Selective inhibition of chymotrypsin-like activity of the immunoproteasome and constitutive proteasome in Waldenstrom macroglobulinemia

Probiotic lactic acid bacteria promote anti-tumor immunity through enhanced major histocompatibility complex class I-restricted antigen presentation machinery in dendritic cells

Lactic acid bacteria (LAB) possess the ability to argument T cell activity through functional modification of antigen presenting cells (APCs), such as dendritic cells (DCs) and macrophages. Nevertheless, the precise mechanism underlying LAB-induced enhancement of antigen presentation in APCs remains incompletely understood. To address this question, we investigated the detailed mechanism underlying the enhancement of major histocompatibility complex (MHC) class I-restricted antigen presentation in DCs using a probiotic strain known as Lactococcus lactis subsp. Cremoris C60. We found that Heat-killed-C60 (HK-C60) facilitated the processing and presentation of ovalbumin (OVA) peptide antigen OVA257-264 (SIINFEKL) via H-2Kb in bone marrow-derived dendritic cells (BMDCs), leading to increased generation of effector CD8+ T cells both in vitro and in vivo. We also revealed that HK-C60 stimulation augmented the activity of 20S immunoproteasome (20SI) in BMDCs, thereby enhancing the MHC class I-restricted antigen presentation machinery. Furthermore, we assessed the impact of HK-C60 on CD8+ T cell activation in an OVA-expressing B16-F10 murine melanoma model. Oral administration of HK-C60 significantly attenuated tumor growth compared to control treatment. Enhanced Ag processing and presentation machineries in DCs from both Peyer's Patches (PPs) and lymph nodes (LNs) resulted in an increased tumor antigen specific CD8+ T cells. These findings shed new light on the role of LAB in MHC class-I restricted antigen presentation and activation of CD8+ T cells through functional modification of DCs.

Discovery of Highly Selective Inhibitors of the Human Constitutive Proteasome β5c Chymotryptic Subunit

We describe our discovery and development of potent and highly selective inhibitors of human constitutive proteasome chymotryptic activity (β5c). Structure-activity relationship studies of the novel class of inhibitors focused on optimization of N-cap, C-cap, and side chain of the chemophore asparagine. Compound 32 is the most potent and selective β5c inhibitor in this study. A docking study provides a structure rationale for potency and selectivity. Kinetic studies show a reversible and noncompetitive inhibition mechanism. It enters the cells to engage the proteasome target, potently and selectively kills multiple myeloma cells, and does so by synergizing with a β5i-selective inhibitor.

Discovery of novel tripeptide propylene oxide proteasome inhibitors for the treatment of multiple myeloma

The ubiquitin proteasome pathway (UPP) plays a critical role in the maintenance of cell homeostasis and the development of diseases, such as cancer and neurodegenerative disease. A series of novel tripeptide propylene oxide compounds as proteasome inhibitors were designed, synthesized and biologically investigated in this manuscript. The enzymatic activities of final compounds against 20S human proteasome were investigated and structure-activity relationship (SAR) was summarized. Some potent compounds were further evaluated to inhibit the proliferation of multiple myeloma (MM) cancer cell lines RPMI8226 and U266B. The results showed that some compounds were active against MM cancer cell lines with IC₅₀ values of less than 50 nM. The microsomal metabolic stabilities in human, rat and mice species were carried out and the results showed that compounds 30 and 31 were stable enough to be in vivo investigated. The in vivo pharmacokinetic results showed that compounds 30 and 31 had acceptable biological parameters for both ig and iv administrations. In vivo antitumor activities of compounds 30 and 31 with the doses of 100 mg/kg and 50 mg/kg BIW were performed by using RPMI8226 xenograft nude mouse model. Toxicities of compounds 30 and 31 were not observed during the experiment and dose dependent effect was obvious and the tumor volume was greatly inhibited.

High immunoproteasome concentration in the plasma of patients with newly diagnosed multiple myeloma treated with bortezomib is predictive of longer OS

PURPOSE

Proteasome inhibitors (PI) bortezomib or carfilzomib among them, play a crucial role in the modern standard therapy for multiple myeloma (MM). In this study, we intended to evaluate whether immunoproteasome (IMP) concentration could act as an effective biomarker which determines the probability of response to treatment with bortezomib, in order to detect groups of patients who are more likely to respond to treatment with PI.

MATERIALS AND METHODS

In our study, we evaluated IMP concentration in the plasma of 40 patients with monoclonal gammopathy of undetermined significance (MGUS) and 116 patients with newly diagnosed MM during treatment with or without PI.

RESULTS

The values of all the studied parameters after the applied chemotherapy in the responders' group of patients declined considerably during the consecutive cycles of chemotherapy compared to their initial levels. On the contrary, in the group of non-responders, we observed no change in the measured IMP parameters during the consecutive cycles of therapy. We also showed that higher baseline IMP concentration might indicate longer overall survival (OS) in all patients.

CONCLUSIONS

Our results indicate that assessing plasma IMP concentration can be applied as a strong biomarker for predicting clinical response to treatment and OS in patients with newly diagnosed MM.

ONX0912, a selective oral proteasome inhibitor, triggering mitochondrial apoptosis and mitophagy in liver cancer

Proteasome inhibitors represent effective anti-tumor drugs. ONX0912 is a novel oral proteasome inhibitor that selectively targets the chymotrypsin-like activity of 20S proteasome subunits β5 and LMP7 （Low molecular mass polypeptide-7）. It has been shown to be effective in hematologic malignancies. However, its anti-tumor effect in solid tumors remains unclear. Here, we discovered that ONX0912 suppressed the expansion of liver cancer cells. ONX0912 treatment led to an increased level of mitochondrial membrane potential collapse and mitochondrial ROS in tumor cells in a concentration- and exposure time-dependent manner, indicating ONX0912 triggers apoptosis through the intrinsic mitochondrial pathway. ONX0912 also induced mitophagy by activating Parkin/Pink pathway. Silencing mitophagy receptor protein, p62, aggravated the ONX0912-mediated apoptosis, which implied a new mechanism for the conversion between autophagy and apoptosis. Furthermore, we found that the ONX0912 target protein, LMP7 was overexpressed in liver cancer tissues compared to their adjacent tissues and increased level of LMP7 predicted worse clinical characteristics and poorer prognosis. In conclusion, we demonstrated that ONX0912 suppressed liver cancer cell expansion by inducing apoptosis and mitophagy. Our data also revealed ONX0912 as a potential clinical therapeutic drug for liver cancer therapy, and inhibition of mitophagy may sensitize the anti-tumor effect of ONX0912.

