Multiple Myeloma Xenograft Models Research Articles

Abstract 2739: XON27, a novel and potent immunotherapy against hematologic malignancies

Abstract Background: Over the past decades, intensive research has led to the development of innovative therapies (monoclonal and bispecific antibodies, CAR T cells) that have increased the survival rate of patients with multiple myeloma (MM) and B cell lymphoma. However, despite this progress, the majority of patients relapse and become refractory due to the development of resistance. Polyclonal antibodies, with their ability to target multiple antigens, can counteract this resistance. Here we evaluate the safety and efficacy of XON27, a first-in-class glyco-humanized polyclonal antibody (GH-pAb), in MM and other blood cancers. Material and Methods: The ability of XON27 to induce antibody-dependent cellular phagocytosis (ADCP), complement-dependent cytotoxicity (CDC) and apoptosis was tested in a panel of hematological malignancy cells and peripheral blood mononuclear cells (PBMC). Specific binding to human blood cancers was assessed using tissue microarrays. To study resistance mechanisms, MM cell lines were cocultured with macrophages in the presence or absence of XON27 and macrophage. To study relapse mechanisms and tumorigenicity, repeated in vitro administration of XON27 was evaluated in KMS-12-BM. The in vivo efficacy of XON27 was evaluated in KMS-12-BM NMRI nude mice model. Pharmacokinetics and safety of this drug were assessed in non-human primate after repeated IV dosing up to 60mg/kg.Results: XON27 induces potent and specific cytotoxicity in several blood malignancy cell lines including human MM cells via multiple mechanisms: CDC (EC50=35.84 ug/ml), apoptosis (IC50=100 ug/ml) and ADCP (up to 40% of cell death at 50 ug/ml). The cytotoxicity induced by XON27 in the KMS-12-BM was significantly more potent compared to daratumumab (anti-CD38) in both CDC and apoptosis assays, XON27 was able to kill up to 100% of cancer cells without affecting PBMC. XON27 showed cross-reactivity with blood cancer patient biopsies without staining healthy tissue. In addition, repeated administrations of XON27 demonstrate its ability to effectively kill tumor cells after each administration. No resistance is induced after repeated treatments. Interestingly, XON27 blocked the proliferation of residual tumor cells for up to 45 days after the second treatment at 50 ug/ml compared to the control condition, demonstrating sustainable effect of XON27 on tumorigenicity. The in vitro efficacy of XON27 was translated into in vivo efficacy in a murine MM xenograft model. It induced a significant reduction in tumor growth of up to 75%. XON27 was also characterized by a high tolerability profile and satisfactory exposure in primates. Conclusion: Although many therapeutic advances have been made in the field of blood cancers, myeloma remains an incurable disease with a real need for new innovative therapies. XON27 represents a promising and selective immunotherapy which may provide an effective and safe treatment against refractory myeloma. Citation Format: Carine Ciron, Pierre Morice, Françoise Shneiker, Odile Duvaux, Firas Bassissi. XON27, a novel and potent immunotherapy against hematologic malignancies [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 2739.

Abstract 6046: CFT8634, a BRD9 BiDAC™ degrader, is active in a subset of multiple myeloma cell line models and synergistic when combined with pomalidomide or dexamethasone

Abstract Recent literature has shown that loss-of-function of BRD9, a component of the noncanonical SWI/SNF (ncSWI/SNF) complex, mediated by RNA interference or by BRD9 degrader compounds can inhibit multiple myeloma (MM) cell lines and primary MM cell proliferation in vitro, as well as inhibit mouse MM xenograft tumor growth in vivo. Additionally, in vitro synergy was observed when a BRD9 degrader was combined with either dexamethasone or pomalidomide. CFT8634 is a potent and selective oral BiDAC™ degrader of BRD9 that entered a clinical trial for the treatment of SMARCB1-perturbed cancers, including synovial sarcoma and SMARCB1-null tumors. Pharmacokinetic and pharmacodynamic data from this trial demonstrated dose-proportional human plasma exposure and robust BRD9 degradation in patients. Here we show that CFT8634 has anti-proliferative activity in a subset of MM cell lines that translates into tumor growth inhibition in MM xenograft models at clinically relevant CFT8634 exposures. We observe that cell lines less sensitive to pomalidomide tend to be significantly more sensitive to CFT8634 treatment. As pomalidomide is a SoC treatment in MM, we interrogated the ability to combine CFT8634 and pomalidomide. CFT8634 demonstrates synergy with pomalidomide in MM cell lines where CFT8634 is anti-proliferative as a single agent. We further show that clinically relevant exposures of CFT8634 demonstrate synergy with pomalidomide in vivo in the NCI-H929 mouse xenograft model. This model is relatively unresponsive to pomalidomide alone, suggesting that CFT8634 can render otherwise recalcitrant MM tumors sensitive to the effects of pomalidomide in combination. Pharmacokinetic and pharmacodynamic analyses show that in combination, CFT8634 and pomalidomide do not interfere with the ability to degrade each other’s targets (BRD9 and IKZF1/3, respectively) despite both utilizing the E3 ligase cereblon. As the corticosteroid dexamethasone is another SoC treatment given in combination with pomalidomide, we explored the ability to combine dexamethasone with CFT8634. CFT8634 demonstrates synergy with dexamethasone in the RPMI-8226 in vivo xenograft model. This combination leads to tumor regressions at clinically relevant doses and outperforms the current combination of pomalidomide with dexamethasone. In conclusion, we demonstrate in vitro and in vivo activity in an expanded set of MM models using the clinical oral BRD9 degrader CFT8634 as a single agent and show in vivo synergy between CFT8634 and SoC agents pomalidomide and dexamethasone at clinically relevant doses. Citation Format: Laura L. Poling, David Cocozziello, Minsng he, Eunju Hurh, Riadh Lobbardi, Katrina L. Jackson, Stewart L. Fisher, Roy M. Pollock. CFT8634, a BRD9 BiDAC™ degrader, is active in a subset of multiple myeloma cell line models and synergistic when combined with pomalidomide or dexamethasone [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 6046.

