Histone deacetylases are critical targets of bortezomib-induced cytotoxicity in multiple myeloma

Quinazoline-chalcone hybrids as HDAC/EGFR dual inhibitors: Design, synthesis, mechanistic, and in-silico studies of potential anticancer activity against multiple myeloma

Two new series of quinazoline-chalcone hybrids were designed, synthesized as histone deacetylase (HDAC)/epidermal growth factor receptor (EGFR) dual inhibitors, and screened in vitro against the NCI 60 human cancer cell line panel. The most potent derivative, compound 5e bearing a 3,4,5-trimethoxyphenyl chalcone moiety, showed the most effective growth inhibition value against the panel of NCI 60 human cancer cell lines. Thus, it was selected for further investigation for NCI 5 log doses. Interestingly, this trimethoxy-substituted analog inhibited the proliferation of Roswell Park Memorial Institute (RPMI)-8226 cells by 96%, at 10 µM with IC50 = 9.09 ± 0.34 µM and selectivity index = 7.19 against normal blood cells. To confirm the selectivity of this compound, it was evaluated against a panel of tyrosine kinase enzymes. Mechanistically, it successfully and selectively inhibited HDAC6, HDAC8, and EGFR with IC50 = 0.41 ± 0.015, 0.61 ± 0.027, and 0.09 ± 0.004 µM, respectively. Furthermore, the selected derivative induced apoptosis via the mitochondrial apoptotic pathway by raising the Bax/Bcl-2 ratio and activating caspases 3, 7, and 9. Also, the flow cytometry analysis of RPMI-8226 cells showed that the trimethoxy-substituted analog produced cell cycle arrest in the G1 and S phases at 55.82%. Finally, an in silico study was performed to explore the binding interaction of the most active compound within the zinc-containing binding site of HDAC6 and HDAC8.

Exploring the role of histone deacetylase and histone deacetylase inhibitors in the context of multiple myeloma: mechanisms, therapeutic implications, and future perspectives

Histone deacetylase inhibitors (HDACis) are a significant category of pharmaceuticals that have developed in the past two decades to treat multiple myeloma. Four drugs in this category have received approval from the U.S. Food and Drug Administration (FDA) for use: Panobinonstat (though canceled by the FDA in 2022), Vorinostat, Belinostat and Romidepsin. The efficacy of this group of drugs is attributed to the disruption of many processes involved in tumor growth through the inhibition of histone deacetylase, and this mode of action leads to significant anti-multiple myeloma (MM) activity. In MM, inhibition of histone deacetylase has many downstream consequences, including suppression of NF-κB signaling and HSP90, upregulation of cell cycle regulators (p21, p53), and downregulation of antiapoptotic proteins including Bcl-2. Furthermore, HDACis have a variety of direct and indirect oxidative effects on cellular DNA. HDAC inhibitors enhance normal immune function, thereby decreasing the proliferation of malignant plasma cells and promoting autophagy. The various biological effects of inhibiting histone deacetylase have a combined or additional impact when used alongside other chemotherapeutic and targeted drugs for multiple myeloma. This helps to decrease resistance to treatment. Combination treatment regimens that include HDACis have become an essential part of the therapy for multiple myeloma. These regimens incorporate drugs from other important classes of anti-myeloma agents, such as immunomodulatory drugs (IMiDs), conventional chemotherapy, monoclonal antibodies, and proteasome inhibitors. This review provides a comprehensive evaluation of the clinical efficacy and safety data pertaining to the currently approved histone deacetylase inhibitors, as well as an explanation of the crucial function of histone deacetylase in multiple myeloma and the characteristics of the different histone deacetylase inhibitors. Moreover, it provides a concise overview of the most recent developments in the use of histone deacetylase inhibitors for treating multiple myeloma, as well as potential future uses in treatment.

Chromatin Profiles Are Prognostic of Clinical Response to Bortezomib-Containing Chemotherapy in Pediatric Acute Myeloid Leukemia: Results from the COG AAML1031 Trial

The addition of the proteasome inhibitor bortezomib to standard chemotherapy did not improve survival in pediatric acute myeloid leukemia (AML) when all patients were analyzed as a group in the Children's Oncology Group phase 3 trial AAML1031 (NCT01371981). Proteasome inhibition influences the chromatin landscape and proteostasis, and we hypothesized that baseline proteomic analysis of histone- and chromatin-modifying enzymes (HMEs) would identify AML subgroups that benefitted from bortezomib addition. A proteomic profile of 483 patients treated with AAML1031 chemotherapy was generated using a reverse-phase protein array. A relatively high expression of 16 HME was associated with lower EFS and higher 3-year relapse risk after AML standard treatment compared to low expressions (52% vs. 29%, p = 0.005). The high-HME profile correlated with more transposase-accessible chromatin, as demonstrated via ATAC-sequencing, and the bortezomib addition improved the 3-year overall survival compared with standard therapy (62% vs. 75%, p = 0.033). These data suggest that there are pediatric AML populations that respond well to bortezomib-containing chemotherapy.

Epigenetic Alterations as Vital Aspects of Bortezomib Molecular Action

Bortezomib (BTZ) is widely implemented in the treatment of multiple myeloma (MM). Its main mechanism of action is very well established. BTZ selectively and reversibly inhibits the 26S proteasome. More precisely, it interacts with the chymotryptic site of the 20S proteasome and therefore inhibits the degradation of proteins. This results in the intracellular accumulation of misfolded or otherwise defective proteins leading to growth inhibition and apoptosis. As well as interfering with the ubiquitin-proteasome complex, BTZ elicits various epigenetic alterations which contribute to its cytotoxic effects as well as to the development of BTZ resistance. In this review, we summarized the epigenetic alterations elicited by BTZ. We focused on modifications contributing to the mechanism of action, those mediating drug-resistance development, and epigenetic changes promoting the occurrence of peripheral neuropathy. In addition, there are therapeutic strategies which are specifically designed to target epigenetic changes. Herein, we also reviewed epigenetic agents which might enhance BTZ-related cytotoxicity or restore the sensitivity to BTZ of resistant clones. Finally, we highlighted putative future perspectives regarding the role of targeting epigenetic changes in patients exposed to BTZ.

Histone deacetylase-based dual targeted inhibition in multiple myeloma

Despite enormous advances in terms of therapeutic strategies, multiple myeloma (MM) still remains an incurable disease with MM patients often becoming resistant to standard treatments. To date, multiple combined and targeted therapies have proven to be more beneficial compared to monotherapy approaches, leading to a decrease in drug resistance and an improvement in median overall survival in patients. Moreover, recent breakthroughs highlighted the relevant role of histone deacetylases (HDACs) in cancer treatment, including MM. Thus, the simultaneous use of HDAC inhibitors with other conventional regimens, such as proteasome inhibitors, is of interest in the field. In this review, we provide a general overview of HDAC-based combination treatments in MM, through a critical presentation of publications from the past few decades related to in vitro and in vivo studies, as well as clinical trials. Furthermore, we discuss the recent introduction of dual-inhibitor entities that could have the same beneficial effects as drug combinations with the advantage of having two or more pharmacophores in one molecular structure. These findings could represent a starting-point for both reducing therapeutic doses and lowering the risk of developing drug resistance.

