Primary Mantle Cell Lymphoma Cells Research Articles

Abstract 3424: Induction of prolonged early G1-arrest by CDK4/CDK6 inhibition reprograms cycling lymphoma cells for enhanced and sustained inhibition of PI3Kδ/AKT.

Abstract The phosphatidylinositol-3-kinase (PI3K) signaling pathway is constitutively activated at a high frequency in cancer. Interest in evaluating the therapeutic utility of selective PI3K subunit inhibition has led to the development of potent PI3Kδ-specific inhibitors. Selective inhibition of PI3Kδ has now emerged as a promising therapy for chronic lymphocytic leukemia and indolent lymphomas. For aggressive non Hodgkin lymphoma such as mantle cell lymphoma (MCL), however, efficacy has been observed but duration of tumor control has been modest, encouraging development of mechanism-based combination therapy. We hypothesize that induction of G1-cell cycle arrest may reprogram non-indolent lymphomas to PI3Kδ inhibition, and test this hypothesis in MCL based on the following: 1) aberrant cyclin D1 and CDK4 expression is the primary cause for unrestrained cell cycle progression and proliferation in MCL; 2) by induction of prolonged early G1 arrest (pG1) through selective inhibition of CDK4/CDK6, we have developed a novel strategy that both inhibits proliferation of tumor cells and sensitizes them to cytotoxic killing; and 3) induction of pG1 by CDK4/CDK6 inhibition has demonstrated encouraging clinical activity, with an excellent toxicity profile, in a phase I clinical trial in MCL. Here we show in primary MCL cells (N=10) by whole transcriptome-sequencing (WTS) that mutations in coding regions are rare in Cyclin D1, CDK4 and other genes that control G1 cell cycle progression or in the PI3K/AKT signaling pathway. PI3Kδ is the predominant PI3K catalytic expressed in MCL cells. Selective inhibition of PI3Kδ transiently reduces AKT phosphorylation but does not inhibit the cell cycle in proliferating MCL cells, implying a potential mechanism for resistance. Induction of pG1 by CDK4/CDK6 inhibition amplifies and sustains PI3Kδ inhibition and induces robust apoptosis. Validating the G1 cell cycle-dependence of PI3Kδ inhibition, all primary MCL cells tested are responsive to PI3Kδ inhibition when they cease to cycle in ex vivo in stromal co-culture. This loss of viability is further accelerated in pG1 induced by CDK4/CDK6 inhibition, despite the presence of cytokines and growth factors that are known to activate PI3K. This study presents the first sequential combination of selective inhibition of CDK4/CDK6 with a selective partner, a PI3Kδ specific inhibitor, in primary human cancer cells and the first WTS-validated therapeutic strategy that leads to sensitization of MCL cells by cell cycle control. Our data demonstrate, for the first time, that the magnitude and duration of PI3K inhibition is G1 cell cycle-dependent, and suggest a strategy to sensitize proliferating lymphoma cells to selective PI3Kδ inhibition by induction of early G1-arrest through selective CDK4/CDK6 inhibition. Citation Format: David Chiron, Peter Martin, Maurizio Di Liberto, Xiangao Huang, Scott A. Ely, Brian J. Lannutti, John P. Leonard, Christopher E. Mason, Selina Chen-Kiang. Induction of prolonged early G1-arrest by CDK4/CDK6 inhibition reprograms cycling lymphoma cells for enhanced and sustained inhibition of PI3Kδ/AKT. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3424. doi:10.1158/1538-7445.AM2013-3424 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Abstract 2432: The bruton's tyrosine kinase inhibitor ibrutinib synergized with the proteasome inhibitor carfilzomib and overcame immunoproteasome-mediated carfilzomib resistance in mantle cell lymphoma .

Abstract Introduction: Mantle cell lymphoma (MCL) is not curable and novel therapeutic agents and their rational combinations are needed. The ubiquitin-proteasome pathway is an attractive target for antitumor therapy, as its persistent activity is associated with tumor formation, growth, metastasis, and drug resistance in many cancer types, including B-cell non-Hodgkin lymphoma. 20S proteasome activity is regulated by the catalytic subunits β1, β2, and β5 or in the case of the immunoproteasome (i20S) by the inducible catalytic subunits LMP2 (β1i), MECL-1(β2i), and LMP7 (β5i). Carfilzomib (CFZ), a proteasome inhibitor, inhibits the proteasome by binding specifically and irreversibly to the catalytic subunit β5/β5i. Materials and Methods: CFZ was supplied by Onyx Pharmaceuticals (South San Francisco, CA). The Btk inhibitor ibrutinib (PCI-32765) was provided by Pharmacyclics (Sunnyvale, CA). Human MCL cell lines (Mino, Jeko-1, Z138, and Rec-1) were either created by our laboratory or obtained from American Type Culture Collection. Primary cells were obtained from newly diagnosed MCL patients with informed consent. Cell viability was assessed by an MTT assay, apoptosis by Annexin V binding assays, and proteasome expression by Western blotting. Results: We found that MCL cells had different responses to CFZ. For the CFZ-sensitive MCL cell lines Mino and Z138 and freshly isolated MCL cells from 6 patients, CFZ significantly induced the growth inhibition and apoptosis at a low dose (IC50 2-6 nM). In contrast, for the CFZ-resistant MCL cell line (Rec-1) and fresh primary MCL cells from patients with clinical resistance, CFZ did not induce cell death (IC50 not reached at 100 nM). Next, Western blot analysis showed that the CFZ-resistant cells lacked expression of the i20S subunits LMP2, LMP7, and MECL-1. By contrast, the CFZ-sensitive cells showed high levels of LMP2, LMP7, and MECL-1. These results suggest that an intact immunoproteasome is necessary for CFZ-induced anti-MCL activity. In an attempt to overcome the CFZ resistance, we studied the effect of ibrutinib in CFZ-resistant MCL cells. Ibrutinib alone was toxic to both CFZ-sensitive and CFZ-resistant MCL cells with IC50 values ranging from 3 to 12.5 μM. Furthermore, we found that ibrutinib synergized with CFZ in CFZ-sensitive cell lines, and primary MCL cells. The Chou-Talay combination index was < 1, indicating synergism between the two drugs. Most importantly, the CFZ-resistant MCL cells Rec-1 were sensitive to ibrutinib, with an IC50 of 6 uM. Conclusion: Our data suggest that LMP2, LMP7, and MECL-1 may serve as potential biomarkers for patients who are likely to be sensitive to CFZ. Our data also suggest that ibrutinib may be useful in patients with CFZ-resistant MCL. Our preclinical data provide a strong rationale for testing the ibrutinib-CFZ combination clinically. Citation Format: Zhishuo Ou, Liang Zhang, Kate Newberry, Luhong Sun, Kirk J. Christopher, Alex Rollo, Archito Tamayo, John Lee, Richard J. Ford, Michael Wang, Lan V. Pham. The bruton's tyrosine kinase inhibitor ibrutinib synergized with the proteasome inhibitor carfilzomib and overcame immunoproteasome-mediated carfilzomib resistance in mantle cell lymphoma . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2432. doi:10.1158/1538-7445.AM2013-2432

