Multiple Myeloma Cell Lines RPMI8226 Research Articles

Daptomycin Inhibits Multiple Myeloma Progression through Downregulating the Expression of RPS19.

This study aimed to explore new therapeutic drugs for multiple myeloma (MM). MM is a common plasma cell malignant proliferative disease, accounting for 15% of hematological malignancies. The role of daptomycin (DAP), a potential anti-tumor drug, remains unclear in MM. In the present research, we investigated the anticancer effect of DAP in MM cell line RPMI 8226. RPMI 8226 cells were treated with DAP (20 μM, 40 μM, and 80 μM) with 20 nM bortezomib (BZ) as a positive control. Cell function was detected using CCK8, flow cytometry, and transwell assay. In MM cells, DAP inhibited proliferation and induced apoptosis. The cell cycle was arrested at the G1 phase after the treatment of DAP. The migration and invasion abilities were also inhibited by DAP treatment in RPMI 8226 cells. Importantly, the mRNA and protein levels of RPS19 were downregulated in DAP-treated RPMI 8226 cells. DAP inhibited the proliferation, migration, and invasion and promoted the apoptosis of MM cells. Mechanistically, the RPS19 expression was significantly decreased in DAPtreated cells. This research provides a potential therapeutic drug for MM therapy.

Specific binding of plant-expressed anti-PD-L1 monoclonal antibody to multiple myeloma cell line RPMI8226

Specific binding of plant-expressed anti-PD-L1 monoclonal antibody to multiple myeloma cell line RPMI8226

Melphalan-Induced Multiple Myeloma Cells Exhibit a Senescent-like Dormant Phenotype

Multiple myeloma (MM) is an incurable plasma cell malignancy. Despite therapeutic advances that have vastly improved survival, all patients are expected to relapse. One mechanism that may contribute to MM relapse is tumor dormancy. Dormant MM cells may persist in the bone marrow, where they exhibit reduced proliferative capacity and resistance to treatment. These cells may then exit dormancy following treatment to drive disease relapse. Dormancy shares many features with cellular senescence, a state of stable growth arrest induced by cell stress. Chemotherapies that produce genotoxic stress have been associated with therapy-induced senescence (TIS). One such genotoxic agent, melphalan (Mel), is routinely administered to MM patients for myeloablation prior to autologous bone marrow transplant. We hypothesized that High Dose Mel (HDM) induces a senescent-like dormant phenotype in surviving MM cells. To test our hypothesis, we developed an in vitro model for HDM. We identified 10µM Mel as a concentration to induce >90% cell toxicity (HDM) in 5TGM1 mouse MM cells over 10 days. 5TGM1-GFP MM cells were cultured with HDM or vehicle (Veh) for 6 hours; cells were then cultured in normal growth medium in the presence of primary mouse (C57BL/6) bone marrow stromal cells (BMSCs). Co-cultures were imaged by fluorescent microscopy every other day to quantify cumulative population doublings (CPD) and cell morphology over the following 10 days. The effect of HDM on CPDs was also evaluated in the human RPMI-8226 MM cell line. 5TGM1-GFP cells were isolated by FACS on day 10 for evaluation of senescence histological characteristics and gene expression. All studies represent n=3 independent experiments unless otherwise indicated. HDM-5TGM1 cells exhibited a significant reduction in mean CPDs over 10 days compared to Veh (HDM 0.32±0.31, Veh 6.72±0.69, p<0.0001), indicating stable growth arrest in HDM treated cells consistent with senescence. HDM-5TGM1 cells were also significantly larger versus Veh (median size in pixels units: HDM 413.2±99.98, Veh 207±8.88, p<0.05), consistent with classical enlarged morphology in senescent cells. Preliminary assessment (n=1) of HDM-RPMI-8226 cells showed similar growth arrest (mean cumulative doublings: HDM 0.058±0.101, Veh 4.185±0.358) and enlargement (mean size in pixel units: HDM 804.1±6.048, Veh 526.9±2.115), suggesting a translatable mechanism in humans. FACS-sorted 5TGM1-GFP cells were stained for telomere associated foci (TAF), a marker of persistent DNA damage characteristic of senescent cells. HDM-5TGM1 cells showed a higher percentage of TAF+ cells (Percent TAF+ cells: HDM 39.7%±9.1%, Veh 10.6%±0.8%, n=2). Sorted HDM-5TGM1 cells also exhibited significant increases over Veh (p<0.001) in senescence markers ( Cdkn1a, Cdkn1c, Glb1), senescence cell anti-apoptosis pathway genes (SCAPs, Bcl2l1), and senescence associated secretory phenotype (SASP) genes ( Ccl5, Icam1, Mmp13). In addition, HDM-5TGM1 cells showed significant increases in myeloid markers that have previously been shown to be increased in dormant 5TGM1 ( Axl, Fcer1g, Mpeg1). Single cell RNA-sequencing was used to further evaluate senescence gene expression changes in growth arrested HDM-5TGM1 cells. Gene set enrichment analysis (GSEA) of genes differentially expressed in HDM-5TGM1 versus Veh cells was performed for custom senescence phenotyping gene sets (Senescence Up, SenUp; Senescence Growth Arrest, SenGA; Inflammatory SASP, iSASP; SCAPs; and Plasma Cell Senescence; PCSen) as well as mouse ortholog versions of a published senescence and biological aging gene set (SenMayo) and KEGG curated gene sets. GSEA of HDM-5TGM1 versus Veh cells confirmed significant (FDR<0.25) upregulation of iSASP, MayoSen, PCSen, SenUp, SCAPs, and SenGA gene sets. Concurrently, GSEA revealed significant downregulation of KEGG DNA replication, cell cycle, and nucleotide excision repair gene sets, supporting our observations of proliferative arrest and persistent DNA damage TAF. Our findings demonstrate that HDM-MM cells exhibit multiple features of senescence, suggesting a potential mechanistic role for TIS in MM dormancy and highlight a novel therapeutic target that may be present in patients post-HDM. Thus, targeting senescence may be a novel approach to eliminate dormant MM cells and prevent relapse.

