Myeloma stem cell concepts, heterogeneity and plasticity of multiple myeloma

Exploring the anti-myeloma potential of composite nanoparticles As4S4/Fe3O4: Insights from in vitro, ex vivo and in vivo studies

Given the profound multiple myeloma (MM) heterogeneity in clonal proliferation of malignant plasma cells (PCs) and anti-MM therapeutic potential of nanotherapies, it is inevitable to develop treatment plan for patients with MM. Two composite nanoparticles (NPs), As4S4/Fe3O4 (4:1) and As4S4/Fe3O4 (1:1) demonstrated effective anti-MM activity in in vitro, ex vivo, and in vivo in xenograft mouse model. Composite NPs triggered activation of p-ERK1/2/p-JNK, and downregulation of c-Myc, p-PI3K, p-4E-BP1; G2/M cell cycle arrest with increase in cyclin B1, histones H2AX/H3, activation of p-ATR, p-Chk1/p-Chk2, p-H2AX/p-H3; and caspase- and mitochondria-dependent apoptosis induction. NPs attenuated the stem cell-like side population in MM cells, both alone and in the presence of stroma. For a higher clinical response rate, As4S4/Fe3O4 (4:1) observed synergism with dexamethasone and melphalan, while As4S4/Fe3O4 (1:1) showed synergistic effects in combination with bortezomib, lenalidomide and pomalidomide anti-MM agents, providing the framework for further clinical evaluation of composite NPs in MM.

Method comparison between hematopoietic progenitor cell and CD34+ cell counts in hematopoietic stem cell collection

BACKGROUND

The reference method for hematopoietic stem cell enumeration is flow cytometric CD34+ cell analysis. We evaluated using the hematopoietic progenitor cell (HPC) count on the Sysmex hematology analyzer to safely replace some flow cytometric measurements performed in peripheral blood samples to guide apheresis timing.

STUDY DESIGN AND METHODS

We compared HPC and CD34+ cell counts in 133 preharvest peripheral blood samples and 124 apheresis products.

RESULTS

Pre-apheresis HPC counts ≥24 × 106/L in healthy donors and ≥36 × 106/L in lymphoma patients predicted adequate mobilization with 100% specificity and positive predictive value, saving 79% and 63% of flow cytometry analyses, respectively. Due to a positive bias (mean bias 50.26; 95% CI 36.24-64.29), a higher threshold was needed in multiple myeloma patients (HPC ≥ 132 × 106/L), saving only 24% of flow cytometry analyses.

CONCLUSION

When the HPC count is above the corresponding threshold, apheresis could be safely initiated without waiting for the flow cytometry result, thereby reducing time-to-decision. Lower HPC values, however, require confirmation by flow cytometry.

Transcriptome of bone marrow-Derived stem cells reveals new inflammatory mediators related to increased survival in patients with multiple myeloma

Although multiple myeloma (MM) is a neoplasm that leads affected individuals to death, little is known about why some patients survive much longer than others. In this context, we investigated the transcriptomic profile of bone marrow hematopoietic stem cells obtained from MM patients and compared the clinical outcomes of death and survival six months after bone marrow transplantation. The leukapheresis products of 39 patients with MM eligible for autologous transplantation were collected and analyzed. After extraction, the RNA was analyzed using the GeneChip Human Exon 1.0 Array method. The transcriptome profile was analyzed in silico, and the differentially expressed signaling pathways of interest were validated. The results showed a difference in the expression of inflammation-related genes, immune response processes, and the oxidative stress pathway. The in silico study also pointed out the involvement of the NFκB transcription factor in the possible modulation of these genes. We chose to validate molecules participating in these processes, including the cytokines TNF-α, IFN-γ, and TGF-β1; in addition, we measured the levels of oxidative stress mediators (pro-oxidant profile and the total antioxidant capacity). TNF-α levels were significantly reduced in patients who died and were over 50 years old at diagnosis, as well as in patients with plasmacytoma. Increased TNF-α was detected in patients with very high levels of β2-microglobulin. IFN-γ reduction was observed in patients with a complete response to treatment compared to those with a very good response. Patients with plasmacytoma who died also had an increased pro-oxidant profile. These data show the profile of inflammatory response markers that are altered in patients with MM who die quickly and serve as a basis for the development of future studies of markers to predict better survival in this disease.

Beyond BCMA: the next wave of CAR T cell therapy in multiple myeloma

Chimeric antigen receptor (CAR) T cell therapy has transformed the treatment landscape of relapsed/refractory multiple myeloma. The current Food and Drug Administration approved CAR T cell therapies idecabtagene vicleucel and ciltacabtagene autoleucel both target B cell maturation antigen (BCMA), which is expressed on the surface of malignant plasma cells. Despite deep initial responses in most patients, relapse after anti-BCMA CAR T cell therapy is common. Investigations of acquired resistance to anti-BCMA CAR T cell therapy are underway. Meanwhile, other viable antigenic targets are being pursued, including G protein-coupled receptor class C group 5 member D (GPRC5D), signaling lymphocytic activation molecule family member 7 (SLAMF7), and CD38, among others. CAR T cells targeting these antigens, alone or in combination with anti-BCMA approaches, appear to be highly promising as they move from preclinical studies to early phase clinical trials. This review summarizes the current data with novel CAR T cell targets beyond BCMA that have the potential to enter the treatment landscape in the near future.

Circulating biosignatures in multiple myeloma and their role in multidrug resistance

A major obstacle to chemotherapeutic success in cancer treatment is the development of drug resistance. This occurs when a tumour fails to reduce in size after treatment or when there is clinical relapse after an initial positive response to treatment. A unique and serious type of resistance is multidrug resistance (MDR). MDR causes the simultaneous cross resistance to unrelated drugs used in chemotherapy. MDR can be acquired through genetic alterations following drug exposure, or as discovered by us, through alternative pathways mediated by the transfer of functional MDR proteins and nucleic acids by extracellular vesicles (M Bebawy V Combes E Lee R Jaiswal J Gong A Bonhoure GE Grau, 23 9 1643 1649, 2009).Multiple myeloma is an incurable cancer of bone marrow plasma cells. Treatment involves high dose combination chemotherapy and patient response is unpredictable and variable due to the presence of multisite clonal tumour infiltrates. This clonal heterogeneity can contribute to the development of MDR. There is currently no approved clinical test for the minimally invasive testing of MDR in myeloma.Extracellular vesicles comprise a group of heterogeneous cell-derived membranous structures which include; exosomes, microparticles (microvesicles), migrasomes and apoptotic bodies. Extracellular vesicles serve an important role in cellular communication through the intercellular transfer of cellular protein, nucleic acid and lipid cargo. Of these, microparticles (MPs) originate from the cell plasma membrane and vary in size from 0.1-1um. We have previously shown that MPs confer MDR through the transfer of resistance proteins and nucleic acids. A test for the early detection of MDR would benefit clinical decision making, improve survival and support rational drug use. This review focuses on microparticles as novel clinical biomarkers for the detection of MDR in Myeloma and discusses their role in the therapeutic management of the disease.

