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Acute myeloid leukemia (AML) cells are highly dependent on oxidative phosphorylation (OxPhos) for survival, and they continually adapt to fluctuations in nutrient and oxygen availability in the bone marrow (BM) microenvironment. We investigated how the BM microenvironment affects the response to OxPhos inhibition in AML by using a novel complex I OxPhos inhibitor, IACS-010759. Cellular adhesion, growth, and apoptosis assays, along with measurements of expression of mitochondrial DNA and generation of mitochondrial reactive oxygen species indicated that direct interactions with BM stromal cells triggered compensatory activation of mitochondrial respiration and resistance to OxPhos inhibition in AML cells. Mechanistically, inhibition of OxPhos induced transfer of mitochondria derived from mesenchymal stem cells (MSCs) to AML cells via tunneling nanotubes under direct-contact coculture conditions. Inhibition of OxPhos also induced mitochondrial fission and increased functional mitochondria and mitophagy in AML cells. Mitochondrial fission is known to enhance cell migration, so we used electron microscopy to observe mitochondrial transport to the leading edge of protrusions of AML cells migrating toward MSCs. We further demonstrated that cytarabine, a commonly used antileukemia agent, increased mitochondrial transfer of MSCs to AML cells triggered by OxPhos inhibition. Our findings indicate an important role of exogenous mitochondrial trafficking from BM stromal cells to AML cells as well as endogenous mitochondrial fission and mitophagy in the compensatory adaptation of leukemia cells to energetic stress in the BM microenvironment.

Healthcare workers (HCWs) are highly exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The actual coronavirus disease (COVID-19) situation, especially in regions that are less affected, has not yet been determined. This study aimed to assess the seroprevalence of SARS-CoV-2 in HCWs working in a frontline hospital in Tokyo, Japan. In this cross-sectional observational study, screening was performed on consented HCWs, including medical, nursing, and other workers, as part of a mandatory health checkup. The screening test results and clinical characteristics of the participants were recorded. The antibody seroprevalence rate among the 4147 participants screened between July 6 and August 21, 2020, was 0.34% (14/4147). There was no significant difference in the seroprevalence rate between frontline HCWs with a high exposure risk and HCWs working in other settings with a low exposure risk. Of those seropositive for SARS-CoV-2, 64% (9/14) were not aware of any symptoms and had not previously been diagnosed with COVID-19. In conclusion, this study provides insights into the extent of infection and immune status in HCWs in Japan, which has a relatively low prevalence of COVID-19. Our findings aid in formulating public health policies to control virus spread in regions with low-intensity COVID-19.

Rapid detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using saliva samples has emerged as a preferred technique since sample collection is easy and noninvasive. In addition, several commercial high-throughput PCR kits that do not require RNA extraction/purification have been developed and are now available for testing saliva samples. However, an optimal protocol for SARS-CoV-2 RT-PCR testing of saliva samples using the RNA extraction/purification-free kits has not yet been established. The aim of this study was to establish optimal preanalytical conditions, including saliva sample collection, storage, and dilution for RNA extraction/purification-free RT-PCR (direct RT-PCR).Patients suspected with COVID-19 from March 02 to August 31, 2020, were enrolled in this study. A total of 248 samples, including 43 nasopharyngeal swabs and 205 saliva samples, were collected from 66 patients (37 outpatients and 29 inpatients) and tested using the 2019 Novel Coronavirus Detection Kit (nCoV-DK, Shimadzu Corporation, Kyoto, Japan).The detection results obtained using nasopharyngeal swabs and saliva samples matched 100%. The sampling time, i.e., either awakening time or post-breakfast, had no significant effect on the viral load of the saliva samples. Although saliva samples are routinely diluted to reduce viscosity, we observed that dilution negatively affected PCR sensitivity. Saliva samples could be stored at room temperature (25°C) for 24 hours or at 4°C for up to 48 hours.This study demonstrated the appropriate conditions of saliva sample collection, processing, and storage, and indicated that the nCoV-DK is applicable to saliva samples, making the diagnosis method simple and safe.

Tyrosine kinase inhibitors (TKIs) are established drugs in the therapy of FLT3-ITD mutated acute myeloid leukemia (AML). However, acquired mutations, such as D835 in the tyrosine kinase domain (FLT3-ITD/D835), can induce resistance to TKIs. A cap analysis gene expression (CAGE) technology revealed that the gene expression of BCL2A1 transcription start sites was increased in primary AML cells bearing FLT3-ITD/D835 compared to FLT3-ITD. Overexpression of BCL2A1 attenuated the sensitivity to quizartinib, a type II TKI, and venetoclax, a selective BCL2 inhibitor, in AML cell lines. However, a type I TKI, gilteritinib, inhibited the expression of BCL2A1 through inactivation of STAT5 and alleviated TKI resistance of FLT3-ITD/D835. The combination of gilteritinib and venetoclax showed synergistic effects in the FLT3-ITD/D835 positive AML cells. The promoter region of BCL2A1 contains a BRD4 binding site. Thus, the blockade of BRD4 with a BET inhibitor (CPI-0610) downregulated BCL2A1 in FLT3-mutated AML cells and extended profound suppression of FLT3-ITD/D835 mutant cells. Therefore, we propose that BCL2A1 has the potential to be a novel therapeutic target in treating FLT3-ITD/D835 mutated AML.

Context: BCL2A1 exerts a pro-survival function in FLT3-ITD/D835-double mutant acute myeloid leukemia (AML) cells and may be a putative novel therapeutic target in FLT3-mutant AML. The combination of gilteritinib, which reduced BCL2A1 with venetoclax, was highly synergistic in FLT3-ITD/D835-double mutant cells. Objective: While FLT3 tyrosine kinase inhibitors (TKI) emerged as a new therapeutic option in AML with internal tandem duplications in the juxtamembrane domain of FLT3 (FLT3-ITD), the prognosis of FLT3-mutated AML is still poor because heterogeneous clonal populations with additional acquired FLT3 and Ras mutations emerge and cause drug resistance. FLT3-ITD plus a point mutation at residue D835 in the tyrosine kinase domain (FLT3-ITD/D835) often cause resistance or decrease sensitivity to TKIs. In this study, we investigated new drug targets in AML with FLT3-ITD and TKD double mutations. Design: We carried out cap analysis of gene expression (CAGE) in primary AML cells from 26 patients to characterize transcriptome differences between FLT3-ITD-positive and FLT3-ITD/D835 double-positive primary AML cells. Selected genes were confirmed and validated with immunoblotting and RT-qPCR using FLT3-ITD-positive and FLT3-ITD/D835-positive MV4-11 cells. Furthermore, we generated FLT3-ITD-postive cells with overexpression of the selected genes using lentivirus vectors. Results: CAGE demonstrated that AML cells harboring FLT3-ITD/D835 double mutations expressed increased BCL2A1 gene transcripts compared to those with FLT3-ITD alone. RT-qPCR and immunoblot analysis also revealed that FLT3-ITD/D835-positive MV4-11 cells expressed higher transcript and protein levels of BCL2A1 than MV4-11 cells with FLT3-ITD mutation alone. Overexpression of BCL2A1 attenuated sensitivity to venetoclax and decreased sensitivity to quizartinib in AML cells with a heterozygous FLT3-ITD mutation (FLT3-wildtype/FLT3-ITD) but not in cells with a homozygous mutation (FLT3-ITD/FLT3-ITD). Gilteritinib targets BCL2A1 through inactivation of STAT5, and combinatorial gilteritinib and venetoclax were highly synergistic in FLT3-ITD/D835 double-positive cells. Furthermore, inhibition of BRD4 with the BET inhibitor CPI-0610 exhibited anti-tumor activity in FLT3-ITD/D835 double-positive AML and suppressed BCL2A1 expression in these cells. Conclusions: This study elucidates overexpression of BCL2A1 as a novel survival mechanism in FLT3-ITD/D835 mutant AML cells and identifies BCL2A1 as a putative novel therapeutic target in FLT3-mutant AML.

