ALBERT

Description: Introduction: Rivaroxaban is a novel, oral, direct Factor Xa inhibitor in development for the prevention of venous thromboembolism (VTE) after major orthopaedic surgery. Two large, phase III, randomized controlled trials compared rivaroxaban with subcutaneous (sc) enoxaparin following total knee replacement (TKR). In the recently published RECORD3 trial, rivaroxaban, 10 mg once daily (od), showed superior efficacy to an enoxaparin regimen of 40 mg od. However, enoxaparin 30 mg twice daily (bid) is the more widely used regimen in North America for VTE prophylaxis following TKR. The RECORD4 trial compared rivaroxaban 10 mg od versus enoxaparin 30 mg bid (both for 12 ± 2 days), for prevention of VTE following TKA. In the modified intent to treat population, the primary outcome (deep vein thrombosis [DVT], pulmonary embolism [PE], and all-cause mortality) occurred in 6.9% of rivaroxaban patients and 10.1% of enoxaparin patients (RRR 32%; p

Description: Introduction: Rivaroxaban is a novel, oral, direct Factor Xa inhibitor submitted to US FDA for approval for the prevention of venous thromboembolism (VTE) after major orthopaedic surgery and is also in development for prevention and treatment of thromboembolic disorders. A recently published Phase III trial, RECORD1, compared rivaroxaban 10 mg once daily (od) with subcutaneous (sc) enoxaparin 40 mg od as VTE prophylaxis over 35 days in patients following total hip replacement (THR). The primary outcome (deep vein thrombosis, pulmonary embolism, and all-cause mortality) occurred in 1.1% of rivaroxaban patients and in 3.7% of enoxaparin patients (RRR 70%; p

Description: 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.

Description: Abstract 1982 Poster Board I-1004 Background: Patients with sickle-cell disease (SCD) receiving chronic transfusions of red blood cells are at risk of developing serious adverse effects. Iron chelating therapies (ICTs) help eliminate iron surplus by binding with plasma iron to form a non-toxic conjugate that can be safely excreted from the body. Two iron chelating agents are currently available in the US: deferoxamine (DFO) is an injectable formulation and deferasirox (Exjade®) is an oral suspension. This study compared the frequency of hospitalizations, persistence, and compliance of SCD patients from Medicaid programs treated with DFO versus deferasirox. Methods: An analysis of patients' electronic claims records from the Florida (1998-2007), Missouri (1993-2008), and New Jersey (1996-2008) Medicaid programs was conducted. Patients with continuous enrollment for at least six months prior to ICT initiation and ≥1 SCD diagnosis were included in the analysis. Patients were divided into four cohorts: patients treated with DFO (any DFO group) and patients treated with deferasirox (any deferasirox group); the latter was further divided into patients initiated on DFO and then switched to deferasirox (deferasirox switchers), and patients treated with deferasirox only (deferasirox only group). Frequency of hospitalization as well as length of stay pre- and post-ICT treatment initiation were assessed. Persistence was defined as time to drug discontinuation with at least one Rx gap, using Kaplan-Meier approach. Compliance was estimated using a medication possession ratio (MPR), calculated as the total days of supply divided by the number of days between the first and last dispensing plus the days of supply of the last dispensing. Results: A total of 217 (mean age=19.4), 275 (20.1), 105 (19.4), and 166 (20.4) patients were included in the any DFO, any deferasirox, deferasirox switchers, and deferasirox only groups, respectively. Exposure period, defined as the time from the date of the first dispensing to the end of the days supply of the last dispensing, was approximately two times longer in the DFO group than in the deferasirox groups (days, DFO: 783, any deferasirox: 353, deferasirox switchers: 416, deferasirox only groups: 317). After ICT initiation, both DFO and deferasirox groups experienced significant reduction in the frequency of hospitalizations relative to pre-treatment (DFO: from 0.92 to 0.64 hospitalizations per patient per month, P=.0010; any deferasirox: from 1.22 to 0.4, P

