IL-3 Dependent Cell Research Articles

SETDB1 Suppresses Interferon Responses and NK Cell-Mediated Immunosurveillance Specifically in Monocytic AML

Acute myeloid leukemia (AML) with monocytic differentiation (monocytic AML) responds poorly to current treatments, including venetoclax-based therapy. To identify novel therapeutic targets in monocytic AML, we conducted in vivo and in vitro CRISPR/Cas9 library screens using a pooled sgRNA library targeting epigenetic regulators with a mouse monocytic AML model driven by SETBP1 and ASXL1 mutations (cSAM: combined expression of SETBP1 and ASXL1 Mutations). We ranked all the epigenetic genes according to the in vivo specific essentiality, and selected several candidates which were more depleted in mice rather than in cell cultures. The top-ranked gene was Setdb1, which encodes a histone H3 lysine 9 (H3K9) methyltransferase. In addition, several H3K9 trimethylation (H3K9me3) regulators, ATF7IP and TRIM33, were also more important in vivo than in vitro in our screens. ATF7IP is a cofactor of SETDB1 to enhance its enzymatic activity. TRIM33 is also involved in H3K9me3 modification. These data suggest the critical role of the SETDB1-ATF7IP-TRIM33 H3K9 methyltransferase complex in the development of AML in vivo. To validate the results of our screenings and to investigate the role of immune cells in our transplantation assay, we next transplanted control and Setdb1-knockout (KO) cSAM cells into three types of mice with different immune systems: the immunocompetent C57BL/6 mice, the immunodeficient NSG mice lacking T, B and natural killer (NK) cells, and the C57BL/6J- Rag2-/- mice lacking mature T and B cells but possessing NK cells. Although Setdb1 depletion did not inhibit the growth of cSAM cells in NSG mice, it showed the strong growth-inhibitory effect in C57BL/6 mice and Rag2-/- mice (Fig 1A). Since both C57BL/6 mice and Rag2-/- mice have NK cells, these data suggest that SETDB1 promotes leukemogenesis by suppressing NK cell-mediated cytotoxicity in vivo. Mechanistically, loss of Setdb1 induced upregulation of NKG2D ligands, interferon-stimulated genes (ISGs), and endogenous retrovirus (ERV) sequences through H3K9me3 reduction, thereby rendering cSAM cells more susceptible to NK cell-mediated cytotoxicity. Setdb1 depletion also induced myeloid maturation of cSAM cells towards macrophages and downregulation of major histocompatibility complex class I (MHC-I), which contributed to the increased susceptibility of Setdb1-depleted cSAM cells to NK cell-mediated cytotoxicity. Next, we investigated whether SETDB1 inactivation also sensitizes human AML cells to NK cells using the co-culture assay with an IL-2 dependent NK cell line NK-92. Loss of SETDB1 rendered monocytic AML cell lines, NOMO-1, THP-1, OCI-AML3, U937, and NB4, more susceptible to NK-92 cell-mediated cytotoxicity. SETDB1 depletion also induced overactivation of interferon signaling and intrinsic apoptosis in these monocytic AML cells. In contrast, non-monocytic AML cells, such as K562, TF-1, and Kasumi-1, were not sensitive to SETDB1 depletion. SETDB1 depletion neither increased the susceptibility to NK cell-mediated cytotoxicity nor induced apoptosis in non-monocytic AML cells. Subsequent analyses revealed that SETDB1 depletion reduced H3K9me3 at the monocyte-specific enhancer regions with ERV sequences to upregulate NK cell-activating ligands and ISGs. Because the “ERV enhancers” are active only in monocyte lineage, SETDB1 is essential specifically in monocytic AML. Finally, we identified MNDA and its mouse counterpart Ifi203 as biomarkers to predict the sensitivity of each AML to SETDB1 depletion. MNDA is one of the ISGs and is involved in myeloid cell differentiation. Human monocytic AML cells that are dependent on SETDB1 expressed higher MNDA at both RNA and protein levels compared to other subtypes of AML. We also found that Ifi203-high mouse AML cells transformed by MLL-AF9 were sensitive to Setdb1 depletion, whereas Setdb1 was dispensable in Ifi203-low mouse AML cells transformed by RUNX1-RUNX1T1. In summary, our findings reveal the critical and selective role of SETDB1 in monocytic AML. SETDB1 mediates H3K9me3 at the monocyte-specific ERV enhancers to repress the expression of NK cell-activating ligands and ISGs, thereby suppressing immunogenicity and apoptosis in monocytic AML (Fig 1B). SETDB1 as well as its binding partners could be promising therapeutic targets to treat monocytic AMLs that are relatively resistant to the current standard therapies.

Ex Vivo Drug Sensitivity Evaluation of a ZMYM2::FGFR1 Fusion-Positive 8p11 Myeloproliferative Syndrome (EMS) Leukemia

Introduction : Fibroblast growth factor receptors (FGFRs) are conserved single transmembrane receptor tyrosine kinases (RTKs) with an extracellular ligand-binding domain and a cytoplasmic tyrosine kinase domain. They play vital roles in cellular proliferation, survival, development, fetal organogenesis, metabolism, and tissue repair. 8p11 myeloproliferative syndrome (EMS) is a hematologic malignancy caused by a translocation of the fibroblast growth factor receptor 1 (FGFR1) gene on chromosome 8p11-12. The most common fusion partner of FGFR1 is the zinc-finger domain ZNF198 (also known as ZMYM2) on chromosome 13q12. Pemigatinib is approved for FGFR fusion positive myeloid/lymphoid neoplasms (MLNs), and other FGFR inhibitors are being tested in clinical trials. However, EMS patients still face a poor prognosis and drug resistance, necessitating further research to overcome these challenges. This study evaluated ex vivo drug screening assay data generated from ZMYM2::FGFR1 positive primary leukemia samples throughout the course of an EMS patient's clinical response and validated these findings on a ZMYM2::FGFR1 positive cell line. Methods : Ex vivo and drug screening experiments were performed on freshly isolated primary patient samples and a ZMYM2::FGFR1-expressing cell line. The fusion was confirmed using FISH, and additional clinical specimens were collected with informed patient consent. Ex vivo drug sensitivity assays were conducted on patient mononuclear cells isolated from blood and bone marrow. IL-3 dependent BaF3 cells were infected with retrovirus containing a ZMYM2::FGFR1-V5 construct. ZMYM2::FGFR1 transformed BaF3 cells were evaluated with single agent and drug combination panels. Sanger sequencing of the FGFR portion of the fusion was performed on patient samples to confirm the breakpoint and identify potential mutations affecting sensitivity to Ponatinib throughout the course of treatment. Results : Sample were obtained with informed consent from a 36-year-old man diagnosed with 8p11 myeloproliferative syndrome and a ZMYM2::FGFR1 fusion along with a RUNX1 R201Q mutation. Ex vivo drug screens performed on isolated mononuclear cells demonstrated sensitivity to Ponatinib and Pemigatinib. He underwent treatment with HyperCVAD plus Ponatinib and subsequently HyperCVAD with Ponatinib and Velcade (Bortezomib) to CR1, FISH for FGFR1 rearrangement was undetected. He was scheduled to proceed with hematopoietic stem cell transplant (HSCT), however his pre-transplant bone marrow biopsy showed return of his FGFR1 translocation by FISH. Ex vivo drug screening assays confirmed resistance to Ponatinib, but continued sensitivity to Pemigatinib. He was transitioned to treatment with single agent Pemigatinib and was able to re-clear his FGFR1 fusion by FISH, and has since undergone hematopoietic stem cell transplantation. He remains in remission on post-transplant Pemigatinib maintenance therapy. Sanger sequencing performed at the time of progression on Ponatinib identified a nucleotide alteration resulting in an amino acid substitution (FGFR1 F686L; ZMYM2::FGFR1 F1171L) within the kinase domain that could contribute to decreased Ponatinib sensitivity. Bortezomib and Axitinib exhibited high efficacy on the patient's sample. Ex vivo drug assays performed on ZMYM2::FGFR1 transformed BaF3 cells confirmed the efficacy of Pemigatinib and Ponatinib. Other FGFR inhibitors, including Olverematinib, AZD4547, Axitinib, Cediranib, Dovitinib, and Lenvatinib, also demonstrated exquisite sensitivity. Despite extensive screening, no other single agents or drug combinations exhibited increased effectiveness in the ZMYM2::FGFR1 transformed BaF3 cells except for Trametinib, a MEK inhibitor, and the combination of Belvarafenib (RAF inhibitor) and Gilteritinib (FLT3 inhibitor). Conclusions : Ex vivo drug sensitivity assays demonstrated the highly selective efficacy of FGFR inhibitors in ZMYM2::FGFR1 fusion-positive leukemia cells and a fusion-expressing BaF3 cell line. Mutations in the FGFR1 kinase domain (ZMYM2::FGFR1 F1171L) could contribute to Ponatinib insensitivity. These ex vivo drug screening results provide further support for ongoing clinical trials which are investigating the use of single agent Pemigatinib and other FGFR1 inhibitors for the treatment of patients with FGFR1-fusion positive leukemias.

