ALBERT

Description: Background: Over the past two decades, peripheral blood stem cells (PBSC) have surpassed bone marrow as the preferred graft source for adult allogeneic transplantation due to its more rapid engraftment and potentially better graft-vs-tumor effects, and because PBSC collection is much less invasive for the donor. The optimal CD34+ PBSC dose is ≥ 4.0x106cells/kg, but doses ≥ 8.0x106cells/kg are suggested by some for reduced-intensity conditioning and haploidentical transplants. There is no established minimum CD34+ PBSC dose, but doses below 2.0x106cells/kg have been associated with a higher risk of engraftment delay and failure. There is significant inter-donor variability in the ability to mobilize PBSCs. Several factors have been identified as predictors of PBSC mobilization in healthy donors including: gender, age, weight, body mass index (BMI), and blood counts before and after mobilization. The impact of the donor’s comorbidities on mobilization is currently unknown. Patients/Methods: We performed retrospective chart review of 488 consecutive adult patients who underwent apheresis for allogeneic stem cell donation at Washington University School of Medicine from 2006 through 2013. Patients who received any collection regimen other than 10mcg/kg of G-CSF daily with 20 liters (+/-10%) apheresis on Day 5 were excluded. Patients who had undergone a previous apheresis for stem cell donation were excluded. Univariate analysis was performed to identify predictors of CD34+ PBSC collection in a single apheresis. Variables analyzed were: gender; age; weight; BMI; donor-to-recipient weight ratio; pre and post-mobilization blood counts (white blood count [WBC], hematocrit, platelets, neutrophils, lymphocytes, and monocytes); pre-mobilization glucose and triglyceride levels; post-mobilization peripheral blood (PB) CD34+count; and medical history significant for hypertension, hyperlipidemia, or diabetes mellitus. Subsequently, a linear regression multivariate analysis was performed with all variables found to be significant in the univariate analysis. 2-tailed tests for significance were used throughout the analysis. Results: 304 patients met the eligibility criteria for analysis. The median age was 53 years (range 18-76), 90% were Caucasian, and 50% were male. The median number of CD34+ cells collected was 7.4 x106/kg (range 0.8-27.1). 97% (295) collected ≥ 2.0x106 CD34+cells/kg, 81% (247) collected ≥ 4.0x106 CD34+cells/kg, and 44% (134) collected ≥ 8.0x106 CD34+ cells/kg. Post-mobilization PB CD34+ count (r= 0.841, p

Description: We sought to determine whether bexarotene can be combined with decitabine in elderly and relapsed AML patients. Both drugs have been shown to be well tolerated in acute myeloid leukemia (AML) patients as single agents, and these agents have non-overlapping mechanisms and side-effect profiles; bexarotene activates transcriptional effects of RXRA through hetero- and homodimers, while decitabine is thought to act through DNA hypomethylation. Furthermore, through Affymetrix expression array profiling of 111 AML patients and Nanostring analysis of 7 MDS and AML patients, we observed consistently elevated levels of RXRA relative to RARA, suggesting that a ligand specific for RXR may be more effective to induce AML differentiation than the RARA ligand ATRA. We treated 18 elderly (≥ 60 years old) or relapsed AML patients in 3+3 dose escalating bexarotene cohorts: 100 mg/m2/day, 200 mg/m2/day, 300 mg/m2/day. All patients were treated with decitabine 20 mg/m2IV on days 1-5 of 28 day cycles. All patients were monitored for hypertriglyceridemia and hypothyroidism, and treated accordingly. The average age was 73, the average performance status was 1, an adverse karyotype was observed in 9 patients, and 12 patients had relapsed after prior therapy. Only one patient experienced a dose limiting toxicity (grade 3 fatigue) and 8 patients were treated with the maximum dose (myelosuppression, infection, differentiation syndrome, hypertriglyceridemia, hyperlipidemia, hypothyroidism, nausea, weight loss and reversible electrolyte abnormalities were not