A novel strategy to generate immunocytokines with activity-on-demand using small molecule inhibitors

Cytokine-based therapeutics have been shown to mediate objective responses in certain tumor entities but suffer from insufficient selectivity, causing limiting toxicity which prevents dose escalation to therapeutically active regimens. The antibody-based delivery of cytokines significantly increases the therapeutic index of the corresponding payload but still suffers from side effects associated with peak concentrations of the product in blood upon intravenous administration. Here we devise a general strategy (named "Intra-Cork") to mask systemic cytokine activity without impacting anti-cancer efficacy. Our technology features the use of antibody-cytokine fusions, capable of selective localization at the neoplastic site, in combination with pathway-selective inhibitors of the cytokine signaling, which rapidly clear from the body. This strategy, exemplified with a tumor-targeted IL12 in combination with a JAK2 inhibitor, allowed to abrogate cytokine-driven toxicity without affecting therapeutic activity in a preclinical model of cancer. This approach is readily applicable in clinical practice.

Time-resolved single-cell transcriptomics defines immune trajectories in glioblastoma

Deciphering the cell-state transitions underlying immune adaptation across time is fundamental for advancing biology. Empirical in vivo genomic technologies that capture cellular dynamics are currently lacking. We present Zman-seq, a single-cell technology recording transcriptomic dynamics across time by introducing time stamps into circulating immune cells, tracking them in tissues for days. Applying Zman-seq resolved cell-state and molecular trajectories of the dysfunctional immune microenvironment in glioblastoma. Within 24 hours of tumor infiltration, cytotoxic natural killer cells transitioned to a dysfunctional program regulated by TGFB1 signaling. Infiltrating monocytes differentiated into immunosuppressive macrophages, characterized by the upregulation of suppressive myeloid checkpoints Trem2, Il18bp, and Arg1, over 36 to 48 hours. Treatment with an antagonistic anti-TREM2 antibody reshaped the tumor microenvironment by redirecting the monocyte trajectory toward pro-inflammatory macrophages. Zman-seq is a broadly applicable technology, enabling empirical measurements of differentiation trajectories, which can enhance the development of more efficacious immunotherapies.

Protocol for the expansion of mouse immune effector cells for in vitro and in vivo studies

Reproducible and efficient expansion of different immune effector cells is required for pre-clinical studies investigating adoptive cell therapies against cancer. Here, we provide a protocol for the rapid expansion of mouse T cells, natural killer (NK) cells, and bone-marrow-derived macrophages (BMDMs). We describe steps for αCD3/αCD8 plate coating, isolating splenocytes, and expanding T cells and NK cells. Further, we detail procedures for bone marrow isolation and BMDM differentiation.

Targeted delivery of tumor necrosis factor in combination with CCNU induces a T cell-dependent regression of glioblastoma

Glioblastoma is the most aggressive primary brain tumor with an unmet need for more effective therapies. Here, we investigated combination therapies based on L19TNF, an antibody-cytokine fusion protein based on tumor necrosis factor that selectively localizes to cancer neovasculature. Using immunocompetent orthotopic glioma mouse models, we identified strong anti-glioma activity of L19TNF in combination with the alkylating agent CCNU, which cured the majority of tumor-bearing mice, whereas monotherapies only had limited efficacy. In situ and ex vivo immunophenotypic and molecular profiling in the mouse models revealed that L19TNF and CCNU induced tumor DNA damage and treatment-associated tumor necrosis. In addition, this combination also up-regulated tumor endothelial cell adhesion molecules, promoted the infiltration of immune cells into the tumor, induced immunostimulatory pathways, and decreased immunosuppression pathways. MHC immunopeptidomics demonstrated that L19TNF and CCNU increased antigen presentation on MHC class I molecules. The antitumor activity was T cell dependent and completely abrogated in immunodeficient mouse models. On the basis of these encouraging results, we translated this treatment combination to patients with glioblastoma. The clinical translation is ongoing but already shows objective responses in three of five patients in the first recurrent glioblastoma patient cohort treated with L19TNF in combination with CCNU (NCT04573192).

A lncRNA identifies Irf8 enhancer element in negative feedback control of dendritic cell differentiation

Transcription factors play a determining role in lineage commitment and cell differentiation. Interferon regulatory factor 8 (IRF8) is a lineage determining transcription factor in hematopoiesis and master regulator of dendritic cells (DC), an important immune cell for immunity and tolerance. IRF8 is prominently upregulated in DC development by autoactivation and controls both DC differentiation and function. However, it is unclear how Irf8 autoactivation is controlled and eventually limited. Here we identified a novel long non-coding RNA transcribed from the +32 kb enhancer downstream of Irf8 transcription start site and expressed specifically in mouse plasmacytoid DC (pDC), referred to as lncIrf8. The lncIrf8 locus interacts with the lrf8 promoter and shows differential epigenetic signatures in pDC versus classical DC type 1 (cDC1). Interestingly, a sequence element of the lncIrf8 promoter, but not lncIrf8 itself, is crucial for mouse pDC and cDC1 differentiation, and this sequence element confers feedback inhibition of Irf8 expression. Taken together, in DC development Irf8 autoactivation is first initiated by flanking enhancers and then second controlled by feedback inhibition through the lncIrf8 promoter element in the +32 kb enhancer. Our work reveals a previously unrecognized negative feedback loop of Irf8 that orchestrates its own expression and thereby controls DC differentiation.

