Induction of differential apoptotic pathways in multiple myeloma cells by class-selective histone deacetylase inhibitors

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.

Overcome the tumor immunotherapy resistance by combination of the HDAC6 inhibitors with antitumor immunomodulatory agents

Tumor immunotherapy is currently subject of intense scientific and clinical developments. In previous decade, therapists used natural immune system from the human body to treat several diseases. Although tumor immune disease is a big challenge, combinatorial therapeutic strategy has been succeeded to show the clinical significance. In this context, we discuss the HDAC6 and tumor immune diseases relationship. Also, we summarized the current state of knowledge that based on the combination treatments of the HDAC6 inhibitors (HDAC6is) with antitumor immunomodulatory agents. We observed that, the combination therapies slow down the tumor immune diseases by blocking the aggresome and proteasome pathway. The combination therapy was able to reduce M2 macrophage and increasing PD-L1 blockade sensitivity. Most importantly, multiple combinations of HDAC6is with other agents may consider as potential strategies to treat tumor immune diseases, by reducing the side effects and improve efficacy for the future clinical development.

HDAC6‑selective inhibitor synergistically enhances the anticancer activity of immunomodulatory drugs in multiple myeloma

Nonselective histone deacetylase (HDAC) inhibitors have therapeutic effects, but exhibit dose‑limiting toxicities in patients with multiple myeloma (MM). The present study investigated the interaction between the HDAC6 inhibitor, A452, and immunomodulatory drugs (IMiDs) on dexamethasone (Dex)‑sensitive and ‑resistant MM cells compared with the current clinically tested HDAC6 inhibitor, ACY‑1215. It was shown that the combination of the HDAC6‑selective inhibitor, A452, with either of the IMiDs tested (lenalidomide or pomalidomide) led to the synergistic inhibition of cell growth, a decrease in the viability of MM cells and in an increase in the levels of apoptosis. Furthermore, enhanced cell death was associated with the inactivation of AKT and extracellular signal‑regulated kinase (ERK)1/2. Of note, A452 in combination with IMiDs induced synergistic MM cytotoxicity without altering the expression of cereblon and thereby, the synergistic downregulation of IKAROS family zinc finger (IKZF)1/3, c‑Myc and interferon regulatory factor 4 (IRF4). Furthermore, combined treatment with A452 and IMiDs induced the synergistic upregulation of PD‑L1. More importantly, this combination treatment was effective in the Dex‑resistant MM cells. Overall, the findings of this study indicate that A452 is more effective as an anticancer agent than ACY‑1215. Taken together, these findings suggest that a combination of the HDAC6‑selective inhibitor, A452, and IMiDs may prove to be beneficial in the treatment of patients with MM.

The Therapeutic Strategy of HDAC6 Inhibitors in Lymphoproliferative Disease

Histone deacetylases (HDACs) are master regulators of chromatin remodeling, acting as epigenetic regulators of gene expression. In the last decade, inhibition of HDACs has become a target for specific epigenetic modifications related to cancer development. Overexpression of HDAC has been observed in several hematologic malignancies. Therefore, the observation that HDACs might play a role in various hematologic malignancies has brought to the development of HDAC inhibitors as potential antitumor agents. Recently, the class IIb, HDAC6, has emerged as one potential selective HDACi. This isoenzyme represents an important pharmacological target for selective inhibition. Its selectivity may reduce the toxicity related to the off-target effects of pan-HDAC inhibitors. HDAC6 has also been studied in cancer especially for its ability to coordinate a variety of cellular processes that are important for cancer pathogenesis. HDAC6 has been reported to be overexpressed in lymphoid cells and its inhibition has demonstrated activity in preclinical and clinical study of lymphoproliferative disease. Various studies of HDAC6 inhibitors alone and in combination with other agents provide strong scientific rationale for the evaluation of these new agents in the clinical setting of hematological malignancies. In this review, we describe the HDACs, their inhibitors, and the recent advances of HDAC6 inhibitors, their mechanisms of action and role in lymphoproliferative disorders.

DNMTi/HDACi combined epigenetic targeted treatment induces reprogramming of myeloma cells in the direction of normal plasma cells

Background

Multiple myeloma (MM) is the second most common hematologic malignancy. Aberrant epigenetic modifications have been reported in MM and could be promising therapeutic targets. As response rates are overall limited but deep responses occur, it is important to identify those patients who could indeed benefit from epigenetic-targeted therapy.

Methods

Since HDACi and DNMTi combination have potential therapeutic value in MM, we aimed to build a GEP-based score that could be useful to design future epigenetic-targeted combination trials. In addition, we investigated the changes in GEP upon HDACi/DNMTi treatment.

Results

We report a new gene expression-based score to predict MM cell sensitivity to the combination of DNMTi/HDACi. A high Combo score in MM patients identified a group with a worse overall survival but a higher sensitivity of their MM cells to DNMTi/HDACi therapy compared to a low Combo score. In addition, treatment with DNMTi/HDACi downregulated IRF4 and MYC expression and appeared to induce a mature BMPC plasma cell gene expression profile in myeloma cell lines.