miRNAs and Multiple Myeloma: Focus on the Pathogenesis, Prognosis, and Drug Resistance

Multiple myeloma (MM) produces clonal plasma cells and aberrant monoclonal antibody accumulation in patients' bone marrow (BM). Around 1% of all cancers and 13% of hematological malignancies are caused by MM, making it one of the most common types of cancer. Diagnostic and therapeutic methods for managing MM are currently undergoing extensive research. MicroRNAs (miRNAs) are short noncoding RNAs that reduce or inhibit the translation of their target mRNA after transcription. Because miRNAs play an influential role in how myeloma develops, resources, and becomes resistant to drugs, miRNA signatures may be used to diagnose, do prognosis, and treat the myeloma response. Consequently, researchers have investigated the levels of miRNA in plasma cells from MM patients and developed tools to test whether they directly impacted tumor growth. This review discusses the latest discoveries in miRNA science and their role in the development of MM. We also emphasize the potential applications of miRNAs to diagnose, prognosticate, and treat MM in the future.

Engineering T-cells with chimeric antigen receptors to combat hematological cancers: an update on clinical trials

Chimeric antigen receptor (CAR) redirected T-cells has shown efficacy in the treatment of B-cell leukemia/lymphoma, however, high numbers of relapses occur due to loss of targeted antigen or intrinsic failure of the CAR T-cells. In this situation modifications of the basic strategy are envisaged to reduce the risk of relapse, some of them are in early clinical exploration. These include simultaneous targeting of multiple antigens or combination of CAR T-cell therapy with other treatment modalities such as checkpoint inhibitors. The review evaluates and discusses these modified advanced therapies and pre-clinical approaches with respect to their potential to control leukemia and lymphoma in the long-term.

CAR T-Cell Therapy for Patients with Multiple Myeloma: Current Evidence and Challenges

The therapeutic landscape of multiple myeloma (MM) has benefited from an emergence of novel therapies over the last decade. By inducing T-cell kill of target cancer cells, chimeric antigen receptor (CAR) T-cell therapies have improved outcomes of patients with hematologic malignancies. B-cell maturation antigen (BCMA) is the current target antigen of choice for most CAR T-cell products under investigation for MM. However, their shortcomings deal with logistical and clinical challenges, including limited availability, manufacturing times, and toxicities. This article provides an overview of recently developed and investigational CAR T-cell therapies for MM, highlighting current evidence and challenges.

FOXM1 regulates glycolysis and energy production in multiple myeloma

The transcription factor, forkhead box M1 (FOXM1), has been implicated in the natural history and outcome of newly diagnosed high-risk myeloma (HRMM) and relapsed/refractory myeloma (RRMM), but the mechanism with which FOXM1 promotes the growth of neoplastic plasma cells is poorly understood. Here we show that FOXM1 is a positive regulator of myeloma metabolism that greatly impacts the bioenergetic pathways of glycolysis and oxidative phosphorylation (OxPhos). Using FOXM1-deficient myeloma cells as principal experimental model system, we find that FOXM1 increases glucose uptake, lactate output, and oxygen consumption in myeloma. We demonstrate that the novel 1,1-diarylethylene small-compound FOXM1 inhibitor, NB73, suppresses myeloma in cell culture and human-in-mouse xenografts using a mechanism that includes enhanced proteasomal FOXM1 degradation. Consistent with the FOXM1-stabilizing chaperone function of heat shock protein 90 (HSP90), the HSP90 inhibitor, geldanamycin, collaborates with NB73 in slowing down myeloma. These findings define FOXM1 as a key driver of myeloma metabolism and underscore the feasibility of targeting FOXM1 for new approaches to myeloma therapy and prevention.

Resistance and recurrence of malignancies after CAR-T cell therapy

The emergence of chimeric antigen receptor T (CAR-T) cell therapy has ushered a new era in cancer therapy, especially the treatment of hematological malignancies. However, resistance and recurrence still occur in some patients after CAR-T cell treatment. CAR-T cell inefficiency and tumor escape have emerged as the main challenges for the long-term disease control of B cell malignancies by this promising immunotherapy. In solid tumor treatment, CAR-T cells must also overcome many hurdles from the tumor or immune-suppressed tumor environment, which have become obstacles to the advancement of CAR-T therapy. Therefore, an understanding of the mechanisms underlying post-CAR treatment failure in patients is necessary. In this review, we characterize some mechanisms of resistance and recurrence after CAR-T cell therapy and correspondingly suggest reasonable treatment strategies.

Checkpoint Inhibitors in Multiple Myeloma: Intriguing Potential and Unfulfilled Promises

Immune dysregulation and alteration of the bone marrow microenvironment allowing plasma cells to escape immune surveillance are well-known factors associated with the proliferation of clonal plasma cells and development of multiple myeloma (MM). Whilst immunotherapeutic approaches are now commonplace in a wide spectrum of malignancies, this aberration of myeloma development gives rise to the biological rationale for the use of immune checkpoint inhibitors (ICIs) in MM. However, the initial experience with these agents has been challenging with limited single agent efficacy, significant toxicity, and side effects. Herein, we review the biological and immunological aspects of MM and ICIs. We discuss the basic biology of immune checkpoint inhibitors, mechanisms of resistance, and drug failure patterns, review the published clinical trial data for ICIs in MM, and look towards the future of ICIs for MM treatment.

Chimeric Antigen Receptor T-Cell Therapeutics for Multiple Myeloma: Moving Into the Spotlight

ABSTRACT

Chimeric antigen receptor (CAR) T-cell therapy has quickly emerged as a highly promising treatment for patients with relapsed and refractory multiple myeloma. There are numerous candidates under development, each with their unique characteristics and points of differentiation. The most recent US Food and Drug Administration approval of the first B-cell maturation antigen-targeted CAR-T cell therapy on March 26, 2021, has paved a path forward for the eventual evaluation of more of these investigational agents undergoing clinical trials. Herein, we highlight, from a clinical development perspective, the CAR-T cell therapies farthest along in development with updated data from the American Society of Hematology 2020 annual meeting. We also discuss potential paths of overcoming resistance to these therapies and the future direction for CAR-T cell therapeutics in multiple myeloma.

Engineering enhanced CAR T-cells for improved cancer therapy

Chimeric antigen receptor (CAR) T-cell therapies have evolved from a research tool to a paradigm-shifting therapy with impressive responses in B cell malignancies. This review summarizes the current state of the CAR T-cell field, focusing on CD19- and B cell maturation antigen-directed CAR T-cells, the most developed of the CAR T-cell therapies. We discuss the many challenges to CAR-T therapeutic success and innovations in CAR design and T-cell engineering aimed at extending this therapeutic platform beyond hematologic malignancies.