Synergy of Ruxolitinib and Carfilzomib in Targeting the PAX5::JAK2 fusion I n Vitro: Potential Therapeutic Advantage for a Subset of Ph-like Acute Lymphoblastic Leukemia

INTRODUCTION PAX5::JAK2 is a gene fusion that drives a subset of Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) and confers aggressive disease, poor prognosis and poor response to treatment. PAX5::JAK2 is present in approximately 12% of Ph-like ALL cases. Targeted therapy is urgently required to improve outcomes. We evaluated the efficacy of JAK inhibitor ruxolitinib (RUX) and proteosome inhibitors carfilzomib (CFZ) and bortezomib (BTZ) as monotherapy and in combination against PAX5::JAK2 transfected Ba/F3 cells in vitro. Downregulation of proteosome genes via reduction in STAT3 phosphorylation is a shared mechanism of RUX and proteosome inhibitors. Given that the PAX5::JAK2 fusion results in increased STAT3 phosphorylation driving proliferation, it was proposed that the combination of proteosome inhibitors and RUX would demonstrate synergy in inhibiting proliferation of PAX5::JAK2 driven leukemic cells. METHODS Mouse derived Ba/F3 cells, an IL-3 dependent B-ALL model, were transfected with the PAX5::JAK2 fusion and demonstrated IL-3 independence. We applied, as single treatments, differing concentrations of RUX and the proteosome inhibitors CFZ and BTZ to PAX5::JAK2 transfected Ba/F3 cells and two control cell lines - IL-3 dependent empty vector Ba/F3 cells and an IL-3 independent KG1a myeloid cell line. Differing concentrations of CFZ and 200nM of RUX were then applied in combination. 200nM of RUX was selected because it is a dose at which the drug has minimal effect as a single agent. Inhibitors were applied to cells for 72 hours then percentage of live and dead cells at each concentration was ascertained by flow cytometry using Annexin V and LIVE/DEAD fixable aqua dead cell stain. Downstream STAT5 and STAT3 activation in basal state, and as a response to treatment, was assessed using phosphoflow. We demonstrated mechanisms of growth inhibition via reduction in STAT5 and STAT3 phosphorylation by the inhibitors. RESULTS RUX, CFZ and BTZ were all effective against PAX5::JAK2 transfected Ba/F3 cells with a median lethal dose (LD50) of 514nM (CI 498-530nM) for RUX, 38nM (CI 36-39nM) for CFZ and 19nM (CI 18-20nM) for BTZ. RUX had a variable effect on IL-3 dependent empty vector control cells which also demonstrate JAK/STAT activation, but no effect on the IL-3 independent KG1a cells. CFZ had a lesser effect on empty vector control cells with a LD50 of 59nM (CI 58-60nM) and no effect on KG1a control cells. BTZ had a significant effect on both control cell lines, predicting off-target toxicity and consequently was not applied in combination with RUX. RUX and CFZ in combination demonstrated an LD50 of 21nM (CI 18-25nM) (see figure 1) which is significantly lower than the LD50s for either agent used as monotherapy. Combination index for RUX and CFZ at 45nM was 0.80 and at 50nM was 0.49, suggesting moderate synergy. Phosphoflow demonstrated reduced pSTAT5 with the application of RUX and CFZ to PAX5::JAK2 transfected Ba/F3 cells with mean fluorescence intensity (MFI) reducing from 351 to 285 in inhibitor treated cells, while for STAT3 MFI reduced from 396 to 249. (see figure 2) There was no effect on MFI for control cell lines. This demonstrates that the mechanism for growth inhibition is inhibition of JAK/STAT signaling due to the reduction in pSTAT3 and pSTAT5. CONCLUSIONS We showed in vitro that RUX, CFZ and BTZ are all potent against the high risk PAX5::JAK2 fusion. RUX and CFZ in combination demonstrated moderate synergy against PAX5::JAK2 and inhibited proliferation through their effect on JAK/STAT pathways. The RUX/CFZ combination, drugs widely available in clinical practice, is particularly promising given the apparent synergistic effect on limiting leukemic cell growth. Such treatments warrant clinical trials for management of the poor prognostic group of Ph-like ALL with PAX5::JAK2, given that they may enhance efficacy and lessen toxicity. Clinical trials have already demonstrated efficacy and safety of RUX and CFZ as single agents in combination with chemotherapy for the treatment of B-ALL which indicates the feasibility of combining the two agents clinically in Ph-like ALL.

Protein Tyrosine Phosphatase Non-Receptor 11 (PTPN11/Shp2) as a Driver Oncogene and a Novel Therapeutic Target in Non-Small Cell Lung Cancer (NSCLC)

PTPN11 encodes the SHP2 protein tyrosine phosphatase that activates the mitogen-activated protein kinase (MAPK) pathway upstream of KRAS and MEK. PTPN11/Shp2 somatic mutations occur frequently in Juvenile myelomonocytic leukaemia (JMML); however, the role of mutated PTPN11 in lung cancer tumourigenesis and its utility as a therapeutic target has not been fully addressed. We applied mass-spectrometry-based genotyping to DNA extracted from the tumour and matched the normal tissue of 356 NSCLC patients (98 adenocarcinomas (LUAD) and 258 squamous cell carcinomas (LUSC)). Further, PTPN11 mutation cases were identified in additional cohorts, including TCGA, Broad, and MD Anderson datasets and the COSMIC database. PTPN11 constructs harbouring PTPN11 E76A, A72D and C459S mutations were stably expressed in IL-3 dependent BaF3 cells and NSCLC cell lines (NCI-H1703, NCI-H157, NCI-H1299). The MAPK and PI3K pathway activation was evaluated using Western blotting. PTPN11/Shp2 phosphatase activity was measured in whole-cell protein lysates using an Shp2 assay kit. The Shp2 inhibitor (SHPi) was assessed both in vitro and in vivo in a PTPN11-mutated cell line for improved responses to MAPK and PI3K targeting therapies. Somatic PTPN11 hotspot mutations occurred in 4/98 (4.1%) adenocarcinomas and 7/258 (2.7%) squamous cells of 356 NSCLC patients. Additional 26 PTPN11 hotspot mutations occurred in 23 and 3 adenocarcinomas and squamous cell carcinoma, respectively, across the additional cohorts. Mutant PTPN11 significantly increased the IL-3 independent survival of Ba/F3 cells compared to wildtype PTPN11 (p < 0.0001). Ba/F3, NCI-H1703, and NCI-H157 cells expressing mutant PTPN11 exhibited increased PTPN11/Shp2 phosphatase activity and phospho-ERK1/2 levels compared to cells expressing wildtype PTPN11. The transduction of the PTPN11 inactivating mutation C459S into NSCLC cell lines led to decreased phospho-ERK, as well as decreased phospho-AKT in the PTPN11-mutated NCI-H661 cell line. NCI-H661 cells (PTPN11-mutated, KRAS-wild type) were significantly more sensitive to growth inhibition by the PI3K inhibitor copanlisib (IC50: 13.9 ± 4.7 nM) compared to NCI-H1703 (PTPN11/KRAS-wild type) cells (IC50: >10,000 nM). The SHP2 inhibitor, in combination with the PI3K targeting therapy copanlisib, showed no significant difference in tumour development in vivo; however, this significantly prevented MAPK pathway induction in vitro (p < 0.0001). PTPN11/Shp2 demonstrated the in vitro features of a driver oncogene and could potentially sensitize NSCLC cells to PI3K inhibition and inhibit MAPK pathway activation following PI3K pathway targeting.

