CellTiter-Glo Luminescent Assay Research Articles

The Development of a Precision Medicine Platform to Overcome Ibrutinib Resistance in Mantle Cell Lymphoma

Background: While mantle cell lymphoma (MCL) initially responds to frontline therapies, this aggressive B-cell malignancy typically relapses or becomes resistant to treatment. Despite high overall response rates to the oral, covalent, first-in-class Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, most patients with relapsed/refractory MCL ultimately experience disease progression. To address the critical issue of BTK inhibitor resistance, novel therapies must be developed. Moreover, diversity in genetic alterations and the possibility that multiple pathway aberrations may contribute to disease progression and resistance makes overcoming this phenomenon with uniform treatment regimens extremely difficult, indicating that a personalized approach should be developed to overcome therapeutic resistance. In this study, molecular profiling of ibrutinib-resistant MCL patient samples has been conducted to identify targetable dysregulated signaling pathways and gene mutations associated with ibrutinib resistance. Clinical drug candidates targeting these potential pathways and their combinations with ibrutinib were analyzed in vitro to identify novel treatments that may potentially overcome ibrutinib resistance. Methods: Twenty-three agents targeting multiple pathways associated with ibrutinib resistance were deliberately chosen based on known targetable pathways in MCL to assess via high throughput drug screening. MCL tumor cells were isolated and purified from clinical apheresis and tumor excisional biopsies under established IRB-approved protocols. The same patient primary cells were subjected to gene expression analysis using a nanoString nCounter panel and whole exome sequencing (WES) to identify targetable dysregulated pathways and somatic mutations within each tumor. In vitro cell viability assays of single agents and drug combinations were tested per patient sample using the CellTiter-Glo luminescent assay (Promega), interrogating dysregulated pathways identified in each tumor. Subcutaneous, intravenous, and subrenal injections of the purified patient tumor cells were performed on NSG mice to create corresponding PDX mouse models for validation experiments. Results: nanoString nCounter analysis identified differentially expressed targetable pathways per patient sample such as BCR signaling, the PI3K/AKT pathway, NOTCH signaling, the cell cycle, and the NF-κB pathway. Correlations were identified between the WES and the nanoString nCounter analysis. For example, PTEN loss was observed in an MCL patient sample with high PI3K/AKT expression, demonstrating the potential underlying mechanism for the observed PI3K/AKT enrichment. Patients were divided into subgroups based on the identified responsive pathways in the in vitro screening. For example, PI3K/AKT pathway inhibitors were shown to be more potent against MCL samples in which the PI3K/AKT pathway was enriched. To further validate this finding, we created an MCL PDX model using a sample with enriched PI3K/AKT expression and successfully recapitulated the splenomegaly and hepatomegaly observed in the MCL patient. The MCL PDX mice were treated with the pan-PI3K inhibitor copanlisib (IP, 10 mg/kg) using a 5 on/2 off dosing schedule, which resulted in significantly reduced spleen (P < 0.001) and liver size (P < 0.01), as well as bone marrow involvement (P < 0.05), compared with the vehicle control (Figure 1). Conclusions: Molecular matching with in vitro drug screening were utilized to develop a precision medicine platform for MCL to combat therapeutic resistance. This platform can be translated into a clinical setting to directly benefit the MCL patient population through treatment with therapies directly tailored to each patient. Disclosures Wang: Pulse Biosciences: Consultancy; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Research Funding, Speakers Bureau; Acerta Pharma: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Dava Oncology: Honoraria; Kite Pharma: Consultancy, Research Funding; Juno Therapeutics: Research Funding; Celgene: Consultancy, Research Funding; MoreHealth: Consultancy, Equity Ownership; BioInvent: Consultancy, Research Funding; Aviara: Research Funding; BeiGene: Research Funding; Loxo Oncology: Research Funding; VelosBio: Research Funding.

Abstract 370: The role of DLX1 as a biomarker and novel target in poor prognostic prostate cancer

Abstract Introduction: Previous work from our lab has identified a molecularly distinct subgroup of primary prostate cancers with biology similar to metastatic prostate cancers. These “met-like” cancers can be identified by a 70 gene classifier and are statistically more likely to result in distant metastases than their “non-met like” counterparts. This study aimed to identify exploitable biology common to both “met-like” primary tumours and metastatic prostate cancer. Experimental procedures: Differential gene expression and Ingenuity pathway analysis (IPA) was used to identify nodal genes upregulated in both “met-like” primary prostate cancers and metastatic prostate cancers. siRNA screening was performed on 40 nodal genes in a panel of normal, primary and metastatic prostate cancers. Cell viability was assessed using cell titer-glo luminescent Assay. Relative levels of apoptosis were assessed using PARP, caspase-8 and caspase-3 cleavage Western Blots. siRNA mediated knockdowns were confirmed by Western Blot and rtPCR. Results: We have identified upregulation of the homeobox transcription factor DLX1 in “met-like” primary prostate cancers and metastatic prostate cancers. High levels of DLX1 expression were found to be independently predicative of biochemical recurrence and metastatic disease in primary prostate cancers. DLX1 knockdown resulted in significantly decreased cell viability in primary and metastatic prostate cancer cell lines with minimal reduction of viability in normal prostate cells. Additionally DLX1 knockdown was shown to result in increased PARP, caspase-8 and caspase-3 cleavage providing evidence of apoptotic cell death. Furthermore knockdown of DLX1 resulted in significantly increased transcript levels of the pro-apoptotic BH3 protein BIK, suggesting its involvement in the observed apoptotic cell death. Conclusion: DLX1 has previously been identified as a marker of prostate cancer metastasis with increased expression being observed in both primary and metastatic prostate cancers. However we have observed increased DLX1 expression in a subset of primary prostate cancers that developed metastatic diseased compared to primary tumors that did not metastasise. The elucidation of apoptotic mechanisms following DLX1 knockdown may uncover potential exploitable biology that may be used for the treatment of prostate cancer. Citation Format: Nicholas Forsythe, Cathal McKinney, Nuala McCabe, Richard D. Kennedy. The role of DLX1 as a biomarker and novel target in poor prognostic prostate cancer [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 370.

