Search

Background: Bleeding and thrombosis remain the primary complications related to the use of extracorporeal membrane oxygenation (ECMO). To date, no single test or parameter has been identified to accurately predict the risk of these hemostatic complications. Thrombin generation may be the key marker for both thrombosis and bleeding, and may be influenced by inflammation. The aims of this study were to evaluate if novel laboratory tests including thrombin generation assay, neutrophil extracellular traps (NETs), microparticles (MPs), and red blood cell (RBC) membrane fragility/adhesion could better predict patients at risk for bleeding and/or thrombosis compared to routine laboratory tests. We hypothesized that ECMO related thrombosis is associated with increased thrombin generation and ECMO related bleeding is associated with decreased thrombin generation. Methods: An IRB approved prospective pilot study of patients requiring ECMO was conducted at Children's Hospital of Michigan. Patients were enrolled within 24 hours of ECMO cannulation after informed consent. Patients aged 0-17 years placed on venoarterial (VA) or venovenous (VV) ECMO were included. Patient demographics, baseline laboratory, clinical data, and novel assays were collected. Presented is the preliminary data of the first 16 patients enrolled. SPSS was used for data analysis. Results: Of the 16 patients, there were 9 males and 7 females with the majority being cannulated for primary respiratory etiologies. Median age was 8.5 months with 6 patients being neonates (38%). Twelve patients (75%) survived the ECMO run, and 11 patients (69%) survived to hospital discharge. Laboratory data was grouped based on "no event" (N=94), "bleeding event" (N=13) and "clotting event" (N=21) days. There were no differences in the number of RBC, fresh frozen plasma, or cryoprecipitate transfusions between events. Platelet transfusions were used at higher volumes in bleeding events, p=0.011. Platelet counts did not differ between groups, whereas fibrinogen levels were significantly lower on days of bleeding events, p≤0.001 (Figure 1A). There were no differences seen in the activated partial thromboplastin time (aPTT) or activated clotting time (ACT) which are routinely used for monitoring anticoagulation. However, the prothrombin time (PT) was significantly prolonged in bleeding events with a median of 16 seconds (p=0.001), which may be related to the lower fibrinogen levels (Figure 1B). Thrombin generation was assessed using the maximum rate of thrombin generation (MRTG) value from the thromboelastograph (TEG) generated velocity curve (Figure 1D). Bleeding events had a significantly lower median MRTG of 7.93 mm/min compared to 12.36 mm/min in the no event group and 12.14 mm/min in the clotting event group (p=0.004). The thrombin generation assay results are in process. NETs were analyzed using an ELISA to detect citrullinated histone-3 (CitH3) levels (ng/mL). There were no significant differences seen in our population, however there is a trend toward increased levels in thrombotic events (Figure 1E). Both absolute MPs and platelet MPs were significantly increased in clotting events compared to bleeding events, p=0.003 and p≤0.001 respectively (Figure 1C). In our population, there was no evidence that hemolysis played a role in thrombosis as assessed by flow based RBC mechanical fragility testing. Of note, flow based RBC adhesion showed a non-significant trend toward increased adhesion to P-selectin. This finding requires further investigation because P-selectin is a primary site for adhesion on endothelial cells and plays a crucial role in coagulation (Figure 1F). Conclusions: Bleeding events on ECMO are associated with increased mortality. Our findings suggest that lower fibrinogen levels, prolonged PT and decreased thrombin generation (as assessed by the TEG) are associated with an increased risk for major bleeding. Increased levels of NETs, MPs and RBC adhesion have a trend towards increased thrombotic events. Thus, although preliminary, our results suggest that novel laboratory tests were effective in identifying bleeding events, and the trends seen in thrombotic events may allow for the use of new medications to reduce clotting in ECMO. The results illustrate the challenges in monitoring ECMO anticoagulation and additional study of novel tests are needed to identify and avoid clinical complications. Disclosures Tarasev: Functional Fluidics:Current Employment, Current equity holder in private company.Hines:Functional Fluidics:Current equity holder in private company.Chitlur:Biovertiv:Honoraria;Pfizer:Honoraria;Novo Nordisk:Consultancy, Honoraria;Takeda:Honoraria;Agios Pharmaceuticals:Research Funding.

