 patients were selected. The enzyme-linked immunosorbent assay results showed that 50.94% OC patients with abnormal Hsp90 level. According to the outcome of Kaplan-Meier curves, the results revealed that the abnormal level of Hsp90 was suggested to poor prognosis (P = 0.001) of OC patients. Furthermore, the result of multivariate Cox proportional hazards regression model analysis also predicted that abnormal Hsp90 level (HR = 2.838, 95%CI = 1.139-7.069, P = 0.025) was linked to poor prognosis, which could be an independent prognostic factor for the prognosis of OC patients. Moreover, top 100 genes screened by Pearson's value associated with Hsp90, indicating that Hsp90 participated in the regulation of ATF5 target genes, PRAGC1A target genes and BANP target genes and also enriched in the metabolic processes of cell response to DNA damage stimulus, response to heat and protein folding.

CONCLUSION

Hsp90 level is positively associated with OC mortality and is a potential prognostic indicator of OC.

Bortezomib Inhibits Multiple Myeloma Cells by Transactivating ATF3 to Trigger miR-135a-5p- Dependent Apoptosis

Multiple myeloma (MM) is a malignant cancer with an increasing in incidence that can be alleviated through bortezomib (BTZ) treatment. Activating transcription factor 3 (ATF3) plays a major role in cancer development. Moreover, microRNAs (miRNAs) regulate carcinogenic pathways, apoptosis, and programmed necrotic cell death. However, the detailed mechanism by which ATF3 modulates BTZ drug sensitivity/resistance remains elusive. In the current study, expression of ATF3 was significantly increased under BTZ treatment in a dose-dependent manner in MM cell lines. In addition, ATF3 could regulate cell apoptosis under BTZ treatment. The effect of ATF3 was negatively regulated by its binding miRNA, miR-135a-5p. When either ATF3 was silenced or miR-135a-5p mimics were added to MM cells, they partially lost sensitivity to BTZ treatment. This was accompanied by low levels of Noxa, CHOP, and DR5, and a decrease in mitochondrial membrane potential. These results revealed the combinatorial regulatory patterns of ATF3 and miR-135a-5p in the regulatory protein interactome, which indicated a clinical significance of the miR-135a-5p-ATF3 protein interaction network in BTZ therapy. This study provides potential evidence for further investigation into BTZ resistance.

Molecular analysis of cell survival and death pathways in the proteasome inhibitor bortezomib-resistant PC3 prostate cancer cell line

The ubiquitin-proteasome pathway is an important protein quality control system involved in intracellular homeostasis. To achieve intracellular homeostasis, proteins that are misfolded as a result of translational errors or genetic mutations must be eliminated by the ubiquitin-proteasome pathway. In our previous publications, we determined that 4T1 breast and B16F10 melanoma cancer cells have differential levels of resistance to proteasome inhibitors. Again, in the previous studies, we reported that 4T1 cell cultures, despite being p53-mutant, underwent apoptosis as a result of bortezomib treatment. The first goal of this study was to verify the resistance levels of parental and resistant PC3 prostate cancer cells to bortezomib using WST-1 test. As a result of treatment with different bortezomib concentrations for 48 h, the IC₅₀ value of the parental cells was determined as 32.8 nM and that of the resistant cells was determined as 346 nM. This result showed that the resistant cells were at least 10.5 times more resistant. In addition, to determine whether the resistance gained was reversible or not, the cells were passaged in a medium without bortezomib for one month. The IC₅₀ value determination by WST-1 test showed that the resistant PC3 cells gained an irreversible bortezomib resistance phenotype. The results of the 3D spheroid experiment showed that the 3D spheroid diameter of resistant cells was significantly higher than that of the parental cells. The studies conducted with Western blot showed that ERK1 MAPK T202 phosphorylation and the conversion of autophagy marker LC3-I to LC3-II were significantly increased in parental cells as compared to the resistant cells. Finally, the results showed that while both maternal embryonic leucine zipper kinase (MELK) inhibitor OTSSP167 and Ca²⁺ chelator BAPTA-AM (also an inhibitor of the expression of antiapoptotic protein GRP78) are promising agents for cancer cells resistant to the proteasome inhibitors, CDK2 inhibitor CVT-313 was found ineffective in both parental and the resistant cells.

An investigation of the mechanisms underlying the proteasome inhibitor bortezomib resistance in PC3 prostate cancer cell line

The phenomenon of acquired resistance to chemotherapeutic agents is a long-standing conundrum in cancer treatment. To help delineate drug resistance mechanisms and pave the way for the development of novel strategies, we generated a PC3 prostate cancer cell line resistant to proteasome inhibitor bortezomib for the first time. The resistant cells were found to have an IC₅₀ value of 359.6 nM, whereas the IC₅₀ value of parental cells was 82.6 nM after 24 h of treatment with varying doses of bortezomib. The resistant cells were also partly cross-resistant to the novel proteasome inhibitor carfilzomib; however, they were not resistant to widely used chemotherapeutic agent vincristine sulfate, indicating that enhanced cellular drug efflux via the multidrug resistance (MDR) transporters is not the molecular basis of the resistance. Since both bortezomib and carfilzomib target and inhibit the chymotrypsin-related activity residing in the β5 subunit of the proteasome (PSMB5), we next examined its expression and found surprisingly no significant alteration in the expression profile of the mature form. However, a significant increase in the accumulation of the precursor form of PSMB5 in response to 100 nM bortezomib was observed in the parental cells without a significant accumulation in the resistant cells. The results presented here thus suggest that the molecular mechanisms causing resistance to proteasome inhibitors need to be examined in-depth to overcome the resistance to ubiquitin-proteasome pathway inhibitors in cancer treatment.

Activation of LXRβ inhibits proliferation, promotes apoptosis, and increases chemosensitivity of gastric cancer cells by upregulating the expression of ATF4

Recently, great advances have been achieved in both surgery and chemotherapy for the treatment of gastric cancer, but there is still poor prognosis for this disease. The aim of this study is to investigate the role of liver X receptor β (LXRβ) in chemosensitivity of gastric cancer SGC7901 cells. From 171 patients with gastric cancer, the gastric cancer and paracancerous tissues were selected to measure the expression of LXRβ and ATF4. Gastric cancer cell lines were cultured and screened to figure out the proliferation and apoptosis of gastric cancer SGC7901 cells with the treatment of LXRβ agonist (GW3965), ATF4 short hairpin RNA (shRNA), and chemotherapy drug paclitaxel. The expression of apoptosis-related gene cleaved caspase-3 was detected by Western blot analysis. First, we found that the expressions of LXRβ and ATF4 in gastric cancer tissues and cells were significantly lower than those in their paracancerous tissues and gastric mucosal epithelial cells. In addition, activation of LXRβ and paclitaxel treatment suppressed proliferation of SGC7901 cells, and the expression of ATF4 was upregulated in a concentration-dependent manner. Furthermore, shRNA significantly inhibited the expression of ATF4 and blocked the chemosensitivity of SGC7901 cells to LXRβ activation. Our study demonstrates that the expression of LXRβ was low in gastric cancer. In addition, activation of LXRβ may inhibit the proliferation of gastric cancer cells, promote apoptosis, and increase chemosensitivity by upregulating the expression of ATF4.