Polo-Like Kinase 1: A Novel Target for the Treatment of Therapy-Resistant Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a B-cell non-Hodgkin lymphoma (NHL) which is one of the most aggressive lymphomas. Despite recent improvements in therapies, the development of therapy-resistance is still a major problem; therefore, in order to understand the molecular basis of therapy-resistance, stable therapy-resistant MCL cell lines have been established by us. Based on the gene expression profiles of these cell lines, Polo-like kinase 1 (PLK1) was chosen as a therapeutic target. In this paper, we demonstrate a significant antilymphoma effect of targeting PLK1 in therapy-resistant MCL cells and primary MCL cells from refractory patients. PLK1 knockdown with the antisense oligonucleotide (ASO)/or small molecule inhibitor BI2536 showed significantly decreased proliferation and increased apoptosis in therapy-resistant MCL cell lines and MCL primary cells. Additionally, the direct protein-protein interaction partners of PLK1 were mapped using ingenuity pathway and confirmed the level of association of these partners with PLK1 based on their expression changes following PLK1 knockdown using real-time PCR. Results suggest that PLK1 is a viable target for the treatment of therapy-resistant MCL.

Targeting early B-cell receptor signaling induces apoptosis in leukemic mantle cell lymphoma

BackgroundWe previously showed that B-cell receptor (BCR) signaling pathways are important for in vitro survival of mantle cell lymphoma (MCL) cells. To further identify early BCR-activated signaling pathways involved in MCL cell survival, we focused our study on BCR-proximal kinases such as LYN whose dysregulations could contribute to the aggressive course of MCL.MethodsPrimary MCL cells were isolated from 14 leukemic patients. Early BCR-induced genes were identified by qRT-PCR array. The basal and BCR-induced phosphorylation of LYN and JNK were evaluated by immunoblottting. Cell survival signals were evaluated by apoptosis using flow cytometry.ResultsWe showed that LYN was constitutively phosphorylated in MCL cell lines and in 9/10 leukemic MCL cases. Treatment with dasatinib or with a specific inhibitor of Src kinases such as PP2 suppressed constitutive LYN activation and increased in vitro spontaneous apoptosis of primary MCL cells. BCR engagement resulted in an increase of LYN phosphorylation leading to activation of c-JUN NH2-terminal kinase (JNK) and over-expression of the early growth response gene-1 (EGR-1). Inhibition of JNK with SP600125 induced apoptosis and reduced level of basal and BCR-induced expression of EGR-1. Furthermore, decreasing EGR1 expression by siRNA reduced BCR-induced cell survival. Treatment with PP2 or with dasatinib suppressed BCR-induced LYN and JNK phosphorylation as well as EGR-1 upregulation and is associated with a decrease of cell survival in all cases analysed.ConclusionsThis study highlights the importance of BCR signaling in MCL cell survival and points out to the efficiency of kinase inhibitors in suppressing proximal BCR signaling events and in inducing apoptosis.

Potential effects of CRM1 inhibition in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma. The disease has no known cure, which prompts the urgent need for novel therapeutic agents. Chromosomal region maintenance 1 (CRM1) may play a role in human neoplasia and serve as a novel target of cancer treatment. This study summarizes MCL pathogenesis and determines the involvement of CRM1 in the regulation of several vital signaling pathways contributing to MCL pathogenesis, including the pathways of cell cycle progression, DNA damage response, phosphoinositide kinase-3, nuclear factor-κB activation, and chromosomal stability. A preclinical study is also presented to compare the CRM1 status in MCL cell lines and primary MCL cells with normal B cells, as well as the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, which make these agents potential targets of novel MCL treatments.

Induction of Early G1-Arrest by CDK4/CDK6 Inhibition Sensitizes Mantle Cell Lymphoma Cells to Selective PI3Kδ Inhibition by GS-1101 Through Enhancing the Magnitude and Duration of p-AKT Inhibition

