ALBERT

Description: Background: Clonal hematopoiesis of indeterminate potential (CHIP) is defined by the detection of mutations in genes like DNA methyltransferase 3A (DNMT3A) and has recently been described to occur in healthy people and to predispose them to myeloid malignancies. DNMT3A is frequently mutated in acute myeloid leukemia (AML) and mutations have been detected in CD3 positive T-cells of some AML patients. In these patients DNMT3A mutations are early events that are likely to arise from CHIP. It is unknown how a history (hx) of CHIP influences the characteristics of AML patients and their response to therapy. We studied this question on the basis of a large cohort of DNMT3A mutated AML patients. Patients and Methods: 171 DNMT3A mutated AML patients (aged 18-87 years) were included in our study. 127 patients were treated intensively in trials of the AMLSHG and AMLSG. 34 patients received non-intensive therapy and for 10 patients the therapy is unknown. 148 patients carried a mutation at arginine R882. At the time of diagnosis and relapse samples were further sequenced for 54 genes involved in leukemia with next generation sequencing (NGS) on the Illumina platform. Library preparation of diagnostic samples was performed with the TruSight Myeloid sequencing panel (Illumina). T-cells (CD3+ CD11b- CD14- CD33-) were purified by flow cytometry from AML samples at the time of diagnosis. DNMT3A mutational analysis of T-cell samples and of mononuclear cells during remission or at relapse was performed also with ultra-deep sequencing using customized DNMT3A NGS primers. Presence of a DNMT3A mutation in sorted T cell populations was used as an indicator of a hx of CHIP. Results: A total of 40 patients (23%) were found to have the DNMT3A mutation in mononuclear cells and T-cells (hx of CHIP), while 131 patients (77%) had a DNMT3A mutation in mononuclear cells, but not T-cells (control cohort). Comparing these two patient cohorts revealed that significantly more patients in the hx of CHIP cohort had secondary AML (p=0.009), were older (p=0.005) and less likely to receive intensive treatment (p=0.047) while other clinical parameters did not significantly differ. Analysing the mutational profile of 54 genes revealed that the number of mutations per patient between these 2 groups was similar (median 5 vs 4 mutations, p=0.39). Patients with a hx of CHIP were significantly more likely to harbour mutations in TET2 (p=0.006), RUNX1 (p=0.004), SF3B1 (p=0.049), U2AF1 (p=0.015) but less likely to be NPM1 mutated (p=0.005). There was no significant difference in the allelic burden of DNMT3A in the CHIP hx (mean 43.6) vs control group (mean 44.5). The mean variant allele frequencies of DNMT3A, RUNX1 and NPM1 were highest (44, 45 and 43 respectively) as compared to other mutated genes like IDH1, IDH2 and FLT3 (32, 37 and 34). In relapse samples (n=11), the identical DNMT3A mutation could always be identified. However, patients with a hx of CHIP (n=2) had comparable allelic frequencies compared to diagnosis of mutated DNMT3A ( 10% difference), while 7 out of 9 patients in the control group had a change in the allelic frequency at the time of relapse (mostly reduction). In all remission samples DNMT3A mutations could be identified with ultra-deep NGS but with variable allelic frequencies (0.13-50.01% in the control group, 0.25-70.14% in the hx of CHIP group). In the cohort of patients with intensive therapy there was no difference in CR rates between hx of CHIP and control groups (82 vs 90%, p=0.31). Overall survival (OS) was not influenced by a hx of CHIP (whole cohort: HR 1.09; 95%CI 0.67-1.79; P=.73; intensively treated cohort: HR 0.72; 95%CI 0.34-1.51; P=.38). Relapse-free survival (RFS) was also not different in the hx of CHIP vs the control group (HR 1.06; 95%CI 0.58-1.93; P=.85; intensively treated cohort only HR 0.91; 95%CI 0.46-1.78; P=.78). However, when looking at the influence of allogeneic stem cell transplantations (HSCT) on outcome in intensively treated patients, patients with a hx of CHIP showed abenefit from HSCT (HR 0.082; 95%CI 0.009-0.75; P= 0.027 Figure 1A) as compared to the control group (HR 0.68; 95%CI 0.39-1.21; P= 0.19, Figure 1B). Conclusion: AML patients with a hx of CHIP, as defined by mutated DNMT3A in T-cells, show a distinct clinical and molecular profile and may benefit from HSCT. Figure 1A. Figure 1A. Figure 1B. Figure 1B. Disclosures Bug: TEVA Oncology, Astellas: Other: Travel Grant; NordMedica, Boehringer Ingelheim, Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene, Novartis: Research Funding. Fiedler:Pfizer, Amgen, Kolltan: Research Funding; Teva, Amgen, Astellas: Other: Travel Grant; Karyopharm: Research Funding. Schlenk:Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Research Funding; Arog: Honoraria, Research Funding; Teva: Honoraria, Research Funding; Boehringer-Ingelheim: Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Research Funding.