Abstract 4225: IL-2Rβ/IL-2R γsynthetic cytokines induce activation of human T and NK cells

Abstract Introduction: Heterodimerization of the intermediate affinity Interleukin-2 Receptors (IL-2R), IL-2Rβ and IL-2Rγ, initiates a signaling cascade in T and NK cells that ultimately results in proliferation and production of Interferon-gamma (IFN-γ). Binding of IL-2 in a dimeric complex with intermediate affinity or in the high affinity trimeric complex, which also includes IL-2Rα and is predominantly expressed on antigen activated T cells and Tregs leads to trans-phosphorylation of signaling motifs on the IL-2Rβ and IL-2Rγ intracellular domains by the associated JAK kinases. The function of the wild type IL-2 is to bring the receptor chains in close proximity to produce an optimal level of phosphorylation and activation of associated STAT transcription factors. Here we established a way to bring IL-2Rβ and IL-2Rγ chains together in a cytokine-independent manner that results in functional activation. Experimental Procedures: Human IL-2Rβ and IL-2Rγ specific heavy chain single domain antibodies (VHH) were generated by camel immunization and screening of VHH libraries prepared from peripheral blood cells for binding. Ten IL-2Rβ VHH segments and six IL-2Rγ VHH segments, all with low nanomolar affinity, were identified and coupled as IL-2Rβ/IL-2Rγ VHH dimers in all possible combinations in both amino-carboxy and carboxy-amino orientations yielding 120 different proteins that were tested in human T and NK cell functional assays. Results: IL-2Rβ/IL-2Rγ VHH dimers were biologically active and induced pSTAT-5 phosphorylation in the IL-2 dependent NK cell line NKL at various levels. The biological activity of these IL-2Rβ/IL-2Rγ VHH dimers was further confirmed on primary cells. IL-2Rβ/IL-2Rγ VHH dimers induced pSTAT5 phosphorylation on NK cells isolated from human peripheral blood and culture with IL-2Rβ/IL-2Rγ VHH dimers resulted in proliferation and production of high but varied levels of IFN-γ. The activity of IL-2Rβ/IL-2Rγ VHH dimers on primary T cells was also examined. Similar to NK cells, IL-2Rβ/IL-2Rγ VHH dimers induced pSTAT5 phosphorylation, proliferation and IFN-γ production by CD4 positive and CD8 positive T cell blasts generated after CD3/CD28 activation of human PBMC. Conclusions: In conclusion, we have generated a series of functional IL-2Rβ/IL-2Rγ VHH dimers representing surrogate cytokine agonists each with unique signaling strengths that will now be further analyzed for potential therapeutic application in tumor immunology and auto-immunity Citation Format: Rene de Waal Malefyt, PJ Aspuria, Sandro Vivona, Priyanka Balasubrahmanyam, Cindy Buffone, Mahalakshmi Ramadass, Romina Riener, Martin Oft, Patrick Lupardus, Robert Kastelein. IL-2Rβ/IL-2R γsynthetic cytokines induce activation of human T and NK cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4225.

Activation of the STAT1-BCL-2/MCL-1 Axis in Leukemic Cells Carrying a SPAG9-JAK2 Fusion

[Background and aim of this study]Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a distinct subtype of B-ALL with poor prognosis. JAK2 related fusion genes have been identified in this subtype, especially in adolescent and young adults (AYA). Previously, we identified SPAG9-JAK2 fusion gene in 14-year-old boy with Ph-like ALL (Kawamura M, et al. Genes Chromosomes Cancer. 2015). In this study, we performed functional analysis of the SPAG9-JAK2 fusion protein, and evaluated the efficacy of treatment with a JAK inhibitor against cells carrying the fusion. In addition, we assessed therapeutic options other than JAK2 inhibition following comprehensive molecular analysis.[Materials and Methods]Full length of SPAG9-JAK2 cDNA was cloned into retroviral construct with Tet-On system. Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with retroviral vector to establish Ba/F3 cells expressing SPAG9-JAK2 (Ba/F3-SPAG9-JAK2) under doxycycline (DOX) dependent manner. Ba/F3-SPAG9-JAK2 were analyzed whether IL-3 independent growth was achieved. Aberrant activation of JAK-STAT pathway achieved by SPAG9-JAK2 was evaluated by western blot. To clarify whether the tyrosine residues of JAK2 in this fusion protein were critical for IL-3-independent proliferation, Ba/F3 cells expressing SPAG9-JAK2 mutants (SPAG9-JAK2 mut) in which both tyrosine residues of JAK2 were replaced with phenylalanine was established. Gene expression analysis using Mouse Genome 430 2.0 Array was performed for comprehensive analysis of gene expression profile related to SPAG9-JAK2. Sensitivity of Ba/F3-SPAG9-JAK2 to ruxolitinib (a JAK inhibitor) was tested in cytotoxic assay and in xenograft model established using Ba/F3-SPAG9-JAK2 cells.[Results and discussions]The expression of SPAG9-JAK2 in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3-SPAG9-JAK2 proliferated without IL-3 in contrast to Ba/F3 cells (p<0.01), suggesting SPAG9-JAK2 had the proliferation activity. Western blot revealed that constitutive phosphorylation of tyrosine residue of SPAG9-JAK2, STAT3/STAT5, suggesting constitutive activation of JAK2-STAT3/STAT5 pathway. SPAG9-JAK2 mut abolished IL-3 independence (p<0.01), but had no influence on STAT3/STAT5 phosphorylation levels detected by western blot. Gene expression analysis revealed that Stat1 was significantly up-regulated in Ba/F3-SPAG9-JAK2 cells compared with mock Ba/F3 cells (fold change 8.04 with p < 0.01) [Fig. 1], confirmed by western blot. STAT1 was also phosphorylated in Ba/F3-SPAG9-JAK2 but not SPAG9-JAK2 mut cells detected by western blot [Fig. 2], suggesting that STAT1 is a key mediator for SPAG9-JAK2-mediated cell proliferation. Consistently, STAT1 induced expression of the anti-apoptotic proteins, BCL-2 and MCL-1, as did SPAG9-JAK2, but not SPAG9-JAK2 mut confirmed by western blot [Fig. 3]. Ruxolitinib abrogated Ba/F3-SPAG9-JAK2-mediated proliferation in vitro (p<0.01), with an 50% inhibitory concentration (IC50) value of 65.9 ± 9.8 nM, causing decrease of JAK2, STAT1/STAT3/STAT5 phospholyration in western blot and apoptosis in annexin V/PI staining. Ruxolitinib prolonged survival time of xenotransplanted mice (p = 0.0213), however, the proliferation of leukemic cells in mouse bone marrow was not suppressed by ruxolitinib. Ba/F3-SPAG9-JAK2 cells showed a dose-dependent response for venetoclax (a BCL-2 inhibitor) with IC50 2.57 ± 1.11 µM and AZD5991 (an MCL-1 inhibitor) with IC50 6.76 ± 3.31 µM. Treatment of Ba/F3-SPAG9-JAK2 cells with a combination of ruxolitinib and venetoclax or AZD5991 resulted in a significant reduction in the IC50 of ruxolitinib (p<0.01) [Fig. 4, 5], with a combined index (CI) value of 0.61 or 0.92, indicating a moderately or weak synergistic effect in vitro.[Conclusion]SPAG9-JAK2 promotes cell proliferation and that tyrosine phosphorylation of the JAK2 kinase domain is critical for IL-3-independent cell growth. Ruxolitinib shows sufficient cytotoxic effects against Ba/F3-SPAG9-JAK2 cells in vitro, but is only partially effective in vivo. Activation of the JAK2-STAT1-BCL-2/MCL-1 axis contributes to aberrant growth promotion by SPAG9-JAK2. BCL-2 or MCL-1 inhibitors in combination with ruxolitinib shows efficacy against Ph-like ALL carrying the SPAG9-JAK2 fusion in vitro. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Leukemic Cells Expressing ETV6-Frk Identified in a Refractory B-ALL Patient Are Sensitive to Dasatinib in Vitro

