Molecular basis of resistance to proteasome inhibitors in hematological malignancies

Different Strategies to Overcome Resistance to Proteasome Inhibitors-A Summary 20 Years after Their Introduction

Proteasome inhibitors (PIs), bortezomib, carfilzomib, and ixazomib, are the first-line treatment for multiple myeloma (MM). They inhibit cytosolic protein degradation in cells, which leads to the accumulation of misfolded and malfunctioned proteins in the cytosol and endoplasmic reticulum, resulting in cell death. Despite being a breakthrough in MM therapy, malignant cells develop resistance to PIs via different mechanisms. Understanding these mechanisms drives research toward new anticancer agents to overcome PI resistance. In this review, we summarize the mechanism of action of PIs and how MM cells adapt to these drugs to develop resistance. Finally, we explore these mechanisms to present strategies to interfere with PI resistance. The strategies include new inhibitors of the ubiquitin-proteasome system, drug efflux inhibitors, autophagy disruption, targeting stress response mechanisms, affecting survival and cell cycle regulators, bone marrow microenvironment modulation, and immunotherapy. We list potential pharmacological targets examined in in vitro, in vivo, and clinical studies. Some of these strategies have already provided clinicians with new anti-MM medications, such as panobinostat and selinexor. We hope that further exploration of the subject will broaden the range of therapeutic options and improve patient outcomes.

A comprehensive review of the PTEN/PI3K/Akt axis in multiple myeloma: From molecular interactions to potential therapeutic targets

Phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt) signaling pathways contribute to the development of several cancers, including multiple myeloma (MM). PTEN is a tumor suppressor that influences the PI3K/Akt/mTOR pathway, which in turn impacts vital cellular processes like growth, survival, and treatment resistance. The current study aims to present the role of PTEN and PI3K/Akt/mTOR signaling in the development of MM and its response to treatment. In addition, the molecular interactions in MM that underpin the PI3K/Akt/mTOR pathway and address potential implications for the development of successful treatment plans are also discussed in detail. We investigate their relationship to both upstream and downstream regulators, highlighting new developments in combined therapies that target the PTEN/PI3K/Akt axis to overcome drug resistance, including the use of PI3K and mitogen-activated protein kinase (MAPK) inhibitors. We also emphasize that PTEN/PI3K/Akt pathway elements may be used in MM diagnosis, prognosis, and therapeutic targets.

Using nanotechnology to progress the utilization of marine natural products in combating multidrug resistance in cancer: A prospective strategy

Achieving targeted, customized, and combination therapies with clarity of the involved molecular pathways is crucial in the treatment as well as overcoming multidrug resistance (MDR) in cancer. Nanotechnology has emerged as an innovative and promising approach to address the problem of drug resistance. Developing nano-formulation-based therapies using therapeutic agents poses a synergistic effect to overcome MDR in cancer. In this review, we aimed to highlight the important pathways involved in the progression of MDR in cancer mediated through nanotechnology-based approaches that have been employed to circumvent them in recent years. Here, we also discussed the potential use of marine metabolites to treat MDR in cancer, utilizing active drug-targeting nanomedicine-based techniques to enhance selective drug accumulation in cancer cells. The discussion also provides future insights for developing complex targeted, multistage responsive nanomedical drug delivery systems for effective cancer treatments. We propose more combinational studies and their validation for the possible marine-based nanoformulations for future development.

Long non-coding RNA MALAT1 in hematological malignancies and its clinical applications

ABSTRACT

Metastasis-associated lung adenocarcinoma transcript 1 ( MALAT1 ) is a well-established oncogenic long non-coding RNA, the higher expression of which is strongly correlated with cancer events such as tumorigenesis, progression, metastasis, drug resistance, and treatment outcome in solid cancers. Recently, a series of studies has highlighted its potential role in hematological malignancies in terms of these events. Similar to solid cancers, MALAT1 can regulate various target genes via sponging and epigenetic mechanisms, but the miRNAs sponged by MALAT1 differ from those identified in solid cancers. In this review, we systematically describe the role and underlying mechanisms of MALAT1 in multiple types of hematological malignancies, including regulation of cell proliferation, metastasis, stress response, and glycolysis. Clinically, MALAT1 expression is related to poor treatment outcome and drug resistance, therefore exhibiting potential prognostic value in multiple myeloma, lymphoma, and leukemia. Finally, we discuss the evaluation of MALAT1 as a novel therapeutic target against cancer in preclinical studies.

NCX1/Ca2+ promotes autophagy and decreases bortezomib activity in multiple myeloma through non-canonical NFκB signaling pathway

Although bortezomib (BTZ) is the cornerstone of anti-multiple myeloma (MM) therapy, the inevitable primary and secondary drug resistance still seriously affects the prognosis of patients. New treatment strategies are in need. Sodium-calcium exchanger 1 (NCX1) is a calcium-permeable ion transporter on the membrane, and our previous studies showed that low NCX1 confers inferior viability in MM cells and suppressed osteoclast differentiation. However, the effect of NCX1 on BTZ sensitivity of MM and its possible mechanism remain unclear. In this study, we investigated the effect of NCX1 on BTZ sensitivity in MM, focusing on cellular processes of autophagy and cell viability. Our results provide evidence that NCX1 expression correlates with MM disease progression and low NCX1 expression increases BTZ sensitivity. NCX1/Ca2+ triggered autophagic flux through non-canonical NFκB pathway in MM cells, leading to attenuated the sensitivity of BTZ. Knockdown or inhibition of NCX1 could potentiate the anti-MM activity of BTZ in vitro and vivo, and inhibition of autophagy sensitized NCX1-overexpressing MM cells to BTZ. In general, this work implicates NCX1 as a potential therapeutic target in MM with BTZ resistance and provides novel mechanistic insights into its vital role in combating BTZ resistance.

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

Proteasome Inhibitors in Multiple Myeloma: Biological Insights on Mechanisms of Action or Resistance Informed by Functional Genomics

During the last 20 years, proteasome inhibitors have been a cornerstone for the therapeutic management of multiple myeloma (MM). This review highlights how MM research has evolved over time in terms of our understanding of the mechanistic basis for the pronounced clinical activity of proteasome inhibitors in MM, compared with the limited clinical applications of this drug class outside the setting of plasma cell dyscrasias.

Acute suppression of translation by hyperthermia enhances anti-myeloma activity of carfilzomib

Hyperthermia is a unique treatment option for cancers. Multiple myeloma (MM) remains incurable and innovative therapeutic options are needed. We investigated the efficacy of hyperthermia and carfilzomib in combination against MM cells. Although MM cell lines exhibited different susceptibilities to pulsatile carfilzomib treatment, mild hyperthermia at 43℃ induced MM cell death in all cell lines in a time-dependent manner. Hyperthermia and carfilzomib cooperatively induced MM cell death even under suboptimal conditions. The pro-survival mediators PIM2 and NRF2 accumulated in MM cells due to inhibition of their proteasomal degradation by carfilzomib; however, hyperthermia acutely suppressed translation in parallel with phosphorylation of eIF2α to reduce these proteins in MM cells. Recovery of β5 subunit enzymatic activity from its immediate inhibition by carfilzomib was observed at 24 h in carfilzomib-insusceptible KMS-11, OPM-2, and RPMI8226 cells, but not in carfilzomib-sensitive MM.1S cells. However, heat treatment suppressed the recovery of β5 subunit activity in these carfilzomib-insusceptible cells. Therefore, hyperthermia re-sensitized MM cells to carfilzomib. Our results support the treatment of MM with hyperthermia in combination with carfilzomib. Further research is warranted on hyperthermia for drug-resistant extramedullary plasmacytoma.

Cyclophosphamide, Bortezomib, and Dexamethasone and Severe Systolic Heart Failure: A Case Report

Multiple myeloma (MM) is a neoplastic proliferation of plasma cells in bone marrow. Pharmacotherapy for the management of patients with MM includes drug classes like proteasome inhibitors, monoclonal antibodies, immunomodulators, alkylating agents, steroids, etc. We present a case of new-onset heart failure with reduced ejection fraction (HFrEF) in a patient with previously normal ejection fraction after treatment with a cyclophosphamide, bortezomib, and dexamethasone (CyBorD) chemotherapeutic regimen. An echocardiogram done after the completion of nine cycles of chemotherapy in a period of about 4.5 months showed severely decreased left ventricular systolic function with an ejection fraction of only 15-20% and grade I diastolic dysfunction. Cardiac catheterization showed no angiographic evidence of vessel occlusion or epicardial disease. HFrEF was managed with the initiation of guideline-directed medical therapy with cardiology clinic follow-up, and the patient was discharged with a plan to start a lenalidomide-based chemotherapeutic regimen with oncology clinic follow-up. It is, therefore, imperative to perform a thorough cardiovascular assessment before initiation of chemotherapy, complemented by periodic and recurrent assessments of cardiovascular function during and after completion of the treatment course, for early detection and prevention of potentially severe cardiovascular toxicities in patients with MM.