AbstractAbstract 791The phosphatidylinositol-3-kinase (PI3K) signaling pathway is constitutively activated at a high frequency in human cancer. As the first PI3K-specific inhibitor, GS-1101 (CAL-101) selectively targets p110δ (PI3Kδ). It has emerged as a promising single-agent therapy for chronic lymphocytic leukemia and indolent lymphomas. For aggressive non-Hodgkin lymphoma such as mantle cell lymphoma (MCL), efficacy has been observed but the extent and duration of tumor control has been modest, encouraging development of mechanism-based combination therapy.Since cell cycle dysregulation is frequently amplified in relapse/refractory diseases, we hypothesize that targeting the cell cycle may sensitize non-indolent lymphomas to inhibition of PI3Kδ by GS-1101, and test this hypothesis in MCL based on the following: 1) dysregulated cyclin D1 and CDK4 expression is a primary cause for unrestrained cell cycle progression and proliferation in MCL; 2) by induction of prolonged early G1 arrest (pG1) through selective inhibition of CDK4/CDK6 with PD 0332991 we have recently developed a novel strategy that both inhibits proliferation of tumor cells and sensitizes them to cytotoxic killing; and 3) induction of pG1 by PD 0332991 demonstrated encouraging clinical activity and an excellent toxicity profile in a phase I single-agent study in MCL.To test this hypothesis, we first demonstrate by whole transcriptome sequencing (WTS, RNA-Seq) that PI3Kδ is the predominant PI3K catalytic subunit expressed, and that only few non-synonymous single-nucleotide variants are present in the coding sequences of genes in the PI3K-AKT pathway in primary MCL tumor cells (N=10), including the analyzed PI3K subunits, AKT1, PTEN and PDK1. Moreover, despite a multitude of genetic abnormalities, mutations in the coding regions of core G1-cell cycle genes, including cyclin D1, CDK4, and CDK4/6 inhibitors CDKN2C (p18INK4c) and CDKN2D (p19INK4d) are also rare in primary MCL cells. Analysis of protein expression by immunoblotting has confirmed the WTS analysis and further demonstrated that AKT is constitutively phosphorylated on serine 473 by mTORC2 (p-AKT) downstream of PI3K in primary MCL cells. These findings reinforce the rationale for combining selective inhibition of PI3Kδ with selective inhibition of CDK4/CDK6 in targeting MCL.GS-1101 treatment does not result in cell cycle arrest in proliferating MCL cell lines (N=6), including Jeko-1 and MAVER-1 cells, which recapitulate the expression of PI3K and G1 cell cycle genes in primary MCL cells based on WTS and immunoblot analyses. GS-1101 transiently reduces p-AKT in proliferating MCL cells, confirming that MCL cells are intrinsically responsive to GS-1101 but also implying a potential mechanism for resistance. Prior induction of pG1 by selective inhibition of CDK4/CDK6 with PD 0332991 reduces p-AKT, amplifies and sustains the loss of p-AKT, and enhances apoptosis in response to GS-1101. Finally, validating the G1 cell cycle-dependence of GS-1101 killing, all primary MCL cells tested are responsive to PI3Kδ inhibition by GS-1101 when they are arrested in early G1 ex vivo in stromal co-culture. This loss of viability is accelerated at a reduced GS-1101 concentration when G1 arrest is accelerated by PD 0332991, despite the presence of cytokines and growth factors that are known to activate PI3K.This study presents the first sequential combination of selective inhibition of CDK4/CDK6 with a selective partner, the PI3Kδ-specific inhibitor GS-1101, in primary human cancer cells, and the first WTS-validated therapeutic strategy that leads to sensitization of MCL cells by cell cycle control and PI3K inhibition. Our data demonstrate, for the first time, that the magnitude and duration of GS-1101 killing is G1 cell cycle-dependent, and suggest a strategy to sensitize proliferating lymphoma cells to selective PI3Kδ inhibition by induction of early G1-arrest through CDK4/CDK6-specific inhibition. Disclosures:Off Label Use: PD 0332991 is a CDK4/CDK6 selective inhibitor GS-1101 is a PI3K-delta specific inhibitor. Martin:Cephalon: Consultancy; Celgene: Consultancy; Millennium: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Huang:Celgene, Corp: Research Funding. Lannutti:Gilead Sciences Inc: Employment. Leonard:Gilead/Calistoga: Consultancy, Honoraria. Mason:HESI Advisory Board: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MorganStanley: Consultancy; Shriner's Hospital: Consultancy; Illumina, Inc.: Ownership interest (inc stock options) in a publicly traded company, Ownership interest (inc stock options) in a publicly traded company Other; PerkinElmer: Consultancy. Chen-Kiang:Bristol Myers Squibb: Consultancy; Pfizer: Research Funding.

Novel Treatment for Therapy-Resistant Mantle Cell Lymphoma Targeting NF-κB and mTOR Signaling Pathways in Vitro and in Vivo

AbstractAbstract 63 Background:Mantle cell lymphoma (MCL) is one of the most aggressive B-cell non-Hodgkin lymphomas (NHL) with a median survival of less than five years. Currently, there is no curative therapy available for refractory MCL because of relapse from therapy-resistant tumor cells. It has been well documented that the NF-κB and mTOR pathways are constitutively active in MCL leading to increased survival, proliferation and decreased apoptosis. Therefore, in an effort to improve therapy for refractory MCL, we investigated the antilymphoma activity in vitro and in vivo and associated molecular mechanism of action of 13–197, a quinoxaline analog that specifically perturbs IκB kinase (IKK) β, an upstream kinase of the NF-κB and mTOR pathways. Methods:Established therapy-resistant from Granta 519 (Ahrens and Chaturvedi et al, Leukemia and Lymphoma doi:10.3109/10428194.2012.691481), other MCL cell lines Mino and Rec-1 and primary MCL cells from patients were used in this study. These MCL cells were treated in vitro with varying concentrations of 13–197 for the different time points. Cellular proliferation/viability, cytomorphology, frequency of cells undergoing apoptosis in treated and control cells were evaluated using 3[H]-thymidine uptake, MTT assay, cytomorphology and Annexin-V staining methods respectively. The status of key molecules in the NF-κB and mTOR pathways were examined in therapy-resistant and parental MCL cells following treatment with 13–197 using western blot analyses. The results of these analyses were compared to untreated control cells as appropriate and statistical significance of the results were determined using student‘t' test. In addition, in vivo therapeutic efficacy of 13–197 was investigated using NOD-SCID mouse bearing therapy-resistant MCL. Results:Our results showed that 13–197 significantly decreased the proliferation and induced a ∼four-fold (P<0.005) increase in apoptosis in parental and therapy-resistant MCL cells compared to control cells. At the molecular level, we observed down-regulation of IκBα phosphorylation and inhibition of NF-κB nuclear translocation by the 13–197 in MCL cells. In addition, NF-κB regulated genes such as cyclin D1, Bcl-XL and Mcl-1 were down-regulated in 13–197-treated cells. 13–197 also inhibited the phosphorylation of S6K and 4E-BP1, the downstream molecules of mTOR pathway that are also activated in refractory MCL. Further, to investigate the therapeutic efficacy of 13–197 against therapy-resistant MCL in vivo, we treated NOD-SCID mice bearing therapy-resistant MCL with 13–197; there was significantly reduced tumor burden in the kidney (p>0.05), liver (p>0.01), and lungs (p>0.03) of 13–197 treated mice compared to vehicle treated mice. Indeed, 13–197 treatment significantly increased the survival (p>0.001) of MCL transplanted mice. Taken together, our results suggest that 13–197 targets IKKβ which leads to both the transcriptional (NF-κB) and translational (mTOR) downregulation of gene products (cyclin D1, Bcl-XL and Mcl-1) misregulated in therapy-resistant MCL. Summary/Conclusions:Overall, results suggest that 13–197 perturbs the NF-κB and mTOR pathways leading significant antilymphoma effects in vitro and in vivo thus demonstrates its potentials to be a therapeutic agent for refractory MCL.(This work was supported by the Lymphoma Research Foundation New York, NY) Disclosures:No relevant conflicts of interest to declare.