[Background]ETV6-FRK is a rare kinase-related fusion gene which was identified only in acute myeloid leukemia (Hosoya N, et al. Genes Chromosomes Cancer. 2005). Herein, we firstly identified ETV6-FRK fusion gene in a patient with high-risk pediatric B cell precursor ALL (B-ALL). Because FRK is Src family tyrosine kinase, we performed functional analysis of ETV6-FRK to establish molecular targeting therapy.[Patient]A 11-year-old boy with B-ALL was refractory to conventional chemotherapy and received allogeneic bone marrow transplantation (allo-BMT) following two courses of blinatumomab. This patient maintains complete remission for three months after allo-BMT. Cytogenetic analysis demonstrated t(6;12)(q21;p13) as a part of complex karyotype. Targeted capture mRNA sequencing identified ETV6-FRK fusion transcript in this patient.[Materials and methods]ETV6-FRK fusion was validated by RT-PCR of the diagnostic leukemic sample from this patient. Full length of ETV6-FRK cDNA was cloned into retroviral vector with Tet-On system. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with retroviral vector to establish Ba/F3 cells expressing ETV6-FRK (Ba/F3-ETV6-FRK) under doxycycline (DOX) dependent manner. Ba/F3-ETV6-FRK was analyzed whether IL-3 independent growth was achieved. To determine whether aberrant activation of FRK-STAT pathway as the downstream effects of ETV6-FRK, activation of FRK-STAT pathway was evaluated by western blot. Finally, in cytotoxic assay, proliferation of Ba/F3-ETV6-FRK was assessed under the media with various concentrations of dasatinib, a tyrosine kinase inhibitor.[Results and discussions]Sequencing of RT-PCR product revealed that ETV6 exon 4 was fused in-frame to FRK exon 3, creating an ETV6-FRK fusion gene. The ETV6-FRK fusion gene produced a chimeric protein consisting of the entire pointed (PNT) oligomerization domain of ETV6 and the kinase domain of FRK (Fig 1). The expression of ETV6-FRK in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3-ETV6-FRK proliferated without IL-3 in contrast to Ba/F3 cells not expressing ETV6-FRK (p<0.01), suggesting ETV6-FRK had proliferation activity. Western blot analysis revealed constitutive phosphorylation of tyrosine residues of ETV6-FRK and STAT5/STAT3/STAT1, suggesting constitutive activation of FRK-STATs pathway was associated with IL-3 independent proliferation activity of ETV6-FRK. Considering that dasatinib, which is Src-kinase inhibitor, could block constitutive phosphorylation of ETV6-FRK, we hypothesized that dasatinib might block the IL-3 independent proliferation of Ba/F3-ETV6-FRK. In vitro killing assay showed that dasatinib suppressed efficiently the proliferation of Ba/F3-ETV6-FRK with 50% inhibitory concentration (IC50) 1.64 ± 0.02 nM, although dasatinib didn't show any effect on Ba/F3 cells not expressing ETV6-FRK (Fig. 2). Annexin V assay determined that 35.8 ± 6.9 % of Ba/F3-ETV6-FRK with dasatinib (10nM, 48hrs) were apoptotic than Ba/F3 cells not expressing ETV6-FRK (Fig. 3, p<0.01). These findings suggested that dasatinib abolished the proliferation activity of ETV6-FRK selectively.[Conclusion]We identified the first patient of pediatric high-risk B-ALL harboring ETV6-FRK fusion by targeted capture mRNA sequencing, who was refractory to the conventional chemotherapy. We also provide the first evidence that dasatinib could abrogate proliferation activity of ETV6-FRK in vitro, suggesting that dasatinib might be effective for the patient with B-ALL carrying a ETV6-FRK fusion. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Oncogenic Cooperation Between IL7R-JAK-STAT Pathway Mutations.

Oncogenic Cooperation Between IL7R-JAK-STAT Pathway Mutations.

Histone Deacetylase Inhibitors Abolish HBZ Protein Expression and Induce Cell Death in HTLV-1 Related Adult T-Cell Leukemia-Lymphoma

Background:Adult T-cell leukemia-lymphoma (ATL) is a malignancy with dismal prognosis caused by HTLV-1. ATL is incurable by conventional drugs. Histone deacetylase (HDAC) inhibitors (HDIs) are broadly active anti-neoplastic agents that can be cautiously exploited in the treatment of viral related lymphomas. HTLV-1 usually establishes lifelong latency in human CD4+ T-cells, which in turn propagate and persist as result of the multifaceted functions of HTLV-1 basic zipper factor (HBZ) through various signaling pathways that promote growth and proliferation, and block apoptosis and cell senescence. All ATL cells harbor at least one copy of latent intact HTLV-1 provirus in most cases, and unlike Tax, all tumors express HBZ from the negative 3‘ proviral strand via SP-1 activity. The HTLV-1 promoter is negatively regulated by HDACs at the 5‘ long terminal repeat (LTR), and by HBZ, which disrupts Tax positive interaction with the transcriptional activator p300/CBP, thus blocking viral transcription. Therefore, treatment of HTLV-1 infected cells with HDIs can induce expression of Tax protein, which is highly immunogenic, and which could promote immune-mediated clearance of ATL cells in vivo.Methods:Low-passage IL-2 dependent ATL cell lines established from patients with acute type ATL and freshly isolated ATL cells were treated with several HDIs (VPA, sodium butyrate, vorinostat, belinostat, panabinostat, and mocetinostat) at various doses and time points. Apoptosis was measured by annexin V and FACS analysis. Expression of HBZ protein, Tax, acetyl and total histone 3 subunits (H3), BIM, caspase 3, caspase 9, Jun B, c-Jun, Jun D, and Sp-1 were measured by Western blots before and after HDI treatment. HBZ and Tax mRNA expression was measured by quantitative RT-PCR. SP-1 binding to HTLV-1 specific oligonucleotide consensus sequence was measured by gel shift assay using nuclear protein extracts before and after HDI treatment.Results:HDIs sequentially increased acetylated H3 levels, blocked HBZ protein, upregulated Tax expression, stabilized BIM, and induced cleavage of pro-caspases 9 and 3 (intrinsic apoptotic pathway), resulting in apoptosis of ATL cells. HDIs tested (VPA and belinostat) blocked expression of Jun-B, which is known to be upregulated by HBZ, while no significant effects were observed on c-Jun and Jun D protein levels. HDIs tested (VPA, belinostat, and panabinostat) did not significantly alter spliced-HBZ RNA levels or affect SP-1 binding to HBZ promoter-specific oligonucleotide sequence, suggesting a post-translational mechanism may contribute to abrogation of HBZ in ATL cells.Conclusions:Our data demonstrate that HDIs target ATL cells in part by abrogating HBZ protein, which could negatively impact the longevity of ATL and HTLV-1 cells in vivo. Long-term clinical use of HDIs might be beneficial for eliminating residual ATL cells after definitive treatment. A pilot clinical trial testing belinostat-based consolidation therapy for aggressive leukemic ATL types is currently ongoing at our institution (available at Clinicaltrials.gov , NCT02737046). DisclosuresNo relevant conflicts of interest to declare.

Targeting T-Cell Malignancies with Chimeric Antigen Receptors Using Two Structurally Different Antigen Binding Domains Against CD5

Patients with relapsed T-cell acute lymphoblastic leukemia (T-ALL) have extremely poor survival when treated with chemotherapy alone. Allogeneic hematopoietic stem cell transplantation (HSCT) offers a chance of cure for these patients, but attaining clinical remission in order to undergo HSCT remains the biggest therapeutic challenge. Chimeric antigen receptor (CAR) T-cell therapy has been used with great success in relapsed/refractory B-ALL patients. The same approach, however, is difficult in targeting T-cell disease given the lack of a T-lymphoblast specific surface antigen. The use of natural killer (NK) cells as the effector cell provides a potential solution. We are testing two different CAR structures directed against CD5, a pan T-cell marker; one consisting of a more traditional immunoglobulin (Ig) based single chain variable fragment (scFv), while the other comprising of a variable lymphocyte receptor (VLR) as the antigen recognition domain. VLRs are single chain crescent shaped proteins that represent the functional unit of the adaptive immune system in jawless vertebrates. Our previous work has shown that a VLR can be used as an alternative for CAR-based antigen recognition. Here, we directly compare a VLR to its scFv counterpart in a CAR setting. The single chain structure of a VLR allows for the rapid creation of novel CARs, compared to the corresponding use of a scFv-CAR, in which the variable heavy and light sequences need further engineering for adapting to CAR technologies. Thus, our hypothesis was that natural killer cells engineered to express an anti-CD5 CAR can specifically be used to target T-cell malignancies, with the VLR-CAR being equal or superior to scFv-based cassettes. We constructed two second generation CARs using the VLR or scFv sequence targeting CD5 as our antigen recognition domain. Both CD5-CAR constructs showed similar activity when tested in CD5-positive Jurkat cells. For our cytotoxicity studies, we used the IL-2 dependent natural killer cell line NK-92. To generate uniform populations of CAR-expressing NK cells we transduced NK-92 cells with a dual lentiviral construct expressing the CD5-CAR and green fluorescent protein (GFP), and then selected for the positively transduced cells using flow sorting for GFP. In vitro cytotoxicity studies showed significantly increased killing using the CD5-CAR expressing NK-92 cells compared to unmodified NK-92 cells (p<0.05), for both VLR and scFv modified cells. We then tested the two CD5-CARs in a T-cell leukemia mouse model. NOD scid gamma (NSG) mice were intravenously injected with luciferase expressing Jurkat leukemia cells to establish the T-cell leukemia xenograft model. Four doses of NK-92 cells were injected over a two week period starting on day 7 post-tumor injection. Bioluminescence imaging was used to monitor tumor burden. The CD5-scFv-CAR NK-92 treated mice group had a significant survival advantage over the other groups (p<0.01). Interestingly, the CD5-VLR-CAR NK-92 treated mice did not have a significant advantage over naïve NK-92 or saline treated groups. Given the superior in vivo cytotoxicity demonstrated in our studies, we plan to use the CD5-scFV-CAR going forward as we transition to primary cells. Overall, these studies provide the foundation to move these studies into preclinical testing as a treatment for relapsed T-ALL. DisclosuresNo relevant conflicts of interest to declare.