Decoding the secrets: how conformational and structural regulators inhibit the human 20S proteasome

Acquired resistance to drugs that modulate specific protein functions, such as the human proteasome, presents a significant challenge in targeted therapies. This underscores the importance of devising new methodologies to predict drug binding and potential resistance due to specific protein mutations. In this work, we conducted an extensive computational analysis to ascertain the effects of selected mutations (Ala49Thr, Ala50Val, and Cys52Phe) within the active site of the human proteasome. Specifically, we sought to understand how these mutations might disrupt protein function either by altering protein stability or by impeding interactions with a clinical administered drug. Leveraging molecular dynamics simulations and molecular docking calculations, we assessed the effect of these mutations on protein stability and ligand affinity. Notably, our results indicate that the Cys52Phe mutation critically impacts protein-ligand binding, providing valuable insights into potential proteasome inhibitor resistance.

Regulatory role of RBM39 in acute myeloid leukemia: Mediation through the PI3K/AKT pathway

BACKGROUND

Acute myeloid leukemia (AML) presents ongoing therapeutic challenges due to its intricate molecular pathogenesis. This study aimed to elucidate the role of RNA binding motif protein 39 (RBM39) in AML cell proliferation, apoptosis, and chemosensitivity, and its potential modulation of the PI3K/AKT pathway.

METHODS

In vitro and in vivo experiments were conducted using AML cell lines (K562 and U937) and bone marrow mononuclear cells (BM-MNCs) from AML patients and healthy donors. RBM39 mRNA and protein levels were measured using qRT-PCR and Western blotting. Cells were transfected with sh-RBM39 or sh-control, and then treated with daunorubicin (DNR) or homoharringtonine (HHT) at varied concentrations. Cell proliferation, chemosensitivity, and apoptosis were assessed through CCK-8 assay and Annexin V-APC/PI staining. RNA sequencing identified differentially expressed genes (DEGs) post RBM39 knockdown. An in vivo xenograft AML model using E7070, a selective RBM39 inhibitor, was employed to evaluate RBM39 modulation effects.

RESULTS

Elevated RBM39 levels were found in AML patients and cell lines compared to controls. RBM39 knockdown promoted apoptosis, curtailed cell proliferation, and enhanced chemosensitivity to DNR and HHT in vitro. Drug-resistant or relapsed AML patients displayed higher RBM39 levels. RNA sequencing after RBM39 knockdown revealed downregulated PI3K/AKT signaling. The xenograft model validated in vitro results, as E7070 treatment suppressed AML xenograft growth via RBM39-mediated PI3K/AKT pathway suppression.

CONCLUSION

RBM39 plays a pivotal role in AML progression through the PI3K/AKT signaling pathway. Targeting RBM39, potentially with E7070, could inhibit proliferation and induce apoptosis in AML cells, offering a promising avenue for future AML research and treatment.

Lysin (K)-specific demethylase 1 inhibition enhances proteasome inhibitor response and overcomes drug resistance in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is an incurable plasma cell malignancy, accounting for approximately 1% of all cancers. Despite recent advances in the treatment of MM, due to the introduction of proteasome inhibitors (PIs) such as bortezomib (BTZ) and carfilzomib (CFZ), relapses and disease progression remain common. Therefore, a major challenge is the development of novel therapeutic approaches to overcome drug resistance, improve patient outcomes, and broaden PIs applicability to other pathologies.

METHODS

We performed genetic and drug screens to identify new synthetic lethal partners to PIs, and validated candidates in PI-sensitive and -resistant MM cells. We also tested best synthetic lethal interactions in other B-cell malignancies, such as mantle cell, Burkitt's and diffuse large B-cell lymphomas. We evaluated the toxicity of combination treatments in normal peripheral blood mononuclear cells (PBMCs) and bone marrow stromal cells (BMSCs). We confirmed the combo treatment' synergistic effects ex vivo in primary CD138+ cells from MM patients, and in different MM xenograft models. We exploited RNA-sequencing and Reverse-Phase Protein Arrays (RPPA) to investigate the molecular mechanisms of the synergy.

RESULTS

We identified lysine (K)-specific demethylase 1 (LSD1) as a top candidate whose inhibition can synergize with CFZ treatment. LSD1 silencing enhanced CFZ sensitivity in both PI-resistant and -sensitive MM cells, resulting in increased tumor cell death. Several LSD1 inhibitors (SP2509, SP2577, and CC-90011) triggered synergistic cytotoxicity in combination with different PIs in MM and other B-cell neoplasms. CFZ/SP2509 treatment exhibited a favorable cytotoxicity profile toward PBMCs and BMSCs. We confirmed the clinical potential of LSD1-proteasome inhibition in primary CD138+ cells of MM patients, and in MM xenograft models, leading to the inhibition of tumor progression. DNA damage response (DDR) and proliferation machinery were the most affected pathways by CFZ/SP2509 combo treatment, responsible for the anti-tumoral effects.

CONCLUSIONS

The present study preclinically demonstrated that LSD1 inhibition could provide a valuable strategy to enhance PI sensitivity and overcome drug resistance in MM patients and that this combination might be exploited for the treatment of other B-cell malignancies, thus extending the therapeutic impact of the project.

siRNA Lipid-Polymer Nanoparticles Targeting E-Selectin and Cyclophilin A in Bone Marrow for Combination Multiple Myeloma Therapy

Introduction

Multiple myeloma (MM) is a hematological blood cancer of the bone marrow that remains largely incurable, in part due to its physical interactions with the bone marrow microenvironment. Such interactions enhance the homing, proliferation, and drug resistance of MM cells. Specifically, adhesion receptors and homing factors, E-selectin (ES) and cyclophilin A (CyPA), respectively, expressed by bone marrow endothelial cells enhance MM colonization and dissemination. Thus, silencing of ES and CyPA presents a potential therapeutic strategy to evade MM spreading. However, small molecule inhibition of ES and CyPA expressed by bone marrow endothelial cells remains challenging, and blocking antibodies induce further MM propagation. Therefore, ES and CyPA are promising candidates for inhibition via RNA interference (RNAi).

Methods

Here, we utilized a previously developed lipid-polymer nanoparticle for RNAi therapy, that delivers siRNA to the bone marrow perivascular niche. We utilized our platform to co-deliver ES and CyPA siRNAs to prevent MM dissemination in vivo.

Results

Lipid-polymer nanoparticles effectively downregulated ES expression in vitro, which decreased MM cell adhesion and migration through endothelial monolayers. Additionally, in vivo delivery of lipid-polymer nanoparticles co-encapsulating ES and CyPA siRNA extended survival in a xenograft mouse model of MM, either alone or in combination with the proteasome inhibitor bortezomib.

Conclusions

Our combination siRNA lipid-polymer nanoparticle therapy presents a vascular microenvironment-targeting strategy as a potential paradigm shift for MM therapies, which could be extended to other cancers that colonize the bone marrow.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00774-y.

CD317 maintains proteostasis and cell survival in response to proteasome inhibitors by targeting calnexin for RACK1-mediated autophagic degradation

Unbalanced protein homeostasis (proteostasis) networks are frequently linked to tumorigenesis, making cancer cells more susceptible to treatments that target proteostasis regulators. Proteasome inhibition is the first licensed proteostasis-targeting therapeutic strategy, and has been proven effective in hematological malignancy patients. However, drug resistance almost inevitably develops, pressing for a better understanding of the mechanisms that preserve proteostasis in tumor cells. Here we report that CD317, a tumor-targeting antigen with a unique topology, was upregulated in hematological malignancies and preserved proteostasis and cell viability in response to proteasome inhibitors (PIs). Knocking down CD317 lowered Ca²⁺ levels in the endoplasmic reticulum (ER), promoting PIs-induced proteostasis failure and cell death. Mechanistically, CD317 interacted with calnexin (CNX), an ER chaperone protein that limits calcium refilling via the Ca²⁺ pump SERCA, thereby subjecting CNX to RACK1-mediated autophagic degradation. As a result, CD317 decreased the level of CNX protein, coordinating Ca²⁺ uptake and thus favoring protein folding and quality control in the ER lumen. Our findings reveal a previously unrecognized role of CD317 in proteostasis control and imply that CD317 could be a promising target for resolving PIs resistance in the clinic.

