Myeloma Patient Samples Research Articles

LILRB4 regulates multiple myeloma development through STAT3-PFKFB1 pathway

Although multiple myeloma (MM) responds well to immunotherapeutic treatment, certain portions of MM are still unresponsive or relapse after immunotherapy. Other immune molecules are needed for the immunotherapy of MM. Here, we revealed that leukocyte immunoglobulin-like receptor B4 (LILRB4) was highly expressed in multiple myeloma cell lines and patient samples and that the expression of LILRB4 was adversely correlated with the overall survival of MM patients. Knockdown of LILRB4 efficiently delayed the growth of MM cells both in vitro and in vivo. Mechanistically, IKZF1 transactivated LILRB4 expression to trigger the downstream of STAT3-PFKFB1 pathways to support MM cell proliferation. Blockade of LILRB4 signaling by blocking antibodies can effectively inhibit MM progression. Our data show that targeting LILRB4 is potentially an additional therapeutic strategy for the immunotherapeutic treatment of MM.

Abstract 1691: p300 catalytic inhibition selectively targets IRF4 oncogenic activity in multiple myeloma

Abstract Multiple myeloma (MM), an incurable plasma cell malignancy, is addicted to oncogenic transcription factor (TF) IRF4 signaling. Lineage TFs like IRF4 are difficult to drug but represent high value oncology targets owing to the depth and context selectivity of their genetic dependency. Using a transcription regulatory network (TRN) based approach to integrate a high dimensional multi-platform dataset, we defined the key regulatory activity of IRF4 and its druggable co-factors. This unbiased analysis identified p300 lysine acetyl transferase (KAT) function as the nearest selective neighbor for therapeutic intervention, with more potent and selective effects than historically observed with p300/CBP bromodomain inhibitors. To further probe this biology, we developed a highly selective inhibitor of the KAT domain of p300 and its close homolog CBP. p300 KAT inhibition led to selective downregulation of IRF4 at the mRNA and protein level as well as reduction in acetylation at highly specific sites co-localized with IRF4, in contrast to more general agents like BET inhibitors. Gene expression reduction was most pronounced at IRF4/p300 co-bound genes, in particular IRF4 itself and MYC. IRF4 and p300 also directly bind to each other and other key MM nodes regulating them at the chromatin, mRNA, and protein levels. p300 KAT inhibition exhibits strong antiproliferative activity across in vitro MM models regardless of cytogenetics or resistance to other therapies. Moreover, this relationship is mediated by the KAT domain and not its acetyl-lysine recognizing bromodomain. Comparative pharmacology studies found that a p300 KAT inhibitor downregulated the IRF4 TRN and induced apoptosis in MM cells more effectively than existing standard of care agents, including IMiDs and glucocorticoid receptor agonists, or p300/CBP bromodomain inhibitors. Combinations of a p300 KAT inhibitor with clinically active molecules such as IMiDs and glucocorticoid agonists showed synergistic impacts on reducing key MM TFs and cell line viability. Ex vivo treatment of primary patient samples demonstrated broad anti-proliferative activity with loss of IRF4 and induction of apoptosis in relapsed-refractory MM patient samples, independent of prior lines of therapy. Importantly, the induction of MM cell apoptosis occurs in the milieu of CD138 negative bone marrow stromal cells while also sparing them from toxicity, supporting a potential therapeutic index. Finally, p300 KAT inhibition demonstrated activity in in vivo MM models with robust tumor growth inhibition at tolerated doses and exposures correlated to reduced p300-dependent substrate acetylation. IRF4 dependency is a hallmark of MM that has been challenging to target with existing therapies, motivating further development of p300 KAT targeting therapeutics. Citation Format: Michael R. McKeown, Giulia Giorgetti, Walter F. Lenoir, Marek J. Kobylarz, Tamara D. Hopkins, Wayne L. Glore, Michelle G. Shum, Yare Calderon, Kameron R. Mori, Hua Gao, Luis A. Carvajal, Nikolaus D. Obholzer, Benjamin W. Trotter, Christopher D. Dinsmore, Nikhil C. Munshi, Peter B. Rahl, Mariateresa Fulciniti, Charles Y. Lin. p300 catalytic inhibition selectively targets IRF4 oncogenic activity in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1691.

Deciphering the Exact Sequence of Endogenous Soluble B Cell Maturation Antigen and Unbiased Quantitation in Multiple Myeloma Patient Samples by LC-MS.

B-cell maturation antigen is a pivotal therapeutic target for multiple myeloma (MM). Membrane-bound BCMA can be cleaved by γ-secretase and shed as soluble BCMA (sBCMA). sBCMA can act as a neutralizing sink to compete with drug, as well as serve as a diagnostic/prognostic biomarker for MM. Antibody-capture based methods, such as enzyme-linked immunosorbent assay (ELISA) and immunoaffinity-liquid chromatography-multiple reaction monitoring (IA-LC-MRM), have been reported and well adopted to measure sBCMA in clinical samples. However, both methods are biased by capturing antibodies. We have used various LC-MS workflows to characterize and quantify endogenous sBCMA in MM patient samples, including bottom-up peptide mapping, intact analysis, IA-based, and reagent-free (RF)-LC-MRM quantitation. We have confirmed that sBCMA contains a variable N-terminus and a C-terminus that extends to the transmembrane domain, ending at amino acid 61. Leveraging an in-house synthesized G-1-61 sBCMA recombinant standard, we developed a RF-LC-MRM method for unbiased sBCMA quantitation in MM patient samples. By comparing the results from RF-LC-MRM with ELISA and IA-LC-MRM, we demonstrated that RF-LC-MRM measures a more complete pool of endogenous sBCMA compared to the antibody-based methods. This work fills the knowledge gap of the exact sequence of endogenous sBCMA for the first time, which differs from the current commercially available standard. Additionally, this work highlights the necessity of identifying the actual sequence of an endogenous soluble target such as sBCMA, both for bioanalytical purposes and to underpin pharmacodynamic measurements.