Discovery and Development of CD70 As a Cellular Therapy Target in High Risk Multiple Myeloma

Background: Even in the BCMA CAR-T era, multiple myeloma (MM) patients with high-risk genotypes have the poorest outcomes. We thus leveraged MMRF CoMMpass data to identify potential novel surface immunotherapeutic targets in high-risk MM. As described below, we focused on CD70, an immunotherapeutic target known to be upregulated on many hematologic and solid tumors but minimally expressed on normal tissue. While CD70 was previously explored in MM (McEarchern et al, Clin Cancer Res (2008)), it was not further investigated due to heterogeneous expression in newly diagnosed samples. Here we revisit this target to suggest cellular therapies against CD70 could be highly beneficial in high-risk MM patients, currently the greatest unmet need in the field. Methods: Primary patient samples were obtained under an IRB-approved protocol. CAR-T lentiviral transduction was performed on paired CD4/CD8 human T cells from at least 3 healthy donors. Effector function was assessed by cytotoxicity against MM cell lines and CAR-T profiling for memory and exhaustion markers. In vivo efficiency was assessed using bioluminescence. ATAC-seq peaks were called using Promo and HOMER (data from Jin et al. Blood (2018)). Machine learning was performed using XGBoost approach applied to CoMMpass RNA-seq data with 80% of samples for training and 20% as test set. Results: Analyzing CoMMpass mRNA data (release IA19) we first evaluated surface protein encoding-genes upregulated in tumors at relapse compared to diagnosis. Among >100 significantly upregulated genes, we focused on CD70 given known promise as an immunotherapy target. Further analysis across genomic subtypes revealed a specific, marked upregulation of CD70 in t(4;14) and gain 1q ( Fig. 1), as well as R-ISS 3 at diagnosis. Flow cytometry profiling of 8 cell line models, including t(4;14) models KHM11, KMS26, and LP1, revealed consistent CD70 protein expression with antigen density similar to BCMA. Profiling of relapsed primary MM samples confirmed that 19 of 28 samples had CD138+ plasma cells positive for CD70 expression. Of 5 patients in whom both BCMA and CD70 were measured, antigen densities were also similar. To target CD70, we then designed 10 unique anti-CD70 CAR-T constructs. 9 of these were scFv-based binders derived from therapeutic antibody fragments currently in preclinical or clinical development. By a structure-guided design based on the CD70:CD27 co-crystal structure (PDB: 7KX0), we also derived a unique truncated fragment of CD27 as an alternative CD70 binding element. All CD70 CARs were efficacious in in vitro cytotoxicity assays targeting MM cell lines AMO1, MM1.S, LP1, and RPMI8226. We then selected the top 3 performing scFv based-CARs as well as our natural ligand (CD27) CAR-T for in vivo studies. All 4 CD70 CAR-Ts prolonged survival of MM.1S-bearing mice compared to empty CAR ( n=5 mice/arm, p<0.005 by log-rank), similar to BCMA CAR-T controls. Remarkably, the CD27-based CAR showed superior expansion (50-85x, p< 0.0001 by ANOVA) and persistence compared to scFv-based ( Fig. 2). These results underscore that targeting CD70 using a natural ligand-based CAR-T represents a promising preclinical candidate for treatment of relapsed and high risk MM. We further investigated why CD70 may be upregulated in high risk MM. Analysis of ChIP-seq in ENCODE and primary MM tumor ATAC-seq was used to nominate a set of transcription factors that bind the CD70 locus. Extending from CoMMpass data, we built a predictive machine learning model for CD70 expression as a function of transcription factor gene expression, nominating key transcription factors TFAP2A, LEF1, MYB, and PAX5 as CD70 regulators; validation is now underway. Additionally, we showed that knockout of NSD2 in t(4;14) models KMS34 and KMS11 led to significantly decreased CD70 surface expression, implicating this central epigenetic driver in CD70 overexpression in this high-risk MM subtype. Finally, we also demonstrated that treatment with the hypomethylating agent azacytidine can drive increased CD70 expression, similar to that shown in AML models. Conclusion: Taken together, targeting CD70 appears to be a highly promising cellular therapeutic strategy for MM, with particularly high utility in high-risk patients after BCMA CAR-T relapse. We are continuing preclinical and future clinical development of this CAR-T strategy, using our natural ligand CD27 design with extended in vivo persistence.

Zinc Oxide Nanoparticles Trigger Autophagy in the Human Multiple Myeloma Cell Line RPMI8226: an In Vitro Study.

Multiple myeloma (MM) is a malignant clonal proliferative plasma cell tumor. Zinc oxide nanoparticles (ZnO NPs) are used for antibacterial and antitumor applications in the biomedical field. This study investigated the autophagy-induced effects of ZnO NPs on the MM cell line RPMI8226 and the underlying mechanism. After RPMI8226 cells were exposed to various concentrations of ZnO NPs, the cell survival rate, morphological changes, lactate dehydrogenase (LDH) levels, cell cycle arrest, and autophagic vacuoles were monitored. Moreover, we investigated the expression of Beclin 1 (Becn1), autophagy-related gene 5 (Atg5), and Atg12 at the mRNA and protein levels, as well as the level of light chain 3 (LC3). The results showed that ZnO NPs could effectively inhibit the proliferation and promote the death of RPMI8226 cells in vitro in a dose- and time-dependent manner. ZnO NPs increased LDH levels, enhanced monodansylcadaverine (MDC) fluorescence intensity, and induced cell cycle arrest at the G2/M phases in RPMI8226 cells. Moreover, ZnO NPs significantly increased the expression of Becn1, Atg5, and Atg12 at the mRNA and protein levels and stimulated the production of LC3. We further validated the results using the autophagy inhibitor 3-methyladenine (3‑MA). Overall, we observed that ZnO NPs can trigger autophagy signaling in RPMI8226 cells, which may be a potential therapeutic approach for MM.

Connexin 43 gap junction affects survival and drug resistance of multiple myeloma side population cells.

