Investigational agent MLN9708/2238 targets tumor-suppressor miR33b in MM cells

An evidence-based review of ixazomib citrate and its potential in the treatment of newly diagnosed multiple myeloma

Proteasome inhibition represents one of the more important therapeutic targets in the treatment of multiple myeloma (MM), since by suppressing nuclear factor-κB activity, which promotes myelomagenesis, it makes plasma cells susceptible to proapoptotic signals. Bortezomib, the first proteasome inhibitor approved for MM therapy, has been shown to increase response rate and improve outcome in patients with relapsed/refractory disease and in the frontline setting, particularly when combined with immunomodulatory drugs and alkylating agents. Among second-generation proteasome inhibitors, ixazomib (MLN9708) is the first oral compound to be evaluated for the treatment of MM. Ixazomib has shown improved pharmacokinetic and pharmacodynamic parameters compared with bortezomib, in addition to similar efficacy in the control of myeloma growth and prevention of bone loss. Ixazomib was found to overcome bortezomib resistance and to trigger synergistic antimyeloma activity with dexamethasone, lenalidomide, and histone deacetylase inhibitors. Phase I/II studies using ixazomib weekly or twice weekly in relapsed/refractory MM patients suggested antitumor activity of the single agent, but more promising results have been obtained with the combination of ixazomib, lenalidomide, and dexamethasone in newly diagnosed MM. Ixazomib has also been used in systemic amyloidosis as a single agent, showing important activity in this difficult-to-treat plasma-cell dyscrasia. More frequent side effects observed during administration of ixazomib were thrombocytopenia, nausea, vomiting, diarrhea, fatigue, and rash, whereas severe peripheral neuropathy was rare. Here, we review the chemical characteristics of ixazomib, as well as its mechanism of action and results from preclinical and clinical trials.

Low serum miR-19a expression as a novel poor prognostic indicator in multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy characterized by the clonal expansion of plasma cells. Despite continuing advances, novel biomarkers are needed for diagnosis and prognosis of MM. In our study, we characterized the diagnostic and prognostic potential of circulating microRNAs (miRNAs) in MM. Serum miRNA levels were analyzed in 108 newly diagnosed symptomatic MM patients and 56 healthy donors (HDs). Our analysis identified 95 dysregulated miRNAs in newly diagnosed MM patients. Of the 95 dysregulated miRNAs, dysregulation of miR-19a, miR-92a, miR-214-3p, miR-135b-5p, miR-4254, miR-3658 and miR-33b was confirmed by quantitative reverse transcription PCR (RT-qPCR). Receiver operating characteristic analysis revealed that a combination of miR-19a and miR-4254 can distinguish MM from HD with a sensitivity of 91.7% and specificity of 90.5%. Decreased expression of miR-19a was positively correlated with international staging system advancement, del(13q14) and 1q21 amplification. Furthermore, downregulation of miR-19a resulted in significantly decreased progression-free survival (PFS) and overall survival (OS). Our analysis indicated that the poor prognostic correlation of miR-19a expression was independent of genetic abnormalities in MM. Multivariate analysis revealed that miR-19a was a significant predictor of shortened PFS and OS. Interestingly, although miR-19a levels portend a poor prognosis, patients with low miR-19a levels had an improved response to bortezomib compared to those with high miR-19a profile. Patients with downregulated miR-19a experienced a significantly extended survival upon bortezomib-based therapy. These data demonstrate that the expression patterns of serum microRNAs are altered in MM, and miR-19a levels are a valuable prognostic marker to identify high-risk MM.

Phase 1 study of weekly dosing with the investigational oral proteasome inhibitor ixazomib in relapsed/refractory multiple myeloma

Proteasome inhibition is an effective treatment strategy for multiple myeloma. With improving survival, attention is increasingly focusing on ease of administration and toxicity profile. Ixazomib is an investigational, orally bioavailable 20S proteasome inhibitor. Sixty patients with relapsed and/or refractory multiple myeloma were enrolled on this phase 1 trial to evaluate safety and tolerability and determine the maximum tolerated dose (MTD) of single-agent, oral ixazomib given weekly for 3 of 4 weeks. Upon MTD determination, patients were enrolled to 4 different cohorts based on relapsed/refractory status and prior bortezomib and carfilzomib exposure. The MTD was determined to be 2.97 mg/m(2). Dose-limiting toxicities were grade 3 nausea, vomiting, and diarrhea in 2 patients, and grade 3 skin rash in 1 patient. Common drug-related adverse events were thrombocytopenia (43%), diarrhea (38%), nausea (38%), fatigue (37%), and vomiting (35%). The observed rate of peripheral neuropathy was 20%, with only 1 grade 3 event reported. Nine (18%) patients achieved a partial response or better, including 8 of 30 (27%) evaluable patients treated at the MTD. Pharmacokinetic studies suggested a long terminal half-life of 3.6 to 11.3 days, supporting once-weekly dosing. This trial was registered at www.clinicaltrials.gov as #NCT00963820.