considered dose limiting). The overall response rate was 22%: 1 patient achieved complete remission with incomplete count recovery (CRi) and 3 patients achieved blast reduction greater than 50% (partial response, PR). In addition, six patients achieved stable disease (SD). Patients with CRi, PR, or SD completed an average of 4.25 cycles, while other patients completed an average of 1.2 cycles. Of note, 3 patients successfully transitioned to allogeneic transplant following therapy (average age 68). We correlated ex vivo bexarotene sensitivity with clinical response. Bone marrow cells were collected on day 0 and day 3 of bexarotene therapy (during cycle 1, decitabine was administered on day 3 after bone marrow collection) and co-cultured with irradiated MS5 murine stromal cells for 72hrs with or without further bexarotene treatment. We used flow cytometry to compare CD11b expression in cells treated with and without bexarotene ex vivo, and compared expression between samples collected on day 0 vs day 3 (in vivo treatment). Bexarotene increased CD11b expression greater in the 4 responding patients vs non-responders (fold increase in CD11b: ex vivo average 2.1 ± 0.3 vs 1.1 ± 0.1 fold, p 〈 0.003; and in vivo 1.6 ± 0.3 vs 0.7 ± 0.2 fold, p 〈 0.03; increase in absolute percentage of CD11b+ cells: ex vivo average 24% ± 2.6% vs 0.7% ± 1%, p 〈 0.001; and in vivo 13.6% ± 4% vs -3.6% ± 2.2%, p 〈 0.002). Furthermore, all 4 responding patients demonstrated an equivalent or increased induction of CD11b when treated ex vivo with ATRA compared with bexarotene. These results show that bexarotene, a retinoid which selectively binds to and activates RXRs, but not RARs, can be safely combined with decitabine in relapsed and refractory AML patients. This combination leads to partial response in a subset of patients, is well tolerated, and can bridge elderly patients to allogeneic transplant. Because ex vivo bexarotene treatment identified all patients achieving a PR, further studies should focus on patients who display ex vivo sensitivity. Finally, the mechanism of RXRA-activated differentiation is likely to be through the RXRA/RARA heterodimer, as all 4 patients who responded to bexarotene also responded to ATRA when tested ex vivo. Disclosures: Welch: Eisai: Research Funding. Off Label Use: Bexarotene for the treatment of AML. Abboud:Ariad, Alexion, Novartis, Teva: Honoraria, Speakers Bureau. Stockerl-Goldstein:Celgene : Speakers Bureau; Millennium: Speakers Bureau.

Description: Patients with relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL) have a poor prognosis and limited treatment options. We evaluated selinexor, an orally bioavailable, first-in-class inhibitor of the nuclear export protein XPO1, in this phase 1 trial to assess safety and determine a recommended phase 2 dose (RP2D). Seventy-nine patients with various NHL histologies, including diffuse large B-cell lymphoma, Richter’s transformation, mantle cell lymphoma, follicular lymphoma, and chronic lymphocytic leukemia, were enrolled. In the dose-escalation phase, patients received 3 to 80 mg/m2 of selinexor in 3- or 4-week cycles and were assessed for toxicities, pharmacokinetics, and antitumor activity. In the dose-expansion phase, patients were treated with selinexor at 35 or 60 mg/m2. The most common grade 3 to 4 drug-related adverse events were thrombocytopenia (47%), neutropenia (32%), anemia (27%), leukopenia (16%), fatigue (11%), and hyponatremia (10%). Tumor biopsies showed decreases in cell-signaling pathways (Bcl-2, Bcl-6, c-Myc), reduced proliferation (Ki67), nuclear localization of XPO1 cargos (p53, PTEN), and increased apoptosis after treatment. Twenty-two (31%) of the 70 evaluable patients had an objective responses, including 4 complete responses and 18 partial responses, which were observed across a spectrum of NHL subtypes. A dose of 35 mg/m2 (60 mg) was identified as the RP2D. These findings suggest that inhibition of XPO1 with oral selinexor at 35 mg/m2 is a safe therapy with encouraging and durable anticancer activity in patients with R/R NHL. The trial was registered at www.clinicaltrials.gov as #NCT01607892.

