scholarly journals Leukemia-on-a-chip: Dissecting the chemoresistance mechanisms in B cell acute lymphoblastic leukemia bone marrow niche

2020 ◽  
Vol 6 (44) ◽  
pp. eaba5536
Author(s):  
Chao Ma ◽  
Matthew T. Witkowski ◽  
Jacob Harris ◽  
Igor Dolgalev ◽  
Sheetal Sreeram ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Chemotherapy Resistance ◽  
Patient Specific ◽  
Bone Marrow Niche ◽  
Cell Acute Lymphoblastic Leukemia

B cell acute lymphoblastic leukemia (B-ALL) blasts hijack the bone marrow (BM) microenvironment to form chemoprotective leukemic BM “niches,” facilitating chemoresistance and, ultimately, disease relapse. However, the ability to dissect these evolving, heterogeneous interactions among distinct B-ALL subtypes and their varying BM niches is limited with current in vivo methods. Here, we demonstrated an in vitro organotypic “leukemia-on-a-chip” model to emulate the in vivo B-ALL BM pathology and comparatively studied the spatial and genetic heterogeneity of the BM niche in regulating B-ALL chemotherapy resistance. We revealed the heterogeneous chemoresistance mechanisms across various B-ALL cell lines and patient-derived samples. We showed that the leukemic perivascular, endosteal, and hematopoietic niche-derived factors maintain B-ALL survival and quiescence (e.g., CXCL12 cytokine signal, VCAM-1/OPN adhesive signals, and enhanced downstream leukemia-intrinsic NF-κB pathway). Furthermore, we demonstrated the preclinical use of our model to test niche-cotargeting regimens, which may translate to patient-specific therapy screening and response prediction.

scholarly journals Bone marrow niche-derived extracellular matrix-degrading enzymes influence the progression of B-cell acute lymphoblastic leukemia

Leukemia ◽  
2020 ◽  
Vol 34 (6) ◽  
pp. 1540-1552 ◽  
Author(s):  
Divij Verma ◽  
Costanza Zanetti ◽  
Parimala Sonika Godavarthy ◽  
Rahul Kumar ◽  
Valentina R. Minciacchi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Extracellular Matrix ◽  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Leukemia Cell ◽  
Bone Marrow Niche ◽  
Significant Prolongation ◽  
Tnf Α ◽  
Cell Acute Lymphoblastic Leukemia

AbstractSpecific and reciprocal interactions with the bone marrow microenvironment (BMM) govern the course of hematological malignancies. Matrix metalloproteinase-9 (MMP-9), secreted by leukemia cells, facilitates tumor progression via remodeling of the extracellular matrix (ECM) of the BMM. Hypothesizing that leukemias may instruct the BMM to degrade the ECM, we show, that MMP-9-deficiency in the BMM prolongs survival of mice with BCR-ABL1-induced B-cell acute lymphoblastic leukemia (B-ALL) compared with controls and reduces leukemia-initiating cells. MMP-9-deficiency in the BMM leads to reduced degradation of proteins of the ECM and reduced invasion of B-ALL. Using various in vivo and in vitro assays, as well as recipient mice deficient for the receptor for tumor necrosis factor (TNF) α (TNFR1) we demonstrate that B-ALL cells induce MMP-9-expression in mesenchymal stem cells (MSC) and possibly other cells of the BMM via a release of TNFα. MMP-9-expression in MSC is mediated by activation of nuclear factor kappa B (NF-κB) downstream of TNFR1. Consistently, knockdown of TNF-α in B-ALL-initiating cells or pharmacological inhibition of MMP-9 led to significant prolongation of survival in mice with B-ALL. In summary, leukemia cell-derived Tnfα induced MMP-9-expression by the BMM promoting B-ALL progression. Inhibition of MMP-9 may act as an adjunct to existing therapies.

