Effects Of Proteasome Inhibitors Research Articles

Cardiac mechanics in response to proteasome inhibition: a prospective study.

Ubiquitin-Proteasome System (UPS) is of paramount importance regarding the function of the myocardial cell. Consistently, inhibition of this system has been found to affect myocardium in experimental models; yet, the clinical impact of UPS inhibition on cardiac function has not been comprehensively examined. Our aim was to gain insight into the effect of proteasome inhibition on myocardial mechanics in humans. We prospectively evaluated 48 patients with multiple myeloma and an indication to receive carfilzomib, an irreversible proteasome inhibitor. All patients were initially evaluated and underwent echocardiography with speckle tracking analysis. Carfilzomib was administered according to Kd treatment protocol. Follow-up echocardiography was performed at the 3rd and 6th month. Proteasome activity (PrA) was measured in peripheral blood mononuclear cells.At 3 months after treatment, we observed early left ventricular (LV) segmental dysfunction and deterioration of left atrial (LA) remodelling, which was sustained and more pronounced than that observed in a cardiotoxicity control group. At 6 months, LV and right ventricular functions were additionally attenuated (P < 0.05 for all). These changes were independent of blood pressure, endothelial function, inflammation, and cardiac injury levels. Changes in PrA were associated with changes in global longitudinal strain (GLS), segmental LV strain, and LA markers (P < 0.05 for all). Finally, baseline GLS < -18% or LA strain rate > 1.71 were associated with null hypertension events. Inhibition of the UPS induced global deterioration of cardiac function.

Abstract 5439: MDM2 inhibitor alrizomadlin (APG-115) stabilizes p53 and synergizes with proteasome inhibitors in multiple myeloma

Abstract Multiple myeloma (MM) accounts for about 2% of all cancers and 18% of all hematologic malignancies in the US. Newly developed treatments (e.g., immunomodulators, proteasome inhibitors, monoclonal antibodies) have significantly improved outcomes, but MM inevitably relapses and is considered incurable. Genomic analysis shows that the TP53 gene encoding tumor suppressor protein p53 is infrequently mutated in patients with MM, of whom about 82% retain wild-type (WT) TP53. Mouse double minute 2 (MDM2) is an E3 ubiquitin ligase that inhibits p53 via proteasome degradation. Proteasome inhibitors might help to stabilize p53 and synergize with MDM2 inhibitors. Therefore, MDM2 inhibitors that activate p53 might constitute an attractive pharmacologic approach to MM. Alrizomadlin (APG-115) is an investigational, new small molecule targeting the p53/MDM2 interaction and is in clinical development for solid and hematologic cancers. This study aimed to evaluate whether alrizomadlin can potentiate the antitumor effects of proteasome inhibitors in MM. In cell-based antiproliferation studies, alrizomadlin demonstrated selective activity against WT TP53 MM cell lines, including MOLP-8, H929, and MM1S, with IC50 values of 0.495 ± 0.132 µM, 0.259 ± 0.251 µM, and 0.325 ± 0.105 µM, respectively. In contrast, alrizomadlin was inactive against TP53-mutant MM cell lines (IC50 &amp;gt;10 µM). In MM cell lines, APG-115 exhibited synergistic activity with anti-MM agents (e.g., carfilzomib, lenalidomide, melphalan, selinexor) and other targeted agents (e.g., panobinostat, bromodomain inhibitor OTX-015, tumor necrosis factor-related apoptotic-inducing ligand). In vivo studies showed that coadministration of alrizomadlin with proteasome inhibitor bortezomib or carfilzomib enhanced tumor regression (vs. single agents) in H929 xenograft models. As to mechanism, alrizomadlin likely disrupts MDM2/p53 interactions and induces accumulation of p53, MDM2, and downstream proteins 4 hours after treatment. The proteasome inhibitors induced dose-related increases in p53 protein expression 24 hours after treatment. The combination of carfilzomib with alrizomadlin further promoted accumulation of p53 and MDM2 and increased phosphorylation of p53. As a transcription factor, p53: (1) activated expression of p21 to cause cell cycle arrest (2) augmented downstream BCL-2-associated X protein (BAX) and p53-upregulated modulator of apoptosis (PUMA), (3) increased cleavage of caspase-3 and poly [ADP-ribose] polymerase 1 (PARP-1; hallmarks of apoptosis), and (4) increased apoptosis and associated antitumor effects. In conclusion, our results demonstrate that the combination of MDM2 inhibitor APG-115 and proteasome inhibitors have synergistic antitumor effects on MM tumors harboring WT TP53. These data lay a foundation for clinical trials of a new and novel therapeutic option for patients with refractory MM. Citation Format: Guangfeng Wang, Eric Liang, Chunyang Tang, Li Rui, Ping Min, Jing Lv, Yangfeng Ge, Fei Zhang, Lvcheng Wang, Jingjin Shang, Dajun Yang, Yifan Zhai. MDM2 inhibitor alrizomadlin (APG-115) stabilizes p53 and synergizes with proteasome inhibitors in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5439.

The anti-tumor effect of proteasome inhibitor MG132 for human adenoid cystic carcinoma: correlate with the emerging role of Nrf2/Keap1 signaling pathway.

BackgroundAdenoid cystic carcinoma (ACC) is one of the most common malignant salivary gland tumors. Moreover, the unique biological characteristics and complex structures of ACC contribute to its poor survival rates. Recently, proteasome inhibitors have been shown to elicit satisfactory therapeutic effects in the treatment of certain solid tumors, but few studies have been implemented to investigate the effects of proteasome inhibitor therapy for ACC.MethodsIn this present study, cell counting kit-8 assay and flow cytometry assay were performed to examine the effects of proteasome inhibitor (MG132) on cell viability and apoptosis. We applied western blot and immunofluorescence staining to explore the expression of the Nrf2/Keap1 signaling pathway and P62, additionally Nrf2 inhibitor (ML385) was utilized to evaluate the role of Nrf2/Keap1 signaling pathway in MG132-induced cell apoptosis.ResultsOur data indicated that MG132 significantly suppressed the growth of ACC-83 cells(MG132 10µM P = 0.0046; 40µM P = 0.0033; 70µM P = 0.0007 versus control) and induced apoptosis (MG132 10µM P = 0.0458; 40µM P = 0.0018; 70µM P = 0.0087 versus control). The application of MG132 induced the up-regulation of Nrf2/Keap1 signaling pathway. Furthermore, inhibition of Nrf2 attenuated the therapeutic effects of MG132 for ACC (both ML385 + MG132 10µM P = 0.0013; 40µM P = 0.0057; 70µM P = 0.0003 versus MG132). P < 0.05 was considered statistically significant.ConclusionsOur results revealed that proteasome inhibitors MG132 could inhibit the cell viability and induce the apoptosis of ACC through Nrf2/Keap1 signaling pathway.

