Combined Effect of Bortezomib and Menadione Sodium Bisulfite on Proteasomes of Tumor Cells: The Dramatic Decrease of Bortezomib Toxicity in a Preclinical Trial

Multikinase inhibitors modulate non-constitutive proteasome expression in colorectal cancer cells

Introduction: Proteasomes are multi-subunit protein complexes responsible for protein degradation in cells. Immunoproteasomes and intermediate proteasomes (together non-constitutive proteasomes) are specific forms of proteasomes frequently associated with immune response, antigen presentation, inflammation and stress. Expression of non-constitutive proteasome subunits has a prognostic value in several types of cancer. Thus, factors that modulate non-constitutive proteasome expression in tumors are of particular interest. Multikinase inhibitors (MKIs) demonstrate promising results in treatment of cancer. At the same time, their immunomodulatory properties and effects on non-constitutive proteasome expression in colorectal cancer cells are poorly investigated. Methods: Proteasome subunit expression in colorectal cancer was evaluated by bioinformatic analysis of available datasets. Two colorectal cancer cell lines, expressing fluorescent non-constitutive proteasomes were treated with multikinase inhibitors: regorafenib and sorafenib. The proteasome subunit expression was assessed by real-time PCR, Western blotting and flow cytometry. The proteasome activity was studied using proteasome activity-based probe and fluorescent substrates. Intracellular proteasome localization was revealed by confocal microscopy. Reactive oxygen species levels following treatment were determined in cells. Combined effect of proteasome inhibition and treatment with MKIs on viability of cells was estimated. Results: Expression of non-constitutive proteasomes is increased in BRAF-mutant colorectal tumors. Regorafenib and sorafenib stimulated the activity and synthesis of non-constitutive proteasomes in examined cell lines. MKIs induced oxidative stress and redistribution of proteasomes within cells. Sorafenib stimulated formation of cytoplasmic aggregates, containing proteolyticaly active non-constitutive proteasomes, while regorafenib had no such effect. MKIs caused no synergistic action when were combined with the proteasome inhibitor. Discussion: Obtained results indicate that MKIs might affect the crosstalk between cancer cells and immune cells via modulation of intracellular proteasome pool. Observed phenomenon should be considered when MKI-based therapy is applied.

Unlocking the potential of 1,4-naphthoquinones: A comprehensive review of their anticancer properties

Cancer encompasses a group of pathologies with common characteristics, high incidence, and prevalence in all countries. Although there are treatments available for this disease, they are not always effective or safe, often failing to achieve the desired results. This is why it is necessary to continue the search for new therapies. One of the strategies for obtaining new antitumor drugs is the use of 1,4-naphthoquinone as a scaffold in synthetic or natural products with antitumor activity. This review focuses on compiling studies related to the antitumor activity of 1,4-naphthoquinone and its natural and synthetic derivatives over the last 10 years. The work describes the main natural naphthoquinones with antitumor activity and classifies the synthetic naphthoquinones based on the structural modifications made to the scaffold. Additionally, the formation of metal complexes using naphthoquinones as a ligand is considered. After a thorough review, 197 synthetic compounds with potent biological activity against cancer have been classified according to their chemical structures and their mechanisms of action have been described.

Menadione and protocatechuic acid: A drug combination with antitumor effects in murine osteosarcoma cells

Osteosarcoma (OS) is a primary malignant bone tumor that has an abnormal expression of oncogenesis and tumor suppressors and causes dysregulation of various signaling pathways. Thus, novel therapeutic strategies for OS are needed to overcome the resistance of traditional treatments. This study evaluated the cytotoxic and anticancer effects of the association between menadione (MEN) and protocatechuic acid (PCA) in murine OS cells (UMR-106). The concentrations were 3.12 μM of isolated MEN, 500 μM of isolated PCA, and their associations. We performed cell viability assays, morphology modification analysis, cell migration by the wound-healing method, apoptosis by flow cytometry, reactive oxygen species (ROS) production, gene expression of NOX by RT-qPCR, and degradation of MMP-2 and 9 by zymography. Our results showed that the association of MEN+PCA was more effective in OS cells than the compounds alone. The association decreased cell viability, delayed cell migration, and decreased the expression of NOX-2 and ROS. In addition, the MEN+PCA association induced a slight increase in the apoptotic process. In summary, the association can enhance the compound's antitumor effects and establish a higher selectivity for tumor cells, possibly caused by significant mitochondrial damage and antioxidant properties.

