Mouse Model Of Multiple Myeloma Research Articles

Irisin prevents trabecular bone damage and tumor invasion in a mouse model of multiple myeloma

Abstract Bone disease associated with multiple myeloma (MM) is characterized by osteolytic lesions and pathological fractures, which remain a therapeutic priority despite new drugs improving MM patient survival. Antiresorptive molecules represent the main option for the treatment of MM-associated bone disease (MMBD), whereas osteoanabolic molecules are under investigation. Among these latter, we here focused on the myokine irisin, which is able to enhance bone mass in healthy mice, prevent bone loss in osteoporotic mouse models, and accelerate fracture healing in mice. Therefore, we investigated irisin effect on MMBD in a mouse model of MM induced by intratibial injection of myeloma cells followed by weekly administration of 100 μg/kg of recombinant irisin for 5 wk. By micro-Ct analysis, we demonstrated that irisin improves MM-induced trabecular bone damage by partially preventing the reduction of femur Trabecular Bone Volume/Total Volume (P = .0028), Trabecular Number (P = .0076), Trabecular Fractal Dimension (P = .0044), and increasing Trabecular Separation (P = .0003) in MM mice. In cortical bone, irisin downregulates the expression of Sclerostin, a bone formation inhibitor, and RankL, a pro-osteoclastogenic molecule, while in BM it upregulates Opg, an anti-osteoclastogenic cytokine. We found that in the BM tibia of irisin-treated MM mice, the percentage of MM cells displays a reduction trend, while in the femur it decreases significantly. This is in line with the in vitro reduction of myeloma cell viability after 48 h of irisin stimulation at both 200 and 500 ng/mL and, after 72 h already at 100 ng/mL rec-irisin. These results could be due to irisin ability to downregulate the expression of Notch 3, which is important for cell-to-cell communication in the tumor niche, and Cyclin D1, supporting an inhibitory effect of irisin on MM cell proliferation. Overall, our findings suggest that irisin could be a new promising strategy to counteract MMBD and tumor burden in one shot.

Decreased RNA-binding protein heterogeneous nuclear ribonucleoprotein U improves multiple myeloma sensitivity to lenalidomide.

Multiple myeloma (MM) is an incurable plasma cell cancer in the bone marrow. Immunomodulatory drugs, such as lenalidomide (LEN) and pomalidomide, are backbone agents in MM treatment, and LEN resistance is commonly seen in the MM clinic. In this study, we presented that heterogeneous nuclear ribonucleoprotein U (hnRNPU) affected MM resistance to LEN via the regulation of target mRNA translation. hnRNPULow MM cells exhibited upregulated CRBN and IKZF1 proteins, stringent IKZF1/3 protein degradation upon LEN addition and increased sensitivity to LEN. RNA pulldown assays and RNA electrophoretic mobility shift assays revealed that hnRNPU bound to the 3'-untranslated region of CRBN and IKZF1 mRNA. A sucrose gradient assay suggested that hnRNPU specifically regulated CRBN and IKZF1 mRNA translation. The competition of hnRNPU binding to its target mRNAs by small RNAs with hnRNPU-binding sites restored MM sensitivity to LEN. hnRNPU function invivo was confirmed in an immunocompetent MM mouse model constructed by the inoculation of Crbn-humanized murine 5TGM1 cells into CrbnI391V/+ mice. Overall, this study suggests a novel mechanism of LEN sensitivity in which hnRNPU represses CRBN and IKZF1 mRNA translation.

Self-sufficient primary natural killer cells engineered to express T cell receptors and interleukin-15 exhibit improved effector function and persistence.

NK cells can be genetically engineered to express a transgenic T-cell receptor (TCR). This approach offers an alternative strategy to target heterogenous tumors, as NK:TCR cells can eradicate both tumor cells with high expression of HLA class I and antigen of interest or HLA class I negative tumors. Expansion and survival of NK cells relies on the presence of IL-15. Therefore, autonomous production of IL-15 by NK:TCR cells might improve functional persistence of NK cells. Here we present an optimized NK:TCR product harnessed with a construct encoding for soluble IL-15 (NK:TCR/IL-15), to support their proliferation, persistence and cytotoxic capabilities. Expression of tumor-specific TCRs in peripheral blood derived NK-cells was achieved following retroviral transduction. NK:TCR/IL-15 cells were compared with NK:TCR cells for autonomous cytokine production, proliferation and survival. NK:BOB1-TCR/IL-15 cells, expressing a HLA-B*07:02-restricted TCR against BOB1, a B-cell lineage specific transcription factor highly expressed in all B-cell malignancies, were compared with control NK:BOB1-TCR and NK:CMV-TCR/IL-15 cells for effector function against TCR antigen positive malignant B-cell lines in vitro and in vivo. Viral incorporation of the interleukin-15 gene into engineered NK:TCR cells was feasible and high expression of the TCR was maintained, resulting in pure NK:TCR/IL-15 cell products generated from peripheral blood of multiple donors. Self-sufficient secretion of IL-15 by NK:TCR cells enables engineered NK cells to proliferate in vitro without addition of extra cytokines. NK:TCR/IL-15 demonstrated a marked enhancement of TCR-mediated cytotoxicity as well as enhanced NK-mediated cytotoxicity resulting in improved persistence and performance of NK:BOB1-TCR/IL-15 cells in an orthotopic multiple myeloma mouse model. However, in contrast to prolonged anti-tumor reactivity by NK:BOB1-TCR/IL-15, we observed in one of the experiments an accumulation of NK:BOB1-TCR/IL-15 cells in several organs of treated mice, leading to unexpected death 30 days post-NK infusion. This study showed that NK:TCR/IL-15 cells secrete low levels of IL-15 and can proliferate in an environment lacking cytokines. Repeated in vitro and in vivo experiments confirmed the effectiveness and target specificity of our product, in which addition of IL-15 supports TCR- and NK-mediated cytotoxicity.

