Optimal induction of myeloma cell death requires dual blockade of phosphoinositide 3-kinase and mTOR signalling and is determined by translocation subtype

Pathogenic signaling in multiple myeloma

Multiple myeloma is a common hematological malignancy of plasma cells, the terminally differentiated B cells that secrete antibodies as part of the adaptive immune response. Significant progress has been made in treating multiple myeloma, but this disease remains largely incurable, and most patients will eventually suffer a relapse of disease that becomes refractory to further therapies. Moreover, a portion of patients with multiple myeloma present with disease that is refractory to all treatments from the initial diagnosis, and no current therapeutic approaches can help. Therefore, the task remains to advance new therapeutic strategies to help these vulnerable patients. One strategy to meet this challenge is to unravel the complex web of pathogenic signaling pathways in malignant plasma cells and use this information to design novel precision medicine strategies to assist these patients most at risk.

NVP-BEZ235-induced autophagy as a potential therapeutic approach for multiple myeloma

BACKGROUND

The PI3K/Akt/mTOR pathway is constitutively activated in human multiple myeloma (MM) cell lines and in freshly isolated plasmocytes from patients with MM. The mTOR signaling pathway has been designated an attractive anti-tumor target in multiple myeloma. NVP-BEZ235, a novel, dual class I PI3K/mTOR inhibitor, is an imidazoquinoline derivative. NVP-BEZ235 binds to the ATP-binding clefts of PI3K and mTOR kinase, thereby inhibiting their activities. Increasing evidence shows that NVP-BEZ235 is able to effectively and specifically reverse the hyperactivation of the PI3K/mTOR pathway, resulting not only in potent antiproliferative and antitumor activities in a broad range of cancer cell lines and experimental tumors but also in autophagy.

METHOD

The antitumor, apoptosis, and autophagy effects of NVP-BEZ235 were measured in three MM cell lines, two leukemia cell lines, and primary CD138+ myeloma cells from MM patients and nude mouse MM models. In addition, the relationships between autophagy, cell death and apoptosis induced by NVP-BEZ235 were analyzed in MM cells. Furthermore, we explored the mechanism of autophagy induced by NVP-BEZ235 in MM cells.

RESULTS

NVP-BEZ235 inhibited proliferation and induced apoptosis and autophagy in MM cells and in primary MM cells from patients and nude mouse MM models. Autophagy played an important role in the cell death and apoptosis of MM cell lines induced by NVP-BEZ235, and the mechanism involved the mTOR2-Akt-FOXO3a-BNIP3 pathway.

CONCLUSIONS

In this study, NVP-BEZ235 showed the strongest antitumor and autophagy induction activity. Moreover, the mechanism involved the mTOR2-Akt-FOXO3a-BNIP3 pathway. Our study lays a theoretical foundation for NVP-BEZ235 clinical application.

Kinase inhibitors as potential agents in the treatment of multiple myeloma

Recent years have witnessed a dramatic increase in the number of therapeutic options available for the treatment of multiple myeloma (MM) - from immunomodulating agents to proteasome inhibitors to histone deacetylase (HDAC) inhibitors and, most recently, monoclonal antibodies. Used in conjunction with autologous hematopoietic stem cell transplantation, these modalities have nearly doubled the disease's five-year survival rate over the last three decades to about 50%. In spite of these advances, MM still is considered incurable as resistance and relapse are common. While small molecule protein kinase inhibitors have made inroads in the therapy of a number of cancers, to date their application to MM has been less than successful. Focusing on MM, this review examines the roles played by a number of kinases in driving the malignant state and the rationale for target development in the design of a number of kinase inhibitors that have demonstrated anti-myeloma activity in both in vitro and in vivo xenograph models, as well as those that have entered clinical trials. Among the targets and their inhibitors examined are receptor and non-receptor tyrosine kinases, cell cycle control kinases, the PI3K/AKT/mTOR pathway kinases, protein kinase C, mitogen-activated protein kinase, glycogen synthase kinase, casein kinase, integrin-linked kinase, sphingosine kinase, and kinases involved in the unfolded protein response.