A p53 score derived from TP53 CRISPR/Cas9 HMCLs predicts survival and reveals a major role of BAX in the response to BH3 mimetics

AbstractTo establish a strict p53-dependent gene-expression profile, TP53−/− clones were derived from TP53+/+ and TP53−/mut t(4;14) human myeloma cell lines (HMCLs) using CRISPR/Cas9 technology. From the 17 dysregulated genes shared between the TP53−/− clones from TP53+/+ HMCLs, we established a functional p53 score, involving 13 genes specifically downregulated upon p53 silencing. This functional score segregated clones and myeloma cell lines as well as other cancer cell lines according to their TP53 status. The score efficiently identified samples from patients with myeloma with biallelic TP53 inactivation and was predictive of overall survival in Multiple Myeloma Research Foundation–coMMpass and CASSIOPEA cohorts. At the functional level, we showed that among the 13 genes, p53-regulated BAX expression correlated with and directly affected the MCL1 BH3 mimetic S63845 sensitivity of myeloma cells by decreasing MCL1-BAX complexes. However, resistance to S63845 was overcome by combining MCL1 and BCL2 BH3 mimetics, which displayed synergistic efficacy. The combination of BH3 mimetics was effective in 97% of patient samples with or without del17p. Nevertheless, single-cell RNA sequencing analysis showed that myeloma cells surviving the combination had lower p53 score, showing that myeloma cells with higher p53 score were more sensitive to BH3 mimetics. Taken together, we established a functional p53 score that identifies myeloma cells with biallelic TP53 invalidation, demonstrated that p53-regulated BAX is critical for optimal cell response to BH3 mimetics, and showed that MCL1 and BCL2 BH3 mimetics in combination may be of greater effectiveness for patients with biallelic TP53 invalidation, for whom there is still an unmet medical need.

Single Cell Multi-Omic Correlation of Single Nucleotide Variants, Copy Number Variation and Surface Epitopes for Clonal Profiling of Myeloma

Introduction Multiple myeloma (MM) is a cancer of plasma cells with approximately 200,000 new diagnoses each year and a 54% 5-year overall survival rate. As myeloma cells expand, clonal genetic differences lead to relapse due to acquired resistance in 100% of patients, mandating regular, long-term surveillance. Improvements in precision medicine for MM have come from monoclonal antibodies and antibody-drug conjugates that specifically target the offending cells. However, while existing diagnostic modalities offer exquisite sensitivity, they are unable to correlate subclonal genetic changes and putative antibody targets on refractory myeloma cells, leaving the clinician to use their best judgment on salvage therapy which can lead to unnecessary expense and toxicity to patients due to ineffective treatment. Specifically knowing actual targets on refractory MM cells would better facilitate precision medicine and potentially improve outcomes. Methods Cryopreserved, human MM patient samples were processed on the Mission Bio Tapestri platform, enabling simultaneous single cell quantification of subclones by single nucleotide variants (SNV), copy number variants (CNV), and surface protein analysis. These single time point samples were thawed from frozen bone marrow mononuclear cells previously enriched for CD38, stained with a 45-plex antibody-oligo cocktail to label common heme-specific surface markers for sequencing analysis, and processed with a 733-plex DNA primer panel that combined whole-genome CNV coverage with MM gene hotspots. Sequencing was performed on an Illumina system with the raw data being analyzed using Mission Bio proprietary algorithms. Results We show complex clonal evolution of MM in individual samples as copy gains and losses that were sequentially acquired and correlated with expression changes of MM markers. Across the cases analyzed, complex branching phylogenetic trees were reconstructed with as many as five subclones and clear associated shifts in MM-marker expression. When averaged across subclones, each sample had CNV profiles that matched patient bulk genome-wide array records, ranging from a single gene-level copy gain to arm-level gains and losses across the majority. The progression of protein expression within different samples could be mapped together on a single plot and correlated with generally higher MM-markers as subclonal genetic variants were acquired, though occasional branches saw reversal. The fraction of other cell phenotypes, such as T-cells and those with low viability, decreased within subclones as mutational burden grew. Conclusion This high-resolution, single cell assay offers a potential new modality for the diagnosis and surveillance of patients with suspected MGUS, SGUS or high-risk MM. We have demonstrated: 1) exceptional results from cryopreserved human specimens, 2) the ability to use genetic lesion profiling to positively identify subclonal MM and, most importantly, 3) correlate cell surface protein expression of potential therapeutic targets with each clonal and subclonal population

Characterization of JNJ-79635322, a Novel BCMAxGPRC5DxCD3 T-Cell Redirecting Trispecific Antibody, for the Treatment of Multiple Myeloma

Background: Multiple myeloma (MM) is a genetically complex and heterogenous malignancy with a poor survival rate and accounts for approximately 10% to 15% of all hematologic cancers. Despite advances in myeloma therapy, MM remains incurable. Deep and durable clinical responses have been observed when targeting the tumor associated antigens BCMA and GPRC5D with immunotherapies. Additionally, data presented at ASCO this year demonstrated a further improvement in ORR when BCMA and GPRC5D bispecifics were given in combination to relapsed or refractory MM patients. These data suggest that broader antigen coverage by redirecting T cells to two tumor surface antigens is an effective means to harness the immune system to deplete cancer cells. Targeting two tumor antigens may also reduce the likelihood of antigen escape as a primary reason for relapse. Here, we describe JNJ-79635322, a trispecific antibody targeting B-cell maturation antigen (BCMA) and G-Protein-coupled receptor class 5 member D (GPRC5D), which are both highly expressed on plasmablasts and plasma cells in myeloma patient samples. Dual antigen recognition on plasma cells with a trispecific T-cell engaging antibody engineered with a CD3 arm has the potential to enhance tumor binding through avidity that could result in efficient depletion of malignant clonal populations and prevent tumor antigen loss mediated resistance. Methods: JNJ-79635322 is a trispecific antibody composed of an anti-CD3 binding domain an anti-BCMA binding domain, and an anti-GPRC5D binding domain. It was selected based on biophysical assessment and showed activity in multiple myeloma models. Results: JNJ-79635322 induced potent cytotoxicity in various myeloma cell lines in vitro with concomitant T-cell activation. Importantly, JNJ-79635322 was able to deplete both dual (BCMA and GPRC5D) and single (BCMA or GPRC5D) target expressing cells efficiently. In addition, dose dependent depletion of H929 myeloma cells was observed in a more physiological healthy fresh whole blood co-culture assay. In vivo, JNJ-79635322 exhibited potent antitumor activity compared to vehicle and antibody controls in a murine MM xenograft prevention model (single target expressing clonal H929 cells) and two tumor regression models (RPMI 8226 and MM.1S cells). Conclusion: JNJ-79635322 is a potential first-in-class trispecific antibody targeting BCMA and GPRC5D with the ability to deplete dual and single target expressing MM clones in preclinical studies vitro and in vivo. A Phase 1 dose-escalating study of JNJ-79635322 in myeloma patients is ongoing (NCT05652335).