Rapid turnover proteins (RTPs), such as transthyretin (TTR), retinol binding protein (RBP), and transferrin (Tf), provide an accurate assessment of nutritional status but are susceptible to inflammation. Lipid-related markers, which have short half-lives in serum, may be better suited for nutritional assessment. We sought to identify sensitive nutritional markers unaffected by inflammation.Fasting serum samples were collected from 30 malnourished inpatients and 25 healthy volunteers. Malnourished inpatients were divided into 2 groups: a low-C-reactive protein (CRP) group (CRP 20 mg/l, n = 15) and a high-CRP group (CRP ≥ 20 mg/l, n = 15). Lipid-related markers, traditional nutritional markers, RTPs, micronutrients, and ketone bodies were measured and compared among the groups.Apolipoprotein (Apo)C-II and ApoC-III concentrations were lower in malnourished inpatients than in the control group. There was no significant difference in ApoC-II and ApoC-III between the low- and high-CRP groups. Carnitine transporters and ketone bodies did not show a significant difference among the three groups. Albumin, TTR, RBP, and Tf concentrations were lowest in the high-CRP group, intermediate in the low-CRP group, and highest in the control group.These results indicate that ApoC-II and ApoC-III are appropriate nutritional biomarkers unaffected by inflammation.

A selective BCL-2 inhibitor venetoclax synergizes with hypomethylating agents (HMA). Combination of venetoclax plus HMAs (decitabine or azacitidine) is FDA approved for the treatment of high-risk newly-diagnosed (ND) AML including older patients and patients unfit intensive chemotherapy. We have reported that combination of venetoclax with ten-day HMA decitabine (DEC10-VEN, NCT03404193) demonstrated high efficacy in ND AML patients, with lower overall response rates in relapsed/refractory (R/R) AML. Specifically, the complete remission (CR/CRi) rates were 84% in ND AML and 42% in R/R AML (DiNardo et al. Lancet Haematol. 2020). The determinants of reduced efficacy in the R/R compared to ND AML are not defined. To characterize the transcriptomic signatures associated with response or resistance to DEC10-VEN in ND vs R/R AML, we performed RNA-seq analysis on samples from genetically diverse 24 AML patients treated on DEC10-VEN clinical trial. The pre-treatment samples from 11 ND patients, including 6 patients who achieved CR/CRi and 5 who failed to respond or subsequently relapsed (non-responders, NR); and from 9 R/R patients, 3 patients who achieved CR/CRi and 6 NR, have been analyzed with a NovaSeq 6000 platform. We first performed the comparative analysis of NR vs CR/CRi cases using pre-treatment samples. In ND AML patients 113 genes were higher and 62 genes were lower, and in R/R group 33 genes were higher and 69 genes were lower, in non-responders than in CR/CRi patients (log fold-change >|2|, FDR < 0.05). In ND AML, the top functional processes identified by Gene Ontology (GO) analysis (FDR < 0.05) in non-responders were genes involved in oxidative phosphorylation (OXPHOS) and cell migration/adhesion, such as upregulation of OXPHOS/energy metabolism-associated genes MT-CO3, COX6B2, NADK and cell-to-cell interactions mediator TSHBS1. In contrast, R/R AML patients that failed to achieve the response had lower transcriptomic signatures of genes associated with immune system such as TLR8, FCER2, TNFAIP3, CCR7, compared to responders. Recently, HMAs have been reported to activate silenced endogenous retroviral (ERV) elements regulated by epigenetic modifications, followed by upregulation of interferon-response genes and activation of energy metabolism through ATP hydrolysis (Fresquet et al. Cancer Discovery, 2021). ERVs re-activation may have dual opposing role in malignant cells including leukemia: (1) inducing "immunogenic cell death" by mounting innate antiviral immune responses; and (2) promoting carcinogenesis through activation of Notch signaling and fostering tumor cell proliferation with energy consumption. We analyzed transcription of 45 well-annotated ERV in 9 samples of 6 pre- and 3 post- DEC10-VEN treatment in R/R AML patients who failed to respond. The differential expression analysis with the custom-built ERV reference genome by STAR demonstrated ERVFRD, HERVK-27 and ERVK3-1 as significantly upregulated after DEC10-VEN treatment. Of note, HERV-K27 is one of human cancer-associated HERV-K proviruses. GO analysis demonstrated that these 3 ERVs are positively associated with innate immune system, Notch, Wnt, TGF beta signaling pathways and fatty acid oxidation. To further determine the potential function of ERVs, we investigated the upregulated genes after DEC10-VEN treatment in R/R AML that failed to respond. The top 10 significantly upregulated GO terms were dominated by immune response and cytoplasmic translation, associated with upregulation of ATP hydrolysis activating gene TNNT1, interferon simulated gene TNFAIP3, Notch1 regulating CAMK2A, TGF beta regulating SMAD7, and endogenous RNA MUEOV that promotes tumor metastasis through TGF beta signaling. Taken together, our transcriptomic analysis suggests that diverse pathways may contribute to the development of resistance to DEC10-VEN in AML cells in ND and R/R patients. In ND patients, high OXPHOS and microenvironment confer resistance to therapy. In R/R AML, baseline immune suppression is aided by the ERVs reactivation by DEC10-VEN therapy, which in turn may promote ATP consumption, energy metabolism, and Notch signaling (Figure 1). These findings are currently being validated and may identify novel mechanisms of resistance to DEC10-VEN treatment in ND and R/R AML. Figure 1 Figure 1. Disclosures DiNardo: Foghorn: Honoraria, Research Funding; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; ImmuneOnc: Honoraria, Research Funding; Forma: Honoraria, Research Funding; AbbVie: Consultancy, Research Funding; Agios/Servier: Consultancy, Honoraria, Research Funding; Celgene, a Bristol Myers Squibb company: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Takeda: Honoraria; Notable Labs: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria. Konopleva: Ablynx: Other: grant support, Research Funding; Stemline Therapeutics: Research Funding; AstraZeneca: Other: grant support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Cellectis: Other: grant support; KisoJi: Research Funding; Calithera: Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Rafael Pharmaceuticals: Other: grant support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support; Forty Seven: Other: grant support, Research Funding; Ascentage: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; Sanofi: Other: grant support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights.