Conclusion

In conclusion, we developed a score for the prediction of primary MM cell sensitivity to DNMTi/HDACi and found that this combination could be beneficial in high-risk patients by targeting proliferation and inducing maturation.

Discovery of selective small-molecule HDAC6 inhibitor for overcoming proteasome inhibitor resistance in multiple myeloma

Multiple myeloma (MM) has proven clinically susceptible to modulation of pathways of protein homeostasis. Blockade of proteasomal degradation of polyubiquitinated misfolded proteins by the proteasome inhibitor bortezomib (BTZ) achieves responses and prolongs survival in MM, but long-term treatment with BTZ leads to drug-resistant relapse in most patients. In a proof-of-concept study, we previously demonstrated that blocking aggresomal breakdown of polyubiquitinated misfolded proteins with the histone deacetylase 6 (HDAC6) inhibitor tubacin enhances BTZ-induced cytotoxicity in MM cells in vitro. However, these foundational studies were limited by the pharmacologic liabilities of tubacin as a chemical probe with only in vitro utility. Emerging from a focused library synthesis, a potent, selective, and bioavailable HDAC6 inhibitor, WT161, was created to study the mechanism of action of HDAC6 inhibition in MM alone and in combination with BTZ. WT161 in combination with BTZ triggers significant accumulation of polyubiquitinated proteins and cell stress, followed by caspase activation and apoptosis. More importantly, this combination treatment was effective in BTZ-resistant cells and in the presence of bone marrow stromal cells, which have been shown to mediate MM cell drug resistance. The activity of WT161 was confirmed in our human MM cell xenograft mouse model and established the framework for clinical trials of the combination treatment to improve patient outcomes in MM.

Progress and Paradigms in Multiple Myeloma

Remarkable progress has been achieved in multiple myeloma, and patient median survival has been extended 3- to 4-fold. Specifically, there have been 18 newly approved treatments for multiple myeloma in the past 12 years, including seven in 2015, and the treatment paradigm and patient outcome have been transformed. The definition of patients benefitting from these therapies has been broadened. Response criteria now include minimal residual disease (MRD), assessed in bone marrow by multicolor flow cytometry or sequencing, and by imaging for extramedullary disease. Initial therapy for transplant candidates is a triplet incorporating novel therapies-that is, lenalidomide, bortezomib, and dexamethasone or cyclophosphamide, bortezomib, and dexamethasone. Lenalidomide maintenance until progression can prolong progression-free and overall survival in standard-risk multiple myeloma, with incorporation of proteasome inhibitor for high-risk disease. Studies are evaluating the value of early versus late transplant and MRD as a therapeutic goal to inform therapy. In nontransplant patients, triplet therapies are also preferred, with doublet therapy reserved for frail patients, and maintenance as described above. The availability of second-generation proteasome inhibitors (carfilzomib and ixazomib), immunomodulatory drugs (pomalidomide), histone deacetylase inhibitors (panobinostat), and monoclonal antibodies (elotuzumab and daratumumab) allows for effective combination therapies of relapsed disease as well. Finally, novel therapies targeting protein degradation, restoring autologous memory anti-multiple myeloma immunity, and exploiting genetic vulnerabilities show promise to improve patient outcome even further. Clin Cancer Res; 22(22); 5419-27. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "MULTIPLE MYELOMA MULTIPLYING THERAPIES".

Histone deacetylase inhibitors in multiple myeloma: from bench to bedside

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

Novel therapeutic strategies for multiple myeloma

Multiple myeloma (MM) is a plasma-cell malignancy which remains incurable despite the recent emergence of multiple novel agents. Importantly, recent genetic and molecular analyses have revealed the complexity and heterogeneity of this disease, highlighting the need for therapeutic strategies to eliminate all clones. Moreover, the bone marrow microenvironment, including stromal cells and immune cells, plays a central role in MM pathogenesis, promoting tumor cell growth, survival, and drug resistance. New classes of agents including proteasome inhibitors, immunomodulatory drugs, monoclonal antibodies, and histone deacetylase inhibitors have shown remarkable efficacy; however, novel therapeutic approaches are still urgently needed to further improve patient outcomes. In this review, we discuss the recent advances and future strategies to ultimately develop MM therapies with curative potential.

