Almada, Luciana L.

CMML is a lethal myeloid neoplasm with no therapies that improve its dismal prognosis. Inhibition of BET family members has been proposed as a therapeutic strategy based on preclinical data identifying BRD4 as a therapeutic target in acute myeloid leukemia. However, despite potent on-target transcriptional remodeling, early phase clinical trials have demonstrated only modest activity secondary to a variety of resistance mechanisms. In ovarian cancer BET inhibitor (BETi) treated cells, compensatory upregulation and addiction to pro-survival kinase networks have been observed. Given that over 50% of CMML cases have mutations upregulating kinase signaling, we hypothesized that BETi resistance is mediated by these networks in CMML and can be targeted therapeutically. We tested this hypothesis by performing a limited screen of kinase inhibitors alone and in combination with the IC20 of the BETi INCB54329 in 8 human leukemia cell lines. This screen revealed that the IC50 of the PIM inhibitor (PIMi) INCB53914 decreased after co-treatment with BETi in a majority of the leukemia cell lines tested. Synergy was validated chemically in U937, TF1 and SKM1 leukemia cells using other selective inhibitors of BET and PIM. We next assessed the activity of the BET-PIM combination in 14-day colony formation assays with 10 unique CMML bone marrow mononuclear cell (BM-MNCs) patient samples(Fig. 1A). These studies revealed that combination therapy significantly suppressed clonogenicity versus BMNCs treated with vehicle or single drug alone. Finally, this synergy was validated in vivo in 36 patient derived xenografts (PDX) from 3 CMML patients, as manifest by reduced leukemic burden/engraftment in CMML PDX treated with combination therapy(Fig. 1B). To explore the mechanism by which BETi and PIMi therapeutically synergize we treated U937 and SKM1 leukemia cells with INCB54329 and measured mRNA and protein levels for all PIM isoforms. Surprisingly, we identified that PIM1 was increased following treatment with INCB54329, other BETi, or a JQ1-derived PROTAC (Fig. 1C). PIM1 upregulation was also manifest in INCB54329 persistor U937 leukemia cells generated by daily BETi treatment for 6 weeks. Testing across a broader panel of leukemia cell lines revealed an inverse correlation between PIM1 induction and decrease in the IC50 of PIMi following BETi treatment, suggesting PIM1 upregulation confers sensitivity to combination therapy. Consistent with this, isogenic SKM1 leukemia cells engineered to overexpress PIM1 were resistant to INCB54329 and were more sensitive to INCB53914 versus controls cells. Recent studies have demonstrated that inhibitory miRNAs, especially those located near super-enhancers, are suppressed by BET inhibition. Given that several miRNAs are known to control PIM1 expression, we hypothesized that paradoxical PIM1 upregulation following BETi treatment was due to down-regulation of select miRNAs. To test this, we treated our leukemia cell models with broad inhibitors of miRNA activity (i.e., AGO and Dicer inhibitors) and observed a dose dependent increase in PIM1 levels similar to that seen with BET inhibition(Fig. 1Di). Further, integrating public H3K27 CHIP-seq and miRNA super enhancer datasets and using computational prediction algorithms, we identified 6 candidate miRNAs that could regulate PIM1 and were predicted to be controlled by BET inhibitors. Of these, only miR-33a levels were reduced in a dose dependent manner in SKM1 cells by BETi treatment(Fig. 1Dii). This was confirmed by genetically silencing all BET proteins, which suppressed miR-33a levels in SKM1 leukemia cells. Finally, miR-33a mimics (but not control miRNAs) abolished BETi-induced upregulation of PIM1(Fig. 1Diii). Collectively, these studies established BET and PIM inhibition as a novel and potent combination therapy for CMML that is mediated by miR-33a-dependent upregulation of PIM1(Fig. 1E). Disclosures Liu: Incyte Corporation: Employment. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Lancet:Daiichi Sankyo: Consultancy, Other: fees for non-CME/CE services ; Agios, Biopath, Biosight, Boehringer Inglheim, Celator, Celgene, Janssen, Jazz Pharmaceuticals, Karyopharm, Novartis: Consultancy; Pfizer: Consultancy, Research Funding. Komrokji:Novartis: Speakers Bureau; JAZZ: Speakers Bureau; JAZZ: Consultancy; Agios: Consultancy; Incyte: Consultancy; DSI: Consultancy; pfizer: Consultancy; celgene: Consultancy. Epling-Burnette:Incyte Corporation: Research Funding. List:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Haura:Incyte Corporation: Research Funding. Reuther:Incyte Corporation: Research Funding. Koblish:Incyte Corporation: Employment.

