A comparative analysis between proteasome and immunoproteasome inhibition in cellular and humoral alloimmunity

The effect of proteasome in heart transplantation: From mechanisms to therapeutic potential

Heart transplantation is a critical treatment for end-stage heart failure. However, its clinical efficacy is hindered by some challenges, such as ischemia-reperfusion injury (IRI) and post-transplant rejection. These complications significantly contribute to graft dysfunction and compromise patient survival. Emerging evidence underscores the involvement of proteasome in the pathophysiology of both IRI and post-transplant rejection. Proteasome inhibition has demonstrated potential in attenuating IRI by limiting oxidative damage and apoptosis while also mitigating rejection through the regulation of adaptive and innate immune responses. Recent advances in the development of proteasome inhibitors, particularly in optimizing specificity and minimizing adverse effects, have further strengthened their prospects for clinical application. This review focuses on the roles of the proteasome and its inhibitors in heart transplantation, with an emphasis on their mechanisms and therapeutic applications in managing IRI and rejection.

Secretome Analysis of Human and Rat Pancreatic Islets Co-Cultured with Adipose-Derived Stromal Cells Reveals a Signature with Enhanced Regenerative Capacities

Pancreatic islet transplantation (PIT) is a promising treatment for type 1 diabetes (T1D) but faces challenges pre- and post-transplantation. Co-transplantation with mesenchymal stromal cells (MSCs), known for their regenerative properties, has shown potential in improving PIT outcomes. This study examined the secretome of islets cultured alone compared to the secretomes of islets co-cultured with adipose-derived stromal cells (ASCs), a subtype of MSCs, under transplantation-relevant stressors: normoxia, cytokines, high glucose, hypoxia, and combined hypoxia and high glucose. Islet co-culture with ASCs significantly altered the proteome, affecting pathways related to energy metabolism, angiogenesis, extracellular matrix organization, and immune modulation. Key signaling molecules (e.g., VEGF, PDGF, bFGF, Collagen I alpha 1, IL-1α, and IL-10) were differentially regulated depending on culture conditions and ASC presence. Functional assays demonstrated that the co-culture secretome could enhance angiogenesis, collagen deposition, and immune modulation, depending on the stress conditions. These findings highlight possible mechanisms through which ASCs may support islet survival and function, offering insights into overcoming PIT challenges. Moreover, this work contributes to identifying biomarkers of the post-transplantation microenvironment, advancing therapeutic strategies for T1D and regenerative medicine.

Bortezomib in cancer therapy: Mechanisms, side effects, and future proteasome inhibitors

The ubiquitin-proteasome pathway (UPP) regulates protein stability and normal cellular functions with the help of autocatalytic proteasome complex. Studies have linked aberrant proteasome activity to malignant cells and found that proteasome inhibitors play a significant role as therapeutic drugs for various types of cancer, specifically multiple myeloma and mantle cell lymphoma. Bortezomib, the first FDA-approved proteasome inhibitor for treating different stages of multiple myeloma, acts on cancer cells by inhibiting the 26S proteasome, modulating NF-κB, phosphorylating Bcl-2, upregulating of NOXA, blocking p53 degradation, activating caspase, generating reactive oxygen species (ROS), and inhibiting angiogenesis. However, its efficacy is limited due to side effects such as peripheral neuropathy (PN), thrombotic microangiopathy (TMA), and acute interstitial nephritis (AIN). Therefore, a better understanding of its precise mechanism of action may help mitigate these side effects. In this review, we have discussed the proposed mechanisms of action and off target effects of Bortezomib, along with the prospects of next generation potential proteasome inhibitor drugs in the treatment of cancer.