Description: Background: About 40% of IDH1 mutated (IDH1mut) acute myeloid leukemia (AML) patients respond to IDH1 inhibitors with a median duration of response of 8.2 months. A better understanding of the biology of IDH1mut leukemia may further improve the treatment of these patients. IDH1mut produces R-2-hydroxyglutarate (R-2HG), which activates PHD1 and PHD2 but have negligible effects on PHD3. In the present study we assessed whether PHD3 plays a role in the pathogenesis of IDH1 mutated leukemia and can be targeted in a patient-derived xenograft (PDX) model of IDH1 mutated AML. Methods: Bone marrow cells from Phdwt and Phd3ko mice were immortalized with HoxA9, and IDH1wildtype (IDH1wt) and IDH1mut respectively, were constitutively expressed. The effects on cell proliferation, apoptosis and colony formation were evaluated in vitro, whereas the leukemic potential was evaluated in vivo by transplantation in syngeneic mice. To show that PHD3 is a therapeutic target, either IDH1mut cells from AML patients were transduced with shRNA against PHD3 and transplanted in immunocompromised mice, or leukemic cells from an AML patient with mutated IDH1 were xenografted in immunocompromised mice and treated with the PHD inhibitor molidustat. Results: In in-vitro functional assays loss of Phd3 specifically impaired proliferation, apoptosis and clonogenic capacity of HoxA9-IDH1mut but not HoxA9-IDH1wt cells. Likewise, in mouse transplantation assays, loss of Phd3 eliminated HoxA9-IDH1mut induced leukemia. However, Phd3 was dispensable to the engraftment and proliferation of HoxA9-IDH1wt cells. Additionally, the IDH1-independent model of MN1-induced leukemia remained unaltered in the absence of Phd3, indicating the specificity of the role of Phd3 in mutant IDH1-induced transformation. To identify molecular pathways that might explain in vitro and in vivo phenotypes gene expression profiling was performed. Immune and stress-response pathways as well as metabolism-related genes were most prominently dysregulated in Phd3ko IDH1-mutant cells. Analysis of dysregulated transcription factors by gene set enrichment analysis revealed a depletion of key oncogenic transcription factors (Myc, Rb, Stk33, and Rps14) in Phd3ko IDH1mut cells compared to Phd3ko IDH1wt cells. To study if IDH1mut signals to Phd3 through R-2HG, we transduced Phd3kocells, with a splice variant of mutant IDH1, which does not produce R-2HG but causes leukemia in mice with similar kinetics as in mice with the full-length IDH1 mutant protein. Interestingly, loss of Phd3 also eliminated leukemia in these mice, which demonstrates that mutant IDH1 signals through Phd3 independently of R-2HG. To study the functional relevance of PHD3 inhibition in patients, cells from an IDH1 mutated AML patient were transduced with an shRNA against PHD3 and were transplanted in immunodeficient NSG mice. Inhibition of PHD3 depleted human AML cells in the IDH1-mutated PDX model. Moreover, the PHD inhibitor molidustat was 50-fold more active in IDH1mut (80 nM) compared to IDH1wt AML patient cells (4000 nM) in colony-forming unit assays. In a xenograft model of IDH1 mutated AML, molidustat significantly prolonged survival compared to control-treated mice (P

