Palmer, Jeanne

Abstract Abstract 467 Background: While donor-recipient disparity at HLA loci is associated with greater risk for severe acute graft vs. host disease (GVHD) and inferior survival after unrelated donor allogeneic hematopoietic cell transplantation (HCT), the impact of amino acid substitution (AAS) at peptide binding pockets of the HLA molecule is incompletely understood. Methods: Adult and pediatric patients who received myeloablative or reduced intensity/non-myeloablative first unrelated bone marrow or peripheral blood stem cell transplantation for AML, ALL, CML or MDS between 1988 and 2009 were included. Donors and patients were fully high resolution matched for HLA-A, B, C, and DRB1 (8/8) or had single mismatch (7/8) at one HLA class I locus. Among 7/8 donor-recipient pairs, cases were categorized based on the presence or absence of the AAS of interest at positions 9, 77, 99, 116, or 156 of the class I molecule. In multivariable analysis accounting for patient, disease, and transplantation variables, we studied the independent impact of AAS at these residues on risk for grade III-IV acute GVHD, chronic GVHD, treatment-related mortality, primary malignancy relapse, and overall survival. We compared 7/8 donor-recipient pairs with AAS of interest to 7/8 pairs without these AAS in the primary analyses. Additionally, we performed this analysis restricted to each HLA class I locus. Results: Donor-recipient pairs were 8/8 matched (n=5282), 7/8 with AAS of interest (n=1713), or 7/8 without AAS of interest (n=318). In multivariable analysis, AAS at position 116 was associated with increased risk for grade III-IV acute GVHD (HR 1.21, 1.04–1.42, p=0.0165). No other significant association was detected between AAS studied and clinical outcomes. In multivariable analysis restricted to each class I HLA locus, we detected the following: Among 7/8 matched pairs with mismatch at HLA-C, AAS at position 116 was associated with increased risk for severe acute GVHD (HR 1.42, 1.13–1.79, p=0.0031) and inferior OS (HR 1.2, 1.01–1.41, p=0.0343). AAS at position 99 was associated with increased TRM (HR 1.37, 1.11–1.69, p=0.0037). Of 7/8 pairs with mismatch at HLA-B, AAS at position 9 was associated with increased chronic GVHD (HR 2.19, 1.31–3.66, p=0.0029). Specific amino acid substitution pairs with frequency > 30 were tested for association with HCT outcomes. None met the significance level of 0.00125, pre-specified for multiple comparisons. Conclusions: These results support the concept that AAS at key peptide-binding residues in the HLA class I molecule are associated with increased risk for severe acute GVHD and lower survival. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Smoking increases the risk of Philadelphia-chromosome negative myeloproliferative neoplasm (MPN) development as well as increases the risk of thrombotic complications, the major cause of mortality in this population (Blood 2017 130:4199). Guidelines suggest that management of more indolent forms of MPNs include the assessment and mitigation of cardiovascular risk, which includes the management of smoking-related risks (NCCN Guidelines. 2017). In this analysis we sought to examine smoking outcomes and opinions from the perspective of the MPN patient, with the goal of helping to guide MPN patient care. Methods: The internet-based survey was developed by a team of MPN investigators and administered via Mayo Clinic's REDCap. Online recruitment was facilitated via multiple MPN-related webpages including the MPN Forum, MPN Net, MPN Research Foundation, and MPN Voice during June of 2018. Surveyed data included disease demographics such as thrombosis, medications, and smoking history. MPN-specific symptoms were assessed utilizing the MPN-10 (Blood. 2011 Jul 14;118(2):401-8). Data: Participant Demographics: Of the 607 patients who clicked the survey link, 435 patients were eligible for the survey and completed the questions regarding smoking history. Of these, 254 (58%) reported no history of tobacco use, 161 (37%) reported being ex-tobacco users, and 20 (5%) reported being current users. Among those who reported current tobacco use, 50% used premade cigarettes, 27% used self-rolled cigarettes, 20% reported vaping, and 3% reported chewing tobacco or snuff use. Respondents were most often from the US (67%), Australia (12%), the UK (6%) or Canada (6%). The distribution of respondents included 28% with myelofibrosis, 44% with polycythemia vera and 27% with essential thrombocythemia. Over one quarter (26%) of patients had experienced a prior thrombosis, with the most frequent thrombosis types being DVT (9%), stroke or transient ischemic attack (8%), abdominal vein thrombosis (5%), myocardial infarction (2%) and cerebral vein thrombosis (2%). When comparing current/former smokers to never smokers, no significant difference in thrombotic frequency was observed. Smoking Correlates: When evaluating MPN symptoms, current/former smokers reported higher severity of fatigue (mean 5.6 