Abstract 1890: HMA800067, a novel CD38-targeting antibody-drug conjugate (ADC), demonstrated superior anti-tumor activity to daratumumab in preclinical B-cell malignancies models

Abstract Introduction: Daratumumab (Dara), an anti-CD38 monoclonal antibody, has been widely used in the treatment of multiple myeloma (MM). However, some of MM patients exhibit primary or acquired resistance to Dara therapy. A CD38 targeting antibody-drug conjugate (ADC) HMA800067 is developed, in which Dara was conjugated with cytotoxic payload via a novel linker, aiming to have superior anti-tumor efficacy to Dara, even in the subjects with resistance to Dara treatment. Methods: HMA800067 was characterized by ELISA-based binding assay, cell internalization assay, antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) assays. The in vitro anti-tumor potency was assessed against a panel of 24 MM and B cell lymphoma cell lines with various CD38 expressions. Bystander effect of HMA800067 was evaluated in co-culture of CD38− SU-DHL-2 cells with CD38+ Ramos cells. In vivo anti-tumor efficacy was investigated in the multiple MM and Diffuse Large B-cell Lymphoma (DLBCL) subcutaneous xenograft models, including some non-responsive to Dara. Results: HMA800067 displayed comparable binding affinity and internalization capability to Dara in CD38+ Ramos cells. And HMA800067 maintained the ability of Dara to induce the death of CD38+ Daudi cells by ADCC and ADCP, which indicated that conjugation did not change the property of Dara in the ADC upon antigen binding. HMA800067 exhibited a CD38-dependent cytotoxic activity with median IC50 of 0.46 nM against a panel of tumor cell lines, with a trend that the higher CD38 expression, the stronger potency could be seen. Bystander killing effect of HMA800067 was observed in CD38− cells when co-cultured with CD38+ cells in vitro. Furthermore, with the low release of payload in plasma and sustainable high exposure of payload in the tumor, HMA800067 demonstrated dose-dependent and superior anti-tumor efficacy to Dara in all tested models, and 10 mg/kg induced complete tumor regression in MM RPMI-8226, DLBCL SU-DHL-6 and SU-DHL-10 models. For example, in SU-DHL-6 xenograft model, the treatment of intravenous injection of HMA800067 at 10 mg/kg single dose induced complete tumor regression in all the animals within 10 days of administration, which was maintained until the end of study (day 49), while 10 mg/kg Dara twice a week for 2 weeks inhibited tumor growth within 20%-40% without any tumor regression during a four-week observation post initial dosing. Conclusion: HMA800067 demonstrated potent anti-tumor activities in vitro and in vivo in multiple B-cell malignant tumor lines, including those with poor response to Dara. These results supported further development of HMA800067, as a superior therapeutic option for treatment of patients with CD38+ B cell malignancies. Citation Format: Yan Xu, Junqing Liang, Shuwen Jiang, Haibin Yang, Hui Zhang, Fangfang Mao, Jiahuan Zhu, Jianlin He, Na Yang, Jian Wang, WeiHan Zhang, Yongxin Ren, Weiguo Su. HMA800067, a novel CD38-targeting antibody-drug conjugate (ADC), demonstrated superior anti-tumor activity to daratumumab in preclinical B-cell malignancies models [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 1890.

TIM-3, LAG-3, or 2B4 gene disruptions increase the anti-tumor response of engineered T cells.

In adoptive T cell therapy, the long term therapeutic benefits in patients treated with engineered tumor specific T cells are limited by the lack of long term persistence of the infused cellular products and by the immunosuppressive mechanisms active in the tumor microenvironment. Exhausted T cells infiltrating the tumor are characterized by loss of effector functions triggered by multiple inhibitory receptors (IRs). In patients, IR blockade reverts T cell exhaustion but has low selectivity, potentially unleashing autoreactive clones and resulting in clinical autoimmune side effects. Furthermore, loss of long term protective immunity in cell therapy has been ascribed to the effector memory phenotype of the infused cells. We simultaneously redirected T cell specificity towards the NY-ESO-1 antigen via TCR gene editing (TCRED) and permanently disrupted LAG3, TIM-3 or 2B4 genes (IRKO) via CRISPR/Cas9 in a protocol to expand early differentiated long-living memory stem T cells. The effector functions of the TCRED-IRKO and IR competent (TCRED-IRCOMP) cells were tested in short-term co-culture assays and under a chronic stimulation setting in vitro. Finally, the therapeutic efficacy of the developed cellular products were evaluated in multiple myeloma xenograft models. We show that upon chronic stimulation, TCRED-IRKO cells are superior to TCRED-IRCOMP cells in resisting functional exhaustion through different mechanisms and efficiently eliminate cancer cells upon tumor re-challenge in vivo. Our data indicate that TIM-3 and 2B4-disruption preserve T-cell degranulation capacity, while LAG-3 disruption prevents the upregulation of additional inhibitory receptors in T cells. These results highlight that TIM-3, LAG-3, and 2B4 disruptions increase the therapeutic benefit of tumor specific cellular products and suggest distinct, non-redundant roles for IRs in anti-tumor responses.

CD46 and CD59 inhibitors enhance complement-dependent cytotoxicity of anti-CD38 monoclonal antibodies daratumumab and isatuximab in multiple myeloma and other B-cell malignancy cells

ABSTRACT Multiple myeloma (MM) is an incurable malignancy of the B-cell lineage. Remarkable progress has been made in the treatment of MM with anti-CD38 monoclonal antibodies such as daratumumab and isatuximab, which can kill MM cells by inducing complement-dependent cytotoxicity (CDC). We showed that the CDC efficacy of daratumumab and isatuximab is limited by membrane complement inhibitors, including CD46 and CD59, which are upregulated in MM cells. We recently developed a small recombinant protein, Ad35K++, which is capable of transiently removing CD46 from the cell surface. We also produced a peptide inhibitor of CD59 (rILYd4). In this study, we tested Ad35K++ and rILYd4 in combination with daratumumab and isatuximab in MM cells as well as in cells from two other B-cell malignancies. We showed that Ad35K++ and rILYd4 increased CDC triggered by daratumumab and isatuximab. The combination of both inhibitors had an additive effect in vitro in primary MM cells as well as in vivo in a mouse xenograft model of MM. Daratumumab and isatuximab treatment of MM lines (without Ad35K++ or rILYd4) resulted in the upregulation of CD46/CD59 and/or survival of CD46high/CD59high MM cells that escaped the second round of daratumumab and isatuximab treatment. The escape in the second treatment cycle was prevented by the pretreatment of cells with Ad35K++. Overall, our data demonstrate that Ad35K++ and rILYd4 are efficient co-therapeutics of daratumumab and isatuximab, specifically in multi-cycle treatment regimens, and could be used to improve treatment of multiple myeloma.