Abstract 4110: Identification of tumor peptides for therapeutic mRNA vaccination in a mouse multiple myeloma model

Abstract Background: Multiple myeloma (MM) is a plasma cell cancer for which immunotherapy holds the promise of durable control. To date, cancer vaccines mainly focused on tumor-associated antigens with survivin eliciting protective T-cell responses in both preclinical and clinical studies. Given the success of mRNA vaccines in medicine, we developed Galsomes, lipid nanoparticles containing mRNA and α-galactosyl ceramide to activate both CD8+ T cells and invariant natural killer (iNK) T cells, both potential anti-MM effectors. Materials and Methods: Mouse 5T33MM cells were studied by PCR and flow cytometry (FCM) for expression of survivin and CD1d, respectively. Intravenous (IV) prime-boost Galsome vaccination was performed with a 7-day interval in C57BL6/KalwRij mice that received an IV injection of 5x106 5T33MM cells 3 days earlier. As a control, mice were injected with saline. After 2 weeks, MM burden was studied by serum electrophoresis and FCM, incl. expression of CD1d and PD-L1 on MM cells. Activation of iNKT cells and survivin-specific T cells was studied by measuring IFN-γ secretion in ELISA and dextramer staining. Immunopeptidomics was used to identify new vaccine candidates for which Galsome vaccination is ongoing. Result: The 5T33MM cells showed expression of survivin and CD1d, making it a suitable model for Galsome vaccination. Two weeks following prime-boost vaccination, the serum M-protein was reduced, though not significantly. In contrast, MM cells were significantly reduced in bone marrow and spleen. Expression of CD1d and PD-L1 on MM cells was high but unchanged by Galsome vaccination. Activation of iNKT cells and survivin-specific T cells following prime vaccination was shown. However, following boost vaccination these cell populations reduced significantly compared to control. We repeated prime-boost vaccination in healthy mice, observing a similar outcome. This suggests that the negative effect of the boost Galsome vaccination was not related to immune dysfunctionality due to MM progression. So, we studied the impact of survivin mRNA in the vaccine, as survivin is also expressed in activated T cells, making them a potential target. We observed that iNKT cells and ovalbumin-specific T cells were more reduced when ovalbumin mRNA was paired with survivin mRNA in the Galsomes. To identify other vaccine candidates, we studied peptides eluted from MHC-I/peptide complexes on 5T33MM cells. We selected 4 vaccine candidates including the MM idiotype based on immunogenicity, pathway classification and abundance. mRNA and Galsomes were prepared, and the efficacy of these Galsomes in 5T33MM mice is currently under evaluation. Conclusion: These data show that Galsome vaccination has the potential to reduce MM cell levels. To reach higher efficacy, careful selection of the vaccine antigen is required. Moreover, combination with other immunotherapies might be needed to reach durable disease control. Citation Format: Arne Van der Vreken, Fabien Thery, Sofie Meulewaeter, Karin Vanderkerken, Elke De Bruyne, Kim De Veirman, Lorenzo Franceschini, Rein Verbeke, Francis Impens, Ine Lentacker, Karine Breckpot, Eline Menu. Identification of tumor peptides for therapeutic mRNA vaccination in a mouse multiple myeloma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4110.

Abstract 3618: High-avidity BCMA CAR and high-affinity, non-cleavable CD16 Fc receptor incorporated in off-the-shelf CAR T cells promote multi-antigen targeting and durable anti-tumor cytotoxicity in the treatment of multiple myeloma

Abstract Immune cell therapy has proven highly effective for the treatment of multiple myeloma (MM). However, key challenges remain that include disease relapse, limited patient access, and inability to effectively combine with existing standard-of-care therapies. Rapid progress in the development of off-the-shelf, multiplexed-engineered, induced pluripotent stem cell (iPSC)-derived cell therapies enables large-scale manufacture of immune cells incorporating multiple novel synthetic controls of cell function to improve cell fitness, enhance cell function, and enable synergistic combination with existing effective therapies such as CD38-targeted antibody (mAb) therapy. We have developed an iPSC-derived chimeric antigen receptor T (CAR-iT) cell therapy that uniquely leverages elements of both adaptive and innate immunity by incorporating a BCMA-targeted CAR (BCMA-CAR) derived from a scFv domain exhibiting high-binding affinity in the low nanomolar range, and a high-affinity, non-cleavable CD16 (hnCD16) Fc receptor to enable antibody-dependent cellular cytotoxicity with mAb therapy. The genetic deletion of CD38 gene was also incorporated to eliminate the possibility for CD38-mediated fratricide, and genetic deletion of TRAC gene was introduced to remove the potential risk of graft-versus-host disease in an allogeneic setting. These CAR iT cells, which were generated from a clonally-derived iPSC line, demonstrated homogenous expression of each genetic edit (>95% BCMA-CAR and hnCD16; <1% CD38 and TCR surface expression). Using a stringent, disseminated xenograft mouse model of multiple myeloma, MM.1S, which was allowed to achieve complete systemic engraftment during the initial 4 days, treatment with BCMA-CAR iT cells demonstrated comparable tumor cell clearance (p=0.0024 vs. vehicle at Day 17) to primary BCMA-CAR T cells (p=0.002 vs. vehicle). In combination with a CD38-targeted mAb to exploit hnCD16 and biallelic CD38 KO, BCMA-CAR iT cells are capable of dual-antigen targeting to address antigen escape and promote durable tumor control. To this end, a single dose of BCMA-CAR iT cells combined with daratumumab exhibited near complete TGI for the duration of the study (p<0.0001 vs. vehicle at Day 37). Together, these studies demonstrate CAR iT cells incorporating a high-avidity BCMA CAR and high-affinity, non-cleavable CD16 Fc receptor can uniquely leverage elements of both adaptive and innate immunity and can be combined with CD38-targeted mAb to potentially outcompete primary BCMA CAR T cells. As these CAR iT cells can be administered off-the-shelf, key challenges associated with current immune cell therapy, such as patient access and inability to synergize with standard-of-care therapies, can be addressed for the treatment of relapsed/refractory MM. Citation Format: John Reiser, Alison O'Connor, Bryan Hancock, Spas Markov, Brian Groff, Alma Gutierrez, Miguel Meza, Mark Jelcik, Yijia Pan, Alex Garcia, Bobby Goulding, Matthew Denholtz, Tom Lee, Ramzey Abujarour, Ryan Bjordahl, Armin Rehm, Raedun Clarke, Jode Goodridge, Bahram Valamehr. High-avidity BCMA CAR and high-affinity, non-cleavable CD16 Fc receptor incorporated in off-the-shelf CAR T cells promote multi-antigen targeting and durable anti-tumor cytotoxicity in the treatment of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3618.

Abstract 7374: Mathematical modeling of targeted radionuclide therapy and CAR-T cell immunotherapy for maximizing therapeutic efficacy in multiple myeloma