Prospective Molecular Characterization of Multiple Myeloma Patient Samples Identifies High-Risk Patients and Informs Treatment Sequences through Resistance Mechanisms to Immunotherapies

Introduction. Multiple myeloma (MM) genetic diagnostics has traditionally been performed using fluorescence in situ hybridization (FISH), giving prognostic information based on immunoglobulin (Ig) translocations and key copy number abnormalities such as 1p, 1q, and 17p. However, in recent years it has become clear that more mutations, biallelic events, and focal deletions are also prognostically important and can be captured better through molecular techniques such as DNA sequencing. In addition, as targeted and immunotherapies become standard, monitoring the molecular targets will be important in determining the optimal sequence of therapies. Methods. Bone marrow aspirates from patients with MGUS/amyloid (n=3), smoldering MM (n=3), newly diagnosed MM (n=15), or progression/relapse MM (n=33) were collected. All patients were enrolled in the Indiana Myeloma Registry and consented for use of data for research purposes. CD138+ MACS cell separation was performed in a clinical pathology laboratory and DNA was extracted from CD138+ cells and patient-matched buccal swabs. 100 ng DNA from both the tumor and control sample were processed using the HyperPlus kit (KAPA Biosystems) and hybridized to the Myeloma Genome Project (MGP) sequencing panel in a CLIA-certified laboratory. The panel consisted of 228 genes for mutation and copy number analysis, as well as the immunoglobulin and MYC loci for translocation analysis. Samples were sequenced using paired-end reads to a median depth of 1063x. Data were analyzed using a clinical workflow and genomic abnormalities reported by a pathologist. Results. Of the 54 patients, Ig translocations were detected in 30 and included the known t(4;14), t(6;14), t(11;14), t(14;16) and t(12;14) as well as rare Ig translocations to partners such as GADD45B, LYN, PPCDC, and RCBTB2, of which over-expression of GADD45B and LYN are potentially targetable. A complex t(1;8;11;14) was also detected involving CCND1, MYC and the IGH loci which would not have been detectable by FISH. High-risk markers, such as gain/amp1q (22.2%) and deletion/mutation TP53 (16.6%) were detected including biallelic TP53 alterations in 5 patients (9.3%), which were mostly deletion plus mutation (4/5) and would not have been detected by traditional techniques. Of the MM patients who had been previously treated (n=33), 27 had received an IMiD and 30 had received a proteasome inhibitor. One patient showed mutation of CRBN (p.N236D) in conjunction with del3p and another patient with mutation of CUL4B (p.E277Ter) with delX indicating complete inactivation of the genes as a resistance mechanism to IMiDs. In addition, 17 patients had received an immunotherapeutic regimen including anti-CD38 or anti-BCMA. Of those that had received an anti-CD38 treatment (n=17), three had deletion of 4p (the location of CD38) including one patient, who had received three previous anti-CD38 regimens, with focal deletion of CD38. Six patients had also received anti-BCMA therapy, of which one had a mutation in the gene encoding BCMA, TNFRSF17, resulting in premature termination within the extracellular domain (p.S48Ter) in 42% of cells. This sample came from a patient who relapsed after an initial response to a BCMA CAR-T, followed by a progression occurring quickly while on a BCMA bispecific antibody Teclistamab, suggesting the loss of BCMA expression as a mechanism of resistance in both treatments. Interestingly, two patients harbored somatic mutations in the transmembrane domains of either CD38 (p.S29I) or TNFRSF17 (p.L60S) prior to the start of the respective treatments indicating that not all mutations seen in these genes are a result of treatment resistance. Conclusions. DNA sequencing approaches are cost-effective alternatives to FISH, the current standard diagnostic technology, to detect genomic abnormalities in multiple myeloma and they can identify clinically meaningful markers related to prognosis and treatment, particularly in the emerging era of immunotherapeutics where antigen evasion is a key mechanism of molecular resistance.

Abstract 207: Ex vivo modeling of multiple myeloma: A novel drug sensitivity screening platform

Abstract Multiple Myeloma (MM) is a heterogeneous malignancy characterized by abnormal clonal plasma cell infiltration in the bone marrow. It is the second most common hematologic malignancy, after non-Hodgkin’s Lymphoma. This deadly disease globally affects 1 to 5 people in every 100,000 people each year. After initial diagnosis, the 5-year survival rate is 44% because there is no curative therapy, and most patients will eventually experience relapse, and some become refractory. Large inter-patient and intra-patient genetic heterogeneity limit the identification of universal drivers of MM. However, several oncogenic dependencies such as primary events related to driver gene mutations and primary translocations can be targeted for better treatment strategies for R/R multiple myeloma. To establish a robust drug sensitivity screening platform, both MM cell lines and cryopreserved primary MM patient samples were used. MM cell lines screen with H929, MM1R and RPMI-8226 was performed to narrow down optimal concentrations of investigative test agents. During assay development, a panel of FDA approved agents for relapsed MM including panobinostat, bortezomib, melphalan, omacetaxine, and selinexor were tested. The cells were seeded at 50,000 cells per well in triplicates in a 96-well plate on day 0. The test agents were added in 9 concentrations with the top concentration being 25 uM with 2-fold dilutions. After 6- days of incubation, a luminescent cell viability assay was performed to calculate relative viability with drug treatment and IC50 was computed by fitting data using a standard four-parameter logistic model. For primary multiple myeloma samples, bone marrow aspirates were collected from Multiple Myeloma patients procured from different providers. BM mononuclear (BMMNC) cells were separated by Ficoll-Hypaque density sedimentation. Unfractionated BMMNC cells were used in these assays to preserve intra-tumor heterogeneity. Primary cells were seeded in triplicates per dose point on day 0 in Champions’ proprietary media. The test agents were also added on day 0 and were incubated for 6 days. On Day 6, the relative cell viability was measured based on Cell Titer Glo readout. The cryopreserved primary MM patient samples were viable in culture for the entire assay duration validating assay feasibility. A panel of FDA approved, standard of care drugs were tested in numerous clinically well-annotated and diverse MM patient models. Primary model selection was based on disease burden including plasma cell count from Core Biopsy and BM aspirates. Multiparametric flow cytometric immunophenotyping was also performed in these primary samples using monoclonal antibodies against CD56, CD19, CD117, CD27, CD138, and CD38. For the first time, we demonstrate the feasibility of a novel, ex-vivo drug sensitivity screening platform with cryopreserved, primary multiple myeloma cells from diverse, clinically well-annotated patient samples. Citation Format: Vaishnavi Sambandam, Sharvari Inamdar, Haoting Hsu, Brandon Walling, Paolo Schiviani, Abhay Andar, Marianna Zipeto, Michael Ritchie, Karin Abarca Heidemann, Maria Mancini. Ex vivo modeling of multiple myeloma: A novel drug sensitivity screening platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 207.

