Vorinostat enhances the antimyeloma effects of melphalan and bortezomib

Stochasticity of anticancer mechanisms underlying clinical effectiveness of vorinostat

The Food and Drug Administration (FDA) has approved vorinostat, also called Zolinza®, for its effectiveness in fighting cancer. This drug is a suberoyl-anilide hydroxamic acid belonging to the class of histone deacetylase inhibitors (HDACis). Its HDAC inhibitory potential allows it to accumulate acetylated histones. This, in turn, can restore normal gene expression in cancer cells and activate multiple signaling pathways. Experiments have proven that vorinostat induces histone acetylation and cytotoxicity in many cancer cell lines, increases the level of p21 cell cycle proteins, and enhances pro-apoptotic factors while decreasing anti-apoptotic factors. Additionally, it regulates the immune response by up-regulating programmed death-ligand 1 (PD-L1) and interferon gamma receptor 1 (IFN-γR1) expression, and can impact proteasome and/or aggresome degradation, endoplasmic reticulum function, cell cycle arrest, apoptosis, tumor microenvironment remodeling, and angiogenesis inhibition. In this study, we sought to elucidate the precise molecular mechanism by which Vorinostat inhibits HDACs. A deeper understanding of these mechanisms could improve our understanding of cancer cell abnormalities and provide new therapeutic possibilities for cancer treatment.

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.

Network-Based Systems Analysis Explains Sequence-Dependent Synergism of Bortezomib and Vorinostat in Multiple Myeloma

Bortezomib and vorinostat exhibit synergistic effects in multiple myeloma (MM) cells when given in sequence, and the purpose of this study was to evaluate the molecular determinants of the interaction using a systems pharmacology approach. A Boolean network model consisting of 79 proteins and 225 connections was developed using literature information characterizing mechanisms of drug action and intracellular signal transduction. Network visualization and structural analysis were conducted, and model simulations were compared with experimental data. Critical biomarkers, such as pNFκB, p53, cellular stress, and p21, were identified using measures of network centrality and model reduction. U266 cells were then exposed to bortezomib (3 nM) and vorinostat (2 μM) as single agents or in simultaneous and sequential (bortezomib for first 24 h, followed by addition of vorinostat for another 24 h) combinations. Temporal changes for nine of the critical proteins in the reduced Boolean model were measured over 48 h, and cellular proliferation was measured over 96 h. A mechanism-based systems model was developed that captured the biological basis of a bortezomib and vorinostat sequence-dependent pharmacodynamic interaction. The model was further extended in vivo by linking in vitro parameter values and dynamics of p21, caspase-3, and pAKT biomarkers to tumor growth in xenograft mice reported in the literature. Network-based methodologies and pharmacodynamic principles were integrated successfully to evaluate bortezomib and vorinostat interactions in a mechanistic and quantitative manner. The model can be potentially applied to evaluate their combination regimens and explore in vivo dosing regimens.

Impact of HDAC Inhibitors on Protein Quality Control Systems: Consequences for Precision Medicine in Malignant Disease

Lysine acetylation is one of the major posttranslational modifications (PTM) in human cells and thus needs to be tightly regulated by the writers of this process, the histone acetyl transferases (HAT), and the erasers, the histone deacetylases (HDAC). Acetylation plays a crucial role in cell signaling, cell cycle control and in epigenetic regulation of gene expression. Bromodomain (BRD)-containing proteins are readers of the acetylation mark, enabling them to transduce the modification signal. HDAC inhibitors (HDACi) have been proven to be efficient in hematologic malignancies with four of them being approved by the FDA. However, the mechanisms by which HDACi exert their cytotoxicity are only partly resolved. It is likely that HDACi alter the acetylation pattern of cytoplasmic proteins, contributing to their anti-cancer potential. Recently, it has been demonstrated that various protein quality control (PQC) systems are involved in recognizing the altered acetylation pattern upon HDACi treatment. In particular, molecular chaperones, the ubiquitin proteasome system (UPS) and autophagy are able to sense the structurally changed proteins, providing additional targets. Recent clinical studies of novel HDACi have proven that proteins of the UPS may serve as biomarkers for stratifying patient groups under HDACi regimes. In addition, members of the PQC systems have been shown to modify the epigenetic readout of HDACi treated cells and alter proteostasis in the nucleus, thus contributing to changing gene expression profiles. Bromodomain (BRD)-containing proteins seem to play a potent role in transducing the signaling process initiating apoptosis, and many clinical trials are under way to test BRD inhibitors. Finally, it has been demonstrated that HDACi treatment leads to protein misfolding and aggregation, which may explain the effect of panobinostat, the latest FDA approved HDACi, in combination with the proteasome inhibitor bortezomib in multiple myeloma. Therefore, proteins of these PQC systems provide valuable targets for precision medicine in cancer. In this review, we give an overview of the impact of HDACi treatment on PQC systems and their implications for malignant disease. We exemplify the development of novel HDACi and how affected proteins belonging to PQC can be used to determine molecular signatures and utilized in precision medicine.

Mesenchymal stem cells in multiple myeloma: a therapeutical tool or target?

Multiple myeloma (MM) is a malignant plasma cell (PC) disorder, characterized by a complex interactive network of tumour cells and the bone marrow (BM) stromal microenvironment, contributing to MM cell survival, proliferation and chemoresistance. Mesenchymal stem cells (MSCs) represent the predominant stem cell population of the bone marrow stroma, capable of differentiating into multiple cell lineages, including fibroblasts, adipocytes, chondrocytes and osteoblasts. MSCs can migrate towards primary tumours and metastatic sites, implying that these cells might modulate tumour growth and metastasis. However, this issue remains controversial and is not well understood. Interestingly, several recent studies have shown functional abnormalities of MM patient-derived MSCs indicating that MSCs are not just by-standers in the BM microenvironment but rather active players in the pathophysiology of this disease. It appears that the complex interaction of MSCs and MM cells is critical for MM development and disease outcome. This review will focus on the current understanding of the biological role of MSCs in MM as well as the potential utility of MSC-based therapies in this malignancy.