Internal tandem duplications in the juxtamembrane domain of FMS-like tyrosine kinase 3 gene (FLT3-ITD) and missense mutations in the gene's tyrosine-kinase domain (FLT3-TKD) play critical roles in the pathophysiology of acute myeloid leukemia (AML). Recent study revealed that AML cells resistant to quizartinib, a type II TKI, consist of heterogeneous clonal populations harboring wild-type FLT3 as well as FLT3-ITD, FLT3-TKD and FLT3-ITD/TKD mutations, and on- and off-target mechanisms may contribute to the resistance to TKIs. To overcome the heterogeneous resistance mechanisms of FLT3-ITD and TKD mutations, various combinatorial therapies have been investigated. For example, BCL-2 inhibition in the presence of TKIs increased survival a murine FLT3-ITD AML model, and a phase Ib/II clinical trial of a combination of quizartinib with venetoclax, a BCL2 inhibitor is ongoing in relapsed/refractory FLT3-mutant AML patients (NCT03735875). To dissect underlying mechanisms of drug-resistance and exploring new targets in refractory AML with FLT3-ITD and TKD mutations, we investigated alterations of transcriptome signatures by analyzing AML samples with FLT3-ITD/D835 dual mutations. Previously, we reported BCL2A1 transcriptomes were upregulated in primary AML cells with FLT3-ITD/D835 dual mutations compared to cells with FLT3-ITD mutations only. This was recapitulated in the MV4-11 cells harboring FLT3-ITD/D835 dual mutations after 6 month-exposure to quizartinib. The MV4-11 cells with the FLT3-ITD/D835 dual mutations became resistant to quizartinib, and the cells also became resistant to venetoclax, a BCL2 inhibitor (Yamatani et al. ASH 2019). In this study, we further investigated BCL2A1 as new target in refractory AML with FLT3-ITD/D835 dual mutations. First, we examined whether overexpression of BCL2A1 induces drug-resistance in MV4-11 and Molm13 cell lines with FLT3-ITD. While parental MV4-11 and Molm13 cells are sensitive to venetoclax and quizartinib, MV4-11 and Molm13 cells transfected with lentivirus carrying BCL2A1 became resistant to venetoclax (IC50: MV4-11 with BCL2A1 over-expression >1000 nM vs. mock vector 0.71 nM; Molm13 with over-expression >1000 nM vs. mock vector 0.38 nM, 72h). In contrast, the sensitivity to quizartinib was retained in the BCL2A1 overexpressing MV4-11 and Molm13 cells. These findings indicate that the overexpression of BCL2A1 could play a role in the acquired resistance to venetoclax, but not to quizartinib. Bromodomain-containing protein 4 (BRD4), a family member of bromodomain and extra-terminal motif (BET) is known to transcriptionally modulate BCL2A1 gene expression. Next, we examined effects of CPI-0610, a BET inhibitor, on MV4-11 cells with FLT3-ITD or the FLT3-ITD/D835 dual mutation. CPI-0610 inhibited cell growth of MV4-11 cells by inducing apoptosis irrespective of co-existing FLT3 mutations (IC50: FLT3-ITD/D835, 255 nM vs. FLT3-ITD, 191 nM, 72h). Immunoblotting analyses confirmed that BET inhibition by CPT-0610 decreased the expression of BCL2A1 in MV4-11 cells FLT3-ITD/D835. WIn conclusion, transcriptome analysis and molecular pharmacological approaches identified alterations in the anti-apoptotic BCL2 family proteins in double-mutant FLT3 leukemias. BCL2A1 upregulation might be involved in drug resistance of FLT3-ITD/D835 dual mutant AML cells, and could be a promising new target in refractory AML with FLT3-ITD/D835 dual mutations. Disclosures Konopleva: Cellectis: Research Funding; Eli Lilly: Research Funding; Calithera: Research Funding; Sanofi: Research Funding; Ascentage: Research Funding; AstraZeneca: Research Funding; Agios: Research Funding; Stemline Therapeutics: Consultancy, Research Funding; Kisoji: Consultancy; Genentech: Consultancy, Research Funding; F. Hoffmann La-Roche: Consultancy, Research Funding; Forty-Seven: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Reata Pharmaceutical Inc.;: Patents & Royalties: patents and royalties with patent US 7,795,305 B2 on CDDO-compounds and combination therapies, licensed to Reata Pharmaceutical; Rafael Pharmaceutical: Research Funding; Ablynx: Research Funding; Amgen: Consultancy. Carter:Syndax: Research Funding; AstraZeneca: Research Funding; Amgen: Research Funding; Ascentage: Research Funding. Andreeff:Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy.

Background Preβ1-high-density lipoprotein (HDL) is a lipid-poor cholesterol acceptor that is converted to lipid-rich HDL by lecithin–cholesterol acyltransferase (LCAT). In patients receiving hemodialysis, preβ1-HDL metabolism is hampered even if HDL cholesterol is normal. Hemodialysis may affect preβ1-HDL metabolism by releasing lipases from the vascular wall due to heparin. Objectives We investigated whether preβ1-HDL metabolism is delayed in patients with chronic kidney disease (CKD) who are not receiving hemodialysis. Methods We examined 44 patients with Stage 3 or higher CKD and 22 healthy volunteers (Control group). The patients with CKD were divided into those without renal replacement therapy (CKD group, n = 22) and those undergoing continuous ambulatory peritoneal dialysis (CAPD group, n = 22). Plasma preβ1-HDL concentrations were determined by immunoassay. During incubation at 37°C, we used 5,5-dithio-bis (2-nitrobenzoic acid) (DTNB) to inhibit LCAT activity and defined the conversion halftime of preβ1-HDL (CHTpreβ1) as the time required for the difference in preβ1-HDL concentration in the presence and absence of 5,5-DTNB to reach half the baseline concentration. Results The absolute and relative preβ1-HDL concentrations were higher, and CHTpreβ1 was longer in the CKD and CAPD groups than in the Control group. Preβ1-HDL concentration was significantly correlated with CHTpreβ1 but not with LCAT activity in patients with CKD and CAPD. Conclusion Preβ1-HDL metabolism is delayed in patients with CKD who are not on hemodialysis. This preβ1-HDL metabolic delay may progress as renal function declines.

We examined the usefulness of five COVID-19 antibody detection tests using 114 serum samples at various time points from 34 Japanese COVID-19 patients. We examined Elecsys Anti-SARS-CoV-2 from Roche, and four immunochromatography tests from Hangzhou Laihe Biotech, Artron Laboratories, Chil, and Nadal. In the first week after onset, Elecsys had 40% positivity in Group S (severe cases) but was negative in Group M (mild-moderate cases). The immunochromatography kits showed 40–60% and 0–8% positivity in Groups S and M, respectively. In the second week, Elecsys showed 75% and 50% positivity, and the immunochromatography tests showed 5–80% and 50–75% positivity in Groups S and M, respectively. After the third week, Elecsys showed 100% positivity in both groups. The immunochromatography kits showed 100% positivity in Group S. In Group M, positivity decreased to 50% for Chil and 75–89% for Artron and Lyher. Elecsys and immunochromatography kits had 91–100% specificity. Elecsys had comparable chronological change of cut-off index values in the two groups from the second week to the sixth week. The current SARS-CoV-2 antibody detection tests do not provide meaningful interpretation of severity and infection status. Its use might be limited to short-term epidemiological studies.