Description: Background: BCR-ABL+ acute lymphoblastic leukemia (ALL) in adults has a poor prognosis with allogeneic stem cell transplantation (SCT) considered the best curative option for suitable patients. BH3 mimetics induce mitochondrial outer membrane permeabilization (MOMP) linked to apoptosis induction by releasing BH3-only proteins BIM and/or BID from the anti-apoptotic factors BCL2, BCL-XL, MCL1, BCLW and BFL1. The BCL2-specific BH3 mimetic venetoclax (ABT-199) may provide an opportunity to improve pharmacotherapy of BCR-ABL+ ALL in particular for elderly patients not suitable for SCT. Aim: We aimed to rationally design optimized combination therapies for BCR-ABL+ ALL based on the molecular mechanisms of apoptosis induction by BH3 mimetics. Methods: We first biochemically characterized binding of BIM, a BH3 only activator of mitochondrial apoptosis, to BCL2, BCLXL and MCL1 and its release by BH3 mimetics in two BCR-ABL+ ALL cell lines. We next visualized and quantitated MOMP-induction by BH3 mimetics in viable cells. We then characterized the effects of dexamethasone and tyrosine kinase inhibitors (TKI) imatinib and dasatinib on BIM expression and calculated dose-effect combination indices (CI) for combination therapies in cell lines and two BCR-ABL+ ALL primograft models co-cultured with mesenchymal stem cells ex vivo. We finally used in vivo bioluminescence and survival analyses in murine xenotransplantation models to evaluate therapeutic efficacy in vivo. Results: In BCR-ABL+ BV173 and SUPB15 cells BIM but not BID binds to BCL2. BIM is rapidly released from BCL2 by venetoclax in a time and dose dependent manner. Release of BIM induces both MOMP (as defined by a decrease in mitochondrial membrane potential) and apoptosis (as defined by PARP cleavage and propidium iodide staining). Furthermore, BIM is strongly required for cytotoxicity of venetoclax, dasatinib and dexamethasone. Primary BCR-ABL+ ALL cells are more resistant against MOMP induction by venetoclax than BCR-ABL-negative ones, and BIM expression is reduced in these cells. Both, TKIs and dexamethasone augment BIM expression in BV173 and SUPB15 cells and act synergistically with venetoclax in cell lines and two BCR-ABL+ primografts (CI for the triple combination therapy of venetoclax, dexamethasone and dasatinib between 0.1 and 0.15, CI〈 1.0 considered synergistic). Triple combinations with venetoclax, dexamethasone and TKIs efficiently attenuate leukemia progression in xenotransplantation models and, notably, the dasatinib- but not the imatinib-containing combination led to treatment- and leukemia-free long-term survival in a BCR-ABL+ mouse model. Conclusions: These data demonstrate efficacy of venetoclax in ALL. Although BCR-ABL inhibits venetoclax cytotoxicity, this inhibition can be overcome by triple combination therapy with venetoclax, dexamethasone and dasatinib. Since the triple combination therapy can be curative in preclinical xenotranplatation models clinical studies with oral chemotherapy-free regimens may be considered in particular for elderly patients not suitable for allogeneic SCT. Disclosures Ganser: Novartis: Membership on an entity's Board of Directors or advisory committees.

