Primary Mantle Cell Lymphoma Cells Research Articles

Targeting CERS6-AS1/FGFR1 axis as synthetic vulnerability to constrain stromal cells supported proliferation in Mantle cell lymphoma.

The interaction between stromal and tumor cells in tumor microenvironment is a crucial factor in Mantle cell lymphoma (MCL) progression and therapy resistance. We have identified a long non-coding RNA, CERS6-AS1, upregulated in MCL and associated with poor overall survival. CERS6-AS1 expression was elevated in primary MCL within stromal microenvironment and in a subset of MCL cells adhered to stromal layer. These stromal-adhered MCL-subsets exhibited cancer stem cell signatures than suspension counterparts. Mechanistically, we found that downregulating CERS6-AS1 in MCL reduced Fibroblast Growth Factor Receptor-1 (FGFR1), expression attributed to loss of its interaction with RNA-binding protein nucleolin. In addition, using in-silico approach, we have discovered a direct interaction between nucleolin and 5'UTR of FGFR1, thereby regulating FGFR1 transcript stability. We discovered a positive association of CERS6-AS1 with cancer stem cell signatures, and Wnt signaling. Building on these, we explored potential therapeutic strategies where combining nucleolin-targeting agent with FGFR1 inhibition significantly contributed to reversing cancer stem cell signatures and abrogated primary MCL cell growth on stromal layer. These findings provide mechanistic insights into regulatory network involving CERS6-AS1, nucleolin, and FGFR1 axis-associated crosstalk between tumor cells and stromal cell interaction and highlights therapeutic potential of targeting a non-coding RNA in MCL.

The dual HCK/BTK inhibitor KIN-8194 impairs growth and integrin-mediated adhesion of BTKi-resistant mantle cell lymphoma

Although Bruton’s tyrosine kinase (BTK) inhibitors (BTKi) have significantly improved patient prognosis, mantle cell lymphoma (MCL) is still considered incurable due to primary and acquired resistance. We have recently shown that aberrant expression of the Src-family tyrosine kinase hematopoietic cell kinase (HCK) in MCL correlates with poor prognosis, and that genetic HCK perturbation impairs growth and integrin-mediated adhesion of MCL cells. Here, we show that KIN-8194, a dual inhibitor of BTK and HCK with in vivo activity against Myd88-L265P-driven diffuse large B-cell lymphoma and Waldenström Macroglobulinemia, has a potent growth inhibitory effect in MCL cell lines and primary MCL cells, irrespective of their sensitivity to BTKi (ibrutinib and acalabrutinib). In BTKi-resistant cells this is mediated by inhibition of HCK, which results in repression of AKT-S6 signaling. In addition, KIN-8194 inhibits integrin-mediated adhesion of BTKi-sensitive and insensitive MCL cells to fibronectin and stromal cells in an HCK-dependent manner. Finally, we show that MCL cells with acquired BTKi resistance retain their sensitivity to KIN-8194. Taken together, our data demonstrate that KIN-8194 inhibits growth and integrin-mediated adhesion of BTKi-sensitive MCL cells, as well as MCL cells with primary or acquired BTKi resistance. This renders KIN-8194 a promising novel treatment for MCL patients.

Exploring BiTE-Integrated CAR T-Cell Therapy to Overcome Tumor Antigen Escape and Reinforce CAR-T Therapy in Mantle Cell Lymphoma

Background T cell engagers (BiTEs) are bispecific T-cell engaging antibodies that redirect T cells to target antigen-expressing tumor cells. Combining a second antigen-targeted bispecific T cell engager (BiTE) with CAR T cells or incorporating bispecific engaging antibody-secreting T cells (engager-T cells) is expected to augment T-cell activation and proliferative capacity, and antitumor cytotoxicity, even towards tumor cells expressing tumor antigens heterogeneously. Here, we report a BiTE-integrated T-cell therapeutic strategy to overcome tumor antigen escape and reinforce the efficacy of CAR-T therapy in mantle cell lymphoma (MCL). Methods CD20-directed bispecific T-cell engager (CD20-BiTE) was constructed with a publicly available VHH fragment from an anti-CD20 single-domain antibody, and anti-CD3 scFv from OKT3 monoclonal antibody. CD19-directed CAR construct is comprised of anti-CD19 scFv from publicly available FMC63 monoclonal antibody, CD8 transmembrane-, 4-1BB costimulatory-, and CD3ζ signaling-domains. Human primary pan-T cells were isolated from PBMC derived from normal human donors (MD Anderson Blood Bank) or patients with MCL. Activated T cells were used for effector functional assay or transduced with lentivirus to produce CAR T or engager-T cells. Effector function of bispecific antibodies and T cells was determined via T-cell activation, cytokine release, and T-cell-dependent cytotoxicity assay in a co-culture model. Results Treatment with CD20-BiTE enhances the effector function of naïve T cells: the BiTE-Fc fusion protein was ectopically expressed in Expi293 and purified by immobilized Protein-A. The binding specificity of scFv(s) of CD20-BiTE was confirmed to bind strongly and specifically to CD20-expressing cells. In vitro functional analyses demonstrated that co-culture of naïve T cells with CD20-exressing cells in the presence of CD20-BiTE induced antigen-specific activation of the T cells (increase in the expression of CD25 and CD69). In the presence of naïve T cells and antigen-positive MCL cells, CD20-BiTE enhanced the secretion of cytokines (IFNγ and TNFα, > 2-fold increase) and CD8 T-cell cytotoxic molecule granzyme B by T cells, in a BiTE-dependent and CD20-specific manner. The enhanced effector function translated into improved antitumor cytotoxicity, as activated T cells treated with CD20-BiTE exerted 43- 72% increase in the killing efficacy of JeKo-1 BTK-KD cells. CD20-BiTE-combined CAR T cells endowed with enhanced antitumor activity overcome tumor antigen escape and resistance to current CD19-CAR T cell therapy: when primary T cells and CD19-CAR T cells were co-cultured with MCL cells, addition of CD20-BiTE potentiated T cell-dependent cytotoxicity ( p < 0.001). Since both CD19-dependent and -independent CAR T cell-resistance often develop during adoptive cell therapy in MCL, we sought to overcome the resistance in MCL by combining a second antigen-targeted CD20-BiTE with CAR T cells or incorporating CD20-BiTE secreting T cells (engager-T cells). Remarkably, when combined with CD19-CAR T cells, CD20-BiTE mediates significant increase in the antitumor cytotoxicity, compared to T cells alone ( p ≤ 0,001 and p < 0.001 for 2nM and 5nM of the BiTE, respectively), in a CD20-specific fashion, in both MCL cells with diminished CD19 expression, and CD19-CAR T-resistant primary MCL cells. Importantly, in a transwell assay, CD19-CAR T cells demonstrated restored potent killing (>3-fold increase over CAR T cells alone) of the CD19-low or CAR T therapy resistant tumor cells, but only when the engager-T cells were present in the insert, suggesting the engaging molecules were able to redirect CD19-CAR T cells to CD20-positive tumor cells regardless of their CD19 expression. The anti-lymphoma efficacy of engager-CAR T cell therapy will be further evaluated in our well-established unique PDX model for MCL. In summary, we have successfully generated a CD20-directed bispecific T-cellengaging antibody and CD20-BiTE engager-T cells that could be combined with CAR T cell therapy, which was demonstrated effective in overcoming tumor antigen escape and resistance to current CD19-CAR T cell therapy in MCL.