VS-5584 mediates potent anti-myeloma activity via the upregulation of a class II tumor suppressor gene, RARRES3 and the activation of Bim

The PI3K/mTOR/AKT pathway is an integral regulator of survival and drug resistance in multiple myeloma (MM). VS-5584 was synthesized with dual-specific and equipotent activity against mTORC1/2 and all four Class I PI3K isoforms so as to durably inhibit this pathway. We show that VS-5584 is highly efficacious against MM cell lines even in the presence of IL-6 and IGF-1 and that this growth inhibition is partially dependent on Bim. Importantly, VS-5584 triggers apoptosis in patient cells with a favorable therapeutic index. Gene expression profiling revealed a VS-5584-induced upregulation of RARRES3, a class II tumor suppressor gene. MM patient databases, UAMS and APEX, show that RARRES3 is under-expressed in 11q13 subsets which correlates with the reduced effectiveness of VS-5584 in 11q13 cell lines. Silencing RARRES3 expression significantly rescues VS-5584-induced cell death and increases cyclin D2 expression but not cyclin D1 or other cyclins implying a role for RARRES3 in cell cycle arrest. In vivo, VS-5584 significantly reduces the tumor burden of MM mouse xenografts. We further identified that VS-5584 synergised with Dexamethasone, Velcade, and exceptionally so with HDAC inhibitor, Panobinostat. Interestingly, this was consistently observed in several patient samples, proposing a promising novel clinical strategy for combination treatment especially in relapsed/refractory patients.

Signaling Pathways and Emerging Therapies in Multiple Myeloma

Multiple myeloma (MM) is a devastating malignancy of antibody-producing plasma cells. In the absence of a single unifying genetic event contributing to disease manifestation, efforts have focused on understanding signaling events deregulated in myeloma plasma cells. MM cells are dependent on both cellular and non-cellular components of the tumor microenvironment such as bone marrow stromal cells, endothelial cells, and cytokines such as interleukin 6 (IL6), vascular endothelial growth factor (VEGF), and insulin-like growth factor (IGF) for their growth and survival. The cumulative effect of such interactions is the aberrant activation of numerous signal transduction pathways within the MM plasma cells leading to uncontrolled growth and prevention of apoptosis. Here, we will review our current understanding of some of the key signal transduction pathways dysregulated in MM and emerging therapies targeting these pathways in MM.

Role of Immunotherapy in Targeting the Bone Marrow Microenvironment in Multiple Myeloma: An Evolving Therapeutic Strategy

Multiple myeloma (referred to henceforth as myeloma) is a B-cell malignancy characterized by unregulated growth of plasma cells in the bone marrow. The treatment paradigm for myeloma underwent significant evolution in the last decade, with an improved understanding of the pathogenesis of the disease as well as the development of therapeutic agents that target not only the tumor cells but also their microenvironment. Despite these therapeutic advances, the prognosis of patients with relapsed or refractory myeloma remains poor. Accordingly, a need exists for new therapeutic avenues that can overcome resistance to current therapies and improve survival outcomes. In addition, myeloma is associated with progressive immune dysregulation, with defects in T-cell immunity, natural killer cell function, and the antigen-presenting capacity of dendritic cells, resulting in a tumor microenvironment that promotes disease tolerance and progression. Together, the immunosuppressive microenvironment and oncogenic mutations activate signaling networks that promote myeloma cell survival. Immunotherapy incorporates novel treatment options (e.g., monoclonal antibodies, antibody-drug conjugates, chimeric antigen receptor T-cell therapy, immune checkpoint inhibitors, bispecific antibodies, and tumor vaccines) either alone or in combination with existing lines of therapies (e.g., immunomodulatory agents, proteasome inhibitors, and histone deacetylase inhibitors) to enhance the host anti myeloma immunity within the bone marrow microenvironment and improve clinical response. Following the U.S. Food and Drug Administration approval of daratumumab and elotuzumab in 2015, more immunotherapeutic agents are expected to be become available as valuable treatment options in the near future. This review provides a basic understanding of the role of immunotherapy in modulating the bone marrow tumor microenvironment and its role in the treatment of myeloma. Clinical efficacy and safety of recently approved therapeutic monoclonal antibodies (daratumumab, elotuzumab) are discussed, along with the therapeutic potential of emerging immunotherapies (antibody-drug conjugates, chimeric antigen receptor T-cell therapy, tumor vaccines, and immune checkpoint inhibitors).