Inhibition of extracellular signal-regulated kinase downregulates endoplasmic reticulum stress-induced apoptosis and decreases brain injury in a cardiac arrest rat model

Cerebral ischemia-reperfusion injury (CIRI) is the predominant cause of neurological disability after cardiac arrest/cardiopulmonary resuscitation (CA/CPR). The endoplasmic reticulum stress (ERs)-induced apoptosis plays an important role in neuronal survival/death in CIRI. Our previous studies reported that the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, alleviates CIRI after CA/CPR. Whether ERs-induced apoptosis is involved in the neuroprotection of PD98059 remains unknown. This study aims to investigate the effects of ERK inhibition by PD98059 on ERs-induced apoptosis after CIRI in the CA/CPR rat model. The baseline characteristics of male adult Sprague-Dawley (SD) rats in all groups were evaluated before CA/CPR. The SD rats that survived from CA/CPR were randomly divided into 3 groups (n=12/group): normal saline group (1 ml/kg), dimethylsulfoxide (DMSO, the solvent of PD98059, 1 ml/kg) group, PD98059 group (0.3 mg/kg). Another 12 SD rats were randomly selected as the Sham group. Twenty-four hours after resuscitation, neural injury was assessed by survival rate, neurological deficit scores (NDS) and Nissl staining; apoptosis of brain cells was detected using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining; mRNA expression and protein levels of ERs-related protein BIP, PERK, ATF4 and CHOP were checked with RT-PCR and Western Blot. The results showed that there were no significant differences in baseline characteristics before CA/CPR among all groups. PD98059 significantly improved survival rate and NDS, increased the Nissl bodies in neurons, reduced apoptosis, downregulated the mRNA transcription and expression levels of BIP, PERK, ATF4 and CHOP at 24 h after CA/CPR. Our results demonstrate that inhibition of ERK by PD98059 alleviates ERs-induced apoptosis via BIP-PERK-ATF4-CHOP signaling pathway and mitigates CIRI in the CA/CPR rat model.

26S Proteasome Non-ATPase Regulatory Subunits 1 (PSMD1) and 3 (PSMD3) as Putative Targets for Cancer Prognosis and Therapy

Ever since the ubiquitin proteasome system was characterized, efforts have been made to manipulate its function to abrogate the progression of cancer. As a result, the anti-cancer drugs bortezomib, carfilzomib, and ixazomib targeting the 26S proteasome were developed to treat multiple myeloma, mantle cell lymphoma, and diffuse large B-cell lymphoma, among others. Despite success, adverse side effects and drug resistance are prominent, raising the need for alternative therapeutic options. We recently demonstrated that knockdown of the 19S regulatory components, 26S proteasome non-ATPase subunits 1 (PSMD1) and 3 (PSMD3), resulted in increased apoptosis of chronic myeloid leukemia (CML) cells, but had no effect on normal controls, suggesting they may be good targets for therapy. Therefore, we hypothesized that PSMD1 and PSMD3 are potential targets for anti-cancer therapeutics and that their relevance stretches beyond CML to other types of cancers. In the present study, we analyzed PSMD1 and PSMD3 mRNA and protein expression in cancerous tissue versus normal controls using data from The Cancer Genome Atlas (TCGA) and the Clinical Proteomic Tumor Analysis Consortium (CPTAC), comparing expression with overall survival. Altogether, our data suggest that PSMD1 and PSMD3 may be novel putative targets for cancer prognosis and therapy that are worthy of future investigation.

The potentiation of menadione on imatinib by downregulation of ABCB1 expression

Imatinib was the first BCR-ABL inhibitor used in clinical practice to treat chronic myeloid leukaemia (CML) and significantly improve the life expectancy of CML patients in the chronic phase. However, a portion of CML patients are resistant to imatinib. This study aimed to determine whether menadione (Vitamin K3) can improve imatinib efficacy in CML and to thoroughly explore the combination regimen mechanism between imatinib and menadione. Menadione improved imatinib efficacy in K562 cells by downregulating ABCB1 expression and increased the intracellular concentration of imatinib, which confirmed that this combination regimen is more effective than imatinib monotherapy. The results demonstrate that menadione and imatinib combination therapy may be a promising approach to refractory CML.

Proteasomes in Patient Rectal Cancer and Different Intestine Locations: Where Does Proteasome Pool Change?