Circadian Clock REV-ERBs Agonist SR9009 Induces Synergistic Antitumor Activity in Multiple Myeloma by Suppressing Glucose-Regulated Protein 78-Dependent Autophagy and Lipogenesis.

Proteasome inhibitors, such as bortezomib, have demonstrated efficacy in the therapeutic management of multiple myeloma (MM). However, it is important to note that these inhibitors also elicit endoplasmic reticulum stress, which subsequently triggers the unfolded protein response (UPR) and autophagy, which have been shown to facilitate the survival of tumor cells. The disruption of the circadian clock is considered a characteristic feature of cancer. However, how disrupted circadian clock intertwines with tumor metabolism and drug resistance is not clearly clarified. This work explores the antitumor effectiveness of bortezomib and the circadian clock agonist SR9009, elucidating their impact on glucose-regulated protein 78 (GRP78), the autophagy process, and lipogenesis. The antitumor effects of bortezomib and SR9009 were evaluated using human MM cell lines (RPMI8226 and U266) in vitro and in vivo nonobese diabetic/severe combined immunodeficient (NOD/SCID) murine xenograft MM model. The assessment of cell viability was conducted using the cell counting kit-8 (CCK8) method, whereas the measurement of cell proliferation was performed with the inclusion of EdU (5-ethynyl-2'-deoxyuridine). Apoptosis was assessed by flow cytometry. The cells were transduced using adenovirus-tf-LC3, which was labeled with dual fluorescence. Subsequently, confocal imaging was employed to observe and examine the autophagosomes. REV-ERBα knockdown leads to upregulation of ATG5 and BENC1 at the protein level with immunoblot. Changes in the expression levels of GRP78, LC3, stearoyl-CoA desaturase 1 (SCD1), and fatty acid synthase (FASN) were assessed through the utilization of quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. Our results showed that both bortezomib and circadian clock REV-ERBs agonist SR9009 decreased MM viability, proliferation rate and induced an apoptotic response in a dose-dependent manner in vitro. However, the two differ greatly in their mechanisms of action. Bortezomib upregulated GRP78 and autophagy LC3, while circadian clock agonist SR9009 inhibited GRP78 and autophagy LC3. Combined SR9009 with bortezomib induced synergistic cytotoxicity against MM cells. REV-ERBα knockdown lead to upregulation of ATG5, BENC1 and significant upregulation of FASN, and SCD1. Mechanically, SR9009 inhibited the core autophagy gene ATG5 and BECN1, and two essential enzymes for de novo lipogenesis FASN and SCD1. SR9009 had synergistic effect with bortezomib and slowed down murine xenograft models of human MM tumor growth in vivo. Taken together, these results demonstrated that the circadian clock component REV-ERBs agonist SR9009 could inhibit GRP78-induced autophagy and de novo lipogenesis processes and had a synergistic effect with proteasome inhibitors in both in vitro and in vivo models of MM. Our findings shed light on how a disrupted circadian clock interacts with metabolic mechanisms to shape proteasome inhibitor drug resistance and suggest that SR9009 may be able to overcome the inherent drug resistance of proteasome inhibitors.

Ex Vivo Enriched Tumor Antigen-Specific T Cells Are Optimal Effectors of T Cell Engagers and Tumor-Specific T Cell Receptor/T Cell Engager Combination Provides Synergistic Efficacy Against Hematologic Malignancies

Multiple myeloma (MM) and acute myeloid leukemia (AML) are blood cancers that remain difficult to treat because a large proportion of patients have disease that does not respond to currently available therapies. NexImmune's Artificial Immune Modulation (AIM) platform mimics natural dendritic cell function by using nanoparticles engineered with MHC molecules loaded with tumor specific peptides (signal 1) and anti-CD28 (signal 2) for activation and expansion of HLA A*02:01 restricted tumor associated antigen (TAA)-specific cytotoxic CD8 T lymphocytes (CTL). Additionally, T cell engager (TCE) therapy allows for TAA-specific, but T cell receptor (TCR) independent T cell cytotoxicity mediated by immunological synapse formation between targeted cancer cells and T cells. Given that T cell function in MM and AML patients is often perturbed and the response to TCE therapy is determined by pre-existing endogenous T cells of the patient, we hypothesized adoptively transferred multi-antigen specific T cells with a rejuvenated phenotype in combination with TCE therapy might produce optimal efficacy. We compared polyclonal CTL with AIM CTL (CTL that were AIM primed and expanded for optimal antigen experience and specificity). We evaluated the preclinical efficacy of B cell maturation antigen (BCMA)xCD3 TCE+MM-specific AIM CTL combination therapy and CD123xCD3 TCE+AML-specific AIM CTL combination therapy both in vitro and in vivo. In co-culture assays with polyclonal CTL and AIM CTL, we investigated the effect of prior antigen exposure on the efficacy of the TCE against tumor cell lines by measuring the responses to T cells alone and in the presence of TCE treatment. We quantified tumor cell survival and thus determined cytotoxicity of the various culture conditions by luciferase assay. Our analysis showed that, as expected, CD4 T cells had little potency. Non-HLA matched control CTL (bulk or enriched for naïve cells) without TCE showed higher cytotoxicity (data not shown), but these cells were much less potent than AIM CTL (data not shown and Fig. 1A). Combined TCR and TCE-mediated target cell killing was most efficient when using AIM CTL as effector cells (Fig. 1B). Correcting the data for TCR mediated killing revealed that antigen-experienced AIM CTL were indeed superior effectors of TCE potency than antigen inexperienced control CTL. This finding was reproducible regardless of the HLA type of the target cells, consistent with the TCR independent mechanism of action of TCE-mediated killing. Nuclear factor of activated T cells (NFAT) transcriptional reporter assays with Jurkat effector cells and AML target cells revealed that TCE treatment decreased NFAT transcriptional activity in TCE effector cells; moreover, TCE treatment in vivo (treating mice with AIM CTL +/- TCE) increased CD3 levels on AIM CTL. Both observations are consistent with reduced TCR mediated T cell activation in the context of TCE therapy. Furthermore, BCMAxCD3 TCE treatment of mice in a MM xenograft model resulted in decreased PD-1 expression on AIM CTL and enhanced the in vivo efficacy of AIM CTL. Our studies show that AIM CTL display strong anti-tumor activity, and even subtherapeutic AIM CTL cell doses can be highly efficacious when armed with a TCE. Importantly, our data indicate that AIM CTL cells are optimal TCE effectors, superior to less experienced, polyclonal CTL (such as the patient's endogenous T cells). Combining AIM CTL with TCE therapy has the additional benefits of complementary targets and mechanisms of action, reducing the risk of immune escape. Moreover, our preclinical studies suggest that TCE treatment reduces NFAT transcriptional activity and PD-1 induction associated with physiological TCR mediated T cell activation. This suggests that TCE mediated T cell activation can partially suppress TCR mediated T cell activation in AIM CTL, resulting in excellent tumor-specific cytolytic activity while inducing a transcriptional signature that preserves T cell fitness. Following withdrawal of TCE therapy, less exhausted AIM CTL will be present, facilitating the persistence of long-lasting anti-tumor activity and immunosurveillance. Combination of AIM CTL (autologous or HLA matched allogeneic) with TCE therapy is therefore a highly promising and innovative strategy for the induction of durable antitumor activity, and this approach has potential for clinical translation as a novel combinatorial immunotherapy.