Diagnostic and therapeutic potential of protease inhibition

Proteases are enzymes that hydrolyze peptide bonds in proteins and peptides; thus, they control virtually all biological processes. Our understanding of protease function has advanced considerably from nonselective digestive enzymes to highly specialized molecular scissors that orchestrate complex signaling networks through a limited proteolysis. The catalytic activity of proteases is tightly regulated at several levels, ranging from gene expression through trafficking and maturation to posttranslational modifications. However, when this delicate balance is disturbed, many diseases develop, including cancer, inflammatory disorders, diabetes, and neurodegenerative diseases. This new understanding of the role of proteases in pathologic physiology indicates that these enzymes represent excellent molecular targets for the development of therapeutic inhibitors, as well as for the design of chemical probes to visualize their redundant activity. Recently, numerous platform technologies have been developed to identify and optimize protease substrates and inhibitors, which were further used as lead structures for the development of chemical probes and therapeutic drugs. Due to this considerable success, the clinical potential of proteases in therapeutics and diagnostics is rapidly growing and is still not completely explored. Therefore, small molecules that can selectively target aberrant protease activity are emerging in diseases cells. In this review, we describe modern trends in the design of protease drugs as well as small molecule activity-based probes to visualize selected proteases in clinical settings.

Autophagy in Hematological Malignancies

Simple Summary

Autophagy is a dynamic and tightly regulated process that seems to have dual effects in cancer. In some contexts, it can induce carcinogenesis and promote cancer cell survival, whereas in others, it acts preventing tumor cell growth and tumor progression. Thus, autophagy functions seem to strictly depend on cancer ontogenesis, progression, and type. Here, we will dive into the current knowledge of autophagy in hematological malignancies and will highlight the main genetic components involved in each cancer type.

Abstract

Autophagy is a highly conserved metabolic pathway via which unwanted intracellular materials, such as unfolded proteins or damaged organelles, are digested. It is activated in response to conditions of oxidative stress or starvation, and is essential for the maintenance of cellular homeostasis and other vital functions, such as differentiation, cell death, and the cell cycle. Therefore, autophagy plays an important role in the initiation and progression of tumors, including hematological malignancies, where damaged autophagy during hematopoiesis can cause malignant transformation and increase cell proliferation. Over the last decade, the importance of autophagy in response to standard pharmacological treatment of hematological tumors has been observed, revealing completely opposite roles depending on the tumor type and stage. Thus, autophagy can promote tumor survival by attenuating the cellular damage caused by drugs and/or stabilizing oncogenic proteins, but can also have an antitumoral effect due to autophagic cell death. Therefore, autophagy-based strategies must depend on the context to create specific and safe combination therapies that could contribute to improved clinical outcomes. In this review, we describe the process of autophagy and its role on hematopoiesis, and we highlight recent research investigating its role as a potential therapeutic target in hematological malignancies. The findings suggest that genetic variants within autophagy-related genes modulate the risk of developing hemopathies, as well as patient survival.

Kinase Inhibition in Multiple Myeloma: Current Scenario and Clinical Perspectives

Multiple myeloma (MM) is a blood cell neoplasm characterized by excessive production of malignant monoclonal plasma cells (activated B lymphocytes) by the bone marrow, which end up synthesizing antibodies or antibody fragments, called M proteins, in excess. The accumulation of this production, both cells themselves and of the immunoglobulins, causes a series of problems for the patient, of a systemic and local nature, such as blood hyperviscosity, renal failure, anemia, bone lesions, and infections due to compromised immunity. MM is the third most common hematological neoplasm, constituting 1% of all cancer cases, and is a disease that is difficult to treat, still being considered an incurable disease. The treatments currently available cannot cure the patient, but only extend their lifespan, and the main and most effective alternative is autologous hematopoietic stem cell transplantation, but not every patient is eligible, often due to age and pre-existing comorbidities. In this context, the search for new therapies that can bring better results to patients is of utmost importance. Protein tyrosine kinases (PTKs) are involved in several biological processes, such as cell growth regulation and proliferation, thus, mutations that affect their functionality can have a great impact on crucial molecular pathways in the cells, leading to tumorigenesis. In the past couple of decades, the use of small-molecule inhibitors, which include tyrosine kinase inhibitors (TKIs), has been a hallmark in the treatment of hematological malignancies, and MM patients may also benefit from TKI-based treatment strategies. In this review, we seek to understand the applicability of TKIs used in MM clinical trials in the last 10 years.

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.

Understanding ER homeostasis and the UPR to enhance treatment efficacy of acute myeloid leukemia

Protein biogenesis, maturation and degradation are tightly regulated processes that are governed by a complex network of signaling pathways. The endoplasmic reticulum (ER) is responsible for biosynthesis and maturation of secretory proteins. Circumstances that alter cellular protein homeostasis, determine accumulation of misfolded and unfolded proteins in the ER, a condition defined as ER stress. In case of stress, the ER activates an adaptive response called unfolded protein response (UPR), a series of pathways of major relevance for cancer biology. The UPR plays a preeminent role in adaptation of tumor cells to the harsh conditions that they experience, due to high rates of proliferation, metabolic abnormalities and hostile environment scarce in oxygen and nutrients. Furthermore, the UPR is among the main adaptive cell stress responses contributing to the development of resistance to drugs and chemotherapy. Clinical management of Acute Myeloid Leukemia (AML) has improved significantly in the last decade, thanks to development of molecular targeted therapies. However, the emergence of treatment-resistant clones renders the rate of AML cure dismal. Moreover, different cell populations that constitute the bone marrow niche recently emerged as a main determinant leading to drug resistance. Herein we summarize the most relevant literature regarding the role played by the UPR in expansion of AML and ability to develop drug resistance and we discuss different possible modalities to overturn this adaptive response against leukemia. To this aim, we also describe the interconnection of the UPR with other cellular stress responses regulating protein homeostasis. Finally, we review the newest findings about the crosstalk between AML cells and cells of the bone marrow niche, under physiological conditions and in response to therapies, discussing in particular the importance of the niche in supporting survival of AML cells by favoring protein homeostasis.

The molecular mechanism and challenge of targeting XPO1 in treatment of relapsed and refractory myeloma

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Significant progress has been made on the treatment of MM during past two decades.

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Acquired drug-resistance continues to drive early relapse in primary refractory MM.

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XPO1 over-expression and cargo mislocalization are associated with drug-resistance.

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XPO1 inhibitor selinexor restores drug sensitivity to subsets of RR-MM cells.

Multiple myeloma (MM) treatment regimens have vastly improved since the introduction of immunomodulators, proteasome inhibitors, and anti-CD38 monoclonal antibodies; however, MM is considered an incurable disease due to inevitable relapse and acquired drug resistance. Understanding the molecular mechanism by which drug resistance is acquired will help create novel strategies to prevent relapse and help develop novel therapeutics to treat relapsed/refractory (RR)-MM patients. Currently, only homozygous deletion/mutation of TP53 gene due to “double-hits” on Chromosome 17p region is consistently associated with a poor prognosis. The exciting discovery of XPO1 overexpression and mislocalization of its cargos in the RR-MM cells has led to a novel treatment options. Clinical studies have demonstrated that the XPO1 inhibitor selinexor can restore sensitivity of RR-MM to PIs and dexamethasone. We will elaborate on the problems of MM treatment strategies and discuss the mechanism and challenges of using XPO1 inhibitors in RR-MM therapies while deliberating potential solutions.

The aspartyl protease DDI2 drives adaptation to proteasome inhibition in multiple myeloma

Proteasome inhibitors, such as bortezomib, are first-line therapy against multiple myeloma (MM). Unfortunately, patients frequently become refractory to this treatment. The transcription factor NRF1 has been proposed to initiate an adaptation program that regulates proteasome levels. In the context of proteasome inhibition, the cytosolic protease DDI2 cleaves NRF1 to release an active fragment that translocates to the nucleus to promote the transcription of new proteasome subunits. However, the contribution of the DDI2-NRF1 pathway to bortezomib resistance is poorly understood. Here we show that upon prolonged bortezomib treatment, MM cells become resistant to proteasome inhibition by increasing the expression of DDI2 and consequently activation of NRF1. Furthermore, we found that many MM cells became more sensitive to proteasome impairment in the context of DDI2 deficiency. Mechanistically, we demonstrate that both the protease and the HDD domains of DDI2 are required to activate NRF1. Finally, we show that partial inhibition of the DDI2-protease domain with the antiviral drug nelfinavir increased bortezomib susceptibility in treated MM cells. Altogether, these findings define the DDI2-NRF1 pathway as an essential program contributing to proteasome inhibition responses and identifying DDI2 domains that could be targets of interest in bortezomib-treated MM patients.

