ALBERT

Description: Background: The biology, pathology and clinical course of CD5+ chronic B cell lymphoproliferative disorders (CD5+ B-CLPD) excluding chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) and mantle cell lymphoma (MCL) are poorly defined. These patients could either have a leukemic variant of a known B cell malignancy or a novel disease entity. Objective: To define the clinical features and pathology of CD5+ B-CLPD, compare these features to CLL, and test the hypothesis that at least some of these patients have a unique B cell malignancy. Methods: The study was conducted with Institutional Review Board permission. We studied 231 patients evaluated in the Division of Hematology at Mayo Clinic Rochester between 1996 and 2008 who had CD5+ monoclonal B cell population in the peripheral blood and/or bone marrow, and in whom CLL and MCL was not diagnosed after flow cytometry, histology and interphase fluorescence in situ hybridization (FISH) examinations. Data were abstracted from patient records and from the Mayo Clinic CLL database. Statistical analysis: To compare differences in characteristics between CD5+ and CLL patients, χ2 statistics were used for qualitative variables (gender, treatment, vital status) and t-tests were used for quantitative variables (age). We performed survival and time to treatment analyses with results displayed using Kaplan-Meier curves and p-values calculated using a log-rank test. Results: We analyzed data on 231 CD5+ B-CLPD patients diagnosed between 7/1/1976 and 5/2/2008 and 1572 CLL patients diagnosed in the same time period. Median follow-up from diagnosis was 2.5 years (range 0 to 25.1 years) for the CD5+ patients and 5.2 years (range 0 to 29.9 years) for CLL patients. CD5+ B-CLPD patients had a median age at diagnosis of 68 years (range 30–94 years) with male predominance (61.5%). One hundred and nine of 231 (52.4%) patients received treatment for their CD5+ B-CLPD and 162 (70.1%) patients were alive at the time of last follow-up. As a group, CD5+ B-CLPD patients had a similar male predominance to CLL but were older at diagnosis. CD5+ B-CLPD patients required their first treatment significantly sooner than CLL patients (median 2.0 years vs. 6.8 years, (p〈 0.001) and a higher percentage of CD5+ B-CLPD patients required treatment (52.4% vs. 37.5%, p

Description: PU.1 is a member of the ETS family of transcription factors and is required for the development of multiple hematopoietic lineages. PU.1-/- mice die from hematopoietic failure at about embryonic day 18.5 (e18.5) and show a complete absence of B cells, mature T cells, and macrophages. This phenotype suggests that PU.1 may function at the level of the hematopoietic stem cell (HSC) or a multilineage progenitor. To investigate the role of PU.1 in the regulation of HSCs, PU.1-/- embryos were analyzed at various stages of embryonic development. The absolute number and frequency of HSCs were determined by flow cytometric analysis of c-Kit+Thy-1.1loLin-Sca-1+ (KTLS) cells. We found that KTLS cells were absent or severely reduced in PU.1-/- fetal liver from e12.5 to e15.5. Progenitor cells with a c-Kit+Lin-AA4.1+ and c-Kit+Lin-CD34+ phenotype were also severely reduced. In addition, PU.1-/- fetal liver at e14.5 lacked common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) but retained megakaryocyteerythroid progenitors (MEPs). Consistent with the loss of HSC activity, a 10-fold reduction in erythroid progenitors (mature erythroid burst-forming units [BFUEs]) was observed between e14.5 and e16.5. These data suggest that PU.1 plays an important role in the maintenance or expansion of HSC number in murine fetal liver. (Blood. 2004;104:3894-3900)

Description: Epigenetic mechanism plays important regulatory roles in hematopoiesis and hematopoietic stem cell (HSC) function. Subunits of Polycomb repressive complex 1 (PRC1), the major histone H2A ubiquitin ligase, are critical for both normal and pathological hematopoiesis; however, it was unclear which H2A deubiquitinase pairs with PRC1 to control H2A ubiquitination (ubH2A) level in vivo and regulates hematopoiesis. Here we investigated the function of Usp16 in mouse hematopoiesis. Deletion of Usp16 in bone marrow resulted in a significant increase of global ubH2A level and mouse lethality. Usp16 deletion was associated with a dramatic reduction of progenitor cell populations and unchanged HSC number, revealing a critical role for Usp16 in HSC differentiation. The HSC differentiation defect was correlated with a great reduction of G1 phase cell population. RNA-seq and RT-qPCR studies revealed that Usp16 regulates the expression of many genes associated with HSC differentiation and self-renewal including cell cycle regulator p21. Significantly, knockdown of p21 largely rescued the undifferentiated phenotype of Usp16 deleted HSCs. Usp16 binds to regions flanking transcription start site and knockdown of PRC1 subunits, which reduced ubH2A levels, largely rescued the altered gene expression pattern associated with Usp16 deletion. Therefore, these studies identified Usp16 as the H2A deubiquitinase that pairs with PRC1 to regulate hematopoiesis in vivo and revealed that Usp16 regulates HSC function by affecting HSC cell cycle progression. Disclosures No relevant conflicts of interest to declare.