AIMS Circulating endothelial progenitor cells (EPCs) play a pivotal role in vasculogenesis and promote angiogenesis by secreting growth factors. Recent studies have suggested that erythropoietin (EPO) may accelerate not only angiogenesis but also vasculogenesis, beyond erythropoiesis. The aim of this study was to investigate whether two erythropoiesis-stimulating agents (ESAs) modulate vascular-related factors and EPC mobilization in patients with chronic kidney disease stage G5 and dialysis (CKD G5 and 5D). MATERIALS AND METHODS We conducted a 12-week prospective study in 63 patients; 21 patients received recombinant human erythropoietin (rhEPO) (EPO group, 4,565.5 ± 1,994.4 IU/week), 21 patients received darbepoetin (DA) (DA group, 40.1 ± 13.8 µg/week), and 21 patients received no ESAs (no-ESA group). Vascular mediators, including EPCs, vascular endothelial growth factor, matrix metalloproteinase-2 (MMP-2), high-sensitivity C-reactive protein, and asymmetric dimethyl arginine, were measured at 0 and 12 weeks. EPCs were measured by flow cytometry as CD45lowCD34+CD133+ cells. We also performed a subanalysis of dialysis (5D) patients (n = 32) in the three groups. RESULTS In the EPO group, EPC count increased significantly from 0 to 12 weeks in a dose-dependent manner (r = 0.62, p = 0.005), and the increase was more conspicuous in the subgroup of dialysis 5D patients. In the DA group, the EPC number did not change at 12 weeks. Neither rhEPO nor DA affected the serum levels of the aforementioned biomarkers other than EPC. ;Conclusion: We speculate that the pleiotropic effects of rhEPO and DA beyond their hematopoietic effects may differ between CKD G5 and 5D patients. .

Acute myeloid leukemia (AML) cells are highly dependent on oxidative phosphorylation (OxPhos) for survival and continually adapt to the bone marrow (BM) microenvironment. We investigated how the BM microenvironment impacts the response to energy-depriving OxPhos inhibition in AML using a novel complex I OxPhos inhibitor (OxPhosi), IACS-010759. We have reported that OxPhosi-resistant primary AML samples demonstrated higher baseline transcription of genes related to cell adhesion, integrin and/or Rho GTPase family genes that modulate intracellular actin dynamics. (Yang et al. ASH 2019) In this study, we performed Cap Analysis of Gene Expression (CAGE) transcriptome analyses using IACS-010759-sensitive and -resistant AML PDXs. CAGE identifies and quantifies the 5' ends of capped mRNA transcripts (= transcription start sites) and allows investigating promoter structures necessary for gene expression. Primary AML cells from 9 AML PDXs were injected into irradiated NSG mice, which were randomized upon documented engraftment to receive IACS-010759 or vehicle (n = 3/group). The antileukemia efficacy of the treatment was monitored by serial measurements of circulating AML cells. Of the 9 models tested, we defined 4 PDXs as sensitive and 5 as resistant to OxPhos inhibitor therapy. In the resistant models, CAGE analysis of OxPhosi-induced changes (comparing pretreatment with posttreatment) identified upregulation of 77 promoters and downregulation of 207 promoters (log 2-fold change > 3.0, FDR < 0.05, EdgeR), including increased promoter expression (>3.0 fold) of genes associated with adhesion (CCR8,ADGRB2, LAG3, BMF, ATN1, PLXDC1), migration (CCR8, NKX3-2, TMEM123, IGLV7-43, FAM171A1, LBX2, TRAV21, PPP2R5C, BMF, PLXDC1), and actin cytoskeleton dynamics (FAM171A1, BMF, BEST1, PLXDC1). Of note, the 6 adhesion-associated promoters that were upregulated by OxPhosi in 5 of the OxPhosi-resistant mouse models were unchanged or downregulated in the 4 OxPhosi-sensitive models. We then used DEGseq, an R package for identifying differentially expressed genes, to identify promoters whose expression was different between OxPhosi-treated and vehicle-treated groups in the OxPhosi-resistant mouse models. DEGseq detected consistent changes of 214 upregulated and 626 downregulated promoters with OxPhosi treatment in all 5 mouse models. KEGG pathway enrichment analysis was performed with these consistently changed genes and revealed that OxPhos inhibitor treatment significantly upregulated the transcripts of cell adhesion pathway. We then confirmed that BM derived mesenchymal stem cells (MSC) protected OxPhosi-sensitive OCI-AML3 cells; the IC50 of IACS-010759 under MSC coculture was 80-fold higher than in monoculture conditions (IC50; 0.04 nM in monoculture vs. 3.25 nM in coculture), and IACS-010759 (10nM) induced 55% reduction of viable cells in coculture condition as compared to 70% reduction in monoculture. We further observed that OCI-AML3 cells adhered to MSCs were more profoundly protected from OxPhosi induced apoptosis than nonadherent cells. These results indicate that BM stromal cells, in particular those in direct contact with leukemia cells, play a key role in the microenvironment-mediated protection of AML cells from metabolic stress caused by OxPhos blockade. We further observed promoter upregulation of ASS1, coding Argininosuccinate Synthase 1 and of LRP1, coding LDL Receptor Related Protein 1. Argininosuccinate Synthase 1 is an epigenetically regulated key enzyme in the biosynthesis of arginine and energy starvation that induces adaptive transcriptional upregulation of ASS1. LDL Receptor Related Protein 1 plays a major role in lipid metabolism and has been reported to be responsible for hemin-induced autophagy in leukemia cells. These might contribute to intrinsic AML resistance to OxPhosi via activation of compensatory metabolic pathways, amino acid metabolism and lipid metabolism. Taken together, our data highlight the importance of direct interaction with BM stromal cells as well as complementally modification of amino acid- and lipid metabolism for the resistance of AML cells to OxPhos inhibition. While the mechanisms of stroma-leukemia interactions are likely complex, reducing the adhesion of AML cells to nurturing stromal cells ameliorates the resistance to the metabolic and energetic consequences of OxPhos inhibition. Disclosures Andreeff: Amgen: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding. Konopleva:Rafael Pharmaceutical: Research Funding; Reata Pharmaceutical Inc.;: Patents & Royalties: patents and royalties with patent US 7,795,305 B2 on CDDO-compounds and combination therapies, licensed to Reata Pharmaceutical; Sanofi: Research Funding; AstraZeneca: Research Funding; Cellectis: Research Funding; AbbVie: Consultancy, Research Funding; Ablynx: Research Funding; Agios: Research Funding; Ascentage: Research Funding; Eli Lilly: Research Funding; Forty-Seven: Consultancy, Research Funding; Stemline Therapeutics: Consultancy, Research Funding; Amgen: Consultancy; F. Hoffmann La-Roche: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Kisoji: Consultancy; Calithera: Research Funding.