CTIM-22. THE COMBINATION OF LOMUSTINE AND THE IMMUNOCYTOKINE L19TNF IS A PROMISING TREATMENT FOR RECURRENT GLIOBLASTOMA

Glioblastoma is the most aggressive primary brain tumor and adults and poorly immunogenic. Treatment options for recurrent glioblastoma after standard of care chemoradiation are limited Several immunotherapeutic strategies including peptide vaccination and immune checkpoint inhibition have so far failed to improve survival and except from potentially regorafenib, no other agent has demonstrated superior activity to lomustine. Therefore, there is an urgent need for more effective treatment strategies for recurrent glioblastoma. Here, we investigate a new treatment combination based on the alkylating chemotherapy lomustine and the tumor-stroma targeting antibody-cytokine fusion protein L19TNF in preclinical glioma models and patients with recurrent glioblastoma. The combination treatment with lomustine and L19TNF demonstrated strong synergistic anti-tumor activity in several immunocompetent orthotopic glioma models curing the majority of tumor-bearing mice, whereas other mono- or combination therapies for example with anti-PD1 had only limited anti-glioma activity. Investigations of the mechanism of action revealed that lomustine plus L19TNF led to intratumoral necrosis, DNA damage and triggered a strong local anti-tumor immune response with increased MHC-I expression, presentation of neoepitopes and increased abundance of tumor-infiltrating lymphoid cells. In the first patients treated within a phase I/II clinical trial (NCT04573192), the treatment was well tolerated, and durable objective tumor responses and disease stabilizations could be observed also in patients with an unmethylated MGMT promoter.

Multifunctional mRNA-Based CAR T Cells Display Promising Antitumor Activity Against Glioblastoma

PURPOSE

Most chimeric antigen receptor (CAR) T-cell strategies against glioblastoma have demonstrated only modest therapeutic activity and are based on persistent gene modification strategies that have limited transgene capacity, long manufacturing processes, and the risk for uncontrollable off-tumor toxicities. mRNA-based T-cell modifications are an emerging safe, rapid, and cost-effective alternative to overcome these challenges, but are underexplored against glioblastoma.

EXPERIMENTAL DESIGN

We generated mouse and human mRNA-based multifunctional T cells coexpressing a multitargeting CAR based on the natural killer group 2D (NKG2D) receptor and the proinflammatory cytokines IL12 and IFNα2 and assessed their antiglioma activity in vitro and in vivo.

RESULTS

Compared with T cells that either expressed the CAR or cytokines alone, multifunctional CAR T cells demonstrated increased antiglioma activity in vitro and in vivo in three orthotopic immunocompetent mouse glioma models without signs of toxicity. Mechanistically, the coexpression of IL12 and IFNα2 in addition to the CAR promoted a proinflammatory tumor microenvironment and reduced T-cell exhaustion as demonstrated by ex vivo immune phenotyping, cytokine profiling, and RNA sequencing. The translational potential was demonstrated by image-based single-cell analyses of mRNA-modified T cells in patient glioblastoma samples with a complex cellular microenvironment. This revealed strong antiglioma activity of human mRNA-based multifunctional NKG2D CAR T cells coexpressing IL12 and IFNα2 whereas T cells that expressed either the CAR or cytokines alone did not demonstrate comparable antiglioma activity.

CONCLUSIONS

These data provide a robust rationale for future clinical studies with mRNA-based multifunctional CAR T cells to treat malignant brain tumors.

OS08.7.A Lomustine and the immunocytokine L19TNF are a promising treatment combination for recurrent glioblastoma

Background

Treatment options for recurrent glioblastoma are limited and with the possible exception of regorafenib, no agent has demonstrated superior activity to lomustine. Therefore, there is an urgent need for more effective treatment strategies for recurrent glioblastoma. Here, we investigated different treatment combinations based on the tumor-stroma targeting antibody-cytokine fusion protein L19TNF in preclinical glioma models and translated the most effective treatment combination to patients with recurrent glioblastoma.

Material and Methods

Orthotopic immunocompetent mouse glioma models were used to study the anti-glioma activity of L19TNF in combination with anti-PD1, bevacizumab or lomustine. Tumor growth was monitored by MRI. Flow cytometry and microscopy were used to characterize tumor-infiltrating-immune cells. MHC immunoaffinity purification and mass spectrometry were used to characterize the MHC immunopeptidome. Genetic mouse models were used to study immune-dependent effects. Subsequently, we translated the most efficient treatment combination to patients with recurrent glioblastoma within a phase I/II clinical trial (NCT04573192).

Results

The combination of L19TNF and lomustine demonstrated strong synergistic anti-tumor activity in two immunocompetent orthotopic glioma models and cured a majority of tumor-bearing mice. In contrast, combinations with anti-PD-1 or bevacizumab had only limited anti-glioma activity. Furthermore, compared to the monotherapies, the combination of L19TNF and lomustine led to the strongest increase in tumor-infiltrating lymphoid cells as demonstrated by flow cytometry and microsopy and to the highest number of peptides presented in the context of MHC-I. The treatment effect was abrograted in different genetic immunodeficient mouse models. The treatment combination of L19TNF and lomustine was well tolerated in the first patients treated within a phase I/II clinical trial and we observed partial tumor responses also in patients with an unmethylated MGMT promoter.

Conclusion

The combination of L19TNF and lomustine demonstrated promising anti-glioma activity and patients are currently recruited within a phase I/II clinical trial for patients with recurrent glioblastoma.

Generation and in vivo validation of an IL-12 fusion protein based on a novel anti-human FAP monoclonal antibody

BACKGROUND

In this study, we describe the generation of a fully human monoclonal antibody (named '7NP2') targeting human fibroblast activation protein (FAP), an antigen expressed in the microenvironment of different types of solid neoplasms.

METHODS

7NP2 was isolated from a synthetic antibody phage display library and was improved by one round of mutagenesis-based affinity maturation. The tumor recognition properties of the antibody were validated by immunofluorescence procedures performed on cancer biopsies from human patients. A fusion protein consisting of the 7NP2 antibody linked to interleukin (IL)-12 was generated and the anticancer activity of the murine surrogate product (named mIL12-7NP2) was evaluated in mouse models. Furthermore, the safety of the fully human product (named IL12-7NP2) was evaluated in Cynomolgus monkeys.

RESULTS

Biodistribution analysis in tumor-bearing mice confirmed the ability of the product to selectively localize to solid tumors while sparing healthy organs. Encouraged by these results, therapy studies were conducted in vivo, showing a potent antitumor activity in immunocompetent and immunodeficient mouse models of cancer, both as single agent and in combination with immune checkpoint inhibitors. The fully human product was tolerated when administered to non-human primates.