Abstract Abstract 769 Despite the many and diverse therapeutic approaches used to treat patients with mantle cell lymphoma (MCL), it remains an incurable disease. Recently, attention has turned into novel therapies targeting MCL-specific oncogenic pathways important for the growth and maintenance of the transformed phenotype. The chromosomal translocation t(11;14)(q13;q32) leading to cyclin-D1 over-expression is the hallmark of MCL. Constitute cyclin-D1 activation in B-lymphocytes maintains retinoblastoma protein in a phosphorylated state and promotes cell cycling, thus initiating the tumorigenesis process. Cyclin-D1 has been postulated as a putative target for therapeutic intervention, however its evaluation has been hampered by the incomplete understanding of the mechanism underlying this cyclin oncogenic function and by the lack of valid MCL models. To investigate these issues, we developed a combined cellular-genomics screening whereby responses to known cytotoxic compounds targeting cancer-related molecular pathways were correlated with genomic, gene expression and proteomic profiles of human MCL cells. Results showed that cyclin-D1 silencing had minimal antitumoral effects but significantly increased the therapeutic efficacy of several compounds, especially the BH3 mimetics that inhibited anti-apoptotic protein BCL-2. To further evaluate this finding we generated a MCL mouse model by transducing a tetracycline-regulatable cyclin-D1-expressing vector in murine pro-B cells, which allowed modulating cyclin-D1 expression levels. These mice generated lymphomas recapitulating most of the cellular, histopathological and molecular features of human MCL. Similar to the previous in vitro findings, cyclin-D1 inhibition in this model did not induce lymphoma regression, but sensitized cells to apoptosis. Analysis of the mechanisms underlying this therapeutic synergy identified a novel role for cyclin-D1 as a pro-survival molecule. Specifically, cyclin-D1 sequestrated the pro-apoptotic effector protein BAX in MCL cells, thereby favoring BCL2 anti-apoptotic function. Accordingly, therapeutic cyclin-D1 inactivation released BAX, thus sensitizing cells to apoptosis and inducing lymphoma regression. Interestingly, pharmacological blockade in vivo of cyclin-D1 with Roscovitine synergistically cooperated with the BH3 mimetic ABT-737 to effectively inhibit MCL tumor growth. In summary, our study reveals a novel role for cyclin-D1 in deregulating apoptosis in MCL cells and highlights the potential benefit of cyclin-D1 targeting, thus providing the rationale for the clinical evaluation of drugs targeting cell proliferation and survival pathways in MCL. Disclosures: Siebert: Abbott: Honoraria.

