Combination therapy of bortezomib with novel targeted agents: an emerging treatment strategy

Combination therapy involving HSP90 inhibitors for combating cancer: an overview of clinical and preclinical progress

The molecular chaperone heat shock protein 90 (HSP90) regulates multiple crucial signalling pathways in cancer by driving the maturation of key signalling components, thereby playing a crucial role in tumorigenesis and drug resistance in cancer. Inhibition of HSP90 results in metastable conformational collapse of its client proteins and their proteasomal degradation. Considerable efforts have been devoted to the development of small-molecule inhibitors targeting HSP90, and more than 20 inhibitors have been evaluated in clinical trials for cancer therapy. However, owing to disadvantages such as organ toxicity and drug resistance, only one HSP90 inhibitor has been approved for use in clinical settings. In recent years, HSP90 inhibitors used in combination with other anti-cancer therapies have shown remarkable potential in the treatment of cancer. HSP90 inhibitors work synergistically with various anti-cancer therapies, including chemotherapy, targeted therapy, radiation therapy and immunotherapy. HSP90 inhibitors can improve the pharmacological effects of the above-mentioned therapies and reduce treatment resistance. This review provides an overview of the use of combination therapy with HSP90 inhibitors and other anti-cancer therapies in clinical and preclinical studies reported in the past decade and summarises design strategies and prospects for these combination therapies. Altogether, this review provides a theoretical basis for further research and application of these combination therapies in the treatment of cancer.

Investigating the complexation propensity of self-assembling dipeptides with the anticancer peptide-drug Bortezomib: a computational study

The investigation of potential self-assembled peptides as carriers for the delivery of anticancer drug Bortezomib is the topic of the present study. The self-assembly of Bortezomib in water is examined using all-atom molecular dynamics simulations and corresponding experimental results from FESEM experiments. In addition, a series of dipeptides with a similar chemical formula to Bortezomib with hydrogel-forming ability are being investigated for their propensity to bind to the drug molecule. Dipeptides are divided into two classes, the protected FF (Fmoc-FF and Z-FF) and the LF-based (Cyclo-LF and LF) ones. The thermodynamic stability of the complexes formed in an aqueous environment, as well as key morphological features of the nanoassemblies are investigated at the molecular level. Binding enthalpy between Bortezomib and dipeptides follows the increasing order: LF < Cyclo-LF < Fmoc-FF < Z-FF under both van der Waals and electrostatic contributions. Protected FF dipeptides have a higher affinity for the drug molecule, which will favor its entrapment, giving them an edge over the LF based dipeptides. By evaluating the various measures, regarding both the binding between the two components and the eventual ability of controlled drug release, we conclude that the protected FF class is a more suitable candidate for drug release of Bortezomib, whereas among its two members, Fmoc-FF appears to be more promising. The selection of the optimal candidates based on the present computational study will be a stepping stone for future detailed experimental studies involving the encapsulation and controlled release of Bortezomib both in vitro and in vivo.

Multitarget antibacterial drugs: An effective strategy to combat bacterial resistance

The rise of antibiotic resistance and the decrease in the discovery of new antibiotics have caused a global health crisis. Of particular concern is the fact that despite efforts to develop new antibiotics, drug discovery is unable to keep up with the rapid development of resistance. This ongoing crisis highlights the fact that single-target drugs may not always exhibit satisfactory therapeutic effects and are prone to target mutations and resistance due to the complexity of bacterial mechanisms. Retrospective studies have shown that most successful antibiotics have multiple targets. Compared with single-target drugs, successfully designed multitarget drugs can simultaneously regulate multiple targets to reduce resistance caused by single-target mutations or expression changes. In addition to a lower risk of drug-drug interactions, multitarget drugs show superior pharmacokinetics and higher patient compliance compared with combination therapies. Therefore, to reduce resistance, many efforts have been made to discover and design multitarget drugs with different chemical structures and functions. Although there have been numerous studies on how to develop drugs and slow down the development of drug resistance, the reduction of bacterial resistance by multitarget antibacterial drugs has not received widespread attention and is rarely mentioned in the peer-reviewed literature. This review summarises the development of antibiotic resistance and the mechanisms proposed for its emergence, examines the potential of multitarget drugs as an effective strategy to slow the development of resistance, and discusses the rationale for multitarget drug therapy. We also describe multitarget antibacterial compounds with the potential to reduce drug resistance and the available strategies to develop multitarget drugs.

Candidate Therapeutics by Screening for Multitargeting Ligands: Combining the CB2 Receptor With CB1, PPARγ and 5-HT4 Receptors

In recent years, the cannabinoid type 2 receptor (CB2R) has become a major target for treating many disease conditions. The old therapeutic paradigm of “one disease-one target-one drug” is being transformed to “complex disease-many targets-one drug.” Multitargeting, therefore, attracts much attention as a promising approach. We thus focus on designing single multitargeting agents (MTAs), which have many advantages over combined therapies. Using our ligand-based approach, the “Iterative Stochastic Elimination” (ISE) algorithm, we produce activity models of agonists and antagonists for desired therapeutic targets and anti-targets. These models are used for sequential virtual screening and scoring large libraries of molecules in order to pick top-scored candidates for testing in vitro and in vivo. In this study, we built activity models for CB2R and other targets for combinations that could be used for several indications. Those additional targets are the cannabinoid 1 receptor (CB1R), peroxisome proliferator-activated receptor gamma (PPARγ), and 5-Hydroxytryptamine receptor 4 (5-HT4R). All these models have high statistical parameters and are reliable. Many more CB2R/CBIR agonists were found than combined CB2R agonists with CB1R antagonist activity (by 200 fold). CB2R agonism combined with PPARγ or 5-HT4R agonist activity may be used for treating Inflammatory Bowel Disease (IBD). Combining CB2R agonism with 5-HT4R generates more candidates (14,008) than combining CB2R agonism with agonists for the nuclear receptor PPARγ (374 candidates) from an initial set of ∼2.1 million molecules. Improved enrichment of true vs. false positives may be achieved by requiring a better ISE score cutoff or by performing docking. Those candidates can be purchased and tested experimentally to validate their activity. Further, we performed docking to CB2R structures and found lower statistical performance of the docking (“structure-based”) compared to ISE modeling (“ligand-based”). Therefore, ISE modeling may be a better starting point for molecular discovery than docking.

