Overcoming inherent resistance to histone deacetylase inhibitors in multiple myeloma cells by targeting pathways integral to the actin cytoskeleton

Different evasion strategies in multiple myeloma

Multiple myeloma is the second most common malignant hematologic malignancy which evolved different strategies for immune escape from the host immune surveillance and drug resistance, including uncontrolled proliferation of malignant plasma cells in the bone marrow, genetic mutations, or deletion of tumor antigens to escape from special targets and so. Therefore, it is a big challenge to efficiently treat multiple myeloma patients. Despite recent applications of immunomodulatory drugs (IMiDS), protease inhibitors (PI), targeted monoclonal antibodies (mAb), and even hematopoietic stem cell transplantation (HSCT), it remains hardly curable. Summarizing the possible evasion strategies can help design specific drugs for multiple myeloma treatment. This review aims to provide an integrative overview of the intrinsic and extrinsic evasion mechanisms as well as recently discovered microbiota utilized by multiple myeloma for immune evasion and drug resistance, hopefully providing a theoretical basis for the rational design of specific immunotherapies or drug combinations to prevent the uncontrolled proliferation of MM, overcome drug resistance and improve patient survival.

Inhibition of PI3K Class IA Kinases Using GDC-0941 Overcomes Cytoprotection of Multiple Myeloma Cells in the Osteoclastic Bone Marrow Microenvironment Enhancing the Efficacy of Current Clinical Therapeutics

Osteoclasts contribute to bone marrow (BM)-mediated drug resistance in multiple myeloma (MM) by providing cytoprotective cues. Additionally, 80% of patients develop osteolytic lesions, which is a major cause of morbidity in MM. Although targeting osteoclast function is critical to improve MM therapies, pre-clinical studies rarely consider overcoming osteoclast-mediated cytoprotection within the selection criteria of drug candidates. We have performed a drug screening and identified PI3K as a key regulator of a signalling node associated with resistance to dexamethasone lenalidomide, pomalidomide, and bortezomib mediated by osteoclasts and BM fibroblastic stromal cells, which was blocked by the pan-PI3K Class IA inhibitor GDC-0941. Additionally, GDC-0941 repressed the maturation of osteoclasts derived from MM patients and disrupted the organisation of the F-actin cytoskeleton in sealing zones required for bone degradation, correlating with decreased bone resorption by osteoclasts. In vivo, GDC-0941 improved the efficacy of dexamethasone against MM in the syngeneic GFP-5T33/C57-Rawji mouse model. Taken together, our results indicate that GDC-0941 in combination with currently used therapeutic agents could effectively kill MM cells in the presence of the cytoprotective BM microenvironment while inhibiting bone resorption by osteoclasts. These data support investigating GDC-0941 in combination with currently used therapeutic drugs for MM patients with active bone disease.

Autophagy and Apoptosis: Current Challenges of Treatment and Drug Resistance in Multiple Myeloma

Over the past two decades, the natural history of multiple myeloma (MM) has evolved dramatically, owing primarily to novel agents targeting MM in the bone marrow microenvironment (BMM) pathways. However, the mechanisms of resistance acquisition remain a mystery and are poorly understood. Autophagy and apoptosis are tightly controlled processes and play a critical role in the cell growth, development, and survival of MM. Genetic instability and abnormalities are two hallmarks of MM. During MM progression, plasma malignant cells become genetically unstable and activate various signaling pathways, resulting in the overexpression of abnormal proteins that disrupt autophagy and apoptosis biological processes. Thus, achieving a better understanding of the autophagy and apoptosis processes and the proteins that crosslinked both pathways, could provide new insights for the MM treatment and improve the development of novel therapeutic strategies to overcome resistance. This review presents a sufficient overview of the roles of autophagy and apoptosis and how they crosslink and control MM progression and drug resistance. Potential combination targeting of both pathways for improving outcomes in MM patients also has been addressed.