Concentration and activation biresponsive strategy in one analysis system with simultaneous use of G4 structure-specific signal probe and enzyme-catalyzed reaction

BACKGROUND

Enzymes with critical effects on life systems are regulated by expression and activation to modulate life processes. However, further insights into enzyme functions and mechanisms in various physiological processes are limited to concentration or activation analysis only. Currently, enzyme analysis has received notable attention, particularly simultaneous analysis of their concentration and activation in one system. Herein, N-methyl mesoporphyrin IX (NMM), a specific dye with notable structural selectivity for parallel G-quadruplex nucleic acid enzyme (G4h DNAzyme), is employed for the analysis of its concentration. In addition, the peroxidase activity of G4h DNAzyme is characterized based on G4h DNAzyme-catalyzed decomposition of H2O2 to continuously consume luminol. Accordingly, an increased fluorescence (FL) response of NMM and a decreased FL response of luminol could be simultaneously employed to analyze the concentration and activation of G4h DNAzyme.

RESULT

Herein, a novel concentration and activation biresponsive strategy is proposed using a G4h DNAzyme-based model that simultaneously employs a G4h structure-specific signal probe for enzyme concentration analysis and G4h DNAzyme-catalyzed reactions for enzyme activation analysis. Under optimal conditions, the biresponsive strategy can be effectively used for the simultaneous analysis of G4h DNAzyme concentration and activation, with detection limits of 718.7 pM and 233.4 nM respectively, delivering acceptable performances both in cell and in vitro.

SIGNIFICANCE

This strategy can not only be applied to concentration and activation analyses of G4h DNAzyme but can also be easily extended to other enzymes by simultaneously combining concentration analysis via target-induced direct reaction and activation analysis via target-induced catalytic reaction, offering deeper insights into various enzymes and enabling their effective implementation in bioanalysis and biochemistry.

Development and anticancer properties of Up284, a spirocyclic candidate ADRM1/RPN13 inhibitor

Bortezomib has been successful for treatment of multiple myeloma, but not against solid tumors, and toxicities of neuropathy, thrombocytopenia and the emergence of resistance have triggered efforts to find alternative proteasome inhibitors. Bis-benzylidine piperidones such as RA190 covalently bind ADRM1/RPN13, a ubiquitin receptor that supports recognition of polyubiquitinated substrates of the proteasome and their subsequent deububiqutination and degradation. While these candidate RPN13 inhibitors (iRPN13) show promising anticancer activity in mouse models of cancer, they have suboptimal drug-like properties. Here we describe Up284, a novel candidate iRPN13 possessing a central spiro-carbon ring in place of RA190's problematic piperidone core. Cell lines derived from diverse cancer types (ovarian, triple negative breast, colon, cervical and prostate cancers, multiple myeloma and glioblastoma) were sensitive to Up284, including several lines resistant to bortezomib or cisplatin. Up284 and cisplatin showed synergistic cytotoxicity in vitro. Up284-induced cytotoxicity was associated with mitochondrial dysfunction, elevated levels of reactive oxygen species, accumulation of very high molecular weight polyubiquitinated protein aggregates, an unfolded protein response and the early onset of apoptosis. Up284 and RA190, but not bortezomib, enhanced antigen presentation in vitro. Up284 cleared from plasma in a few hours and accumulated in major organs by 24 h. A single dose of Up284, when administered to mice intra peritoneally or orally, inhibited proteasome function in both muscle and tumor for >48 h. Up284 was well tolerated by mice in repeat dose studies. Up284 demonstrated therapeutic activity in xenograft, syngeneic and genetically-engineered murine models of ovarian cancer.

Emerging New Approaches in Desensitization: Targeted Therapies for HLA Sensitization

There is an urgent need for therapeutic interventions for desensitization and antibody-mediated rejection (AMR) in sensitized patients with preformed or de novo donor-specific HLA antibodies (DSA). The risk of AMR and allograft loss in sensitized patients is increased due to preformed DSA detected at time of transplant or the reactivation of HLA memory after transplantation, causing acute and chronic AMR. Alternatively, de novo DSA that develops post-transplant due to inadequate immunosuppression and again may lead to acute and chronic AMR or even allograft loss. Circulating antibody, the final product of the humoral immune response, has been the primary target of desensitization and AMR treatment. However, in many cases these protocols fail to achieve efficient removal of all DSA and long-term outcomes of patients with persistent DSA are far worse when compared to non-sensitized patients. We believe that targeting multiple components of humoral immunity will lead to improved outcomes for such patients. In this review, we will briefly discuss conventional desensitization methods targeting antibody or B cell removal and then present a mechanistically designed desensitization regimen targeting plasma cells and the humoral response.