CFT8634, a Clinical Stage BRD9 Bi DAC™ Degrader, Is Active in a Subset of Multiple Myeloma Cell Line Models and Synergistic When Combined with Pomalidomide

Recent literature has shown that loss-of-function of BRD9, a component of the noncanonical SWI/SNF (ncSWI/SNF) complex, mediated either by RNA interference or by BRD9 tool degrader compounds can inhibit multiple myeloma (MM) cell lines and primary MM cell proliferation in vitro, as well as inhibit mouse MM xenograft tumor growth in vivo. Additionally, in vitro synergy in MM proliferation assays was observed when a tool BRD9 degrader was combined with the standard of care (SoC) agents, dexamethasone or pomalidomide. Given the continued unmet need of the MM patient population, we explored the therapeutic potential of CFT8634 in this indication. CFT8634, a potent and selective oral BiDAC™ degrader of BRD9, is currently in a Phase 1/2 clinical trial (NCT05355753) for the treatment of SMARCB1-perturbed cancers, including synovial sarcoma and SMARCB1-null tumors. Pharmacokinetic and pharmacodynamic data to date from the ongoing trial of CFT8634 has demonstrated dose-proportional human plasma exposure and robust BRD9 degradation in patient tumor samples thereby establishing proof of mechanism in patients. Here we show that CFT8634 has anti-proliferative activity in a subset of MM cell lines that translates into tumor growth inhibition in MM xenograft models at clinically relevant CFT8634 exposures. We observe that cell lines less sensitive to pomalidomide tend to be significantly more sensitive to CFT8634 treatment. As pomalidomide is a SoC treatment in MM, we interrogated the ability to combine CFT8634 and pomalidomide. CFT8634 demonstrates synergy with pomalidomide in MM cell lines where CFT8634 is anti-proliferative as a single agent. We further show that clinically relevant exposures of CFT8634 demonstrate synergy with pomalidomide in vivo in the NCI-H929 mouse xenograft model (Figure 1). This model is relatively unresponsive to pomalidomide alone, suggesting that CFT8634 can render otherwise recalcitrant MM tumors sensitive to the effects of pomalidomide in combination. Pharmacokinetic and pharmacodynamic analyses show that in combination, CFT8634 and pomalidomide do not interfere with the ability to degrade each other's targets (BRD9 and IKZF1/3, respectively) despite both utilizing the E3 ligase cereblon. In conclusion, we demonstrate in vitro and in vivo activity in an expanded set of MM models using the clinical oral BRD9 degrader CFT8634 as a single agent and show in vivo synergy between CFT8634 and pomalidomide at clinically relevant doses. Our findings suggest that combining CFT8634 with pomalidomide may be a viable therapeutic strategy in treating MM patients.

Discovery of a Novel, First-in-Class Bfl-1 BH3 Mimetic with Pro-Apoptotic Activity

Background: Intrinsic apoptosis is regulated by the B Cell lymphoma 2 (BCL-2) protein family. Anti-apoptotic family members, such as BCL-2, MCL-1 and BFL-1, sequester their pro-apoptotic counterparts through a highly conserved BH3 binding groove. Disruption of this balance leads to mitochondrial pore formation and subsequent cell death. To evade apoptosis, tumors often upregulate the expression of one or more anti-apoptotic family members and as such they have become attractive targets for anti-cancer drug development. BFL-1 (‘Bcl-2 related gene expressed in fetal liver’, gene name BCL2A1) is a lesser-known anti-apoptotic family member, physiologically mainly expressed in the hematopoietic system. BCL2A1 overexpression has been reported in many types of B cell lymphoma. Diffuse Large B Cell Lymphoma (DLBCL) patient sample analysis showed that BCL2A1 expression levels are second only to MCL1 within the anti-apoptotic family. Expression of BFL-1 was shown to be upregulated in MYC+/BCL2+ double hit lymphoma cell lines treated with the BCL-2 inhibitor, Venetoclax, in vivo. Interestingly, BFL-1 positive lymphomas are less sensitive to inhibition of BCL-2 and MCL-1. Hence, targeting BFL-1 is a rational and attractive strategy in DLBCL to improve clinical outcome. Methods: Using hit identification screens followed by iterative structure-activity relationship (SAR) analyses and structure-based design, compound A, a first-in-class, selective BFL-1 BH3 mimetic, was identified. Compound A was evaluated using biochemical, cellular in vitro and in vivo tumor efficacy models. Results: Compound A is a highly potent and selective compound in biochemical assays. In BFL-1 sensitive lymphoma cell lines characterized by high BFL-1 protein expression, compound A was shown to displace BAK and BIM from BFL-1, leading to downstream cleavage of caspase 3 and cell death. Interestingly, these cellular models were resistant to Venetoclax. Compound A exhibited tumor growth inhibition in an engineered BFL-1 overexpressing, MCL-1 KO human multiple myeloma xenograft model. However, in the high BFL-1 expressing SU-DHL-2 DLBCL human xenograft model, compound A did not induce significant PD (cleaved caspase 3) and efficacy in vivo. Conclusion: First-in-class selective BFL-1 BH3 mimetics are shown to specifically inhibit cell growth of lymphoma cell lines in vitro and can induce efficacy in vivo in a BFL-1 overexpressing model. Further studies may be useful to determine whether compound A elicits anti-tumor efficacy in lymphoma alone or in combination with other anti-apoptotic agents.

