Mcl-1 Stability Determines Mitotic Cell Fate of Human Multiple Myeloma Tumor Cells Treated with the Kinesin Spindle Protein Inhibitor ARRY-520

NAT10 regulates mitotic cell fate by acetylating Eg5 to control bipolar spindle assembly and chromosome segregation

Cell fate of mitotic cell is controlled by spindle assembly. Deficient spindle assembly results in mitotic catastrophe leading to cell death to maintain cellular homeostasis. Therefore, inducing mitotic catastrophe provides a strategy for tumor therapy. Nucleolar acetyltransferase NAT10 has been found to regulate various cellular processes to maintain cell homeostasis. Here we report that NAT10 regulates mitotic cell fate by acetylating Eg5. NAT10 depletion results in multinuclear giant cells, which is the hallmark of mitotic catastrophe. Live-cell imaging showed that knockdown of NAT10 dramatically prolongs the mitotic time and induces defective chromosome segregation including chromosome misalignment, bridge and lagging. NAT10 binds and co-localizes with Eg5 in the centrosome during mitosis. Depletion of NAT10 reduces the centrosome loading of Eg5 and impairs the poleward movement of centrosome, leading to monopolar and asymmetrical spindle formation. Furthermore, NAT10 stabilizes Eg5 through its acetyltransferase function. NAT10 acetylates Eg5 at K771 to control Eg5 stabilization. We generated K771-Ac specific antibody and showed that Eg5 K771-Ac specifically localizes in the centrosome during mitosis. Additionally, K771 acetylation is required for the motor function of Eg5. The hyper-acetylation mimic Flag-Eg5 K771Q but not Flag-Eg5 rescued the NAT10 depletion-induced defective spindle formation and mitotic catastrophe, demonstrating that NAT10 controls mitosis through acetylating Eg5 K771. Collectively, we identify Eg5 as an important substrate of NAT10 in the control of mitosis and provide K771 as an essential acetylation site in the stabilization and motor function of Eg5. Our findings reveal that targeting the NAT10-mediated Eg5 K771 acetylation provides a potential strategy for tumor therapy.

A review on the treatment of multiple myeloma with small molecular agents in the past five years

Multiple myeloma is currently incurable, and the incidence rate is increasing year by year worldwide. Although in recent years the combined treatment plan based on proteasome inhibitors and immunomodulatory drugs has greatly improved the treatment effect of multiple myeloma, most patients still relapse and become resistant to current treatments. To solve this problem, scientists are committed to developing drugs with higher specificity, such as iberdomide, which is highly specific to ikaros and aiolos. This review aims to focus on the small molecular agents that are being researched/clinically used for the treatment of multiple myeloma, including the target mechanism, structure-activity relationship and application prospects of small molecular agents.

Filanesib plus bortezomib and dexamethasone in relapsed/refractory t(11;14) and 1q21 gain multiple myeloma

Filanesib is a first-in-class kinesin spindle protein inhibitor which demonstrated safety and encouraging activity in combination with bortezomib and dexamethasone in relapsed/refractory multiple myeloma in a preliminary analysis of dose-escalation phase results. This multicenter study included first a dose-escalation phase to determine maximum tolerated dose of two schedules of filanesib, bortezomib, and dexamethasone and a subsequent dose-expansion phase using the maximum tolerated doses. In the dose-expansion phase, 28 patients were evaluable for safety and efficacy. The most common grade ≥3 adverse events were neutropenia (21%) and anemia (18%), which were noncumulative and reversible, and hypertension (18%). The overall response rate was 43% with median duration of response not yet reached (range, 2.8-23.7+ months) with median follow-up of 6.3 months. A post hoc analysis incorporated 29 dose-escalation phase patients who received therapeutic filanesib doses, with an overall response rate of 39% and median duration of response of 18.0 months among the 57 total patients with median progression-free survival of 8.5 months. Notably, the PFS of high risk patients was comparable at 8.5 months, driven by the patients with 1q21 gain, characterized by increased MCL-1 expression, with a PFS of 9.1 months versus 3.5 months for the remainder of high risk patients. Patients with t(11;14) also had an encouraging PFS of 15.0 months. The combination of filanesib, bortezomib, and dexamethasone continues to show safety and encouraging activity in relapsed/refractory multiple myeloma, particularly in those patients with 1q21 gain and t(11;14).

Therapeutic targeting of KSP in preclinical models of high-risk neuroblastoma

Neuroblastoma is a childhood malignancy with often dismal prognosis; relapse is common despite intense treatment. Here, we used human tumor organoids representing multiple MYCN-amplified high-risk neuroblastomas to perform a high-throughput drug screen with approved or emerging oncology drugs. Tumor-selective effects were calculated using drug sensitivity scores. Several drugs with previously unreported anti-neuroblastoma effects were identified by stringent selection criteria. ARRY-520, an inhibitor of kinesin spindle protein (KSP), was among those causing reduced viability. High expression of the KSP-encoding gene KIF11 was associated with poor outcome in neuroblastoma. Genome-scale loss-of-function screens in hundreds of human cancer cell lines across 22 tumor types revealed that KIF11 is particularly important for neuroblastoma cell viability. KSP inhibition in neuroblastoma patient-derived xenograft (PDX) cells resulted in the formation of abnormal monoastral spindles, mitotic arrest, up-regulation of mitosis-associated genes, and apoptosis. In vivo, KSP inhibition caused regression of MYCN-amplified neuroblastoma PDX tumors. Furthermore, treatment of mice harboring orthotopic neuroblastoma PDX tumors resulted in increased survival. Our results suggested that KSP inhibition could be a promising treatment strategy in children with high-risk neuroblastoma.