Bone-Targeted Bortezomib Inhibits Bortezomib-Resistant Multiple Myeloma in Mice by Providing Higher Levels of Bortezomib in Bone

Limited treatment options exist for cancer within the bone, as demonstrated by the inevitable, pernicious course of metastatic and blood cancers. The difficulty of eliminating bone-residing cancer, especially drug-resistant cancer, necessitates novel, alternative treatments to manipulate tumor cells and their microenvironment, with minimal off-target effects. To this end, bone-targeted conjugate (BP-Btz) was generated by linking bortezomib (Btz, an anticancer, bone-stimulatory drug) to a bisphosphonate (BP, a targeting ligand) through a cleavable linker that enables spatiotemporally controlled delivery of Btz to bone under acidic conditions for treating multiple myeloma (MM). Three conjugates with different linkers were developed and screened for best efficacy in mouse model of MM. Results demonstrated that the lead candidate BP-Btz with optimal linker could overcome Btz resistance, reduced tumor burden, bone destruction, or tumor metastasis more effectively than BP or free Btz without thrombocytopenia and neurotoxicity in mice bearing myeloma. Furthermore, pharmacokinetic and pharmacodynamic studies showed that BP-Btz bound to bone matrix, released Btz in acidic conditions, and had a higher local concentration and longer half-life than Btz in bone. Our findings suggest the potential of bone-targeted Btz conjugate as an efficacious Btz-resistant MM treatment mechanism. © 2021 American Society for Bone and Mineral Research (ASBMR).

Indirubin-3'-monoxime acts as proteasome inhibitor: Therapeutic application in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is still an incurable malignancy of plasma cells. Proteasome inhibitors (PIs) work as the backbone agent and have greatly improved the outcome in majority of newly diagnosed patients with myeloma. However, drug resistance remains the major obstacle causing treatment failure in clinical practice. Here, we investigated the effects of Indirubin-3'-monoxime (I3MO), one of the derivatives of Indirubin, in the treatment of MM.

METHODS

MM patient primary samples and human cell lines were examined. I3MO effects on myeloma treatment and the underling molecular mechanisms were investigated via in vivo and in vitro study.

FINDINGS

Our results demonstrated the anti-MM activity of I3MO in both drug- sensitive and -resistance MM cells. I3MO sensitizes MM cells to bortezomib-induced apoptosis. Mechanistically, I3MO acts as a multifaceted regulator of cell death, which induced DNA damage, cell cycle arrest, and abrogates NF-κB activation. I3MO efficiently down-regulated USP7 expression, promoted NEK2 degradation, and suppressed NF-κB signaling in MM. Our study reported that I3MO directly bound with and caused the down-regulation of PA28γ (PSME3), and PA200 (PSME4), the proteasome activators. Knockdown of PSME3 or PSME4 caused the inhibition of proteasome capacity and the overload of paraprotein, which sensitizes MM cells to bortezomib-mediated growth arrest. Clinical data demonstrated that PSME3 and PSME4 are over-expressed in relapsed/refractory MM (RRMM) and associated with inferior outcome.

INTERPRETATION

Altogether, our study indicates that I3MO is agent triggering proteasome inhibition and represents a promising therapeutic strategy to improve patient outcome in MM.

FUNDINGS

A full list of funding can be found in the acknowledgements.

Revisiting Proteasome Inhibitors: Molecular Underpinnings of Their Development, Mechanisms of Resistance and Strategies to Overcome Anti-Cancer Drug Resistance

Proteasome inhibitors have shown relevant clinical activity in several hematological malignancies, namely in multiple myeloma and mantle cell lymphoma, improving patient outcomes such as survival and quality of life, when compared with other therapies. However, initial response to the therapy is a challenge as most patients show an innate resistance to proteasome inhibitors, and those that respond to the therapy usually develop late relapses suggesting the development of acquired resistance. The mechanisms of resistance to proteasome inhibition are still controversial and scarce in the literature. In this review, we discuss the development of proteasome inhibitors and the mechanisms of innate and acquired resistance to their activity—a major challenge in preclinical and clinical therapeutics. An improved understanding of these mechanisms is crucial to guiding the design of new and more effective drugs to tackle these devastating diseases. In addition, we provide a comprehensive overview of proteasome inhibitors used in combination with other chemotherapeutic agents, as this is a key strategy to combat resistance.

Constitutive Activation of p62/Sequestosome-1-Mediated Proteaphagy Regulates Proteolysis and Impairs Cell Death in Bortezomib-Resistant Mantle Cell Lymphoma

Simple Summary

To decipher the molecular mechanism underlying the resistance of a significant fraction of mantle cell lymphoma (MCL) patients to the first-in-class proteasome inhibitor bortezomib (BTZ), we have characterized the ubiquitin-related proteome (i.e., ubiquitome) of a set of MCL cell lines with different degrees of sensitivity to the drug by coupling a tandem ubiquitin-binding entity (TUBE) approach to mass spectrometry, followed by phenotypic and functional validations in both in vitro and in vivo models of MCL. We identified an enrichment of autophagy–lysosome system (ALS) components in BTZ-resistant cells, which was associated with constitutive intracellular inactivation of proteasome subunits by a process called proteaphagy. Blockade of this phenomenon by the pharmacological or genetic inactivation of the autophagy receptor p62/SQSTM1 reactivated normal proteasomal activity and restored the BTZ antitumor effect in in vitro and in vivo models of BTZ resistance.

Abstract

Protein ubiquitylation coordinates crucial cellular events in physiological and pathological conditions. A comparative analysis of the ubiquitin proteome from bortezomib (BTZ)-sensitive and BTZ-resistant mantle cell lymphoma (MCL) revealed an enrichment of the autophagy–lysosome system (ALS) in BTZ-resistant cells. Pharmacological inhibition of autophagy at the level of lysosome-fusion revealed a constitutive activation of proteaphagy and accumulation of proteasome subunits within autophagosomes in different MCL cell lines with acquired or natural resistance to BTZ. Inhibition of the autophagy receptor p62/SQSTM1 upon verteporfin (VTP) treatment disrupted proteaphagosome assembly, reduced co-localization of proteasome subunits with autophagy markers and negatively impacted proteasome activity. Finally, the silencing or pharmacological inhibition of p62 restored the apoptosis threshold at physiological levels in BTZ-resistant cells both in vitro and in vivo. In total, these results demonstrate for the first time a proteolytic switch from the ubiquitin–proteasome system (UPS) to ALS in B-cell lymphoma refractory to proteasome inhibition, pointing out a crucial role for proteaphagy in this phenomenon and paving the way for the design of alternative therapeutic venues in treatment-resistant tumors.

A review on the treatment of multiple myeloma with small molecular agents in the past five years

Multiple myeloma is currently incurable, and the incidence rate is increasing year by year worldwide. Although in recent years the combined treatment plan based on proteasome inhibitors and immunomodulatory drugs has greatly improved the treatment effect of multiple myeloma, most patients still relapse and become resistant to current treatments. To solve this problem, scientists are committed to developing drugs with higher specificity, such as iberdomide, which is highly specific to ikaros and aiolos. This review aims to focus on the small molecular agents that are being researched/clinically used for the treatment of multiple myeloma, including the target mechanism, structure-activity relationship and application prospects of small molecular agents.

The Role of Proteasome Inhibitors in Treating Acute Lymphoblastic Leukaemia

Acute lymphoblastic leukaemia (ALL) is an aggressive haematolymphoid malignancy. The prognosis of ALL is excellent in paediatric population, however the outcome of relapse/refractory disease is dismal. Adult ALL has less favourable prognosis and relapse/refractory disease is not uncommonly encountered. Bortezomib is the first generation proteasome inhibitor licensed to treat plasma cell myeloma and mantle cell lymphoma with favourable side effect profile. Efficacy of bortezomib had been proven in other solid tumors. Clinical studies showed promising response for proteasome inhibitors in treating relapse/refractory ALL. Thus, proteasome inhibitors are attractive alternative agents for research in treating ALL. In the review article, we will introduce different proteasome inhibitors and their difference in pharmacological properties. Moreover, the mechanism of action of proteasome inhibitors on ALL will be highlighted. Finally, results of various clinical studies on proteasome inhibitors in both paediatric and adult ALL will be discussed. This review article provides the insights on the use of proteasome inhibitors in treating ALL with a summary of mechanism of action in ALL which facilitates future research on its use to improve the outcome of ALL.

