Large B-cell Lymphoma Cell Lines Research Articles

The impact of diffuse large B-cell lymphoma-derived exosomes on macrophage polarisation and cytokine release

IntroductionThe pro-tumoural role of M2 macrophages has been described in various cancers and is associated with poor clinical outcomes. Exosomes derived from cancers can shuttle information among tumour cells, immune cells, and the microenvironment, leading to microenvironment remodelling. The mechanism involved in exosomes influencing macrophages polarisation is still unclear.Material and methodsWe established a macrophage model derived from THP-1 monocytes. To mimic the in vivo microenvironment, we generated an indirect co-culture system of macrophages with diffuse large B-cell lymphoma (DLBCL) cell lines, OCI-LY1 and OCI-LY3 cells. In addition, pre-treated macrophages with exosomes derived from OCI-LY1/3 lymphoma cells were used in our study. The changes in macrophage polarisation stage, surface receptor expression, and cytokine expression at the mRNA level were analysed. Moreover, the effect of macrophages on drug-induced lymphoma cell apoptosis in the indirect co-culture system was assessed. Furthermore, protein analysis of NF-κB and p-p65 in macrophages exposed to exosomes was performed by western blot.ResultsDLBCL-derived exosomes had different effects on macrophages at different differentiation stages; these macrophages had different effects on drug-induced apoptosis of lymphoma cells in indirect co-culture. Moreover, NF-κB signalling molecules were involved in this process.ConclusionsThe results indicate that DLBCL-derived exosomes can lead to more M2 phenotypes, promote tumour growth, and play a substantial role in tumour progression, invasion, and drug-resistance.

IL-17 regulates the expression of major histocompatibility complex II and VEGF in DLBCL mice on tumor growth

Objective: To investigate the effect of interleukin-17 (IL-17) on vascular endothelial growth factor (VEGF) and major histocompatibility complex II (MHC II) expression in diffuse large B-cell lymphoma (DLBCL) and the relationship thereof with tumor development. Methods: CD4 + CD62L + naive cells from spleen of BALB/c mice were purified by the immunomagnetic beads method. T-cells were cultured in vitro with anti-CD3, anti-CD28, transforming growth factor-β (TGF-β), and interleukin-6 (IL-6). The human germinal center B-cell-like diffuse large B-cell lymphoma (GCB-DLBCL) cell line SUDHL-4 was cultured and inoculated into severe combined immune deficiency (SCID) mice to establish a DLBCL mice model. Tumor-bearing mice were inoculated with Th17 cells. DLBCL was detected by ELISA. The expression of IL-17, VEGF, and MHC II were detected by immunohistochemistry (IH). Results: After Th17 cells were inoculated, the IL-17 expression level was higher than that of the control group, the VEGF expression level as lower than that of the control group, and the MHC II expression level was higher than that of the control group. There was a significant negative correlation between IL-17 and VEGF, and there was a significant positive correlation between IL-17 and MHC II. Conclusion: The VEGF and MHC II expression levels can be used as an index to judge the DLBCL disease status. IL-17 can produce negative regulation of VEGF and positive regulation of MHC II, thereby affecting the DLBCL disease process. Detection of IL-17, VEGF, and MHC II expression levels have value in judging the DLBCL disease status and progression. Keywords: Diffuse large B cell lymphoma, Th17, interleukin 17, vascular endothelial growth factor, major histocompatibility complex II

Parsaclisib Is a Next-Generation Phosphoinositide 3-Kinase δ Inhibitor with Reduced Hepatotoxicity and Potent Antitumor and Immunomodulatory Activities in Models of B-Cell Malignancy.

The clinical use of first-generation phosphoinositide 3-kinase (PI3K)δ inhibitors in B-cell malignancies is hampered by hepatotoxicity, requiring dose reduction, treatment interruption, and/or discontinuation of therapy. In addition, potential molecular mechanisms by which resistance to this class of drugs occurs have not been investigated. Parsaclisib (INCB050465) is a potent and selective next-generation PI3Kδ inhibitor that differs in structure from first-generation PI3Kδ inhibitors and has shown encouraging anti-B-cell tumor activity and reduced hepatotoxicity in phase 1/2 clinical studies. Here, we present preclinical data demonstrating parsaclisib as a potent inhibitor of PI3Kδ with over 1000-fold selectivity against other class 1 PI3K isozymes. Parsaclisib directly blocks PI3K signaling-mediated cell proliferation in B-cell lines in vitro and in vivo and indirectly controls tumor growth by lessening immunosuppression through regulatory T-cell inhibition in a syngeneic lymphoma model. Diffuse large B-cell lymphoma cell lines overexpressing MYC were insensitive to proliferation blockade via PI3Kδ signaling inhibition by parsaclisib, but their proliferative activities were reduced by suppression of MYC gene transcription. Molecular structure analysis of the first- and next-generation PI3Kδ inhibitors combined with clinical observation suggests that hepatotoxicity seen with the first-generation inhibitors could result from a structure-related off-target effect. Parsaclisib is currently being evaluated in multiple phase 2 clinical trials as a therapy against various hematologic malignancies of B-cell origin (NCT03126019, NCT02998476, NCT03235544, NCT03144674, and NCT02018861). SIGNIFICANCE STATEMENT: The preclinical properties described here provide the mechanism of action and support clinical investigations of parsaclisib as a therapy for B-cell malignancies. MYC overexpression was identified as a resistance mechanism to parsaclisib in DLBCL cells, which may be useful in guiding further translational studies for the selection of patients with DLBCL who might benefit from PI3Kδ inhibitor treatment in future trials. Hepatotoxicity associated with first-generation PI3Kδ inhibitors may be an off-target effect of that class of compounds.