CONCLUSIONS

The results obtained in this work provided a rationale for future clinical translation activities using IL12-7NP2.

CRISPR/Cas9 editing in conditionally immortalized HoxB8 cells for studying gene regulation in mouse dendritic cells

HoxB8 multipotent progenitors (MPP) are obtained by expression of the estrogen receptor hormone binding domain (ERHBD) HoxB8 fusion gene in mouse BM cells. HoxB8 MPP generate (i) the full complement of DC subsets (cDC1, cDC2, and pDC) in vitro and in vivo and (ii) allow CRISPR/Cas9-mediated gene editing, for example, generating homozygous deletions in cis-acting DNA elements at high precision, and (iii) efficient gene repression by dCas9-KRAB for studying gene regulation in DC differentiation.

DDRE-21. LOMUSTINE AND TARGETED-CYTOKINE THERAPY: A BENEFICIAL LIAISON FOR RECURRENT GLIOBLASTOMA

Treatment options for recurrent glioblastoma are limited and except from regorafenib (potentially), no other agent has demonstrated superior activity to lomustine. Therefore, there is an urgent need for more effective treatment strategies for recurrent glioblastoma.

We investigated the combination of lomustine or bevacizumab that are frequently used for recurrent glioblastoma with L19TNF (onfekafusp alfa), a systemically administered tumor-stroma targeting antibody-cytokine fusion protein that enables a targeted delivery of tumor-necrosis factor (TNF)a to the tumor. In immunocompetent orthotopic glioma mouse models, the combination of lomustine and L19TNF demonstrated the strongest anti-tumor activity, acted in synergy and cured a majority of tumor-bearing mice, whereas lomustine or L19TNF monotherapy only had only very limited anti-tumor activity. Ex vivo profiling of the tumors and tumor-infiltrating immune cells from immunocompetent or immunodeficient hosts demonstrated immune-dependent cytotoxic and cytostatic effects on the glioma cells, and a strong increase of tumor-infiltrating immune cells upon combination therapy in immunocompetent models. Based on these encouraging results, we translate this combinatorial therapy to patients with recurrent glioblastoma. For the first patients, the treatment with lomustine and L19TNF was well tolerated and led to stable disease with a reduction in tumor perfusion. More patients are recruited in an ongoing phase I/II clinical trial with lomustine and L19TNF for patients with recurrent glioblastoma (NCT04573192).

Sulfopin is a covalent inhibitor of Pin1 that blocks Myc-driven tumors in vivo

The peptidyl-prolyl isomerase, Pin1, is exploited in cancer to activate oncogenes and inactivate tumor suppressors. However, despite considerable efforts, Pin1 has remained an elusive drug target. Here, we screened an electrophilic fragment library to identify covalent inhibitors targeting Pin1's active site Cys113, leading to the development of Sulfopin, a nanomolar Pin1 inhibitor. Sulfopin is highly selective, as validated by two independent chemoproteomics methods, achieves potent cellular and in vivo target engagement and phenocopies Pin1 genetic knockout. Pin1 inhibition had only a modest effect on cancer cell line viability. Nevertheless, Sulfopin induced downregulation of c-Myc target genes, reduced tumor progression and conferred survival benefit in murine and zebrafish models of MYCN-driven neuroblastoma, and in a murine model of pancreatic cancer. Our results demonstrate that Sulfopin is a chemical probe suitable for assessment of Pin1-dependent pharmacology in cells and in vivo, and that Pin1 warrants further investigation as a potential cancer drug target.

Resistance of t(17;19)-acute lymphoblastic leukemia cell lines to multiagents in induction therapy

t(17;19)(q21‐q22;p13), responsible for TCF3‐HLF fusion, is a rare translocation in childhood B‐cell precursor acute lymphoblastic leukemia(BCP‐ALL). t(1;19)(q23;p13), producing TCF3‐PBX1 fusion, is a common translocation in childhood BCP‐ALL. Prognosis of t(17;19)‐ALL is extremely poor, while that of t(1;19)‐ALL has recently improved dramatically in intensified chemotherapy. In this study, TCF3‐HLF mRNA was detectable at a high level during induction therapy in a newly diagnosed t(17;19)‐ALL case, while TCF3‐PBX1 mRNA was undetectable at the end of induction therapy in most newly diagnosed t(1;19)‐ALL cases. Using 4 t(17;19)‐ALL and 16 t(1;19)‐ALL cell lines, drug response profiling was analyzed. t(17;19)‐ALL cell lines were found to be significantly more resistant to vincristine (VCR), daunorubicin (DNR), and prednisolone (Pred) than t(1;19)‐ALL cell lines. Sensitivities to three (Pred, VCR, and l‐asparaginase [l‐Asp]), four (Pred, VCR, l‐Asp, and DNR) and five (Pred, VCR, l‐Asp, DNR, and cyclophosphamide) agents, widely used in induction therapy, were significantly poorer for t(17;19)‐ALL cell lines than for t(1;19)‐ALL cell lines. Consistent with poor responses to VCR and DNR, gene and protein expression levels of P‐glycoprotein (P‐gp) were higher in t(17;19)‐ALL cell lines than in t(1;19)‐ALL cell lines. Inhibitors for P‐gp sensitized P‐gp‐positive t(17;19)‐ALL cell lines to VCR and DNR. Knockout of P‐gp by CRISPRCas9 overcame resistance to VCR and DNR in the P‐gp‐positive t(17;19)‐ALL cell line. A combination of cyclosporine A with DNR prolonged survival of NSG mice inoculated with P‐gp‐positive t(17;19)‐ALL cell line. These findings indicate involvement of P‐gp in resistance to VCR and DNR in Pgp positive t(17;19)‐ALL cell lines. In all four t(17;19)‐ALL cell lines, RAS pathway mutation was detected. Furthermore, among 16 t(1;19)‐ALL cell lines, multiagent resistance was usually observed in the cell lines with RAS pathway mutation in comparison to those without it, suggesting at least a partial involvement of RAS pathway mutation in multiagent resistance of t(17;19)‐ALL.