vs 5.0, p=0.02) and inactivity (mean 4.0 vs 3.1, p=0.03) compared to nonsmokers. Additionally, current/former smokers were more likely to experience early satiety (69% vs 58%, p=0.03), inactivity (80% vs 71%, p=0.04), concentration difficulties (82% vs 73%, p=0.04), and reduced quality of life (mean 6.1 vs 6.5, p=0.03) compared to nonsmokers. Although not significant, a trend of higher symptomatology was observed for former/current smokers compared to nonsmokers (MPN-10 total symptom score [TSS] mean 30.4 vs 27.0, p=0.07). Former/current smokers were also more likely than nonsmokers to report heavy alcohol consumption (>7 drinks per week in 9.6% vs 4.0%, p=0.03) and using opioids for pain management (24% vs 11%, p=0.001). Smoking Opinions and Care: As shown in Table 1, less than half of current/former smokers (43%) reported having their physician discuss tobacco use with them. Less than 40% of MPN current or previous smokers were aware of the risk of MPN development due to smoking, although the majority (83%) were aware of the increased thrombotic risk. Less than one quarter (43/181) of current/former smokers reported having utilized pharmacologic therapy to aid cessation. Conclusions MPN patients with current or previous tobacco use demonstrate significantly higher symptom burden than non-smoking counterparts. In terms of patient care, less than half of patients who are current or previous smokers recall having a physician discuss their smoking habits with them. These results highlight the need for enhanced MPN patient counseling by health care providers, both regarding the risks of smoking and available methods to aid cessation. Disclosures Scherber: Orphan Pharmaceuticals: Honoraria; Incyte: Consultancy. Dueck:Phytogine: Employment; Pfizer: Honoraria; Bayer: Employment. Palmer:Novartis: Research Funding. Mesa:Incyte: Research Funding; Galena: Consultancy; Gilead: Research Funding; Ariad: Consultancy; Celgene: Research Funding; Novartis: Consultancy; CTI: Research Funding; Promedior: Research Funding.

Abstract Introduction - Allogenic hematopoietic cell transplantation (HCT) remains potential curative treatment for hematologic malignancies. Anti-thymocyte globulin (ATG) is an immunoglobulin directed to human T lymphocytes, and may decrease the risk of chronic graft versus host disease (cGVHD). Use of ATG has been associated with higher incidence of disease relapse and infection. While the optimal dosing of ATG has not been well established, higher doses (≥ 7.5 mg/kg) have a stronger association with infection and disease relapse. Our institution utilizes low dose rabbit ATG at 2.5 mg/kg for in-vivo T-cell depletion. In this retrospective study we evaluated outcomes in patients receiving low dose ATG to those not undergoing in-vivo T-cell depletion with the hypothesis that low dose ATG protects against cGVHD without impacting infectious complications or relapse. Patients and Methods - We evaluated all patients with 8/8 HLA Matched unrelated Donors (MUD) undergoing HCT between 2007 and 2016. Patients were divided in to two cohorts, those receiving low dose ATG to those that did not. Both cohorts received standard GVHD prophylaxis with calcineurin inhibition plus methotrexate or mycophenolate. The primary outcome was overall survival (OS). Secondary outcomes included relapse free survival (RFS), EBV reactivation, CMV reactivation, CMV disease, invasive fungal infection, incidence of acute GVHD (aGVHD) grades III-IV, and moderate to severe cGVHD. A subset analysis was performed to assess relapse free survival (RFS) in patients with myeloid malignancies. Descriptive statistics were utilized for baseline characteristics; and a series of univariate and multivariant Cox proportional hazard regression models were conducted for outcomes of interest. A Kaplan-Meier (K-M) survival curve was used to depict probability of survival by ATG cohort. Results - We identified 209 patients, with 129 (62%) in ATG group and 80 (38%) in non-ATG group. At baseline, there were no differences in the age at transplant, sex, ABO incompatibility, or performance status. The ATG cohort had fewer low disease risk index (DRI) patients and more patients with intermediate or high DRI (2.4%, 64.6%, 28.3% vs 18.4%, 51.3%, 23.7% respectively), and Fisher's Exact test showed that this difference between ATG groups was statistically significant, p = <0.001. The ATG cohort also had significantly different rates of myeloablative (MA) conditioning regimens from the non-ATG cohort with fewer receiving MA (31% vs 53% p < 0.01). No statistically significant differences in OS were observed between the two ATG cohorts at up to 5 years post-transplant (p=0.35; Fig. 1). The primary predictor of OS was DRI very high vs low [HR 6.0 (2-18) p < 0.01]. The ATG exposed cohort had significantly lower risk of cGVHD [HR 0.17 (0.08-0.37) p = <0.001]. There was no difference in risk of death from relapse, incidence of EBV or CMV reactivation, CMV disease, invasive fungal infection, or grade