Exocytosis of polyubiquitinated proteins in bortezomib-resistant leukemia cells: a role for MARCKS in acquired resistance to proteasome inhibitors

PSMB5 mutations and upregulation of the β5 subunit of the proteasome represent key determinants of acquired resistance to the proteasome inhibitor bortezomib (BTZ) in leukemic cells in vitro. We here undertook a multi-modality (DNA, mRNA, miRNA) array-based analysis of human CCRF-CEM leukemia cells and BTZ-resistant subclones to determine whether or not complementary mechanisms contribute to BTZ resistance. These studies revealed signatures of markedly reduced expression of proteolytic stress related genes in drug resistant cells over a broad range of BTZ concentrations along with a high upregulation of myristoylated alanine-rich C-kinase substrate (MARCKS) gene expression. MARCKS upregulation was confirmed on protein level and also observed in other BTZ-resistant tumor cell lines as well as in leukemia cells with acquired resistance to other proteasome inhibitors. Moreover, when MARCKS protein expression was demonstrated in specimens derived from therapy-refractory pediatric leukemia patients (n = 44), higher MARCKS protein expression trended (p = 0.073) towards a dismal response to BTZ-containing chemotherapy. Mechanistically, we show a BTZ concentration-dependent association of MARCKS protein levels with the emergence of ubiquitin-containing vesicles in BTZ-resistant CEM cells. These vesicles were found to be extruded and taken up in co-cultures with proteasome-proficient acceptor cells. Consistent with these observations, MARCKS protein associated with ubiquitin-containing vesicles was also more prominent in clinical leukemic specimen with ex vivo BTZ resistance compared to BTZ-sensitive leukemia cells. Collectively, we propose a role for MARCKS in a novel mechanism of BTZ resistance via exocytosis of ubiquitinated proteins in BTZ-resistant cells leading to quenching of proteolytic stress.

Potent anti-tumor activity of a syringolin analog in multiple myeloma: a dual inhibitor of proteasome activity targeting β2 and β5 subunits

Proteasome inhibitors (PI), mainly targeting the β5 subunit of the 20S proteasome, are widely used in the treatment of multiple myeloma (MM). However, PI resistance remains an unresolved problem in the therapy of relapsed and refractory MM. To develop a new PI that targets other proteasome subunits, we examined the anti-MM activity of a novel syringolin analog, syringolog-1, which inhibits the activity of both the β5 and β2 subunits. Syringolog-1 exhibited marked cytotoxicity against various MM cell lines and anti-tumor activity towards bortezomib (Btz)-resistant MM cells through the dual inhibition of chymotrypsin-like (β5 subunit) and trypsin-like (β2 subunit) activities. MM cells, including Btz-resistant cells, showed elevated CHOP and NOXA expression after syringolog-1 treatment, indicating the induction of excessive endoplasmic reticulum stress during syringolog-1 treatment. Similar activities of syringolog-1 were also observed in freshly prepared MM cells derived from patients. To clarify the anti-tumor mechanism of dual inhibition of both the β5 and β2 subunits of the proteasome, PSMB5 and PSMB7 were co-inhibited in MM cells. This resulted in increased apoptosis of MM cells accompanied by accumulation of ubiquitinated proteins compared to inhibition of either PSMB7 or PSMB5 alone, indicating an enhanced effect by double inhibition of β2 and β5 activities. In conclusion, this syringolin analog, a dual inhibitor of proteasome β2 and β5 activities, exhibited potent anti-tumor effects on MM cells and may be useful for overcoming Btz-resistance in the treatment of MM.

Soluble and Cell-Cell-Mediated Drivers of Proteasome Inhibitor Resistance in Multiple Myeloma

It is becoming clear that myeloma cell-induced disruption of the highly organized bone marrow components (both cellular and extracellular) results in destruction of the marrow and support for multiple myeloma (MM) cell proliferation, survival, migration, and drug resistance. Since the first phase I clinical trial on bortezomib was published 15 years ago, proteasome inhibitors (PIs) have become increasingly common for treatment of MM and are currently an essential part of any anti-myeloma combination therapy. PIs, either the first generation (bortezomib), second generation (carfilzomib) or oral agent (ixazomib), all take advantage of the heavy reliance of myeloma cells on the 26S proteasome for their degradation of excessive or misfolded proteins. Inhibiting the proteasome can create a crisis specifically for myeloma cells due to their rapid production of immunoglobulins. PIs have relatively few side effects and can be very effective, especially in combination therapy. If PI resistance can be overcome, these drugs may prove even more useful to a greater range of patients. Both soluble and insoluble (contact mediated) signals drive PI-resistance via activation of various intracellular signaling pathways. This review discusses the currently known mechanisms of non-autonomous (microenvironment dependent) mechanisms of PI resistance in myeloma cells. We also introduce briefly cell-autonomous and stress-mediated mechanisms of PI resistance. Our goal is to help researchers design better ways to study and overcome PI resistance, to ultimately design better combination therapies.

IL-2 imprints human naive B cell fate towards plasma cell through ERK/ELK1-mediated BACH2 repression

Plasma cell differentiation is a tightly regulated process that requires appropriate T cell helps to reach the induction threshold. To further understand mechanisms by which T cell inputs regulate B cell fate decision, we investigate the minimal IL-2 stimulation for triggering human plasma cell differentiation in vitro. Here we show that the timed repression of BACH2 through IL-2-mediated ERK/ELK1 signalling pathway directs plasma cell lineage commitment. Enforced BACH2 repression in activated B cells unlocks the plasma cell transcriptional program and induces their differentiation into immunoglobulin M-secreting cells. RNA-seq and ChIP-seq results further identify BACH2 target genes involved in this process. An active regulatory region within the BACH2 super-enhancer, under ELK1 control and differentially regulated upon B-cell activation and cellular divisions, helps integrate IL-2 signal. Our study thus provides insights into the temporal regulation of BACH2 and its targets for controlling the differentiation of human naive B cells.

T cells help B cells to differentiate into antibody-producing plasma cells. Here the authors show that T cells produce interleukin-2 to activate ERK/ELK1 and suppress BACH2 expression by modulating the BACH2 super-enhancer, thereby altering BACH2 downstream transcription programs for plasma cell differentiation.

The p97 Inhibitor CB-5083 Is a Unique Disrupter of Protein Homeostasis in Models of Multiple Myeloma

Inhibition of the AAA ATPase, p97, was recently shown to be a novel method for targeting the ubiquitin proteasome system, and CB-5083, a first-in-class inhibitor of p97, has demonstrated broad antitumor activity in a range of both hematologic and solid tumor models. Here, we show that CB-5083 has robust activity against multiple myeloma cell lines and a number of in vivo multiple myeloma models. Treatment with CB-5083 is associated with accumulation of ubiquitinated proteins, induction of the unfolded protein response, and apoptosis. CB-5083 decreases viability in multiple myeloma cell lines and patient-derived multiple myeloma cells, including those with background proteasome inhibitor (PI) resistance. CB-5083 has a unique mechanism of action that combines well with PIs, which is likely owing to the p97-dependent retro-translocation of the transcription factor, Nrf1, which transcribes proteasome subunit genes following exposure to a PI. In vivo studies using clinically relevant multiple myeloma models demonstrate that single-agent CB-5083 inhibits tumor growth and combines well with multiple myeloma standard-of-care agents. Our preclinical data demonstrate the efficacy of CB-5083 in several multiple myeloma disease models and provide the rationale for clinical evaluation as monotherapy and in combination in multiple myeloma. Mol Cancer Ther; 16(11); 2375-86. ©2017 AACR.