Combination Therapy With Histone Deacetylase Inhibitors (HDACi) for the Treatment of Cancer: Achieving the Full Therapeutic Potential of HDACi

Genetic and epigenetic changes in DNA are involved in cancer development and tumor progression. Histone deacetylases (HDACs) are key regulators of gene expression that act as transcriptional repressors by removing acetyl groups from histones. HDACs are dysregulated in many cancers, making them a therapeutic target for the treatment of cancer. Histone deacetylase inhibitors (HDACi), a novel class of small-molecular therapeutics, are now approved by the Food and Drug Administration as anticancer agents. While they have shown great promise, resistance to HDACi is often observed and furthermore, HDACi have shown limited success in treating solid tumors. The combination of HDACi with standard chemotherapeutic drugs has demonstrated promising anticancer effects in both preclinical and clinical studies. In this review, we summarize the research thus far on HDACi in combination therapy, with other anticancer agents and their translation into preclinical and clinical studies. We additionally highlight the side effects associated with HDACi in cancer therapy and discuss potential biomarkers to either select or predict a patient's response to these agents, in order to limit the off-target toxicity associated with HDACi.

Cell Signaling Model Connects Vorinostat Pharmacokinetics and Tumor Growth Response in Multiple Myeloma Xenografts

Multiple myeloma is a fatal hematological malignancy with high rates of drug resistance and relapse. Vorinostat, a histone deacetylase inhibitor, has shown promise in enhancing efficacy when combined with current myeloma therapies. In this study, temporal changes of critical proteins and cell proliferation were measured in myeloma cells exposed to vorinostat. A model linking biomarker dynamics to cell proliferation was developed that captured vorinostat effects on signal transduction and cell viability. The model structure and parameters were fixed to describe tumor dynamics in vivo, and tumor-specific growth and death rate parameters were estimated. The signaling model captured tumor growth inhibition in murine xenografts for a range of dose levels and regimens. This model may be used as a mechanistic bridge to link vorinostat exposure to molecular events and pharmacodynamic (PD) outcomes. It may also provide a translational platform to explore vorinostat activity as a single agent and in combination regimens.

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.

Final Results of a Phase 1 Study of Vorinostat, Pegylated Liposomal Doxorubicin, and Bortezomib in Relapsed or Refractory Multiple Myeloma

INTRODUCTION/BACKGROUND

Deacetylase inhibitors have synergistic activity in combination with proteasome inhibitors and anthracyclines in preclinical models of multiple myeloma (MM). We therefore evaluated the safety and efficacy of the deacetylase inhibitor vorinostat in combination with pegylated liposomal doxorubicin (PLD) and bortezomib in relapsed/refractory MM.

PATIENTS AND METHODS

Thirty-two patients were treated with PLD and bortezomib in combination with escalating doses of vorinostat on days 4 to 11 or 1 to 14.

RESULTS

The maximum tolerated dose of vorinostat was 400 mg on days 4 to 11. Neutropenia and thrombocytopenia attributable to protocol therapy were seen in 59% and 94% of patients, of which 37% and 47% were of grade 3 or higher severity, respectively. Constitutional and gastrointestinal adverse events of all grades were common, the majority of which were less than grade 3 in severity. The overall response rate (partial response rate or better) was 65% and the clinical benefit rate (minimal response rate or better) 74%. The overall response rate was 83%, 71%, and 45% for patients with bortezomib-naive, -sensitive, and -refractory MM, respectively. The median progression-free survival was 13.9 months and the 3-year overall survival 77%. Whole blood proteasome activity assays demonstrated a potential impact of vorinostat on the chymotryptic-like activity of the proteasome.

CONCLUSION

Further evaluation of PLD, bortezomib, and deacetylase inhibitor combinations is warranted, with special attention directed toward strategies to improve tolerability.

Enhancement of pomalidomide anti-tumor response with ACY-241, a selective HDAC6 inhibitor

Thalidomide-based Immunomodulatory Drugs (IMiDs^®), including lenalidomide and pomalidomide, are effective therapeutics for multiple myeloma. These agents have been approved with, or are under clinical development with, other targeted therapies including proteasome inhibitors, αCD38 monoclonal antibodies, as well as histone deacetylase (HDAC) inhibitors for combination therapy. HDAC inhibitors broadly targeting Class I and IIb HDACs have shown potent preclinical efficacy but have frequently demonstrated an undesirable safety profile in combination therapy approaches in clinical studies. Therefore, development of more selective HDAC inhibitors could provide enhanced efficacy with reduced side effects in combination with IMiDs^® for the treatment of B-cell malignancies, including multiple myeloma. Here, the second generation selective HDAC6 inhibitor citarinostat (ACY-241), with a more favorable safety profile than non-selective pan-HDAC inhibitors, is shown to synergize with pomalidomide in in vitro assays through promoting greater apoptosis and cell cycle arrest. Furthermore, utilizing a multiple myeloma in vivo murine xenograft model, combination treatment with pomalidomide and ACY-241 leads to increased tumor growth inhibition. At the molecular level, combination treatment with ACY-241 and pomalidomide leads to greater suppression of the pro-survival factors survivin, Myc, and IRF4. The results presented here demonstrate synergy between pomalidomide and ACY-241 in both in vitro and in vivo preclinical models, providing further impetus for clinical development of ACY-241 for use in combination with IMiDs for patients with multiple myeloma and potentially other B-cell malignancies.

Sequential Exposure of Bortezomib and Vorinostat is Synergistic in Multiple Myeloma Cells

PURPOSE

To examine the combination of bortezomib and vorinostat in multiple myeloma cells (U266) and xenografts, and to assess the nature of their potential interactions with semi-mechanistic pharmacodynamic models and biomarkers.