Bispecific T Cell Engagers for the Treatment of Multiple Myeloma: Achievements and Challenges

MM is the second most common hematological malignancy and represents approximately 20% of deaths from hematopoietic cancers. The advent of novel agents has changed the therapeutic landscape of MM treatment; however, MM remains incurable. T cell-based immunotherapy such as BTCEs is a promising modality for the treatment of MM. This review article discusses the advancements and future directions of BTCE treatments for MM.

Usefulness of hematopoietic progenitor cell monitoring to predict autologous peripheral blood stem cell harvest timing: A single-center retrospective study

INTRODUCTION

In autologous peripheral blood stem cell harvest (APBSCH), CD34-positive cells have been measured to assess the numbers of hematopoietic stem cells, but measurement requires specialized equipment. Recently, there was a report that peripheral blood hematopoietic progenitor cells (HPCs) are useful indicators of the presence of hematopoietic stem cells. We examined the usefulness of HPC monitoring to predict APBSCH timing.

METHODS

We retrospectively analyzed the relationship between HPC and collected CD34-positive cells in 84 consecutive patients who underwent APBSCH.

RESULTS

According to the receiver operating characteristics curve for the collection of ≥2 × 106 CD34-positive cells/kg, the HPC cut-off value on the day before collection was 21/μL, while that on the day of collection was 41/μL. No significant factors were found in the univariate analysis except for the HPC count on the day before collection (p < 0.001) and the day of collection (p < 0.001). According to the multivariate analysis, the HPC count on the day before collection (p < 0.001) and the day of collection (p < 0.001) were also factors that strongly influenced the quantity of CD34-positive cells collected.

CONCLUSION

Our results suggest that the HPC count on not only the day of collection but also the day before collection is a good indicator for appropriate APBSCH timing.

Exosomal miR-1305 in the oncogenic activity of hypoxic multiple myeloma cells: a biomarker for predicting prognosis

Background: Exosomes have emerged as important mediators of tumor progression, and a prognostic role for serum exosomal miRNAs has been suggested in multiple myeloma (MM). Given the association of hypoxia with tumor aggressiveness, including cancer stem cell-like phenotypes, we explored exosomal miRNAs from MM cells under hypoxic conditions and analyzed their diverse roles both in promoting oncogenic activity and in predicting prognosis.

Methods: The human MM cell line, RPMI 8226, was cultured under hypoxic conditions and their exosome production and exosomal miRNA profiles were compared with those of normoxic parental cells. The survival outcome of myeloma patients was compared using serum levels of exosomal miRNAs, and the effects of exosomal miRNAs on the target genes of MM cells and adjacent immune cells were analyzed.

Results: Increased expression of stem cell markers and exosome production were observed in hypoxic MM cells. Exosome miRNA analysis identified a higher expression of miR-1305 in exosomes isolated from hypoxic MM cells than in those of normoxic parental cells. The overall survival of patients with high exosomal miR-1305 was poorer than it was in patients with low exosomal miR-1305. In hypoxic MM cells, an increase of exosomal miR-1305 led to a decrease of cellular miR-1305 and increased expression of the miR-1305 target genes, MDM2, IGF1 and FGF2 resulted in the promotion of oncogenic activity of MM. Exosomal miR-1305 was also transferred from MM cells to macrophages, and miR-1305-transferred macrophages showed tumor-promoting, M2-macrophage phenotypes.

Conclusions: Exosome-mediated secretion of miR-1305 in MM cells promoted oncogenic activity of hypoxic MM cells and high serum levels of exosomal miR-1305.

Efficacy and Safety of CAR-Modified T Cell Therapy in Patients with Relapsed or Refractory Multiple Myeloma: A Meta-Analysis of Prospective Clinical Trials

Background: In recent years, chimeric antigen receptor-modified T (CAR-T) cell therapy for B-cell leukemia and lymphoma has shown high clinical efficacy. Similar CAR-T clinical trials have also been carried out in patients with refractory/relapsed multiple myeloma (RRMM). However, no systematic review has evaluated the efficacy and safety of CAR-T cell therapy in RRMM. The purpose of this study was to fill this literature gap. Methods: Eligible studies were searched in PUBMED, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), CNKI, and WanFang from data inception to December 2019. For efficacy assessment, the overall response rate (ORR), minimal residual disease (MRD) negativity rate, strict complete response (sCR), complete response (CR), very good partial response (VGPR), and partial response (PR) were calculated. The incidence of any grade cytokine release syndrome (CRS) and grade ≥3 adverse events (AEs) were calculated for safety analysis. The effect estimates were then pooled using an inverse variance method. Results: Overall, 27 studies involving 497 patients were included in this meta-analysis. The pooled ORR and MRD negativity rate were 89% (95% Cl: 83-94%) and 81% (95% Cl: 67-91%), respectively. The pooled sCR, CR, VGPR, and PR were 14% (95% Cl: 5-27%), 13% (95% Cl: 4-26%), 23% (95% Cl: 14-33%), and 15% (95% Cl: 10-21%), respectively. Subgroup analyses of ORR by age, proportion of previous autologous stem cell transplantation (ASCT), and target selection of CAR-T cells revealed that age ≤ 55 years (≤55 years vs. > 55 years, p = 0.0081), prior ASCT ≤70% (≤70% vs. > 70%, p = 0.035), and bispecific CAR-T cells (dual B-cell maturation antigen (BCMA)/BCMA + CD19 vs specific BCMA, p = 0.0329) associated with higher ORR in patients. Subgroup analyses of remission depth by target selection suggested that more patients achieved a better response than VGPR with dual BCMA/BCMA + CD19 CAR-T cells compared to specific BCMA targeting (p = 0.0061). In terms of safety, the pooled incidence of any grade and grade ≥ 3 CRS was 76% (95% CL: 63-87%) and 11% (95% CL: 6-17%). The most common grade ≥ 3 AEs were hematologic toxic effects. Conclusion: In heavily treated patients, CAR-T therapy associates with promising responses and tolerable AEs, as well as CRS in RRMM. However, additional information regarding the durability of CAR-T cell therapy, as well as further randomized controlled trials, is needed.

CAR T cell therapies for patients with multiple myeloma

Despite several therapeutic advances over the past decade, multiple myeloma (MM) remains largely incurable, indicating a need for new treatment approaches. Chimeric antigen receptor (CAR) T cell therapy works by mechanisms distinct from those of other MM therapies and involves the modification of patient or donor T cells to target specific cell-surface antigens. B cell maturation antigen (BCMA) is expressed only on plasma cells, a small subset of B cells and MM cells, which makes it a suitable target antigen for such therapies. At the time of writing, data from >20 clinical trials involving anti-BCMA CAR T cells have demonstrated that patients with relapsed and/or refractory MM can achieve objective responses. These early investigations have been instrumental in demonstrating short-term safety and efficacy; however, most patients do not have disease remission lasting >18 months. Attempts to reduce or delay the onset of relapsed disease are underway and include identifying additional CAR T cell target antigens and methods of enhancing BCMA expression on MM cells. Engineering CAR T cells to enhance both the activity and safety of treatment continues to be a promising avenue for improvement. In this Review we summarize data from clinical trials that have been carried out to date, describe novel antigens that could be targeted in the future, and highlight potential future innovations that could enhance the efficacy and/or reduce the toxicities associated with CAR T cell therapies.