HSP70-Hrd1 axis precludes the oncorepressor potential of N-terminal misfolded Blimp-1s in lymphoma cells

B lymphocyte-induced maturation protein-1 (Blimp-1) ensures B-cell differentiation into the plasma cell stage, and its instability constitutes a crucial oncogenic element in certain aggressive cases of activated B cell-like diffuse large B-cell lymphoma (ABC-DLBCL). However, the underlying degradation mechanisms and their possible therapeutic relevance remain unexplored. Here, we show that N-terminal misfolding mutations in ABC-DLBCL render Blimp-1 protein susceptible to proteasome-mediated degradation but spare its transcription-regulating activity. Mechanistically, whereas wild-type Blimp-1 metabolism is triggered in the nucleus through PML-mediated sumoylation, the degradation of lymphoma-associated mutants is accelerated by subversion of this pathway to Hrd1-mediated cytoplasmic sequestration and ubiquitination. Screening experiments identifies the heat shock protein 70 (HSP70) that selects Blimp-1 mutants for Hrd1 association, and HSP70 inhibition restores their nuclear accumulation and oncorepressor activities without disrupting normal B-cell maturation. Therefore, HSP70-Hrd1 axis represents a potential therapeutic target for restoring the oncorepressor activity of unstable lymphoma-associated Blimp-1 mutants.

The transcriptional repressor Blimp-1 has an important role in B-cell differentiation. Here the authors show that lymphoma-associated Blimp-1 mutants are selectively recognized by HSP70-Hrd1, which leads to their accelerated degradation and propose HSP70 inhibition as a therapeutic approach for certain lymphomas.

Suppression of 19S proteasome subunits marks emergence of an altered cell state in diverse cancers

The use of proteasome inhibitors to target cancer's dependence on altered protein homeostasis has been greatly limited by intrinsic and acquired resistance. Analyzing data from thousands of cancer lines and tumors, we find that those with suppressed expression of one or more 19S proteasome subunits show intrinsic proteasome inhibitor resistance. Moreover, such proteasome subunit suppression is associated with poor outcome in myeloma patients, where proteasome inhibitors are a mainstay of treatment. Beyond conferring resistance to proteasome inhibitors, proteasome subunit suppression also serves as a sentinel of a more global remodeling of the transcriptome. This remodeling produces a distinct gene signature and new vulnerabilities to the proapoptotic drug, ABT-263. This frequent, naturally arising imbalance in 19S regulatory complex composition is achieved through a variety of mechanisms, including DNA methylation, and marks the emergence of a heritably altered and therapeutically relevant state in diverse cancers.

Synergistic cytotoxic effects of bortezomib and CK2 inhibitor CX-4945 in acute lymphoblastic leukemia: turning off the prosurvival ER chaperone BIP/Grp78 and turning on the pro-apoptotic NF-κB

The proteasome inhibitor bortezomib is a new targeted treatment option for refractory or relapsed acute lymphoblastic leukemia (ALL) patients. However, a limited efficacy of bortezomib alone has been reported. A terminal pro-apoptotic endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is one of the several mechanisms of bortezomib-induced apoptosis. Recently, it has been documented that UPR disruption could be considered a selective anti-leukemia therapy. CX-4945, a potent casein kinase (CK) 2 inhibitor, has been found to induce apoptotic cell death in T-ALL preclinical models, via perturbation of ER/UPR pathway. In this study, we analyzed in T- and B-ALL preclinical settings, the molecular mechanisms of synergistic apoptotic effects observed after bortezomib/CX-4945 combined treatment. We demonstrated that, adding CX-4945 after bortezomib treatment, prevented leukemic cells from engaging a functional UPR in order to buffer the bortezomib-mediated proteotoxic stress in ER lumen. We documented that the combined treatment decreased pro-survival ER chaperon BIP/Grp78 expression, via reduction of chaperoning activity of Hsp90. Bortezomib/CX-4945 treatment inhibited NF-κB signaling in T-ALL cell lines and primary cells from T-ALL patients, but, intriguingly, in B-ALL cells the drug combination activated NF-κB p65 pro-apoptotic functions. In fact in B-cells, the combined treatment induced p65-HDAC1 association with consequent repression of the anti-apoptotic target genes, Bcl-xL and XIAP. Exposure to NEMO (IKKγ)-binding domain inhibitor peptide reduced the cytotoxic effects of bortezomib/CX-4945 treatment. Overall, our findings demonstrated that CK2 inhibition could be useful in combination with bortezomib as a novel therapeutic strategy in both T- and B-ALL.

Selective targeting of BCL6 induces oncogene addiction switching to BCL2 in B-cell lymphoma

The BCL6 oncogene plays a crucial role in sustaining diffuse large B-cell lymphomas (DLBCL) through transcriptional repression of key checkpoint genes. BCL6-targeted therapy kills lymphoma cells by releasing these checkpoints. However BCL6 also directly represses several DLBCL oncogenes such as BCL2 and BCL-XL that promote lymphoma survival. Herein we show that DLBCL cells that survive BCL6-targeted therapy induce a phenomenon of “oncogene-addiction switching” by reactivating BCL2-family dependent anti-apoptotic pathways. Thus, most DLBCL cells require concomitant inhibition of BCL6 and BCL2-family members for effective lymphoma killing. Moreover, in DLBCL cells initially resistant to BH3 mimetic drugs, BCL6 inhibition induces a newly developed reliance on anti-apoptotic BCL2-family members for survival that translates in acquired susceptibility to BH3 mimetic drugs ABT-737 and obatoclax. In germinal center B cell-like (GCB)-DLBCL cells, the proteasome inhibitor bortezomib and the NEDD inhibitor MLN4924 post-transcriptionally activated the BH3-only sensitizer NOXA thus counteracting the oncogenic switch to BCL2 induced by BCL6-targeting. Hence our study indicates that BCL6 inhibition induces an on-target feedback mechanism based on the activation of anti-apoptotic BH3 members. This oncogene-addition switching mechanism was harnessed to develop rational combinatorial therapies for GCB-DLBCL.

Small molecule inhibitor screen identifies synergistic activity of the bromodomain inhibitor CPI203 and bortezomib in drug resistant myeloma

Purpose

Despite significant therapeutic progress in multiple myeloma, drug resistance is uniformly inevitable and new treatments are needed. Our aim was to identify novel, efficacious small-molecule combinations for use in drug resistant multiple myeloma.