Abstract 780: High expression of miR-155 promotes prostate cancer aggressiveness in African-Americans compared to Caucasians

Abstract Background: African-Americans have higher risk for developing prostate cancer and when diagnosed, the cancer is more aggressive and African-Americans are more than twice as likely to die of the disease compared to Caucasians. To clarify the mechanisms involved in this disparity, we analyzed the role of miR-155 in African-American and Caucasian prostate cancer tissues and cell lines. Materials and Methods: Human tissue samples from African-Americans and Caucasians clinical FFPE (Formaldehyde Fixed Paraffin Embedded) were used to analyzed miR-155 expression by Real Time PCR. We selected prostate cancer cell lines from Caucasians (DU-145, LNCaP, PC3), African-American (E006AA-hT) and normal epithelial cell line (PWR-1E) which express different levels of miR-155, to mimic the tissue samples and help identify the mechanisms related to racial disparity. We knocked down miR-155 in cells lines and performed cell viability assays using a CellTiter-Glo luminescent assay. For migration analysis, miR-155 knockdown cells were seeded in chambers and we measured the capacity of cell motility towards a chemo-attractant. To identify miR-155 mediated downstream regulators, three target prediction algorithms (miRDB, Targetscan and miRecords) were used. Results: We found miR-155 expression to be higher in African-American prostate cancer tissues compared to Caucasian patients with localized disease. Also, expression of miR-155 in African-American cell line, E006AA-hT, was significantly higher compared to Caucasian cell lines, DU-145, LNCaP and PC3. To determine the role of miR-155 in the differences between African-Americans and Caucasians, miR-155 was knocked down in E006AA-hT and DU-145 cells. miR-155 knockdown in E006AA-hT cells caused a decrease in cell viability compared with negative control, while there was no difference in DU-145 cells. We observed inhibition of migration E006AA-hT miR-155 knockdown cells but not on DU-145 miR-155 knockdown cells, suggesting that miR-155 knockdown have the more potent effect on African-American cell line. We analyzed three target prediction algorithms and found that four genes overlapped, SPI1, JARID2, ETS1 and CEBPB that may play a pivotal role in the treatment of aggressive African-American prostate cancers. Conclusion: We conclude that high levels of miR-155 is associated with prostate cancer aggressiveness in African-Americans. Citation Format: Marisa Shiina, Yutaka Hashimoto, Priyanka Kulkarni, Pritha Dasgupta, Varahram Shahryari, Guoren Deng, Divya Bhagirath, Laura Tabatabai, Sharanjot Saini, Shahana Majid, Soichiro Yamamura, Yuichiro Tanaka, Rajvir Dahiya. High expression of miR-155 promotes prostate cancer aggressiveness in African-Americans compared to Caucasians [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 780.

Urolithin A induces prostate cancer cell death in p53-dependent and in p53-independent manner.

Pomegranate and walnuts are widely consumed dietary sources and contain several bioactive compounds, including the ellagitannins (ETs). ETs are polyphenols that are metabolized in the gut microbiota to urolithin A (UA). p53 is a tumor suppressor that lost its activity through MDM2 activation in about half cancers. The purpose of this study was to investigate the influence of UA on the p53-MDM2 interaction pathway in prostate cancer cell lines. Three human prostate cancer cell lines were used that harbor different p53 genotypes; LNCaP (p53+/+), 22RV1(p53-/+) and PC3 (p53-/-). Cell viability was determined by CellTiter-Glo Luminescent assay. Apoptosis was confirmed by measuring annexin V by flow cytometry. The expression of p53, its target proteins, and apoptotic markers were measured by western blotting. Real-time qPCR was used to measure the gene expression of p21, a main target gene of p53. Co-immunoprecipitation-immunoblotting was used to assess the inhibition of interactions between p53 and MDM2 and to assess the effect of UA on MDM2-mediated p53 polyubiquitination. We found UA inhibited CaP cells' viability and induced apoptosis. For 22RV1 and LNCaP, we found UA increased p53 protein expression and its main target protein, p21, and MDM2, forming an autoregulatory feedback loop. In addition, UA increased the p53 proapoptotic proteins PUMA and NOXA. Moreover, UA inhibited the interaction between p53 and MDM2 and inhibited MDM2-mediated p53 polyubiquitination. UA downregulated MDM2 and XIAP protein expression in PC3 cells and upregulated p21 and p14ARF in a p53-independent manner. The influencing of UA on p53-MDM2 pathway may partly contribute to its anticancer effect.

Identification of the Raf kinase inhibitor TAK-632 and its analogues as potent inhibitors of necroptosis by targeting RIPK1 and RIPK3.

Necroptosis is a form of programmed, caspase-independent, cell death, mediated by receptor-interacting protein kinases, RIPK1 and RIPK3, and the mixed lineage kinase domain-like (MLKL). Necroptosis contributes to the pathophysiology of various inflammatory, infectious, and degenerative diseases. Thus, identification of low MW inhibitors for necroptosis has broad therapeutic relevance. Here, we identified that the pan-Raf inhibitor TAK-632 was also an inhibitor of necroptosis. We have further generated a more selective, highly potent analogue of TAK-632 by targeting RIPK1 and RIPK3. Cell viability was measured by MTT, propidium staining, or CellTiter-Glo luminescent assays. Effects of TAK-632 on necroptosis signalling pathways were investigated by western blotting, immunoprecipitation, and in vitro kinase assays. Downstream targets of TAK-632 were identified by a drug affinity responsive target stability assay and a pull-down assay with biotinylated TAK-632. A mouse model of TNF-α-induced systemic inflammatory response syndrome (SIRS) was further used to explore the role of TAK-632 in protecting against necroptosis-associated inflammation in vivo. TAK-632 protected against necroptosis in human and mouse cells but did not protect cells from apoptosis. TAK-632 directly bound with RIPK1 and RIPK3 to inhibit kinase activities of both enzymes. In vivo, TAK-632 alleviated TNF-induced SIRS. Furthermore, we performed a structure-activity relationship analysis of TAK-632 analogues and generated SZM594, a highly potent inhibitor of RIPK1/3. TAK-632 is an inhibitor of necroptosis and represents a new lead compound in the development of highly potent inhibitors of RIPK1 and RIPK3.

The HACE1-NRF2 Axis a Novel Target in Acute Myeloid Leukemia

Acute Myeloid Leukemia (AML) is a genetically heterogenous disease characterized by clonal expansion of immature myeloid progenitors cells in the bone marrow (BM). Despite this genetic heterogeneity, AML patients share Leukemia associated oncogenes such as NF-E2-related factor 2 (Nrf2) (Rushworth SA et al.). NRF2 is a transcription factor that activates genes with antioxidant response elements (ARE)-containing promoters and protects cancer cells from apoptosis. Inhibition of NRF2 or antioxidant defense increases the level of Radical Oxygen Species (ROS), leading to tumor supression (Chio IIC et al.). Recently, the E3 Ubiquitin-Protein Ligase HACE1, a tumor suppressor in solid tumors, was demonstrated to promote the expression of NRF2 in Huntigton disease (Rotblat B et al.). Thus, we hypothesized a role for HACE1 as an oncogenic factor acting through NRF2 activation in myeloid malignancies and provide first data supporting the HACE1-NRF2 axis to be a novel target in acute myeloid leukemias.Material and methodsThe mRNA expression data from AML patients (296 samples) vs normal Hematopoietic Stem Cells (HSC) (6 samples) were exported from the bloodSpot database. HACE1 mRNA and protein expression was measured by q-RT-PCR and western blot in 12 commercially available Myeloid Malignancies cell lines. The HACE1 inducible knock down (KD) was carried out by Sleeping Beauty Transposon system in U937 and NOMO-1 cell lines. The cell viability was analyzed by Cell Titer Glo Luminescent assay. Apoptosis was measured by Annexin V (AV)/Propidium Iodide (PI) assay.Results and discussionHACE1 mRNA is downregulated in AML patients compared to HSC (***p<0.001, Bloodspot database). However mRNA and HACE1 protein expression do not correlate in AML cell lines, suggesting post translational modifications. High HACE1 protein expression was observed in most AML cell lines. HACE1 KD reduced drastically the cell viability of U937 cells through caspase activation and NRF2 degradation. However, no effect on cell viability was observed in NOMO-1 cells. Recently, non-programmed cell death necroptosis induction has been described by TNFR1 activation in HACE1 knock out Mouse Embrionic Fibroblast cells (Tortola L et al.). In line with this study, we observed that TNF induces strong cell death in HACE1 KD NOMO-1 cells within 48 hours.In addition HACE1 KD promotes autophagy through p62 degradation (late autophagy marker) in U937 cells. Autophagy has recently been described to contribute to the differentiation and death of AML cells, and to the promotion of immunostimulatory signals activating immune responses against cancer cells (Chen L et al.; Pietrocola F et al.). Thus HACE1 might be a potential target to induce autophagy, providing a novel therapeutical target in the treatment of myeloid malignancies.Finally, HACE1 KD in our hands promoted sensitization of U937 and NOMO-1 cells to cytatarabine, the backbone therapy in AML patients. This treatment promotes HACE1 protein expression at 24 and 48 hours in NOMO-1 cells, which may explain the better response rates of HACE1 KD cells to cytarabine.Taken together, we provide first evidence of HACE1 being a novel oncogene in AML and that the HACE1-NRF2 axis is a promising target in the treatment of Acute Myeloid Leukemias. DisclosuresHaferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