Combination of ACY1215, a Selective Histone Deacetylase 6 (HDAC6) Inhibitor with the Bruton Tyrosine Kinase (BTK) Inhibitor, Ibrutinib, Represents a Novel Therapeutic Strategy in Mantle Cell Lymphoma (MCL)

AbstractAbstract 1660Recently, we have found that HDAC6 is overexpressed in MCL cell lines and in primary human MCL cells. Knocking-down HDAC6 in MCL cells with a shRNA lentiviral system resulted in cell cycle arrest and apoptosis induction. Interestingly, MCL cells lacking HDAC6 displayed a significantly decreased STAT3 phosphorylation and abrogation of IL-10 gene transcriptional activity. ACY1215 is a novel, selective, orally bioavailable HDAC6 inhibitor. Treatment of MCL cell lines with this agent resulted in decreased cell viability and proliferation. In addition, ACY1215 inhibits IL-10 production in a dose dependent manner.Bruton tyrosine kinase (BTK) is a member of Tec family of kinases with a very distinct role in B-cell antigen receptor (BCR) signaling. The selective BTK-inhibitor PCI-32765 has shown promising pre-clinical and clinical activity in MCL. In addition to their direct anti-lymphoma effects, disruption of BTK also induces positive immunological changes such as inhibition of the immunosuppressive STAT3/IL-10 signaling pathway1.The above observations led us to determine whether the direct antitumor effects and the immunological properties of ACY1215 and PCI-32765 could be potentiated when these agents are used in combination. First, the viability of MCL cells was decreased when they were treated in vitro with either PCI-32765 or ACY1215. However, combination of these two agents resulted in a 3-fold increase in apoptosis induction, pointing to a synergistic effect of BTK and HDAC6 inhibition in MCL. The additional findings that this approach can increase the immunogenicity of MCL cells and anti-MCL immune responses has provided the proper framework for combining the selective HDAC6 inhibitor ACY1215 with BTK inhibition as a novel therapeutic strategy in MCL. Disclosures:Chen-Kiang:Bristol Myers Squibb: Consultancy; Pfizer: Research Funding. Jones:Acetylon Pharmaceuticals, Inc: Employment.

Superior efficacy of a combined epigenetic therapy against human mantle cell lymphoma cells.

A deregulated epigenome contributes to the transformed phenotype of mantle cell lymphoma (MCL). This involves activity of the polycomb repressive complex (PRC) 2, containing three core proteins, EZH2, SUZ12, and EED, in which the SET domain of EZH2 mediates the histone methyltransferase activity. We determined the effects of 3-deazaneplanocin A (DZNep), an S-adenosylhomocysteine hydrolase inhibitor, and/or pan-histone deacetylase inhibitor panobinostat (PS) on cultured and primary MCL cells. Following treatment with DZNep and/or PS, apoptosis and the levels and activity of EZH2 and PRC2 proteins in cultured and primary MCL cells were determined. Treatment with DZNep depleted EZH2, SUZ12, and 3MeK27H3 in the cultured human MCL cells. DZNep also increased expression of p21, p27, and FBXO32, whereas it depleted Cyclin D1 and Cyclin E1 levels in MCL cells. In addition, DZNep treatment induced cell-cycle arrest and apoptosis in cultured and primary MCL cells. Furthermore, as compared with treatment with each agent alone, cotreatment with DZNep and PS caused greater depletion of EZH2, SUZ12, 3MeK27H3, and Cyclin D1 levels, whereas it induced greater expression of FBXO32, p16, p21, and p27. Combined treatment with DZNep and PS synergistically induced apoptosis of cultured and primary MCL cells while relatively sparing normal CD34 + cells. Cotreatment with DZNep and PS also caused significantly greater inhibition of tumor growth of JeKo-1 xenografts in NOD/SCID mice. These preclinical in vitro and in vivo findings show that cotreatment with DZNep and PS is an active combined epigenetic therapy worthy of further in vivo testing against MCL.

Transcription and translation are primary targets of Pim kinase inhibitor SGI-1776 in mantle cell lymphoma

AbstractProviral integration site for Moloney murine leukemia virus (Pim) kinases are serine/threonine/tyrosine kinases and oncoproteins that promote tumor progression. Three isoforms of Pim kinases have been identified and are known to phosphorylate numerous substrates, with regulatory functions in transcription, translation, cell cycle, and survival pathways. These kinases are involved in production, proliferation, and survival of normal B cells and are overexpressed in B-cell malignancies such as mantle cell lymphoma (MCL). SGI-1776 is a small mol-ecule and Pim kinase inhibitor with selectivity for Pim-1. We hypothesize that Pim kinase function can be inhibited by SGI-1776 in MCL and that inhibition of phosphorylation of downstream substrates will disrupt transcriptional, translational, and cell cycle processes and promote cell death. SGI-1776 treatment in 4 MCL cell lines resulted in apoptosis induction. Phosphorylation of transcription (c-Myc) and translation targets (4E-BP1), tested in Jeko-1 and Mino, was declined. Consistent with these data, Mcl-1 and cyclin D1 protein levels were decreased. Importantly, similar to cell line data, MCL primary cells but not normal cells showed similar inhibition of substrate phosphorylation and cytotoxicity from SGI-1776 treatment. Genetic knockdown of Pim-1/Pim-2 affected similar proteins in MCL cell lines. Collectively these data demonstrate Pim kinases as therapeutic targets in MCL.

Potential effects of CRM1 inhibition in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma. The disease has no known cure, which prompts the urgent need for novel therapeutic agents. Chromosomal region maintenance 1 (CRM1) may play a role in human neoplasia and serve as a novel target of cancer treatment. This study summarizes MCL pathogenesis and determines the involvement of CRM1 in the regulation of several vital signaling pathways contributing to MCL pathogenesis, including the pathways of cell cycle progression, DNA damage response, phosphoinositide kinase-3, nuclear factor-κB activation, and chromosomal stability. A preclinical study is also presented to compare the CRM1 status in MCL cell lines and primary MCL cells with normal B cells, as well as the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, which make these agents potential targets of novel MCL treatments.