Experimental Design

A panel of 116 small molecule inhibitors was used to screen resistant myeloma cell lines for potential therapeutic targets. Agents found to have enhanced activity in the bortezomib or melphalan resistant myeloma cell lines were investigated further in combination. Synergistic combinations of interest were evaluated in primary patient cells.

Results

The overall single-agent drug sensitivity profiles were dramatically different between melphalan and bortezomib resistant cells, however, the bromodomain inhibitor, CPI203, was observed to have enhanced activity in both the bortezomib and melphalan resistant lines compared to their wild-type counterparts. The combination of bortezomib and CPI203 was found to be synergistic in both the bortezomib and melphalan resistant cell lines as well as in a primary multiple myeloma sample from a patient refractory to recent proteasome inhibitor treatment. The CPI203-bortezomib combination led to enhanced apoptosis and anti-proliferative effects. Finally, in contrast to prior reports of synergy between bortezomib and other epigenetic modifying agents, which implicated MYC downregulation or NOXA induction, our analyses suggest that CPI203-bortezomib synergy is independent of these events.

Conclusion

Our preclinical data supports a role for the clinical investigation of the bromodomain inhibitor CPI203 combined with bortezomib or alkylating agents in resistant multiple myeloma.

Elucidation and Pharmacological Targeting of Novel Molecular Drivers of Follicular Lymphoma Progression

Follicular lymphoma, the most common indolent subtype of non-Hodgkin lymphoma, is associated with a relatively long overall survival rate ranging from 6 to 10 years from the time of diagnosis. However, in 20% to 60% of follicular lymphoma patients, transformation to aggressive diffuse large B-cell lymphoma (DLBCL) reduces median survival to only 1.2 years. The specific functional and genetic determinants of follicular lymphoma transformation remain elusive, and genomic alterations underlying disease advancement have only been identified for a subset of cases. Therefore, to identify candidate drivers of follicular lymphoma transformation, we performed systematic analysis of a B-cell-specific regulatory model exhibiting follicular lymphoma transformation signatures using the Master Regulator Inference algorithm (MARINa). This analysis revealed FOXM1, TFDP1, ATF5, HMGA1, and NFYB to be candidate master regulators (MR) contributing to disease progression. Accordingly, validation was achieved through synthetic lethality assays in which RNAi-mediated silencing of MRs individually or in combination reduced the viability of (14;18)-positive DLBCL (t-DLBCL) cells. Furthermore, specific combinations of small-molecule compounds targeting synergistic MR pairs induced loss of viability in t-DLBCL cells. Collectively, our findings indicate that MR analysis is a valuable method for identifying bona fide contributors to follicular lymphoma transformation and may therefore guide the selection of compounds to be used in combinatorial treatment strategies.

MicroRNAs in diffuse large B-cell lymphoma

The aberrant expression of microRNAs (miRs) has a significant impact on the biological characteristics of lymphocytes, and is important in the pathogenesis of diffuse large B-cell lymphoma (DLBCL). It has been demonstrated, using miR profiling and detecting distinct miR signatures, that certain miRs may accurately distinguish different subtypes and prognostic classifications of DLBCL, as well as distinguish DLBCL from other more indolent lymphomas, including follicular lymphoma. miRs are excellent biomarkers for cancer diagnosis and prognosis. In DLBCL, specific miR expression profiles in the tissues of patients are associated with prognosis and clinical outcome. Over the past decade, there has been substantial investigation concerning the pathogenetic, diagnostic and prognostic roles of miRs in DLBCL. The aim of the present review is to describe the aberrant expression of miRs in DLBCL, and the functions, potential clinical use and possible therapeutic targets of miRs in this disease.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin's lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.

Lower expression of activating transcription factors 3 and 4 correlates with shorter progression-free survival in multiple myeloma patients receiving bortezomib plus dexamethasone therapy

Bortezomib (BTZ), a proteasome inhibitor, is widely used in the treatment of multiple myeloma (MM), but a fraction of patients respond poorly to this agent. To identify factors predicting the duration of progression-free survival (PFS) of MM patients on BTZ treatment, the expression of proteasome and endoplasmic reticulum (ER) stress-related genes was quantified in primary samples from patients receiving a combination of BTZ and dexamethasone (BD). Fifty-six MM patients were stratified into a group with PFS<6 months (n=33) and a second group with PFS⩾6 months (n=23). Of the 15 genes analyzed, the expression of activating transcription factor 3 (ATF3) and ATF4 was significantly lower in patients with shorter PFS (P=0.0157 and P=0.0085, respectively). Chromatin immunoprecipitation analysis showed that these ATFs bind each other and transactivate genes encoding the pro-apoptotic transcription factors, CHOP and Noxa, which promote ER stress-associated apoptosis. When either ATF3 or ATF4 expression was silenced, MM cells partially lost sensitivity to BTZ treatment. This was accompanied by lower levels of Noxa, CHOP and DR5. Thus low basal expression of ATF3 and ATF4 may attenuate BTZ-induced apoptosis. Hence, ATF3 and ATF4 could potentially be used as biomarkers to predict efficacy of BD therapy in patients with MM.

Mitochondrial thioredoxin reductase regulates major cytotoxicity pathways of proteasome inhibitors in multiple myeloma cells

It is generally accepted that intracellular oxidative stress induced by proteasome inhibitors is a byproduct of endoplasmic reticulum (ER) stress. Here we report a mechanism underlying the ability of proteasome inhibitors bortezomib (BTZ) and carfilzomib (CFZ) to directly induce oxidative and ER stresses in multiple myeloma (MM) cells via transcriptional repression of a gene encoding mitochondrial thioredoxin reductase (TXNRD2). TXNRD2 is critical for maintenance of intracellular red-ox status and detoxification of reactive oxygen species. Depletion of TXNRD2 to the levels detected in BTZ- or CFZ-treated cells causes oxidative stress, ER stress and death similar to those induced by proteasome inhibitors. Reciprocally, restoration of near-wildtype TXNRD2 amounts in MM cells treated with proteasome inhibitors reduces oxidative stress, ER stress and cell death by ~46%, ~35% and ~50%, respectively, compared with cells with unrestored TXNRD2 levels. Moreover, cells from three MM cell lines selected for resistance to BTZ demonstrate elevated levels of TXNRD2, indirectly confirming its functional role in BTZ resistance. Accordingly, ectopic expression of TXNRD2 in MM cell xenografts in immunocompromised mice blunts therapeutic effects of BTZ. Our data identify TXNRD2 as a potentially clinically relevant target, inhibition of which is critical for proteasome inhibitor-dependent cytotoxicity, oxidative stress and ER stress.