Combined treatment with crizotinib and temsirolimus is an effective strategy in mantle cell lymphoma and can overcome acquired resistance to temsirolimus.

Constitutive activation of the PI3K/AKT/mTOR-pathway plays an important role in the pathogenesis of mantle cell lymphoma (MCL), leading to approval of the mTOR inhibitor temsirolimus for relapsed or refractory MCL. Yet, despite favorable initial response rates, early relapses under treatment have been observed. Therefore, understanding the underlying mechanisms of temsirolimus resistance and developing strategies to overcome it is highly warranted. Here, we established a new temsirolimus-resistant MCL cell line to evaluate the molecular background of resistance to this drug. Transcriptome profiling and gene set enrichment analysis comparing temsirolimus-sensitive and -resistant cell lines showed significant upregulation of PI3K/AKT/mTor-, RAS signaling- and the RTK-dependent PDGFR-, FGFR-, Met- and ALK-signaling-pathways in the resistant cells. Furthermore, MET, known as important proto-oncogene and mediator of drug resistance, was among the most upregulated genes in the resistant cells. Importantly, Met protein was overexpressed in both, MCL cells with acquired as well as intrinsic temsirolimus resistance, but could not be detected in any of the temsirolimus sensitive ones. Combined pharmacological inhibition of mTOR and Met signaling with temsirolimus and the RTK inhibitor crizotinib significantly restored sensitivity to temsirolimus. Furthermore, this combined treatment proved to be synergistic in all MCL cell lines investigated and was also active in primary MCL cells. In summary, we showed for the first time that overexpression of MET plays an important role for mediating temsirolimus resistance in MCL and combined treatment with temsirolimus and crizotinib is a very promising therapeutic approach for MCL and an effective strategy to overcome temsirolimus resistance.

Roles of PI3Kγ and PI3Kδ in mantle cell lymphoma proliferation and migration contributing to efficacy of the PI3Kγ/δ inhibitor duvelisib

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma that is incurable with existing therapies, and therefore presents a significant unmet clinical need. The ability of this disease to overcome therapy, including those that target the B cell receptor pathway which has a pathogenic role in MCL, highlights the need to develop new treatment strategies. Herein, we demonstrate that a distinguishing feature of lymph node resident MCL cells is the expression of phosphatidylinositol 3-kinase γ (PI3Kγ), a PI3K isoform that is not highly expressed in other B cells or B-cell malignancies. By exploring the role of PI3K in MCL using different PI3K isoform inhibitors, we provide evidence that duvelisib, a dual PI3Kδ/γ inhibitor, has a greater effect than PI3Kδ- and PI3Kγ-selective inhibitors in blocking the proliferation of primary MCL cells and MCL cell lines, and in inhibiting tumour growth in a mouse xenograft model. In addition, we demonstrated that PI3Kδ/γ signalling is critical for migration of primary MCL cells and cell lines. Our data indicates that aberrant expression of PI3Kγ is a critical feature of MCL pathogenesis. Thus, we suggest that the dual PI3Kδ/γ duvelisib would be effective for the treatment of mantle cell lymphoma.

Combined Inhibition of CDK2 and BCL2 Overrides Resistance to Targeting BTK and CDK4/6 in Mantle Cell Lymphoma Therapy

Mantle cell lymphoma (MCL) remains incurable due to the development of drug resistance, despite the plethora of therapies available. Each successive treatment failure is associated with a more rapidly proliferating disease and fewer treatment options. Understanding the drug-resistance mechanism and developing effective, well-tolerated, new therapies for MCL are urgently needed. Unrestrained proliferation of MCL cells is mainly driven by aberrant cyclin D1 expression and dysregulated CDK4 activity that promotes cell cycle progression from G1 to S. In our phase 1 clinical trial inhibiting CDK4/6 with palbociclib and BTK with ibrutinib (PALIBR) in recurrent MCL, the complete response rate (CR) was 42% compared to 21% in response to ibrutinib alone, despite a comparable 67% overall response rate. Moreover, 5 patients remain on therapy (2 CR and 3 PR) for ~ 8 years, suggesting that CDK4/6 inhibition deepens and prolongs the clinical response to BTK inhibition in MCL. However, resistance emerges in some patients. To elucidate the underpinnings, we undertook integrative longitudinal genomic analysis of sequential tissue and blood specimens (n=53) of 27 MCL patients before, during therapy and on progression, and 4 treatment-naïve MCL patients and 4 normal subjects as controls. Whole exome and whole transcriptome sequencing of freshly isolated MCL cells and B cells revealed that resistance to PALIBR is rooted in homozygous deletion of RB1 (direct target of CDK4/6) or compound copy number variation (cCNV) - concurrent hemizygous loss of RB1 and CDKN2A (p16, CDK4/6 inhibitor) and gain of CDK4. In other resistant patients, the RB protein is silenced by translational termination mutation. Single-cell RNA-sequencing (scRNA-seq, 210,000 cells) of corresponding PBMCs using a unique in-house MCL RNA reference library reveals that MCL cells comprise 4 transcriptomically distinct clusters. Cluster 1 (C1) is similar to quiescent normal B cells; C2 resembles hyper-activated B cells enriched for signatures of BCR and cytokine signaling; C3 represents non-proliferating, long-lived MCL cells; and C4 is highly proliferative, expanding with disease progression. RNA velocity analysis further uncovered that C2 fuels the transition to C4 with disease progression, whereas C3 is a terminal node (Fig 1). In C2 and C3 MCL cells, CDK2 is highly elevated, indicating evasion of CDK4/6 inhibition, and PIK3IP1 (negative PI3K regulator) is silenced, suggesting that compensatory PI3K activation in BTKi resistance (Chiron et al, Cancer Discovery 2014) is secondary to loss of cell cycle control. BCL2 is markedly elevated in C2, greater in C3 MCL cells along with increases in anti-apoptotic BCL2L1(BCL-XL) and BCL-2A1 and decreases in pro-apoptotic PMAIP1 (NOXA) expression. This suggests combined CDK2 and BCL2 inhibition as a rational approach to override CDK4/6i and BTKi resistance. Indeed, combined inhibition of CDK2 with PF-07104091 and BCL2 with venetoclax (PF-VEN) cooperatively impaired growth and killed ibrutinib-resistant MAVER-1 cells, more effectively in the isogenic derivative MAVER-1R cells which we generated to recapitulate cCNV in PALIBR resistance - depletion of RB protein through translational termination mutation (W99, AAF 75%) in RB1, loss of CDKN2A and gain of CDK4. Mechanistically, MAVER-1R cells are accelerated in G1 to S progression, based on elevation of CDK2 and TK1 expression and cell cycle profiling. They are intrinsically apoptotic and vulnerable to BCL2 inhibition due to a marked reduction in cells expressing anti-apoptotic BCL2L1 and IRF4, and universal expression of pro-apoptotic PMAIP1 (NOXA). Importantly, combined CDK2 and BCL2 inhibition synergistically kills MCL cells of a patient resistant to PALIBR ex vivo. In summary, by longitudinal genomic analysis, we have provided the first evidence that 1) resistance to CDK4/6i and BTKi stems from MCL intrinsic cCNV; 2) MCL cells comprise 4 major transcriptomically distinct clusters; cluster 2 expressing copious CDK2 and BCL2 is pivotal in fueling proliferation of MCL cells in resistance; 3) cluster 3 cells also accumulate with resistance due to longevity; 4) combined inhibition of CDK2 and BCL2 overrides resistance to CDK4i and BTKi, in MCL cell lines and primary MCL cells from PALIBR resistant patient. Combined inhibition of CDK2 and BCL2, therefore, represents a mechanism-based strategy to overcome CDK4/6i and BTKi resistance in MCL therapy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