Counteracting Autophagy Overcomes Resistance to Everolimus in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is an aggressive B-lymphoid neoplasm with poor response to conventional chemotherapy and short survival. The phosphatidylinositol 3-kinase/Akt/mTOR survival pathway is constitutively activated in MCL cells, thereby making the mTOR inhibition an attractive therapeutic strategy. The first clinical studies of everolimus (RAD001), an mTOR inhibitor, in relapsed MCL patients have reported a significant response. Our aim was to analyze the mechanism related to everolimus resistance/sensitivity in MCL cells. Sensitivity to everolimus was analyzed in MCL cell lines and primary MCL cells. Everolimus mechanism of action was determined by flow cytometry and Western blot. Particularly, autophagy was studied by LC3BI/II expression, autophagolysosomes detection by flow cytometry and fluorescence microscopy, and siRNA-mediated gene silencing. Everolimus exerted antitumoral effect on MCL cells while sparing normal cells. In MCL cell lines, this phenomenon was associated to G(1) cell-cycle arrest, dephosphorylation of the mTOR downstream targets, 4E-BP1 and S6RP, and rephosphorylation of Akt. A synergistic cytotoxic effect was observed between everolimus and an Akt inhibitor, which overcame the compensatory reactivation within the mTOR signaling pathway. Interestingly, MCL cells with low response to this combination showed high levels of autophagy. Accordingly, selective triple knockdown of the autophagy genes ATG7, ATG5 and ATG3, and pretreatment with the autophagy inhibitor hydroxychloroquine, efficiently overcame the resistance to Akt/mTOR inhibitors, leading to the activation of the mitochondrial apoptotic pathway. These results suggest that autophagy induction protects MCL cells from Akt/mTOR targeting and counteracting autophagy may represent an attractive strategy for sensitizing MCL cells to everolimus-based therapy.

Verapamil synergistically enhances cytotoxicity of bortezomib in mantle cell lymphoma via induction of reactive oxygen species production

Verapamil synergistically enhances cytotoxicity of bortezomib in mantle cell lymphoma via induction of reactive oxygen species production

Targeting malignant B cells with an immunotoxin against ROR1

The selective cell surface expression of receptor tyrosine kinase-like orphan receptor 1 (ROR1) in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) has made ROR1 a novel and promising target for therapeutic monoclonal antibodies (mAbs). Four mouse mAbs generated by hybridoma technology exhibited specific binding to human ROR1. Epitope mapping studies showed that two mAbs (2A2 and 2D11) recognized N-terminal epitopes in the extracellular region of ROR1 and the other two (1A1 and 1A7) recognized C-terminal epitopes. A ROR1- immunotoxin (BT-1) consisting of truncated Pseudomonas exotoxin A (PE38) and the VH and VL fragments of 2A2-IgG was made recombinantly. Both 2A2-IgG and BT-1 showed dose-dependent and selective binding to primary CLL and MCL cells and MCL cell lines. Kinetic analyses revealed 0.12-nM (2A2-IgG) to 65-nM (BT-1) avidity/affinity to hROR1, depicting bivalent and monovalent interactions, respectively. After binding to cell surface ROR1, 2A2-IgG and BT-1 were partially internalized by primary CLL cells and MCL cell lines, and BT-1 induced profound apoptosis of ROR1-expressing MCL cell lines in vitro (EC50 = 16 pM–16 nM), but did not affect ROR1-negative cell lines. Our data suggest that ROR1-immunotoxins such as BT-1 could serve as targeted therapeutic agents for ROR1-expressing B cell malignancies and other cancers.

Abstract 2078: Treatment with auranofin induces oxidative and lethal endoplasmic reticulum (ER) stress exerting single agent activity against mantle cell lymphoma cells

Abstract Auranofin (AF) (Ridaura®) is an oral, FDA-approved, lipophilic, gold-containing compound used for the treatment of rheumatoid arthritis. In the present studies, we determined for the first time the lethal activity of AF (100 to 1000 nM) and its underlying mechanism(s) in cultured and primary Mantle Cell Lymphoma (MCL) cells. We demonstrate that treatment with AF in JeKo-1 and Z138C cells induced 2 to 3.5 fold increase in reactive oxygen species (ROS) levels (assessed by flow cytometry), decrease in thioredoxin reductase (TRR) activity (mean reduction of 35-40%) without alteration in the expression of TRR. These findings were associated with induction of nuclear factor erythroid 2-related factor 2 (NRF2) activity marked by substantial increase in heme oxygenase-1 (HMOX1) expression. Microarray analysis revealed that AF treatment significantly upregulated ER stress and oxidative stress inducible genes including that of the ER-stress induced pro-apoptotic transcription factor CHOP (CAAT/enhancer binding protein homologous protein), ATF3 (Activated Transcription Factor 3) and Glutamate-cysteine ligase (GCL), modifier subunit (GCLM), the rate-limiting enzyme in the glutathione (GSH) biosynthesis. Exposure to AF induced significantly more apoptosis in primary MCL cells, as compared to CD19+ normal B cells, CD34+ human cord blood and bone marrow progenitor cells (&amp;lt; 15% apoptosis) (p &amp;lt; 0.01). Based on the observations that AF treatment induced oxidative and ER stress, we determined whether exposure to AF increased the intracellular levels of misfolded and polyubiquitylated proteins, which would disrupt the cytosolic complex consisting of the heat shock protein (hsp) 90, heat shock factor (hsf) 1, histone deacetylase 6 (HDAC6) and p97/VCP, resulting in hyperacetylation and inhibition of the chaperone function of hsp90. Indeed, treatment with AF disrupted the association between hsp90 and HDAC6, HSF1 and p97, resulting in hyperacetylation of hsp90 and depletion of the levels of hsp90 client proteins including HDAC6, AKT and Cyclin D1 in MCL cells. Co-treatment of MCL cells with AF and the proteasome inhibitor carfilzomib (CZ) resulted in synergistic apoptosis in cultured MCL cells and significantly more apoptosis in primary MCL cells, than treatment with each agent alone. Based on the induction of GCLM and anti-oxidant response genes following AF treatment, we tested the anti-MCL activity of the combination of AF and the GCL inhibitor Buthionine sulphoximine (BSO), against MCL cells. Co-treatment with BSO and AF resulted in significantly more apoptosis of MCL cells than treatment with each agent alone. Collectively, our data creates a strong rationale for determining the in vivo activity of AF in patients with MCL as a single agent and in combination with other ER and oxidative stress-inducing agents, especially GCL inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2078. doi:1538-7445.AM2012-2078

Combined Targeting of Chromatin Modifying Enzymes LSD1, EZH2 and Histone Deacetylases (HDACs) Has Superior Efficacy Against Human Mantle Cell Lymphoma Cells