III-IV acute GVHD. Low dose ATG was not associated with inferior RFS, including in subset analysis of patients with myeloid malignancies [HR 0.85 (0.5-1.4) p = 0.549]. Conclusions - Our study shows no significant difference in survival or death from relapse for patients who receive ATG. Importantly, patients receiving ATG had a lower rate of cGVHD with no increased rates of infectious complications. Low dose ATG did not appear to increase the risk of relapse, even when considering only myeloid malignancies. These findings suggest that low dose ATG can improve cGVHD with no impact on survival, relapse, or infectious complications. Additional prospective trials using low dose ATG compared to no ATG are warranted. Disclosures Palmer: Novartis: Research Funding.

Abstract Background: Treatment options for elderly acute myeloid leukemia (AML) patients, despite various novel therapies, are still limited. Relapse is common after chemotherapy, and progression on lower intensity treatment with hypomethylating agents is inevitable in all patients even after initial response. Lysine deacetylase inhibitors (KDIs or HDAC inhibitors) have shown limited single-agent clinical activity in AML. Therefore, to develop potential novel treatment options for AML, we aimed to identify synergistic KDI-based drug combinations to build upon the single-agent activity and clinical-availability of KDIs. We performed RNA-interference (RNAi) drug modifier screens of the kinome and phosphatome with the KDI vorinostat in AML cells in order to identify targets to inhibit in combination with KDIs. Based on pathway analysis of RNAi screen results that highlighted an unexpected role for p38/JNK/SAPK signaling in vorinostat activity in AML, we explored the putative p38 substrate-selective MK2 inhibitor CMPD1 combined with KDIs, and demonstrated potent synergistic activity in AML regardless of molecular, cytogenetic or lineage background. As published evidence suggests that CMPD1 can also act as a microtubule-destabilizing/targeting agent (MTA), and that MK2 can associate with microtubules and cytoskeleton-associated proteins, we examined several MTAs in combination with KDIs in AML, including vinca alkaloid microtubule-destabilizing agents vinblastine/vincristine, and taxol as a microtubule-stabilizing agent. Results: Vinblastine and vincristine dose-dependently synergized with vorinostat similarly to CMPD1 in all AML cell lines tested, with vinblastine being more potently synergistic than vincristine. Taxol only potentiated KDI activity in approximately half of AML cell lines. Importantly, preliminary data suggest preferential, dose-dependent synergy of KDIs and vinca alkaloid MTAs in the CD34+ progenitor AML cell fraction, as compared to the paired CD34-depleted fraction from the same primary AML sample in ex vivo culture. This preferential CD34+ activity was similar to that observed with CMPD1 combined with KDIs in ex vivo models. Consistent with synergistic activity of MTAs and KDIs, multiple RNAi screen hits also converged on microtubule dynamics. Subsequently, we identified the LKB1 signaling network, a critical integrator of cellular stress metabolism and hematopoietic stem cell quiescence/homeostasis, as a determinant of vorinostat activity in AML. Of 14 known kinases directly regulated by LKB1, 4 belong to microtubule-associated protein (MAP) or microtubule-affinity regulating kinases (MARK) families (e.g. screen hit MARK4). RNAi screen hits also converged on regulation of microtubule proteins, or directly on microtubule proteins themselves, (e.g. atypical MAPK4 and MAPK6 which phosphorylate microtubule-associated protein 2, or TAOK2 which has a kinase-independent role in stabilizing microtubules). Additionally, several RNAi hits such as PACSIN1 and -2, and MAST2 and -4 link the actin cytoskeleton to microtubule dynamics. Discussion: Herein we show that several types of clinically-used MTAs (i.e. vinca alkaloids or taxanes) potently synergize with KDIs in AML, and that this synergy can occur preferentially in primary CD34+ cells, as compared to the CD34-negative AML compartment. Although at high in vitro doses microtubule-destabilizing agents such as vinca alkaloids, and microtubule-stabilizing agents such as taxanes, can both induce apoptosis via mitotic perturbation, many publications show that low therapeutic MTA doses can induce apoptosis in tumor cells in vivo independent of mitosis. Therefore, we hypothesize that clinically-available KDIs (i.e. vorinostat, panobinostat) and MTAs (i.e. vinca alkaloids or taxanes) represent novel combinations with the potential to target the AML progenitor pool even in a non-proliferate state, and thus have the potential to eradicate minimal residual disease. Disclosures Mesa: Celgene: Research Funding; Incyte Corporation: Research Funding; Ariad: Consultancy; Galena: Consultancy; Novartis: Consultancy; Promedior: Research Funding; CTI: Research Funding; Gilead: Research Funding. Tibes:Italfarmaco S.p.A.: Consultancy, Honoraria.