Proteasome inhibition targets the KMT2A transcriptional complex in acute lymphoblastic leukemia

Rearrangments in Histone-lysine-N-methyltransferase 2A (KMT2Ar) are associated with pediatric, adult and therapy-induced acute leukemias. Infants with KMT2Ar acute lymphoblastic leukemia (ALL) have a poor prognosis with an event-free-survival of 38%. Herein we evaluate 1116 FDA approved compounds in primary KMT2Ar infant ALL specimens and identify a sensitivity to proteasome inhibition. Upon exposure to this class of agents, cells demonstrate a depletion of histone H2B monoubiquitination (H2Bub1) and histone H3 lysine 79 dimethylation (H3K79me2) at KMT2A target genes in addition to a downregulation of the KMT2A gene expression signature, providing evidence that it targets the KMT2A transcriptional complex and alters the epigenome. A cohort of relapsed/refractory KMT2Ar patients treated with this approach on a compassionate basis had an overall response rate of 90%. In conclusion, we report on a high throughput drug screen in primary pediatric leukemia specimens whose results translate into clinically meaningful responses. This innovative treatment approach is now being evaluated in a multi-institutional upfront trial for infants with newly diagnosed ALL.

Epigenetic Crosstalk between Malignant Plasma Cells and the Tumour Microenvironment in Multiple Myeloma

In multiple myeloma, cells of the bone marrow microenvironment have a relevant responsibility in promoting the growth, survival, and drug resistance of multiple myeloma plasma cells. In addition to the well-recognized role of genetic lesions, microenvironmental cells also present deregulated epigenetic systems. However, the effect of epigenetic changes in reshaping the tumour microenvironment is still not well identified. An assortment of epigenetic regulators, comprising histone methyltransferases, histone acetyltransferases, and lysine demethylases, are altered in bone marrow microenvironmental cells in multiple myeloma subjects participating in disease progression and prognosis. Aberrant epigenetics affect numerous processes correlated with the tumour microenvironment, such as angiogenesis, bone homeostasis, and extracellular matrix remodelling. This review focuses on the interplay between epigenetic alterations of the tumour milieu and neoplastic cells, trying to decipher the crosstalk between these cells. We also evaluate the possibility of intervening specifically in modified signalling or counterbalancing epigenetic mechanisms.

High Histone Deacetylase 2/3 Expression in Non-Functioning Pituitary Tumors

Epigenetic modification of chromatin is involved in non-malignant pituitary neoplasia by causing abnormal expression of tumor suppressors and oncogenes. These changes are potentially reversible, suggesting the possibility of targeting tumor cells by restoring the expression of epigenetically silenced tumor suppressors. The role of the histone deacetylase (HDAC) family in pituitary tumorigenesis is not known. We report that HDAC2 and 3, Class I HDAC members, are highly expressed in clinically non-functioning pituitary adenomas (NFPAs) compared to normal pituitary (NP) samples as determined by RT-PCR and immunohistochemical staining (IHC). Treatment of a human NFPA derived folliculostellate cell line, PDFS, with the HDAC3 inhibitor RGFP966 for 96 hours resulted in inhibition of cell proliferation by 70%. Furthermore, the combination of RGFP966 with a methyltransferase/DNMT inhibitor, 5’-aza-2’-deoxycytidine, led to the restoration of the expression of several tumor suppressor genes, including STAT1, P16, PTEN, and the large non-coding RNA tumor suppressor MEG3, in PDFS cells. Our data support the hypothesis that both histone modification and DNA methylation are involved in the pathogenesis of human NFPAs and suggest that targeting HDACs and DNA methylation can be incorporated into future therapies.

Epigenetics-Associated Risk Reduction of Hematologic Neoplasms in a Nationwide Cohort Study: The Chemopreventive and Therapeutic Efficacy of Hydralazine

Background

Although several epigenetic drugs have been reported to have therapeutic efficacy for some hematologic neoplasms (HNs) in clinical trials, few achieved disease-free survival benefit. The traditional drug discovery pathway is costly and time-consuming, and thus, more effective strategies are required. We attempted to facilitate epigenetic drug repositioning for therapy of HNs by screening the Human Epigenetic Drug Database (HEDD) in the web, conducting a bench-work cytotoxicity test and a retrospective nationwide cohort study prior to a clinical trial.

Methods

Four FDA-approved epigenetic drugs with antitumor properties and completion of clinical phase II trials were selected from HEDD. Hydralazine (HDZ) and valproate (VAL) among the four were selected with higher cytotoxicity to HN cells, no matter whether carrying the JAK2V617F mutation or not. Both of them were chosen for a cohort study using the Longitudinal Health Insurance Database (LHID) 2000–2015 (N = 1,936,512), a subset of the National Health Insurance Research Database (NHIRD, N= 25.68 millions) in Taiwan.

Results

In the initial cohort, HDZ or VAL exposure subjects (11,049) and matching reference subjects (44,196) were enrolled according to maximal daily consumption (300/2,100 mg per day of HDZ/VAL). The HN incidence in HDZ and VAL exposure groups reduced from 4.97% to 3.90% (p <.001) and 4.45% (p = .075), respectively. A further cohort study on HDZ at a lower range of the WHO defined daily dose (<34 mg per day) and HN incidence of HDZ exposure subjects (75,612) reduced from 5.01% to 4.16% (p = 1.725 × 10 ^-18) compared to the reference subjects (302,448).

Conclusions

An association of a chronically prescribed HDZ, even prescribed low dose, with reduction of overall incidence rate and in most subgroups of HN was observed in our study. Repositioning HDZ for HN management may be feasible. This is the first nationwide cohort study of the epigenetics-associated risk evaluation of overall HN in the existing literature, showing an effective method with a wider scope to inform contemporary clinical trials of epigenetic drugs in the future.

Expression of histone deacetylase (HDAC) family members in bortezomib-refractory multiple myeloma and modulation by panobinostat

AIM

Multiple myeloma (MM) is a hematological malignancy of antibody-producing mature B cells or plasma cells. The proteasome inhibitor, bortezomib, was the first-in-class compound to be FDA approved for MM and is frequently utilized in induction therapy. However, bortezomib refractory disease is a major clinical concern, and the efficacy of the pan-histone deacetylase inhibitor (HDACi), panobinostat, in bortezomib refractory disease indicates that HDAC targeting is a viable strategy. Here, we utilized isogenic bortezomib resistant models to profile HDAC expression and define baseline and HDACi-induced expression patterns of individual HDAC family members in sensitive vs. resistant cells to better understanding the potential for targeting these enzymes.