P2.13-21 MET Addiction Can be Circumvented Through EGFR Inhibition Via AXL in MET-Amplified Primary Resistant EGFR-Mutant NSCLCX.

Primary resistance to EGFR-TKI is observed in approximately 10% of patients with activating EGFR mutations. In a patient harboring L858R mutation and high cMET amplification (MET copy number 7.3, CEP7 ratio 3.4) who progressed after just 4 weeks of erlotinib (ERL), significant tumor regression was achieved with MET inhibition alone (Crizotinib, CRZ). We confirmed this phenotype in the corresponding patient-derived cell line model (A482) and identified EGFR-AXL interaction as a mechanism that can circumvent clonal cMET addiction. We generated patient-derived cell lines from the patient’s baseline neck excision biopsy (A482) and evaluated the effect of mono and combination therapy (ERL, CRZ, ERL-CRZ) on A482, including viability (CellTiter-Glo Luminescent Assay, Promega), colony forming (Crystal Violet Assay), downstream signaling (Western blots) and adaptive pathways (Human Phosho-Receptor Tyrosine Kinase Array Kit, RandD systems). AXL was identified as a key mediator of resistance and subsequently subjected to further functional validation. Finally, we examined the prevalence of this clinical phenomenon in a retrospective series of MET amplified EGFR-mutant NSCLC. Cell viability assays confirmed the patient-derived cell line to be more sensitive to CRZ as compared to ERL alone or with combination CRZ-ERL. Upregulation of AXL, RET and FGFR3 expression were identified as adaptive changes 24 hours upon ERL exposure. A targeted pharmacologic screen revealed A482 to be exquisitely sensitive to combination EGFR and AXL inhibition. Immunoprecipitation revealed a direct interaction between EGFR and AXL, which upon treatment with ERL resulted in attenuation of cMET addiction. Co-existing cMET amplification with demonstrated suboptimal response to EGFR TKI was found in 3% of EGFR-mutant NSCLC in a retrospective series of patients. Targeting the EGFR-AXL axis through EGFR inhibition alone can lead to paradoxical MET pathway activation, while the combination of EGFR and AXL inhibition can circumvent downstream signaling in MET amplified EGFR-mutant NSCLC. AXL expression levels can potentially identify patients in whom combination or monotherapy with MET inhibitors may be most beneficial. Our data highlights the challenge in interpreting genomic alterations alone; and how cellular context can lead to differential sensitivities to EGFR and MET inhibitors alone and/or in combination in MET amplified EGFR-mutant NSCLC.

Abstract 471: High expression of miR-182 promotes prostate cancer aggressiveness in African-Americans compared to Caucasians

Abstract Background: African-Americans (AfA) have higher risk for developing prostate cancer and when diagnosed, the cancer is more aggressive with worse survival compared to Caucasians (CA). To clarify the mechanisms involved in this disparity, we analyzed the role of miR-182 in AfA and CA prostate cancer tissues and cells. Materials and Methods: We analyzed miR-182 expression in AfA and CA prostate cancer tissue samples by Real Time PCR. We selected two cell lines, DU-145 (CA) and MDA-PCa-2b (AfA), which express different levels of miR-182, to mimic the tissue samples and help identify the mechanisms related to racial disparity. We generated lentivirus stable miR-182 knockdown cells lines and performed cell viability assays using a CellTiter-Glo luminescent assay. For cell cycle analysis, cells were stained with PI/RNase staining buffer and analyzed for DNA content by BD FACSVerse. Cancer pathway-focused gene expression profiling was done using a human RT2 Profiler Cancer Pathway Finder and Oncogenes and Tumor Suppressor Genes PCR Array. Results: We found miR-182 expression to be higher in AfA prostate cancer tissues compared to CA patients with localized disease. Also, expression of miR-182 in AfA cell line, MDA-PCa-2b, was significantly higher compared to CA cell line, DU-145. To determine the role of miR-182 in the differences between AfA and CA, miR-182 was knocked down in MDA-PCa-2b and DU- 145 cells. miR-182 knockdown in MDA-PCa-2b cells effectively inhibited cell migration, invasion and colony formation compared to control cells, while there was no difference in DU-145 cells. Knockdown of miR-182 caused a decrease in MDA-PCa-2b cell viability compared with negative control. In addition, the cell cycle profile showed an increase in the G1 phase of MDA-PCa-2b cells (control 7.3% compared to miR-182 knockdown cells 18.6%), whereas no change was observed in DU-145 cells. Similar to these results, wound healing was significantly slower in the miR-182 knockdown MDA-PCa-2b cells compared to controls. PCR array analysis was performed to determine the molecular effects of miR-182 knockdown in MDA-PCa-2b and DU-145 cells. We found from our PCR array data some potential targets genes regulated by miR-182. Conclusion: We conclude that high levels of miR-182 is associated with prostate cancer aggressiveness in African-Americans. Citation Format: Marisa Shiina, Yutaka Hashimoto, Guoren Deng, Varahram Shahryari, Majid Shahana, Soichiro Yamamura, Priyanka Kulkarni, Pritha Dasgupta, Divya Bhagirath, Sharanjot Sharan, Yuichiro Tanaka, Rajvir Dahiya. High expression of miR-182 promotes prostate cancer aggressiveness in African-Americans compared to Caucasians [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 471.