Abstract Introduction Venetoclax (ABT-199) is an approved BCL-2 inhibitor for the treatment of patients with chronic lymphocytic leukemia (CLL). Multiple clinical trials are underway to explore its efficacy in additional indications. While venetoclax demonstrated high remission rates in combination with azacitidine in early stage clinical trials, the question of durability of responses and primary and acquired resistance remain, especially given the modest activity and rapid development of resistance as a single agent. One reported mechanism of intrinsic resistance is high expression of other BCL-2 family proteins, including MCL-1. We and others have demonstrated that the CDK9 inhibitor, alvocidib, can mediate transcriptional repression of anti-apoptotic MCL-1. It has also been shown that alvocidib can increase pro-apoptotic BIM, a dual activator and sensitizer BH3-only protein that can directly induce apoptosis and simultaneously inactivate anti-apoptotic BCL-2 family proteins such as MCL-1 and BCL-2, thus having the same effect on mitochondria-associated apoptosis as MCL-1 down-regulation, with the potential to directly induce apoptosis. An alvocidib-containing cytotoxic chemotherapy regimen demonstrated favorable remission rates in high-risk AML patients over standard therapy in a randomized Phase 2 trial indicating its potential role and safety in AML. We hypothesized that alvocidib and venetoclax would synergize against AML cells by shifting the overall balance of pro- and anti-apoptotic BCL-2 proteins in favor of apoptosis and thus represent a novel active treatment regimen in AML. Aims This study seeks to examine the efficacy of a treatment regimen containing alvocidib and venetoclax in multiple preclinical studies, including in vivo models of AML. Methods Cell viability assays interrogating alvocidib and venetoclax activity in cell lines were performed using CellTiter-Glo according to manufacturer's protocol. mRNA/miRNA expression changes were assessed using standard RT-PCR technique. Protein expression changes were assessed using standard western immunoblotting technique. To assess the efficacy of an alvocidib and venetoclax combination on tumor growth in an in vivo model, the OCI-AML3 xenograft mouse model and ex vivo studies with AML patient samples were performed. Results Herein we demonstrate that alvocidib inhibits both mRNA and protein expression of MCL-1 in a time and concentration-dependent fashion in 3 out of 4 AML cell lines analyzed, while in cells where alvocidib did not reduce MCL-1 protein levels (i.e. MOLM-13) a dose-dependent decrease in miR17-92, and concomitant increase in BIM protein was observed after 24 hours of alvocidib treatment. The alvocidib-venetoclax combination resulted in very strong synergistic reductions of cell viability (with combination indices [CI] of 0.4 to 0.7), both in venetoclax-sensitive and resistant cells. The venetoclax-sensitive lines, MV4-11 and MOLM-13, exhibited 5- to 10-fold reduction of venetoclax EC50 values in the low nM range when combined with only 80 nM alvocidib. Importantly, venetoclax-resistant lines, OCI-AML3 and THP-1, exhibited at least 20-fold reduction of venetoclax EC50 values from near 1 µM to 10-50 nM, when combined with 80 nM alvocidib.In the venetoclax-resistant OCI-AML3 xenograft model, single agent alvocidib and venetoclax achieved tumor growth inhibition (TGI) of 9.7 and 31.5%, respectively, while the combination achieved 87.9% TGI at the same dose levels of individual drugs. Conclusions Taken together, our data suggest that the combination of alvocidib with venetoclax is highly synergistic in vitro and in vivo, in both venetoclax-sensitive and -resistant AML across a heterogeneous genomic background. The particularly high level of synergy achieved in venetoclax-resistant cell lines highlights the central importance of both BCL-2 and MCL-1-mediated cell survival in AML. Importantly, the addition of alvocidib to venetoclax treatment reduced IC50s to clinically achievable concentrations. Therefore, we conclude that an alvocidib/venetoclax combination may be a novel approach for the treatment of AML and warrants further pre-clinical and clinical validation. Disclosures Whatcott: Tolero Pharmaceuticals: Employment. Kim:Tolero Pharmaceuticals: Employment. Haws:Tolero Pharmaceuticals: Employment. Mesa:Celgene: Research Funding; Galena: Consultancy; Promedior: Research Funding; Ariad: Consultancy; Novartis: Consultancy; CTI: Research Funding; Incyte: Research Funding; Gilead: Research Funding. Peterson:Tolero Pharmaceuticals: Employment. Siddiqui-Jain:Tolero Pharmaceuticals: Employment. Weitman:Tolero Pharmaceuticals: Employment. Bearss:Tolero Pharmaceuticals: Employment, Equity Ownership, Patents & Royalties. Warner:Tolero Pharmaceuticals: Employment, Equity Ownership, Patents & Royalties.

