Anti-myeloma Activity Research Articles

Prevalence of t(11;14) Multiple Myeloma in Real-World Setting: Interim Analysis from the Medici Study

Introduction: Multiple myeloma (MM) is the second most common hematologic malignancy characterized by bone marrow infiltration by monoclonal plasma cells (PC). Several well-defined genetic abnormalities have been identified as relevant with the disease. Although novel therapies have improved overall survival most patients with MM will eventually relapse or become refractory (RR). Therefore, there is an emerging need for better therapeutic regimens including personalized medicine based on specific biomarkers. Venetoclax (Ven) is a selective and potent oral B-cell lymphoma-2 (BCL-2) inhibitor that has shown significant antimyeloma activity in patients with t(11;14) RRMM (Kumar et al. Blood 2017; 130 (22): 2401-2409). In the phase 3 BELLINI (NCT02755597) study, patients with t(11;14) RRMM showed improved response rates and progression-free survival when treated with Ven in combination with bortezomib and dexamethasone compared to placebo-bortezomib-dexamethasone (Kumar et al. Lancet Oncol. 2020; 21:1630-1642). These results suggest that t(11;14)-based selection of patients with MM may represent a potential biomarker for venetoclax-based treatment regimens. An ongoing phase 3 study, CANOVA (NCT03539744), is evaluating the combination of Ven and dexamethasone in patients with t(11;14) RRMM compared to standard of care pomalidomide-dexamethasone (Mateos et al. J Clin Oncol 2020; 38: no. 15_suppl) . Understanding the prevalence of t(11;14) MM in a real-world setting will provide important insights for targeted therapy in this patient subpopulation. Therefore, the MEDICI study was designed to evaluate the real-world prevalence of t(11;14) as detected by interphase fluorescence in situ hybridization (FISH) technology in patients with MM. Methods: MEDICI (NCT04721002) is an ongoing, prospective, multicenter minimally interventional study. The primary objective is to determine the prevalence of t(11;14) in both newly diagnosed (ND) and RRMM as determined by interphase FISH analysis of monoclonal bone marrow (BM) PCs. All patients (≥18 years) included in the study signed informed consent. BM aspirates (BMA) were collected as part of standard of care procedures performed at diagnosis and disease relapse. Patients with no BMA sample at the time of diagnosis or confirmation of relapse were excluded from the trial. The primary endpoint was the t(11;14) status of the earliest bone marrow sample collected at initial diagnosis or across subsequent lines of therapies. CD138-enriched BMA samples were evaluated for t(11;14) by FISH (Abbott Molecular). Results: Sixty-two patients were included at the time of the interim analysis (data cut-off 09 March 2022). Median age was 67.5 years, 51.6% were male and 95.2% were Caucasian. Patients with ECOG performance status ≤2/>2/unknown was 83.9%/8.1%/8.1%. ISS stage across patients were stage I (30.6%), stage II (22.6%), stage III (33.9%) and unknown (12.9%) respectively. Del 17p was observed in 6.5% of patients and gain of chromosome 1q in 25.8% of patients. There were 36 and 26 patients with NDMM and RRMM respectively. One patient had longitudinal samples. The overall prevalence of patients with t(11;14) MM was 30.0%, which was similar between NDMM (25.0%) and RRMM (37.5%) patients (Table). The distribution of patients across the observed t(11;14) FISH fusion (F) categories (1F/2F/≥3F) for NDMM was 33.3%/22.2%/22.2% and 44.4%/55.6%/0.0% in RRMM pts (Table). Across lines (L) of therapy, the distribution of t(11;14)+ patients were similar between 1L (25.0%) , 2L (35.7%), and 3L+ (36.4%) (Table). The distribution of t(11;14)+ patients across disease stage was also similar between stage I (31.6%), stage II (28.6%), and stage III (25.0%) respectively. There were 8 patients with unknown stage of disease, 3 among them were t(11;14)+. Conclusion: Interim analysis of MEDICI demonstrated that prevalence of t(11;14) was consistent across ND and RRMM setting and independent of line of therapy and disease stage. This study is currently ongoing, and further updates will be provided upon presentation. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Mechanistic Studies and a Retrospective Cohort Study: The Interaction between PPAR Agonists and Immunomodulatory Agents in Multiple Myeloma.

Our previous study demonstrated that peroxisome proliferator-activated receptor (PPAR) agonists downregulated cereblon (CRBN) expression and reduced the anti-myeloma activity of lenalidomide in vitro and in vivo. We aimed to determine whether DNA methylation and protein degradation contribute to the effects of PPAR agonists. CRBN promoter methylation status was detected using methylation-specific polymerase chain reaction. The CRBN protein degradation rate was measured using a cycloheximide chase assay. Metabolomic analysis was performed in multiple myeloma (MM) cells treated with PPAR agonists and/or lenalidomide. Our retrospective study determined the effect of co-administration of PPAR agonists with immunomodulatory drugs on the outcomes of patients with MM. CpG islands of the CRBN promoter region became highly methylated upon treatment with PPAR agonists, whereas treatment with PPAR antagonists resulted in unmethylation. The CRBN protein was rapidly degraded after treatment with PPAR agonists. Lenalidomide and fenofibrate showed opposite effects on acylcarnitines and amino acids. Co-administration of immunomodulatory drugs and PPAR agonists was associated with inferior treatment responses and poor survival. Our study provides the first evidence that PPAR agonists reduce CRBN expression through various mechanisms including inducing methylation of CRBN promoter CpG island, enhancing CRBN protein degradation, and affecting metabolomics of MM cells.