Verticillin A increases the BIMEL/MCL-1 ratio to overcome ABT-737-resistance in human colon cancer cells by targeting the MEK/ERK pathway

ABT-737, a small molecule BH-3 mimetic, is less effective against human colon cancers due to its resistance. Verticillin A is a natural compound, which was previously purified from verticillium-infected mushrooms. Hence, we aimed at overcoming the ABT737 resistance observed in CRC tumors by combining Verticillin A with ABT-737 and figuring out the potential mechanism. In this study, we observed that Verticillin A could sensitize colon cancer to ABT-737-induced cell death through induction of mitochondrial-dependent apoptosis. Verticillin A could significantly increase the BIMEL/MCL-1 ratio to overcome ABT737 resistance through the suppression of the MEK/ERK pathway. In addition, up-regulation of BIM protein levels to activate BAX translocation results in apoptosis induction. Altogether, our work suggested the potential application of Verticillin A as a MEK inhibitor in BH3-mimetic-based therapy.

MCL-1 inhibitors, fast-lane development of a new class of anti-cancer agents

Cell death escape is one of the most prominent features of tumor cells and closely linked to the dysregulation of members of the Bcl-2 family of proteins. Among those, the anti-apoptotic family member myeloid cell leukemia-1 (MCL-1) acts as a master regulator of apoptosis in various human malignancies. Irrespective of its unfavorable structure profile, independent research efforts recently led to the generation of highly potent MCL-1 inhibitors that are currently evaluated in clinical trials. This offers new perspectives to target a so far undruggable cancer cell dependency. However, a detailed understanding about the tumor and tissue type specific implications of MCL-1 are a prerequisite for the optimal (i.e., precision medicine guided) use of this novel drug class. In this review, we summarize the major functions of MCL-1 with a special focus on cancer, provide insights into its different roles in solid vs. hematological tumors and give an update about the (pre)clinical development program of state-of-the-art MCL-1 targeting compounds. We aim to raise the awareness about the heterogeneous role of MCL-1 as drug target between, but also within tumor entities and to highlight the importance of rationale treatment decisions on a case by case basis.

New drugs in early development for treating multiple myeloma: all that glitters is not gold

INTRODUCTION

The last twenty years have introduced new therapeutic agents for multiple myeloma (MM); these include proteasome inhibitors (PIs), immunomodulatory drugs (IMDs) and monoclonal antibodies (mAbs). However, MM remains incurable, hence there is an unmet need for new agents for the treatment of advanced refractory disease. New agents could also be used in early lines to achieve improved, more sustained remission.

AREAS COVERED

We review the most promising agents investigated in early-phase trials for the treatment of MM and provide an emphasis on new agents directed against well-known targets (new PIs, IMDs and anti-CD38 mAbs). Drugs that work through distinct and numerous mechanisms of action (e.g. pro-apoptotic agents and tyrosine kinase inhibitors) and innovative immunotherapeutic approaches are also described. The paper culminates with our perspective on therapeutic approaches on the horizon for this disease.

EXPERT OPINION

IMD iberdomide and the export protein inhibitor selinexor demonstrated efficacy in heavily pretreated patients who had no other therapeutic options. We expect that immunotherapy with anti-BCMA BTEs and ADCs will revolutionize the approach to treating the early stages of the disease. Data on venetoclax in t(11;14)-positive patients may pave the way for personalized therapy. Not all new agents under early clinical evaluation will be investigated in regulatory phase III trials; one of the most important challenges is to identify those that could make a difference.

Thiadiazole derivatives as anticancer agents

In spite of substantial progress made toward understanding cancer pathogenesis, this disease remains one of the leading causes of mortality. Thus, there is an urgent need to develop novel, more effective anticancer therapeutics. Thiadiazole ring is a versatile scaffold widely studied in medicinal chemistry. Mesoionic character of this ring allows thiadiazole-containing compounds to cross cellular membrane and interact strongly with biological targets. Consequently, these compounds exert a broad spectrum of biological activities. This review presents the current state of knowledge on thiadiazole derivatives that demonstrate in vitro and/or in vivo efficacy across the cancer models with an emphasis on targets of action. The influence of the substituent on the compounds' activity is depicted. Furthermore, the results from clinical trials assessing thiadiazole-containing drugs in cancer patients are summarized.

Filanesib in combination with pomalidomide and dexamethasone in refractory MM patients: safety and efficacy, and association with alpha 1-acid glycoprotein (AAG) levels. Phase Ib/II Pomdefil clinical trial conducted by the Spanish MM group

This phase I/II trial evaluated the combination of the kinesin spindle protein inhibitor filanesib with pomalidomide and dexamethasone in relapsed or refractory multiple myeloma (RRMM) patients. Forty-seven RRMM patients with a median of three prior lines (2-8) and 94% refractory to lenalidomide were included: 14 in phase I and 33 in phase II. The recommended dose was 1·25 mg/m² of filanesib on days 1, 2, 15, 16, with pomalidomide 4 mg on days 1-21 and dexamethasone 40 mg weekly. The defined threshold for success was achieved, with 18 out of 31 patients obtaining at least minor response (MR) in the phase II. In the global population, 51% of patients achieved at least partial response (PR) and 60% ≥MR, resulting in a median progression-free survival (mPFS) of seven months and overall survival (OS) of 19 months. The main toxicity was haematological. Importantly, patients with low serum levels of alpha 1-acid glycoprotein (AAG) at baseline (<800 mg/l) had a superior response (overall response rate of 62% vs. 17%; P = 0·04), which also translated into a longer mPFS (9 vs. 2 months; P = 0·014). In summary, filanesib with pomalidomide and dexamethasone is active in RRMM although with significant haematological toxicity. Most importantly, high levels of AAG can identify patients unlikely to respond to this strategy. Trial registration: clinicaltrials.gov identifier: NCT02384083.