Abstract Background: Resistance of cancer cells to monotherapies has led to the development of sequential or combination therapy regimens. However, dosing and scheduling of these therapies is challenging due to the numerous dosing and scheduling combinations that can be given. Mathematical models are thus critical tools for addressing this challenge as multiple therapy combinations can be tested in silico to finalize a patient-specific therapeutic regimen in vivo. Here we develop a mathematical framework for combining targeted radiation therapy (TRT) with Chimeric Antigen Receptor (CAR)-T cell immunotherapy and demonstrate the use of in silico techniques to schedule these therapies for maximizing survival. Methods: In the mathematical framework tumor growth is assumed to be exponential and the effect of radiation on both tumor cells and CAR-T cells is modeled using the linear-quadratic model of cell survival to radiation. A predator-prey model is used to characterize the dynamics of tumor and CAR-T cells. Using a preclinical disseminated mouse model of multiple myeloma (MM1S), we evaluate tumor response to 200 nCi of 225Ac-DOTA-Daratumumab (TRT) and 1 million cells of CS1 CAR-T cell therapy both as monotherapies as well as in combination. Tumor burden tracked using bioluminescence imaging from six groups of mice is used to calibrate model parameters: (a) No treatment. (b) Day 7 TRT. (c) Day 7 CAR-T cell therapy. (d) Day 7 TRT + Day 18 CAR-T cell therapy. (e) Day 7 TRT + Day 25 CAR-T cell therapy. (f) Day 7 TRT + Day 32 CAR-T cell therapy. Response to therapy is evaluated using progression-free survival (PFS), overall survival (OS) and time to minimum tumor burden (tmin), all of which are calculated using the predicted in silico tumor burden dynamics and the tumor burden at the start of first therapy. We evaluate these response metrics for various dosing and scheduling regimens. Results: Therapy intervals that were too short or too long are shown to be detrimental for therapeutic efficacy. TRT too close to CAR-T cell therapy results in radiation related CAR-T cell killing, while the interval being too long results in tumor regrowth, negatively impacting tumor control and survival. If a single dose is split into multiple doses, the splitting is advantageous only if the first therapy delivered can produce a significant benefit as a monotherapy. Based on the model parameters we estimate the minimum required TRT activity and CAR-T cell dose to demonstrate an improvement in PFS. Conclusions: The proposed model demonstrates the impact of different dosing and scheduling regimens of TRT and CAR-T therapy on survival metrics. It is a potent tool for translating preclinical results to the clinic and eventually tailor therapy regimens for patients. Citation Format: Vikram Adhikarla, Dennis Awuah, Enrico Caserta, Megan Minnix, Maxim Kuznetsov, Amrita Krishnan, Jeffrey Y. Wong, John E. Shively, Xiuli Wang, Flavia Pichiorri, Russell C. Rockne. Mathematical modeling of targeted radionuclide therapy and CAR-T cell immunotherapy for maximizing therapeutic efficacy in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7374.

Abstract 1238: ISB 2001, a BCMA and CD38 dual targeting T cell engager, demonstrates superior cytotoxicity relative to teclistamab in the samples of patient relapsing from CD38 and BCMA targeted immunotherapies

Abstract Immune therapies targeting single tumor associated antigens (TAA) demonstrated efficacy against multiple myeloma (MM). However, durable responses are still limited1 potentially due to expansion of clones with low target expression2 We have previously demonstrated that simultaneous targeting of BCMA and CD38 on MM tumor cells with heterogenous expression of these antigens using dual targeting ISB 2001, enables superior killing relative to mono-targeting T cell engagers (TCE) 3. Here we present a further characterization of a dual targeting TCE utilizing bone marrow aspirates from multiple myeloma patients. In relapsed/refractory (r/r) patients, which received CD38 targeted therapy, daratumumab cytotoxicity was substantially reduced due to low CD38 expression. Teclistamab is considered the next line of treatment in such patients. However, ISB 2001 consistently demonstrated increased cytotoxicity compared to teclistamab in both newly diagnosed patient and r/r patient samples. Remarkably, ISB 2001 also induced stronger cytotoxic response in one patient relapsing after BCMA targeted therapy, suggesting that the dual targeting ISB 2001 TCE can overcome the escape mechanisms. ISB 2001 was also compared to the combination of teclistamab and daratumumab in cytotoxic assay using healthy donors. ISB 2001 shows superiority to both teclistamab and daratumumab as single agents, as well as when they were used in combination. Additionally, ISB 2001 was compared against a combination of daratumumab and teclistamab in a humanized mouse model of multiple myeloma with a low expression of both CD38 and BCMA, mimicking potential tumor escaping clones. ISB 2001 induced complete eradication of the tumors in almost all animals, whereas the combination only showed partial tumor protection, underscoring that dual targeting by a TCE is superior to two therapeutic agents individually targeting the same antigens. Based on the promising preclinical in vitro, ex vivo and in vivo data, we have advanced ISB 2001 into clinical studies. For calculating the first-in-human (FIH) dose, we have developed a quantitative systems pharmacology (QSP) model. The calculated FIH dose was 50-100 fold higher than that generated by a traditional minimum anticipated biological effect level calculation. Therefore, using this approach will substantially reduce patient exposure to sub-efficacious doses of ISB 2001. This plan was accepted by the HREC in Australia and the FDA in the US to initiate a Phase 1 FIH study of ISB 2001 for the treatment of relapsed/refractory multiple myeloma (NCT05862012)4. 1. Munshi, N. C. et al. 384, 705-716 (2021). 2. Nijhof, I. S. et al. Blood 128, 12 (2016). 3. (https://doi.org/10.1182/blood-2022-159353) 4. Abstract# 3396, ASH 2023, Hanlon Sia at al. Citation Format: Laura Carretero-Iglesia, Maria Pihlgren, Jeremy Berret, Adam Drake, Daniela Pais, Cyrille Dreyfus, Vinu Menon, Thomas Matthes, Claire Edwards, James Edwards, Catherine Pellat-Deceunynck, Philippe Moreau, Cyrille Touzeau, Tomomi Matsuura, Piet van der Graaf, Lida Pacaud, Cyril Konto, Eugene Zhukovsky, Mario Perro. ISB 2001, a BCMA and CD38 dual targeting T cell engager, demonstrates superior cytotoxicity relative to teclistamab in the samples of patient relapsing from CD38 and BCMA targeted immunotherapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1238.

Abstract 4180: Evaluation of CD38 pharmacodynamics in multiple myeloma using PET with a Ga-68 labelled peptide