Abstract Abstract 613 Uncontrolled immunoglobulin (Ig) secretion by malignant cells is a characteristic feature of lymphoplasmacytic malignancies and associates with significant morbidity. IL6 has been shown to promote Ig secretion by malignant B cells, however, the mechanisms mediating this cellular event remain elusive. Here, we identified a CCL5 induced pathway that upregulates IL6 secretion in B cell/plasma cell malignancies including Waldenström macroglobulinemia (WM). Characterization of this mechanism revealed that activation of the CCL5 pathway increases IL6 expression and promoter activity in stromal cells (HS-5, Saka and primary stromal cells from WM patients). Conversely, stable RNAi knockdown of the CCL5 receptor CCR3 in stromal cells led to significantly reduced IL6 promoter activity and expression. Further analysis using a combination of bioinformatics analysis, genetic analysis and chromatin immunoprecipitation assays (ChIP) identified GLI2 as the mediator of this CCL5-IL6 functional interaction. CCL5 induces GLI2 expression via activation of the PI3K/AKT pathway. Constitutively active PI3K and AKT mutants increase expression of GLI2 through the canonical NFkB pathway. ChIP assay showed p65 binds to the GLI2 promoter and increases GLI2 levels in stromal cells. Dominant negative molecules antagonizing these pathways effectively blocked CCR3 induction of GLI2 expression. Interestingly, this CCL5-induced pathway was independent of the Hedgehog signaling. Blockade of this cascade using pharmacological or genetic tools did not affect CCL5 activation of GLI2 in stromal cells. To validate the biological significance of this newly identified CCL5-GLI2-IL6 signaling axis in the regulation of IgM secretion, we used an in vitro coculture system and an in vivo mouse model. Coculture of primary WM stromal cells, HS-5 or Saka cells with primary WM malignant cells or BCWM.1, an IgM producing cell line, led to a significant increase in IL6 and IgM secretion. Similar results were obtained in vivo using athymic nu/nu mice subcutaneously injected with BCWM.1 and HS-5 cells. We then confirmed the requirement of GLI2 in vitro and in vivo. We infected HS-5 cells with a lentivirus containing shRNA targeting GLI2 or a scramble control and cocultured them with BCWM.1 cells. Knockdown of GLI2 decreased IL6 and IgM secretion in coculture. This was confirmed in vivo by infecting HS-5 cells or primary WMsc with lentivirus targeting GLI2 or scrambled shRNA and coinjecting with BCWM.1 cells into athymic nu/nu mice. Mice injected with cells lacking GLI2 had lower IgM levels in the serum and tumors compared with mice injected with HS-5 cells with an intact GLI2, further supporting the hypothesis that CCL5 requires an intact GLI2 to increase IL6 and consequently IgM. Finally, we confirmed the importance of this phenomenon in other B cell/plasma cell malignancies such as MGUS and MM. Primary stromal cultures from these neoplasms were infected with lentivirus targeting GLI2 or scrambled shRNA and cocultured with BCWM.1 cells. Similar to WM, there was a significant decrease in IL6 and IgM secretion in the absence of GLI2 suggesting the role of this molecule is conserved in other B cell/plasma cell malignancies. In summary, our data identifies a novel role for GLI2, an effector of the Hedgehog signaling pathway, in mediating the interaction between CCL5 and IL6 in the tumor microenvironment that modulates Ig secretion by malignant B cells. Therefore therapies targeting this signaling axis in the tumor microenvironment might provide efficacy in patients with Ig-mediated diseases. Disclosures: No relevant conflicts of interest to declare.

Abstract Immunoglobulin (Ig) secretion by terminally differentiated B-cells is important in the immune response to pathogens. Its over production is a defining characteristic of many B-cell malignancies, including Waldenström Macroglobulinemia (WM), where elevated IgM is associated with significant morbidity and poor prognosis. Thus, the identification and characterization of the mechanisms controlling Ig secretion are of great importance for the development of future therapeutic approaches for these diseases. Here, we define a novel pathway involving the oncogenic transcription factor, GLI2, modulating IgM secretion via regulation of IL-6 receptor alpha subunit (IL6Rα) expression in WM cells. We have previously identified components of the Hedgehog (HH)-GLI pathway as modulators of Ig secretion. Pharmacological (GANT61) and genetic (shRNA) inhibition of GLI proteins resulted in no significant effect on cell proliferation or viability, while there was a significant reduction in IgM secretion (60%) in BCWM.1 (p<0.0001), (55%) in MWCL-1 (p<0.0001) and (50%) in RPCI-WM1 (p<0.0001) cells. Interestingly, this occurred independent of HH signaling as manipulation of HH had no effect on IgM secretion, cell growth or viability. Screening for a mechanism identified IL6Rα as a downstream direct target of GLI activity. GANT61 treatment significantly reduces IL6Rα promoter activity in BCWM.1 (p=0.0002), MWCL-1 (P=0.0003) and RPCI-WM1 (p<0.0001) cells. GLI2 knockdown using two independent shGLI2 constructs resulted in reduced IL6Rα mRNA expression (p<0.0001) determined by qPCR, and IL6Rα protein expression examined by FACS analysis. Similarly, GLI2 knockdown diminished IL6Rα promoter activity in BCWM.1 (p=0.0218), MWCL-1 (p=0.0008) and RPCI-WM1 (p=0.0002) cells. Using bioinformatics analysis, we identified three candidate GLI2 binding sites in the IL6Rα promoter region. Using chromatin immunoprecipitation assay (ChIP) followed by qPCR, we confirmed that GLI2 directly binds to the IL6Rα promoter region (-1294 / -1065). Finally, we were able to rescue the reduction in IgM secretion in GLI2 knockdown group by overexpressing IL6Rα (p=0.0142). Taken together, these data reveal a novel mechanism where GLI2 modulates IgM secretion in WM through the regulation of IL6Rα expression. Given the poor prognosis associated with elevated IgM in WM patients, components of this new signaling axis could be important therapeutic targets. Disclosures No relevant conflicts of interest to declare.