METHODS

Gene expression of HDAC family members in two sets of isogenic bortezomib sensitive or resistant myeloma cell lines was examined. These cell lines were subsequently treated with HDAC inhibitors: panobinostat or vorinostat, and HDAC expression was evaluated. CRISPR/Cas9 knockdown and pharmacological inhibition of specific HDAC family members were conducted.

RESULTS

Interestingly, HDAC6 and HDAC7 were significantly upregulated and downregulated, respectively, in bortezomib-resistant cells. Panobinostat was effective at inducing cell death in these lines and modulated HDAC expression in cell lines and patient samples. Knockdown of HDAC7 inhibited cell growth while pharmacologically inhibiting HDAC6 augmented cell death by panobinostat.

CONCLUSION

Our data revealed heterogeneous expression of individual HDACs in bortezomib sensitive vs. resistant isogenic cell lines and patient samples treated with panobinostat. Cumulatively our findings highlight distinct roles for HDAC6 and HDAC7 in regulating cell death in the context of bortezomib resistance.

Recent developments in the medicinal chemistry of single boron atom-containing compounds

Various boron-containing drugs have been approved for clinical use over the past two decades, and more are currently in clinical trials. The increasing interest in boron-containing compounds is due to their unique binding properties to biological targets; for example, boron substitution can be used to modulate biological activity, pharmacokinetic properties, and drug resistance. In this perspective, we aim to comprehensively review the current status of boron compounds in drug discovery, focusing especially on progress from 2015 to December 2020. We classify these compounds into groups showing anticancer, antibacterial, antiviral, antiparasitic and other activities, and discuss the biological targets associated with each activity, as well as potential future developments.

Chidamide, a subtype-selective histone deacetylase inhibitor, enhances Bortezomib effects in multiple myeloma therapy

Drug resistance is the major cause for disease relapse and patient death in multiple myeloma (MM). It is an urgent need to develop new therapies to overcome drug resistance in MM. Chidamide (CHI), a novel oral HDAC inhibitor targeting HDAC1, 2, 3 and 10, has shown potential therapeutic effect in MM. In this study, we determined that CHI exhibited significant anti-tumor effect on MM cells both in vitro and in vivo, which was positively correlated with the expression of HDAC1. Meanwhile, CHI enhanced Bortezomib (BTZ) effects synergistically in MM cells and a combination of CHI with BTZ induced myeloma cell apoptosis and G0/G1 arrest in vitro and in vivo. Mechanistically, the synergistic anti-tumor effect of CHI and BTZ was related with the increased production of reactive oxygen species (ROS) dependent DNA damage and the changes of cell apoptosis and cycle pathways. Our data indicate that CHI may be a suitable drug to sensitize BTZ in MM cells, which provides novel insight into the therapy for MM patients.

Borinostats: solid-phase synthesis of carborane-capped histone deacetylase inhibitors with a tailor-made selectivity profile

The elevated expression of histone deacetylases (HDACs) in various tumor types renders their inhibition an attractive strategy for epigenetic therapeutics. One key issue in the development of improved HDAC inhibitors (HDACis) is the selectivity for single HDAC isoforms over unspecific pan inhibition to minimize off-target toxicity. Utilizing the carborane moiety as a fine-tuning pharmacophore, we herein present a robust solid phase synthetic approach towards tailor-made HDACis meeting both ends of the selectivity spectrum, namely pan inhibition and highly selective HDAC6 inhibition.

Investigating the Interplay between Myeloma Cells and Bone Marrow Stromal Cells in the Development of Drug Resistance: Dissecting the Role of Epigenetic Modifications

Simple Summary

Despite advances made in the last two decades, multiple myeloma (MM) is still an incurable disease. The genetic complexity of MM and the presence of intra-clonal heterogeneity are major contributors to disease relapse and the development of treatment resistance. Additionally, the bone marrow microenvironment is known to play a pivotal role in MM disease progression. Together with genetic modifications, epigenetic changes have been shown to influence MM development and progression. However, epigenetic treatments for MM are still lacking. This is mainly due to the high rate of adverse events of epigenetic drugs in clinical practice. In this review, we will focus on the role of epigenetic modifications in MM disease progression and the development of drug resistance, as well as their role in shaping the interplay between bone marrow stromal cells and MM cells. The current and future treatment strategies involving epigenetic drugs will also be addressed.

Abstract

Multiple Myeloma (MM) is a malignancy of plasma cells infiltrating the bone marrow (BM). Many studies have demonstrated the crucial involvement of bone marrow stromal cells in MM progression and drug resistance. Together with the BM microenvironment (BMME), epigenetics also plays a crucial role in MM development. A variety of epigenetic regulators, including histone acetyltransferases (HATs), histone methyltransferases (HMTs) and lysine demethylases (KDMs), are altered in MM, contributing to the disease progression and prognosis. In addition to histone modifications, DNA methylation also plays a crucial role. Among others, aberrant epigenetics involves processes associated with the BMME, like bone homeostasis, ECM remodeling or the development of treatment resistance. In this review, we will highlight the importance of the interplay of MM cells with the BMME in the development of treatment resistance. Additionally, we will focus on the epigenetic aberrations in MM and their role in disease evolution, interaction with the BMME, disease progression and development of drug resistance. We will also briefly touch on the epigenetic treatments currently available or currently under investigation to overcome BMME-driven treatment resistance.

Inhibition of hsa_circ_0003489 shifts balance from autophagy to apoptosis and sensitizes multiple myeloma cells to bortezomib via miR-874-3p/HDAC1 axis

BACKGROUND

Circular RNAs (circRNAs) crucially regulate tumor progression. In this study, we examined the functional roles and mechanisms of hsa_circ_0003489 in multiple myeloma (MM).

METHODS

Upon altering the expressions of hsa_circ_0003489, miR-874-3p, and/or histone deacetylase 1 (HDAC1) in MM1.R cells and treating them with bortezomib (BTZ), cell viability was examined by CCK-8 assay; cell proliferation by Ki-67 immunofluorescence; apoptosis by TUNEL staining, flow cytometry, and western blot; and autophagy by electron microscopy and western blot. The interaction between hsa_circ_0003489 and miR-874-3p as well as that between miR-874-3p and HDAC1 was examined by expressional analysis, dual luciferase reporter assay, and RNA immunoprecipitation. The in vivo impacts of hsa_circ_0003489 on MM growth and sensitivity to BTZ were examined using an MM xenograft mouse model.

RESULTS

Knocking down hsa_circ_0003489 significantly inhibited the viability, cell proliferation, and autophagy, while promoting the apoptosis of MM cells in vitro and MM xenograft in vivo. Suppressing hsa_circ_0003489 also further boosted the cytotoxic effects of BTZ in MM cells and reversed its promoting effect on autophagy. Mechanically, hsa_circ_0003489 acted as a sponge of miR-874-3p and positively regulated the expression of miR-874-3p target, HDAC1. MiR-874-3p and HDAC1 essentially mediated the effects of hsa_circ_0003489 on cell viability, proliferation, apoptosis, and autophagy.