A special problem in the surgery of rectal cancer is connected with a need for appropriate removal of intestine parts, along with the tumor, including the fragment close to the sphincter. To determine the length of fragments to remove, it is necessary to reveal areas without changes in molecule functioning, specific for tumor. The purpose of the present study was to investigate functioning the proteasomes, the main actors in protein hydrolysis, in patient rectal adenocarcinoma and different intestine locations. Chymotrypsin-like and caspase-like activities, open to complex influence of different factors, were analyzed in 43-54 samples by Suc-LLVY-AMC- and Z-LLE-AMC-hydrolysis correspondingly. Both activities may be arranged by the decrease in the location row: cancer→adjacent tissue→proximal (8-20 cm from tumor) and distal (2 and 4 cm from tumor) sides. These activities did not differ noticeably in proximal and distal locations. Similar patterns were detected for the activities and expression of immune subunits LMP2 and LMP7 and expression of 19S and PA28αβ activators. The largest changes in tumor were related to proteasome subtype containing LMP2 and PA28αβ that was demonstrated by native electrophoresis. Thus, the results indicate a significance of subtype LMP2-PA28αβ for tumor and absence of changes in proteasome pool in distal fragments of 2-4 cm from tumor.

Ouabain and Digoxin Activate the Proteasome and the Degradation of the ERα in Cells Modeling Primary and Metastatic Breast Cancer

Simple Summary

Breast cancer (BC) treatment relies on the detection of the estrogen receptor α (ERα). ERα-expressing BC patients are treated with anti-estrogen drugs (i.e., tamoxifen and fulvestrant). Despite their proven efficacy, these drugs cause serious side effects in a significant fraction of the patients, including both tumor insurgence in secondary organs, and resistant phenotypes, which result in a relapsing disease with scarce treatment options. Thus, new drugs for treatment of primary and metastatic BC (MBC) are needed. Here, we report the characterization of two cardiac glycosides (CGs) (i.e., ouabain and digoxin), approved by the FDA for treatment of heart disease, as novel ‘anti-estrogen’-like drugs. We found that these drugs induce ERα degradation, and prevent the proliferation of cellular models of primary and metastatic BC cells. Remarkably, we discovered that these CGs are activators of the proteasome, and therefore may be repurposed for treatment not only of BC, but also for other proteasome-based diseases.

Abstract

Estrogen receptor α expressing breast cancers (BC) are classically treated with endocrine therapy. Prolonged endocrine therapy often results in a metastatic disease (MBC), for which a standardized effective therapy is still lacking. Thus, new drugs are required for primary and metastatic BC treatment. Here, we report that the Food and Drug Administration (FDA)-approved drugs, ouabain and digoxin, induce ERα degradation and prevent proliferation in cells modeling primary and metastatic BC. Ouabain and digoxin activate the cellular proteasome, instigating ERα degradation, which causes the inhibition of 17β-estradiol signaling, induces the cell cycle blockade in the G2 phase, and triggers apoptosis. Remarkably, these effects are independent of the inhibition of the Na/K pump. The antiproliferative effects of ouabain and digoxin occur also in diverse cancer models (i.e., tumor spheroids and xenografts). Additionally, gene profiling analysis reveals that these drugs downregulate the expression of genes related to endocrine therapy resistance. Therefore, ouabain and digoxin behave as ‘anti-estrogen’-like drugs, and are appealing candidates for the treatment of primary and metastatic BCs.

Estrogen Receptors and Ubiquitin Proteasome System: Mutual Regulation

This review provides information on the structure of estrogen receptors (ERs), their localization and functions in mammalian cells. Additionally, the structure of proteasomes and mechanisms of protein ubiquitination and cleavage are described. According to the modern concept, the ubiquitin proteasome system (UPS) is involved in the regulation of the activity of ERs in several ways. First, UPS performs the ubiquitination of ERs with a change in their functional activity. Second, UPS degrades ERs and their transcriptional regulators. Third, UPS affects the expression of ER genes. In addition, the opportunity of the regulation of proteasome functioning by ERs—in particular, the expression of immune proteasomes—is discussed. Understanding the complex mechanisms underlying the regulation of ERs and proteasomes has great prospects for the development of new therapeutic agents that can make a significant contribution to the treatment of diseases associated with the impaired function of these biomolecules.

Proteasomes and Several Aspects of Their Heterogeneity Relevant to Cancer

The life of every organism is dependent on the fine-tuned mechanisms of protein synthesis and breakdown. The degradation of most intracellular proteins is performed by the ubiquitin proteasome system (UPS). Proteasomes are central elements of the UPS and represent large multisubunit protein complexes directly responsible for the protein degradation. Accumulating data indicate that there is an intriguing diversity of cellular proteasomes. Different proteasome forms, containing different subunits and attached regulators have been described. In addition, proteasomes specific for a particular tissue were identified. Cancer cells are highly dependent on the proper functioning of the UPS in general, and proteasomes in particular. At the same time, the information regarding the role of different proteasome forms in cancer is limited. This review describes the functional and structural heterogeneity of proteasomes, their association with cancer as well as several established and novel proteasome-directed therapeutic strategies.