METHODS

U266 proliferation was examined for a range of bortezomib and vorinostat exposure times and concentrations (alone and in combination). A non-competitive interaction model was used with interaction parameters that reflect the nature of drug interactions after simultaneous and sequential exposures. p21 and cleaved PARP were measured using immunoblotting to assess critical biomarker dynamics. For xenografts, data were extracted from literature and modeled with a PK/PD model with an interaction parameter.

RESULTS

Estimated model parameters for simultaneous in vitro and xenograft treatments suggested additive drug effects. The sequence of bortezomib preincubation for 24 hours, followed by vorinostat for 24 hours, resulted in an estimated interaction term significantly less than 1, suggesting synergistic effects. p21 and cleaved PARP were also up-regulated the greatest in this sequence.

CONCLUSIONS

Semi-mechanistic pharmacodynamic modeling suggests synergistic pharmacodynamic interactions for the sequential administration of bortezomib followed by vorinostat. Increased p21 and cleaved PARP expression can potentially explain mechanisms of their enhanced effects, which require further PK/PD systems analysis to suggest an optimal dosing regimen.

Therapeutic Targeting of miR-29b/HDAC4 Epigenetic Loop in Multiple Myeloma

Epigenetic abnormalities are common in hematologic malignancies, including multiple myeloma, and their effects can be efficiently counteracted by a class of tumor suppressor miRNAs, named epi-miRNAs. Given the oncogenic role of histone deacetylases (HDAC) in multiple myeloma, we investigated whether their activity could be antagonized by miR-29b, a well-established epi-miRNA. We demonstrated here that miR-29b specifically targets HDAC4 and highlighted that both molecules are involved in a functional loop. In fact, silencing of HDAC4 by shRNAs inhibited multiple myeloma cell survival and migration and triggered apoptosis and autophagy, along with the induction of miR-29b expression by promoter hyperacetylation, leading to the downregulation of prosurvival miR-29b targets (SP1, MCL-1). Moreover, treatment with the pan-HDAC inhibitor SAHA upregulated miR-29b, overcoming the negative control exerted by HDAC4. Importantly, overexpression or inhibition of miR-29b, respectively, potentiated or antagonized SAHA activity on multiple myeloma cells, as also shown in vivo by a strong synergism between miR-29b synthetic mimics and SAHA in a murine xenograft model of human multiple myeloma. Altogether, our results shed light on a novel epigenetic circuitry regulating multiple myeloma cell growth and survival and open new avenues for miR-29b-based epi-therapeutic approaches in the treatment of this malignancy. Mol Cancer Ther; 15(6); 1364-75. ©2016 AACR.

Clinical use and applications of histone deacetylase inhibitors in multiple myeloma

The incorporation of various novel therapies has resulted in a significant survival benefit in newly diagnosed and relapsed patients with multiple myeloma (MM) over the past decade. Despite these advances, resistance to therapy leads to eventual relapse and fatal outcomes in the vast majority of patients. Hence, there is an unmet need for new safe and efficacious therapies for continued improvement in outcomes. Given the role of epigenetic aberrations in the pathogenesis and progression of MM and the success of histone deacetylase inhibitors (HDACi) in other malignancies, many HDACi have been tried in MM. Various preclinical studies helped us to understand the antimyeloma activity of different HDACi in MM as a single agent or in combination with conventional, novel, and immune therapies. The early clinical trials of HDACi depicted only modest single-agent activity, but recent studies have revealed encouraging clinical response rates in combination with other antimyeloma agents, especially proteasome inhibitors. This led to the approval of the combination of panobinostat and bortezomib for the treatment of relapsed/refractory MM patients with two prior lines of treatment by the US Food and Drug Administration. However, it remains yet to be defined how we can incorporate HDACi in the current therapeutic paradigms for MM that will help to achieve longer disease control and significant survival benefits. In addition, isoform-selective and/or class-selective HDAC inhibition to reduce unfavorable side effects needs further evaluation.

Phase 1 trial of carfilzomib (PR-171) in combination with vorinostat (SAHA) in patients with relapsed or refractory B-cell lymphomas

A phase 1 study with carfilzomib and vorinostat was conducted in 20 B-cell lymphoma patients. Vorinostat was given orally twice daily on days 1, 2, 3, 8, 9, 10, 15, 16, and 17 followed by carfilzomib (given as a 30-min infusion) on days 1, 2, 8, 9, 15, and 16. A treatment cycle was 28 days. Dose escalation initially followed a standard 3 + 3 design, but adapted a more conservative accrual rule following dose de-escalation. The maximum tolerated dose was 20 mg/m2 carfilzomib and 100 mg vorinostat (twice daily). The dose-limiting toxicities were grade 3 pneumonitis, hyponatremia, and febrile neutropenia. One patient had a partial response and two patients had stable disease. Correlative studies showed a decrease in NF-κB activation and an increase in Bim levels in some patients, but these changes did not correlate with clinical response.

Lenalidomide and vorinostat maintenance after autologous transplant in multiple myeloma

Single-agent post-autologous transplant maintenance therapy with lenalidomide is standard of care for patients with multiple myeloma. The tolerability and effectiveness of combination post-transplant maintenance therapy is unknown, so we investigated lenalidomide and vorinostat (suberoylanilide hydroxamic acid) in this setting, hypothesizing that the regimen would be well tolerated and associated with an improved post-transplant response. This trial followed a standard 3 × 3 dose escalation phase 1 design. Vorinostat was administered beginning day +90 post-haematopoietic stem cell transplantation for days 1-7 and 15-21, and lenalidomide was started at 10 mg days 1-21, both on a 28-d cycle. The primary endpoint was maximum tolerated dose and dose limiting toxicities were assessed during the first cycle. Treatment was well tolerated in 16 enrolled patients. During Cycle 1, the most common toxicities included cytopenias, gastrointestinal complaints and fatigue. Seven patients improved their transplant response after starting combination therapy. The median follow-up was 38·4 months, and the median progression-free survival and overall survival have yet to be reached. This oral post-transplant maintenance regimen was well tolerated. This is the first trial to publish results on the use of a histone deacetylase inhibitor in the maintenance setting, and it provides rationale for the ongoing randomized trial in maintenance (ISRCTN 49407852).