Importance of CaMKII activation in the regulation of adiposomes and ATP concentration in rat skeletal muscle

Lipid droplets, also referred to as adiposomes, are intracellular organelles that are found in most cells. They store oil-based reserves of metabolic energy and components of membrane lipids. Adenosine triphosphate (ATP), produced in the mitochondria, is used to supply energy to the cells. Both lipid droplets and ATP play fundamental roles in energy metabolism, as such critical in the pathogenesis of metabolic diseases like diabetes and obesity. Therefore, understanding their regulation can be a key pathway to understanding the aetiology of obesity and diabetes. Predominantly, CaMKII has been linked to the regulation of mitochondrial and glucose transport genes associated with diabetes and obesity. In this study, the role of exercise-induced CaMKII on the regulation of lipid droplets and ATP concentrations in rat skeletal muscle was investigated. Five to six week-old male Wistar rats were used in this study. Transmission Electron Microscopy (TEM) was performed to determine lipid droplet number/size and mitochondria size. ATP concentration was measured using CellTiter-Glo luminescent assay. This study showed that lipid droplet size and number were decreased in exercised rats when compared to the control rats. Furthermore, the results showed an increase in mitochondrial size and the concentration of ATP by exercise due to CaMKII activation. The results indicate that CaMKII activation by exercise could potentially give a new therapeutic approach to the treatment or prevention of metabolic diseases such as diabetes and obesity.

SAHA-induced TRAIL-sensitisation of Multiple Myeloma cells is enhanced in 3D cell culture

BackgroundMultiple Myeloma (MM) is currently incurable despite many novel therapies. Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) is a potential anti-tumour agent although effects as a single agent are limited. In this study, we investigated whether the Histone Deacetylase (HDAC) inhibitor SAHA can enhance TRAIL-induced apoptosis and target TRAIL resistance in both suspension culture, and 3D cell culture as a model of disseminated MM lesions that form in bone. MethodsThe effects of SAHA and/or TRAIL in 6 Multiple Myeloma cell lines were assessed in both suspension cultures and in an Alginate-based 3D cell culture model. The effect of SAHA and/or TRAIL was assessed on apoptosis by assessment of nuclear morphology using Hoechst 33342/Propidium Iodide staining. Viable cell number was assessed by CellTiter-Glo luminescence assay, Caspase-8 and -9 activities were measured by Caspase-Glo™ assay kit. TRAIL-resistant cells were generated by culture of RPMI 8226 and NCI-H929 by acute exposure to TRAIL followed by selection of TRAIL-resistant cells. ResultsTRAIL significantly induced apoptosis in a dose-dependent manner in OPM-2, RPMI 8226, NCI-H929, U266, JJN-3 MM cell lines and ADC-1 plasma cell leukaemia cells. SAHA amplified TRAIL responses in all lines except OPM-2, and enhanced TRAIL responses were both via Caspase-8 and -9. SAHA treatment induced growth inhibition that further increased in the combination treatment with TRAIL in MM cells. The co-treatment of TRAIL and SAHA reduced viable cell numbers all cell lines. TRAIL responses were further potentiated by SAHA in 3D cell culture in NCI-H929, RPMI 8226 and U266 at lower TRAIL + SAHA doses than in suspension culture. However TRAIL responses in cells that had been selected for TRAIL resistance were not further enhanced by SAHA treatment. ConclusionsSAHA is a potent sensitizer of TRAIL responses in both TRAIL sensitive and resistant cell lines, in both suspension and 3D culture, however SAHA did not sensitise TRAIL-sensitive cell populations that had been selected for TRAIL-resistance from initially TRAIL-sensitive populations. SAHA may increase TRAIL sensitivity in insensitive cells, but not in cells that have specifically been selected for acquired TRAIL-resistance.

Abstract 2073: A systematic investigation of the effect of scheduling of targeted combination therapies on response and dynamics of relapse in triple negative breast cancer cells

Abstract Cancer treatment typically involves administration of combination of targeted therapies, but initial response is often followed by disease relapse. The efficacy of a treatment regimen depends on the complex interplay between cancer growth dynamics, drug specificity and kinetics, treatment dose and its scheduling. In standard high-throughput drug screening assays, cells are treated with a single drug cocktail bolus and cell viability is assessed after 2-3 days, thus not considering treatment interactions and long-term effects. Recently we have reported a promising synergistic combination of crizotinib (ALK/MET inhibitor) and ABT-263 (BCL2/BCL-XL inhibitor) against triple negative breast cancer cells. To understand the effect of the sequence and combination doses of crizotnib and ABT-263, we designed a comprehensive experimental plan that involved a total of 567 treatment regimens by varying treatment duration with the first drug (1, 2, or 3 days), followed by drug withdrawal and recovery period (2, 5 or 10 days) and then by a second cycle of treatment and recovery periods over a 26-day period. Cell viability was assessed by the CellTiter-Glo luminescence assay. Interestingly, ABT-263 alone induced higher cytotoxicity than an equivalent dose of crizotinib, but the remaining viable cells recovered much faster after ABT-263 withdrawal than cells after crizotinib withdrawal. Furthermore, cells exposed to higher doses of ABT-263 eventually become less sensitive to crizotinib. Among sequential regimens, crizotinib followed by ABT-263 was significantly more effective than ABT-263 followed by crizotinib, and combinations that included lower doses of ABT-263 were most effective. Taken together, our results show a significant interaction between the two targeted therapies, and suggest that it may be possible to select treatment scheduling that can delay drug resistance and tumor relapse in vivo. Note: This abstract was not presented at the meeting. Citation Format: Gauri A. Patwardhan, Vikram B. Wali, Lajos Pusztai, Christos Hatzis. A systematic investigation of the effect of scheduling of targeted combination therapies on response and dynamics of relapse in triple negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2073. doi:10.1158/1538-7445.AM2017-2073

Abstract 1533: Transcriptional inhibition of brachyury in chordoma is associated with adoption of quiescent phenotype

Abstract BACKGROUND: Brachyury is a mesoderm specification transcription factor involved in notochord development and overexpressed in a variety of cancers, including chordoma. High levels of brachyury protein expression in cancers is associated with a poor prognosis in part due to its role in mediating epithelial-mesenchymal transition (EMT). TG02 is a multikinase inhibitor that targets transcriptional regulation of cyclin-dependent kinases (CDKs). Because chordoma is characterized by a relative paucity of genomic mutations and largely driven by the super-enhancer activity of brachyury expression, we investigated the downstream effect of a transcriptional inhibitor, TG02, in chordomas. METHODS: Established chordoma cell lines, UCH-1 and UM-Chor1, were exposed to increasing concentrations of TG02 to determine effect on brachyury protein expression. qPCR was used to analyze brachyury mRNA expression as well as the mesenchymal proteins, vimentin and fibronectin, typically associated with brachyury expression in tumor cells. Cell migration was evaluated using wound healing assay. CellTiterGlo Luminescence Assay was used to quantify cell viability. RESULTS: TG02 down-regulated protein expression of brachyury in a dose-dependent manner. Attenuation of brachyury expression was seen within 4 hours and persisted for 5 days upon single exposure to a clinically relevant concentration of TG02. Brachyury downregulation did not affect cell count or viability, and was associated with a quiescent phenotype, including impaired migration. Expression of vimentin and fibronectin, both associated with EMT, was also suppressed within 4 hours of TG02 treatment and persisted for 24 hours. CONCLUSIONS: Inhibition of brachyury expression and its downstream signaling is associated with quiescent behavior of chordoma cells. Pharmacologically induced transcriptional targeting of brachyury using TG02, a potent CDK9 inhibitor, represents a potential therapeutic strategy. Citation Format: Ashlee N. Seldomridge, Jinkyu Jung, Heather M. Sonnemann, Amber Giles, Kristan Meetze, Mark R. Gilbert, Claudia M. Palena, Deric M. Park. Transcriptional inhibition of brachyury in chordoma is associated with adoption of quiescent phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1533. doi:10.1158/1538-7445.AM2017-1533