Acidification of intracellular pH in MM tumor cells overcomes resistance to hypoxia-mediated apoptosis in vitro and in vivo.

Multiple myeloma (MM) is an incurable cancer of malignant plasma cells that engraft in the bone marrow (BM). It is more than likely that the poorly investigated physical parameters of hypoxia and pH in the tumor microenvironment (TME) is critical for MM survival. Here, we explore the effects of a hypoxic environment on pH regulation and its role in MM survival. We used in vitro models of MM, in which the culturing medium was modified to specific pH and pO2 levels and then measured the effects on cell survival that was correlated with changes in intracellular (pHi) and extracellular pH (pHe). In a MM xenograft model, we used PET/CT to study hypoxia-mediated effects on tumor growth. Hypoxia-mediated apoptosis of MM cells is correlated with acidic intracellular pHi (less than < 6.6) that is dependent on HIF activity. Using a polyamide HIF responsive element binding compound, a carbonic anhydrase inhibitor (acetazolamide), and an NHE-1 inhibitor (amiloride) acidified the pHi and lead to cell death. In contrast, treatment of cells with an alkalization agent, Na-lactate, rescued these cells by increasing the pHi (pH > 6.6). Finally, treatment of mice with acetazolamide decreased cell growth in the tumor nodules. Targeting hypoxia and HIF have been proposed as an anti-tumor therapy but the clinical efficacy of such strategies are modest. We propose that targeting the pHi may be more effective at treating cancers within a hypoxic TME.

Bclxl Prevents Progressive Exhaustion in BCMA CAR T Cells with Maintenance of High TCF1 Expressing T Cells

Although BCMA targeted CAR T cell therapies are highly effective in the treatment of multiple myeloma (MM), patients with high disease burden have not fully benefited from this therapy with shorter disease remissions despite initial responses. It is postulated that high disease burden results in chronic antigenic stimulation of CAR T cells with the induction of exhaustion-associated gene signatures and CAR T cells contraction, limiting their in vivo potency. We have previously reported that BCL2L1 (gene encoding for BCLxL) armoring of BCMA CAR T cells enhanced CAR T cells functional fitness and improved proliferation and cytotoxicity after chronic antigenic stimulation in vitro, as well as superior tumor clearance in xenograft models of MM. In the current study we aimed to define the molecular mechanisms that mediates BCL2L1-armored CAR T cell and examine the effect of BCLxL variants on CAR T cells fitness. In in vivo studies, NSG mice were systemically injected with OPM2 cells (stably transduced with firefly luciferase) and led to develop large MM disease burden, treatment with BCLxL armored (BCMA_BCL2L1) vs unarmored CARs (BCMA_CAR) or control T cells completely eliminated the MM disease and significantly improved animal survival. In animals treated with armored CARs (BCMA_BCL2L1) no disease recurrence was noted 180 days post treatment (in contrast to unarmored CARs where disease recurrence was noted within 60 days). BCLxL also improved CARs persistence, with armored CAR T cells being detectable in the marrow of these mice 7 and 14 days post treatment. Of note, BCLxL armored CAR T cells did not demonstrate uncontrolled proliferation as they were no longer detectable on day 120 post-infusion. Furthermore, CITEseq profiling on harvested human T cells 7 days post CAR T cells infusion to diseased mice revealed a differential T cell repertoires and phenotypes between BCMA_CAR and BCMA_BCL2L1 CARs. While unarmored CARs were significantly enriched for exhausted T cells (CD8_Tex), BCMA_BCL2L1 CAR T were enriched with early activated non-exhausted CD8 T cells, precursor exhausted T cells (CD8_Tpex) and naïve CD4 and CD8 T cells. Importantly, single cell genes set enrichment analysis (ssGSEA) revealed a differential metabolic signature with higher oxidative phosphorylation in BCMA_BCL2L1 CAR T cells compared to unarmored CARs. These findings suggested that armoring CAR T cells with BCL2L1 maintain CAR T cells in an activated and precursor exhausted T cell states with improved mitochondrial and metabolic fitness, preventing terminal T cells exhaustion. To further evaluate the impact of BCLxL in suppressing BCMA CAR T cells' exhaustion, we engineered BCMA CAR T cells with armored expression of two BCLxL mutants (BCLxL Δ26-83 or BCLxL Δ46-83) harboring large or small deletions involving a BCLxL regulatory loop. These mutants were previously reported to enhance BCLxL function (Chang et al The EMBO Journal 1997,16:968-977). Under chronic antigenic stimulation (CAS) or hypoxic conditions, wild type or mutants BClxL overexpression in BCMA CAR T cells resulted in higher proliferation rates compared to unarmored CARs. Compared to wild type BClxL, BCLxL Δ26-83 and BCLxL Δ46-83 mutants demonstrated higher proliferation capacity post CARs or under hypoxic conditions. Intriguingly, majority of BCLxL-overexpressing BCMA CAR-T cells, particularly BCMA CAR-T BCLxL_Δ26-83 cells, maintained a central memory (T CM) phenotype following a long co-culture with MM tumor cells with lower levels of exhaustion markers. Importantly BCLxL-overexpressing BCMA CAR-T cells had substantially higher level of TCF1 with lower TOX/TOX2 expression compared to unarmored BCMA CAR T cells. TCF1 high population was also enriched in unstimulated BCLxL-overexpressing BCMA CAR T cells suggesting a positive regulatory impact of BCL2L1 on TCF1 expression, either through direct or indirect pathways. Expectedly, TCF1 high BCMA CAR-T cells overexpressing a BCLxL were mainly associated with the naive/T CM phenotype. In summary, we have identified a role for BCLxL and two mutant variants lacking a loop regulatory domain (BCLxL Δ26-83 or BCLxL Δ46-83), in maintenance of BCMA CAR T cells in central memory and precursor exhausted states with retained high TCF1 expression, even under hypoxic and chronic antigenic stimulation conditions. These studies further support the clinical development of a BCL2L1 armored CAR T cells for the treatment of MM.