Proteasome inhibition alters mitotic progression through the upregulation of centromeric α-Satellite RNAs.

Cell cycle progression requires control of the abundance of several proteins and RNAs over space and time to properly transit from one phase to the next and to ensure faithful genomic inheritance in daughter cells. The proteasome, the main protein degradation system of the cell, facilitates the establishment of a proteome specific to each phase of the cell cycle. Its activity also strongly influences transcription. Here, we detected the upregulation of repetitive RNAs upon proteasome inhibition in human cancer cells using RNA‐seq. The effect of proteasome inhibition on centromeres was remarkable, especially on α‐Satellite RNAs. We showed that α‐Satellite RNAs fluctuate along the cell cycle and interact with members of the cohesin ring, suggesting that these transcripts may take part in the regulation of mitotic progression. Next, we forced exogenous overexpression and used gapmer oligonucleotide targeting to demonstrate that α‐Sat RNAs have regulatory roles in mitosis. Finally, we explored the transcriptional regulation of α‐Satellite DNA. Through in silico analyses, we detected the presence of CCAAT transcription factor‐binding motifs within α‐Satellite centromeric arrays. Using high‐resolution three‐dimensional immuno‐FISH and ChIP‐qPCR, we showed an association between the α‐Satellite upregulation and the recruitment of the transcription factor NFY‐A to the centromere upon MG132‐induced proteasome inhibition. Together, our results show that the proteasome controls α‐Satellite RNAs associated with the regulation of mitosis.

Global deterioration of cardiovascular mechanics by carfilzomib treatment is associated with proteasome activity in patients with relapsed multiple myeloma

Abstract Background Carfilzomib (CFZ) is a second generation irreversible proteasome inhibitor that has been shown to improve overall survival in patients with relapsed or refractory multiple myeloma (MM) but is associated with cardiac toxicity in MM. Because ubiquitin-proteasome system (UPS) is involved in cardiovascular homeostasis exploring the effects of proteasome inhibition on cardiac mechanics, in a clinical setting, would provide novel insight of the clinical role of UPS in cardiovascular disease. Aim To gain a thorough understanding of proteasome inhibition on myocardial mechanics in a clinical setting. Methods We prospectively evaluated 48 patients with relapsed or refractory MM and an indication to receive CFZ treatment [median age: 67.5, interquartile range (64–73), 66.7% men]. All patients underwent cardiac ultrasonography at an initial visit, at the first day of the 3rd month (C3D1, n=25) and at the last day of cycle 6 (C6D16, n=48). Pulse wave velocity (PWV) was used to assess arterial stiffness and calculate arterial-ventricular coupling (VAC) by the ratio (PWV/global longitudinal strain (GLS)). Carfilzomib was administered at 27mg/m2 on days 1 (C1D1) and 2 (C1D2) of cycle 1 and at 56mg/m2 thereafter. Blood was drawn at baseline, C3D1 and C6D16 to measure proteasome activity (PrA). Patients were followed up for carfilzomib–related cardiovascular adverse events. Results Regarding systolic function, between baseline and C6D16, we noticed deterioration in left ventricular ejection fraction (LVEF) (57.7±5.4% vs 56.1±7.19%, p=0.022), GLS (−20.51±2.78 vs −18.88±3.45%, p=0.003), S wave of LV longitudinal strain rate and radial strain (p&amp;lt;0.05 for both). Markers of LV diastolic function also deteriorated at 6 months including early diastolic (Ea) mitral annular velocity (7.27±1.83cm/sec vs 6.7±1.64cm/sec, p=0.008) and E wave of LV longitudinal strain rate (1.1±0.37sec-1 vs 0.95±0.36sec-1, p=0.010). Left atrial volume (LAV) and index (LAVi) increased both at 3 and 6 months (p&amp;lt;0.05). Peak LA strain at reservoir phase (peak atrial longitudinal strain, PALS) was also decreased at 6th and 3rd month measurements (p&amp;lt;0.05), whereas LA strain rate at reservoir function (s wave) was decreased, compared to baseline, only at 6th month (p=0.001). RV longitudinal strain also decreased between 3rd and 6th month (p=0.039). Furthermore, PWV/GLS also deteriorated at 6 months (−0.56±0.13 vs −0.64±0.21, p=0.001). By linear mixed models analysis, we found that changes in proteasome activity were associated with changes in PWV/GLS (p=0.017), LAV (p=0.015) and LAVi (p=0.009), and PALS (p=0.014). Conclusion CFZ treatment was associated with global deterioration of markers of myocardial systolic and diastolic function and VAC. The observed association of changes in proteasome activity with VAC and left atrial function and structure supports a direct effect of proteasome inhibition on the cross-talk between LV and arterial function and LV diastolic function. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): Amgen

Out of Control: The Role of the Ubiquitin Proteasome System in Skeletal Muscle during Inflammation.

The majority of critically ill intensive care unit (ICU) patients with severe sepsis develop ICU-acquired weakness (ICUAW) characterized by loss of muscle mass, reduction in myofiber size and decreased muscle strength leading to persisting physical impairment. This phenotype results from a dysregulated protein homeostasis with increased protein degradation and decreased protein synthesis, eventually causing a decrease in muscle structural proteins. The ubiquitin proteasome system (UPS) is the predominant protein-degrading system in muscle that is activated during diverse muscle atrophy conditions, e.g., inflammation. The specificity of UPS-mediated protein degradation is assured by E3 ubiquitin ligases, such as atrogin-1 and MuRF1, which target structural and contractile proteins, proteins involved in energy metabolism and transcription factors for UPS-dependent degradation. Although the regulation of activity and function of E3 ubiquitin ligases in inflammation-induced muscle atrophy is well perceived, the contribution of the proteasome to muscle atrophy during inflammation is still elusive. During inflammation, a shift from standard- to immunoproteasome was described; however, to which extent this contributes to muscle wasting and whether this changes targeting of specific muscular proteins is not well described. This review summarizes the function of the main proinflammatory cytokines and acute phase response proteins and their signaling pathways in inflammation-induced muscle atrophy with a focus on UPS-mediated protein degradation in muscle during sepsis. The regulation and target-specificity of the main E3 ubiquitin ligases in muscle atrophy and their mode of action on myofibrillar proteins will be reported. The function of the standard- and immunoproteasome in inflammation-induced muscle atrophy will be described and the effects of proteasome-inhibitors as treatment strategies will be discussed.