Combination of Histone Deacetylase Inhibitor Panobinostat (LBH589) with β-Catenin Inhibitor Tegavivint (BC2059) Exerts Significant Anti-Myeloma Activity Both In Vitro and In Vivo

Over the last three decades changes in the treatment paradigm for newly diagnosed multiple myeloma (MM) have led to a significant increase in overall survival. Despite this, the majority of patients relapse after one or more lines of treatment while acquiring resistance to available therapies. Panobinostat, a pan-histone deacetylase inhibitor, was approved by the FDA in 2015 for patients with relapsed MM but how to incorporate panobinostat most effectively into everyday practice remains unclear. Dysregulation of the Wnt canonical pathway, and its key mediator β-catenin, has been shown to be important for the evolution of MM and the acquisition of drug resistance, making it a potentially attractive therapeutic target. Despite concerns regarding the safety of Wnt pathway inhibitors, we have recently shown that the β-catenin inhibitor Tegavivint is deliverable and effective in in vivo models of MM. In this study we show that the combination of low concentrations of panobinostat and Tegavivint have significant in vitro and in vivo anti-MM effects including in the context of proteasome inhibitor resistance, by targeting both aerobic glycolysis and mitochondrial respiration and the down-regulation of down-stream β-catenin targets including myc, cyclinD1, and cyclinD2. The significant anti-MM effect of this novel combination warrants further evaluation for the treatment of MM patients with relapsed and/or refractory MM.

Combining histone deacetylase inhibitors (HDACis) with other therapies for cancer therapy

Histone deacetylases (HDACs) play an important role in regulating the expression of genes involved in tumorigenesis and tumor maintenance, and hence they have been considered as key targets in cancer therapy. As a novel category of antitumor agents, histone deacetylase inhibitors (HDACis) can induce cell cycle arrest, apoptosis, and differentiation in cancer cells, ultimately combating cancer. Although in the United States, the use of HDACis for the treatment of certain cancers has been approved, the therapeutic efficacy of HDACis as a single therapeutic agent in solid tumorshas been unsatisfactory and drug resistance may yet occur. To enhance therapeutic efficacy and limit drug resistance, numerous combination therapies involving HDACis in synergy with other antitumor therapies have been studied. In this review, we describe the classification of HDACs. Moreover, we summarize the antitumor mechanism of the HDACis for targeting key cellular processes of cancers (cell cycle, apoptosis, angiogenesis, DNA repair, and immune response). In addition, we outline the major developments of other antitumor therapies in combination with HDACis, including chemotherapy, radiotherapy, phototherapy, targeted therapy, and immunotherapy. Finally, we discuss the current state and challenges of HDACis-drugs combinations in future clinical studies, with the aim of optimizing the antitumor effect of such combinations.

Panobinostat From Bench to Bedside: Rethinking the Treatment Paradigm for Multiple Myeloma

Relapsed and refractory multiple myeloma (RRMM) presents a therapeutic challenge due to the development of drug resistance. Panobinostat is an oral histone deacetylase inhibitor (HDACi) that affects multiple cellular pathways and has demonstrated the ability to resensitize refractory-multiple myeloma cells in preclinical studies, as well as in patients with RRMM in clinical trials. Synergy of panobinostat with a number of different classes of antimyeloma drugs (proteasome inhibitors, immunomodulatory drugs and monoclonal antibodies) has also been shown. Panobinostat is a promising HDACi for the treatment of multiple myeloma. Here, we present a comprehensive review of preclinical and clinical studies of panobinostat.

A novel dual HDAC and HSP90 inhibitor, MPT0G449, downregulates oncogenic pathways in human acute leukemia in vitro and in vivo

Acute leukemia is a highly heterogeneous disease; therefore, combination therapy is commonly used for patient treatment. Drug–drug interaction is a major concern of combined therapy; hence, dual/multi-target inhibitors have become a dominant approach for cancer drug development. HDACs and HSP90 are involved in the activation of various oncogenic signaling pathways, including PI3K/AKT/mTOR, JAK/STAT, and RAF/MEK/ERK, which are also highly enriched in acute leukemia gene expression profiles. Therefore, we suggest that dual HDAC and HSP90 inhibitors could represent a novel therapeutic approach for acute leukemia. MPT0G449 is a dual effect inhibitor, and it showed cytotoxic effectiveness in acute leukemia cells. Molecular docking analysis indicated that MPT0G449 possessed dual HDAC and HSP90 inhibitory abilities. Furthermore, MPT0G449 induced G₂ arrest and caspase-mediated cell apoptosis in acute leukemia cells. The oncogenic signaling molecules AKT, mTOR, STAT3, STAT5, MEK, and ERK were significantly downregulated after MPT0G449 treatment in HL-60 and MOLT-4 cells. In vivo xenograft models confirmed the antitumor activity and showed the upregulation of acetyl-histone H3 and HSP70, biomarkers of pan-HDAC and HSP90 inhibition, with MPT0G449 treatment. These findings suggest that the dual inhibition of HDAC and HSP90 can suppress the expression of oncogenic pathways in acute leukemia, and MPT0G449 represents a novel therapeutic for anticancer treatment.