Description: INTRODUCTION On average 5 recurrent mutations are present in each patient with acute myeloid leukemia (AML). Many mutated genes are implicated as tumor suppressor genes, but their contribution to leukemia stem cell (LSC) survival and chemoresistance is often unknown. We hypothesized that ectopic expression of the wildtype sequence of these genes will restore the function of the tumor suppressor gene and will lead to reduced clonal expansion and increased chemosensitivity. AIM To evaluate the contribution of recurrently mutated genes to leukemia stem cell survival and chemoresistance in human AML cells in vitro and in vivo. METHODS We performed a loss-of-function screening in primary human AML cells and cell lines by lentiviral expression of a pool of 22 wildtype genes associated with AML pathogenesis, which can restore gene function of a repressed pathway or a dysfunctional tumor suppressor gene. The 22 full-length cDNAs were labelled with a genetic barcode, which can be amplified with a common primer for all 22 genes. The readout of the screening was reduced representation of the barcode DNA after in vitro culture or in vivo growth in patient-derived xenograft (PDX) models, which was amplified from DNA and quantified by next-generation sequencing (NGS). Five PDX models with favorable, normal or complex cytogenetics and 3-5 recurrent mutations per model were screened in order to identify cDNAs that could potentially limit the proliferative capacity of LSCs in vivo (5 mice per model). Nine to 16 weeks after transplantation, DNA from blood, bone marrow and spleen were analyzed by NGS. We also screened two CD34+-enriched cord blood samples in vitro. After transduction with the cDNA pool, cells were cultured for 11 days and the barcode representation was analyzed by NGS at days 2, 4, 7, 9 and 11. Finally, we screened the human leukemia cell lines U937and PB14, a newly established cell line from an AML patient with mutations in FLT3, NPM1, RAD21, GSE1, and ROBO2. Cells were treated with cytarabine, doxorubicin or venetoclax for a 3-day period, followed by a 4-day recovery period to allow outgrowth of resistant clones and accumulation of cDNAs that conferred drug resistance. RESULTS Our loss-of-function screening with overexpressed wildtype genes revealed that expression of ETV6 and PTPN11 depleted LSCs in 3 of 5 PDX models and that expression of CEBPA and KDM6A depleted the progeny of normal CD34+ cells in cord blood. ASXL1, EZH2, CUX1, SMC1A and SMC3 had a general negative effect on stem cell self-renewal in both leukemic and normal CD34+ cells. Relative frequencies of the leukemia-specific genes ETV6 and PTPN11 were reduced 3 to 16-fold and 2 to 3-fold, respectively. Both genes were not mutated in the 3 patients' diagnostic samples, but had reduced RNA expression by 10-70% compared to healthy control peripheral blood mononuclear cells. Relative frequencies of cord blood-specific CEBPA was reduced 4-fold and KDM6A 5-fold. We then evaluated whether activation of a repressed pathway can increase sensitivity to cytarabine, doxorubicin or venetoclax in U937 and PB14 cells after 1 or 2 weeks of treatment. All three drugs showed better cytotoxic effects upon p53 expression in both cell lines by a factor of 1.4 to 2.5 fold. Cytarabine and venetoclax improved elimination of leukemic cells that had been transduced with U2AF1 in PB14 cells, which are U2AF1 wildtype. Venetoclax improved elimination of U937 cells that had been transduced with ETV6 or KDM6A, which are wildtype for these genes, while RNA expression was reduced more than 50% in these cells compared to other leukemic cell lines (NB4 and MV4-11). CONCLUSION Functional cDNA screening in PDX models in vivo is feasible and can reveal selective vulnerabilities of leukemic compared to normal stem cells. Our approach was validated by the finding that p53 expression improved chemosensitivity for all drugs tested in two leukemia cell lines, which is expected from the known function of p53 as a critical tumor suppressor gene. Similarly, overexpression of the transcriptional corepressor ETV6 in leukemia cells with low ETV6 expression was found to inhibit leukemia stem cell proliferation in vivo and to sensitize U937 cells to venetoclax. Therefore, activation of ETV6 should be explored as a novel strategy to inhibit LSCs and improve treatment response. Disclosures Ganser: Novartis: Membership on an entity's Board of Directors or advisory committees. Heuser:Janssen: Consultancy; StemLine Therapeutics: Consultancy; Bayer Pharma AG: Consultancy, Research Funding; Tetralogic: Research Funding; Sunesis: Research Funding; Daiichi Sankyo: Research Funding; Karyopharm: Research Funding; BergenBio: Research Funding; Astellas: Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding.