High Expression of MEF2D-Fusion Protein Is Caused By Escaping from the Suppression By miRNA and Leads to Suppress Transcriptional Activity of PAX5

We previously discovered new fusion genes, MEF2D-BCL9 and MEF2D-HNRNPUL1, in 9% of adolescent and young adult B-cell acute lymphoblastic leukemia (ALL; Yasuda T, et al. , Nature Genetics, 2016;48:569-574). Vector driving expression of MEF2D-fusion protein was markedly higher than the expression of wild-type MEF2D (MEF2D W) protein driven by the same expression vector system; however, the mechanism and significance of the high-expression have been yet to be clarified.We first confirmed fusion specific MEF2D high expression was occurred in MEF2D fusion-positive ALL cell lines, Kasumi-7 and Kasumi-9. Protein half-life and the effect of proteasome inhibitor on protein expression were not significantly different between MEF2D W and MEF2D-fusion, suggesting that stability of protein was not different between them. We speculated that MEF2D fusion gene lost the miRNA target that existed in C-terminal half of MEF2D mRNA and that the high-expression of MEF2D fusion protein was caused by escaping from the suppression by miRNA (Figure A). In order to investigate this speculation, we made several expression vectors of MEF2D that express same partial MEF2D protein but transcript different length of mRNA. That is, we introduced a mutation substituting stop codon for D336, the breakpoint of MEF2D-HNRNPUL1 fusion protein, into the expression vector of wild-type MEF2D and designated it as MEF2D (full D336Stop). We deleted C-terminal legion from it with various lengths (Figure B). The protein expression level of MEF2D (1-335) from MEF2D (full D336Stop) vector was similar to that of MEF2D W; however, the protein expression level was markedly increased when DNA region coding amino acid (aa) 377-418 was deleted from the expression vector (Figure C), indicating that protein expression of MEF2D (1-335) was down regulated by miRNA targeting mRNA coding aa 377-418. We identified a candidate of responsible miRNA by database search. Transfection of miRNA mimic of the candidate miRNA decreased the protein expression of MEF2D W but not that of MEF2D fusion. Introduction of mutation at the binding site of the candidate miRNA increased the protein expression of MEF2D W. We examined the effect of MEF2D fusion protein on transcriptional activity of various B cell differentiation regulators and found that MEF2D-fusion protein suppressed transcriptional activity of PAX5 in luciferase assays in dose-dependent manner and that MEF2D W protein did not significantly affect it. These results suggested that the high-expression of MEF2D fusion protein impaired B cell differentiation through the inhibition of PAX5 function. This is the first report that a mutation of a coding gene causes high expression of the protein coded by the gene through escape from suppression by miRNA. These results shed a new insight into the mechanism of leukemia development by MEF2D fusion gene and pathological significance of miRNA-related disorder. [Display omitted] DisclosuresNaoe:Otsuka Pharmaceutical Co.,Ltd.: Honoraria, Research Funding; Nippon Boehringer Ingelheim Co.: Honoraria, Research Funding; Fujifilm Corporation: Patents & Royalties, Research Funding; Dainippon Sumitomo Pharma Co.,LTD.: Research Funding; Astellas Pharma Inc.: Research Funding; Toyama Chemikal Co.,Ltd.: Research Funding. Kiyoi:Bristol-Myers Squibb: Honoraria, Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; Meiji Seika Pharma Co.,Ltd.: Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; MSD K.K.: Research Funding; Celgene Corporation: Consultancy, Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Nippon Boehringer Ingelheim Co., Ltd.: Research Funding; Astellas Pharma Inc.: Consultancy, Research Funding; JCR Pharmaceuticals Co.,Ltd.: Research Funding; Novartis Pharma K.K.: Research Funding; FUJIFILM Corporation: Patents & Royalties, Research Funding; ONO Pharmaceutical Co., Ltd.: Research Funding; Phizer Japan Inc.: Honoraria, Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding.

Pre-Clinical Development of Targeted Therapies for Double Hit (DH) Diffuse Large B-Cell Lymphoma (DLBCL)

Background: Gene expression profile classifies DLBCL into three subtypes with distinct pathogenesis and clinical outcomes: activated B-cell (ABC), germinal center B-cell (GCB) and primary mediastinal B-cell lymphoma (PMBL). DH-DLBCL is a distinct subgroup, with a poor clinical outcome, harboring concurrent gene translocations involving the C-MYC and either/both BCL2 or BCL6 proto-oncogenes. DH-DLBCL has inferior response rates to rituximab-based chemotherapy, and a shorter progression-free survival (PFS)/overall survival (OS). In addition, pts with DH-DLBCL who are refractory to frontline chemoimmunotherapy fare dismally; a retrospective review at our institute yielded survival rates of zero and median OS of 6 months in these patients, highlighting the need for novel therapies. DH-DLBCL is characterized by de-regulation of apoptosis and cell cycle progression, leading to rapid proliferation of neoplastic cells, and resistance to apoptotic stimuli. Upregulation of the anti-apoptotic protein Mcl-1 is implicated in chemotherapy resistance and poor clinical outcomes in ABC-DLBCL. Transcriptional regulation of MCL1 by c-MYC might further potentiate Mcl-1 induced resistance to chemotherapy in DH-DLBCL. Specific inhibitors targeting cell pro-survival proteins might provide a novel and alternative therapeutic approach in rituximab-chemotherapy resistant DH-DLBCL. We hypothesize that dual inhibition of anti-apoptotic proteins Bcl-2 and Mcl-1 using readily available agents (Venetoclax and Proteasome inhibitors) is an effective strategy in inducing lymphoma cell death. Materials and Methods: We conducted pre-clinical in vitro and in vivo models targeting Bcl-2 with Venetoclax and Mcl-1 with either a c-Myc inhibitor (JQ-1) or Proteasome inhibitor (Carfilzomib) in DHL. Val, DOHH-2, and ROS-50 cells were exposed to Venetoclax (0-10 uM), JQ-1 (0-100 uM) and Carfilzomib (CFZ) (0-50 nM) for 24, 48 and 72 hours. IC50 drug concentrations were calculated for each agent. Subsequently, DHL cells were exposed to Venetoclax in combination with JQ-1 or CFZ for 48 hours. Cell viability was determined by Cell Titerglo. Coefficient of synergy was calculated using CalcuSyn. In addition, induction of apoptosis was evaluated by flow cytometry (Annexin V/PI staining) and changes in Bcl-2 family members and Caspase activation were determined by Western blotting. Primary tumor cells isolated from B-cell lymphoma patients (N= 15) including DHL were exposed ex vivo to Venetoclax +/- Carfilzomib. For in vivo experiments 6-8 weeks old severe combined immunodeficiency (SCID) mice were inoculated with 10x106 ROS-50 cells via tail vein injection (IV). Subsequently, animals were treated with Venetoclax (100mg/kg/dose via gastric lavage on days 3-7 and 10-14); Carfilzomib (2mg/kg/dose IV days 3, 4, 10, 11), or both agents. A group of untreated animals was used as a control. Differences in survival were evaluated between treatment groups. Results: In vitro, Venetoclax, JQ-1, and CFZ induced cell death in a dose- and time-dependent manner. Significant synergistic activity was observed by combining both Venetoclax and CFZ and to a lesser degree with JQ-1. Similar findings were observed in primary tumor cells isolated from B-cell lymphoma patients. Annexin/PI staining with the combination of Venetoclax and CFZ resulted in caspase dependent apoptosis. Western blotting confirmed changes in Bcl-2 family members favoring an apoptotic state as well as PARP cleavage following in vitro exposure to Venetoclax and CFZ. In vivo the combination of Venetoclax with Carfilzomib resulted in significant increased survival increase (P<0.05) when compared to single agent Venetoclax or CFZ. Conclusion: Our data suggests that Venetoclax exhibits strong synergistic activity with Carfilzomib in vitro and in vivo . Perhaps related to the synergy observed between Venetoclax and CFZ, is the effects of proteasome inhibition on Mcl-1 levels. Combination therapy targeting the proteasome inhibition and BCL-2 may provide an alternative therapeutic approach in DH-DLBCL. DisclosuresNo relevant conflicts of interest to declare.

