Next-generation proteasome inhibitor MLN9708 sensitizes breast cancer cells to doxorubicin-induced apoptosis

The ubiquitin-proteasome system in the regulation of tumor dormancy and recurrence

Tumor recurrence is a mechanism triggered in sparse populations of cancer cells that usually remain in a quiescent state after strict stress and/or therapeutic factors, which is affected by a variety of autocrine and microenvironmental cues. Despite thorough investigations, the biology of dormant and/or cancer stem cells is still not fully elucidated, as for the mechanisms of their reawakening, while only the major molecular patterns driving the relapse process have been identified to date. These molecular patterns profoundly interfere with the elements of cellular proteostasis systems that support the efficiency of the recurrence process. As a major proteostasis machinery, we review the role of the ubiquitin-proteasome system (UPS) in tumor cell dormancy and reawakening, devoting particular attention to the functions of its components, E3 ligases, deubiquitinating enzymes and proteasomes in cancer recurrence. We demonstrate how UPS components functionally or mechanistically interact with the pivotal proteins implicated in the recurrence program and reveal that modulators of the UPS hold promise to become an efficient adjuvant therapy for eradicating refractory tumor cells to impede tumor relapse.

Long non-coding RNAs as the critical regulators of PI3K/AKT, TGF-β, and MAPK signaling pathways during breast tumor progression

Breast cancer (BC) as one of the most common causes of human deaths among women, is always considered one of the global health challenges. Despite various advances in diagnostic and therapeutic methods, a significant percentage of BC patients have a poor prognosis due to the lack of therapeutic response. Therefore, investigating the molecular mechanisms involved in BC progression can improve the therapeutic and diagnostic strategies in these patients. Cytokine and growth factor-dependent signaling pathways play a key role during BC progression. In addition to cytokines and growth factors, long non-coding RNAs (lncRNAs) have also important roles in regulation of such signaling pathways. Therefore, in the present review we discussed the role of lncRNAs in regulation of PI3K/AKT, MAPK, and TGF-β signaling pathways in breast tumor cells. It has been shown that lncRNAs mainly have an oncogenic role through the promotion of these signaling pathways in BC. This review can be an effective step in introducing the lncRNAs inhibition as a probable therapeutic strategy to reduce tumor growth by suppression of PI3K/AKT, MAPK, and TGF-β signaling pathways in BC patients. In addition, considering the oncogenic role and increased levels of lncRNAs expressions in majority of the breast tumors, lncRNAs can be also considered as the reliable diagnostic markers in BC patients.

Nanomedicine for autophagy modulation in cancer therapy: a clinical perspective

In recent years, progress in nanotechnology provided new tools to treat cancer more effectively. Advances in biomaterials tailored for drug delivery have the potential to overcome the limited selectivity and side effects frequently associated with traditional therapeutic agents. While autophagy is pivotal in determining cell fate and adaptation to different challenges, and despite the fact that it is frequently dysregulated in cancer, antitumor therapeutic strategies leveraging on or targeting this process are scarce. This is due to many reasons, including the very contextual effects of autophagy in cancer, low bioavailability and non-targeted delivery of existing autophagy modulatory compounds. Conjugating the versatile characteristics of nanoparticles with autophagy modulators may render these drugs safer and more effective for cancer treatment. Here, we review current standing questions on the biology of autophagy in tumor progression, and precursory studies and the state-of-the-art in harnessing nanomaterials science to enhance the specificity and therapeutic potential of autophagy modulators.

DNMT2/TRDMT1 gene knockout compromises doxorubicin-induced unfolded protein response and sensitizes cancer cells to ER stress-induced apoptosis

The acidic, hypoxic and nutrient-deprived tumor microenvironment may induce endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) may exert an important cytoprotective role by promoting folding of newly synthesized proteins and cancer cell survival. The lack of DNMT2/TRDMT1 methyltransferase-mediated C38 tRNA methylation compromises translational fidelity that may result in the accumulation of misfolded and aggregated proteins leading to proteotoxic stress-related cell death. In the present study, DNMT2/TRDMT1 gene knockout-mediated effects were investigated during doxorubicin (DOX)-induced ER stress and PERK-, IRE1- and ATF6-orchestrated UPR in four genetically different cellular models of cancer (breast and cervical cancer, osteosarcoma and glioblastoma cells). Upon DOX stimulation, DNMT2/TRDMT1 gene knockout impaired PERK activation and modulated NSUN and 5-methylcytosine RNA-based responses and microRNA profiles. The lack of DNMT2/TRDMT1 gene in DOX-treated four cancer cell lines resulted in decreased levels of four microRNAs, namely, miR-23a-3p, miR-93-5p, miR-125a-5p and miR-191-5p involved in the regulation of several pathways such as ubiquitin-mediated proteolysis, amino acid degradation and translational misregulation in cancer. We conclude that DNMT2/TRDMT1 gene knockout, at least in selected cellular cancer models, affects adaptive responses associated with protein homeostasis networks that during prolonged ER stress may result in increased sensitivity to apoptotic cell death.

Ursolic Acid Enhances Cytotoxicity of Doxorubicin-Resistant Triple-Negative Breast Cancer Cells via ZEB1-AS1/miR-186-5p/ABCC1 Axis

Background: Triple-negative breast cancer (TNBC) is the most serious subtype of breast cancer (BC) and has been a great health threat to females. Although chemotherapeutic agent contributes a lot to TNBC treatment, drug resistance has been a great obstacle for chemotherapies. Ursolic acid (UA), a pentacyclic triterpenoid compound, was reported to reverse paclitaxel resistance in BC. However, whether UA could affect the resistance of TNBC cells to other drugs such as doxorubicin (DOX) remains to be discovered. Materials and Methods: MTT assay, EdU assay, colony formation assay, and flow cytometry analysis were implemented to detect the viability, proliferation, and apoptosis of DOX-resistant MDA-MB-468 and MDA-MB-436 cells with or without UA treatment. Mechanism assays including RIP, RNA pull-down, and luciferase reporter assays verified the interaction between RNAs. Results: UA treatment hindered the growth and mitigated the DOX resistance of DOX-resistant MDA-MB-468 and MDA-MB-436 cells. Mechanistically, multidrug resistance-associated protein 1 (ABCC1) expression was downregulated by UA treatment. MiR-186-5p was verified to target ABCC1. Further, UA-inhibited ZEB1-AS1 (zinc finger E-box binding homeobox 1 antisense RNA 1) was verified as a competitive endogenous RNA (ceRNA) to upregulate ABCC1 through sponging miR-186-5p. Importantly, UA treatment impaired the malignant phenotypes of DOX-resistant MDA-MB-468 and MDA-MB-436 cells through ZEB1-AS1/ABCC1 axis. Conclusion: UA promotes TNBC cell sensitivity to DOX through inactivating ZEB1-AS1/miR-186-5p/ABCC1 signaling.