A Novel Small Molecular Prostaglandin Receptor EP4 Antagonist, L001, Suppresses Pancreatic Cancer Metastasis

Metastatic pancreatic cancer remains a major clinical challenge, emphasizing the urgent need for the exploitation of novel therapeutic approaches with superior response. In this study, we demonstrate that the aberrant activation of prostaglandin E₂ (PGE₂) receptor 4 (EP4) is a pro-metastatic signal in pancreatic cancer. To explore the therapeutic role of EP4 signaling, we developed a potent and selective EP4 antagonist L001 with single-nanomolar activity using a panel of cell functional assays. EP4 antagonism by L001 effectively repressed PGE₂-elicited cell migration and the invasion of pancreatic cancer cells in a dose-dependent manner. Importantly, L001 alone or combined with the chemotherapy drug gemcitabine exhibited remarkably anti-metastasis activity in a pancreatic cancer hepatic metastasis model with excellent tolerability and safety. Mechanistically, EP4 blockade by L001 abrogated Yes-associated protein 1 (YAP)-driven pro-metastatic factor expression in pancreatic cancer cells. The suppression of YAP’s activity was also observed upon L001 treatment in vivo. Together, these findings support the notions that EP4–YAP signaling axis is a vital pro-metastatic pathway in pancreatic cancer and that EP4 inhibition with L001 may deliver a therapeutic benefit for patients with metastatic pancreatic cancer.

Rational Design and Synthesis of Novel Dual PROTACs for Simultaneous Degradation of EGFR and PARP

Inspired by the success of dual-targeting drugs, especially bispecific antibodies, we propose to combine the concept of proteolysis targeting chimera (PROTAC) and dual targeting to design and synthesize dual PROTAC molecules with the function of degrading two completely different types of targets simultaneously. A library of novel dual-targeting PROTAC molecules has been rationally designed and prepared. A convergent synthetic strategy has been utilized to achieve high synthetic efficiency. These dual PROTAC structures are characterized using trifunctional natural amino acids as star-type core linkers to connect two independent inhibitors and E3 ligands together. In this study, gefitinib, olaparib, and CRBN or VHL E3 ligands were used as substrates to synthesize novel dual PROTACs. They successfully degraded both the epidermal growth factor receptor (EGFR) and poly(ADP-ribose) polymerase (PARP) simultaneously in cancer cells. Being the first successful example of dual PROTACs, this technique will greatly widen the range of application of the PROTAC method and open up a new field for drug discovery.

Ciclopirox and bortezomib synergistically inhibits glioblastoma multiforme growth via simultaneously enhancing JNK/p38 MAPK and NF-κB signaling

Ciclopirox (CPX) is an antifungal drug that has recently been reported to act as a potential anticancer drug. However, the effects and underlying molecular mechanisms of CPX on glioblastoma multiforme (GBM) remain unknown. Bortezomib (BTZ) is the first proteasome inhibitor-based anticancer drug approved to treat multiple myeloma and mantle cell lymphoma, as BTZ exhibits toxic effects on diverse tumor cells. Herein, we show that CPX displays strong anti-tumorigenic activity on GBM. Mechanistically, CPX inhibits GBM cellular migration and invasion by reducing N-Cadherin, MMP9 and Snail expression. Further analysis revealed that CPX suppresses the expression of several key subunits of mitochondrial enzyme complex, thus leading to the disruption of mitochondrial oxidative phosphorylation (OXPHOS) in GBM cells. In combination with BTZ, CPX promotes apoptosis in GBM cells through the induction of reactive oxygen species (ROS)-mediated c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinase (MAPK) signaling. Moreover, CPX and BTZ synergistically activates nuclear factor kappa B (NF-κB) signaling and induces cellular senescence. Our findings suggest that a combination of CPX and BTZ may serve as a novel therapeutic strategy to enhance the anticancer activity of CPX against GBM.

Drug Repurposing Screen Identifies Novel Classes of Drugs with Anticancer Activity in Mantle Cell Lymphoma

AIM AND OBJECTIVE

Mantle Cell Lymphoma (MCL) is typically an aggressive and rare disease with poor prognosis, therefore new effective therapeutics are urgently needed. Drug repurposing for cancer treatment is becoming increasingly more attractive as an alternative approach to discover clinically approved drugs that demonstrate antineoplastic effect. The objective of this study was to screen an approved drug library and identify candidate compounds with an antineoplastic effect in MCL cells using High-Throughput Screening (HTS) technique.

MATERIALS AND METHODS

Using the HTS technique, nearly 3,800 clinically approved drugs and drug candidates were screened in Jeko and Mino MCL cell lines. We also demonstrated the selectivity window of the candidate compounds in six normal cell lines. Further validations were performed in caspase-3/7 apoptosis assay and three-dimensional (3D) multicellular aggregates model using Z138 cell line.

RESULTS

We identified 98 compounds showing >50% inhibition in either MCL cell line screened, they were distributed across eight unique therapeutic categories and have different mechanisms of action (MOA). We selected alisertib, carfilzomib, pracinostat and YM155 for further validation based on their antiproliferative activity in two MCL cell lines, selectivity to normal cell lines, and drug developing stages in terms of clinical research. Alisertib and carfilzomib showed antiproliferative effect on MCL cell with EC50 = 6 nM and >100-fold selectivity to normal cell lines, especially for alisertib which demonstrated >1000-fold selectivity to 5 out of 6 normal cell lines. Pracinostat and YM155 had potency of 11 and 12 nM in MCL cell with >20-fold selectivity to normal cell lines. All four compounds had been tested in caspase-dependent apoptosis assay. We further validated and demonstrated their anti-MCL effect on cell proliferation and (3D) multicellular aggregates model using Z138 cell line.

CONCLUSION

This is the first study to examine such a large library of clinically approved compounds for the identification of novel drug candidates for MCL treatment, the results could be rapidly translated into clinical practice in patients with MCL.

The Biology of Myxofibrosarcoma: State of the Art and Future Perspectives

BACKGROUND

Myxofibrosarcoma (MFS) is among the most highly complex sarcoma types. Molecular cytogenetic studies have identified a high level of genomic complexity.

SUMMARY

This review provides an update of the current research related to MFS, with particular emphasis on emerging mechanisms of tumorigenesis and their potential therapeutic impact. Many novel possible molecular markers have been identified, not only for prognostication in MFS, but also to serve as possible therapeutic targets, and thereby improve clinical outcomes. However, the molecular pathogenesis of MFS remains incompletely understood. Key Messages: Patients suffering from advanced MFS might benefit from expanded molecular evaluation in order to detect specific expression profiles and identify drug-able targets. Moreover, immunotherapy represents an intriguingly perspective due to the presence of "T-cell inflamed" tumor microenvironment.