Chimeric Antigen Receptor T-cell Therapy for Multiple Myeloma

Relapsed/refractory multiple myeloma (MM) remains a significant clinical challenge, despite a wide array of approved therapeutic agents. Immunotherapy offers an advantage in this setting. Chimeric antigen receptor (CAR) modified T-cells have transformed care for patients with hematologic malignancies. CAR-T cells targeting CD-19 B-cell lymphoma cells have shown prominent activity in lymphoma and acute lymphoblastic leukemia. Recently, the CAR-T cell platform for MM demonstrated therapeutic benefit. Hence, it is rapidly progressing. The most commonly tested target for MM is the B-cell maturation antigen. Complexities involved in the generation and use of CAR-T cells for MM include the identification of appropriate target antigens that are specific, and tumor type restricted, in addition to the optimization of CAR constructs to mitigate toxicities including cytokine release syndrome. CAR-T cells hold immense promise as a therapeutic modality for the treatment of MM. In this article, we provide an updated review of clinical trials of MM-specific CAR-T cells.

c-MYC expression and maturity phenotypes are associated with outcome benefit from addition of ixazomib to lenalidomide-dexamethasone in myeloma

OBJECTIVES

In the TOURMALINE-MM1 phase 3 trial in relapsed/refractory multiple myeloma, ixazomib-lenalidomide-dexamethasone (IRd) showed different magnitudes of progression-free survival (PFS) benefit vs placebo-Rd according to number and type of prior therapies, with greater benefit seen in patients with >1 prior line of therapy or 1 prior line of therapy without stem cell transplantation (SCT).

METHODS

RNA sequencing data were used to investigate the basis of these differences.

RESULTS

The PFS benefit of IRd vs placebo-Rd was greater in patients with tumors expressing high c-MYC levels (median not reached vs 11.3 months; hazard ratio [HR] 0.42; 95% CI, 0.26, 0.66; P < .001) compared with in those expressing low c-MYC levels (median 20.6 vs 16.6 months; HR 0.75; 95% CI, 0.42, 1.2). Expression of c-MYC in tumors varied based on the number and type of prior therapy received, with the lowest levels observed in tumors of patients who had received 1 prior line of therapy including SCT. These tumors also had higher expression levels of CD19 and CD81.

CONCLUSIONS

PFS analyses suggest that lenalidomide and ixazomib target tumors with different levels of c-MYC, CD19, and CD81 expression, thus providing a potential rationale for the differential benefits observed in the TOURMALINE-MM1 study. This trial was registered at www.clinicaltrials.gov as: NCT01564537.

The Society for Immunotherapy of Cancer consensus statement on immunotherapy for the treatment of multiple myeloma

Outcomes in multiple myeloma (MM) have improved dramatically in the last two decades with the advent of novel therapies including immunomodulatory agents (IMiDs), proteasome inhibitors and monoclonal antibodies. In recent years, immunotherapy for the treatment of MM has advanced rapidly, with the approval of new targeted agents and monoclonal antibodies directed against myeloma cell-surface antigens, as well as maturing data from late stage trials of chimeric antigen receptor CAR T cells. Therapies that engage the immune system to treat myeloma offer significant clinical benefits with durable responses and manageable toxicity profiles, however, the appropriate use of these immunotherapy agents can present unique challenges for practicing physicians. Therefore, the Society for Immunotherapy of Cancer convened an expert panel, which met to consider the current role of approved and emerging immunotherapy agents in MM and provide guidance to the oncology community by developing consensus recommendations. As immunotherapy evolves as a therapeutic option for the treatment of MM, these guidelines will be updated.

Development of CAR-T cell therapies for multiple myeloma

Currently available data on chimeric antigen receptor (CAR)-T cell therapy has demonstrated efficacy and manageable toxicity in heavily pretreated multiple myeloma (MM) patients. The CAR-T field in MM is rapidly evolving with >50 currently ongoing clinical trials across all phases, different CAR-T design, or targets. Most of the CAR-T trials are performed in China and the United States, while European centers organize or participate in only a small fraction of current clinical investigations. Autologous CAR-T cell therapy against B cell maturation antigen shows the best evidence of efficacy so far but main issues remain to be addressed: duration of response, longer follow-up, prolonged cytopenia, patients who may benefit the most such as those with extramedullary disease, outcome prediction, and the integration of CAR-T cell therapy within the MM treatment paradigm. Other promising targets are, i.a.,: CD38, SLAMF7/CS1, or GPRC5D. Although no product has been approved to date, cost and production time for autologous products are expected to be the main obstacles for broad use, for which reason allogeneic CAR-T cells are currently explored. However, the inherent risk of graft-versus-host disease requires additional modification which still need to be validated. This review aims to present the current status of CAR-T cell therapy in MM with an overview on current targets, designs, and stages of CAR-T cell development. Main challenges to CAR-T cell therapy will be highlighted as well as strategies to structurally improve the CAR-T cell product, and thereby its efficacy and safety. The need for comparability of the most promising therapies will be emphasized to balance risks and benefits in an evidence-based but personalized approach to further improve outcome of patients with MM.

Chimeric antigen receptor T-cell therapy for multiple myeloma

Chimeric antigen receptor (CAR) T cell therapy, an immunotherapy using gene-modified T cells, has recently made a big success. CAR T cells targeting CD19 is highly effective against B cell malignancies. Next good target for CAR T therapy is multiple myeloma. B cell maturation antigen has been proved to be a good target for CAR T cell therapy in early-phase clinical trials. We are also developing CAR T cells targeting a protein conformation that is preferentially detected in myeloma cells. In this review, I will summarize the state of art in the field of CAR T cell therapy against myeloma, and also present our effort to develop a new CAR T cell therapy.

Chimeric antigen receptor T cell therapies for multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy and remains incurable despite the advent of numerous new drugs such as proteasome inhibitors (PIs), immunomodulatory agents (IMiDs), and monoclonal antibodies. There is an unmet need to develop novel therapies for refractory/relapsed MM. In the past few years, chimeric antigen receptor (CAR)-modified T cell therapy for MM has shown promising efficacy in preclinical and clinical studies. Furthermore, the toxicities of CAR-T cell therapy are manageable. This article summarizes recent developments of CAR-T therapy in MM, focusing on promising targets, new technologies, and new research areas. Additionally, a comprehensive overview of antigen selection is presented along with preliminary results and future directions of CAR-T therapy development.