Evaluation of an Undocumented Polyherbal (Faradin®) Used for the Treatment of Sickle Cell Disease in West Africa. Part I: Phytochemistry and Ex-vivo Anti-sickling Study

Background: An undocumented complementary and alternative medicine (CAM)- Faradin® - was screened for its phytochemicals, anti-sickling effect using a clinical protocol, and toxicity. Faradin is a polyherbal made up of Zanthoxylum zanthoxyloides, Alnus glutinosa and Alchornea cordofolia. Methods: The polyherbal and the individual components (coded V, M, and F) were separately screened for phytochemicals such as alkaloids, phenols, flavonoids, sterols and coumarins, using standard tests. Institutional Review Board approved clinicalprotocolinvolving4 female de-identified sickle cell patients was used for the ex-vivo anti-sickling evaluation. The negative control was phosphate-buffered saline (PBS)-washed erythrocytes treated with 2% sodium metabisulfite (SMB) to cause a hypoxic state and result in HBSS polymerization or sickling. As positive control, 2% w/v p-hydroxy benzoic acid (PHBA) solution was used. The anti-sickling effect was studied by incubating the washed erythrocytes in various concentrations of Faradin - Faradin: water v/v ratios (2.5:1 – 10:1) - for 4 hours followed by further incubation with SMB for 1½ hrs. The respective samples were examined under an optical microscope and the number of sickled cells counted. Cell viability to Faradin was also done using human primary hepatocytes (HPP) and Cell Titer-Glo Luminescent assay. Results: Faradin tested positive for flavonoids, phenols, coumarins, alkaloids and antioxidants. The V component tested positive for coumarins, alkaloids and antioxidants. The M component was positive for phenols, alkaloids and antioxidants while the F component tested positive for flavonoids, phenols and antioxidants. For the anti-sickling study, the negative control (SMB treated erythrocytes) showed 20-28% increase in sickling relative to the PBS-washed. The positive control caused a reversal of sickling by decreasing the percent sickled cells from 21% to 8%. There was a dose-dependent decrease in percent sickled cells; the highest dose reduced the percent sickled cells from 21% to 2%. The activity was likely due to the phenols, polyphenols, flavonoids and antioxidants in the CAM. Cell viability of Faradin® was greater than 85%. Conclusions: Thecombined phytochemicals in the polyherbal contributed to the reversal of sickling that is similar to the positive control. Faradin has a high potential for clinical effectiveness in the management of SCD.

Synthetic lethality in chronic lymphocytic leukaemia with DNA damage response defects by targeting the ATR pathway

BackgroundDNA damage response (DDR) defects, particularly TP53 and biallelic ataxia telangiectasia mutated (ATM) aberrations, are associated with genomic instability, clonal evolution, and chemoresistance in chronic lymphocytic leukaemia (CLL). Therapies capable of providing long-term disease control in CLL patients with DDR defects are lacking. Using AZD6738, a novel ATR inhibitor, we investigated ATR pathway inhibition as a synthetically lethal strategy for targeting CLL cells with these defects. MethodsThe effect of AZD6738 was assessed by western blotting and immunofluorescence of key DDR proteins. Cytotoxicity was assessed by CellTiter-Gloluminescence assay (Promega, Madison, WI, USA) and by propidium iodide exclusion. Primary CLL cells with biallelic TP53 or ATM inactivation were xenotransplanted into NOD/Shi-scid/IL-2Rγ mice. After treatment with AZD6738 or vehicle, tumour load was measured by flow cytometric analysis of infiltrated spleens, and subclonal composition by fluorescence in-situ hybridisation for 17p(TP53) or 11q(ATM) deletion. FindingsAZD6738 provided potent and specific inhibition of ATR signalling with compensatory activation of ATM/p53 pathway in cycling CLL cells in the presence of genotoxic stress. In p53 or ATM defective cells, AZD6738 treatment resulted in replication fork stalls and accumulation of unrepaired DNA damage, as evidenced by γH2AX and 53BP1 foci formation, which was carried through into mitosis, resulting in cell death by mitotic catastrophe. AZD6738 displayed selective cytotoxicity towards ATM or p53 deficient CLL cells, and was highly synergistic in combination with cytotoxic chemotherapy. This finding was confirmed in primary xenograft models of DDR-defective CLL, where treatment with AZD6738 resulted in decreased tumour load and selective reduction of CLL subclones with ATM or TP53 alterations. InterpretationWe have provided mechanistic insight and demonstrated in-vitro and in-vivo efficacy of a novel therapeutic approach that specifically targets p53-null or ATM-null CLL cells. Such an approach can potentially help to avert clonal evolution, a major cause of therapeutic resistance and disease relapse. FundingLeukaemia & Lymphoma Research.

Abstract B54: Difluoromethylornithine treatment affects the LIN28/Let-7 axis resulting in reduced glycolytic metabolism in neuroblastoma