Description: Background: ADGRE2, CCR1, CD70, and LILRB2 expressed on the surface of myeloid blasts but not normal hematopoietic stem cells, T cells or other tissues have been recently suggested as candidate chimeric antigen receptor (CAR) targets for engineered T cells in acute myeloid leukemia (AML) patients. Aim: To validate the expression pattern of the recently identified candidate CAR targets ADGRE2, CCR1, CD70, and LILRB2 on leukemic blasts in a cohort of newly diagnosed AML patients. Methods: 109 patients with de novo (n=87) or secondary (n=22) AML were included in the analysis. Patients were classified according to the 2008 WHO classification and cytogenetically characterized by chromosome banding analysis. Molecular analyses were performed by Sanger and next-generation sequencing (NGS) with a panel of 46 genes. Bone marrow or peripheral blood samples from the time of first diagnosis were obtained to perform multi-color flow cytometry analysis evaluating the expression levels of ADGRE2 (also known as EMR2 or CD132), CCR1 (also known as CD191), CD70 and LILRB2 (also known as CD85d) antigens on the surface of myeloid blasts. Patients with expression of the marker on ≥20% of blast cells were defined positive. Informed consent was obtained from all patients in accordance to the declaration of Helsinki and institutional guidelines. Results: ADGRE2, CCR1, CD70 and LILRB2 were expressed in 100%, 70%, 27.5%, 27.5% of patients with a median expression on myeloid blasts of 87.8% (range 30.4-99.8%), 43.9% (range 21.1-86.2%), 29.0% (range 20.0-55.4%), and 35.6% (range 20.7-90.6%), respectively. A subset analysis was performed to determine expression levels of the candidate targets in CD3 positive cells. Of patients with positive marker expression on blast cells ADGRE2, CCR1, CD70 and LILRB2 were expressed on 14.5% (range 0.0-64.2%), 19.9% (0.0-73.0%), 15.3% (range 0.0-35.1%), and 2% (range 0.1-18.4%) of CD3+ T cells, respectively. The proportion of patients with ≥80% expression on blasts was 61.5% (n=67), 0.9% (n=1) and 3.7% (n=4) for ADGRE2, CCR1 and LILRB2, respectively. Of those 53.7%, 0%, and 100% had marker expression

Description: Molecular measurable residual disease (MRD) assessment is not established in approximately 60% of acute myeloid leukemia (AML) patients because of the lack of suitable markers for quantitative real-time polymerase chain reaction. To overcome this limitation, we established an error-corrected next-generation sequencing (NGS) MRD approach that can be applied to any somatic gene mutation. The clinical significance of this approach was evaluated in 116 AML patients undergoing allogeneic hematopoietic cell transplantation (alloHCT) in complete morphologic remission (CR). Targeted resequencing at the time of diagnosis identified a suitable mutation in 93% of the patients, covering 24 different genes. MRD was measured in CR samples from peripheral blood or bone marrow before alloHCT and identified 12 patients with persistence of an ancestral clone (variant allele frequency [VAF] 〉5%). The remaining 96 patients formed the final cohort of which 45% were MRD+ (median VAF, 0.33%; range, 0.016%-4.91%). In competing risk analysis, cumulative incidence of relapse (CIR) was higher in MRD+ than in MRD− patients (hazard ratio [HR], 5.58; P 〈 .001; 5-year CIR, 66% vs 17%), whereas nonrelapse mortality was not significantly different (HR, 0.60; P = .47). In multivariate analysis, MRD positivity was an independent negative predictor of CIR (HR, 5.68; P 〈 .001), in addition to FLT3-ITD and NPM1 mutation status at the time of diagnosis, and of overall survival (HR, 3.0; P = .004), in addition to conditioning regimen and TP53 and KRAS mutation status. In conclusion, NGS-based MRD is widely applicable to AML patients, is highly predictive of relapse and survival, and may help refine transplantation and posttransplantation management in AML patients.