Rational drug combination design in patient-derived avatars reveals effective inhibition of hepatocellular carcinoma with proteasome and CDK inhibitors

Background

Hepatocellular carcinoma (HCC) remains difficult to treat due to limited effective treatment options. While the proteasome inhibitor bortezomib has shown promising preclinical activity in HCC, clinical trials of bortezomib showed no advantage over the standard-of-care treatment sorafenib, highlighting the need for more clinically relevant therapeutic strategies. Here, we propose that rational drug combination design and validation in patient-derived HCC avatar models such as patient-derived xenografts (PDXs) and organoids can improve proteasome inhibitor-based therapeutic efficacy and clinical potential.

Methods

HCC PDXs and the corresponding PDX-derived organoids (PDXOs) were generated from primary patient samples for drug screening and efficacy studies. To identify effective proteasome inhibitor-based drug combinations, we applied a hybrid experimental-computational approach, Quadratic Phenotypic Optimization Platform (QPOP) on a pool of nine drugs comprising proteasome inhibitors, kinase inhibitors and chemotherapy agents. QPOP utilizes small experimental drug response datasets to accurately identify globally optimal drug combinations.

Results

Preliminary drug screening highlighted the increased susceptibility of HCC PDXOs towards proteasome inhibitors. Through QPOP, the combination of second-generation proteasome inhibitor ixazomib (Ixa) and CDK inhibitor dinaciclib (Dina) was identified to be effective against HCC. In vitro and in vivo studies demonstrated the synergistic pro-apoptotic and anti-proliferative activity of Ixa + Dina against HCC PDXs and PDXOs. Furthermore, Ixa + Dina outperformed sorafenib in mitigating tumor formation in mice. Mechanistically, increased activation of JNK signaling mediates the combined anti-tumor effects of Ixa + Dina in HCC tumor cells.

Conclusions

Rational drug combination design in patient-derived avatars highlights the therapeutic potential of proteasome and CDK inhibitors and represents a feasible approach towards developing more clinically relevant treatment strategies for HCC.

Dormancy in Breast Cancer, the Role of Autophagy, lncRNAs, miRNAs and Exosomes

Breast cancer (BC) is the most frequently diagnosed cancer in women for which numerous diagnostic and therapeutic options have been developed. Namely, the targeted treatment of BC, for the most part, relies on the expression of growth factors and hormone receptors by these cancer cells. Despite this, close to 30% of BC patients may experience relapse due to the presence of minimal residual disease (MRD) consisting of surviving disseminated tumour cells (DTCs) from the primary tumour which can colonise a secondary site. This can lead to either detectable metastasis or DTCs entering a dormant state for a prolonged period where they are undetectable. In the latter, cells can re-emerge from their dormant state due to intrinsic and microenvironmental cues leading to relapse and metastatic outgrowth. Pre- and clinical studies propose that targeting dormant DTCs may inhibit metastasis, but the choice between keeping them dormant or forcing their “awakening” is still controversial. This review will focus on cancer cells’ microenvironmental cues and metabolic and molecular properties, which lead to dormancy, relapse, and metastatic latency in BC. Furthermore, we will focus on the role of autophagy, long non-coding RNAs (lncRNAs), miRNAs, and exosomes in influencing the induction of dormancy and awakening of dormant BC cells. In addition, we have analysed BC treatment from a viewpoint of autophagy, lncRNAs, miRNAs, and exosomes. We propose the targeted modulation of these processes and molecules as modern aspects of precision medicine for BC treatment, improving both novel and traditional BC treatment options. Understanding these pathways and processes may ultimately improve BC patient prognosis, patient survival, and treatment response.

Screening and Identification of HTNVpv Entry Inhibitors with High-throughput Pseudovirus-based Chemiluminescence

Hantaviruses, such as Hantaan virus (HTNV) and Seoul virus, are the causative agents of Hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS), and are important zoonotic pathogens. China has the highest incidence of HFRS, which is mainly caused by HTNV and Seoul virus. No approved antiviral drugs are available for these hantaviral diseases. Here, a chemiluminescence-based high-throughput-screening (HTS) assay was developed and used to screen HTNV pseudovirus (HTNV_pv) inhibitors in a library of 1813 approved drugs and 556 small-molecule compounds from traditional Chinese medicine sources. We identified six compounds with in vitro anti-HTNV_pv activities in the low-micromolar range (EC₅₀ values of 0.1–2.2 ​μmol/L; selectivity index of 40–900). Among the six selected compounds, cepharanthine not only showed good anti-HTNV_pv activity in vitro but also inhibited HTNV_pv-fluc infection in Balb/c mice 5 ​h after infection by 94% (180 ​mg/kg/d, P ​< ​0.01), 93% (90 ​mg/kg/d, P ​< ​0.01), or 92% (45 ​mg/kg/d, P ​< ​0.01), respectively, in a bioluminescent imaging mouse model. A time-of-addition analysis suggested that the antiviral mechanism of cepharanthine involves the membrane fusion and entry phases. Overall, we have established a HTS method for antiviral drugs screening, and shown that cepharanthine is a candidate for HCPS and HFRS therapy. These findings may offer a starting point for the treatment of patients infected with hantaviruses.

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A chemiluminescence-based high-throughput-screening (HTS) assay was used to screen HTNV pseudovirus (HTNV_pv) inhibitors.

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Cepharanthine showed good anti-HTNV_pv activity in vitro and in vivo.

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A time-of-addition analysis suggested that cepharanthine involves the membrane fusion and entry phases.