Inhibition of Oncogenic Transcription Factor REL by the Natural Product Derivative Calafianin Monomer 101 Induces Proliferation Arrest and Apoptosis in Human B-Lymphoma Cell Lines

Increased activity of transcription factor NF-κB has been implicated in many B-cell lymphomas. We investigated effects of synthetic compound calafianin monomer (CM101) on biochemical and biological properties of NF-κB. In human 293 cells, CM101 selectively inhibited DNA binding by overexpressed NF-κB subunits REL (human c-Rel) and p65 as compared to NF-κB p50, and inhibition of REL and p65 DNA binding by CM101 required a conserved cysteine residue. CM101 also inhibited DNA binding by REL in human B-lymphoma cell lines, and the sensitivity of several B-lymphoma cell lines to CM101-induced proliferation arrest and apoptosis correlated with levels of cellular and nuclear REL. CM101 treatment induced both phosphorylation and decreased expression of anti-apoptotic protein Bcl-XL, a REL target gene product, in sensitive B-lymphoma cell lines. Ectopic expression of Bcl-XL protected SUDHL-2 B-lymphoma cells against CM101-induced apoptosis, and overexpression of a transforming mutant of REL decreased the sensitivity of BJAB B-lymphoma cells to CM101-induced apoptosis. Lipopolysaccharide-induced activation of NF-κB signaling upstream components occurred in RAW264.7 macrophages at CM101 concentrations that blocked NF-κB DNA binding. Direct inhibitors of REL may be useful for treating B-cell lymphomas in which REL is active, and may inhibit B-lymphoma cell growth at doses that do not affect some immune-related responses in normal cells.

Cellular uptake kinetics of bortezomib in relation to efficacy in myeloma cells and the influence of drug transporters

PURPOSE

Despite overall successful application to multiple myeloma patients, clinical efficacy of the proteasome inhibitor bortezomib is typically challenged by primary and secondary resistance of unknown origin. So far, the potential impact of intracellular concentrations on drug efficacy of bortezomib and the influence of drug transporters are unknown.

METHODS

We determined cellular bortezomib kinetics in nine myeloma cell lines using ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry. The potential influence of drug transporters on the uptake kinetics observed in these cell lines was investigated by testing substrate characteristics of bortezomib for several transporters in over-expressing model cells. Additionally, transporter mRNA expression was quantified in myeloma cell lines by real-time polymerase chain reaction (RT-PCR).

RESULTS

All myeloma cells revealed an extensive intracellular bortezomib accumulation (47.5-183 ng/ml) exceeding extracellular concentrations (0.04-0.17 ng/ml) by more than factor 1,000. Only organic anion-transporting polypeptide 1B1 facilitated the uptake in over-expressing cells, however, to a negligible extent (factor 1.36). Bortezomib efflux via P-glycoprotein was confirmed by demonstrating reduced sensitivity (IC50 11.6 vs. 2.8 ng/ml) and intracellular concentrations (-56.1%) in over-expressing cells compared to controls. RT-PCR revealed a varying but overall weak transporter expression in the studied myeloma cells without any correlation to intracellular concentrations. Although principally valid as demonstrated in the P-glycoprotein over-expressing cell model, there was no significant correlation between intracellular concentrations and bortezomib efficacy in myeloma cell lines.

CONCLUSION

Differences in intracellular concentrations in myeloma cell lines neither result from variable transporter expression nor represent the main factor determining bortezomib efficacy in vitro.

Bortezomib for the treatment of non-Hodgkin's lymphoma

INTRODUCTION

Bortezomib , the first proteasome inhibitor (PI) to be evaluated in humans, is approved in the USA and Europe for the treatment of patients with multiple myeloma, and in the USA for patients with relapsed mantle cell lymphoma (MCL).

AREAS COVERED

This review examines the role of bortezomib in the therapy of non-Hodgkin's lymphoma (NHL). Bortezomib may be particularly effective against the NF-κB-dependent activated B-cell subtype of diffuse large B-cell lymphoma. The combination of bortezomib with rituximab and dexamethasone represents a standard approach for the treatment of Waldenström's macroglobulinemia, and that with bendamustine and rituximab has demonstrated excellent efficacy in follicular lymphoma. Combinations with other novel agents, such as inhibitors of cyclin-dependent kinases or histone deacetylases, also hold substantial promise in NHL. Unmet needs in NHL, competitor compounds, chemistry, pharmacokinetics, pharmacodynamics and safety and tolerability of bortezomib are also discussed.

EXPERT OPINION

The success of bortezomib in MCL has validated the proteasome as a therapeutic target in NHL. Rational combinations, for example, with Bruton's tyrosine kinase inhibitors or BH3-mimetics, may hold the key to optimizing the therapeutic potential of PIs in NHL. Future trials are likely to involve newer agents with improved pharmacodynamic (e.g., carfilzomib, marizomib) or pharmacokinetic (e.g., ixazomib, oprozomib) properties.

Reversal of bortezomib resistance in myelodysplastic syndrome cells by MAPK inhibitors

The myelodysplastic syndromes (MDS) comprise a heterogeneous group of malignant neoplasms with distinctive clinicopathological features. Currently, there is no specific approach for the treatment of MDS. Here, we report that bortezomib (BTZ), a proteasome inhibitor that has been used to treat plasma cell myeloma, induced G2/M phase cycle arrest in the MDS cell line SKM-1 through upregulation of Wee1, a negative regulator of G2/M phase transition. Treatment by BTZ led to reduced SKM-1 cell viability as well as increased apoptosis and autophagy. The BTZ-induced cell death was associated with reduced expression of p-ERK. To elucidate the implications of downregulation of p-ERK, we established the BTZ resistant cell line SKM-1R. Our data show that resistance to BTZ-induced apoptosis could be reversed by the MEK inhibitors U0126 or PD98059. Our results suggest that MAPK pathway may play an important role in mediating BTZ resistance.

Magnetic fluid hyperthermia enhances cytotoxicity of bortezomib in sensitive and resistant cancer cell lines

The proteasome inhibitor bortezomib (BZ) has shown promising results in some types of cancer, but in others it has had minimal activity. Recent studies have reported enhanced efficacy of BZ when combined with hyperthermia. However, the use of magnetic nanoparticles to induce hyperthermia in combination with BZ has not been reported. This novel hyperthermia modality has shown better potentiation of chemotherapeutics over other types of hyperthermia. We hypothesized that inducing hyperthermia via magnetic nanoparticles (MFH) would enhance the cytotoxicity of BZ in BZ-sensitive and BZ-resistant cancer cells more effectively than hyperthermia using a hot water bath (HWH). Studies were conducted using BZ in combination with MFH in two BZ-sensitive cell lines (MDA-MB-468, Caco-2), and one BZ-resistant cell line (A2780) at two different conditions, ie, 43°C for 30 minutes and 45°C for 30 minutes. These experiments were compared with combined application of HWH and BZ. The results indicate enhanced potentiation between hyperthermic treatment and BZ. MFH combined with BZ induced cytotoxicity in sensitive and resistant cell lines to a greater extent than HWH under the same treatment conditions. The observation that MFH sensitizes BZ-resistant cell lines makes this approach a potentially effective anticancer therapy platform.