CONCLUSION

The hsa_circ_0003489/miR-874-3p/HDAC1 axis critically regulates the balance between apoptosis and autophagy. Silencing hsa_circ_0003489 sensitizes MM cells to BTZ by inhibiting autophagy and thus may boost the therapeutic effects of BTZ.

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.

TAK1 is a pivotal therapeutic target for tumor progression and bone destruction in myeloma

Along with tumor progression, the bone marrow microenvironment is skewed in multiple myeloma (MM), which underlies the unique pathophysiology of MM and confers aggressiveness and drug resistance in MM cells. TGF-b-activated kinase-1 (TAK1) mediates a wide range of intracellular signaling pathways. We demonstrate here that TAK1 is constitutively overexpressed and phosphorylated in MM cells, and that TAK1 inhibition suppresses the activation of NF-κB, p38MAPK, ERK and STAT3 in order to decrease the expression of critical mediators for MM growth and survival, including PIM2, MYC, Mcl- 1, IRF4, and Sp1, along with a substantial reduction in the angiogenic factor VEGF in MM cells. Intriguingly, TAK1 phosphorylation was also induced along with upregulation of vascular cell adhesion molecule-1 (VCAM-1) in bone marrow stromal cells (BMSC) in cocultures with MM cells, which facilitated MM cell-BMSC adhesion while inducing IL-6 production and receptor activator of nuclear factor κ-B ligand (RANKL) expression by BMSC. TAK1 inhibition effectively impaired MM cell adhesion to BMSC to disrupt the support of MM cell growth and survival by BMSC. Furthermore, TAK1 inhibition suppressed osteoclastogenesis enhanced by RANKL in cocultures of bone marrow cells with MM cells, and restored osteoblastic differentiation suppressed by MM cells or inhibitory factors for osteoblastogenesis overproduced in MM. Finally, treatment with the TAK1 inhibitor LLZ1640-2 markedly suppressed MM tumor growth and prevented bone destruction and loss in mouse MM models. Therefore, TAK1 inhibition may be a promising therapeutic option targeting not only MM cells but also the skewed bone marrow microenvironment in MM.

The Landscape of Signaling Pathways and Proteasome Inhibitors Combinations in Multiple Myeloma

Multiple myeloma is a malignancy of terminally differentiated plasma cells, characterized by an extreme genetic heterogeneity that poses great challenges for its successful treatment. Due to antibody overproduction, MM cells depend on the precise regulation of the protein degradation systems. Despite the success of PIs in MM treatment, resistance and adverse toxic effects such as peripheral neuropathy and cardiotoxicity could arise. To this end, the use of rational combinatorial treatments might allow lowering the dose of inhibitors and therefore, minimize their side-effects. Even though the suppression of different cellular pathways in combination with proteasome inhibitors have shown remarkable anti-myeloma activities in preclinical models, many of these promising combinations often failed in clinical trials. Substantial progress has been made by the simultaneous targeting of proteasome and different aspects of MM-associated immune dysfunctions. Moreover, targeting deranged metabolic hubs could represent a new avenue to identify effective therapeutic combinations with PIs. Finally, epigenetic drugs targeting either DNA methylation, histone modifiers/readers, or chromatin remodelers are showing pleiotropic anti-myeloma effects alone and in combination with PIs. We envisage that the positive outcome of patients will probably depend on the availability of more effective drug combinations and treatment of early MM stages. Therefore, the identification of sensitive targets and aberrant signaling pathways is instrumental for the development of new personalized therapies for MM patients.

The proteostasis guardian HSF1 directs the transcription of its paralog and interactor HSF2 during proteasome dysfunction

Protein homeostasis is essential for life in eukaryotes. Organisms respond to proteotoxic stress by activating heat shock transcription factors (HSFs), which play important roles in cytoprotection, longevity and development. Of six human HSFs, HSF1 acts as a proteostasis guardian regulating stress-induced transcriptional responses, whereas HSF2 has a critical role in development, in particular of brain and reproductive organs. Unlike HSF1, that is a stable protein constitutively expressed, HSF2 is a labile protein and its expression varies in different tissues; however, the mechanisms regulating HSF2 expression remain poorly understood. Herein we demonstrate that the proteasome inhibitor anticancer drug bortezomib (Velcade), at clinically relevant concentrations, triggers de novo HSF2 mRNA transcription in different types of cancers via HSF1 activation. Similar results were obtained with next-generation proteasome inhibitors ixazomib and carfilzomib, indicating that induction of HSF2 expression is a general response to proteasome dysfunction. HSF2-promoter analysis, electrophoretic mobility shift assays, and chromatin immunoprecipitation studies unexpectedly revealed that HSF1 is recruited to a heat shock element located at 1.397 bp upstream from the transcription start site in the HSF2-promoter. More importantly, we found that HSF1 is critical for HSF2 gene transcription during proteasome dysfunction, representing an interesting example of transcription factor involved in controlling the expression of members of the same family. Moreover, bortezomib-induced HSF2 was found to localize in the nucleus, interact with HSF1, and participate in bortezomib-mediated control of cancer cell migration. The results shed light on HSF2-expression regulation, revealing a novel level of HSF1/HSF2 interplay that may lead to advances in pharmacological modulation of these fundamental transcription factors.

Old drugs, new uses: Drug repurposing in hematological malignancies

Discovery and development of novel anti-cancer drugs are expensive and time consuming. Systems biology approaches have revealed that a drug being developed for a non-cancer indication can hit other targets as well, which play critical roles in cancer progression. Since drugs for non-cancer indications would have already gone through the preclinical and partial or full clinical development, repurposing such drugs for hematological malignancies would cost much less, and drastically reduce the development time, which is evident in case of thalidomide. Here, we have reviewed some of the drugs for their potential to repurpose for treating the hematological malignancies. We have also enlisted resources that can be helpful in drug repurposing.

Loss of HDAC3 results in nonreceptive endometrium and female infertility

Endometriosis is a disease in which tissue that normally grows inside the uterus grows outside the uterus and causes chronic pelvic pain and infertility. However, the exact mechanisms of the pathogenesis of endometriosis-associated infertility are unknown. Epigenetic dysregulation has recently been implicated in infertility. Here, we report a reduction of histone deacetylase 3 (HDAC3) protein amounts in eutopic endometrium of infertile women with endometriosis compared to a control group. To investigate the effect of HDAC3 loss in the uterus, we generated mice with conditional ablation of Hdac3 in progesterone receptor (PGR)-positive cells (Pgr^cre/+Hdac3^f/f ; Hdac3^d/d ). Loss of Hdac3 in the uterus of mice results in infertility due to implantation failure and decidualization defect. Expression microarray and ChIP-seq analyses identified COL1A1 and COL1A2 as direct targets of HDAC3 in both mice and humans. Reduction of HDAC3 abrogated decidualization in a primary culture of human endometrial stromal cells (hESCs) similar to that observed in infertile patients with endometriosis. Whereas attenuation of HDAC3 resulted in p300 recruitment to Col1a1 and Col1a2 genes in the uterus of mice as well as hESCs, inhibition of p300 permitted hESCs to undergo decidualization. Collectively, we found attenuation of HDAC3 and overexpression of collagen type I in the eutopic endometrium of infertile patients with endometriosis. HDAC3 loss caused a defect of decidualization through the aberrant transcriptional activation of Col1a1 and Col1a2 genes in mice and COL1A1 and COL1A2 genes in humans. Our results suggest that HDAC3 is critical for endometrial receptivity and decidualization.