Kinome Expression Profiling in Multiple Myeloma Identifies New Therapeutic Targets

Multiple Myeloma (MM) account for approximately 10% of hematological malignancies and is the second most common hematological disorder. Active research on MM allowed great improvement in treatment, including proteasomes inhibitors or immunomodulatory agents, that enhanced significantly the patients median survival from 3-4 years in the 90's to 7-8 years nowadays. However there is a vital need for additional therapies since until today, MM is a condition that cannot be cured, and all patients finally relapse. Although numbers of kinases inhibitors are currently in preclinical and clinical development in cancers, kinases have only be poorly studied in MM. Thus only one study (Tiedeman RE Blood 2010) examined the kinome in MM by using a screening of siRNA in Human Myeloma Cell lines (HMCL).Here, in contrast to Tiedeman et al., we evaluated the potential of kinase involvement directly on patient outcome. We first performed kinome in silico analysis in three independent cohorts of patients, and identified 36 kinases significantly and identically involved in MM patient's survival. We built a Kinome Index (KI) from the 36 kinases expression, and showed that KI: 1) is related to OS and EFS prognosis in 3 independent cohorts, 2) is linked to proliferation and poor prognosis subgroups of MM molecular classification, 3) is associated with relapse. Among the 36 targets, 7 had available inhibitors and were not already consistently studied in MM (PBK, SRPK1, CDC7-DBF4, MELK, CHK1, PLK4, MPS1/TTK). We then tested the therapeutic interest of these 7 kinase inhibitors using 4 HMCLs representing two IL-6 independent (AMO1, OPM2) and two IL-6 dependent (XG1, XG21) cell lines. All tested inhibitors significantly reduced viability of the cells, and had IC50 from the nanomolar (for MELKi, CHK1i and PLK4i) to the micromolar range (for PBKi, SRPK1i, CDC7-DBF4i and MPS1/TTKi). Annexin, PARP and cell cycle analysis following treatment with selected concentration of the inhibitors in AMO1, showed significant increase in apoptosis, associated for most of them with a perturbation of the cell cycle. Treatment of primary myeloma cells from patients with MELKi, CHK1i and PLK4i induced MM cell death while they didn't impacted significantly the cellular microenvironment. Similarly experiments using murine MM cells, from 5TMM models, confirmed the potential of these three inhibitors.Next, IC20 of the different inhibitors were tested in co-treatment with melphalan, lenaledomide or velcade in XG1, XG21, AMO1 and OPM2 to challenge the capabilities of the selected kinases inhibitors to synergize with major routinely used therapeutics. We didn't observed any synergy for the co-treatments with bortezomib. However, CHK1i, MELKi, PBKi, DBF4i synergized with melphalan to induce MM cell death. Furthermore, CHK1i, MELKi, PLK4i, PBKi, SRPK1i demonstrated also a synergistic effect when combined with lenalidomide, highlighting their potential therapeutic interest in MM. Analysis of apoptosis and cell cycle following co-treatments with melphalan and lenaledomide using AMO1 cell line demonstrated an increase in PARP cleavage and annexin V staining in association with significant cell cycle deregulation. One of the outstanding co-treatment effects was the reversion of the natural AMO1's resistance to lenaledomide with CHK1, MELK and PBK inhibitors used at their IC20. We then tested their therapeutic interest to overcome melphalan drug resistance using wild-type (XG7-WT) and melphalan-resistant (XG7-Mres) cell lines. PLK4 and DBF4 inhibitors demonstrated higher activity on XG7-Mres cells compared to their WT control. In addition CHK1, PBK and DBF4 inhibitors (IC20) were able to re-sensitize XG7-Mres to melphalan at a similar level than XG7-WT. Altogether we identified 36 new potential kinases deregulated in MM in association with a poor prognostic value. Seven of them represent potential new MM therapeutic targets alone or in combination with conventional therapies in high-risk MM patients. DisclosuresBruyer:Diag2tec: Employment. Cartron:Sanofi, BMS, Jansen, celgene, Roche, Gilead: Equity Ownership; Celgene: Consultancy, Employment; Roche: Consultancy, Equity Ownership, Honoraria, Research Funding. Hose:Sanofi: Research Funding; EngMab: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees.

Germline Gain-of-Function JAK3 Mutation in Familial Chronic Lymphoproliferative Disorder of NK Cells

Chronic lymphoproliferative disorder of NK-cells (CLPD-NK) predominantly occurs in adults with a median age of diagnosis at 60 years. It is characterized by a persistent increase (≥2 x 109/L, for &amp;gt; 6 months) of mature NK-cells in peripheral blood with an indolent clinical course similar to T-cell large granular lymphocytic leukemia (T-LGL). Somatic gain-of-function (GOF) mutations in STAT3 have been identified in approximately one-third of patients with CLPD-NK. On the other hand, somatic GOF mutations in JAK3 recurrently occur in various types of T-cell neoplasms and exert a GOF effect, unlike biallelic germline loss-of-function mutations found in severe combined immunodeficiency (Figure 1). Here we report on the discovery of a germline GOF JAK3 mutation as a first germline cause of CLPD-NK. Two individuals from one nonconsanguineous family (mother and son) presented at ages 35 and 12 years old with NK cell lymphoproliferation, lymphadenopathy, splenomegaly and autoimmune symptoms. The mother had history of vasculitis while the son was diagnosed with CVID, recurrent multilineage autoimmune cytopenia and subsequently developed psoriasis at 18 years old. The immunological phenotype was assessed in depth in the son and revealed hypogammaglobulinemia with normal vaccine response, expanded NK cells (between 40-60% of total lymphocytes), decreased FOXP3 expression in regulatory T cells and B cell subsets showing decreased total and isotype-switched memory B cells. Flow cytometry revealed expanded population of aberrant NK cells with normal KIR panel. Marrow studies revealed normal karyotype, cellularity and maturation but prominent large granular lymphocytes with benign cytology. Genomic studies identified a novel germline heterozygous JAK3 variant (c.1520A&amp;gt;C/p.Q507P) located at the linker between SH2 and pseudokinase domain (Figure 1). No additional somatic mutations were found. The JAK3 variant was not present in gnomAD database but previously reported as somatic mutation in a patient with T cell prolymphocytic leukemia (Bergmann, Genes Chromosomes Cancer 2014) and predicted to exert a GOF effect. It is well known that JAK3 activation promotes STAT signaling, a known key player in lymphoproliferation. To better understand the biological effect in patient cells, we performed pSTAT5 phosphorylation assay in primary blood lymphocytes after IL2 stimulation, revealing increased pSTAT5 phosphorylation in patient's NK cells. The IL3-dependent BaF3 cell line (containing human wild type JAK3) has been previously used as a robust model to study the effect of JAK3 mutations (Elliott et al. Blood 2011). We therefore introduced the p.Q507P mutation using CRISPR/Cas9 system and used known GOF mutation p.A572V as positive control. While untransduced BaF3 cells died without IL3, p.Q507P-mutant BaF3 cells survived and rapidly expanded without IL3, showing comparable results to positive control. Finally, using western blot we identified constitutive phosphorylation as expected mechanism underlying the lymphoproliferation p.Q507P-mutant cells. In summary, we identify JAK3 as the first germline cause underlying familial CLPD-NK and describe a novel primary immune dysregulatory disorder characterized by non-malignant NK lymphoproliferation with CVID and autoimmune dysregulation. These findings broaden the genetic spectrum of primary immunodeficiency and immune dysregulatory conditions. Disclosures Takemoto: Genentech: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: DSMB Aplastic Anemia Trial. Nichols:Incyte corporation: Research Funding.