Abstract The mammalian target of rapamycin (mTOR), a kinase that regulates proliferation and apoptosis, has been extensively evaluated as a therapeutic target in hematologic malignancies. Rapamycin analogues, which partially inhibit mTOR complex 1 (mTORC1), showed limited anti-tumor activity due to feedback mechanisms involving mTORC2 and incomplete inhibition of mTORC1. Thus, attention has turned to agents targeting both mTOR complexes by binding the mTOR kinase domain. The purpose of this study was to delineate the mechanisms of mTOR dual inhibitor induced apoptosis in human neoplastic lymphoid cells in vitro. MTS assays and propidium iodide staining followed by flow cytometry for subdiploid populations demonstrated that OSI-027 and MLN0128 inhibited cell proliferation and induced apoptosis in a wide range of lymphoid cell lines including Jurkat, Nalm-6, Molt-4, and SeAX. Raptor and Rictor knockdown in Jurkat and Nalm-6 increased cell death, suggesting both mTOR complexes play a role in apoptosis. 4EBP1 phosphorylation was inhibited by mTOR dual inhibitors, but not by rapamycin. Expression of 4EBP1 T37A/T46A and 4EBP1 T37A/T46A/S65A/T70A, which mimic dephosphorylated 4EBP1, increased Puma mRNA and protein levels as well as apoptosis. Moreover, 4EBP1 knockdown abrogated mTOR dual inhibitor induced Puma upregulation and cell death, further supporting the role of 4EBP1 dephosphorylation in mTORC1 dependent apoptosis. In accord with the known dependence of c-Myc translation on the eIF4E/eIF4G complex, we also observed c-Myc downregulation after treatment with OSI-027, MLN0128 and 4EGI-1, but not rapamycin. Puma induction mirrored c-Myc downregulation under a variety of conditions, including expression of nonphosphorylatable 4EBP1 in parental Jurkat cells or wt 4EBP1 in 4EBP1 deficient cells. Furthermore, c-Myc knockdown induced Puma mRNA and protein as well as increased apoptosis. Collectively, these results support a model in which mTORC1 inhibition, acting through 4EBP1, induces Puma upregulation and apoptosis through c-Myc downregulation. In order to assess the parallel mTORC2-dependent Bim-mediated apoptotic mechanism, we utilized reporter assays and RNAseq experiments. OSI-027-induced Bim promoter activity decreased markedly when the nucleotides -29 to -18 were removed, suggesting that this response element is critical for OSI-027-induced promoter activation. In silico analysis identified eight transcription factors, including SP1, Egr-1, and Myb, that potentially bind this 12-bp region. In RNAseq experiments, we detected a 9-fold increase in Egr-1. Egr-1 upregulation was confirmed by qRT-PCR and immunoblotting after dual inhibitors treatment or Rictor knockdown. Moreover, dominant negative Egr-1 or Egr-1 knockdown diminished dual inhibitor-induced Bim promoter activation and Bim upregulation. Chromatin immunoprecipitation assays demonstrated that OSI-027 enhances binding of Egr-1 to a region of the Bim promoter including bp -29 to -18, further confirming that Egr-1 functions as a direct transcriptional activator for Bim upon mTOR dual inhibitor treatment. NFκB is a known transcription factor for Egr-1 and we observed increased p65 in the nucleus and increased NFκB transcriptional activity after dual inhibitor treatment. Overexpression of S32A/S36A IκB impaired the ability of dual inhibitors to induce NFκB transcriptional activation, Egr-1 mRNA and protein, Bim promoter activation and Bim mRNA and protein upregulation. Collectively, these results suggest that mTORC2 inhibition induces Bim upregulation and apoptosis through NFκB and Egr-1 transactivation. When fresh clinical ALL isolates were exposed to OSI-027 or MLN0128 ex vivo, inhibition of 4EBP1 phosphorylation along with upregulation of Egr-1 and Bim and/or c-Myc downregulation accompanied by Puma induction occurred, indicating that the pathways identified in ALL cell lines can also potentially be engaged in clinical ALLs. These observations not only provide new insight into the survival roles of mTOR in lymphoid malignancies, but also identify alterations that potentially modulate the action of mTOR dual inhibitors. Disclosures No relevant conflicts of interest to declare.