Phenotypic deconvolution in heterogeneous cancer cell populations using drug-screening data

Tumor heterogeneity is an important driver of treatment failure in cancer since therapies often select for drug-tolerant or drug-resistant cellular subpopulations that drive tumor growth and recurrence. Profiling the drug-response heterogeneity of tumor samples using traditional genomic deconvolution methods has yielded limited results, due in part to the imperfect mapping between genomic variation and functional characteristics. Here, we leverage mechanistic population modeling to develop a statistical framework for profiling phenotypic heterogeneity from standard drug-screen data on bulk tumor samples. This method, called PhenoPop, reliably identifies tumor subpopulations exhibiting differential drug responses and estimates their drug sensitivities and frequencies within the bulk population. We apply PhenoPop to synthetically generated cell populations, mixed cell-line experiments, and multiple myeloma patient samples and demonstrate how it can provide individualized predictions of tumor growth under candidate therapies. This methodology can also be applied to deconvolution problems in a variety of biological settings beyond cancer drug response.

Targeted Nanotherapy of Hematologic Malignancies Using Gold Nanoframework-Based Delivery of a Novel NF-Kb Inhibitor

Hematologic malignancies account for one third of all cancers worldwide. Traditional chemo- or radiotherapy of these often highly aggressive cancers is limited by poor bio-selectivity and a narrow safety window, correlating with a risk for serious side effects and the development of refractory disease. Precision molecular therapeutics and highly targeted nanotechnological approaches can be employed as an alternative to overcome these challenges and successfully produce targeted anti-tumor responses, especially in the setting of disseminated disease. Herein, we report the formulation of a therapeutic nanocomposite comprising of a hyaluronic acid (HA)-coated gold nanoframework delivery system and encapsulated IT848, a novel small molecule with potent anti-lymphoma and -myeloma properties that targets the transcriptional activity of nuclear factor kappa B (NF-κB). We show that IT848 inhibits NF-κB activity through inhibition of DNA binding of all five NF-κB subunits. IT848 treatment of lymphoma and myeloma cell lines and patient samples inhibited proliferation and induced caspase-dependent and independent apoptosis. In addition to direct NF-κB inhibitory effects, IT848 treatment altered the redox homeostasis of cancer cells through depletion of the reduced glutathione pool, selectively inducing oxidative stress in cancer but not in healthy cells. IT848 significantly improved survival in an immunocompetent mouse model of multiple myeloma when combined with PD-1 inhibition, and correlative immune studies revealed that this clinical benefit was associated with suppression of regulatory T cell infiltration of the tumor microenvironment. We optimized the safety profile as well as the efficacy of IT848 by adapting HA-coated gold nanoparticles as an integrative platform for CD44-targeted delivery of IT848. Among a plethora of functionalized nanomaterials used for drug delivery, gold nanoparticles/nanoframeworks (AuNF) demonstrate excellent efficacy as drug carriers, photothermal or contrast agents, and radiosensitizers. Furthermore, easy synthesis and apt control over particle size, shape, porosity, and surface chemistry, together with their excellent biocompatibility make these particles ideal vehicles for small molecules such as IT848. HA-functionalized and IT848-loaded AuNFs were synthesized via a simple, reproducible, and inexpensive liposome-assisted technique that can easily be scaled up, a critical feature for clinical relevance. AuNFs were loaded with IT848 and surface functionalized with HA to formulate nanotherapeutics that were able to efficiently deliver the payload with high specificity to myeloma and lymphoma cell lines in vitro. In vivo studies characterized biodistribution, pharmacokinetics and safety of HA-AuNFs, and we demonstrated significantly superior specificity and efficacy of HA-AuNF formulated IT848 versus free IT848 in lymphoma mouse models (Figure 1). Our results indicate that active targeted delivery of IT848 using AuNFs via HA-CD44 ligand-receptor mediated endocytosis is a promising strategy to augment IT848 uptake by CD44-overexpressing tumor cells, mitigate rapid clearance of nanoparticles from the body and yield a highly desirable and sustained (as compared to free IT848) anti-tumor therapeutic effect. Our HA-AuNF-based drug delivery approach offers infrequent (weekly) low dose administration and robust efficacy with minimal toxicity risk. In fact, i.v. administration of IT848-loaded HA-AuNFs once or twice a week was not associated with any signs of toxicity, while traditional intraperitoneal administration of free IT848 twice a week over a 2-week period typically leads to ascites development in up to 50% of the recipients. Collectively, both our in vitro and in vivo results affirm that our AuNF system facilitates targeted drug delivery, improving the drug safety profile, and enhancing the efficacy of our novel NF-kB inhibitor molecule with minimal dosing. Our data therefore provide a strong preclinical rationale for the clinical development of HA-AuNF formulated IT848 as a therapeutic modality for the treatment of hematological malignancies. Additional studies are needed to develop curative treatment regimens based on synergistic, highly active, and well-tolerated combinatorial approaches with other targeted agents such as immune checkpoint inhibitors, hypomethylating agents, or CAR-T cells. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Novel Antigens LMA and Kma Are Expressed on Malignant Bone Marrow Plasma Cells from Patients with Relapsed Refractory Multiple Myeloma and Plasma Cell Dyscrasias