Abstract 525: A novel anti-PD1-IL15 immunocytokine potentiates anti-tumor T cell activity of PD-1 checkpoint inhibition and IL-2R-beta-gamma agonism

Abstract Therapeutic antibodies targeting immune checkpoint inhibitors (ICI) such as PD-1/PD-L1 effectively expand and reactivate T cells in patients, leading to long-lasting response in multiple tumor types. However, only a fraction of patients responded to approved ICIs, majority are either resistant or quickly become refractory. Other immunotherapy modalities including immunostimulatory cytokines IL-2, IL-12 and IL-15 demonstrated clinical benefits as monotherapy or in combination with ICIs. Cytokines exhibit in general a short half-life and systemic toxicities that limit their use as the optimal doses in treating cancer. An antibody-based immunocytokine fusion such as Kadmon lead candidate KD033 (anti-PDL1/IL15) and Roche anti-PD1/CEA/FAP-IL2v can extend the half-life of cytokine and reduce systemic toxicities. In this study, a fully human single-chain variable fragment (scFv) antibody against mouse PD1 (mPD1) have been isolated from the phage display library. The variable domains of these antibodies were fused to either human IgG1a or mouse IgG2a constant domain first, and then fused to either human IL15 receptor alpha sushi domain-hIL15 complex (hSD15) or mouse IL15 receptor alpha sushi domain-mIL15 complex (mSD15). These variations of fusion have been tested in in vitro binding and functional assays, and in vivo in PD1/PDL1 resistant mouse syngeneic model LL2 (Lewis Lung Carcinoma). We demonstrated that hSD15 fusion antibody can stimulate both IL2 dependent human and murine cells growth, surprisingly, mSD15 fusion antibody can only stimulate murine cell growth. Although mSD15 fusion antibody EC50 was 10 folds better than hSD15 fusion antibody in stimulating mouse spleen cell growth in vitro, it did not show a better efficacy than hSD15 fusion antibody in LL2 model. In vivo, mSD15 fusion antibody had higher maximum tolerate dose than hSD15 fusion antibody (up to 12mg/kg). In addition, anti-mPD1/mSD15 showed better efficacy than either the mIL15 and anti-mPD1 alone or the combination of anti-mPD1 plus mIL15 in vitro and in vivo. Together these preclinical data have confirmed that PD1-IL15 could be a promising next generation IL-15 fusion for cancer immunotherapy. Citation Format: Dan Lu, Zhanna Polonskaya, Tzi-Pei Chang, Stella Martomo, Xenia Luna, Zhikai Zhang, Faical Miyara, Jeedar Patel. A novel anti-PD1-IL15 immunocytokine potentiates anti-tumor T cell activity of PD-1 checkpoint inhibition and IL-2R-beta-gamma agonism [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 525.

Discovery & Characterization of Therapeutically Targetable Ntrk Point Mutations in Leukemia

Discovery & Characterization of Therapeutically Targetable Ntrk Point Mutations in Leukemia

Leukemic Cell with a Novel Kinase Fusion Gene SPAG9-JAK2 Exhibits High Sensitivity to Ruxolitinib

[Background and aim of this study] Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a distinct subtype of B-ALL with poor prognosis. JAK2 related fusion genes with diverse partner genes have been identified in this subtype, especially in adolescent and young adults (AYA). Previously, we identified SPAG9-JAK2 fusion gene in 14-year-old boy with Ph-like ALL (Kawamura M, et al. Genes Chromosomes Cancer. 2015). JAK2 fusion protein is putative therapeutic target of Ph-like ALL with JAK2 rearrangement, so it should be clarified whether JAK inhibitor is effective for the leukemic cells with JAK2 fusion genes. In this study, we performed functional analysis of SPAG9-JAK2 to establish molecular targeting therapy for the patients with SPAG9-JAK2. [Materials and Methods] Full length of SPAG9-JAK2 cDNA was cloned into retroviral construct with Tet-On system. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with retroviral vector to establish Ba/F3 cells expressing SPAG9-JAK2 (Ba/F3-SPAG9-JAK2) under doxycycline (DOX) dependent manner. Once Ba/F3-SPAG9-JAK2 was established, cells were analyzed whether IL-3 independent growth was achieved. To determine whether aberrant activation of JAK-STAT pathway achieved by SPAG9-JAK2, activation of JAK-STAT pathway was evaluated by western blot. In addition, gene expression analysis using Mouse Genome 430 2.0 Array was performed for comprehensive analysis of gene expression profile related to SPAG9-JAK2. Finally, in cytotoxic assay, proliferation of Ba/F3-SPAG9-JAK2 was assessed under the media with various concentrations of ruxolitinib (JAK inhibitor, RUX). [Results and discussions] The expression of SPAG9-JAK2 in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3-SPAG9-JAK2 could proliferate without IL-3 in contrast to Ba/F3 cells (p&lt;0.0001), suggesting that SPAG9-JAK2 had the IL-3 independent proliferation activity of Ba/F3 cells. Western blot revealed that constitutive phosphorylation of tyrosine residue of SPAG9-JAK2, Stat5, and Stat3, suggesting that constitutive activation of JAK2-STAT pathway contributes to IL-3 independent proliferation activity. Gene expression analysis revealed that, in Ba/F3-SPAG9-JAK2, expression of 187 genes among 45,037 probes was increased (log 2 ratio, ≥2.0) and the expression of 371 genes was decreased (log 2 ratio, ≤2.0), compared with those in Ba/F3. Pathway analysis revealed that the expression level of several genes related to type II interferon signaling pathway, p53 signaling pathway, Il4 receptor signaling pathway and G1 to S cell cycle control in Ba/F3-SPAG9-JAK2. In detail, Stat1, Stat2, Ptpn6, Irf1 and Cxcr4 were significantly up-regulated and Cdkn2a and Cdkn2b were significantly down-regulated in Ba/F3-SPAG9-JAK2. These findings were in accordance with activation of JAK-STAT pathway and aberrant growth promotion of Ba/F3-SPAG9-JAK2. Considering that JAK inhibitors could block constitutive phosphorylation of SPAG9-JAK2, RUX might block the IL-3 independent proliferation of Ba/F3-SPAG9-JAK2. Cytotoxic assay revealed that 100nM of RUX suppressed the proliferation of Ba/F3-SPAG9-JAK2 completely (p&lt;0.00001), although 100nM RUX didn't show any effect on Ba/F3. Annexin V assay also determined that 100 nM RUX induced more apoptosis in Ba/F3-SPAG9-JAK2 than Ba/F3 (p&lt;0.01). These findings suggest that RUX abolishes the proliferation activity of SPAG9-JAK2 selectively and is possibly effective for ALL with SPAG9-JAK2. [Conclusion] Although in vivo study is required, our in vitro study clearly demonstrated that RUX could be effective for the B-ALL patients withSPAG9-JAK2. Further studies are on-going to determine other therapeutic target of B-ALL with SPAG9-JAK2. Figure Disclosures No relevant conflicts of interest to declare.

The Clinical and Functional Relevance of the Transforming AKT E17K Mutation in T-ALL

INTRODUCTION. The importance of IL-7R signaling has been thoroughly studied in the context of both normal T-cell development and leukemogenesis. Upon IL-7 induced heterodimerization of the IL-7Rα and the γc chain, downstream signaling routes regulate survival and proliferation of differentiating T-cells. JAK-STAT, MAPK-ERK and PI3K-AKT pathways are aberrantly activated in T-cell acute lymphoblastic leukemia (T-ALL) patients by recurrent gain-of-function mutations of the IL-7R signaling pathway. IL-7R signaling mutations are a result of mutations in IL7Ra, JAK1/3, PTPN11, NF1, STAT5B, N/KRAS, PI3K or AKT that are found in nearly 35% of pediatric T-ALL patients and are associated with steroid resistance and inferior event-free survival. Here we focus on downstream AKT activation in relation to cellular transformation and steroid resistance. We previously demonstrated that AKTE17K transforms IL3-dependent BaF3 cells in contrast to wild type AKT, while wild type AKT drives steroid resistance in SUP-T1 T-ALL cells in contrast to mutant AKTE17K. AIM. Our aim was to identify functional differences between AKT and AKTE17K molecules in respect to cellular transformation and steroid resistance. We assessed activation level, cellular localization and downstream signaling events that may explain these functional differences. RESULTS. For this study, we used doxycycline-inducible SUP-T1 cell lines that overexpress wild type AKT or mutant AKTE17K molecules. Using immunohistochemistry, we revealed abundant cytoplasmic localization of wild type AKT but predominant plasma membrane localization of AKTE17K and extends previous findings by others. Furthermore, we found evidence for phosphorylation of wild type AKT on serine-473 (S473) and threonine-308 (T308) residues in both cytoplasmic and nuclear fractions, indicating that part of induced AKT becomes activated. In contrast, expression of AKTE17K was accompanied with abundant phosphorylation of T308 while having relatively low levels of S473 phosphorylation. The T308/S473 phosphorylation ratio was 5 times higher for AKTE17K compared to wild type AKT. These results are in line with current views on AKT activation that S473 phosphorylation facilitates the opening of the AKT pleckstrin homology domain and membrane docking, after which AKT is phosphorylated (activated) on the T308 residue by PDK1. The constitutive plasma membrane localization and open conformation of AKTE17K as a result of its E17K pleckstrin homology domain mutation leaves it independent of S473 phosphorylation and results in enhanced T308 phosphorylation by PDK1. Consequently, AKTE17K mutant cells may exhibit reduced cellular sensitivity to allosteric AKT inhibitors but not to type I ATP-competitive inhibitors. Indeed, SUP-T1 cells expressing wild type AKT or mutant AKTE17K are equally sensitivity to the ATP-competitive AZD5363 inhibitor, but AKTE17K cells display reduced sensitivity to the MK2206 allosteric inhibitor compared to AKT wild type cells. In an attempt to explain enhanced steroid resistance by expression of wild type AKT but not mutant AKTE17K, we found no differences in AKT-mediated S134 phosphorylation of the NR3C1 steroid receptor or impaired nuclear import of NR3C1 following steroid treatment (Piovan et al., Cancer Cell 2013). This indicates that AKT induces steroid resistance by other mechanisms in our SUP-T1 cell system. CONCLUSIONS. In contrast to wild type AKT overexpression, we demonstrated that AKTE17K has (i) transforming activity, (ii) does not yield cellular resistance to steroid treatment, (iii) is predominantly localized at the plasma membrane, (iv) has high T308 over S473 phosphorylation and (v) is less sensitive to the MK2206 allosteric AKT-inhibitor. These observed differences are likely caused by the constitutively open AKTE17K conformation. Since no differences in NR3C1 phosphorylation or nuclear shuttling were observed in our model, we hypothesize other mechanisms underlie the provoked steroid resistance by AKT wild type overexpression. To identify these novel mechanisms, we are currently performing an unbiased phospho-protein array to identify differentially phosphorylated AKT substrates. Disclosures No relevant conflicts of interest to declare.