Rac2 GTPase Activation Is Necessary for Development of p190-BCR-ABL-Induced B-Cell Acute Lymphoblastic Leukemia

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3790-3790
Author(s):  
Abel Sanchez-Aguilera ◽  
Ami tava Sengupta ◽  
Joseph P Mastin ◽  
Kyung H Chang ◽  
David A Williams ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
B Cells ◽  
Tyrosine Kinase ◽  
B Cell ◽  
Rho Gtpases ◽  
Lymphoblastic Leukemia ◽  
Hematopoietic Stem ◽  
Cell Acute Lymphoblastic Leukemia

Abstract The fusion gene BCR-ABL, resulting from t(9;22) reciprocal chromosomal translocations, encodes a constitutively active tyrosine kinase. Two different isoforms of BCR-ABL, p190 and p210, are associated to two completely different diseases. In the tyrosine kinase inhibitor (TKI) era, while p210-BCR-ABL-induced CML is highly responsive to TKI, p190-BCR-ABL still induces a poor prognosis B-cell acute lymphoblastic leukemia (B-ALL). The only difference between these two forms of BCR-ABL is the existence of a DH/Cdc24/PH domain in p210-BCR-ABL, which acts as a guanine nucleotide exchange factor (GEF) able to activate Rho GTPases. Rac is a subfamily of Rho GTPases with regulatory activity on hematopoietic stem cell and progenitor (HSC/P) functions. We have previously shown that Rac2 and further the combination of Rac1 and Rac2 mediate downstream signals in p210 BCR-ABL-induced myeloproliferation (Thomas EK, et al., Cancer Cell, 2007). Interestingly, despite the absence of a GEF domain in p190-BCR-ABL, Rac is activated, suggesting the activation of other GEF(s). Here we have analyzed whether Vav and Rac family members are involved in p190-BCR-ABL-induced B-ALL. We have used a combination of in vitro (Ba/F3 pro-B cells transduced with p190 or p210 BCR-ABL) and in vivo (murine transduction-transplantation model of p190 BCR-ABL-induced B-ALL) approaches. In Ba/F3 cells, both p190 BCR-ABL and p210 BCR-ABL activated Rac and the Rac effector p21 activated kinase (PAK), and their proliferation and survival appeared severely decreased in response to the Rac activation inhibitor NSC23766. Stat3, Stat5 and Jnk, but not ERK, p38 or NF-kB, were constitutively hyperactivated in p190 BCRABL-expressing Ba/F3 cells and primary murine B-ALL cells. Intracellular flow cytometry analysis demonstrated that Stat5 was specifically activated in the pro/pre-B leukemic cell population, compared to normal B cells. In the murine model of B-ALL, loss of Rac2, but not Rac3, prolonged survival and impaired leukemia development. Like in Ba/F3 cells, primary B-CFU and outgrowth in Witte-Whitlock assays of leukemic primary cells from mice was severely decreased by the addition of NSC23766 to the culture. Although Vav was activated by both p190- and p210-BCR-ABL, since NSC23766 does not block the activation by Vav1, we hypothesized that other GEFs were involved. Indeed, the loss of Vav1 or even combined loss of Vav1 and Vav2 did not impair BCR-ABL-mediated lymphoid leukemogenesis in vivo. Vav3, another member in the Vav family which uses a different mechanism of activation of Rac GTPases was a likely candidate. In fact, loss of Vav3 alone was able to significantly prolong the survival and attenuate development of p190 BCR-ABL-driven B-ALL. In conclusion, the results of this study indicate that Rac activation is necessary for the development of B-ALL induced by p190-BCR-ABL in vitro and in vivo, and validate a new signaling pathway as a therapeutic target for BCR-ABL-induced B-ALL.

Drug Screening of Primary Human Pediatric Pre-B Cell Acute Lymphoblastic Leukemia (pre-B ALL) Cells in Their Stromal Niche

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 4295-4295
Author(s):  
Jae-Hung Shieh ◽  
Tsann-Long Su ◽  
Jason Shieh ◽  
Malcolm A.S. Moore
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
Culture System ◽  
Lymphoblastic Leukemia ◽  
Nsg Mice ◽  
Cd34 Cells ◽  
Cell Acute Lymphoblastic Leukemia