Simultaneous proteasome and autophagy inhibition synergistically enhances cytotoxicity of doxorubicin in breast cancer cells

Ubiquitin-proteasome system (UPS) and autophagy are interconnected proteolysis pathways implicated in doxorubicin resistance of breast cancer cells. Following anticancer treatments, autophagy either plays a cytoprotective role or augments treatment-induced cytotoxicity. However, the role of autophagy in breast cancer cells cotreated with doxorubicin and ixazomib remains unclear. The expression of autophagy proteins (LC3A/B and Beclin-1) and UPS protein (ubiquitin) in MDA-MB-231 and MCF-7 cells following doxorubicin, ixazomib, and/or hydroxychloroquine were determined by western blot. The combinatorial effects and combination index (CI) of triple-combination were determined by cell viability assay and CompuSyn software, respectively. Doxorubicin and ixazomib cotreatment increased Beclin-1 (3.8- and 3.5-fold) and LC3-II expression (13.5- and 1.9-fold) in MDA-MB-231 and MCF-7 cells, respectively. Adding lysosomal inhibitor hydroxychloroquine to doxorubicin and ixazomib further increased LC3-II expression to 45.0- and 16.5-fold in MDA-MB-231 and MCF-7 cells, respectively, confirming autophagy induction. The triple-combination synergistically inhibited cell growth, achieving CI 0.672 and 0.157 in MDA-MB-231 and MCF-7 cells, respectively. The triple-combination also induced ubiquitinated proteins accumulation (2.5-fold and 3.0-fold) in MDA-MB-231 and MCF-7 cells, respectively. These results suggest that the autophagy induced by doxorubicin and ixazomib cotreatment serves cytoprotective role in breast cancer cells. Simultaneous UPS and autophagy inhibition synergistically enhanced doxorubicin-mediated cytotoxicity.

Production of Epoxyketone Peptide-Based Proteasome Inhibitors by Streptomyces sp. BRA-346: Regulation and Biosynthesis

Streptomyces sp. BRA-346 is an Actinobacteria isolated from the Brazilian endemic tunicate Euherdmania sp. We have reported that this strain produces epoxyketone peptides, as dihydroeponemycin (DHE) and structurally related analogs. This cocktail of epoxyketone peptides inhibits the proteasome chymotrypsin-like activity and shows high cytotoxicity to glioma cells. However, low yields and poor reproducibility of epoxyketone peptides production by BRA-346 under laboratory cultivation have limited the isolation of epoxyketone peptides for additional studies. Here, we evaluated several cultivation methods using different culture media and chemical elicitors to increase the repertoire of peptide epoxyketone production by this bacterium. Furthermore, BRA-346 genome was sequenced, revealing its broad genetic potential, which is mostly hidden under laboratory conditions. By using specific growth conditions, we were able to evidence different classes of secondary metabolites produced by BRA-346. In addition, by combining genome mining with untargeted metabolomics, we could link the metabolites produced by BRA-346 to its genetic capacity and potential regulators. A single biosynthetic gene cluster (BGC) was related to the production of the target epoxyketone peptides by BRA-346. The candidate BGC displays conserved biosynthetic enzymes with the reported eponemycin (EPN) and TMC-86A (TMC) BGCs. The core of the putative epoxyketone peptide BGC (ORFs A-L), in which ORF A is a LuxR-like transcription factor, was cloned into a heterologous host. The recombinant organism was capable to produce TMC and EPN natural products, along with the biosynthetic intermediates DH-TMC and DHE, and additional congeners. A phylogenetic analysis of the epn/tmc BGC revealed related BGCs in public databases. Most of them carry a proteasome beta-subunit, however, lacking an assigned specialized metabolite. The retrieved BGCs also display a diversity of regulatory genes and TTA codons, indicating tight regulation of this BGC at the transcription and translational levels. These results demonstrate the plasticity of the epn/tmc BGC of BRA-346 in producing epoxyketone peptides and the feasibility of their production in a heterologous host. This work also highlights the capacity of BRA-346 to tightly regulate its secondary metabolism and shed light on how to awake silent gene clusters of Streptomyces sp. BRA-346 to allow the production of pharmacologically important biosynthetic products.

Autophagy, Oxidative Stress and Cancer Development

Simple Summary

Autophagy, as an important cellular repair mechanism, is important for the prevention of several diseases, including metabolic and neurologic disorders, and cancer. Hence, dysfunctional autophagy has been linked to these diseases, and in recent years researchers have tried to outline therapeutic targets in autophagy-related pathways as a treatment. With this review of the literature, we want to give an overview about the connection between oxidative stress, autophagy and cancer.

Abstract

Autophagy is an important cellular repair mechanism, aiming at sequestering misfolded and dysfunctional proteins and damaged cell organelles. Dysfunctions in the autophagy process have been linked to several diseases, like infectious and neurodegenerative diseases, type II diabetes mellitus and cancer. Living organisms are constantly subjected to some degree of oxidative stress, mainly induced by reactive oxygen and nitrogen species. It has been shown that autophagy is readily induced by reactive oxygen species (ROS) upon nutrient deprivation. In recent years, research has increasingly focused on outlining novel therapeutic targets related to the autophagy process. With this review of the literature, we want to give an overview about the link between autophagy, oxidative stress and carcinogenesis.

p62 Promotes the Mitochondrial Localization of p53 through Its UBA Domain and Participates in Regulating the Sensitivity of Ovarian Cancer Cells to Cisplatin

Chemotherapeutic drug-induced p53-dependent crosstalk among tumor cells affects the sensitivity of tumor cells to chemotherapeutic drugs, contributing to chemoresistance. Therefore, pharmacological targeting of p53 may contribute to overcoming drug resistance. The localization of p53 is closely related to its function. Thus, we assessed the effect of p62 on the coordination of p53 mitochondrial localization under chemotherapeutic drug treatment in ovarian cancer cells. We found that the combined use of the proteasome inhibitor epoxomicin and cisplatin led to the accumulation of p53 and sequestosome1(p62) in the mitochondria, downregulated mitochondrial DNA (mtDNA) transcription, inhibited mitochondrial functions, and ultimately promoted apoptosis by enhancing cisplatin sensitivity in ovarian cancer cells. Moreover, the ubiquitin-associated (UBA) domain of p62 was involved in regulating the mitochondrial localization of p53. Our findings suggest that the interaction between p62 and p53 may be a mechanism that determines the fate of tumor cells. In conclusion, p62 coordinated the mitochondrial localization of p53 through its UBA domain, inhibited mtDNA transcription, downregulated mitochondrial function, and promoted ovarian cancer cell death. Our study demonstrates the important role of p53 localization in tumor cell survival and apoptosis, and provides new insights into understanding the anti-tumor mechanism of targeting the ubiquitin–proteasome system in tumor cells.