CARD11 and BCL2A1 Join Forces to Promote Resistance to Ibrutinib/Venetoclax Combination in Lymphoma Patients

Background Mantle cell lymphoma (MCL) is a hard to cure malignancy with conventional chemotherapy. We previously reported that combinations targeting CD20 (obinutuzumab), BTK (ibrutinib) and BCL2 (venetoclax) counteracted both tumor intrinsic anomalies and dialogs within corrupted MCL ecosystems. Importantly, this chemo-free combination provided durable complete responses in patients both at relapse or naïve of treatments (OAsIs trial, NCT02558816). Despite high initial response rates, nearly 1/3 of patients rapidly relapsed. To understand this in vivo resistance, we performed targeted sequencing and single-cell RNA-seq to identify key actors involved. Methods Tumor DNA from patients enrolled in the OAsIs trial were sequenced at baseline (n=12) or relapse (n=5) (Capture xGen technology, IDT). Forty-nine genes and the 9p21 region, described for their impact in lymphoma resistance, were targeted for recurrent SNVs/CNVs. Single cell RNA-seq (3' gene expression, 10X genomics) was performed before treatment (n=4) or after relapse (n=3). Integrated omics analysis was performed to define resistance signatures, at the single cell resolution and associated to gain of function (GOF) mutations. Functional analysis (i.e., reporter assay, BH3-profiling, drug testing) using primary MCL cells and cell lines were performed. Results Targeted sequencing of tumor cells at relapse highlighted an enrichment of CARD11 GOF mutations (p=0.01). The selective advantage of CARD11MUT cells under OAsIs pressure was further documented with a patient who achieved a complete response before relapsing 12 months after inclusion. Whereas CARD11MUT tumor cells were in a minority (0.0005 %) at the onset of treatment, all the cells carried a heterozygous mutation at relapse (VAF: 50.56%). scRNA-seq of the same longitudinal samples identified a minor cluster (187/4860 sequenced cells) enriched at relapse that was characterized by expression of NFKB1 target genes consistent with constitutive CARD11 activity (Enrichr p<5x10-4). By combining scRNA-seq and mutations, we identified a signature associated with CARD11 GOF, which we named "OAsIs-R" signature. Applied to additional patients' samples, this novel signature allowed the segregation of OAsIs sensitive from resistant cells (scRNA-seq). Of major interest, OAsIs-R signature was also predictive for OS/PFS in MCL patients treated with conventional chemotherapy (GSE93291 and in-house cohorts). Among the top genes of OAsIs-R signature, we further focused on BCL2A1. We first highlighted its frequent expression in MCL primary cells (n=63) and cell lines (n=7). BCL2A1 overexpression, BH3-profiling (FS2 peptide) and ex vivo drug testing (AnnexinV) further validated a key role of CARD11-related BCL2A1 dysregulation in OAsIs resistance. Ibrutinib deeply reduced BCL2A1 level in CARD11WT cell lines but not in CARD11MUT cells (RNA expression inhibition: 82%, n=4 vs. 0%, n=4), leading to synergistic apoptosis when associated to venetoclax in BCL2A1+ but not in BCL2A1- cells (mean synergy score: 17 vs. 1, n=6). Using reporter assay experiments we showed that CARD11 mutations directly led to an increase activity of BCL2A1 promoter (2 fold more activity, Mut vs. wt), reinforcing the need to target its activity to counteract resistance. Among druggable strategies to inhibit CARD11, selective inhibition of its partner MALT1, essential for CARD11-BCL10-MALT1 (CBM) activity, is currently tested in early phase clinical trials. We demonstrated that MALT1 protease inhibition led to the reduction of genes involved in OAsIs resistance, including BCL2A1 (RNA inhibition: 40%, n=6), and induced synergistic cell death in combination with venetoclax (mean synergy score: 20, n=4), irrespective of CARD11 mutational status. Conclusions In summary, our data uncovered control of the mitochondrial apoptosis by CARD11 through BCL2A1 expression. This network has critical implication in the resistance to BTK/BCL2 targeted inhibition. Indeed, CARD11 GOF mutations led not only to BCR-independence and consequently ibrutinib resistance but also to BCL2A1-mediated venetoclax resistance. Nevertheless, our data show that targeting the CBM through MALT1 inhibition reverts this resistance and that MALT1 targeting appears as a promising therapeutic option for counteracting MCL resistance, especially in the context of acquired CARD11 mutation. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Establishment of a Patient-Derived Organoid Culture Platform for Mantle Cell Lymphoma Drug Sensitivity and CAR T Cell Anti-Tumor Activity Assay

Background: With BTK inhibitors and brexucabtagene autoleucel CAR-T cell therapy approved by FDA to treat B-cell malignancies, survival of patients with mantle cell lymphoma (MCL) has been greatly improved. However, frequent therapeutic relapses in patients remains as an unmet medical challenge. Preclinical tumor mouse models such as patient-derived xenografts (PDXs) are often used for drug sensitivity and treatment prediction. However, these conventional cancer models are time-consuming and expensive. In recent years, development and application of patient-derived organoid (PDO) models have led to many discoveries in various types of solid tumors. PDO models have demonstrated many advantages over PDX models. For example, PDOs can be established using biopsies as small as needle biopsies yet with much higher success rates. However, a PDO model has not been reported yet in MCL or in a few other hematologic malignancies. Therefore, in this study, with successful establishment of MCL PDO models, we optimized our protocols and applied this model for drug sensitivity screens and rapid evaluation of immunotherapies. Methods: Patient samples were lysed with RBC lysis buffer and washed with PBS, then cell pellets were resuspended in culture medium containing cytokine cocktails. The cell suspension was aliquoted into V-bottom 96-well plates and spun. The cell aggregates within 50% Matrigel were gently transferred into multiple-well plates as needed. After solidification of the cell-Matrigel mixture, pre-warmed culture medium was added to cover them. The PDOs in 24 or 96-well plates were treated with drug or co-cultured with CAR T cells for 3-5 days. The cell viability and T cell killing activity were determined using CellTiter-Glo 3D assay kits. Results: We successfully established and optimized an organoid culture procedure and culture medium for diverse types of biopsy from patients with MCL. The success rate of MCL organoid development from diverse MCL biopsies was greater than 90%, much higher than for PDX. H&E staining of both tumors and their derived organoids revealed similar histological features (Figure 1A). To examine the drug sensitivity of primary MCL cells, organoid cultures derived from the patient apheresis biopsies that were either BTK inhibitor-sensitive (naive) or multiple drug resistant (to acalabrutinib, rituximab, and venetoclax) were treated with the BTK inhibitors ibrutinib or pirtobrutinib or else doxorubicin (as a control) for 48 h. Cell viability assays indicated that MCL cells in organoid cultures maintained the responses of the original tumor cells to drugs used in clinical treatment. We also demonstrated that the MCL organoids had the same major cell lineage populations as the original biopsy. These results support the notion that the PDO in vitro assay has great potential to evaluate and predict patient responses. In addition, we applied this PDO platform to evaluate CAR T cell anti-tumor activity by co-culturing the primary MCL cells with CD19-targeting CAR T cells in organoids for 3 days. To visualize and quantitate tumor killing potential, the MCL cells were labelled with the green dye 5-chloromethyl fluorescein diacetate. The cocultures were examined by imaging and FACS analysis. Compared to the same batch of peripheral blood monocytes used to generating CAR T cells, the CD19-CAR T cells very effectively eradicated CD19+ MCL cells from the co-cultures (Figure 1B), indicating that the PDO platform is a promising in vitro assay for rapid examining CAR T cell activity. Importantly, we validated drug responses in parallel in PDO and PDX models derived from the same tumors. Our preliminary results displayed high consistency between these assay systems, suggesting that PDO-based assay provides an encouraging platform for predicting clinical treatment response. Conclusion: We have successfully established and optimized an MCL PDO platform that can be used to perform reliable and fast assays for drug sensitivity and CAR T cell anti-tumor activity in vitro. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