3101 Background: PDO is a promising translational tool that recapitulates the biology and drug response of donor cancer patient. However, an unmet need is to have PDO drug-screening data available for treatment decision making in clinic. We conducted a pilot study to determine whether PDO testing results will be available at critical treatment decision points in metastatic GI cancer patients. Methods: Metastatic GI cancer patients undergoing core-needle biopsy were eligible. Tumor cells isolated from ≤4 fresh biopsy tissues were grown in a Matrigel-based culture. PDO response to anti-cancer drugs were evaluated; and when available, correlated with donors’ clinical response to the same agent(s). PDO response was defined as IC50 < 0.1 × published Cmax of the drug clinically; stable as IC50 between 0.1 to 10 × Cmax. Radiographic response was per RECIST criteria. Results: We enrolled 27 refractory metastatic GI cancer patients (9 colorectal [CRC], 9 pancreas, and 9 biliary tract). Median lines of therapy were 4, 2, and 2; the success rate of organoid establishment was 89%, 44%, and 55%, respectively. The median time from biopsy to availability of drug-testing data was 64 days (range: 24 to 93 days). The median time from biopsy to next CT re-staging in donors was 64 days. The established PDOs shared histological and genomic features with donor clinical tissue. PDO and clinical responses to the same agent(s) were correlated in 2 CRC donors including (1) BRAFV600E-mutated PDO responded to vemurafenib + panitumumab, as did the donor who had partial response (PDO drug-testing data were available 55 days post-biopsy, 23 days prior to restaging scan); (2) KRAS/FGF-dual amplified PDO had stable disease status to regorafenib, as did the biopsied lesion from the donor (73 days post-biopsy, 5 days post-scan). Conclusions: We showed the feasibility of completing PDO drug sensitivity testing in metastatic GI cancer patients within a short time that could impact clinical decision making, particularly in CRC. PDO drug response showed correlation with clinical response. With further refinement, PDO can be a powerful tool for personalizing cancer therapy in metastatic GI cancer patients.

Objective Despite advances in the identification of epigenetic alterations in pancreatic cancer, their biological roles in the pathobiology of this dismal neoplasm remain elusive. Here, we aimed to characterise the functional significance of histone lysine methyltransferases (KMTs) and demethylases (KDMs) in pancreatic tumourigenesis. Design DNA methylation sequencing and gene expression microarrays were employed to investigate CpG methylation and expression patterns of KMTs and KDMs in pancreatic cancer tissues versus normal tissues. Gene expression was assessed in five cohorts of patients by reverse transcription quantitative-PCR. Molecular analysis and functional assays were conducted in genetically modified cell lines. Cellular metabolic rates were measured using an XF24-3 Analyzer, while quantitative evaluation of lipids was performed by liquid chromatography-mass spectrometry (LC-MS) analysis. Subcutaneous xenograft mouse models were used to evaluate pancreatic tumour growth in vivo. Results We define a new antitumorous function of the histone lysine (K)-specific methyltransferase 2D (KMT2D) in pancreatic cancer. KMT2D is transcriptionally repressed in human pancreatic tumours through DNA methylation. Clinically, lower levels of this methyltransferase associate with poor prognosis and significant weight alterations. RNAi-based genetic inactivation of KMT2D promotes tumour growth and results in loss of H3K4me3 mark. In addition, KMT2D inhibition increases aerobic glycolysis and alters the lipidomic profiles of pancreatic cancer cells. Further analysis of this phenomenon identified the glucose transporter SLC2A3 as a mediator of KMT2D-induced changes in cellular, metabolic and proliferative rates. Conclusion Together our findings define a new tumour suppressor function of KMT2D through the regulation of glucose/fatty acid metabolism in pancreatic cancer.