Abstract Abstract 4295 Pre-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common leukemia in children and is treatable. However, no in vitro nor in vivo models are available to investigate their pathophysiology other than a number of established cell lines that grow in the absence of any cytokine dependence or stromal interaction. We developed a serum-free MS-5 cell (a murine bone marrow stromal cell line) co-culture system that is capable of expanding human primary pre-B ALL CD34+CD19+ cells in vitro. To define a population of pre-B ALL initiating cells, our study reveals that a sorted CD34bright population displays a slow proliferation and maintains a high % of CD34+ cells. In contrast, CD34dim cells/CD34− cells fraction shows a higher proliferation but expanded cells lost CD34 antigens. A group of alkylating molecules (BO-1055, -1090, 1099, -1393 and -1509) was evaluated for proliferation of the pre-B ALL CD34+ cells, the pre-B ALL CD34− cells, human mesenchymal stem cells (hMSC), murine MSC (MS-5 cells and Op9 cells), human bone marrow derived endothelial cells (BMEC), and human cord blood (CB) CD34+ cells, as well as for a week 5 cobblestones area forming (CAFC) assay with CB CD34+ cells. BO-1055 molecule efficiently suppressed the growth of pre-B ALL CD34+ cells (IC50 = 0.29 μM) and CD34− cells (IC50 = 0.31 μM). In contrast, IC50 of BMEC, MSC, CB CD34+ cells and CAFC are >10, >25, 8, and >5 μM, respectively. Pre-B ALL cells expressing green fluorescent protein (GFP) and luciferase (GFP-Lu-pre-B ALL) were created, and a xenograft of the GFP-Lu-pre-B ALL cells to NOD/SCID IL2R gamma null (NSG) mice was established. The in vivo effect of BO-1055 to the GFP-Lu-pre-B ALL cells in NSG mice is under investigation. Our stromal culture system supports primary pre-B ALL cells and closely recapitulates the growth of primary human pre-B ALL cells in their niche in vivo. Based on this co-culture system, we identified BO-1055 as a potential therapeutic agent with an excellent toxicity window between pre-B ALL cells and normal tissues including BMEC, MSC and hematopoietic progenitor/stem cells. The in vitro stromal co-culture system combined with the xenograft model of GFP-Lu-pre-B ALL cells provides an efficient and powerful method to screen new drugs for pre-B ALL therapy. Disclosures: No relevant conflicts of interest to declare.

Zebrafish Xenotransplantation and Focused Chemical Genomics: A Preclinical Therapeutic Model For T-Cell Acute Lymphoblastic Leukemia

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 2670-2670
Author(s):  
Victoria L Bentley ◽  
Chansey J Veinotte ◽  
Dale Corkery ◽  
Marissa A Leblanc ◽  
Karen Bedard ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Human Cancer ◽  
Lymphoblastic Leukemia ◽  
Zebrafish Embryos ◽  
Chemical Genomics ◽  
Cell Acute Lymphoblastic Leukemia

Abstract T-cell acute lymphoblastic leukemia (T-ALL) is a high-risk subset of ALL, for which there is a need for new therapeutic strategies and efficient preclinical screening methods. We have pioneered an innovative zebrafish human cancer xenotransplantation (XT) model to examine drug-tumor interactions in vivo. T-ALL cell lines and primary patient T-ALL samples were microinjected into 48-hour zebrafish embryos, a stage at which the adaptive immune system has not yet developed. Fluorescent labelling of tumor cells prior to injection and use of casper pigment mutant fish facilitates evaluation of drug response both by direct observation in transparent fish and enumeration of human cells following embryo dissociation. Proliferation rates are rapidly determined by directly counting fluorescent cells using in silico-based programs and/or utilizing immunohistochemical approaches to distinguish human cancer cells from host cell populations. T-ALL cell lines harboring defined mutations in the NOTCH1, phosphoinositide 3-kinase (PI3K)/AKT and mTOR pathways differentially responded to targeted inhibition using the γ-secretase inhibitor Compound E, triciribine, and rapamycin, when xenografted into embryos, consistent with responses in vitro. Primary patient-derived T-ALL bone marrow samples similarly engrafted and proliferated in zebrafish embryos. Using this in vivo chemical genomic approach, a targetable mutation sensitive to γ-secretase inhibition was identified from the diagnostic bone marrow sample of a child with T-ALL, which was confirmed by exome Sanger sequencing, and validated as a gain-of-function mutation in the NOTCH1 gene by luciferase assay and Western blot. Focused chemical genomics using the zebrafish T-ALL XT model provides a means of tailoring therapy using a real time in vivo assay that more accurately recapitulates the tumor microenvironment than in vitro methods and more rapidly than mouse xenografts. Moreover, the efficiency and cost-effectiveness of this innovative platform provides a novel intermediary for the prioritization of much-needed drug candidates in the preclinical pipeline. Disclosures: No relevant conflicts of interest to declare.