CHOP induces activating transcription factor 5 (ATF5) to trigger apoptosis in response to perturbations in protein homeostasis

Environmental stresses that disrupt protein homeostasis induce phosphorylation of eIF2, triggering repression of global protein synthesis coincident with preferential translation of ATF4, a transcriptional activator of the integrated stress response (ISR). Depending on the extent of protein disruption, ATF4 may not be able to restore proteostatic control and instead switches to a terminal outcome that features elevated expression of the transcription factor CHOP (GADD153/DDIT3). The focus of this study is to define the mechanisms by which CHOP directs gene regulatory networks that determine cell fate. We find that in response to proteasome inhibition, CHOP enhances the expression of a collection of genes encoding transcription regulators, including ATF5, which is preferentially translated during eIF2 phosphorylation. Transcriptional expression of ATF5 is directly induced by both CHOP and ATF4. Knockdown of ATF5 increases cell survival in response to proteasome inhibition, supporting the idea that both ATF5 and CHOP have proapoptotic functions. Transcriptome analysis of ATF5-dependent genes reveals targets involved in apoptosis, including NOXA, which is important for inducing cell death during proteasome inhibition. This study suggests that the ISR features a feedforward loop of stress-induced transcriptional regulators, each subject to transcriptional and translational control, which can switch cell fate toward apoptosis.

Oppositional regulation of Noxa by JNK1 and JNK2 during apoptosis induced by proteasomal inhibitors

Proteasome inhibitors (PIs) potently induce apoptosis in a variety of tumor cells, but the underlying mechanisms are not fully elucidated. Comparing PI-induced apoptosis susceptibilities of various mouse embryonic fibroblast (MEF) lines differing in their c-jun N-terminal kinase (JNK) 1 and 2 status, we show that several hallmarks of apoptosis were most rapidly detectable in JNK2-/- cells, whereas they appeared only delayed and severely reduced in their intensities in cells expressing JNK2. Consistent with our finding that PI-induced apoptosis requires de novo protein synthesis, the proteasomal inhibitor MG-132 induced expression of the BH3-only protein Noxa at the transcriptional level in a JNK1-dependent, but JNK2-opposing manner. As the knockdown of Noxa blocked only the rapid PI-induced apoptosis of JNK2-/- cells, but not the delayed death occurring in JNK1-/- and JNK1+/+ cells, our data uncover a novel PI-induced apoptosis pathway that is regulated by the JNK1/2-dependent expression of Noxa. Furthermore, several transcription factors known to modulate Noxa expression including ATF3, ATF4, c-Jun, c-Myc, HIF1α, and p53 were found upregulated following MG-132 exposure. From those, only knockdown of c-Myc rescued JNK2-/- cells from PI-induced apoptosis, however, without affecting expression of Noxa. Together, our data not only show that a rapid execution of PI-induced apoptosis requires JNK1 for upregulation of Noxa via an as yet unknown transcription factor, but also that JNK2 controls this event in an oppositional manner.

The role of the ubiquitin proteasome system in lymphoma

The ubiquitin-proteasome system (UPS) maintains the integrity of cellular processes by controlling protein degradation pathways. The role of the UPS in proliferation, cell cycle, differentiation, DNA repair, protein folding, and apoptosis is well documented, and a wide range of protein activities in these signaling pathways can be manipulated by UPS inhibitors, which include many anti-cancer agents. Naturally occurring and synthetic drugs designed to target the UPS are currently used for hematological cancers, including lymphoma. These drugs largely interfere with the E1 and E2 regions of the 26S proteasome, blocking proteasomal activity and promoting apoptosis by enhancing activities of the extrinsic (death receptors, Trail, Fas) and intrinsic (caspases, Bax, Bcl2, p53, nuclear factor-kappa B, p27) cell death programs. This review focuses on recent clinical developments concerning UPS inhibitors, signaling pathways that are affected by down-regulation of UPS activities, and apoptotic mechanisms promoted by drugs in this class that are used to treat lymphoma.

The resistance mechanisms of proteasome inhibitor bortezomib

The proteasome inhibitor, bortezomib, a boronic dipeptide which reversibly inhibit the chymotrypsin-like activity at the β5-subunit of proteasome (PSMB5), has marked efficacy against multiple myeloma and several non-Hodgkin's lymphoma subtypes, and has a potential therapeutic role against other malignancy diseases. However, intrinsic and acquired resistance to bortezomib may limit its efficacy. In this article, we discuss recent advances in the molecular understanding of bortezomib resistance. Resistance mechanisms discussed include mutations of PSMB5 and the up-regulation of proteasome subunits, alterations of gene and protein expression in stress response, cell survival and antiapoptotic pathways, and multidrug resistance.

Single cell imaging of the heat shock response during proteasome inhibitor-induced apoptosis in colon cancer cells suggests that magnitude and length rather than time of onset determines resistance to apoptosis

Targeting the proteasome is a valuable approach for cancer therapy, potentially limited by pro-survival pathways induced in parallel to cell death. Whether these pro-survival pathways are activated in all cells, show different activation kinetics in sensitive versus resistant cells, or interact functionally with cell death pathways is unknown. We monitored activation of the heat shock response (HSR), a key survival pathway induced by proteasome inhibition, relative to apoptosis activation in HCT116 colon cancer cells expressing green fluorescent protein (GFP) under the control of the Hsp70 promoter. Single cell and high content time-lapse imaging of epoxomicin treatment revealed that neither basal activity, nor the time of onset of the HSR differed between resistant and sensitive populations. However, resistant cells had significantly higher and prolonged reporter activity than those that succumbed to cell death. p53 deficiency protected against cell death but failed to modulate the HSR. In contrast, inhibition of the HSR significantly increased the cytotoxicity of epoxomicin. Our data provide novel insights into the kinetics and heterogeneity of HSR during proteasome inhibition, suggesting that the HSR modulates cell death signaling unidirectionally.

Quantitative profiling of caspase-cleaved substrates reveals different drug-induced and cell-type patterns in apoptosis

Proapoptotic drugs are a mainstay of cancer drug treatment. These drugs stress cells and ultimately trigger the activation of caspases, cysteine-class proteases that cleave after aspartic acid and deconstruct the cell. It is well known that cells respond differently to proapoptotic cancer drug treatments. Here, using a global and unbiased quantitative N-terminomics technology, we show that ~500 products of caspase cleavage and their kinetics vary dramatically between cell type and cytotoxic drug treatment. It is likely that variations arise from differences in baseline proteome composition of the cell type and the alterations induced by drug treatments to yield a unique cohort of proteins that caspases finally target. Many targets are specific to both drug treatment and cell type, providing candidate-specific biomarkers for apoptosis. For example, in multiple myeloma cells treated with the proteasome inhibitor bortezomib, levels of activating transcription factor-4 increase dramatically early in drug treatment and then decrease upon cleavage by activated caspases. Thus, caspase-derived cleavage products are a sensitive reflection of cell-type and drug-induced stress, and provide useful fingerprints for mechanisms of drug action and response.