Pevonedistat, a NEDD8‐activating enzyme inhibitor, induces apoptosis and augments efficacy of chemotherapy and small molecule inhibitors in pre‐clinical models of diffuse large B‐cell lymphoma

We studied the biological activity of pevonedistat, a first‐in‐class NEDD8‐activating enzyme (NAE) inhibitor, in combination with various cytotoxic chemotherapy agents and small molecule inhibitors in lymphoma preclinical models. Pevonedistat induced cell death in activated B‐cell (ABC) diffuse large B‐cell lymphoma (DLBCL) cell lines and to a lesser degree in germinal center B‐cell (GCB) DLBCL cell lines. In pevonedistat sensitive cells, we observed inhibition of NF‐κB activity by p65 co‐localization studies, decreased expression of BCL‐2/Bcl‐XL, and upregulation of BAK levels. Pevonedistat enhanced the activity of cytarabine, cisplatin, doxorubicin, and etoposide in ABC‐, but not in the GCB‐DLBCL cell lines. It also exhibited synergy with ibrutinib, selinexor, venetoclax, and A‐1331852 (a novel BCL‐XL inhibitor). In vivo, the combination of pevonedistat and ibrutinib or pevonedistat and cytarabine prolonged survival in SCID mice xenograft models when compared with monotherapy controls. Our data suggest that targeting the neddylation pathway in DLBCL is a viable therapeutic strategy and support further clinical studies of pevonedistat as a single agent or in combination with chemotherapy or novel targeted agents.

AID assists DNMT1 to attenuate BCL6 expression through DNA methylation in diffuse large B-cell lymphoma cell lines

The BCL6 proto-oncogene encodes a transcriptional repressor, which is required for germinal centers (GCs) formation and lymphomagenesis. Previous studies have been reported that the constitutive expression of BCL6 leads to diffuse large B cell lymphoma (DLBCL) through activation-induced cytidine deaminase (AID) mediated chromosomal translocations and mutations. However, other DLBCLs (45%) without structural variants were characterized by abnormally high level of BCL6 expression through an unknown mechanism. Herein, we report that deficiency in AID or methyltransferase 1 (DNMT1) triggers high level of BCL6 expression. AID-DNMT1 complex binds to −0.4 kb −0 kb region of BCL6 promoter and contributes to generate BCL6 methylation which results in inhibition of BCL6 expression. The proteasome pathway inhibitor MG132 induces accumulation of AID and DNMT1, causes decreased BCL6 expression, and leads to cell apoptosis and tumor growth inhibition in DLBCL cell xenograft mice. These findings propose mechanistic insight into an alternative cofactor role of AID in assisting DNMT1 to maintain BCL6 methylation, thus suppress BCL6 transcription in DLBCL. This novel mechanism will provide a new drug selection in the therapeutic approach to DLBCL in the future.

Mechanism of Sorafenib and Decitabine Inducing Apoptosis of Diffuse Large B-Cell Lymphoma Cells

To investigate the effect of sorafenib combined with decitabine on the viability and apoptosis of diffuse large B-cell lymphoma cell line OCI-LY1 and its mechanism. Sorafenib at 1.5μmol/L or decitabine at 25μmol/L was used to treat the cells alone or in combination. The viability of OCI-LY1 cells was detected by CCK8 assay; the PI positive cells were observed by fluorescence microscopy; the cell proliferation and ROS levels were measured by flow cytometry; The expression levels of proteins related to apoptosis were detected by Western blot. Compared with the control group, treatment with sorafenib and decitabine alone or in combination inhibited the cell proliferation, activated ROS formation and induced apoptosis finally. Sorafenib in combination with decitabine produced a synergistic effect. Western blot analysis showed that sorafenib combined with decitabine significantly up-regulated the levels of Bax/Bcl-2, P53, C-Caspase3 and C-PARP and activated apoptosis by inhibiting PI3K-AKT pathway. Sorafenib combined with decitabine induces the apoptosis of diffuse large B-cell lymphoma cell line OCI-LY1 by inhibiting PI3K-AKT pathway and activating P53.

BCL-W is dispensable for the sustained survival of select Burkitt lymphoma and diffuse large B-cell lymphoma cell lines

AbstractDysregulated expression of BCL-2 family proteins allows cancer cells to escape apoptosis. To counter this, BH3-mimetic drugs that target and inhibit select BCL-2 prosurvival proteins to induce apoptosis have been developed for cancer therapy. Venetoclax, which targets BCL-2, has been effective as therapy for patients with chronic lymphocytic leukemia, and MCL-1–targeting BH3-mimetic drugs have been extensively evaluated in preclinical studies for a range of blood cancers. Recently, BCL-W, a relatively understudied prosurvival member of the BCL-2 protein family, has been reported to be abnormally upregulated in Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), and Hodgkin lymphoma patient samples. Therefore, to determine if BCL-W would be a promising therapeutic target for B-cell lymphomas, we have examined the role of BCL-W in the sustained growth of human BL- and DLBCL-derived cell lines. We found that CRISPR/CAS9-mediated loss or short hairpin RNA-mediated knockdown of BCL-W expression in selected BL and DLBCL cell lines did not lead to spontaneous apoptosis and had no effect on their sensitivity to a range of BH3-mimetic drugs targeting other BCL-2 prosurvival proteins. Our results suggest that BCL-W is not universally required for the sustained growth and survival of human BL and DLBCL cell lines. Thus, targeting BCL-W in this subset of B-cell lymphomas may not be of broad therapeutic benefit.