Adipocytes are the prevalent stromal cell type in adult bone marrow (BM), and leukemia cells continuously adapt to deficiency of nutrients acquiring chemoresistant profiles in the BM microenvironment. We have previously shown that fatty acid metabolism is a key energy pathway for survival of acute myeloid leukemia (AML) cells in the adipocyte-abundant BM microenvironment. The novel fatty acid β-oxidation (FAO) inhibitor avocatin B, an odd-numbered carbon lipid derived from the avocado fruit, induced apoptosis and growth inhibition in mono-cultured AML cells. In AML cells co-cultured with BM adipocytes, FAO inhibition with avocatin B caused adaptive stimulation of free fatty acid (FFA) uptake through upregulation of FABP4 mRNA, enhanced glucose uptake and switch to glycolysis. These changes reflect the compensatory response to a shortage of FFA supply to the mitochondria, and facilitate the protection of AML cells from avocatin B–induced apoptosis in the presence of BM adipocytes. However, the combination treatment of avocatin B and conventional anti-AML therapeutic agent cytarabine (AraC) increased reactive oxygen species and demonstrated highly synergistic effects on AML cells under BM adipocyte co-culture condition. These findings highlight the potential for combination regimens of AraC and FAO inhibitors that target bone marrow-resident chemoresistant AML cells.

Acute myeloid leukemia (AML) cells highly depend on oxidative phosphorylation (OxPhos) to satisfy their heightened demands for energy, and the complex I OxPhos inhibitor IACS-010759 (Molina, Nat. Med. 2018) is currently in Phase 1 clinical trial in AML. In this study, we investigated how the bone marrow (BM) microenvironment affects the response to OxPhos inhibition in AML. To characterize the molecular mechanisms of sensitivity to OxPhos inhibition, we performed Cap Analysis of Gene Expression analysis (CAGE) on 31 genetically diverse primary AML samples (20 were defined as sensitive and 11 as resistant to IACS-010759; cut off >3.0 fold annexin V(+) by 100 nM IACS-010759/DMSO at 72 hours). CAGE identified higher expression of transcription start sites (TSS) for 17 genes in IACS-010759 resistant AML samples compared to sensitive (fold change >2.0, FDR < 0.05, EdgeR), which were related to cell adhesion, integrin and/or Rho GTPase family genes that modulate intracellular actin dynamics. We next investigated the interactions between IACS-010759 sensitive OCI-AML3 cells and BM-derived mesenchymal stem cells (MSC). Under conditions mimicking the BM microenvironment, IACS-010759 upregulated the pathways of focal adhesion and ECM-receptor interaction in OCI-AML3 cells (KEGG analysis based on CAGE). In turn, MSC co-culture increased oxygen consumption by AML, induced generation of mitochondrial ROS (control 4.4% vs IACS 44.4%), increased mtDNA (2-fold by q-PCR) and upregulation of mitochondrial proteins VDAC and cytochrome C, translating into dampened growth-inhibitory effects of IACS-010759. We further demonstrated that OCI-AML3 cells adhering to MSCs were fully protected from IACS-010759 induced apoptosis (IACS-induced specific apoptosis: non-adherent cells 16.2% ± 1.6% vs adherent cells 1.6% ± 0.7%, p=0.008, 30nM, 72hours). Similarly, adherent cells were fully protected from apoptosis induced by combination of IACS and AraC. These findings indicate that direct interactions with MSC trigger compensatory activation of mitochondrial respiration, increase in mitochondrial mass and resistance to OxPhos inhibition in AML. We next hypothesized that the trafficking of mitochondria from BM stroma cells to AML cells could represent a putative mechanism of an acquired resistance to OxPhos inhibition. To visualize mitochondria, OCI-AML3 and MSC were stably transfected with mitochondria-targeted PDHA1-GFP and -dsRed, respectively. We discovered that IACS-010759 induced transfer of MSC-derived mitochondria to OCI-AML3 cells (% of GFP/dsRed double-positive OCI-AML, control 4.1 ± 1.7 vs IACS 26.2 ± 13.4, p=0.002) via tunneling nanotubes (TNTs) detected by confocal and electron microscopy (Fig.1). Mitochondria transfer was only observed in the direct contact but not in the transwell co-cultures, and was abrogated by ICAM-1 neutralizing antibody and TNT blockade with Cytochalasin B. Likewise, combination of IACS with AraC increased mitochondrial transfer. We further found that IACS-010759 induced autophagy in OCI-AML3 cells co-cultured with MSC, as noted by increased conversion of LC3-I to LC3-II, which was further enhanced by the lysosome inhibitor Bafilomycin. Additionally, we observed autophagosome formation enwrapping MSC-derived mitochondria (Fig.1F), along with the degradation of an outer mitochondrial membrane protein Tom20. Finally, IACS-010759-induced transfer of mtDNA in BM-resident AML cells was confirmed in vivo in humanized AML PDX models (n=2). Daily oral treatment of mice harboring human AML with IACS-010759 (5.0 mg/kg/day, 21 days) increased the ratio of murine/human mtDNA in human AML cells isolated from BM, in 5 days on/2 days off PDX models tested (2.1 ± 0.3 fold, n=2). In conclusion, the findings of this study indicate an important role of mitochondria trafficking from BM stromal cells to AML cells in a compensatory adaptation to OxPhos inhibition in BM microenvironment. We propose that blocking of mitochondrial transfer could enhance the anti-AML efficacy of OxPhos targeting agents. Disclosures Zhang: The University of Texas M.D.Anderson Cancer Center: Employment. Kuruvilla:The University of Texas M.D.Anderson Cancer Center: Employment. Andreeff:BiolineRx: Membership on an entity's Board of Directors or advisory committees; Breast Cancer Research Foundation: Research Funding; Oncolyze: Equity Ownership; Oncoceutics: Equity Ownership; Senti Bio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Eutropics: Equity Ownership; Reata: Equity Ownership; Aptose: Equity Ownership; 6 Dimensions Capital: Consultancy; Daiichi Sankyo, Inc.: Consultancy, Patents & Royalties: Patents licensed, royalty bearing, Research Funding; Jazz Pharmaceuticals: Consultancy; Celgene: Consultancy; Amgen: Consultancy; AstaZeneca: Consultancy; CPRIT: Research Funding; NIH/NCI: Research Funding; Center for Drug Research & Development: Membership on an entity's Board of Directors or advisory committees; Cancer UK: Membership on an entity's Board of Directors or advisory committees; NCI-CTEP: Membership on an entity's Board of Directors or advisory committees; German Research Council: Membership on an entity's Board of Directors or advisory committees; Leukemia Lymphoma Society: Membership on an entity's Board of Directors or advisory committees; NCI-RDCRN (Rare Disease Cliln Network): Membership on an entity's Board of Directors or advisory committees; CLL Foundation: Membership on an entity's Board of Directors or advisory committees. Konopleva:Astra Zeneca: Research Funding; Agios: Research Funding; Eli Lilly: Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Cellectis: Research Funding; Amgen: Consultancy, Honoraria; F. Hoffman La-Roche: Consultancy, Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Ascentage: Research Funding; Kisoji: Consultancy, Honoraria; Reata Pharmaceuticals: Equity Ownership, Patents & Royalties; Ablynx: Research Funding; Forty-Seven: Consultancy, Honoraria; Calithera: Research Funding; Stemline Therapeutics: Consultancy, Honoraria, Research Funding.