Effect of Proteasome Inhibitors and/or Immunomodulatory Drugs on the Risk of Early Death of 991 Newly Diagnosed Symptomatic Multiple Myeloma Patients: A Single Centre Retrospective Analysis

Introduction and aim : Several clinical trials have shown that the incorporation of novel agents (i.e., proteasome inhibitor, bortezomib and immunomodulatory drugs, thalidomide and lenalidomide) in the treatment of newly diagnosed symptomatic multiple myeloma (MM) patients improves their time to first response and survival outcomes. Nevertheless, some patients still die within 3 months (early death, ED) from starting treatment. Thus, we investigated the effect of novel agents- containing first line treatments on the risk of ED of MM patients.Study design : retrospective analysis of a cohort of 991 newly diagnosed symptomatic MM patients consecutively treated at a single Institution from 1997 until 2015 at the Hematology Division of the Ospedale Papa Giovanni XXIII (formerly, Ospedali Riuniti) of Bergamo, Italy.Results : during the entire period of analysis (18 years), 708 patients (71.4%) died. They were 374 men and 334 women, aged 25-94 years (median 68 years). Types of MM were: IgG (n=357), IgA (n=138), light chain (n=125), plasmacytoma (n=23), non-secretory (n=16), plasma cell leukemia (n=11), IgD (n=6), IgM (n=4), unknown (n=28). Durie and Salmon clinical stages were: I (n=75), II (n=111), III (n=479), unknown (n=43). A/B stages were: A (n=518, 73%), B (n=147, 21%), unknown (n=43, 2%). Treatments were as follows: conventional chemotherapy (CC) (n=255, 36%), CC + autotransplantation (ASCT) (n=150, 21%), novel agents (n=181, 26%), novel agents + ASCT (n=122, 17%). Ninety-two patients (9.3%) experienced an early death (ED cohort) and the other 616 patients died > 90 days from starting treatment (late death, LD, cohort) (91.7%). Univariate and multivariate analysis (Table) showed that patients in the ED cohort were significantly older and had more commonly stage B MM compared to patients in the LD cohort. Incorporation of at least a novel agent in the first line treatment resulted in a significant reduction of ED. This beneficial effect was only seen in patients not enrolled in ASCT programs (p<0.001, Odds Ratio, OR, 0.37, 95% Confidence Interval, CI, 0.20-0.69 and p=0.009, OR 0.42, 95%CI 0.22-0.81, by univariate and multivariate analysis, respectively). Progression of MM was the cause of all ED events. Only one patient in the ED cohort started a second line of treatment.Conclusions : Administration of first line regimens containing at least a novel agent significantly reduced the ED rate of patients with MM. Particularly, this improved survival was beneficial in patients not enrolled in ASCT programs. [Display omitted] DisclosuresRambaldi:Novartis, Amgen, Celgene, Sanofi: Other: Travel, Accomodations, Expenses; Novartis, Roche/Genentech, Amgen, Italfarmaco: Consultancy.

Targeting phosphoinositide 3-kinases and histone deacetylases in multiple myeloma

BackgroundMultiple myeloma (MM) is a type of hematological malignancy affecting the functions of plasma cells. The treatment of MM patients has changed dramatically with the use of new agents. However, unfortunately, it is still incurable. Therefore, a new approach for treating MM is still needed to improve patient outcomes.MethodsBecause the histone deacetylase (HDAC) and phosphoinositide 3-kinase (PI3K) pathway is a key signal in cancer cell biology, we investigated whether dual HDAC and PI3K inhibitors could suppress the myeloma cells.ResultsGene expression of HDACs is high in myeloma cells. CUDC-907, a dual inhibitor of PI3K and HDAC, inhibits HDAC activity. Akt activity and expression of BCL-XL, MCL-1, and NF-κB p65 were reduced by CUDC-907 in a dose-dependent manner. The number of apoptotic and caspase 3/7-positive cells also increased in the myeloma cells. Combined treatment of myeloma cells with carfilzomib and CUDC-907 increased cytotoxicity compared to that observed with each drug alone.ConclusionsData from this study suggested that the administration of CUDC-907 might be a powerful strategy against myeloma cells, to enhance the cytotoxic effects of proteasome inhibitors.

Proteasome inhibition creates a chromatin landscape favorable to RNA Pol II processivity.