LMP7 polymorphism may modify the presentation and clinical impact of minor histocompatibility antigens in matched related hematopoietic stem cell transplantation

Differential expression of minor histocompatibility antigens between the recipient and donor determines their disparity and can be modified by immunoproteasomes that regulate their processing and presentation. We examined the impact of HA-1 and HA-8 disparity, and immunoproteasome LMP7 polymorphism in 130 pairs. In multivariate analysis, HA-1 disparity showed a statistically significant association with an increased incidence of acute graft-versus-host disease (aGVHD) II-IV (p = 0.043, HR: 3.71, 95%CI = 1.04-13.26), while LMP7-Q/Q showed a trend toward increased incidence of aGVHD compared to LMP7-Q/K and K/K genotypes (p = 0.087, HR: 2.36, 95%CI = 0.88-6.31). All HA-1 and HA-8 disparate patients who developed aGVHD had the LMP7-Q/Q genotype. No significant association could be detected between HA-1, HA-8, or LMP7 and chronic GVHD, relapse-free survival (RFS), overall survival (OS), or transplant-related mortality (TRM). In conclusion, we suggested an association between the HA-1 disparity and the risk of developing aGVHD with a possible modifying effect of LMP7.

In Mixed Lymphocyte Reaction, the Hypoxia-Inducible Factor Prolyl-Hydroxylase Inhibitor Roxadustat Suppresses Cellular and Humoral Alloimmunity

Hypoxia-inducible factor (HIF) prolyl-hydroxylase inhibitors are currently used for the treatment of renal anemia. Since HIF affects immune cells, we evaluated the effect of such a drug, the roxadustat, on adaptive immunity. Cell proliferation was assessed in a two-way mixed lymphocyte reaction (MLR) with BrdU assay. In CD4+ T cells isolated from the two-way MLRs, western blotting was performed to detect the impact of roxadustat on HIF-1α and HIF-2α, the apoptotic marker cleaved caspase-3, and the master transcription factors of CD4+ T cells differentiation towards Th1, Th2, Th17, Treg and Tfh subsets. The signature cytokines of the above CD4+ T-cell subsets IFN-γ, IL-4, IL-17, IL-10, and IL-21 were measured in the supernatants. For assessing humoral immunity, we developed a suitable antibody-mediated complement-dependent cytotoxicity assay. Roxadustat stabilized HIF-1α and HIF-2α, suppressed cell proliferation, inhibited CD4+ T-cell differentiation into Th1 and Th17 subsets, while it favored differentiation towards Th2, Treg and Tfh. Roxadustat suppressed humoral immunity too. These immunosuppressive properties of roxadustat indicate that the recently introduced HIF prolyl-hydroxylase inhibitors in medical therapeutics may render the patients vulnerable to infections. This possibility should be further evaluated in clinical trials.

Recent insights how combined inhibition of immuno/proteasome subunits enables therapeutic efficacy

The proteasome is a multicatalytic protease in the cytosol and nucleus of all eukaryotic cells that controls numerous cellular processes through regulated protein degradation. Proteasome inhibitors have significantly improved the survival of multiple myeloma patients. However, clinically approved proteasome inhibitors have failed to show efficacy against solid tumors, neither alone nor in combination with other therapies. Targeting the immunoproteasome with selective inhibitors has been therapeutically effective in preclinical models for several autoimmune diseases and colon cancer. Moreover, immunoproteasome inhibitors prevented the chronic rejection of allogeneic organ transplants. In recent years, it has become apparent that inhibition of one single active center of the proteasome is insufficient to achieve therapeutic benefits. In this review we summarize the latest insights how targeting multiple catalytically active proteasome subunits can interfere with disease progression in autoimmunity, growth of solid tumors, and allograft rejection.