Structure-Activity Relationships of Noncovalent Immunoproteasome β5i-Selective Dipeptides

The immunoproteasome (i-20S) has emerged as a therapeutic target for autoimmune and inflammatory disorders and hematological malignancies. Inhibition of the chymotryptic β5i subunit of i-20S inhibits T cell activation, B cell proliferation, and dendritic cell differentiation in vitro and suppresses immune responses in animal models of autoimmune disorders and allograft rejection. However, cytotoxicity to immune cells has accompanied the use of covalently reactive β5i inhibitors, whose activity against the constitutive proteasome (c-20S) is cumulative with the time of exposure. Herein, we report a structure-activity relationship study of a class of noncovalent proteasome inhibitors with picomolar potencies and 1000-fold selectivity for i-20S over c-20S. Furthermore, these inhibitors are specific for β5i over the other five active subunits of i-20S and c-20S, providing useful tools to study the functions of β5i in immune responses. The potency of these compounds in inhibiting human T cell activation suggests that they may have therapeutic potential.

Proteotoxic stress promotes entrapment of ribosomes and misfolded proteins in a shared cytosolic compartment

Cells continuously monitor protein synthesis to prevent accumulation of aberrant polypeptides. Insufficient capacity of cellular degradative systems, chaperone shortage or high levels of mistranslation by ribosomes can result in proteotoxic stress and endanger proteostasis. One of the least explored reasons for mistranslation is the incorrect functioning of the ribosome itself. To understand how cells deal with ribosome malfunction, we introduced mutations in the Expansion Segment 7 (ES7L) of 25S rRNA that allowed the formation of mature, translationally active ribosomes but induced proteotoxic stress and compromised cell viability. The ES7L-mutated ribosomes escaped nonfunctional rRNA Decay (NRD) and remained stable. Remarkably, ES7L-mutated ribosomes showed increased segregation into cytoplasmic foci containing soluble misfolded proteins. This ribosome entrapment pathway, termed TRAP (Translational Relocalization with Aberrant Polypeptides), was generalizable beyond the ES7L mutation, as wild-type ribosomes also showed increased relocalization into the same compartments in cells exposed to proteotoxic stressors. We propose that during TRAP, assembled ribosomes associated with misfolded nascent chains move into cytoplasmic compartments enriched in factors that facilitate protein quality control. In addition, TRAP may help to keep translation at its peak efficiency by preventing malfunctioning ribosomes from active duty in translation.

Drug Development Targeting the Ubiquitin-Proteasome System (UPS) for the Treatment of Human Cancers

Cancer cells are characterized by a higher rate of protein turnover and greater demand for protein homeostasis compared to normal cells. In this scenario, the ubiquitin-proteasome system (UPS), which is responsible for the degradation of over 80% of cellular proteins within mammalian cells, becomes vital to cancer cells, making the UPS a critical target for the discovery of novel cancer therapeutics. This review systematically categorizes all current reported small molecule inhibitors of the various essential components of the UPS, including ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), the 20S proteasome catalytic core particle (20S CP) and the 19S proteasome regulatory particles (19S RP), as well as their mechanism/s of action and limitations. We also discuss the immunoproteasome which is considered as a prospective therapeutic target of the next generation of proteasome inhibitors in cancer therapies.

The emergence of drug resistance to targeted cancer therapies: Clinical evidence

For many decades classical anti-tumor therapies included chemotherapy, radiation and surgery; however, in the last two decades, following the identification of the genomic drivers and main hallmarks of cancer, the introduction of therapies that target specific tumor-promoting oncogenic or non-oncogenic pathways, has revolutionized cancer therapeutics. Despite the significant progress in cancer therapy, clinical oncologists are often facing the primary impediment of anticancer drug resistance, as many cancer patients display either intrinsic chemoresistance from the very beginning of the therapy or after initial responses and upon repeated drug treatment cycles, acquired drug resistance develops and thus relapse emerges, resulting in increased mortality. Our attempts to understand the molecular basis underlying these drug resistance phenotypes in pre-clinical models and patient specimens revealed the extreme plasticity and adaptive pathways employed by tumor cells, being under sustained stress and extensive genomic/proteomic instability due to the applied therapeutic regimens. Subsequent efforts have yielded more effective inhibitors and combinatorial approaches (e.g. the use of specific pharmacologic inhibitors with immunotherapy) that exhibit synergistic effects against tumor cells, hence enhancing therapeutic indices. Furthermore, new advanced methodologies that allow for the early detection of genetic/epigenetic alterations that lead to drug chemoresistance and prospective validation of biomarkers which identify patients that will benefit from certain drug classes, have started to improve the clinical outcome. This review discusses emerging principles of drug resistance to cancer therapies targeting a wide array of oncogenic kinases, along with hedgehog pathway and the proteasome and apoptotic inducers, as well as epigenetic and metabolic modulators. We further discuss mechanisms of resistance to monoclonal antibodies, immunomodulators and immune checkpoint inhibitors, potential biomarkers of drug response/drug resistance, along with possible new therapeutic avenues for the clinicians to combat devastating drug resistant malignancies. It is foreseen that these topics will be major areas of focused multidisciplinary translational research in the years to come.

An oral second-generation proteasome inhibitor oprozomib significantly inhibits lung cancer in a p53 independent manner in vitro

The destruction of proteins via the ubiquitin-proteasome system is a multi-step, complex process involving polyubiquitination of substrate proteins, followed by proteolytic degradation by the macromolecular 26S proteasome complex. Inhibitors of the proteasome promote the accumulation of proteins that are deleterious to cell survival and are promising anticancer agents. Oprozomib (OPZ), an oral second-generation proteasome inhibitor, has been shown to inhibit the growth of several cancers in preclinical and clinical trials, including multiple myeloma and head and neck cancers, but its effects on lung cancer has not yet been determined. In this study, we evaluated the inhibitory effects of OPZ on lung cancer cell lines in vitro. The results showed that OPZ significantly suppressed cell proliferation and strongly induced apoptosis in both tested lung cancer cells independent of p53 expression. OPZ was able to cause obvious caspase 3 and PARP cleavages and stabilize p53 and its transcriptional targets p21, PUMA, and Noxa. Moreover, OPZ was capable of sensitizing lung cancer cells to the conventional chemotherapeutic drug cisplatin. Our study provides preclinical data and sheds light on the potential applications of proteasome inhibitor OPZ in lung cancer treatment.