Thrombospondin-1 counteracts the p97 inhibitor CB-5083 in colon carcinoma cells

p97 has recently emerged as a therapeutic target for cancer due to its essential functions in protein homeostasis. CB-5083 is a first-in-class, potent and selective ATP-competitive p97 inhibitor that induces proteotoxic stress in cancer cells. Potential mechanisms regulating the sensitivity of cells to p97 inhibition remain poorly studied. Here, we demonstrate that Thrombospondin-1 (THBS1) is a CB-5083-upregulated gene that helps confer resistance of HCT116 cells to CB-5083. Our immunoblotting and immunofluorescence data showed that CB-5083 significantly increases the steady-state abundance of THBS1. Blockade of THBS1 induction sensitized cells to CB-5083-mediated growth inhibition. Suppression of THBS1 caused an increase of CB-5083-induced sub-G1 population and caspase 3/7 activity suggesting that its function is linked to the survival of cancer cells in response to p97 inhibition. Altogether our data provide new evidence that THBS1 is important for the susceptibility of cells to p97 inhibition.

Deep graph embedding for prioritizing synergistic anticancer drug combinations

Drug combinations are frequently used for the treatment of cancer patients in order to increase efficacy, decrease adverse side effects, or overcome drug resistance. Given the enormous number of drug combinations, it is cost- and time-consuming to screen all possible drug pairs experimentally. Currently, it has not been fully explored to integrate multiple networks to predict synergistic drug combinations using recently developed deep learning technologies. In this study, we proposed a Graph Convolutional Network (GCN) model to predict synergistic drug combinations in particular cancer cell lines. Specifically, the GCN method used a convolutional neural network model to do heterogeneous graph embedding, and thus solved a link prediction task. The graph in this study was a multimodal graph, which was constructed by integrating the drug-drug combination, drug-protein interaction, and protein-protein interaction networks. We found that the GCN model was able to correctly predict cell line-specific synergistic drug combinations from a large heterogonous network. The majority (30) of the 39 cell line-specific models show an area under the receiver operational characteristic curve (AUC) larger than 0.80, resulting in a mean AUC of 0.84. Moreover, we conducted an in-depth literature survey to investigate the top predicted drug combinations in specific cancer cell lines and found that many of them have been found to show synergistic antitumor activity against the same or other cancers in vitro or in vivo. Taken together, the results indicate that our study provides a promising way to better predict and optimize synergistic drug pairs in silico.

Inhibition of the PI3K/AKT signaling pathway sensitizes diffuse large B-cell lymphoma cells to treatment with proteasome inhibitors via suppression of BAG3

Proteasome inhibitors represent a novel class of drugs that have clinical efficacy against hematological and solid cancer types, including acute myeloid leukaemia, myelodysplastic syndrome an non-small cell lung cancer. It has been demonstrated that the anti-apoptotic protein B-cell lymphoma-2-associated athanogene 3 (BAG3) is induced by proteasome inhibitors in various cancer cells and serves an important role in chemotherapy resistance. The phosphatidylinositol 3-kinase (PI3K)/RAC-α serine/threonine-protein kinase (AKT) pathway is constitutively activated in a number of lymphoid malignancy types, including diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma. In the present study, the aim was to elucidate the role of the PI3K/AKT signaling pathway in the induction of BAG3, following exposure to a proteasome inhibitor in DLBCL cell lines. Bortezomib and MG132 were used as proteasome inhibitors. Western blotting was used to evaluate the roles of proteasome inhibitors and the PI3K/AKT pathway in BAG3 induction in DLBCL cells (LY1 and LY8), and LY294002 was used to block the PI3K/AKT pathway. Cell viability was detected using a Cell Counting Kit-8 assay. Apoptosis of LY1 and LY8 cells was quantified by Annexin V/7-amino-actinomycin D flow cytometry. The BAG3 protein was markedly induced upon exposure to bortezomib and MG132 in a dose-dependent manner. The PI3K/AKT inhibitor LY294002 significantly suppressed the induction of BAG3 by proteasome inhibitors. Inhibition of the PI3K/AKT pathway decreased the proliferation and increased the apoptosis induced by proteasome inhibitors. The present results indicated that the PI3K/AKT pathway is associated with the activation of BAG3 expression in DLBCL cells, and is involved in the protective response against proteasome inhibition.

(Immuno)proteasomes as therapeutic target in acute leukemia

The clinical efficacy of proteasome inhibitors in the treatment of multiple myeloma has encouraged application of proteasome inhibitor containing therapeutic interventions in (pediatric) acute leukemia. Here, we summarize the positioning of bortezomib, as first-generation proteasome inhibitor, and second-generation proteasome inhibitors in leukemia treatment from a preclinical and clinical perspective. Potential markers for proteasome inhibitor sensitivity and/or resistance emerging from leukemia cell line models and clinical sample studies will be discussed focusing on the role of immunoproteasome and constitutive proteasome (subunit) expression, PSMB5 mutations, and alternative mechanisms of overcoming proteolytic stress.

PSMD7 downregulation induces apoptosis and suppresses tumorigenesis of esophageal squamous cell carcinoma via the mTOR/p70S6K pathway

PSMD7, a 19S proteasome subunit, is overexpressed in most carcinoma cells. It forms a dimer with PSMD14 that functions in the removal of attached ubiquitin chain. However, there is little knowledge about the cellular mechanism of PSMD7 and its exact biological function, especially in cancer cells. In this study, we explored the role of PSMD7 in proliferation, cell cycle, apoptosis, and proteasomal proteolysis in the esophageal squamous cell carcinoma (ESCC) cell line EC9706. Our results showed that PSMD7 was highly expressed in ESCC cells. Downregulation of PSMD7 by lentivirus‐mediated shRNA led to decreased proliferation, increased cell apoptosis, and reduced proteasomal function. Notably, lower expression level of mTOR and p70S6K and suppressed activity of mTOR/p70S6K pathway were detected after PSMD7 downregulation. By contrast, increased expression of p‐mTOR^Ser2448 and p‐p70S6K^{Thr421/Ser424} was discovered upon PSMD7 overexpression in Het‐1A cells. Furthermore, PSMD7 downregulation contributed to decelerated tumor growth, inhibition of proteasomal function, induced cell apoptosis and attenuated activity of mTOR/p70S6K pathway in vivo. These findings suggest that PSMD7 and the mTOR/p70S6K pathway may be a promising candidate for developing therapies for ESCC.