SDF-1α/CXCR4 signaling plays a key role in leukemia/bone marrow microenvironment interactions. We previously reported that bone marrow–derived stromal cells inhibit chemotherapy-induced apoptosis in acute myeloid leukemia (AML). Here we demonstrate that the CXCR4 inhibitor AMD3465 antagonized stromal-derived factor 1α (SDF-1α)–induced and stroma-induced chemotaxis and inhibited SDF-1α–induced activation of prosurvival signaling pathways in leukemic cells. Further, CXCR4 inhibition partially abrogated the protective effects of stromal cells on chemotherapy-induced apoptosis in AML cells. Fetal liver tyrosine kinase-3 (FLT3) gene mutations activate CXCR4 signaling, and coculture with stromal cells significantly diminished antileukemia effects of FLT3 inhibitors in cells with mutated FLT3. Notably, CXCR4 inhibition increased the sensitivity of FLT3-mutated leukemic cells to the apoptogenic effects of the FLT3 inhibitor sorafenib. In vivo studies demonstrated that AMD3465, alone or in combination with granulocyte colony-stimulating factor, induced mobilization of AML cells and progenitor cells into circulation and enhanced antileukemic effects of chemotherapy and sorafenib, resulting in markedly reduced leukemia burden and prolonged survival of the animals. These findings indicate that SDF-1α/CXCR4 interactions contribute to the resistance of leukemic cells to signal transduction inhibitor– and chemotherapy-induced apoptosis in systems mimicking the physiologic microenvironment. Disruption of these interactions with CXCR4 inhibitors represents a novel strategy of sensitizing leukemic cells by targeting their protective bone marrow microenvironment.

Background: Acute leukemias are the most common cancers in childhood. Despite multi-agent chemotherapy protocols and the introduction of novel molecularly targeted therapies which have resulted in improved survival over the last few decades, relapsed acute lymphoblastic leukemia remains the second most common pediatric cancer diagnosis. In addition, morbidities from current chemotherapy regimens are unacceptably high. Abundant evidence point to a major role for mediators of the unfolded protein response (UPR) in normal and leukemic white blood cell biology. We have demonstrated that activation of the UPR is a productive approach to inhibit the proliferation of solid tumor cell lines in vitro and to reducing xenograft burden in vivo. The UPR consists of genetically distinct mechanisms that serve to clear misfolded proteins from the endoplasmic reticulum (ER) and enhance protein folding, or induce apoptosis if the initiating stress is prolonged or robust. ML291 is a novel UPR-inducing sulfonamidebenzamide, identified through cell-based high throughput screening and iterative SAR-guided chemical synthesis, that overwhelms the adaptive capacity of the UPR and induces apoptosis in a variety of solid cancer models. Objective: To determine the ability of ML291 to activate the UPR and induce apoptosis in a panel of leukemia cell lines, and to use CHOP-null K562 cells to elucidate the relative contribution of the UPR. We hypothesized that ML291 might activate the PERK/eIF2a/CHOP (apoptotic) arm of the UPR and reduce leukemic cell burden in vitro and in vivo. Methods: MTT and luciferase-based proliferation assays, flow cytometry and RT-qPCR were used to evaluate cell growth, UPR activation and apoptosis in a panel of leukemia cell lines that included AML, ALL and CML in cells exposed to ML291. CRISPR-Cas9 genome editing was used to delete CHOP in K562 (human myeloid leukemia) cells. Deletion was validated by immunoblot analysis and these cells were subjected to the same proliferation and gene analyses described above. The in vivo response to ML291 therapy was evaluated in an established zebrafish xenograft assay (Corkery et al. BJH 2011) in which embryos were xenotransplanted with wild type or CHOP knockdown K562 cells and embryos bathed in ML291. Results: Immunoblot and RT-qPCR analysis revealed an accumulation of proteins and increased gene expression for downstream UPR genes, including CHOP, GRP78/BiP, GADD34 and XBP1 in leukemia cells following ML291 treatment, indicating the activation of the UPR. Increased expression of the apoptotic genes, NOXA, PUMA and DR5 was also observed post-treatment with ML291; and dose response proliferation assays performed after 24 hours revealed IC50 concentrations of 1 - 30µM across cell lines. CHOP deleted K562 cells were protected from cell death when cultured with increasing concentrations of ML291, and were significantly less able to translocate phosphatidylserine across the cell membrane and activate the caspase cascade. When zebrafish embryos xenotransplanted with K562-wild type or -CHOP-null cells were bathed in water containing 5mM ML291 for three days, there was a significant reduction in leukemia cell burden exclusively in theK562 wild type xenografts. Conclusion: Collectively these data indicate that intact PERK/eIF2a/CHOP signaling is required for efficient leukemic cell apoptosis in response to ML291 in vitro and in vivo, and support the hypothesis that small molecule enforcement of the UPR might be a productive therapeutic approach in leukemia. Disclosures No relevant conflicts of interest to declare.