Abstract Background: Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for primary myelofibrosis (PMF). Reduced intensity conditioning (RIC) allows otherwise ineligible patients to proceed with HSCT. Host factors in PMF such as bone marrow (BM) fibrosis, massive splenomegaly, and transfusion related allo-immunization increase the risk of engraftment failure, especially with RIC. Spleen directed therapy (SDT) is often used in PMF patients with splenomegaly to help with engraftment, however little data exists supporting this practice. This study was carried out to investigate the role for SDT and the predictors of outcomes with RIC HSCT for PMF. Methods :After IRB approval, the Mayo Clinic HSCT registry was queried for patients with PMF that underwent RIC allo-HSCT from 2005-2014. Disease and transplant related data were retrospectively abstracted and analyzed for HSCT related outcomes. SDT was defined as a therapeutic strategy with specific intent to overcome an enlarged spleen prior to HSCT and included splenectomy, splenic artery embolization, splenic irradiation, or JAK inhibitor therapy that was stopped <30 days before HSCT. Survival estimates were calculated using the Kaplan-Meier method and means were compared using the log-rank test. Univariate and multivariate analyses were performed using Cox regression modeling. Results :51 patients (67% males) with WHO defined PMF with palpable splenomegaly that underwent RIC allo-HSCT were included in the study; median age 57 years (range, 35-68). The median follow-up was 12.2 months, and at last follow up, 19 deaths (37%) and 4 relapses (8%) were documented. The median OS for the group was not reached (mean 34.2 months); 88% at 100 days and 60% at 2 years. 17 deaths were attributed to non-relapse mortality (NRM). There were 3 engraftment failures (6%). 32 patients (63%) developed acute GVHD (grades II-IV) and 24 patients (47%) developed chronic GVHD (all grades). Twenty-one patients (41%) received SDT; 10 (48%) splenectomy, 2 (9%) splenic irradiation, and 9 (43%) JAK inhibitor therapy (ruxolitinib). The SDT group had a median spleen size of 14.5 cm (range, 1-29 cm) below the left costal margin (LCM) and 13 patients (62%) with spleen size >10 cm below LCM, while the no SDT group had a median spleen size of 7 cm (range, 1-19 cm) and 12 patients (40%) with spleen size >10 cm below LCM; p = 0.01. Seven (64%) of 11 patients receiving splenic irradiation (n = 1) or JAK inhibitor therapy (n = 6) were eligible for IWG-MRT spleen response, and 2 (29%) responded (both in JAK inhibitor group). Of the remaining 5 patients, 2 had a response not meeting IWG-MRT criteria. There were no differences in age (p = 0.09), gender (p = 1.0), DIPSS + score (p = 0.35), or HCT-CI (p = 0.61) between the two groups. There was a statistically significant difference in engraftment failure, with all 3 engraftment failures occurring in the SDT group (2 splenectomy patients, 1 splenic irradiation patient; p = 0.02). Engraftment failures were not attributable to insufficient cell dose, donor specific antibodies, or identifiable host factors. The patient with engraftment failure who underwent splenic irradiation had persistent massive splenomegaly. There were similar outcomes with regards to relapse rates, NRM, and acute and chronic GVHD. In the SDT group, the median OS was 13.3 months; 81% at 100 days and 33% at 2 years. In the no SDT group, the median OS was not reached; 94% at 100 days and 68% at 2 years; p=0.13. In a univariate survival analysis that included age, gender, SDT, DIPSS+ score, HCT-CI, CMV status, ABO status, HLA matching, donor source, graft source, engraftment status, and acute and chronic GVHD, predictors of survival were engraftment failure (p = 0.02) and major/bidirectional ABO incompatibility (p = 0.02). Similar results were obtained when JAK inhibitor therapy was considered separately from other forms of SDT. In a multivariate analysis, engraftment failure (HR 8.2, 1.8-27.2; p = 0.01) and major/bidirectional ABO incompatibility (HR 4.1, 1.4-10.9; p = 0.009) retained independent prognostic significance. Discussion:In patients with PMF and splenomegaly, there was no demonstrable benefit from SDT. Predictors of post-HSCT survival included engraftment failure and major/bidirectional ABO incompatibility. These findings need validation in a larger cohort of patients. Disclosures Al-Kali: Celgene: Research Funding. Mesa:Gilead: Research Funding; Incyte Corporation: Research Funding; Pfizer: Research Funding; Genentech: Research Funding; CTI Biopharma: Research Funding; Promedior: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; NS Pharma: Research Funding.