IKKα is required in the intestinal epithelial cells for tumour stemness

Background:

Colorectal cancer is a common cause of death in developed countries. Progression from adenoma to invasive carcinoma requires accumulation of mutations starting with the Adenomatous Polyposis Coli (Apc) gene. NF-κB signalling is a key element in cancer, mainly related to the activity of IKKβ. IKKα kinase also participates in this process by mechanisms that are primarily unknown.

Methods:

We generated a compound mouse model with mutation in Apc and lacking intestinal epithelial IKKα, produced intestinal organoids and tumour spheroids with different genetic backgrounds, and performed immunohistochemistry and RNA-seq analysis.

Results:

Deficiency of IKKα prevents adenoma formation, with adenomas lacking IKKα showing reduced proliferation. In contrast, IKKα status did not affect normal intestinal function. The same divergent phenotype was found in the organoid–spheroid model. We also found that epithelial IKKα controls stemness, proliferation and apoptosis-related expression.

Conclusions:

IKKα is a potential therapeutic target for Apc mutant colorectal cancer patients.

Identification of HSP90 inhibitors as a novel class of senolytics

Aging is the main risk factor for many chronic degenerative diseases and cancer. Increased senescent cell burden in various tissues is a major contributor to aging and age-related diseases. Recently, a new class of drugs termed senolytics were demonstrated to extending healthspan, reducing frailty and improving stem cell function in multiple murine models of aging. To identify novel and more optimal senotherapeutic drugs and combinations, we established a senescence associated β-galactosidase assay as a screening platform to rapidly identify drugs that specifically affect senescent cells. We used primary Ercc1 -/- murine embryonic fibroblasts with reduced DNA repair capacity, which senesce rapidly if grown at atmospheric oxygen. This platform was used to screen a small library of compounds that regulate autophagy, identifying two inhibitors of the HSP90 chaperone family as having significant senolytic activity in mouse and human cells. Treatment of Ercc1 -/∆ mice, a mouse model of a human progeroid syndrome, with the HSP90 inhibitor 17-DMAG extended healthspan, delayed the onset of several age-related symptoms and reduced p16INK4a expression. These results demonstrate the utility of our screening platform to identify senotherapeutic agents as well as identified HSP90 inhibitors as a promising new class of senolytic drugs.The accumulation of senescent cells is thought to contribute to the age-associated decline in tissue function. Here, the authors identify HSP90 inhibitors as a new class of senolytic compounds in an in vitro screening and show that administration of a HSP90 inhibitor reduces age-related symptoms in progeroid mice.

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.

Peripheral neuropathy outcomes and efficacy of subcutaneous bortezomib when combined with thalidomide and dexamethasone in the treatment of multiple myeloma

Due to the safety, convenience and efficacy of subcutaneous administration of bortezomib (scBor), it is becoming increasingly common to treat multiple myeloma (MM) using this treatment method. The current retrospective study suggested a lower incidence of peripheral neuropathy (PN) outcomes and superior efficacy following treatment with scBor combined with thalidomide and dexamethasone (VTD) in MM when compared with intravenous Bor (ivBor) treatment. The data of 81 patients from the Affiliated Hospital of Nantong University between September 2011 and February 2014 were analyzed, including 37 scBor and 44 ivBor patients administered a median (range) of 5.5 (3-8) and 6 (3-10) chemotherapy cycles, respectively. Adverse events (AEs) were assessed according to the National Cancer Institute (NCI) Common Terminology Criteria for AEs, and response and progression were assessed by the International Myeloma Working Group criteria. Evidence of histopathology using transmission electron microscopy (TEM) was obtained from an in vivo model of adult Sprague Dawley (SD) rats. Following bortezomib-based VTD chemotherapy, patients had achieved very good partial remission or demonstrated no significant difference between the scBor and ivBor treatment groups (75.6 vs. 84.1%, respectively; P=0.350). The 1-year progression-free survival (83.8 vs. 84.1%, scBor vs. ivBor; P=0.921) and 1-year overall survival (OS) (91.9 vs. 90.9%, respectively; P=0.926) were also similar. PN rates of all the NCI grades were 51.3 and 61.3% (P=0.371); grade ≥2, 35.1 and 56.8% (P=0.052); and grade ≥3, 32.7 and 20.5% (P=0.015) in the subcutaneous and intravenous treatment groups, respectively, which suggests that severe PN may be less common following scBor treatment. There were no severe injection site reactions in the scBor-treated group. The incidence of adverse events were comparable between the two groups, including thrombocytopenia, anemia, fatigue and gastrointestinal symptoms such as nausea and vomiting. Furthermore, TEM images of the SD rat sciatic nerves revealed that all rats suffered PN to varying degrees, except the control group, and that the PN of ivBor-treated rats (in the presence and the absence of thalidomide) was more severe than that of scBor-treated rats. It was concluded that a subcutaneous dose of bortezomib of 1.3 mg/m² may result in a lower incidence and severity of PN, with equivalent efficacy, as a component of combination VTD chemotherapy.

Final overall survival results of a randomized trial comparing bortezomib plus pegylated liposomal doxorubicin with bortezomib alone in patients with relapsed or refractory multiple myeloma

BACKGROUND

Previous results from an interim analysis of an open-label, randomized, phase 3 study demonstrated that bortezomib combined with pegylated liposomal doxorubicin (PLD) was superior to bortezomib monotherapy in patients with relapsed/refractory multiple myeloma who had previously received one or more lines of therapy. Protocol-defined final survival data from that study are provided here.

METHODS

Patients were randomized (1:1) to receive either bortezomib alone (1.3 mg/m(2) intravenously on days 1, 4, 8, and 11 of every 21-day cycle) or bortezomib-PLD (bortezomib plus PLD 30 mg/m(2) intravenously on day 4). The primary endpoint was the time to progression. Secondary efficacy endpoints included overall survival (OS), progression-free survival, and the overall response rate.

RESULTS

In total, 646 patients (bortezomib-PLD, n = 324; bortezomib alone, n = 322) were randomized between December, 2004, and March, 2006. On the clinical cutoff date (May 16, 2014) for the final survival analysis, at a median follow-up of 103 months, 79% of patients had died (bortezomib-PLD group: 253 of 324 patients; 78%; bortezomib alone group: 257 of 322 patients; 80%). The median OS in the bortezomib-PLD group was 33 months (95% confidence interval [CI], 28.9-37.1) versus 30.8 months (95% CI, 25.2-36.5) in the bortezomib alone group (hazard ratio, 1.047; 95% CI, 0.879-1.246; P = .6068). Salvage therapies included conventional and novel drugs, which were well balanced between the two treatment groups.