Description: Background: The nuclear export protein XPO1 is overexpressed in all types of hematological malignancies. The SINE selinexor (KPT-330) is a novel, first-in-class, slowly reversible XPO1 antagonist that forces the nuclear retention and activation of over tumor suppressor proteins (TSPs) such as p53, IkB, FOXO and p21. Forced nuclear retention of TSPs leads to their reactivation, which can counteract a multitude of oncogenic pathways that perpetuate the neoplastic phenotype. In addition, XPO1 inhibition prevents the eIF4e-mediated export of messenger mRNA for a variety of oncoproteins (FLT3, c-KIT, cyclin D1, c-MYC, Bcl2), leading to decreased expressed to further provide anti-cancer activity. An ongoing Phase 1 (NCT01607892) open label, dose escalation, multi-center study in hematological malignancies was designed to evaluate the safety and tolerability of selinexor as well as response rate as the secondary objective. A maximum tolerated dose (MTD) was not identified yet in this study, but based on the ongoing Phase1 study of selinexor in pts with solid tumors, a MTD of 65 mg/m2 twice weekly was determined. The goal of the analyses reported here was to identify the recommended Phase 2 dose (RP2D) based on both tolerability and efficacy in patients with heavily pretreated hematological malignancies. Methods: A subset (N=157) of the Phase 1 patient population received oral selinexor twice weekly (8 doses/28-d cycle). General clinical observations suggested that doses of selinexor 〉35 mg/m2 (〉 ~60 mg flat dose) are associated with suboptimal tolerability. Therefore, based on the actual dose administered, patients were divided into groups receiving 45-65 mg (median 60 mg; N=59) and 〉65 mg (70-160 mg; median 90 mg, N=98) for comparison of safety and efficacy endpoints. The majority of the patients have heavily pretreated myeloma, NHL, and AML. Results: 157 pts received 45-160 mg selinexor twice weekly (89 M/68 F, median age 66 yr; median 4 prior regimens). The most common adverse events (AEs) were fatigue (66%), nausea (64%), anorexia (55%), vomiting (38%), which were mostly gr 1/2, and thrombocytopenia (44%), which was mostly grade 3/4. Incidence of certain selinexor-related high grade (3/4) adverse events was greater in pts receiving 〉65 mg selinexor vs those receiving 45-65 mg (Table 1). Grade 3 nausea (4%), anorexia (3%), vomiting (3%) and hypokalemia (3%) were observed in the 〉65 mg group but were not seen in the 45-65 mg group. Grade 3 and 4 anemia were 19% vs 14% and 4% vs 2% for the 〉65 mg vs 45-65 mg groups, respectively. Grade 3 and 4 thrombocytopenia was similar in both groups, but slightly higher in the 〉65 mg group, with 8% and 24 % in the 45-65 mg group vs 12% and 27% in the 〉65 mg group. Neutropenia was also very similar in Grade 3 and 4 toxicity for both groups with 10% and 12% in the 45-65 mg group vs 11% and 10% in the 〉65 mg group. In contrast, high grade cataract was only seen in the 45-65 mg group (8%; 3 gr 3, 1 gr 4). Selinexor-induced weight loss, as compared to baseline, was maximal by the end of cycle 2 in both dose groups, without further loss through at least cycle 4, but the 〉65 mg group lost on average 〉5-fold more weight (average of 3.8 ± 1.1 kg vs 0.7 ± 0.1 kg in the 65 mg group from 56 d- 126 d; p65 mg group; p=0. 05). In contrast, overall efficacy in the two dose groups was comparable, with 5 complete responses (CRs, 10%) and an overall response rate (ORR) of 23% in the 45-65 mg group and 4 CRs (5%) and ORR of 24% in the 〉65 mg group. A listing of all responses for both groups can be seen in Table 2. Conclusions: While efficacy is comparable, doses of selinexor from 45-65 mg (median 60 mg) are better tolerated than doses 〉65 mg, based upon decreased weight loss, incidence of high grade AEs, and greater numbers of days on study. Based on this superior risk-benefit, a flat dose of 60 mg selinexor, twice weekly, is the RP2D for patients with hematological cancers. Similar results have been observed for solid tumors. Disclosures Chen: Celgene: Consultancy, Honoraria, Research Funding. Jacoby:Novo Nordisk: Consultancy; Sunesis: Research Funding. Stone:AROG: Consultancy; Celator: Consultancy; Novartis: Research Funding; Pfizer: Consultancy; Juno: Consultancy; Celgene: Consultancy; Karyopharm: Consultancy; Amgen: Consultancy; Agios: Consultancy; Roche/Genetech: Consultancy; Abbvie: Consultancy; Sunesis: Consultancy, Other: DSMB for clinical trial; Merck: Consultancy. Baz:Sanofi: Research Funding; Celgene Corporation: Research Funding; Karyopharm: Research Funding; Millennium: Research Funding. Gabrail:Sanofi: Honoraria, Speakers Bureau; Janssen: Speakers Bureau; BI: Honoraria, Speakers Bureau; Onyx: Honoraria, Speakers Bureau. Wang:Celgene: Research Funding. Martin:Janssen: Consultancy, Honoraria; Acerta: Consultancy; Gilead: Consultancy; Celgene: Consultancy; Novartis: Consultancy; Bayer: Consultancy. Siegel:Celgene Corporation: Consultancy, Speakers Bureau; Amgen: Speakers Bureau; Takeda: Speakers Bureau; Novartis: Speakers Bureau; Merck: Speakers Bureau. Marshall:Karyopharm: Employment. Saint-Martin:Karyopharm: Employment. Carlson:Karyopharm: Employment. Shacham:Karyopharm: Employment, Equity Ownership. Kauffman:Karyopharm: Employment, Equity Ownership. Kuruvilla:Gilead: Consultancy; Hoffmann LaRoche: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Merck: Honoraria; Bristol-Myers Squibb: Honoraria; Lundbeck: Honoraria; Karyopharm: Honoraria.