scholarly journals PF161 THIOREDOXIN SYSTEM INHIBITORS ARE EFFECTIVE AGAINST B CELL ACUTE LYMPHOBLASTIC LEUKEMIA IN VITRO AND IN VIVO

HemaSphere ◽  
2019 ◽  
Vol 3 (S1) ◽  
pp. 32-33
Author(s):  
K. Fidyt ◽  
A. Pastorczak ◽  
A. Goral ◽  
A. Muchowicz ◽  
L. Komorowski ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Thioredoxin System ◽  
Cell Acute Lymphoblastic Leukemia

scholarly journals An Fc-Engineered CD19 Antibody Engages Macrophages and Is Effective in Xenograft Models of Pediatric Acute Lymphoblastic Leukemia

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 277-277
Author(s):  
Denis M Schewe ◽  
Ameera Alsadeq ◽  
Gunnar Cario ◽  
Simon Vieth ◽  
Thomas Valerius ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
Lymphoblastic Leukemia ◽  
Antibody Therapy ◽  
Patient Specific ◽  
Rank Test ◽  
Xenograft Models ◽  
Overt Leukemia

Abstract Introduction: CD19 antibody therapy may represent an attractive treatment option in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Since conventional CD19 antibodies have failed in clinical trials, different strategies are evaluated to target CD19 more efficiently. Beside the bispecific T cell engager blinatumomab and chimeric antigen receptor T-cells, antibody drug conjugates and antibodies with engineered fragments crystallisable(Fc)for improved effector cell engagement are under investigation. Here, we demonstrate the efficacy of Fc-engineered CD19 antibodies in minimal residual disease (MRD) xenograft models of pediatric BCP-ALL. We further suggest an important contribution of macrophages for this type of therapy. Methods: An Fc-engineered CD19 antibody carrying amino acid mutations S239D/I332E (CD19-DE) and its native CD19-IgG1 variant were generated according to published sequences. CD19-DE was analyzed in patient-derived leukemia xenografts from infants with MLL-rearranged BCP-ALL, which were established by intrafemoral transplantation of 100 cells per animal in NOD-SCID-gamma-/- (NSG) mice lacking a functional lymphatic compartment. CD19-DE was injected intraperitoneally (1 mg/kg on days +1, +3, +6, +10, +13, and every 21 days thereafter; MRD-model). In some experiments leukemia development (defined as >1% peripheral blasts; overt leukemia model) was awaited before CD19-DE was applied alone, or in combination with a regimen mimicking standard induction chemotherapy (Dexamethasone days 1-5, Vincristine day 1 and PEG-Asparaginase day 1 every 28 days). MRD status was determined by analysis of bone marrow DNA for patient-specific immunoglobulin (Ig)-rearrangements and MLL-fusion genes by polymerase chain reaction. In order to test the role of macrophages as effector cells, macrophages were depleted by intraperitoneal injection of liposomal clodronate. In vitro phagocytosis of BCP-ALL primary cells from xenografts was determined by fluorescence microscopy. For that purpose, macrophages were differentiated from human monocytes with macrophage colony-stimulating factor and BCP-ALL cells were labelled with a fluorescent membrane dye. Results: CD19-DE was efficient in prolonging the survival of NSG xenografts of two patients tested in the MRD-model (p = 0.0072 and p = 0.0015, Kaplan-Meier log rank test, Figure A/B). Interestingly, analyses of bone marrow DNA from the surviving mice for two patient specific Ig-rearrangements and the respective MLL-fusion revealed that 4/5 mice were MRD-negative by Ig-rearrangement and 3/5 mice were MRD-negative by MLL-fusion. In order to identify effector mechanisms, antibody therapy was performed in the MRD-model with and without depletion of macrophages. Macrophage depletion in vivo resulted in a reversal of the beneficial effects of CD19-DE as measured by increases in splenic volumes and percentage of human blasts in the bone marrow, suggesting an important role for macrophages in CD19 antibody therapy. CD19-DE was next analyzed for its ability to engage human macrophages in phagocytosis assays with primary BCP-ALL blasts from xenograft mice in vitro. CD19-DE effectively triggered phagocytosis of BCP-ALL cells, whereas a corresponding native CD19 IgG1 antibody did not (ANOVA, p < 0.0001, Figure C; data points indicate results with macrophages from 5 different donors), which emphasizes the importance of Fc-engineering for the efficacy of CD19 antibodies. Finally, therapy with CD19-DE was initiated in the overt leukemia model alone and in combination with chemotherapy. CD19-DE was still efficient in prolonging survival as compared to control animals (p = 0.0003, Figure D), but the effects were less pronounced. Importantly, the combination of antibody therapy and cytoreductive chemotherapy resulted in prolonged survival of 90% of the animals as compared to control animals (p < 0.0001) or animals treated with chemotherapy alone (p = 0.0054; Figure D). Conclusion: These preclinical in vivo data obtained in xenograft models of BCP-ALL suggest a high therapeutic potential of Fc-engineered CD19 antibodies and indicate an important role for macrophages in that context. Administration of Fc-engineered CD19 antibodies in an MRD situation or concomitant application of the antibody and cytoreductive chemotherapy may represent promising approaches in the therapy of pediatric BCP-ALL. Figure Figure. Disclosures Gramatzki: Janssen: Other: Travel/Accommodation/Expenses, Research Funding.