Proteasome activity is required for diverse cellular processes, including transcriptional and epigenetic regulation. However, inhibiting proteasome activity can lead to an increase in transcriptional output that is correlated with enriched levels of trimethyl H3K4 and phosphorylated forms of RNA polymerase (Pol) II at the promoter and gene body. Here, we perform gene expression analysis and ChIP followed by sequencing (ChIP-seq) in MCF-7 breast cancer cells treated with the proteasome inhibitor MG132, and we further explore genome-wide effects of proteasome inhibition on the chromatin state and RNA Pol II transcription. Analysis of gene expression programs and chromatin architecture reveals that chemically inhibiting proteasome activity creates a distinct chromatin state, defined by spreading of the H3K4me3 mark into the gene bodies of differentially-expressed genes. The distinct H3K4me3 chromatin profile and hyperacetylated nucleosomes at transcription start sites establish a chromatin landscape that facilitates recruitment of Ser-5- and Ser-2-phosphorylated RNA Pol II. Subsequent transcriptional events result in diverse gene expression changes. Alterations of H3K36me3 levels in the gene body reflect productive RNA Pol II elongation of transcripts of genes that are induced, underscoring the requirement for proteasome activity at multiple phases of the transcriptional cycle. Finally, by integrating genomics data and pathway analysis, we find that the differential effects of proteasome inhibition on the chromatin state modulate genes that are fundamental for cancer cell survival. Together, our results uncover underappreciated downstream effects of proteasome inhibitors that may underlie targeting of distinct chromatin states and key steps of RNA Pol II-mediated transcription in cancer cells.

Targeting the p62-ZZ/N-End Rule Pathway in Multiple Myeloma Overcomes Proteasome Inhibitor-Resistance Via Induction of Necroptosis and Enhances the Bone Anabolic Effects of Proteasome Inhibitors

Multiple myeloma (MM) is incurable and 80% of MM patients develop MM bone disease (MMBD). MMBD lesions do not heal due to the persistent suppression of bone formation, which markedly increases mortality and contributes to MM drug resistance. Current treatments for MMBD, such as bisphosphonates and denosumab, target bone destruction but do not result in new bone formation. Although proteasome inhibitors (PIs) have greatly improved survival of MM patients, they only have transient bone anabolic effects. Further, development of drug resistance to PIs remains a major clinical problem. We previously showed that the ZZ domain of p62 (sequestosome-1),plays an important role in both MM growth and suppression of osteoblast (OB) differentiation in the MM microenvironment, by regulating multiple signaling pathways and acting as a cargo-receptor for autophagy. Recently, our collaborators showed that the p62-ZZ is a high-affinity N-recognin of the N-end rule pathway (NERP). p62-ZZ also serves as the molecular switch for necroptotic versus apoptotic cell death pathways. We previously reported that MM cells or TNFα prevent OB differentiation by inducing persistent epigenetic repression of the Runx2-P1 promoter in MM patient bone marrow stromal cells (BMSCs), via the transcriptional repressor Gfi1. We found that blocking p62-ZZ by saturating it with a novel synthetic p62-ZZ/NERP competing ligand, XRK3F2, prevented and reversed MM-induced Gfi1 occupancy at the Runx2-P1 promoter, allowing BMSCs to increase OB marker gene expression and to mineralize. These results suggest that targeting the p62-ZZ/N-end rule pathway would enhance the bone anabolic effects of PIs. To test this hypothesis, we first exposed normal OBs to different doses of bortezomib (Btz) or XRK3F2 or their combination. The combination significantly increased OB differentiation markers Runx2 (60%), Osterix (20%) and ATF4 (60%), and induced mineral deposition compared with either drug alone. The combination also blocked TNFα up-regulation of Gfi1 and suppression of OB differentiation. Interestingly, none of the concentrations tested decreased OB viability. Studies with MM patient-BMSCs showed that XRK3F2 reversed suppression of OB differentiation induced by MM cells, allowing them to mineralize. Importantly, our preliminary in vivo data showed that administration of XRK3F2 to mice with established MM induced dramatic cortical bone formation in MM-containing bones but had no effect on tumor burden. We and others previously showed that MM cells subjected to sustained proteasomal inhibition, rely on p62-mediated autophagic degradation to reduce the proteotoxic load caused by excessive immunoglobulin synthesis. We recently found that targeting the p62-ZZ domain in human MM cells, increases Btz-induced MM cell death, independently of their p53 status. The combination also significantly reduced cell viability in Btz resistant cells although no caspase 3 activation was observed, suggesting a caspase-3 independent cell death. To determine the mechanism(s) responsible for MM cell death induced by the combination, we pretreated MM cell lines and primary CD138+ MM cells with Z-DEVD (20μM), bafilomycin (Baf, 40nM), or necrostatin1 (NEC1, 50μM). The anti-MM effects of XRK3F2 or Btz+XRK3F2 were fully blocked by NEC1, an inhibitor of necroptosis, but not by inhibitors of caspase-dependent apoptosis (Z-DEVD) or autophagy (Baf), supporting that p62-ZZ regulates necroptosis in MM cells. RNAseq analysis of the additive effect of Btz+XRK3F2 on gene expression showed a total of 583 differentially regulated genes, including 374 significantly down-regulated and 209 significantly upregulated. GO term analysis of up-regulated DEGs identified an enrichment in the endoplasmic reticulum (ER) stress and ER unfolded protein response, and regulation of transcription in response to stress and autophagy. In summary, our results demonstrate that targeting the p62-ZZ/N-end rule pathway in combination with PIs in MM significantly reduces MM cell viability by activating multiple death pathway and overcomes PI-resistance of MM cells. In addition, targeting the p62-ZZ in OBs potentiates the bone anabolic action of PIs and reverses the persistent OB suppression induced by MM cells to allow bone formation. Thus, p62-ZZ plays a critical role in MM and bone cells and identifies p62-ZZ as an important molecular target for the treatment of MMBD. Disclosures Xie: Oxis Biotech: Consultancy; ID4Pharma: Other: Founder. Roodman:Amgen: Membership on an entity's Board of Directors or advisory committees.