Oncogenic Mechanisms of CBL E3 Ubiquitin Ligase Mutations in Myeloid Malignancies

CBL encodes an E3 ubiquitin ligase and signaling adaptor that acts downstream of cytokine receptors. Recurrent CBL mutations are found in a variety of myeloid disorders, including 10-15% of chronic myelomonocytic leukemia (CMML) cases, and specifically disrupt the protein's RING domain, which is responsible for E3 ligase activity; adaptor domains of CBL, including the tyrosine kinase-binding domain (TKB), proline-rich region (PRR) and C-terminal phosphotyrosine (pY) residues, remain intact in the context of RING mutations. In prior studies, CBL RING mutations were associated with hyperactivation of signaling pathways that drive cell proliferation. However, the precise mechanism by which CBL mutants act remains incompletely understood. Here we combined functional assays and mass spectrometry (MS) to comprehensively define the phosphoproteome, CBL interactome and molecular mechanism of signaling hyperactivation in a panel of cell lines expressing an allelic series of CBL RING mutants. We identified the SRC family kinase LYN as a key driver of signaling by CBL RING mutants; furthermore, we demonstrated in vitro and in vivo efficacy of LYN inhibition by dasatinib in CBL-mutant cell lines and primary CMML patient samples. We generated cell lines expressing wild-type (WT) or RING-mutant CBL using IL3-dependent mouse 32D cells and GM-CSF-dependent human TF1 cells. Cells expressing CBL RING mutants Y371H, C384Y or R420Q had a proliferative advantage over CBL WT or CBL knockout cells. To determine the role of CBL's adaptor domains in the proliferative advantage conferred by CBL RING mutants, we generated double mutants comprising the C384Y RING mutation in cis with mutations in the TKB domain (G306E), PRR (Δ477-688) or pY residues (Y700/731/774F). The proliferative advantage of cells expressing CBL C384Y was significantly reduced with mutation of the TKB domain, PRR or pY residues, indicating that CBL's adaptor domains are critical for the proliferative advantage of cells expressing RING-mutant CBL. To assess the effects of CBL RING mutation on signaling, we used MS to measure global protein phosphorylation in 32D cells expressing CBL WT or CBL C384Y. Activation of LYN and the PI3 kinase (PI3K) pathway were most significantly increased in cells expressing CBL C384Y compared to CBL WT; western blot confirmed increased phosphorylation of LYN, the PI3K p85 subunit and AKT in cells expressing CBL Y371H, C384Y or R420Q. We next employed immunoprecipitation (IP) followed by MS to characterize the global CBL interactome in 32D cells expressing CBL WT or RING mutants Y371H, C384Y or R420Q. In line with the phosphoproteomic analysis, LYN showed significantly increased binding to CBL RING mutants; the PI3K p85 subunit also showed increased binding to CBL RING mutants. Thus, global proteomic analyses revealed that increased binding of LYN and p85 to CBL RING mutants was directly associated with hyperactivation of LYN and PI3K-AKT signaling pathways. Deletion of CBL's PRR reduced interactions with both LYN and p85, and the CBL-p85 interaction required CBL Y731. Genetic ablation or inhibition of LYN by dasatinib decreased binding of p85 to CBL, suggesting that increased CBL Y731 phosphorylation by LYN enabled the CBL-p85 interaction. Indeed, CBL Y731 phosphorylation and AKT activation were diminished by deletion of CBL's PRR, LYN knockout or LYN inhibition by dasatinib. Altogether, these data demonstrated that enhanced LYN activation in cells expressing RING-mutant CBL drives increased CBL phosphorylation, p85 recruitment and downstream AKT signaling. Given the central role of LYN in signaling by CBL RING mutants, we hypothesized that LYN inhibition by dasatinib would abrogate the hyperproliferation of cells expressing CBL RING mutants. Dasatinib blocked the proliferative advantage of 32D and TF1 cells expressing CBL RING mutants. In addition, dasatinib significantly reduced the number of methylcellulose colonies formed by bone marrow mononuclear cells from 2 patients with CBL-mutated CMML; dasatinib treatment of mice xenografted with the same CMML cells resulted in a substantial decrease in leukemia burden compared to vehicle-treated mice. In summary, we have defined a mechanism by which LYN promotes PI3K-AKT signaling through CBL RING mutants. Our data provide rationale for exploring the therapeutic potential of LYN and/or PI3K-AKT inhibition in patients with CBL-mutated myeloid malignancies. Disclosures Ebert: Celgene: Research Funding; Deerfield: Research Funding.

A Novel PAX5-KIDINS220 Fusion Protein Activates Multiple Signals Associated with Therapeutic Resistance

Background: It is well known that PAX5 related fusion proteins are mainly associated with leukemogenesis of B cell precursor acute lymphoblastic leukemia (B-ALL) through dominant negative effect against normal PAX5, resulting in impairment of B cell differentiation. However, different biological property of PAX5 fusion protein which is related to B-ALL has not been fully investigated. Here, we performed functional analysis of novel fusion protein, PAX5-KIDINS220 (P-K220) which was identified in pediatric Ph-like ALL patient. Methods: Full length of P-K220 fusion gene was cloned into pRetroX-Tight-Pur retroviral vector. We also established the PAX5-N construct that contained only PAX5 region (1-306 aa) of P-K220 so that we could analyze the importance of KIDINS220 in P-K220. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with this retroviral vector to establish Ba/F3 cells expressing P-K220 or PAX5-N under doxycycline (DOX) dependent manner. P-K220 was also cloned into pAcGFP1-C1 vector and pMSCVneo vector to perform localization assay and luciferase reporter assay. Gene expression analysis was performed using Mouse Genome 430 2.0 Array. In cytotoxic assay using co-culture system with murine mesenchymal stromal cell, MS-5, Ba/F3 cells that were pre-stained with Carboxyfluorescein diacetate succinimidyl ester (CFSE) were seeded on MS-5 stromal cell, then 10 nM vincristine (VCR) was applied. 72 hours later, flow cytometric analysis was performed to determine the fraction and proliferation ability of viable Ba/F3 cells. The proliferation ability was estimated by CFSE fluorescence that attenuates depending on cell proliferation. Results and discussions: P-K220 and PAX5-N were successfully expressed in Ba/F3 cells, confirmed by western blotting. Localization assay revealed that GFP tagged P-K220 was localized in a nucleus of HEK293-T cells under confocal microscopy, suggesting that P-K220 acted as a transcriptional factor. Luciferase reporter assay revealed that P-K220 protein inhibited PAX5 transcriptional activity in dominant negative fashion. Although P-K220 was identified in Ph-like ALL patient and activated JAK2-STAT5 pathway through reduction of Socs5 expression, Ba/F3 cells expressing P-K220 protein did not acquire IL-3 independency. P-K220 attenuated proliferation of Ba/F3 cells (p=0.02), which was in contrast to PAX5-JAK2. To reveal which pathways were affected by P-K220, gene expression analysis was performed. Gene set enrichment analysis revealed that multiple pathways related to chemotaxis, migration, such as IL-15 pathway, were activated in P-K220 expressing Ba/F3 cells. RQ-PCR and western blotting confirmed P-K220 induced expression of IL-15 in RNA (p=0.018) and protein level, suggesting that P-K220 might be associated with infiltration of leukemic cells into extramedullary site. Next, we examined whether P-K220 was associated with sensitivity of chemotherapeutic agents, such as vincristine (VCR), cytarabine, prednisolone, methotrexate, and 6-mercaptoprine. P-K220 expressing Ba/F3 cells showed higher VCR IC50 (0.4 nM vs 2.5 nM) and decreased Annexin V positive fraction under the condition of 10 nM VCR (39.4 % vs 23.8 %, p=0.04). In co-culture analysis with MS-5 stromal cell under the 10 nM VCR, the fraction of viable Ba/F3 cells that adhered to MS-5 was significantly increased with expression of P-K220 than PAX5-N or Dox (-) (11.6% vs 7.3% vs 6.8%, p<0.001), and proliferation ability was also significantly increased with expression of P-K220, that was estimated by mean CFSE fluorescence (479.6 vs 990.0 vs 909.7, p<0.001), suggesting P-K220 was associated with VCR resistance. Gene expression analysis and RQ-PCR revealed that P-K220 induced expression of Abcc5 which was reported to be associated with VCR resistance (p=0.003). Conclusion: P-K220 did not induce high proliferation of Ba/F3 cells even though identified in Ph-like ALL patient. However, P-K220 might be associated with treatment resistance through the infiltration of leukemic cells into extramedullary sites partly via activation of IL-15 pathway and resistance to VCR via induction of Abcc5. DisclosuresNo relevant conflicts of interest to declare.