DNMT3A-Mediated Oxidative Phosphorylation and Ibrutinib Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL), a B cell non-Hodgkin lymphoma, is incurable with current treatment modalities. Targeting Bruton tyrosine kinase (BTK) in the early B cell receptor signaling pathway by ibrutinib has shown remarkable anti-tumor activity, with the overall response rate of 68% in relapsed/refractory MCL patients. However, almost all the responders relapsed after ibrutinib treatment, with the 1-year survival rate of 22%. To overcome primary and acquired resistance to ibrutinib, novel treatment strategies are urgently needed. The presence of a relapse-specific C481S mutation in BTK associated with acquired ibrutinib resistance has been frequently identified in chronic lymphocytic leukemia but is rare in clinical MCL specimens based on sequencing results. Thissuggests that non-genetic aberrations likely play a role in ibrutinib resistance. The recent emergence of mitochondrial oxidative phosphorylation (OXPHOS) as a driver of ibrutinib resistance warrants the necessity to identify the components that govern OXPHOS in MCL. This study identifies the de novo DNA methyltransferase 3A (DNMT3A) as a mediator of mitochondrial biogenesis and OXPHOS in MCL. Using multiomics and functional approaches, we found that DNMT3A is required and sufficient to confers ibrutinib resistance in MCL. We show that DNMT3A promotes MCL growth by enhancing mitochondrial biogenesis, mitochondrial functions and OXPHOS. These effects are mediated by its interaction with MEF2B, a transcriptional activator of MYC, to enhance MYC-mediated transcription of genes involved in mitochondrial biogenesis. More importantly, the level of DNMT3A protein increases after ibrutinib treatment in primary MCL, which is consistent with a previous finding that the expression of DNMT3A was higher in ibrutinib-resistant than in ibrutinib-sensitive MCL patients. We demonstrate that DNMT3A knockout sensitizes ibrutinib-resistant cells to ibrutinib treatment. Conversely, the overexpression of DNMT3A cDNA de-sensitizes ibrutinib-sensitive cell lines. Interestingly, the overexpression of a catalytically dead DNMT3A confers resistance to ibrutinib in ibrutinib-sensitive cell lines, suggesting that DNMT3A-mediated ibrutinib resistance is independent of its enzymatic activity. Finally, we demonstrate that targeting DNMT3A by a low dose of decitabine, which induces the degradation of DNMT3A protein, synergizes with IM156, an inhibitor of mitochondrial complex I and currently in phase I clinical trial, in killing ibrutinib-resistant cell lines and primary MCL cells. Currently, we are testing this synergistic effect using patient-derived xenograft mouse models. Therefore, our study reveals a novel noncatalytic function of DNMT3A and suggests that DNMT3A is a potential biomarker and molecular target in treating MCL (Figure 1). Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Targeting Sumoylation with Subasumstat (TAK-981), a Selective Inhibitor of SUMO-Activating Enzyme (SAE), Induces Mitochondrial Dysfunction in Preclinical Models of Non-Hodgkin Lymphoma (NHL)

SUMOylation is a post-translational modification which leads to covalent attachment of small ubiquitin-like modifiers (SUMO) proteins to lysine residues of a target protein. SUMOylation is essential for the regulation of genomic integrity, gene expression and intracellular signaling. Many tumors exhibit deregulation of SUMOylation pathway. Subasumstat, (TAK-981), a novel selective inhibitor of SUMO-activating enzyme (SAEi), has entered early phase II clinical trials. Here we studied SAEi in pre-clinical models of B-cell non-Hodgkin's lymphoma (NHL). TAK-981 was provided by Takeda Development Center Americas, Inc. (Lexington, MA). Diffuse large B-cell lymphoma (DLBCL) cell lines (OCI-LY3, VAL, U-2932, SU-DHL10), and primary mantle cell lymphoma (MCL) cells were assayed for survival, mitochondrial function, and metabolic phenotype. In vivo experiments were performed using DLBCL cell line xenografts and MCL PDX models. Treatment with TAK-981 restricted growth of DLBCL cell lines with an IC50~10 nM. SAEi led to rapid (within 2 h) protein desumoylation in a dose dependent manner, prominently in the ~90 kDa region. TAK-981 induced pronounced double strand DNA breaks in DLBCL cells (comet assay) and cell cycle arrest (propidium iodine). RNA-Seq and ATAC-Seq analysis of TAK-981-treated DLBCL cells revealed upregulation of the DNA damage, NF-κB, and OXPHOS signaling pathways. We noted that in addition to cytoplasmic proteins, mitochondrial proteins were heavily de-SUMOylated upon treatment of NHL cells with TAK-981. In vitro exposure to TAK-981 resulted in mitochondrial membrane depolarization, loss of mitochondrial integrity (by electron microscopy) and a change of mitochondrial dynamics as assessed by expression of mitochondrial proteins (eg, Drp1). Seahorse respirometry analysis revealed dramatic downmodulation of OXPHOS following SAEi. Furthermore, metabolomic profiling of DLBCL cells treated with TAK-981 showed downmodulation of TCA substrates, while glycolysis substrates remained unchanged. The mitochondrial disruption observed following TAK-981 treatment was accompanied by rapid accumulation of reactive oxygen species, a mechanism that has been previously shown to lead to DNA damage in cancer cells. Consistent with cell line data, exposure of primary MCL cells to TAK-981 in stromal conditions (CD40L- or BAFF expressing stroma) induced apoptosis and reduced OXPHOS. Next, we conducted genome-wide CRISPR-Cas9 loss-of-function library screens and identified that loss of genes in the NFκB, TP53, DNA damage and centromere/telomere gene pathways contributed to resistance to SAEi in DLBCL cells. By means of genetic knockout we demonstrated that TP53 and its transcriptional target BAX contributed to TAK-981-induced G2 arrest and apoptosis, further implicating mitochondrial dysfunction in sensitivity to SAEi. For in vivo experiments, we used DLBCL xenografts. OCI-LY3 and U-2932 cells were inoculated subcutaneously in NSG mice. Once tumors reached 100 mm3, mice received 10 twice-weekly IV doses of 7.5 mg/kg TAK-981 (over 5 weeks), leading to resolution of flank tumors and improved survival compared with control. Finally, we used an MCL PDX model where MCL cells were inoculated intravenously. Once cells became detectable in the blood, mice were treated as above. Treatment with TAK-981 resulted in delayed tumor expansion in blood and spleen and extended animal survival. TAK-981-exposed splenocytes exhibited a reduction of maximal respiration by Seahorse analysis. Conclusions. Pharmacologic SAEi with TAK-981 demonstrated pre-clinical activity in NHL models in vitro and in vivo, accompanied by DNA damage, mitochondrial dysfunction, and metabolic reprogramming.