1,2,3-Triazole-Chalcone hybrids: Synthesis, in vitro cytotoxic activity and mechanistic investigation of apoptosis induction in multiple myeloma RPMI-8226

A new series of 1,2,3-triazole-chalcone hybrids has been synthesized and screened in vitro against a panel of 60 human cancer cell lines according to NCI (USA) protocol. Compound 4d having 3, 4-dimethoxyphenyl chalcone moiety, the most potent derivative, inhibited the growth of RPMI-8226 and SR leukemia cell lines by 99.73% and 94.95% at 10 μM, respectively. Also, it inhibited the growth of M14 melanoma, K-562 leukemia, and MCF7 breast cancer cell lines by more than 80% at the same test concentration. 4d showed IC₅₀ values less than 1 μM on six types of tumor cells and high selectivity index reached to 104 fold on MCF7. Compound 4d showed superior activity than methotrexate and gefitinib against the most sensitive leukemia cell lines in addition to higher or comparable activity against the rest sensitive cell lines. Flow cytometry analysis in RPMI-8226 cells revealed that compound 4d caused cell cycle arrest at G2/M phase and induced apoptosis in a dose dependant manner. Mechanistic evaluation referred this apoptosis induction to triggering mitochondrial apoptotic pathway through inducing ROS accumulation, increasing Bax/Bcl-2 ratio and activation of caspases 3, 7 and 9.

Efficacy of Panobinostat for the Treatment of Multiple Myeloma

Panobinostat represents a potent oral nonselective pan-histone deacetylase inhibitor (HDAC) with activity in myeloma patients. It has been approved by the FDA and EMA in combination with bortezomib and dexamethasone for the treatment of multiple myeloma, in patients who have received at least two prior regimens, including bortezomib and an immunomodulatory agent. In order to further explore its clinical potential, it is evaluated in different combinations in relapsed/refractory and newly diagnosed multiple myeloma. This review focuses on available data about panobinostat's pharmacology and its role in clinical practice. This review will reveal panobinostat's efficacy as antimyeloma treatment, describing drug evolution from preclinical experimental administration to administration in phase III trials, which established its role in current clinical practice. Based on the latest data, we will present its mechanism of action, its efficacy, and most important issues regarding its toxicity profile. We will further try to shed light on its role in current and future therapeutic landscape of myeloma patients. Panobinostat retains its role in therapy of multiple myeloma because of its manageable toxicity profile and its efficacy, mainly in heavily pretreated multiple myeloma patients. These characteristics make it valuable also for novel regimens in combination with second-generation proteasome inhibitors, IMiDs, and monoclonal antibodies. Results of ongoing trials are expected to shed light on drug introduction in different therapeutic combinations or even at an earlier level of disease course.

Targeting the Cancer Epigenome with Histone Deacetylase Inhibitors in Osteosarcoma

Epigenetic deregulation is an emerging hallmark of cancer that enables tumor cells to escape surveillance by tumor suppressors and ultimately progress. The structure of the epigenome consists of covalent modifications of chromatin components, including acetylation by histone acetyltransferases (HATs) and deacetylation by histone deacetylases (HDACs). Targeting these enzymes with inhibitors to restore epigenetic homeostasis has been explored for many cancers. Osteosarcoma, an aggressive bone malignancy that primarily affects children and young adults, is notable for widespread genetic and epigenetic instability. This may explain why therapy directed at unique molecular pathways has failed to substantially improve outcomes in osteosarcoma over the past four decades. In this review, we discuss the potential of targeting the cancer epigenome, with a focus on histone deacetylase inhibitors (HDACi) for osteosarcoma. We additionally highlight the safety and tolerance of HDACi, combination chemotherapy with HDACi, and the ongoing challenges in the development of these agents.

Soluble SLAMF7 promotes the growth of myeloma cells via homophilic interaction with surface SLAMF7

SLAMF7 is expressed mainly on multiple myeloma (MM) cells and considered an ideal target for immunotherapeutic approaches. Indeed, elotuzumab, an anti-SLAMF7 antibody, is used for the treatment of MM in combination with immunomodulatory drugs. SLAMF7 is cleaved via unknown mechanisms and detected as a soluble form (sSLAMF7) exclusively in the serum of MM patients; however, little is known about the role of sSLAMF7 in MM biology. In this study, we found that sSLAMF7 enhanced the growth of MM cells via homophilic interaction with surface SLAMF7 and subsequent activation of the SHP-2 and ERK signaling pathways. Elotuzumab suppressed sSLAMF7-induced MM cell growth both in vitro and in vivo. Promoter analyses identified IKZF1 (Ikaros) as a pivotal transcriptional activator of the SLAMF7 gene. Pharmacological targeting of Ikaros by lenalidomide and its analog pomalidomide downregulated SLAMF7 expression and ameliorated the response of MM cells to sSLAMF7. Elotuzumab blocked the growth-promoting function of sSLAMF7 when combined with lenalidomide in a murine xenograft model. Neutralization of sSLAMF7 is a novel antimyeloma mechanism of elotuzumab, which is enhanced by immunomodulatory drugs via downregulation of surface SLAMF7 expression on MM cells. These findings may provide important information for the optimal use of elotuzumab in MM treatment.

Anti-tumor Activity and Epigenetic Impact of the Polyphenol Oleacein in Multiple Myeloma

Olive oil contains different biologically active polyphenols, among which oleacein, the most abundant secoiridoid, has recently emerged for its beneficial properties in various disease contexts. By using in vitro models of human multiple myeloma (MM), we here investigated the anti-tumor potential of oleacein and the underlying bio-molecular sequelae. Within a low micromolar range, oleacein reduced the viability of MM primary samples and cell lines even in the presence of bone marrow stromal cells (BMSCs), while sparing healthy peripheral blood mononuclear cells. We also demonstrated that oleacein inhibited MM cell clonogenicity, prompted cell cycle blockade and triggered apoptosis. We evaluated the epigenetic impact of oleacein on MM cells, and observed dose-dependent accumulation of both acetylated histones and α-tubulin, along with down-regulation of several class I/II histone deacetylases (HDACs) both at the mRNA and protein level, providing evidence of the HDAC inhibitory activity of this compound; conversely, no effect on global DNA methylation was found. Mechanistically, HDACs inhibition by oleacein was associated with down-regulation of Sp1, the major transactivator of HDACs promoter, via Caspase 8 activation. Of potential translational significance, oleacein synergistically enhanced the in vitro anti-MM activity of the proteasome inhibitor carfilzomib. Altogether, these results indicate that oleacein is endowed with HDAC inhibitory properties, which associate with significant anti-MM activity both as single agent or in combination with carfilzomib. These findings may pave the way to novel potential anti-MM epi-therapeutic approaches based on natural agents.