Identification of transcription factor binding sites using ATAC-seq

Transposase-Accessible Chromatin followed by sequencing (ATAC-seq) is a simple protocol for detection of open chromatin. Computational footprinting, the search for regions with depletion of cleavage events due to transcription factor binding, is poorly understood for ATAC-seq. We propose the first footprinting method considering ATAC-seq protocol artifacts. HINT-ATAC uses a position dependency model to learn the cleavage preferences of the transposase. We observe strand-specific cleavage patterns around transcription factor binding sites, which are determined by local nucleosome architecture. By incorporating all these biases, HINT-ATAC is able to significantly outperform competing methods in the prediction of transcription factor binding sites with footprints.

CTLA4 Promotes Tyk2-STAT3-Dependent B-cell Oncogenicity

CTL-associated antigen 4 (CTLA4) is a well-established immune checkpoint for antitumor immune responses. The protumorigenic function of CTLA4 is believed to be limited to T-cell inhibition by countering the activity of the T-cell costimulating receptor CD28. However, as we demonstrate here, there are two additional roles for CTLA4 in cancer, including via CTLA4 overexpression in diverse B-cell lymphomas and in melanoma-associated B cells. CTLA4-CD86 ligation recruited and activated the JAK family member Tyk2, resulting in STAT3 activation and expression of genes critical for cancer immunosuppression and tumor growth and survival. CTLA4 activation resulted in lymphoma cell proliferation and tumor growth, whereas silencing or antibody-blockade of CTLA4 in B-cell lymphoma tumor cells in the absence of T cells inhibits tumor growth. This inhibition was accompanied by reduction of Tyk2/STAT3 activity, tumor cell proliferation, and induction of tumor cell apoptosis. The CTLA4-Tyk2-STAT3 signal pathway was also active in tumor-associated nonmalignant B cells in mouse models of melanoma and lymphoma. Overall, our results show how CTLA4-induced immune suppression occurs primarily via an intrinsic STAT3 pathway and that CTLA4 is critical for B-cell lymphoma proliferation and survival. Cancer Res; 77(18); 5118-28. ©2017 AACR.

Abstract 5488: APOBEC signature mutation generates an oncogenic enhancer that drives LMO1 expression in T-ALL

Oncogenic driver mutations are those that provide a proliferative or survival advantage to neoplastic cells resulting in clonal selection. Although most cancer causing mutations have been detected in the protein-coding regions of the cancer genome, driver mutations have recently also been discovered within noncoding genomic sequences. Thus, a current challenge is to gain precise understanding of how these unique genomic elements function in cancer pathogenesis, while clarifying mechanisms of gene regulation and identifying new targets for therapeutic intervention. Here we report a C-to-T single nucleotide transition that occurs as a somatic mutation in noncoding sequences 4 kb upstream of the transcriptional start site of the LMO1 oncogene in primary samples from patients with T-cell acute lymphoblastic leukaemia. This single nucleotide alteration conforms to an APOBEC-like cytidine deaminase mutational signature, and generates a new binding site for the MYB transcription factor, leading to the formation of an aberrant transcriptional enhancer complex that drives high levels of expression of the LMO1 oncogene. Since APOBEC-signature mutations are common in a broad spectrum of human cancers, we suggest that noncoding nucleotide transitions such as the one described here may activate potent oncogenic enhancers not only in T-lymphoid cells but in other cell lineages as well.

Citation Format: Zhaodong Li, Brian Abraham, Alla Berezovskaya, Nadine Farah, Yu Liu, Theresa Leon, Adele Fielding, Shi Hao Tan, Takaomi Sanda, Abraham Weintraub, Benshang Li, Shuhong Shen, Jinghui Zhang, Marc Mansour, Richard Young, Thomas Look. APOBEC signature mutation generates an oncogenic enhancer that drives LMO1 expression in T-ALL [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 5488. doi:10.1158/1538-7445.AM2017-5488

Abstract 802: Loss of function of Arid1a synergizes with MYCN in neuroblastoma pathogenesis

ARID1A is a key component of the SWI/SNF-A (BAF) chromatin-remodeling complex that is known to modulate chromatin structure and gene transcription. Recent exome and whole-genome resequencing has identified SWI/SNF as the most frequently mutated chromatin remodeler in human cancers, and ARID1A as the most highly mutated component among the SWI/SNF subunits, primarily in solid tumors. In high-risk neuroblastoma, ARID1A is mutationally inactivated in one allele in ~1% of patient tumors. In addition, ARID1A is deleted in one allele in at least 85% of cases with chromosome 1p deletions, which is the most common deletion found in neuroblastoma. Thus, ARID1A appears to function as a haploinsufficient tumor suppressor in a substantial fraction of high-risk neuroblastomas. The arid1a gene is duplicated in zebrafish, and the two genes are hence named arid1aa and arid1ab. We targeted each allele of the two genes using CRISPR/Cas genome editing system and recovered stable lines with loss-of-function mutations in each arid1a gene. arid1ab but not arid1aa homozygous mutation showed embryonic lethality. We bred these lines with a transgenic zebrafish line expressing high levels of MYCN in the peripheral sympathetic nervous system driven by the dopamine beta-hydroxylase promoter. Loss of one copy of either arid1aa or arid1ab dramatically accelerated the onset and increased the penetrance of MYCN-induced neuroblastoma. Loss of additional copies of arid1aa or arid1ab accelerated the tumor onset even futher, with the most rapid onset in compound heterosygotes of both genes. The compound heterosygotes showed increased fraction of sympathoadrenal cells in active cell cycle compared to the MYCN transgenic fish with wild type arid1a allales. Our long-term goal is to use the zebrafish model to elucidate the mechanisms underlying the highly dose-dependent tumor suppressor role of this component of the BAF chromatin remodeling complex in neuroblastoma, as a first step toward designing targeted therapies synthetic lethal with reduced expression levels of ARID1A.