Drug Targeting of Genomic Instability in Multiple Myeloma

Genomic instability can be observed at both chromosomal and chromatin levels. Instability at the macro level includes centrosome abnormalities (CA) resulting in numerical as well as structural chromosomal changes, whereas instability at the micro level is characterized by defects in DNA repair pathways resulting in microsatellite instability (MIN) or mutations. Genomic instability occurs during carcinogenesis without impairing survival and growth, though the precise mechanisms remain unclear. Solid tumors arising from most cells of epithelial origin are characterized by genomic instability which renders them resistant to chemotherapy and radiotherapy. This instability is also observed in 25% of myeloma patients and has been shown to be highly prognostic, independently of the international staging system (ISS). However, a biomarker of aberrant DNA repair and loss of heterozygosity (LOH), was only observed at a frequency of 5% in newly diagnosed patients. Several new molecules targeting the pathways involved in genomic instability are under development and some have already entered clinical trials. Poly(ADP-ribose) polymerase-1 (PARP) inhibitors have been FDA-approved for the treatment of breast cancer type 1 susceptibility protein (BRCA1)-mutated metastatic breast cancer, as well as ovarian and lung cancer. Topoisomerase inhibitors and epigenetic histone modification-targeting inhibitors, such as HDAC (Histone Deacetylase) inhibitors which are novel agents that can target genomic instability. Several of the small molecule inhibitors targeting chromosomal level instability such as PARP, Akt, Aurora kinase, cyclin dependent kinase or spindle kinase inhibitors have been tested in mouse models and early phase I/II trials. ATM, ATR kinase inhibitors and DNA helicase inhibitors are also promising novel agents. However, most of these drugs are not effective as single agents but appear to act synergistically with DNA damaging agents such as radiotherapy, platinum derivatives, immunomodulators, and proteasome inhibitors. In this review, new drugs targeting genomic instability and their mechanisms of action will be discussed.

The Multiple Myeloma Drug Pipeline-2018: A Review of Small Molecules and Their Therapeutic Targets

Treatment of multiple myeloma (MM), a neoplasm of plasma cells, formerly dependent on alkylating drugs, corticosteroids, and autologous stem cell transplantation, has changed dramatically in the past 20 years because 3 new classes of small molecule drugs (arbitrarily defined as having a molecular weight of < 900 kDa)-immunomodulators, proteasome inhibitors, and histone deacetylase blockers-have been introduced for the disease. Therapeutic options for MM expanded further in 2015 when 2 new monoclonal antibodies (daratumumab and elotuzumab) were approved by the Food and Drug Administration for MM. Although MM remains incurable, the cumulative effect of these advances has resulted in a near-doubling of the 5-year survival rate since the late 1980s. Despite these advances, therapy for MM continues to pose substantial challenges because resistance to therapy frequently develops, and relapse and recurrence are all too common. The present review focused on the pipeline for new small molecules in various stages of development and their associated cellular targets. In addition to newer versions of alkylators, immunomodulators, proteasome inhibitors, and histone deacetylase inhibitors, the present review considered the prospects for adding new classes of small molecules to the MM armamentarium, which offer the potential for oral efficacy, relative simplicity of preparation, and prospects for improvement in the cost-to-benefit ratio. Included are agents that affect myeloma epigenetics and the ubiquitination-proteasome system and the unfolded protein response, apoptotic mechanisms, chromosomal abnormalities, nuclear protein transport, and various kinases involved in cellular signaling pathways.

Emerging alternatives to tyrosine kinase inhibitors for treating chronic myeloid leukemia

INTRODUCTION

BCR-ABL-directed tyrosine kinase inhibitors (TKIs) have revolutionised therapy for chronic myeloid leukemia. However, despite the availability and efficacy of this class of agents, lifelong treatment is still required in a significant proportion of patients Areas covered: We give an overview of the currently available BCR-ABL-directed TKIs and other conventional therapies for CML. We proceed to review the current market and some of the scientific rationale for new drug development before outlining a number of novel therapies, considered broadly as immunotherapies and targeted agents. Published English-language literature was reviewed regarding currently available TKIs; clinical trials repositories were reviewed to identify novel agents recently investigated or under active study. Expert opinion: We recommend discussion with patients and enrolment on an appropriate clinical trial where feasible. In situations where no trials are available, or if patients decline enrolment, we recommend use of an appropriate BCR-ABL directed TKI, selected on the basis of an evaluation of patient risk factors and side effect profile. Allogeneic stem cell transplant continues to have a role though this is generally limited to cases with advanced phases of disease or in cases with resistance-conferring mutations.

Anti-mitotic chemotherapeutics promote apoptosis through TL1A-activated death receptor 3 in cancer cells

The commonly used antimitotic chemotherapeutic agents such as taxol and vinblastine arrest cell cycle progression by disrupting mitotic spindles, and cause cancer cells to undergo apoptosis through ‘mitotic catastrophe’. The molecular mechanisms by which these drugs induce apoptosis and their relevance to clinical efficacy are not known. Facilitated by a new spindle poison diazonamide, we found that apoptosis induced by these agents requires death receptor 3 (DR3). Mitotic arrest by these agents induces lysosome-dependent secretion of the DR3 ligand, TL1A. Engagement of TL1A with DR3 stimulates the formation of FADD-containing and caspase-8-containing death-inducing signaling complex (DISC), which subsequently activates apoptosis in cells that express DR3. Expression of DR3 and TL1A correlates with the apoptotic response of human tumor xenograft models and human cancer cell lines to antimitotic drugs, providing further evidence that these drugs kill cancer cells through the DR3/TL1A-mediated pathway. These results suggest that TL1A and DR3 may hold promise to be used as biomarkers for predicting clinical response to antimitotic therapeutics.