Introduction Previous studies have identified the lambda myeloma antigen (LMA) and kappa myeloma antigen (KMA) on the surface of malignant plasma cells in myeloma patient bone marrow samples, human myeloma cell lines and other plasma cell dyscrasias1-3. LMA and KMA are not present on normal B cells and are found on occasional mononuclear cells in tonsillar tissue and secondary mucosal lymphoid tissue. Targeting KMA and LMA through cellular and other immunological therapies has the potential advantage of leaving a population of normal plasma cells untouched and minimising the risk of serious post-treatment infection. Characteristics of the antibodies called KappaMab and LambdaMabs (10B3 and 7F11) that bind to specific conformational epitopes in the constant regions of these surface-bound light chains have been described in clinical trials and in vitro experiments1, 2, 4-6. Here, we present data on a larger series of patients with plasma cell dyscrasias, demonstrating the expression of LMA on plasma cells from patients in whom myeloma evolves from monoclonal gammopathy of unknown significance (MGUS). We also describe the difference in phenotype between LMA and KMA expressing malignant plasma cells and the frequent expression of KMA in relapsed refractory myeloma patient (RRMM) samples. Methods Patient BM samples (κ=49 and λ=31) were analysed using multiparametric FCM immunophenotyping with APC labelled LambdaMab (10B3) and KappaMab Fab'2 fragments, CD38, CD138, CD269 (BCMA), CD319 (SLAM F7), CD56 and CD45 monoclonal antibodies. Plasma cells were identified as previously described by initial gating using CD38 and CD138. LMA and KMA expression was determined and compared with the other cell markers. Results Nine of 12 (75%) newly diagnosed λ-type patients with MGUS or SMM expressed LMA on the surface of BM plasma cells. Longitudinal data from two patients was available. One patient showed LMA expression and antigen density increasing on the surface of bone marrow plasma cells during progression from MGUS (2020) to smoldering myeloma (SMM) (2022) (% of plasma cells positive for LMA rose from 61% to 92%, antigen density increased from 532 to 5164 molecules of PE/cell). In a second individual, LMA expression and antigen density increased on bone marrow plasma cells during progression from SMM (2020) to myeloma (2022) (% of plasma cells positive for LMA rose from 94% to 100%, antigen density increased from 3981 to 8941 molecules of PE/cell). KMA expression continued to be observed on plasma cells in 4 of 6 patients after autologous stem cell transplant. KMA was expressed in 86% of patients with ĸRRMM (n=14). LMA expression was observed in 2 of 4 patients with λRRMM. Both KMA and LMA antigen densities were higher than BCMA in the RRMM population (KMA mean 1802, range 468-7943 vs BCMA mean 1306, range 350-2630 molecules of PE/cell), (LMA mean 2439, range 263-6664 vs BCMA mean 817, range 537-1065 molecules of PE/cell). Conclusions In an enlarged cohort of patients with myeloma, we have confirmed that KMA and LMA are expressed at all stages of disease. Our data examining longitudinal expression in individual patients suggests that expression of LMA on BM plasma cells increases from MGUS to MM. The majority of patients with relapsed refractory kappa myeloma expressed KMA. Further data is required to confirm LMA expression in this population. The antigen density of both LMA and KMA is higher than BCMA on RRMM BM plasma cells. KMA and LMA expression is independent of serum Ig and FLC levels and % marrow plasma cells. These data show that KappaMab and LambdaMab have therapeutic potential in the treatment of myeloma patients, especially in the setting of relapsed refractory disease where the combination of high antigen density and restriction of the target antigen to the malignant subpopulation of plasma cells will confer valuable clinical benefit.

Newly Diagnosed, Untreated, Multiple Myeloma (MM) Patient Samples Already Harbor Cereblon (CRBN) Exon 10 Deletions Associated with Drug Resistance

Background: Acquisition of drug resistance, particularly immunomodulatory drugs (IMiDs) in MM is one of the most important challenges in patient treatment today. Early on in the disease, the plasma cells in the MM clone are often sensitive to chemotherapy. However, over time, after exposure to chemotherapy, the cells acquire increasing genomic complexity and mutations leading to resistance to therapy and ultimately patient death. Cereblon (CRBN) is a binding protein, which is required for the action of the widely used IMiDs such as lenalidomide and pomolidomide. CRBN is also essential to the newer CRBN E3 ligase modulator drugs and proteolysis targeting chimeras. We recently described an algorithm based on digital gene expression profiling of purified CD138(+) MM cells from patients at different clinical stages that we term the "MM-IP-7", which correlated with clinical drug resistance, poor survival, and disease progression following combination treatment containing IMIDs and/or PIs (XY Zhu et al, eHaem 2022). Given the recent description of genetic changes in the CRBN gene that are associated with IMiD resistance particularly the exon 10-spliced CRBN transcripts that increase in incidence in parallel with IMiD-refractory states (S. Gooding et al, Blood 2021), we sought to build an integrated, single-platform test to measure both gene expression levels and genetic deletions. Methods: We designed a novel CRBN splicing isoform probe with homology to both exon 9 and exon 11. This probe will thus capture CRBN mRNA sequences in which exon 10 is deleted and portions of exons 9 and 11 and juxtaposed. We also included probes to CRBN overall (Exons 5 and 6). These probes were combined with the MM-IP-7 probes to create a dual gene expression and genetic assay that was used to analyze 30 cases of newly diagnosed MM, 30 cases of end stage MM, and 3 MM cell lines (MM1.S, OPM2, XG1). To define increased exon 10 deleted allele frequency, we calculated the ratio of exon 10 deletion/total exon 10. Cases with apparent exon 10 deletion by expression profiling, were further evaluated with RT-PCR. Results: 40% MM samples in the end stage group versus 23% of samples in the newly diagnosed group were identified with more than 20% exon 10 deleted mRNA as compared to total CRBN mRNA levels. Three cases were shown to have more than 45% exon 10 deleted mRNA, including two newly diagnosed cases and one end stage case. RT-PCR confirmed exon 10 deletion in a newly diagnosed patient sample with sufficient remaining RNA that was tested (cloning and sequencing for confirmation are underway). Cell line results showed very low exon 10 splicing variant, which correlated with our mRNAseq data for these lines. Conclusions: Our findings demonstrate that inclusion of probes bridging CRBN exon 10 deletion with homology to exons 9 and 11, is feasible approach to use on the gene expression platform, which allows for combined evaluation of expression and genetic changes. CRBN exon 10 deletion is a known treatment resistance feature in MM, which may already be present at diagnosis and selected by subsequent therapy with possible therapeutic planning implications. Additional studies to confirm the results and expand the study set are underway.

