Rituximab-resistant Cell Lines Research Articles

Abstract 1751: Prognostic value of CD20/CD73 ratio in sensitive and relapsed/refractory diffuse large B-cell lymphoma cell lines

Abstract Purpose: Developing novel therapy strategies to treat relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL) is critically needed. Previous studies in our group found despite dysregulation of apoptotic pathway in resistant DLBCL, upregulation in glycose metabolism and energetic ATP production were also found in r/r DLBCL. Therefore, decreasing or blockage ATP production may provide a novel method to overcome resistance in lymphoma. ATP/ADP is hydrolyzed into AMP by NTPDases, and AMP into adenosine and phosphate by ecto-5’-nucleotidase, known as CD73. CD73 is the rate limiting enzyme anchored the surface of tumor and immune cell. The expression level of CD73 on the tumor was reported significantly associated with inferior prognosis in variety of cancers. Moreover, expression level of CD73 on immune cell has been shown immunosuppression in multiple cancers. Targeting CD73 by monoclonal antibody or small inhibitor currently underwent multiple clinical trials. However, the role of CD73 in r/r DLBCL and the relationship between CD73 and CD20 have not been explored. Methods: Germinal center B-cell like, activated B-cell like lymphoma, Burkitt’s lymphoma and rituximab resistant cell lines generated in our lab were used. Surface expression of CD73 and CD20 were determined by staining anti-CD73 FITC and anti-CD20 Per-cy5.5 antibodies and running flow cytometry. The expression levels of CD73 and CD20 were detected by media fluorescence index (MFI). The CD20/CD73 ratio was calculated by CD73 MFI/CD20 MFI. Result: Previously our group found surface CD20 levels exhibited a linear correlation with rituximab induced cellular mediated cytotoxicity. The CD20 MFI of germinal center B-cell like, activated B-cell like lymphoma, Burkitt’s lymphoma and rituximab resistant cell lines were: DHL4 8652, DOHH2 6472, TMD8 3981, RL 2849, Raji 2011, U2932 604, RL 4RH 599 and Raji 4RH 576. The higher MFI of CD20, the more sensitive to rituximab treatment. Here we discovered that the surface level of CD73 had an inverse correlation with CD20 level in these cell lines. In detail, CD73 MFI were: DHL4 464, DOHH2 387, TMD8 363, RL 299, Raji 611, U2932 486, RL 4RH 631 and Raji 4RH 702. The CD20/CD73 ratio of cell lines from high to low were DOHH2, DHL4, TMD8, RL, Raji, U2932, Raji 4RH and RL 4RH, respectively. This CD20/CD73 ratio in each of cell lines was found more straight forward to represent the sensitivity of rituximab or chemo drug treatment in vitro condition. Conclusion: Our study was first time to reveal the association between CD20/CD73 ratio and immune-chemo response in lymphoma cell lines, especially in resistant lymphoma in vitro condition. This may give us prognostic value of CD20/CD73 ratio in predicting lymphoma response to immune/chemotherapy in clinical setting. Further study to find CD20 and CD73 association in the clinical setting and mechanism of action need to be warranted. Citation Format: Juan J. Gu, Cory Mavis, Jessica Wang, Taylor Mandeville, Francisco Hernandez-Ilizaliturri. Prognostic value of CD20/CD73 ratio in sensitive and relapsed/refractory diffuse large B-cell lymphoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1751.

XIAP Knockdown Can Increase the Activity of Caspase 3 and 7, and Restore the Apoptotic Response in Cell Line Models of Rituximab Relapse/Refractory B-Cell Lymphoma

Rituximab-chemotherapy relapse/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) patients have lower response rates to second-line chemotherapy, and have a poor overall prognosis. Pre-clinical models of rituximab resistance demonstrated that the acquirement of resistance to anti-CD20 antibodies leads to concomitant resistance to chemotherapy drugs, suggesting the existence of share pathways of resistance between rituximab and chemotherapy agents. To better understand the mechanisms responsible for rituximab/chemotherapy cross-resistance we developed several rituximab resistance cell lines (RRCL), which also display significant resistance to a wide range of chemotherapy agents. RRCLs exhibit a deregulation in the apoptotic response pathway at several levels. Previous work by our group demonstrated that the X linked inhibitor of apoptosis (XIAP) is a key regulator of chemotherapy resistance in RRCLs. Moreover, we have established that knocking down XIAP in RRCLs can enhance the anti-tumor cytotoxic effect of chemotherapy, but a clear mechanistic role for XIAP in RRCLs has yet to be established. To investigate how XIAP regulates chemotherapy response in resistant lymphoma models we first looked at expression levels of XIAP and its binding partners in RRCLs and rituximab sensitive cell lines (RSCL). Although we observed no change in XIAP expression between the RRCL Raji 4RH and RSCL Raji, we did observe changes in several of the XIAP interacting proteins. Protein levels for both of the primary apoptotic effector caspases (caspase 3 and caspase 7) were substantially decreased in the Raji 4RH cell line compared to Raji cells. In addition, when we exposed Raji and Raji 4RH cells to gemcitabine (50uM) for 28 hours we observed substantially less release of cytochrome C from the mitochondria in Raji 4RH compared to Raji. Cytochrome C is an essential part of the apoptosome, which functions as a primary activator of caspases 3 and 7. Both of these observations support the hypothesis that impaired effector caspase activation and signaling contributes to chemotherapy resistance in RRCLs. To determine if targeting XIAP could restore caspase activation in RRCLs we used a transient siRNA knockdown of XIAP in the Raji 4RH cell line. Cells were treated with either the XIAP targeting siRNA, or a scramble sequence control, and then exposed to chemotherapy for 36 hours. Cellular viability was measured with the Promega CellTiter-Glo ATP assay, while caspase 3 and 7 activity was determined with the Caspase 3/7-Glo assay, also purchased from Promega. XIAP knockdown increased caspase activity by more than 500% compared to controls when cells were exposed to etoposide (20uM). This correlated with a 60% decrease in cellular viability in cells with an XIAP knockdown. In addition, the addition of the caspase inhibitor QVD-OPh along with the RIP kinase inhibitor necrostatin-1 (both at 10uM) was enough to restore cellular viability to the same levels observed in scramble treated controls exposed to the same dose of etoposide. Additional experiments looking at activation of caspases 2 and 6 in Raji 4RH cells following XIAP knockdown did not show any difference compared to scramble controls. In summary, XIAP appears to directly inhibit the caspase dependent apoptotic response in RRCLs. In addition, targeting XIAP can restore the apoptotic response in cell line models of rituximab resistant disease. These results support the hypothesis that selective XIAP inhibitors, currently in development, may be highly active against rituximab rel/ref B-cell lymphoma. DisclosuresNo relevant conflicts of interest to declare.