The NAD + Metabolic Dependency Restriction Overcomes Drug-Resistance Phenotype of Multiple Myeloma CELLS

Introduction: We previously reported that Nicotinamide Adenine Dinucleotide (NAD +), a master regulator of catabolic metabolism and several enzymatic activities, plays a crucial role for Multiple Myeloma (MM) cells growth; indeed, small molecules targeting the rate-limiting NAD + producer enzyme NAMPT, have potent anti-MM activity. However, targeting dysregulated metabolic landscape of tumors has proven to be a major challenge as suggested by existence of alternative NAD + production routes which confer resistance to NAMPT inhibitors. As result here we focused on whole NAD + metabolic dependency of MM cells by investigating relevance of a comprehensive NAD + metabolic restriction as strategy to enhance activity of currently used anti-MM strategies. Methods: whole transcriptomic analysis of the NADome signature was performed on MM patients by probing MMRF CoMMpass study; its correlation with clinical data (OS and PFS) was also investigated. Next, GSEA algorithm on biological modules was run on MM patients carrying low- vs high-NADome signature. Chemical and genome editing-approaches using CRISPR-Cas9-based strategy were both used to investigate relevance of our findings. Then, an anti-MM drugs screen was used to challenge fully-NAD depleted MM cells using different viability tools. Mechanistic studies were also performed using qPCR, western blot, immunofluorescence analyses, targeted enzymatic assays and in-vivo xenograft MM models. Finally, clinical benefits of our findings were accomplished by challenging publicly available dataset on ASCT-treated MM patients. Results: RNAseq analysis on CoMMPass dataset sharply divided MM patients according to their comprehensive NADome signaling landscape: high-NAD producers showed poorer outcome than those expressing low mRNA levels, both in terms of PFS and OS as well. In line with these data, a panel of MM cell lines showed that pervasive NAPRT levels reduced NAMPT inhibitors activity thus supporting a complete NAD +-depletion for more effective strategies also in in-vivo xenograft models. PROGENy analysis revealed an increased NF-KB activity in NAPRT-depleted cells which in turn resulted in higher oxygen reactive species generation from these cells. Indeed, NAPRT KO cells showed oxidative damage accumulation, with increased malondialdehyde (MDA) activity and lower endogenous antioxidant defenses as suggested by glutathione reductase, glutathione peroxidase and ratio of reduced GSH to oxidized glutathione (GSSG) ratio measurements. Next, mitochondrial-energetic status was also tested by measuring electron transport chain (ETC) Complex I and Complex II activities: a shift towards oxidative metabolism was observed. Overall these data phenocopy the energetic status observed in drug-resistant cells; as result NAPRT-KO makes MM cells resistant to Melphalan. In such a context, the use of NAMPT-inhibitors was able to overcome drug-resistance by re-sensitizing cells to anti-MM activity of DNA damaging agents. Finally, a focused analysis on ASCT-treated MM patients, revealed poor outcome for “high-NAD + producers” thus supporting clinical relevance for NAD + metabolic restriction in these patients. Conclusions. Our data provide evidence that NAD + biosynthesis shapes metabolic phenotypes of MM cells, with its impairment resulting in metabolic reprogramming and cells viability injury. As result, a comprehensive NAD + depletion with dual NAPRT and NAMPT inhibition primes MM cells to alkylating agents which still represent the backbone strategy for ASCT-eligible patients.

Heme Attenuates T Cell Exhaustion and Drives Effector Function: Implications for Immune and Adoptive T Cell Therapy

Introduction: Though frontline agents have been effective in multiple myeloma (MM) therapy, a significant proportion of MM patients relapse and succumb to refractory disease. B-cell maturation antigen (BCMA)-directed chimeric antigen receptor (CAR) T therapy represents an exciting novel therapeutic strategy for MM but still suffers from limited in vivo T cell expansion and CAR T cytotoxicity. Altering the CAR T manufacturing process to produce CAR T cells with less exhausted phenotypes and robust killing is an active area of research. Mitochondrial function and energetics play a central role in regulating T cell fate and function, and heme (iron-protoporphyrin IX) is critical for maintaining electron transport chain activity and oxidative phosphorylation. Heme can be sourced from the extracellular milieu, diet, or intrinsic heme biosynthesis and has a multitude of cellular functions throughserving as a cofactor for enzymatic and metabolic reactions. Additionally, heme is catabolized by heme oxygenase 1, producing the antioxidants biliverdin and bilirubin critical to preserving cellular redox homeostasis. In the present study, we investigate the effects of heme on CAR T cell efficacy. Our results suggest that heme supplementation during ex vivo CAR T manufacturing or supplementation during CAR T-tumor cell engagement can lead to decreased T cell exhaustion and increased tumor killing. Methods: Human healthy donor and MM patient T cells were activated and expanded with α-CD3/CD28 and IL-2 for 7 days +/- hemin, after which immunostaining and metabolic assays were conducted. For CAR T manufacture, T cells were transduced with CAR construct starting on day 3 and were co-cultured with antigen-expressing tumor cells in vitro on day 7-8. Cytotoxicity and cytokine production were assayed after 24 hours of co-culture. Results: In a dose-dependent manner, heme supplementation significantly decreases proportions of LAG3 + and TIM3 + and decreases proportions of CD62L + and TCF1 + cells in both CD4 + and CD8 + subsets isolated from healthy donor and MM patient peripheral blood. Supportive of these observations, inhibition of de novo heme biosynthesis leads to the opposite effect with an increase in proportions of PD1 +, LAG3 +, TIM3 +, and CD62-L + cells. CAR T cells manufactured with heme (heme-CAR T cells) have significantly reduced terminally exhausted phenotypes (PD1 +/LAG3 +/TIM3 +) and increased enrichment of effector memory cells (CD62L -CD45RA -) in both CD4 + and CD8 + subsets. Inquiry of cellular energetics of heme supplemented CAR T cells reveals reduced reactive oxygen species (ROS) and increased mitochondrial membrane potential, consistent with previous reports showing increased membrane potential in effector T cells for greater production of cytokines such as IL-17A, IL-17F, and IFNγ. In co-culture with tumor cells in vitro, heme-CAR T cells have higher tumor-specific lysis and production of TNFα and IL-2. CAR T-tumor cell engagement in the presence of heme resulted in significantly decreased proportions of exhausted CAR T cells and increased production of TNFα. Heme also increases BCMA surface expression in several MM cell lines, highlighting a viable strategy for enhancing BCMA CAR T engagement with MM. Lastly, MM patient bone marrow-localized T cells demonstrate significantly decreased terminally exhausted phenotypes and increased differentiation into effector subsets when expanded with heme. Conclusion: We show that heme increases effector T and CAR T cell function and decreases T cell exhaustion. Increased cytotoxicity of heme-supplemented CAR T cells was associated with reduced ROS and increased membrane potential. Ongoing in vivo studies aim to characterize the efficacy of heme-supplemented CAR T cells in MM xenograft models. Our studies have broader implications for investigating heme supplementation in ex vivo CAR T manufacturing for a wide range of hematological cancers and underscore the need for further investigation of heme uptake and metabolism for strategic enhancement of T-cell based immunotherapies.