Description: Mutations in the metabolic enzymes isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) are frequently found in patients with glioma, acute myeloid leukemia (AML), melanoma, thyroid cancer, cholangiocellular carcinoma and chondrosarcoma. Mutant IDH produces R-2-hydroxyglutarate (R2HG), which induces histone- and DNA-hypermethylation through inhibition of epigenetic regulators, thus linking metabolism to tumorigenesis. We recently established an in vivo mouse model and investigated the function of mutant IDH1. By computational drug screening, we identified an inhibitor of mutant IDH1 (HMS-101), which inhibits mutant IDH1 cell proliferation, decreases R2HG levels in vitro, and efficiently blocks colony formation of AML cells from IDH1 mutated patients but not of normal CD34+ bone marrow cells. In the present study we investigated the effect of the inhibitor in our IDH1/HoxA9-induced mouse model of leukemia in vivo. To identify the maximally tolerated dose of HMS-101, we treated normal C57BL/6 mice with variable doses of HMS-101 for 9 days and measured the serum concentration. Mice receiving 0.5 mg and 1mg intraperitoneally once a day tolerated the drug well with mean plasma concentrations of 0.1 to 0.3 µM. To evaluate the effect of HMS-101 in the IDH1 mouse model, we transduced IDH1 R132C in HoxA9-immortalized murine bone marrow cells. Sorted transgene positive cells were then transplanted into lethally irradiated mice. After 5 days of transplantation, mice were treated with HMS-101 intraperitoneally for 5 days/week. The R/S-2HG ratio in serum was reduced 3-fold in HMS-101 treated mice after 8 weeks of treatment compared to control treated mice. HMS-101 or PBS treated mice had similar levels of transduced leukemic cells in peripheral blood at 2 and 6 weeks after transplantation. However, from week 6 to week 15 leukemic cells in peripheral blood decreased from 76% to 58, 63% to 29%, 67% to 7%, and 74% to 38% in 4/6 mice treated with HMS-101. In one mouse the percentage of leukemic cells was constant, and in one mouse it increased from week 6 to week 15 after transplantation. Leukemic cells increased constantly in peripheral blood until death in control treated mice. While the control cohort developed severe leukocytosis, anemia and thrombocytopenia around 8 to 10 weeks post transplantation, mice treated with HMS-101 still had normal WBC, RBC and platelet counts at 15 weeks after transplantation. Moreover, the HMS-101 treated mice had significantly more differentiated Gr1+CD11b+ cells in peripheral blood than control mice at 6 weeks and 15 weeks after transplantation and at death (P=.01). Morphologic evaluation of blood cells at 15 weeks or death from HMS-101 treated mice revealed a high proportion of mature neutrophils that were GFP positive and thus derived from IDH1 transduced cells, whereas control treated mice had monocytic morphology with a high proportion of immature cells. Importantly, HMS-101 treated mice survived significantly longer with a median latency of 87 days (range 80-118), whereas PBS-treated mice died with a median latency of 66 days (range 64-69) after transplantation (P

Description: Background: Relapse occurs in 30-40% of AML patients undergoing allogeneic hematopoietic stem cell transplantation (alloHSCT). Detecting molecular relapse before clinical relapse offers the opportunity of early interventions (e.g. donor lymphocyte infusions, reduction of immunosuppression etc.). Next-generation sequencing (NGS)-based error-corrected sequencing approaches have shown promising results in AML patients prior to alloHSCT, which identified MRD in 45% of patients and predicted a cumulative incidence of relapse of 66% versus 17% in MRD negative patients at 5 years. However, NGS-based MRD is not well studied in patients after alloHSCT. Aim: To evaluate the prognostic impact of MRD on day 90 and day 180 after alloHSCT in AML patients in morphologic complete remission (CR) using error-corrected NGS applicable to the majority of AML patients. Patients and Methods: We quantified MRD in 138 patients who underwent myeloablative (MA, n=47) or reduced-intensity conditioned (RIC, n=91) alloHSCT for AML on day 90 and 180 after alloHSCT. All patients had at least one mutation at the time of diagnosis that was identified by NGS with a myeloid panel on the Illumina platform. Amplicon-based error-corrected sequencing and bioinformatics analysis was applied to samples on day 90 (n=133) and day 180 (n=125) after alloHSCT as described previously (Thol et al. Blood 2018). In the first approach we analysed 1-2 diagnostic mutations (=limited marker approach). In the second approach an extended marker set with (2-4) markers was used (=extended marker approach). Genomic DNA from peripheral blood (PB) was used for the majority of analyses (PB n= 394; bone marrow n=17). Cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) were evaluated by competing risk analysis. Results: The median follow up time of the cohort was 5.5 years. The mean limit of detection was a variant allele frequency (VAF) of 0.012% using error correction and 0.071 when using forward/reverse read error correction. MRD positivity on day 90 and/or day 180 was detected in 22 out of 138 patients (16%) with the limited marker approach, while MRD was found in 28 patients (20.3%) with the extended marker approach. Using the limited marker approach, the 5-year CIR was 52% for MRD positive and 30% for MRD negative patients (P=0.001), while NRM was similar between both groups (Figure 1A). Overall survival (OS) was shorter in MRD positive patients compared to MRD negative patients (P=.044, Figure 1B). In multivariate analysis using variables significant in univariate analysis (P