Abstract Introduction: Multiple myeloma (MM) is a disease of plasma cells that primarily arises in the bone marrow. CD38 is a receptor expressed uniformly and with high density in MM. Several CD38 targeted therapeutics are in clinic for MM. However, how those therapeutics engage or modulate CD38 is poorly understood particularly in lesions that cannot be assessed with routine blood testing. CD38 specific radiotracers for positron emission tomography (PET) could be helpful for detection of MM and for assessing therapy response early by measuring CD38 pharmacodynamics non-invasively. Here, we report the development of a first-in-class peptide-based PET radiotracer, [68Ga]AJ206, evaluation of its pharmacokinetics (PK), specificity for non-invasive CD38 detection, and its potential to evaluate therapy induced CD38 pharmacodynamics in mouse models of MM. Methods: A bicyclic peptide, AJ206, was synthesized and its binding affinity for CD38 was determined by surface plasmon resonance. AJ206 was labelled with Gallium-68 in high radiochemical yields and purity. In vitro uptake of [68Ga]AJ206 was carried out in four MM cell lines with variable CD38 expression (MOLP8, MM1S, RPMI8226, and U266). PK and biodistribution of [68Ga]AJ206 were evaluated by PET in cell line derived xenografts, in patient derived xenografts (PDXs) and in a disseminated disease model. PET data was corroborated by ex vivo biodistribution studies. [68Ga]AJ206 in vivo specificity for CD38 was confirmed by co-injection of non-radioactive AJ206 (1 mg/kg) and cross-correlative immunohistochemistry (IHC) of matched xenografts. Furthermore, ability of [68Ga]AJ206 to quantify CD38 pharmacodynamics was established by treating PDX models with all-trans retinoic acid (ATRA) and cross validating PET imaging observations with IHC. Results: AJ206 exhibits high affinity (KD,19 nM) for human CD38. In vitro binding assays showed variable [68Ga]AJ206 uptake in MM cells that correlated with receptor density measured by flow cytometry. Dynamic PET-MR imaging revealed high and specific uptake of [68Ga]AJ206 in MOLP8 tumor within 5 min that retained for at least 90 min. In contrast, [68Ga]AJ206 exhibited rapid clearance from normal tissues providing high contrast images at 60 minutes and a high tumor-to-muscle ratio of 27.1±2.7. Tumor uptake was reduced by > 80 % in mice receiving blocking dose, confirming the specificity of the radiotracer. Also, [68Ga]AJ206 could detect CD38 expression in different MM xenografts, PDXs and disseminated disease models which was corroborated by flow cytometry and IHC findings. Moreover, [68Ga]AJ206 successfully quantified the increased CD38 expression in PDXs following ATRA treatment. Conclusion: [68Ga]AJ206 is a CD38 specific high affinity peptide-based PET imaging agent that can be used to non-invasively quantify CD38 pharmacodynamics in MM, with potential applications in other diseases with CD38 involvement. Citation Format: Ajay Kumar Sharma, Kuldeep Gupta, Akhilesh Mishra, Gabriela Lofland, Ian Marsh, Dhiraj Kumar, Gabriel Ghiaur, Philip Imus, Steven P. Rowe, Robert Hobbs, Christian B. Gocke, Sridhar Nimmagadda. Evaluation of CD38 pharmacodynamics in multiple myeloma using PET with a Ga-68 labelled peptide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4180.

Abstract 3609: Chimeric cytokine receptors increase memory phenotypes and improve expansion and efficacy of CAR-T cell therapies

Abstract Cytokine activation of T cells can promote T cell proliferation, memory and improve T cell function in driving tumor cell killing. However, systemic administration of cytokines at therapeutic doses is also associated with unacceptable toxicities. To overcome this limitation, we have engineered a system of private cytokine signaling to affect T cell homeostasis, identity, and function. Specifically, we have engineered chimeric cytokine receptors (CCRs) composed of single-chain variable fragments (scFvs) that bind specifically to small molecules such as fluorescein or DOTA. These scFvs are fused to transmembrane and intracellular domains of all members of the common gamma-chain (γ-chain) family of cytokine receptors. CCRs that permit private cytokine signaling were introduced into known CAR-T cell therapies and their impact on CAR-T cell phenotype, function, and anti-tumor activity was tested. First, CCR-containing T cells were tested for activation-induced changes in phenotype and expansion following stimulation with small molecule conjugates in vitro. The most promising results were obtained using either the IL-7Rα- or IL-2Rβ/γ-containing CCR’s. CCR-containing constructs were then transduced into one of two different anti-BCMA CAR-T constructs, ide-cel or cilta-cel, using a lentiviral transduction system. CAR-T cells containing each CCR were then compared with CAR-T cells lacking CCRs for phenotype and function in vitro. Results indicated that engineering the IL-7Rα CCR with both of these CAR-T’s led to increased expansion, cytokine secretion and improved tumor cell killing. Next, CAR-T cells expressing the IL-7Rα CCR were compared to CAR-T cells lacking CCR for efficacy and durability in a mouse model of human multiple myeloma. IL-7Rα CCR-expressing CAR-T cells demonstrated improved long-term tumor control compared to ide-cel and cilta-cel alone. In addition, IL-7Rα CCR-expression increased T cell numbers in blood, spleen and bone marrow of tumor-bearing mice. These increases were particularly evident in the CD8+population of CAR-T cells in vivo. These results demostrate that private cytokine signaling using small-molecule activatable CCRs can improve efficacy and durability of CAR-T cells. We are testing these CCRs in mouse models of human solid tumors to assess their ability to overcome the immunosuppressive microenvironment. Citation Format: John R. Newcomb, Jun Ren, Sakeena Syed, Zachary Caruolo, Lindsay Webb, Craig McKay, Stephanie Kwei, Carl Novina, Fred Mermelstein. Chimeric cytokine receptors increase memory phenotypes and improve expansion and efficacy of CAR-T cell therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3609.

The Combinatorial Effect of Ad-IL-24 and Ad-HSV-tk/GCV on Tumor Size, Autophagy, and UPR Mechanisms in Multiple Myeloma Mouse Model.

Multiple myeloma is a type of malignant neoplasia whose treatment has changed over the past decade. This study aimed to investigate the effects of combination of Adenovector-carrying interleukin-24 and herpes simplex virus 1 thymidine kinase/ganciclovir on tumor growth, autophagy, and unfolded protein response mechanisms in mouse model of multiple myeloma.Six groups of mice, including Ad-HSV-tk/GCV, Ad-IL-24, Ad-HSV-tk/IL-24, Ad-GFP, and positive and negative controls, were investigated, and each group was injected every 72 h. The tumor size was measured several times. The expression of LC3B evaluated through western blotting and ASK-1, CHOP, Caspase-3, and ATF-6 genes in the UPR and apoptosis pathways were also analyzed by the quantitative polymerase chain reaction (qPCR) method.The present results showed that the injection of Ad-HSV-tk/GCV, Ad-HSV-tk/IL-24, and metformin reduced the tumor size. The expression of LC3B was significantly higher in the treatment groups and positive control groups compared to the negative control group. The expression of CHOP, caspase-3, and ATF-6 genes was significantly higher in the Ad-IL-24 group compared to the other treatment groups. Besides, the ASK-1 expression was significantly lower in the Ad-IL-24 group as compared to the other groups. Overall, the results indicated that the presence of the HSV-tk gene in the adenovectors reduced the size of tumors and induced autophagy by triggering the expression of LC3B protein. The presence of the IL-24 might affect tumor growth but not as much the therapeutic effect of HSV-tk. Furthermore, the results indicated that co-administration of IL-24 and HSV-tk had no synergistic effect on tumor size control.

An orthotopic syngeneic mouse model of bortezomib-resistant multiple myeloma.

While bortezomib has significant benefits in multiple myeloma (MM) therapy, the disease remains incurable due to the invariable development of bortezomib resistance. This emphasises the need for advanced models for preclinical evaluation of new therapeutic approaches for bortezomib-resistant MM. Here, we describe the development of an orthotopic syngeneic bortezomib-resistant MM mouse model based on the most well-characterised syngeneic MM mouse model derived from spontaneous MM-forming C57BL/KaLwRij mice. Using bortezomib-resistant 5TGM1 cells, we report and characterise a robust syngeneic mouse model of bortezomib-resistant MM that is well suited to the evaluation of new therapeutic approaches for proteasome inhibitor-resistant MM.