Lymphoma cell-killing activity and cytokine release by CD20-directed bispecific IgM antibody-based T-cell engager (IGM-2323).

e15007 Background: Bispecific antibodies which tether T-cells to cancer cells, and additionally activate T-cell mediated killing, have shown promise in treating B-cell malignancies. Dose intensity, however, is limited by cytokine release from the activated T-cells. Side effects include fever, hypotension, and hypoxia. Methods: A novel type of bispecific antibody (IGM-2323) was constructed using the pentameric IgM framework. Recombinant IgM heavy chains and kappa light chains with high affinity variable domains derived from an anti-CD20 IgG, were co-expressed with a J-chain fused to anti-CD3 single chain Fv domain. IGM-2323 has 10 binding domains for CD20, and one binding domain for CD3. Results: IGM-2323 binds to the CD20 antigen with > 1000-fold increased avidity relative to an IgG antibody format. IGM-2323 in human cell cultures shows highly potent T cell dependent cytotoxicity (EC50 20 pM), even on cells with very low cell surface expression of CD20, rituximab-resistant lymphoma cell lines, and patient derived CLL cells. Significantly, IGM-2323 exhibits vastly reduced cytokine release, with equivalent T cell dependent killing of CD20-expressing cancer cells, as compared to corresponding IgG-based T cell bispecifics made with the same binding domains. IGM-2323 mediated killing can occur at low T-cell/cancer cell ratios, as low as (1:5). In addition, IGM-2323 mediates complement dependent cytotoxicity (CDC) of CD20-expressing cells with > 100-fold higher potency than IgG. IgM-based bispecific (anti-CD20 x anti-CD3) completely depletes circulating B cells in cynomolgus monkeys at doses of > 300 µg per kg. Furthermore, durable depletion of B cells in spleen and lymphoid tissues was noted with multiple doses of > 1 mg/kg. Importantly, in these studies no observable adverse effects were seen, despite repeated doses at up to 25 mg/kg (the highest dose tested). Low levels of transiently increased circulating IL-6 and no increased levels of circulating TNF-α and IFN-γ were observed in these primate studies. Conclusions: These data indicate that IgM-based bispecifics can induce T cell engagement and very potent cytotoxicity that can be dissociated from cytokine release syndrome in the primate model. These preclinical data demonstrate the potential for broad application of this novel modular IgM-based bispecific antibody format. A Phase I dose-escalation study of IGM-2323 in patients with relapsed/refractory Non-Hodgkin’s lymphoma has been initiated (NCT04082936) and is currently enrolling patients.

Targeting MDM2 and XIAP By Idasanutlin in Diffuse Large B-Cell Lymphoma

Purpose: The combination of rituximab and chemotherapy has improved overall survival of diffuse large B-cell lymphoma (DLBCL) patients in recent decades. Relapsed/refractory DLBCL patients previously treated with rituximab-containing regimen had significantly poorer response to salvage therapy. To study the mechanisms of this resistance, our laboratory developed several rituximab resistant cell lines. Previous study from our group found demonstrated an aberrant imbalance in the levels of pro- and anti-apoptotic proteins in these cell lines, including Bak/Bak, Mcl-1/BCLxL/Survivin and inhibitor of apoptosis (IAP) family proteins resulting in acquired chemotherapy resistance. MDM2 is an E3 ligase which regulates the degradation of multiple cellular protein targets such as pRB, HIF-1, p73, NF-kB, and E2F1 as well as FOXO3a. It is also the major negative regulator of p53. Recently, we found that MX69 (a MDM2 inhibitor), which blocks the MDM2 protein-XIAP RNA interaction, led to both MDM2 and XIAP degradation, and induced apoptosis-dependent cell killing activity. Moreover, MX69 re-sensitized resistant DLBCL cell lines to chemotherapy agents or small inhibitors (i.e. Venetoclax) in vitro. However, MX69 cannot be used clinically stressing the need to use a clinically available MDM2 inhibitor. To this end, we evaluated Idasanutlin, an investigational Nutlin family MDM2 antagonist, in B-cell lymphoma pre-clinical models. Methods: We used a panel of different DLBCL subtypes cell lines including activated B-cell lymphoma cell lines (TMD8, U2932); germinal center B-cell lymphoma (DOHH2, VAL, OCILY2, DH4, DH6, ROS50); rituximab-sensitive cell lines (Raji and RL); and rituximab/-resistant cell lines (Raji 4RH and RL 4RH). Cells were exposed to escalating doses of Idasanutlin (1nM-100µM) without or with other chemotherapeutic agents for 24, 48 and 72 hrs. Differences in cell viability were evaluated utilizing PrestoBlue. IC50 was calculated by GraphPad and Coefficient of synergy was calculated using CalcuSyn. Low mitochondrial potential was detected by staining cell with DiOC6 10ng/ml for 30 minutes and followed by flow cytometric analysis. Western blot was used to detect the changes of MDM2, XIAP and PUMA expression before and after exposure to Idasanutlin 1uM for 24h. Results:In vitro exposure Idasanutlin to DLBCL cell lines demonstrated a dose- and time-dependent cell death. IC50 dosage of the cells was ranged from 0.7uM to 63.07uM at 48h. Low dose of Idasanutlin (1uM) was able to disrupt mitochondria and induced low mitochondrial membrane potential in both ABC and GCB cell lines. At molecular level, Idasanutlin reduced expression level of MDM2 in TMD8, U2932, VAL, OCILy2 DHL4 and ROS50 cell lines. XIAP was reduced in Val and DHL4. Meanwhile, PUMA, the downstream of p53 activation, was increased after Idasanutlin exposure. Idasanutlin enhanced the anti-tumor activity of proteasome inhibitors (carfilzomib, ixazomib), Bcl-2 inhibitor venetoclax and Bryton kinase inhibitor ibrutinib. Conclusion: Idasanutlin showed potent anti-tumor activity as a single agent in DLBCL pre-clinical setting. Idasanutlin was able to decrease cellular mitochondrial membrane potential. At molecular level, Idasanutlin decreased MDM2 and XIAP protein level and induced PUMA expression. Moreover, Idasanutlin enhanced anti-tumor activities of other small inhibitors. Taking together, Idasanutlin could be used as a novel and promising drug in the clinical setting of DLBCL with relapsed/refractory disease. Disclosures No relevant conflicts of interest to declare.

Abstract 723: MX69 induces apoptosis by inhibiting XIAP in both rituximab sensitive and resistant lymphomas

Abstract Background: X-linked inhibitor of apoptosis protein (XIAP) has been implicated in development of resistance to chemotherapy via its direct inhibition of caspases 3,7 and 9. It is overexpressed in several lymphoma cell lines including rituximab-resistant cell lines (RRCL), Raji4RH and RL4RH, produced by our group. We have previously demonstrated that XIAP is critical for chemotherapy-resistance and survival in RRCL by knocking down XIAP using siRNA interference which demonstrated that XIAP is critical for chemotherapy-sensitivity and survival in RRCL. MDM2 inhibition activates p53 transcription and inhibits translation of XIAP, thus promoting apoptosis of cancer cells. Here, we targeted XIAP at a translational level by inhibiting it with MX69, a dual inhibitor of MDM2 and XIAP. Materials and Methods: Cell lines representing Burkitt’s lymphoma (BL), activated B-cell like diffuse large B-cell lymphoma (ABC-DLBCL, germinal center B-cell like DLBCL (GCB-DLBCL), mantle cell lymphoma (MCL) and B-cell lymphoblastic leukemia were exposed to MX69 as a single agent (0-80 uM) over 24, 48 and 72 hrs and IC50 concentrations were calculated. Subsequently, Raji, Raji4RH, RL, RL4RH, HBL-2, TMD-8, Daudi and Reh cell lines were exposed to MX69 (0-80 uM), in combination with doxorubicin (0-1 uM), cytarabine (0-50 uM), vincristine (0-10 nM), etoposide (0-50 uM), carboplatin (0-10 uM), ixazomib (0-1.5 uM), ibrutinib (0-10 uM) and venetoclax (0-10 uM) for 48 hours. Cell viability was determined by Cell Titer-Glo. Coefficient of synergy was calculated using CalcuSyn. Induction of apoptosis was evaluated by flow cytometry (Annexin V/PI stain). MDM2, p53, XIAP and PARP protein expression was determined by Western blotting. Results: MX69 induced cell death in a dose- and time-dependent manner in all cell lines. Annexin/PI staining showed caspase-dependent apoptosis with MX69 in all cell lines. Western blotting confirmed significant inhibition of MDM2, XIAP and changes in p53 and PARP following exposure to MX69. MX69 demonstrated significant synergistic activity when combined with doxorubicin, ixazomib, ibrutinib or venetoclax; synergy was strongest for the MX69- venetoclax combination. Conclusion: Our data suggests that in vitro exposure to MX69 resulted in anti-tumor activity in a wide variety of B-cell lymphoma cells lines (including BL, DLBCL, MCL). Perhaps related to its anti-tumor effects, MX69 inhibited XIAP levels. These findings are similar to prior siRNA XIAP knockdown experiments. Strong synergistic activity was observed when XIAP was combined with various chemotherapy agents and small molecules inhibitors (such as venetoclax, ixazomib or ibrutinib). Ex vivo experiments using primary tumor cells isolated from lymphoma patients and lymphoma mouse models have been planned. Targeting MDM2 and XIAP can be an attractive therapeutic strategy in patients with rituximab-sensitive or -resistant B-cell lymphoma. Citation Format: Sumera Khan, Cory Mavis, Ahmad Hanif, Juan Gu, Pallawi Torka, Francisco Hernandez-Ilizaliturri. MX69 induces apoptosis by inhibiting XIAP in both rituximab sensitive and resistant lymphomas [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 723.