In vitro and ex vivo anti-myeloma effects of nanocomposite As4S4/ZnS/Fe3O4

Nanoparticles in medicine can integrate actively targeted imaging agents and drug delivery vehicles, and combining multiple types of therapeutics in a single particle has numerous advantages, especially in multiple myeloma. MM is an incurable hematological disorder characterized by clonal proliferation of plasma cells in the bone marrow. In this study, we evaluated the anti-myeloma activity of 3 nanocomposites (3NPs): As4S4/ZnS/Fe3O4 (1:4:1), As4S4/ZnS/Fe3O4 with folic acid (FA), and As4S4/ZnS/Fe3O4 with FA and albumin with reduced survival MM cell lines and primary MM samples by each of 3NP. Cytotoxic effects of 3NPs were associated with caspase- and mitochondria-dependent apoptosis induction and reduced c-Myc expression. Modulation of cell cycle regulators, such as p-ATM/ATM and p-ATR/ATR, and increases in p-Chk2, cyclin B1, and histones were accompanied by G2/M arrest triggered by 3NPs. In addition, 3NPs activated several myeloma-related signaling, including JNK1/2/3, ERK1/2 and mTOR. To overcome BM microenvironment-mediated drug resistance, nanocomposites retained its anti-MM activity in the presence of stroma. 3NPs significantly decreased the stem cell-like side population in MM cells, even in the context of stroma. We observed strong synergistic effects of 3NPs combined with lenalidomide, pomalidomide, or melphalan, suggesting the potential of these combinations for future clinical studies.

Progressive lower extremity weakness as the initial presentation of isolated large thoracic plasmacytoma

Plasmacytoma is a tumor of monoclonal plasma cells of bone or soft tissue that can occur anywhere in the body without evidence of systemic multiple myeloma. It may present as solitary or multiple masses and is classified as osseous if arising from bone or extraosseous if arising from soft tissue. Osseous plasmacytoma is the most common form of plasmacytoma with predominance in active hematopoietic bones, including vertebrae, femur, pelvis, and ribs. The diagnosis is made with a tissue biopsy. Different imaging modalities allow for tumor localization, and magnetic resonance imaging (MRI) is the gold standard to detect spinal cord compression. Corticosteroids provide analgesia, reduce vasogenic edema, and have anti-myeloma activity which may result in better neurological outcomes in cases of acute spinal cord compression. Corticosteroids should be started promptly once cord compression is suspected. We report a case of progressive lower extremity weakness as the initial presentation of a thoracic plasmacytoma. The patient was started on a high-dose corticosteroid after acute cord compression was suspected. Magnetic resonance imaging confirmed cord compression. T1-T2 corpectomy with C5-T5 posterior spinal fusion for decompression and stabilization was done. He was successfully discharged to an inpatient rehabilitation facility with plans for definitive radiotherapy. Worsening back pain and lower extremity weakness in elderly patients should raise concerns for acute cord compression. Early intervention to relieve compression is crucial to preserve neurological functions.
 
 Keywords: plasmacytoma, weakness, steroids, multiple myeloma

ISG20L2 suppresses bortezomib antimyeloma activity by attenuating bortezomib binding to PSMB5.

The proteasome inhibitors (PIs) bortezomib and carfilzomib, which target proteasome 20S subunit beta 5 (PSMB5) in cells, are widely used in multiple myeloma (MM) treatment. In this study, we demonstrated the role of interferon-stimulated 20 kDa exonuclease-like 2 (ISG20L2) in MM PI resistance. Gain- and loss-of-function studies showed that ISG20L2 suppressed MM cell sensitivity to PIs in vitro and in vivo. Patients with ISG20L2lo MM had a better response to PIs and a longer overall survival than patients with ISG20L2hi MM. Biotinylated bortezomib pull-down assays showed that ISG20L2 competed with PSMB5 in binding to bortezomib. The surface plasmon resonance assay confirmed the direct binding of bortezomib to ISG20L2. In ISG20L2hi MM cells, ISG20L2 attenuated the binding of bortezomib to PSMB5, resulting in lower inhibition of proteasome activity and therefore less bortezomib-induced cell death. Overall, we identified a potentially novel mechanism by which ISG20L2 conferred bortezomib resistance on MM. The expression of ISG20L2 correlated with MM PI responses and patient treatment outcomes.

Elevated SFXN2 limits mitochondrial autophagy and increases iron-mediated energy production to promote multiple myeloma cell proliferation.

Human sideroflexin 2 (SFXN2) belongs to the SFXN protein family, which is a mitochondrial outer membrane protein involved in mitochondrial iron metabolism. Mitochondria are indispensable for cellular energy production and iron metabolism. However, it remains elusive how SFXN2 modulates mitochondrial homeostasis and cellular iron metabolism in multiple myeloma (MM). In this study, we first found that SFXN2 was significantly elevated and correlated to poor outcomes in MM patients from clinical datasets. SFXN2 overexpression promoted MM cell proliferation and suppressed starvation-induced autophagy/mitophagy, while SFXN2 knockdown aggravated mitochondria damage and autophagic processes in ARP1 and H929 MM cell lines. Furthermore, inhibition of SFXN2 exerted effectively anti-myeloma activity in vivo by using myeloma xenograft model. Mechanism studies indicated that heme oxygenase 1 (HO1) with anti-oxidant function contributed to the process of autophagy suppression and cellular proliferation mediated by SFXN2. Our study revealed the critical role of SFXN2 in regulating mitochondrial bioenergetics, mitophagy, cellular iron metabolism, and redox homeostasis in interconnected and intricate way. Collectively, these findings not only provide insights into the metabolic reprogramming of tumor cells, but also highlight the therapeutic potential of SFXN2 in combination with iron metabolism as target for prognosis and treatment in MM patients.

Mechanism of immunomodulatory drug resistance and novel therapeutic strategies in multiple myeloma

ABSTRACT Objective The mechanism of immunomodulatory drugs (IMiDs) resistance to multiple myeloma (MM) cells has been gradually demonstrated by recently studies, and some potential novel strategies have been confirmed to have antimyeloma activity and be associated with IMiD activity in MM. Methods This article searched the Pubmed library, reviewed some recently studies related to IMiD resistance to MM cells and summarized some potent agents to improve IMiD resistance to MM cells. Results Studies have confirmed that cereblon is a primary direct protein target of IMiDs. IRF4 not only is affected by the IKZF protein but also can directly inhibit the expression of BMF and BIM, thereby promoting the survival of MM cells. Additionally, the expression of IRF4 and MYC also plays an important role in three important signaling pathways (Wnt, STAT3 and MAPK/ERK) related to IMiD resistance. Notably, MYC, a downstream factor of IRF4, may be upregulated by BRD4, and upregulation of MYC promotes cell proliferation in MM and disease progression. Recently, some novel therapeutic agents targeting BRD4, a histone modification-related ‘reader’ of epigenetic marks, or other important factors (e.g. TAK1) in relevant signaling pathways have been developed and they may provide new options for relapse/refractory MM therapy, such as BET inhibitors, CBP/EP300 inhibitors, dual-target BET-CBP/EP300 inhibitors, TAK1 inhibitors, and they may provide new options for relapsed/refractory MM therapy. Conclusions Accumulated studies have revealed that some key factors associated with the mechanism of IMiD resistance to MM cells. Some agents represent promising new therapeutics of MM to regulate the IRF4/MYC axis by inhibiting BRD4 expression or signaling pathway activation.