Selective MCL-1 inhibitor ABBV-467 is efficacious in tumor models but is associated with cardiac troponin increases in patients

BackgroundMCL-1 is a prosurvival B-cell lymphoma 2 family protein that plays a critical role in tumor maintenance and survival and can act as a resistance factor to multiple anticancer therapies. Herein, we describe the generation and characterization of the highly potent and selective MCL-1 inhibitor ABBV-467 and present findings from a first-in-human trial that included patients with relapsed/refractory multiple myeloma (NCT04178902).MethodsBinding of ABBV-467 to human MCL-1 was assessed in multiple cell lines. The ability of ABBV-467 to induce tumor growth inhibition was investigated in xenograft models of human multiple myeloma and acute myelogenous leukemia. The first-in-human study was a multicenter, open-label, dose-escalation study assessing safety, pharmacokinetics, and efficacy of ABBV-467 monotherapy.ResultsHere we show that administration of ABBV-467 to MCL-1-dependent tumor cell lines triggers rapid and mechanism-based apoptosis. In vivo, intermittent dosing of ABBV-467 as monotherapy or in combination with venetoclax inhibits the growth of xenografts from human hematologic cancers. Results from a clinical trial evaluating ABBV-467 in patients with multiple myeloma based on these preclinical data indicate that treatment with ABBV-467 can result in disease control (seen in 1 patient), but may also cause increases in cardiac troponin levels in the plasma in some patients (seen in 4 of 8 patients), without other corresponding cardiac findings.ConclusionsThe selectivity of ABBV-467 suggests that treatment-induced troponin release is a consequence of MCL-1 inhibition and therefore may represent a class effect of MCL-1 inhibitors in human patients.

Unrevealed roles of extracellular enolase‑1 (ENO1) in promoting glycolysis and pro‑cancer activities in multiple myeloma via hypoxia‑inducible factor 1α.

The involvement of enolase‑1 (ENO1), intracellularly or extracellularly, has been implicated in cancer development. Moreover, anticancer activities of an ENO1‑targeting antibody has demonstrated the pathological roles of extracellular ENO1 (surface or secreted forms). However, although ENO1 was first identified as a glycolytic enzyme in the cytosol, to the best of our knowledge, extracellular ENO1 has not been implicated in glycolysis thus far. In the present study, the effects of extracellular ENO1 on glycolysis and other related pro‑cancer activities were investigated in multiple myeloma (MM) cells invitro and invivo. Knockdown of ENO1 expression reduced lactate production, cell viability, cell migration and surface ENO1 expression in MM cells. Notably, addition of extracellular ENO1 protein in cancer cell culture enhanced glycolytic activity, hypoxia‑inducible factor 1‑α (HIF‑1α) expression, glycolysis‑related gene (GRG) expression and pro‑cancer activities, such as cell migration, cell viability and tumor‑promoting cytokine secretion. Consistently, these extracellular ENO1‑induced cellular effects were inhibited by an ENO1‑specific monoclonal antibody (mAb). In addition, extracellular ENO1‑mediated glycolysis, GRG expression and pro‑cancer activities were also reduced by HIF‑1α silencing. Lastly, administration of an ENO1 mAb reduced tumor growth and serum lactate levels in an MM xenograft model. These results suggested that extracellular ENO1 (surface or secreted forms) enhanced a HIF‑1α‑mediated glycolytic pathway, in addition to its already identified roles. Therefore, the results of the present study highlighted the therapeutic potential of ENO1‑specific antibodies in treating MM, possibly via glycolysis inhibition, and warrant further studies in other types of cancer.

The Potential of JAG Ligands as Therapeutic Targets and Predictive Biomarkers in Multiple Myeloma.

The NOTCH ligands JAG1 and JAG2 have been correlated in vitro with multiple myeloma (MM) cell proliferation, drug resistance, self-renewal and a pathological crosstalk with the tumor microenvironment resulting in angiogenesis and osteoclastogenesis. These findings suggest that a therapeutic approach targeting JAG ligands might be helpful for the care of MM patients and lead us to explore the role of JAG1 and JAG2 in a MM in vivo model and primary patient samples. JAG1 and JAG2 protein expression represents a common feature in MM cell lines; therefore, we assessed their function through JAG1/2 conditional silencing in a MM xenograft model. We observed that JAG1 and JAG2 showed potential as therapeutic targets in MM, as their silencing resulted in a reduction in the tumor burden. Moreover, JAG1 and JAG2 protein expression in MM patients was positively correlated with the presence of MM cells in patients' bone marrow biopsies. Finally, taking advantage of the Multiple Myeloma Research Foundation (MMRF) CoMMpass global dataset, we showed that JAG2 gene expression level was a predictive biomarker associated with patients' overall survival and progression-free survival, independently from other main molecular or clinical features. Overall, these results strengthened the rationale for the development of a JAG1/2-tailored approach and the use of JAG2 as a predictive biomarker in MM.