Apoptosis Induction byHistone Deacetylase Inhibitors in Cancer Cells: Role of Ku70

Histone deacetylases (HDACs) are a group of enzymes that regulate gene transcription by controlling deacetylation of histones and non-histone proteins. Overexpression of HDACs is found in some types of tumors and predicts poor prognosis. Five HDAC inhibitors are approved for the treatment of cutaneous T-cell lymphoma, peripheral T-cell lymphoma, and multiple myeloma. Treatment with HDAC inhibitors regulates gene expression with increased acetylated histones with unconfirmed connection with therapy. Apoptosis is a key mechanism by which HDAC inhibitors selectively kill cancer cells, probably due to acetylation of non-histone proteins. Ku70 is a protein that repairs DNA breaks and stabilizes anti-apoptotic protein c-FLIP and proapoptotic protein Bax, which is regulated by acetylation. HDAC inhibitors induce Ku70 acetylation with repressed c-FLIP and activated Bax in cancer cells. Current studies indicate that Ku70 is a potential target of HDAC inhibitors and plays an important role during the induction of apoptosis.

Role of RACK1 on cell proliferation, adhesion, and bortezomib-induced apoptosis in multiple myeloma

Receptor for activated C kinase 1 (RACK1), a scaffold protein, plays a crucial role in the progression of various cancers. However, the biological function and underlying mechanism of RACK1 in multiple myeloma (MM) cells remain unclear. The present study aimed to explore the function of RACK1 on the cell proliferation, adhesion, and bortezomib-induced apoptosis in MM. We found that RACK1 was significantly overexpressed in myeloma cell lines and primary myeloma cells compared with normal bone marrow plasma cells. Moreover, immunofluorescence revealed that RACK1 was primarily expressed in the cytoplasm of MM cells. Knockdown of RACK1 impaired growth of MM cells, blocked entry into the S-phase of the cell cycle, and resulted in reduced cell adhesion rates. More importantly, knockdown of RACK1 decreased the proliferation of MM cells by activating P-P38 and P-ERK in the MAPK/ERK signaling pathway. We also found that altered expression of RACK1 is associated with bortezomib-mediated MM cell apoptosis. In summary, these results may provide a possible target for therapy in MM.

The biological significance of histone modifiers in multiple myeloma: clinical applications

Multiple myeloma (MM) is a clonal plasma cell disorder that is characterized by a variety of genetic alterations. Recent studies have highlighted not only the importance of these genetic events but also epigenetic aberrations including DNA methylation, histone modifications, and non-coding RNAs in the biology of MM. Post-translational modifications of histone, such as methylation and acetylation, contribute to chromatin dynamics, and are modulated by histone modifying enzymes, and dysregulation of these enzymes is implicated in the pathogenesis of cancers, including MM. Histone modifiers also have non-histone substrates and enzymatically independent roles, which are also involved in tumorigenesis. Here we review and provide comprehensive insight into the biologic significance of histone methyl- and acetyl-modifiers in MM, and further provide an overview of the clinical applications of histone modifier inhibitors, especially histone deacetylase inhibitors. These findings underline the emerging roles of histone modifiers in the pathogenesis of MM, and further highlight the possibility of novel epigenetic therapies in MM.

The bitter side of epigenetics: variability and resistance to chemotherapy

One of the major obstacles to the development of effective new cancer treatments and the main factor for the increasing number of clinical trial failures appears to be the paucity of accurate, reproducible and robust drug resistance testing methods. Most research assessing the resistance of cancers to chemotherapy has concentrated on genetic-based molecular mechanisms, while the role of epigenetics in drug resistance has been generally overlooked. This is rather surprising given that an increasing body of evidence pointing to the fact that epigenetic mechanism alterations appear to play a pivotal role in cancer initiation, progression and development of chemoresistance. This resulted in a series of clinical trials involving epi-drug as single treatment or combined with cancer conventional drugs. In this review, we provided the main mechanisms by which the epigenetic regulators control the resistance to cancer drugs.

HDAC and Ku70 axis- an effective target for apoptosis induction by a new 2-cyano-3-oxo-1,9-dien glycyrrhetinic acid analogue

Methyl 2-cyano-3,12-dioxo-18β-olean-1,9(11)-dien-30-oate (CDODO-Me, 10d) derived from glycyrrhetinic acid and methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO-Me) derived from oleanoic acid are potent apoptosis inducers developed to clinical trials. Both compounds have high affinity for reduced  glutathione (GSH), which needs to be overcome to improve their target selectivity. We generated a new 10d analogue methyl 2-cyano-3-oxo-18β-olean-1,9(11), 12-trien-30-oate (COOTO, 10e), which retains high apoptosis inducing ability, while displaying decreased affinity for GSH, and explored the acting targets. We found that it induces Noxa level, reduces c-Flip level and causes Bax/Bak activation. Silencing of either Noxa or Bak significantly attenuated apoptosis induction of 10e. We linked these events due to targeting HDAC3/HDAC6 and Ku70 axis. 10e treatment reduced the levels of HDAC3 and HDAC6 with increased DNA damage/repair marker gamma-H2AX (γ-H2AX) and acetylated Ku70. c-Flip dissociates from acetylated Ku70 undergoing degradation, while Bax dissociates from acetylated Ku70 undergoing activation. Silencing of either HDAC3 or HDAC6 enhanced 10e-induced apoptosis. We reveal a new action cascade of this category of compounds that involves targeting of HADC3/6 proteins and Ku70 acetylation.

Expression of ribosomal and actin network proteins and immunochemotherapy resistance in diffuse large B cell lymphoma patients

Diffuse large B cell lymphoma (DLBCL) patients with early relapse or refractory disease have a very poor outcome. Immunochemotherapy resistance will probably, also in the era of targeted drugs, remain the major cause of treatment failure. We used proteomic mass spectrometry to analyse the global protein expression of micro-dissected formalin-fixed paraffin-embedded tumour tissues from 97 DLBCL patients: 44 with primary refractory disease or relapse within 1 year from diagnosis (REF/REL), and 53 who were progression-free more than 5 years after diagnosis (CURED). We identified 2127 proteins: 442 were found in all patients and 102 were differentially expressed. Sixty-five proteins were overexpressed in REF/REL patients, of which 46 were ribosomal proteins (RPs) compared with 2 of the 37 overexpressed proteins in CURED patients (P = 7·6 × 10^-10 ). Twenty of 37 overexpressed proteins in CURED patients were associated with actin regulation, compared with 1 of 65 in REF/REL patients (P = 1·4 × 10^-9 ). Immunohistochemical staining showed higher expression of RPS5 and RPL17 in REF/REL patients while MARCKS-like protein, belonging to the actin network, was more highly expressed in CURED patients. Even though functional studies aimed at individual proteins and protein interactions to evaluate potential clinical effect are needed, our findings suggest new mechanisms behind immunochemotherapy resistance in DLBCL.