Phase II trial of single-agent panobinostat consolidation improves responses after sub-optimal transplant outcomes in multiple myeloma

Panobinostat is a pan-deacetylase inhibitor that modulates the expression of oncogenic and immune-mediating genes involved in tumour cell growth and survival. We evaluated panobinostat-induced post-transplant responses and identified correlative biomarkers in patients with multiple myeloma who had failed to achieve a complete response after autologous transplantation. Patients received panobinostat 45 mg administered three-times weekly (TIW) on alternate weeks of 28-day cycles commencing 8-12 weeks post-transplant. Twelve of 25 patients (48%) improved their depth of response after a median (range) of 4·3 (1·9-9·7) months of panobinostat. In responders, T-lymphocyte histone acetylation increased after both three cycles (P < 0·05) and six cycles (P < 0·01) of panobinostat when compared to baseline, with no differences in non-responders. The reduction in the proportion of CD127+ CD8+ T cells and CD4:CD8 ratio was significantly greater, after three and six cycles of panobinostat compared to pre-transplant, in non-responders when compared to responders. Whole marrow RNA-seq revealed widespread transcriptional changes only in responders with baseline differences in genes involved in ribosome biogenesis, oxidative phosphorylation and metabolic pathways. This study confirmed the efficacy of panobinostat as a single agent in multiple myeloma and established acetylation of lymphocyte histones, modulation of immune subsets and transcriptional changes as pharmacodynamic biomarkers of clinical benefit.

TOP2A expression predicts responsiveness to carfilzomib in myeloma and informs novel combinatorial strategies for enhanced proteasome inhibitor cell killing

Microarray was utilized to determine if a genetic signature associated with resistance to carfilzomib (CFZ) could be identified. Twelve human myeloma (MM) cell lines (HMCLs) were treated with CFZ and a cell-viability profile was assessed categorizing HMCLs as sensitive or resistant to CFZ. The gene expression profiles (GEP) of untreated resistant versus sensitive HMCLs revealed 29 differentially expressed genes. TOP2A, an enzyme involved in cell cycle and proliferation, was overexpressed in carfilzomib-resistant HMCLs. TOP2A protein expression levels, evaluated utilizing trephine biopsy specimens acquired prior to treatment with proteasome inhibitors, were higher in patients failing to achieve a response when compared to responding patients. Logistic-regression analysis confirmed that TOP2A protein expression was a highly significant predictor of response to PIs (AUC 0.738). Further, the combination of CFZ with TOP2A inhibitors, demonstrated synergistic cytotoxic effects in vitro, providing a rationale for combining topoisomerase inhibitors with CFZ to overcome resistance in MM.

A Synergistic Anticancer FAK and HDAC Inhibitor Combination Discovered by a Novel Chemical-Genetic High-Content Phenotypic Screen

We mutated the focal adhesion kinase (FAK) catalytic domain to inhibit binding of the chaperone Cdc37 and ATP, mimicking the actions of a FAK kinase inhibitor. We reexpressed mutant and wild-type FAK in squamous cell carcinoma (SCC) cells from which endogenous FAK had been deleted, genetically fixing one axis of a FAK inhibitor combination high-content phenotypic screen to discover drugs that may synergize with FAK inhibitors. Histone deacetylase (HDAC) inhibitors represented the major class of compounds that potently induced multiparametric phenotypic changes when FAK was rendered kinase-defective or inhibited pharmacologically in SCC cells. Combined FAK and HDAC inhibitors arrest proliferation and induce apoptosis in a subset of cancer cell lines in vitro and efficiently inhibit their growth as tumors in vivo Mechanistically, HDAC inhibitors potentiate inhibitor-induced FAK inactivation and impair FAK-associated nuclear YAP in sensitive cancer cell lines. Here, we report the discovery of a new, clinically actionable, synergistic combination between FAK and HDAC inhibitors.