The efficacy and mechanism of proteasome inhibitors in solid tumor treatment

BACKGROUND

The ubiquitin-proteasome system (UPS) is critical in cellular protein degradation and widely involved in the regulations of cancer hallmarks. Targeting the UPS pathway has emerged as a promising novel treatment in hematological malignancies and solid tumors.

OBJECTIVE

This review mainly focuses on the preclinical results of proteasome inhibitors in solid tumors.

METHODS

We analyzed the published articles associated with the anticancer results of proteasome inhibitors alone or combination chemotherapy in solid tumors. Important data presented in abstract form were also discussed in this review.

RESULTS/CONCLUSION

Proteasome inhibitors, such as bortezomib and carfilzomib, are highly effective in treating solid tumors. The anticancer efficacy is not limited to affect the proteasomal inhibition-associated signaling pathways but also widely involves the signaling pathways related to cell cycle, apoptosis, and epithelial-mesenchymal transition (EMT). In addition, proteasome inhibitors overcome the conventional chemo-resistance of standard chemotherapeutics by inhibiting signaling pathways, such as NF-κB or PI3K/Akt. Combination chemotherapy of proteasome inhibitors and standard chemotherapeutics are widely investigated in multiple relapsed or chemo-resistant solid tumor types, such as breast cancer and pancreatic cancer. The proteasome inhibitors re-sensitize the standard chemotherapeutic regimens and induce synergistic anticancer effects. The development of novel proteasome inhibitors and delivery systems also improves the proteasome inhibitors' anticancer efficacy in solid tumors. This review summarizes the current preclinical results of proteasome inhibitors in solid tumors and reveals the potential anticancer mechanisms.

Knockdown of circ_0006528 Suppresses Cell Proliferation, Migration, Invasion, and Adriamycin Chemoresistance via Regulating the miR-1236-3p/CHD4 Axis in Breast Cancer

BACKGROUND

Adriamycin (ADM) is one of the postoperative chemotherapy drugs for breast cancer (BCa) patients. Circular RNAs have been shown to modulate ADM resistance in many cancers. However, it is unclear whether circ_0006528 can modulate the ADM chemoresistance in BCa.

METHODS

Levels of circ_0006528, microRNA-1236-3p (miR-1236-3p), and chromodomain helicase DNA-binding protein 4 (CHD4) were detected by quantitative real-time polymerase chain reaction or western blot. Cell proliferation, the half maximal inhibitory concentration (IC50) value of ADM, and cell migration and invasion were evaluated by cell counting kit-8 and transwell assays, respectively. The interaction among circ_0006528, miR-1236-3p, and CHD4 was confirmed using dual-luciferase reporter assays. Tumor formation in nude mice was performed to explore the effect of circ_0006528 in vivo.

RESULTS

Higher levels of circ_0006528 and CHD4 and lower level of miR-1236-3p were found in ADM-resistant BCa tissues and cells, and patients with high circ_0006528 had a shorter overall survival. Circ_0006528 could directly bind to miR-1236-3p, and circ_0006528 knockdown or miR-1236-3p overexpression could suppress cell proliferation, migration, invasion, and ADM resistance in ADM-resistant BCa cells. Moreover, circ_0006528-regulated CHD4 expression by sponging miR-1236-3p, and CHD4 elevation reversed the inhibitory effect of circ_0006528 knockdown on ADM-resistant BCa cells. Consistently, circ_0006528 inhibition retarded ADM-resistant BCa tumor growth in vivo by decreasing CHD4 and increasing miR-1236-3p.

CONCLUSIONS

Downregulation of circ_0006528 restrained cell proliferation, migration, invasion, and drug resistance of ADM-resistant BCa cells through inhibiting CHD4 and inducing miR-1236-3p.

Does the proteasome inhibitor bortezomib sensitize to DNA-damaging therapy in gastroenteropancreatic neuroendocrine neoplasms? - A preclinical assessment in vitro and in vivo

BACKGROUND

Well-differentiated gastroenteropancreatic neuroendocrine neoplasms are rare tumors with a slow proliferation. They are virtually resistant to many DNA-damaging therapeutic approaches, such as chemo- and external beam therapy, which might be overcome by DNA damage inhibition induced by proteasome inhibitors such as bortezomib.

METHODS AND RESULTS

In this study, we assessed several combined treatment modalities in vitro and in vivo. By cell-based functional analyses, in a 3D in ovo and an orthotopic mouse model, we demonstrated sensitizing effects of bortezomib combined with cisplatin, radiation and peptide receptor radionuclide therapy (PRRT). By gene expression profiling and western blot, we explored the underlying mechanisms, which resulted in an impaired DNA damage repair. Therapy-induced DNA damage triggered extrinsic proapoptotic signaling as well as the induction of cell cycle arrest, leading to a decreased vital tumor volume and altered tissue composition shown by magnetic resonance imaging and F-18-FDG-PET in vivo, however with no significant additional benefit related to PRRT alone.

CONCLUSIONS

We demonstrated that bortezomib has short-term sensitizing effects when combined with DNA damaging therapy by interfering with DNA repair in vitro and in ovo. Nevertheless, due to high tumor heterogeneity after PRRT in long-term observations, we were not able to prove a therapeutic advantage of bortezomib-combined PRRT in an in vivo mouse model.