Pharmacodynamics and pharmacokinetics of proteasome inhibitors for the treatment of multiple myeloma

Introduction: Multiple myeloma (MM) is the second most commonly diagnosed hematologic malignancy and has an increasing incidence and prevalence globally, and proteasome inhibitors (PIs) form the backbone of some of our most effective regimens for all phases of this disease in fit and frail patients. Areas covered: Strong understanding of the proteasome complex is increasingly important as the rapid development of new PIs and innovative myeloma therapies complicate the use of old and new combination regimens. We focus herein on the pharmacodynamics and pharmacokinetics of the approved PIs and others in development, including their safety and efficacy in corresponding clinical studies. Expert opinion: Advancements such as the first oral PI, ixazomib, with a more convenient route of administration and improved toxicity profile led to an improved quality of life, patient compliance, and all-oral combination regimens which are efficacious for long-term management of standard and high-risk MM. Novel pan-PIs, such as marizomib, hold the promise of superior clinical activity due to irreversible targeting of all multicatalytic proteinase complex subunits. Development of clinically validated biomarkers of PI sensitivity/resistance is required to inform utilization of the most optimal and effective, rationally targeted PI treatments for all MM patients.

A Phase Ib/II Study of Oprozomib in Patients with Advanced Multiple Myeloma and Waldenström Macroglobulinemia

PURPOSE

The oral proteasome inhibitor oprozomib has shown preclinical antitumor activity. Here, we report phase Ib/II study results investigating single-agent oprozomib in patients with relapsed multiple myeloma and Waldenström macroglobulinemia.

PATIENTS AND METHODS

The primary objectives were to determine the MTD, safety, and tolerability of oprozomib (phase Ib) as well as overall response rate (ORR; phase II). Oprozomib was administered once daily on days 1, 2, 8, and 9 (2/7 schedule) or days 1 to 5 (5/14 schedule) of a 14-day cycle.

RESULTS

In patients with multiple myeloma or Waldenström macroglobulinemia (n = 71), the determined MTDs were 300 mg/day (2/7 schedule) and 240 mg/day (5/14 schedule). Median oprozomib treatment duration for patients with multiple myeloma was 11.4 weeks (2/7 schedule, 240/300 mg/day), 5.4 weeks (5/14, 240 mg/day), and 10.1 weeks (5/14, 150/180 mg/day). For patients with Waldenström macroglobulinemia, these values were 34.6 weeks (2/7 schedule, 240/300 mg/day) and 8.1 weeks (5/14 schedule, 240 mg/day). The most common grade ≥3 adverse events (AE) in phase Ib included gastrointestinal and hematologic AEs. Three AE-related deaths in phase II prompted enrollment into 2/7 and 5/14 step-up dosing schedules (240/300 mg/day and 150/180 mg/day, respectively). In phase II, ORRs in 95 response-eligible multiple myeloma patients were 41.0%, 28.1%, and 25.0% in the 2/7, 240/300-mg/day; 5/14, 150/180-mg/day; and 5/14, 240-mg/day cohorts, respectively. ORRs in 31 response-eligible Waldenström macroglobulinemia patients were 71.4% and 47.1% for the 2/7 and 5/14 cohorts, respectively.

CONCLUSIONS

This study demonstrated promising efficacy of single-agent oprozomib in patients with relapsed multiple myeloma and Waldenström macroglobulinemia.

A Practical Review of Proteasome Pharmacology

The ubiquitin proteasome system (UPS) degrades individual proteins in a highly regulated fashion and is responsible for the degradation of misfolded, damaged, or unneeded cellular proteins. During the past 20 years, investigators have established a critical role for the UPS in essentially every cellular process, including cell cycle progression, transcriptional regulation, genome integrity, apoptosis, immune responses, and neuronal plasticity. At the center of the UPS is the proteasome, a large and complex molecular machine containing a multicatalytic protease complex. When the efficiency of this proteostasis system is perturbed, misfolded and damaged protein aggregates can accumulate to toxic levels and cause neuronal dysfunction, which may underlie many neurodegenerative diseases. In addition, many cancers rely on robust proteasome activity for degrading tumor suppressors and cell cycle checkpoint inhibitors necessary for rapid cell division. Thus, proteasome inhibitors have proven clinically useful to treat some types of cancer, especially multiple myeloma. Numerous cellular processes rely on finely tuned proteasome function, making it a crucial target for future therapeutic intervention in many diseases, including neurodegenerative diseases, cystic fibrosis, atherosclerosis, autoimmune diseases, diabetes, and cancer. In this review, we discuss the structure and function of the proteasome, the mechanisms of action of different proteasome inhibitors, various techniques to evaluate proteasome function in vitro and in vivo, proteasome inhibitors in preclinical and clinical development, and the feasibility for pharmacological activation of the proteasome to potentially treat neurodegenerative disease.

Pluripotent Stem Cell Model of Nakajo-Nishimura Syndrome Untangles Proinflammatory Pathways Mediated by Oxidative Stress

Nakajo-Nishimura syndrome (NNS) is an immunoproteasome-associated autoinflammatory disorder caused by a mutation of the PSMB8 gene. Although dysfunction of the immunoproteasome causes various cellular stresses attributed to the overproduction of inflammatory cytokines and chemokines in NNS, the underlying mechanisms of the autoinflammation are still largely unknown. To investigate and understand the mechanisms and signal pathways in NNS, we established a panel of isogenic pluripotent stem cell (PSC) lines with PSMB8 mutation. Activity of the immunoproteasome in PSMB8-mutant PSC-derived myeloid cell lines (MT-MLs) was reduced even without stimulation compared with non-mutant-MLs. In addition, MT-MLs showed an overproduction of inflammatory cytokines and chemokines, with elevated reactive oxygen species (ROS) and phosphorylated p38 MAPK levels. Treatment with p38 MAPK inhibitor and antioxidants decreased the abnormal production of cytokines and chemokines. The current PSC model revealed a specific ROS-mediated inflammatory pathway, providing a platform for the discovery of alternative therapeutic options for NNS and related immunoproteasome disorders.

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An isogenic PSC panel for Nakajo-Nishimura syndrome was prepared

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Mutant myeloid cell lines showed increased proinflammatory response

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p38 MAPK inhibitor and antioxidant treatment restored the proinflammatory phenotype

Proteasome-associated deubiquitinases and cancer

Maintenance of protein homeostasis is a crucial process for the normal functioning of the cell. The regulated degradation of proteins is primarily facilitated by the ubiquitin proteasome system (UPS), a system of selective tagging of proteins with ubiquitin followed by proteasome-mediated proteolysis. The UPS is highly dynamic consisting of both ubiquitination and deubiquitination steps that modulate protein stabilization and degradation. Deregulation of protein stability is a common feature in the development and progression of numerous cancer types. Simultaneously, the elevated protein synthesis rate of cancer cells and consequential accumulation of misfolded proteins drives UPS addiction, thus sensitizing them to UPS inhibitors. This sensitivity along with the potential of stabilizing pro-apoptotic signaling pathways makes the proteasome an attractive clinical target for the development of novel therapies. Targeting of the catalytic 20S subunit of the proteasome is already a clinically validated strategy in multiple myeloma and other cancers. Spurred on by this success, promising novel inhibitors of the UPS have entered development, targeting the 20S as well as regulatory 19S subunit and inhibitors of deubiquitinating and ubiquitin ligase enzymes. In this review, we outline the manner in which deregulation of the UPS can cause cancer to develop, current clinical application of proteasome inhibitors, and the (pre-)clinical development of novel inhibitors of the UPS.