In Vitro Culture Reveals Microenvironment-Dependent Growth, Heterogeneity and Hierarchical Structure of Primary Human Pediatric Pre-B Cell Acute Lymphoblastic Leukemia (pre-B ALL) Cells

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1483-1483
Author(s):  
Jae Hung Shieh ◽  
Peter G Steinherz ◽  
Jason Shieh ◽  
Malcolm A.S. Moore
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Hierarchical Structure ◽  
Culture System ◽  
Lymphoblastic Leukemia ◽  
Nsg Mice ◽  
Cd34 Antigen ◽  
Cell Acute Lymphoblastic Leukemia

Abstract Abstract 1483 In Vitro culture reveals microenvironment-dependent growth, heterogeneity and hierarchical structure of primary human pediatric pre-B cell acute lymphoblastic leukemia (pre-B ALL) cells. J.-H. Shieh1, P. Steinherz2, J Shieh3 and M. A.S. Moore1. 1Moore Laboratory. Cell Biology Program and 2Leukemia and Lymphoma Studies, Department of Pediatrics, Memorial-Sloan Kettering Cancer Center, New York, NY. 3Department of Biology, Brandeis Univ., Waltham, MA Pre-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common leukemia in children. Although this pediatric pre-B ALLs are treatable, no in vitro nor in vivo models are available to investigate their pathophysiology other than a number of established cell lines that grow in the absence of any cytokine dependence or stromal interaction. To address this issue, we systemically evaluated the effects of various tissue culture parameters to the growth of primary pre-B ALL cells. A serum-free MS-5 cells (a murine bone marrow stromal cell line) co-culture system is capable of expanding the pre-B ALL CD34+CD19+ cells and supporting their differentiation to CD34−CD19+ B cells. This expansion requires a contact between the stromal cells and the pre-B ALL cells, and is inhibited by fetal bovine serum and IL-6 in a dose-dependent manner. c-Kit ligand and Flt3 ligand can reverse the IL-6 inhibition. Expansion of individual CD34+CD19+ cells revealed a hierarchical structure with respect to CD34 antigen expression and an heterogeneity in cell proliferation. When the pre-B ALL cells were sorted into CD34dim and CD34bright populations, the CD34dim cells were capable of a faster proliferation but gradually lost their CD34 antigen. In contrast, the CD34bright cells were more slowly proliferating and retained their CD34 antigen. We transduced the B-ALL cells with a fusion gene expressing green fluorescent protein (GFP) and luciferase (GFP-Lu-pre-B ALL). These GFP-Lu-pre-B ALL cells display the similar in vitro characteristics and in vivo xenograftment to NOD/SCID IL2R gamma null (NSG) mice as the non-transduced pre-B ALL cells. One hundred, 103, 104 or 105 GFP-LU-pre-B ALL CD34+ cells were i.v. transplanted to NSG mice. Both 104 and 105 cells resulted in the engraftment of the leukemia cells in limbs and cranium as judged by imaging after 6 weeks, and 103 cells engrafted after 13 weeks. When the 105 cells-transplanted mice were sacrificed after 14 weeks, the harvested peripheral blood, spleen (3–4×108cells/spleen) and bone marrow (5−10×106 cells/femur) displayed 2–3%, 51–55% and 75–81% of human CD34+CD19+ cells, respectively. Human CD34−CD19+ cells were 1–2%, 12–13% and 15–21%, respectively. Therefore, our stromal culture system supports leukemic stem cell/leukemia initiating cell proliferation and closely recapitulates the growth of primary human pre-B ALL cells in their niche in vivo, and reveals the heterogeneity and hierarchical structure of human pre-B ALL cells. The in vitro stromal co-culture system combined with the xenograft model of GFP-Lu-pre-B ALL cells provides powerful tools to dissect the pathophysiology of human pre-B ALL, and to screen new drugs for pre-B ALL therapy. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Ibrutinib inhibits pre-BCR+ B-cell acute lymphoblastic leukemia progression by targeting BTK and BLK