The Proteasome Inhibitor Ixazomib Inhibits the Formation and Growth of Pulmonary and Abdominal Osteosarcoma Metastases in Mice

Osteosarcoma is the most common form of primary bone cancer. Over 20% of osteosarcoma patients present with pulmonary metastases at diagnosis, and nearly 70% of these patients fail to respond to treatment. Previous work revealed that human and canine osteosarcoma cell lines are extremely sensitive to the therapeutic proteasome inhibitor bortezomib in vitro. However, bortezomib has proven disappointingly ineffective against solid tumors including sarcomas in animal experiments and clinical trials. Poor tumor penetration has been speculated to account for the inconsistency between in vitro and in vivo responses of solid tumors to bortezomib. Here we show that the second-generation proteasome inhibitor ixazomib, which reportedly has enhanced solid tumor penetration compared to bortezomib, is toxic to human and canine osteosarcoma cells in vitro. We used experimental osteosarcoma metastasis models to compare the efficacies of ixazomib and bortezomib against primary tumors and metastases derived from luciferase-expressing KRIB or 143B human osteosarcoma cell lines in athymic mice. Neither proteasome inhibitor reduced the growth of primary intramuscular KRIB tumors, however both drugs inhibited the growth of established pulmonary metastases created via intravenous inoculation with KRIB cells, which were significantly better vascularized than the primary tumors. Only ixazomib slowed metastases from KRIB primary tumors and inhibited the growth of 143B pulmonary and abdominal metastases, significantly enhancing the survival of mice intravenously injected with 143B cells. Taken together, these results suggest ixazomib exerts better single agent activity against osteosarcoma metastases than bortezomib. These data provide hope that incorporation of ixazomib, or other proteasome inhibitors that penetrate efficiently into solid tumors, into current regimens may improve outcomes for patients diagnosed with metastatic osteosarcoma.

Molecular mechanisms of apoptosis and autophagy elicited by combined treatment with oridonin and cetuximab in laryngeal squamous cell carcinoma

Combined oridonin (ORI), a natural and safe kaurene diterpenoid isolated from Rabdosia rubescens, and cetuximab (Cet), an anti-EGFR monoclonal antibody, have been reported to exert synergistic anti-tumor effects against laryngeal squamous cell carcinoma (LSCC) both in vitro and in vivo by our group. In the present study, we further found that ORI/Cet treatment not only resulted in apoptosis but also induced autophagy. AMPK/mTOR signaling pathway was found to be involved in the activation of autophagy in ORI/Cet-treated LSCC cells, which is independent of p53 status. Additionally, chromatin immunoprecipitation (ChIP) assay showed that ORI/Cet significantly increased the binding NF-κB family member p65 with the promotor of BECN 1, and p65-mediated up-regulation of BECN 1 caused by ORI/Cet is coupled to increased autophagy. On the other hand, we demonstrated that either Beclin 1 SiRNA or autophagy inhibitors could increase ORI/Cet induced-apoptosis, indicating that autophagy induced by combination of the two agents plays a cytoprotective role. Interestingly, 48 h after the combined treatment, autophagy began to decrease but apoptosis was significantly elevated. Our findings suggest that autophagy might be strongly associated with the antitumor efficacy of ORI/Cet, which may be beneficial to the clinical application of ORI/Cet in LSCC treatment.

BET Inhibitors Synergize with Carfilzomib to Induce Cell Death in Cancer Cells via Impairing Nrf1 Transcriptional Activity and Exacerbating the Unfolded Protein Response

Currently, proteasome inhibitors bortezomib, carfilzomib, and ixazomib are successfully used in clinics to treat multiple myeloma. However, these agents show limited efficacy against solid tumors. Identification of drugs that can potentiate the action of proteasome inhibitors could help expand the use of this therapeutic modality to solid tumors. Here, we found that bromodomain extra-terminal (BET) family protein inhibitors such as JQ1, I-BET762, and I-BET151 synergize with carfilzomib in multiple solid tumor cell lines. Mechanistically, BET inhibitors attenuated the ability of the transcription factor Nrf1 to induce proteasome genes in response to proteasome inhibition, thus, impeding the bounce-back response of proteasome activity, a critical pathway by which cells cope with proteotoxic stress. Moreover, we found that treatment with BET inhibitors or depletion of Nrf1 exacerbated the unfolded protein response (UPR), signaling that was initiated by proteasome inhibition. Taken together, our work provides a mechanistic explanation behind the synergy between proteasome and BET inhibitors in cancer cell lines and could prompt future preclinical and clinical studies aimed at further investigating this combination.

A novel FoxM1-PSMB4 axis contributes to proliferation and progression of cervical cancer

The abnormally high activity of the proteasome system is closely related to the occurrence and development of various tumors. PSMB4 is a non-catalytic subunit for the proteasome assembly. Although the reports from genetic screening have demonstrated it's a driver gene for cell growth in several types of solid tumor, its expression pattern and regulatory mechanisms in malignant diseases are still elusive. Here, we found that PSMB4 is overexpressed in cervical cancer tissues. And knockdown of PSMB4 significantly inhibited cervical cancer cell proliferation. The mechanistic study revealed that FoxM1, a master regulator of cell division, binds directly to the promoter region of PSMB4 and regulates the PSMB4 expression in the mRNA level. In addition, the data analysis from TCGA showed a positive correlation between FxoM1 and PSMB4 in cervical cancer. Furthermore, the loss of functional and rescue experiments confirmed that PSMB4 is required for FoxM1-driven cervical cancer cell proliferation. Collectively, our study explains the phenomenon of dysregulated expression of PSMB4 in cervical cancer tissues and verifies its driver effect on cancer cell proliferation. More importantly, it highlights a FoxM1-PSMB4 axis could be a potential target for the treatment of cervical cancer.

Knockdown of lncRNA-HOTAIR downregulates the drug-resistance of breast cancer cells to doxorubicin via the PI3K/AKT/mTOR signaling pathway

The resistance to chemotherapeutic drugs is a critical feature of breast cancer recurrence and metastasis. Long non-coding RNAs (LncRNAs) serve key roles in tumor drug resistance. LncRNA-HOX transcript antisense RNA (HOTAIR) has been reported to be overexpressed in certain types of cancer and may be closely associated with tumor resistance. The current study aimed to investigate the role of lncRNA-HOTAIR in the regulation of breast cancer resistance to doxorubicin (DOX). A breast cancer cell line (MCF-7) and DOX-resistant breast cancer cell line (DOXR-MCF-7) were utilized in the current study. DOXR-MCF-7 cells were transfected with lncRNA-HOTAIR small interfering RNA (siRNA) and control siRNA. Subsequently, MTT and colony formation assays were performed to assess cell proliferation. Cell apoptosis was also evaluated via flow cytometry. In addition, western blotting and reverse transcription-quantitative polymerase chain reaction were performed to detect the expression of caspase-3, B-cell lymphoma 2, Bcl-2-associated X protein, phosphoinositide 3-kinase (PI3K), protein kinase B (AKT) and mechanistic target of rapamycin (mTOR), and the phosphorylation of PI3K, AKT, and mTOR. The data indicated that lncRNA-HOTAIR silencing decreased cell proliferation and increased apoptosis in MCF-7 and DOXR MCF-7 cells. Furthermore, lncRNA-HOTAIR silencing significantly decreased the phosphorylation of PI3K, AKT and mTOR, indicating that the knockdown of lncRNA-HOTAIR effectively attenuates the resistance of breast cancer cells to DOX by inhibiting the PI3K/AKT/mTOR pathway. In summary, the present study indicated that the knockdown of lncRNA-HOTAIR weakened the resistance of breast cancer cells to DOX via PI3K/AKT/mTOR signaling, suggesting that lncRNA-HOTAIR may be a novel intervention target to reverse DOX-resistance in breast cancer.