CRL4CRBN E3 Ligase Complex as a Therapeutic Target in Multiple Myeloma

Simple SummaryImmunomodulatory drugs (IMiDs) are effective in the treatment of multiple myeloma (MM) and other hematological malignancies. Cereblon (CRBN), a target of IMiDs, forms the CRL4 E3 ubiquitin ligase complex (CRL4CRBN) with DDB1, CUL4A and RBX1. The insight into the molecular mechanism of IMiDs action has advanced dramatically since the identification of cereblon (CRBN) as their direct target. Targeting CRBN by IMiDs modifies CRL4CRBN substrate specificity towards non-physiological protein targets which are subsequently ubiquitinated and degraded by the proteasome. To date, IMiDs are the only known group of protein degraders used in clinical practice. This review provides the current state of knowledge about thalidomide and its derivatives’ mechanisms of action, and highlights the future perspectives for targeted protein degraders.Multiple myeloma (MM) is the second most common hematological malignancy with a recurrent clinical course. The introduction of immunomodulatory drugs (IMiDs) was one of the milestones in MM therapy leading to a significant improvement in patients’ prognosis. Currently, IMiDs are the backbone of MM therapy in newly diagnosed and relapsed/refractory settings. It is now known that IMiDs exert their anti-myeloma activity mainly by binding cereblon (CRBN), the substrate receptor protein of the CRL4 E3 ubiquitin ligase (CRL4CRBN) complex. By binding CRBN, IMiDs alter its substrate specificity, leading to ubiquitination and proteasomal degradation of proteins essential for MM cell survival. Following the success of IMiDs, it is not surprising that the possibility of using the CRL4CRBN complex’s activity to treat MM is being further explored. In this review, we summarize the current state of knowledge about novel players in the MM therapeutic landscape, namely the CRBN E3 ligase modulators (CELMoDs), the next generation of IMiDs with broader biological activity. In addition, we discuss a new strategy of tailored proteolysis called proteolysis targeting chimeras (PROTACs) using the CRL4CRBN to degrade typically undruggable proteins, which may have relevance for the treatment of MM and other malignancies in the future.

Immune checkpoint inhibition improves antimyeloma activity of bortezomib and STING agonist combination in Vk*MYC preclinical model

Multiple myeloma (MM), a hematological malignancy of plasma cells, has remained incurable despite the development of novel therapies that improve patients’ outcome. Recent evidence indicates that the stimulator of interferon genes (STING) pathway may represent a novel target for induction of antitumor immune response in multiple myeloma. Here, we investigated antitumor effects of STING agonist with bortezomib with or without checkpoint inhibitor in the treatment of MM. Methods: STING expression in bone marrow plasma cells of 58 MM patients was examined by immunohistochemical staining. The effectiveness of the proposed therapy was evaluated in vivo in a syngeneic transplantable mouse model of MM (Vĸ*MYC) in immunocompetent mice. Flow cytometry was used to assess tumor burden and investigate activation of immune response against MM. ELISA was performed to measure serum inflammatory cytokines concentrations upon treatment. Results: Combining a STING agonist [2′3′-cGAM(PS)2] with bortezomib significantly decreased tumor burden and improved the survival of treated mice compared to either of the compounds used alone. The combination treatment led to secretion of pro-inflammatory cytokines and increased the percentage of neutrophils, activated dendritic cells and T cells in the tumor microenvironment. However, it resulted also in increased expression of PD-L1 on the surface of the immune cells. Addition of anti-PD1 antibody further potentiated the therapeutic effects. Conclusions: Our findings indicate high antimyeloma efficacy of the three-drug regimen comprising bortezomib, STING agonist, and a checkpoint inhibitor.

P-021: 7C6 is a novel monoclonal antibody that induces enhanced anti-myeloma activity of cytokine induced memory-like (CIML) NK cells by blocking MICA/B shedding and antibodydependent cell cytotoxicity

P-021: 7C6 is a novel monoclonal antibody that induces enhanced anti-myeloma activity of cytokine induced memory-like (CIML) NK cells by blocking MICA/B shedding and antibodydependent cell cytotoxicity

PPAR agonists attenuate lenalidomide's anti-myeloma activity in vitro and in vivo

Many patients with multiple myeloma (MM) have comorbidities and are treated with PPAR agonists. Immunomodulatory agents (IMiDs) are the cornerstones for MM therapy. Currently, little is known about how co-administration of PPAR agonists impacts lenalidomide treatment in patients with MM. Here, we determined the effects of PPAR agonists on anti-myeloma activities of lenalidomide in vitro and in a myeloma xenograft mouse model. Genetic overexpression and CRISPR/cas9 knockout experiments were performed to determine the role of CRBN in the PPAR-mediated pathway. A retrospective cohort study was performed to determine the correlation of PPAR expression with the outcomes of patients with MM. PPAR agonists down-regulated CRBN expression and reduced the anti-myeloma efficacy of lenalidomide in vitro and in vivo. Co-treatment with PPAR antagonists increased CRBN expression and improved sensitivity to lenalidomide. PPAR expression was higher in bone marrow cells of patients with newly diagnosed MM than in normal control bone marrow samples. High PPAR expression was correlated with poor clinical outcomes. Our study provides the first evidence that PPARs transcriptionally regulate CRBN and that drug-drug interactions between PPAR agonists and IMiDs may impact myeloma treatment outcomes.

What's Old is New: The Past, Present and Future Role of Thalidomide in the Modern-Day Management of Multiple Myeloma.