Citation Format: Hui Shi, Ting Tao, Cigall Kadoch, Thomas Look. Loss of function of Arid1a synergizes with MYCN in neuroblastoma pathogenesis [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 802. doi:10.1158/1538-7445.AM2017-802

Abstract 5152: Zebrafish models of myeloid malignancies produced through tet2 and asxl1 genomic editing

Myelodysplastic syndromes (MDS) are one of the most common and most difficult to treat of all hematologic malignancies. MDS are diverse clonal disorders of hematopoietic stem cells in the bone marrow that cause dysplastic differentiation in developing progenitors leading to ineffective hematopoiesis, dangerously low circulating blood counts, and evolution to acute myeloid leukemia (AML). We sought to create a faithful zebrafish model of MDS, to study the altered molecular pathways and mechanisms underlying this disease and to provide a means to identify synthetic lethal relationships that can be exploited with small molecule inhibitors to selectively eliminate the mutant cells. Somatic loss-of-function mutations of the Ten-ElevenTranslocation-2 (TET2) and Additional Sex Combs Like 1 (ASXL1) genes are the most frequent clonal somatically acquired genetic abnormalities that have been identified in human MDS and other myeloid malignancies, such as chronic myelomonocytic leukemia (CMML). To generate a zebrafish model of MDS with tet2 and asxl1 loss, we used genome-editing technology to disrupt the zebrafish tet2 and asxl1 genes. The resultant tet2m/m mutant zebrafish are viable and fertile and exhibited normal embryonic and larval hematopoiesis, but developed myelodysplastic syndrome progressing to anemia at 24 months of age. asxl1 m/m mutant zebrafish are embryonic lethal with bone malformations. asxl1 m/m embryos show reduced numbers of hematopoietic and progenitor stem cells (HSPCs), a phenotype which is rescued by Tet2 loss. Combined loss of tet2 and asxl1 in the zebrafish leads to CMML at 5 months of age. These zebrafish lines provide animal models for small molecule and genetic screens in definitive HSPCs to identify synthetic lethal relationships and to dissect the pathways in hematopoietic cells that are altered by loss of function of tet2 and asxl1.

Citation Format: Evisa Gjini, Marc Mansour, Jeffry Sander, Shuning He, Myunggon Ko, Yi Zhou, Scott Rodig, Keith Joung, Leonard Zon, Anjana Rao, Thomas Look. Zebrafish models of myeloid malignancies produced through tet2 and asxl1 genomic editing. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5152. doi:10.1158/1538-7445.AM2015-5152

Abstract 4445: Selective inhibitor of nuclear exporter CRM1/XPO1, Selinexor (KPT-330), exhibits remarkable activity against AML leukemia-initiating cells while sparing normal hematopoietic cells

Current treatments for acute myeloid leukemia (AML) often fail to induce long-term remissions and are toxic to normal tissues, prompting the need to develop new targeted therapies. The frequent disease relapse that is observed in patients with AML is thought to occur because of the inability of the existing drugs to target the self-renewing leukemia-initiating cells (LICs). An attractive new strategy for AML therapy is inhibition of the nuclear export protein exporter 1 (XPO1), or CRM1. XPO1 regulates export of proteins that contain leucine-rich nuclear export signals (NES), including protein adaptors that mediate transport of RNA. XPO1 cargo encompass tumor suppressor proteins, cell cycle regulators, and apoptotic proteins. Recently, small molecule inhibitors of nuclear export (SINE) that inhibit the export function of XPO1 by targeting Cys528 in its NES-binding groove, were developed using an in silico molecular modeling. Selinexor (KPT-330), the orally bioavailable SINE compound, is in Phase 1 and 2 studies in adult patients with AML (NCT01607892 and NCT02088541) and in a Phase 1 study for relapsed childhood ALL and AML initiated in March 2014 (NCT02091245).

To define the anti-leukemic activity of selinexor against primary AML blasts and LICs in a clinically relevant setting, we established mouse models of primary human leukemia, or patient-derived xenografts (PDX), in which leukemic blasts from AML patients were transplanted into immunodeficient NOD-SCID-IL2Rcγnull (NSG) mice. Mice engrafted with leukemic blasts were treated with either vehicle or selinexor. Selinexor was highly active against blast cells from two of the three patients with poor-prognosis disease (cytogenetically normal AML with FLT3-ITD (AML-CN) and complex karyotype AML (AML-CK1 and AML-CK2)), as evidenced by a reduction in leukemic engraftment in primary mice after 4 weeks of treatment. Secondary transplantation assays indicated that selinexor greatly reduced the frequency of LICs in PDX models derived from all three patients (6- to 430- fold reduction compared to controls), indicating that this agent not only targets the bulk leukemic cells, but also eliminates LICs. These findings show that selinexor has potent activity against LICs, even when it has only moderate activity against the bulk AML cell population. Furthermore, preliminary results of combination studies of selinexor with Ara-C, a standard chemotherapeutic agent, demonstrate synergistic effect of the two drugs against LICs in a PDX model of AML-CN. Importantly, 4 weeks of selinexor treatment demonstrated minimal toxicity in mice engrafted with normal human CD34+ hematopoietic cells. These findings demonstrate that inhibition of nuclear export with selinexor overcomes an important obstacle to cure of AML, which is to destroy the very critical LIC compartment while sparing normal hematopoietic cells.

Citation Format: Julia Etchin, Bonnie Thi Le, Alla Berezovskaya, Amy S. Conway, Weihsu C. Chen, Alex Kentsis, Marc R. Mansour, Richard M. Stone, Ilene A. Galinsky, Daniel J. DeAngelo, Dilara McCauley, Michael Kauffman, Sharon Shacham, Jean CY Wang, Andrew L. Kung, Thomas Look. Selective inhibitor of nuclear exporter CRM1/XPO1, Selinexor (KPT-330), exhibits remarkable activity against AML leukemia-initiating cells while sparing normal hematopoietic cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4445. doi:10.1158/1538-7445.AM2015-4445

Abstract PR02: Targeting NOTCH1 and C-MYC in humanized models of relapsed and induction failure pediatric T-ALL