Leukemic Cell Expressing a Novel Kinase Fusion Protein NCOR1-LYN Exhibits High Sensitivity to Dasatinib and Rapamycin

[Background and aim of this study]Kinase fusion protein is putative therapeutic target of hematological malignancies. Previously, we identified NCOR1-LYN fusion gene in which NCOR1 exon 34 was fused in-frame to LYN exon 7 in a pediatric patient with Ph-like acute lymphoblastic leukemia (ALL) treated according to Japan Childhood Leukemia Study Group ALL-02 protocol (Yano M, et al. Br J Haematol 2015). Because rearrangement of LYN is the recurrent genetic abnormality in high risk B-ALL, targeting therapy for LYN rearranged ALL could be attractive. Thus, in this study, we performed functional analysis of NCOR1-LYN fusion protein to get insight of biological property of this fusion protein to establish targeting therapy for LYN rearranged ALL.[Materials and Methods]Full length of NCOR1-LYN cDNA was cloned into pRetroX-Tight-Pur retroviral vector. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with this retroviral vector to establish Ba/F3 cells expressing NCOR1-LYN under doxycycline (DOX) dependent manner. Once Ba/F3 cells expressing NCOR1-LYN were established, cells were analyzed whether IL-3 independent growth was achieved. To determine whether the tyrosine residues of LYN (Y397 and Y508) in this fusion protein were critical for IL-3-independent proliferation, Ba/F3 cells expressing NCOR1-LYN mutants in which both tyrosine residues of LYN were replaced with phenylalanine (Y397F and Y508F) was established. In cytotoxic assay, proliferation of Ba/F3 cells expressing NCOR1-LYN was assessed under the media with tyrosine kinase inhibitors (TKI), such as imatinib and dasatinib. To determine changes of gene expression pattern in Ba/F3 cells expressing NCOR1-LYN, gene expression analysis was performed using Mouse Genome 430 2.0 Array.[Results and discussions]The expression of NCOR1-LYN in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3 cells expressing NCOR1-LYN could proliferate without IL-3 in contrast to Ba/F3 cells not expressing NCOR1-LYN couldn't, suggesting that NCOR1-LYN could induce IL-3 independent proliferation of Ba/F3 cells. Western blot analysis also revealed that constitutive tyrosine phosphorylation of NCOR1-LYN fusion protein was present, intriguing that constitutive phosphorylation of tyrosine residues in LYN was associated with IL-3 independent proliferation activity of NCOR1-LYN. Consistent with our hypothesis, Ba/F3 cells expressing NCOR1-LYN mutant (Y397F and Y508F), which didn't show constitutive phosphorylation of NCOR1-LYN, could not proliferate without IL-3.Considering that TKIs could block constitutive phosphorylation of LYN, TKIs might block the IL-3 independent proliferation of Ba/F3 cells expressing NCOR1-LYN. Cytotoxic assay revealed that 1nM of dasatinib suppressed the proliferation of Ba/F3 cells expressing NCOR1-LYN completely (p<0.01), although imatinib didn't show any effect. Annexin V assay also determined that 96% of Ba/F3 cells treated with dasatinib (10nM, 48hrs) were Annexin positive. However, dasatinib didn't show any effect on Ba/F3 cells not expressing NCOR1-LYN. These findings suggest that dasatinib abolishes the proliferation activity of NCOR1-LYN selectively.To determine other signaling pathways to be targeted in Ba/F3 cells expressing NCOR1-LYN, Gene Set Enrichment Analysis (GSEA) was performed. GSEA revealed that multiple signaling pathways including mTOR pathway, MYC, E2A and EZH2 related pathways. Because mTOR pathway was activated in Ba/F3 cells expressing NCOR1-LYN (NOM p-value<0.01), mTOR inhibitor might suppress the proliferation activity of NCOR1-LYN. Consistent with our hypothesis, cytotoxic assay revealed that rapamycin (20nM) could suppress the proliferation of Ba/F3 cells expressing NCOR1-LYN efficiently compared to Ba/F3 cells not expressing NCOR1-LYN.[Conclusion]Our in vitro study clearly demonstrated that dasatinib and rapamycin could be effective for the patient with B-ALL harboring LYN rearrangement. DisclosuresNo relevant conflicts of interest to declare.

Towards Improved Models of NPM-ALK Induced T-Cell Lymphoma

Time- and tissue-specific expression of transgenes is essential for the accurate representation of human disease in in vivo models. To improve flexibility but also fidelity of ALK+ ALCL models, we developed new approaches enabling lineage specific expression of NPM-ALK cDNAs, as well as a novel system for CRISPR/Cas induced Npm-Alk recombination. First, we have designed a new system for lineage-restricted expression of transgenes based on a retroviral vector incorporating a translational stop-cassette flanked by loxP recombination sites. Conditional transgene expression in chimeric mice is rapidly achieved through retroviral infection and subsequent transplantation of hematopoietic stem cells (HSC) derived from transgenic mice expressing Cre-recombinase from a lineage specific promoter. To validate the model, we directed expression of NPM-ALK, the fusion oncogene present in anaplastic large cell lymphoma (ALCL), to T-cells by infecting hematopoietic stem cells from Lck-Cre transgenic mice with a retroviral construct containing the Npm-Alk cDNA preceded by a translational stop cassette. The approach efficiently induced T-cell lymphomas within 12-16 weeks closely resembling the human disease including the expression of the ALCL hallmark antigen CD30.Since NPM-ALK overexpressed from a cDNA acts as a very strong oncogene transforming a range of cell types, we were interested to develop a more physiologic model based on chromosomal recombination, enabling NPM-ALK expression from the endogenous Npm promoter. To achieve this, we have designed guide RNAs (gRNAs) directed to either the intron between exon 4 and 5 for Npm1 on mouse chr. 11, or the intron between exons 19 and 20 for Alk on mouse chr. 17., enabling targeted translocation between the two chromosomes. For further analysis, the IL-3 dependent murine pro-B cell line Ba/F3 stably expressing the Cas9 recombinase was transduced with the respective gRNAs and subsequently grown in the absence of IL-3 to allow positive selection of cells transformed by productive t(11;17) NA recombination. A PCR reaction on genomic DNA using primers covering the translocation breakpoint resulted in a product and Sanger sequencing of the amplicon confirmed the intended recombination at the targeted genomic positions. The translocation was also detectable by fluorescence in-situ hybridization (FISH), and Western blot analysis demonstrated expression of a highly phosphorylated Npm-Alk fusion protein. To further probe for oncogene dependency, we treated Npm-Alk translocated cells and control cells with a specific Alk inhibitor, resulting in rapid cell depletion of the Npm-Alk translocated cells, but not controls.The described Cre/loxP-based system represents a versatile tool for the rapid functional analysis of gene function in a defined lineage or in a developmental stage in vivo, and faithfully recapitulates many features of ALCL. Furthermore, using Crispr/Cas to induce targeted double-strand breaks, we have been able to generate specific Npm-Alk translocations in murine cells, paving the way for novel models which may help to further define the initial pathogenetic event underlying lymphomagenesis in ALCL. DisclosuresNo relevant conflicts of interest to declare.