Description: Abstract 3253 Poster Board III-1 Chronic myelogenous leukemia (CML) is a hematopoietic stem cell (HSC) malignancy induced by p210-BCR-ABL and is characterized by myeloproliferation in the bone marrow (BM) and egress of leukemic stem cells and progenitors (LSC/P) to extramedullary sites. Persistence of BCR-ABL+ HSCs in patients under imatinib suggests that inhibition of ABL-kinase alone is not sufficient to completely eliminate the LSC/P population. Rac GTPases represent integrative molecular switches for p210-BCR-ABL-induced HSC transformation and combined pharmacological and genetic attenuation of Rac GTPases significantly prolong survival in vivo, as reported in a retroviral transduction/transplantation model (Thomas EK & Cancelas JA et al, Cancer Cell 2008). Here, we analyzed the role of Rac2 GTPase in the leukemic maintenance and in the interaction of LSC/P with the leukemic microenvironment in vivo. We used a stem cell leukemia (Scl) promoter-driven, tet-off, Scl-tTA x TRE-BCR-ABL (Scl/p210-BCR-ABL) binary transgenic mouse model (Koschmieder S et al., Blood 2005), where expression of BCR-ABL is restricted to the HSC/P compartment, allowing the study of the intrinsic molecular changes in LSC/P during leukemogenesis. In these mice, Scl-driven expression of BCR-ABL is active in HSC (Lin-/Sca1+/c-kit+; LSK) and progenitors (Lin-/c-kit+/Sca-1-; LK), and CML development is associated with the activation of downstream signaling effectors CrkL, p38-MAPK and JNK. Additionally, Scl/p210-BCR-ABL mice had increased cycling of LSK cells and expansion of circulating and splenic, but not BM, LSC/P, suggesting egress of LSC/Ps from the marrow. These mice share all the characteristics of HSC/P transformation in CML, including increased HSC/P proliferation and survival, severely reduced adhesion to fibronectin, increased migration towards CXCL12, increased cell surface expression of CD44 and decreased expression of L-selectin. Myeloproliferative disease (MPD) in these mice is transplantable into recipient mice, and CML splenocytes have a 10-fold increase in homing to the spleen than towards BM (P

Description: Abstract 3251 Poster Board III-1 Chronic myelogenous leukemia (CML) is a hematopoietic stem cell (HSC) malignancy induced by p210-BCR-ABL and characterized by myeloproliferation followed by poor-prognosis acute blastic transformation. Persistence of BCR-ABL+ HSCs in patients under tyrosine kinase inhibitor therapy suggests that inhibition of ABL-kinase alone is not sufficient to completely eliminate the leukemic stem cells and progenitor (LSC/P) population and a group of patients continue developing accelerated/blastic phase despite therapy. Expression of p210-BCR-ABL is necessary and sufficient to develop CML but the molecular mechanisms necessary for its blastic transformation remain elusive. The polycomb group gene Bmi1 plays an essential role in regulating the proliferative capacity of both normal and leukemic stem cells (Lessard J, et al. Nature 2003). Recently, expression of Bmi1 has been found significantly elevated in CD34+ cells of patients with advanced phases compared with patients in chronic-phase CML (Mohty M et al. Blood 2007). We therefore intend to determine whether Bmi1 expression in CML stem cells and progenitors, isolated from Scl/p210-BCR-ABL-expressing mice, is sufficient to accelerate significantly the development of blastic phase. Since simultaneous co-expression of Bmi1 and BCR-ABL in normal HSC/P may not faithfully recapitulate the progression events in CML transformation, we have over-expressed Bmi1 in a model of stem cell-dependent chronic phase CML. This model is based on the tetracycline-dependent expression of p210-BCR-ABL driven by the Scl promoter (Scl-tTA x TRE-BCR-ABL, Koschmieder S et al. Blood 2005), where expression of BCR-ABL is restricted to the HSC/P compartment. Scl-driven expression of BCR-ABL is predominantly active in HSC (Lin-/Sca1+/c-kit+; LSK) and progenitors (Lin-/c-kit+; LK) and is transplantable into secondary recipients (Sengupta A et al., ASH 2008). Expression of Bmi1 into Scl/p210-BCR-ABL-expressing cells significantly increases the HSC/P proliferation (2.5 fold) and also increases the frequency of colony forming cells (CFU-Cs) after serial propagation in liquid culture, compared to Bmi1 (4.6-fold) or BCR-ABL-expressing CML cells alone (517-fold). Furthermore, Bmi1 expression into Scl/p210 leukemic progenitors increases the hypermigratory phenotype of leukemic progenitors (3-fold increase over 5.5-fold increase induced by BCR/ABL alone; P