Mitotic arrest-induced phosphorylation of Mcl-1 revisited using two-dimensional gel electrophoresis and phosphoproteomics: nine phosphorylation sites identified

Microtubule targeting agents (MTAs) characteristically promote phosphorylation and degradation of Mcl-1, and this represents a critical pro-apoptotic signal in mitotic death. While several phosphorylation sites and kinases have been implicated in mitotic arrest-induced Mcl-1 phosphorylation, a comprehensive biochemical analysis has been lacking. Contrary to previous reports suggesting that T92 phosphorylation by Cdk1 regulates Mcl-1 degradation, a T92A Mcl-1 mutant expressed in HeLa cells was phosphorylated and degraded with the same kinetics as wild-type Mcl-1 following vinblastine treatment. Similarly, when Mcl-1 with alanine replacements of all five putative Cdk sites (S64, T92, S121, S159, T163) was expressed, it was also phosphorylated and degraded in response to vinblastine. To analyze Mcl-1 phosphorylation in more detail, two-dimensional gel electrophoresis (2D-PAGE) was performed. While untreated cells expressed mainly unphosphorylated Mcl-1 with two minor phosphorylated species, Mcl-1 from vinblastine treated cells migrated during 2D-PAGE as a train of acidic spots representing nine or more phosphorylated species. Immunopurification and mass spectrometry of phosphorylated Mcl-1 derived from mitotically arrested HeLa cells revealed nine distinct sites, including several previously unreported. Mcl-1 bearing substitutions of all nine sites had a longer half-life than wild-type Mcl-1 under basal conditions, but still underwent phosphorylation and degradation in response to vinblastine treatment, and, like wild-type Mcl-1, was unable to protect cells from MTA treatment. These results reveal an unexpected complexity in Mcl-1 phosphorylation in response to MTAs and indicate that previous work has severely underestimated the number of sites, and thus encourage major revisions to the current model.

Cell death response to anti-mitotic drug treatment in cell culture, mouse tumor model and the clinic

Anti-mitotic cancer drugs include classic microtubule-targeting drugs, such as taxanes and vinca alkaloids, and the newer spindle-targeting drugs, such as inhibitors of the motor protein; Kinesin-5 (aka KSP, Eg5, KIF11); and Aurora-A, Aurora-B and Polo-like kinases. Microtubule-targeting drugs are among the first line of chemotherapies for a wide spectrum of cancers, but patient responses vary greatly. We still lack understanding of how these drugs achieve a favorable therapeutic index, and why individual patient responses vary. Spindle-targeting drugs have so far shown disappointing results in the clinic, but it is possible that certain patients could benefit if we understand their mechanism of action better. Pre-clinical data from both cell culture and mouse tumor models showed that the cell death response is the most variable point of the drug action. Hence, in this review we focus on current mechanistic understanding of the cell death response to anti-mitotics. We first draw on extensive results from cell culture studies, and then cross-examine them with the more limited data from animal tumor models and the clinic. We end by discussing how cell type variation in cell death response might be harnessed to improve anti-mitotic chemotherapy by better patient stratification, new drug combinations and identification of novel targets for drug development.

The kinesin spindle protein inhibitor filanesib enhances the activity of pomalidomide and dexamethasone in multiple myeloma

Kinesin spindle protein inhibition is known to be an effective therapeutic approach in several malignancies. Filanesib (ARRY-520), an inhibitor of this protein, has demonstrated activity in heavily pre-treated multiple myeloma patients. The aim of the work herein was to investigate the activity of filanesib in combination with pomalidomide plus dexamethasone backbone, and the mechanisms underlying the potential synergistic effect. The ability of filanesib to enhance the activity of pomalidomide plus dexamethasone was studied in several in vitro and in vivo models. Mechanisms of this synergistic combination were dissected by gene expression profiling, immunostaining, cell cycle and short interfering ribonucleic acid studies. Filanesib showed in vitro, ex vivo, and in vivo synergy with pomalidomide plus dexamethasone treatment. Importantly, the in vivo synergy observed in this combination was more evident in large, highly proliferative tumors, and was shown to be mediated by the impairment of mitosis transcriptional control, an increase in monopolar spindles, cell cycle arrest and the induction of apoptosis in cells in proliferative phases. In addition, the triple combination increased the activation of the proapoptotic protein BAX, which has previously been associated with sensitivity to filanesib, and could potentially be used as a predictive biomarker of response to this combination. Our results provide preclinical evidence for the potential benefit of the combination of filanesib with pomalidomide and dexamethasone, and supported the initiation of a recently activated trial being conducted by the Spanish Myeloma group which is investigating this combination in relapsed myeloma patients.

Practical Approaches to the Management of Dual Refractory Multiple Myeloma

The outcome of myeloma patients' dual refractory to lenalidomide and bortezomib is generally poor and represents a significant clinical challenge with a clear need for new therapeutic approaches. This has prompted the development of next-generation proteasome inhibitors and immunodulatory drugs (IMiDs), as well as new classes of drugs with novel mechanisms of action. As a result, several of these agents have received regulatory approval that have shown promising activity in the dual refractory setting including the second-generation proteasome inhibitor carfilzomib and third-generation IMiD pomalidomide. Moreover, the regulatory approval of several first-in-class drugs for myeloma such as the histone deacetylase (HDAC) inhibitor panobinostat and the anti-CD38 monoclonal antibody daratumumab has further broadened the therapeutic landscape for these patients. Collectively, these advances have provided new treatment strategies in dual refractory myeloma as well as important insights for the development of future studies with rationally designed drug combinations to target this challenging patient population.

A Phase 1 and 2 study of Filanesib alone and in combination with low-dose dexamethasone in relapsed/refractory multiple myeloma

BACKGROUND

Filanesib (ARRY-520) is a highly selective inhibitor of kinesin spindle protein, which has demonstrated preclinical antimyeloma activity.