Phase 1 study of twice-weekly ixazomib, an oral proteasome inhibitor, in relapsed/refractory multiple myeloma patients

Ixazomib is the first investigational oral proteasome inhibitor to be studied clinically. In this phase 1 trial, 60 patients with relapsed/refractory multiple myeloma (median of 4 prior lines of therapy; bortezomib, lenalidomide, thalidomide, and carfilzomib/marizomib in 88%, 88%, 62%, and 5%, respectively) received single-agent ixazomib 0.24 to 2.23 mg/m(2) (days 1, 4, 8, 11; 21-day cycles). Two dose-limiting toxicities (grade 3 rash; grade 4 thrombocytopenia) occurred at 2.23 mg/m(2). The maximum tolerated dose was 2.0 mg/m(2), which 40 patients received in 4 expansion cohorts. Patients received a median of 4 cycles (range, 1-39); 18% received ≥12 cycles. Eighty-eight percent had drug-related adverse events, including nausea (42%), thrombocytopenia (42%), fatigue (40%), and rash (40%); drug-related grade ≥3 events included thrombocytopenia (37%) and neutropenia (17%). Grade 1/2 drug-related peripheral neuropathy occurred in 12% (no grade ≥3). Two patients died on the study (both considered unrelated to treatment). The terminal half-life of ixazomib was 3.3 to 7.4 days; plasma exposure increased proportionally with dose (0.48-2.23 mg/m(2)). Among 55 response-evaluable patients, 15% achieved partial response or better (76% stable disease or better). These findings have informed the subsequent clinical development of ixazomib in multiple myeloma. This trial was registered at www.clinicaltrials.gov as #NCT00932698.

MicroRNA: important player in the pathobiology of multiple myeloma

Recent studies have revealed a pivotal role played by a class of small, noncoding RNAs, microRNA (miRNA), in multiple myeloma (MM), a plasma cell (PC) malignancy causing significant morbidity and mortality. Deregulated miRNA expression in patient's PCs and plasma has been associated with tumor progression, molecular subtypes, clinical staging, prognosis, and drug response in MM. A number of important oncogenic and tumor suppressor miRNAs have been discovered to regulate important genes and pathways such as p53 and IL6-JAK-STAT signaling. miRNAs may also form complex regulatory circuitry with genetic and epigenetic machineries, the deregulation of which could lead to malignant transformation and progression. The translational potential of miRNAs in the clinic is being increasingly recognized that they could represent novel biomarkers and therapeutic targets. This review comprehensively summarizes current progress in delineating the roles of miRNAs in MM pathobiology and management.

Linking the activity of bortezomib in multiple myeloma and autoimmune diseases

Since their introduction to the clinic 10 years ago, proteasome inhibitors have become the cornerstone of anti-multiple myeloma therapy. Despite significant progress in understanding the consequences of proteasome inhibition, the unique activity of bortezomib is still unclear. Disappointing results from clinical trials with bortezomib in other malignancies raise the question of what makes multiple myeloma so sensitive to proteasome inhibition. Successful administration of bortezomib in various immunological disorders that exhibit high antibody production suggests that the balance between protein synthesis and degradation is a key determinant of sensitivity to proteasome inhibition because a high rate of protein production is a shared characteristic in plasma and myeloma cells. Initial or acquired resistance to bortezomib remains a major obstacle in the clinic as in vitro data from cell lines suggest a key role for the β5 subunit mutation in resistance; however the mutation was not found in patient samples. Recent studies indicate the importance of selecting for a subpopulation of cells that produce lower amounts of paraprotein during bortezomib therapy.

Use of regulators and inhibitors of Pim-1, a serine/threonine kinase, for tumour therapy (review)

Pim-1 is a proto-oncogene that encodes a serine/threonine kinase that is overexpressed in a range of haematopoietic malignancies and solid cancers. Pim-1 expression is tightly regulated by multiple biomolecules at different levels. Several lines of evidence have indicated that dysregulation of Pim-1 can interfere with the cell cycle and apoptosis to promote malignant transformation of a number of types of tumour. Thus, investigation of Pim-1 regulation may provide important theoretical guidance for the development of molecular targeting therapies and drug treatments for Pim-1‑associated diseases. Regulators of Pim-1 expression, include microRNAs, oestrogen, inecalcitol, adenosine triphosphate (ATP) mimetic inhibitors and ATP competitive inhibitors of Pim-1. Combinations of inhibitors of Pim-1 expression and Pim-1‑specific inhibitors may provide novel therapies for cancer patients and directions for cancer treatment.