Abstract Background: Overexpression of LIN28 correlates with poor outcome in neuroblastoma (NB). The LIN28/Let-7 axis affects many cellular processes including cell differentiation and glycolytic metabolism. MYCN overexpression correlates with decreased Let-7 miRNA which results in an increase in LIN28 protein. Recent studies have shown that ODC inhibition decreases LIN28 levels. We propose that therapy targeting ODC will affect the LIN28/Let-7 axis, thus suppressing the glycolytic metabolic activity of NB tumor cells. We also propose that cells overexpressing LIN28 will have greater sensitivity to Difluoromethylornithine (DFMO) treatment which inhibits ODC and decreases cellular polyamines. Methods: Two MYCN high-expression cell lines, BE(2)-C and SMS-KCNR, and one MYCN low-expression cell line, CHLA90, were grown in RPMI-1640 medium with 10% fetal bovine serum for 24 hours prior to treatment with DFMO. Cells were treated with 5 mM or 10 mM DFMO from 48-96 hours followed by cell viability assay, ATP per cell, and western blot analysis and 6 hours for qPCR analysis. Cell viability was measured using Calcein AM fluorescence assay. IC50 values were calculated using GraphPad software. ATP per cell was measured by combining Cell Titer GLO luminescence assay with CyQuant fluorescence assay. Western blot analysis was used to measure LIN28B and MYCN protein levels. TaqMan PCR reagents were used to measure Let-7 miRNA levels using qPCR analysis. SMS-KCNR cells were injected subcutaneously into nude mice for in vivo xenograft studies. Mice were drugged with 2% DFMO in drinking water when tumors reached 200mm3. Tumor volumes were measured using both caliper and micro-CT, and tumor glycolytic metabolism was determined by Maximum Standard Uptake Value (SUVMax) in the tumors through longitudinal 18F-FDG micro PET/CT scans on days 19 and 32. Results: treatment with high and low dose DFMO resulted in decreased LIN28B protein levels in all three cell lines at 48, 72, and 96 hours timepoints. MYCN protein levels decreased in MYCN high-expression cell lines, BE(2)-C and SMS-KCNR, with high and low dose DFMO treatments, but did not change in MYCN low-expression cell line CHLA90. Let-7 miRNA levels were increased in both MYCN high-expression cell lines after 6 hours of high dose DFMO treatment and no change was seen in CHLA90 cells. Sensitivity to DFMO correlated with LIN28B expression levels in all three cell lines (BE(2)-C&amp;gt;SMS-KCNR&amp;gt;CHLA90). BE(2)-C cells were most sensitive to DFMO treatment with an IC50 of 3.01 mM followed by SMS-KCNR cells (10.61 mM), and CHLA90 cells, which showed resistance (25.76 mM). In addition, ATP per cell levels were most significantly reduced in BE(2)-C cells after treatment with DFMO followed by SMS-KCNR and CHLA90 cells. In vivo 18F-FDG PET/CT studies showed decreased SUVMax in the DFMO treatment group indicating reduced glycolytic metabolism. Conclusions: Treatment with DFMO reverses the LIN28/Let-7 axis with a decrease in LIN28B protein expression and an increase in Let-7 miRNA expression. This axis has been shown to play a role in metabolic activity of cells. Decreased metabolic activity and decreased tumor growth is seen in NB cells both in vitro and in vivo following DFMO treatment. NB cell lines with higher levels of LIN28B and MYCN expression are more sensitive to DFMO treatment. These studies suggest that targeting of the LIN28/Let-7 pathway may offer a new method of treating neuroblastoma. Citation Format: Ann Kendzicky, Maria Rich, Anderson Peck, Zhao Ping, Elizabeth VanSickle, Heather McClung, Anthony Chang, Giselle Sholler. Difluoromethylornithine treatment affects the LIN28/Let-7 axis resulting in reduced glycolytic metabolism in neuroblastoma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B54.

Effect of Dentin Conditioning with Intracanal Medicaments on Survival of Stem Cells of Apical Papilla

IntroductionRegenerative endodontics is a valuable treatment modality for immature teeth with pulpal necrosis. A common feature in regenerative cases is the use of intracanal medicaments. Although these medicaments are chosen because of their antibacterial properties, their enduring effect on dentin (conditioning) and the subsequent impact on stem cell survival has never been evaluated. In this study, we hypothesized that triple antibiotic paste (TAP), double antibiotic paste (DAP), or Ca(OH)2 has an indirect adverse effect on the survival of stem cells of apical papilla (SCAP) by dentin conditioning. MethodsHuman dentin disks were created with a standardized root canal diameter of 3.2 mm. The disks were then exposed to either TAP or DAP (at concentrations of 1 mg/mL or 1000 mg/mL), Ca(OH)2 (Ultracal), or Hank's balanced salt solution for 7 or 28 days. Next, the medicaments were removed with copious irrigation, followed by placement of SCAP in a Matrigel scaffold in the lumen of the disks. The bioengineered constructs were cultured for 7 days, followed by determination of cellular viability by using the CellTiter-Glo luminescence assay. Data were analyzed using 1-way analysis of variance with Bonferroni post hoc test. ResultsExposure of dentin to TAP or DAP at 1000 mg/mL resulted in no viable SCAP, whereas the use of these medicaments at 1 mg/mL had no adverse effect on cell viability. In contrast, Ca(OH)2 treatment significantly increased SCAP survival and proliferation when compared with the control group. ConclusionsDentin conditioning with TAP and DAP at commonly used clinical concentration (approximately 1000 mg/mL) alters dentin in such a way as to prevent SCAP survival. This lethal indirect effect of both TAP and DAP can be largely avoided if these medicaments are used at the 1 mg/mL concentration. Conversely, dentin conditioning with Ca(OH)2 promotes SCAP survival and proliferation.

Deletions In TBL1XR1 Results In Glucocorticoid Resistance By Decreasing Glucocorticoid Signaling In Childhood B-Lymphoblastic Leukemia

IntroductionThe prognosis for children with acute lymphoblastic leukemia who relapse is poor and discovery of the underlying mechanisms that lead to drug resistance is a top priority. Relapsed blasts have intrinsic chemoresistance compared to diagnosis blasts especially to glucocorticoids (Klumper et. al, 1995). Furthermore, resistance to glucocorticoids is associated with a poor prognosis in childhood ALL (Dördelmann M et. al, Blood 1999, Schmiegelow K et. al, Leukemia 2001, Tissing WJ et. al, Leukemia 2003). We have previously identified recurrent deletions with concordant decreased gene expression in TBL1XR1 in 10.7% of patients at relapse (Hogan et. al, 2011). TBL1XR1 codes for the TBLR1 protein which is responsible for the dismissal and degradation of nuclear corepressor (N-CoR) complex proteins including N-CoR1, SMRT, GPS2, and histone deacetylases (HDAC) (Perissi V et. al, Cell 2004). We hypothesized that TBL1XR1 deletions may result in resistance to glucocorticoid agonist, prednisolone through up-regulation of N-CoR complex proteins. MethodsB-precursor ALL cell lines Reh, and RS4;11 were transduced with lentiviral constructs containing control and TBL1XR1 targeting shRNAs. Knockdown was confirmed by RT-PCR and western blotting. Stable cell lines were treated with prednisolone, doxorubicin, 6-thioguanine, or etoposide for 24-48 hours. Cell viability and apoptosis were measured by cell titer glo luminescence assay (promega) and annexin V-PE and 7-Amino-actinomycin D (7AAD) staining (Annexin V-PE Apoptosis Detection Kit, BD Pharmingen, San Diego, CA, USA) respectively. To determine changes in global gene expression by TBL1XR1 knockdown, stable Reh cell lines were treated with prednisolone or vehicle for 8 hours and then collected for RNA extraction (Qiagen, RNeasy mini kit) and microarray analysis. Microarray data was validated by RT-PCR. To elucidate the mechanism of resistance we performed small-scale biochemical fractionation and chromatin immunoprecipitation (ChIP) detecting levels of glucocorticoid receptor (GR), TBLR1, N-CoR1, and HDAC3 residing on the chromatin as well as gene specific glucocorticoid response elements (GREs). ResultsIn this study, we demonstrate that knockdown of TBL1XR1 results in resistance to the glucocorticoid agonist prednisolone but not other classes of chemotherapeutic agents. We discovered that 51 of the 117 genes induced by prednisolone in control cells had decreased induction of at least 50%. We validated a subset of prednisolone induced genes including, GILZ, TXNIP, ZEB1, ST6GALNAC3, IL21R, and CCPG1 by RT-PCR. To explore the mechanism of TBL1XR1 mediated decrease in GR signaling we determined the effect of TBL1XR1 depletion of GR recruitment to total bulk chromatin. In TBL1XR1 knockdown cells, no GR was detected in the chromatin associated fractions in vehicle or prednisolone treatment conditions, despite similar levels of GR protein between control and TBL1XR1 knock down lines. We show that the decreased GR levels is associated with an increased level of NCoR1 detected in the chromatin fraction of TBLR1 depleted cells; however no change in HDAC3 levels were observed. We confirmed these results by interrogating the gene regulatory regions of GILZ and TXNIP by ChIP. In TBL1XR1 depleted lines a decrease in GR occupancy in prednisolone stimulated cells was observed compared to control lines. We also observed increased levels of N-CoR1, and HDAC3 occupying these GREs. To interrogate the functional relationship between increased NCoR1 and HDAC3 levels on the gene regulatory region as a result of TBL1XR1 knockdown we depleted NCoR1 or inhibited HDAC3 using a pan HDAC inhibitor SAHA and examined the impact of prednisolone treatment on cell viability and induction of GILZ. We found that upon NCoR1 depletion or HDAC inhibition, TBL1XR1 knockdown line was no longer resistant to prednisolone and the induction of GILZ was restored.ConclusionsReduction of TBL1XR1 results in prednisolone resistance in ALL by decreasing GR occupancy on gene regulatory regions through the upregulation of the NCoR co-repressor complex at these sites. Our work and others has provided insight into the importance of transcription regulatory complexes in steroid resistance in ALL (and perhaps other malignancies) as well as opportunities for novel therapeutic approaches. Disclosures:No relevant conflicts of interest to declare.