METHODS

This open-label Phase 1/2 study determined the maximum tolerated dose of Filanesib administered on Days 1 and 2 of 14-Day Cycles in patients with multiple myeloma (MM) and included expansion cohorts with and without dexamethasone (40 mg/week). Patients in the dose-escalation (N = 31) and Phase 2 single-agent (N = 32) cohorts had received prior bortezomib as well as prior thalidomide and/or lenalidomide. Patients in the Phase 2 Filanesib plus dexamethasone cohort (N = 55) had received prior alkylator therapy and had disease refractory to lenalidomide, bortezomib, and dexamethasone. Prophylactic filgrastim was incorporated during dose escalation and was used throughout Phase 2.

RESULTS

Patients in each cohort had received a median of ≥6 prior therapies. The most common dose-limiting toxicities were febrile neutropenia and mucosal inflammation. In Phase 2, Grade 3 and 4 cytopenias were reported in approximately 50% of patients. Nonhematologic toxicities were infrequent. Phase 2 response rates (partial responses or better) were 16% (single agent) and 15% (Filanesib plus dexamethasone). All responding patients had low baseline levels of α1-acid glycoprotein, a potential selective biomarker.

CONCLUSIONS

Filanesib 1.50 mg/m² /day administered with prophylactic filgrastim has a manageable safety profile and encouraging activity in heavily pretreated patients This study is registered at www.clinicaltrials.gov as NCT00821249. Cancer 2017;123:4617-4630. © 2017 American Cancer Society.

Mitosis and mitochondrial priming for apoptosis

Cell division is a period of danger for cells, as inaccurate segregation of chromosomes can lead to loss of cell viability or aneuploidy. In order to protect against these dangers, cells ultimately initiate mitochondrial apoptosis if they are unable to correctly exit mitosis. A number of important chemotherapeutics exploit this response to delayed mitotic exit, but despite this, the molecular mechanism of the apoptotic timer in mitosis has proved elusive. Some recent studies have now shed light on this, showing how passage through the cell cycle fine-tunes a cell's apoptotic sensitivity such that it can respond appropriately when errors arise.

The therapeutic potential of cell cycle targeting in multiple myeloma

Proper cell cycle progression through the interphase and mitosis is regulated by coordinated activation of important cell cycle proteins (including cyclin-dependent kinases and mitotic kinases) and several checkpoint pathways. Aberrant activity of these cell cycle proteins and checkpoint pathways results in deregulation of cell cycle progression, which is one of the key hallmarks of cancer. Consequently, intensive research on targeting these cell cycle regulatory proteins identified several candidate small molecule inhibitors that are able to induce cell cycle arrest and even apoptosis in cancer cells. Importantly, several of these cell cycle regulatory proteins have also been proposed as therapeutic targets in the plasma cell malignancy multiple myeloma (MM). Despite the enormous progress in the treatment of MM the past 5 years, MM still remains most often incurable due to the development of drug resistance. Deregulated expression of the cyclins D is observed in virtually all myeloma patients, emphasizing the potential therapeutic interest of cyclin-dependent kinase inhibitors in MM. Furthermore, other targets have also been identified in MM, such as microtubules, kinesin motor proteins, aurora kinases, polo-like kinases and the anaphase promoting complex/cyclosome. This review will provide an overview of the cell cycle proteins and checkpoint pathways deregulated in MM and discuss the therapeutic potential of targeting proteins or protein complexes involved in cell cycle control in MM.

Hepatocellular carcinoma repression by TNFα-mediated synergistic lethal effect of mitosis defect-induced senescence and cell death sensitization

Hepatocellular carcinoma (HCC) is a cancer lacking effective therapies. Several measures have been proposed to treat HCCs, such as senescence induction, mitotic inhibition, and cell death promotion. However, data from other cancers suggest that single use of these approaches may not be effective. Here, by genetic targeting of Survivin, an inhibitor of apoptosis protein (IAP) that plays dual roles in mitosis and cell survival, we identified a tumor necrosis factor alpha (TNFα)-mediated synergistic lethal effect between senescence and apoptosis sensitization in malignant HCCs. Survivin deficiency results in mitosis defect-associated senescence in HCC cells, which triggers local inflammation and increased TNFα. Survivin inactivation also sensitizes HCC cells to TNFα-triggered cell death, which leads to marked HCC regression. Based on these findings, we designed a combination treatment using mitosis inhibitor and proapoptosis compounds. This treatment recapitulates the therapeutic effect of Survivin deletion and effectively eliminates HCCs, thus representing a potential strategy for HCC therapy.

CONCLUSION

Survivin ablation dramatically suppresses human and mouse HCCs by triggering senescence-associated TNFα and sensitizing HCC cells to TNFα-induced cell death. Combined use of mitotic inhibitor and second mitochondrial-derived activator of caspases mimetic can induce senescence-associated TNFα and enhance TNFα-induced cell death and synergistically eliminate HCC. (Hepatology 2016;64:1105-1120).

Inhibition of Bcl-xL sensitizes cells to mitotic blockers, but not mitotic drivers

Cell fate in response to an aberrant mitosis is governed by two competing networks: the spindle assembly checkpoint (SAC) and the intrinsic apoptosis pathway. The mechanistic interplay between these two networks is obscured by functional redundancy and the ability of cells to die either in mitosis or in the subsequent interphase. By coupling time-lapse microscopy with selective pharmacological agents, we systematically probe pro-survival Bcl-xL in response to various mitotic perturbations. Concentration matrices show that BH3-mimetic-mediated inhibition of Bcl-xL synergises with perturbations that induce an SAC-mediated mitotic block, including drugs that dampen microtubule dynamics, and inhibitors targeting kinesins and kinases required for spindle assembly. By contrast, Bcl-xL inhibition does not synergize with drugs which drive cells through an aberrant mitosis by overriding the SAC. This differential effect, which is explained by compensatory Mcl-1 function, provides opportunities for patient stratification and combination treatments in the context of cancer chemotherapy.