Proteasome inhibitors - molecular basis and current perspectives in multiple myeloma

Inhibition of proteasome, a proteolytic complex responsible for the degradation of ubiquitinated proteins, has emerged as a powerful strategy for treatment of multiple myeloma (MM), a plasma cell malignancy. First-in-class agent, bortezomib, has demonstrated great positive therapeutic efficacy in MM, both in pre-clinical and in clinical studies. However, despite its high efficiency, a large proportion of patients do not achieve sufficient clinical response. Therefore, the development of a second-generation of proteasome inhibitors (PIs) with improved pharmacological properties was needed. Recently, several of these new agents have been introduced into clinics including carfilzomib, marizomib and ixazomib. Further, new orally administered second-generation PI oprozomib is being investigated. This review provides an overview of main mechanisms of action of PIs in MM, focusing on the ongoing development and progress of novel anti-proteasome therapeutics.

A novel small molecule inhibitor of deubiquitylating enzyme USP14 and UCHL5 induces apoptosis in multiple myeloma and overcomes bortezomib resistance

Proteasome inhibitors have demonstrated that targeting protein degradation is effective therapy in multiple myeloma (MM). Here we show that deubiquitylating enzymes (DUBs) USP14 and UCHL5 are more highly expressed in MM cells than in normal plasma cells. USP14 and UCHL5 short interfering RNA knockdown decreases MM cell viability. A novel 19S regulatory particle inhibitor b-AP15 selectively blocks deubiquitylating activity of USP14 and UCHL5 without inhibiting proteasome activity. b-AP15 decreases viability in MM cell lines and patient MM cells, inhibits proliferation of MM cells even in the presence of bone marrow stroma cells, and overcomes bortezomib resistance. Anti-MM activity of b-AP15 is associated with growth arrest via downregulation of CDC25C, CDC2, and cyclin B1 as well as induction of caspase-dependent apoptosis and activation of unfolded protein response. In vivo studies using distinct human MM xenograft models show that b-AP15 is well tolerated, inhibits tumor growth, and prolongs survival. Combining b-AP15 with suberoylanilide hydroxamic acid, lenalidomide, or dexamethasone induces synergistic anti-MM activity. Our preclinical data showing efficacy of b-AP15 in MM disease models validates targeting DUBs in the ubiquitin proteasomal cascade to overcome proteasome inhibitor resistance and provides the framework for clinical evaluation of USP14/UCHL5 inhibitors to improve patient outcome in MM.

(18)F-FDG-PET/CT imaging in an IL-6- and MYC-driven mouse model of human multiple myeloma affords objective evaluation of plasma cell tumor progression and therapeutic response to the proteasome inhibitor ixazomib

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and computed tomography (CT) are useful imaging modalities for evaluating tumor progression and treatment responses in genetically engineered mouse models of solid human cancers, but the potential of integrated FDG-PET/CT for assessing tumor development and new interventions in transgenic mouse models of human blood cancers such as multiple myeloma (MM) has not been demonstrated. Here we use BALB/c mice that contain the newly developed iMyc(ΔEμ) gene insertion and the widely expressed H2-L(d)-IL6 transgene to demonstrate that FDG-PET/CT affords an excellent research tool for assessing interleukin-6- and MYC-driven plasma cell tumor (PCT) development in a serial, reproducible and stage- and lesion-specific manner. We also show that FDG-PET/CT permits determination of objective drug responses in PCT-bearing mice treated with the investigational proteasome inhibitor ixazomib (MLN2238), the biologically active form of ixazomib citrate (MLN9708), that is currently in phase 3 clinical trials in MM. Overall survival of 5 of 6 ixazomib-treated mice doubled compared with mice left untreated. One outlier mouse presented with primary refractory disease. Our findings demonstrate the utility of FDG-PET/CT for preclinical MM research and suggest that this method will play an important role in the design and testing of new approaches to treat myeloma.

New orally active proteasome inhibitors in multiple myeloma

Bortezomib is the first proteasome inhibitor approved for the therapy of multiple myeloma (MM). Although Bortezomib has renovated the treatment of MM, a considerable proportion of subjects fail to respond to Bortezomib treatment and almost all patients relapse from this drug either alone or when used in combination therapies. However, the good clinical outcome of Bortezomib treatment in MM patients gave impulsion for the development of second generation proteasome inhibitors with the ambition of improving efficacy of proteasome inhibition, enhancing antitumor activity, and decreasing toxicity, as well as providing flexible dosing schedules and patient convenience. This review provides an overview of the role of oral proteasome inhibitors including Marizomib, Oprozomib, Delanzomib, chemical proteasome inhibitors, and cinnabaramides, in the therapy of MM, focusing on developments over the past five years. These emerging drugs with different mechanisms of action have exhibited promising antitumor activity in patients with relapsed/refractory MM, and they are creating chances to target multiple pathways, overcome resistance, and improve clinical outcomes, mainly for those subjects who are refractory to approved agents. Future steps in the clinical development of oral inhibitors include the optimization of the schedule and the definition of their antitumor activity in MM.