Drug resistance remains a major challenge for multiple myeloma (MM) treatment, and side population (SP) cells may play a key role in this resistance. The function of connexin 43 (Cx43)-mediated gap junction intercellular communication (GJ-IC) in MM cells is poorly understood. Bone marrow mesenchymal stem cells (BMSCs) from different sources were isolated and cultured. SP cells of MM cell line RPMI 8266 were separated by flow cytometry. Real-time reverse transcriptase-polymerase chain reaction and Western blot were used to detect Cx43 mRNA and protein expression in BMSCs, RPMI 8266 and SP cells from different sources. The effects of BMSCs from different sources on SP cell cycle, in vitro colony formation ability, stem cell-related gene expression and drug resistance, and the addition of 18α glycyrrhetinic acid (18αGA) as a pathway inhibitor were observed. Here, we demonstrate that MM cells expressed Cx43 and contained a high percentage of SP cells. We observed an increase in the survival and proliferative capacity of SP cells compared with RPMI 8226 cells, but treatment with 18αGA decreased SP cell survival and proliferation (all P<0.05). MM cells were sensitive to dexamethasone- and bortezomib-induced apoptosis; however, this sensitivity was significantly decreased when MM cells were co-cultured with BMSCs, and 18αGA partly recovered this cytotoxicity (all P<0.05). Collectively, our data suggest that GJ-IC between BMSCs and MM cells is one of the important regulatory mechanisms underlying MM cells survival, proliferation, and drug sensitivity.

Abstract 6033: RA123, a new GLS1 allosteric inhibitor demonstrates in vitro and in vivo activity in multiple myeloma models

Abstract The conditional essential amino acid glutamine is utilized by tumors to sustain bioenergetic requirements in a nutrient-poor microenvironment. Based on this specific tumor need, efforts have been made to target the glutamine metabolism using glutaminase inhibitors. In this study, we present in vitro and in vivo studies demonstrating activities and target engagement of a new specific GLS1 allosteric inhibitor (RA123). In vitro, RA123 was tested in imid-resistant, CD38 low RPMI8226 multiple myeloma cell line using the ATP Cell titer Glo assay over a 72h treatment period. In vivo, RA123 was tested in mice xenografted with RPMI8226 multiple myeloma cell line. Compound was given at three different under a BID (twice a day) regimen. Tumor growth under treatment was monitored by caliper measurement for 20 days. A terminal PK/PD study on the same model was setup measuring impact of the drug on the glutamine and glutamate tumor content post 24 hours after the last administration. Over the same period, PK measurements were planned to document drug exposure in the plasma and in the tumor. Finally, in a stand-alone study, target engagement was documented using imaging modality. [18F]FSPG PET radiotracer was used to visualize and quantify impact of RA123 on tumor (RPMI8226) glutamate pool. RA123 was given at three doses under a BID regimen. Treatment was administered for 3 days, and PET signal was recorded at baseline and at end of day 3. In vitro study demonstrated that RA123 was able to induce cell killing of RPMI8226 after 72 hours of treatment. These data translated in vivo by a dose-dependent effect on cell growth. In a terminal PK/PD study, RA123 confirmed a dose-dependent impact on glutamine and glutamate tumor levels which correlated with both plasma and tumor exposure. Further confirmation of target engagement was observed with reduced PET uptake post- RA123 treatment at the three doses tested. In conclusion, this study demonstrated that RA123, a new specific GLS1 allosteric inhibitor was able to impact multiple myeloma tumor cell growth both in vitro and in vivo. This effect was associated with reduced glutamate pools and accumulation of glutamine levels within the tumor cells. Citation Format: Christophe Henry, Dimitri Gorge-Bernat, Pascal Pannier, Isabelle Meaux, Jane Cheng, Fangxian Sun, Olivier Pasquier, Philippe Lienard, Erwan Jouannot, Thierry Gouyon, Geneviève Estenne-Bouhtou, Bailin Zhang, Bérangère Thiers, Laurent Debussche, David Machnik. RA123, a new GLS1 allosteric inhibitor demonstrates in vitro and in vivo activity in multiple myeloma models [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 6033.

Design and discovery of novel dipeptide boronic acid ester proteasome inhibitors, an oral slowly-released prodrug for the treatment of multiple myeloma

Multiple myeloma (MM), the second most common hematological malignancy, is a disease characterized by a clonal expansion of malignant plasma cells that accumulate in the bone marrow. Ixazomib citrate was the first commercially available oral proteasome inhibitor for the treatment of MM. However, it immediately hydrolyzed into the active form on exposure to aqueous solution and so it was a pseudo prodrug. Herein, a series of dipeptide boronic acid esters as novel oral proteasome inhibitors were designed, synthesized and biologically investigated for the inhibition of the β5 subunit of 20S proteasome. Based on the enzymatic results, structure-activity relationships (SAR) were discussed in detail. Some potent compounds were further evaluated to inhibit the proliferation of MM cell line RPMI-8226. The results showed that some compounds were active against RPMI-8226 with IC50 values of less than 10 nM. The solution stability showed that ixazomib citrate was completely hydrolyzed to its active form ixazomib within 2 min in the simulated gastric juice. However, among the screened compounds, prodrug 18u was stable enough in simulated gastric juice and simulated intestinal juice, and its hydrolysis rate was 59.7% and 3.6% after 2 h, respectively. In addition, 18u exhibited good microsome stabilities and pharmacokinetic properties and displayed strong antiproliferative activity against the RPMI-8226 cell line (5.6 nM). Furthermore, compound 18u exhibited strong in vivo anticancer efficacy in human MM (RPMI-8226) xenograft mouse model.