Abstract 3863: Specifically targeting PDIA1 with indene inhibitors leads to bortezomib-potentiation in multiple myeloma

Abstract Protein disulfide isomerase (PDI) is an emerging therapeutic target in oncology. PDI inhibitors have demonstrated a unique propensity to overcome resistance to existing cancer therapies, although drug candidates have not yet progressed to the stage of clinical development. We recently reported the discovery of lead indene compound E64FC26 as a potent pan-PDI inhibitor that enhances the cytotoxic effects of proteasome inhibitors (PIs) in panels of Multiple Myeloma (MM) cells and MM mouse models [1]. An extensive medicinal chemistry program has led to the generation of a diverse library of indene-containing molecules with varying degrees of PI-potentiating activity. The results show detailed structure activity relationships (SAR) with a high degree of correlation between potency of PDIA1 inhibition and bortezomib (Btz) potentiation in MM cells. Inhibition of PDIA1 in MM leads to ER and oxidative stress characterized by the accumulation of misfolded poly-ubiquitinated proteins and the induction of UPR biomarkers ATF4, CHOP, and Nrf2. Furthermore, an advanced derivative, E64FC65, was identified as a PDIA1 selective inhibitor as it was significantly weaker against PDIA3, PDIA4, TXNDC5, PDIA6, and thioredoxin when compared to E64FC26 (Table 1). We purified the redox-active a and a’ thioredoxin-like domains of PDI and found that E64FC65 only inhibited the a domain while E64FC26 inhibited both a and a’ domains. The PDI isoform and domain selectivity of E64FC65 imparted increased anti-cancer activity while reducing toxicity against primary activated human T-cells. Additionally, E64FC65 exhibited improved pharmaceutical properties in ADME assays. This work shows the generation of a PDIA1 a domain specific indene inhibitor that potentiates Btz cytotoxicity in MM cells while abrogating toxicity in normal cells. E64FC65 is thus a favorable PDI inhibitor candidate for further development. Citation Format: Reeder M. Robinson, Leticia Reyes, Ravyn Duncan, Nathan Dolloff. Specifically targeting PDIA1 with indene inhibitors leads to bortezomib-potentiation in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3863.

The Effects of Proteasome Inhibitors on Telomerase Activity and Regulation in Multiple Myeloma Cells.

The importance of telomerase, the enzyme that maintains telomere length, has been reported in many malignancies in general and in multiple myeloma (MM) in particular. Proteasome inhibitors are clinically used to combat effectively MM. Since the mechanism of action of proteasome inhibitors has not been fully described we sought to clarify its potential effect on telomerase activity (TA) in MM cells. Previously we showed that the first generation proteasome inhibitor bortezomib (Brt) inhibits TA in MM cells by both transcriptional and post-translational mechanisms and has a potential clinical significance. In the current study we focused around the anti- telomerase activity of the new generation of proteasome inhibitors, epoxomicin (EP) and MG-132 in order to clarify whether telomerase inhibition represents a class effect. We have exposed MM cell lines, ARP-1, CAG, RPMI 8226 and U266 to EP or MG and the following parameters were assessed: viability; TA, hTERT expression, the binding of hTERT (human telomerase reverse transcriptase) transcription factors and post-translational modifications. Epoxomicin and MG-132 differentially downregulated the proliferation and TA in all MM cell lines. The downregulation of TA and the expression of hTERT were faster in CAG than in ARP-1 cells. Epoxomicin was more potent than MG-132 and therefore further mechanistic studies were performed using this compound. The inhibition of TA was mainly transcriptionally regulated. The binding of three positive regulator transcription factors: SP1, c-Myc and NF-κB to the hTERT promoter was decreased by EP in CAG cells as well as their total cellular expression. In ARP-1 cells the SP1 and c-MYC binding and protein levels were similarly affected by EP while NF-κB was not affected. Interestingly, the transcription factor WT-1 (Wilms’ tumor-1) exhibited an increased binding to the hTERT promoter while its total cellular amount remained unchanged. Our results combined with our previous study of bortezomib define telomerase as a general target for proteasome inhibitors. The inhibitory effect of TA is exerted by several regulatory levels, transcriptional and post translational. SP1, C-Myc and NF-κB were involved in mediating these effects. A novel finding of this study is the role of WT-1 in the regulation of telomerase which appears as a negative regulator of hTERT expression. The results of this study may contribute to future development of telomerase inhibition as a therapeutic modality in MM.

Effects of proteasome inhibitors on cytokines, metalloproteinases and their inhibitors and collagen type-I expression in periprosthetic tissues and fibroblasts from loose arthroplasty endoprostheses

ABSTRACTObjective: Aseptic loosening is a major problem in total joint replacement. Implant wear debris provokes a foreign body host response and activates cells to produce a variety of mediators and ROS, leading to periprosthetic osteolysis. Elevated ROS levels can harm proteasome function. Proteasome inhibitors have been reported to alter the secretory profile of cells involved in inflammation and also to induce ROS production. In this work, we aimed to document the effects of proteasome inhibitors MG-132 and Epoxomicin, on the production of factors involved in aseptic loosening, in periprosthetic tissues and fibroblasts, and investigate the role of proteasome impairment in periprosthetic osteolysis.Materials and methods: IL-6 levels in tissue cultures were determined by sandwich ELISA. MMP-1, -3, -13, -14 and TIMP-1 levels in tissue or cell cultures were determined by indirect ELISA. Results for MMP-1 and TIMP-1 in tissue cultures were confirmed by Western blotting. MMP-2 and MMP-9 levels were determined by gelatin zymography. Gene expression of IL-6, MMP-1,-3,-14, TIMP-1 and collagen type-I was determined by RT-PCR.Results: Results show that proteasome inhibition induces the expression of ΜΜΡ-1, -2, -3, -9 and suppresses that of IL-6, MMP-14, -13, TIMP-1 and collagen type I, enhancing the collagenolytic and gelatinolytic activity already present in periprosthetic tissues, as documented in various studies.Conclusions: These findings suggest that proteasome impairment could be a contributing factor to aseptic loosening. Protection and enhancement of proteasome efficacy could thus be considered as an alternative strategy toward disease treatment.