The interactions between the bone marrow (BM) microenvironment and acute myeloid leukemia (AML) is known to promote survival of AML cells. In this study, we used reverse phase-protein array (RPPA) technology to measure changes in multiple proteins induced by stroma in leukemic cells. We then investigated the potential of an mTOR kinase inhibitor, PP242, to disrupt leukemia/stroma interactions, and examined the effects of PP242 in vivo using a mouse model. Using RPPA, we confirmed that multiple survival signaling pathways, including the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), were up-regulated in primary AML cells cocultured with stroma. PP242 effectively induced apoptosis in primary samples cultured with or without stroma. Mechanistically, PP242 attenuated the activities of mTORC1 and mTORC2, sequentially inhibited phosphorylated AKT, S6K, and 4EBP1, and concurrently suppressed chemokine receptor CXCR4 expression in primary leukemic cells and in stromal cells cultured alone or cocultured with leukemic cells. In the in vivo leukemia mouse model, PP242 inhibited mTOR signaling in leukemic cells and demonstrated a greater antileukemia effect than rapamycin. Our findings indicate that disrupting mTOR/AKT signaling with a selective mTOR kinase inhibitor can effectively target leukemic cells within the BM microenvironment.

The interactions between hematopoietic cells and the bone marrow (BM) microenvironment play a critical role in normal and malignant hematopoiesis and drug resistance. These interactions within the BM niche are unique and could be important for developing new therapies. Here, we describe the development of extramedullary bone and bone marrow using human mesenchymal stromal cells and endothelial colony-forming cells implanted subcutaneously into immunodeficient mice. We demonstrate the engraftment of human normal and leukemic cells engraft into the human extramedullary bone marrow. When normal hematopoietic cells are engrafted into the model, only discrete areas of the BM are hypoxic, whereas leukemia engraftment results in widespread severe hypoxia, just as recently reported by us in human leukemias. Importantly, the hematopoietic cell engraftment could be altered by genetical manipulation of the bone marrow microenvironment: Extramedullary bone marrow in which hypoxia-inducible factor 1α was knocked down in mesenchymal stromal cells by lentiviral transfer of short hairpin RNA showed significant reduction (50% ± 6%; P = .0006) in human leukemic cell engraftment. These results highlight the potential of a novel in vivo model of human BM microenvironment that can be genetically modified. The model could be useful for the study of leukemia biology and for the development of novel therapeutic modalities aimed at modifying the hematopoietic microenvironment.