MAF protein mediates innate resistance to proteasome inhibition therapy in multiple myeloma

Multiple myeloma (MM) patients with the t(14;16) translocation have a poor prognosis, and unlike other molecular subgroups, their outcome has not improved with the introduction of bortezomib (Bzb). The mechanism underlying innate resistance of MM to Bzb is unknown. In the present study, we have investigated how MAF overexpression impacts resistance to proteasome inhibitor (PI) therapy (Bzb and carfilzomib). High levels of MAF protein were found in t(14;16) cell lines; cell lines from the t(4;14) subgroup had intermediate levels, whereas cell lines from the other subgroups had low levels. High expression of MAF protein in t(14;16) was associated with significantly higher PI half-maximum inhibitory concentration values compared with other molecular subgroups. PI exposure abrogated glycogen synthase kinase 3β (GSK3β)-mediated degradation of MAF protein, resulting in increased MAF protein stability and PI resistance. Subsequent studies using loss-of-function and gain-of-function models showed that silencing MAF led to increased sensitivity to PIs, enhanced apoptosis, and activation of caspase-3, -7, -8, -9, poly (ADP-ribose) polymerase, and lamin A/C. In contrast, overexpression of MAF resulted in increased resistance to PIs and reduced apoptosis. These results define the role of MAF and GSK3 in the resistance of t(14;16) MM to PIs and identifies a novel mechanism by which MAF protein levels are regulated by PIs, which in turn confers resistance to PIs.

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.

Effects of topoisomerase inhibitors that induce DNA damage response on glucose metabolism and PI3K/Akt/mTOR signaling in multiple myeloma cells

Hallmarks of cancer cells comprise altered glucose metabolism (aerobic glycolysis) and differences in DNA damage response (DDR). Glucose transporters (GLUT), glycolytic enzymes such as hexokinase (HK) and metabolic pathways (e.g. PI3K/Akt/mTor) have been shown to be upregulated in multiple myeloma and other cancer cell lines. Here we have investigated the effects of clinically used inhibitors of topoisomerases, of DDR and of the PI3K/Akt/mTor pathway on glucose metabolism and on cell survival in multiple myeloma cells. The effects of DNA damaging topoisomerase inhibitors (doxorubicin, etoposide, topotecan), non-DNA damaging agents (bortezomib, vincristine) as well as of molecular inhibitors of DNA damage related kinases PIKKs (KU55933 [ATM], NU7026 [DNA-PKCs]) and PI3K/Akt/mTor signaling (BEZ235 [PI3K/mTor], MK-2206 [Akt]) were analyzed 24 hours after treatment of OPM-2 multiple myeloma cells. For this purpose we monitored [18F]-FDG uptake, cell viability using an ATP assay and expression of GLUT-1, hexokinase II (HKII), cleaved caspase-3 and cleaved PARP via Western-blotting. All topoisomerase inhibitors used could upregulate expression of GLUT-1 and HKII in OPM-2 cells, resulting in elevated [18F]-FDG uptake and promotion of cell survival. In contrast, bortezomib and vincristine induced a decline in [18F]-FDG uptake combined with early induction of apoptosis. Combination treatment with topoisomerase inhibitors and molecular inhibitors of PIKK and PI3K could reverse elevated [18F]-FDG uptake, as observed after application of topoisomerase inhibitors only, and aggravate induction of apoptosis. Thus, elevated glucose consumption in OPM-2 cells can be reversed by targeting both DDR and PI3K/Akt/mTOR signaling, thus providing a promising strategy in the treatment of cancer.