Immunomodulatory drugs (IMiDs) have become an integral part of therapy for both newly diagnosed and relapsed/refractory multiple myeloma (RRMM). IMiDs bind to cereblon, leading to the degradation of proteins involved in B-cell survival and proliferation. Thalidomide, a first-generation IMiD, has little to no myelosuppressive potential, negligible renal clearance, and long-proven anti-myeloma activity. However, thalidomide's adverse effects (e.g., somnolence, constipation, and peripheral neuropathy) and the advent of more potent therapeutic options has led to the drug being less frequently used in many countries, including the US and Canada. Newer-generation IMiDs, such as lenalidomide and pomalidomide, are utilized far more frequently. In numerous previous trials, salvage therapy with thalidomide (50-200 mg/day) plus corticosteroids (with or without selected cytotoxic or targeted agents) has been shown to be effective and well-tolerated in the RRMM setting. Hence, thalidomide-based regimens remain important alternatives for heavily pretreated patients, especially for those who have no access to novel therapies and/or are not eligible for their use (due to renal failure, high-grade myelosuppression, or significant comorbidities). Ongoing and future trials may provide further insights into the current role of thalidomide, especially by comparing thalidomide-containing regimens with protocols based on newer-generation IMiDs and by investigating thalidomide's association with novel therapies (e.g., antibody-drug conjugates, bispecific antibodies, and chimeric antigen receptor Tcells).

S181: MODAKAFUSP ALFA (TAK-573): UPDATED CLINICAL, PHARMACOKINETIC (PK), AND IMMUNOGENICITY RESULTS FROM A PHASE 1/2 STUDY IN PATIENTS (PTS) WITH RELAPSED/REFRACTORY MULTIPLE MYELOMA (RRMM)

Background: Modakafusp alfa (TAK-573) is a first-in-class immunocytokine designed to deliver attenuated interferon alpha-2b to CD38+ cells. In this phase 1/2 study (NCT03215030), the maximum tolerated dose of modakafusp alfa was defined as 3 mg/kg every 4 weeks (Q4W); preliminary data from 29 pts treated at 1.5 mg/kg Q4W (5 in dose escalation, 24 in dose expansion) showed single-agent, anti-myeloma activity with an overall response rate (ORR) of 38% after a median follow-up of 4.2 months (mos) (Vogl ASH 2021, #898). Aims: We present a clinical update on the efficacy and safety of modakafusp alfa 1.5 mg/kg Q4W after a median follow-up of 4.5 mos. We also present PK, immunogenicity, and dose-exposure-response data from the overall study. Methods: Eligible pts had received ≥3 prior lines of treatment. Pts received modakafusp alfa as a 1–4-hour IV infusion at 10 dose levels from 0.001–6 mg/kg at weekly (cycles 1–2 only; 0.001–0.75 mg/kg), every-2-week (0.2–0.3 mg/kg), every-3-week (Q3W; 0.4–0.75 mg/kg), or Q4W (0.75–6 mg/kg) dosing intervals; an expansion cohort was opened at 1.5 mg/kg Q4W after anti-myeloma activity was observed in 3/5 pts in the escalation cohort at that dose. Serum samples prepared from blood were used for PK and anti-modakafusp alfa antibody (ADA) assessments. Modakafusp alfa concentrations were determined via a validated enzyme-linked immunosorbent assay; ADA were detected using a validated bridging electrochemiluminescence assay. Results: As of Oct 2021, 30 pts had received modakafusp alfa 1.5 mg/kg Q4W. The median number of prior lines was 7 (range 3–16); 90% of pts were refractory to an anti-CD38 monoclonal antibody (mAb), while 37% were exposed to an anti-B-cell maturation agent (BCMA). Grade (G) 3–4 treatment-emergent adverse events (TEAEs) were reported in 25 pts (83%); the most frequent G3–4 TEAEs were neutropenia in 19 (63%), thrombocytopenia in 13 (43%), leukopenia in 12 (40%), anemia in 9 (30%), and decreased lymphocyte count in 9 (30%) pts. As reported previously, 1 pt in the 1.5 mg/kg Q4W cohort had a G3 bleeding event, while 3 pts had G3 infections. Among all pts, the ORR was 40% (complete response, 7%; very good partial response, 20%; partial response, 13%); among anti-CD38 mAb-refractory and anti BMCA-exposed pts, the ORR was 37% and 27%, respectively. Median progression-free survival was 6 mos and median duration of response had not been reached (Kaplan-Meier estimate, 91% at 6 mos). Based on pooled available data for the Q3W and Q4W cohorts (all doses) within the escalation and expansion phases, there was a strong trend for a dose-exposure-response relationship for ORR, with the apparent inflection point at 1.5 mg/kg Q4W dosing. No apparent relationship between dose-exposure-response and G3/4 thrombocytopenia or neutropenia was observed across all doses, whereas a correlation between dose-exposure-response and incidence of infusion-related reactions across the 0.4–6 mg/kg Q3W and Q4W dosing cohorts was found. There was an apparent non-linear (more than dose proportional) increase in exposure in the dose range of 0.1–3 mg/kg with a geometric mean terminal half-life of 13 hours in serum for modakafusp alfa 1.5 mg/kg. Based on the available data, 14% and 60% of pts were ADA positive at baseline and post-treatment, respectively. Summary/Conclusion: Modakafusp alfa has a novel mechanism of action and has shown encouraging activity with a manageable safety profile in pts with RRMM. Characterization of the potential clinical impact of immunogenicity is ongoing. The optimal dose for single-agent modakafusp alfa will be further investigated in a phase 2 study.

P897: UPDATED RESULTS FROM THE ONGOING PHASE 1 STUDY OF ELRANATAMAB, A BCMA TARGETED T-CELL REDIRECTING IMMUNOTHERAPY, FOR PATIENTS WITH RELAPSED OR REFRACTORY MULTIPLE MYELOMA