Synergistic effects of nelfinavir and bortezomib on proteotoxic death of NSCLC and multiple myeloma cells

Exploiting protein homeostasis is a new therapeutic approach in cancer. Nelfinavir (NFV) is an HIV protease inhibitor that induces endoplasmic reticulum (ER) stress in cancer cells. Under conditions of ER stress, misfolded proteins are transported from the ER back to the cytosol for subsequent degradation by the ubiquitin–proteasome system. Bortezomib (BZ) is a proteasome inhibitor and interferes with degradation of misfolded proteins. Here, we show that NFV and BZ enhance proteotoxicity in non-small cell lung cancer (NSCLC) and multiple myeloma (MM) cells. The combination synergistically inhibited cell proliferation and induced cell death. Activating transcription factor (ATF)3 and CCAAT-enhancer binding protein homologous protein (CHOP), markers of ER stress, were rapidly increased, and their siRNA-mediated knockdown inhibited cell death. Knockdown of double-stranded RNA activated protein kinase-like ER kinase, a signal transducer in ER stress, significantly decreased apoptosis. Pretreatment with the protein synthesis inhibitor, cycloheximide, decreased levels of ubiquitinated proteins, ATF3, CHOP, and the overall total cell death, suggesting that inhibition of protein synthesis increases cell survival by relieving proteotoxic stress. The NFV/BZ combination inhibited the growth of NSCLC xenografts, which correlated with the induction of markers of ER stress and apoptosis. Collectively, these data show that NFV and BZ enhance proteotoxicity in NSCLC and MM cells, and suggest that this combination could tip the precarious balance of protein homeostasis in cancer cells for therapeutic gain.

Activating transcription factor 4 increases chemotherapeutics resistance of human hepatocellular carcinoma

It has been reported that activating transcription factor 4 (ATF4) increases the processes of tumor growth, metastasis and drug resistance. However, the role played by ATF4 in chemoresistance of hepatocellular carcinoma (HCC) remains unknown. Clarification of this role of ATF4 in HCC could greatly benefit the efficacy of clinical treatment of HCC. In this study, we found that ATF4 was overexpressed in about 50.7% of HCC tissues. In fact knockdown of ATF4 significantly increased the cytotoxicity of cisplatin in both in vitro and in vivo assays, while overexpression of this molecule dramatically decreased the sensitivity of HCC cell lines to cisplatin. Additionally, we found that synthesis of glutathione was significantly reduced in HCC cell lines subjected to ATF4 knockdown. Taken together, these results demonstrate that ATF4 can increase resistance to cisplatin in HCC by increased biosynthesis of glutathione, and that this may be a potent novel target for the future development of anti-HCC drugs.

HSPA2 overexpression protects V79 fibroblasts against bortezomib-induced apoptosis

Human HSPA2 is a member of the HSPA (HSP70) family of heat-shock proteins, encoded by the gene originally described as testis-specific. Recently, it has been reported that HSPA2 can be also expressed in human somatic tissues in a cell-type specific manner. The aim of the present study was to find out whether HSPA2 can increase the resistance of somatic cells to the toxic effect of heat shock, proteasome inhibitors, and several anticancer cytostatics. We used a Chinese hamster fibroblast V79 cell line because these cells do not express the HSPA2 and cytoprotective HSPA1 proteins under normal culture conditions and show limited ability to express HSPA1 in response to heat shock and proteasome inhibitors. We established, by retroviral gene transfer, a stable V79/HSPA2 cell line, which constitutively overexpressed HSPA2 protein. The major observation of our study was that HSPA2 increased long-term survival of cells subjected to heat shock and proteasome inhibitors. We found, that HSPA2 confers resistance to bortezomib-induced apoptosis. Thus, we showed for the first time that in somatic cells HSPA2 can be a part of a system protecting cells against cytotoxic stimuli inducing proteotoxic stress.

Measures of association for identifying microRNA-mRNA pairs of biological interest

MicroRNAs are a class of small non-protein coding RNAs that play an important role in the regulation of gene expression. Most studies on the identification of microRNA-mRNA pairs utilize the correlation coefficient as a measure of association. The use of correlation coefficient is appropriate if the expression data are available for several conditions and, for a given condition, both microRNA and mRNA expression profiles are obtained from the same set of individuals. However, there are many instances where one of the requirements is not satisfied. Therefore, there is a need for new measures of association to identify the microRNA-mRNA pairs of interest and we present two such measures. The first measure requires expression data for multiple conditions but, for a given condition, the microRNA and mRNA expression may be obtained from different individuals. The new measure, unlike the correlation coefficient, is suitable for analyzing large data sets which are obtained by combining several independent studies on microRNAs and mRNAs. Our second measure is able to handle expression data that correspond to just two conditions but, for a given condition, the microRNA and mRNA expression must be obtained from the same set of individuals. This measure, unlike the correlation coefficient, is appropriate for analyzing data sets with a small number of conditions. We apply our new measures of association to multiple myeloma data sets, which cannot be analyzed using the correlation coefficient, and identify several microRNA-mRNA pairs involved in apoptosis and cell proliferation.

Molecular mechanisms of bortezomib resistant adenocarcinoma cells

Bortezomib (Velcade™) is a reversible proteasome inhibitor that is approved for the treatment of multiple myeloma (MM). Despite its demonstrated clinical success, some patients are deprived of treatment due to primary refractoriness or development of resistance during therapy. To investigate the role of the duration of proteasome inhibition in the anti-tumor response of bortezomib, we established clonal isolates of HT-29 adenocarcinoma cells adapted to continuous exposure of bortezomib. These cells were ∼30-fold resistant to bortezomib. Two novel and distinct mutations in the β5 subunit, Cys63Phe, located distal to the binding site in a helix critical for drug binding, and Arg24Cys, found in the propeptide region were found in all resistant clones. The latter mutation is a natural variant found to be elevated in frequency in patients with MM. Proteasome activity and levels of both the constitutive and immunoproteasome were increased in resistant cells, which correlated to an increase in subunit gene expression. These changes correlated with a more rapid recovery of proteasome activity following brief exposure to bortezomib. Increased recovery rate was not due to increased proteasome turnover as similar findings were seen in cells co-treated with cycloheximide. When we exposed resistant cells to the irreversible proteasome inhibitor carfilzomib we noted a slower rate of recovery of proteasome activity as compared to bortezomib in both parental and resistant cells. Importantly, carfilzomib maintained its cytotoxic potential in the bortezomib resistant cell lines. Therefore, resistance to bortezomib, can be overcome with irreversible inhibitors, suggesting prolonged proteasome inhibition induces a more potent anti-tumor response.

KLF9 is a novel transcriptional regulator of bortezomib- and LBH589-induced apoptosis in multiple myeloma cells

Bortezomib, a therapeutic agent for multiple myeloma (MM) and mantle cell lymphoma, suppresses proteosomal degradation leading to substantial changes in cellular transcriptional programs and ultimately resulting in apoptosis. Transcriptional regulators required for bortezomib-induced apoptosis in MM cells are largely unknown. Using gene expression profiling, we identified 36 transcription factors that displayed altered expression in MM cells treated with bortezomib. Analysis of a publically available database identified Kruppel-like family factor 9 (KLF9) as the only transcription factor with significantly higher basal expression in MM cells from patients who responded to bortezomib compared with nonresponders. We demonstrated that KLF9 in cultured MM cells was up-regulated by bortezomib; however, it was not through the induction of endoplasmic reticulum stress. Instead, KLF9 levels correlated with bortezomib-dependent inhibition of histone deacetylases (HDAC) and were increased by the HDAC inhibitor LBH589 (panobinostat). Furthermore, bortezomib induced binding of endogenous KLF9 to the promoter of the proapoptotic gene NOXA. Importantly, KLF9 knockdown impaired NOXA up-regulation and apoptosis caused by bortezomib, LBH589, or a combination of theses drugs, whereas KLF9 overexpression induced apoptosis that was partially NOXA-dependent. Our data identify KLF9 as a novel and potentially clinically relevant transcriptional regulator of drug-induced apoptosis in MM cells.