Abstract Background Myeloid neoplasms (MN) occurring secondary to treatment of non-malignant disease, especially autoimmune diseases (AID), and the overlap between them, is an increasing clinically important observation. Confounding variables for myeloid transformation include the nature of autoimmune disease as an incessant, chronically activated inflammatory cascade that has been associated with an increased risk of myeloid malignancy, and disease modifying therapies, often with cytotoxic and immunosuppressive drugs. Thus, the addition of therapeutic agents for treatment of AID theoretically amplifies the opportunity for MN to develop in genetically susceptible individuals. To our knowledge, there is no large study evaluating a comprehensive primary AID population that developed MDS or AML with detailed assessment of therapeutic interventions for AID. The presented study queries the association of cytotoxic, anti-inflammatory, and immune-modulating agents to treat AID as risk factors for developing myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML). Methods In a 10-year period from 2004-2014, a total of 40,011 patients with an ICD-9 coded diagnosis of AID were seen at Mayo Clinic Arizona and Florida campuses; 311 patients from this population had a concomitant coded diagnosis of MDS and/or AML. In an IRB approved, retrospective chart review, we confirmed 86 cases meeting strict inclusion criteria for AID and confirmed MDS or AML. We performed a case-control match from the same primary autoimmune population for age, gender, and autoimmune specific diagnosis at a 2:1 ratio querying for therapeutic interventions. Results Myeloid neoplasm specifics in our case cohort of 86 patients were 55 MDS, 21 de novo AML, and 10 AML with history of MDS. Average age was 72 years with a slight male predominance (57%). Rheumatoid arthritis (26.4%), psoriasis (20.7%), systemic lupus (13.8%), was the most common autoimmune profiles. Median onset of autoimmune disease to diagnosis of myeloid neoplasm was 6 years (range 1-54 years). Up to 26% controls documented no systemic agent for treatment of autoimmune disease and similarly 12.8% of the case cohort (p=0.142). Case and control populations treated with systemic therapies had similar exposures by category for immune-modulating agents (33.7% and 37.8% respectively) and cytotoxic therapies (47.7 and 44.8% respectively). A total of 57/86 cases (66.3%) received either a cytotoxic or immune-modulating agent. In comparison, 105/172 (61.1%) controls received either agent; p=0.495. Azathioprine was the only statistically significant agent exposure observed more frequently in the study cohort than controls with an OR of 7.05 (p= < 0.001). There was no increased incidence of MDS or AML in TNF-antagonist treated patients. No significant correlation for duration of agent exposure by drug category was observed. Discussion In a large primary AID population, azathioprine exposure was associated with a 7 fold risk of MDS or AML (p=< 0.001). Notable, but not statistically significant case cohort trends among cytotoxic agents was exposure to cyclophosphamide (OR 3.58) followed by mitoxantrone (OR 2.73). Methotrexate, mercaptopurine, and mycophenolate had favorable odd ratios, but these were not statistically significant. No association was found for TNF-inhibitory agents. Finally, there was no association of drug exposure time to the incidence in development of MDS or AML. Disclosures Dueck: Bayer: Honoraria. Mesa:Gilead: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Incyte Corporation: Research Funding; Galena: Consultancy; Ariad: Consultancy; CTI: Research Funding; Promedior: Research Funding. Al-Kali:Onconova Therapeutics, Inc.: Research Funding; Celgene: Research Funding. Foran:Millennium Pharmaceuticals, Inc.: Research Funding; novartis: Honoraria; karyopharm: Honoraria; medscape: Honoraria; pfizer: Honoraria; boehringer ingelheim: Research Funding; agios: Research Funding; Cellerant: Research Funding.