Identification of long noncoding RNA NEAT1 as a key gene involved in the extramedullary disease of multiple myeloma by bioinformatics analysis

ABSTRACTObjectiveLong non-coding RNAs (lncRNAs) are involved in tumorigenesis and play a key role in cancer progression. To determine whether lncRNAs are involved in extramedullary disease of multiple myeloma (EMD), we analyzed the expression profile of lncRNAs in EMD.MethodsThree pairs of EMD patients and their intramedullary MM cells were screened by microarray first. We extracted data from gene chips and made an identification of lncRNAs and mRNAs with significant differences between EMD group and non EMD group. WGCNA confirmed the EMD related gene module and drew a heat map to further determine the key gene lncRNA-NEAT1. In the meantime, bone marrow and extramedullary samples (hydrothorax and ascites) were collected from 2 MM patients and subjected to single-cell RNA-seq. Single cell Transcriptome analysis was conducted to verify the gene expression difference of malignant plasma cells derived from intramedullary and extramedullary. Then we verified high expression level of lncRNA-NEAT1 in EMD patients by using quantitative real-time PCR (qRT-PCR) and analyzed the correlation between expression patterns and survival and molecular genetics analysis of the LncRNA (NEAT1) involved in MM patients. At last, cell experiments were conducted to observe the effects of down-regulation of NEAT1on the proliferation, cell cycle and PTEN pathway related proteins of multiple myeloma cell lines U266 and RPMI8226.ResultsWe identified one of the EMD related key gene is lncRNA-NEAT1. Compared with patients without extramedullary lesions, intramedullary MM cells in EMD patients expressed NEAT1 highly. The outcome of parallel single-cell RNA sequencing (RNA-seq) revealed NEAT1 level of plasma cells came from pleural effusion /ascites increased significantly compared with myeloma-stricken bone marrow. By survival and molecular genetic analysis, NEAT1 gene expression was not associated with OS and PFS in MM patients. However, the expression of NEAT1 is related to adverse therapeutic reactions and the progression of MM. We found that the expressions of NEAT1 were negatively associated with albumin levels and were positively associated with gain of chromosome 1q, IGH-CCND1, IGH@-FGFR3/WHSC1,and IGH-MAF gene fusion, respectively. At the level of cell experiment, CCK-8, soft agar clone formation experiment and CFSE staining showed that down regulating NEAT1 could inhibit the proliferation of U266 and RPMI8226 cells; Cell cycle detection showed that down-regulation of NEAT1 would interfere with the cell cycle process, and RPMI 8226 cells were blocked in G1 phase. Western blot analysis showed that when the expression of NEAT1 was down regulated in U266 and RPMI 8226 cells, the expression of PTEN and p-PTEN (phosphorylated phosphatase and tensin homologue) was up-regulated, and the expression of PI3K, p-PI3K (human phosphorylated inositol 3 kinase), Akt, p-Akt (phosphorylated protein kinase B).Discuccion and conclusionThis study provides novel insights into the lncRNA-NEAT1 and reveals that NEAT1 maybe a potential lncRNA biomarkers in EMD.

The JAK Inhibitor Pacritinib Suppresses the Checkpoint Proteins Pvrig and Tigit Expression on T Cells in Multiple Myeloma Patients

Introduction: Immunotherapies blocking immune checkpoints have been effective in cancer treatment, but these drugs have significant toxicities. Previously, we have shown the JAK1/2 inhibitor ruxolitinib has beneficial effects for treating multiple myeloma (MM) patients. We have also found that it reduces expression of two immune checkpoint proteins, PD-L1 and B7-H3, in MM bone marrow (BM). Pacritinib is another JAK inhibitor that specifically targets JAK2, but not JAK1. We hypothesized pacritinib may inhibit other immune checkpoints in MM. The immune checkpoint proteins TIGIT and PVRIG have been shown to be over-expressed in MM BM, and we evaluated whether pacritinib could reduce expression of these checkpoint inhibitors and the effect of this JAK inhibitor on MM growth. Methods: The human MM cell lines U266, RPMI8226 and MM1s were obtained from ATCC. Mononuclear cells (MCs) were isolated from MM patients' BM aspirates. Cell viability was quantified using the MTS cell proliferation assay. We determined the IC curves for the MM cell lines RPMI8226, U266, and MM1S and fresh BMMCs from the MM patients using this JAK inhibitor and other anti-MM drugs. Specifically, we examined the anti-proliferative effects of pacritinib alone and in combination with dexamethasone, pomalidomide or bortezomib using these 3 MM cell lines and 1 patient's fresh MM BMMCs. In addition, 5 fresh MMBMMCs (3 patients with progressive disease [PD] and 2 patients in complete remission [CR]) were treated with pacritinib alone for 48 hours in vitro, followed by flow cytometric analysis to determine TIGIT and PVRIG expression using an Attune flow cytometer. Results: MM tumor cells from the 3 human myeloma cell lines were exposed to increasing concentrations of pacritinib from 0.1 to 100 µM. The results of anti-MM effects on cell viability showed that pacritinib alone inhibited MM tumor cell proliferation in all three MM cell lines (RPMI8226, U266 and MM1S) in a concentration dependent manner. We also found the viability in one PD patient was significantly decreased when pacritinib was combined with dexamethasone or bortezomib compared to these drugs alone, but there was no effect when this JAK inhibitor was combined with pomalidomide. Next, flow cytometric analysis showed PVRIG and TIGIT expression in MM BMMCs were significantly decreased after pacritinib treatment in vitro for 48 hours in both PD and CR patients, demonstrating that pacritinib inhibited PVRIG and TIGIT in MMBM. Specifically, pacritinib reduced the expression of both PVRIG and TIGIT on CD8+ T cells. Thus, blockade of PVRIG and TIGIT on CD8+ T cells with pacritinib may restore T cell anti-tumor activity. Summary: We demonstrated that pacritinib can inhibit expression of PVRIG and TIGIT in MM BM, and specifically blocks PVRIG and TIGIT expression on CD8+ T cells. We also show the anti-MM effects of pacritinib both alone and in combination with other anti-MM drugs. Pacritinib can be potentially beneficial for treating myeloma patients due to its inhibitory role on PVRIG and TIGIT expression which may enhance tumor cell killing by CD8+ T cells.