Multi-Level Control of Myeloma Cell Proliferation and Genomic Instability By the PDZ Binding Kinase (PBK)

Genomic instability and cell proliferation play important roles in the development and progression of cancer. We identified a six-gene kinase signature that correlated with overall genomic instability in multiple human cancers including multiple myeloma (MM). PDZ Binding Kinase (PBK) was one of the top kinases in this signature. Inhibiting PBK downregulated E2F and FOXM1-related pathways and impacted several members of the DREAM complex, which represses cell cycle genes during quiescence. We further evaluated whether PBK affects entry into mitosis by controlling FOXM1 phosphorylation and affects genome stability. Using co-immunoprecipitation and chromatin immunoprecipitation assays, we observed that PBK binds to and phosphorylates FOXM1, leading to upregulation of FOXM1 target genes. Overexpression of PBK increased the association of LIN54 (a major component of the MuvB complex) with phosphorylated-FOXM1 and inhibited LIN54 interaction with E2F4 in the DREAM complex. Consistently, PBK knockdown or inhibitor increased the LIN54-E2F4 interaction and inhibited the LIN54 and phosphorylated-FOXM1 interaction. The inhibitor also impaired tumor growth in vitro and significantly increased the efficacy of a chemotherapeutic agent ( P = 0.0011) in a subcutaneous mouse model of MM. Overall, these data indicate that PBK phosphorylates FOXM1, then FOXM1 interacts with MuvB which is associated with the start of mitosis, dissociating it from E2F4 in the DREAM complex, thus allowing entry into mitosis and subsequent tumor growth. Given that phosphorylation of FOXM1 also activates the expression of major DNA repair genes (including RAD51, EXO1), we investigated whether PBK affects genome stability. Surprisingly, we observed that PBK also directly phosphorylates DNA repair/HR genes, such as flap structure-specific nuclease 1 (FEN1), and that PBK inhibition reduces spontaneous and chemotherapy (melphalan)-induced genomic instability ( P < 0.05). A significant upregulation of PBK has also been observed in MM patient samples at relapse (after melphalan treatment) relative to paired samples collected at diagnosis (GSE19554). To further investigate the consequences of elevated PBK in vivo, we transformed the normalized PBK expression into a Z-score and used this to divide patients (in MMRF-COMPASS) into three groups based on PBK expression (i.e., high, medium and low PBK expression groups). Patients with high PBK expression had poor overall survival as compared to those with medium and low PBK expression ( P=1.127e−13). DNA replication, mismatch repair, homologous recombination, cell cycle and Fanconi anemia were the top upregulated pathways in patients with high PBK expression. Known drivers of DNA replication, including those involved in the initiation of once-per-cell cycle replication and several DNA repair and HR genes, which are part of different genomic instability signatures (such as RAD51, RAD51C, RAD54B, RAD54L, EXO1, BRCA1, FEN1, ATAD2, CENPA, MAD2L1, TTK), were significantly overexpressed in patients with high PBK expression. Interestingly, FOXM1, which can impact both replication and genome stability was also overexpressed (Log2 Fold change of 1.8; P adj = 1.27E-86). In summary, we demonstrate that PBK drives DNA replication and genomic instability in MM cells by acting at multiple levels. Therefore, PBK inhibitors investigated here have the potential to impair growth and increase the efficacy of chemotherapeutic agents while reducing spontaneous as well as chemotherapeutic agent-induced genomic instability in MM.

Cells of the Osteoblast Lineage Cross-Talk with Myeloid-Derived Suppressor Cells to Promote Multiple Myeloma Growth

Multiple myeloma (MM) is a plasma cell malignancy that thrives in the bone marrow (BM) and is highly influenced by the BM tumor microenvironment. Osteolytic bone disease is a hallmark of MM and is partly due to osteoblast (OB) inhibition. MM cells suppress osteoblast maturation and function via inhibition of the critical Runt-related transcription factor 2 (Runx2) in immature OBs. However, immature cells of the osteoblast lineage (e.g. pre-osteoblasts) remain present and even increased in the MM bone microenvironment and their contribution to the progression of MM has not been well understood. We previously developed a syngeneic mouse model of MM in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2 -/- mice), and demonstrated that OB-Runx2 deficiency creates a highly inflammatory BM microenvironment that is responsible for MM cell bone-homing to new bone sites. We therefore hypothesize that pre-osteoblasts play a role as promoters of MM cell survival and proliferation. To determine the direct effect of pre-osteoblasts on MM cells, we established co-cultures of pre-osteoblasts with MM cells. 5TGM1 murine MM cells were cocultured with MC3T3 murine pre-osteoblasts and newborn mouse calvarial pre-osteoblasts respectively. Within 48hrs of co-culture, each of pre-osteoblast populations slightly stimulated proliferation of 5TGM1 MM cells. These data suggest that pre-osteoblasts do not directly affect myeloma growth in vitro. Therefore, we next focus our studies on the role of pre-osteoblasts in MM progression in vivo. Firstly, we used OB-Runx2 deficient mouse model to assess the impact of pre-osteoblast accumulation on MM progression in vivo. 2x10 5 5TGM1-Luciferase MM cells were injected into the right tibia of OB-Runx2 -/- mice and control mice. Bioluminescence imaging and serum IgG2bκ (a soluble marker of 5TGM1 MM cells) ELISA demonstrated that, compared with controls, OB-Runx2 -/- mice had a much larger tumor burden. Following, to more thoroughly evaluate the role of pre-osteoblasts in early stage of MM cell engraftment in bones, we used MC3T3 murine pre-osteoblasts to modulate pre-osteoblast populations at the sites of MM engraftment. 2x10 5 5TGM1-Luciferase MM cells were injected directly into the right tibia of NSG mice with or without equal numbers of MC3T3 pre-osteoblasts. Tumors grew significantly larger when co-injected with 5TGM1 MM cells and MC3T3 pre-osteoblasts than injected with 5TGM1 MM cells alone, which was confirmed by luciferin imaging and serum IgG2bκ ELISA. These data suggest that pre-osteoblasts provide critical support for MM progression in vivo. Given that pre-osteoblasts have no direct effect on the growth of MM cells in vitro, we hypothesized that the pre-osteoblastic niche may regulate MM cells via other intermediary cells in BM. We previously showed that OB-Runx2 deficiency induces an immunosuppressive BM microenvironment that is marked by an increase of myeloid-derived suppressor cells (MDSCs). To investigate whether pre-osteoblasts support MM cell survival and proliferation through the functional crosstalk with MDSCs, 5TGM1 MM cells were co-cultured with MC3T3 pre-osteoblasts and mouse calvarial pre-osteoblasts respectively in the presence or absence of MDSCs. Interestingly, pre-osteoblasts significantly promoted the proliferation of MM cells under the existence of MDSCs. To extend these findings in vivo, we next determined whether MDSC depletion can alleviate the promoting effect of pre-osteoblasts on MM progression. Gemcitabine (GEM) is an FDA-approved anti-cancer agent and MDSC inhibitor used in the treatment of solid tumors but not commonly used in MM therapy. We again injected 5TGM1-Luciferase MM cells into the right tibia of NSG mice with or without co-injection of MC3T3 pre-osteoblasts. We treated tumor-bearing mice with PBS or GEM (i.p. 30 mg/kg/week) for 4 weeks. Bioluminescence imaging and serum IgG2bκ ELISA demonstrated that GEM could overcome the proliferative effect of pre-osteoblasts on MM cells in mouse model, and this effect was independent of NK, B and T cells. Taken together, using in vivo and in vitro models, we show that pre-osteoblasts have a positive regulatory impact on MM cells through communication with MDSCs. Ongoing mechanistic studies aim to delineate how pre-osteoblasts modulate the functions of MDSCs to promote MM progression.