Description: For many subtypes of AML including cases with the inv(16), mutations that give rise to the leukemic phenotype occur, at least in part, in the hematopoietic stem/progenitor (HSPC) cell subset, as suggested by studies showing that primitive CD34+ CD38- bone marrow cells can function as leukemia-initiating cells (LIC) when transferred into immunodeficient mice. A significant challenge has been that LIC share many of the same cell-surface markers as their normal HSPC counterparts, thus making it difficult to purify and functionally characterize either subset from the bulk bone marrow of leukemia patients. Here we report the FACS analysis of several previously reported human LIC markers on bone marrow samples from inv(16) AML patients and show that a combination of TIM3, CLL1, and CD33 can significantly enrich for a rare population of CD34+ CD38- cells that lack the inv(16) fusion mRNA when tested by nested RT-PCR. Heterogeneous expression of these markers among different patient samples often causes incomplete elimination of the fusion mRNA when FACS-sorting the CD34+ CD38- population as single TIM3-, CLL1-, or CD33- subsets. The combination of TIM3 with CLL1 and/or CD33 leads to a more consistent elimination of the fusion mRNA from the FACS-sorted CD34+ CD38- subsets. Results from methylcellulose assays showed that the TIM3- CLL1- CD33- subset of CD34+CD38- cells could form multiple colony types, including CFU-GEMM, that were all negative for the fusion mRNA by RT-PCR. In contrast, colonies derived from bulk bone marrow were all positive for the fusion mRNA. The TIM3- CLL1- CD33- subset of CD34+CD38- cells displayed greater than 600-fold enrichment for progenitor activity compared to bulk bone marrow but did not form additional colonies upon serial re-plating. These results have important implications for the therapeutic targeting of inv(16)+ hematopoietic stem/progenitor cells in patients with relapsed and refractory disease and for purification of normal HSPC from leukemic bone marrow samples. Disclosures No relevant conflicts of interest to declare.

Description: The inversion of chromosome 16 in the inv(16)(p13q22) is one of the most frequent cytogenetic abnormalities observed in acute myeloid leukemia (AML). The inv(16) fuses the core binding factor (CBF) beta subunit with the coiled-coil rod domain of smooth muscle myosin heavy chain (SMMHC). Expression of CBFβ-SMMHC in mice does not promote AML in the absence of secondary mutations. Patient samples with the inv(16) also possess mutually exclusive activating mutations in either N-RAS, K-RAS, or the receptor tyrosine kinases, c-KIT and FLT3, in almost 70% of cases. To test whether an activating mutation of FLT3 (FLT3-ITD) would cooperate with CBFβ-SMMHC to promote AML, we coexpressed both mutations in hematopoietic progenitor cells used to reconstitute lethally irradiated mice. Analysis of transplanted animals showed strong selection for CBFβ-SMMHC/FLT3-ITD–expressing cells in bone marrow and peripheral blood. Compared with animals transplanted with only CBFβ-SMMHC–expressing cells, FLT3-ITD further restricted early myeloid differentiation and promoted peripheralization of primitive myeloblasts as early as 2.5 weeks after transplantation. FLT3-ITD also accelerated disease progression in all CBFβ-SMMHC/FLT3-ITD–reconstituted animals, which died of a highly aggressive and transplantable AML within 3 to 5 months. These results indicate that FLT3-activating mutations can cooperate with CBFβ-SMMHC in an animal model of inv(16)-associated AML.

Description: Helios is a zinc-finger protein belonging to the Ikaros family of transcriptional regulators. It is expressed, along with Ikaros, throughout early stages of thymocyte development where it quantitatively associates with Ikaros through C-terminal zinc-finger domains that mediate heterodimerization between Ikaros family members. To understand the role of Helios in T-cell development, we used a retroviral vector to express full-length Helios or a Helios isoform that lacked the N-terminal DNA-binding domain in hematopoietic progenitor cells of reconstituted mice. Constitutive expression of full-length Helios resulted in an inhibition of T-cell development at the double-negative stage within the thymus. Although expression of the DNA-binding mutant of Helios did not contribute to developmental abnormalities at early times after transplantation, 60% of animals that expressed the Helios DNA-binding mutant developed an aggressive and transplantable T-cell lymphoma 4 to 10 months after transplantation. These results demonstrate a vital function for Helios in maintaining normal homeostasis of developing T cells and formally show that non–DNA-binding isoforms of Helios are lymphomagenic if aberrantly expressed within the T-cell lineage.