A phase 1 clinical trial evaluating marizomib, pomalidomide and low-dose dexamethasone in relapsed and refractory multiple myeloma (NPI-0052-107): final study results

Marizomib (MRZ) is an irreversible, pan-subunit proteasome inhibitor (PI) in clinical development for relapsed/refractory multiple myeloma (RRMM) and glioma. This study analysed MRZ, pomalidomide (POM) and low-dose dexamethasone (Lo-DEX) [PMD] in RRMM to evaluate safety and determine the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D). Intravenous MRZ (0·3-0·5 mg/m² ) was administered over 2 h on days 1, 4, 8, 11; POM (3-4 mg) on days 1-21; and Lo-DEX (5 or 10 mg) on days 1, 2, 4, 5, 8, 9, 11, 12, 15, 16, 22 and 23 of every 28-day cycle. Thirty-eight patients were enrolled that had received a median of 4 (range 1-10) prior lines of therapy; all patients received prior lenalidomide and bortezomib. No dose-limiting toxicities (DLTs) were observed and 0·5 mg/m² MRZ was determined to be the RP2D. The most common treatment-related ≥Grade 3 adverse events were: neutropenia (11/38 patients: 29%), pneumonia (4/38 patients 11%), anaemia (4/38 patients; 11%) and thrombocytopenia (4/38 patients; 11%). The overall response rate and clinical benefit rate was 53% (19/36) and 64% (23/36), respectively. In conclusion, PMD was well tolerated and demonstrated promising activity in heavily pre-treated, high-risk RRMM patients.

Immunoproteasome in the blood plasma of children with acute appendicitis, and its correlation with proteasome and UCHL1 measured by SPR imaging biosensors

The aim of this study was to determinate the immunoproteasome concentration in the blood plasma of children with appendicitis, and its correlation with circulating proteasome and ubiquitin carboxyl-terminal hydrolase L1 (UCHL1). Twenty-seven children with acute appendicitis, managed at the Paediatric Surgery Department, were included randomly into the study (age 2 years 9 months up to 14 years, mean age 9·5 ± 1 years). There were 10 girls and 17 boys; 18 healthy, age-matched subjects, admitted for planned surgeries served as controls. Mean concentrations of immunoproteasome, 20S proteasome and UCHL1 in the blood plasma of children with appendicitis before surgery 24 h and 72 h after the appendectomy were higher than in the control group. The immunoproteasome, 20S proteasome and UCHL1 concentrations in the blood plasma of patients with acute appendicitis were highest before surgery. The immunoproteasome, 20S proteasome and UCHL1 concentration measured 24 and 72 h after the operation decreased slowly over time and still did not reach the normal range (P < 0·05). There was no statistical difference between immunoproteasome, 20S proteasome and UCHL1 concentrations in children operated on laparoscopically and children after classic appendectomy. The immunoproteasome concentration may reflect the metabolic response to acute state inflammation, and the process of gradual ebbing of the inflammation may thus be helpful in the assessment of the efficacy of treatment. The method of operation - classic open appendectomy or laparoscopic appendectomy - does not influence the general trend in immunoproteasome concentration in children with appendicitis.

Novel Proteasome Inhibitors and Histone Deacetylase Inhibitors: Progress in Myeloma Therapeutics

The unfolded protein response is responsible for the detection of misfolded proteins and the coordination of their disposal and is necessary to maintain the cellular homoeostasis. Multiple myeloma cells secrete large amounts of immunoglobulins, proteins that need to be correctly folded by the chaperone system. If this process fails, the misfolded proteins have to be eliminated by the two main garbage-disposal systems of the cell: proteasome and aggresome. The blockade of either of these systems will result in accumulation of immunoglobulins and other toxic proteins in the cytoplasm and cell death. The simultaneous inhibition of the proteasome, by proteasome inhibitors (PIs) and the aggresome, by histone deacetylase inhibitors (HDACi) results in a synergistic increase in cytotoxicity in myeloma cell lines. This review provides an overview of mechanisms of action of second-generation PIs and HDACi in multiple myeloma (MM), the clinical results currently observed with these agents and assesses the potential therapeutic impact of the different agents in the two classes. The second-generation PIs offer benefits in terms of increased efficacy, reduced neurotoxicity as off-target effect and may overcome resistance to bortezomib because of their different chemical structure, mechanism of action and biological properties. HDACi with anti-myeloma activity in clinical development discussed in this review include vorinostat, panobinostat and selective HDAC6 inhibitor, ricolinostat.

Methods for 20S Immunoproteasome and 20S Constitutive Proteasome Determination Based on SPRI Biosensors

The 20S proteasome, released into the circulation, is a novel cancer biomarker. It exists in two forms: the constitutive proteasome (20Sc) and the immunoproteasome (20Si), which both have separate diagnostic significance. The aim of this work was to develop new methods for 20Si and 20Sc determination. Five alternative specific biosensors usable with the surface plasmon resonance imaging (SPRI) technique for 20Si determination have been developed. Specific 20Si entrapment on the biosensor surface from an analyzed solution was achieved by means of an immobilized specific 20Si receptor. Four of the biosensors contain newly synthesized specific 20Si receptors, while the fifth contains the inhibitor ONX 0914. A method for 20Sc determination using an SPRI biosensor containing PSI inhibitor has been developed. By the introduction of an inhibitor blocking 20Si, 20Sc is selectively determined. All of the methods developed for 20Si and 20Sc determination exhibit good selectivity and satisfactory precision, recoveries and dynamic response ranges. 20Si and 20Sc were determined in blood plasma samples from healthy donors and patients with acute leukemia. In the case of these patients 20Si was the major component, and its level was more than one order of magnitude higher than in the healthy donors.