Curcumin Inhibits the Proliferation, Migration, Invasion, and Apoptosis of Diffuse Large B-Cell Lymphoma Cell Line by Regulating MiR-21/VHL Axis

PurposeCurcumin exerts its anti-cancer effects, partly by targeting special microRNAs, in human cancers. MiR-21 is a key oncomir in carcinogenesis of multiple human cancers. Here, we aimed to further explore the mechanistic insight into the link between curcumin and miR-21 on diffuse large B-cell lymphoma (DLBCL).Materials and MethodsQuantitative real-time PCR assays were performed to assess the levels of miR-21 and Von Hippel-Lindau (VHL) mRNA. In situ hybridization assay was used for miR-21 expression visualization in lymphoma tissues. Western blot was used for determination of VHL protein, Ki-67, caspase-3, and cleaved caspase-3 levels. Dual-luciferase reporter assay and RNA immunoprecipitation assay were employed to confirm the direct target of miR-21. MTT assay, flow cytometric analysis, and transwell assay were used to evaluate cell proliferation, apoptosis, and migration and invasion capacities, respectively.ResultsCurcumin repressed the proliferation, migration, and invasion abilities and promoted apoptosis in SU-DHL-8 cells. Curcumin inhibited miR-21 expression and curcumin exerted its anti-proliferation, anti-migration, anti-invasion, and pro-apoptosis effects by miR-21 in SU-DHL-8 cells. VHL was a direct target of miR-21. Moreover, curcumin exerted its regulatory effects on SU-DHL-8 cells by VHL.ConclusionCurcumin exerted its anti-proliferation, anti-migration, anti-invasion, and pro-apoptosis functions, at least partly, by repressing miR-21 and regulating VHL expression in DLBCL cell line. Our findings provided a possible molecular mechanism of curcumin-mediated anti-cancer effect.

Targeting Polo-like Kinase 4 for Therapeutic Benefit in the Patients with Diffuse Large B-Cell Lymphoma

Abstract: Polo-like kinase 4 (PLK4) is a serine/threonine kinase that plays a critical role in regulating centriole duplication. PLK4 overexpression causes centriole amplification and genomic instability, which is the hallmark of cancer. Thus, PLK4 has been suggested as a tumor promoter role in solid malignancies. CFI-400945 is a highly selective small-molecule inhibitor of PLK4. CFI-400945 treatment results in centriole duplication defects, which leads to mitotic catastrophe and cell death. The antineoplastic effects of CFI-400945 have been reported in many cancers and this inhibitor has entered Phase I clinical trials for solid tumors. However, the role of PLK4 and cellular effects of CFI-40045 in hematological malignancies remains elusive. In the present study, we found that PLK4 expression is up-regulated at both transcriptional and translational levels in diffuse large B-cell lymphoma (DLBCL) cell lines (Fig. 1a, Fig. 1b). DLBCL patients displayed high protein levels of PLK4 as visualized by immunohistochemistry (Fig. 1c). In vitro, treatment of DLBCL cell lines with CFI-400945 induced a decrease in cell proliferation and an increase in cell apoptosis and a block at the G2-M transition in a dose-dependent manner (Fig. 1d, Fig. 1e, Fig. 1f). Furthermore, we found that the antineoplastic effects of CFI-400945 in DLBCL cell lines were due to the increased DNA damage, as observed by increased accumulation of γH2AX through phosphorylation of CHK1/CHK2 (Fig. 1g). Since PLK4 inhibition affects DNA damage, we next aimed to explore the effects of PLK4 expression on sensitivity of DNA damage-inducing drugs (e.g., doxorubicin). We found that silencing of PLK4 via shRNA improve the anti-tumor effects of doxorubicin in DLBCL cell lines (Fig. 1h, Fig. 1i). PLK4 inhibition in combination with doxorubicin significantly increased phosphorylation of H2AX compared to cells treated with doxorubicin alone (Fig. 1j). In summary, our data indicates that PLK4 is aberrantly expressed in DLBCL cell lines and tissues. Targeting PLK4 with the selective inhibitor CFI-400945 suppresses cell proliferation and induces apoptotic deaths and causes DNA damage in vitro. Our findings established PLK4 as a potential therapeutic target in DLBCL. Silencing of PLK4 expression induces accumulation of DNA damage and enhances the cytotoxic effects of doxorubicin. Thus, the levels of PLK4 may serve as a determinant of doxorubicin sensitivity and a predictive biomarker of the patients with DLBCL treated with R-CHOP based therapy. Figure 1 Disclosures No relevant conflicts of interest to declare.