Autophagy in breast cancer metastatic dormancy: Tumor suppressing or tumor promoting functions?

Breast cancer is the second leading cause of cancer-associated death in women in the United States, with more than 90% of those deaths attributed to metastasis. Breast cancer metastasis is incurable and possesses few treatment options and a poor overall prognosis due in part to confounding metastatic attributes, particularly the acquisition of dormancy-associated phenotypes. Dormant disseminated tumor cells (DTCs) can persist for years-to-decades before recurring as highly aggressive, secondary lesions. Dormancy-associated phenotypes are exhibited by breast cancer stem cells (BCSCs), which undergo tumor initiation and unlimited self-renewal. In addition to their specialized abilities to circumvent chemotherapeutic insults, BCSCs also upregulate autophagy during metastatic dormancy as a means to survive in nutrient poor conditions and environmental stress. As such, therapeutic targeting of autophagy is actively being pursued as an attractive strategy to alleviate metastatic disease and the recurrence of dormant BCSCs. Here we review the molecular and cellular features of autophagy, as well as its paradoxical role in both suppressing and promoting mammary tumor development and metastatic progression. Finally, we highlight the clinical challenges associated with therapeutic targeting of autophagy in metastatic breast cancers.

Delanzomib, a novel proteasome inhibitor, sensitizes breast cancer cells to doxorubicin-induced apoptosis

Background

Delanzomib, a novel proteasome inhibitor, has demonstrated promising efficacy and antitumor ability in human multiple myeloma cell lines and patient‐derived cells. However, the potential therapeutic effects of delanzomib on breast cancer remain unknown. In this study, we show that delanzomib has antitumor effects and synergizes with doxorubicin (Dox) in human breast cancer cell lines.

Methods

Cell proliferation assay and flow cytometry were used to evaluate cell viability and apoptosis in eight human breast cancer cell lines after treatment with delanzomib or Dox. Essential molecules of the p53, MAPK, and apoptosis signaling pathways were analyzed by Western blotting.

Results

Delanzomib induced cell death and demonstrated synergism with Dox in all tested breast cancer cell lines. In addition, delanzomib enhanced the Dox‐induced phosphorylation of p38/JNK and the expression of transcriptional target proteins of p53, such as p21, p27, NOXA, and PUMA.

Conclusion

The combined regimen of the proteasome inhibitor delanzomib with Dox chemotherapy may become an effective strategy for breast cancer therapy.

Ixazomib in combination with carboplatin in pretreated women with advanced triple-negative breast cancer, a phase I/II trial of the AGMT (AGMT MBC-10 trial)

Background

Triple-negative breast cancer (TNBC) comprises a heterogeneous group of diseases which are generally associated with poor prognosis. Up to now, no targeted treatment beyond anti-VEGF therapy has been approved for TNBC and cytotoxic agents remain the mainstay of treatment. Ixazomib is a selective and reversible inhibitor of the proteasome, which has been mainly investigated in the treatment of multiple myeloma. In a preclinical study TNBC cells were treated with the first-generation proteasome inhibitor bortezomib in combination with cisplatin and synergistic efficacy was demonstrated. Clinical data are available for carboplatin plus bortezomib in metastatic ovarian and lung cancers showing remarkable antitumor activity and good tolerability (Mol Cancer 11:26 2012, J Thorac Oncol 4:87–92 2009, J Thorac Oncol 7:1032–1040, 2012). Based on this evidence, the phase I/II MBC-10 trial will evaluate the toxicity profile and efficacy of the second-generation proteasome inhibitor ixazomib in combination with carboplatin in patients with advanced TNBC.

Methods

Patients with metastatic TNBC pretreated with at least one prior line of chemotherapy for advanced disease with a confirmed disease progression and measurable disease according to RECIST criteria 1.1 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 utilizes an alternate dose escalation accelerated titration design. After establishing the maximum tolerated dose (MTD), the efficacy and safety of the combination will be further evaluated (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 progression-free survival, safety, and quality of life. This trial is open for patient enrollment since November 2016 in six Austrian cancer centers. Accrual is planned to be completed within 2 years.

Discussion

Based on preclinical and clinical findings an ixazomib and carboplatin combination is thought to be effective in metastatic TNBC patients. 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.

Trial registration

EudraCT Number: 2016–001421-13 received on March 31, 2016, ClinicalTrials.gov Identifier: NCT02993094 first posted on December 15, 2016. This trial was registered prospectively.

Mitosis inhibitors in anticancer therapy: When blocking the exit becomes a solution

Current microtubule-targeting agents (MTAs) remain amongst the most important antimitotic drugs used against a broad range of malignancies. By perturbing spindle assembly, MTAs activate the spindle assembly checkpoint (SAC), which induces mitotic arrest and subsequent apoptosis. However, besides toxic side effects and resistance, mitotic slippage and failure in triggering apoptosis in various cancer cells are limiting factors of MTAs efficacy. Alternative strategies to target mitosis without affecting microtubules have, thus, led to the identification of small molecules, such as those that target spindle Kinesins, Aurora and Polo-like kinases. Unfortunately, these so-called second-generation of antimitotics, encompassing mitotic blockers and mitotic drivers, have failed in clinical trials. Our recent understanding regarding the mechanisms of cell death during a mitotic arrest pointed out apoptosis as the main variable, providing an opportunity to control the cell fates and influence the effectiveness of antimitotics. Here, we provide an overview on the second-generation of antimitotics, and discuss possible strategies that exploit SAC activity, mitotic slippage/exit and apoptosis induction, in order to improve the efficacy of anticancer strategies that target mitosis.