Description: Oncogenic NRAS mutations are highly prevalent in hematologic malignancies. In acute myeloid leukemia (AML), genetic analysis supports the hypothesis that NRAS mutations cooperate with antecedent molecular lesions in leukemogenesis. Furthermore, NRAS mutations identified at diagnosis may disappear at relapse, raising questions regarding the potential clinical benefits of inhibiting oncogenic N-Ras in AML. To directly investigate the consequences of Nras inactivation in normal hematopoiesis, we used the Mx1-Cre transgene to inactivate a conditional mutant Nras allele and analyzed hematopoiesis and hematopoietic stem and progenitor cells (HSPC) under normal and stressed conditions. We show that HSPCs lacking Nras expression are functionally equivalent to normal HSPCs in the adult mouse. Importantly, shRNA-mediated knockdown in human AML cell lines and primary mouse leukemias with oncogenic NRAS/Nras mutations revealed dependence on continued oncogene expression in vitro and in vivo. Next, we interrogated the functional consequences of pharmacologic inhibition of the canonical Ras effector pathways, the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways,alone and in combination. Recipient mice transplanted with five independent primary mouse AMLs generated by infecting NrasG12D “knock in” mice with the MOL4070LTR retrovirus (Li et al, Blood 2011; 117:2022) were treated with the allosteric MEK inhibitors PD0325901 (PD901) or trametinib or the PI3K inhibitor GDC-0941. Both MEK inhibitors significantly prolonged survival and reduced proliferation and blast colony formation, but did not induce apoptosis, differentiation, or promote clonal evolution. PI3K inhibition alone was ineffective in vivo and combinations of MEK and PI3K inhibitors were no better than MEK inhibition alone. All mice ultimately succumbed from progressive leukemia. These data, along with observations that Nras is dispensable for normal hematopoiesis, validate oncogenic N-Ras signaling as a therapeutic target in AML and support testing combination regimens that include MEK inhibitors in leukemias harboring NRAS mutations. Disclosures No relevant conflicts of interest to declare.

Description: The most common chromosomal translocation in acute promyelocytic leukemia (APL), t15;17(q22;q21), creates PMLRAR andRARPML fusion genes. We previously developed a mouse model of APL by expressing PMLRAR in murine myeloid cells. In order to examine the mechanisms by which PMLRAR can initiate leukemia, we have now generated transgenic mice expressingPMLRARm4 and RARm4, proteins that are unable to activate transcription in response to retinoic acid.PMLRARm4 transgenic mice developed myeloid leukemia, demonstrating that transcriptional activation by PMLRAR is not required for leukemic transformation. The characteristics of the leukemias arising in the PMLRARm4 transgenic mice varied from those previously observed in our PMLRAR transgenic mice, indicating that ligand responsiveness may influence the phenotype of the leukemic cells. The leukemias that arose in PMLRARm4transgenic mice did not differentiate in response to retinoic acid therapy. This result supports the hypothesis that a major therapeutic effect of retinoic acid is mediated directly through thePMLRAR protein. However, a variable effect on survival suggested that this agent may be of some benefit in APL even when leukemic cells are resistant to its differentiative effects. Transgenic mice expressing high levels of RARm4 have not developed leukemia, providing evidence that the PML domain ofPMLRAR plays a specific and critical role in the pathogenesis of APL.

Description: There is conflicting information about the influence of body mass index (BMI) on the pharmacokinetics, toxicity, and outcome of chemotherapy. We compared pharmacokinetics, outcome, and toxicity data across 4 BMI groups (underweight, BMI ≤ 10th percentile; normal; at risk of overweight, BMI ≥ 85th and 〈 95th percentile; overweight, BMI ≥ 95th percentile) in 621 children with acute lymphoblastic leukemia (ALL) treated on 4 consecutive St Jude Total Therapy studies. Chemotherapy doses were not adjusted to ideal BMI. Estimates of overall survival (86.1% ± 3.4%, 86.0% ± 1.7%, 85.9% ± 4.3%, and 78.2% ± 5.5%, respectively; P = .533), event-free survival (76.2% ± 4.2%, 78.7% ± 2.1%, 73.4% ± 5.5%, and 72.7% ± 5.9%, respectively; P = .722), and cumulative incidence of relapse (16.0% ± 3.7%, 14.4% ± 1.8%, 20.6% ± 5.1%, and 16.7% ± 5.1%, respectively; P = .862) did not differ across the 4 groups. In addition, the intracellular levels of thioguanine nucleotides and methotrexate polyglutamates did not differ between the 4 BMI groups (P = .73 and P = .74, respectively). The 4 groups also did not differ in the overall incidence of grade 3 or 4 toxicity during the induction or postinduction periods. Further, the systemic clearance of methotrexate, teniposide, etoposide, and cytarabine did not differ with BMI (P 〉 .3). We conclude that BMI does not affect the outcome or toxicity of chemotherapy in this patient population with ALL.