Regulation of expression of SG2NA isoforms in human cancer cell lines

The Striatin family members (Striatin, SG2NA and Zinedin) have characteristic protein‐protein interaction domains as a caveolin‐binding domain, a coiled‐coil motif and a calmodulin‐binding domain at its N‐terminus and WD40 domain at carboxyl end. SG2NA was first reported in Lung and Bladder cancer patient serum as a Nuclear Autoantigen and its expression was found to be up regulated during the S and G2 phase of cell cycle. Mouse SG2NA generates five isoforms (87, 82, 78, 52 and 35kDas) by alternative splicing, intron retention and RNA editing. SG2NA isoforms are differentially expressed in mouse tissues viz., brain, heart, lung, liver and skeletal muscle. Besides alternative splicing and polyadenylation, sg2na expression is also regulated by post‐translational stability as its dephosphorylated form is more stable than the phosphorylated form. Further its role in Cancer progression and survival was established by its knockdown study. In the present study two splice variants (78 kDa and 87 kDa) of human sg2na were characterized. Further the expression of SG2NA isoforms in different human cancer cell lines (HEK293T, A549, H1299, HepG2, Hep3B, DU145, HELA) were assessed at the protein and RNA level which shows dyanamic expression. The expression of SG2NA isoforms varies among different cancer cell lines. In case of human cancer cell lines the expression of larger isoform i.e. 87 kDa was prominent unlike mouse which suggests that this SG2NA isoform in human is not undergoing proteasomal degradation. The ambiguity between mRNA and protein level in different cancer cell lines indicate its regulation at the post‐transcriptional or post‐translation level. There was no effect of proteasome inhibition on the stability of SG2NA in all the cells tested. The post‐transcriptional regulation study of SG2NA in different cancer cell lines would be a useful to show its expression and role in cancer progression.Support or Funding InformationDBT‐BUILDER, Government of India, awarded to the Jawaharlal Nehru University.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of Proteasome Inhibition in the Anti-Tumor Activity of Venetoclax in Mantle Cell Lymphoma Pre-Clinical Models

Background: At the molecular level, mantle cell lymphoma (MCL) is characterized by the deregulation of Bcl-2 family members (Mcl-1, BIM) and cell cycle (cyclin D1) regulatory proteins. Perhaps related to this, the clinical outcome of MCL continues to be poor specially for those patients with disease progression after high dose chemotherapy and autologous stem cell rescue and/or BTK inhibitors, stressing the need to develop novel therapeutic strategies or optimize current available options. Venetoclax (V), a highly selective Bcl-2 inhibitor, has shown modest activity against relapsed/refractory MCL. Over-expression of Mcl-1 has been postulated to be a mechanism of resistance to V limiting its anti-tumor activity in subtypes of lymphoma including MCL. The lethality by proteasome inhibitors (PIs) has been associated with changes in the Bcl-2 family members (Bax, Noxa, Mcl-1 and Bcl-XL) in lymphoma pre-clinical models, making them ideal agents to combine with V. To this end, we studied the anti-tumor activity of combining PIs with V in MCL pre-clinical models. Materials and Methods: A panel cytarabine sensitive (Rec-1, Jeko, Granta, HBL-2, Z-138 and Mino) and resistant (araC) cell lines (Jeko araC, HBL-2 araC, and Mino araC) were exposed to V, Bortezomib (BTZ), carfilzomib (CFZ), or ixazomib (IXZ) for 24, 48 and 72 hours. Cell viability was calculated measuring the ATP content. IC50 drug concentrations were calculated for each agent. Subsequently, MCL cell lines were exposed to escalating doses of V (0.001uM-5uM) and CFZ (1.5625nM-50nM), BTZ (3.125nM-100nM) or IXZ (3.125nM-100nM). In addition, primary tumor cells isolated from B-cell lymphoma patients (N=21) including MCL patients were exposed to V +/- BTZ or CFZ for 48 hrs. Cell viability was determined by Cell Titerglo. Coefficient of synergy were calculated using CalcuSyn software program. Induction of apoptosis was detected by Annexin V/Propidium iodine staining and PARP cleavage. Changes in Bcl-2 and cell cycle regulatory proteins were evaluated by Western blotting in HBL-2 cells. For in vivo experiments, 6-8 weeks old severe combined immunodeficiency (SCID) mice were inoculated with 10x106 HBL-2 cells via tail vein injection (IV). Subsequently, SCID mice were treated with V (100mg/kg/dose via gastric lavage on days 3-7, 10-14 and 17-21) or IXZ (6mg/kg/dose IV days 3, 6, 10, 13, 17 and 20) or combination of both agents. A group of untreated animals was used as a control. Differences in survival were evaluated between treatment groups. Results: In vitro exposure of MCL cell lines to either V, BTZ, CFZ, and IXZ induced cell death in a dose- and time-dependent manner. Significant synergistic activity was observed by combining both V with CFZ or IXZ at known sub-therapeutic and therapeutic doses of individual agents measured by ATP content and apoptosis potential. Anti-tumor activity was observed in cytarabine sensitive and resistant cell lines. Similar findings were observed in primary tumor cells isolated from B-cell lymphoma patients. In vitro exposure of MCL cell lines with the lowest IC50 (HBL-2) to V and PIs (BTZ, CFZ, or IXZ) resulted in the upregulation of Noxa, BIM, Mcl-1 cleavage form (pro-apoptotic) and downregulation of Bcl-XL leading to PARP cleavage and apoptosis. In vivo treatment of MCL bearing SCID mice with V resulted in significant anti-tumor activity when compared to single agent IXZ treated or control animals. Of interest, MCL bearing SCID animals treated with V and IXZ exhibited a better disease control and the survival was longer than SCID animals treated with V or IXZ single agent (P<0.05). Conclusion: Our data suggests that V exhibits strong synergistic activity with PIs, especially with CFZ (in vitro) or IXZ (in vitro and in vivo). Together, our data supports the evaluation of V in combination with readily available novel PIs (IXZ or CFZ) in relapsed/refractory MCL. (Supported by LRF grant 555463, an NIH grant R01 CA136907-01A1 and a grant from The Roswell Park Cancer Institute Alliance Foundation) DisclosuresNo relevant conflicts of interest to declare.

Abstract CT160: Ixazomib in combination with carboplatin in pretreated women with advanced triple negative breast cancer, an ongoing phase I/II trial (AGMT MBC-10 trial)