TRIAL REGISTRATION

NCT00729118.

Combination of proteasome and HDAC inhibitor enhances HPV16 E7-specific CD8+ T cell immune response and antitumor effects in a preclinical cervical cancer model

Background

Bortezomib, a proteasome inhibitor and suberoylanilide hydroxamic acid (SAHA, also known as Vorinostat), a histone deacetylase inhibitor, have been recognized as potent chemotherapeutic drugs. Bortezomib and SAHA are FDA-approved for the treatment of cutaneous T cell lymphoma and multiple myeloma/mantle cell lymphoma, respectively. Furthermore, the combination of the bortezomib and SAHA has been tested in a variety of preclinical models and in clinical trials and may be ideal for the treatment of cancer. However, it remains unclear how this treatment strategy affects the host immune response against tumors.

Results

Here, we used a well-defined E6/E7-expressing tumor model to examine how the immune system can be motivated to act against tumor cells expressing tumor antigens. We demonstrate that the combination of bortezomib and SAHA elicits potent antitumor effects in TC-1 tumor-bearing mice. Additionally, we are the first to show that treatment with bortezomib and SAHA leads to tumor-specific immunity by rendering tumor cells more susceptible to killing by antigen-specific CD8+ T cells than treatment with either drug alone.

Conclusions

The current study serves an important foundation for the future clinical application of both drugs for the treatment of cervical cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-014-0111-1) contains supplementary material, which is available to authorized users.

The potential of panobinostat as a treatment option in patients with relapsed and refractory multiple myeloma

Panobinostat is an investigational and potent histone deacetylase inhibitor (HDACi) that has shown promise as an antimultiple myeloma agent in the preclinical setting. In this review, we discuss the rationale for the use of panobinostat as a combination therapy for multiple myeloma and provide an overview of recent and ongoing clinical trials testing the safety and efficacy of panobinostat for the treatment of the disease.

Not too little, not too much-just right! (Better ways to give high dose melphalan)

Of the 13 286 autologous haematopoietic cell transplant procedures reported in the US in 2010-2012 for plasma cell disorders, 10 557 used single agent, high-dose melphalan. Despite 30 years of clinical and pharmacokinetic (PK) experience with high-dose melphalan, and its continuing central role as cytoreductive therapy for large numbers of patients with myeloma, the pharmacodynamics and pharmacogenomics of melphalan are still in their infancy. The addition of protectant agents such as amifostine and palifermin allows dose escalation to 280 mg/m(2), but at these doses it is cardiac, rather than gut, toxicity that is dose-limiting. Although combination with additional alkylating agents is feasible, the additional TRM may not be justified when so many post-consolidation therapies are available for myeloma patients. Current research should optimise the delivery of this single-agent chemotherapy. This includes the use of newer formulations and real-time PKs. These strategies may allow a safe and effective platform for adding synergistic novel therapies and provide a window of lymphodepletion for the addition of immunotherapies.

Role of Bcl-xL/Beclin-1 in interplay between apoptosis and autophagy in oxaliplatin and bortezomib-induced cell death

Recent studies indicate that a complex relationship exists between autophagy and apoptosis. In this study we investigated a regulatory relationship between autophagy and apoptosis in colorectal cancer cells utilizing molecular and biochemical approaches. For this study, human colorectal carcinoma HCT116 and CX-1 cells were treated with two chemotherapeutic agents-oxaliplatin, which induces apoptosis, and bortezomib, which triggers both apoptosis and autophagy. A combinatorial treatment of oxaliplatin and bortezomib caused a synergistic induction of apoptosis which was mediated through an increase in caspase activation. The combinational treatment of oxaliplatin and bortezomib promoted the JNK-Bcl-xL-Bax pathway which modulated the synergistic effect through the mitochondria-dependent apoptotic pathway. JNK signaling led to Bcl-xL phosphorylation at serine 62, oligomerization of Bax, alteration of mitochondrial membrane potential, and subsequent cytochrome c release. Overexpression of dominant-negative mutant of Bcl-xL (S62A), but not dominant-positive mutant of Bcl-xL (S62D), suppressed cytochrome c release and synergistic death effect. Interestingly, Bcl-xL also affected autophagy through alteration of interaction with Beclin-1. Beclin-1 was dissociated from Bcl-xL and initiated autophagy during treatment with oxaliplatin and bortezomib. However, activated caspase 8 cleaved Beclin-1 and suppressed Beclin-1-associated autophagy and enhanced apoptosis. A combinatorial treatment of oxaliplatin and bortezomib-induced Beclin-1 cleavage was abolished in Beclin-1 double mutant (D133AA/D149A) knock-in HCT116 cells, restoring the autophagy-promoting function of Beclin-1 and suppressing the apoptosis induced by the combination therapy. In addition, the combinatorial treatment significantly inhibited colorectal cancer xenografts' tumor growth. An understanding of the molecular mechanisms of crosstalk between apoptosis and autophagy will support the application of combinatorial treatment to colorectal cancer.

The role of histone deacetylase inhibitors in patients with relapsed/refractory multiple myeloma

Clinical outcomes for patients with multiple myeloma (MM) have improved substantially since the introduction of novel agents including the proteasome inhibitor bortezomib and the immunomodulatory drugs thalidomide and lenalidomide. However, most patients with MM eventually relapse, and prognosis remains poor among patients with relapsed and/or refractory disease. Combination therapy using agents with different mechanisms of action is emerging as an attractive treatment approach in oncology to increase efficacy and/or overcome resistance to standard treatment regimens. This review discusses unmet needs in the treatment of MM and the development of histone deacetylase inhibitors as a treatment modality for MM.