AbstractBackground: Pathogenic germline mutations in the CDKN2A tumor suppressor gene are rare and associated with highly penetrant familial melanoma and pancreatic cancer in non-Hispanic whites (NHW). To date, the prevalence and impact of CDKN2A rare coding variants (RCV) in racial minority groups remain poorly characterized. We examined the role of CDKN2A RCVs on the risk of pancreatic cancer among minority subjects.Methods: We sequenced CDKN2A in 220 African American (AA) pancreatic cancer cases, 900 noncancer AA controls, and 183 Nigerian controls. RCV frequencies were determined for each group and compared with that of 1,537 NHW patients with pancreatic cancer. Odds ratios (OR) and 95% confidence intervals (CI) were calculated for both a case–case comparison of RCV frequencies in AAs versus NHWs, and case–control comparison between AA cases versus noncancer AA controls plus Nigerian controls. Smaller sets of Hispanic and Native American cases and controls also were sequenced.Results: One novel missense RCV and one novel frameshift RCV were found among AA patients: 400G&gt;A and 258_278del. RCV carrier status was associated with increased risk of pancreatic cancer among AA cases (11/220; OR, 3.3; 95% CI, 1.5–7.1; P = 0.004) compared with AA and Nigerian controls (17/1,083). Further, AA cases had higher frequency of RCVs: 5.0% (OR, 13.4; 95% CI, 4.9–36.7; P &lt; 0.001) compared with NHW cases (0.4%).Conclusions: CDKN2A RCVs are more common in AA than in NHW patients with pancreatic cancer and associated with moderately increased pancreatic cancer risk among AAs.Impact: RCVs in CDKN2A are frequent in AAs and are associated with risk for pancreatic cancer. Cancer Epidemiol Biomarkers Prev; 27(11); 1364–70. ©2018 AACR.

Abstract Existing antiangiogenic approaches to treat metastatic hepatocellular carcinoma (HCC) are weakly effectual, prompting further study of tumor angiogenesis in this disease setting. Here, we report a novel role for sulfatase 2 (SULF2) in driving HCC angiogenesis. Sulf2-deficient mice (Sulf2 KO) exhibited resistance to diethylnitrosamine-induced HCC and did not develop metastases like wild-type mice (Sulf2 WT). The smaller and less numerous tumors formed in Sulf2 KO mice exhibited a markedly lower microvascular density. In human HCC cells, SULF2 overexpression increased endothelial proliferation, adhesion, chemotaxis, and tube formation in a paracrine fashion. Mechanistic analyses identified the extracellular matrix protein periostin (POSTN), a ligand of αvβ3/5 integrins, as an effector protein in SULF2-induced angiogenesis. POSTN silencing in HCC cells attenuated SULF2-induced angiogenesis and tumor growth in vivo. The TGFβ1/SMAD pathway was identified as a critical signaling axis between SULF2 and upregulation of POSTN transcription. In clinical HCC specimens, elevated levels of SULF2 correlated with increased microvascular density, POSTN levels, and relatively poorer patient survival. Together, our findings define an important axis controlling angiogenesis in HCC and a mechanistic foundation for rational drug development. Cancer Res; 77(3); 632–45. ©2016 AACR.

Key Points Agents that inhibit both complexes containing the mammalian target of rapamycin are particularly toxic to acute lymphocytic leukemia cells. This killing reflects engagement of a 4EBP1/c-MYC/PUMA axis downstream of mTORC1 and an NF-κB/EGR1/BIM axis downstream of mTORC2.