An Expanded Treatment Protocol of Panobinostat Plus Bortezomib and Dexamethasone in Patients With Previously Treated Myeloma

BACKGROUND

Panobinostat was recently approved by the US Food and Drug Administration and European Commission in combination with bortezomib and dexamethasone for patients with multiple myeloma who have received ≥ 2 regimens, including bortezomib and an immunomodulatory drug. The PANEX (panobinostat expansion) treatment protocol provided access to panobinostat and gathered additional safety data before commercial availability.

PATIENTS AND METHODS

In treatment phase 1, patients received panobinostat 20 mg 3 times per week plus bortezomib 1.3 mg/m² twice weekly with dexamethasone 20 mg on the days of and after bortezomib treatment. Patients with no change or better in treatment phase 1 proceeded to treatment phase 2, when bortezomib was reduced to once weekly. Unlike in the phase III trial, PANORAMA-1 (panobinostat or placebo with bortezomib and dexamethasone in patients with relapsed multiple myeloma), bortezomib could be administered either subcutaneously or intravenously.

RESULTS

Thirty-nine patients with a median number of previous treatments of 4 (range, 1-12) were enrolled; most received subcutaneous bortezomib (87%). The overall response rate (partial response or better) was 56%. Grade 3/4 adverse events included thrombocytopenia (47%), fatigue (31%), dehydration (26%), and diarrhea (18%). Among the patients who received subcutaneous bortezomib, relatively low rates of peripheral neuropathy (all grade, 15%) and notable grade 3/4 adverse events (thrombocytopenia, 47%; diarrhea, 12%) were observed.

CONCLUSION

Overall, data from the PANEX trial support regulatory approval of panobinostat plus bortezomib and dexamethasone and suggest the potential tolerability benefits of subcutaneous bortezomib in this regimen.

A vicious cycle between acid sensing and survival signaling in myeloma cells: acid-induced epigenetic alteration

Myeloma (MM) cells and osteoclasts are mutually interacted to enhance MM growth while creating acidic bone lesions. Here, we explored acid sensing of MM cells and its role in MM cell response to acidic conditions. Acidic conditions activated the PI3K-Akt signaling in MM cells while upregulating the pH sensor transient receptor potential cation channel subfamily V member 1 (TRPV1) in a manner inhibitable by PI3K inhibition. The acid-activated PI3K-Akt signaling facilitated the nuclear localization of the transcription factor Sp1 to trigger the expression of its target genes, including TRPV1 and HDAC1. Consistently, histone deacetylation was enhanced in MM cells in acidic conditions, while repressing a wide variety of genes, including DR4. Indeed, acidic conditions deacetylated histone H3K9 in a DR4 gene promoter and curtailed DR4 expression in MM cells. However, inhibition of HDAC as well as either Sp1 or PI3K was able to restore DR4 expression in MM cells suppressed in acidic conditions. These results collectively demonstrate that acid activates the TRPV1-PI3K-Akt-Sp1 signaling in MM cells while inducing HDAC-mediated gene repression, and suggest that a positive feedback loop between acid sensing and the PI3K-Akt signaling is formed in MM cells, leading to MM cell response to acidic bone lesions.

Lysine-specific demethylase 1 inhibitors prevent teratoma development from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are creating great expectations for regenerative medicine. However, safety strategies must be put in place to guard against teratoma formation after transplantation of hiPSC-derived cells into patients. Recent studies indicate that epigenetic regulators act at the initial step of tumorigenesis. Using gain-of-function and loss-of-function approaches, we show here that the expression and function of lysine-specific demethylase 1 (LSD1) are tightly regulated in hiPSCs, and their deregulation underlies the development of teratomas. Consistent with these results, we demonstrate that an LSD1 inhibitor, S2157, prevented teratoma formation from hiPSCs transplanted into immunodeficient mice. This novel action of LSD1 and the effects of its inhibition potentially allow for the development of new clinical applications and therapeutic strategies using hiPSCs.

Novel tropolones induce the unfolded protein response pathway and apoptosis in multiple myeloma cells

Tropolones are small organic compounds with metal-directing moieties. Tropolones inhibit the proliferation of cancer cell lines, possibly through their effects on metalloenzymes such as select histone deacetylases (HDACs). Pan-HDAC inhibitors are therapeutically beneficial in the treatment of multiple myeloma, however there is interest in the use of more selective HDAC inhibitor therapy to minimize adverse side effects. We hypothesized that tropolones might have anti-myeloma activities. To this end, a series of novel α-substituted tropolones were evaluated for effects on multiple myeloma cells. While all tested tropolones showed some level of cytotoxicity, MO-OH-Nap had consistently low IC50 values between 1-11 μM in all three cell lines tested and was used for subsequent experiments. MO-OH-Nap was found to induce apoptosis in a concentration-dependent manner. Time course experiments demonstrated that MO-OH-Nap promotes caspase cleavage in a time frame that was distinct from the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). Furthermore, MO-OH-Nap- and SAHA-treated cells possess unique gene expression patterns, suggesting they promote apoptosis via different mechanisms. In particular, MO-OH-Nap increases the expression of markers associated with endoplasmic reticulum stress and the unfolded protein response. Synergistic cytotoxic effects were observed when cells were treated with the combination of MO-OH-Nap and the proteasome inhibitor bortezomib. However, treatment with MO-OH-Nap did not abrogate the bortezomib-induced increase in aggresomes, consistent with an HDAC6-independent mechanism for the observed synergy. Collectively, these finding support further investigation into the usefulness of α-substituted tropolones as anti-myeloma agents.

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.

Novel Proteasome Inhibitors and Histone Deacetylase Inhibitors: Progress in Myeloma Therapeutics

The unfolded protein response is responsible for the detection of misfolded proteins and the coordination of their disposal and is necessary to maintain the cellular homoeostasis. Multiple myeloma cells secrete large amounts of immunoglobulins, proteins that need to be correctly folded by the chaperone system. If this process fails, the misfolded proteins have to be eliminated by the two main garbage-disposal systems of the cell: proteasome and aggresome. The blockade of either of these systems will result in accumulation of immunoglobulins and other toxic proteins in the cytoplasm and cell death. The simultaneous inhibition of the proteasome, by proteasome inhibitors (PIs) and the aggresome, by histone deacetylase inhibitors (HDACi) results in a synergistic increase in cytotoxicity in myeloma cell lines. This review provides an overview of mechanisms of action of second-generation PIs and HDACi in multiple myeloma (MM), the clinical results currently observed with these agents and assesses the potential therapeutic impact of the different agents in the two classes. The second-generation PIs offer benefits in terms of increased efficacy, reduced neurotoxicity as off-target effect and may overcome resistance to bortezomib because of their different chemical structure, mechanism of action and biological properties. HDACi with anti-myeloma activity in clinical development discussed in this review include vorinostat, panobinostat and selective HDAC6 inhibitor, ricolinostat.