Background: Elranatamab (PF-06863135), a bispecific molecule that engages B-cell maturation antigen (BCMA) on multiple myeloma (MM) and CD3 on T-cells, induces targeted proliferation and activation of T cells to redirect the immune response against MM. Aims: The Phase 1 study, MagnetisMM-1 (NCT03269136), aims to characterize the safety, pharmacokinetics (PK), pharmacodynamics and efficacy of elranatamab as a single agent or in combination with immunomodulatory agents for patients (pts) with relapsed or refractory MM. Methods: After informed consent, elranatamab was given subcutaneously weekly or every 2 weeks (Q2W) at doses from 80 to 1000µg/kg. A subset of pts received a single priming dose (600µg/kg or 44mg equivalent) followed 1 week later by the recommended Phase 2 dose (RP2D; 1000µg/kg or 76mg equivalent) thereafter. Treatment-emergent adverse events (TEAEs) were graded by Common Terminology Criteria for Adverse Events (v4.03) and cytokine release syndrome (CRS) by American Society for Transplantation and Cellular Therapy criteria. PK, cytokine and soluble BCMA profiling, and lymphocyte subset analyses were performed. Response was evaluated by International Myeloma Working Group (IMWG) criteria. Minimal residual disease (MRD) was assessed by next generation sequencing at a sensitivity of 1×10-5 in accordance with IMWG criteria. Results: A total of 55 pts received elranatamab monotherapy at doses ≥215µg/kg as of 1-Nov-2021. Median age was 64 years (range 42-80), 27% of pts were Black/African American or Asian, and 27% had high risk cytogenetics at baseline. Median number of prior lines of therapy was 6 (range 2-15), 91% were triple-class refractory, 22% received prior BCMA-targeted therapy, and 56% had prior stem cell transplant. The most common TEAEs (all causality) were CRS, neutropenia, anemia, injection site reaction, and lymphopenia. With a single priming dose and premedication, the incidence of CRS at the RP2D was 67% and divided equally between Grade 1 and 2, with no events greater than Grade 2. PK exposure was dose dependent, and elranatamab 1000µg/kg Q2W achieved exposure associated with anti-myeloma activity. Elranatamab therapy induced peripheral T-cell proliferation with a median time to response of 36 days (range 7-73), and the level of soluble BCMA decreased with disease response. With a median follow up of 8.1 months (range 0.3-21) and including only IMWG confirmed responses, overall response rate (ORR) was 64% (95% CI 50-75%), and 31% of pts achieved complete response or better. For responders (n=35), the probability of being event free at 6 months was 91% (95% CI 73-97%). Single-agent elranatamab induced durable clinical and molecular responses, and updated results including serial MRD assessment will be presented. Summary/Conclusion: Elranatamab demonstrates a manageable safety profile and achieves durable clinical and molecular responses for pts with relapsed or refractory MM.

P848: TINOSTAMUSTINE (EDO-S101), AN ALKYLATOR AND HISTONE DEACETYLASE INHIBITOR, ENHANCES THE EFFICACY OF DARATUMUMAB IN PRECLINICAL MODELS OF MULTIPLE MYELOMA

Background: Tinostamustine (EDO-S101) is a novel alkylating and deacetylase inhibiting molecule designed to improve drug access to DNA strands, induce DNA damage and counteract its repair in cancer cells. It has shown anti-myeloma (MM) activity in different preclinical models both in monotherapy and in combination with bortezomib. Aims: To evaluate whether tinostamustine enhances the anti-myeloma effect of daratumumab. Methods: Tinostamustine was provided by Mundipharma and daratumumab was obtained from pharmacy surplus of the University Hospital of Salamanca. Mechanisms of action of daratumumab were studied by flow cytometry (FCM) in MM cell lines pretreated with tinostamustine and cultured as specified: 1) with F(ab)2 fragments (direct apoptosis via crosslinking); 2) with 10% human serum (CDC assays); 3) co-cultures of MM and NK cells (ADCC assays). Expression of CD38 and NKG2D ligands (MICA and MICB) after tinostamustine treatment was evaluated by FCM, WB and qPCR. The effects of tinostamustine + daratumumab combination were also studied ex vivo in bone marrow (BM) samples from MM patients, and in vivo in two plasmacytoma models developed in CB17-SCID and NK-cell-humanized NSG mice. Results: Pretreatment of U266, JJN3, MM.1S, NCI-H929, RPMI-8226 and MOLP-8 cell lines with tinostamustine (1-2.5 μM) for 48 h increased CD38 expression. Tinostamustine-pretreated myeloma cells showed a higher level of daratumumab binding, as demonstrated by anti-human-IgG1-AF488 staining. Also, tinostamustine (1-2.5 μM) increased MICA and MICB expression in MM cell lines. In ex vivo cultures, tinostamustine increased expression of CD38 in 4 out of 10 patients and MICA in 3 out of 5 patients. Next, the influence of tinostamustine pretreatment (2.5 μM) on several daratumumab mechanisms was evaluated. In apoptosis via crosslinking, the percentage of apoptotic cells in presence of daratumumab was higher in tinostamustine-pretreated MOLP-8 cells vsDMSO-pretreated cells (90.57%±7.35 vs 60.36%±2.86; p<0.001). Likewise, pretreatment with tinostamustine increased the percentage of Annexin-V+/7AAD+ MOLP-8 cells in CDC assays with daratumumab, although not reaching statistical significance (93.22%±1.05 vs73.39%±11.93). In MM-NK co-cultures in absence of daratumumab (NK cell-mediated direct cytotoxicity), the percentages of apoptotic cells in tinostamustine-pretreated vs DMSO-pretreated cells were: 83.64%±5.28 vs 61.58%±6.81 in MOLP-8 cells (p<0.05); 54.27%±5.99 vs 34.24%±7.37 for RPMI-8226 (p<0.05); and 26.15%±4 vs 12.32%±1.97 in MM.1S (p<0.05). However, in the presence of daratumumab (ADCC) these percentages showed a similar tendency although not significant: 88.57%±3.77 vs 78.89%±5.57 in MOLP-8; 70.75%±5.69 vs 58.28%±7.52 for RPMI-8226; and 56.74%±7.25 vs 45.68%±7.1 in MM.1S. Ex vivo experiments with patients’ BM samples (n = 10) showed that simultaneous combination of daratumumab + tinostamustine significantly increased the percentage of eliminated MM cells compared to individual treatments, with an acceptable toxicity on healthy lymphocytes (Figure 1a). Finally, in the CB17-SCID model, tinostamustine treatment (24 h) followed by daratumumab administration controlled tumor growth significantly better than daratumumab alone (Figure 1b). The combination prolonged the median survival as compared to vehicle, and monotherapy with tinostamustine or daratumumab (Figure 1b). Similar results were obtained in the NSG model. Image:Summary/Conclusion: Our preclinical data demonstrate that tinostamustine increases the anti-myeloma effect of daratumumab presumably due to enhanced expression of CD38 and MICA.