Suppression of BCL6 function by HDAC inhibitor mediated acetylation and chromatin modification enhances BET inhibitor effects in B-cell lymphoma cells

Multiple genetic aberrations in the regulation of BCL6, including in acetyltransferase genes, occur in clinically aggressive B-cell lymphomas and lead to higher expression levels and activity of this transcriptional repressor. BCL6 is, therefore, an attractive target for therapy in aggressive lymphomas. In this study romidepsin, a potent histone deacetylase inhibitor (HDACi), induced apoptosis and cell cycle arrest in Burkitt and diffuse large B-cell lymphoma cell lines, which are model cells for studying the mechanism of action of BCL6. Romidepsin caused BCL6 acetylation at early timepoints inhibiting its function, while at later timepoints BCL6 expression was reduced and target gene expression increased due to chromatin modification. MYC contributes to poor prognosis in aggressive lymphoma. MYC function is reduced by inhibition of chromatin readers of the bromodomain and extra-terminal repeat (BET) family, which includes BRD4. The novel combination of romidepsin and JQ1, a BRD4 inhibitor was investigated and showed synergy. Collectively we suggest that the combination of HDACi and BRD4i should be pursued in further pre-clinical testing.

Depletion of the transcriptional coactivators CREB-binding protein or EP300 downregulates CD20 in diffuse large B-cell lymphoma cells and impairs the cytotoxic effects of anti-CD20 antibodies

Monoclonal antibodies targeting CD20 are central in the treatment of B-cell lymphomas. In diffuse large B-cell lymphoma (DLBCL), inactivating mutations of the histone acetyltransferases CREB-binding protein (CBP) and EP300 are common. Moreover, knockdown of CBP in DLBCL has been shown to result in aberrant transcriptional silencing. Expression of CD20 is sensitive to epigenetic manipulation, and histone deacetylase inhibitors have been found to potentiate treatment with anti-CD20 antibodies. Therefore, we studied the role of CBP and EP300 depletion on CD20 expression and effects of the anti-CD20 antibodies rituximab and obinutuzumab in DLBCL cells. Levels of CBP and EP300 were reduced by shRNA in the germinal centre-derived diffuse large B-cell lymphoma cell line SU-DHL4. The levels of CD20 mRNA and protein were determined by quantitative polymerase chain reaction, Western blot, and flow cytometry. Binding of the transcription factors PU.1 and FOXO1 to the CD20 promoter was determined by chromatin immunoprecipitation coupled with quantitative polymerase chain reaction. Response to the monoclonal anti-CD20 antibodies rituximab and obinutuzumab in CBP- or EP300-depleted cells was assessed by complement-dependent cell death, direct cell death, and antibody-dependent cellular cytotoxicity (ADCC). Our results suggest that depletion of CBP and EP300 levels leads to a strong reduction of CD20 expression, accompanied by reduced binding of PU.1 to the CD20 promoter. In CBP-depleted, but not EP300-depleted cells, increased binding of FOXO1 to the CD20 promoter was observed. Interestingly, CBP or EP300 depletion leads to decreased complement-dependent cell death and direct cell death in response to rituximab and obinutuzumab, which was most pronounced in response to rituximab in CBP-depleted cells. Our data suggest that inactivating mutations of CBP, and to a lesser extent EP300, may impair the response to anti-CD20 antibodies. However, these observations should be analyzed in future clinical trials.

Preferential targeting of MCL-1 by a hydrocarbon-stapled BIM BH3 peptide.

BCL-2 family proteins are central regulators of apoptosis and represent prime therapeutic targets for overcoming cell death resistance in malignancies. However, plasticity of anti-apoptotic members, such as MCL-1, often allows for a switch in cell death dependency patterns that lie outside the binding profile of targeted BH3-mimetics. Therefore discovery of therapeutics that effectively inactivate all anti-apoptotic members is a high priority. To address this we tested the potency of a hydrocarbon stapled BIM BH3 peptide (BIM SAHBA) to overcome both BCL-2 and MCL-1 apoptotic resistance given BIM’s naturally wide ranging affinity for all BCL-2 family multidomain members. BIM SAHBA effectively killed diffuse large B-cell lymphoma (DLBCL) cell lines regardless of their anti-apoptotic dependence. Despite BIM BH3’s ability to bind all BCL-2 anti-apoptotic proteins, BIM SAHBA’s dominant intracellular target was MCL-1 and this specificity was exploited in sequenced combination BH3-mimetic treatments targeting BCL-2, BCL-XL, and BCL-W. Extending this MCL-1 functional dependence, mouse embryonic fibroblasts (MEFs) deficient in MCL-1 were resistant to mitochondrial changes induced by BIM SAHBA. This study demonstrates the importance of understanding BH3 mimetic functional intracellular affinities for optimized use and highlights the diagnostic and therapeutic promise of a BIM BH3 peptide mimetic as a potential MCL-1 inhibitor.

Expression of co-inhibitory molecules B7-H4 and B7-H1 in Epstein-Barr virus positive diffuse large B-cell lymphoma and their roles in tumor invasion

To investigate the relationship between immunoregulatory molecules B7-H4 and B7-H1 in Epstein-Barr positive diffuse large B-cell lymphoma (EBV+DLBCL). Immunohistochemistry was used to detect the expression of B7-H4 and B7-H1 in tumor tissues of 13 patients with EBV+DLBCL. The expression levels of B7-H4 and B7-H1 in four diffuse large B-cell lymphoma cell lines (SU-DHL-4, SU-DHL-10, SU-DHL-6, Pfeiffer) were analyzed by flow cytometry. Transwell invasion assays were conducted to observe the invasive ability of cell lines. B7-H4 and B7-H1 were expressed in 84.62% and 100% tumor specimens of EBV+DLBCL. The overexpression of B7-H4 and B7-H1 was found in 46.15% and 23.08% tumor samples of EBV+DLBCL. There was a medium negative correlation between the expression levels of B7-H4 and B7-H1 (r = -0.667, P = 0.013, spearman rank correlation). The expression levels of B7-H1 in four diffuse large B-cell lymphoma cell lines were positively correlated with their invasive ability, whereas the expression levels of B7-H4 were not. Here, we provide evidence for the negative relationship between B7-H4 and B7-H1 in EBV+DLBCL. The expression of B7-H1 in EBV+DLBCL appears to be the dominant factor which affects tumor aggressiveness. When B7-H1 expression weakens, the molecule B7-H4 may become the dominant factor of prognosis in patients with EBV+DLBCL.