Abstract 2429PRC (polycomb repressive complex) 2 contains three core protein components, i.e., EZH2, SUZ12 and EED, of which EZH2 has the SET domain with its intrinsic histone methyltransferase activity that mediates the trimethylation (Me3) of lysine (K) 27 on histone (H) 3-a repressive chromatin mark for gene expression. We have previously reported that treatment with the S-adenosylhomocysteine hydrolase and EZH2 inhibitor, DZNep as well as treatment with the pan-histone deacetylase inhibitor panobinostat (PS, Novartis Pharma) deplete PRC2 complex proteins. LSD1 (KDM1A) is a demethylase of H3K4Me2, and inhibiton of LSD1 leads to increase in H3K4Me3-a permissive mark for gene expression. In the present studies, we determined the chromatin-modifying and cytotoxic effects of LSD1 inhibition alone and in combination with PS or DZNep in cultured (JeKo-1 and Z138C) and primary human Mantle Cell Lymphoma (MCL) cells. Treatment with the non-amine oxidase reversible inhibitor of LSD1 CIT0665 (250 to 1000 nM), or the more potent analogue HCI2509 (20 to 250 nM), dose-dependently increased the levels of H3K4Me2 & Me3, p21 and p27, while decreasing the levels of cyclin D1, which was associated with inhibition of cell proliferation and accumulation of the MCL cells in the G1 phase of the cell cycle. Abrogation of LSD1 by a specific shRNA treatment also induced similar chromatin, cell cycle and growth inhibitory effects. Exposure to CIT0665 or HCI2509 disrupted the binding of LSD1 with the co-repressor CoREST and HDAC1, without affecting the levels of these proteins. As noted above, treatment with PS (10 to 50 nM) dose-dependently depleted the levels of not only EZH2, SUZ12 and the PRC1 complex protein BMI1, but also of LSD1 in MCL cells. PS treatment alone also depleted the levels of AKT, cRAF, CDK4 and cyclin D1, as well as induced cell cycle growth inhibition and apoptosis of MCL cells. Co-treatment with PS enhanced the chromatin modifying effects of CIT0665 or HCI2509. The combination synergistically induced apoptosis of the cultured MCL cells (combination indices, CI <1.0). This was associated with greater induction of p27 and depletion of cyclin D1. Treatment with PS and HCI2509 also synergistically induced loss of viability of primary MCL cells (CI <1.0). We have previously reported that DZNep dose-dependently depleted EZH2, SUZ12 and BMI1 expression, inhibited H3K27Me3 levels, induced p21, p27 and FBXO32 (muscle atrophy F-box protein, also called atrogin-1) levels in cultured and primary MCL cells. Here, we determined the effects of co-treatment with HCI2509 and DZNep in MCL cells. Combined treatment with HCI2509, although not synergistic, enhanced the apoptosis of MCL cells induced by DZNep. Taken together these findings indicate that combined targeted depletion of the level and activity of LSD1 by PS and CIT0665 or HCI2509 along with PS-mediated depletion of PRC2 proteins, BMI and HDACs exerts superior activity against MCL cells. These studies also support the in vivo testing of combined epigenetic therapies in the treatment of MCL. Disclosures:Sharma:Novartis: Research Funding.

Novel CRM-1 Inhibitors for Therapy In Mantle Cell Lymphoma

Abstract 2734Chromosomal Region Maintenance 1 (CRM1) overexpression has been associated with cancer progression and mortality in several human cancers, suggesting that activation of nuclear export may play a role in human neoplasia and may serve as a novel target for the treatment of cancers. This overexpression of CRM1 may be related to the export of most tumor suppressor and growth regulatory proteins out of the nucleus, thereby functionally inactivating them. Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma that is not yet curable. The objective of our study was to investigate the status of CRM1 in MCL, both in MCL cell lines and primary MCL cells, in comparison to normal B cells, and to evaluate the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, and to elucidate the mechanism of CRM1 inhibitor-mediated MCL cell apoptosis. We used 8 established MCL cell lines and primary cells from 4 patients with relapsed/refractory MCL. KPT185 and KPT276 are novel, highly selective, drug-like small molecular CRM1 inhibitors. Western Blot analysis showed that CRM1 was expressed in both the cytoplasm and nuclei of 8 MCL cell lines. CRM1 was mainly detected in nuclei of normal resting B cells; In contrast, CRM1 was primarily detected in the cytoplasm of freshly isolated primary MCL cells from patients with relapsed/refractory MCL. In 3H-thymidine incorporation assays, inhibition of CRM1 by KPT185 resulted in a significant dose-dependent growth inhibition of 8 MCL cells, with IC50 values range between 10 nM to 120 nM. The blastoid-variant MCL cell lines (Z-138 and Rec-1) were significantly more sensitive to KPT185 than the non-blastoid variant MCL cell lines. Flow cytometry analysis with fluorescence-labeled Annexin V and propidium iodide showed that KPT185 induced MCL cells apoptosis in both time- and dose-dependent manners, but had no effect on cell cycle arrest. MCL cells treated with KPT185 for 12 hours showed caspase 3 activation and PARP cleavage. As shown in Western blot and confocal microscopy, blocking CRM1 activity by KPT185 in MCL cells up-regulated the protein expression of p53, a known CRM1-mediated export protein, and also induced CRM1 translocation to the nucleus and decreased CRM1 expression. In severe combined immunodeficient (SCID) mice bearing palpable Z-138 tumors, treatment with KPT-276 (similar structure to KPT-185 but improved animal pharmacokinetics), 50mg/kg or 150 mg/kg PO QDx5 each week, or cyclophosphamide 100 mg/kg on days 1–3, was initiated. Tumor growth was significantly inhibited (>75%) in all of treatment groups compared with vehicle control. Neutropenia and other cytotoxic-agent specific effects have not been observed in treated animals. In conclusion, CRM1 inhibitors inhibited growth of MCL cells in vitro and in vivo, and induced apoptosis of MCL cells via inhibition of CRM1 expression and blockage of its translocation with functional nuclear proteins. Our data suggest that novel CRM1 inhibitors provide a potential therapy for patients with relapsed/refractory MCL. Disclosures:No relevant conflicts of interest to declare.