Blood ◽  
2017 ◽  
Vol 129 (9) ◽  
pp. 1155-1165 ◽  
Author(s):  
Ekaterina Kim ◽  
Christian Hurtz ◽  
Stefan Koehrer ◽  
Zhiqiang Wang ◽  
Sriram Balasubramanian ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
Cell Growth ◽  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Leukemia Cell ◽  
Key Points ◽  
Cell Acute Lymphoblastic Leukemia ◽  
In Vivo Effects

Key Points In B-ALL, cells that express a functional pre-BCR ibrutinib abrogate leukemia cell growth in vitro and in vivo. Effects of ibrutinib in B-ALL not only are mediated through inhibition of BTK but also involve BLK inhibition.

scholarly journals Preclinical Evaluation of a Novel Dual Targeting PI3Kδ/BRD4 Inhibitor, SF2535, in B-Cell Acute Lymphoblastic Leukemia

2021 ◽  
Vol 11 ◽  
Author(s):  
Yongsheng Ruan ◽  
Hye Na Kim ◽  
Heather A. Ogana ◽  
Zesheng Wan ◽  
Samantha Hurwitz ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Akt Pathway ◽  
Dual Inhibitor ◽  
Cell Counts ◽  
Cell Acute Lymphoblastic Leukemia

The PI3K/Akt pathway—and in particular PI3Kδ—is known for its role in drug resistant B-cell acute lymphoblastic leukemia (B-ALL) and it is often upregulated in refractory or relapsed B-ALL. Myc proteins are transcription factors responsible for transcribing pro-proliferative genes and c-Myc is often overexpressed in cancers. The chromatin regulator BRD4 is required for expression of c-Myc in hematologic malignancies including B-ALL. Previously, combination of BRD4 and PI3K inhibition with SF2523 was shown to successfully decrease Myc expression. However, the underlying mechanism and effect of dual inhibition of PI3Kδ/BRD4 in B-ALL remains unknown. To study this, we utilized SF2535, a novel small molecule dual inhibitor which can specifically target the PI3Kδ isoform and BRD4. We treated primary B-ALL cells with various concentrations of SF2535 and studied its effect on specific pharmacological on-target mechanisms such as apoptosis, cell cycle, cell proliferation, and adhesion molecules expression usingin vitro and in vivo models. SF2535 significantly downregulates both c-Myc mRNA and protein expression through inhibition of BRD4 at the c-Myc promoter site and decreases p-AKT expression through inhibition of the PI3Kδ/AKT pathway. SF2535 induced apoptosis in B-ALL by downregulation of BCL-2 and increased cleavage of caspase-3, caspase-7, and PARP. Moreover, SF2535 induced cell cycle arrest and decreased cell counts in B-ALL. Interestingly, SF2535 decreased the mean fluorescence intensity (MFI) of integrin α4, α5, α6, and β1 while increasing MFI of CXCR4, indicating that SF2535 may work through inside-out signaling of integrins. Taken together, our data provide a rationale for the clinical evaluation of targeting PI3Kδ/BRD4 in refractory or relapsed B-ALL using SF2535.

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