Description: Hematopoietic cells from patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) contain gene mutations that are variably distributed between the founding clone and daughter subclone(s). Traditional response criteria in MDS and AML are based on bone marrow morphology and may not accurately reflect antitumor activity and clinical benefit in patients treated with hypomethylating agents. We used digital sequencing of serial bone marrow samples to monitor tumor burden and to characterize the changes in the clonal structure of MDS and AML that occur during treatment with epigenetic therapy. We hypothesized that digital sequencing may provide an alternative measure of antitumor activity and identify the persistence or emergence of resistant clones during treatment which mediate disease relapse. We conducted a phase I/II study in older adults (age ≥ 60) with advanced MDS (IPSS ≥ 1.5) or AML. Subjects received a combination of decitabine 20 mg/m2 on d1-5 with the histone deacetylase inhibitor, panobinostat 10-40 mg po 3x/week every 28 days for up to 12 cycles. Serial bone marrow samples were collected for digital sequencing at baseline, after every 2 cycles of treatment and at the time of relapse. A total of 52 patients, 14 with MDS and 38 with AML were enrolled in this study. For AML patients, 10% achieved a complete remission (CR+CRi) with an additional 18% of patients achieving a morphologic leukemia-free state (mLFS) using IWG response criteria. For patients with MDS, 14% achieved a CR and 21% achieved a marrow CR. We identified 9 MDS and 16 AML patients that had banked, paired bone marrow and skin (as a source of normal DNA) samples and a somatic mutation in at least 1 of 54 recurrently mutated MDS/ AML genes. DNA was enriched for 285 genes commonly mutated in MDS and AML (n=24 patients) or whole exome probes spiked-in with the 285 genes (enhanced exome sequencing; EES) (n=7 patients), and sequenced on a HiSeq2000 instrument with 2x101bp reads. We detected an average of 4.9 SNVs and indels per patient (range 1-15) when only the 285 gene panel was used, compared to 27.4 mutations per patient (range 9-43) using EES. Ten genes were mutated in at least 3 pre-study samples. The presence of a TP53 mutation (N=8) was associated with a trend towards achieving a response (p=0.09). We then analyzed variant allele frequencies (VAF) of mutations in serial samples. We observed five distinct patterns that were associated with different clinical responses, including i) AML patients achieving a CR+CRi (n=2): mutation VAFs were undetectable by cycle 2 using standard sequencing, ii) AML with mLFS (n=2): mutation VAFs remained detectable but decreased to 30%. We observed responding patients can have persistent measurable clonal hematopoiesis for at least one year without disease progression. Sequencing also revealed selective AML subclone clearance in a patient with treatment failure, nominating a set of mutations that may mark super-responder clones. We observed that the blast percentage decreases prior to mutation VAFs in some patients, suggesting that the differentiation of blasts could falsely underestimate tumor burden. Finally, sequencing revealed that tumor burden can be measured even in patients achieving a CR. Using an ultra-sensitive barcode sequencing approach, we sequenced 1 MDS and 1 AML patient achieving a clinical and molecular CR (based on standard sequencing). We detected extremely rare TP53 mutations months to years prior to disease relapse (VAFs = 0.23% in MDS and 0.05% in AML during a CR - equivalent to a sensitivity of 1 in 2000 heterozygous mutant cells). While patients can live with persistent clonal hematopoiesis in a CR or stable disease, ultimately we find evidence that expansion of a rare subclone drives relapse or progression from MDS to secondary AML. Digital sequencing provides an alternative measure of disease response which may augment traditional clinical response criteria and should be explored in future clinical trials. Disclosures Uy: Novartis: Research Funding. Off Label Use: Panobinostat in MDS/AML. Duncavage:Cofactor Genomics: Consultancy; DI&P Consulting: Consultancy. Jacoby:Sunesis: Research Funding; Novo Nordisk: Consultancy. Abboud:Teva Phamaceutical: Research Funding.