CONCLUSIONS

Despite inducing a superior time to progression, long-term follow-up revealed that PLD-bortezomib did not improve OS compared with bortezomib alone in patients with relapsed/refractory multiple myeloma. The inability to sustain the early observed survival advantage may have been caused by the effects of subsequent lines of therapy, and underscores the need for long-term follow-up of phase 3 trials while recognizing the challenge of having adequate power to detect long-term differences in OS. Cancer 2016;122:2050-6. © 2016 American Cancer Society.

Role of Nrf2, HO-1 and GSH in Neuroblastoma Cell Resistance to Bortezomib

The activation of Nrf2 has been demonstrated to play a crucial role in cancer cell resistance to different anticancer therapies. The inhibition of proteasome activity has been proposed as a chemosensitizing therapy but the activation of Nrf2 could reduce its efficacy. Using the highly chemoresistant neuroblastoma cells HTLA-230, here we show that the strong reduction in proteasome activity, obtained by using low concentration of bortezomib (BTZ, 2.5 nM), fails in reducing cell viability. BTZ treatment favours the binding of Nrf2 to the ARE sequences in the promoter regions of target genes such as heme oxygenase 1 (HO-1), the modulatory subunit of γ-glutamylcysteine ligase (GCLM) and the transporter for cysteine (x-CT), enabling their transcription. GSH level is also increased after BTZ treatment. The up-regulation of Nrf2 target genes is responsible for cell resistance since HO-1 silencing and GSH depletion synergistically decrease BTZ-treated cell viability. Moreover, cell exposure to all-trans-Retinoic acid (ATRA, 3 μM) reduces the binding of Nrf2 to the ARE sequences, decreases HO-1 induction and lowers GSH level increasing the efficacy of bortezomib. These data suggest the role of Nrf2, HO-1 and GSH as molecular targets to improve the efficacy of low doses of bortezomib in the treatment of malignant neuroblastoma.

Matrices for combined delivery of proteins and synthetic molecules

With the increasing advancement of synergistic, multimodal approaches to influence the treatment of infectious and non-infectious diseases, we witness the development of enabling techniques merging necessary complexity with leaner designs and effectiveness. Systems- and polypharmacology ask for multi-potent drug combinations with many targets to engage with the biological system. These demand drug delivery designs for one single drug, dual drug release systems and multiple release matrices in which the macromolecular structure allows for higher solubilization, protection and sequential or combined release profiles. As a result, nano- and micromaterials have been evolved from mono- to dual drug carriers but are also an essential part to establish multimodality in polymeric matrices. Surface dynamics of particles creating interfaces between polymer chains and hydrogels inspired the development not only of biomedical adhesives but also of injectable hydrogels in which the nanoscale material is both, adhesive and delivery tool. These complex delivery systems are segmented into two delivery subunits, a polymer matrix and nanocarrier, to allow for an even higher tolerance of the incorporated drugs without adding further synthetic demands to the nanocarrier alone. The opportunities in these quite novel approaches for the delivery of small and biological therapeutics are remarkable and selected examples for applications in cancer and bone treatments are discussed.

Combination Treatment with Sublethal Ionizing Radiation and the Proteasome Inhibitor, Bortezomib, Enhances Death-Receptor Mediated Apoptosis and Anti-Tumor Immune Attack

Sub-lethal doses of radiation can modulate gene expression, making tumor cells more susceptible to T-cell-mediated immune attack. Proteasome inhibitors demonstrate broad anti-tumor activity in clinical and pre-clinical cancer models. Here, we use a combination treatment of proteasome inhibition and irradiation to further induce immunomodulation of tumor cells that could enhance tumor-specific immune responses. We investigate the effects of the 26S proteasome inhibitor, bortezomib, alone or in combination with radiotherapy, on the expression of immunogenic genes in normal colon and colorectal cancer cell lines. We examined cells for changes in the expression of several death receptors (DR4, DR5 and Fas) commonly used by T cells for killing of target cells. Our results indicate that the combination treatment resulted in increased cell surface expression of death receptors by increasing their transcript levels. The combination treatment further increases the sensitivity of carcinoma cells to apoptosis through FAS and TRAIL receptors but does not change the sensitivity of normal non-malignant epithelial cells. Furthermore, the combination treatment significantly enhances tumor cell killing by tumor specific CD8⁺ T cells. This study suggests that combining radiotherapy and proteasome inhibition may simultaneously enhance tumor immunogenicity and the induction of antitumor immunity by enhancing tumor-specific T-cell activity.

Targeting the AAA ATPase p97 as an Approach to Treat Cancer through Disruption of Protein Homeostasis

p97 is a AAA-ATPase with multiple cellular functions, one of which is critical regulation of protein homeostasis pathways. We describe the characterization of CB-5083, a potent, selective, and orally bioavailable inhibitor of p97. Treatment of tumor cells with CB-5083 leads to accumulation of poly-ubiquitinated proteins, retention of endoplasmic reticulum-associated degradation (ERAD) substrates, and generation of irresolvable proteotoxic stress, leading to activation of the apoptotic arm of the unfolded protein response. In xenograft models, CB-5083 causes modulation of key p97-related pathways, induces apoptosis, and has antitumor activity in a broad range of both hematological and solid tumor models. Molecular determinants of CB-5083 activity include expression of genes in the ERAD pathway, providing a potential strategy for patient selection.

A phase 2 study of weekly temsirolimus and bortezomib for relapsed or refractory B-cell non-Hodgkin lymphoma: A Wisconsin Oncology Network study

BACKGROUND

Proteasome inhibitors and mammalian target of rapamycin inhibitors each have activity in various B-cell malignancies and affect distinct cellular pathways. Their combination has demonstrated synergy in vitro and in mouse models.

METHODS

The authors conducted a single-arm, phase 2 trial of combined temsirolimus and bortezomib in patients with relapsed and refractory B-cell non-Hodgkin lymphoma (NHL) using a dosing scheme that was previously tested in multiple myeloma. The patients received bortezomib and temsirolimus weekly on days 1, 8, 15, and 22 of a 35-day cycle.

RESULTS

Of 39 patients who received treatment, 3 achieved a complete response (7.7%; 95% confidence interval [CI], 1.6%-21%), and 9 had a partial response (PR) (23%; 95% CI, 11%-39%). Thus, the overall response rate (12 of 39 patients) was 31% (95% CI, 17%-48%), and the median progression-free survival was 4.7 months (95% CI, 2.1-7.8 months; 2 months for patients with diffuse large B-cell lymphoma [n = 18], 7.5 months for those with mantle cell lymphoma [n = 7], and 16.5 months for those with follicular lymphoma [n = 9]). Two extensively treated patients with diffuse large B-cell lymphoma achieved a complete response. There were no unexpected toxicities from the combination.