Description: Chronic myelogenous leukemia (CML) is a stem cell malignancy induced by p210 BCR-ABL and characterized by myeloproliferation in BM and egression of leukemic stem cells and progenitors (LSC/P) to extramedullary sites. Persistence of BCR-ABL+ HSC in patients under Imatinib suggests inhibition of ABL-kinase alone is not sufficient to eliminate the LSC/P. One of the major hallmarks of CML induced by signaling downstream BCR-ABL is the loss of control of the hematopoietic microenvironment on LSC/P. Expression of p210 BCR-ABL has been associated with loss of adhesion to the bone marrow, impaired migration in response to CXCL12 and decreased retention in the BM. In order to study the putative LSC/P niches in steady-state chronic-phase leukemia, we have analyzed the ability of LSC/P to proliferate and get retained in the bone marrow (BM) in an inducible model of CML. Binary transgenic SCL-tTA/TRE-BCR-ABL mice (Koschmieder S et al., Blood 2005) express p210 BCR-ABL in LSC/P upon doxycycline withdrawal (CML mice). Induced myeloproliferation was associated with activation of the downstream signaling effectors CrkL and p38-MAPK and expansion of circulating (Table 1) and splenic LSC/P but not in BM, suggesting massive LSC/P egression from the marrow (Table 2). Proliferation analysis showed that myeloid expansion in the spleen was secondary to increased cycling of Lin−Sca1+c-Kit+ (LSK) cells (3.1-fold increase in S-phase cells, P

Description: Truncation mutations in the granulocyte colony stimulating factor receptor (G-CSFR), common in severe congenital neutropenia (SCN), lead to excessive stem cell proliferation in response to G-CSF. These G-CSFR mutants are (at least indirectly) implicated in the progression of these patients to acute leukemia. Since SCN patients require continuous G-CSF treatment throughout their lifespan, we hypothesize that excessive stem cell proliferation can lead to DNA damage. Stem cells are relatively quiescent and rarely enter the cell cycle under normal conditions. During the cell cycle cells generate approximately 5000 single strand DNA lesions per nucleus (Vilenchik and Knudson, 2003). Approximately 1% of these lesions are ultimately converted to double strand DNA breaks (DSBs). Hematopoietic stem cells are found within the Sca+ ckit+ Lin- (KLS) population. Wild type and mice bearing a mutant G-CSFR similar to that found in patients with SCN were treated with G-CSF. After 21 days of treatment with G-CSF (10 ug/kg/day), the KLS population in the bone marrow increased four-fold in wild type mice and eight-fold in mutant mice. We isolated Lin-Sca+ bone marrow cells from these G-CSF treated mice and evaluated for the presence of double stranded DNA breaks by staining with anti-phospho-H2AX by immunofluorescence. H2AX is a histone whose phosphorylated form localizes to the site of double stranded DNA breaks. The results showed that there is an 8-fold increase in the DSB in wild type Lin-Sca+ and 10-fold in mutant Lin-Sca+ when compared to cells from untreated mice. This data suggests that excessive proliferation can contribute to an increase in DSBs in hematopoietic stem cells. Investigation of potential mechanisms contributing to DSB formation are ongoing. Understanding the causes and trends of chromosomal instability would improve our understanding of leukemogenesis and potentially reveal novel treatment strategies.

Description: Abstract 449 The Philadelphia chromosome-positive (Ph+) hematologic malignancies are characterized by the reciprocal translocation between the BCR serine/threonine kinase and the ABL tyrosine kinase genes. Fifty percent of adult B-cell Ph+ acute lymphoblastic leukemia (B-ALL) and most cases of pediatric Ph+ B-ALL express the p190 BCR-ABL isoform, which causes abnormal expansion of lymphoid progenitors and a poor prognosis despite the administration of tyrosine kinase inhibitors. A major signaling pathway activated by BCR-ABL is the Rac/Rho GTPase signaling pathway. We had previously demonstrated that p210-BCR-ABL activates Rac GTPases and the deficiency of Rac2, or even more, the deficiency of both Rac1 and Rac2, impairs myeloid leukemogenesis induced by p210 BCR-ABL in vitro and in vivo (Thomas EK et al., Cancer Cell 2007). The p190-BCR-ABL isoform also activates Rac GTPases and the deficiency of Rac2 induces resistance to develop proB-ALL (Sanchez-Aguilera et al., ASH 2008). Since p190-BCR-ABL is devoid of guanine nucleotide exchange factor (GEF) activity through the absence of the BCR Dbl-homology (DH) domain, it probably requires the recruitment of intermediate GEFs to activate Rac GTPases. The Vav family of GEF has been shown to bind the SH3/SH2 domains of ABL and become activated. Three isoforms of Vav (Vav1, Vav2 and Vav3) are expressed in hematopoietic cells. Several studies have indicated that Vav3 has a role distinct from Vav1 or Vav2. Here, we hypothesized that the hematopoietic specific Rho GTPase, Rac2, may mediate key signals in the transformation of B-cell progenitors upon Vav-mediated activation. We have found that both Vav1 and Vav3 are overexpressed and hyperphosphorylated in p190 BCR-ABL expressing human B-ALL cells as well as in BCR-ABL transduced murine proB cells. While the combined deficiency of Vav1 and Vav2 does not impair leukemogenesis in vivo, Vav3 deficiency reverses p190-BCR-ABL induced transformation phenotypes. Specifically, Vav3 deficiency in p190-BCR-ABL expressing proB-ALL cells associated with a significant reduction of Rho and Rac activation (75% and 56%), apoptosis induction (4-fold) and impaired ex-vivo expansion (33% reduction). In addition, p190-BCR-ABL-induced adhesion-to-fibronectin defect and hypermigratory response to CXCL12 were corrected by deletion of Vav3 (2.1-fold increase and 60% decrease, respectively), suggesting that Vav3 deficiency reverses the transformation-associated phenotype associated to BCR-ABL expression. Collectively, our work identifies a critical role of Rac2 and its activator Vav3 for p190 BCR-ABL induced B-cell progenitor leukemic transformation and may define a novel therapeutic target for this poor prognosis disease. Disclosures: Cancelas: CERUS CO: Research Funding; CARIDIAN BCT: Research Funding; HEMERUS INC: Research Funding.