The SMAC mimetic LCL-161 displays antitumor activity in preclinical models of rituximab-resistant B-cell lymphoma

AbstractClinical observations suggest the existence of shared resistance pathways between rituximab and chemotherapy agents. To explore the mechanisms of rituximab resistance, our group created rituximab-resistant cell lines (RRCLs), which display altered expression of several inhibitor of apoptosis (IAP) family proteins. Here, we provide evidence to support pharmacologically targeting IAPs in lymphoma with LCL-161, a small molecule mimetic of the second mitochondria-derived activator of caspases (SMAC). The antitumor effect of LCL-161 was determined using luminescent adenosine triphosphate assays, flow cytometry, SCID mouse xenografts, and ex vivo patient biopsy sample studies. In vitro exposure to LCL-161 also resulted in a dose-dependent decrease in IAP levels, along with synergistic enhancement of the antitumor effect of cytotoxic chemotherapy, in rituximab-sensitive cell lines and RRCLs. In addition, LCL-161 increased the cytotoxic effect of the proteasome inhibitor carfilzomib in ex vivo lymphoma patient samples. The combination of LCL-161 with the chemotherapy regimen rituximab, gemcitabine, and vinorelbine (RGV) improved in vivo survival compared with RGV alone in severe combined immunodeficient mice implanted with RRCLs but not in animals implanted with rituximab-sensitive cell lines. In summary, LCL-161 exhibits synergistic antitumor activity in both in vitro and in vivo models of resistant lymphoma. Our data support further preclinical investigation of LCL-161 as a novel antilymphoma agent.

Targeting XIAP Via Degradation of MDM-2 By MX69 in Aggressive Lymphomas

Background: The addition of Rituximab to front-line therapy has improved clinical outcomes in diffuse large B-cell lymphoma (DLBCL), but it has also altered the biology of relapsed/refractory disease. To better understand the mechanisms responsible for Rituximab associated chemotherapy cross-resistance our group developed and characterized several Rituximab resistance cell lines (RRCL). We previously demonstrated using SiRNA interference, that X-linked inhibitor of apoptosis (XIAP) is critical for chemotherapy sensitivity and survival in RRCL. MX69, a dual inhibitor of Mdm2 and XIAP that indirectly downregulates XIAP, is undergoing pre-clinical testing. MX69 affects XIAP levels by its effects on the ubiquitination and degradation of endogenous MDM-2, resulting in decrease XIAP translation and activation of caspase 3, 7 and 9 as well as PARP cleavage leading to apoptosis of cancer cells. In our current work, we pharmacologically inhibited XIAP in lymphoma pre-clinical models using MX69.Materials and Methods: A panel of Burkitt's Lymphoma (BL, including RRCL), germinal center B-cell (GCB)-DLBCL (including RRCL), activated B-cell (ABC)-DLBCL, Mantle cell Lymphoma (MCL) and Pre-B cell Leukemia cell lines were exposed to MX69 as a single agent (0-80uM) over 24, 48, 72 hrs and IC50 concentrations were calculated for each cell line. Changes in Mdm2, p53, XIAP and PARP expressions were determined following MX69 exposure (at IC50 doses) for 24 hrs. Induction of apoptosis was evaluated by Annexin V/propidium iodine staining. Subsequently, cell lines were exposed to MX69 (0-80 uM), in combination with Doxorubicin (0-1uM), Cytarabine(0-50uM), Vincristine (0-10nM), Etoposide(0-50uM), Carboplatin (0-20uM), Ixazomib (0-1.5uM), Ibrutinib (0-20uM) and Venetoclax (0-10uM) for 48 hours. Cell viability was determined by Cell Titerglo. Coefficient of synergy was calculated using CalcuSyn.Results: In vitro, MX69 single agent exposure induced cell death in a dose and time-dependent manner in all cell lines tested. Western blotting studies confirmed downregulation of Mdm2, XIAP and changes in P53 and PARP, following in vitro exposure to MX69. Induction of apoptosis was observed by flow cytometry in all cell lines tested. The combination of MX69 with Doxorubicin, Cytarabine, Vincristine, Ixazomib, Carboplatin, Etoposide, Ibrutinib, and Venetoclax resulted in significant synergistic activity. The strongest CI of synergy was observed when cell lines were exposed to MX69 and Venetoclax, Ixazomib, Etoposide or Ibrutinib.Conclusion: Our data suggests that in vitro exposure of a wide variety of B-cell lymphoma cell lines (including BL, DLBCL, MCL or RRCL) to MX69 resulted in anti-tumor activity. Perhaps related to its anti-tumor effects, MX69 inhibited XIAP levels. These findings are similar to prior SiRNA XIAP knockdown experiments. Strong synergistic activity was observed when XIAP was combined with various chemotherapy agents and small molecules inhibitors (such as Venetoclax, ixazomib or ibrutinib). Ex vivo experiments using primary tumor cells isolated from lymphoma patients and lymphoma mouse models are been planned. Targeting Mdm2 and XIAP can be an attractive therapeutic strategy in patients with Rituximab-sensitive or -resistant B-cell lymphoma. DisclosuresNo relevant conflicts of interest to declare.

A Novel Anti-IgM/HLA-DR Bispecific Antibody for Treatment of Refractory B Cell Malignancies