The promise of chimeric antigen receptor (CAR) T cell therapy in multiple myeloma

A cure for multiple myeloma (MM), a malignancy of plasma cells, remains elusive. Nearly all myeloma patients will eventually relapse and develop resistance to currently available treatments. There is an unmet medical need to develop novel and effective therapies that can induce sustained responses. Early phase clinical trials using chimeric antigen receptor (CAR) T cell therapy have shown great promise in the treatment of relapsed and/or refractory MM. In this review article, we provide an overview of the CAR constructs, the gene transfer vector systems, and approaches for T cell activation and expansion. We then summarize the outcomes of several early phase clinical trials of CAR T cell therapy in MM and the novel CAR T targets that are under development. Finally, we explore the potential mechanisms that result in disease relapse after CAR T therapy and propose future directions in CAR T therapy in MM.

A multiple myeloma classification system that associates normal B-cell subset phenotypes with prognosis

Despite the recent progress in treatment of multiple myeloma (MM), it is still an incurable malignant disease, and we are therefore in need of new risk stratification tools that can help us to understand the disease and optimize therapy. Here we propose a new subtyping of myeloma plasma cells (PCs) from diagnostic samples, assigned by normal B-cell subset associated gene signatures (BAGS). For this purpose, we combined fluorescence-activated cell sorting and gene expression profiles from normal bone marrow (BM) Pre-BI, Pre-BII, immature, naïve, memory, and PC subsets to generate BAGS for assignment of normal BM subtypes in diagnostic samples. The impact of the subtypes was analyzed in 8 available data sets from 1772 patients' myeloma PC samples. The resulting tumor assignments in available clinical data sets exhibited similar BAGS subtype frequencies in 4 cohorts from de novo MM patients across 1296 individual cases. The BAGS subtypes were significantly associated with progression-free and overall survival in a meta-analysis of 916 patients from 3 prospective clinical trials. The major impact was observed within the Pre-BII and memory subtypes, which had a significantly inferior prognosis compared with other subtypes. A multiple Cox proportional hazard analysis documented that BAGS subtypes added significant, independent prognostic information to the translocations and cyclin D classification. BAGS subtype analysis of patient cases identified transcriptional differences, including a number of differentially spliced genes. We identified subtype differences in myeloma at diagnosis, with prognostic impact and predictive potential, supporting an acquired B-cell trait and phenotypic plasticity as a pathogenetic hallmark of MM.

Assessment of haematopoietic progenitor cell counting with the Sysmex® XN-1000 to guide timing of apheresis of peripheral blood stem cells

BACKGROUND

Successful peripheral blood stem cell (PBSC) collection depends on optimal timing of apheresis, as usually determined by flow cytometry CD34-positive (⁺) cell count in peripheral blood (PB). Since this method is costly and labour-intensive, we evaluated the use of the Hematopoietic Progenitor Cell count programme on a Sysmex^® XN haematologic analyser (XN-HPC) as a rapid and inexpensive alternative for predicting CD34⁺ cell count in PB samples.

MATERIALS AND METHODS

Haematopoietic progenitor cell and CD34⁺ cell counts were compared using 273 PB samples collected from 78 healthy donors and 72 patients who underwent PBSC transplantation. We assessed the effectiveness of the XN-HPC in safely predicting pre-harvest CD34⁺ counts. The most efficient cut-off values of XNHPC were identified. We also evaluated the imprecision (coefficient of variation, CV) and functional sensitivity.

RESULTS

Imprecision of the XN-HPC count was <6.3% on daily measurement of three levels of quality control material. Functional sensitivity was 8.9×10⁶/L. A cut-off value of ≥62×10⁶/L XN-HPC for multiple myeloma (MM) patients and ≥30×10⁶/L for all other subjects had both 100% specificity and 100% positive predictive value for identifying samples with CD34⁺ cells ≥20×10⁶/L. An XN-HPC threshold of <13×10⁶/L identified preharvest CD34⁺ cell count <10×10⁶/L with 100% sensitivity and 100% negative predictive value.

DISCUSSION

The XN-HPC is a fast, easy and inexpensive test that can safely improve apheresis workflow thus possibly replacing other more expensive CD34 counts currently performed and promoting optimal timing of PBSC collection.

Super-resolution microscopy reveals ultra-low CD19 expression on myeloma cells that triggers elimination by CD19 CAR-T

Immunotherapy with chimeric antigen receptor-engineered T-cells (CAR-T) is under investigation in multiple myeloma. There are reports of myeloma remission after CD19 CAR-T therapy, although CD19 is hardly detectable on myeloma cells by flow cytometry (FC). We apply single molecule-sensitive direct stochastic optical reconstruction microscopy (dSTORM), and demonstrate CD19 expression on a fraction of myeloma cells (10.3–80%) in 10 out of 14 patients (density: 13–5,000 molecules per cell). In contrast, FC detects CD19 in only 2 of these 10 patients, on a smaller fraction of cells. Treatment with CD19 CAR-T in vitro results in elimination of CD19-positive myeloma cells, including those with <100 CD19 molecules per cell. Similar data are obtained by dSTORM analyses of CD20 expression on myeloma cells and CD20 CAR-T. These data establish a sensitivity threshold for CAR-T and illustrate how super-resolution microscopy can guide patient selection in immunotherapy to exploit ultra-low density antigens.

CD19 CAR-T cells have achieved some success in treating myeloma patients despite the limited detection of the CD19 antigen. Here, the authors show using dSTORM that 10/14 myeloma samples studied express ultra-low levels of CD19, which are sufficient for engaging CAR-T cells in vitro.

Emerging immune targets for the treatment of multiple myeloma

We reviewed emerging immune strategies for multiple myeloma (MM) therapy excluding US FDA approved drugs. In relapsed refractory MM, isatuximab (anti-CD38) monotherapy achieved overall response (OR) of 24%. Other monoclonal antibodies that have shown efficacy in combination therapy include siltuximab (OR: 66%), indatuximab (OR: 78%), isatuximab (OR: 64.5%), pembrolizumab (OR: 60%), bevacizumab (OR: 70%), dacetuzumab (OR: 39%) and lorvotuzumab (OR: 56.4%). No OR was observed with monotherapy using BI-505, siltuximab, bevacizumab, AVE-1642, figitumumab, atacicept, milatuzumab, dacetuzumab, lucatumumab, IPH2101, lorvotuzumab, BT062 and nivolumab. We included seven clinical trials on chimeric antigen receptor (CAR) T cells. CAR T-cell targets include BCMA, CD19, KLC and CD138. A recent experience of CAR T-cell (B-cell maturation antigen) therapy in advanced MM has shown global response of 100%. The future of monoclonal antibodies and adoptive T cells for MM treatment seems promising.