A phase 1/2 study of oral panobinostat combined with melphalan for patients with relapsed or refractory multiple myeloma

Panobinostat is a histone deacetylase inhibitor that has shown synergistic preclinical anti-myeloma activity when combined with other agents, recently exhibiting synergy with the alkylating agent melphalan (Sanchez et al., Leuk Res 35(3):373-379, 2011). This phase 1/2 trial investigated the safety and efficacy of panobinostat in combination with melphalan for relapsed/refractory multiple myeloma patients. There were four different trial treatment schedules due to tolerability issues, with the final treatment schedule (treatment schedule D) consisting of panobinostat (15 or 20 mg) and melphalan (0.05 or 0.10 mg/kg), both administered on days 1, 3, and 5 of a 28-day cycle. A total of 40 patients were enrolled; 3 in treatment schedule A, 9 in schedule B, 7 in schedule C, and finally 21 schedule D. Patients had been treated with a median of four regimens (range, 1-16) and two prior bortezomib-containing regimens (range, 0-9). Maximum-tolerated dose was established at 20 mg panobinostat and 0.05 mg/kg melphalan in treatment schedule D. Overall, 3 patients (7.5 %) achieved ≥partial response (two very good PRs and one PR) while 23 exhibited stable disease and 14 showed progressive disease. All three responders were enrolled in cohort 2 of treatment schedule B (panobinostat 20 mg thrice weekly continuously with melphalan 0.05 mg/kg on days 1, 3, and 5). Neutropenia and thrombocytopenia were common, with 30.8 and 23.1 % of patients exhibiting ≥grade 3, respectively. Panobinostat + melphalan appears to have tolerability issues in a dosing regimen capable of producing a response. Care must be taken to balance tolerability and efficacy with this combination.

Histone deacetylase inhibitors in multiple myeloma: rationale and evidence for their use in combination therapy

Multiple myeloma (MM) arises from abnormal proliferation and survival (ie, a high proliferative index and a low apoptotic index) of mature immunoglobulin-producing plasma cells in the bone marrow. Development of novel therapeutic options, such as proteasome inhibitors and immunomodulatory agents (IMiDs), has improved treatment outcomes. However, patients often develop relapsed and refractory MM, thus requiring alternative treatment approaches. Histone acetyltransferases and histone deacetylases (HDACs) control the acetylation status of proteins and affect a broad array of physiologic processes (eg, cell cycle, apoptosis, and protein folding) involved in cell growth and survival. The discovery that HDACs might have a role in various hematologic malignancies, including MM, has led to the development of HDAC inhibitors as potential antitumor agents. Preclinical evidence from studies of HDAC inhibitors in combination with proteasome inhibitors (eg, bortezomib and carfilzomib), other antimyeloma agents, including IMiDs (eg, lenalidomide), and cytotoxic agents (eg, melphalan, pegylated liposomal doxorubicin), provides a strong scientific rationale for the evaluation of these regimens. Results from early stage clinical trials further support the use of HDAC inhibitors as a therapeutic option for MM, in combination with current and emerging antimyeloma agents. In this review, we examine the role of protein acetylation that underlies the antimyeloma effects of HDAC inhibitors, discuss the preclinical rationale for the use of HDAC inhibitors in combination with other antimyeloma agents, and provide an overview of the current clinical evidence supporting the use of HDAC inhibitors as a therapeutic option in MM.

Effect of the HDAC inhibitor vorinostat on the osteogenic differentiation of mesenchymal stem cells in vitro and bone formation in vivo

AIM

Vorinostat, a histone deacetylase (HDAC) inhibitor currently in a clinical phase III trial for multiple myeloma (MM) patients, has been reported to cause bone loss. The purpose of this study was to test whether, and to what extent, vorinostat influences the osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro and bone formation in vivo.

METHODS

Bone marrow-derived MSCs were prepared from both normal donors and MM patients. The MSCs were cultured in an osteogenic differentiation induction medium to induce osteogenic differentiation, which was evaluated by alkaline phosphatase (ALP) staining, Alizarin Red S staining and the mRNA expression of osteogenic markers. Naïve mice were administered vorinostat (100 mg/kg, ip) every other day for 3 weeks. After the mice were sacrificed, bone formation was assessed based on serum osteocalcin level and histomorphometric analysis.

RESULTS

Vorinostat inhibited the viability of hMSCs in a concentration-dependent manner (the IC50 value was 15.57 μmol/L). The low concentration of vorinostat (1 μmol/L) did not significantly increase apoptosis in hMSCs, whereas pronounced apoptosis was observed following exposure to higher concentrations of vorinostat (10 and 50 μmol/L). In bone marrow-derived hMSCs from both normal donors and MM patients, vorinostat (1 μmol/L) significantly increased ALP activity, mRNA expression of osteogenic markers, and matrix mineralization. These effects were associated with upregulation of the bone-specifying transcription factor Runx2 and with the epigenetic alterations during normal hMSCs osteogenic differentiation. Importantly, the mice treated with vorinostat did not show any bone loss in response to the optimized treatment regimen.

CONCLUSION

Vorinostat, known as a potent anti-myeloma drug, stimulates MSC osteogenesis in vitro. With the optimized treatment regimen, any decrease in bone formation was not observed in vivo.

Preclinical data and early clinical experience supporting the use of histone deacetylase inhibitors in multiple myeloma

Histone deacetylases (HDACs) mediate protein acetylation states, which in turn regulate normal cellular processes often dysregulated in cancer. These observations led to the development of HDAC inhibitors that target tumors through multiple effects on protein acetylation. Clinical evidence demonstrates that treatment with HDAC inhibitors (such as vorinostat, panobinostat, and romidepsin) in combination with other antimyeloma agents (such as proteasome inhibitors and immunomodulatory drugs) has promising antitumor activity in relapsed/refractory multiple myeloma patients. This mini-review highlights the role of protein acetylation in the development of cancers and the rationale for the use of HDAC inhibitors in this patient population.