Although prognosis has improved for children with T cell acute lymphoblastic leukemia (T-ALL), 20-30% of patients undergo induction failure (IF) or relapse. Leukemia-initiating cells (L-ICs) are hypothesized to be resistant to chemotherapy and to mediate relapse. We and others have shown that Notch1 directly regulates c-Myc and c-Myc is a known regulator of quiescence in stem and progenitor populations, leading us to examine whether c-Myc inhibition results in efficient targeting of T-ALL-initiating cells. We demonstrate that c-Myc suppression by shRNA or pharmacological approaches prevents leukemia initiation in mice by reducing the L-IC population. Consistent with its anti-L-IC activity in mice, treatment with the BET bromodomain BRD4 inhibitor JQ1 reduces C-MYC expression and inhibits the growth of relapsed and induction failure (IF) pediatric T-ALL samples in vitro. Although treatment of relapsed T-ALL cells with gamma secretase inhibitors (GSI) or JQ1 reduces, it does not abrogate C-MYC mRNA levels, indicating a role for dual NOTCH and MYC inhibition in relapsed disease. To test this possibility, we engrafted immunodeficient NSG mice with relapsed pediatric T-ALL cells and treated them with vehicle, GSI, JQ1 or with GSI and JQ1 and monitored survival. Although JQ1 or GSI treatment alone significantly prolonged survival, the combination therapy was more effective at extending survival. These findings reveal a requirement for MYC in mouse and human L-IC maintenance and provide evidence that NOTCH1 and MYC inhibition may be an effective therapy for relapsed/IF T-ALL patients.

This abstract is also presented as Poster A48.

Citation Format: Justine E. Roderick, Jessica Tesell, Alejandro Gutierrez, Thomas Look, Jun Qi, James E. Bradner, Michelle A. Kelliher. Targeting NOTCH1 and C-MYC in humanized models of relapsed and induction failure pediatric T-ALL. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr PR02.

SCF(FBW7) regulates cellular apoptosis by targeting MCL1 for ubiquitylation and destruction

The effective use of targeted therapy is highly dependent upon the identification of responder patient populations. Loss of the Fbw7 tumor suppressor is frequently found in various types of human cancers including breast cancer, colon cancer 1 and T-cell acute lymphoblastic leukemia (T-ALL)2. In line with these genomic data, engineered deletion of Fbw7 in mouse T cells results in T-ALL3–5, validating Fbw7 as a T-ALL tumor suppressor. The precise molecular mechanisms by which Fbw7 exerts anti-tumor activity remain areas of intensive investigation and are thought to relate in part to Fbw7-mediated destruction of key cancer relevant proteins including c-Jun6, c-Myc 7, Cyclin E 8 and Notch-19, all of which possess oncogenic activity and are overexpressed in various human cancers including leukemia. Besides accelerating cell growth 10, overexpression of either c-Jun, c-Myc or Notch-1 can also provoke programmed cell death 11. Thus, considerable uncertainty surrounds how Fbw7-deficient cells evade cell death in the setting of upregulated c-Jun, c-Myc and/or Notch-1. Here we report that SCF^Fbw7 governs cellular apoptosis by targeting the pro-survival Bcl-2 family member, Mcl-1, for ubiquitination and destruction in a GSK3 phosphorylation-dependent manner. Human T-ALL cell lines showed a close relationship between Fbw7 loss and Mcl-1 overexpression. Correspondingly, T-ALL cell lines with defective Fbw7 are particularly sensitive to the multi-kinase inhibitor, sorafenib, but resistant to the Bcl-2 antagonist, ABT-737. On the genetic level, Fbw7 reconstitution or Mcl-1 depletion restores ABT-737 sensitivity, establishing Mcl-1 as a therapeutically relevant bypass survival mechanism for Fbw7-deficient cells to evade apoptosis. Therefore, our work provides novel molecular insight into Fbw7-direct tumor suppression with direct implications for the targeted treatment of Fbw7-deficient T-ALL patients.

NOTCH2 links protein kinase C delta to the expression of CD23 in chronic lymphocytic leukaemia (CLL) cells

One characteristic of chronic lymphocytic leukaemia (CLL) lymphocytes is high expression of CD23, which has previously been identified as a downstream target for NOTCH2 signalling. The mechanisms regulating NOTCH2-dependent CD23 expression, however, are largely unknown. This study showed that peripheral CLL cells overexpressed transcriptionally active NOTCH2 (N2(IC)), irrespective of their prognostic marker profile. When placed in culture, NOTCH2 activity was spontaneously decreased in 25 out of 31 CLL cases (81%) within 24 h. DNA-bound N2(IC) complexes could be maintained by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) or by gamma-interferon (IFN-gamma), two CLL characteristic inducers of CD23 expression. Inhibition of PKC-delta by RNA interference or by rottlerin antagonised PMA-induced NOTCH2 activation and also suppressed NOTCH2 activity in CLL cases with constitutively activated NOTCH2 signalling. In 23 out of 29 CLL cases tested (79%), DNA-bound N2(IC) complexes were found to be resistant to the gamma-secretase inhibitor (GSI) DAPT, suggesting that GSIs will be only effective in a subset of CLL cases. These data suggest that deregulation of NOTCH2 signalling is critically involved in maintaining the malignant phenotype of CLL lymphocytes and point to a link between PKC-delta and NOTCH2 signalling in the leukemic cells.

Down-regulation of the Notch pathway mediated by a gamma-secretase inhibitor induces anti-tumour effects in mouse models of T-cell leukaemia

BACKGROUND AND PURPOSE

gamma-Secretase inhibitors (GSIs) block NOTCH receptor cleavage and pathway activation and have been under clinical evaluation for the treatment of malignancies such as T-cell acute lymphoblastic leukaemia (T-ALL). The ability of GSIs to decrease T-ALL cell viability in vitro is a slow process requiring >8 days, however, such treatment durations are not well tolerated in vivo. Here we study GSI's effect on tumour and normal cellular processes to optimize dosing regimens for anti-tumour efficacy.

EXPERIMENTAL APPROACH

Inhibition of the Notch pathway in mouse intestinal epithelium was used to evaluate the effect of GSIs and guide the design of dosing regimens for xenograft models. Serum Abeta(40) and Notch target gene modulation in tumours were used to evaluate the degree and duration of target inhibition. Pharmacokinetic and pharmacodynamic correlations with biochemical, immunohistochemical and profiling data were used to demonstrate GSI mechanism of action in xenograft tumours.