Killing by Degradation: Regulation of Apoptosis by the Ubiquitin-Proteasome-System

Apoptosis is a cell suicide process that is essential for development, tissue homeostasis and human health. Impaired apoptosis is associated with a variety of human diseases, including neurodegenerative disorders, autoimmunity and cancer. As the levels of pro- and anti-apoptotic proteins can determine the life or death of cells, tight regulation of these proteins is critical. The ubiquitin proteasome system (UPS) is essential for maintaining protein turnover, which can either trigger or inhibit apoptosis. In this review, we will describe the E3 ligases that regulate the levels of pro- and anti-apoptotic proteins and assisting proteins that regulate the levels of these E3 ligases. We will provide examples of apoptotic cell death modulations using the UPS, determined by positive and negative feedback loop reactions. Specifically, we will review how the stability of p53, Bcl-2 family members and IAPs (Inhibitor of Apoptosis proteins) are regulated upon initiation of apoptosis. As increased levels of oncogenes and decreased levels of tumor suppressor proteins can promote tumorigenesis, targeting these pathways offers opportunities to develop novel anti-cancer therapies, which act by recruiting the UPS for the effective and selective killing of cancer cells.

The Role of Chaperone-Mediated Autophagy in Bortezomib Resistant Multiple Myeloma

Background: Multiple myeloma (MM) remains incurable despite high-dose chemotherapy, autologous stem cell transplants and novel agents. Even with the improved survival of MM patients treated with novel agents, including bortezomib (Bz), the therapeutic options in relapsed/refractory MM remain limited. The majority of MM patients eventually develop resistance to Bz, although the mechanisms of the resistance are poorly understood. Methods: Lysosomal associated membrane protein 2A (LAMP2A) mRNA and protein expression levels were assessed in ex vivo patient samples and a Bz-resistant MM cell line model by in real-rime PCR, western blotting and immunohistochemistry. In vitro modelling of chaperone-mediated autophagy (CMA) activity in response to ER stress were assessed by western blotting and confocal microscopy. The effects of CMA inhibition on MM cell viability and Bz sensitivity in MM cells were assessed by Annexin V/7AAD apoptosis assays using flow cytometry. Results: In this study, there is evidence that CMA, a chaperone-mediated protein degradation pathway, is upregulated in Bz-resistant MM and the inhibition of CMA sensitises resistant cells to Bz. The protein levels of LAMP2A, the rate-limiting factor of the CMA pathway, are significantly increased in MM patients resistant to Bz and within our Bz-resistant cell line model. Bz-resistant cell lines also possessed higher basal CMA activity than the Bz-sensitive parent cell line. In MM cell lines, CMA activity was upregulated in response to ER stress induced by Bz. The inhibition of CMA sensitises Bz-resistant cells to Bz and the combination of CMA inhibition and Bz in vitro had a more cytotoxic effect on myeloma cells than Bz alone. Conclusion: In summary, the upregulation of CMA is a potential mechanism of resistance to Bz and a novel target to overcome Bz-resistant MM.

Gene expression profiling as a prognostic tool in multiple myeloma

Multiple myeloma (MM) is an aggressive plasma cell malignancy with high degrees of variability in outcome, some patients experience long remissions, whilst others survive less than two years from diagnosis. Therapy refractoriness and relapse remain challenges in MM management, and there is a need for improved prognostication and targeted therapies to improve overall survival (OS). The past decade has seen a surge in gene expression profiling (GEP) studies which have elucidated the molecular landscape of MM and led to the identification of novel gene signatures that predict OS and outperform current clinical predictors. In this review, we discuss the limitations of current prognostic tools and the emerging role of GEP in diagnostics and in the development of personalised medicine approaches to combat drug resistance.

USP32 confers cancer cell resistance to YM155 via promoting ER-associated degradation of solute carrier protein SLC35F2

Background: The most commonly preferred chemotherapeutic agents to treat cancers are small-molecule drugs. However, the differential sensitivity of various cancer cells to small molecules and untargeted delivery narrow the range of potential therapeutic applications. The mechanisms responsible for drug resistance in a variety of cancer cells are also largely unknown. Several deubiquitinating enzymes (DUBs) are the main determinants of drug resistance in cancer cells.

Methods: We used CRISPR-Cas9 to perform genome-scale knockout of the entire set of genes encoding ubiquitin-specific proteases (USPs) and systematically screened for DUBs resistant to the clinically evaluated anticancer compound YM155. A series of in vitro and in vivo experiments were conducted to reveal the relationship between USP32 and SLC35F2 on YM155-mediated DNA damage in cancer cells.

Results: CRISPR-based dual-screening method identified USP32 as a novel DUB that governs resistance for uptake of YM155 by destabilizing protein levels of SLC35F2, a solute-carrier protein essential for the uptake of YM155. The expression of USP32 and SLC35F2 was negatively correlated across a panel of tested cancer cell lines. YM155-resistant cancer cells in particular exhibited elevated expression of USP32 and low expression of SLC35F2.

Conclusion: Collectively, our DUB-screening strategy revealed a resistance mechanism governed by USP32 associated with YM155 resistance in breast cancers, one that presents an attractive molecular target for anti-cancer therapies. Targeted genome knockout verified that USP32 is the main determinant of SLC35F2 protein stability in vitro and in vivo, suggesting a novel way to treat tumors resistant to small-molecule drugs.

Ixazomib induces apoptosis and suppresses proliferation in esophageal squamous cell carcinoma through activation of the c-Myc/NOXA pathway

Esophageal squamous cell carcinoma (ESCC) is one of the major subtypes of esophageal cancer. More than half of the ESCC patients in the world are in China, and the 5-year survival rate is less than 10%. As a new oral proteasome inhibitor, ixazomib has shown strong therapeutic effect in many solid tumors. In this study, we aimed to investigate the effects of ixazomib on the proliferation inhibition and apoptosis of ESCC cells.We used four human ESCC cell lines, cell viability assay, cell cycle and apoptosis assay, RT-PCR, Western blot, immunohistochemistry and ESCC xenografts model to clarify the roles of the therapeutic effect and mechanism of ixazomib in ESCC. Ixazomib significantly inhibited the proliferation and induced apoptosis in ESCC cells. RT-PCR results showed that the expression of endoplasmic reticulum stress-related gene NOXA and c-Myc significant increase after treatment with ixazomib in ESCC cell. Then we knockdown the NOXA and c-Myc by siRNA, the therapeutic effect of ixazomib markedly decrease, which confirmed that c-Myc/NOXA pathway played a key role in the treatment of ESCC with ixazomib. In vivo, the xenograft ESCC model mice were given 10 mg/kg of ixazomib every other day for 30 days. The results showed that the tumor size in the treatment group was significantly smaller than the control group. These results suggested that ixazomib is known to suppress proliferation and induce apoptosis in an ESCC cell lines, and this effect was likely mediated by increased activation of the c-Myc/NOXA signaling pathways. Significance Statement Esophageal squamous cell carcinoma (ESCC) is the common worldwide malignant tumors,but conventional chemotherapeutics suffer from a number of limitations. In this study, our results suggested that ixazomib is known to suppress proliferation and induce apoptosis in an ESCC cell lines. Therefore, ixazomib may be a potential new stratgegy for ESCC therapy.

miR-338-5p-ZEB2 axis in Diagnostic, Therapeutic Predictive and Prognostic Value of Gastric Cancer