Low expression of pro-apoptotic Bcl-2 family proteins sets the apoptotic threshold in Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM) is a proliferative disorder of IgM-secreting, lymphoplasmacytoid cells that inhabit the lymph nodes and bone marrow. The disease carries a high prevalence of activating mutations in MyD88 (91%) and CXCR4 (28%). Because signaling through these pathways leads to Bcl-xL induction, we examined Bcl-2 family expression in WM patients and cell lines. Unlike other B-lymphocyte-derived malignancies, which become dependent on expression of anti-apoptotic proteins to counter expression of pro-apoptotic proteins, WM samples expressed both pro- and anti-apoptotic Bcl-2 proteins at low levels similar to their normal B-cell and plasma cell counterparts. Three WM cell lines expressed pro-apoptotic Bcl-2 family members Bim or Bax and Bak at low levels, which determined their sensitivity to inducers of intrinsic apoptosis. In two cell lines, miR-155 upregulation, which is common in WM, was responsible for the inhibition of FOXO3a and Bim expression. Both antagonizing miR-155 to induce Bim and proteasome inhibition increased the sensitivity to ABT-737 in these lines indicating a lowering of the apoptotic threshold. In this manner, treatments that increase pro-apoptotic protein expression increase the efficacy of agents treated in combination in addition to direct killing.

Validation of the 2nd Generation Proteasome Inhibitor Oprozomib for Local Therapy of Pulmonary Fibrosis

Proteasome inhibition has been shown to prevent development of fibrosis in several organs including the lung. However, effects of proteasome inhibitors on lung fibrosis are controversial and cytotoxic side effects of the overall inhibition of proteasomal protein degradation cannot be excluded. Therefore, we hypothesized that local lung-specific application of a novel, selective proteasome inhibitor, oprozomib (OZ), provides antifibrotic effects without systemic toxicity in a mouse model of lung fibrosis. Oprozomib was first tested on the human alveolar epithelial cancer cell line A549 and in primary mouse alveolar epithelial type II cells regarding its cytotoxic effects on alveolar epithelial cells and compared to the FDA approved proteasome inhibitor bortezomib (BZ). OZ was less toxic than BZ and provided high selectivity for the chymotrypsin-like active site of the proteasome. In primary mouse lung fibroblasts, OZ showed significant anti-fibrotic effects, i.e. reduction of collagen I and α smooth muscle actin expression, in the absence of cytotoxicity. When applied locally into the lungs of healthy mice via instillation, OZ was well tolerated and effectively reduced proteasome activity in the lungs. In bleomycin challenged mice, however, locally applied OZ resulted in accelerated weight loss and increased mortality of treated mice. Further, OZ failed to reduce fibrosis in these mice. While upon systemic application OZ was well tolerated in healthy mice, it rather augmented instead of attenuated fibrotic remodelling of the lung in bleomycin challenged mice. To conclude, low toxicity and antifibrotic effects of OZ in pulmonary fibroblasts could not be confirmed for pulmonary fibrosis of bleomycin-treated mice. In light of these data, the use of proteasome inhibitors as therapeutic agents for the treatment of fibrotic lung diseases should thus be considered with caution.

Proteasome inhibitors

Proteasome inhibitors have a 20 year history in cancer therapy. The first proteasome inhibitor, bortezomib (Velcade, PS-341), a break-through multiple myeloma treatment, moved rapidly through development from bench in 1994 to first approval in 2003. Bortezomib is a reversible boronic acid inhibitor of the chymotrypsin-like activity of the proteasome. Next generation proteasome inhibitors include carfilzomib and oprozomib which are irreversible epoxyketone proteasome inhibitors; and ixazomib and delanzomib which are reversible boronic acid proteasome inhibitors. Two proteasome inhibitors, bortezomib and carfilzomib are FDA approved drugs and ixazomib and oprozomib are in late stage clinical trials. All of the agents are potent cytotoxics. The disease focus for all the proteasome inhibitors is multiple myeloma. This focus arose from clinical observations made in bortezomib early clinical trials. Later preclinical studies confirmed that multiple myeloma cells were indeed more sensitive to proteasome inhibitors than other tumor cell types. The discovery and development of the proteasome inhibitor class of anticancer agents has progressed through a classic route of serendipity and scientific investigation. These agents are continuing to have a major impact in their treatment of hematologic malignancies and are beginning to be explored as potential treatment agent for non-cancer indications.

Trial Watch: Proteasomal inhibitors for anticancer therapy

The so-called "ubiquitin-proteasome system" (UPS) is a multicomponent molecular apparatus that catalyzes the covalent attachment of several copies of the small protein ubiquitin to other proteins that are generally (but not always) destined to proteasomal degradation. This enzymatic cascade is crucial for the maintenance of intracellular protein homeostasis (both in physiological conditions and in the course of adaptive stress responses), and regulates a wide array of signaling pathways. In line with this notion, defects in the UPS have been associated with aging as well as with several pathological conditions including cardiac, neurodegenerative, and neoplastic disorders. As transformed cells often experience a constant state of stress (as a result of the hyperactivation of oncogenic signaling pathways and/or adverse microenvironmental conditions), their survival and proliferation are highly dependent on the integrity of the UPS. This rationale has driven an intense wave of preclinical and clinical investigation culminating in 2003 with the approval of the proteasomal inhibitor bortezomib by the US Food and Drug Administration for use in multiple myeloma patients. Another proteasomal inhibitor, carfilzomib, is now licensed by international regulatory agencies for use in multiple myeloma patients, and the approved indications for bortezomib have been extended to mantle cell lymphoma. This said, the clinical activity of bortezomib and carfilzomib is often limited by off-target effects, innate/acquired resistance, and the absence of validated predictive biomarkers. Moreover, the antineoplastic activity of proteasome inhibitors against solid tumors is poor. In this Trial Watch we discuss the contribution of the UPS to oncogenesis and tumor progression and summarize the design and/or results of recent clinical studies evaluating the therapeutic profile of proteasome inhibitors in cancer patients.

Novel treatment options for Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM), first described by Jan Waldenström in 1944, is a lymphoplasmacytic lymphoma characterized by the presence of an immunoglobulin M monoclonal gammopathy in the blood and monoclonal small lymphocytes and lymphoplasmacytoid cells in the bone marrow. WM is a rare and indolent disease but remains incurable. In this review we discuss the pathogenesis of WM and focus on novel treatment options that target pathways deregulated in this disease. Recent studies have helped us identify specific genetic mutations that are commonly seen in WM and might prove to be important therapeutic targets in the future. We discuss the role of epigenetics and the changes in the bone marrow microenvironment that are important in the pathogenesis of WM. The commonly used drugs are discussed with a focus on novel agents that are currently being used as single agents or in combination to treat WM. We finally focus on some agents that have shown preclinical efficacy and might be available in the near future.