DZNep-mediated apoptosis in B-cell lymphoma is independent of the lymphoma type, EZH2 mutation status and MYC, BCL2 or BCL6 translocations.

Enhancer of zeste homolog 2 (EZH2) tri-methylates histone 3 at position lysine 27 (H3K27me3). Overexpression and gain-of-function mutations in EZH2 are regarded as oncogenic drivers in lymphoma and other malignancies due to the silencing of tumor suppressors and differentiation genes. EZH2 inhibition is sought to represent a good strategy for tumor therapy. In this study, we treated Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) cell lines with 3-deazaneplanocin—A (DZNep), an indirect EZH2 inhibitor which possesses anticancer properties both in-vitro and in-vivo. We aimed to address the impact of the lymphoma type, EZH2 mutation status, as well as MYC, BCL2 and BCL6 translocations on the sensitivity of the lymphoma cell lines to DZNep-mediated apoptosis. We show that DZNep inhibits proliferation and induces apoptosis of these cell lines independent of the type of lymphoma, the EZH2 mutation status and the MYC, BCL2 and BCL6 rearrangement status. Furthermore, DZNep induced a much stronger apoptosis in majority of these cell lines at a lower concentration, and within a shorter period when compared with EPZ-6438, a direct EZH2 inhibitor currently in phase II clinical trials. Apoptosis induction by DZNep was both concentration-dependent and time-dependent, and was associated with the inhibition of EZH2 and subsequent downregulation of H3K27me3 in DZNep-sensitive cell lines. Although EZH2, MYC, BCL2 and BCL6 are important prognostic biomarkers for lymphomas, our study shows that they poorly influence the sensitivity of lymphoma cell lines to DZNep-mediated apoptosis.

Differential Activity of ATR and WEE1 Inhibitors in a Highly Sensitive Subpopulation of DLBCL Linked to Replication Stress.

DNA damage checkpoint kinases ATR and WEE1 are among key regulators of DNA damage response pathways protecting cells from replication stress, a hallmark of cancer that has potential to be exploited for therapeutic use. ATR and WEE1 inhibitors are in early clinical trials and success will require greater understanding of both their mechanism of action and biomarkers for patient selection. Here, we report selective antitumor activity of ATR and WEE1 inhibitors in a subset of non-germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL) cell lines, characterized by high MYC protein expression and CDKN2A/B deletion. Activity correlated with the induction of replication stress, indicated by increased origin firing and retardation of replication fork progression. However, ATR and WEE1 inhibitors caused different amounts of DNA damage and cell death in distinct phases of the cell cycle, underlying the increased potency observed with WEE1 inhibition. ATR inhibition caused DNA damage to manifest as 53BP1 nuclear bodies in daughter G1 cells leading to G1 arrest, whereas WEE1 inhibition caused DNA damage and arrest in S phase, leading to earlier onset apoptosis. In vivo xenograft DLBCL models confirmed differences in single-agent antitumor activity, but also showed potential for effective ATR inhibitor combinations. Importantly, insights into the different inhibitor mechanisms may guide differentiated clinical development strategies aimed at exploiting specific vulnerabilities of tumor cells while maximizing therapeutic index. Our data therefore highlight clinical development opportunities for both ATR and WEE1 inhibitors in non-GCB DLBCL subtypes that represent an area of unmet clinical need. SIGNIFICANCE: ATR and WEE1 inhibitors demonstrate effective antitumor activity in preclinical models of DLBCL associated with replication stress, but new mechanistic insights and biomarkers of response support a differentiated clinical development strategy.

Abstract 2500: Transient CDK9 inhibition with AZD4573 modulates Bfl-1 in preclinical lymphoma models