The Role of Intracellular Signaling Pathways in the Pathogenesis of Multiple Myeloma and Novel Therapeutic Approaches

The introduction of novel agents, such as bortezomib, thalidomide, and lenalidomide, into daily practice has dramatically improved clinical outcomes and prolonged survival of patients with multiple myeloma (MM). However, despite these advanced clinical benefits, MM remains an incurable hematological malignancy. Therefore, development of new agents and novel therapeutic strategies is urgently needed. Recent advances toward understanding the mechanism of myeloma cell growth and drug resistance in the bone marrow milieu have provided clues for the development of next-generation agents aimed at improving patient outcomes. In this review article, we discuss new possible agents for the treatment of MM based on recent advances in the understanding of signaling pathways in myeloma cells.

Synergistic targeting of Sp1, a critical transcription factor for myeloma cell growth and survival, by panobinostat and proteasome inhibitors

Panobinostat, a pan-deacetylase inhibitor, synergistically elicits cytotoxic activity against myeloma (MM) cells in combination with the proteasome inhibitor bortezomib. Because precise mechanisms for panobinostat's anti-MM action still remain elusive, we aimed to clarify the mechanisms of anti-MM effects of panobinostat and its synergism with proteasome inhibitors. Although the transcription factor Sp1 was overexpressed in MM cells, the Sp1 inhibitor terameprocol induced MM cell death in parallel with reduction of IRF4 and cMyc. Panobinostat induced activation of caspase-8, which was inversely correlated with reduction of Sp1 protein levels in MM cells. The panobinostat-mediated effects were further potentiated to effectively induce MM cell death in combination with bortezomib or carfilzomib even at suboptimal concentrations as a single agent. Addition of the caspase-8 inhibitor z-IETD-FMK abolished the Sp1 reduction not only by panobinostat alone but also by its combination with bortezomib, suggesting caspase-8-mediated Sp1 degradation. The synergistic Sp1 reduction markedly suppressed Sp1-driven prosurvival factors, IRF4 and cMyc. Besides, the combinatory treatment reduced HDAC1, another Sp1 target, in MM cells, which may potentiate HDAC inhibition. Collectively, caspase-8-mediated post-translational Sp1 degradation appears to be among major mechanisms for synergistic anti-MM effects of panobinostat and proteasome inhibitors in combination.

Targeting histone deacetylases in T-cell lymphoma

Histone deacetylase inhibitors (HDACi) are epigenetic modifiers with single-agent activity in patients with cutaneous and peripheral T-cell lymphoma (CTCL, PTCL). The mechanisms for this preferential activity remain unclear, and although some would term this as 'class effect,' there are differences in efficacy and safety, likely a result of the varying chemical structures/classes, histone and non-histone targets, potencies, and clinical dosing for each. Three HDACi have single-agent approval in relapsed/refractory TCL in the United States: romidepsin in CTCL and PTCL, vorinostat in CTCL, and belinostat in PTCL. Although comparison of these agents is difficult due to differences in patient populations, through this review we aimed to provide a detailed overview of the clinical data for HDACi in TCL and their use in clinical practice. Despite early concerns, data demonstrate the cardiac safety of HDACi, while highlighting the need to maintain electrolytes in the normal range and monitor QT interval when initially co-administering antiemetics or other drugs that prolong QT. To further improve response rates and durability of responses, HDACi are under clinical investigation in combination with chemotherapy regimens and various novel agents.

The Role of Panobinostat Plus Bortezomib and Dexamethasone in Treating Relapsed or Relapsed and Refractory Multiple Myeloma: A European Perspective

Panobinostat is an oral pan-histone deacetylase inhibitor developed by Novartis. Panobinostat acts via epigenetic modification and inhibition of the aggresome pathway. In August 2015, the European Commission authorized panobinostat for use in combination with bortezomib and dexamethasone for the treatment of relapsed or relapsed and refractory multiple myeloma (MM) in patients who have received ≥2 prior regimens including bortezomib and an immunomodulatory drug. In January 2016, the National Institute for Health and Care Excellence recommended panobinostat for use in the same combination and patient population. The authorization and recommendation were based on results from the pivotal phase 3 PANORAMA 1 (NCT01023308) clinical trial, which demonstrated an improvement in median progression-free survival of 7.8 months for the three-drug combination compared with placebo plus bortezomib and dexamethasone in this patient population. This review will discuss the current treatment landscape for relapsed/refractory MM, the mechanism of action of panobinostat, clinical data supporting the European authorization, concerns about safety and strategies for mitigating toxicity, and how panobinostat fits into the current MM landscape in Europe.

FUNDING

Editorial support, funded by Novartis Pharmaceuticals.

A phase II study of belinostat (PXD101) in relapsed and refractory aggressive B-cell lymphomas: SWOG S0520

Recent advances in diffuse large B-cell lymphomas (DLBCL) have underscored the importance of tumor microenvironment in escaping host anti-tumor responses. One mechanism is loss of major histocompatibility Class II antigens (MHCII) associated with decreased tumor infiltrating T lymphocytes (TIL) and poor survival. Transcription of MHCII is controlled by CIITA which in turn is regulated by histone acetylation. In this study, we hypothesized that HDAC inhibition with belinostat increases MHCII, CIITA expression, TIL and improves patient outcomes. Primary objective was evaluation of toxicity and response. Twenty-two patients were enrolled for the study. Belinostat was well tolerated with mild toxicity. Two partial responses were observed at 5, 13 months after registration for an overall response rate (ORR) (95% CI) of 10.5% (1.3-33.1%), and three patients had stable disease for 4.7, 42.3+, and 68.4 + months with minimum 3-year follow-up. Included correlative studies support the hypothesis and serve as the basis for SWOG S0806 combining vorinostat with R-CHOP.

Use of class I histone deacetylase inhibitor romidepsin in combination regimens

Histone deacetylase (HDAC) inhibitors are epigenetic-modifying agents that have shown promise as anticancer therapies. Several HDAC inhibitors have been approved by the US Food and Drug Administration (FDA) as single-agent therapies to treat T-cell lymphoma. The synergistic combination of HDAC inhibitors with other anticancer agents has the potential to constitute treatment regimens with enhanced efficacy. Romidepsin is a structurally unique, potent, bicyclic class 1 selective HDAC inhibitor approved by the FDA for the treatment of patients with peripheral T-cell lymphoma who have had at least 1 prior therapy and patients with cutaneous T-cell lymphoma who have had at least 1 prior systemic therapy. Here, we review data that support the use of romidepsin in combination with other anticancer agents for the treatment of various malignancies. Promising results have emerged from early clinical studies, supporting the potential for romidepsin combination regimens to constitute safe and effective treatments for cancer.