Introduction: IgM composes a part of the B cell receptor, and its expression is restricted to B cell lineage cells. There have been several reports that refractory B cell malignant cells frequently express IgM. For example, activated B cell-like (ABC) diffuse large cell lymphoma (DLBCL) is a subtype with a poor prognosis following R-CHOP treatment (Lenz et al., N Engl J Med, 2008), and the tumor cells generally express IgM-type immunoglobulin (Ruminy et al., Leukemia, 2011). In addition, IgM-expressing chronic lymphocytic leukemia (CLL) was also found to have a poor prognosis (D'Avola et al., Blood, 2016). Therefore, IgM is a promising therapeutic target for refractory B cell malignancies. However, anti-IgM antibodies may not function fully in the body due to the presence of soluble IgM. To improve the selectivity to the IgM expressing cells, we produced a bispecific antibody bound to IgM and HLA-DR, which are both expressed by B cells, and it was able to bind IgM+HLA-DR+ cells in the presence of soluble IgM. Thus, the aim of the present study was to examine the in vitro anti-tumor activity of the anti-IgM/HLA-DR bispecific antibody against B cell lymphoma, and to clarify its efficacy and tolerability in non-human primates (NHP).Methods: BTA106 is the bispecific antibody that can bind to IgM and HLA-DR, and BTA111 is glycoengineered BTA106. To investigate their direct inhibitory effects and Fc-mediated effects against B cell lymphoma cell lines, a growth inhibition assay, antibody-dependent cell cytotoxicity (ADCC) assay and complement dependent cytotoxicity (CDC) assay were performed. In the growth inhibition assay and CDC assay, cell proliferation was measured by WST-8. In the ADCC assay, human peripheral blood mononuclear cells were used as effector cells. Dead cells were stained with propidium iodide and measured by flow cytometry. JeKo-1 (Mantle cell lymphoma, MCL), Ramos (Burkitt's lymphoma, BL), RL (DLBCL), B104 (B cell lymphoma) and two rituximab-resistant cell lines, RL-4RH (Czuczman et al., Clin Cancer Res., 2008) and RRBL1 (generously provided by Dr. Tomita, Tomita et al., Int J Hematol., 2007), were used. To clarify the efficacy and tolerability of BTA106 in NHP, a dose escalation study and single-dose administration study were performed using cynomolgus monkeys.Results: BTA106 and BTA111 demonstrated direct growth inhibition activity, and CDC and ADCC activity, although their intensities differed among cell lines. In the case of rituximab-resistant cell lines, RRBL1 and RL-4RH, BTA106 and BTA111 exhibited weak or no growth inhibitory effects, but their CDC and ADCC activity was superior to that of rituximab. Development of resistance to rituximab is also a poor prognostic factor and remains problematic. Thus, BTA106 and BTA111 are expected as therapeutic antibodies to overcome rituximab resistance.A dose escalation study and single dose study were performed in cynomolgus monkeys. BTA106 greatly reduced peripheral B cells. Moreover, after the administration of BTA106, lymph follicles disappeared in axillary lymph nodes. In these studies, decreased locomotor activity and vomiting were observed; however, these symptoms resolved 2 hrs after injection. Other BTA106-related clinical toxicities or changes in body weight were not observed.Conclusions: In the in vitro studies, BTA106 and BTA111 demonstrated significant anti-tumor effects on rituximab-sensitive and -resistant B cell lymphoma cell lines. The efficacy and toxicity studies in cynomolgus monkeys revealed that BTA106 depletes peripheral and lymph node B cells, and it was well tolerated. BTA111 was considered to be significantly more effective than BTA106 due to glycoengineering, which induced high ADCC activity. These data suggest that BTA111 is an effective and potent therapeutic antibody for B cell malignancies, especially rituximab-resistant B cell lymphoma. Currently, a repeated administration study of BTA111 with cynomolgus monkeys to evaluate its efficacy and toxicity is ongoing. DisclosuresOhashi:Zenyaku Kogyo Co., Ltd.: Employment. Miyashita:Zenyaku Kogyo Co., Ltd.: Employment. Nagata:Zenyaku Kogyo Co., Ltd.: Employment. Tatebe:Zenyaku Kogyo Co., Ltd.: Employment. Otsuka:Zenyaku Kogyo Co., Ltd.: Employment. Suzuki:Zenyaku Kogyo Co., Ltd.: Employment. Sasaki:Zenyaku Kogyo Co., Ltd.: Employment. Enami:Zenyaku Kogyo Co., Ltd.: Employment. Tsukada:Zenyaku Kogyo Co., Ltd.: Employment. Fukushima:Zenyaku Kogyo Co., Ltd.: Employment.

Up-regulation of hexokinase II contributes to rituximab-chemotherapy resistance and is a clinically relevant target for therapeutic development.

In order to identify cellular pathways associated with therapy-resistant aggressive lymphoma, we generated rituximab-resistant cell lines (RRCL) and found that the acquirement of rituximab resistance was associated with a deregulation in glucose metabolism and an increase in the apoptotic threshold leading to chemotherapy resistance. Hexokinase II (HKII), the predominant isoform overexpressed in cancer cells, has dual functions of promoting glycolysis as well as inhibiting mitochondrial-mediated apoptosis. We found that RRCL demonstrated higher HKII levels. Targeting HKII resulted in decreased mitochondrial membrane potential, ATP production, cell viability; and re-sensitization to chemotherapy agents. Analyzed gene expression profiling data from diffuse large B-cell lymphoma patients, high-HKII levels were associated with a shorter progression free survival (PFS) and/or overall survival (OS). Our data suggest that over-expression of HKII is associated with resistance to rituximab and chemotherapy agents in aggressive lymphoma and identifies this enzyme isoform as a potential therapeutic target.

Mitotic catastrophe and cell cycle arrest are alternative cell death pathways executed by bortezomib in rituximab resistant B-cell lymphoma cells.

The ubiqutin-proteasome system (UPS) plays a role in rituximab-chemotherapy resistance and bortezomib (BTZ) possesses caspase-dependent (i.e. Bak stabilization) and a less characterized caspase–independent mechanism-of-action(s). Here, we define BTZ-induced caspase-independent cell death pathways. A panel of rituximab-sensitive (RSCL), rituximab-resistant cell lines (RRCL) and primary tumor cells derived from lymphoma patients (N = 13) were exposed to BTZ. Changes in cell viability, cell-cycle, senescence, and mitotic index were quantified. In resting conditions, RRCL exhibits a low-proliferation rate, accumulation of cells in S-phase and senescence. Exposure of RRCL to BTZ reduces cell senescence, induced G2-M phase cell-cycle arrest, and is associated with mitotic catastrophe. BTZ stabilized p21, CDC2, and cyclin B in RRCL and in primary tumor cells. Transient p21 knockdown alleviates BTZ-induced senescence inhibition, G2-M cell cycle blockade, and mitotic catastrophe. Our data suggest that BTZ can induce apoptosis or mitotic catastrophe and that p21 has a pivotal role in BTZ activity against RRCL.

The XIAP Inhibitor BMT-062789 Displays Anti-Tumor Activity in Cell Line Models of De Novo and Rituximab Relapse/Refractory Lymphoma

The addition of rituximab to front line therapy for aggressive lymphomas has improved clinical outcomes, but it has also altered the biology of relapsed/refractory disease. To better understand the mechanisms responsible for rituximab associated chemotherapy cross-resistance our group developed several rituximab resistance cell lines (Raji 4RH and RL 4RH), which also display significant resistance to a wide range of chemotherapy agents. These rituximab resistant cell lines (RRCL)s exhibit multiple deregulations in the BCL-2 and inhibitor of apoptosis (IAP) protein families, including loss of the pro-apoptotic proteins Bax and Bak. We previously demonstrated that the X linked inhibitor of apoptosis protein (XIAP) is critically required for chemotherapy resistance in the RRCLs, and that an shRNA knockdown of XIAP increased chemotherapy response in both in vitro and in vivo models of rituximab resistant lymphoma. BMT-062789 is a heterodimeric mimetic of the second mitochondrial activator of caspases (SMAC) developed by Bristol-Myers Squibb, which can inhibit both the caspase 9 and caspase 3/7 binding domains of XIAP. BMT-062789 demonstrated dose and time dependent single agent anti-tumor effect (as measured by the Cell TiterGlo luminescent viability assay) in a panel of lymphoma cell lines, with IC50 values of less than 5uM for all cell lines tested except the rituximab resistant cell line Raji 4RH. The Burkitt's lymphoma cell line Daudi and diffuse large B-cell lymphoma cell line U2932 were particularly sensitive to BMT-062789 with IC50 values of 0.91uM and 0.76uM respectively. To investigate if the observed anti-tumor effect of BMT-062789 was due to increased apoptosis we exposed rituximab sensitive (Raji, RL) and rituximab resistant (Raji 4RH, RL 4RH) cells to escalating doses of BMT-062789 with or without the addition of 20uM etoposide for 48 hours. The induction of apoptosis was measured by flow cytometry with an Annexin-V:PE-Cy7 conjugate and Sytox blue (a DNA stain). 2uM BMT-062789 alone triggered apoptosis in 75% of Raji cells and 65% of RL cells. It is also worth adding that 2uM BMT-062789 induced higher rates of apoptosis than 20uM etoposide alone in both cell lines. The combination of 2uM BMT-062789 and 20uM etoposide together triggered apoptosis in 80% of Raji cells and 85% of RL cells, indicating that BMT-062789 may be able to augment the anti-tumor activity of conventional chemotherapy. More importantly, the combination of BMT-062789 and etoposide was also able to induce apoptosis in the rituximab resistant cell line models Raji 4RH and RL 4RH. 3uM BMT-062789 in combination with 20uM etoposide triggered apoptosis in 90% of Raji 4RH cells and 55% of the RL 4RH cells, which is a substantial improvement compared to 15% apoptosis with 20uM etoposide alone in each cell line. Additional studies are in progress to evaluate the anti-tumor effect of BMT-062789 in ex vivo samples from lymphoma patients with de novo and relapse/refractory disease. In summary, the novel heterodimeric XIAP inhibitor BMT-062789 has anti-tumor effect at low micromolar concentrations in lymphoma cell line models, including models of rituximab resistant disease. These results support earlier studies by our group indicating that XIAP is critical for survival in models of rituximab resistant lymphoma, and establish that XIAP inhibitors may have potential clinical value for the treatment of both de novo, and rituximab relapse/refractory lymphomas. DisclosuresNo relevant conflicts of interest to declare.