P942: DREAMM-9: PHASE I STUDY OF BELANTAMAB MAFODOTIN PLUS STANDARD OF CARE IN PATIENTS WITH TRANSPLANT-INELIGIBLE NEWLY DIAGNOSED MULTIPLE MYELOMA

Background: The bortezomib, lenalidomide, and dexamethasone (VRd) regimen is a standard of care for newly diagnosed multiple myeloma (NDMM). Belantamab mafodotin (belamaf) is a B-cell maturation antigen-binding antibody-drug conjugate that eliminates myeloma cells by a multimodal mechanism: direct cell kill and anti-myeloma tumor immune response. Belamaf has demonstrated deep and durable responses as a monotherapy in the DREAMM-2 study of patients (pts) with relapsed/refractory multiple myeloma (RRMM). Preclinical evidence of belamaf in combination with bortezomib or lenalidomide suggests enhanced anti-myeloma activity, providing rationale for this treatment combination. Aims: To evaluate the safety and tolerability of this combination in adult pts with transplant-ineligible (TI) NDMM and establish the recommended Phase III dose. Methods: DREAMM-9 (NCT04091126) is an ongoing Phase I, open-label, randomized study of belamaf + VRd. The belamaf dose cohorts currently being evaluated are Cohort 1 (1.9 mg/kg Q3/4W), Cohort 2 (1.4 mg/kg Q6/8W), Cohort 3 (1.9 mg/kg Q6/8W), Cohort 4 (1.0 mg/kg Q3/4W), and Cohort 5 (1.4 mg/kg Q3/4W). Belamaf is given with VRd Q3W until Cycle 8, and with Rd Q4W thereafter. After evaluation of safety data for Cohort 1, Cohorts 2–5 were opened in parallel and enrolled pts were randomized 1:1:1:1. Primary endpoint is safety. Secondary endpoints include efficacy, tolerability, and pharmacokinetics (PK). Results: As of data cutoff (07 Dec 2021), 64 pts were analyzed across all cohorts. Median age (range) was 73.0 (51–88) years, 55% were male, 80% were white, 8% had extramedullary disease, 59% were International Staging System stage II or III, 20% had amp1q, and 17% had high-risk cytogenetics (≥1 of: t(4;14), t(14;16), del17p). The median duration of follow-up varied: Cohort 1 (17.4 months [mo]), Cohort 2 (5.9 mo), Cohort 3 (6.1 mo), Cohort 4 (4.7 mo), Cohort 5 (5.8 mo). Median number of belamaf cycles were: Cohort 1 (6), Cohort 2 (3), Cohort 3 (3.5), Cohort 4 (4.5), and Cohort 5 (5). Most common adverse events (AEs) across cohorts included thrombocytopenia (49%), constipation (43%), diarrhea (32%), and peripheral sensory neuropathy (30%). AEs related to study treatment were experienced by 61 (97%) pts. Belamaf-related grade 3/4 AEs occurred in 24 (38%) pts. Belamaf dose reductions occurred in 11 (18%) pts, with dose delays in 10 (16%) pts. Three pts experienced a fatal severe AE (unrelated to study treatment); 2 due to COVID-19 infection, 1 due to pancreatic adenocarcinoma. Early deep responses were observed; 67–92% pts achieved ≥very good partial response (VGPR) (Table), with median time to VGPR of 2.1–2.9 months across cohorts. Of pts with ≥VGPR, 17 were minimal residual disease (MRD) negative, 10 in Cohort 1. As of data cutoff, 8–75% of pts achieved best response of complete response (CR) or stringent CR (sCR). Grade 3 corneal exam findings were reported in 25–58% of pts; grade 3 visual acuity changes were reported in 21–75% of pts. No grade 4 corneal exam findings or visual acuity changes were reported in pts receiving belamaf Q6/8W, compared with 0–17% and 0–8%, respectively, in the Q3/4W cohorts. Belamaf PK profile was similar to that in pts with RRMM, accounting for baseline characteristics. Image:Summary/Conclusion: Belamaf + VRd demonstrated high response rates in pts with TI NDMM, with a high rate of MRD negativity indicating deep responses. No new safety signals were observed relative to DREAMM-2. Study is ongoing to evaluate the safety and efficacy of variable dose intensities of belamaf in combination with VRd.

S178: SAFETY AND EFFICACY OF BELANTAMAB MAFODOTIN IN COMBINATION WITH RD IN NEWLY DIAGNOSED, TRANSPLANT INELIGIBLE MULTIPLE MYELOMA PATIENTS: A PHASE 1/2 STUDY BY THE HELLENIC SOCIETY OF HEMATOLOGY