LMP1 expression in bone marrow trephines of patients with multiple myeloma confers a survival advantage

Multiple myeloma (MM) is a heterogeneous disease of the bone marrow (BM). Its association with Epstein-Barr virus (EBV) remains enigmatic. Aim of our study was to determine expression of latent membrane protein 1 (LMP1), aldehyde dehydrogenase 1 (ALDH1), CD117 and their association with 5-year survival in MM patients. Seven percent of cases expressed LMP1 in MM cells with no association with survival. Whereas, LMP1 expression in CD138- non-neoplastic cells was observed in 80% of the cases, conferring a survival advantage of 1.75 years (mean 3.75 ± 0.28, 95% CI 3.19-4.3). LMP1 in CD138- non-neoplastic cells was associated with CD117 expression in MM cells. Combinatorial analysis of LMP1 and CD117 stratified patients into good prognostic group LMP1+/CD117- (mean survival 4.16 ± 0.39 years) and a worst prognostic group; LMP1-/CD117+ (mean survival 1.02 ± 0.29 years). Our study showed that LMP1 expression in CD138- non-neoplastic cells of BM in MM patients confers a survival advantage.

Cellular Immunotherapy in the Treatment of Hematopoietic Malignancies

Cancer immunotherapy has been shown to be an efficacious therapeutic approach in the treatment of cancers including hematopoietic malignancies. Induction of T cell cytotoxicity against tumors by adoptive cell therapies (ACT), cancer vaccines, gene therapies, and monoclonal antibody therapies has been intensively studied. In particular, immune checkpoint blockade and chimeric antigen receptor T (CAR-T) cell therapies are the recent clinical successes in cancer immunotherapy. This article introduces the main concepts and addresses the most relevant clinical modalities of cellular immunotherapies for hematological malignancies: antigen non-specific T cell therapy, genetically modified T cell receptor (TCR) T cell therapy, chimeric antigen receptor (CAR) T cell therapy, and CAR-T cell clinical trials in leukemia, lymphoma, and multiple myeloma. Clinical trials have shown encouraging results, but future studies may need to incorporate novel CAR constructs or targets with enhanced safety and efficacy to ensure long-term benefits.

Macrophage Inhibitory Factor-1 (MIF-1) controls the plasticity of multiple myeloma tumor cells

Multiple Myeloma (MM) is the second most common hematological malignancy with a median survival of 5–10 years. While current treatments initially cause remission, relapse almost always occurs, leading to the hypothesis that a chemotherapy-resistant cancer stem cell (CSC) remains dormant, and undergoes self-renewal and differentiation to reestablish disease. Our finding is that the mature cancer cell (CD138+, rapidly proliferating and chemosensitive) has developmental plasticity; namely, the ability to dedifferentiate back into its own chemoresistant CSC progenitor, the CD138–, quiescent pre-plasma cell. We observe multiple cycles of differentiation and dedifferentiation in the absence of niche or supportive accessory cells, suggesting that soluble cytokines secreted by the MM cells themselves are responsible for this bidirectional interconversion and that stemness and chemoresistance are dynamic characteristics that can be acquired or lost and thus may be targetable. By examining cytokine secretion of CD138- and CD138+ RPMI-8226 cells, we identified that concomitant with interconversion, Macrophage Migration Inhibitory Factor (MIF-1) is secreted. The addition of a small molecule MIF-1 inhibitor (4-IPP) or MIF-1 neutralizing antibodies to CD138+ cells accelerated dedifferentiation back into the CD138- progenitor, while addition of recombinant MIF-1 drove cells towards CD138+ differentiation. A similar increase in the CD138- population is seen when MM tumor cells isolated from primary bone marrow aspirates are cultured in the presence of 4-IPP. As the CD138+ MM cell is chemosensitive, targeting MIF-1 and/or the pathways that it regulates could be a viable way to modulate stemness and chemosensitivity, which could in turn transform the treatment of MM.

Building upon the success of CART19: chimeric antigen receptor T cells for hematologic malignancies

Chimeric antigen receptor T cell (CART) therapy has dramatically changed the therapeutic prospects for B cell malignancies. Over the last decade CD19-redirected CART have demonstrated the ability to induce deep, long-lasting remissions and possibly cure patients with relapsing B cell neoplasms. Such impressive results with CART19 fostered efforts to expand this technology to other incurable malignancies that naturally do not express CD19, such as acute myeloid leukemia (AML), Hodgkin lymphoma (HL) and multiple myeloma (MM). However, to reach this goal, several hurdles have to be overcome, in particular: (i) the apparent lack of suitable targets as effective as CD19; (ii) the immunosuppressive tumor microenvironment; (iii) intra-tumoral heterogeneity and antigen-negative relapses. Therefore, new strategies that allow safer and more potent CART platforms are under development and may provide grounds for new exciting breakthroughs in the field.

The application of CAR-T cell therapy in hematological malignancies: advantages and challenges

Chimeric antigen receptor T cell (CAR-T cell) therapy is a novel adoptive immunotherapy where T lymphocytes are engineered with synthetic receptors known as chimeric antigen receptors (CAR). The CAR-T cell is an effector T cell that recognizes and eliminates specific cancer cells, independent of major histocompatibility complex molecules. The whole procedure of CAR-T cell production is not well understood. The CAR-T cell has been used predominantly in the treatment of hematological malignancies, including acute lymphoblastic leukemia, chronic lymphocytic leukemia, lymphoma, and multiple myeloma. Solid tumors including melanoma, breast cancer and sarcoma offer great promise in CAR-T cell research and development. CD19 CAR-T cell is most commonly used, and other targets, including CD20, CD30, CD38 and CD138 are being studied. Although this novel therapy is promising, there are several disadvantages. In this review we discuss the applications of CAR-T cells in different hematological malignancies, and pave a way for future improvement on the effectiveness and persistence of these adoptive cell therapies.

Anti-CD19 CAR T cells with high-dose melphalan and autologous stem cell transplantation for refractory multiple myeloma

BACKGROUND

Multiple myeloma is usually fatal due to serial relapses that become progressively refractory to therapy. CD19 is typically absent on the dominant multiple myeloma cell population but may be present on minor subsets with unique myeloma-propagating properties. To target myeloma-propagating cells, we clinically evaluated autologous T cells transduced with a chimeric antigen receptor (CAR) against CD19 (CTL019).

METHODS

Subjects received CTL019 following salvage high-dose melphalan and autologous stem cell transplantation (ASCT). All subjects had relapsed/refractory multiple myeloma and had previously undergone ASCT with less than 1 year progression-free survival (PFS).

RESULTS

ASCT + CTL019 was safe and feasible, with most toxicity attributable to ASCT and no severe cytokine release syndrome. Two of 10 subjects exhibited significantly longer PFS after ASCT + CTL019 compared with prior ASCT (479 vs. 181 days; 249 vs. 127 days). Correlates of favorable clinical outcome included peak CTL019 frequency in bone marrow and emergence of humoral and cellular immune responses against the stem-cell antigen Sox2. Ex vivo treatment of primary myeloma samples with a combination of CTL019 and CAR T cells against the plasma cell antigen BCMA reliably inhibited myeloma colony formation in vitro, whereas treatment with either CAR alone inhibited colony formation inconsistently.