Profiling bortezomib resistance identifies secondary therapies in a mouse myeloma model

Multiple myeloma is a hematologic malignancy characterized by the proliferation of neoplastic plasma cells in the bone marrow. Although the first-to-market proteasome inhibitor bortezomib (Velcade) has been successfully used to treat patients with myeloma, drug resistance remains an emerging problem. In this study, we identify signatures of bortezomib sensitivity and resistance by gene expression profiling (GEP) using pairs of bortezomib-sensitive (BzS) and bortezomib-resistant (BzR) cell lines created from the Bcl-XL/Myc double-transgenic mouse model of multiple myeloma. Notably, these BzR cell lines show cross-resistance to the next-generation proteasome inhibitors, MLN2238 and carfilzomib (Kyprolis) but not to other antimyeloma drugs. We further characterized the response to bortezomib using the Connectivity Map database, revealing a differential response between these cell lines to histone deacetylase (HDAC) inhibitors. Furthermore, in vivo experiments using the HDAC inhibitor panobinostat confirmed that the predicted responder showed increased sensitivity to HDAC inhibitors in the BzR line. These findings show that GEP may be used to document bortezomib resistance in myeloma cells and predict individual sensitivity to other drug classes. Finally, these data reveal complex heterogeneity within multiple myeloma and suggest that resistance to one drug class reprograms resistant clones for increased sensitivity to a distinct class of drugs. This study represents an important next step in translating pharmacogenomic profiling and may be useful for understanding personalized pharmacotherapy for patients with multiple myeloma.

A phase I trial of vorinostat and bortezomib in children with refractory or recurrent solid tumors: a Children's Oncology Group phase I consortium study (ADVL0916)

BACKGROUND

A pediatric Phase I trial was performed to determine the maximum-tolerated dose, dose-limiting toxicities (DLTs), and pharmacokinetics (PK) of vorinostat and bortezomib, in patients with solid tumors.

PROCEDURE

Oral vorinostat was administered on days 1-5 and 8-12 of a 21-day cycle (starting dose 180 mg/m(2) /day with dose escalations to 230 and 300 mg/m(2) /day). Bortezomib (1.3 mg/m(2) i.v.) was administered on days 1, 4, 8, and 11 of the same cycle. PK and correlative biology studies were performed during Cycle 1.

RESULTS

Twenty-three eligible patients [17 male, median age 12 years (range: 1-20)] were enrolled of whom 17 were fully evaluable for toxicity. Cycle 1 DLTs that occurred in 2/6 patients at dose level 3 (vorinostat 300 mg/m(2) /day) were Grade 2 sensory neuropathy that progressed to Grade 4 (n = 1) and Grade 3 nausea and anorexia (n = 1). No objective responses were observed. There was wide interpatient variability in vorinostat PK parameters. Bortezomib disposition was best described by a three-compartment model that demonstrated rapid distribution followed by prolonged elimination. We did not observe a decrease in nuclear factor-κB activity or Grp78 induction after bortezomib treatment in peripheral blood mononuclear cells from solid tumor patients.

CONCLUSION

The recommended Phase 2 dose and schedule is vorinostat (230 mg/m(2) /day PO on days 1-5 and 8-12) in combination with bortezomib (1.3 mg/m(2) /day i.v. on days 1, 4, 8, and 11 of a 21-day cycle) in children with recurrent or refractory solid tumors.

Targeting histone deacetylases: development of vorinostat for the treatment of cancer

Reversible histone acetylation on lysine residues, regulated by the opposing activities of histone acetyltransferases and histone deacetylases (HDACs), plays an important role in the regulation of gene expression. Aberrant gene expression resulting from increased HDAC activity and histone hypoacetylation has been observed in human tumors and genetic knockdown studies support a role of HDACs in cancer. Treatment with small-molecule inhibitors of HDAC activity results in anti-tumor effects in a variety of transformed cell lines. Several HDAC inhibitors are in clinical development and show anti-tumor activity in cancer patients. Vorinostat (suberoylanilide hydroxamic acid) was the first HDAC inhibitor approved for the treatment of cancer and will be the focus of this article.

Preclinical activity, pharmacodynamic, and pharmacokinetic properties of a selective HDAC6 inhibitor, ACY-1215, in combination with bortezomib in multiple myeloma

Histone deacetylase (HDAC) enzymatic activity has been linked to the transcription of DNA in cancers including multiple myeloma (MM). Therefore, HDAC inhibitors used alone and in combination are being actively studied as novel therapies in MM. In the present study, we investigated the preclinical activity of ACY-1215, an HDAC6-selective inhibitor, alone and in combination with bortezomib in MM. Low doses of ACY-1215 combined with bortezomib triggered synergistic anti-MM activity, resulting in protracted endoplasmic reticulum stress and apoptosis via activation of caspase-3, caspase-8, and caspase-9 and poly (ADP) ribosome polymerase. In vivo, the anti-MM activity of ACY-1215 in combination with bortezomib was confirmed using 2 different xenograft SCID mouse models: human MM injected subcutaneously (the plasmacytoma model) and luciferase-expressing human MM injected intravenously (the disseminated MM model). Tumor growth was significantly delayed and overall survival was significantly prolonged in animals treated with the combination therapy. Pharmacokinetic data showed peak plasma levels of ACY-1215 at 4 hours after treatment coincident with an increase in acetylated α-tubulin, a marker of HDAC6 inhibition, by immunohistochemistry and Western blot analysis. These studies provide preclinical rationale for acetylated α-tubulin use as a pharmacodynamic biomarker in future clinical trials.