Description: Background: NUP98-NSD1 positive AML is a poor prognostic subgroup within pediatric and adult AML (Thol et al., 2013). However, targeted therapeutics for these AML patients are not available to date. As a result of the NUP98-NSD1 fusion, NSD1 causes H3K36 hypermethylation of HOXA genes, which contributes to myeloid progenitor cell immortalization and results in AML (Wang et al., 2007). Therefore, we hypothesized that inhibition of the methyltransferase activity of NSD1 could be an effective treatment strategy for NUP98-NSD1 AML patients. Here, we assessed the efficacy of NSD1 inhibitor suramin and NUP98-NSD1-directed siRNA-containing lipid nanoparticles (LNP) in a preclinical patient-derived xenograft (PDX) model of NUP98-NSD1 leukemia. Methods: A NUP98-NSD1 positive AML patient was screened through nested PCR and Sanger sequencing. Bone marrow cells from this patient were serially transplanted into NSG (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) mice to establish a NUP98-NSD1 PDX model. During serial transplantations, an alternative NUP98-NSD1 fusion gene appeared. Flow-cytometry was used to check the engraftment and immunophenotype of engrafted cells. Effective siRNAs against each of the two fusion genes were developed. The microfluidic mixing technology, Nanoassemblr was used to package siRNA into LNPs and the Zetasizer was used to characterize them. Fifteen days after transplantation, suramin and solvent treatment were initiated in 9 mice per group with 10 mg/kg suramin (2 days/week for 10 weeks). For LNP treatment, treatment was initiated 3 weeks after transplantation with a once daily dose of 2.5 mg/kg on days 1-3 and then every third day thereafter for a total of 17 injections. Results: Besides the NUP98-NSD1 translocation, our patient had a FLT3-ITD mutation and a normal karyotype. In our PDX model, the engraftment of human leukemia cells reached up to 90% after ten weeks of transplantation. In successive transplantations up to the 6th generation, the NUP98-NSD1 fusion was confirmed in leukemic cells, supporting the importance of the fusion for leukemia development and stability of the model. In later transplantations, a minor clone of NUP98-NSD1 was identified. A high blast count, high WBC count, increased spleen weight, and a low hemoglobin and platelet count at death demonstrated the development of acute leukemia. High expression of myeloid markers (e.g. CD33, 99%, N=9) and negligible expression of lymphoid markers (CD3, 2%; CD19, 2%; N=9) confirmed acute myeloid leukemia. In the suramin treatment study, the mean human leukemic cell engraftment was similar between the control and treatment groups at the start of treatment (0.51%, N=9 and 0.71%, N=9, respectively), but was lower in suramin treated mice after 4 and 8 weeks of treatment (4 weeks: CTRL, 4,8%; suramin, 2,66%, P=0.1; 8 weeks: CTRL, 87,3%; suramin: 66,5%, P=0.016). No significant effect was seen on the immunophenotype of suramin and control treated leukemia cells. Suramin treatment significantly prolonged the median survival of mice compared to control mice (126 vs 114 days after transplantation, P=0.008). To establish the siRNA-LNP treatment, we identified one siRNA against each NUP98-NSD1 clone that reduced expression levels by 78% and 89.5% in the major and minor clones, respectively. The effective siRNAs were modified to increase their in vivo stability and were packaged into LNPs and used in vivo. We started the treatment when the engraftment was similar in both control LNP and NUP98-NSD1 LNP groups (0.93%, N=7 and 1.25%, N=6, respectively). After 3 weeks of treatment, LNP uptake was 99.3% and 99.2% in the CTRL LNP and NUP98-NSD1 LNP groups, respectively. The mean engraftment was lower in NUP98-NSD1 LNP mice after 5 and 8 weeks of treatment (5 weeks: CTRL LNP, 15%; NUP98-NSD1 LNP, 4.6%, P= 0.08; 8 weeks: CTRL LNP, 94.8%; NUP98-NSD1 LNP, 55.83%, P=0.007). Importantly, the NUP98-NSD1 siRNA-LNP treated mice showed a significant survival benefit compared to CTRL siRNA-LNP treated mice (106 vs 82 days after transplantation, P=0.02). Conclusions: In summary, our findings demonstrate that targeted inhibition of NUP98-NSD1 either through siRNA-LNP or suramin delays leukemia development in vivo and prolongs the survival of mice carrying a NUP98-NSD1 positive AML. Our results provide the rationale for the evaluation of NSD1 methyltransferase inhibitors and siRNA-LNP formulations in NUP98-NSD1 positive AML. Disclosures Heuser: Bayer Pharma AG, Berlin: Research Funding; Synimmune: Research Funding.