Inhibition Of The Wnt Pathway Leads To Improved Chemosensitivity In Pediatric Acute Lymphoblastic Leukemia

Abstract Introduction While childhood acute lymphoblastic leukemia (ALL) is highly curable, up to 20% of children will relapse, with dismal prognosis, warranting the need for novel therapies. Previously, using an integrated genomic approach on matched diagnosis-relapse samples, we identified overactivation of the Wnt pathway as a mechanism of disease recurrence at relapse (Hogan et al, Blood 2011). Aberrant Wnt signaling has been linked to cancers of the liver, colon, breast, skin and more recently hematologic malignancies. To validate our findings and determine if Wnt inhibition could restore chemosensitivity in relapsed ALL, we sought to examine directly whether Wnt is activated at relapse in paired samples (examining expression of activated b-catenin and its downstream target Survivin (BIRC5) using multiparameter phosphoflow cytometry) and tested the efficacy of a recently developed small molecule Wnt inhibitor, iCRT14, that specifically interferes with the b-catenin-TCF interaction (Gonzalves et al, PNAS 2011), in ALL cell lines and patient samples. Methods B and T-ALL cell lines were treated with iCRT14 and the expression of target genes were determined by quantitative RT-PCR.10 paired diagnosis-relapse patient samples obtained from the Children’s Oncology Group were washed, fixed and stained simultaneously with caspase 3, CD10, activated b-catenin and survivin and the change in expression of activated b-catenin and survivin from diagnosis to relapse was measured by multiparameter phosphoflow cytometry in each patient by gating on the caspase 3 negative, CD10 positive leukemic blasts. To test the effect of Wnt inhibition on chemosensitivity, B-ALL cell lines were pretreated with iCRT14 for 48 hours prior to incubation with traditional chemotherapy for an additional 24 hours. The response to increasing doses of iCRT14 and chemo, alone and in combination, was assessed by cell viability (Cell Titer-Glo Luminescent Assay (Promega)) and apoptosis (FACS analysis with AnnexinV-PE/7AAD staining (BD Bioscience)). Protein levels of apoptotic markers were assessed. Also, 4 newly diagnosed and 4 relapsed patient samples were treated ex vivo with iCRT14 (20 and 30 uM) and prednisolone, alone and in combination. Drug combination results were analyzed using the Calcusyn program which calculates a Combination Index (CI): CI&gt;1.1=antagonism, 0.9-1.1=additive and &lt;0.9=synergy. Results Previously, we reported that treatment of ALL cell lines with iCRT14, downregulated the mRNA expression of the Wnt target genes BIRC5, axin 2, and c-myc (Romanos et al, ASPHO 2012 # 414). Comparison of Mean Fluorescent Intensity of activated b-catenin and survivin in the 10 pairs showed upregulation of activated b-catenin at relapse in 6 of 10 patients. Survivin expression was increased in 6 patients and in 4 patients the upregulation of activated b-catenin and survivin was concordant. iCRT14 pretreatment of cell lines followed by chemotherapy (prednisolone, etoposide, doxorubicin, cytarabine and 6TG) demonstrated additive to synergistic effects on viability. UOCB1 cells showed synergism with all 5 chemotherapy agents (CI=0.1-0.88). Nalm6 cells were very sensitive to iCRT, hence the combination with chemotherapy showed additive to synergistic effects (CI=0.05-1.I). In Reh cells, all agents besides cytarabine showed robust synergism (CI=0.03-0.55). FACS analysis revealed that iCRT14 alone contributed significantly to apoptosis and combination with chemotherapy further increased cell death with &gt;80% apoptosis by hour 72 with the maximal chemotherapy dose in all cell lines. Change in the protein levels of cleaved PARP and cleaved caspase 3 was seen. The 4 diagnosis patients were very sensitive to prednisolone as expected, precluding synergism with iCRT14. The relapsed patient samples were much less sensitive to prednisolone alone (40% decrease in viability in relapsed patients vs 80% in new diagnoses). Interestingly, all the relapsed patients showed enhanced chemosensitivity with Wnt inhibition. 3 out of 4 relapsed patients showed strong synergism (CI=0.03-0.6) with both doses of iCRT14 and 1 patient showed additive to synergistic effects (CI=0.7 and 1). Conclusion Overactivation of the Wnt pathway may lead to chemoresistance in relapsed ALL. Wnt Inhibition restores chemosensitivity and induces apoptosis in ALL cell lines and primary patient samples making it a potential therapeutic approach. Disclosures: No relevant conflicts of interest to declare.