Inhibitors of the immunoproteasome: current status and future directions

The ubiquitin-proteasome system (UPS) plays a vital role in maintaining protein homeostasis and regulating numerous cellular processes. The proteasome, a multi-protease complex, is the key component of the UPS and has been validated as a therapeutic target by the FDA's approval of bortezomib and carfilzomib. These proteasome inhibitor drugs have substantially improved outcomes in patients with hematological malignancies and are currently being investigated for other types of cancer as well as several other diseases. These approved proteasome inhibitors target the catalytic activity of both the constitutive proteasome and the immunoproteasome indiscriminately, and their inhibitory effects on the constitutive proteasome in normal cells are believed to contribute to unwanted side effects. In addition, selective immunoproteasome inhibition has been proposed to have unique effects on other diseases, including those involving aberrant immune function. Initially recognized for its role in the adaptive immune response, the immunoproteasome is often upregulated in disease states such as inflammatory diseases and cancer, suggesting functions beyond antigen presentation. In an effort to explore the immunoproteasome as a potential therapeutic target in these diseases, the development of immunoproteasome-specific inhibitors has become the focus of recent studies. Owing to considerable efforts by both academic and industry groups, immunoproteasome-selective inhibitors have now been identified and tested against several disease models. These inhibitors also provide a valuable set of chemical tools for investigating the biological function of the immunoproteasome. In this review, we will focus on the recent efforts towards the development of immunoproteasome-selective inhibitors.

Proteasome inhibitors - molecular basis and current perspectives in multiple myeloma

Inhibition of proteasome, a proteolytic complex responsible for the degradation of ubiquitinated proteins, has emerged as a powerful strategy for treatment of multiple myeloma (MM), a plasma cell malignancy. First-in-class agent, bortezomib, has demonstrated great positive therapeutic efficacy in MM, both in pre-clinical and in clinical studies. However, despite its high efficiency, a large proportion of patients do not achieve sufficient clinical response. Therefore, the development of a second-generation of proteasome inhibitors (PIs) with improved pharmacological properties was needed. Recently, several of these new agents have been introduced into clinics including carfilzomib, marizomib and ixazomib. Further, new orally administered second-generation PI oprozomib is being investigated. This review provides an overview of main mechanisms of action of PIs in MM, focusing on the ongoing development and progress of novel anti-proteasome therapeutics.

Autophagy in plasma cell pathophysiology

Plasma cells (PCs) are the effectors responsible for antibody (Ab)-mediated immunity. They differentiate from B lymphocytes through a complete remodeling of their original structure and function. Stress is a constitutive element of PC differentiation. Macroautophagy, conventionally referred to as autophagy, is a conserved lysosomal recycling strategy that integrates cellular metabolism and enables adaptation to stress. In metazoa, autophagy plays diverse roles in cell differentiation. Recently, a number of autophagic functions have been recognized in innate and adaptive immunity, including clearance of intracellular pathogens, inflammasome regulation, lymphocyte ontogenesis, and antigen presentation. We identified a previously unrecognized role played by autophagy in PC differentiation and activity. Following B cell activation, autophagy moderates the expression of the transcriptional repressor Blimp-1 and immunoglobulins through a selective negative control exerted on the size of the endoplasmic reticulum and its stress signaling response, including the essential PC transcription factor, XBP-1. This containment of PC differentiation and function, i.e., Ab production, is essential to optimize energy metabolism and viability. As a result, autophagy sustains Ab responses in vivo. Moreover, autophagy is an essential intrinsic determinant of long-lived PCs in their as yet poorly understood bone marrow niche. In this essay, we discuss these findings in the context of the established biological functions of autophagy, and their manifold implications for adaptive immunity and PC diseases, in primis multiple myeloma.

Anti-leukemic activity and mechanisms underlying resistance to the novel immunoproteasome inhibitor PR-924

PR-924 is a novel prototypic immunoproteasome inhibitor bearing markedly enhanced specificity for the β5i immunoproteasome subunit, compared to the classical proteasome inhibitor bortezomib. Here, we assessed the growth inhibitory potential of PR-924 in three human hematologic malignancy cell lines (CCRF-CEM, THP1, and 8226) and their bortezomib-resistant sublines. Parental cells displayed equal sensitivity to PR-924 (IC₅₀: 1.5-2.8 μM), whereas their bortezomib-resistant tumor lines displayed a 10-12 fold cross-resistance to PR-924. However, PR-924 cross-resistance factors for bortezomib-resistant sublines were markedly lower compared to the resistance factors to bortezomib. Proteasome inhibition experiments confirmed that PR-924 specifically inhibited β5i activity, even far below concentrations that exerted anti-proliferative activity. We further determined whether PR-924 activity might be compromised by acquisition of drug resistance phenomena. Indeed, CEM cells rendered stepwise resistant to 20 μM PR-924 (CEM/PR20) displayed 13-fold PR-924-resistance and 10-fold cross-resistance to bortezomib. CEM/PR20 cells were devoid of mutations in the PSMB8 gene (encoding β5i), but acquired Met45Ile mutation in the PSMB5 gene (encoding constitutive β5), consistent with β5 mutations observed in bortezomib-resistant cells. Furthermore, compared to parental CEM cells, CEM/PR20 cells exhibited 2.5-fold upregulation of constitutive proteasome subunit expression, whereas immunoproteasome subunit expression was 2-fold decreased. In conclusion, PR-924 displayed potent anti-leukemic activity including toward bortezomib-resistant leukemia cells. Despite the specificity of PR-924 to the β5i immunoproteasome subunit, its anti-leukemic effect required concentrations that blocked both β5 and β5i subunits. This is underscored by the emergence of mutations in PSMB5 rather than in PSMB8.

Interferon-γ-induced upregulation of immunoproteasome subunit assembly overcomes bortezomib resistance in human hematological cell lines

Background

Despite encouraging results with the proteasome inhibitor bortezomib in the treatment of hematologic malignancies, emergence of resistance can limit its efficacy, hence calling for novel strategies to overcome bortezomib-resistance. We previously showed that bortezomib-resistant human leukemia cell lines expressed significantly lower levels of immunoproteasome at the expense of constitutive proteasomes, which harbored point mutations in exon 2 of the PSMB5 gene encoding the β5 subunit. Here we investigated whether up-regulation of immunoproteasomes by exposure to interferon-γ restores sensitivity to bortezomib in myeloma and leukemia cell lines with acquired resistance to bortezomib.

Methods

RPMI-8226 myeloma, THP1 monocytic/macrophage and CCRF-CEM (T) parental cells and sub lines with acquired resistance to bortezomib were exposed to Interferon-γ for 24-48 h where after the effects on proteasome subunit expression and activity were measured, next to sensitivity measurements to proteasome inhibitors bortezomib, carfilzomib, and the immunoproteasome selective inhibitor ONX 0914. At last, siRNA knockdown experiments of β5i and β1i were performed to identify the contribution of these subunits to sensitivity to proteasome inhibition. Statistical significance of the differences were determined using the Mann-Whitney U test.