Identification of biomarkers and their functions in dasatinib-resistant pancreatic cancer using bioinformatics analysis

Dasatinib is a tyrosine kinase inhibitor, which inhibits tumor proliferation by blocking SRC pathways and is considered as a potential treatment of various epithelial neoplasms, including pancreatic cancer. However, dasatinib efficacy is largely limited due to drug resistance. In the present study, bioinformatics strategies were used to investigate the potential mechanisms of dasatinib-resistance in pancreatic cancer. The gene expression profiles of the Panc0403, Panc0504, Panc1005 (dasatinib-sensitive), SU8686, MiaPaCa2 and Panc1 (acquired dasatinib-resistant) cell lines were obtained from the gene expression omnibus database. The differentially expressed genes (DEGs) were then selected using R software. In addition, gene ontology (GO) and pathway enrichment analysis were performed through the Database for Annotation, Visualization and Integrated Discovery. A protein-protein interaction (PPI) network was constructed and analyzed to determine the hub genes using the Search Tool for the Retrieval of Interacting Genes database. A total of 472 DEGs, including vimentin, transmembrane 4 l six family member 18 and S100 calcium binding protein P, were identified. Enrichment analysis by GO function demonstrated that DEGs were associated with extracellular components, signal regulation and binding factors. The analysis of the Kyoto Encyclopedia of Genes and Genomes demonstrated that several adenocarcinoma pathways were enriched, including the phosphoinositide 3-kinases/protein kinase B and mitogen-activated protein kinase signaling pathways. Some hub genes were highlighted following the PPI network construction, including Rac family small GTPase 1, laminin subunit α3, integrin subunit β4, integrin subunit α2, collagen type VI α1 chain, collagen type I α2 chain, arrestin β1 and synaptotagmin 1, which may be associated with pancreatic adenocarcinoma prognosis. A total of five out of eight hub genes were highly associated with the overall survival rate (P<0.05). In conclusion, the present study reported novel insights into the mechanisms of dasatinib resistance. Identification of these hub genes may be considered as potential novel treatment targets for dasatinib-resistance in pancreatic cancer.

HDAC5-LSD1 axis regulates antineoplastic effect of natural HDAC inhibitor sulforaphane in human breast cancer cells

Our recent studies have shown that cross-talk between histone deacetylase 5 (HDAC5) and lysine-specific demethylase 1 (LSD1) facilitates breast cancer progression. In this work, we demonstrated that regulatory activity at -356 to -100 bp promoter element plays a critical role in governing HDAC5 transcription. By using DNA affinity precipitation and mass spectrometry, we identified a group of factors that bind to this element. Among these factors, Upstream Transcription Factor 1 (USF1) was shown to play a critical role in controlling HDAC5 transcription. Through screening a panel of epigenetic modifying drugs, we showed that a natural bioactive HDAC inhibitor, sulforaphane, downregulated HDAC5 transcription by blocking USF1 activity. Sulforaphane facilitated LSD1 ubiquitination and degradation in an HDAC5-dependent manner. A comparative microarray analysis demonstrated a genome wide cooperative effect of HDAC5 and LSD1 on cancer-related gene expression. shRNA knockdown and sulforaphane inhibition of HDAC5/LSD1 exhibited similar effects on expression of HDAC5/LSD1 target genes. We also showed that coordinated cross-talk of HDAC5 and LSD1 is essential for the antitumor efficacy of sulforaphane. Combination treatment with sulforaphane and a potent LSD1 inhibitor resulted in synergistic growth inhibition in breast cancer cells, but not in normal breast epithelial cells. Furthermore, combined therapy with sulforaphane and LSD1 inhibitor exhibited superior inhibitory effect on MDA-MB-231 xenograft tumor growth. Taken together, our work demonstrates that HDAC5-LSD1 axis is an effective drug target for breast cancer. Inhibition of HDAC5-LSD1 axis with sulforaphane blocks breast cancer growth and combined treatment with LSD1 inhibitor improves the therapeutic efficacy of sulforaphane.