Expression of the glucagon-like peptide-1 receptor and its role in regulating autophagy in endometrial cancer

Background

A previous report showed that a glucagon-like peptide-1 receptor (GLP-1R) agonist (exenatide) induced apoptosis in endometrial cancer cells. However, the pathophysiological role of GLP-1R in endometrial cancer has not been fully elucidated. Here, we investigated the effects of the GLP-1R agonist liraglutide in endometrial cancer cells and examined the association between GLP-1R expression and clinicopathological characteristics in endometrial cancer patients.

Methods

Human Ishikawa endometrial cancer cells were treated with different concentrations of liraglutide. To assess the effects of liraglutide, cell viability, colony formation, flow cytometry, Western blotting, and immunofluorescence assays were performed. Autophagy induction was examined by analyzing LC3 and p62 expression and autophagosome accumulation. Moreover, using a tissue microarray, we analyzed GLP-1R expression in 154 endometrial cancer tissue samples by immunohistochemistry.

Results

In accordance with the previous report, liraglutide inhibited Ishikawa cell growth in a dose-dependent manner. Liraglutide significantly induced autophagy, and phosphorylated AMPK expression was elevated. Immunohistochemical analysis revealed that GLP-1R expression was associated with positive estrogen receptor and progesterone receptor status, and higher GLP-1R expression was significantly correlated with better progression-free survival.

Conclusions

The use of liraglutide to target autophagy in endometrial cancer cells may be a novel potential treatment for endometrial cancer. Furthermore, higher GLP-1R expression may be associated with better prognosis in endometrial cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4570-8) contains supplementary material, which is available to authorized users.

Next-generation proteasome inhibitor oprozomib enhances sensitivity to doxorubicin in triple-negative breast cancer cells

Doxorubicin (DOX) is the most common chemotherapeutic drug for treatment of breast cancer but intrinsic and acquired resistance frequently occurs and severe side effects occur at high doses. DOX might induce activation of NF-κB causing this resistance, in which case proteasome inhibitors could inhibit activation of NF-κB by blocking inhibitory factor κB-alpha degradation. Triple-negative breast cancer (TNBC) is highly progressive and there are no established therapeutic targets against TNBC. Although some proteasome inhibitors have been shown to have antitumor effects in breast cancer, the effect of orally bioavailable proteasome inhibitor oprozomib on TNBC proliferation remains unclear. In the present study, we investigated the role of oprozomib in two TNBC lines, MDA-MB-231 and BT-549. Oprozomib had cytotoxic effects on TNBC cells and increased DOX-induced cytotoxic effects and apoptosis by enhancing DOX-induced JNK/p38 MAPK phosphorylation and inhibiting DOX-induced inhibitory factor êB alpha degradation. These results suggest that oprozomib has potent antitumor effects on TNBC in vitro and can sensitize TNBC cells to DOX treatment. The combination of DOX and oprozomib may be an effective and feasible therapeutic option for TNBC.

SIRT7 depletion inhibits cell proliferation, migration, and increases drug sensitivity by activating p38MAPK in breast cancer cells

SIRT7 is a member of the sirtuin family of proteins that are known to be associated with tumor development. However, the functional roles and molecular mechanisms underlying the function of SIRT7 in breast cancer cell survival and tumor development remain unclear. Recent studies demonstrated that SIRT7 is upregulated in breast cancer cells and tissues. In the present study, we systematically explored the roles of SIRT7 in the growth of breast cancer cells and tumors both in vitro and in vivo. Our results showed that SIRT7 plays a major role in facilitating cell survival by promoting cell proliferation and inhibiting apoptosis. SIRT7 depletion significantly inhibited cell invasion and wound healing by blocking cell cycle progression and inducing cell apoptosis. Meanwhile, SIRT7 depletion can increase the sensitivity of breast cancer cells to doxorubicin (DOX). Xenograft model studies showed that stable silencing of SIRT7 inhibited tumor growth and enhanced tumor sensitivity to DOX. Further research revealed that p38MAPK is involved in SIRT7-mediated regulation of breast cancer cell proliferation and tumor growth. Taken together, our results showed that SIRT7 plays a critical role in breast cancer cell survival, migration, and tumor growth, and increased the efficiency of DOX treatment both in vitro and in vivo. Therefore, SIRT7 is a promising therapeutic target in breast cancer treatment.

Second-generation proteasome inhibitor carfilzomib enhances doxorubicin-induced cytotoxicity and apoptosis in breast cancer cells

Proteasome inhibition is an attractive approach for anticancer therapy. Doxorubicin (DOX) is widely used for treatment in a number of cancers including breast cancer; however, the development of DOX resistance largely limits its clinical application. One of the possible mechanisms of DOX-resistance is that DOX might induce the activation of NF-κB. In this case, proteasome inhibitors could inhibit the activation of NF-κB by blocking inhibitory factor κB (IκB) degradation. Carfilzomib, a second-generation proteasome inhibitor, overcomes bortezomib resistance and lessens its side-effects. Currently, the effect of carfilzomib on breast cancer cell proliferation remains unclear. In this study, we exploited the role of carfilzomib in seven breast cancer cell lines, MCF7, T-47D, MDA-MB-361, HCC1954, MDA-MB-468, MDA-MB-231, and BT-549, representing all major molecular subtypes of breast cancer. We found that carfilzomib alone had cytotoxic effects on the breast cancer cells and it increased DOX-induced cytotoxic effects and apoptosis in combination by enhancing DOX-induced JNK phosphorylation and inhibiting DOX-induced IκBα degradation. The results suggest that carfilzomib has potent antitumor effects on breast cancer in vitro and can sensitize breast cancer cells to DOX treatment. DOX in combination with carfilzomib may be an effective and feasible therapeutic option in the clinical trials for treating breast cancer.

Positioning of proteasome inhibitors in therapy of solid malignancies

Targeting of the protein degradation pathway, in particular, the ubiquitin-proteasome system, has emerged as an attractive novel cancer chemotherapeutic modality. Although proteasome inhibitors have been most successfully applied in the treatment of hematological malignancies, they also received continuing interest for the treatment of solid tumors. In this review, we summarize the current positioning of proteasome inhibitors in the treatment of common solid malignancies (e.g., lung, colon, pancreas, breast, and head and neck cancer), addressing topics of their mechanism(s) of action, predictive factors and molecular mechanisms of resistance.