Abstract Background: Triple-negative breast cancer (TNBC) comprises a heterogeneous group of diseases which are generally associated with poor prognosis. Recently, the PARP inhibitor olaparib was approved as first targeted treatment beyond antiVEGF therapy for the BRCA1/2 mutated subgroup of TNBC. However, cytotoxic agents still remain the mainstay of treatment for this breast cancer subtype. Ixazomib is a selective and reversible inhibitor of the proteasome, which has been mainly investigated as treatment of multiple myeloma. In a preclinical cell line model for TNBC the first-generation proteasome inhibitor bortezomib showed synergistic efficacy with cisplatin. Clinical data are available for carboplatin plus bortezomib in metastatic ovarian and lung cancers showing remarkable antitumor activity (47% and 38% response rate, respectively) and good tolerability. In solid tumors cytotoxic effect of proteasome inhibitors is thought to be mediated through different mechanisms: (1) Inhibition of the Fanconi Anemia and BRCA1 DNA repair mechanism (2) Inhibition of p53 degradation (3) Inhibition of NF-kappa B signaling cascade. Based on this evidence, the phase I/II MBC-10 trial will evaluate the toxicity profile and efficacy of the oral second-generation proteasome inhibitor ixazomib in combination with carboplatin in patients with advanced TNBC. Trial Design: Patients with metastatic TNBC pretreated with at least one prior line of chemotherapy for advanced disease with a confirmed disease progression and measurable disease are eligible for this study. Patients will receive ixazomib in combination with carboplatin on days 1, 8, and 15 in a 28-day cycle. The phase I part of this study uses an alternate dose escalation accelerated titration design. After establishing the maximum tolerated dose (MTD), accrual continues to evaluate the efficacy and safety of the combination (phase II, including 41 evaluable patients). All patients will continue on study drugs until disease progression, unacceptable toxicity or discontinuation for any other reason. Primary endpoint of the phase II is overall response rate, secondary endpoints include safety profile, progression-free survival and quality of life. The MBC-10 trial is accompanied by a broad biomarker program investigating predictive biomarkers for treatment response and potential resistance mechanisms to the investigational drug combination. This trial is open for patient enrollment since November 2016 in six Austrian cancer centers. Accrual is planned to be completed within two years. ClinicalTrials.gov Identifier: NCT02993094 Citation Format: Gabriel Rinnerthaler, Simon P. Gampenrieder, Andreas Petzer, Renate Pusch, Daniela Voskova, Dieter Rossmann, Marija Balic, Daniel Egle, Holger Rumpold, Christian F. Singer, Thomas Melchardt, Hanno Ulmer, Brigitte Mlineritsch, Richard Greil. Ixazomib in combination with carboplatin in pretreated women with advanced triple negative breast cancer, an ongoing phase I/II trial (AGMT MBC-10 trial) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT160.

Abstract OT3-07-01: Ixazomib in combination with carboplatin in pretreated women with advanced triple negative breast cancer, an ongoing phase I/II trial (AGMT MBC-10 trial)

Abstract Background:Triple-negative breast cancer (TNBC) comprises a heterogeneous group of diseases which are generally associated with poor prognosis. Recently, the PARP inhibitor olaparib was approved as first targeted treatment beyond antiVEGF therapy for the BRCA1/2 mutated subgroup of TNBC. However, cytotoxic agents still remain the mainstay of treatment for this breast cancer subtype. Ixazomib is a selective and reversible inhibitor of the proteasome, which has been mainly investigated as treatment of multiple myeloma. In a preclinical cell line model for TNBC the first-generation proteasome inhibitor bortezomib showed synergistic efficacy with cisplatin. Clinical data are available for carboplatin plus bortezomib in metastatic ovarian and lung cancers showing remarkable antitumor activity (47% and 38% response rate, respectively) and good tolerability. In solid tumors cytotoxic effect of proteasome inhibitors is thought to be mediated through different mechanisms: (1) Inhibition of the Fanconi Anemia and BRCA1 DNA repair mechanism (2) Inhibition of p53 degradation (3) Inhibition of NF-kappa B signaling cascade. Based on this evidence, the phase I/II MBC-10 trial will evaluate the toxicity profile and efficacy of the oral second-generation proteasome inhibitor ixazomib in combination with carboplatin in patients with advanced TNBC. Trial Design: Patients with metastatic TNBC pretreated with at least one prior line of chemotherapy for advanced disease with a confirmed disease progression and measurable disease are eligible for this study.Patients will receive ixazomib in combination with carboplatin on days 1, 8, and 15 in a 28-day cycle. The phase I part of this study uses an alternate dose escalation accelerated titration design. After establishing the maximum tolerated dose (MTD), accrual continues to evaluate the efficacy and safety of the combination (phase II, including 41 evaluable patients). All patients will continue on study drugs until disease progression, unacceptable toxicity or discontinuation for any other reason. Primary endpoint of the phase II is overall response rate, secondary endpoints include safety profile, progression-free survival and quality of life. The MBC-10 trial is accompanied by a broad biomarker program investigating predictive biomarkers for treatment response and potential resistance mechanisms to the investigational drug combination. This trial is open for patient enrollment since November 2016 in six Austrian cancer centers. Accrual is planned to be completed within two years. ClinicalTrials.gov Identifier: NCT02993094 Citation Format: Rinnerthaler G, Gampenrieder SP, Petzer A, Burgstaller S, Voskova D, Rossmann D, Balic M, Egle D, Rumpold H, Singer CF, Petru E, Melchardt T, Ulmer H, Mlineritsch B, Greil R. Ixazomib in combination with carboplatin in pretreated women with advanced triple negative breast cancer, an ongoing phase I/II trial (AGMT MBC-10 trial) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT3-07-01.

Amelioration of autoimmunity with an inhibitor selectively targeting all active centres of the immunoproteasome.

Multicatalytic endopeptidase complex-like-1 (β2i), low molecular mass polypeptide (LMP) 2 (β1i) and LMP7 (β5i) are the proteolytically active subunits of the immunoproteasome, a special type of proteasome mainly expressed in haematopoietic cells. Targeting LMP7 has been shown to be therapeutically effective in preclinical models of autoimmune diseases. In this study, we investigated the selectivity and biological activity of LU-005i, a recently described inhibitor of the immunoproteasome. The specificity of LU-005i and other immunoproteasome-selective inhibitors was characterized using fluorogenic peptide substrates. The effect of proteasome inhibition on cytokine release was investigated in endotoxin-stimulated mouse splenocytes or human peripheral blood mononuclear cells (PBMCs). The effect of proteasome inhibition on inflammatory bowel disease in the dextran sulfate sodium (DSS)-induced colitis model was assessed by measuring weight loss and colon length. LU-005i is the first human and mouse immunoproteasome-selective inhibitor that targets all three proteolytically active immunoproteasome subunits. LU-005i inhibited cytokine secretion from endotoxin-stimulated mouse splenocytes or human PBMCs. Furthermore, differentiation of naïve T helper cells to T helper 17 cells was impaired in the presence of LU-005i. Additionally, LU-005i ameliorated DSS-induced colitis. This study with a novel pan-immunoproteasome inhibitor substantiates that the immunoproteasome is a promising drug target for the treatment of inflammatory diseases and that exclusive inhibition of LMP7 is not necessary for therapeutic effectiveness. Our results will promote the design of new generations of immunoproteasome inhibitors with optimal therapeutic efficacy for clinical use in the treatment of autoimmunity and cancer.