Genetic mutations in FLT3 (fms-like tyrosine kinase-3) play an important role in the pathogenesis of acute myeloid leukemia (AML). FLT3 internal tandem duplications (FLT3-ITD) occur in approximately 25% of all AML cases and various tyrosine kinase inhibitors (TKIs) targeting FLT3-ITD such as quizartinib, crenolanib, and gilteritinib have been developed. Although these selective FLT3 inhibitors were thought to be promising, their effects turned out to be temporary due to the rapid development of resistance associated with clonal switching. Acquired FLT3 point mutations at D835 in the activation loop of tyrosine kinase domain are often accountable for clonal switching at least for Type II TKIs. In addition, adjunct mutations in other genes are also found to be associated with TKI resistance. To investigate the underlying molecular mechanism of this secondary, mutation-driven acquired resistance, we first analyzed co-occurring mutations in the leukemia cells obtained from 26 AML patients with FLT3-ITD (n=14) or FLT3-ITD/D835 dual (n=12) mutations, and performed cap analysis of gene expression (CAGE) sequencing, which identifies and quantifies the 5' ends of capped mRNA transcripts (transcription start sites) and allows investigating promoter structures necessary for gene expression. Patients with FLT3-ITD/D835 harbored a higher number of co-mutations such as ASXL1 and RUNX1 compared to AML with FLT3-ITD (FLT3-ITD/D835: 2.83 ± 0.52, FLT3-ITD: 0.49 ± 0.13, p To recapitulate the observations obtained with primary human AML samples, we generated MV4;11 cells with acquired FLT3-ITD/D835 mutations (MV4;11-QR cells) by culturing FLT3-ITD MV4;11 leukemia cells in the presence of quizartinib (1.5 nM), a selective FLT3 inhibitor, for 6 months. While quizartinib (0.2 nM) suppressed the proliferation of 50% of the parental MV4;11 at 72 hours, much higher concentrations of quizartinib (10 nM) was required to suppress the proliferation of MV4;11-QR cells. Quantitative RT-PCR and immunoblot analysis revealed that MV4;11-QR cells expressed higher transcript and protein levels of BCL2A1 than MV4;11 parental cells, while BCL2 levels were similar in both cells and MCL1 and BCLxL expression were lower in the MV4;11-QR than in the parental cells. Next, to investigate the molecular properties of AML cells bearing FLT3-ITD or FLT3-ITD/D835 without other co-mutations, we created Ba/F3 cells stably expressing FLT3-ITD or FLT3-ITD/D835. Of notes, the FLT3-ITD/D835 Ba/F3 cells expressed markedly higher BCL2 transcript and protein levels with lower expression of BCLxL than in FLT3-ITD Ba/F3 cells. No significant difference of MCL1 expression was observed. The sensitivity to quizartinib was massively decreased in the FLT3-ITD/D835 Ba/F3 cells (IC50: FLT3-ITD/D835 >1000nM vs. FLT3-ITD, 0.8nM, at 48h). Finally, we examined the efficacy of the BCL-2 specific inhibitor venetoclax in FLT3-ITD/D835 dual mutated cells with or without upregulation of BCL2 or BCL2A1, the latter shown to confer resistance to venetoclax by sequestering released BIM (Esteve-Arenys, Oncogene. 2018). As expected, venetoclax caused more profound cell growth inhibition and apoptosis induction in BCL2 upregulated FLT3-ITD/D835 Ba/F3 compared to FLT3-ITD Ba/F3 cells (IC50: FLT3-ITD/D835 301nM vs. FLT3-ITD >1000 nM, 96 h). However, FLT3-ITD/D835 bearing MV4;11-QR cells with upregulated BCL2A1 were less sensitive to venetoclax than MV4;11 parental cells (IC50: MV4;11-QR, 149nM vs. MV4;11, 33 nM, 72 h). In conclusion, these results demonstrate that acquisition of D835 mutation in FLT3-ITD mutated AML is often accompanied with multiple co-occurring genetic mutations, and depends on anti-apoptotic BCL-2 associated pro-survival mechanisms. BCL2A1 upregulation might be involved in pathogenesis of acquired drug resistance of FLT3-ITD/D835 dual mutant AML cells, and is a promising new target in FLT3-ITD/D835 refractory AML with complex mutations. Disclosures Carter: Amgen: Research Funding; AstraZeneca: Research Funding; Ascentage: Research Funding. Shah:Bristol-Myers Squibb: Research Funding. Konopleva:Genentech: Honoraria, Research Funding; Ascentage: Research Funding; Kisoji: Consultancy, Honoraria; Reata Pharmaceuticals: Equity Ownership, Patents & Royalties; Ablynx: Research Funding; Astra Zeneca: Research Funding; Agios: Research Funding; Calithera: Research Funding; Stemline Therapeutics: Consultancy, Honoraria, Research Funding; Forty-Seven: Consultancy, Honoraria; Eli Lilly: Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Cellectis: Research Funding; Amgen: Consultancy, Honoraria; F. Hoffman La-Roche: Consultancy, Honoraria, Research Funding. Andreeff:Daiichi Sankyo, Inc.: Consultancy, Patents & Royalties: Patents licensed, royalty bearing, Research Funding; Jazz Pharmaceuticals: Consultancy; Celgene: Consultancy; Amgen: Consultancy; AstaZeneca: Consultancy; 6 Dimensions Capital: Consultancy; Reata: Equity Ownership; Aptose: Equity Ownership; Eutropics: Equity Ownership; Senti Bio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Oncoceutics: Equity Ownership; Oncolyze: Equity Ownership; Breast Cancer Research Foundation: Research Funding; CPRIT: Research Funding; NIH/NCI: Research Funding; Center for Drug Research & Development: Membership on an entity's Board of Directors or advisory committees; Cancer UK: Membership on an entity's Board of Directors or advisory committees; NCI-CTEP: Membership on an entity's Board of Directors or advisory committees; German Research Council: Membership on an entity's Board of Directors or advisory committees; Leukemia Lymphoma Society: Membership on an entity's Board of Directors or advisory committees; NCI-RDCRN (Rare Disease Cliln Network): Membership on an entity's Board of Directors or advisory committees; CLL Foundation: Membership on an entity's Board of Directors or advisory committees; BiolineRx: Membership on an entity's Board of Directors or advisory committees.