Description: Background: Although hypomethylating agents are the mainstay of treatment for myelodysplastic syndromes (MDS), these agents produce remissions in a minority of patients and are not curative. Vosaroxin is a first-in-class quinolone derivative that intercalates DNA and inhibits topoisomerase II activity, which is active and tolerable in acute myeloid leukemia (AML). The novel combination of vosaroxin and azacitidine was found to be synergistic in primary myeloblasts. This phase I/cohort expansion trial was conducted to study the combination of vosaroxin and azacitidine for patients with MDS. Methods: Patients with MDS ≥ 18 years of age with cytopenias requiring transfusions, an IPSS score of intermediate-1 or greater, or CMML were eligible. The primary objective was to determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of vosaroxin when given in combination with a fixed dose of azacitidine (75 mg/m2 /day). Vosaroxin was administered on days 1 and 4, and azacitidine on days 1-7 of a 28 day cycle, for up to 6 cycles in a 3+3 design. Results: Thirteen patients were enrolled in the dose escalation phase. No patients received prior hypomethylating therapy. The median age was 65 years (range 38-77) with IPSS scores of intermediate-1 (INT-1), (n=4); intermediate-2 (INT-2), (n=7); and high risk (HR), (n=2). At the initial dose of 50mg/m2 /day vosaroxin, 2 of 6 patients experienced a DLT (grade 4 hyperbilirubinemia, and grade 4 neutropenia 〉42 days). Additional incidences of ≥ grade 3 non-hematologic toxicity in this cohort included: febrile neutropenia (n=6), dysphagia (n=1), mucositis (n=3), infections (n=9), sepsis (n=3), and bleeding (n=3). The vosaroxin dose was de-escalated to 34 mg/m2 /day, resulting in 1 of 6 patients with a DLT (grade 4 mucositis). Incidences of ≥ grade 3 non-hematologic toxicity in this cohort included febrile neutropenia (n=4) and infection (n=4). No patients died within 30 days of treatment. Twelve patients completed at least one cycle and were evaluable for response, assessed by modified IWG criteria (Table). Best response for each patient was as follows: stable disease, n=3; stable disease with hematologic improvement (HI)-neutrophils, n=1; marrow complete remission (CR), n=3; marrow CR with HI-platelets; n=2; marrow CR with HI-neutrophils, n=1; marrow CR with HI-erythroid, n=1; and marrow CR with HI-platelets and neutrophils, n=1. Of these twelve patients, five (42%) have proceeded on to allogeneic stem cell transplantation. Conclusions: The MTD of vosaroxin in MDS patients was 34 mg/m2 /day when given on days 1 and 4 with a fixed dose of 75 mg/m2 of azacitidine on days 1-7. The major non-hematologic toxicities of febrile neutropenia, infections, and mucositis were expected based on the disease population and prior experiences with vosaroxin. The combination of vosaroxin and azacitidine showed promising activity with responses rates comparable or better than those generally observed with azacitidine alone. Additionally, the transplant rate observed was encouraging in this patient population with a median age of 65 years. A cohort expansion with plans to enroll an additional 20 patients at the MTD to further evaluate the tolerability and activity of the combination of vosaroxin and azacitidine in MDS patients is ongoing. In addition, correlative studies of the DNA damage response to the combination of vosaroxin and azacitidine from primary patient samples are in progress. Table 1.Best responsea, n (%)Evaluable patients (N=12)mCR/ mCR-HI8 (67)mCR3 (25)mCR-HI-erythroid1 (8)mCR-HI-neutrophils1 (8)mCR-HI-platelets2 (17)mCR-HI-neutrophil/platelets1 (8)Stable disease4 (33)mCR, marrow complete remission; HI, hematologic improvement.aResponse categories defined according to the modified IWG criteria (Cheson 2006). Disclosures Jacoby: Sunesis: Research Funding; Novo Nordisk: Consultancy. Off Label Use: Vosaroxin is currently under clinical development for the treatment of AML.. Abboud:Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding; Pfizer: Research Funding; Merck: Research Funding; Teva Pharmaceuticals: Research Funding; Gerson Lehman Group: Consultancy. Uy:Novartis: Research Funding.