Comparison of the Analytical Performance of EXENT®, a Mass Spectrometry-Based Assessment of M-Protein, to SPEP and NGS-Based MRD in Multiple Myeloma Patient Samples

Background: serum protein electrophoresis (SPEP) and B-cell receptor next generation gene sequencing (NGS) are methodologies used to monitor the amount of a monoclonal protein in multiple myeloma (MM) patients and to evaluate minimal residual disease (MRD), respectively. Mass spectrometry (MS) is a methodology currently being explored to provide a serum/plasma-based quantitative assessment of M-protein, which could also serve as a surrogate of MRD. Here we present the analytical performance of SPEP and MRD compared to the MALDI-TOF MS-based assay EXENT. Methods: SPEP, NGS (Clonoseq v 2.0, Adaptive Biotechnologies), and MS (EXENT®, The Binding Site) assays were performed to assess M-protein in 65 serum samples from 22 MM patients who participated in a phase 3 clinical trial (CASTOR, NCT02136134), in which patients received Daratumumab, Bortezomib and Dexamethasone (DVd) or Bortezomib and Dexamethasone (Vd). Irrespective of treatment, serum samples collected at three time points were selected from each subject, including 1) baseline prior to treatment, 2) available sample at or most approximately prior to the first confirmed complete response (CR) according to IMWG criteria with SPEP equaled 0, and 3) last available sample prior to disease progression (PD) with SPEP equaled 0. M-protein concentration measured by EXENT was compared to that measured by SPEP. Data was analyzed by using either all obtained values (n=62) or only non-zero values (n=18) by EXENT or SPEP. NGS-based MRD results (n=26) used for the comparison were those sampled within 60 days of the samples used for the EXENT analysis. Results: M-protein concentration by EXENT significantly correlated with SPEP measurements by using all obtained values (r=0.986, p<0.0001). The correlation was also significant when non-zero values were used in the analysis (r=0.969, P<0.0001). The lower limit of quantification (LLOQ) of EXENT was 0.015 g/L, while that of SPEP was approximately 1 g/L. With the better sensitivity, EXENT was able to detect M-protein up to 167 days prior to PD when SPEP detected none (figure). MS-based assessments were concordant with NGS-based MRD results. A 76.9% (20 of 26) agreement was observed when comparing EXENT with MRD at a sensitivity of 10-5. EXENT purified samples were reflexed to analysis by the more sensitive MS-based methodology LC-MS. The agreement between LC-MS and MRD at a sensitivity of 10-6 was 92.3% (24 of 26). In addition, we observed several useful features unique to MS-based assays. These include distinguishing daratumumab from the endogenous M-protein, detecting isotype switching, and the ability of detecting light chain glycosylation. Conclusion: EXENT significantly correlated with SPEP while EXENT demonstrated a higher sensitivity in quantification of M-protein in serum than SPEP. A high degree of agreement was observed between EXENT/LC-MS and NGS-based MRD. With its non-invasive nature and early detection of relapse, EXENT can be used as a complementary assay in MM patient management to guide bone marrow based MRD assessment. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Inhibition of NF-κB DNA Binding Suppresses Myeloma Growth via Intracellular Redox and Tumor Microenvironment Modulation.

Multiple myeloma is a plasma cell malignancy that is still largely incurable, despite considerable progress in recent years. NF-κB is a well-established therapeutic target in multiple myeloma, but none of the currently available treatment options offer direct, specific pharmacologic targeting of NF-κB transcriptional activity. Thus, we designed a novel direct NF-κB inhibitor (IT848) as a drug candidate with strong potential for clinical translation and conducted comprehensive in vitro and in vivo mechanistic studies in multiple myeloma cell lines, primary multiple myeloma cells, xenograft models, and immunocompetent mouse models of multiple myeloma. Here, we show that IT848 inhibits NF-κB activity through inhibition of DNA binding of all five NF-κB subunits. IT848 treatment of multiple myeloma cell lines and patient samples inhibited proliferation and induced caspase-dependent and independent apoptosis. In addition to direct NF-κB inhibitory effects, IT848 treatment altered the redox homeostasis of multiple myeloma cells through depletion of the reduced glutathione pool, selectively inducing oxidative stress in multiple myeloma but not in healthy cells. Multiple myeloma xenograft studies confirmed the efficacy of IT848 as single agent and in combination with bortezomib. Furthermore, IT848 significantly improved survival when combined with programmed death protein 1 inhibition, and correlative immune studies revealed that this clinical benefit was associated with suppression of regulatory T-cell infiltration of the bone marrow microenvironment. In conclusion, IT848 is a potent direct NF-κB inhibitor and inducer of oxidative stress specifically in tumor cells, displaying significant activity against multiple myeloma cells in vitro and in vivo, both as monotherapy as well as in combination with bortezomib or immune checkpoint blockade.