CONCLUSION

CTL019 may improve duration of response to standard multiple myeloma therapies by targeting and precipitating secondary immune responses against myeloma-propagating cells.

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT02135406.

FUNDING

Novartis, NIH, Conquer Cancer Foundation.

CARs and other T cell therapies for MM: The clinical experience

Harnessing the endogenous immune system to eliminate malignant cells has long been an intriguing approach. After considerable success in the treatment of B-cell acute lymphoblastic leukemia, chimeric antigen receptor (CAR)-modified T cells have entered early clinical evaluation in the field of multiple myeloma (MM). The choice of suitable non-CD19 target antigens is challenging and a variety of myeloma-associated surface molecules have been under preclinical investigation. Most recent clinical protocols have focused on targeting B-cell maturation antigen (BCMA), and early results are promising. The trials differ in receptor constructs, patient selection, dosing strategies and conditioning chemotherapy and will thus pave the way to eventually define the optimal parameters. Other sources for autologous T-cell therapy of MM include affinity-enhanced T-cell receptor-modified cells and marrow infiltrating lymphocytes. In summary, adoptive T-cell transfer for the treatment of MM is still in its infancy, but if early response rates indicate durability, will be a paradigm changing therapeutic modality for the treatment of MM.

Successful Autologous Hematopoietic Stem Cell Transplantation Followed by Bortezomib Maintenance in a Patient with Relapsed CD138-low Multiple Solitary Plasmacytomas Harboring a 17p Deletion

Solitary bone plasmacytoma (SBP) tends to progress to multiple myeloma (MM); however, progression to multiple solitary plasmacytomas (MSP) is rare. We report a case of CD138-low MSP with 17p deletion in a patient with relapsed SBP. 17p deletion is associated with a poor outcome in patients with MM, and the low expression of CD138 in myeloma cells is associated with drug resistance and a poor prognosis. The patient was successfully treated with bortezomib plus dexamethasone induction therapy and autologous hematopoietic stem cell transplantation followed by bortezomib maintenance therapy. Consequently, bortezomib treatment was stopped and a stringent complete response has been maintained.

Blocking EZH2 methylation transferase activity by GSK126 decreases stem cell-like myeloma cells

EZH2 is a critical epigenetic regulator that is deregulated in various types of cancers including multiple myeloma (MM). In the present study, we hypothesized that targeting EZH2 might induce apoptosis in myeloma cells including stem cell-like cells (CSCs). We investigated the effect of EZH2 inhibition on MM cells using a potent inhibitor (GSK126). The results showed that GSK126 effectively abrogated the methylated histone 3 (H3K27me3) level in MM.1S and LP1 cells, and inhibited the number of live cells and colony formation in soft agar of six MM cell lines. GSK126 induced massive apoptosis in MM.1S, LP1 and RPMI8226 cells. Progressive release of mitochondrial cytochrome c and AIF into the cytosol was detected in GSK126-treated MM cells. GSK126 treatment elicited caspase-3-dependent MCL-1 cleavage with accumulation of proapoptotic truncated MCL-1. These results suggested that GSK126 triggers the intrinsic mitochondrial apoptosis pathway. Enhanced apoptosis was observed in the combination of GSK126 with bortezomib. Using ALDH and side population (SP) assays to characterize CSCs, we found that GSK126 eliminated the stem-like myeloma cells by blocking the Wnt/β-catenin pathway. The in vivo anti-tumor effect of GSK126 was confirmed by using RPMI8226 cells in a xenograft mouse model. In conclusion, our findings suggest that EZH2 inactivation by GSK126 is effective in killing MM cells and CSCs as a single agent or in combination with bortezomib. Clinical trial of GSK126 in patients with MM may be warranted.

Potential of oncolytic viruses in the treatment of multiple myeloma

Multiple myeloma (MM) is a clonal malignancy of plasma cells that is newly diagnosed in ~30,000 patients in the US each year. While recently developed therapies have improved the prognosis for MM patients, relapse rates remain unacceptably high. To overcome this challenge, researchers have begun to investigate the therapeutic potential of oncolytic viruses as a novel treatment option for MM. Preclinical work with these viruses has demonstrated that their infection can be highly specific for MM cells and results in impressive therapeutic efficacy in a variety of preclinical models. This has led to the recent initiation of several human trials. This review summarizes the current state of oncolytic therapy as a therapeutic option for MM and highlights a variety of areas that need to be addressed as the field moves forward.

Role of micro-RNAs in drug resistance of multiple myeloma

While novel therapeutic approaches have profoundly improved survival of multiple myeloma (MM) patients, drug resistance and treatment refractoriness still persists. This obstacle highly demands thorough investigation into the root and underlying molecular mechanisms to develop more effective strategies. The advent of micro-RNAs (miRNAs) in the study of cancer biology and pathogenesis in recent years has revolutionized therapy in this field and particularly opened new windows to further understanding of tumor drug resistance. However; in spite of the fact that miRNAs involvement in MM pathogenesis and progression has been substantially evidenced, miRNA investigation in MM drug resistance is still in its infancy. Our knowledge of the potential role of miRNAs in MM drug resistance comes from few recent reports confirming that some miRNAs including miR-137/197, miR-21 and miR-221/222 could negatively modulate drug sensitivity of MM cells. Further continuous researches are required to exploit miRNAs to elucidate the critical mechanisms controlling drug resistance in MM. In this review, we will highlight the most recent observations on the role of miRNAs in MM drug resistance. Moreover, approaches and insights into clinical application of miRNAs to overcome MM drug resistance will be discussed.

Multiple myeloma cancer stem cells

Multiple myeloma (MM) remains incurable despite much progress that has been made in the treatment of the disease. MM cancer stem cell (MMSC), a rare subpopulation of MM cells with the capacity for self-renewal and drug resistance, is considered to lead to disease relapse. Several markers such as side population (SP) and ALDH1+ have been used to identify MMSCs. However, ideally and more precisely, the identification of the MMSCs should rely on MMSCs phenotype. Unfortunately the MMSC phenotype has not been properly defined yet. Drug resistance is the most important property of MMSCs and contributes to disease relapse, but the mechanisms of drug resistance have not been fully understood. The major signaling pathways involved in the regulation of self-renewal and differentiation of MMSCs include Hedgehog (Hh), Wingless (Wnt), Notch and PI3K/Akt/mTOR. However, the precise role of these signaling pathways needs to be clarified. It has been reported that the microRNA profile of MMSCs is remarkably different than that of non-MMSCs. Therefore, the search for targeting MMSCs has also been focused on microRNAs. Complex and mutual interactions between the MMSC and the surrounding bone marrow (BM) microenvironment sustain self-renewal and survival of MMSC. However, the required molecules for the interaction of the MMSC and the surrounding BM microenvironment need to be further identified. In this review, we summarize the current state of knowledge of MMSCs regarding their phenotype, mechanisms of drug resistance, signaling pathways that regulate MMSCs self-renewal and differentiation, abnormal microRNAs expression, and their interactions with the BM microenvironment.