Description: Background: Atypical chronic myeloid leukemia (aCML) is a rare disorder classified as one of the MPN/MDS overlap syndromes. aCML usually presents like CML but lacks the pathognomonic BCR-ABL fusion found in CML. Most patients progress to acute myeloid leukemia (AML) with a median time to AML of 11.2 months and have a median overall survival of only 12.4 months (Wang et al. Blood 2014). Recurrently mutated genes found in aCML patients include SETBP1 , CSF3R, NRAS, EZH2, ASXL1, ETNK1, and U2AF1. The pathogenesis of aCML is poorly understood and neither specific nor effective treatments besides hematopoietic stem cell transplantation are available. We therefore aimed at developing a patient derived xenotransplantation model that allows serial transplantation and expansion of human leukemic cells and evaluation of novel treatments and drugs in vivo. Patient and Methods: Bone marrow cells were harvested from a patient diagnosed with atypical CML based on persistent leukocytosis, immature circulating myeloid precursors (16% metamyelocytes, 8% myelocytes, 9% blasts), marked dysgranulopoiesis, minimal monocytosis and basophilia, hypercellular bone marrow with high myeloid/erythroid ratio and 6% myeloid blasts, dysplasia in megakaryocytes and erythroid progenitors, and absence of BCR-ABL and mutated JAK2. The patient had moderate anemia and normal platelet counts and cytogenetic analysis showed a normal karyotype. Eight hundred thousand bone marrow cells were injected intravenously in NOD/SCID IL-2 receptor γ (NSG) deficient mice. We monitored these mice for human cell engraftment by regular eye bleeds every 4 weeks. Bone marrow and spleen cells from engrafted mice were retransplanted in secondary and tertiary mice of the NSG strain transgenic for SCF, IL3 and GM-CSF (NSGS). Patient cells were analyzed for mutations in fifty four genes by next generation sequencing and mutations were confirmed by Sanger sequencing in primary patient cells and cells from tertiary mice. Results: Human CD45+ cells from the aCML patient showed increasing engraftment over time in the NSG mouse reaching 16% in peripheral blood and 35% in spleen at 26 weeks after transplantation. In secondary (n=2) and tertiary (n=4) mice we used NSGS recipient mice and observed considerably accelerated engraftment kinetics leading to 19, 21 and 73% human cells in peripheral blood, spleen and bone marrow, respectively, between 12 and 15 weeks after transplantation. The myeloid marker CD33 was expressed in 86% of human bone marrow cells, while lymphoid markers CD3 and CD19 were absent. The stem and progenitor phenotype CD34+CD38- was found in 11% of human cells. The progenitor marker CD123 was expressed in 42% of cells, while the myeloid marker CD14 was expressed in 6% of cells. Hemoglobin levels and platelet counts were considerably lower in secondary and tertiary recipients of aCML cells compared to control animals. Spleens were enlarged at time of sacrifice with an average spleen weight of 150 mg. Morphological evaluation of bone marrow cells in tertiary recipients revealed a characteristic picture for aCML with 39% neutrophils, 8% blasts and 53% myeloid progenitors and monocytes. Molecular analysis identified mutations in ASXL1, RUNX1 and EZH2 with variant allele frequencies of 49, 48 and 46 percent, respectively that were confirmed in human cells from tertiary recipient mice. Thus, we show that primary aCML cells can be expanded and serially transplanted in immunodeficient mice and suggest clonal stability of this model. Conclusion: We provide the first patient derived xenotransplantation model for atypical CML, which preserves the phenotypic and molecular characteristics of the primary disease and allows serial transplantation and expansion of aCML cells. This model will serve to better understand the pathogenesis of aCML and to test urgently needed novel treatment approaches. Disclosures No relevant conflicts of interest to declare.