Description: Abstract 3366 The gross chromosomal aberrations in treatment-related acute myeloid leukemia/myelodysplastic syndrome (t-AML/t-MDS) cells suggest that disease initiation and progression may result from the inability of cells to appropriately respond to double-strand DNA breaks (DSBs) induced by prior exposure to radiation, alkylator, or topoisomerase II inhibitor therapy. We hypothesize that dysregulation of DSB repair by homology-directed repair (HDR) or nonhomologous end joining (NHEJ) contributes to the development of t-AML/t-MDS. Dysregulation of DSB repair in t-AML/t-MDS may result from inherited variants or acquired mutations in HDR/NHEJ pathway genes. To directly test this possibility, we used next-generation sequencing technology and an array CGH platform to identify inherited and somatic genetic variants, including small indels and copy number alterations, in 21 canonical HDR and 9 NHEJ DNA repair genes, as well as a subset of 7 DNA damage response genes using tumor DNA and paired normal DNA obtained from 30 t-AML/t-MDS patients. All the data has been acquired and the analysis is ongoing. Because dysregulation of DNA repair pathways can result from epigenetic changes or post-translational modifications in DNA repair genes and would not be detected using sequencing and array CGH, we are also performing functional studies to interrogate DSB repair using primary bone marrow cells from 16 of these t-AML/t-MDS patients and CD34+ cells from 5 normal healthy controls. We performed a flow-based assay for DSB formation and repair by measuring the phosphorylated form of the variant histone H2AX (pH2AX), which is rapidly phosphorylated upon DSB formation, in myeloblasts (CD45 dim, low side scatter) and lymphocytes (a surrogate for normal cells) from leukemic bone marrow. Baseline measurements of unmanipulated primary bone marrow cells and a time course to measure the kinetics of DSB repair after gamma irradiation are used to assess a cell's basal DSB burden and the response to acute damage. We have validated this assay in a defined genetic system using isogenic cells deficient or not in BRCA2, a gene central to the HDR pathway, and were able to demonstrate that cells lacking BRCA2 have elevated pH2AX levels at 4–24 hours post DSB induction compared to controls (p=0.01). In addition, we have evaluated the ability of the cells to form nuclear foci of pH2AX and RAD51 (a protein central to the repair of DSB by HDR) by quantifying the relative numbers of immunofluorescent nuclear foci upon irradiation. We have performed these functional assays for 8 t-AML/t-MDS samples and 3 normal donors. We identified one t-AML/t-MDS sample whose myeloblasts show 2–3 fold greater pH2AX at baseline, compared to control CD34+ cells (p=0.006). Interestingly, the clearance of pH2AX is significantly faster in this sample compared to controls (p=0.001) despite showing elevated baseline pH2AX levels. This patient had a translocation involving chromosome 11q23. One additional patient in our cohort with an 11q23 translocation also showed similar increased baseline pH2AX levels. In addition, we identified abnormalities in a third t-AML/t-MDS sample that trends towards impaired maximal pH2AX induction (p=0.052). Furthermore, myeloblasts from a fourth t-AML/t-MDS sample, a known heterozygous BRCA2 mutation carrier, show a trend towards delayed pH2AX clearance (p=0.07). As predicted, bone marrow cells from this BRCA2 carrier also have 3.5 fold less RAD51 nuclear foci formation compared to control cells (8.6% vs 30%). Collectively, these results show that primary t-AML bone marrow cells can be used to assess the functional integrity of DSB response, and suggest that a large proportion of samples (4/8) may contain genetic alterations in DNA DSB response and/or repair genes. Functional studies of an additional 8 samples are ongoing. Next generation sequencing and array CGH data for the 37 HDR/NHEJ genes has been completed and will be correlated with the functional studies for each sample. Identification of abnormal DSB repair in leukemic patients may not only elucidate the molecular pathogenesis of the disease, but may provide rationale for testing agents to achieve selective killing of leukemic cells, as defects in one DNA repair pathway may increase reliance on another, making these cancer cells particularly susceptible to killing by inhibitors targeting the extant pathway(s). Disclosures: No relevant conflicts of interest to declare.