JQ1, a c-MYC Inhibitor Targets Hexokinase II and Enhances the Cytotoxic Effects of Chemotherapeutic Agents in Diffuse Large B-Cell Lymphoma (DLBCL)

Background: Results from thecollaborative trial in relapsed aggressive lymphoma (CORAL) study demonstrated a poor clinical among patients treated with second-line chemo-immunotherapy in the post-rituximab era, stressing the need to identify and/or optimize novel targeted agents. C-myc expression was found correlate with a poor clinical outcome in patients with newly diagnosed or relapsed/refractory DLBCL. Previously, we found that JQ1 overcomes rituximab-chemotherapy resistance in lymphoma pre-clinical models. JQ1 exhibited synergistic activity when combined with chemotherapy agents. We also demonstrated that hexokinase II was highly expressed in rituximab resistant cell lines (RRCL), and its expression was associated with a deregulation in the glucose metabolism and an increase in the apoptotic threshold leading to chemotherapy resistance. In our current work, we evaluated molecular studies dissecting the cellular pathways affected by JQ1.Methods: A panel of rituximab-sensitive (RSCL) and RRCL cell lines were exposed to escalating doses of JQ1 (0-8μM) for 24, 48 and 72h. Changes in cell viability and cell cycle distribution were evaluated using the Presto Blue assay and flow cytometry respectively. IC50 was calculated by Graphpad Prism 6 software. Loss of mitochondrial membrane potential (Δψm) following JQ1 exposure was assessed by DiOC6 staining. Changes in c-MYC, HKII, HKI, Voltage dependent anion channel protein (VDAC) and p21 expression levels were determined by western blotting. HKII was silencing using siRNA interference in RRCL (Raji-4RH) and changes in HKII, HKI, VDAC, c-MYC and p21 protein expression was determined. HKII knockdown or scramble Raji-4RH cells were exposed to different chemotherapy agents and JQ1; cell viability and mitochondrial membrane potential was accessed.Result:JQ1 induced a dose-and time- dependent cell death in cell lines. In vitro exposure cells to JQ1 resulted in a loss of mitochondrial potential and induced G1 cell cycle arrest. In vitro exposure to JQ1 decreased c-MYC and HKII expression levels and induced of p21 expression. Complete silencing of HKII re-sensitized cell to chemotherapy (doxorubicin, vincristine and bortezomib). On the other hand, HKII knockout abrogated JQ1 anti-tumor activity.Conclusion: Our data suggests that JQ1 had anti-tumor activity against rituximab-sensitive or resistant pre-clinical models. The inhibition of HKII following JQ1 exposure may contribute to lower the mitochondrial membrane potential and enhance the chemotherapeutic effect. Our finding highlights a better understanding in the molecular events triggered by JQ1 as a potential role in the treatment of B-cell malignancies. DisclosuresNo relevant conflicts of interest to declare.

The Adhesion Molecule ICAM-1 in Diffuse Large B-Cell Lymphoma Post-Rituximab Era: Relationship with Prognostic Importance and Rituximab Resistance

Background: Intercellular adhesion molecule-1 (ICAM-1) is a cell-surface receptor involving in cell-to-cell adhesion and as well as co-stimulatory molecule involved in T-cell lymphocyte infiltration and activation. In the pre-rituximab era, high level of ICAM-1 was reported to be a prognostic indicator of better clinical outcomes in diffuse large B-cell lymphoma (DLBCL). The value of ICAM-1 expression in the post-rituximab era remains unclear. To investigate the impact of ICAM-1 expression in DLBCL, we conducted a retrospective study in R+CHOP treated patients.Methods: Patients (N=102) with histologically proven DLBCL treated at Fudan University Shanghai Cancer Center with available diagnostic biopsy material were identified. Forty-three patients were treated with CHOP and 59 patients with R+CHOP. ICAM-1 expression was determined by immunohistochemistry (IHC). ICAM-1 expression was quantified by staining intensity or percentage of positive cells. Tumors were considered positive when at least 75% of tumor cells expressed ICAM-1. Progression free survival (PFS) and overall survival (OS) was plotted by Kaplan-Meier method and curves were compared with the long-rank test in both groups. Correlation between the ICAM-1 expression and clinical variables were tested by Pearson Chi Square test and a two-sided P value of <0.05 was considered to be statistically significant. Finally, ICAM-1 expression was determined in a panel of rituximab-sensitive (RSCL) and rituximab-resistant lymphoma cell lines (RRCL) by western blot. Correlation of ICAM-1 expression and rituximab anti-tumor activity was determined by standard complement-mediated cytotoxicity (CMC) and antibody-dependent cellular cytotoxicity (ADCC) assays.Result: ICAM-1 expressionwas detected in 28 (27.5%) DLBCL patients. The rest of the patients tested negative for ICAM-1 (N=74; 72.5%). Differences in ICAM-1 expression were observed according to cell of origin DLBCL subtype. ICAM-1 expression was higher among germinal center B-cell (GCB) DLBCL (41.4%) vs. non-GCB subtype patients (19.6%, P=0.019). The response rates for R-CHOP and CHOP were, respectively, 89.4% and 77.7% (P=0.409) in ICAM-1 positive patients and 92.5% and 73.5% (p=0.027) in ICAM-1 negative patients. As previously described, ICAM-1 expression was associated with an improved PFS/OS (P=0.03/ P=0.05) in CHOP-treated DLBCL. On the other hand, no differences in PFS/OS were observed between ICAM-1 positive or negative DLBCL patients treated with R+CHOP. The addition of rituximab to CHOP chemotherapy resulted in an improved PFS in ICAM-1 negative DLBCL (P=0.018). On the other hand, the clinical outcome of ICAM-1 positive DLBCL patients treated with CHOP chemotherapy was similar than R+CHOP treated patients. Finally, loss of ICAM-1 expression level was found in our rituximab resistant cell lines, along with reduction of rituximab activity.Conclusion: Before therituximab era, ICAM-1 low expression correlated with worse PFS and OS. In our retrospective clinical analysis, we found that rituximab significantly improved the overall response rate and PFS in ICAM-1 negative subset patients. Our data also indicated that ICAM-1 expression level was higher in GCB than non-GCB subtypes, and this may contribute to better rituximab response in GCB cell types. Gradually exposed lymphoma cell to rituximab lost ICAM-1 expression and may contribute to the resistance to rituximab and chemotherapy agents. Further investigation of ICAM-1 expression needed to be study to enhance the rituximab therapy in lymphoma. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

CD19 Target Activated Natural Killer (CD19.TaNK) Cellular Therapy: A Novel immunotherapeutic Approach to the Treatment of Non-Hodgkin Lymphoma (NHL)