Modakafusp Alfa (TAK-573), a Novel CD38-Targeting Attenuated Interferon-Alpha Immunocytokine, Kills MM Cells Via NK Cell Activation

Background Despite recent success of monoclonal antibodies (mAb) and T cell redirecting therapies, relapsed/refractory (RR) multiple myeloma (MM) patients remain in urgent need of new therapies with distinct mechanisms of action (MoA). Modakafusp alfa, previously known as TAK-573, is a novel immune-targeted attenuated cytokine specifically designed to deliver interferon-alpha to CD38-expressing cells via a CD38-targeting IgG4 mAb. Preliminary results of a first in human phase 1 trial with modakafusp alfa monotherapy (1.5mg/kg, every four weeks) in RRMM patients (90% anti-CD38 mAb refractory; 37% anti-BCMA agent exposed) indicate a promising 40% overall response with manageable toxicity (Kaufman et al. EHA 2022 abstract S181). Prior studies suggest a unique and multimodal MoA of modakafusp alfa, including anti-proliferative effects on tumor cells as well as stimulation of CD38-positive immune effector cells. Towards a thorough understanding of these immunomodulatory effects, specifically regarding the activation of innate immunity, we here studied the effects of modakafusp alfa on the anti-MM activity of NK cells, which highly express CD38. Aims We assessed the ex vivo activity of modakafusp alfa on NK cell activation, degranulation, and antibody-independent cytotoxicity. In addition, we investigated the impact of modakafusp alfa on NK cell-mediated, antibody-dependent cellular cytotoxicity (ADCC) against MM cells using daratumumab (anti-CD38) or elotuzumab (anti-SLAMF7). Methods NK cell activation was explored by flow cytometry after 24-hour incubation of peripheral blood mononuclear cells (PBMC) from healthy donors with modakafusp alfa or negative/specificity controls. These pre-incubated PBMCs were also used to examine NK cell degranulation after subsequent 4 hour stimulation with K562 or PMA/Ionomycin, or in a 16-hour cytotoxicity assay against K562. In addition, modakafusp alfa pre-incubated PBMCs or enriched NK cells were assessed for antibody-independent cytotoxicity or daratumumab/elotuzumab-mediated ADCC in 24-48 hour assays against MM cell lines RPMI-8226, MM.1S or UM9. Alternatively, modakafusp alfa was directly added to the assays without pre-incubation steps. Results We found that incubation of PBMCs with modakafusp alfa for 24 hours resulted in upregulation of activation markers CD38 and CD69 on the surface of NK cells. In addition, modakafusp alfa pre-incubation significantly improved the degranulation of NK cells after 4-hour stimulation with K562 or PMA/Ionomycin. Importantly, overnight pre-incubation of PBMCs or enriched NK cells with modakafusp alfa showed enhanced antibody-independent cytotoxicity against K562 tumor cells and MM cell lines RPMI-8226, MM.1S or UM9. Consequently, this also resulted in augmented killing of MM cells in the presence of daratumumab or elotuzumab. We observed similar effects when modakafusp alfa was directly added to the cytotoxicity assays without pre-incubation of immune effector cells. Conclusions Modakafusp alfa rapidly activates NK cells, and improves their degranulation and anti-MM effectivity. This important MoA also results in improved efficacy of daratumumab or elotuzumab in short-term cytotoxicity assays. Our findings warrant clinical investigation of combining modakafusp alfa with NK cell-exploiting immunotherapies.

Identification and in-vitro analysis of potential proteasome inhibitors targeting PSMβ5 for multiple myeloma

The proteasome subunit β5 (PSMβ5) is a chief target of proteasome inhibitors (PIs) for treatment of multiple myeloma (MM). The relevance of PSMβ5 mutations and their functional impact on the development of resistance to PIs have been demonstrated recently. Therefore, this present study deals with an in-depth E-pharmacophore based screening and repurposing of FDA-approved drugs that could target PSMβ5 for MM. Our molecular docking-based investigation revealed risedronate and zoledronate as potential alternative therapeutic molecules for targeting the PSMβ5 gene. Risedronate and zoledronate displayed high binding affinity (−9.51 and −8.56 kcal/mol respectively) to PSMβ5. Moreover, 100 ns molecular dynamics simulation analysis of docking complexes revealed risedronate and zoledronate with a superior binding free energies and stable interactions with PSMβ5. The RMSD plot shows that the risedronate-PSMβ5 (mean: 0.24 nm) and zoledronate-PSMβ5 (mean: 0.25 nm) complexes are identical and stays stable until 100 ns. We further validated the activity of zoledronate in MM cell lines RPMI8226 and U266 where zoledronate showed significant anti-proliferative and apoptotic activity. Importantly, zoledronate showed an enhanced anti-proliferative activity when combined with bortezomib in MM cell lines. Thus, this study demonstrates that combining bortezomib with zoledronate could have a significant impact on reducing MM cell growth and can be an alternative strategy for treating MM.