KEY RESULTS

Three days of >70% Notch pathway inhibition was sufficient to provide an anti-tumour effect and was well tolerated. GSI-induced conversion of mouse epithelial cells to a secretory lineage was time- and dose-dependent. Anti-tumour efficacy was associated with cell cycle arrest and apoptosis that was in part due to Notch-dependent regulation of mitochondrial homeostasis.

CONCLUSIONS AND IMPLICATIONS

Intermittent but potent inhibition of Notch signalling is sufficient for anti-tumour efficacy in these T-ALL models. These findings provide support for the use of GSI in Notch-dependent malignancies and that clinical benefits may be derived from transient but potent inhibition of Notch.

Identification of additional cytogenetic and molecular genetic abnormalities in acute myeloid leukaemia with t(8;21)/AML1-ETO

AML1-ETO collaborates with further genetic abnormalities to induce acute myeloid leukaemia (AML). We analysed 99 patients with an AML1-ETO rearrangement for additional aberrations. Frequent genetic abnormalities were, loss of a sex chromosome (56/99, 56.5%) and del(9)(q22) (24/99, 24.2%). The most frequent molecular aberrations were mutations of KITD816 (3/23, 13%) and NRAS (8/89, 8.9%). Further molecular abnormalities were FLT3 mutations (3/87, 3.4%), AML1 (1/26, 3.8%) and PU1 (1/14, 7.1%). MLL-PTD, KRAS and CEBPA mutations were not found. These clinical findings support the model that AML1-ETO collaborates with other genetic alterations, such as mutations of receptor tyrosine kinases, to induce AML.

Making waves in cancer research: new models in the zebrafish

The zebrafish (Danio rerio) has proven to be a powerful vertebrate model system for the genetic analysis of developmental pathways and is only beginning to be exploited as a model for human disease and clinical research. The attributes that have led to the emergence of the zebrafish as a preeminent embryological model, including its capacity for forward and reverse genetic analyses, provides a unique opportunity to uncover novel insights into the molecular genetics of cancer. Some of the advantages of the zebrafish animal model system include fecundity, with each female capable of laying 200-300 eggs per week, external fertilization that permits manipulation of embryos ex utero, and rapid development of optically clear embryos, which allows the direct observation of developing internal organs and tissues in vivo. The zebrafish is amenable to transgenic and both forward and reverse genetic strategies that can be used to identify or generate zebrafish models of different types of cancer and may also present significant advantages for the discovery of tumor suppressor genes that promote tumorigenesis when mutationally inactivated. Importantly, the transparency and accessibility of the zebrafish embryo allows the unprecedented direct analysis of pathologic processes in vivo, including neoplastic cell transformation and tumorigenic progression. Ultimately, high-throughput modifier screens based on zebrafish cancer models can lead to the identification of chemicals or genes involved in the suppression or prevention of the malignant phenotype. The identification of small molecules or gene products through such screens will serve as ideal entry points for novel drug development for the treatment of cancer. This review focuses on the current technology that takes advantage of the zebrafish model system to further our understanding of the genetic basis of cancer and its treatment.

DNA index of glial tumors in children. Correlation with tumor grade and prognosis

BACKGROUND

Although DNA index (DI) has prognostic significance in a variety of pediatric malignancies, there are few data regarding its utility in central nervous system (CNS) tumors. We have previously shown that patients with hyperdiploid medulloblastoma have a significantly better survival than those whose tumors are diploid. Here, we examine the effect of DI and tumor grade on the progression free survival (PFS) of 57 patients with a variety of glial neoplasms.

METHODS

DI was determined by flow cytometry on freshly obtained tumor tissue from the initial diagnostic specimens; a DI = 1.0 was defined as diploid (DIP), 1.0 < DI < 1.1 as near diploid (NDIP), and DI > 1.1 as hyperdiploid (HYP). Tumors were histologically graded according to the World Health Organization classification.

RESULTS

There were 21 Grade I tumors, 20 Grade II, 8 Grade III, and 8 Grade IV. Among the 41 low grade tumors (Grade I-II), 39 were DIP or NDIP, and 2 were HYP. Among the 16 high grade tumors (Grade III-IV), 9 were DIP, 2 NDIP, and 5 HYP. The 4-year PFS of low grade tumors was 70% (standard deviation [SD] 12%) versus 8% (SD 7%) for high grade tumors. There was a significant correlation between low grade tumor histology and a DIP/NDIP DI (P = 0.015), and univariate analysis suggested improved PFS was associated with DIP/NDIP tumors (P = 0.05). However, DI did not remain a significant prognostic factor after being stratified by tumor grade (P = 0.87).

CONCLUSIONS

Unlike medulloblastoma, DI is not an independent prognostic factor in pediatric glial tumors.

The retinoblastoma protein binds to a family of E2F transcription factors

E2F is a transcription factor that helps regulate the expression of a number of genes that are important in cell proliferation. Recently, several laboratories have isolated a cDNA clone that encodes an E2F-like protein, known as E2F-1. Subsequent characterization of this protein showed that it had the properties of E2F, but it was difficult to account for all of the suggested E2F activities through the function of this one protein. Using low-stringency hybridization, we have isolated cDNA clones that encode two additional E2F-like proteins, called E2F-2 and E2F-3. The chromosomal locations of the genes for E2F-2 and E2F-3 were mapped to 1p36 and 6q22, respectfully, confirming their independence from E2F-1. However, the E2F-2 and E2F-3 proteins are closely related to E2F-1. Both E2F-2 and E2F-3 bound to wild-type but not mutant E2F recognition sites, and they bound specifically to the retinoblastoma protein in vivo. Finally, E2F-2 and E2F-3 were able to activate transcription of E2F-responsive genes in a manner that was dependent upon the presence of at least one functional E2F binding site. These observations suggest that the E2F activities described previously result from the combined action of a family of proteins.