Background: Continued improvement in the treatment of NHL is desired, especially via the incorporation of 'targeted' immunotherapy agents. This is especially important in B-cell NHL (bNHL) as resistance to rituximab anti-CD20 antibody, and now second-generation antibodies (e.g., obinutuzumab), may occur. Activated NK-92 (aNK-92) is a continuously growing cell line consisting of "pure" (100%) activated NK cells. These cells were subsequently bioengineered to express human anti-CD19 chimeric antigen receptor (CAR) recognizing CD19+ B cells. The goal of this project was to investigate the specificity and the efficacy of a novel 'off the shelf' targeted immunotherapy, CD19.TaNK, in a multitude of B-cell NHL cell lines, including anti-CD20 antibody resistant cell lines.Methods: Using gene expression profiling, Gene Set Enrichment Analysis and Ingenuity Pathway Analysis, we first investigated the expression of NK activation and inhibitory ligands in varied lymphoma cells. The bNHL cell lines, SUDHL10 (DLBCL), L540, L428 (Hodgkin lymphoma), HF1 (follicular), Raji (Burkitt's), and Mino (mantle cell) were purchased from ATCC and maintained in RPMI1640 medium. aNK and CD19.TaNK were supplied by NantKwest, Inc and were maintained in Myelocult supplemented with recombinant human IL-2 (500IU/ml). NK cell mediated cytotoxicity was determined using lactate dehydrogenase (LDH) release glucose-6-phosphate dehydrogenase (G6PD) release (aCella-tox assay). Briefly, 10,000 target bNHL cells were co-cultured with effector NK cells, at clinically relevant effector to target ratios (E:T 1:1-10:1) for 4 hours, and the supernatant was assayed for LDH or G6PD release. Percent cytotoxicity was determined based on the experimental levels of LDH or G6PD release from NK mediated bNHL cell lysis compared to maximum LDH or G6PD release from target cells. To determine if resistance to anti-CD20 antibodies would interfere with sensitivity to CD19.TaNK therapy, rituximab and obinutuzumab resistant bNHL cell lines (SUDHL4, SHUDHL10, and Raji) were established; cells were exposed to incremental increasing concentrations of antibody drugs (5-20μg/ml) over a period of 8 weeks. CD19, CD20 and CD30 expression in bNHL cells was determined by flow cytometry. Additionally, the efficacy of primary NK cells were determined against CD20 monoclonal antibody sensitive and resistant cell lines utilizing droplet microfluidics based assessment.Results: We observed that bNHL cell lines expressed a multitude of ligands associated with stimulating NK cell activity, while expression of inhibitory ligands was minimal. This indicates that NK cell interaction with bNHL cells is predicted to lead to overall robust antitumor immune response (Figure). Using LDH and G6PD release assays in bNHL cell lines, we observed increased cytolytic activity in an E:T ratio dependent manner, with Raji and L428 cells being the most sensitive to CD19.TaNK at 1:1 E:T ratio. Development of resistance to anti-CD20 antibodies (rituximab and obinutuzumab) resulted in significantly decreased down regulation of CD20, but not CD19 or CD30, as detected by flow cytometry. After direct contact with primary NK cells, we observed that rituximab resistant SUDHL10 cells were poorly sensitive (7%), while in rituximab sensitive cells, there was 22% cell loss. Moreover, at 4 hours using CD19.TaNK therapy (1:5 ratios), there was marked cytolytic activity with consistent high LDH release seen across all bNHL cell lines without differences noted regardless of rituximab or obinutuzumab resistance (ie, SUDHL4, SHUDHL10, and Raji). These results were further confirmed using live cell video microscopy measuring the cytolytic activity of CD19.TaNK versus bNHL cells.Conclusion: We identified that bNHL cells contain high expression levels of NK activation ligands and low amounts of inhibitory ligands and that CD19.TaNK immunotherapy had potent single-agent anti-tumor activity against a spectrum of bNHL cells. Furthermore, CD19.TaNK maintained high cytolytic activity in bNHL cells resistant to standard CD20 antibody therapy, which were poorly sensitive to innate NK cells. Ongoing analyses include systems biology studies to determine potential biologic mechanisms of activity of CD19.TaNK therapy as well as well as to help guide optimum combinatorial therapy. [Display omitted] DisclosuresBoissel:NantKwest, Inc.: Employment. Evens:Takeda: Other: Advisory board.

Itraconazole, an Oral Antifungal Drug, Is Active in Chemotherapy Resistant B-Cell Non-Hodgkin Lymphoma and Enhances the Anti-Tumor Activity of Chemotherapy Agents

Background: Relapsed/refractory diffuse large B-cell lymphoma (DLBCL) patients previously treated with rituximab-based therapy have poor clinical outcome, according to the results from collaborative trial in relapsed aggressive lymphoma (CORAL) study. It stresses the need to identify and/or optimize novel targeted agents. To better understand the molecular mechanisms underlining the acquired resistance to rituximab, we generated and characterized several rituximab-resistant DLBCL cell lines (RRCLs). Itraconazole, an oral antifungal agent, was reported had novel anticancer activity in basal cell carcinoma, non-small cell lung cancer and prostate cancer. In our current work, we define and characterize the anticancer activity of itraconazole in preclinical rituximab-sensitive or -resistant lymphoma models.Methods: A panel of rituximab-sensitive (RSCL) and rituximab-resistant (RRCL) cell lines were exposed to escalating doses of itraconazole (0-20μM) for 24, 48 and 72h. Changes in cell viability and cell cycle distribution were evaluated using the Presto Blue assay and flow cytometry respectively. IC50 was calculated by Graphpad Prism6 software. Loss of mitochondrial membrane potential (Δψm) following itraconazole exposure was assessed by DiOC6 and flow cytometry. Subsequently lymphoma cells were exposed to itraconazole or vehicle and various chemotherapy agents such as doxorubicin (1µM), dexamethasone (1µM), cDDP (20μg/ml), bortezomib (20nM), carfilzomib (20nM) or MLN2238 (20nM) for 48 hours. Coefficient of synergy was calculated using the CalcuSyn software. Changes in hexokinase II (HKII), Voltage dependent anion channel protein (VDAC), LC3 and BCL-xL expression levels were determined by western blotting after exposure cells to itraconazole. VDAC-HKII interactions following in vitro exposure to itraconazole were determined by immunoprecipitation of VDAC and probing for HKII in RSCL and RRCLs.Result:Itraconazole consistently showed potent, specific, dose-and time- dependent inhibition of all our sensitive and resistant lymphoma cell lines. In vitro exposure cells to itraconazole resulted in a loss of mitochondrial membrane potential and caused G2 cell cycle arrest. Itraconazole significantly had a synergistic anti-tumor effect combined with various chemotherapeutic agents, including doxorubicin, dexamethasone, cisplatin and different generations of proteasome inhibitors (bortezomib, carfilzomib or ixazomib) in both RSCL and RRCL. Western blot and immunoprecipitation studies demonstrated that following exposure to itraconazole, HKII bound less to mitochondrial specific protein VDAC. Complete silencing of HKII (using HKII siRNA interference) resulted in a rescue of loss in the mitochondrial membrane potential induced by intraconazole.Conclusion: Taking together, our data suggest that itraconazole had a potent anti-tumor activity against rituximab-sensitive or resistant pre-clinical models. The disruption of HKII from mitochondria following itraconazole exposure may contribute to lower the mitochondrial membrane potential and enhance the chemotherapeutic efficacy. Our finding highlights itraconazole as a potential therapeutic agent in the treatment of B-cell malignancies, and strongly supports clinical translation of its use. DisclosuresNo relevant conflicts of interest to declare.