Abstract AZD4573 is a selective cyclin-dependent kinase 9 (CDK9) inhibitor under clinical development in patients with hematological malignancies. Transient CDK9 inhibition serves as an orthogonal approach for targeting Mcl-1, a labile anti-apoptotic protein essential for the survival of cancer cells. Across-broad hematological cancer models, anti-tumor responses with AZD4573 strongly correlate with selective Mcl-1 inhibitors, such as AZD5991 (R2=0.8). Despite compelling evidence for an Mcl-1 dependent mechanism of action, we also observed a subset of lymphoma models more sensitive to CDK9 inhibition compared to Mcl-1 inhibition, suggesting acute CDK9 inhibition could be targeting other labile proteins beyond Mcl-1 to induce apoptosis. We identified Bfl-1 as one such potential target and demonstrate lymphoma models expressing Bfl-1 are highly sensitive to CDK9 inhibition. Bfl-1 belongs to the Bcl-2 family of anti-apoptotic proteins and was detected in over 20% of lymphoma cell lines evaluated (n=33). Cycloheximide experiments indicate Bfl-1 has a short protein half-life (<1h), similar to Mcl-1. Therefore, treatment with 100nM of AZD4573 in diffuse large B-cell lymphoma cell lines OCILY10 and TMD8 caused rapid down-regulation of both Mcl-1 and Bfl-1 by 4h, resulting in caspase cleavage by 6h. Evaluation of caspase activation following 6h treatment revealed an average maximum effect of 87% for AZD4573 compared to 45% with Mcl-1 inhibition, suggesting these cell lines are not exclusively Mcl-1-dependent. The hypothesis that survival of lymphoma cells may be co-dependent on both Mcl-1 and Bfl-1 was evaluated by siRNA knockdown. Following a dose-dependent suppression of Bfl-1 protein (>80%) in OCILY10 and TMD8 cells, viability loss was minimal (<30% reduction relative to control). However, when Bfl-1 knockdown cells were treated for 6h with an Mcl-1 inhibitor, the maximum caspase activation increased to over 90% in both cell lines, phenocopying a similar magnitude achieved with AZD4573-mediated CDK9 inhibition. In these models, depletion of both Bfl-1 and Mcl-1 was necessary to induce maximum apoptosis, with studies ongoing to evaluate single-gene Bfl-1 dependency in additional lymphoma models. Consistent with the in vitro phenotype, intermittent dosing of the ABC-DLBCL xenografts OCILY10 and TMD8 with AZD4573 caused robust tumor regressions (198 and 184% TGI, respectively). AZD4573-mediated anti-tumor activity was associated with pharmacodynamic reductions of pSer2-RNAPII, Mcl-1 and Bfl-1, followed by caspase activation. Collectively, these findings support the ability to target Bfl-1 via CDK9 inhibition. Given the current absence of clinical small molecule Bfl-1 inhibitors and expanded monotherapy activity compared to selective Mcl-1 inhibition in a subset of preclinical models, CDK9 inhibitors have tremendous therapeutic potential in the treatment of patients with Bfl-1-expressing lymphoma. Citation Format: Scott Boiko, Theresa Proia, Maryann San Martin, Lisa Drew, Wenlin Shao, Justin Cidado. Transient CDK9 inhibition with AZD4573 modulates Bfl-1 in preclinical lymphoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2500.

Abstract 2497: FCN-338, a novel and selective Bcl-2 inhibitor, exhibits potent anti-tumor activity in B-cell lymphoma

Abstract B-cell lymphoma-2 (Bcl-2) family proteins are key regulators of apoptosis, which is vital for proper tissue development and cellular homeostasis. Apoptosis occurs via activation of two different pathways: the extrinsic pathway, triggered by a death ligand binding to a death receptor, such as TNF-α to TNFR1; and the intrinsic pathway, regulated by Bcl-2 family proteins and their complex protein-protein interactions. Bcl-2 family proteins are functionally classified as either anti-apoptotic, such as Bcl-2, Bcl-xL and Mcl-1, or pro-apoptotic, including Bid, Bim, Bad, Bak and Bax. Anti-apoptotic Bcl-2 family members are often found to be up-regulated in many types of human cancers, such as different subtypes of B-cell lymphoma and diverse solid tumors, and are frequently been correlated with decreased susceptibility to chemotherapeutics and to increased radio-resistance. Overexpression of Bcl-2 proteins is an independent indicator of poor prognosis in tumors including chronic lymphocytic leukemia (CLL), prostate cancer, and small cell lung cancer (SCLC). Therefore, targeting Bcl-2 and its pro-survival relatives that form the core anti-apoptotic machinery, has emerged as a promising therapeutic approach in cancer. To that end, we have developed a novel and selective Bcl-2 inhibitor, FCN-338, with nanomolar affinity to Bcl-2 and physicochemical properties suitable for oral administration. FCN-338 exhibits much greater affinity to Bcl-2 than Bcl-xL, suggesting its good potential to avoid thrombocytopenia caused by the inhibition of Bcl-xL. FCN-338 has shown remarkable anti-proliferation potency against a panel of Bcl-2-addicted human B-cell lymphoma cell lines, including DOHH2 follicular lymphoma (FL) cell line (IC50 2 nM), Mino diffuse large B-cell lymphoma (DLBCL) cell line (IC50 23 nM), and RS4;11 acute lymphoblastic leukemia (ALL) cell line (IC50 35 nM), but not in Bcl-xL-dependent H146 SCLC cell line (IC50 >4,500 nM). Correspondingly, in vivo efficacy of FCN-338 was demonstrated in a variety of xenograft models derived from FL, DLBCL and ALL tumors. FCN-338 dramatically caused tumor regression in a dose-dependent manner. In the non-clinical studies, FCN-338 exhibits much improved pharmacokinetic properties with higher T1/2, dose-normalized AUC and bioavailability in dogs compared with the FDA-approved Bcl-2 inhibitor ABT-199. Preferable safety profiles of FCN-338 were shown with no potential hERG inhibitory effect and less drug-drug interaction potential, as evidenced by no inhibitory effect (IC50 >50 μM) on CYP2C9 enzyme compared with ABT-199 (IC50 1.05 μM). Together, our findings highlight the therapeutic potential of FCN-338 to be used as effective therapy across a broad range of Bcl-2-addicted B-cell malignancies. Citation Format: Shu Lin, Xingdong Zhao, Hongbin Liu, Huajie Zhang, Zhifang Chen, Lihua Jiang, Yanxin Liu, Min Lin, Yue Rong, Rui Tan, Zuwen Zhou, Zongyao Zou, Yuwei Gao, Weibo Wang. FCN-338, a novel and selective Bcl-2 inhibitor, exhibits potent anti-tumor activity in B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2497.