Multiple Myeloma Induced IL-6 Reprograms Lipid Metabolism through a CD36 Dependent Mechanism

Multiple Myeloma (MM) requires a high metabolic turnover to allow for expansion and paraprotein production. MM metabolism is complex relying on various metabolic pathways to fuel its survival including fatty acid (FA) oxidation (1, 2). The liver is a master regulator of fatty acid metabolism and distribution. It also stores FA as lipid droplets during steady state or produces ketone bodies during a starvation state (3). This study aimed to determine whether MM alters FA uptake within the liver and by what mechanism this occurs. To investigate the role of FA metabolism we used a mouse model of MM (5TGM1 (GFP) cells into KaLwRij mice). Analysis of serum from 5TGM1 (GFP) engrafted KaLwRij mice showed increased FFA when compared to control animals. RT-qPCR of RNA isolated from liver samples showed a decrease in genes involved in FA uptake and metabolism. These genes included the long chain fatty acid transporter CD36, which belongs to the class B scavenger receptors and is essential for uptake of LCFA in hepatocytes. In vitro modelling showed that primary hepatocytes cultured in conditioned media from 5TGM1 cells had significantly reduced expression of CD36. Furthermore, serum isolated from MM patients (n=6) downregulated CD36 expression in the human hepatocarcinoma cell line, HepG2. These data support the hypothesis that MM induces a factor that alters lipid metabolism in the liver. To detemine the factor that MM secretes, and which regulates FA uptake in the liver, a cytokine array of the serum from 5TGM1 (GFP) engrafted KaLwRij mice was compared to control serum. Pathway analysis revealed interleukin-6 (IL-6) as possible key factor involved in regulating liver FA uptake. In vitro gene expressions analysis of mouse primary hepatocytes revealed that addition of IL-6 to the medium inhibited expression of CD36 and also showed that primary hepatocytes had decreased reliance on FA oxidation when treated with IL-6. Furthermore. 5TGM1 (GFP) engrafted KaLwRij mice showed increased serum IL-6 levels compared to controls. Finally, using the IL-6 neutralising antibody, we observed that this blocked CD36 downregulation in HepG2 cultured with MM patient serum. Here we demonstrate that MM changes FA metabolism in the liver through upregulation of IL-6. Gene expression of FA genes identifies CD36 is down regulated in hepatocytes in response to IL-6. These data suggest that MM is able to redirect FFA away from the liver by down regulating CD36, which mediates FFA uptake in the liver. References Panaroni C, Fulzele K, Mori T, Siu KT, Onyewadume C, Maebius A, et al. Multiple myeloma cells induce lipolysis in adipocytes and uptake fatty acids through fatty acid transporter proteins. Blood. 2022;139(6):876-88.Tirado-Vélez JM, Joumady I, Sáez-Benito A, Cózar-Castellano I, Perdomo G. Inhibition of fatty acid metabolism reduces human myeloma cells proliferation. PLoS One. 2012;7(9):e46484.Hodson L, Gunn PJ. The regulation of hepatic fatty acid synthesis and partitioning: the effect of nutritional state. Nat Rev Endocrinol. 2019;15(12):689-700.

Targeted Inhibition of Myeloperoxidase (MPO): A New Therapeutic Strategy for the Treatment of Multiple Myeloma

Despite major improvements in therapeutic strategies for patients with multiple myeloma (MM), effective treatment still remains a persistent challenge, as patients ultimately relapse and succumb to the disease. In the last decade, studies have highlighted the reciprocal interaction between MM plasma cells (PC) and the bone marrow (BM) microenvironment in regulating immune evasion, disease progression and persistence. As MM PC rely on BM stromal cells and their secreted factors for their survival and growth, the therapeutic targeting of the BM microenvironment may prove to be a novel and successful strategy for myeloma care in the future. Myeloid-derived suppressor cells (MDSC), a heterogenous population of myeloid cells are described to promote MM progression through immunosuppression and induction of angiogenesis. Myeloperoxidase (MPO), a key inflammatory enzyme important in host defence, is reported to be the most highly upregulated gene in MDSCs in murine cancer models. Recently, the accumulation of MPO within the tumour microenvironment has attracted much attention with a number of studies describing a role for MPO in regulating cancer development due to its potent pro-oxidative and proinflammatory properties. Our most recent findings have revealed new functional roles for myeloid-derived MPO in the BM microenvironment of MM. Specifically, we demonstrate that myeloid cell populations are increased within the BM of 5TGM1 tumour-bearing mice and that MM PC may directly influence Mpo gene expression in BM-derived myeloid cells. Mechanistically, we report that MPO has the capacity to induce the expression of key MM growth factors, and exerts potent immune suppression by inhibiting anti-tumour T-cell responses. Remarkably, in the syngeneic KaLwRij/5TGM1 mouse model of MM, targeted inhibition of MPO with the suicide substrate 4-Aminobenzoic acid hydrazide (4-ABAH) demonstrated a significant reduction in overall MM tumour burden. Here, we investigate for the first time the efficacy of an orally bioavailable irreversible small molecule inhibitor of MPO (MPOi) in the preclinical Vk*MYC murine model of myeloma. Twelve-week-old C57BL/6J mice were intravenously inoculated with Vk*MYC (Vk14451-GFP) cells and tumour progression was monitored by serum paraprotein electrophoresis (SPEP), whilst endpoint GFP+ tumour cells in the bone marrow were quantitated by flow cytometry. To characterise myeloid cell populations and associated Mpo expression in the Vk*MYC tumour landscape, we utilised flow cytometry to quantitate CD11b+ cells and used magnetic activated cell separation to isolate these populations and characterise the expression of Mpo by qPCR. Our studies confirm that CD11b+ myeloid cells are significantly increased in the BM of Vk*MYC tumour-bearing mice (p<0.01), accompanied by an upregulation of MPO mRNA expression (p<0.001). To assess the efficacy of MPOi in MM, mice were treated with MPOi or vehicle alone twice daily by oral gavage, with treatment initiated at the time of Vk*MYC inoculation. Notably, mice receiving MPOi presented with significantly reduced endpoint tumour burden (9 weeks post tumour cell inoculation). We observed a 15.2% and 31.4% reduction in MM tumour as determined by hind limb GFP% (p<0.05) and SPEP (p<0.01) respectively, compared to vehicle control. Additionally, mRNA analysis of complete BM revealed an upregulation of the critical cytokine IFN gamma (p<0.05) and the downregulation of the potent proangiogenic factor VEGF (p<0.05) in mice treated with MPOi, suggesting MPO inhibition in MM may be an advantageous means to regulate the BM microenvironment and impede disease progression. However, when MPOi treatment was initiated at first signs of detectable disease, (as identified by the presence of a monoclonal spike by SPEP; 5 weeks post tumour cell inoculation), no difference in endpoint tumour burden was observed. This suggests that targeted inhibition of MPO using MPOi may be more effective in at early stages of MM development. In conclusion, the findings presented in this study indicate that inhibiting MPO activity with MPOi, as a single agent therapy, attenuates MM tumour growth in the Vk*Myc mouse model. With limited therapies used in the clinic that target the stromal microenvironment, these findings suggest MPOi could be investigated as a potential novel treatment option that may be included in combination with current frontline therapeutic agents.