Mechanism of action of proteasome inhibitors and deacetylase inhibitors and the biological basis of synergy in multiple myeloma

Novel agents, including the proteasome inhibitor bortezomib, have significantly improved the response and survival of patients with multiple myeloma over the last decade. Despite these advances, many patients relapse or do not benefit from the currently available therapies; thus, multiple myeloma remains an incurable disease. Deacetylase inhibitors (DACi), including panobinostat and vorinostat, have recently emerged as novel agents being evaluated in the treatment of multiple myeloma. Deacetylases are a group of enzymes with effects on various intracellular proteins, including histones, transcription factors, and molecular chaperones. Although DACi inhibit cell growth and induce apoptosis in multiple myeloma cells as a single agent, synergistic activity has been observed when they were used in combination with bortezomib. The mechanistic basis of synergy is multifactorial and includes disruption of protein degradation and inhibition of the interaction of multiple myeloma cells with the tumor microenvironment. This review summarizes recent advancements in the understanding of the mechanism of action of proteasome inhibitors and DACi in multiple myeloma and examines the biological basis of their synergistic effects. Data from the studies summarized here have been used as the rationale for the implementation of phase II and III clinical trials of DACi, alone and combined with bortezomib, in relapsed and refractory multiple myeloma.

Tracking human multiple myeloma xenografts in NOD-Rag-1/IL-2 receptor gamma chain-null mice with the novel biomarker AKAP-4

BACKGROUND

Multiple myeloma (MM) is a fatal malignancy ranking second in prevalence among hematological tumors. Continuous efforts are being made to develop innovative and more effective treatments. The preclinical evaluation of new therapies relies on the use of murine models of the disease.

METHODS

Here we describe a new MM animal model in NOD-Rag1null IL2rgnull (NRG) mice that supports the engraftment of cell lines and primary MM cells that can be tracked with the tumor antigen, AKAP-4.

RESULTS

Human MM cell lines, U266 and H929, and primary MM cells were successfully engrafted in NRG mice after intravenous administration, and were found in the bone marrow, blood and spleen of tumor-challenged animals. The AKAP-4 expression pattern was similar to that of known MM markers, such as paraproteins, CD38 and CD45.

CONCLUSIONS

We developed for the first time a murine model allowing for the growth of both MM cell lines and primary cells in multifocal sites, thus mimicking the disease seen in patients. Additionally, we validated the use of AKAP-4 antigen to track tumor growth in vivo and to specifically identify MM cells in mouse tissues. We expect that our model will significantly improve the pre-clinical evaluation of new anti-myeloma therapies.

Experimental approaches in the treatment of multiple myeloma

Myeloma therapy has undergone significant advances in recent years resulting in a marked improvement in survival. Knowledge of the active pathways involved in myeloma pathogenesis has led to the discovery of novel agents and greatly expanded the potential armamentarium available for treatment. This better understanding of the disease and resistance mechanisms has resulted in new agent classes that are being evaluated in preclinical and early clinical studies. In addition, dosing for existing agents is being optimized, and they are being given in new combinations. In this article, we review experimental agents that are showing promise in multiple myeloma treatment. New biological agents in clinical trials hold the promise of efficacy through novel mechanisms of action, with a significant reduction of dose-limiting toxicities compared with classic cytotoxic chemotherapeutics. Second-generation proteasome inhibitors and immunomodulatory agents are furthest along in clinical development, and histone deacetylase inhibitors, heat shock protein 90 inhibitors, Akt inhibitors and monoclonal antibodies are some of the other agents entering later-phase clinical trials. We also review developments in targeting the myeloma stem cell as an exciting new treatment direction.

Suberoylanilide hydroxamic acid (SAHA; vorinostat) causes bone loss by inhibiting immature osteoblasts

Histone deacetylase (Hdac) inhibitors are used clinically to treat cancer and epilepsy. Although Hdac inhibition accelerates osteoblast maturation and suppresses osteoclast maturation in vitro, the effects of Hdac inhibitors on the skeleton are not understood. The purpose of this study was to determine how the pan-Hdac inhibitor, suberoylanilide hydroxamic acid (SAHA; a.k.a. vorinostat or Zolinza(TM)) affects bone mass and remodeling in vivo. Male C57BL/6J mice received daily SAHA (100mg/kg) or vehicle injections for 3 to 4weeks. SAHA decreased trabecular bone volume fraction and trabecular number in the distal femur. Cortical bone at the femoral midshaft was not affected. SAHA reduced serum levels of P1NP, a bone formation marker, and also suppressed tibial mRNA levels of type I collagen, osteocalcin and osteopontin, but did not alter Runx2 or osterix transcripts. SAHA decreased histological measures of osteoblast number but interestingly increased indices of osteoblast activity including mineral apposition rate and bone formation rate. Neither serum (TRAcP 5b) nor histological markers of bone resorption were affected by SAHA. P1NP levels returned to baseline in animals which were allowed to recover for 4weeks after 4weeks of daily SAHA injections, but bone density remained low. In vitro, SAHA suppressed osteogenic colony formation, decreased osteoblastic gene expression, induced cell cycle arrest, and caused DNA damage in bone marrow-derived adherent cells. Collectively, these data demonstrate that bone loss following treatment with SAHA is primarily due to a reduction in osteoblast number. Moreover, these decreases in osteoblast number can be attributed to the deleterious effects of SAHA on immature osteoblasts, even while mature osteoblasts are resistant to the harmful effects and demonstrate increased activity in vivo, indicating that the response of osteoblasts to SAHA is dependent upon their differentiation state. These studies suggest that clinical use of SAHA and other Hdac inhibitors to treat cancer, epilepsy or other conditions may potentially compromise skeletal structure and function.

Potentiation of apoptosis by histone deacetylase inhibitors and doxorubicin combination: cytoplasmic cathepsin B as a mediator of apoptosis in multiple myeloma

Background:

Although inhibitors of histone deacetylase inhibitors (HDACis) in combination with genotoxins potentiate apoptosis, the role of proteases other than caspases in this process remained elusive. Therefore, we examined the potentiation of apoptosis and related mechanisms of HDACis and doxorubicin combination in a panel of myeloma cell lines and in 25 primary myelomas.