Description: Introduction: The clinical diagnosis of myelodysplastic syndrome (MDS) relies on the presence of persistent cytopenias, not otherwise explained, and evidence of morphologic dysplasia in the bone marrow. Low grade MDS (bone marrow blasts

Description: Background: The need to repeat peripheral blood stem cell (PBSC) mobilization and collection arises infrequently in healthy donors, but may be required due to insufficient initial collection, graft failure, or relapse of the recipient’s disease. Currently no published data exists on the efficacy of remobilization of healthy PBSC donors. Studies of remobilization in patients undergoing autologous transplantation (ASCT) have largely focused on the use of alternative mobilization agents such as chemotherapy or plerixafor. Boeve et al (Bone Marrow Transplant, 2004) reported that remobilization with G-CSF in patients undergoing ASCT who failed initial mobilization with G-CSF, resulted in higher numbers of CD34+ cells collected than the initial collection, though this required a doubling of the dose of G-CSF. Patients/Methods: We performed retrospective chart review of 977 consecutive adult (〉18 yrs) donors who underwent apheresis for PBSC donation at Washington University School of Medicine from 1995 through 2013. We identified 66 donors who had undergone more than one mobilization. Two cohorts of donors were identified for analysis: Group 1 included donors mobilized initially and again subsequently with G-CSF (10 ug/kg/day), or GM-CSF (5 ug/kg/day) + G-CSF (10 ug/kg/day). Group 2 consisted of donors mobilized with a CXCR4 antagonist, plerixafor (240-320 ug/kg) or POL6326 (1000-2500 ug/kg), and subsequently were remobilized with G-CSF (10 ug/kg/day). Statistical Analysis: Spearman correlations were performed to analyze the relationship between peak peripheral blood (PB) CD34+/uL level; the number of CD34+ cells collected per kg (recipient weight); and the number of CD34+ cells per L of apheresis collected during initial mobilization (MOB1) and remobilization (MOB2); and the interval (days) between MOB1 and MOB2. One-way ANOVA with repeated measures analyses were performed to determine the relationship of PB CD34+/uL, CD34+/kg and CD34+/L during MOB1 and MOB2. Results: Group 1 included 30 donors. The median age was 49 years (range 18-75) and 15 were male. The median number of days between MOB1 and MOB2 was 140 (range 26-2238). All 30 donors were remobilized due to graft failure or relapse of the recipient’s disease. PB CD34+/uL, CD34+/kg and CD34+/L all correlated between MOB1 and MOB2. The mean PB CD34/uL at MOB1 was 69 compared to 37 at MOB2 (p= 0.029); the mean CD34/kg collected at MOB1 was 5.6x106 compared to 3.3x106 at MOB2 (p= 0.002); and the mean CD34/L collected at MOB1 was 24.0x106 compared to 17.6x106at MOB2 (p= 0.023). The interval between MOB1 and MOB2 did not correlate with any of the MOB2 variables. Results from the analysis are summarized in Table 1. Group 2 included 32 donors. The median age was 51 years (range 21-67) and 18 were male. The median number of days between MOB1 and MOB2 was 20 (range 4-1123). 18 donors were remobilized due to mobilization failure, while 14 were remobilized due to graft failure or relapse of the recipient’s disease. The mean PB CD34/uL at MOB1 was 15 compared to 68 at MOB2 (p〈 0.001); the mean CD34/kg collected at MOB1 was 2.5x106 compared to 7.1x106 at MOB2 (p〈 0.001); and the mean CD34/L collected at MOB1 was 10.6x106 compared to 30.1x106at MOB2 (p〈 0.001). The interval between MOB1 and MOB2 did not correlate with any of the MOB2 variables. Results from the analysis are summarized in Table 2. Conclusion: Remobilization with G-CSF or GM-CSF and G-CSF after initial successful mobilization with the same regimen results in poorer mobilization while remobilization with G-CSF after initial mobilization with a CXCR4 antagonist results in dramatically improved mobilization. The reason for this remains unclear, but in this study the interval between collections was not associated with successful remobilization. Abstract 850. Table 1 Group 1 MOB 1 MOB 2 One-way ANOVA Spearman Correlation PB CD34/ul 69 (13-417) 37 (1-115) F(1.0, 29.0) = 5.26, p= 0.029 r= 0.615, p〈 0.001 CD34/kg (x106) 5.6 (0.8-13.8) 3.3 (0.3-10.6) F(1.0, 29.0) = 11.77, p= 0.002 r= 0.483, p= 0.007 CD34/L (x106) 24.0 (4.5-72.0) 17.6 (2.8-41.3) F(1.0, 29.0) = 5.74, p= 0.023 r= 0.566, p〈 0.001 Abstract 850. Table 2 Group 2 MOB 1 MOB 2 One-way ANOVA Spearman Correlation PB CD34/ul 15 (2-54) 68 (14-358) F(1.0, 31.0) = 23.16, p〈 0.001 r= 0.433, p= 0.013 CD34/kg (x106) 2.5 (0.2-19.7) 7.1 (1.7-42.4) F(1.0, 31.0) = 33.84, p〈 0.001 r= 0.769, p〈 0.001 CD34/L (x106) 10.6 (1.4-67.1) 30.1 (6.0-165.0) F(1.0, 31.0) = 34.70, p〈 0.001 r= 0.774, p〈 0.001 Disclosures No relevant conflicts of interest to declare.