CONCLUSIONS

The current results demonstrate that the combination of a mammalian target of rapamycin inhibitor and a proteasome inhibitor is safe and has activity in patients with heavily pretreated B-cell NHL. Further studies with this combination are warranted in specific subtypes of NHL.

Proteasome inhibition reverses hedgehog inhibitor and taxane resistance in ovarian cancer

The goal of this study was to determine whether combined targeted therapies, specifically those against the Notch, hedgehog and ubiquitin-proteasome pathways, could overcome ovarian cancer chemoresistance. Chemoresistant ovarian cancer cells were exposed to gamma-secretase inhibitors (GSI-I, Compound E) or the proteasome inhibitor bortezomib, alone and in combination with the hedgehog antagonist, LDE225. Bortezomib, alone and in combination with LDE225, was evaluated for effects on paclitaxel efficacy. Cell viability and cell cycle analysis were assessed by MTT assay and propidium iodide staining, respectively. Proteasome activity and gene expression were determined by luminescence assay and qPCR, respectively. Studies demonstrated that GSI-I, but not Compound E, inhibited proteasome activity, similar to bortezomib. Proteasome inhibition decreased hedgehog target genes (PTCH1, GLI1 and GLI2) and increased LDE225 sensitivity in vitro. Bortezomib, alone and in combination with LDE225, increased paclitaxel sensitivity through apoptosis and G2/M arrest. Expression of the multi-drug resistance gene ABCB1/MDR1 was decreased and acetylation of α-tubulin, a marker of microtubule stabilization, was increased following bortezomib treatment. HDAC6 inhibitor tubastatin-a demonstrated that microtubule effects are associated with hedgehog inhibition and sensitization to paclitaxel and LDE225. These results suggest that proteasome inhibition, through alteration of microtubule dynamics and hedgehog signaling, can reverse taxane-mediated chemoresistance.

Curcumin and its analogue induce apoptosis in leukemia cells and have additive effects with bortezomib in cellular and xenograft models

Combination therapy of bortezomib with other chemotherapeutics is an emerging treatment strategy. Since both curcumin and bortezomib inhibit NF-κB, we tested the effects of their combination on leukemia cells. To improve potency, a novel Mannich-type curcumin derivative, C-150, was synthesized. Curcumin and its analogue showed potent antiproliferative and apoptotic effects on the human leukemia cell line, HL60, with different potency but similar additive properties with bortezomib. Additive antiproliferative effects were correlated well with LPS-induced NF-κB inhibition results. Gene expression data on cell cycle and apoptosis related genes, obtained by high-throughput QPCR, showed that curcumin and its analogue act through similar signaling pathways. In correlation with in vitro results similar additive effect could be obsereved in SCID mice inoculated systemically with HL60 cells. C-150 in a liposomal formulation given intravenously in combination with bortezomib was more efficient than either of the drugs alone. As our novel curcumin analogue exerted anticancer effects in leukemic cells at submicromolar concentration in vitro and at 3 mg/kg dose in vivo, which was potentiated by bortezomib, it holds a great promise as a future therapeutic agent in the treatment of leukemia alone or in combination.

Molecular characterization of the boron adducts of the proteasome inhibitor bortezomib with epigallocatechin-3-gallate and related polyphenols

The green tea polyphenol epigallocatechin-3-gallate (EGCG) was reported to effectively antagonize the ability of Bortezomib (BZM) to induce apoptosis in cancer cells. This interaction was attributed to the formation of a covalent adduct between a phenolic moiety of EGCG with the boronic acid group of Bortezomib. However, the structural details of this boron adduct and the molecular factors that contribute to its formation and its ability to inhibit Bortezomib's activity remain unclear. This paper describes the use of NMR spectroscopy and cell assays to characterize the structures and properties of the boron adducts of EGCG and related polyphenols. The observed boron adducts included both boronate and borate derivatives, and their structural characteristics were correlated with cell-based evaluation of the ability of EGCG and other phenols to antagonize the anticancer activity of Bortezomib. The enhanced stability of the BZM/EGCG adduct was attributed to electronic and steric reasons, and a newly identified intramolecular interaction of the boron atom of BZM with the adjacent amide bond. The reported approach provides a useful method for determining the potential ability of polyphenols to form undesired adducts with boron-based drugs and interfere with their actions.

Computational polypharmacology analysis of the heat shock protein 90 interactome

The design of a single drug molecule that is able to simultaneously and specifically interact with multiple biological targets is gaining major consideration in drug discovery. However, the rational design of drugs with a desired polypharmacology profile is still a challenging task, especially when these targets are distantly related or unrelated. In this work, we present a computational approach aimed at the identification of suitable target combinations for multitarget drug design within an ensemble of biologically relevant proteins. The target selection relies on the analysis of activity annotations present in molecular databases and on ligand-based virtual screening. A few target combinations were also inspected with structure-based methods to demonstrate that the identified dual-activity compounds are able to bind target combinations characterized by remote binding site similarities. Our approach was applied to the heat shock protein 90 (Hsp90) interactome, which contains several targets of key importance in cancer. Promising target combinations were identified, providing a basis for the computational design of compounds with dual activity. The approach may be used on any ensemble of proteins of interest for which known inhibitors are available.

Integrin-mediated resistance to epidermal growth factor receptor-targeted therapy: an inflammatory situation

Targeting the function of epidermal growth factor receptor (EGFR) has failed as an effective clinical option for breast cancer. Understanding the drivers of inherent resistance has been a challenge. One possible mechanism is the acquisition of stem-like properties through the process of epithelial-mesenchymal transition. A recent study by Seguin and colleagues adds to our understanding of this process by demonstrating a functional role for unligated αvβ3 integrin in mediating a stem-like phenotype and facilitating resistance to EGFR-targeted therapy via enhanced downstream coupling to a KRAS:RalB:NF-κB pathway. Importantly, the identified mechanism may reveal a possible strategy for sensitizing breast cancer cells to EGFR-targeted therapies.

An analysis of the safety profile of proteasome inhibitors for treating various cancers

INTRODUCTION

Emerging evidence demonstrates that the ubiquitin-proteasome pathway is a promising target for cancer therapy. Bortezomib (Velcade) exhibits great efficacy against multiple myeloma (MM) since the first clinical application. However, there are still several limitations associated with the use of bortezomib, including severe toxicities. To overcome bortezomib's shortcomings and to improve its safety profile, several second-generation proteasome inhibitors, for example, carfilzomib, ixazomib, oprozomib and marizomib, have been developed and currently tested in various clinical trials.