Sensitizing human multiple myeloma cells to the proteasome inhibitor bortezomib by novel curcumin analogs

The proteasome plays a vital role in the degradation of proteins involved in several pathways including the cell cycle, cellular proliferation and apoptosis and is a validated target in cancer treatment. Bortezomib (Velcade^®, PS-341) is the first US FDA approved proteasome inhibitor anticancer drug used in the treatment of refractory multiple myeloma. In spite of its improved efficacy compared to alternative therapies, about 60% of patients do not respond to bortezomib due to the emergence of resistance. We hypothesized that novel small molecules could enhance the proteasome-inhibitory and anticancer activities of bortezomib in resistant multiple myeloma cells in vitro and in vivo. The dietary polyphenol curcumin has been shown to exert anti-cancer activity in several cancer cell lines, but the effects of curcumin in solid tumors have been modest primarily due to poor water solubility and poor bioavailability in tissues remote from the gastrointestinal tract. Here we show that the water-soluble analog of curcumin #12, but not curcumin, in combination with bortezomib could enhance the proteasome-inhibitory effect in multiple myeloma cells. Furthermore, the sensitivity of the myeloma cells to cytotoxic killing in the presence of otherwise sublethal concentrations of bortezomib was enhanced by incubation with the curcumin analog #12. These findings justify further investigation into those combinations that may yield potential therapeutic benefit.

Response of myeloma to the proteasome inhibitor bortezomib is correlated with the unfolded protein response regulator XBP-1

BACKGROUND

Multiple myeloma, a malignancy of the antibody-secreting plasma cells, remains incurable by current therapy. However, the proteasome inhibitor bortezomib and other new drugs are revolutionizing its treatment. It remains unclear why myelomas are peculiarly sensitive to bortezomib, or what causes primary or acquired resistance. The 'unfolded protein response' is necessary for folding and assembly of immunoglobulin chains in both normal and malignant plasma cells, as well as for the disposal of incorrectly folded or unpaired chains via the ubiquitin-proteasome pathway. We tested the hypothesis that levels of transcription factor XBP-1, a major regulator of the unfolded protein response, predict response to bortezomib.

DESIGN AND METHODS

Expression of XBP-1 and other regulators of the unfolded protein response were measured in myeloma and other cancer cell lines and two cohorts of patients with refractory myeloma and correlated with sensitivity/response to bortezomib. Bortezomib-resistant myeloma cell lines were derived and the effects on expression of unfolded protein response regulators, immunoglobulin secretion, proteasome activity and cross-resistance to cytotoxic drugs and tunicamycin determined. The consequences of manipulation of XBP-1 levels for sensitivity to bortezomib were tested.

RESULTS

Low XBP-1 levels predicted poor response to bortezomib, both in vitro and in myeloma patients. Moreover, myeloma cell lines selected for resistance to bortezomib had down-regulated XBP-1 and immunoglobulin secretion. Expression of ATF6, another regulator of the unfolded protein response, also correlated with bortezomib sensitivity. Direct manipulation of XBP-1 levels had only modest effects on sensitivity to bortezomib, suggesting it is a surrogate marker of response to bortezomib rather than a target itself.

CONCLUSIONS

The unfolded protein response may be a relevant target pathway for proteasome inhibitors in the treatment of myeloma and its regulator XBP-1 is a potential response marker. (The BIR study was registered with Australian Clinical Trial Registry Number 12605000770662).

The expression of the endoplasmic reticulum stress sensor BiP/GRP78 predicts response to chemotherapy and determines the efficacy of proteasome inhibitors in diffuse large b-cell lymphoma

Activation of the endoplasmic reticulum (ER) stress pathway is associated with poor response to doxorubicin-containing regimens, such as rituximab, cyclophosphamide, hydroxydaunorubicin (doxorubicin), vincristine and prednisone (R-CHOP), in patients with diffuse large B-cell lymphoma (DLBCL). Bortezomib, a proteasome inhibitor, interferes with ER responses and improves survival in patients with aggressive hematologic malignant tumors, although its use in DLBCL patients remains controversial. The 78-kDa glucose-regulated protein (GRP78), also known as immunoglobulin heavy chain binding protein (BiP), is an ER stress sensor involved in the resistance to doxorubicin and bortezomib, but its role in the response to chemotherapy in DLBCL has not been explored before. We show that high BiP/GRP78 expression is related to worse overall survival (median overall survival, 5.2 versus 3.4 years). Moreover, cell death after R-CHOP in DLCBL cell lines is associated with decreased BiP/GRP78 expression. Conversely, DLBCL cell lines are primarily resistant to bortezomib, probably owing to BiP/GRP78 overexpression. Small-interfering RNA silencing of BiP/GRP78 renders all cell lines sensitive to bortezomib. R-CHOP with bortezomib (R-CHOP-BZ) reduces BiP/GRP78 expression and overcomes bortezomib resistance, mimicking the small-interfering RNA silencing of BiP/GRP78. Accordingly, R-CHOP-BZ is the most effective treatment, providing a rationale for the use of this combinational therapy to improve DLBCL patient survival. Moreover, this study provides preclinical evidence that the germinal center B-cell-like subtype DLBCL is sensitive to bortezomib combined with immunochemotherapy.

The Hsp90 inhibitor IPI-504 overcomes bortezomib resistance in mantle cell lymphoma in vitro and in vivo by down-regulation of the prosurvival ER chaperone BiP/Grp78

Despite the promising introduction of the proteasome inhibitor bortezomib in the treatment of mantle cell lymphoma (MCL), not all patients respond, and resistance often appears after initial treatment. By analyzing a set of 18 MCL samples, including cell lines with constitutive or induced resistance to bortezomib, we found a high correlation between loss of sensitivity to the proteasome inhibitor and up-regulation of the prosurvival chaperone BiP/Grp78. BiP/Grp78 stabilization was ensured at a posttranscriptional level by an increase in the chaperoning activity of heat shock protein of 90 kDa (Hsp90). In bortezomib-resistant cells, both BiP/Grp78 knockdown and cell pretreatment with the Hsp90 inhibitor of the ansamycin class, IPI-504, led to synergistic induction of apoptotic cell death when combined with bortezomib. Cell exposure to the IPI-504-bortezomib combination provoked the dissociation of Hsp90/BiP complexes, leading to BiP/Grp78 depletion, inhibition of unfolded protein response, and promotion of NOXA-mediated mitochondrial depolarization. The IPI-504-bortezomib combination also prevented BiP/Grp78 accumulation, thereby promoting apoptosis and inhibiting the growth of bortezomib-resistant tumors in a mouse model of MCL xenotransplantation. These results suggest that targeting unfolded protein response activation by the inhibition of Hsp90 may be an attractive model for the design of a new bortezomib-based combination therapy for MCL.