Abstract 3164: Detection and CAR T-cell directed targeting of inflammation-responsive Wnt pathway receptors on multiple myeloma cancer stem-like cells

Abstract Multiple myeloma (MM) is the second most common hematological malignancy characterized by a malignant expansion of abnormal antibody-producing cells. Despite available treatments, relapsed disease is a common occurrence with patients receiving survival predictions of less than one year. Relapsed MM is often refractory to multiple lines of therapy and occurs due to the uncontrolled regeneration of a population of malignant cells displaying progenitor-cell-like phenotypes. Selectively targeting this cancer stem cell (CSC) population provides an effective way to limit incidence of relapsed disease, improving the prognosis for high-risk patients. In MM, the defining characteristics of CSCs remain poorly understood, though signaling pathways promoting ‘stemness’ that are often deregulated in CSCs, such as interleukin-6 (IL-6) signaling, as well as canonical and non-canonical Wnt signaling are also aberrantly activated in MM. In this context, the central objective of this project was to explore the functionality of two proteins which have been shown to be downstream targets of IL-6/JAK2/STAT3 signaling and potentiate Wnt signaling, the embryonic G-protein coupled receptor LGR4 and the fetal-oncogene tyrosine kinase like orphan receptor-1 (ROR1), as CSC biomarker candidates, and explore the feasibility of CSC targeting therapeutics for MM. Receptor expression was assessed by quantitative PCR and flow cytometry in primary plasma cell dyscrasia patient samples across the spectrum of disease, as well as in human myeloma cell lines (HMCLs). Whole transcriptome sequencing analyses were carried out in HMCLs induced to overexpress LGR4, which enriched genes associated with ion transport and embryonic development. Cell adhesion and extracellular matrix genes were downregulated, along with genes associated with metabolic and mitochondrial pathways. Results of ROR1 gene expression and flow cytometry studies suggest that a subset of MM patient samples harbor a low-frequency ROR1-positive cell population, and expression is enriched in an in vitro model of acquired drug resistance. Overexpression of interferon regulatory factor-4 (IRF4) - a myeloma cell-enriched transcription factor that we recently showed promotes myeloma regeneration - also contributed to increased human ROR1 protein levels. HMCLs with high endogenous ROR1 expression were sensitive to in vitro killing by anti-ROR1 CAR T-cell treatment, which employs an scFv generated from the fully humanized ROR1-specific monoclonal antibody cirmtuzumab, at effector:target cell ratios (ET) as low as 0.33:1. Together, these results suggest a central role for Wnt signaling in MM stem cell phenotypes and activation of embryonic transcriptional pathways, while also paving the way towards development of clinical therapies that target a CSC population in MM. Citation Format: Lara C. Avsharian, Christopher S. Oh, Ashni A. Vora, Jayde Fernandez, Caitlin Shin, Navyaa Sinha, Charles Prussak, Leslie Crews. Detection and CAR T-cell directed targeting of inflammation-responsive Wnt pathway receptors on multiple myeloma cancer stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3164.

Abstract 5299: A therapeutic antibody against G-protein-coupled receptor class 5 member D to treat multiple myeloma

Abstract Multiple myeloma (MM) comprised 0.9% of all new cancer cases and 1.2% of cancer death in 2020 and is the second most common hematological neoplasm in adults. Primary refractory to treatment and relapse resulted in a high death rate of MM patients. Bispecific antibodies (BsAbs) are attracting candidate drugs against multiple myeloma by targeting CD3 on T cells and MM specific cell surface markers such as B cell maturation antigen (BCMA), CD38, and G Protein-Coupled Receptor Class C Group 5 Member D (GPRC5D). In the current study, we developed a humanized antibody targeting GPRC5D (clone number G-02-9D7). The antibody was derived from hybridoma of mouse immunized with GPRC5D overexpressed mouse cell line. Compared to the GPRC5D antibody in clinical (JNJ-64407564), this antibody has a higher affinity to 293T cells overexpressing GPRC5D (EC50=1.9nM vs. 3nM), MM cell lines, and MM patient samples. In addition, this antibody did not bind to GPRC5A, B, and C and had weaker non-specific binding to human serum albumin than JNJ-64407564. Bispecific antibody derived from the GRPC5D antibody and CD3 antibody (clone number: sp34) induced specific cytotoxicity of MM cells in the presence of T cells from PBMC. This bispecific antibody stimulated the release of cytokines from T cells such as INF-γ, IL-2, IL-8, and TNF-α. In NCI-H929 prophylactic xenograft mouse model with PBMC transplantation, tumor growth could be prevented by administration weekly with this bispecific antibody as low as 0.1ug per mouse. In the presence of T cells, the bispecific antibody also resulted in complete remission of established MM.1S tumor in xenografted NSG mouse with the injection of 1ug antibody weekly. At last, MM patient bone marrow samples cultured in vitro with this bispecific antibody increased cell death of the CD138+ population. In summary, the GPRC5D antibody could efficiently target Multiple myeloma tumor cells. Citation Format: Feng He, Kefei Wu, Jiabei Liang, Jianhui Li, Hao Peng, Guojin Wu, Jinying Ning. A therapeutic antibody against G-protein-coupled receptor class 5 member D to treat multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5299.

Abstract 6251: Evaluation of a dual-targeting BCMA-CS1 HLE BiTE® molecule for multiple myeloma

Abstract Multiple myeloma (MM) is a cancer of the antibody-producing plasma cells (PC). MM is invariably fatal due to frequent disease relapse and/or treatment refractoriness, and therapies that provide deeper and more durable responses are needed. BiTE® (Bispecific T Cell Engager) molecules are immunotherapy agents that redirect a patient’s T cells to lyse tumor cells by simultaneously engaging a tumor associated antigen (TAA) on cancer cells and CD3ε on T cells. Clinical activity has been observed in MM using BiTE® molecules and other T cell engagers that target B-cell maturation antigen (BCMA). BCMA is an attractive MM TAA due to its broad prevalence and restricted normal tissue profile, mainly PCs and plasmablasts. However, heterogenous expression in MM cancer cells, potential antigen loss, and the presence of high levels of soluble BCMA in MM patient sera present challenges that may prevent BCMA-only-targeted therapies from achieving their full potential. To address these issues, we generated a BiTE® molecule capable of engaging BCMA and a second MM TAA, CS1 (also known as SLAMF7). This BiTE® molecule also contains an Fc-based domain to provide half-life extension (HLE). Here, we evaluated the in vitro and in vivo properties of this BCMA-CS1 HLE BiTE® molecule. The BCMA-CS1 HLE BiTE® molecule had nanomolar binding affinity for human BCMA, CS1, and CD3ε and the non-human primate (NHP) orthologues. In vitro, we observed picomolar activity against human MM cell lines with a range of BCMA and CS1 expression in a T cell dependent cellular cytotoxicity (TDCC) assay using human T cells or NHP peripheral blood mononuclear cells. The BCMA-CS1 HLE BiTE® molecule retained TDCC activity in the presence of soluble BCMA up to 2500 ng/mL as well as against human MM cells engineered to express only BCMA or CS1. In vivo, this BiTE® molecule inhibited tumor growth in a MM xenograft model. We also evaluated the BCMA-CS1 HLE BiTE® molecule in NHP over 15 days (IV dosing; intra-animal dose escalation from 60→240 μg/kg or 180→540 μg/kg on days 1 and 8). We observed hallmarks of BiTE® molecule activity in all groups, including transient decreases in circulating lymphocytes and moderate increases in cytokines like MCP-1. We measured the PC-specific transcripts BCMA and J-chain in NHP bone marrow and blood as surrogates for PC levels using ddPCR. These transcripts were reduced in both treatment groups (≥90%) with the strongest effects occurring in the 180→540 μg/kg group. Lastly, we showed that CS1 is highly and broadly expressed in MM patient samples and is restricted to a few normal hematopoietic cell types including PCs, NK cells, T cells, and some monocytes. These data suggest that the BCMA-CS1 HLE BiTE® molecule has potent in vitro and in vivo activity and may provide therapeutic benefit for MM patients by expanding the population of MM cancer cells that can be eliminated by a BiTE® molecule while overcoming common mechanisms that can impair BCMA-only-targeted MM therapies. Citation Format: Elizabeth T. Andrews, Stephanie C. Casey, Mohammad Farhad Amani, Grit Lorenczewski, Mozhgan Farshbaf, Lisa Winkel, Matthias Klinger, John M. Harrold, Famke Aeffner, Ana Goyos, Matthias Friedrich, Tara Arvedson, Matthew G. Chun. Evaluation of a dual-targeting BCMA-CS1 HLE BiTE® molecule for multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6251.