Role of epigenetics-microRNA axis in drug resistance of multiple myeloma

Despite administration of novel therapies, multiple myeloma (MM) remains incurable with resistance to drugs leading to relapse in most patients. Thus, it is critical to understand the detailed mechanisms underlying the drug resistance of MM and develop more effective therapeutic strategies. Genetic abnormalities are well known to play a central role in MM pathogenesis and therapy resistance; however, epigenetic aberrations mainly affecting the patterns of DNA methylation/histone modifications of genes (especially tumor suppressors) and miRNAs have also been shown to be involved. Importantly, while epigenetic silencing of miRNAs in MM is well documented, some epigenetic markers are known to be direct targets of miRNAs particularly the recently described "epimiRNAs". Drugs targeting epigenetic modifiers (e.g., HDACs, EZH2) can sensitize MM-resistant cells to anti-myeloma drugs and reversibility of epigenetic changes makes these drugs promising therapeutic agents. Therefore, combination of miRNA mimics with inhibitors of epigenetic modifiers would be a more potent therapeutic strategy in MM patients in relapse or refractory to treatments. In this review, we will discuss the findings of recent investigations on epigenetics/miRNA regulatory axis in development of drug resistance in MM and highlight possible approaches for therapeutic applications of such interaction.

Histone deacetylase inhibitors in multiple myeloma: from bench to bedside

Histone deacetylases (HDACs) deacetylate the lysine residues of both histones and non-histone proteins. Histone acetylation results in a loose local chromatin structure that regulates gene-specific transcription. Non-histone proteins can also be acetylated, leading to dynamic changes in their activity and stability. For these reasons, HDAC inhibition has emerged as a potential approach for the treatment of MM. Specifically, combination treatment with HDAC inhibitors and proteasome inhibitors or immunomodulatory drugs shows remarkable anti-MM activity in both preclinical and clinical settings. However, the clinical studies using non-selective HDAC inhibitors also cause unfavorable side effects in patients, leading us to develop more isoform- and/or class-selective HDAC inhibitors to enhance tolerability without diminishing anti-MM activity, thereby improving patient outcome in MM.

Histone Deacetylase Inhibitors Delivery using Nanoparticles with Intrinsic Passive Tumor Targeting Properties for Tumor Therapy

Fast clearance, metabolism and systemic toxicity are major limits for the clinical use of anti-cancer drugs. Histone deacetylase inhibitors (HDACi) present these defects despite displaying promising anti-tumor properties on tumor cells in vitro and in in vivo model of cancers. Specific delivery of anti-cancer drugs into the tumor should improve their clinical benefit by limiting systemic toxicity and by increasing the anti-tumor effect. In this work, we describe a simple and flexible polymeric nanoparticle platform highly targeting the tumor in vivo and triggering impressive tumor weight reduction when functionalized with HDACi. Our nanoparticles were produced by Ring-Opening Metathesis Polymerization of azido-polyethylene oxide-norbornene macromonomers and functionalized using click chemistry. Using an orthotopic model of peritoneal invasive cancer, a highly selective accumulation of the particles in the tumor was obtained. A combination of epigenetic drugs involving a pH-responsive histone deacetylase inhibitor (HDACi) polymer conjugated to these particles gave 80% reduction of tumor weight without toxicity whereas the free HDACi has no effect. Our work demonstrates that the use of a nanovector with theranostic properties leads to an optimized delivery of potent HDACi in tumor and then, to an improvement of their anti-tumor properties in vivo.

Activation of insulin-like growth factor receptor signaling mediates resistance to histone deacetylase inhibitors

Histone deacetylases (HDACs) are considered promising targets in the treatment of hematologic malignancies and several types of solid tumors, including non-small cell lung cancer (NSCLC). However, the efficacy of HDAC inhibitors in solid tumors is marginal, and the mechanisms underlying resistance to HDAC inhibitors are largely unknown. Here, we demonstrate the involvement of type 1 insulin-like growth factor receptor (IGF-1R) signaling in resistance to HDAC inhibitors in NSCLC. Using MTT and soft-agar colony formation assays, we selected NSCLC cell lines that exhibited intrinsic resistance to vorinostat. Treatment with vorinostat activated IGF-1R signaling in vorinostat-resistant but not vorinostat-sensitive NSCLC cells. Other HDAC inhibitors, including trichostatin A, sodium butyrate, and depsipeptide, also activated IGF-1R signaling in vorinostat-resistant NSCLC cells. Blockade of IGF-1R signaling via IGF-1R monoclonal antibodies (mAbs) or through knockdown of IGF-1R via RNA interference sensitized vorinostat-resistant cells to HDAC inhibition. Finally, IGF-1R mAbs sensitized xenograft tumors of vorinostat-resistant cells to vorinostat treatment in vivo. These findings suggest that IGF-1R activation is generally involved in resistance to HDAC inhibitors and that targeting IGF-1R is an effective strategy for overcoming resistance to HDAC inhibitors in NSCLC.