Entinostat, a Novel Histone Deacetylase (HiDAC) Inhibitor Is Active in B-Cell Lymphoma and Enhances the Anti-Tumor Activity of Rituximab, Chemotherapy Agents and Proteasome Inhibitors

Abstract 1649Deacetylases (DACs) are enzymes that remove the acetyl groups from target protein lysines leading to regulation of gene transcription and other cellular processes. Entinostat is a novel and potent class I DAC inhibitor undergoing pre-clinical and clinical testing. We previously demonstrated that entinostat was active against a panel of rituximab-sensitive (RSCL) and –resistant cell lines (RRCL); and enhanced the anti-tumor activity of chemotherapy agents. In the current work, we studied the mechanisms-of-action of entinostat and its effect on rituximab activity and proteasome inhibition. Our results indicate that entinostat potentiates both rituximab and proteasome inhibitor activity in NHL cells through a dual caspase dependent and independent mechanism-of-action. Studies were conducted in RSCL, RRCL and in primary tumor cells isolated from patients with B-cell non-Hodgkin’s lymphoma (n = 43). For studies with a proteasome inhibitor, cells were exposed to escalating doses of entinostat +/− bortezomib of up to 72 hrs. Studies were repeated with or without a pan-caspase inhibitor (Q-VD-OPh, 5uM). Changes in mitochondrial potential and ATP synthesis were determined by alamar blue reduction and cell titer glo luminescent assays, respectively. Flow cytometric analysis was used to determine changes in cell cycle. Protein lysates from entinostat +/− BTZ exposed cells were evaluated for changes in members of Bcl-2 and cell cycle family proteins. Microarray analysis was performed to discern differences in gene expression between RRCL and RSCL after incubation with entinostat. Separately, we studied the effects of entinostat in vitro and in vivo on rituximab-associated complement-mediated cytotoxicity (CMC) or antibody-dependent cellular cytotoxicity (ADCC). NHL cells were exposed to entinostat or DMSO 0.01% for 48hrs and then labeled with 51Cr. Labeled target cells were then exposed to rituximab or isotype control (10mg/ml) and human serum (25%) (CMC) or PBMCs (Effector:Target ratio, 40:1) (ADCC). For in vivo studies, 6–8 week old SCID mice were inoculated with 1′106 Raji cells via tail vein injection and after a period of 72 hours animals were divided into six cohorts: control, entinostat alone at 5mg/kg/dose, entinostat alone at 20mg/kg/dose alone, rituximab single agent at 10mg/kg/dose, rituximab and entinostat at 5mg/kg/dose and rituximab + entinostat at 20mg/kg/dose. Entinostat was administered by gastric lavage daily on days +3–8 and +11–16, and rituximab was administered via tail vein injection on days +3, +8, +11, and +16. Difference in survival between treatment groups was performed by Kaplan-Meier analysis. Entinostat exhibited dose-dependent activity as a single agent against RSCL, RRCL and patient-derived primary lymphoma cells. In vitro exposure of lymphoma cells to entinostat resulted in an increase in G1 and a decrease in S phase. Synergistic activity was observed by combining entinostat with BTZ but not rituximab in vitro. Microarray data demonstrated that p21 was up-regulated after exposure to entinostat. Additionally, we found an upregulation of ICAM2, down-regulation of E2F2 but no changes in CD20 mRNA. Findings were confirmed at the protein level. Caspase inhibition diminished entinostat anti-tumor activity in RSCL but not in RRCL suggesting that entinostat has a dual mechanism-of-action and can induce cell death by caspase-dependent and independent pathways (i.e. cell cycle arrest). Furthermore, In vivo treatment of SCID mice with high dose entinostat in combination with rituximab led to prolongation of the mean survival (87 days, 72–103 95% C.I. P=0.05) compared to rituximab (67 days, 52–82 95% C.I.) entinostat 20 mg/kg (19 days, 19–20 95% C.I.) alone. Our data suggests that entinostat is active against RSCL and RRCL and potentiates the anti-tumor activity of BTZ or rituximab. In addition, entinostat appears to have a dual mechanism of action that supports its clinical development in rituximab-sensitive or resistant lymphomas. Ongoing studies are aimed to further define the molecular events responsible for entinostat mechanisms-of-action and optimize its spectrum of anti-tumor activity. (Research, in part, supported by a NIH grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute). Disclosures:No relevant conflicts of interest to declare.

Entinostat, a Novel Histone Deacetylase (HiDAC) Inhibitor Enhances the Anti-Tumor Activity of Bortezomib (BTZ) in Rituximab-Chemotherapy Sensitive and Resistant Lymphoma Cell Lines,

Abstract 3734Deacetylases (DACs) are enzymes that remove the acetyl groups from target proteins [histones (class I) and non-histone proteins (class II)], leading to regulation of gene transcription and other cellular processes. Entinostat (MS-275) is a novel and potent DAC class I inhibitor undergoing pre-clinical and clinical testing. In order to better characterize the role of DAC inhibitors in the treatment of refractory/resistant (r/r) B-cell lymphoma, we studied the anti-tumor activity of entinostat as a single agent or in combination with the proteasome inhibitor bortezomib (BTZ) against a panel of rituximab-[chemotherapy]-sensitive cell lines (RSCL), rituximab-[chemotherapy]-resistant cell lines (RRCL), and primary lymphoma cells isolated from patients with treatment-naïve or r/r B-cell lymphoma. In addition, we characterized the mechanisms responsible for entinostat’s anti-tumor activity. Non-Hodgkin lymphoma (NHL) cell lines were exposed to escalating doses of entinostat (0.1 to 20uM) +/− BTZ (1–10nM). Changes in mitochondrial potential and ATP synthesis were determined by alamar blue reduction and cell titer glo luminescent assays, respectively. Changes in cell cycle were determined by flow cytometric analysis. Subsequently, protein lysates were isolated from entinostat +/− BTZ exposed cells and changes in members of Bcl-2 and cell cycle family proteins were evaluated by Western blotting. Finally, to characterize entinostat’s mechanisms-of-action, lymphoma cells were exposed to entinostat with or without pan-caspase (Q-VD-OPh, 5mM) and changes in cell viability were detected. Entinostat exhibited dose-dependent activity as a single agent against RSCL, RRCL and patient-derived primary tumor cells (N=32). In addition, in vitro exposure of lymphoma cells to entinostat resulted in an increase in G1 and a decrease in S phase. Moreover synergistic activity was observed by combining entinostat with BTZ in vitro. The pharmacological interactions between entinostat and proteasome inhibitor could be explained in part by each agent’s effects on the expression levels of cell cycle proteins. In vitro exposure of lymphoma cells to entinostat resulted in p21 upregulation and p53 down-regulation, whereas BTZ exposure lead to up-regulation of Bak and Noxa and downregulation of Mcl-1 and Bcl-XL. Caspase inhibition diminished entinostat anti-tumor activity in RSCL but not in RRCL. Together this data suggests that entinostat has a dual mechanism-of-action and can induce cell death by caspase-dependent and independent pathways. Our data suggests that entinostat as a single agent is active against rituximab-chemotherapy sensitive and resistant lymphoma cells and potentiates the anti-tumor activity of BTZ. A better understanding in the molecular events (caspase-dependent and -independent) triggered by entinostat in combination with proteasome inhibition is important in order to develop optimal combination strategies using these novel agents in future clinical trials. Disclosures:Czuczman:Millennium: Honoraria, Research Funding. Hernandez-Ilizaliturri:Genmab: Research Funding; Amgen: Research Funding; Celgene: Consultancy.