Screening for neuroblastoma in North America. 2-year results from the Quebec Project

The Quebec Neuroblastoma Screening Project was initiated to assess the clinical and biological aspects of screening infants for the presence of neuroblastoma in North America. All children born in the province of Quebec from May 1, 1989 to April 30, 1994 are eligible for participation. This report provides results from 22 months' accrual of infants who were screened using urine-saturated filter paper for determination of the catecholamine metabolites vanillylmandelic acid (VMA) and homovanillic acid (HVA). More than 157,000 infants have been screened to date at 3 weeks of age, representing 92% of the entire birth population of Quebec. Over 98,000 infants have been screened a second time at 6 months of age, which made up 76% of the Quebec birth cohort. After a two-stage initial screening, 340 (0.13%) infants (182 at 3 weeks and 158 at 6 months) required second laboratory examinations because of elevated levels of urinary VMA, HVA, or both. Twenty infants from the 3-week screening (0.01%) and nine from the 6-month screening (0.01%) were subsequently referred to one of four Quebec pediatric oncology centers for neuroblastoma evaluation. Seven of 20 children from the 3-week screening and two of nine children from the 6-month screening have been identified as having neuroblastoma. During the same period, 14 additional children in the birth cohort were diagnosed clinically with neuroblastoma; eight were diagnosed prior to screening at 3 weeks of age, three children had negative results at 3 weeks of age, two had negative results at 3 weeks and at 6 months of age, and one had never been screened.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of breakpoints in t(8;21) acute myelogenous leukemia and isolation of a fusion transcript, AML1/ETO, with similarity to Drosophila segmentation gene, runt

We have developed a restriction map of the chromosome 21 breakpoint region involved in t(8;21)(q22;q22.3) acute myelogenous leukemia (AML) and have isolated a genomic junction clone containing chromosome 8 and 21 material. Using probes from these regions, rearrangements have been identified in each of nine cases of t(8;21) AML examined. In addition, we have isolated cDNA clones from a t(8;21) AML cDNA library that contain fused sequences from chromosome 8 and 21. The chromosome 8 component, referred to as ETO (for eight twenty-one), is encoded over a large genomic region, as suggested by the analysis of corresponding yeast artificial chromosomes (YACs). The DNA sequence of the chromosome 21 portion of the fusion transcript is derived from the normal AML1 gene. A striking similarity (67% identity over 387 bp, with a corresponding 69% amino acid identity) was detected between AML1 and the Drosophila segmentation gene, runt. The critical consequence of the translocation is the juxtaposition of 5' sequences of AML1 to 3' sequences of ETO, oriented telomere to centromere on the der(8) chromosome.

Ploidy of lymphoblasts is the strongest predictor of treatment outcome in B-progenitor cell acute lymphoblastic leukemia of childhood: a Pediatric Oncology Group study

PURPOSE

Using the technique of recursive partitioning and amalgamation analysis with verification, the Pediatric Oncology Group (POG) investigated the independent prognostic significance of previously published prognostic factors significantly associated with event-free survival (EFS) in B-progenitor cell acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Age, leukocyte count, sex, immunophenotype (expression of cytoplasmic immunoglobulin [Ig] and of surface antigens CD10 and CD34), and DNA index (ratio of the flow cytometry-determined DNA content of leukemia cells to that of normal diploid cells) were the variables used in the evaluation of four antimetabolite-based chemotherapy regimens in 1,535 children with the newly diagnosed B-progenitor cell ALL between February 1986 and May 1990.

RESULTS

There were three subgroups at widely different risks of treatment failure. A DNA index greater than 1.16 was the most prognostic feature. The final prognostic subgrouping was as follows: (1) DNA index greater than 1.16; (2) DNA index less than or equal to 1.16, age less than 11.0 years, and leukocyte count less than 50 x 10(9)/L; and (3) DNA index less than or equal to 1.16, (age greater than 11.0 years, and/or leukocyte count greater than 50 x 10(9)/L). These groups made up 20%, 53%, and 27% of the patients and had 4-year EFS rates (SE) of 90.1% (6.3%), 80.5% (5.1%), and 50.4% (7.6%), respectively.

CONCLUSIONS

Use of the DNA index, leukocyte count, and age--data that are relatively inexpensive and simple to obtain--may be sufficient to stratify patients with B-progenitor cell ALL for risk-directed therapy. Patients at an extremely low risk of failing therapy (approximately 20% of cases in this study) can thus be identified and spared the toxic short-term and late effects of more intensive therapies that may be needed for children with less favorable clinical and biologic features.

Increased adenosine deaminase (ADA) activity and a shift from ADA-dependent to ADA-independent phases during T-cell activation: a paradox

During activation of WF rat splenic T-cells, a change occurs with respect to susceptibility to a toxic accumulation of adenosine or deoxyadenosine (dADO) in the presence of adenosine deaminase (ADA) blockade. Addition of nucleoside 1 hour after the initiation of a concanavalin A response in the presence of 2'deoxycoformycin (DCF) markedly inhibited the response, whereas delay of addition of the nucleoside for 24-48 hours resulted in minimal or no inhibition. Inhibition was not simply the result of prolonged incubation of cells in the presence of nucleoside and was apparently not attributable to an effect on proliferating cells. Addition of interleukin 2 (IL-2) to cultures containing DCF and dADO did not reverse the inhibitory effect, which suggests that IL-2-producing T-cells also were not the target of nucleoside toxicity. A twofold increase in ADA activity that occurred during T-cell activation was nonessential for the survival of mitogen-activated T-cells in the presence of toxic concentrations of dADO and did not account for an apparent increased resistance of these cells to nucleoside toxicity. These paradoxical observations prompted an analysis of ADA activity in various populations of activated T-cells enriched with cells in G0/G1, S, or G2+M cell-cycle phases, which indicated that increased ADA activity was not associated with a specific period during cell-cycle traverse, but, rather, coincided with cell enlargement in preparation for mitosis. In conclusion, either an early event in T-cell mitogenesis is highly susceptible to nucleoside toxicity or a mechanism independent of ADA is acquired during T-cell activation that allows proliferating T-cells to resist toxic concentrations of nucleoside.