Naïve CD4+ T Cells Modified to Express a ROR1-Specific CAR Mediate Anti-Tumor Activity and Provide Superior Help to CD8+ ROR1-CAR T Cells

Abstract 643The engineering of T cells modified to express single-chain antibody-derived chimeric antigen receptors (CARs) that recognize surface molecules expressed on malignant B cells independent from HLA is an area of intense research. The successful use of CAR-modified T cells to treat B-cell malignancies requires the definition of T cells or T-cell subsets that possess an intrinsic ability to confer potent and durable anti-tumor responses, and would ideally be directed against an antigen with selective expression on malignant, but not on normal B cells.Current efforts have focused on the use of bulk CD8+ cytotoxic T cells (CTL) for CAR-modification because the role of CTL in mediating tumor rejection is well established, or unselected PBMC that contain both CD8+ and CD4+ T cells. However, without selection, the progeny and composition of the final cell product is poorly controlled, and the rational use of CD4+ CAR T cells that play a central role in sustaining CD8+ T cell responses to pathogens remains unexplored. We have shown that ROR1, an oncofetal tyrosine kinase receptor, is uniformly expressed on chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), and developed a ROR1-CAR from an anti-ROR1 mAb that confers specific recognition of malignant, but not mature normal B cells when expressed in CD8+ T cells [Hudecek et al. 2010]. Here, we derived CD4+ ROR1-CAR T cells from unselected, and sort purified naïve (N), central (CM) and effector memory (EM) CD4+ T cells and characterized direct tumor recognition and the ability to augment CD8+ ROR1-CAR CTL.We purified CD4+ and CD8+ T cells from the peripheral blood of healthy donors (n=3) and CLL patients (n=3) and transduced them with ROR1-CAR encoding lentiviral vector. In all cases, we achieved higher transduction efficiencies of CD4+ compared to CD8+ T cells. CAR-modified T cells were enriched from the cultures using a truncated EGFR encoded within the CAR vector downstream of a T2A sequence as a selection marker. ROR1-CAR expression on the surface of T cells was confirmed by flow cytometry using recombinant ROR1-Fc fusion protein. In functional assays, CD4+ CAR T cells conferred specific but weak cytolytic activity compared with CD8+ CAR T cells against ROR1+ tumors including primary CLL, JeKo-1 MCL, and K562 cells transfected with ROR1. Multiplex cytokine analysis detected high-level production of Th1 cytokines including IFN-g, IL-2 and TNF-α, and CFSE staining showed superior proliferation after stimulation with tumor compared to CD8+ CAR CTL, suggesting CD4+ CAR T cells exert typical helper effector functions after stimulation through the CAR.Polyclonal CD4+ T cells contain various frequencies of N, CM, and EM subsets that have distinct functional properties. Thus, we compared the cytolytic activity, cytokine profile and proliferative capacity of CAR T cells derived from flow-sort purified CD4+ N, CM and EM subsets. CD4+ CAR T cells derived from the N CD45RA+CD45RO-CD62L+ subset exhibited the strongest cytotoxicity, produced the highest levels of Th1 cytokines, especially IL-2, and proliferated most vigorously in response to ROR1+ tumor cells, suggesting they may be able to confer the strongest direct anti-tumor effect, and be best suited to provide help to CD8+ CAR CTL. Indeed, in co-culture experiments, the addition of CAR-transduced, but not untransduced CD4+ T cells derived from N rather than memory subsets also resulted in maximum proliferation of CD8+ CAR CTL. Consistent with our analysis of cytokine production, blocking with anti-IL-2 and anti-IL-2Ra mAbs was able to impair but did not completely abrogate this helper effect, demonstrating that help provided by CD4+ CAR T cells was at least in part mediated by IL-2. In vivo experiments demonstrated profound anti-tumor efficacy of CD4+ ROR1-CAR modified T cells in NOD/SCIDgc−/− (NSG) mice that had been engrafted with firefly luciferase transduced JeKo-1 MCL tumor cells. Experiments to compare the anti-tumor efficacy of CAR-modified CD4+ T cells derived from individual N, CM and EM subsets, alone or in combination with CD8+ CAR CTLs are in progress.Collectively, our data illustrate how cell-intrinsic qualities can inform the rational design of cell products containing both tumor-specific CD8+ and CD4+ T cells to improve outcomes of cancer immunotherapy, and suggest that deriving engineered CD4+ T cells from the naïve subset may be most advantageous for tumor therapy. Disclosures:Maloney:GSK: Consultancy, Honoraria.

Juxtaposing CD20 and CD74 with Novel Bispecific Antibodies Evokes Potent Cytotoxicity in Mantle Cell Lymphoma (MCL)

Abstract 599 Introduction:Initial response rates with first-line conventional or high-dose chemotherapy, are high in MCL, but most patients relapse. With 3,500 new cases detected every year in the US, there is an unmet medical need for new therapeutic interventions in MCL. Combination of two different targeting mAbs to achieve improved efficacy without increased toxicity was demonstrated first in NHL patients given both rituximab (anti-CD20 chimeric antibody) and epratuzumab (humanized anti-CD22 IgG). Recently, the potential advantage of targeting both CD20 and CD74 was reported in a preclinical study showing that combining rituximab and milatuzumab (humanized anti-CD74 IgG) together with a crosslinking antibody resulted in anti-tumor activity in MCL lines and patient samples in vitro (Alinari L, et al. Blood 2011; 117:4530-41). Here we describe the generation of two novel bispecific hexavalent antibodies [HexAbs; IgG-(Fab)4] constructed from veltuzumab (humanized anti-CD20 IgG) and milatuzumab (anti-CD74 IgG), and show both are capable of inducing potent cytotoxicity in mantle cell lymphoma (MCL) and other lymphoma/leukemia cell lines, as well as primary MCL and CLL patient samples, without requiring a crosslinking antibody. To identify these HexAbs, we assign each of them a code of X-(Y)-(Y), where × and Y are specific numbers given to differentiate the antibodies, and a designated number enclosed in a parenthesis representing the antibody as a stabilized Fab dimmer (e.g., 20-(74)-(74) designates the bispecific HexAb comprising a divalent anti-CD20 IgG of veltuzumab and a pair of stabilized dimers of Fab derived from milatuzumab). Methods: The two bispecific HexAbs, 74-(20)-(20) and 20-(74)-(74), as well as the two monospecific HexAbs, 74-(74)-(74) and 20-(20)-(20), were generated by the Dock-and-Lock method by reacting cognate CH3-AD2-IgG and CH1-DDD2-Fab modules under mild redox conditions and purified by Protein A. The in vitro activities were determined by cell viability and Annexin V binding assays. In addition, the role of signal transduction, homotypic adhesion, actin reorganization, and lysosomal volume changes were evaluated. Results: Each HexAb was purified to >95 % homogeneity and were stable in vitro and in serum. Both 20-(74)-(74) and 74-(20)-(20) potently inhibited the growth of MCL lines, JeKo-1, Granta-519 and Mino, at 10 nM. In contrast, neither parental antibody, alone or in combination, nor the two monospecific counterparts, 74-(74)-(74) and 20-(20)-(20), inhibited the growth of JeKo-1 under the same conditions, suggesting the requirement of apposing CD74 and CD20 for the observed cytotoxicity. Treatment of primary MCL and CLL patient cells with 74-(20)-(20) and 20-(74)-(74) induced 25–30% apoptosis, compared to 10–15% apoptosis with parental IgGs, alone or in combination. The two bispecific anti-CD20/CD74 HexAbs, but not the parental mAbs, induced strong homotypic adhesion, actin reorganization to cell-cell junctions, loss of mitochondrial membrane potential, generation of ROS, deactivation of the PI3K/Akt signaling pathway, as well as rapid and sustained activation of ERK and JNK MAPKs, and enlargement of lysosomes followed by release of cathepsin B in target cells. In SCID mice bearing JeKo-1 xenografts, both 20-(74)-(74) and 74-(20)-(20) were effective at the 370-μg dose level, resulting in 60% and 30% increases in median survival time, respectively, compared to saline controls (P = 0.001). Conclusion: Juxtaposing CD20 and CD74 in close proximity by HexAbs induces potent in vitro cytotoxicity in MCL lines and primary samples. These novel bispecific mAbs warrant further evaluation in B-cell lymphomas that are refractory or poorly responsive to anti-CD20 antibodies. Disclosures:Gupta:Immunomedics, Inc.: Employment. Goldenberg:Immunomedics, Inc.: Employment, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties. Rossi:Immunomedics, Inc.: Employment. Cardillo:Immunomedics, Inc.: Employment. Furman:Centocor Ortho Biotech Research & Development: Research Funding. Chang:Immunomedics, Inc.: Employment, Equity Ownership, Patents & Royalties.