Rational combination treatment with histone deacetylase inhibitors and immunomodulatory drugs in multiple myeloma

Immunomodulatory drugs (IMiDs) thalidomide, lenalidomide (Len) and pomalidomide trigger anti-tumor activities in multiple myeloma (MM) by targetting cereblon and thereby impacting IZF1/3, c-Myc and IRF4. Histone deacetylase inhibitors (HDACi) also downregulate c-Myc. We therefore determined whether IMiDs with HDACi trigger significant MM cell growth inhibition by inhibiting or downregulating c-Myc. Combination treatment of Len with non-selective HDACi suberoylanilide hydroxamic acid or class-I HDAC-selective inhibitor MS275 induces synergic cytotoxicity, associated with downregulation of c-Myc. Unexpectedly, we observed that decreased levels of cereblon (CRBN), a primary target protein of IMiDs, was triggered by these agents. Indeed, sequential treatment of MM cells with MS275 followed by Len shows less efficacy than simultaneous treatment with this combination. Importantly ACY1215, an HDAC6 inhibitor with minimal effects on class-I HDACs, together with Len induces synergistic MM cytotoxicity without alteration of CRBN expression. Our results showed that only modest class-I HDAC inhibition is able to induce synergistic MM cytotoxicity in combination with Len. These studies may provide the framework for utilizing HDACi in combination with Len to both avoid CRBN downregulation and enhance anti-MM activities.

Pleiotropic roles in cancer biology for multifaceted proteins FKBPs

BACKGROUND

FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.

SCOPE OF THE REVIEW

The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.

MAJOR CONCLUSIONS

Some family members appear to promote disease while others are protective against tumorigenesis.

GENERAL SIGNIFICANCE

FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.

Early or delayed transplantation for multiple myeloma in the era of novel therapy: does one size fit all?

For the last 20 years, high-dose therapy with autologous stem cell transplantation (ASCT) for multiple myeloma has been considered a standard frontline treatment for younger patients with adequate organ function. With the introduction of novel agents, specifically thalidomide, bortezomib, and lenalidomide, the role of ASCT has changed in several ways. First, novel agents have been incorporated successfully as induction regimens, increasing the response rate before ASCT, and are now being used as part of both consolidation and maintenance with the goal of extending progression-free and overall survival. These approaches have shown considerable promise with significant improvements in outcome. Furthermore, the efficacy of novel therapeutics has also led to the investigation of these agents upfront without the immediate application of ASCT, and compelling preliminary results have been reported. Next-generation novel agents and the use of monoclonal antibodies have raised the possibility of not only successful salvage strategies to facilitate delayed transplantation for younger patients, but also the prospect of an nontransplantation approach achieving the same outcome. Moreover, this could be achieved without incurring acute toxicity or long-term complications that are inherent to high-dose alkylation, and melphalan exposure in particular. At present, the role of ASCT has therefore become an area of debate: should it be used upfront in all eligible patients, or should it be used as a salvage treatment at the time of progression for patients achieving a high quality of response with initial therapy? There is a clear need to derive a consensus that is useful for clinicians considering both protocol-directed and non-protocol-directed options for their patients. Participation in ongoing prospective randomized trials is considered vital. While preliminary randomized data from studies in Europe favor early ASCT with novel agents, differences in both agents and the combinations used, as well as limited information on overall survival and benefit for specific patient subsets, suggest that one size does not fit all. Specifically, the optimal approach to treatment of younger patients eligible for ASCT remains a key area for further research. A rigid approach to its use outside of a clinical study is difficult to justify and participation in prospective studies should be a priority.

Early or delayed transplantation for multiple myeloma in the era of novel therapy: does one size fit all?

For the last 20 years, high-dose therapy with autologous stem cell transplantation (ASCT) for multiple myeloma has been considered a standard frontline treatment for younger patients with adequate organ function. With the introduction of novel agents, specifically thalidomide, bortezomib, and lenalidomide, the role of ASCT has changed in several ways. First, novel agents have been incorporated successfully as induction regimens, increasing the response rate before ASCT, and are now being used as part of both consolidation and maintenance with the goal of extending progression-free and overall survival. These approaches have shown considerable promise with significant improvements in outcome. Furthermore, the efficacy of novel therapeutics has also led to the investigation of these agents upfront without the immediate application of ASCT, and compelling preliminary results have been reported. Next-generation novel agents and the use of monoclonal antibodies have raised the possibility of not only successful salvage strategies to facilitate delayed transplantation for younger patients, but also the prospect of an nontransplantation approach achieving the same outcome. Moreover, this could be achieved without incurring acute toxicity or long-term complications that are inherent to high-dose alkylation, and melphalan exposure in particular. At present, the role of ASCT has therefore become an area of debate: should it be used upfront in all eligible patients, or should it be used as a salvage treatment at the time of progression for patients achieving a high quality of response with initial therapy? There is a clear need to derive a consensus that is useful for clinicians considering both protocol-directed and non-protocol-directed options for their patients. Participation in ongoing prospective randomized trials is considered vital. While preliminary randomized data from studies in Europe favor early ASCT with novel agents, differences in both agents and the combinations used, as well as limited information on overall survival and benefit for specific patient subsets, suggest that one size does not fit all. Specifically, the optimal approach to treatment of younger patients eligible for ASCT remains a key area for further research. A rigid approach to its use outside of a clinical study is difficult to justify and participation in prospective studies should be a priority.