MiR-770 suppresses the chemo-resistance and metastasis of triple negative breast cancer via direct targeting of STMN1

Chemo-resistance and metastasis of triple negative breast cancer (TNBC) contributed the most of treatment failure in the clinic. MicroRNAs (miRNAs) have been proved to be involved in many biological processes and diseases. In this study, we aimed to determine the role of miR-770 in the regulation of chemo-resistance and metastasis of TNBC. Clinically, miR-770 was highly expressed in chemo-sensitive tissues and predicted a better prognosis of TNBC. Functionally, ectopic expression of miR-770 suppressed the doxorubicin-resistance of TNBC cell lines via regulation of apoptosis and tumor microenvironment, which was mediated by exosomes. Moreover, miR-770 overexpression inhibited the migration and invasion. Rescue of STMN1 could partly reverse the effect of miR-770 in TNBC behaviors. Furthermore, we also demonstrated that overexpression of miR-770 inhibited DOX resistance and metastasis in vivo. Taken together, our results proved that miR-770 could suppress the doxorubicin-resistance and metastasis of TNBC cells, which broaden our insights into the underlying mechanisms in chemo-resistance and metastasis, and provided a new prognostic marker for TNBC cells.

miR-125b regulates the drug-resistance of breast cancer cells to doxorubicin by targeting HAX-1

MircroRNAs (miRNAs) are considered as essential regulators in the tumorigenesis and chemoresistance of multiple cancer types. In the present study, it was demonstrated that the expression levels of miR-125b were significantly downregulated in the tissues of patients with breast cancer (BC), as well as the BC cell lines in vitro. To study the association between chemoresistance and miR-125b in BC, doxorubicin (DOX)-resistant MCF-7 (MCF-7/R) cells were established, and gain- and loss-of-function experiments were performed. It was demonstrated that the overexpression of miR-125b increased the sensitivity of MCF-7/R cells to DOX. Furthermore, it was revealed that the sensitization of miR-125b mimics to DOX-induced cell death was regulated by the hematopoietic cell-specific protein 1-associated protein X-1 (HAX-1) vector and HAX-1 small interfering RNA. These results emphasized the notable function of miR-125b and its target of HAX-1 in regulating DOX-resistance. In addition, it was demonstrated that the miR-125b mimics promoted the loss of the mitochondrial membrane potential and the generation of reactive oxygen species induced by DOX treatment in MCF-7/R cells. These data suggest that the miR-125b-HAX-1-mitochondria pathway has a notable function in the treatment of DOX-resistant BC cells, which may provide a novel target for the chemotherapy of BC.

Targeting autophagy in cancer

Autophagy is a mechanism by which cellular material is delivered to lysosomes for degradation, leading to the basal turnover of cell components and providing energy and macromolecular precursors. Autophagy has opposing, context-dependent roles in cancer, and interventions to both stimulate and inhibit autophagy have been proposed as cancer therapies. This has led to the therapeutic targeting of autophagy in cancer to be sometimes viewed as controversial. In this Review, we suggest a way forwards for the effective targeting of autophagy by understanding the context-dependent roles of autophagy and by capitalizing on modern approaches to clinical trial design.

Anti-cancer agents and reactive oxygen species modulators that target cancer cell metabolism

Traditionally the perspective on reactive oxygen species (ROS) has centered on the role they play as carcinogenic or cancer-causing radicals. Over the years, characterization and functional studies have revealed the complexity of ROS as signaling molecules that regulate various physiological cellular responses or whose levels are altered in various diseases. Cancer cells often maintain high basal level of ROS and are vulnerable to any further increase in ROS levels beyond a certain protective threshold. Consequently, ROS-modulation has emerged as an anticancer strategy with synthesis of various ROS-inducing or responsive agents that target cancer cells. Of note, an increased carbohydrate uptake and/or induction of death receptors of cancer cells was exploited to develop glycoconjugates that potentially induce cellular stress, ROS and apoptosis. This mini review highlights the development of compounds that target cancer cells by taking advantage of redox or metabolic alteration in cancer cells.

Identification of the anticancer effects of a novel proteasome inhibitor, ixazomib, on colorectal cancer using a combined method of microarray and bioinformatics analysis

Purpose

The study aimed to explore the anticancer effects of a novel proteasome inhibitor, ixazomib, on colorectal cancer (CRC) using a combined method of microarray and bioinformatics analysis.

Materials and methods

Cell proliferation was tested by Cell Counting Kit-8 (CCK-8) assay for SW620 cells treated with different concentrations of ixazomib and different treatment times. The microarray analysis was conducted for six samples, including three samples of SW620 cells untreated with ixazomib and three samples of SW620 cells treated with ixazomib. The differentially expressed genes (DEGs) between untreated and treated samples were identified by the Linear Models for Microarray data (LIMMA) package in R language. The Gene Ontology (GO) functional and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed for the DEGs using the Database for Annotation, Visualization and Integrated Discovery (DAVID) and KEGG Orthology-Based Annotation System (KOBAS) online tool. The protein–protein interaction (PPI) network was constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, and module analysis was performed for the PPI network.

Results

Ixazomib could inhibit the proliferation of SW620 cells in a dose-dependent and time-dependent manner. A total of 743 DEGs, including 203 upregulated DEGs such as HSPA6 and 540 downregulated DEGs such as APCDD1, were identified. Eighty-three GO terms were enriched for DEGs, which were mainly related to protein folding, apoptotic process, transcription factor activity, and proteasome. Thirty-seven KEGG pathways were perturbed, including pathway of apoptosis and cell cycle. Forty-six hub genes, such as TP53, JUN, and ITGA2, were screened out, and three modules with important functions were mined from the PPI network.

Conclusion

The novel proteasome inhibitor ixazomib significantly inhibited the proliferation of human CRC SW620 cells. It exerted anticancer effects through targeting the expression of DEGs, such as HSPA6, APCDD1, TP53, and JUN, and affecting the signaling pathways including apoptosis and cell cycle pathway, which demonstrated the promising potential of ixazomib for CRC therapy.