MiRNAs have been widely reported to be involved in the occurrence and development of cancers. So far, some studies have revealed that miR-338-5p has the functions of tumorigenesis and tumor suppression. However, the role of miR-338-5p in the pathogenesis, progression and treatment of gastric cancer (GC) has not been reported. MiRNAs microarray analysis showed for the first time that miR-338-5p was significantly lower-expression in cisplin-resistant GC cells SGC7901/DDP, and cell viability assay and flow cytometry confirmed that overexpression of miR-338-5p could significantly increase cisplatin-sensitivity of SGC7901/DDP and BGC823 cells. Subsequently, we found that the expression of miR-338-5p in postoperative cancer tissues of GC patients was also significantly lower than the corresponding paracancer tissues. The expression of miR-338-5p in peripheral blood serum of GC patients is generally lower than that of healthy people. Moreover, the low expression of miR-338-5p in the cancer tissues and serum of GC patients was closely associated with larger tumor volume, lymph node metastasis, later stage, and even poorer survival, which was confirmed by close 5-year cases follow-up. ZEB2, as a predictive target of miR-338-5p, its expression was negatively regulated by miR-338-5p and can promote cisplatin-resistance in SGC7901/DDP and BGC823 cells. The expression of ZEB2 in cisplatin-resistant SGC7901/DDP cells and GC tissues were significantly higher than SGC7901 cells and paracancer tissues, respectively. Moreover, the expression of ZEB2 in tumor tissues was negatively correlated with miR-338-5p in tumor tissues and peripheral blood serum of GC patients, and the abnormally high expression of ZEB2 in prospective case studies is positively related with more serious clinical pathology and worse survival. More meaningfully, in a retrospective case study, we found that high ZEB2 expression predicts worse clinical efficacy of platinum chemotherapy. Thus, miR-338-5p-ZEB2 axis have novel diagnostic, therapeutic predictive, and prognostic value in GC patients.

At the Cutting Edge against Cancer: A Perspective on Immunoproteasome and Immune Checkpoints Modulation as a Potential Therapeutic Intervention

Immunoproteasome is a noncanonical form of proteasome with enzymological properties optimized for the generation of antigenic peptides presented in complex with class I MHC molecules. This enzymatic property makes the modulation of its activity a promising area of research. Nevertheless, immunotherapy has emerged as a front-line treatment of advanced/metastatic tumors providing outstanding improvement of life expectancy, even though not all patients achieve a long-lasting clinical benefit. To enhance the efficacy of the currently available immunotherapies and enable the development of new strategies, a broader knowledge of the dynamics of antigen repertoire processing by cancer cells is needed. Therefore, a better understanding of the role of immunoproteasome in antigen processing and of the therapeutic implication of its modulation is mandatory. Studies on the potential crosstalk between proteasome modulators and immune checkpoint inhibitors could provide novel perspectives and an unexplored treatment option for a variety of cancers.

VLX1570 induces apoptosis through the generation of ROS and induction of ER stress on leukemia cell lines

A novel proteasome deubiquitinase inhibitor, VLX1570, has been highlighted as a promising therapeutic agent mainly for lymphoid neoplasms and solid tumors. We examined in vitro effects of VLX1570 on eight myeloid and three lymphoid leukemia cell lines. From cell culture studies, 10 out of 11 cell lines except K562 were found to be susceptible to VLX1570 treatment and it inhibited cell growth mainly by apoptosis. Next, to identify the signaling pathways associated with apoptosis, we performed gene expression profiling using HL‐60 with or without 50 nmol/L of VLX1570 for 3 hours and demonstrated that VLX1570 induced the genetic pathway involved in “heat shock transcription factor 1 (HSF1) activation”, “HSF1 dependent transactivation”, and “Regulation of HSF1 mediated heat shock response”. VLX1570 increased the amount of high molecular weight polyubiquitinated proteins and the expression of HSP70 as the result of the suppression of ubiquitin proteasome system, the expression of heme oxygenase‐1, and the amount of phosphorylation in JNK and p38 associated with the generation of reactive oxygen species (ROS) induced apoptosis and the amount of phosphorylation in eIF2α, inducing the expression of ATF4 and endoplasmic reticulum (ER) stress dependent apoptosis protein, CHOP, and the amount of phosphorylation slightly in IRE1α, leading to increased expression of XBP‐1s in leukemia cell lines. In the present study, we demonstrate that VLX1570 induces apoptosis and exerts a potential anti‐leukemic effect through the generation of ROS and induction of ER stress in leukemia cell lines.

Proteasomal adaptations to FDA-approved proteasome inhibitors: a potential mechanism for drug resistance?

With proteasome inhibitors (PIs) becoming clinically available since 2003, outcomes for patients with multiple myeloma (MM) have dramatically changed, improving quality of life and survival. Despite the impressive treatment success, however, almost all MM patients who initially respond to these PIs eventually develop resistance. Furthermore, a portion of MM patients is inherently unresponsive to the PIs. Extensive mechanistic investigations identified several non-proteasomal signaling pathways suspected to be linked to the PI resistance, for which several excellent reviews are currently available. On the other hand, it is still unclear how cancer cells under high PI environments adapt to spare proteasome activity essential for survival and proliferation regardless of cancer evolution stages. This review outlines current progress towards understanding the proteasomal adaptations of cells in response to PI treatment to maintain necessary proteasome activity. A better understanding of cellular proteasomal changes in response to the PIs could provide a rationale to develop new therapeutics that could be used to overcome resistance to existing PI drugs.

Additive Benefits of Radium-223 Dichloride and Bortezomib Combination in a Systemic Multiple Myeloma Mouse Model

Osteolytic bone disease is a hallmark of multiple myeloma (MM) mediated by MM cell proliferation, increased osteoclast activity, and suppressed osteoblast function. The proteasome inhibitor bortezomib targets MM cells and improves bone health in MM patients. Radium-223 dichloride (radium-223), the first targeted alpha therapy approved, specifically targets bone metastases, where it disrupts the activity of both tumor cells and tumor-supporting bone cells in mouse models of breast and prostate cancer bone metastasis. We hypothesized that radium-223 and bortezomib combination treatment would have additive effects on MM. In vitro experiments revealed that the combination treatment inhibited MM cell proliferation and demonstrated additive efficacy. In the systemic, syngeneic 5TGM1 mouse MM model, both bortezomib and radium-223 decreased the osteolytic lesion area, and their combination was more effective than either monotherapy alone. Bortezomib decreased the number of osteoclasts at the tumor-bone interface, and the combination therapy resulted in almost complete eradication of osteoclasts. Furthermore, the combination therapy improved the incorporation of radium-223 into MM-bearing bone. Importantly, the combination therapy decreased tumor burden and restored body weights in MM mice. These results suggest that the combination of radium-223 with bortezomib could constitute a novel, effective therapy for MM and, in particular, myeloma bone disease.

The Effect of Phase Transition Temperature on Therapeutic Efficacy of Liposomal Bortezomib

AIMS

Here, three liposomal formulations of DPPC/DPPG/Chol/DSPE-mPEG2000 (F1), DPPC/DPPG/Chol (F2) and HSPC/DPPG/Chol/DSPE-mPEG2000 (F3) encapsulating BTZ were prepared and characterized in terms of their size, surface charge, drug loading, and release profile. Mannitol was used as a trapping agent to entrap the BTZ inside the liposomal core. The cytotoxicity and anti-tumor activity of formulations were investigated in vitro and in vivo in mice bearing tumor.

BACKGROUND

Bortezomib (BTZ) is an FDA approved proteasome inhibitor for the treatment of mantle cell lymphoma and multiple myeloma. The low solubility of BTZ has been responsible for the several side effects and low therapeutic efficacy of the drug. Encapsulating BTZ in a nano drug delivery system; helps overcome such issues. Among NDDSs, liposomes are promising diagnostic and therapeutic delivery vehicles in cancer treatment.

OBJECTIVE

Evaluating anti-tumor activity of bortezomib liposomal formulations.

METHODS

Data prompted us to design and develop three different liposomal formulations of BTZ based on Tm parameter, which determines liposomal stiffness. DPPC (Tm 41°C) and HSPC (Tm 55°C) lipids were chosen as variables associated with liposome rigidity. In vitro cytotoxicity assay was then carried out for the three designed liposomal formulations on C26 and B16F0, which are the colon and melanoma cancer mouse-cell lines, respectively. NIH 3T3 mouse embryonic fibroblast cell line was also used as a normal cell line. The therapeutic efficacy of these formulations was further assessed in mice tumor models.

RESULT

MBTZ were successfully encapsulated into all the three liposomal formulations with a high entrapment efficacy of 60, 64, and 84% for F1, F2, and F3, respectively. The findings showed that liposomes mean particle diameter ranged from 103.4 to 146.8nm. In vitro cytotoxicity studies showed that liposomal-BTZ formulations had higher IC50 value in comparison to free BTZ. F2-liposomes with DPPC, having lower Tm of 41°C, showed much higher anti-tumor efficacy in mice models of C26 and B16F0 tumors compared to F3-HSPC liposomes with a Tm of 55°C. F2 formulation also enhanced mice survival compared with untreated groups, either in BALB/c or in C57BL/6 mice.