AREAS COVERED

A literature search was carried out using PubMed and Google Scholar. The activity and safety profiling of proteasome inhibitors in treatment of various cancers were reviewed.

EXPERT OPINION

Bortezomib, as a single or in combination therapy, demonstrates efficacy against MM or other hematological malignancies in clinical settings. However, it encounters two major problems, the acquired resistance and the severe side effects. Future direction in bortezomib-based therapy should focus on how to increase or retain its efficacy but improve its safety profile through, for example, rational combination therapies. Second-generation proteasome inhibitors have shown benefits in both overcoming bortezomib resistance and reducing related side effects, although these encouraging results should be further confirmed in a larger clinic population.

Polypharmacology: challenges and opportunities in drug discovery

At present, the legendary magic bullet, i.e., a drug with high potency and selectivity toward a specific biological target, shares the spotlight with an emerging and alternative polypharmacology approach. Polypharmacology suggests that more effective drugs can be developed by specifically modulating multiple targets. It is generally thought that complex diseases such as cancer and central nervous system diseases may require complex therapeutic approaches. In this respect, a drug that "hits" multiple sensitive nodes belonging to a network of interacting targets offers the potential for higher efficacy and may limit drawbacks generally arising from the use of a single-target drug or a combination of multiple drugs. In this review, we will compare advantages and disadvantages of multitarget versus combination therapies, discuss potential drug promiscuity arising from off-target effects, comment on drug repurposing, and introduce approaches to the computational design of multitarget drugs.

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

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

Sorafenib enhances proteasome inhibitor-induced cell death via inactivation of Akt and stress-activated protein kinases

BACKGROUND

Advanced hepatocellular carcinoma (HCC) responds poorly to conventional systemic therapies. Therefore, new effective therapy strategies are urgently needed. Molecular targeted therapies have entered the field of anti-neoplastic treatment and are being used on their own and in combination with other drugs. Sorafenib inhibits proliferation and angiogenesis of HCC by suppressing the Raf serine/threonine kinases and the receptor tyrosine kinases. The proteasome inhibitor bortezomib has shown activity in a variety of solid tumors, including HCC. However, the precise anti-proliferative mechanisms of these agents remain unclear.

METHODS

We treated human hepatoma cell lines (Huh7 and Hep3B) and immortalized human hepatocyte (OUMS29) with sorafenib and/or proteasome inhibitors, including epoxomicin and acetyl-leucyl-leucyl-norleucinal. Cytotoxic effects were examined by morphometric analyses of apoptosis and necrosis. Apoptosis was also evaluated by Western blotting of keratin18, PARP and caspase3. The activity of Akt and stress-activated protein kinases was examined by Western blotting.

RESULTS

Both sorafenib and proteasome inhibitors induced apoptosis in Huh7 and OUMS29. However, sorafenib attenuated proteasome inhibitor-induced apoptosis. Sorafenib induced necrosis, especially in combination with proteasome inhibitors. Sorafenib induced down-regulation of Akt synergistically in combination with proteasome inhibitors in Huh7. Sorafenib inhibited both the JNK and p38 pathways in a time- and dose-dependent manner. In addition, sorafenib also inhibited proteasome inhibitor-mediated JNK and p38 activation in both Huh7 and OUMS29.

CONCLUSIONS

Sorafenib enhances the anti-proliferative effect of proteasome inhibitors in part by inactivating the Akt signaling pathway and modulating stress-activated protein kinases. The combination of these agents could be an ideal molecular targeted therapy for HCC.

Recent insights into NF-κB signalling pathways and the link between inflammation and prostate cancer

Inflammation is involved in regulation of cellular events in prostate carcinogenesis through control of the tumour micro-environment. A variety of bone marrow-derived cells, including CD4+ lymphocytes, macrophages and myeloid-derived suppressor cells, are integral components of the tumour micro-environment. On activation by inflammatory cytokines, NF-κB complexes are capable of promoting tumour cell survival through anti-apoptotic signalling in prostate cancer (PCa). Positive feedback loops are able to maintain NF-κB activation. NF-κB activation is also associated with the metastatic phenotype and PCa progression to castration-resistant prostate cancer (CRPC). A novel role for inhibitor of NF-κB kinase (IKK)-α in NF-κB-independent PCa progression to metastasis and CRPC has recently been uncovered, providing a new mechanistic link between inflammation and PCa. Expansion of PCa progenitors by IKK-α may be involved in this process. In this review, we offer the latest evidence regarding the role of the NF-κB pathway in PCa and discuss therapeutic attempts to target the NF-κB pathways. We point out the need to further dissect inflammatory pathways in PCa in order to develop appropriate preventive measures and design novel therapeutic strategies.

Therapeutic potential of histone deacetylase inhibitors in pancreatic cancer

Pancreatic cancer is a devastating disease with a dismal prognosis. Surgical resection is the only curative option but is heavily hampered by delayed diagnosis. Due to few therapeutic treatments available, novel and efficacious therapy is urgently needed. Histone deacetylase inhibitors (HDACIs) are emerging as a prominent class of therapeutic agents for pancreatic cancer and have exhibited significant anticancer potential with negligible toxicity in preclinical studies. Clinical evaluations of HDACIs are currently underway. HDACIs as monotherapy in solid tumors have proven less effective than hematological malignancies, the combination of HDACIs with other anticancer agents have been assessed for advanced pancreatic cancer. In this review, we describe the molecular mechanism underpin the anticancer effect of HDACIs in pancreatic cancer and summarize the recent advances in the rationale for the combination strategies incorporating HDACIs. In addition, we discuss the importance of identifying predictors of response to HDACI-based therapy.