Results:

At IC₅₀ concentrations, sodium butyrate (an HDACi) or doxorubicin alone caused little apoptosis. However, their combination potentiated apoptosis and synergistically reduced the viability of myeloma cells independent of p53 and caspase 3–7 activation. Potentiated apoptosis correlated with nuclear translocation of apoptosis-inducing factor, suggesting the induction of caspase 3- and 7-independent pathways. Consistent with this, butyrate and doxorubicin combination significantly increased the activity of cytoplasmic cathepsin B. Inhibition of cathepsin B either with a small-molecule inhibitor or downregulation with a siRNA reversed butyrate- and doxorubicin-potentiated apoptosis. Finally, ex vivo, clinically relevant concentrations of butyrate or SAHA (suberoylanilide hydroxamic acid, vorinostat, an HDACi in clinical testing) in combination with doxorubicin significantly (P<0.0001) reduced the survival of primary myeloma cells.

Conclusions:

Cathepsin B has a prominent function in mediating apoptosis potentiated by HDACi and doxorubicin combinations in myeloma. Our results support a molecular model of lysosomal–mitochondrial crosstalk in HDACi- and doxorubicin-potentiated apoptosis through the activation of cathepsin B.

The DAC system and associations with multiple myeloma

Despite the clear progress achieved in recent years in the treatment of MM, most patients eventually relapse and therefore novel therapeutic options are still necessary for these patients. In this regard, several drugs that target specific mechanisms of the tumor cells are currently being explored in the preclinical and clinical setting. This manuscripts offers a review of the rationale and current status of the antimyeloma activity of one of the most relevant examples of these targeted drugs: deacetylase inhibitors (DACi). Several studies have demonstrated the prooncogenic activity of deacetylases (DACs) through the targeting not only of histones but also of non histone proteins relevant to tumor progression, such as p53, E2F family members, Bcl-6, Hsp90, HIF-1α or Nur77. This fact together with the DACs overexpression present in several tumors, has prompted the development of some DACi with potential antitumor effect. This situation is also evident in the case of MM as two mechanisms of DACi, the inhibition of the epigenetic inactivation of p53 and the blockade of the unfolded protein response, through the inhibition of the aggressome formation (by targeting DAC6) and the inactivation of the chaperone system (by acetylating HSP-90), provides the rationale for the exploration of the potential antimyeloma activity of these compounds. Several DACi with different chemical structure and different selectivity for targeting the DAC families have been tested in MM. Their preclinical activity in monotherapy has been quite exciting and has been described to be mediated by various mechanisms: the induction of apoptosis and cell cycle arrest mainly by the upregulation of p21; the interferece with the interaction between plasma cells and the microenvironment, by reducing the expression and signalling of several cytokines or by inhibiting angiogenesis. Finally they also have a role in protecting murine models from myeloma bone disease. Neverteless, the clinical activity in monotherapy of these drugs in relapsed/refractory MM patients has been very modest. This has prompted the development of combinations such as the one with bortezomib or lenalidomide and dexamethasone, which have already been taken into the clinics with positive preliminary results.

Discovery of 2-(6-{[(6-fluoroquinolin-2-yl)methyl]amino}bicyclo[3.1.0]hex-3-yl)-N-hydroxypyrimidine-5-carboxamide (CHR-3996), a class I selective orally active histone deacetylase inhibitor

A novel series of HDAC inhibitors demonstrating class I subtype selectivity and good oral bioavailability is described. The compounds are potent enzyme inhibitors (IC₅₀ values less than 100 nM), and improved activity in cell proliferation assays was achieved by modulation of polar surface area (PSA) through the introduction of novel linking groups. Employing oral pharmacokinetic studies in mice, comparing drug levels in spleen to plasma, we selected compounds that were tested for efficacy in human tumor xenograft studies based on their potential to distribute into tumor. One compound, 21r (CHR-3996), showed good oral activity in these models, including dose-related activity in a LoVo xenograft. In addition 21r showed good activity in combination with other anticancer agents in in vitro studies. On the basis of these results, 21r was nominated for clinical development.

Antitumor effects of (S)-HDAC42, a phenylbutyrate-derived histone deacetylase inhibitor, in multiple myeloma cells

PURPOSE

Epigenetic agents are among the newly targeted therapeutic strategies being studied with intense interest for patients with multiple myeloma. Here, we demonstrate the antitumor activity of a phenylbutyrate-based histone deacetylase (HDAC) inhibitor, (S)-HDAC42, and identify its possible targets in myeloma cells.

METHODS

The antiproliferative effect of (S)-HDAC42 was compared with suberoylanilide hydroxamic acid (SAHA) in three myeloma cell lines, IM-9, RPMI-8226, and U266. Flow cytometry and terminal transferase dUTP nick-end labeling (TUNEL) assay were used to demonstrate the induction of apoptosis by (S)-HDAC42. Moreover, the proposed mechanisms of action, such as modulation of Akt, NF-κB pathway, and cell cycle-related proteins, were investigated by western blotting.

RESULTS

(S)-HDAC42 exhibited four- to sevenfold higher potency relative to SAHA in suppressing myeloma cell viabilities. The apoptotic effect induced by (S)-HDAC42 was through both intrinsic and extrinsic pathways, as evidenced by increased cleavage of caspase-3, caspase-8, and caspase-9 and release of cytochrome c from mitochondria. In addition to HDAC inhibition, (S)-HDAC42 also disturbed signaling pathways governing cell survival, including downregulating Akt phosphorylation and NF-κB signaling. The modulation of cell cycle-related proteins by (S)-HDAC42 suggested its inhibitory effect on cell cycle propagation.

CONCLUSION

These data suggest the translational value of (S)-HDAC42 in developing new therapeutic strategies for myeloma, which warrants further investigations.