MUC1 regulates expression of multiple microRNAs involved in pancreatic tumor progression, including the miR-200c/141 cluster

MUC1 is a transmembrane glycoprotein that modulates transcription via its cytoplasmic domain. We evaluated the capacity of MUC1 to regulate the global transcription of microRNAs in pancreatic cancer cells expressing MUC1. Results indicated that MUC1 regulated expression of at least 103 microRNAs. We evaluated further regulation of the microRNA transcript cluster miR-200c/141, which was among the most highly regulated microRNAs. We found that MUC1 directly interacted with ZEB1, a known transcriptional repressor of the miR-200c/141 cluster, at the promoter of miR-200c/141, and further reduced transcript production. These data indicate that signaling through MUC1 influences cancer progression by regulating transcription of microRNAs that are associated with the process of metastasis.

Novel agents for multiple myeloma to overcome resistance in phase III clinical trials

The incorporation of novel agents such as bortezomib and lenalidomide into initial therapy for multiple myeloma has improved the response rate of induction regimens. Also, these drugs are being increasingly used in the peri-transplant setting for transplant-eligible patients, and as part of consolidation and/or maintenance after front-line treatment, including in transplant-ineligible patients. Together, these and other strategies have contributed to a prolongation of progression-free survival (PFS) and overall survival (OS) in myeloma patients, and an increasing proportion are able to sustain a remission for many years. Despite these improvements, however, the vast majority of patients continue to suffer relapses, which suggests a prominent role for either primary, innate drug resistance, or secondary, acquired drug resistance. As a result, there remains a strong need to develop new proteasome inhibitors and immunomodulatory agents, as well as new drug classes, which would be effective in the relapsed and/or refractory setting, and overcome drug resistance. This review will focus on novel drugs that have reached phase III trials, including carfilzomib and pomalidomide, which have recently garnered regulatory approvals. In addition, agents that are in phase II or III, potentially registration-enabling trials will be described as well, to provide an overview of the possible landscape in the relapsed and/or refractory arena over the next 5 years.

Biological effects of the Pim kinase inhibitor, SGI-1776, in multiple myeloma

BACKGROUND

Pim kinases are constitutively active serine/threonine/tyrosine kinases that are overexpressed in hematological malignancies such as multiple myeloma. Pim kinase substrates are involved in transcription, protein translation, cell proliferation, and apoptosis. SGI-1776 is a potent Pim kinase inhibitor that has proven to be cytotoxic to leukemia and lymphoma cells. Based on this background, we hypothesized that SGI-1776 treatment would result in myeloma cytotoxicity.

MATERIALS AND METHODS

To test this, myeloma cell lines and primary CD138(+) cells from myeloma patients were treated with SGI-1776 in a dose- and time-dependent manner, and effect on cell death and proliferation, induction of autophagy, and changes in cell cycle profile were measured.

RESULTS

SGI-1776 treatment resulted in limited apoptosis in cell lines (mean 30%) and CD138(+) cells (< 10%) assessed using Annexin-V/propidium iodide. Limited effect was observed in cell cycle profile or growth in cell lines. However, DNA synthesis was decreased by 70% at 3 μM (all time points) in U266 though this was not observed in MM.1S. In accordance, immunoblot analyses revealed no change in transcription (c-Myc and H3), or apoptotic (Bad) proteins that are substrates of Pim kinases. In contrast, autophagy, assessed using acridine orange staining, was induced with SGI-1776 treatment in both cell lines (U266, 25%-70%; MM.1S, 8%-52%) and CD138(+) cells (19%-21%). Immunoblot analyses of the autophagy LC3b marker and translation initiation proteins (phospho-p70S6K and 4E-BP1) corroborated autophagy induction.

CONCLUSION

These data indicate that SGI-1776 treatment in myeloma cell lines and CD138(+) myeloma cells elicits its deleterious effects through inhibition of translation and induction of autophagy.

Aberrant microRNA expression in multiple myeloma

Multiple myeloma (MM) is a devastating disease with a complex biology, and in spite of improved survivability by novel treatment strategies over the last decade, MM is still incurable by current therapy. MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression at a post-transcriptional level. More than half of all protein coding genes are estimated to be controlled by miRNAs, and their expression is frequently deregulated in many diseases, including cancer. Recent studies have reported aberrant miRNA expression patterns in MM, and the function of individual miRNAs in MM has been investigated in detail in cell culture and animal models. Here, we review the current knowledge on the role of miRNAs in MM pathogenesis and discuss their potential as prognostic biomarkers and targets for treatment.