Ironomycin Induces Mantle Cell Lymphoma Cell Death By Targeting Iron Metabolism Addiction

Mantle-cell lymphoma (MCL) accounts for approximately 5 to 7% of all lymphomas, and in North America and Europe. MCL remains an aggressive and incurable cancer with existing therapies, presenting a significant unmet clinical need. Accumulating evidence reveals that abnormal iron metabolism plays an important role in tumorigenesis and in cancer progression of many tumors. In cancer cells, the demand for iron increases in response to sustained deregulation of cell proliferation and DNA synthesis. Based on these data, we searched to identify alterations of iron homeostasis in MCL that could be exploited to develop novel therapeutic strategies. Analysis of the iron metabolism gene expression profile of a cohort of patients with MCL (n=71) established the iron score (IS), a gene expression-based risk score enabling identification of patients with MCL with a poor outcome who might benefit from a suitable targeted therapy. We analyzed the therapeutic interest of ironomycin, a new promising iron depleting molecule. Ironomycin is known to sequester iron in the lysosome and to induce ferroptosis (Mai TT et al. Nature Chemistry 2017). Preclinical studies in Acute Myeloid Leukemia (Garciaz et al., 2022 Cancer Discovery) and Diffuse Large B-Cell Lymphoma (Devin et al., 2022 Can Res) have revealed the therapeutic interest of ironomycin in treating hematological malignancies. In a panel of 6 MCL cell lines, ironomycin inhibited MCL cell growth at nanomolar concentrations compared with typical iron chelators. Then, we investigated if ironomycin induces cell death through apoptosis. Flow cytometry analysis revealed that ironomycin treatment resulted in AnnV+/7AAD+ and AnnV+/7AAD- death profiles in MCL. This effect was partially inhibited by the pan-caspase inhibitor Q-VD-Oph. Ironomycin also induced caspases 8 and 9 cleavage, and the activation of caspases 3/7. Furthermore, we found that ironomycin induces ferroptosis with lipid peroxidation and the production of ROS monitored by the fluorescence probe CM-H2DCFDA. Ironomycin induced cell death is inhibited by the ferroptosis inhibitor, ferrostatin-1. The treatment did not induce ferritinophagy, as there was no significant change on the expression of LC3B-II, ferritin and the transferrin receptor (CD71).Taken together, these data indicate that ironomycin kills MCL cells by apoptosis mediated by caspase activation and ferroptosis. Ironomycin significantly decreased cell proliferation rate, with a reduced percentage of cells in S-phase together with Ki67 and Cyclin D1 downregulation. Western blot analysis showed an increase of Chk1 and Chk2 phosphorylation, two central factors of DNA damage response, and an increase of the phosphorylation of γ-H2AX, indicative of DNA damage. With major importance, we validated the therapeutic interest of ironomycin in primary MCL cells of patients (n=5). Ironomycin (20 nM) demonstrated a significant higher toxicity in MCL cells compared to normal cells from the microenvironment. Furthermore, ironomycin presented a low toxicity on hematopoietic progenitors (CFU assays, n=5) compared to conventional treatment. We tested the therapeutic interest to combine ironomycin with conventional chemotherapy used in MCL. Interestingly, we identified a synergistic effect when ironomycin is combined with Ibrutinib BTK inhibitor. Furthermore, Significant synergistic effects were also observed by combining ironomycin with BH3 mimetics or Doxorubicin. Altogether, these data underline that MCL patients my benefit from targeting iron homeostasis using ironomycin alone or in combination with conventional MCL treatments.

A ROR1 Small Molecule Inhibitor (KAN0441571C) Induced Significant Apoptosis of Mantle Cell Lymphoma (MCL) Cells.

The receptor tyrosine kinase orphan receptor 1 (ROR1) is absent in most normal adult tissues but overexpressed in various malignancies and is of importance for tumor cell survival, proliferation, and metastasis. In this study, we evaluated the apoptotic effects of a novel small molecule inhibitor of ROR1 (KAN0441571C) as well as venetoclax (BCL-2 inhibitor), bendamustine, idelalisib (PI3Kδ inhibitor), everolimus (mTOR inhibitor), and ibrutinib (BTK inhibitor) alone or in combination in human MCL primary cells and cell lines. ROR1 expression was evaluated by flow cytometry and Western blot (WB). Cytotoxicity was analyzed by MTT and apoptosis by Annexin V/PI staining as well as signaling and apoptotic proteins (WB). ROR1 was expressed both in patient-derived MCL cells and human MCL cell lines. KAN0441571C alone induced significant time- and dose-dependent apoptosis of MCL cells. Apoptosis was accompanied by decreased expression of MCL-1 and BCL-2 and cleavage of PARP and caspase 3. ROR1 was dephosphorylated as well as ROR1-associated signaling pathway molecules, including the non-canonical WNT signaling pathway (PI3Kδ/AKT/mTOR). The combination of KAN0441571C and ibrutinib, venetoclax, idelalisib, everolimus, or bendamustine had a synergistic apoptotic effect and significantly prevented phosphorylation of ROR1-associated signaling molecules as compared to KAN0441571C alone. Our results suggest that targeting ROR1 by a small molecule inhibitor, KAN0441571C, should be further evaluated particularly in combination with other targeting drugs as a new therapeutic approach for MCL.

Abstract A02: Probing the roles of SUMOylation in B-cell lymphoma cells by using a selective SUMO inhibitor subasumstat (TAK-981)