HSV1716 Infects Multiple Myeloma Cells and Leads to CD138 Downregulation

Multiple myeloma (MM) is a plasma cell malignancy that accounts for approximately 10% of all hematological cancers. MM is classified as incurable due to a high relapse rate after the initial therapy and failure to achieve long-term minimal residual disease (MRD). Therefore, new therapies and combinations are needed. Oncolytic viruses (OVs) are genetically modified viruses that preferentially infect and lyse malignantly transformed cells. HSV1716 is a replication-restricted herpes-simplex virus type I (HSV-1)-based OV (HSV-OV) which has been evaluated in several clinical trials. HSV-OVs have been shown to infect and kill MM cell lines and primary malignant plasma cells. Furthermore, HSV-OV mediated target cell killing was demonstrated to be enhanced by natural killer (NK) cells, an immune cell subset that naturally recognizes malignantly transformed or virally infected cells. The underlying mechanisms behind HSV-OV-enhanced NK-tumor cell killing, however, have not yet been elucidated. Here, we aim to monitor phenotypic changes of MM cells upon HSV1716 infection and thus explore the basis for NK cell recognition of HSV-OV infected target MM cells. The MM cell lines RPMI8226 and MM1S were infected with HSV1716 at various multiplicities of infection (MOIs) over a three-day timecourse. Target cell death and expression of viral glycoproteins were measured at different timepoints by flow cytometry. HSV1716 caused oncolysis of 60% of RPMI8226, and 70% of MM1S cells 48h post-infection (p.i.) at an MOI of 0.5. Under these conditions, the expression of viral glycoprotein E on live cells reached 74% on RPMI8226 cells and 37% on MM1S cells. Primary NK (pNK) cells were isolated from healthy donor peripheral blood mononuclear cells (PBMCs) and co-cultured with infected and uninfected MM cells for 4 hours. CD107a as a marker for NK cell degranulation, as well as the release of IFNγ and TNF were measured on CD3-CD56+ pNK cells by flow cytometry. CD107a expression increased from 15.6% (+/- 0.9%) to 56.2% (+/- 2.4%) following infection of RPMI8226 cells and from 15.6% (+/- 3.4%) to 59.2% (+/- 4.5%) following infection of MM1S cells. Similarly, the expression of IFNγ and TNF increased by four- and three-fold, respectively, as compared to uninfected target cells. To monitor changes in the expression of NK cell ligands on infected MM cells, a 16-color flow cytometry panel was designed. RPMI8226 and MM1S cells were infected at different MOIs, and ligand expression was analyzed at 24h, 48h, and 72h p.i.. Most significantly, an early and progressive downregulation of CD138 expression from 96% on uninfected cells to 79 % (24h MOI 0.5), 70% (48h MOI 0.5), and 22% (72h MOI 0.5) on live RPMI8226 cells and from 99% on uninfected cells to 82% (24h MOI 0.5), 65% (48h MOI 0.5) and 23% (72h MOI 0.5) on live MM1S cells was observed. Of note, the expression of CD38 remained stable at each of these timepoints. While downregulation of HLA class I molecules was observed, the expression of other NK cells ligands on RPMI8226 or MM1S cells did not notably differ between infected and uninfected cells. Together, our data confirm that HSV-OV enhances NK cell-mediated killing of MM cells. While expression of ligands for activating NK cell receptors was not altered on infected versus uninfected RPMI8226 and MM1S cells, a strong downregulation of CD138 with maintained CD38 expression was observed upon HSV1716 infection. The implementation of oncolytic virotherapy as an immunotherapeutic platform for cancer treatment adds a new and promising therapeutic tool for combination therapies to the treatment options of MM.

Evaluation of Repotrectinib's Anti-MM Effects in Combination with Bortezomib, Carfilzomib, Cyclophosphamide, and Dexamethasone in Vitro and Ex Vivo

Introduction: The proteasome inhibitors bortezomib and carfilzomib are anticancer drugs which are indicated for the treatment of multiple myeloma (MM). The alkylating agent cyclophosphamide is also an effective drug against MM. Glucocorticoids including dexamethasone induce MM cell apoptosis and are effective in MM. However, the disease remains incurable with currently available therapies. Repotrectinib (Turning Point Therapeutics, San Diego, CA) is a novel next-generation ROS1/TRK/ALK-tyrosine kinase inhibitor (TKI). Repotrectinib also inhibits the Janus kinase (JAK) 2 and indirectly down-regulates STAT5 phosphorylation in the SET2 cancer cell line harboring a JAK2 V617F tyrosine kinase mutation (Drilon et al 2018). We have previously shown the preclinical anti-MM effects of JAK1/2 inhibitors in combination with corticosteroids and other anti-MM drugs in vitro and in vivo. Although activation of JAK2 and PI3K signaling is often detected in hematological malignancies, there is no data regarding the potential anti-MM effects of repotrectinib alone or in combination with other anti-MM drugs. Thus, we evaluated the anti-myeloma effects of repotrectinib alone and in combination with bortezomib, carfilzomib, cyclophosphamide, and dexamethasone in vitro using MM cell lines and ex vivo using the human MM xenograft model LAG- λ1. Methods: The human MM cell lines U266, RPMI8226 and MM1S were obtained from ATCC. MCs were isolated from MM patients' BM aspirates. Cell viability was quantified using the MTS assay. For the ex vivo studies, cells were isolated from the MM xenograft LAG-λ1 after it was established in SCID mice. We determined the IC curves using the MM cell lines and fresh BMMCs from 6 MM patients. Next, we combined repotrectinib with other active anti-MM drugs (carfilzomib, bortezomib, cyclophosphamide, and dexamethasone) using these same three MM cell lines and BMMCs from 6 MM patients to evaluate the anti-proliferative effects of these combinations. Results: We first evaluated the anti-MM effects of repotrectinib in combination with bortezomib or carfilzomib by using the MM1S, RPMI-8226, and U266 MM cell lines. Specifically, the results with repotrectinib in combination with carfilzomib showed enhanced anti-MM effects when compared to repotrectinib alone or carfilzomib alone. We also determined the anti-MM effects of repotrectinib alone and in combination with carfilzomib by using isolated LAG- λ1 MM xenograft cells. Repotrectinib alone inhibited tumor cell proliferation in a concentration dependent manner (IC50 4.5 µM) and in combination with carfilzomib synergistically inhibited LAG- λ1 MM tumor cell proliferation. These results were not seen when it was combined with bortezomib. We studied BMMCs from 3 PD and 3 CR patients using a cell proliferation assay. The results showed that repotrectinib alone minimally inhibited MM tumor cell proliferation among patients with PD. Repotrectinib combined with carfilzomib showed enhanced anti-proliferative effects compared with either drug alone among BMMCs from PD patients but not those in CR. In contrast, bortezomib did not show this enhanced anti-proliferative effect. We also determined the anti-MM effects of repotrectinib in combination with cyclophosphamide using ex vivo and in vivo studies. The results showed that repotrectinib in combination with cyclophosphamide enhanced the inhibition of LAG- λ1 MM tumor cell and fresh MM BMMC proliferation compared with repotrectinib or cyclophosphamide alone. We further determined the anti-MM effects of repotrectinib in combination with dexamethasone. The results showed that repotrectinib in combination with dexamethasone reduced LAG- λ1 MM cell proliferation in a concentration dependent manner and enhanced inhibition in 2 PD patients' samples but not the other PD patient or 3 CR patients' samples. Summary Single agent repotrectinib decreased MM tumor cell proliferation in all 3 MM cell lines and reduced LAG- λ1 tumor cell proliferation ex vivo. Repotrectinib also reduced proliferation of BMMCs from MM patients with PD but not those in CR. Repotrectinib in combination with carfilzomib, cyclophosphamide or dexamethasone showed enhanced anti-proliferative effects compared with the drugs alone. The results suggest that this kinase inhibitor may have activity in treating MM patients in combination with other active anti-MM agents. Further evaluation is warranted.