Internal tandem duplications (ITD) in the juxtamembrane domain of FMS-like tyrosine kinase 3 (FLT3) cause ligand-independent constitutive activation of FLT3 kinase and its downstream signaling. FLT3-ITD mutations confer poor prognosis with high relapse rates in AML patients. FLT3-targeted therapies using tyrosine kinase inhibitors (TKIs) often induce additional point mutations within the tyrosine kinase domains (FLT3-TKD mutations), most commonly found at D835 activation loop. Additional FLT3-TKD mutations that cause secondary resistance emerge in at least 20% of patients with TKI treatment. To elucidate the alterations of transcriptome signatures of FLT3-ITD and TKD double mutations in AML, we performed cap analysis of gene expression (CAGE) sequencing for 26 primary AML samples (14 with FLT3-ITD, 12 with FLT3-ITD/D835). CAGE detects and quantifies the specific transcriptional start site (TSS) transcripts, which enables high-throughput gene expression profiling and promoter usage analysis. Altered transcription of TSS in FLT3-ITD/D835 AML samples were detected by comparison with TSS in FLT3-ITD samples, and upregulation of 310 TSS and downregulation of 22 TSS were mapped (FDR < 0.05, EdgeR). Based on Gene Ontology (GO) analysis, up-regulated genes were enriched in "apoptotic process", "intracellular signal transduction" and "immune system development", including pro-survival BCL2A1 and drug resistance related S100A8 and PRKCH. To validate these transcriptional changes, we utilized isogenic paired Ba/F3 cells transfected with FLT3-ITD or FLT3-ITD/D835. CAGE detected upregulation of 1945 TSS and downregulation of 1470 TSS in FLT3-ITD/D835 compared to FLT3-ITD cells (FDR < 0.05). TSS transcriptions of Bcl-2, Prkca, NF-κB1, Myc, and Cdkn1a (p21) were upregulated in FLT3-ITD/D835 cells. GO analysis consistently highlighted higher activation of NF-κB signaling and its downstream Bcl-2 in FLT3-ITD/D835 than in FLT3-ITD cells both for primary AML samples and Ba/F3 cells. To determine a correlation between activated promoters and transcription factors in FLT3-ITD/D835 cells, we performed an unbiased search for enriched sequence motifs using HOMER software. HOMER revealed that the promoter 4 of BCL2A1 contained a common motif of transcription factor STAT6, known to associate with NF-κB and cooperatively bound to their respective promoter elements. Ingenuity Pathway Analysis also highlighted higher activation of STAT6 in FLT3-ITD/D835 AML cells compared to FLT3-ITD. Immunoblot analysis confirmed higher expression of Bcl-2, c-Myc, p27, and lower expression of Bcl-xL and Mcl-1 in FLT3-ITD/D835 Ba/F3 compared to FLT3-ITD Ba/F3 cells. FLT3-ITD and FLT3-ITD/D835 cells showed similar expression level of Bax and Bid. We found that FLT3-ITD/D835 Ba/F3 cells proliferated slower than FLT3-ITD cells (growth rate; FLT3-ITD/D835 9.8±2.4 fold, FLT3-ITD 19.8±1.2 fold, p=0.003, 48 h) with G0/G1 accumulation (FLT3-ITD/D835 61.5±10.1%, FLT3-ITD 31.3±11.2%, p Finally, we hypothesized that targeting Bcl-2 may effectively overcome the acquired resistance of FLT3-ITD/D835 cells. Venetoclax (ABT-199/GDC-0199), a clinically available Bcl-2 selective inhibitor, as single agent was not capable of eliminating FLT3-ITD AML due to altered activation of FLT3 downstream signaling and Mcl-1 upregulation. FLT3-ITD/D835 cells showed higher expression of the Bcl-2 gene and/protein and were less dependent on FLT3 signaling compared to FLT3-ITD cells (Tabe, ASH 2017). As expected, venetoclax caused more profound cell growth inhibition and apoptosis induction in FLT3-ITD/D835 Ba/F3 than in FLT3-ITD Ba/F3 cells (IC50 2.98 μM vs 13.9 μM, ED50 28.8 μM vs 173 μM, 48 h). In conclusion, we identified Bcl-2 transcriptional activation as a novel mechanism by which the acquired D835 mutation in FLT3-ITD AML cells facilitates anti-apoptotic network activation and confers TKI resistance. Bcl-2 inhibition by venetoclax represents a putative therapeutic strategy in FLT3-ITD/TDK double-mutated AML cells. Disclosures Shah: Bristol-Myers Squibb: Research Funding; ARIAD: Research Funding. Konopleva:Stemline Therapeutics: Research Funding. Andreeff:AstraZeneca: Research Funding.

FMS-like tyrosine kinase 3 with internal tandem duplication (FLT3-ITD), the most frequent mutation in acute myeloid leukemia (AML), results in the constitutive ligand-independent activation of FLT3 receptor downstream signaling. FLT3-targeted therapies using tyrosine kinase inhibitors (TKIs) demonstrate single agent activity in these patients but long-term efficacy is limited by emerging resistance in part due to acquired point mutations in the tyrosine kinase domains (TKD) of the FLT3 gene, most commonly found at D835 within the activation loop. Exportin 1 (XPO1) mediates the nucleo-cytoplasmic transport, and is overexpressed in AML cells with FLT3-ITD mutations (Kojima, Blood, 2013). We have reported that the clinically available XPO1 inhibitor selinexor effectively inhibits cell proliferation in both FLT3-ITD and FLT3-ITD/D835 mutated cells through upregulation of TP53 and blockade of c-Myc signaling (Tabe, ASH, 2017). In this study, we aimed at developing novel mechanism-based combination therapies for TKI-resistant FLT3-ITD cells with acquired TKD mutation. First we investigated the transcriptional changes associated with XPO1 and FLT3 inhibition in FLT3-ITD and FLT3-ITD/D835 mutated cells. We utilized paired isogenic FLT3-ITD or FLT3-ITD/D835Y transfected Ba/F3 cell lines and performed the cap analysis of gene expression (CAGE) that identifies and quantifies gene expression at the transcription start sites (TSS). FLT3-ITD cells are sensitive and FLT3-ITD/D835 cells are resistant to FLT3 inhibitor quizartinib. CAGE detected the shared upregulation of 3833 TSS genes induced by selinexor in FLT3-ITD and FLT3-ITD/D835 cells (FDR Based on these findings, we focused on Bcl-2 as a novel therapeutic target in FLT3-ITD/D835 cells, and investigated the anti-leukemia efficacy of combined inhibition of Bcl-2 and XPO1. We utilized the clinically available selective Bcl-2 inhibitor venetoclax and observed synergistic anti-proliferative and pro-apoptotic effects of venetoclax and selinexor in FLT3-ITD/D835 (Combination Index, CI: 0.39 and 0.45). Simultaneous inhibition of Bcl-2 by venetoclax and FLT3 by quizartinib showed no synergistic or additive effects in FLT3-ITD/D835 cells. Western blot analysis showed that the combination of venetoclax / selinexor reduced Bcl-2 and Mcl-1 in FLT3-ITD/D835 cells, and activated cleaved caspase3. In FLT3-ITD cells, the venetoclax / selinexor combination induced only small decrease of Bcl-2, did not change Mcl-1 and Bcl-xL, and increased cleaved caspase3. These changes were not observed in wt-FLT3 transfected Ba/F3 cells. Collectively, CAGE analysis of transcription start sites identified the primary mechanism underlying the synergistic activity of concomitant inhibition of Bcl-2 and XPO1 in FLT3-ITD/D835 cells as related to the regulation of Bcl-2, Mcl-1, Bcl-xL and c-Myc. These findings suggest that Bcl-2 inhibition by venetoclax combined with XPO1 inhibition by selinexor could be developed into a promising therapeutic strategy for TKI-resistant AML patients with FLT3-ITD and secondary acquired TKD mutations. Disclosures Konopleva: Stemline Therapeutics: Research Funding. Andreeff:AstraZeneca: Research Funding.