Abstract SUMOylation is a post-translational modification that leads to covalent attachment of small ubiquitin-like modifiers (SUMO) proteins to a target protein. SUMOylation is essential for the regulation of genomic integrity, gene expression and intracellular signaling. Many tumors exhibit deregulation of SUMOylation pathway. TAK-981, a novel selective inhibitor of SUMO-activating enzyme (SAEi) has entered early phase II clinical trials. Here we studied SAEi in pre-clinical models of non-Hodgkin lymphoma (NHL). TAK-981 was provided by Takeda (Lexington, MA). Diffuse large B-cell lymphoma (DLBCL) cell lines and primary mantle cell lymphoma (MCL) cells were assayed for survival, mitochondrial function and metabolic phenotype. In vivo experiments were performed using DLBCL cell line xenografts and MCL PDX models. Treatment with TAK-981 restricted growth of DLBCL lines and led to rapid protein de-SUMOylation in a dose-dependent manner. TAK-981 induced pronounced DNA break in DLBCL cells (comet assay) and cell cycle arrest (propidium iodide). RNA-Seq and ATAC-Seq analysis of TAK-981-treated OCI-LY3 and U-2932 cells revealed upregulation of the NFκB, and OXPHOS signaling pathways. We noted that mitochondrial proteins were heavily de-SUMOylated upon treatment of NHL cells with TAK-981. In vitro exposure to TAK-981 resulted in mitochondrial membrane depolarization, loss of mitochondrial integrity (EM) and a change of mitochondrial dynamics (ICC for p-Drp1), accompanied by rapid accumulation of reactive oxygen species. Seahorse respirometry revealed dramatic downmodulation of OXPHOS. Metabolomic profiling of DLBCL cells treated with TAK981 exhibited downmodulation of TCA substrates. Exposure of primary MCL cells to TAK-981 in stromal conditions (CD40L- or BAFF expressing stroma) induced apoptosis and reduced OXPHOS. Next, we conducted genome-wide CRISPR-Cas9 loss-of-function library screens and identified that loss of genes in the NFκB, TP53 and DNA damage pathways contributed to resistance to SAEi in DLBCL cells. By means of genetic knockout we demonstrated that TP53 and its transcriptional target BAX contributed to TAK-981-induced G2 arrest and apoptosis, further implicating mitochondrial dysfunction in sensitivity to SAEi. For in vivo experiments, OCI-LY3 and U-2932 cells were inoculated subcutaneously in NSG mice. Once tumors reached 100 mm3, mice received twice-weekly IV doses of 7.5 mg/kg TAK-981 (over 5 weeks), leading to resolution of flank tumors and improved survival compared with control. Finally, we used an MCL PDX model where MCL cells were inoculated intravenously. Once cells became detectable in the blood, mice were treated as above. Treatment with TAK-981 resulted in delayed tumor expansion in blood and spleen and extended animal survival. TAK-981 exposed splenocytes exhibited a reduction of maximal respiration by Seahorse. In summary, pharmacologic SAEi with TAK-981 demonstrated pre-clinical activity in NHL models in vitro and in vivo, accompanied by DNA damage, mitochondrial dysfunction and metabolic reprogramming. Citation Format: Tingting Liu, Vi Lam, Duanchen Sun, Elana Thieme, Tamilla Nechiporuk, Daniel Bottomly, Olga V Danilova, Nur Bruss, Martina Cusan, Lili Wang, Shannon K McWeeney, Jeffrey W Tyner, Steve Kurtz, Zheng Xia, Alexey Danilov. Probing the roles of SUMOylation in B-cell lymphoma cells by using a selective SUMO inhibitor subasumstat (TAK-981) [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A02.

Abstract 3160: Establishment and characterization of a new mantle cell lymphoma cell line with a NOTCH2 mutation, ArBo

Abstract Cell lines represent a very useful tool for cancer research. In mantle cell lymphoma (MCL), the number of characterized cell lines remains small. We have recently established a novel blastoid MCL cell line, isolated from a malignant pleural effusion of a patient with MCL. A sample of the malignant pleural effusion was obtained with informed consent, and mononuclear cells were isolated. Following a few days of in-vitro culture, cells started to grow rapidly resulting in an estimated doubling time of 48h. The cells survived multiple freeze/thaw cycles and have been maintained in culture for the last 8 months. Hence the establishment of a novel blastoid MCL cell line, named Arbo. Both Arbo and the primary MCL cells obtained from the pleural effusion were negative for EBV DNA by qPCR. Flow cytometry showed kappa-restricted cells that were positive for CD5, 19, 20, 22, and 23, and negative for CD2, 3, 7, 10, and 71. FMC7 was positive in Arbo and negative in primary cells, as opposed to CD38 that was negative in Arbo and positive in the primary cells. Arbo’s karyotype was complex contrasting with the normal 46XY karyotype found in the primary MCL cells. The presence of t(11;14)(q13;q32) was confirmed by FISH, additionally overexpression of cyclin-D1 was confirmed by western blot. Whole exome sequencing (WES) was performed on DNA collected from Arbo revealing a total of 148,059 SNPs. Mutations were detected in the ATM, TP53 and NOTCH2(C19W and R2400*) genes. Mutations in NOTCH2 have not been described in other MCL cell lines, while they were identified in 5.2% of MCL patients. Immunoblotting for NOTCH2 confirms the expression of the protein by the cell line. Additionally, expression of CD23, which has been shown to be induced through NOTCH2 signaling, was confirmed by flow cytometry. To further characterize the effect of NOTCH2 on the survival of Arbo cells and CD23 expression, we cultured the cell line with increasing concentrations of the NOTCH2 transactivation inhibitor gliotoxin. We observed a dose-dependent inhibition of cell growth with an IC50 of 100 nM. Additionally, a dose dependent decrease in the expression of CD23 was observed by flow cytometry following treatment with gliotoxin. To determine the dependence of Arbo on B-cell receptor (BCR) signaling for survival, we cultured the cells with increasing concentrations of the BTK inhibitor ibrutinib for 48h. Inhibition of cell growth was observed in a dose-dependent manner resulting in an IC50 of 0.4 µM. In conclusion, Arbo is a novel blastoid MCL cell line with a NOTCH2 mutation that is fully characterized and will be made available to the research community. Supported by a grant from the Ladies Leukemia League, Inc., of the Gulf South Region. Citation Format: Ishwarya Satyavarapu, Firas M. Safa, Terri Rasmussen, Nakhle Saba. Establishment and characterization of a new mantle cell lymphoma cell line with a NOTCH2 mutation, ArBo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3160.

CD24 Is a Potential Immunotherapeutic Target for Mantle Cell Lymphoma.

CD24 and its ligand Siglec-10 were described as an innate immune checkpoint in carcinoma. Here, we investigated this axis in B-cell lymphoma by assessing CD24 expression and evaluating pro-phagocytic effects of CD24 antibody treatment in comparison to hallmark immune checkpoint CD47. In mantle cell lymphoma (MCL) and follicular lymphoma patients, high mRNA expression of CD24 correlated with poor overall survival, whereas CD47 expression did not. Conversely, CD24 expression did not correlate with survival in diffuse large B-cell lymphoma (DLBCL), whereas CD47 did. CD24 was also highly expressed on MCL cell lines, where treatment with CD24 antibody clones SN3 or ML5 potently induced phagocytosis, with SN3 yielding >90% removal of MCL cells and triggering phagocytosis of primary patient-derived MCL cells by autologous macrophages. Treatment with CD24 mAb was superior to CD47 mAb in MCL and was comparable in magnitude to the effect observed in carcinoma lines. Reversely, CD24 mAb treatment was less effective than CD47 mAb treatment in DLBCL. Finally, phagocytic activity of clone SN3 appeared at least partly independent of antibody-dependent cellular phagocytosis (ADCP), suggesting CD24/Siglec-10 checkpoint activity, whereas clone ML5 solely induced ADCP. In conclusion, CD24 is an immunotherapeutic target of potential clinical relevance for MCL, but not DLBCL.

The IL32/BAFF axis supports prosurvival dialogs in the lymphoma ecosystem and is disrupted by NIK inhibition.