A Phase I/II Study of Vorinostat (SAHA), Cladribine (2-CdA), and Rituximab Shows Significant Activity in Previously Untreated Mantle Cell Lymphoma

Abstract 441Background: Despite significant progress in the treatment of mantle cell lymphoma (MCL), relapse remains the norm and additional therapies are needed especially for patients who are not candidates for aggressive treatment approaches. Increasingly, it has become evident that epigenetic modifications, including DNA hypomethylation and histone deacetylase inhibition, are critical to the pathogenesis and treatment of hematologic malignancies; important to cancer biology; and may be essential to the development of treatment resistance in B-cell malignancies. Further development and understanding of new and effective treatment regimens that target the epigenome are needed.2-CdA has activity in a variety of B and T cell malignancies. In addition to its cytotoxic effects, our preliminary work shows that 2-CdA has hypomethylating properties in lymphoid malignancies. When primary MCL and CLL cells -before and 96 hours after cladribine treatment-were analyzed by HELP (HpaII tiny fragment Enrichment by Ligation mediated PCR), an array based genome-wide methylation assay, 2-CdA affected DNA hypomethylation. One of the genes hypomethylated was identified as DUSP2, a dual specificity phosphatase gene that is a p53 target gene. DUSP2 dephosphorylates phosphoserine/threonine and phosphotyrosine residues, negatively regulating mitogen-activated protein (MAP) kinases ERK1 and ERK2, which are associated with cellular proliferation and differentiation in B-NHL.Vorinostat (SAHA) is a histone deacetylase inhibitor (HDACi), which has shown modest single agent activity in lymphoma and is FDA approved for use in cutaneous T cell lymphoma (CTCL). MCL cell lines treated with cladribine activated DUSP2 mRNA and when treated with the HDAC inhibitor SAHA synergistically increased transcription of DUSP mRNA. Furthermore, MCL treated with cladribine in vitro showed inhibition of global histone methylation. Our hypothesis is that cladribine and vorinostat synergistically activate silenced genes such as but not limited to DUSP 1 and 2 that are important for tumor cell death. The mechanism of rapid tumor cell death is under investigation, and does not appear to involve the classical apoptosis pathway. Given the need for novel therapies and the potential synergy seen with 2-CdA and SAHA, we initiated a Phase I/II trial combining SAHA, 2-CdA, and rituximab (SCR) for the treatment of B-cell non-Hodgkin's Lymphoma (NHL). The Phase I portion has been completed while Phase II is actively enrolling patients including those with newly diagnosed MCL.Methods: Phase I enrolled 10 patients with relapsed/refractory NHL. The MTD of vorinostat for the Phase I was 400 mg (D 1–14) combined with 2-CdA 5mg/m2 IV (D 1–5), and R 375 mg/m2 IV (weekly × 4 for cycle 1 and 1x/month) every 28 days for up to 6 cycles. Phase II eligibility includes relapsed NHL as well as previously untreated mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Primary outcome is response rate (ORR). Scientific correlatives include analysis of CD20 expression, histone acetylation, gene microarray and HELP methylation analysis, ERK phosphorylation, and Q-PCR of potential target genes.Results: 52 patients (Phase I/II) have been enrolled and 45 patients have been treated. The ORR in evaluable relapsed patients (3 DLBCL, 10 MCL, 1 FL, 1 MZL, 7 CLL) is 32% (7/22). Among these relapsed patients, complete remissions (CR) have been observed in MCL as well as follicular and marginal zone lymphomas. Of the 20 previously untreated MCL patients, 19 have completed ≥ 2 cycles and are evaluable for response. ORR is 100% (19/19) with 79% (15/19) CR. Toxicities by CTCAE 3.0 criteria have primarily included reversible myelosuppression, fatigue, dehydration, 1 gr. 4 thrombo-embolic event (probably related), and 1 grade 5 pulmonary hemorrhage in a patient with relapsed pulmonary lymphoma. One previously untreated mantle cell lymphoma patient has ongoing Gr. 3 thrombocytopenia six weeks after completing therapy. Preliminary analysis of ongoing correlative studies is available in 1 MCL patient and shows DUSP2 upregulation.Conclusions: The SCR regimen shows activity across a number of B-cell malignancies and shows particular therapeutic promise in patients with previously untreated mantle cell lymphoma. Correlative studies are ongoing and will be presented. Future studies should continue to explore this regimen in previously untreated mantle cell lymphoma. Disclosures:Off Label Use: vorinostat (SAHA) is not FDA approved for the treatment of B cell lymphomas. Okada:Merck: Speakers Bureau. Epner:Merck: Speakers Bureau.