PIM and AKT kinase inhibitors show synergistic cytotoxicity in acute myeloid leukaemia that is associated with convergence on mTOR and MCL1 pathways

PIM kinases (PIM1, 2 and 3) are involved in cell proliferation and survival signalling and are emerging targets for the therapy of various malignancies. We found that a significant proportion of primary acute myeloid leukaemia (AML) samples showed PIM1 and PIM2 expression by quantitative reverse transcription polymerase chain reaction. Therefore, we investigated the effects of a novel ATP-competitive pan-PIM inhibitor, AZD1897, on AML cell growth and survival. PIM inhibition showed limited single agent activity in AML cell lines and primary AML cells, including those with or without FLT3-internal tandem duplication (ITD) mutation. However, significant synergy was seen when AZD1897 was combined with the Akt inhibitor AZD5363, a compound that is in early-phase clinical trials. AML cells from putative leukaemia stem cell subsets, including CD34+38- and CD34+38+ fractions, were equivalently affected by dual PIM/Akt inhibition when compared with bulk tumour cells. Analysis of downstream signalling pathways showed that combined PIM/Akt inhibition downregulated mTOR outputs (phosphorylation of 4EBP1 and S6) and markedly reduced levels of the anti-apoptotic protein MCL1. The combination of PIM and Akt inhibition holds promise for the treatment of AML.

AKT as a therapeutic target in multiple myeloma

INTRODUCTION

Multiple myeloma remains an incurable malignancy with poor survival. Novel therapeutic approaches capable of improving outcomes in patients with multiple myeloma are urgently required. AKT is a central node in the phosphatidylinositol-3-kinase/AKT/mammalian target of rapamycin signaling pathway with high expression in advanced and resistant multiple myeloma. AKT contributes to multiple oncogenic functions in multiple myeloma which may be exploited therapeutically. Promising preclinical data has lent support for pursuing further development of AKT inhibitors in multiple myeloma. Lead drugs are now entering the clinic.

AREAS COVERED

The rationale for AKT inhibition in multiple myeloma, pharmacological subtypes of AKT inhibitors in development, available results of clinical studies of AKT inhibitors and suitable drug partners for further development in combination with AKT inhibition in multiple myeloma are discussed.

EXPERT OPINION

AKT inhibitors are a welcome addition to the armamentarium against multiple myeloma and promising clinical activity is being reported from ongoing trials in combination with established and/or novel treatment approaches. AKT inhibitors may be set to improve patient outcomes when used in combination with synergistic drug partners.

PI3K-dependent multiple myeloma cell survival is mediated by the PIK3CA isoform

Constitutive phosphatidylinositide 3-kinase (PI3K) signalling has been implicated in multiple myeloma (MM) pathophysiology and is regarded as an actionable target for pharmacological intervention. Isoform-specific PI3K inhibition may offer the most focused treatment approach and could result in greater clinical efficacy and reduced side effects. We therefore performed isoform-specific knockdown of PIK3CA, PIK3CB, PIK3CD, and PIK3CG to analyse their individual contributions to MM cell survival and downstream signalling. In addition, we tested the effectivity of the novel PI3K isoform-specific inhibitors BYL-719 (PIK3CA), TGX-221 (PIK3CB), CAL-101 (PIK3CD), and CAY10505 (PIK3CG). We found the PIK3CA isoform to be of paramount importance for constitutive Akt activity in MM cells, and - in contrast to inhibition of other class I isoforms - only the blockade of PIK3CA was sufficient to induce cell death in a sizeable subgroup of MM samples. Furthermore, pharmacological PIK3CA inhibition in combination treatments of BYL-719 and established anti-myeloma agents resulted in strongly enhanced MM cell death. Our data thus clearly indicate therapeutic potential of PIK3CA inhibitors and support their clinical evaluation in multiple myeloma.