Targeting the X-Linked Inhibitor of Apoptosis Protein (XIAP) Can Promote Tumor Cell Death, and Increase the Cytotoxic Effects of Chemotherapy Agents in in Vitro and In Vivo Models of Rituximab-Resistant Lymphoma

In diffuse large B-cell lymphoma (DLBCL) the addition of rituximab to front line multi-agent therapy has changed the biology and clinical outcome of patients with relapsed/refractory disease. To better understand the mechanisms responsible for rituximab/chemotherapy cross-resistance we developed several rituximab resistance cell lines, which also display significant resistance to a wide range of chemotherapy agents. These therapy resistant cell lines (TRCL)s have multiple deregulations the apoptotic response pathway, including a loss of Bak and Bax. We previously demonstrated that small molecule mimetics of the second mitochondrial activator of caspases (SMAC), which antagonizes the inhibitor of apoptosis (IAP) family of proteins, could boost response to chemotherapy agents and extend survival in TRCL xenograft animal models. To investigate how SMAC mimetics overcome chemotherapy resistance in TRCL (RL-4RH and Raji-4RH) models we used RNA interference to transiently knockdown expression of individual IAPs (cIAP1, cIAP2, livin, survivin, and XIAP), and then exposed those cells to a panel of chemotherapy agents. Apoptosis induction was analyzed by flow cytometry staining for annexin V and Sytox blue (a DNA stain). While SMAC mimetics can decrease levels of the cellular inhibitor of apoptosis proteins (cIAP1/cIAP2), siRNA knockdown of cIAP1/cIAP2 did not increase chemotherapy-induced apoptosis. On the other hand, siRNA knockdown of XIAP in TRCLs substantially increased rates of apoptosis compared to cells transfected with non-targeting siRNA (5% in controls vs. 22% in XIAP knockdown RL-4RH cells). An additional 24% of XIAP knockdown RL-4RH cells showed signs of necrosis compared to 0.5% in control RL-4RH. Results were confirmed by western blot (PARP cleavage). In addition, siRNA XIAP knockdown re-sensitized TRCLs (Raji-4RH and RL-4H) to the cytotoxic effects of multiple chemotherapy agents (gemcitabine, etoposide, and vincristine). To investigate if XIAP knockdown could improve chemotherapy response in vivo we created a TRCL (Raji-4RH) that stably expresses XIAP targeting shRNA along with luciferase to enable in vivo imaging. SCID mice were inoculated with either the Raji-4RH XIAP knockdown or Raji-4RH non-targeting shRNA control cell line (10x106 cells per animal given i.v.). Tumors were allowed to engraft for 7 days prior to treatment administration. Animal were either given no treatment, or rituximab in combination with ifosfamide, carboplatin, etoposide (RICE) and mesna. Following treatment animals were imaged on a weekly basis to track tumor progression. At the time of the submission disease progression was present in animals in the observation groups, and in animals inoculated with non-targeting control shRNA Raji-4RH treated with RICE. InterestingHowever, animals inoculated with XIAP knockdown Raji-4RH and treated with RICE therapy remain tumor free with no detectable disease. In summary, XIAP acts as a key cell survival regulator in rituximab-chemotherapy resistant lymphoma models. Downregulation of XIAP can enhance chemotherapy activity and promote tumor cell death. Additionally, XIAP knockdown appears to enhance the activity of RICE, a commonly used regiment in the relapsed/refractory setting for DLBCL patients. Our results support the hypothesis that selective XIAP inhibitors, currently in development, may be highly active against relapsed/refractory B-cell lymphoma. DisclosuresCzuczman:Immunogen: Other: Advisory board; Boehringer-Ingelheim: Other: Advisory Board; MorphoSys: Consultancy; Celgene: Employment.

Cooperation Between the CD20 Receptor and hIFN-Alpha Receptor in Overriding the Blocked CD20 Cell-Signaling in Rituximab-Resistant B-NHL By the Fusion Protein Anti-CD20-hIFN-Alpha

Introduction: The standard treatment of B-NHL consists of rituximab in combination with CHOP (RCHOP) and results in a significant clinical response. Rituximab inhibits cell-proliferation and inhibits cell survival/anti-apoptic signaling pathways. A subset of patients does not initially respond and a subset of responding patients develops resistance to RCHOP. The genetic engineering of a fusion protein, α-CD20-hIFN-α, was found to be active in the rituximab-resistant B-NHL cell lines.Objective: To investigate the underlying mechanism by which α-CD20-hIFN-α signals in the resistant lines.Hypothesis: We hypothesized that the treatment with the α-CD20-hIFN-α may result in the cooperation of both α-CD20 and hIFN-α and their interactions with corresponding receptors that will result in overriding α-CD20 blocked cell signaling.Methods: Rituximab-resistant cell lines, R-2F7 and R-Ramos, were used as models. Cell signaling was determined by western. Sensitivity to drug-induced apoptosis was done by activation of caspase 3 by flow cytometry.Results: Treatment of the R lines with α-CD20-hIFN-α resulted in the inhibition of cell growth and sensitization to doxorubicin-induced apoptosis. Treatment with single agents alone or combination was not effective. Treatment with the α-CD20-hIFN-α resulted in the inhibition of the NFκB and the p38 MAPK pathways. In addition, the hIFN-mediated signaling pathway, namely, PKC-d, was also inhibited by the α-CD20-hIFN-α.The role of PKC-d in drug sensitization was corroborated by the use of the specific inhibitor, Rotterin, which reversed the drug sensitization by α-CD20-hIFN-α and doxorubicinConclusion: The ability of the α-CD20-hIFN-α to inhibit cell survival and anti-apoptotic pathways, that was not achieved with single agents or combination, suggested that there may be a crosslinking of the CD20 and hIFN-α receptors by α-CD20-hIFN-α and results in triggering the cells via both receptors and inhibiting intracellular survival pathways and sensitization to drug apoptosis.Clinical Implication: The findings also suggest the potential therapeutic application of the combination of α-CD20-hIFN-α and drugs for the treatment of patients resistant to RCHOP. DisclosuresNo relevant conflicts of interest to declare.

JQ1, a Potent c-MYC Inhibitor Overcomes Rituximab-Chemotherapy Resistance in Lymphoma Pre-Clinical Models

Background: The poor clinical outcomes of patients with aggressive B-cell lymphoma in the post-rituximab era, stress the need to identify and/or optimize novel targeted agents. Several retrospective and prospective clinical studies had demonstrated that C-myc expression correlates with a poor clinical outcome in patients with newly diagnosed or relapsed/refractory diffuse large B-cell lymphoma (DLBCL). To this end, we evaluated the therapeutic effects of targeting C-myc using JQ1, a novel bromodomain inhibitor in rituximab-sensitive or -resistant models.Methods: A panel of rituximab-sensitive (RSCL) or rituximab-resistant (RSCL) cell lines was exposed to JQ1 (0-100 µM) for 24-72 hrs. Changes in cell viability and cell cycle distribution were evaluated using the Presto Blue assay and flow cytometry respectively. IC50 values were calculated using the GraphPad Prism6 software. Subsequently lymphoma cells were exposed to JQ1 or vehicle and various chemotherapy agents such as doxorubicin (0.5, 1, 2µM), dexamethasone (1µM), Ibrutinib (1µM), bortezomib (10-20nM) or carfilzomib (10nM) for 48 hours. Coefficient of synergy was calculated using the CalcuSyn software.Results:In vitro exposure of RRCL and to a lesser degree RSCL to JQ1 resulted in a dose- and time-dependent cell death. Strong synergistic activity was observed when JQ1 was combined with doxorubicin, dexamethasone bortezomib or carfilzomib in vitro. Cell cycle analysis demonstrated that in vitro of RSCL or RRCL to JQ1 resulted in G1 cell cycle arrest.Conclusions: In summary, our data suggests that targeting C-myc expression using JQ1 results in anti-tumor activity against RSCL and RRCL. In addition, JQ1 exhibited synergistic activity when combined with chemotherapy agents (doxorubicin or dexamethasone) or targeted agents (bortezomib or carfilzomib). On going studies are aimed to study the mechanisms by which c-myc inhibition results in cell death in RSCL and RRCL. JQ1 is a distinct targeted agent undergoing clinical evaluation in patients with relapsed/refractory lymphomas. Molecular studies dissecting the cellular pathways affected by JQ1 are important in order to further advance the clinical development of c-myc inhibitors in lymphoid malignancies. (Research, in part, supported by a NIH grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute and The Eugene and Connie Corasanti Lymphoma Research Fund) DisclosuresCzuczman:Boehringer-Ingelheim: Other: Advisory Board; Immunogen: Other: Advisory board; MorphoSys: Consultancy; Celgene: Employment.