Suppression of TRIP13 Induces Metabolic Changes and Potentiates Ferroptosis in Multiple Myeloma

Introduction Despite the remarkable success of combination treatments, multiple myeloma (MM) still poses significant challenges, with a high percentage of patients experiencing relapse over time. Additional metabolic alterations are found in relapsed and refractory MM; however, their impacts have not been fully elucidated. Expression of thyroid hormone receptor interactor 13 (TRIP13) has been identified by Gene Expression Profile (GEP)-70 to correlate with poor prognosis in MM. TRIP13 is an AAA ATPase that regulates the spindle assembly checkpoint in mitosis. Based on GEP data from 34 paired baseline and relapse samples, TRIP13 continuously increased from baseline to first and to second relapse. Overexpression of TRIP13 induces bortezomib resistance. In this study, we aimed to investigate how TRIP13 might regulate MM cell metabolism and to use this information to develop a novel combination strategy to overcome MM resistance. Methods Knockout (KO) of TRIP13 in OPM2 and MM1.S cells was generated by dual gRNAs CRISPR-Cas9 editing deleting a fragment between exon 4 and exon 5. Cell growth curves and response to bortezomib were recorded in the control and TRIP13-KO cells. Metabolomics was performed to reveal cellular metabolic alterations. Seahorse analysis was used to test the mitochondrial stress and glycolysis stress. To investigate whether TRIP13 KO promotes ferroptosis, an intracellular iron-dependent cell death characterized by the accumulation of lipid peroxides, we applied C11-BODIY staining after treatment with Erastin, a ferroptosis-inducer. Expression levels of cyclooxygenase 2 (encoded by PTGS2, a hallmark of ferroptosis), cystine transporter (xCT), and intracellular glutathione peroxidase 4 (GPX4) were analyzed. In addition, the protein levels of iron metabolic molecules, including iron importer transferrin receptor protein 1 (TFRC), iron exporter ferroportin 1 (FPN1), ferritin heavy chain 1 (FTH1), and nuclear receptor coactivator 4 (NCOA4) were assessed. To study whether TRIP13 KO delays MM progression in an immune-competent MM mouse model, Vκ12653 murine MM cells were genetically modified by CRISPR-mediated TRIP13-KO and then injected into C57BL/6 mice. Mouse survival was monitored. Results The cell-doubling rate of TRIP13-KO cells was decreased by 50% compared to control cells. After 24 hours of treatment with 5 nM bortezomib, cell viability of TRIP13-KO cells decreased by 31% compared with control cells. The metabolomic studies revealed that TRIP13-KO OPM2 and MM1.S cells both had significantly decreased intracellular L-serine (FC = 0.57) but increased pyruvate (FC = 1.79), citric acid (FC = 1.76), and isocitric acid (FC = 1.64), indicating TRIP13 may regulate serine metabolism, mitochondrial function, and cellular redox balance. Seahorse analysis indicated that TRIP13-KO MM cells showed decreased glycolysis (decreased by 30%, p < 0.001) and glycolytic capacity (decreased by 33%, p < 0.001) while oxidative phosphorylation showed little change. Moreover, lipid peroxidation and PTGS2 were increased in TRIP13-KO cells after Erastin treatment, indicating that these cells were more vulnerable to ferroptosis. Mechanistically, inhibition of TRIP13 decreased GPX4, FPN1, FTH1, and increased NCOA4, while overexpression of TRIP13 showed the opposite changes, suggesting that targeting TRIP13 sensitizes MM cells to ferroptosis by impairing cellular redox balance and increasing the labile-iron pool. Lastly, TRIP13-KO significantly prolonged mouse survival in the Vκ12653 mouse model (median survival: TRIP13-KO 93 days vs. Control 60.5 days, p < 0.001). Conclusion Our study revealed that TRIP13 plays a critical role in regulating MM cell metabolism. By suppressing TRIP13, we observed increased sensitivity of MM cells to bortezomib, leading to enhanced ferroptosis-mediated cell death and prolonged mouse survival. These findings strongly suggest that targeting TRIP13 could be a promising approach in MM therapy. Moving forward, our future investigations will concentrate on unraveling the precise molecular mechanisms underlying TRIP13-mediated alterations in cell metabolism. Additionally, we plan to explore the potential synergistic effects of TRIP13 inhibition in combination with metabolic targeted treatments, such as venetoclax, to further enhance therapeutic outcomes in MM.

Discovery and Evaluation of C6-Substituted Pyrazolopyrimidine-Based Bisphosphonate Inhibitors of the Human Geranylgeranyl Pyrophosphate Synthase and Evaluation of Their Antitumor Efficacy in Multiple Myeloma, Pancreatic Ductal Adenocarcinoma, and Colorectal Cancer.