Effect of BECN1 Expression on Proliferation and Invasion of Human Myeloma Cell Line RPMI-8226

To investigate the effect of BECN1 expression on proliferation and invasion of human multiple myeloma (MM) cell line RPMI-8226. RPMI-8226 cells were cultured in vitro, the recombinant plasmid pcDNA3.1-BECN1 was constructed and transfected into RPMI-8226 cells, then the cells were divided into three groups: control group, negative transfection group and BECN1 transfection group. The expression of BECN1 mRNA in cells of each group was detected by real-time fluorescent quantitative polymerase chain reaction (qRT-PCR); the effect of BECN1 overexpression on cell proliferation inhibition rate was detected by cell counting kit 8 (CCK-8); the effect of BECN1 overexpression on the colony formation rate was detected by plate cloning assay; the effect of BECN1 overexpression on cell invasion was detected by Transwell assay; the effects of BECN1 overexpression on the expression of cell proliferation, invasion and autophagy-related proteins were detected by Western blot. The expression of BECN1 mRNA in BECN1 transfection group was significantly higher than that in control group and negative transfection group (P<0.05); the inhibition rate of cell proliferation and the expression of autophagy-related proteins Beclin1, Atg5 and invasion-related protein E-cadherin in BECN1 transfection group were significantly higher than those in control group and negative transfection group; the colony formation rate, invasion number and the expression of proliferation-related proteins CyclinD1, β-catenin and invasion-related protein N-cadherin were significantly lower than those in control group and negative transfection group (P<0.05). Overexpression of BECN1 can inhibit the proliferation and invasion of human MM cells RPMI-8226, which may be a potential research target of MM.

PEG@ Carbon Nanotubes Composite as an Effective Nanocarrier of Ixazomib for Myeloma Cancer Therapy

In this work, the preparation of a PEG@ multi-walled carbon nanotubes (MWCNTs) composite has shown a great potential effect in tumor therapy using graphite powder at room temperature. PEGylated MWCNTs were created and used as a carrier for targeting the antineoplastic drug Ixazomib to myeloma cancer cells (abnormal plasma cells). Ixazomib (MLN2238) was covalently encapsulated into functionalized carbon nanotubes modified with polyethylene glycol (PEG 600) to obtain MWCNTs-PEG-MLN2238. The Ixazomib@ MWCNTs-PEG composite shows promising results as an effective nanocarrier and using a small amount of MWCNTs-PEG-Ixazomib that has a low toxicity compared with that of Ixazomib alone. A multifunctional MWCNTs-PEG-Ixazomib composite is used to test biological effects on multiple myeloma cell lines RPMI 8226 using the MTT assay to enhance treatment efficiency. The cytotoxicity of free Ixazomib citrate (69% cell viability of RPMI8226 cells) was higher than that of MWCNTs-PEG-Ixazomib (91% cell viability) at the same maximum concentration of Ixazomib citrate (50 µg/ml). In this work, we performed a study of preparation of MWCNTs with an acceptable Ixazomib loading efficiency and determination of the drug systemic toxicity for the first time. In this study, the preparation of MWCNTs with acceptable Ixazomib loading efficiency and determination of the drug systemic toxicity was performed for the first time. The MTT assay results show decreasing the toxicity of Ixazomib after loading with the MWCNTs-PEG composite. The MWCNTs-PEG @ Ixazomib show promising results as an effective carrier of Ixazomib and lead to a decrease in the cost of using Ixazomib.Graphical

Melatonin Induced Apoptosis of RPMI 8226 Cells through Endoplasmic Reticulum Stress

To investigate the effect of melatonin (MLT) on the proliferation and apoptosis of human multiple myeloma cell line RPMI 8226 and its possible mechanism. RPMI 8226 cells were cultured in vitro, and different concentrations of MLT were treated on RPMI 8226 cells. The effects of MLT on RPMI 8226 cell proliferation were detected by CCK-8 assay and methylcellulose cloning assay, and the effects of MLT on cell apoptosis were detected by AnnexinV-FITC /PI, flow cytometry. Western blot was used to determine the expression of apoptosis and endoplasmic reticulum stress-related proteins in each group, and CCK-8 assay was used to determine the effect of MLT combined with bortezemib on the viability of RPMI 8226 cells. MLT inhibited the proliferation of RPMI 8226 cells in a dose- and time-dependent manner (r=-0.9777，r=-0.9951). With the increase of MLT concentration, the number of clones decreased, the apoptosis of RPMI 8226 cells increased (P<0.05), the expression of anti-apoptotic protein XIAP decreased, the expression of apoptotic proteins Bax and Caspase3 increased, and the expression of endoplasmic reticulum stress-related proteins increased. Compared with the control group, the survival of RPMI 8226 cells in the MLT and BTZ combined group significantly decreased (P<0.01). MLT can inhibit the proliferation of RPMI 8226 cells, promote the apoptosis of RPMI 8226 cells, and enhance the anti-tumor effect of BTZ on RPMI 8226 cells. The mechanism may be related to endoplasmic reticulum stress.