Description: Background: The use of post-transplantation cyclophosphamide (PTCy) as a single agent for graft-versus-host disease (GVHD) prophylaxis in HLA matched transplant patients has had varied results. Two recent studies at Johns Hopkins University noted favorable incidences of both GVHD and non-relapse mortality (NRM) in both matched related and unrelated donor allogeneic hematopoietic cell transplant (allo-HCT) recipients (Kanakry CG, et al, JCO, 2013 and Kanakry CG et al, Blood, 2014). In contrast to this data, a phase II study at MD Anderson reported higher rates of grade II-IV acute GVHD and NRM, with worse overall survival in patients receiving PTCy as the sole GVHD prophylaxis compared to their matched cohort receiving a calcineurin-inhibitor (CNI) and methotrexate (MTX) as immunosuppression (Alousi AM et al, BBMT, 2015). Another study in Australia had to be stopped for safety reasons due to high GVHD and NRM when using PTCy as sole GVHD prophylaxis (Bradstock KF, BBMT, 2015). There is no published data on the use of MMF plus tacrolimus in combination with PTCy in HLA matched allo-HCT recipients. We hypothesized that addition of MMF and Tacrolimus to PTCy in HLA matched allo-HCT recipients will lead to significantly improved transplant outcomes. To answer this question we retrospectively analyzed data from patients who received this regimen at a single institution. Methods. We performed a retrospective analysis of 31 HLA matched allo-HCT patients who received PTCy at 50 mg/m2 on days +3 and +4 in addition to MMF and tacrolimus immunosuppression from December 2012 till June 2015 at Washington University School of Medicine in Saint Louis. All of these patients received G-CSF mobilized peripheral blood grafts. Patients included AML (n=13), ALL (n=5), MDS (n=5), CML (n=2), aplastic anemia (n=2) and NHL (n=1), myelofibrosis (n=1). Twelve of the patients underwent a matched related donor (MRD) transplant and 19 underwent a matched unrelated donor (MUD) transplant. Two of the MUD transplants had a HLA match grade of 8 of 10 and the other 17 were a 10 out of 10 match. Twenty-eight of the patients received a graft collected via peripheral blood stem cell mobilization and the other three had a donor graft collected via bone marrow harvest. Cumulative incidence of aGVHD was estimated using Gray's sub-distribution method to account for death without aGVHD as a competing event, and the cumulative incidences of non-relapse mortality (NRM) and relapse were estimated treating each other as competing event, while OS was estimated using Kaplan-Meier limit method. Results: This regimen was associated with acceptable GVHD in our patients. Incidence of grade II-IV acute GVHD was 28% (21.3% for MRD; 31.5% for MUD) at day 100 and 28% at 1 year. Incidence of Grade III-IV acute GVHD was 13.5% at both 100 days and 1 year. Limited chronic GVHD was 25.9% and extensive GVHD was 14.8% at 1 year. Similarly we found acceptable NRM and relapse in these patients, NRM was 10.2% and 19.7% at 100 days and 1 year respectively and cumulative incidence of relapse at 100 days and 1 year were 17.8% and 29.0% respectively. Overall survival at 1 year for all patients was 52%. Summary: Here we report favorable results from a regimen combining MMF and Tacrolimus on PTCy platform in HLA matched MRD and MUD transplant recipients. Relatively low GVHD and NRM results are particularly encouraging in view of almost exclusive use of G-CSF mobilized T cell replete grafts with much higher T cell content. Though limited by the relatively small number of patients, our results suggest combining MMF plus Tacrolimus with PTCy platform in HLA matched allogeneic transplant patients is safe and associated with acceptable transplant outcomes. Disclosures Vij: Onyx: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Millennium: Honoraria, Speakers Bureau; BMS: Consultancy; Takeda: Consultancy, Research Funding; Novartis: Consultancy; Sanofi: Consultancy; Janssen: Consultancy; Merck: Consultancy. Uy:Novartis: Research Funding. Abboud:Teva Pharmaceuticals: Research Funding; Gerson Lehman Group: Consultancy; Merck: Research Funding; Pfizer: Research Funding; Novartis: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees. Schroeder:Celgene: Other: Azacitidine provided for this trial by Celgene; Incyte: Consultancy. Jacoby:Sunesis: Research Funding; Novo Nordisk: Consultancy.