CONCLUSION

Our findings indicated that F2-DPPC-liposomal formulations prepared with Tm close to body temperature seem to be effective in reducing the side effects and increasing the therapeutic efficacy of BTZ and merits further investigation.

Encapsulation and pH-responsive release of bortezomib by dopamine grafted hyaluronate nanogels

Hydrophobic drugs loaded nanogels were always associated with low encapsulation efficiency and immature burst release. In this work, dopamine grafted hyaluronate nanogels were designed for bortezomib (BTZ), a hydrophobic anticancer drug and a proteasome inhibitor. It was found that there was a more efficient loading and pH-controlled release of BTZ due to the presence of dopamine groups on the skeleton of the nanogels. The drug loading content (DLC) were up to 8.58% as the nanogels modified with 29% dopamine, compared to the DLC of less than 1% for nanogels without dopamine modification. It was the pH-sensitive nature of the borated bonds between BTZ and catechol groups that endowed the pH-responsive release behavior of BTZ in vitro. In vitro study proved good biocompatibility and efficient cell uptake of the nanogels. In vivo anti-tumor experiments demonstrated that bortezomib loading into the nanogel significantly enhanced the therapeutic effect of the drug. After 14-day treatment, the average tumor volume of BTZ loaded nanogel group was reduced by 200% more than that of free BTZ group. Combined with CD44 receptor targeting ability of hyaluronate and the merits of nanogel, the catechol modified hyaluronate nanogel exhibited as an efficient chemotherapeutic formulation of BTZ for cancer treatment.

Bisphosphonates for delivering drugs to bone

Advances in the design of potential bone-selective drugs for the treatment of various bone-related diseases are creating exciting new directions for multiple unmet medical needs. For bone-related cancers, off-target/non-bone toxicities with current drugs represent a significant barrier to the quality of life of affected patients. For bone infections and osteomyelitis, bacterial biofilms on infected bones limit the efficacy of antibiotics because it is hard to access the bacteria with current approaches. Promising new experimental approaches to therapy, based on bone-targeting of drugs, have been used in animal models of these conditions and demonstrate improved efficacy and safety. The success of these drug-design strategies bodes well for the development of therapies with improved efficacy for the treatment of diseases affecting the skeleton. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Pre-Clinical Evaluation of the Proteasome Inhibitor Ixazomib against Bortezomib-Resistant Leukemia Cells and Primary Acute Leukemia Cells

At present, 20-30% of children with acute leukemia still relapse from current chemotherapy protocols, underscoring the unmet need for new treatment options, such as proteasome inhibition. Ixazomib (IXA) is an orally available proteasome inhibitor, with an improved safety profile compared to Bortezomib (BTZ). The mechanism of action (proteasome subunit inhibition, apoptosis induction) and growth inhibitory potential of IXA vs. BTZ were tested in vitro in human (BTZ-resistant) leukemia cell lines. Ex vivo activity of IXA vs. BTZ was analyzed in 15 acute lymphoblastic leukemia (ALL) and 9 acute myeloid leukemia (AML) primary pediatric patient samples. BTZ demonstrated more potent inhibitory effects on constitutive β5 and immunoproteasome β5i proteasome subunit activity; however, IXA more potently inhibited β1i subunit than BTZ (70% vs. 29% at 2.5 nM). In ALL/AML cell lines, IXA conveyed 50% growth inhibition at low nanomolar concentrations, but was ~10-fold less potent than BTZ. BTZ-resistant cells (150-160 fold) displayed similar (100-fold) cross-resistance to IXA. Finally, IXA and BTZ exhibited anti-leukemic effects for primary ex vivo ALL and AML cells; mean LC50 (nM) for IXA: 24 ± 11 and 30 ± 8, respectively, and mean LC50 for BTZ: 4.5 ± 1 and 11 ± 4, respectively. IXA has overlapping mechanisms of action with BTZ and showed anti-leukemic activity in primary leukemic cells, encouraging further pre-clinical in vivo evaluation.

Linking Serine/Glycine Metabolism to Radiotherapy Resistance

Simple Summary

Hyperactivation of the de novo serine/glycine biosynthesis across different cancer types and its critical contribution in tumor initiation, progression, and therapy resistance indicate the relevance of serine/glycine metabolism-targeted therapies as therapeutic intervention in cancer. In this review, we specifically focus on the contribution of the de novo serine/glycine biosynthesis pathway to radioresistance. We provide a future perspective on how de novo serine/glycine biosynthesis inhibition and serine-free diets may improve the outcome of radiotherapy. Future research in this field is needed to better understand serine/glycine metabolic reprogramming of cancer cells in response to radiation and the influence of this pathway in the tumor microenvironment, which may provide the rationale for the optimal combination therapies.

Abstract

The activation of de novo serine/glycine biosynthesis in a subset of tumors has been described as a major contributor to tumor pathogenesis, poor outcome, and treatment resistance. Amplifications and mutations of de novo serine/glycine biosynthesis enzymes can trigger pathway activation; however, a large group of cancers displays serine/glycine pathway overexpression induced by oncogenic drivers and unknown regulatory mechanisms. A better understanding of the regulatory network of de novo serine/glycine biosynthesis activation in cancer might be essential to unveil opportunities to target tumor heterogeneity and therapy resistance. In the current review, we describe how the activation of de novo serine/glycine biosynthesis in cancer is linked to treatment resistance and its implications in the clinic. To our knowledge, only a few studies have identified this pathway as metabolic reprogramming of cancer cells in response to radiation therapy. We propose an important contribution of de novo serine/glycine biosynthesis pathway activation to radioresistance by being involved in cancer cell viability and proliferation, maintenance of cancer stem cells (CSCs), and redox homeostasis under hypoxia and nutrient-deprived conditions. Current approaches for inhibition of the de novo serine/glycine biosynthesis pathway provide new opportunities for therapeutic intervention, which in combination with radiotherapy might be a promising strategy for tumor control and ultimately eradication. Further research is needed to gain molecular and mechanistic insight into the activation of this pathway in response to radiation therapy and to design sophisticated stratification methods to select patients that might benefit from serine/glycine metabolism-targeted therapies in combination with radiotherapy.

Oxidatively modified low-density lipoproteins are potential mediators of proteasome inhibitor resistance in multiple myeloma

Proteasome inhibitor (PI) therapy has improved the survival of multiple myeloma (MM) patients. However, inevitably, primary or acquired resistance to PIs leads to disease progression; resistance mechanisms are unclear. Obesity is a risk factor for MM mortality. Oxidized LDL (OxLDL), a central mediator of atherosclerosis that is elevated in metabolic syndrome (co-occurrence of obesity, insulin resistance, dyslipidemia and hypertension), has been linked to an increased risk of solid cancers and shown to stimulate pro-oncogenic/survival signaling. We hypothesized that OxLDL is a mediator of chemoresistance and evaluated its effects on MM cell killing by PIs. OxLDL potently suppressed the ability of the boronic acid-based PIs bortezomib (BTZ) and ixazomib, but not the epoxyketone-based PI carfilzomib, to kill human MM cell lines and primary cells. OxLDL suppressed BTZ-induced inhibition of proteasome activity and induction of pro-apoptotic signaling. These cytoprotective effects were abrogated when lipid hydroperoxides (LOOHs) associated with OxLDL were enzymatically reduced. We also demonstrated the presence of OxLDL in the MM bone marrow microenvironment as well as numerous granulocytes and monocytes capable of cell-mediated LDL oxidation through myeloperoxidase. Our findings suggest that OxLDL may be a potent mediator of boronic acid-based PI resistance, particularly for MM patients with metabolic syndrome, given their elevated systemic levels of OxLDL. LDL cholesterol-lowering therapy to reduce circulating OxLDL, and pharmacologic targeting of LOOH levels or resistance pathways induced by the modified lipoprotein, could deepen the response to these important agents and offer clinical benefit to MM patients with metabolic syndrome.