Cytotoxic Effects of the Schweinfurthin Analog 5′-Methylschweinfurthin G in Malignant Plasma Cells

Introduction: Multiple myeloma (MM) is a B plasma cell malignancy currently incurable, and novel therapeutics are needed. Evidences regarding the effect of natural compound schweinfurthins suggest that hematological cancers showed growth inhibitory effects to this family of compounds at single nanomolar concentrations. In this study, we evaluated the cytotoxicity of the schweinfurthin synthetic analog 5′-methylschweinfurthin G (MeSG) in MM cell lines, to better understand the validity of this compound as a therapeutic candidate for further studies in MM. Methods: MeSG toxicity against MM cell lines RPMI-8226, MM.1S, and H-929 was evaluated. Trypan blue exclusion and MTT assays measured cell viability and mitochondrial activity, respectively. Flow cytometry was performed to detect apoptotic mitochondria. Flow cytometry and Western blotting techniques were used to investigate apoptosis and to examine the cell cycle. Western blotting was used to determine AKT activation upon MeSG treatment. Results: We provide evidence that in all MM cells analyzed, MeSG exerts diverse cytotoxic effects. MeSG treatment of MM.1S and H-929, but not in RPMI-8226, causes a loss of mitochondria membrane potential. MeSG causes an arrest in G2/M, especially in RPMI-8226, supported by decreased levels of cyclin-B1 and early increased levels of p21. Finally, there is a diverse response to the MeSG treatment for AKT phosphorylation. MM.1S and H-929 showed a marked decrease in AKT phosphorylation at earlier time points compared to the RPMI-8226 line. Conclusions: MeSG cytotoxicity has been confirmed in all of 3 cell lines studied. Results suggest an early event of increased reactive oxygen species, and/or involvement of cholesterol homeostasis via decreased AKT activation, both of which are currently under investigation.

Abstract 237: Evaluation of cell membrane lipid-extracted nanoliposomes (CLENs) as a potential drug platform for targeting multiple myeloma

Abstract Background: Multiple myeloma (MM) is a plasma cell malignancy that primarily affects the elderly. MM is the second most common hematologic cancer with approximately 25,000-30,000 new cases diagnosed annually in the United States. A challenge associated with MM therapy is unwanted drug uptake by normal healthy cells. Nanoparticles provide a promising outlook to mitigate these issues, offering more selective drug uptake, while minimizing toxicity associated with treatment. The objective of this study was to develop, optimize and evaluate physicochemical and In vitro properties of MM-CLENs in comparison to conventional liposomes and relevant cell controls. Methods: RPMI-8226 MM cell line was selected cellular model for MM disease. RPMI-8226 cells were cultured and expanded In vitro for cellular extraction purposes. Lipid extraction (LE) procedures were performed to generate the RPMI-8226 LE ingredient. Other lipid ingredients used in preparation of RPMI-8226 CLENs included DOPC, cholesterol, and DPPE-Rhodamine (fluorescence indicator). Phase I included physicochemical characterization and cellular uptake studies of CLENs preparations with varying concentration of RPMI-8226-LE (0 to 40 mol%) content. Phase II began with the optimized concentration of LE determined in Phase I, along with varying concentrations of cholesterol (0 to 40 mol %) content for the nano-targeting studies in vitro. The control cell lines represent other hematological diseases, K-562-GFP (chronic myeloid leukemia), CCRF-CEM (acute lymphoblastic leukemia), and U937 (lymphoma). Results: Phase I and II physicochemical characterization and In vitro studies, revealed that the optimized preparation of RPMI-8226-CLENs consisted of 5% LE, and 5% cholesterol content. Optimal preparation consisted of DOPC: Cholesterol: LE (90:5:5) with an average values for particle size and zeta potential of 178±38 nm (n=4), and -14±4 mV (n=4), respectively. The inclusion of LE in conventional DOPC:cholesterol liposomes resulted in significantly improved uptake of the CLENs by RPMI-8226 cells in vitro (P&amp;lt; 0.001). However, preliminary selectivity studies suggest no significant difference in the uptake of RPMI-8226-CLENs by RPMI-8226 when compared to control cells (K-562-GFP, CCRF-CEM and U937). Conclusion: Studies involving RPMI-8226 CLENs are currently underway. Such studies include target selectivity, and influence of additional components of CLENs as a function of the microenvironment. Citation Format: Christina T. Tran, Eden Park, Pedro L. Rodriguez-Flores, Robert B. Campbell. Evaluation of cell membrane lipid-extracted nanoliposomes (CLENs) as a potential drug platform for targeting 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 237.

Abstract 556: Novel anti-TACI single and dual-targeting CAR T cells overcome BCMA antigen loss in multiple myeloma

Abstract Anti-BCMA CAR T cell therapy has had success clinically against multiple myeloma, recently leading to FDA approval. However, the median progression free survival is 8.8 months, suggesting that targeting BCMA alone may not be sufficient. Reports of BCMA-negative relapse have occurred, highlighting the need for therapeutics that can overcome antigen loss. We have generated a novel antibody against a second target in multiple myeloma, transmembrane activator and CAML interactor (TACI). This antibody specifically recognizes TACI-positive cells (with either endogenous or exogenous expression) and has no recognition of non-B cell peripheral blood mononuclear cells. We designed novel second-generation CAR T cells based on the single chain variable fragment (scFv) from this antibody. We observe that anti-TACI CARs are cytotoxic in vitro at comparable levels to anti-BCMA CAR against multiple myeloma cell lines MM1S and RPMI-8226. Anti-TACI CARs are also functional in vivo and expand in peripheral blood of xenograft multiple myeloma models. We generated BCMA-knockout MM1S cells and observe that while anti-BCMA CAR treated mice have outgrowth of tumor, anti-TACI CAR treated animals retain anti-tumor activity. To overcome potential antigen loss of either BCMA or TACI, we designed tandem bispecific CAR T cells based on both single-targeting CAR designs. These BCMA and TACI dual-targeting CARs are functional in vitro and in vivo, even in the context of single antigen loss. We monitor the activation (CD69), exhaustion (PD-1, TIM-3, LAG-3), and memory (CCR7, CD45RA) phenotype over time to investigate the differences of single versus dual-targeting CAR T cells. We also study the ability of these CAR T cells to bind soluble antigen, as well as their binding avidity to tumor cells. We observe that the anti-TACI scFv more proximal to the CD3ζ signaling domain has a stronger effect on CAR functionality than when this scFv is more distal. Our studies provide a potential superior therapeutic option which remains efficacious in the context of BCMA antigen loss. Citation Format: Rebecca C. Larson, Ana Castano, Amanda A. Bouffard, Michael C. Kann, Andrea Schmidts, Kathleen M. Gallagher, Marcela V. Maus. Novel anti-TACI single and dual-targeting CAR T cells overcome BCMA antigen loss in 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 556.