New investigational drugs with single-agent activity in multiple myeloma

The treatment of multiple myeloma (MM) is rapidly evolving. In the United States, four drugs (panobinostat, ixazomib, daratumumab and elotuzumab) were approved for the treatment of MM in 2015. As a result of improved diagnosis and therapy, there has been a dramatic improvement in the outcome of MM in the last decade, probably more than any other malignancy. Numerous agents continue to be studied in preclinical models and in clinical trials, with many demonstrating clinical efficacy that appears promising enough to have a trajectory for regulatory approval. The purpose of this article is to summarize the current data and provide perspective on new investigational agents with promising single-agent activity in MM. The agents reviewed include Isatuximab, an anti-CD38 monoclonal antibody; marizomib, a new proteasome inhibitor; oprozomib, an oral proteasome inhibitor; filanesib (ARRY-520), a kinesin spindle protein inhibitor; dinaciclib, a cyclin-dependent kinase inhibitor; venetoclax (ABT-199), a selective BCL-2 inhibitor; and LGH-447, pan PIM kinase inhibitor.

Hierarchy for targeting prosurvival BCL2 family proteins in multiple myeloma: pivotal role of MCL1

New therapeutic targets are needed to address the poor prognosis of patients with high-risk multiple myeloma. Myeloma cells usually express a range of the prosurvival BCL2 proteins. To define the hierarchy of their relative importance for maintaining the survival of myeloma cells, we targeted each of them in a large panel of cell lines, using pharmacological inhibitors or gene editing or by peptide-based approaches, alone or in combination. The majority of well-established immortalized cell lines (17/25) or low-passage myeloma cell lines (5/7) are readily killed when MCL1 is targeted, even including those cell lines sensitive to BCL2 inhibition. Targeting MCL1 also constrained the growth of myeloma in vivo. We also identified a previously unrecognized subset of myeloma that is highly BCLXL-dependent, and has the potential for cotargeting MCL1 and BCLXL. As MCL1 is pivotal for maintaining survival of most myelomas, it should be prioritized for targeting in the clinic once high-quality, validated inhibitors become available.

A phase 1 dose-escalation study of filanesib plus bortezomib and dexamethasone in patients with recurrent/refractory multiple myeloma

BACKGROUND

Filanesib is a kinesin spindle protein inhibitor that has demonstrated encouraging activity in patients with recurrent/refractory multiple myeloma. Preclinical synergy with bortezomib was the rationale for the current phase 1 study.

METHODS

The current study was a multicenter study with an initial dose-escalation phase to determine the maximum tolerated dose of 2 schedules of filanesib plus bortezomib with and without dexamethasone, followed by a dose-expansion phase.

RESULTS

With the addition of prophylactic filgastrim, the maximum planned dose was attained: 1.3 mg/m² /day of bortezomib plus 40 mg of dexamethasone on days 1, 8, and 15 of a 28-day cycle, with filanesib given intravenously either at a dose of 1.5 mg/m² /day (schedule 1: days 1, 2, 15, and 16) or 3 mg/m² /day (schedule 2: days 1 and 15). The most common adverse events (assessed for severity using version 4.0 of the National Cancer Institute Common Terminology Criteria for Adverse Events) were transient, noncumulative neutropenia and thrombocytopenia with grade 3/4 events reported in 44% (16% in cycle 1 with filgastrim) and 29% of patients, respectively. A low (≤11%) overall rate of nonhematological grade 3/4 toxicity was observed. With a median of 3 prior lines of therapy and 56% of patients with disease that was refractory to proteasome inhibitors, the overall response rate was 20% (55 patients), and was 29% in 14 patients with proteasome inhibitors-refractory disease receiving filanesib at a dose of ≥1.25 mg/m² (duration of response, 5.2 to ≥21.2 months).

CONCLUSIONS

The current phase 1 study established a dosing schedule for the combination of these agents that demonstrated a favorable safety profile with a low incidence of nonhematologic toxicity and manageable hematologic toxicity. The combination of filanesib, bortezomib, and dexamethasone appears to have durable activity in patients with recurrent/refractory multiple myeloma. Cancer 2016;122:3327-3335. © 2016 American Cancer Society.

Mcl-1 dynamics influence mitotic slippage and death in mitosis

Microtubule-binding drugs such as taxol are frontline treatments for a variety of cancers but exactly how they yield patient benefit is unclear. In cell culture, inhibiting microtubule dynamics prevents spindle assembly, leading to mitotic arrest followed by either apoptosis in mitosis or slippage, whereby a cell returns to interphase without dividing. Myeloid cell leukaemia-1 (Mcl-1), a pro-survival member of the Bcl-2 family central to the intrinsic apoptosis pathway, is degraded during a prolonged mitotic arrest and may therefore act as a mitotic death timer. Consistently, we show that blocking proteasome-mediated degradation inhibits taxol-induced mitotic apoptosis in a Mcl-1-dependent manner. However, this degradation does not require the activity of either APC/C-Cdc20, FBW7 or MULE, three separate E3 ubiquitin ligases implicated in targeting Mcl-1 for degradation. This therefore challenges the notion that Mcl-1 undergoes regulated degradation during mitosis. We also show that Mcl-1 is continuously synthesized during mitosis and that blocking protein synthesis accelerates taxol induced death-in-mitosis. Modulating Mcl-1 levels also influences slippage; overexpressing Mcl-1 extends the time from mitotic entry to mitotic exit in the presence of taxol, while inhibiting Mcl-1 accelerates it. We suggest that Mcl-1 competes with Cyclin B1 for binding to components of the proteolysis machinery, thereby slowing down the slow degradation of Cyclin B1 responsible for slippage. Thus, modulating Mcl-1 dynamics influences both death-in-mitosis and slippage. However, because mitotic degradation of Mcl-1 appears not to be under the control of an E3 ligase, we suggest that the notion of network crosstalk is used with caution.