Description: Abstract 601 Background. DCC-2036 is a novel and potent tyrosine kinase inhibitor (TKI) which binds to a novel region called the switch pocket, thereby preventing BCR-ABL from adopting a conformationally active state. Efficacy against multiple imatinib-resistant BCR-ABL mutants has been demonstrated both in vitro and in vivo (Chan et al., Cancer Cell 2011;19:556). Importantly, DCC-2036 retains full potency against the T315I mutant in preclinical efficacy studies. Methods. This study was designed to find the maximal tolerated dose (MTD) of DCC-2036 when administered daily as a single-agent on a 28-day cycle. Eligible patients included adults with Ph+ CML/ALL who were refractory/intolerant to ≥2 TKI's or were T315I positive. Initially DCC-2036 capsules were administered orally once daily (QD) at increasing dose levels. Only 1 patient was enrolled in each of the lowest dose cohorts of 57mg QD and 114 mg QD. For higher doses, 3– 6 patients were enrolled into each ascending dose cohort with standard dose limiting toxicity (DLT) rules evaluating safety in cycle 1 to determine dose escalation. A transition from unformulated capsules (C) to formulated tablets (T) occurred after the 1200 mg QD dose level. Paired blood samples were obtained for PK and PD assessments. Results. 30 patients (16 males, 14 females; median age 59, range 31 – 80) with CML including 19 in Chronic (CP); 8 in Accelerated (AP) and 3 in Blast (BP) Phase were enrolled. Enrolled patients had received 1–6 prior CML treatments, and 11 patients had the T315I mutation. To date, a total of 212.5 (median 5.6; range 0.2 – 23.4) 28-day cycles were administered over 10 dose levels either as C (7 dose levels) or T (3 dose levels). The 7 C dose levels were studied first and included 57 mg QD through 1200 mg QD. Following transition to T, evaluation continued with 100 mg QD, 100 mg twice daily (BID), and 200 mg BID. Two reversible DLTs (Grade 3 peripheral neuropathy and Grade 4 lower extremity weakness) occurred during the initial treatment cycle at the 200 mg T BID dose level. Evaluation of 6 patients at the 150 mg T BID dose level determined that dose to be the MTD. Preliminary safety data show that other Grade (Gr) 3/4 adverse events (AEs) were Gr 3 slurred speech and Gr 3 eruptive nevi. Gr 1/2 AEs included dry mouth, constipation, diarrhea, paresthesias, and retinal vein occlusion. There was 1 case of Gr 2 pancreatitis that recurred on rechallenge in a patient with previous pancreatitis with nilotinib. Preliminary responses include one major molecular response in a CP patient with T315I mutation who started on capsules and transitioned to 100 mg T QD. There was one complete cytogenetic response in a CP patient at 100 mg T BID, and one partial cytogenetic response in a CP patient who started on capsules and transitioned to 100 mg T BID. One patient with AP CML and T315I mutation had a complete hematologic response at 450 mg C QD. Another patient with AP CML had a partial hematologic response after receiving 200 mg BID for 1 cycle and then downdosing to 100 mg T BID. Four out of 8 patients receiving 100 mg tablets and evaluable for efficacy (completed 3 cycles of treatment) had responses. PK results indicate dose-related, nonlinear increases in both peak plasma concentration (Cmax) and exposure (AUC). PD results reveal both acute and steady state post-treatment reductions in phospho-protein levels on Days 1 and 8. Marked reductions in pSTAT5 and pCRKL have been observed in subjects with both CP and AP and appear to be required for clinical response. Conclusion. The MTD of DCC-2036 tablets is 150 mg BID. Preliminary results suggest that DCC-2036 is well tolerated and has anti-leukemia activity in subjects with refractory CML and T315I positive disease. PD results are consistent with inhibition of BCR-ABL signaling in this first-in-man study of a switch pocket tyrosine kinase inhibitor. Disclosures: Cortes: Novartis: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Chemgenex: Consultancy, Research Funding; Deciphera Pharmaceuticals: Research Funding. Bixby:Novartis: Speakers Bureau; Bristol Myers Squibb: Speakers Bureau; GlaxoSmithKline: Speakers Bureau. Rafferty:Deciphera Pharmaceuticals: Employment. Berger:Deciphera Pharmaceuticals: Employment. Wise:Deciphera Pharmaceuticals LLC: Employment. Rutkoski:Deciphera Pharmaceuticals: Employment. Smith:Deciphera Pharmaceuticals: Employment. Van Etten:Deciphera Pharmaceuticals: Consultancy, Research Funding.