Aggressive B-cell malignancies, such as mantle cell lymphoma (MCL), are microenvironment-dependent tumors and a better understanding of the dialogs occurring in lymphoma-protective ecosystems will provide new perspectives to increase treatment efficiency. To identify novel molecular regulations, we performed a transcriptomic analysis based on the comparison of circulating MCL cells (n=77) versus MCL lymph nodes (n=107) together with RNA sequencing of malignant (n=8) versus normal B-cell (n=6) samples. This integrated analysis led to the discovery of microenvironment-dependent and tumor-specific secretion of interleukin-32 beta (IL32β), whose expression was confirmed in situ within MCL lymph nodes by multiplex immunohistochemistry. Using ex vivo models of primary MCL cells (n=23), we demonstrated that, through the secretion of IL32β, the tumor was able to polarize monocytes into specific MCL-associated macrophages, which in turn favor tumor survival. We highlighted that while IL32β-stimulated macrophages secreted several protumoral factors, they supported tumor survival through a soluble dialog, mostly driven by BAFF. Finally, we demonstrated the efficacy of selective NIK/alternative-NFkB inhibition to counteract microenvironment-dependent induction of IL32β and BAFF-dependent survival of MCL cells. These data uncovered the IL32β/BAFF axis as a previously undescribed pathway involved in lymphoma-associated macrophage polarization and tumor survival, which could be counteracted through selective NIK inhibition.

Dual BTK/SYK inhibition with CG-806 (luxeptinib) disrupts B-cell receptor and Bcl-2 signaling networks in mantle cell lymphoma

Aberrant B-cell receptor (BCR) signaling is a key driver in lymphoid malignancies. Bruton tyrosine kinase (BTK) inhibitors that disrupt BCR signaling have received regulatory approvals in therapy of mantle cell lymphoma (MCL). However, responses are incomplete and patients who experience BTK inhibitor therapy failure have dire outcomes. CG-806 (luxeptinib) is a dual BTK/SYK inhibitor in clinical development in hematologic malignancies. Here we investigated the pre-clinical activity of CG-806 in MCL. In vitro treatment with CG-806 thwarted survival of MCL cell lines and patient-derived MCL cells in a dose-dependent manner. CG-806 blocked BTK and SYK activation and abrogated BCR signaling. Contrary to ibrutinib, CG-806 downmodulated the anti-apoptotic proteins Mcl-1 and Bcl-xL, abrogated survival of ibrutinib-resistant MCL cell lines, and partially reversed the pro-survival effects of stromal microenvironment-mimicking conditions in primary MCL cells. Dual BTK/SYK inhibition led to mitochondrial membrane depolarization accompanied by mitophagy and metabolic reprogramming toward glycolysis. In vivo studies of CG-806 demonstrated improved survival in one of the two tested aggressive MCL PDX models. While suppression of the anti-apoptotic Bcl-2 family proteins and NFκB signaling correlated with in vivo drug sensitivity, OxPhos and MYC transcriptional programs were upregulated in the resistant model following treatment with CG-806. BAX and NFKBIA were implicated in susceptibility to CG-806 in a whole-genome CRISPR-Cas9 library screen (in a diffuse large B-cell lymphoma cell line). A high-throughput in vitro functional drug screen demonstrated synergy between CG-806 and Bcl-2 inhibitors. In sum, dual BTK/SYK inhibitor CG-806 disrupts BCR signaling and induces metabolic reprogramming and apoptosis in MCL. The Bcl-2 network is a key mediator of sensitivity to CG-806 and combined targeting of Bcl-2 demonstrates synergy with CG-806 warranting continued exploration in lymphoid malignancies.

The Novel Multitarget Small-Molecule Inhibitor SRX3177 Overcomes Ibrutinib Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is an aggressive, rare, and difficult to treat subtype of non-Hodgkin's Lymphoma (NHL) that accounts for about 6% of all cases. Although there is no defined standard of care for MCL treatment, some combination of chemo-immunotherapy and rituximab maintenance with or without autologous stem cell transplantation is generally employed depending on the age and fitness of the patient. Despite recent development of novel therapeutics, there is inevitable disease relapse with progressively declining efficacy and increasing frequency of resistance with single agent targeted therapy. Here, we describe the novel multitarget inhibitor SRX3177 which simultaneously hits three oncogenic targets: phosphatidylinositol-3 kinase (PI3K), cyclin-dependent kinases 4 and 6 (CDK4/6), and the epigenetic reader protein BRD4. This in silico designed, thieno-pyranone (TP) scaffold-based small molecule inhibitor orthogonally disrupt three targets within the cancer cell with one agent.Targeting the cell cycle with small molecule inhibitors represents a reasonable attempt to treat MCL, as cell cycle-associated genes like ATM, TP53, CDKN2A, CCND1 and CDK4/6 are most frequently mutated in patients. Palbociclib is a well-known single agent CDK4/6 inhibitor that has been employed in both solid and hematological malignancies. Due to its cytostatic nature, treatment with single agent palbociclib often results in the emergence of treatment-resistant clones. Therefore, a combination strategy would theoretically be more effective and can overcome the development of resistance. Moreover, prolonged G1 arrest by CDK4/6 inhibition sensitizes lymphoma cells to PI3K inhibition, suggesting a synthetic lethality relationship between these two agents. Inhibiting the chromatin reader protein BRD4 causes downregulation of target genes c-MYC and BCL2, further increasing cytotoxic capabilities. Hence, we developed SRX3177 as a potent CDK4/6/PI3K/BRD4 triple inhibitor to synergistically inhibit cell cycle progression and induce cancer cell apoptosis.SRX3177 is an ATP competitive CDK4/6 inhibitor (IC 50: CDK4 = 2.54 nM, CDK6 = 3.26 nM), PI3K inhibitor (IC 50: PI3Kα = 79.3 nM, PI3Kδ = 83.4 nM), and BRD4 inhibitor (IC 50: BD1 = 32.9 nM, BD2 = 88.8 nM). We have tested the efficacy of SRX3177 against a panel of MCL cell lines and report that SRX3177 induces a strong antiproliferative activity with maximal IC 50 0f 340 nM in JeKo-1, 29 nM in Mino cells, and 630 nM for Rec-1 cells while IC 50 values for cell lines Granta and JVM-2 were 1.3 µM and 1.5 µM, respectively. Further, we show that SRX3177 is more potent to tumor cells than the individual PI3K (BKM120), BTK (Ibrutinib), BRD4 (JQ1), and CDK4/6 (palbociclib) inhibitors, and dual PI3K/BRD4 inhibitor SF2523 (backbone for SRX3177) in JeKo-1 cells. Next, we examine the cytotoxic effect of SRX3177 in ibrutinib/palbociclib resistant primary MCL cells. Our results show that SRX3177 triggers cytotoxic response at 500 nM and 1000 nM as compared to the lack of cytotoxicity of combination Ibrutinib and palbociclib at 150 nM and 1000 nM (Fig 1). SRX3177 induces a strong apoptotic response and cell cycle arrest in JeKo-1 and Mino cells at 24hrs. Annexin V/7AAD apoptosis staining confirmed the induction of PCD by SRX3177with increase in c-PARP. Western blot analysis shows SRX3177 treatment blocks both PI3K/AKT signaling and Rb phosphorylation. Moreover, analysis by chromatin immunoprecipitation revealed that SRX3177 effectively blocked BRD4 binding to both the promoter and enhancer of c-MYC (p≤0.01 and p≤0.001) and BCL2 (p≤0.05). SRX3177 also suppresses the c-MYC and BCL2 transcriptional program in both a time- and dose-dependent manner. Our findings also demonstrate a SRX3177-dependent reduction in c-MYC half-life via induction of proteasomal-mediated degradation. This degradation is associated with decreased phosphorylation of c-MYC at Ser62 and increased phosphorylation of c-MYC at Thr58 - indicative of differential regulation of c-MYC stability. Finally, we show that SRX3177 overcomes chronic ibrutinib resistance in Jeko-1 cells with a maximal IC 50 of 150 nM as compared to 64 µM with ibrutinib. Hence, the triple inhibitor SRX3177 has superior potency to ibrutinib in MCL cell lines and succeeds in overcoming ibrutinib-resistance at nanomolar doses. Taken together, our data supports the development of SRX3177 as a novel therapeutic agent for treatment of MCL. [Display omitted] DisclosuresMartin: ADCT: Consultancy. Park: Takeda: Research Funding; G1 Therapeutics: Consultancy; Teva: Consultancy, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding, Speakers Bureau; Gilead: Speakers Bureau; Rafael Pharma: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Morphosys: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding. Durden: SignalRx Pharmaceuticals: Current holder of individual stocks in a privately-held company.