Background: Belantamab mafodotin (belamaf), a multi-modal antibody-drug conjugate targeting BCMA, has shown efficacy and tolerability in pretreated patients (pts) with relapsed/refractory multiple myeloma. In pts refractory to immunomodulatory drugs, proteasome inhibitors, and antiCD38, belamaf plus pomalidomide and dexamethasone induced a very good partial response (VGPR) or better of 69.2% and a median progression-free survival of 16.2 months (Trudel S, ASH 2021). Preclinical evidence suggests that belamaf plus lenalidomide enhances antimyeloma activity, with no overlapping toxicities. Aims: To evaluate the safety and efficacy of belamaf plus lenalidomide and dexamethasone (Rd) in transplant-ineligible (TI) pts with newly diagnosed multiple myeloma (NDMM). Methods: The ongoing, prospective, open-label, 2-part, phase 1/2 BelaRd study (NCT04808037) aims to enroll 66 pts with TI NDMM from a Greek center. Eligible are adult pts with Eastern Cooperative Oncology Group status 0–2 and adequate organ function. Part 1 (dose selection) evaluates the safety/tolerability of 3 belamaf doses (2.5, 1.9, and 1.4 mg/kg on Day 1 of every other 28-day cycle) plus Rd (each dose regimen administered to a cohort of 6 pts) over ≥4 weeks of follow up; subsequently, an additional 6 pts are enrolled in each dose cohort to establish the recommended phase 2 dose (RP2D). Part 2 (dose expansion) evaluates the safety and clinical activity of belamaf RP2D plus Rd in 30 additional pts. This descriptive analysis presents the safety data for all Part 1 pts and the efficacy data for all Part 1 pts with ≥2 post-baseline efficacy assessments by the cut-off date (14/01/2022). Results: Of 36 pts included, 35 (97.2%) continued study treatment by the cut-off date, and 1 (2.8%) had died due to a belamaf unrelated adverse event (AE). The pt median age was 72.5 years (range 64.0–86.0). Of pts with available data (30 [83.3%]), pts at revised International Staging System stages I, II, and III were 6 [20.0%], 21 [70.0%], and 3 [10.0%], respectively, and 3 (10.0%) had high-risk cytogenetics (i.e., del17p13, t(4;14), t[14;16]). Median duration of therapy was 4.2 months (range 0.5–11.9) and median number of cycles reached was 5.0 (range 1.0–11.0). Twenty-two (61.1%) pts experienced at least one grade (Gr) 3–4 AE. One (2.8%) pt experienced a Gr 5 AE (pneumonia), unrelated to belamaf. Most common (≥ 10.0% of pts) Gr 3–4 AE were fatigue (13 [36.1%] pts), visual acuity reduced (6 [16.7%] pts), and rash (5 [13.9%] pts). Gr 3–4 thrombocytopenias and infections were not reported, as were any Gr infusion-related reactions (Table). Pts with Gr 1–2 ocular symptoms, visual acuity reduced, and keratopathy, were 27 (75.0%), 21 (58.3%), and 18 (50.0%), respectively. Pts with Gr 3–4 ocular symptoms, visual acuity reduced, and keratopathy were 0 (0.0%), 5 (13.9%) and 0 (0.0%), respectively. Of all pts, 28 (77.8%) were evaluable for efficacy (Table). At a median follow up of 4.2 months (range 0.5–11.9), the overall response rate was 96.4% (27/28 pts; complete response [CR]: 14.3% [4/28 pts]; VGPR: 35.7% [10/28 pts]; partial response [PR]: 46.4% [13/28 pts]); no disease progression was reported. Of pts achieving VGPR, 6/10 (60.0%) had negative status serum/urine immunofixation electrophoresis. Median time to PR or better was 1.0 months (range 0.9–2.0). Image:Summary/Conclusion: In pts with TI NDMM, belamaf every 2 months plus Rd showed an improved safety profile, especially at lower doses. Rapid and deep hematological responses were recorded.

P860: THE DE NOVO DNA METHYLTRANSFERASE DNMT3B PLAYS AN IMPORTANT ROLE IN MM CELL GROWTH, CLONOGENICITY AND DRUG RESPONSE

Background: Multiple myeloma (MM) is an incurable plasma cell malignancy due to the development of drug resistance (DR). In about half of the MM patients, modifications are observed in epigenetic modifiers (epiplayers) at the time of diagnosis and this frequency is further increased at relapse, indicating an important role for epiplayers in MM cell DR. However, so far, only for two epiplayers, MMSET and EZH2, a clear role in MM cell DR development has been established. With the aim to identify new, clinically relevant epiplayers involved in MM progression and relapse, we recently compared the RNASeq data from matched newly diagnosed and relapsed patients from the MMRF CoMMpass study. We found that the epiplayer DNMT3B is significantly increased in relapsed patients, suggesting a possible role for DNMT3B in MM relapse. Aims: The aim of this study is to explore the role of DNMT3B in MM cell biology and drug response. Methods: Publicly available gene expression profiling data of three independent cohorts of newly diagnosed MM patients (GSE4581, E-MTAB-372, MMRF-COMMPASS), one cohort of relapsed patients (GSE9782), BM plasma cells (E-MTAB-372), primary MM cells (E- MTAB-372), and human MM cell lines (HMCLs; E-TABM-1088 and E-TABM-937) was used. DNMT3B specific targeting was achieved by using the DNMT3B specific inhibitor Nanaomycin A and genetic inhibition using doxycycline inducible shRNA against DNMT3B. Viability and apoptosis were assessed using a CellTiter-Glo assay and an AnnexinV/7AAD staining respectively. In addition, BrdU incorporation and cell cycle analysis was evaluated to assess cell proliferation. Clonogenic capacity was evaluated by a colony formation assay. Results: We found that DNMT3B mRNA levels increase during disease progression and high DNMT3B mRNA expression correlates with a worse disease outcome in both newly diagnosed and relapsed patients, indicating a role for DNMT3B in MM progression and DR. In line, Nanaomycin A treatment (up to 72h) led to a significant and dose-dependent decrease in cell viability and proliferation and increase in apoptosis in the XG-2, XG-7 and AMO-1 HMCLs. We also validated the anti-MM activity of Nanaomycin A on human primary MM cells. Since DNMT3B is thought to play a significant role in cancer cell stemness, we next evaluated the effect on clonogenicity. A significant and dose-dependent decrease in the number of colonies was observed when low doses of Nanaomycin A were added to AMO-1 (100 and 200 nM) and XG-2 (30 and 50 nM) cells on the day of plating (day 0), but not when added 7 days after plating (day 7). In contrast, treatment with a high Nanaomycin A concentration (800 nM) significantly reduced the number of colonies at both timepoints, indicating that high Nanaomycin A doses are cytotoxic whereas low doses impair the proliferation and clonogenicity of the MM cells. The anti-clonogenic effect of DNMT3B targeting was confirmed by DNMT3B knockdown in AMO-1 cells. Finally, combining Nanaomycin A (100 nM) with bortezomib (Bz, 4 nM) resulted in a significant decrease in colony formation compared to either Nanaomycin A or Bz treatment alone. Summary/Conclusion: Taken together, our findings indicate that DNMT3B is a novel promising target to overcome or delay relapse in MM. DNMT3B targeting impairs MM cell proliferation and clonogenicity and sensitizes the cells to the proteasome inhibitor Bz. In the near future, the anti-myeloma activity of DNMT3B targeting will be validated in vivo using the 5TMM murine MM models and the underlying mechanisms will be further determined.