Systematic optimization of targeted and multiplexed MS-based screening workflows for protein biomarkers.

Background: The capability of targeted MS-based methods to simultaneously measure multiple analytes with high selectivity and sensitivity greatly facilitates the discovery and quantitation of novel biomarkers. However, the complexity of biological samples is a major bottleneck that requires extensive sample preparation. Results: This paper reports a generic workflow to optimize surrogate peptide-based protein biomarker screening for seven human proteins in a multiplexed manner without the need for any specific affinity reagents. Each step of the sample processing and LC-MS methods is systematically assessed and optimized for better analytical performance. Conclusion: The established method is used for the screening of multiple myeloma patient samples to determine which proteins could be robustly measured and serve as potential biomarkers of the disease.

Deubiquitylase USP12 induces pro-survival autophagy and bortezomib resistance in multiple myeloma by stabilizing HMGB1.

Despite the establishment of novel therapeutic interventions, multiple myeloma (MM) remains invariably incurable due to development of drug resistance and subsequent relapse, which are attributed to activation of oncogenic pathways such as autophagy. Deubiquitinating enzymes (DUBs) are promising targets to overcome resistance to proteasome inhibitor-based treatment. Ubiquitin-specific protease-12 (USP12) is a DUB with a known prognostic value in several cancers. We found that USP12 protein levels were significantly higher in myeloma patient samples than in non-cancerous human samples. Depletion of USP12 suppressed cell growth and clonogenicity and inhibited autophagy. Mechanistic studies showed that USP12 interacted with, deubiquitylated and stabilized the critical autophagy mediator HMGB1 (high mobility group box-1) protein. Knockdown of USP12 decreased the level of HMGB1 and suppressed HMGB1-mediated autophagy in MM. Furthermore, basal autophagy activity associated with USP12/HMGB1 was elevated in bortezomib (BTZ)-resistant MM cell lines. USP12 depletion, concomitant with a reduced expression of HMGB1, suppressed autophagy and increased the sensitivity of resistant cells to BTZ. Collectively, our findings have identified an important role of the deubiquitylase USP12 in pro-survival autophagy and resultant BTZ resistance in MM by stabilizing HMGB1, suggesting that the USP12/HMGB1 axis might be pursued as a potential diagnostic and therapeutic target in human MM.

SUMOylation inhibition enhances dexamethasone sensitivity in multiple myeloma

BackgroundMultiple myeloma (MM) is an incurable plasma cell malignancy. Although Dexamethasone (Dex) is the most widely used therapeutic drug in MM treatment, patients develop Dex resistance leading to progressive disease, demanding an urgent need to investigate the mechanisms driving Dex resistance and develop new reagents to address this problem. We propose SUMOylation as a potential mechanism regulating Dex resistance and SUMOylation inhibition can enhance Dex sensitivity in MM.MethodsUsing MM cell lines and primary MM samples from relapsing MM patients, we evaluated the effects of knockdown of SUMO E1 (SAE2) or using TAK-981, a novel and specific SUMO E1 inhibitor, on Dex sensitivity. Xenograft mouse models were generated to determine the in vivo anti-MM effects of TAK-981 as a single agent and in combination with Dex. miRNA-seq, RNA-seq and GSEA analysis were utilized for evaluating key factors mediating Dex resistance. Chromatin immunoprecipitation (ChIP) assay was performed to determine the binding occupancy of c-Myc on promoter region of miRs.ResultsWe observed a significant negative correlation between SUMO E1 (SAE2) expression and Dex sensitivity in primary MM samples. Knockdown of SAE2 or using TAK-981 significantly enhances myeloma sensitivity to Dex in MM cell lines. Moreover, the enhanced anti-MM activity by TAK-981 and Dex combination has been validated using primary relapsing MM patient samples and xenograft mouse models. SUMOylation inhibition increased glucocorticoid receptor (GR) expression via downregulation miR-130b. Using RNA and microRNA sequencing, we identified miR-551b and miR-25 as important miRs mediating Dex resistance in MM. Overexpression of miR-551b and miR-25 caused resistance to Dex, however, knockdown of miR-551b and miR-25 significantly enhanced Dex sensitivity in MM. SAE2 knockdown or TAK-981 treatment downregulated the expression of miR-551b and miR-25, leading to induction of miR targets ZFP36, ULK1 and p27, resulting in apoptosis and autophagy. We demonstrated c-Myc as a major transcriptional activator of miR-130b, miR-551b and miR-25 and SUMOylation inhibition downregulates these miRs level by decreasing c-Myc level.ConclusionOur study proves SUMOylation plays a crucial role in Dex resistance in MM and SUMOylation inhibition appears to be an attractive strategy to advance to the clinic for MM patients.