In vitro biomimetic models for glioblastoma-a promising tool for drug response studies

The poor response of glioblastoma to current treatment protocols is a consequence of its intrinsic drug resistance. Resistance to chemotherapy is primarily associated with considerable cellular heterogeneity, and plasticity of glioblastoma cells, alterations in gene expression, presence of specific tumor microenvironment conditions and blood-brain barrier. In an attempt to successfully overcome chemoresistance and better understand the biological behavior of glioblastoma, numerous tri-dimensional (3D) biomimetic models were developed in the past decade. These novel advanced models are able to better recapitulate the spatial organization of glioblastoma in a real time, therefore providing more realistic and reliable evidence to the response of glioblastoma to therapy. Moreover, these models enable the fine-tuning of different tumor microenvironment conditions and facilitate studies on the effects of the tumor microenvironment on glioblastoma chemoresistance. This review outlines current knowledge on the essence of glioblastoma chemoresistance and describes the progress achieved by 3D biomimetic models. Moreover, comprehensive literature assessment regarding the influence of 3D culturing and microenvironment mimicking on glioblastoma gene expression and biological behavior is also provided. The contribution of the blood-brain barrier as well as the blood-tumor barrier to glioblastoma chemoresistance is also reviewed from the perspective of 3D biomimetic models. Finally, the role of mathematical models in predicting 3D glioblastoma behavior and drug response is elaborated. In the future, technological innovations along with mathematical simulations should create reliable 3D biomimetic systems for glioblastoma research that should facilitate the identification and possibly application in preclinical drug testing and precision medicine.

Multi-omics tumor profiling technologies to develop precision medicine in multiple myeloma

Multiple myeloma (MM), the second most common hematologic cancer, is caused by accumulation of aberrant plasma cells in the bone marrow. Its molecular causes are not fully understood and its great heterogeneity among patients complicates therapeutic decision-making. In the past decades, development of new therapies and drugs have significantly improved survival of MM patients. However, resistance to drugs and relapse remain the most common causes of mortality and are the major challenges to overcome. The advent of high throughput omics technologies capable of analyzing big amount of clinical and biological data has changed the way to diagnose and treat MM. Integration of omics data (gene mutations, gene expression, epigenetic information, and protein and metabolite levels) with clinical histories of thousands of patients allows to build scores to stratify the risk at diagnosis and predict the response to treatment, helping clinicians to make better educated decisions for each particular case. There is no doubt that the future of MM treatment relies on personalized therapies based on predictive models built from omics studies. This review summarizes the current treatments and the use of omics technologies in MM, and their importance in the implementation of personalized medicine.

Multi-omics tumor profiling technologies to develop precision medicine in multiple myeloma

Multiple myeloma (MM), the second most common hematologic cancer, is caused by accumulation of aberrant plasma cells in the bone marrow. Its molecular causes are not fully understood and its great heterogeneity among patients complicates therapeutic decision-making. In the past decades, development of new therapies and drugs have significantly improved survival of MM patients. However, resistance to drugs and relapse remain the most common causes of mortality and are the major challenges to overcome. The advent of high throughput omics technologies capable of analyzing big amount of clinical and biological data has changed the way to diagnose and treat MM. Integration of omics data (gene mutations, gene expression, epigenetic information, and protein and metabolite levels) with clinical histories of thousands of patients allows to build scores to stratify the risk at diagnosis and predict the response to treatment, helping clinicians to make better educated decisions for each particular case. There is no doubt that the future of MM treatment relies on personalized therapies based on predictive models built from omics studies. This review summarizes the current treatments and the use of omics technologies in MM, and their importance in the implementation of personalized medicine.

The Prognostic Value of Whole-Blood PSMB5, CXCR4, POMP, and RPL5 mRNA Expression in Patients with Multiple Myeloma Treated with Bortezomib

Simple Summary

The mRNA expression of nine previously described genes that may affect resistance to multiple myeloma (MM), viz., ABCB1, CXCR4, MAF, MARCKS, POMP, PSMB5, RPL5, TXN, and XBP1, was compared between bortezomib-refractory and bortezomib-sensitive patients. RPL5 was the only gene to be significantly down-regulated in MM patients compared with non-MM individuals, while POMP was significantly up-regulated in the bortezomib-refractory patients. Multivariate analysis found the best independent predictors of progression-free survival to be high PSMB5 and CXCR expression and autologous stem cell transplantation, and that high expression of POMP and RPL5 were associated with shorter survival.

Abstract

Proteasome inhibitors, like bortezomib, play a key role in the treatment of multiple myeloma (MM); however, most patients eventually relapse and eventually show multiple drug resistance, and the molecular mechanisms of this resistance remain unclear. The aim of our study is to assess the expression of previously described genes that may influence the resistance to bortezomib treatment at the mRNA level (ABCB1, CXCR4, MAF, MARCKS, POMP, PSMB5, RPL5, TXN, and XBP1) and prognosis of MM patients. mRNA expression was determined in 73 MM patients treated with bortezomib-based regimens (30 bortzomib-sensitive and 43 bortezomib-refractory patients) and 11 healthy controls. RPL5 was significantly down-regulated in multiple myeloma patients as compared with healthy controls. Moreover, POMP was significantly up-regulated in MM patients refractory to bortezomib-based treatment. In multivariate analysis, high expression of PSMB5 and CXCR and autologous stem cell transplantation were independent predictors of progression-free survival, and high expression of POMP and RPL5 was associated with shorter overall survival.

Identification of resistance pathways and therapeutic targets in relapsed multiple myeloma patients through single-cell sequencing

Multiple myeloma (MM) is a neoplastic plasma-cell disorder characterized by clonal proliferation of malignant plasma cells. Despite extensive research, disease heterogeneity within and between treatment-resistant patients is poorly characterized. In the present study, we conduct a prospective, multicenter, single-arm clinical trial (NCT04065789), combined with longitudinal single-cell RNA-sequencing (scRNA-seq) to study the molecular dynamics of MM resistance mechanisms. Newly diagnosed MM patients (41), who either failed to respond or experienced early relapse after a bortezomib-containing induction regimen, were enrolled to evaluate the safety and efficacy of a daratumumab, carfilzomib, lenalidomide and dexamethasone combination. The primary clinical endpoint was safety and tolerability. Secondary endpoints included overall response rate, progression-free survival and overall survival. Treatment was safe and well tolerated; deep and durable responses were achieved. In prespecified exploratory analyses, comparison of 41 primary refractory and early relapsed patients, with 11 healthy subjects and 15 newly diagnosed MM patients, revealed new MM molecular pathways of resistance, including hypoxia tolerance, protein folding and mitochondria respiration, which generalized to larger clinical cohorts (CoMMpass). We found peptidylprolyl isomerase A (PPIA), a central enzyme in the protein-folding response pathway, as a potential new target for resistant MM. CRISPR-Cas9 deletion of PPIA or inhibition of PPIA with a small molecule inhibitor (ciclosporin) significantly sensitizes MM tumor cells to proteasome inhibitors. Together, our study defines a roadmap for integrating scRNA-seq in clinical trials, identifies a signature of highly resistant MM patients and discovers PPIA as a potent therapeutic target for these tumors.

Targeted Nanoparticles Harboring Jasmine-Oil-Entrapped Paclitaxel for Elimination of Lung Cancer Cells

Selectively targeted drug delivery systems are preferable chemotherapeutic platforms, as they specifically deliver the drug cargo into tumor cells, while minimizing untoward toxic effects. However, these delivery systems suffer from insufficient encapsulation efficiency (EE), encapsulation capacity (EC), and premature drug release. Herein, we coencapsulated paclitaxel (PTX) and Jasmine oil (JO) within PEG-PCL nanoparticles (NPs), with an average diameter < 50 nm, selectively targeted to non-small cell lung cancer (NSCLC) cells, via S15-aptamer (APT) decoration. JO was selected as an "adhesive" oily core to enhance PTX entrapment, as JO and PTX share similar hydrophobicity and terpenoid structure. JO markedly enhanced EE of PTX from 23% to 87.8% and EC from 35 ± 6 to 74 ± 8 µg PTX/mg PEG-PCL. JO also markedly increased the residual amount of PTX after 69 h, from 18.3% to 65%. Moreover, PTX cytotoxicity against human NSCLC A549 cells was significantly enhanced due to the co-encapsulation with JO; the IC50 value for PTX encapsulated within JO-containing APT-NPs was 20-fold lower than that for APT-NPs lacking JO. Remarkably, JO-containing APT-NPs displayed a 6-fold more potent cell-killing, relatively to the free-drug. Collectively, these findings reveal a marked synergistic contribution of JO to the cytotoxic activity of APT-NP-based systems, for targeted PTX delivery against NSCLC, which may be readily applied to various hydrophobic chemotherapeutics.