Description: Abstract 562 In the bone marrow (BM) cavity, the migratory traffic of hematopoietic stem cells and progenitors (HSC/P) from the endosteal niches to circulation and viceversa depends on their response to chemokine gradients and interaction with endothelial and mesenchymal pre-osteoblastic cells located at the endosteal niches, forming the hematopoietic microenvironment (HM). Several lines of evidence have pointed out the possible role of the gap junction-forming protein connexin-43 (Cx43) in the control of stem cell and progenitor migration. Our group previously demonstrated that Cx43 expression in the hematopoietic microenvironment (HM) is critical in the fetal liver and BM hematopoietic regeneration after administration of 5-fluorouracil (5-FU) and other investigators have shown that Cx43 is crucial controlling the migration of neural progenitors along radial glial during brain development. We hypothesized that Cx43 could regulate the bidirectional migration of HSC/P in the BM stroma. Since Cx43 is expressed by mesenchymal cells, endothelial cells and hematopoietic stem cells and progenitors, we decided to analyze the Cx43 contribution in the control of HSC/P migration in cell-specific conditional knock-out mice. To achieve this objective, we have used mice that were selectively deficient for Cx43 in the osteoblast/stromal cells (Collagen 1a-Creflox/flox; O/S-Cx43-deficient), in endothelial cells (Tek-Creflox/flox; E-Cx43-deficient) or in hematopoietic cells (Vav1-Creflox/flox; H-Cx43-deficient). O/S-Cx43-deficient mice have been shown to be a model of osteoblast loss of function (Chung DJ et al., J. Cell. Sci., 2006) and E-Cx43-deficient mice have been shown to be a model of arterial hypotension induced by both increase nitric oxide and angiotensin levels (Liao Y et al, PNAS 2001). Analysis with reporter crossings with Rosa-loxP-Stop-LoxP-LacZ mice showed anatomical specificity of the Cre recombinase expression in different cell types of BM, and western-blot and RT-PCR expression indicated practical abolishment of the expression of Cx43 in each of the specific cell types. First, we analyzed whether there were changes in the levels of circulating progenitors in O/S-, E- or H-Cx43-deficient mice. While H-Cx43-deficient mice did not show any change in the levels of circulating HSC/P, E-Cx43-deficient mice showed a 3.5-fold and 4.7-fold, respectively, increase of circulating CFU-C and competitive repopulating units while maintaining normal repopulation ability of BM HSC. O/S-Cx43-deficient mice showed a 30% reduction in basal conditions which was more accentuated when administered G-CSF (50% reduction on day +6), compared with their WT counterparts. Interestingly, while osteoblast loss-of-function was induced in O/S Cx43-deficient mice, the intramarrow expression levels of CXCL12a/b and mesenchymal progenitor content (CFU-F) were increased (4- and 2-fold, respectively). In correlation with the increased levels of CXCL12, the distance to endosteum of transplanted CFSE+/lin-/c-kit+ BM cells into non-myeloablated O/S-Cx43-deficient mice was dramatically decreased (36.1±4.3 vs 23.2±2.1 mm, p