PS1302 THE CD58-CD2 AXIS CONTROLS KILLING OF B CELLS BY CYTOTOXIC T CELLS

Background: DuoBody-CD3xCD20 (GEN3013) is a bispecific antibody (bsAb) recognizing the T-cell antigen CD3 and the B-cell antigen CD20, that triggers potent T-cell-mediated lysis of CD20-expressing cells. DuoBody-CD3xCD20 is a full-length bispecific IgG1 generated by controlled Fab-arm exchange (Labrijn et al. PNAS 2013, Nat Prot 2014), with an effector function-silenced Fc region. Aims: Preclinical characterization of DuoBody-CD3xCD20. Methods: T-cell activation and cytotoxicity induced by DuoBody-CD3xCD20 in vitro, in comparison with a known CD3xCD20 bsAb, was measured by flow cytometry, 48 hours after incubation of healthy donor T cells with CD20-expressing cell lines (E:T ratio 2:1). Anti-tumor activity of DuoBody-CD3xCD20 in vivo was assessed in xenograft models. In a co-engraftment model, Raji tumor cells were co-inoculated with healthy donor PBMCs subcutaneously (SC) in NOD-SCID mice, followed by intravenous (IV) antibody treatment. In a MiXeno model, JEKO-1 tumor cells were inoculated SC in NCG mice, followed by intraperitoneal injection of human PBMCs. Treatment was initiated when tumors reached an average size of 100 mm3. Human immune system (HIS mice) were inoculated with Daudi lymphoma cells IV or with Raji lymphoma cells SC, followed by treatment from day 3. Activity of DuoBody-CD3xCD20 after SC or IV administration to cynomolgus monkeys was assessed as part of nonclinical safety studies. Results: DuoBody-CD3xCD20 induced potent activation and cytotoxic activity of CD4+ and CD8+ T cells in the presence of CD20-expressing cells in vitro. T-cell-mediated cytotoxicity was observed in a diverse panel of diffuse large B-cell and mantle cell lymphoma cell lines, with EC50 values ranging from 0.2 to 5.0 pM. Direct comparison in vitro demonstrated that DuoBody-CD3xCD20 was ∼100-fold more potent than another CD3xCD20 bsAb that is currently tested in clinical trials. DuoBody-CD3xCD20 potently inhibited outgrowth of CD20-expressing tumors (Raji) in vivo, even in the presence of high doses of Fc-inactive rituximab, demonstrating that the anti-tumor activity of DuoBody-CD3xCD20 was not inhibited by an excess of circulating CD20 antibodies that compete for target binding. In addition, DuoBody-CD3xCD20 induced regression of established mantle cell lymphoma (JEKO-1) tumors and delayed tumor growth and enhanced survival in the HIS xenograft models. In cynomolgus monkeys, profound and long-lasting B-cell depletion (≥ 70 days) from peripheral blood and lymphoid organs was induced by DuoBody-CD3xCD20 at dose levels > 0.1 mg/kg. B-cell depletion was reversible, with time to recovery correlating with the treatment dose. A transient decline in peripheral T cells was observed, as well as T cell activation. At the same dose levels, SC and IV administration of DuoBody-CD3xCD20 induced comparable B cell depletion. Importantly, peak plasma levels were reduced and delayed after SC administration, which was associated with reduced plasma cytokine levels. Summary/Conclusion: DuoBody-CD3xCD20 induced potent anti-tumor activity in vitro and in vivo, also in the presence of competing CD20 antibodies. DuoBody-CD3xCD20 was ∼100-fold more potent in vitro than another CD3xCD20 bsAb that is in clinical development. SC administration in cynomolgus monkeys induced profound B-cell depletion, which was associated with reduced plasma cytokine levels compared to IV administration. A First-in-Human trial to evaluate the safety and preliminary efficacy of DuoBody-CD3xCD20 by SC administration in patients with B-cell malignancies is currently enrolling (NCT03625037).

MEF2B is a member of the BCL6 gene transcriptional complex and induces its expression in diffuse large B-cell lymphoma of the germinal center B-cell-like type

Myocyte enhancer-binding factor 2B (MEF2B) has been implicated as a transcriptional regulator for BCL6. However, details about the interaction between MEF2B and BCL6 during expression, as well as the relationship of MEF2B to the expression of other germinal center (GC) markers, have not yet been fully explained. Using germinal center B-cell-like diffuse large B-cell lymphoma (GC-DLBCL) and activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines, we analyzed the expression of MEF2B and its associations with BCL6, CD10, and ERK. Furthermore, small interfering RNA (siRNA) was used to study the possible effects of MEF2B knockdown on these proteins and cell growth. Analysis of the BCL6 transcriptional complex was performed using electrophoretic mobility shift assay. The correlation between MEF2B expression and the genetic type of DLBCL was assessed using immunohistochemistry on 111 patient samples, and via in silico analysis of publicly available microarray (Gene Expression Omnibus (GEO)) datasets. Our results indicate that the expression of MEF2B protein is important for the growth of GC-DLBCL cells, as evidenced by MEF2B knockdown inhibition of cell growth and the subsequent suppression of BCL6, CD10, and ERK phosphorylation. Analysis of BCL6 transcription factors in nuclear extracts of MEF2-expressing DLBCL cells showed involvement of MEF2B with AP-2α and BCL6 proteins in the formation of the BCL6 gene transcriptional complex. Indeed, differential expression of MEF2B in the GC-DLBCL is statistically significant compared to the ABC-DLBCL in the GEO datasets, as well as in tissue microarray, as indicated via immunohistochemistry (Visco–Young algorithm). Our findings indicate that MEF2B is an essential component of the BCL6 gene transcriptional complex for the regulation of DLBCL growth via the promotion of BCL6 expression. Beyond its regulatory role in DLBCL growth, MEF2B expression correlated positively with BCL6 and CD10 expression, and was preferentially expressed in the GBC-DLBCL group.