Novel approaches to treatment of double-refractory multiple myeloma

Multiple myeloma (MM) refractory to both proteasome inhibitors and immunomodulatory agents (IMiDs; double-refractory myeloma) has a poor prognosis. With the more frequent use of these agents as part of initial therapy, and then in the maintenance setting until disease progression, such drug resistance is an emerging problem of great significance. New therapeutic strategies are clearly needed for this patient population, including the development of more potent agents within existing antimyeloma drug classes, exploration of rational combinations of both novel and conventional drugs, and validation of new myeloma drug targets. Several approaches have shown substantial promise, including use of the second-generation proteasome inhibitor carfilzomib and the third-generation IMiD pomalidomide, which led to the recent regulatory approval of both agents. In addition, the kinesin-spindle protein KSP inhibitor ARRY-520 has shown activity as a first-in-class drug in myeloma therapeutics, whereas the histone deacetylase (HDAC) inhibitors vorinostat and panobinostat have demonstrated efficacy when used in rational combinations. This overview provides a summary of novel agents that have shown activity in double-refractory myeloma in recent phase II and III clinical trials, and a framework for future studies that will help to improve outcomes in this patient population.

Targeting the Mitotic Catastrophe Signaling Pathway in Cancer

Mitotic catastrophe, as defined in 2012 by the International Nomenclature Committee on Cell Death, is a bona fide intrinsic oncosuppressive mechanism that senses mitotic failure and responds by driving a cell to an irreversible antiproliferative fate of death or senescence. Thus, failed mitotic catastrophe can promote the unrestrained growth of defective cells, thereby representing a major gateway to tumour development. Furthermore, the activation of mitotic catastrophe offers significant therapeutic advantage which has been exploited in the action of conventional and targeted anticancer agents. Yet, despite its importance in tumour prevention and treatment, the molecular mechanism of mitotic catastrophe is not well understood. A better understanding of the signals that determine cell fate following failed or defective mitosis will reveal new opportunities to selectively target and enhance the programme for therapeutic benefit and reveal biomarkers to predict patient response. This review is focused on the molecular mechanism of mitotic catastrophe induction and signalling and highlights current strategies to exploit the process in cancer therapy.

DUB-ling down on B-cell malignancies

In this issue of Blood, Peterson et al demonstrate that inhibition of both Usp9x and Usp24 results in efficient degradation of Mcl-1, induction of apoptosis, and inhibition of tumor growth in B-cell malignancies.

First-in-human phase 1 study of filanesib (ARRY-520), a kinesin spindle protein inhibitor, in patients with advanced solid tumors

Purpose Filanesib (ARRY-520) is a highly selective, targeted inhibitor of kinesin spindle protein (KSP) inhibitor that induces mitotic arrest and subsequent tumor cell death. This first-in-human Phase 1 study evaluated dose-limiting toxicities (DLTs) and determined a maximum tolerated dose (MTD) for filanesib administered as a 1-h intravenous infusion on 2 treatment schedules in patients with advanced solid tumors. The pharmacokinetics (PK), pharmacodynamics and preliminary efficacy of filanesib were also evaluated. Methods Filanesib was administered on Day 1 of each 3-week cycle (Initial Schedule) or Days 1 and 2 of each 2-week cycle (Alternate Schedule). A standard 3 + 3 dose-escalation design was employed. An expansion cohort was conducted at the MTD of the Initial Schedule. Filanesib PK was evaluated in plasma (both schedules) and urine (Initial Schedule only). Monopolar spindle formation was evaluated in biopsies taken from patients in the expansion cohort. Results Forty-one patients received filanesib. The MTD was equivalent for both the Initial and Alternate Schedules (2.50 mg/m(2)/cycle). The prevalence of neutropenia as a DLT for both schedules necessitated adding prophylactic filgrastim to another dose escalation on the Alternate Schedule (highest tolerated dose 3.20 mg/m(2)/cycle). Neurotoxicity related to filanesib was not observed. Dose-proportional increases in filanesib exposure were observed. The half-life for filanesib was ~70 h. Monopolar spindles in patient biopsy samples indicated KSP inhibition. Stable disease was the best tumor response observed in 18 % (7/39) of evaluable patients. Conclusion Filanesib provided exposures with acceptable tolerability and evidence of target-specific pharmacodynamic effects.

How I treat relapsed myeloma

Multiple myeloma (MM) is a plasma cell malignancy leading to significant life-expectancy shortening. Although the incorporation of the novel agents thalidomide, bortezomib, and lenalidomide in the front-line therapy has resulted in significant improvement, almost all patients relapse, making the treatment of relapse a real challenge. In the present article, when and how to treat relapsed MM is discussed. Treatment can be safely delayed in a subset of patients with asymptomatic relapse, whereas those with symptomatic relapse, advanced disease at diagnosis, or significant paraproteinemic increase require prompt rescue therapy. The benefit of retreatment and the use of a sequential approach for successive relapses considering drug synergism are highlighted. For patients with aggressive relapses and for those who have exhausted all available options, continued therapy until disease progression is recommended, particularly when using regimens with a long-term safety profile. Patients with a duration response to a first autologous stem cell transplantation (ASCT) longer than 2 years may benefit from a second ASCT. Patients with aggressive disease and/or poor cytogenetics at diagnosis relapsing within the first 2 years from ASCT should be considered for an allogeneic transplantation. Finally, a number of newer promising drugs are being actively investigated and the enrolment of patients in clinical trials is encouraged.