Novel C6-substituted pyrazolo[3,4-d]pyrimidine- and C2-substituted purine-based bisphosphonate (C6-PyraP-BP and C2-Pur-BP, respectively) inhibitors of the human geranylgeranyl pyrophosphate synthase (hGGPPS) were designed and evaluated for their ability to block the proliferation of multiple myeloma (MM), pancreatic ductal adenocarcinoma (PDAC), and colorectal cancer (CRC) cells. Pyrazolo[3,4-d]pyrimidine analogs were identified that induce selective intracellular target engagement leading to apoptosis and downregulate the prenylation of Rap-1A in MM, PDAC, and CRC cells. The C6-PyraP-BP inhibitor RB-07-16 was found to exhibit antitumor efficacy in xenograft mouse models of MM and PDAC, significantly reducing tumor growth without substantially increasing liver enzymes or causing significant histopathologic damage, usually associated with hepatotoxicity. RB-07-16 is a metabolically stable compound in cross-species liver microsomes, does not inhibit key CYP 450 enzymes, and exhibits good systemic circulation in rat. Collectively, the current studies provide encouraging support for further optimization of the pyrazolo[3,4-d]pyrimidine-based GGPPS inhibitors as potential human therapeutics for various cancers.

Inhibition of Sphingosine Kinase 2 Enhances Immunotherapy in Mouse Model of Multiple Myeloma

Introduction: Sphingolipid metabolism, in particular the ceramide:sphigosine 1-phophate (S1P) rheostat, is increasingly recognized as a key pathway in cancer biology, inflammation and immune responses. Sphingosine kinase (SK) 1 and 2 catalyze the formation of S1P. We previously reported that SK2 but not SK1 was overexpressed in multiple myeloma (MM) cells. Treatment with opaganib, an SK2-specific inhibitor, downregulated the expression of c-Myc and Mcl-1, resulting in apoptosis of MM cells. A phase I clinical trial of opaganib in patients with relapsed/refractory MM demonstrated the safety and evidence of anti-myeloma activity of SK2 inhibition. However, the roles of SK2 in host's anti-tumor immunity are unclear. We herein determined the effects of SK2 on the functions of T cells and myeloid derived suppressor cells (MDSCs), the underlying mechanisms, and potential clinical application of SK2 inhibition in enhancing immunotherapy. Methods: For tumor models, transplantable mouse VK*Myc myeloma cells, CT-2A gliomas cells, B16F10 melanoma cells, or TRAMP C2 prostate cancer cells were implanted into SK2 -/- knockout (KO), SK1 -/- KO or WT mice. Multi-color flow cytometry was used to measure various immune cells. Anti-CD8 antibody (clone YST-169.4) and anti-Gr-1 antibody (clone RB6-8C5) were used to deplete CD8 T cells and MDSCs in vivo, respectively. Adaptive transfer of enriched CD8 T cells and bone marrow derived MDSCs was performed. Cytokines and chemokines were measured by multiplex assay. Transcriptome sequencing and omics analyses were performed on mouse primary CD8 T cells and MDSCs. CRISPR/Cas9 genetic knockout experiments were used to validate genes identified from the sequencing results. Mouse BCMA CAR T model was established using syngeneic VK*Myc myeloma cells and anti-mouse BCMA CAR T cells. Additionally, the combinatorial effects of opaganib and 4-1BB agonist were examined in VK* Myc myeloma mouse model. Results: When we injected VK*Myc myeloma cells IV into SK1 -/- KO, SK2 -/- KO or WT mice, none of SK2 -/- KO mice developed myeloma or died from myeloma whereas 85-90% of WT recipient mice and all SK1 -/- KO mice developed myeloma and died. Similarly, tumor development was significantly attenuated in SK2 -/- KO mice when CT-2A gliomas cells (intracranial injection), B16F10 melanoma cells (IV) or TRAMP C2 prostate cancer cells (IV) were implanted, demonstrating broad anti-tumor effects of SK2 deletion. We found that the homing of myeloma cells was not affected in SK2 -/- KO mice. SK2 -/- KO recipient mice showed significantly increased number of CD8 T cells and decreased number of MDSCs. Depletion of CD8 T cells using CD8 antibody rendered SK2 -/- KO mice susceptible to myeloma development and administration of anti-Gr-1 antibody increased CD8 T cells and made SK2 WT mice resistant to myeloma development. Adaptive transfer of SK2 -/- KO CD8 T cells suppressed myeloma development, indicative of a critical role of SK2 in T cell regulation. Cytokine profiling revealed significantly increased level of IFNγ and IL-12 and suppressed level of IL-6, GM-CSF, CCL2, TNFα, and IL-10 in SK2 -/- KO recipient mice. CD8 T cells isolated from SK2 -/- KO mice were more proliferative in response to CD3/CD28 antibody stimulation, had higher expression of CD69, Granzyme B and IFNγ but lower level of PD-1, LAG-3, TIGIT and TIM-3, and were more cytotoxic against myeloma cells. Differential gene expression analyses showed up-regulation of IL-36gamma and kallikrein 1-related peptidase b22 (KLK1B22) in SK2 -/- KO CD8 T cells. Knockout of IL-36gamma or KLK1B22 with CRISPR/Cas9 reversed the effects of SK2 deletion on T cell activation and exhaustion, demonstrating the important role of IL-36gamma and KLK1B22 in SK2 mediated T cell regulation. Compared to T cells from WT mice, T cells from SK2 -/- KO mice exhibited enhanced anti-myeloma activities in our VK*Myc myeloma anti-BCMA CAR T mouse model. Finally, treatment of mice with opaganib increased the number of T cells and decreased the number of MDSCs and showed synergistic anti-myeloma activities when combined with 4-1BB agonist in VK*Myc myeloma model. Conclusions: Our study demonstrated that inhibition of SK2 enhances anti-tumor immunity by promoting CD8 T cell activation likely through IL-36gamma and KLK1B22. These studies provide rationale for clinical trials investigating the combination of opaganib with CAR T therapy or other immunotherapy in cancer treatment.

P-330 The third-generation genetic engineered mouse model of late-stage multiple myeloma

P-330 The third-generation genetic engineered mouse model of late-stage multiple myeloma

PPFIBP1 activates NF-κB signaling to enhance chemoresistance of multiple myeloma

Easily developed chemoresistance is a major characteristic of multiple myeloma (MM) and the main obstacle in curing MM in the clinic, but the key regulators have not been fully identified. In the current study, we find that PPFIA Binding Protein 1 (PPFIBP1) is highly expressed in the plasma cells from MM patients, and higher PPFIBP1 expression predicts poorer outcomes. PPFPIBP1 enhances chemoresistance of MM cells to the treatment of bortezomib (BTZ), a proteasome inhibitor, and manipulation of PPFPIBP1 can alter chemosensitivity of MM cells to BTZ. Mechanistic studies reveal that PPFPIBP1 directly binds and stabilizes RelA, promotes the cyto-nuclear translocation of RelA, and activates NF-κB signaling pathway. Targeting PPFPIBP1 in a xenograft mouse model of MM prohibits tumor growth and prolongs overall survival of mice. Taken together, our findings suggest that PPFIBP1 is a crucial regulator of chemoresistance to PIs in MM cells, and shed light on developing therapeutic strategies to overcome chemoresistance by targeting PPFIBP1.