Targeting MYC-Driven B-Cell Lymphoma By Inhibition of the Histone Methyltransferase DOT1L

Aberrant activation of the MYC proto-oncogene is a recurrent feature in human B-cell lymphomas of diverse sub-types, correlating with adverse prognosis and therapy resistance. Direct pharmacological MYC-targeting has proved difficult, but recent studies have shown that targeting chromatin regulators critical for MYC-driven oncogenesis may provide alternative avenues for therapeutic intervention. Recently, it has been demonstrated that MYC-driven oncogenesis in certain solid tumors is dependent on the histone 3 lysine 79 (H3K79) methyltransferase DOT1L. We hypothesized that B-cell lymphomas with hyperactive MYC-signaling might be responsive to DOT1L inhibition. In order to test this hypothesis, we tested the effect of the DOT1L inhibitor Pinometostat (EPZ-5676) on a panel of human B-cell lymphoma cell lines featuring elevated MYC. Pinometostat treatment reduced global H3K79 methylation levels, accompanied by a time and dose-dependent decrease in proliferation of several Burkitt's lymphoma cell lines including P493-6, Daudi and Raji. We observed that key MYC-target genes including CDK4, PPAT and NPM1 were significantly downregulated upon Pinometostat treatment, suggesting that DOT1L is required for the transcriptional activation of MYC-target genes in these cells. Pinometostat-treated B-lymphoma cells showed a significant decrease of cells in S-phase compared to controls as assessed by BrdU-labeling assays. Similar results were also obtained in a panel of B-cell lymphoma cell lines with MYC-rearrangements including mantle cell lymphoma (MCL) cell lines Jeko-1, JVM2, Mino-1 and Maver-1 and the diffused large B-cell lymphoma (DLBCL) cell line Karpas 422.Next, we sought to investigate whether the DOT1L-dependence of MYC-driven B-cell lymphoma could be reproduced in a well-defined model of MYC-driven B-cell lymphoma. Towards this end, we utilized a mouse model in which expression of the Cre recombinase from a B cell specific promoter leads to ectopic expression of a transgenic human MYC allele and concomitant deletion of the tumor suppressor Pten in B cells. Similar to our in vitro studies, Pinometostat treatment led to a significant reduction in proliferation of B-cell lymphoma cells from these mice with an IC50 of 0.5 µM.Furthermore, we sought to ascertain whether these findings reflected on-target effects related to DOT1L inhibition. Therefore, we deleted DOT1L using CRISPR/Cas9 in B-cell lymphoma cell lines and assessed the effect on proliferation using competitive-proliferation assays. We observed that DOT1L-deletion progressively diminished the relative growth of anti-DOT1L sgRNA-expressing P493-6 and Jeko1 cells compared to non-targeted cells invitro. In order to test the requirement for DOT1L in lymphoma propagation in vivo, we performed intravenous injections of equal number of Jeko-1 cells with either anti-DOT1L or anti-Renilla control sgRNAs into sub-lethally irradiated non-obese diabetic/severe combined immunodeficiency mice (NOD/SCID) mice. Mice injected with control anti-Renilla sgRNAs succumbed to disease with a median latency of 34 days while the latency of disease in the anti-DOT1L sgRNA cohort was 45 days. In summary, DOT1L depletion significantly delayed disease latency in this invivo disseminated model of B-cell lymphoma (P=0.02).We then performed transcriptomic analyses of Pinometostat-treated B-cell lymphoma cell lines compared to DMSO-treated counterparts using RNA-seq. Gene-set enrichment analysis (GSEA) of RNA-seq data from three different B-cell lymphoma cell lines demonstrated that Pinometostat treatment significantly decreased the expression of MYC-target genes. In order to investigate the intriguing role of DOT1L in regulating MYC-target gene expression, we used ChIP-seq to assess the genome-wide occupancy of MYC following DOT1L inhibitor treatment. Strikingly, our studies demonstrated that DOT1L inhibition significantly reduced the chromatin occupancy of MYC.Taken together, our experiments demonstrate the role of DOT1L in MYC-driven B-cell lymphoma pathogenesis invitro and invivo. Furthermore, our genome-wide studies demonstrate the importance of DOT1L for genomic MYC occupancy. Based on these findings, we propose that therapeutic DOT1L targeting may be a viable strategy in MYC-driven B-cell lymphoma. DisclosuresWeigert:Roche: Research Funding; Novartis: Research Funding. Rickert:Pfizer: Employment. Ren:Elli Lilly: Consultancy, Membership on an entity's Board of Directors or advisory committees; Arima Genomics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Deshpande:Salgomed Therapeutics: Membership on an entity's Board of Directors or advisory committees; A2A Pharma: Membership on an entity's Board of Directors or advisory committees.