Chimeric antigen receptor T cells targeting FcRH5 provide robust tumour-specific responses in murine xenograft models of multiple myeloma

BCMA-targeting chimeric antigen receptor (CAR) T cell therapy demonstrates impressive clinical response in multiple myeloma (MM). However, some patients with BCMA-deficient tumours cannot benefit from this therapy, and others can experience BCMA antigen loss leading to relapse, thus necessitating the identification of additional CAR-T targets. Here, we show that FcRH5 is expressed on multiple myeloma cells and can be targeted with CAR-T cells. FcRH5 CAR-T cells elicited antigen-specific activation, cytokine secretion and cytotoxicity against MM cells. Moreover, FcRH5 CAR-T cells exhibited robust tumoricidal efficacy in murine xenograft models, including one deficient in BCMA expression. We also show that different forms of soluble FcRH5 can interfere with the efficacy of FcRH5 CAR-T cells. Lastly, FcRH5/BCMA-bispecific CAR-T cells efficiently recognized MM cells expressing FcRH5 and/or BCMA and displayed improved efficacy, compared with mono-specific CAR-T cells in vivo. These findings suggest that targeting FcRH5 with CAR-T cells may represent a promising therapeutic avenue for MM.

Immunotherapeutic Development of a Tri-Specific NK Cell Engager Recognizing BCMA

Chemotherapy-refractive multiple myeloma (MM) is serious and life-threatening, and better treatments are urgently needed. BCMA is a prominent marker on the cell surface of MM cells, rendering it an accepted target for antibody therapy. Considering that MM is a liquid tumor and immunotherapy has enjoyed success against leukemia, we devise an approach designed to enhance NK cell activity against MM. Ordinarily, NK cells function to naturally survey the body and eliminate malignant cells. Our platform approach is designed to enhance NK function. A tri-specific immune-engaging TriKE is manufactured, consisting of a camelid nanobody VHH antibody fragment recognizing CD16 expressed on NK cells and an scFv antibody fragment specifically recognizing BCMA. These two fragments are crosslinked by the human cytokine interleukin-15 (IL-15) known to have prominent activating effects on NK cells. The molecule, when tested by flow cytometry, shows activation of NK cells in their numbers and activity. Additionally, the molecule demonstrates anti-cancer effects in an in vivo xenograft model of human MM. We believe that the drug will have the capability of enhancing NK cells at the site of the immune synapse, i.e., the effector:target cell interface, and this will promote cancer remissions.

In vivo bone marrow microenvironment siRNA delivery using lipid–polymer nanoparticles for multiple myeloma therapy

Multiple myeloma (MM), a hematologic malignancy that preferentially colonizes the bone marrow, remains incurable with a survival rate of 3 to 6 mo for those with advanced disease despite great efforts to develop effective therapies. Thus, there is an urgent clinical need for innovative and more effective MM therapeutics. Insights suggest that endothelial cells within the bone marrow microenvironment play a critical role. Specifically, cyclophilin A (CyPA), a homing factor secreted by bone marrow endothelial cells (BMECs), is critical to MM homing, progression, survival, and chemotherapeutic resistance. Thus, inhibition of CyPA provides a potential strategy to simultaneously inhibit MM progression and sensitize MM to chemotherapeutics, improving therapeutic response. However, inhibiting factors from the bone marrow endothelium remains challenging due to delivery barriers. Here, we utilize both RNA interference (RNAi) and lipid-polymer nanoparticles to engineer a potential MM therapy, which targets CyPA within blood vessels of the bone marrow. We used combinatorial chemistry and high-throughput in vivo screening methods to engineer a nanoparticle platform for small interfering RNA (siRNA) delivery to bone marrow endothelium. We demonstrate that our strategy inhibits CyPA in BMECs, preventing MM cell extravasation in vitro. Finally, we show that siRNA-based silencing of CyPA in a murine xenograft model of MM, either alone or in combination with the Food and Drug Administration (FDA)-approved MM therapeutic bortezomib, reduces tumor burden and extends survival. This nanoparticle platform may provide a broadly enabling technology to deliver nucleic acid therapeutics to other malignancies that home to bone marrow.

Non-canonical role for the ataxia-telangiectasia-Rad3 pathway in STAT3 activation in human multiple myeloma cells.

The goal of this study was to characterize the relationship between ATR and STAT3 interactions in human multiple myeloma (MM) cells. Various MM cell lines, including IL-6-dependent cells were exposed to ATR inhibitors and effects on STAT3 Tyr705 and Ser727 were monitored by WB analysis and ImageStream analysis. Parallel studies examined induction of cell death, STAT3 DNA binding activity, and expression of STAT3 downstream targets (BCL-XL, MCL-1, c-MYC). Validation was obtained in ATR shRNA knock-down cells, and in cells ectopically expressing BCL-XL, MCL-1, or c-MYC. Analogous studies were performed in primary MM cells and in a MM xenograft model. Multiple pharmacologic ATR inhibitors inhibited STAT3 Tyr705 (but not Ser727) phosphorylation at low uM concentrations and down-regulated BCL-XL, MCL-1, c-MYC in association with cell death induction. Compatible results were observed in ATR shRNA knock-down cells. Cell death induced by ATR inhibitors was significantly attenuated in cells ectopically expressing constitutively active STAT3, BCL-XL, MCL-1, or c-MYC. Concordant results were observed in primary human MM cells and in an in vivo MM xenograft model. Collectively, these findings argue for a non-canonical role for the ATR kinase in STAT3 activation in MM cells, and suggest that STAT3 inactivation contributes to the lethal actions of ATR inhibitors in MM.