Results

Interferon-γ exposure markedly increased immunoproteasome subunit mRNA to a significantly higher level in bortezomib-resistant cells (up to 30-fold, 10-fold, and 6-fold, in β1i, β5i, and β2i, respectively) than in parental cells. These increases were paralleled by elevated immunoproteasome protein levels and catalytic activity, as well as HLA class-I. Moreover, interferon-γ exposure reinforced sensitization of bortezomib-resistant tumor cells to bortezomib and carfilzomib, but most prominently to ONX 0914, as confirmed by cell growth inhibition studies, proteasome inhibitor-induced apoptosis, activation of PARP cleavage and accumulation of polyubiquitinated proteins. This sensitization was abrogated by siRNA silencing of β5i but not by β1i silencing, prior to pulse exposure to interferon-γ.

Conclusion

Downregulation of β5i subunit expression is a major determinant in acquisition of bortezomib-resistance and enhancement of its proteasomal assembly after induction by interferon-γ facilitates restoration of sensitivity in bortezomib-resistant leukemia cells towards bortezomib and next generation (immuno) proteasome inhibitors.

Waldenström macroglobulinemia: from biology to treatment

Waldenström macroglobulinemia (WM) is distinct B-cell lymphoproliferative disorder primarily characterized by bone marrow infiltration of lymphoplasmacytic cells along with production of a serum monoclonal (IgM). In this review, we describe the biology of WM, the diagnostic evaluation for WM with a discussion of other conditions that are in the differential diagnosis and clinical manifestations of the disease as well as current treatment options. Within the novel agents discussed are everolimus, perifosine, enzastaurin, panobinostat, bortezomib and carfilzomib, pomalidomide and ibrutinib. Many of the novel agents have shown good responses and have a better toxicity profile compared to traditional chemotherapeutic agents, which makes them good candidates to be used as primary therapies for WM in the future.

Targeting the ubiquitin proteasome system in haematological malignancies

The ubiquitin proteasome system (UPS) plays a central role in cellular protein homeostasis through the targeted destruction of damaged/misfolded proteins and regulatory proteins that control critical cellular functions. The UPS comprises a sequential series of enzymatic activities to covalently attach ubiquitin to proteins to target them for degradation through the proteasome. Aberrancies within this system have been associated with transformation and tumourigenesis and thus, the UPS represents an attractive target for the development of anti-cancer therapies. The use of the first-in-class proteasome inhibitor, bortezomib, in the treatment of Plasma Cell Myeloma and Mantle Cell Lymphoma has validated the UPS as a therapeutic target. Following on its success, efforts are focused on the development of second-generation proteasome inhibitors and small molecule inhibitors of other components of the UPS. This review will provide an overview of the UPS and discuss current and novel therapies targeting the UPS.

Effect of novel proteasome and immunoproteasome inhibitors on dendritic cell maturation, function, and expression of IκB and NFκB

Dendritic cells (DC) play a central role in the pathophysiology of graft versus host disease (GvHD). Their antigen presenting capacity is nuclear factor κB- (NF-κB) dependent. Consequently, DC have emerged as a potential target for the prevention of GvHD and clinical trials with bortezomib are underway. We explored the activity of novel proteasome and immunoproteasome inhibitors on healthy volunteer peripheral blood DC. After incubation with the drug or drug combination, DC were stimulated with lipopolysaccharide, stained for maturation surface markers and then analyzed by flow cytometry. We found that the different molecule(s) inhibited DC maturation marker expression to variable degrees, with the constitutive proteasome-selective agent being the least active. In a DC and allogeneic CD4+ mixed lymphocyte reaction, DC incubation with the studied proteasome and immunoproteasome inhibitor(s), impeded T cell proliferation as measured by BrDU incorporation. Finally, we found that DC incubation with the drug(s) enhanced IκB expression and that oprozomib inhibited NF-κB expression. We concluded that based on its activity and oral bioavailability, oprozomib merits further investigation in an animal GvHD prevention model. We also suggest that altering IκB and NF-κB expressions may, in DC, represent a new mechanism of action of proteasome and immunoproteasome inhibitors.

Higher ratio immune versus constitutive proteasome level as novel indicator of sensitivity of pediatric acute leukemia cells to proteasome inhibitors

The ex vivo sensitivity of pediatric leukemia cells to the proteasome inhibitor bortezomib was compared to 3 next generation proteasome inhibitors: the epoxyketone-based irreversible proteasome inhibitors carfilzomib, its orally bio-available analog ONX 0912, and the immunoproteasome inhibitor ONX 0914. LC50 values were determined by MTT cytotoxicity assays for 29 childhood acute lymphoblastic leukemia and 12 acute myeloid leukemia patient samples and correlated with protein expression levels of the constitutive proteasome subunits (β5, β1, β2) and their immunoproteasome counterparts (β5i, β1i, β2i). Acute lymphoblastic leukemia cells were up to 5.5-fold more sensitive to proteasome inhibitors than acute myeloid leukemia cells (P<0.001) and the combination of bortezomib and dexamethasone proved additive/synergistic in the majority of patient specimens. Although total proteasome levels in acute lymphoblastic leukemia and acute myeloid leukemia cells did not differ significantly, the ratio of immuno/constitutive proteasome was markedly higher in acute lymphoblastic leukemia cells over acute myeloid leukemia cells. In both acute lymphoblastic leukemia and acute myeloid leukemia, increased ratios of β5i/β5, β1i/β1 and β2i/β2 correlated with increased sensitivity to proteasome inhibitors. Together, differential expression levels of constitutive and immunoproteasomes in pediatric acute lymphoblastic leukemia and acute myeloid leukemia constitute an underlying mechanism of sensitivity to bortezomib and new generation proteasome inhibitors, which may further benefit from synergistic combination therapy with drugs including glucocorticoids.