The IL32/BAFF Axis Supports Prosurvival Dialog in the Lymphoma Ecosystem and Is Disrupted By NIK Inhibition

BackgroundAggressive B-cell lymphomas, such as Mantle cell lymphoma (MCL), are microenvironment-dependent tumors but, in contrast to tumoral intrinsic anomalies, complex interplays within their ecosystems are largely ignored. A better understanding of these dialogs could provide new perspectives integrating the key role of the microenvironment to increase treatment efficiency of this hard to cure B-cell malignancy.MethodsTo identify novel molecular regulations occurring in lymphoma protective ecosystems, we performed a transcriptomic analysis based on the comparison of publicly available datasets from circulating (PB, n=77) versus MCL lymph nodes (LN, n=107) together with deep RNA sequencing of purified CD19+CD5+ MCL (n=8) versus normal B-cells (n=6). This integrated analysis led to the discovery of microenvironment-dependent and tumor-specific secretion of the cytokine IL32β by lymphoma cells. Using in situ multiplex immunohistochemistry , ex vivo models of primary MCL cells (n=23) and IL32 KO MCL cell lines (Crispr/Cas9), we studied the regulation and the functional impact of IL32β in the MCL context, especially in the dialog with tumor-associated macrophages.ResultsAmong the 6887 genes differentially expressed in MCL LN compared to PB in vivo, 70% were confirmed in CD19+ MCL cells cocultured ex vivo and 39% were tumor-specific, that is to say not upregulated in cocultured normal B cells (NBC). Top-genes scoring revealed that IL32 was the most upregulated genes within the “Tumor-specific” transcriptional program. Using ex vivo models of primary MCL cells, we demonstrated that the microenvironment-dependent secretion of IL32β was controlled by the CD40/NFKB2 axis whereas its tumor specificity was the consequence of IL32 promoter hypomethylation in MCL compared to NBC.IL32 protein expression was confirmed in MCL LN in situ by multiplex IHC. The latter allowed the concurrent detection of MCL cells, T cells, macrophages and IL32. Consistently with the microenvironment-dependent induction of IL32 in MCL, we observed that IL32 expression was enriched in situ in tumor zones infiltrated with T cells, compared to tumor-exclusive zones.Based on in vitro experiments using IL32 KO MINO cells (Crispr/Cas9), we demonstrated that, through the secretion of IL32β, the tumor was able to corrupt its microenvironment by polarizing monocytes into specific protumoral CD163 mid MCL-associated macrophages, which secrete both pro- (e.g. IL6, OSM, IL1a/b) and anti- inflammatory (e.g. IL10, IDO, IL18, IL4L1) soluble factors. We next highlighted that IL32β-stimulated macrophages supported tumor survival mostly through a soluble dialog, which is driven by BAFF.Finally, we demonstrated the efficacy of selective NIK/alternative-NFkB inhibition to counteract both microenvironment-dependent induction of IL32β (RNA expression inhibition: 62 % ; n= 3) and BAFF-dependent survival of MCL cells (survival support inhibition : 47 % ; n=6).ConclusionsIn summary, our data uncovered the IL32β/BAFF axis as a previously undescribed pathway involved in MCL-associated macrophage polarization and tumor survival. Dependent on alternative-NFkB signaling, tumor-specific secretion of IL32β led to the corruption of the microenvironment through the polarization of monocytes into specific MCL-associated macrophages, which in turn favor tumor survival. While IL32β-stimulated macrophages secreted several protumoral factors, they supported MCL survival through BAFF and consequent alternative-NFkB activation in tumor cells. Our data shows that targeting IL32b, BAFF or the alternative NFkB pathway through NIK inhibition could also be of major interest for counteracting the multiple cross-talks that occur in the MCL microenvironment and, especially, the CD40L + T-cell / MCL / CD163 + MCL-associated macrophage triad. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Pharmacologic Targeting of Mcl-1 Induces Mitochondrial Dysfunction and Apoptosis in B-Cell Lymphoma Cells in a TP53- and BAX-Dependent Manner.

Bcl-2 has been effectively targeted in lymphoid malignancies. However, resistance is inevitable, and novel approaches to target mitochondrial apoptosis are necessary. AZD5991, a selective BH3-mimetic in clinical trials, inhibits Mcl-1 with high potency. We explored the preclinical activity of AZD5991 in diffuse large B-cell lymphoma (DLBCL) and ibrutinib-resistant mantle cell lymphoma (MCL) cell lines, MCL patient samples, and mice bearing DLBCL and MCL xenografts using flow cytometry, immunoblotting, and Seahorse respirometry assay. Cas9 gene editing and ex vivo functional drug screen assays helped identify mechanisms of resistance to Mcl-1 inhibition. Mcl-1 was expressed in DLBCL and MCL cell lines and primary tumors. Treatment with AZD5991 restricted growth of DLBCL cells independent of cell of origin and overcame ibrutinib resistance in MCL cells. Mcl-1 inhibition led to mitochondrial dysfunction as manifested by mitochondrial membrane depolarization, decreased mitochondrial mass, and induction of mitophagy. This was accompanied by impairment of oxidative phosphorylation. TP53 and BAX were essential for sensitivity to Mcl-1, and oxidative phosphorylation was implicated in resistance to Mcl-1 inhibition. Induction of prosurvival proteins (e.g., Bcl-xL) in stromal conditions that mimic the tumor microenvironment rendered protection of primary MCL cells from Mcl-1 inhibition, while BH3-mimetics targeting Bcl-2/xL sensitized lymphoid cells to AZD5991. Treatment with AZD5991 reduced tumor growth in murine lymphoma models and prolonged survival of MCL PDX mice. Selective targeting Mcl-1 is a promising therapeutic approach in lymphoid malignancies. TP53 apoptotic network and metabolic reprogramming underlie susceptibility to Mcl-1 inhibition.