Kinesin spindle protein inhibitor SB743921 induces mitotic arrest and apoptosis and overcomes imatinib resistance of chronic myeloid leukemia cells

Inhibition of the cell mitotic pathway may provide a novel means for therapeutic intervention in chronic myeloid leukemia (CML). Kinesin spindle protein (KSP), a microtubule-associated motor protein which is essential for cell cycle progression, is overexpressed in bcr-abl+ CML cells. Retrovirus mediated bcr-abl transduction increases KSP expression in cord blood CD34 + cells. SB743921 is a selective KSP inhibitor which is being investigated in ongoing clinical trials for treatment of myeloma, leukemia and solid tumors. Treatment of CML cells with SB743921 resulted in reduced proliferation and colony forming cell (CFC) formation ability. SB743921 also actively blocked cell cycle progression, leading to apoptosis in both primary CML cells and cell lines. KSP inhibition sensitized CML cells to imatinib-induced apoptosis. Importantly, SB743921 inhibited the proliferation of various CML cells including T315I mutation-harboring cells. Furthermore, we demonstrated that SB743921 treatment suppressed ERK and AKT activity in CML cells. These data indicate that SB743921 may become a novel treatment agent for patients with CML.

Novel targeted agents in the treatment of multiple myeloma

New, next-generation targeted treatment strategies are required to improve outcomes in patients with multiple myeloma (MM). Monoclonal antibodies, cell signaling inhibitors, and selective therapies targeting the bone marrow microenvironment have demonstrated encouraging results with generally manageable toxicity in therapeutic trials of patients with relapsed and refractory disease, each critically informed by preclinical studies. A combination approach of these newer agents with immunomodulators and/or proteasome inhibitors as part of a treatment platform seems to improve the efficacy of anti-MM regimens, even in heavily pretreated patients. Future studies are required to better understand the complex mechanisms of drug resistance in MM.

Salvage therapy of multiple myeloma: the new generation drugs

During the past decade, overall results of treatment of multiple myeloma (MM) have been improved and survival curves are now significantly better with respect to those obtained with historical treatment. These improvements are linked to a deeper knowledge of the biology of disease and to the introduction in clinical practice of drugs with different mechanism of action such as proteasome inhibitors and immunomodulatory drugs (IMiDs). However, MM remains in most cases an incurable disease. For patients who relapse after treatment with novel agents, the prognosis is dismal and new drugs and therapeutic strategies are required for continued disease control. In this review, we summarize new insights in salvage therapy for relapsed/refractory MM as emerging from recent clinical trials exploring the activity of bendamustine, new generation proteasome inhibitors, novel IMiDs, monoclonal antibodies, and drugs interfering with growth pathways.

Post-slippage multinucleation renders cytotoxic variation in anti-mitotic drugs that target the microtubules or mitotic spindle

One common cancer chemotherapeutic strategy is to perturb cell division with anti-mitotic drugs. Paclitaxel, the classic microtubule-targeting anti-mitotic drug, so far still outperforms the newer, more spindle-specific anti-mitotics in the clinic, but the underlying cellular mechanism is poorly understood. In this study we identified post-slippage multinucleation, which triggered extensive DNA damage and apoptosis after drug-induced mitotic slippage, contributes to the extra cytotoxicity of paclitaxel in comparison to the spindle-targeting drug, Kinesin-5 inhibitor. Based on quantitative single-cell microscopy assays, we showed that attenuation of the degree of post-slippage multinucleation significantly reduced DNA damage and apoptosis in response to paclitaxel, and that post-slippage apoptosis was likely mediated by the p53-dependent DNA damage response pathway. Paclitaxel appeared to act as a double-edge sword, capable of killing proliferating cancer cells both during mitotic arrest and after mitotic slippage by inducing DNA damage. Our results thus suggest that to predict drug response to paclitaxel and anti-mitotics in general, 2 distinct sets of bio-markers, which regulate mitotic and post-slippage cytotoxicity, respectively, may need to be considered. Our findings provide important new insight not only for elucidating the cytotoxic mechanisms of paclitaxel, but also for understanding the variable efficacy of different anti-mitotic chemotherapeutics.

Current strategies for treatment of relapsed/refractory multiple myeloma

In spite of significant advances in the management of multiple myeloma (MM), the disease remains incurable and nearly all patients ultimately relapse and require salvage chemotherapy. As such, relapsed and relapsed-refractory MM remains a critical area of research pertaining to biological mechanisms of progression and chemotherapy resistance, as well as to the development of new pharmacologic agents and immunologic approaches for the disease. The immunomodulatory agents and proteasome inhibitors represent the cornerstone of treatment in this setting, with combination regimens incorporating these drugs demonstrating encouraging rates and duration of response, including the newer agents, pomalidomide and carfilzomib. In addition, novel drug classes have shown promising activity in RR MM, including the orally-administered proteasome inhibitors ixazomib and oprozomib; monoclonal antibodies such as the anti-CS1 monoclonal antibody elotuzumab and anti-CD38 monoclonal antibody daratumumab; and histone deacetylase inhibitors such as panobinostat and rocilinostat.

Decoding the pathophysiology and the genetics of multiple myeloma to identify new therapeutic targets

In recent years, significant progress has been achieved in the characterization of the transcriptional profiles, gene mutations and structural chromosomal lesions in myeloma cells. These studies have identified many candidate therapeutic targets, which are recurrently deregulated in myeloma cells. However, these targets do not appear, at least individually, to represent universal driver(s) of this disease. Furthermore, evaluation of these recurrent lesions does not suggest that they converge to a single molecular pathway. Detailed integration of molecular and functional data for these candidate targets and pathways will hopefully dissect which of them play more critical roles for each of the different individual molecular defined subtypes of this disease. This review focuses on how recent updates in our understanding of myeloma pathogenesis and molecular characterization may impact ongoing and future efforts to develop new therapeutics for this disease.