Acute myeloid leukemia (AML) cells are highly dependent on oxidative phosphorylation (OxPhos) for survival and continually adapt to fluctuations in nutrient and oxygen availability in the bone marrow (BM) microenvironment. The first-in-class OxPhos inhibitor IACS-010759 (Molina, Nat. Medicine 2018) is currently in Phase 1 clinical trial in AML. To identify biomarkers of sensitivity or resistance to OxPhos inhibition, we performed Cap Analysis of Gene Expression analysis (CAGE) in primary AML samples (11 sensitive and 3 resistant to IACS-010759) and 6 AML cell lines (OCI-AML3, MOLM13, THP-1, U937, MV4;11, HL60). CAGE identified 41 gene transcripts that were significantly higher in IACS-010759 resistant primary AML samples than in sensitive samples (fold change >3.0, FDR We next studied OxPhos inhibition under conditions mimicking BM microenvironment, by co-culturing AML cells with healthy BM-derived mesenchymal stem cells (MSC). Anti-proliferative effects of IACS-010759 were reduced by co-culture with MSC (IC50 0.01nM vs 2.1nM OCI-AML3, 65.4nM vs >10µM MOLM13). MSC co-culture increased OCR and glycoPER, and IACS-010759 decreased OCR / increased glycoPER in both cell lines. To determine the mechanism of resistance to IACS-010759 under MSC co-culture conditions, we studied the mitochondrial exchange between AML cells and MSC. We observed the bidirectional mitochondrial transfer between MSCs and AML cells. Using AML and MSC cells stably infected with mitochondria-targeted PDHA1 (GFP in AML, dsRed in MSC) to visualize the mitochondria, we found that IACS-010759 treatment facilitated transfer of AML-derived mitochondria into the adhered MSCs (24h), and MSC-derived mitochondria transferred to floating AML cells (48-72h) along with formation of tunneling nanotubes (TNTs) of AML cells, in sensitive OCI-AML3 cells (PDHA1-GFP/DsRed double positive %, control vs IACS; 9.0% vs 23.3 %). Mitochondria transfer from MSCs to AML cells was minimally observed in MOLM13 cells with elevated basal OxPhos (4.0% vs 5.0%). We next investigated IACS-010759-induced metabolic changes in AML cells interacting with bone marrow (BM) stromal cells. Capillary electrophoresis-time-of-flight mass spectrometry (CE-TOFMS) metabolite analysis further detected that IACS-010759 suppressed multiple anaplerotic amino acids in OCI-AML3 cells including glutamine and glutamic acid, which was reversed by MSC co-culture along with increase in intra-autophagosomal LC3-II in OCI-AML3 cells. These findings were not observed in MOLM13. Microenvironment-induced activation of glutamine metabolism and autophagy-associated amino acid metabolism could be additional compensatory mechanisms in response to OxPhos inhibition by IACS-010759 in BM microenvironment. Taken together, basal metabolic energetic capacity including elevated OxPhos and high compensatory glycolysis confer the AML-intrinsic resistance to IACS-010759, which can be reversed by simultaneous glycolysis inhibition. BM microenvironment facilitates secondary resistance to OxPhos inhibition through modulation of amino acid metabolism and direct mitochondrial transfer. Inhibition of these processes could enhance the anti-AML efficacy of OxPhos inhibition. Disclosures Andreeff: AstraZeneca: Research Funding. Konopleva:Stemline Therapeutics: Research Funding.

Electrospray ionization mass spectrometry is used in lipidomics studies. The present research established a top-down liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) shotgun analysis method for phospholipids (PLs) using a normal-phase column or a C30 reverse-phase column with the data-dependent MS/MS scanning mode. A normal-phase column can separate most of the major different classes of PLs. By using LC/ESI-MS/MS with a normal-phase column, approximately 50 molecular species were identified in a PL mixture from rat liver. When the reverse-phase column was used, the PLs could be separated depending on their hydrophobicity, essentially the length of their fatty acyl chains and the number of unsaturated bonds in them. The LC/ESI-MS/MS method using a C30 reverse-phase column was applied to phosphatidylcholine (PC) and phosphatidylethanolamine (PE) mixtures as test samples. Molecular species with the same molecular mass but with different pairs of fatty acyl chains were separately identified. As a result, about 60 PC and 50 PE species were identified. PLs from rat liver were subjected to LC/ESI-MS/MS using the C30 reverse-phase column and about 110 molecular species were identified. Off-line two-dimensional LC/ESI-MS/MS with the normal-phase and C30 reverse-phase columns allowed more accurate identification of molecular species by using one-dimensional C30 reverse-phase LC/ESI-MS/MS analysis of the collected fractions.

Analyses of molecular species of phospholipids containing choline (Ch), such as phosphatidylcholine (PC) and sphingomyelin (SM), are reported. Neutral loss scanning was applied for the selective detection of these lipids using a quadrupole-linear ion trap mass spectrometer. By using ammonium formate as an elution buffer, both PC and SM were detected as [M+HCOO]- ions in the negative ion mode. Upon collisional activation, the [M+HCOO]- adduct ions underwent facile elimination of HCO2, to yield an ion which, in turn, readily underwent collisional-induced dissociation (CID) to eliminate CH3 to yield an [M-CH3]- ion. By selecting the proper conditions for scanning for neutral loss of 60 Da (HCO2+CH3), SM species were identified separately from PCs. Further, by selection of this [M-CH3]- ion as the precursor ion, the identities of the fatty acyl chains of PC species can be effectively obtained by MS3 experiments. Furthermore, by the MS3 analyses of [M-CH3]- specifically obtained from SM molecules, identification of sphingosine or sphinganine derivatives and their N-acyl species can also be effectively obtained. This systematic analysis of PCs and SMs by conditional neutral loss scanning, with subsequent analyses by MS3, using a linear ion trap mass spectrometer in the negative ion mode, appears to be a very effective and sensitive method. Further, MS/MS in the positive ion mode at relatively low collision energy was also effective for the identification of positional specificities in individual molecular PC species from their lysoPC-related fragments. The present paper deals only with qualitative identification of individual molecular species, and the related quantitative studies are now underway.