Primary therapy of Waldenstrom macroglobulinemia (WM) with weekly bortezomib, low-dose dexamethasone, and rituximab (BDR): long-term results of a phase 2 study of the European Myeloma Network (EMN)

In this phase 2 multicenter trial, we evaluated the activity of bortezomib, dexamethasone, and rituximab (BDR) combination in previously untreated symptomatic patients with Waldenström macroglobulinemia (WM). To prevent immunoglobulin M (IgM) "flare," single agent bortezomib (1.3 mg/m(2) IV days 1, 4, 8, and 11; 21-day cycle), was followed by weekly IV bortezomib (1.6 mg/m(2) days 1, 8, 15, and 22) every 35 days for 4 additional cycles, followed by IV dexamethasone (40 mg) and IV rituximab (375 mg/m(2)) in cycles 2 and 5. Fifty-nine patients were treated; 45.5% and 40% were high and intermediate risk per the International Prognostic Scoring System for WM. On intent to treat, 85% responded (3% complete response, 7% very good partial response, 58% partial response [PR]). In 11% of patients, an increase of IgM ≥25% was observed after rituximab; no patient required plasmapheresis. After a minimum follow-up of 32 months, median progression-free survival was 42 months, 3-year duration of response for patients with ≥PR was 70%, and 3-year survival was 81%. Peripheral neuropathy occurred in 46% (grade ≥3 in 7%); only 8% discontinued bortezomib due to neuropathy. BDR is rapidly acting, well tolerated, and nonmyelotoxic, inducing durable responses in previously untreated WM.

New proteasome inhibitors in myeloma

Proteasome inhibition has a validated role in cancer therapy since the successful introduction of bortezomib for the treatment of multiple myeloma (MM) and mantle cell lymphoma, leading to the development of second-generation proteasome inhibitors (PI) for MM patients in whom currently approved therapies have failed. Five PIs have reached clinical evaluation, with the goals of improving efficacy and limiting toxicity, including peripheral neuropathy (PN). Carfilzomib, an epoxyketone with specific chymothrypsin-like activity, acts as an irreversible inhibitor and was recently FDA approved for the response benefit seen in relapsed and refractory MM patients previously treated with bortezomib, thalidomide and lenalidomide. ONX-0912 is now under evaluation as an oral form with similar activity. The boronate peptides MLN9708 and CEP-18770 are orally bioactive bortezomib analogs with prolonged activity and greater tissue penetration. NPI-0052 (marizomib) is a unique, beta-lactone non-selective PI that has been shown to potently overcome bortezomib resistance in vitro. All of these second-generation PIs demonstrate encouraging anti-MM activity and appear to reduce the incidence of PN, with clinical trials ongoing.

The bone marrow microenvironment in waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) is a low-grade B-cell lymphoproliferative disorder characterized primarily by specific homing and growth of tumor cells within the bone marrow niches. The progressive growth of tumor cells throughout the bone marrow indicates that the tumor cells are capable of homing and adhering to specific niches that allow growth, survival and drug resistance. In this review we highlight the interaction of the tumor cells in WM and the bone marrow microenvironment including bone marrow stromal cells, endothelial cells and mast cells. Migration, adhesion and downstream activation of signaling pathways leads to cell trafficking and cell dissemination in WM. Future therapeutic agents need to target not only the tumor clone, but also its close interaction with the bone marrow microenvironment.

MYD88 L265P mutation in Waldenstrom macroglobulinemia

Mutation of the MYD88 gene has recently been identified in activated B-cell-like diffuse cell lymphoma and enhanced Janus kinase/signal transducer and activator of transcription (JAK-STAT) and nuclear factor κB (NF-κB) signaling pathways. A whole exome-sequencing study of Waldenstrom macroglobulinemia (WM) suggested a high frequency of MYD88 L265P mutation in WM. The genetic background is not fully deciphered in WM, although the role of NF-κB and JAK-STAT has been demonstrated. We analyzed MYD88 mutation in exon 5 and characterized the clinical significance of this genetic alteration in 67 WM patients. Clinical features; immunophenotypic markers; and conventional cytogenetic, fluorescence in situ hybridization, and single nucleotide polymorphism array data were analyzed. MYD88 L265P mutation was acquired in 79% of patients. Overall, we have identified alteration of the MYD88 locus in 91% of WM patients, including 12% with gain on chromosome 3 at the 3p22 locus that included the MYD88 gene. Patients with absence of MYD88 mutation were WM characterized with a female predominance, a splenomegaly, gain of chromosome 3, and CD27 expression. Importantly, inhibition of MYD88 signaling induced cytotoxicity and inhibited cell growth of cell lines issued from patients with WM. In conclusion, these results confirm a high frequency of MYD88 L265P mutation in WM. The discovery of MYD88 L265P mutation may contribute to a better understanding of the physiopathogeny of WM.

Molecular mechanisms of acquired proteasome inhibitor resistance

The development of proteasome inhibitors (PIs) has transformed the treatment of multiple myeloma and mantle cell lymphoma. To date, two PIs have been FDA approved, the boronate peptide bortezomib and, most recently, the epoxyketone peptide carfilzomib. However, intrinsic and acquired resistance to PIs, for which the underlying mechanisms are poorly understood, may limit their efficacy. In this Perspective, we discuss recent advances in the molecular understanding of PI resistance through acquired bortezomib resistance in human cell lines and evolved salinosporamide A (marizomib) resistance in bacteria. Resistance mechanisms discussed include the up-regulation of proteasome subunits and mutations of the catalytic β-subunits. Additionally, we explore potential strategies to overcome PI resistance.

Carfilzomib and ONX 0912 inhibit cell survival and tumor growth of head and neck cancer and their activities are enhanced by suppression of Mcl-1 or autophagy

PURPOSE

Carfilzomib is a selective, irreversible inhibitor of the chymotrypsin-like activity of the proteasome and is undergoing clinical evaluation in myeloma. ONX 0912 (oprozomib) is an orally bioavailable derivative. The activities of carfilzomib and ONX 0912 against solid tumor malignancies are less well understood. We investigated the impact and mechanisms of action of carfilzomib and ONX 0912 in preclinical models of head and neck squamous cell carcinoma (HNSCC).

EXPERIMENTAL DESIGN

The effects of carfilzomib and ONX 0912 on HNSCC cell survival and xenograft tumor growth were evaluated. The impact and mechanisms of both agents on apoptosis and autophagy induction were also investigated. The contribution of the unfolded protein response (UPR) to autophagy induction and the role of autophagy in attenuating HNSCC cell death were determined.

RESULTS

Carfilzomib and ONX 0912 potently induced apoptosis in HNSCC cell lines via upregulation of pro-apoptotic Bik. Upregulation of Mcl-1 by these agents served to dampen their efficacies. Carfilzomib and ONX 0912 also induced autophagy, mediated, in part, by activation of the UPR pathway involving upregulation of ATF4 transcription factor. Autophagy induction served a prosurvival role. Oral administration of ONX 0912 inhibited the growth of HNSCC xenograft tumors in a dose-dependent manner.

CONCLUSIONS

These results show that carfilzomib and ONX 0912 are potently active against HNSCC cells, and the activities of these agents can be enhanced via suppression of Mcl-1 or inhibition of autophagy. Oral ONX 0912 exhibits in vivo activity against HNSCC tumors and may represent a useful therapeutic agent for this malignancy.