Proteasome inhibition by bortezomib increases IL-8 expression in androgen-independent prostate cancer cells: the role of IKKα

Expression of the proinflammatory and proangiogenic chemokine IL-8, which is regulated at the transcriptional level by NF-κB, is constitutively increased in androgen-independent metastatic prostate cancer and correlates with poor prognosis. Inhibition of NF-κB-dependent transcription was used as an anticancer strategy for the development of the first clinically approved 26S proteasome inhibitor, bortezomib (BZ). Even though BZ has shown remarkable antitumor activity in hematological malignancies, it has been less effective in prostate cancer and other solid tumors; however, the mechanisms have not been fully understood. In this article, we report that proteasome inhibition by BZ unexpectedly increases IL-8 expression in androgen-independent prostate cancer PC3 and DU145 cells, whereas expression of other NF-κB-regulated genes is inhibited or unchanged. The BZ-increased IL-8 expression is associated with increased in vitro p65 NF-κB DNA binding activity and p65 recruitment to the endogenous IL-8 promoter. In addition, proteasome inhibition induces a nuclear accumulation of IκB kinase (IKK)α, and inhibition of IKKα enzymatic activity significantly attenuates the BZ-induced p65 recruitment to IL-8 promoter and IL-8 expression, demonstrating that the induced IL-8 expression is mediated, at least partly, by IKKα. Together, these data provide the first evidence, to our knowledge, for the gene-specific increase of IL-8 expression by proteasome inhibition in prostate cancer cells and suggest that targeting both IKKα and the proteasome may increase BZ effectiveness in treatment of androgen-independent prostate cancer.

Synergistic induction of apoptosis in multiple myeloma cells by bortezomib and hypoxia-activated prodrug TH-302, in vivo and in vitro

Recently, we showed that hypoxia is a critical microenvironmental factor in multiple myeloma, and that the hypoxia-activated prodrug TH-302 selectively targets hypoxic multiple myeloma cells and improves multiple disease parameters in vivo. To explore approaches for sensitizing multiple myeloma cells to TH-302, we evaluated in this study the antitumor effect of TH-302 in combination with the clinically used proteasome inhibitor bortezomib. First, we show that TH-302 and bortezomib synergistically induce apoptosis in multiple myeloma cell lines in vitro. Second, we confirm that this synergism is related to the activation of caspase cascades and is mediated by changes of Bcl-2 family proteins. The combination treatment induces enhanced cleavage of caspase-3/8/9 and PARP, and therefore triggers apoptosis and enhances the cleavage of proapoptotic BH3-only protein BAD and BID as well as the antiapoptotic protein Mcl-1. In particular, TH-302 can abrogate the accumulation of antiapoptotic Mcl-1 induced by bortezomib, and decreases the expression of the prosurvival proteins Bcl-2 and Bcl-xL. Furthermore, we found that the induction of the proapoptotic BH3-only proteins PUMA (p53-upregulated modulator of apoptosis) and NOXA is associated with this synergism. In response to the genotoxic and endoplasmic reticulum stresses by TH-302 and bortezomib, the expression of PUMA and NOXA were upregulated in p53-dependent and -independent manners. Finally, in the murine 5T33MMvv model, we showed that the combination of TH-302 and bortezomib can improve multiple disease parameters and significantly prolong the survival of diseased mice. In conclusion, our studies provide a rationale for clinical evaluation of the combination of TH-302 and bortezomib in patients with multiple myeloma.

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

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

Subcutaneous bortezomib: in multiple myeloma

A subcutaneous formulation of bortezomib is now indicated in the EU and the US for the treatment of patients with multiple myeloma. This article reviews pharmacological, therapeutic efficacy and tolerability data relevant to the utilization of subcutaneous bortezomib (Velcade(®)) in the treatment of patients with multiple myeloma. In a randomized, nonblind, phase III study, subcutaneous bortezomib was noninferior to intravenous bortezomib in the treatment of adults with relapsed multiple myeloma, as determined by the overall response rate after four cycles of therapy (primary endpoint). No significant differences between the subcutaneous and intravenous bortezomib formulations were observed in the median time to first response, median progression-free survival, median time to progression and 1-year overall survival. Compared with intravenous bortezomib, subcutaneous bortezomib confers a significant advantage with respect to the incidence of peripheral neuropathy (all grades, grade ≥2 and grade ≥3). As a consequence, it provides a new treatment option for patients with multiple myeloma, particularly those with pre-existing neuropathy or at a high risk of developing peripheral neuropathy.

Targeting the ubiquitin+proteasome system in solid tumors

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

An historic perspective of proteasome inhibition

The ubiquitin-proteasome system (UPS) and associated signaling pathways are regarded today as an exciting area of development for novel therapeutics. However, two decades ago, following the discovery and elucidation of ubiquitin and the 26S proteasome as key mediators of protein turnover, the concept of inhibiting the UPS was not even considered a feasible therapeutic approach due to the assumption that inhibition of this pathway would have widespread deleterious effects. Subsequent clinical developments with the first-in-class proteasome inhibitor bortezomib have radically overturned that view, with the proteasome now recognized as a validated target and proteasome inhibition demonstrated to be a highly successful treatment for a number of hematologic malignancies. Here we provide a historic perspective on the emergence of proteasome inhibition, sharing some of the lessons learned along the way. We describe the development of bortezomib and the elucidation of the effects of its novel mechanism of action, and place the cutting-edge work described elsewhere in this issue in the context of these historic developments.

Specific small molecule inhibitors of Skp2-mediated p27 degradation

In the ubiquitin proteasome system, the E3 ligase SCF-Skp2 and its accessory protein, Cks1, promote proliferation largely by inducing the degradation of the CDK inhibitor p27. Overexpression of Skp2 in human cancers correlates with poor prognosis, and deregulation of SCF-Skp2-Cks1 promotes tumorigenesis in animal models. We identified small molecule inhibitors specific to SCF-Skp2 activity using in silico screens targeted to the binding interface for p27. These compounds selectively inhibited Skp2-mediated p27 degradation by reducing p27 binding through key compound-receptor contacts. In cancer cells, the compounds induced p27 accumulation in a Skp2-dependent manner and promoted cell-type-specific blocks in the G1 or G2/M phases. Designing SCF-Skp2-specific inhibitors may be a novel strategy to treat cancers dependent on the Skp2-p27 axis.

Proteasome inhibition alleviates SNARE-dependent neurodegeneration

Activation of the proteasomal degradation of misfolded proteins has been proposed as a therapeutic strategy for treating neurodegenerative diseases, but it is unclear whether proteasome dysfunction contributes to neurodegeneration. We tested the role of proteasome activity in neurodegeneration developed by mice lacking cysteine string protein-α (CSPα). Unexpectedly, we found that proteasome inhibitors alleviated neurodegeneration in CSPα-deficient mice, reversing impairment of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-complex assembly and extending life span. We tested whether dysfunctional SNARE-complex assembly could contribute to neurodegeneration in Alzheimer's and Parkinson's disease by analyzing postmortem brain tissue from these patients; we found reduced SNARE-complex assembly in the brain tissue samples. Our results suggest that proteasomal activation may not always be beneficial for alleviating neurodegeneration and that blocking the proteasome may represent a potential therapeutic avenue for treating some forms of neurodegenerative disease.