Multifaceted roles of GSK-3 and Wnt/β-catenin in hematopoiesis and leukemogenesis: opportunities for therapeutic intervention

Glycogen synthase kinase-3 (GSK-3) is well documented to participate in a complex array of critical cellular processes. It was initially identified in rat skeletal muscle as a serine/threonine kinase that phosphorylated and inactivated glycogen synthase. This versatile protein is involved in numerous signaling pathways that influence metabolism, embryogenesis, differentiation, migration, cell cycle progression and survival. Recently, GSK-3 has been implicated in leukemia stem cell pathophysiology and may be an appropriate target for its eradication. In this review, we will discuss the roles that GSK-3 plays in hematopoiesis and leukemogenesis as how this pivotal kinase can interact with multiple signaling pathways such as: Wnt/β-catenin, phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/Akt/mammalian target of rapamycin (mTOR), Ras/Raf/MEK/extracellular signal-regulated kinase (ERK), Notch and others. Moreover, we will discuss how targeting GSK-3 and these other pathways can improve leukemia therapy and may overcome therapeutic resistance. In summary, GSK-3 is a crucial regulatory kinase interacting with multiple pathways to control various physiological processes, as well as leukemia stem cells, leukemia progression and therapeutic resistance. GSK-3 and Wnt are clearly intriguing therapeutic targets.

Emerging pathways as individualized therapeutic target of multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to the growing knowledge of disease pathobiology.

AREAS COVERED

Intrinsic genetic lesions, as well as the bone marrow microenvironment, contribute to the activation of proliferation and survival pathways, impairment of cell death mechanisms and drug resistance. The phosphatidylinositol 3-kinase (PI3K) and the Ras/mitogen-activated protein kinase (MAPK) cascades are the signaling pathways mainly involved in the MM development. In the last decade, several molecules interfering with growth and survival promoting signaling have been developed.

EXPERT OPINION

Despite the availability of novel therapeutics, MM still evolves into a drug-resistant phase and most patients die of progressive disease. Therefore, there is an urgent need of novel therapeutic strategies. Among a plethora of new investigational agents, microRNA (miRNA) represents the basis for the design of novel therapeutic strategies which basically rely on miRNA inhibition or miRNA replacement approaches and take benefit respectively from the use of miRNA inhibitors or synthetic miRNAs as well as from lipid-based nanoparticles as carriers for in vivo delivery.

Combined targeting of MEK/MAPK and PI3K/Akt signalling in multiple myeloma

So-called RAS-dependent pathways, such as those signalling via mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) and phosphoinositide-3 kinase (PI3K)/Akt, are implicated in proliferation and survival of multiple myeloma (MM) cells. However, the effects of their combined blockade and its potential therapeutic utility for the treatment of RAS-mutated MM have not systematically been analysed. Here, we tested the functional consequences of single versus combined inhibition of the MEK/MAPK and PI3K/Akt pathways in a large series of primary MM samples (n = 55) and MM cell lines (n = 11). Additionally, the anti-myeloma activity of different treatments was analysed with respect to the RAS mutation status. PI3K/Akt blockade was generally more pro-apoptotic than blockade of MEK/MAPK both in cell lines and in primary MM samples. Simultaneous blockade of both pathways led to significantly enhanced anti-myeloma activity in 75% of primary MM samples, whereas the remainder was largely resistant. Resistance to combination blockade was exclusively observed in RAS wildtype cases, whereas sensitivity was noted in RAS wildtype and in RAS mutated MM. These results suggest that oncogenic RAS is a predictor of sensitivity to combination treatment with PI3K/Akt and MEK/MAPK inhibitors and that such an approach might therefore be beneficial for this genetically well-defined subgroup of MM patients.