Chimeric antigen receptor T-cell therapies for multiple myeloma

Multiple myeloma (MM) is a nearly always incurable malignancy of plasma cells, so new approaches to treatment are needed. T-cell therapies are a promising approach for treating MM, with a mechanism of action different than those of standard MM treatments. Chimeric antigen receptors (CARs) are fusion proteins incorporating antigen-recognition domains and T-cell signaling domains. T cells genetically engineered to express CARs can specifically recognize antigens. Success of CAR-T cells (CAR-Ts) against leukemia and lymphoma has encouraged development of CAR-T therapies for MM. Target antigens for CARs must be expressed on malignant cells, but expression on normal cells must be absent or limited. B-cell maturation antigen is expressed by normal and malignant plasma cells. CAR-Ts targeting B-cell maturation antigen have demonstrated significant antimyeloma activity in early clinical trials. Toxicities in these trials, including cytokine release syndrome, have been similar to toxicities observed in CAR-T trials for leukemia. Targeting postulated CD19+ myeloma stem cells with anti-CD19 CAR-Ts is a novel approach to MM therapy. MM antigens including CD138, CD38, signaling lymphocyte-activating molecule 7, and κ light chain are under investigation as CAR targets. MM is genetically and phenotypically heterogeneous, so targeting of >1 antigen might often be required for effective treatment of MM with CAR-Ts. Integration of CAR-Ts with other myeloma therapies is an important area of future research. CAR-T therapies for MM are at an early stage of development but have great promise to improve MM treatment.

CARs in the Lead Against Multiple Myeloma

The recent clinical success of CD19-directed chimeric antigen receptor (CAR) T cell therapy in chronic and acute leukemia has led to increased interest in broadening this technology to other hematological malignancies and solid tumors. Now, advances are being made using CAR T cell technology to target myeloma antigens such as B cell maturation antigen (BCMA), CD138, and kappa-light chain as well as CD19 on putative myeloma stem cells. To date, only a limited number of multiple myeloma patients have received CAR T cell therapy but preliminary results have been encouraging. In this review, we summarize the recently reported results of clinical trials conducted utilizing CAR T cell therapy in multiple myeloma (MM).

Withanolide D Exhibits Similar Cytostatic Effect in Drug-Resistant and Drug-Sensitive Multiple Myeloma Cells

In spite of recent therapeutic advances, multiple myeloma (MM) remains a malignancy with very low curability. This has been partly attributed to the existence of a drug-resistant subpopulation known as cancer stem cells (CSCs). MM-CSCs are equipped with the necessary tools that render them highly resistant to virtually all conventional therapies. In this study, the growth inhibitory effects of withanolide D (WND), a steroidal lactone isolated from Withania somnifera, on drug-sensitive tumoral plasma cells and drug-resistant MM cells have been investigated. In MTT/XTT assays, WND exhibited similar cytostatic effects between drug-resistant and drug-sensitive cell lines in the nM range. WND also induced cell death and apoptosis in MM-CSCs and RPMI 8226 cells, as examined by the calcein/ethidium homodimer and annexin V/propidium iodide stainings, respectively. To determine whether P-glycoprotein (P-gp) efflux affected the cytostatic activity of WND, P-gp was inhibited with verapamil and results indicated that the WND cytostatic effect in MM-CSCs was independent of P-gp efflux. Furthermore, WND did not increase the accumulation of the fluorescent P-gp substrate rhodamine 123 in MM-CSCs, suggesting that WND may not inhibit P-gp at the tested relevant doses. Therefore, the WND-induced cytostatic effect may be independent of P-gp efflux. These findings warrant further investigation of WND in MM-CSC animal models.

A phase 1 trial of 90Y-Zevalin radioimmunotherapy with autologous stem cell transplant for multiple myeloma

This phase 1 study (clinical trial NCT00477815) was conducted to determine the maximum tolerated dose (MTD) of yttrium-90 ibritumomab tiuxetan (⁹⁰Y-Zevalin) with high dose melphalan (HDM) therapy in multiple myeloma (MM) patients undergoing autologous stem cell transplantation (ASCT). In a 3+3 trial design, 30 patients received rituximab 250 mg/m² with indium-111 ibritumomab tiuxetan (¹¹¹In-Zevalin) for dosimetry (day -22); rituximab 250 mg/m² with escalating doses of ⁹⁰Y-Zevalin (day -14); melphalan 100 mg/m² (days -2,-1) followed by ASCT (day 0) and sargramostim (GM-CSF, day 0) until neutrophil engraftment. Each patient's ¹¹¹In-Zevalin dosimetry data were used to calculate the dose of ⁹⁰Y-Zevalin (in mCi) to deliver 10, 12, 14, 16, 18 or 20 Gy to the liver. Dose limiting toxicities were seen in 3 patients. The overall response rate was 73% (22/30) with stringent complete response in 2 patients; complete response, 5; very good partial response, 12; and partial response, 3. The median PFS was 16.5 months and the median overall survival was 63.4 months. In MM, the MTD of ⁹⁰Y-Zevalin with HDM is 18 Gy to the liver. The addition of radiation with novel delivery methods such as radioimmunotherapy combined with standard transplant regimens warrants further study.

Cutting edge genomics reveal new insights into tumour development, disease progression and therapeutic impacts in multiple myeloma

Multiple Myeloma (MM) is a haematological malignancy characterised by the clonal expansion of plasma cells (PCs) within the bone marrow. Despite advances in therapy, MM remains a largely incurable disease with a median survival of 6 years. In almost all cases, the development of MM is preceded by the benign PC condition Monoclonal Gammopathy of Undetermined Significance (MGUS). Recent studies show that the transformation of MGUS to MM is associated with complex genetic changes. Understanding how these changes contribute to evolution will present targets for clinical intervention. We discuss three models of MM evolution; the linear, the expansionist and the intraclonal heterogeneity models. Of particular interest is the intraclonal heterogeneity model. Here, distinct populations of MM PCs carry differing combinations of genetic mutations. Acquisition of additional mutations can contribute to subclonal lineages where "driver" mutations may influence selective pressure and dominance, and "passenger" mutations are neutral in their effects. Furthermore, studies show that clinical intervention introduces additional selective pressure on tumour cells and can influence subclone survival, leading to therapy resistance. This review discusses how Next Generation Sequencing approaches are revealing critical insights into the genetics of MM development, disease progression and treatment. MM disease progression will illuminate possible mechanisms underlying the tumour.