Dual Inhibition of PKC Delta By Carfilzomib (CFZ) and Ibrutinib Results in Synergistic Activity in Rituximab-Chemotherapy Sensitive and Resistant Lymphoma Pre-Clinical Models and in Primary Tumor Cells Isolated from B-Cell Lymphoma Patients

Introduction: A better understanding in the role of the B-cell receptor-signaling pathway in lymphomagenesis led to the clinical development of ibrutinib is an orally bioavailable Bruton's tyrosine kinase inhibitor (BTKi). Ibrutinib has clinical activity in several subtypes of B-cell lymphoma (follicular lymphoma, mantle cell lymphoma and certain diffuse large B-cell lymphoma [DLBCL] subtypes). Recently, an increasing number of ibrutinib-treated patients are developing disease progression, stressing the need to optimize its therapeutic potential. To this end, we evaluated the biological effects and interactions of ibrutinib and CFZ, a non-reversible proteasome inhibitor in several lymphoma pre-clinical models including primary tumor cells isolated from lymphoma patients.Methods: A panel of rituximab-sensitive (RSCL) and rituximab-resistant (RRCL) cell lines as well as primary tumor cells isolated from B-cell lymphoma patients (N=20) were exposed to ibrutinib and/or CFZ. Changes in cell viability were evaluated by Presto Blue and Titer Glo assays respectively. Coefficient of synergy was determined using the CalcuSyn software. To further study the mechanisms responsible for the biological effects of ibrutinib and CFZ, RSCL and RRCL were exposed to Ibrutinib+/- CFZ for 48hr. Changes in apoptosis, mitochondrial potential, and cell cycle distribution were evaluated by flow cytometry by AnnexinV-PI, DiOC6 or PI staining respectively. Subsequently, protein lysates were isolated from ibrutinib+/- CFZ exposed RSCL or RRCL and changes in downstream targets (PKCδ a member of diacylglycerol-dependent, calcium-independent serine/threonine-specific protein kinases PKC isoform know to be a substrate of caspase 3 and able to mediate apoptosis), Bcl-2 family members and cell cycle regulatory proteins were evaluated by Western blotting.Results: In vitro exposure of RSCL, RRCL, and primary tumor cells to ibrutinib and CFZ resulted in synergistic anti-tumor activity. In addition, the combination of ibrutinib and CFZ resulted in a more pronounced decrease in the mitochondrial potential, higher degree of apoptosis (as demonstrated by flow cytometry and caspase 3 or PARP cleavage) and increase in G1 cell cycle arrest when compared to single agent ibrutinib or CFZ. Perhaps related to these findings, we found that exposure of lymphoma cells to Ibrutinib and CFZ resulted in an increase in caspase 3, the active form of PKCδ and BAX levels. Using caspase inhibitor Q-VD-OPh rescued the combination killing effect of ibrutinib and CFZ, as well as abrogated induction of the active form of PKCδ. In addition, Ibrutinib in combination with CFZ decreased cyclin E and CDK2 levels.Conclusions: Together our data suggests that ibrutinib and CFZ had a strong synergistic anti-tumor activity against rituximab-chemotherapy sensitive and resistant lymphoma cells and patient samples. At the molecular level, the combination of ibrutinib and CFZ affects the balance of the apoptotic machinery and key regulatory proteins of the cell cycle that could play an important role in the synergistic effects observed. Further signaling and in vivo studies are necessary to evaluate the therapeutic role of ibrutinib in combination with carfilzomib in B-cell lymphoma (Research, in part, supported by a NIH grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute and The Eugene and Connie Corasanti Lymphoma Research Funds). DisclosuresCzuczman:MorphoSys: Consultancy; Celgene: Employment; Immunogen: Other: Advisory board; Boehringer-Ingelheim: Other: Advisory Board.

Metformin Induces p53-Dependent Mitochondrial Stress in Therapy-Sensitive and -Resistant Lymphoma Pre-Clinical Model and Primary Patients Sample with B-Cell Non-Hodgkin Lymphoma (NHL)

Introduction: Metformin, a guanidine originally derived for Galega officinalis (French lilac), has been widely prescribed to type II diabetics since 1950 and well known for its safety toxicity profile. Recently, metformin use was associated with a decrease in risk cancer development and lower cancer-related mortality among breast, colorectal, prostrate, lung, hepatic and ovarian cancer patients. Our group previously reported that the use of metformin during front-line chemo-immunotherapy (i.e. R+CHOP) improved the clinical outcome of diffuse large B-cell lymphoma (DLBCL). The mechanism(s) of action underlying the antitumor effect of metformin remains not to be fully elucidated. Previous research done in our laboratory revealed that metformin inhibited cell proliferation through repressing PCNA and p21 proteins. Here, we report that metformin activates tumor suppressor p53 by suppressing MDMX in pre-clinical lymphoma models.Methods: A panel of rituximab-sensitive (RSCL), rituximab-resistant (RRCL) cell lines and primary tumor cells isolated from B-cell lymphoma patients were exposed to escalating doses of metformin (0-64mM). Changes in cell viability were determined by Presto Blue (Sigma) assay in cell lines and Titer Glo in patient samples. Changes in MDMX, MDM2 and p53 expression levels were determined by western blotting after exposure cells to metformin. MDMX-MDM2-p53 interactions and p53 ubiquitination following in vitro exposure to metformin were determined by immunoprecipitation of p53 and probing for MDMX, MDM2, ubiquitin and p53 in RSCL and RRCLs. Loss of Dψm or induction of apoptosis following metformin exposure were assessed by DiOC6 or Annexin V/PI staining and flow cytometry. Oxidative stress induced by metformin was measured by flow cytometry using dihydrorhodamine-123 (DHR-123) dye.Result: Metformin induced a dose-and time- dependent cell death in cell lines and primary patient tumor cells. In vitro exposure of lymphoma cell to metformin resulted in a decrease in MDMX levels. Immunoprecipitation studies demonstrated that following exposure to metformin, MDMX bound less to p53 leading to less p53 ubiquitination. In vitro exposure of RSCL or RRCL to metformin resulted in the expression of p53 regulated BH3 single domain proteins (Noxa and Puma). Moreover, metformin repressed mitochondrial potential, induced reactive oxidative species (ROS) generation and triggered apoptosis.Conclusion: Our data suggests that metformin had anti-tumor activity against RSCL, RRCL and primary tumor cells isolated from lymphoma patients. The down-regulation of MDMX and re-activation p53 function following metformin exposure may contribute to the disruption in the mitochondria potential, generation of ROS and induction of apoptosis observed in our models RSCL and RRCL. Our finding highlights a potential role for metformin in the treatment of B-cell malignancies. (Research, in part, supported by a NIH grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute and The Eugene and Connie Corasanti Lymphoma Research Funds) DisclosuresCzuczman:MorphoSys: Consultancy; Boehringer-Ingelheim: Other: Advisory Board; Celgene: Employment; Immunogen: Other: Advisory board.