PB2032: MAGNETISMM-9: AN OPEN-LABEL, MULTICENTER, NON-RANDOMIZED PHASE 1/2 STUDY OF ELRANATAMAB IN PATIENTS WITH RELAPSED/REFRACTORY MULTIPLE MYELOMA

Background: Elranatamab (PF-06863135) is a humanized bispecific antibody that targets both B cell maturation antigen (BCMA) on multiple myeloma (MM) cells and CD3 on T cells resulting in T cell- mediated cytotoxicity. In preclinical studies, elranatamab has demonstrated anti-myeloma activity and delayed disease progression. In the ongoing phase 1 MagnetisMM-1 study, elranatamab has demonstrated clinical efficacy and a manageable safety profile in patients with relapsed/refractory MM (Bahlis et al, J Clin Oncol 2021). Elranatamab maximum tolerated dose has not yet been reached. Subcutaneous elranatamab at the recommended dose of 76 mg once weekly on a 28-day cycle with a 2 step-up priming dose regimen administered during the first week is currently being evaluated in a phase 2 study, MagnetisMM-3 (Lesokhin et al, Blood, 2021). Aims: To evaluate an alternative priming regimen to further mitigate cytokine release syndrome incidence and severity, and to evaluate subcutaneous elranatamab every 2 weeks and every 4 weeks in patients with relapsed/refractory MM. Methods: MagnetisMM-9 (start date: October 2021; estimated completion date: April 2025) is an open-label, multicenter, non-randomized phase 1/2 study. In part 1 of the study, patients will receive premedications and 2 step-up priming doses on cycle 1 day 1 (4 mg) and day 4 (20 mg), followed by elranatamab 76 mg once weekly for 6 cycles, and a dose every 2 weeks thereafter if partial response or better is achieved and maintained. In part 2, higher doses of elranatamab (>76 mg) at increased intervals between doses will be evaluated. The primary endpoint is grade ≥2 cytokine release syndrome rate during cycle 1. Secondary endpoints include dose-limiting toxicities (part 2 only), objective response rate, duration of response, progression-free survival, overall survival, minimal residual disease negativity rate, safety, and pharmacokinetics. Eligible patients should be 18 years of age or older with a MM diagnosis and measurable disease according to International Myeloma Working Group criteria, refractory to at least one proteasome inhibitor, one immunomodulatory drug, and one anti-CD38 antibody, relapsed/refractory to their last treatment regimen, and have an Eastern Cooperative Oncology Group performance status ≤1. Key exclusion criteria are smoldering MM, active plasma cell leukemia, amyloidosis, POEMS syndrome, stem cell transplant within 12 weeks of enrollment, active, uncontrolled bacterial, fungal, or viral infections, or any other active malignancy within 3 years prior to enrollment (except for adequately treated basal cell or squamous cell skin cancer, or carcinoma in situ), or previous treatment with an anti-BCMA bispecific antibody. The study is open at centers in the USA, UK, Japan, and Taiwan. ClinicalTrials.gov ID: NCT05014412. Results: Results not available (trial-in-progress) Summary/Conclusion: Conclusion not available (trial-in-progress)

PB2011: CHIDAMIDE COMBINED WITH THALIDOMIDE, CYCLOPHOSPHAMIDE AND DEXAMETHASONE (TC2D) AS AN ORAL QUADRUPLET REGIMEN FOR RELAPSED/REFRACTORY MYELOMA PATIENTS: INITIAL RESULTS OF A PHASE IIA, MULTICENTER TRIAL

Background: Research has showed histone deacetylase (HDAC) is overexpressed in plasma cells. Panobinostat was the first HDAC inhibitor (HDACi) approved by FDA for patients with relapse and refractory multiple myeloma (RRMM) in 2015. Chidamide is an oral subtype-selective HDACi, independently developed in China and approved for peripheral T-cell lymphoma. Preclinical findings have demonstrated the anti-myeloma activities of chidamide in vitro and in vivo. Aims: Here we report the initial efficacy and safety of this prospective, phase IIa, multicenter clinical trial with the chidamide based oral quadruplet regimen in patients with RRMM (ChiCTR2000035100). Methods: The TC2D regimen (thalidomide 100mg on days 1-28, chidamide 5mg on days 1-24, cyclophosphamide 50mg on days 1-24, dexamethasone 20mg on days 1,8,15,22) was administered to patients with RRMM of a 28-day cycle. Overall response rate (ORR) was based on patients whose response ≥MR and clinical beneficial rate (CBR) was calculated in patients completed at least 3 cycles and reached ≥SD. Results: A total of 32 patients were enrolled as of June 30, 2021, with a median age of 63.5 years (range 49–74). 82% (19/23) of which had unfavorable cytogenetics (defined by the presence of del (17p) or p53 mutation, t (4:14), t (14:16), t (14:20), amp (1q)). 75% were double refractory to bortezomib and lenalidomide. 43% (14/32) were heavily pre-treated (>3 lines). 59% (19/32) of patients completed ≥ 3cycles at the cut-off date (Table 1). With the median follow-up of 6 months (range 0.7–19.5), the median progression free survival (PFS) was 3.3 months and the 6-mon PFS rate was 27.5% (Fig 1a). Median overall survival (OS) has not reached yet, 6-mon survival rate was 82%, and the estimated 12-month survival rate was 65% (Fig 1b). Study end points were death (8 cases, 25%) and disease progression (24 cases, 75%). Patients who received ≥3 cycles of treatment had a superior median PFS (3.8 vs 1.4 months, P=0.01) than < 3 cycles. Of the 28 patients whose follow-up time more than 3 months, ORR was 25% and CBR was 46.4%, respectively. Better CBR (56.3% vs. 33.3%) and ORR (31.3% vs. 16.7%) were observed in patients received less than 3 prior lines, although with no significant statistical difference. Stratified analysis of PFS and OS showed no significant differences in sex, age, clinical classification, cytogenetic risk, prognosis score (DS and ISS staging system), and the status of ASCT. Grade 3/4 adverse events were mainly hematological toxicity (neutropenia 28%, anemia 34%, thrombocytopenia 15.6%), which could be tolerated. Fatigue was reported in 68.8% (22/32) of the patients. The incidence of all-cause infection was 37.5% (12/32). There were no treatment related deaths observed. Image:Summary/Conclusion: To our knowledge, this is the first report of chidamide-based oral quadruplet regimen for patients with RRMM. Preliminary results suggested efficacy and relatively high safety, and different groups of patients could benefit from this regimen. A longer treatment period may strengthen this effect. The most common adverse events were hematological toxicity which could be controlled. Choices of treatment are also influenced by physical and emotional impact of hospitalization or frequent hospital visits, which reflects the patient’s ability to continue their treatment and quality of life. Hospitalization and intravenous fluids are not involved in this regimen, which bring far more convenience and could be a cost-effective alternative for patients. Updated results will be presented at the following trial.