Proteasome Inhibitor Drugs

Proteasomes are large, multicatalytic protein complexes that cleave cellular proteins into peptides. There are many distinct forms of proteasomes that differ in catalytically active subunits, regulatory subunits, and associated proteins. Proteasome inhibitors are an important class of drugs for the treatment of multiple myeloma and mantle cell lymphoma, and they are being investigated for other diseases. Bortezomib (Velcade) was the first proteasome inhibitor to be approved by the US Food and Drug Administration. Carfilzomib (Kyprolis) and ixazomib (Ninlaro) have recently been approved, and more drugs are in development. While the primary mechanism of action is inhibition of the proteasome, the downstream events that lead to selective cell death are not entirely clear. Proteasome inhibitors have been found to affect protein turnover but at concentrations that are much higher than those achieved clinically, raising the possibility that some of the effects of proteasome inhibitors are mediated by other mechanisms.

Inhibiting the immunoproteasome's β5i catalytic activity affects human peripheral blood-derived immune cell viability

Small molecule inhibitors selectively targeting the immunoproteasome subunit β5i are currently being developed for the treatment of autoimmune disorders. However, patients carrying loss-of-function mutations in the gene encoding β5i (Psmb8) suffer from the proteasome-associated autoinflammatory syndromes (PRAAS) emphasizing the need to study pharmacological inhibition of immunoproteasome function in human cells. Here, we characterized the immunomodulatory potential of the selective β5i inhibitor ONX 0914 and Bortezomib, a pan-proteasome inhibitor, in human peripheral blood mononuclear cells (PBMCs). Both compounds efficiently blocked pro-inflammatory cytokine secretion in human whole blood and PBMC cultures stimulated with toll-like receptor (TLR) agonists. Furthermore, the compounds inhibited T cell cytokine production induced by recall antigen CMVpp65 or by polyclonal stimulation. The viability of PBMCs, however, was rapidly decreased in the presence of ONX 0914 and Bortezomib demonstrated by decreased residual cytosolic ATP and increased Annexin V surface binding. Interestingly, HLA-DR + monocytes were rapidly depleted from the cultures in the presence of ONX 0914 as a β5i-selective inhibitor and Bortezomib. In conclusion, the anti-inflammatory potential of β5i-selective inhibitors is correlating with a cytotoxicity increase in human PBMC subsets ex vivo. Our results provide important insights into the anti-inflammatory mechanism of action of β5i-inhibitors which currently hold the promise as a novel therapy for autoinflammatory diseases.

Assessment of Humoral Alloimmunity in Mixed Lymphocyte Reaction

Humoral alloimmunity remains a significant and unresolved problem that constrains allograft survival. Thus, there is a need for the development of an easy, preferably non-radioactive, and inexpensive protocol for assessing the effect of various drug treatments on humoral alloimmunity. In order to satisfy this demand, we developed such a protocol in which de novo alloantibodies production is induced in one-way mixed lymphocyte reaction (MLR). The amount and capacity of the generated alloantibodies in the supernatant of each one-way MLR is assessed using an antibody-mediated cell dependent cytotoxicity (CDC) assay. The principle of the assay relies on the assessment of cellular survival of resting PBMCs isolated from the same donors, supplemented with the alloantibodies from the one-way MLR supernatant. The lesser is the cellular survival, the higher the production of alloantibodies in one-way MLR and consequently the more potent the humoral alloimmunity.

On the role of the immunoproteasome in transplant rejection

The immunoproteasome is expressed in cells of hematopoietic origin and is induced during inflammation by IFN-γ. Targeting the immunoproteasome with selective inhibitors has been shown to be therapeutically effective in pre-clinical models for autoimmune diseases, colitis-associated cancer formation, and transplantation. Immunoproteasome inhibition prevents activation and proliferation of lymphocytes, lowers MHC class I cell surface expression, reduces the expression of cytokines of activated immune cells, and curtails  T helper 1 and 17 cell differentiation. This might explain the in vivo efficacy of immunoproteasome inhibition in different pre-clinical disease models for autoimmunity, cancer, and transplantation. In this review, we summarize the effect of immunoproteasome inhibition in different animal models for transplantation.