Abstract Background: Pegylated interferon alpha-2a (Peg INF2a) has been demonstrated to be active therapy for high-risk essential thrombocythemia (ET), polycythemia vera (PV), and early myelofibrosis (MF). We retrospectively analyzed the outcomes of Peg INF2a therapy in myeloproliferative (MPN) patients treated outside the constraints of a clinical trial. Methods: Charts were analyzed for demographic and clinical data. Toxicity to therapy was assessed per CTCAE 3.0 criteria. Therapeutic responses for ET and PV were calculated by the revised ELN/IWG-MRT criteria including complete remission (CR), partial resmission (PR), no response (NR), or progressive disease (PD). Responses in MF were calculated by EUNMET: complete response (CR), major response (MR), moderate response (MoR), minor response (MiR) and NRand the revised IWG-MRT/ELN criteria: CR, PR, clinical improvement (CI), stable disease (SD) or PD. Results: Patients: 75 patients were identified overall. There were 36 PV patients (48%), 20 ET patients (26.7%), and 19 MF patients (25.6%). Thirteen MF patients were post-PV/ET MF. The median age at diagnosis was 51.5 yrs (range 28.8-75.1). JAK2 V617 mutation was present in 53 patients (70.7%). Median baseline hemoglobin (g/dL), leukocyte (x10 9), and platelet count (x109) for PV was 13.6, 8.6, 369, for ET was 12.5, 6.8, 517, and for MF was 11.4, 8.0, and 420, respectively. DIPSS risk category for the 19 MF patients: Low in 6 (31.5%) patients, Intermediate-1 in 3 (15.7%), Intermediate-2 in 8 (42%), and High in 2 (10.5%) patients. The majority of patients (82.2%) had received at least one prior cytoreductive therapy for their disease. Therapy: Median starting dose of Peg INF2a was 45 micrograms/week (range 45-90). The median peak dose was 90 micrograms/week (range 45-270). The median tolerated dose was 60 micrograms/week (range 5.6-180). The median duration of treatment was 24 months (range 3.6-85). Toxicity: Overall the Peg INF2a was well tolerated. Hematological toxicity included: leukopenia at grade 1 in 13 patients (17.3%), grade 2 in 5 patients (6.7%), and grade 3 in 1 patient (1.3%), anemia at grade 1 in 10 patients (13.3%) and grade 2 in 1 patient (1.3%), thrombocytopenia at grade 1 in 13 patients (17.3%) and grade 2 in 1 patient (1.3%). The most common non-hematologic toxicity included: fatigue at grade 1 in 14 patients (18.7%) and grade 2 in 4 patients (5.3%), transaminitis at grade 1 in 6 patients (8%) and grade 2 in 3 patients (4%), myalgias at grade 1 in 4 patients (5.3%). Response: See Table #1 PV/ET: 56 patients were evaluated by ELN/IWG-MRT criteria overall: A complete remission (CR) was seen in 8 patients (14.3%), a partial remission (PR) in 18 patients (32.1%), either a CR or PR in 18 patients (32.1%) when histologic remissions were unable to be documented due to lack of restaging bone marrow examination, no response in 11 patients (19.6%), and progressive disease in 1 patient (1.8%). Of the 12 patients receiving at least1 phlebotomy per month, 10 patients (83.3%) became phlebotomy independent with therapy. Of the 20 ET patients, 12 patients (60%) had platelet normalization (<400 x 109). MF: 19 patients were evaluated by IWG-ELN criteria: a PR was seen in 2 patients (10.5%), CI in 4 patients (21.1%), SD in 12 patients (63.2%), and PD in 1 patient (5.3%). Utilizing EUNMET critieria: 1 patient (5.3%) with a CR, 5 patients (26.3%) with a MR, 3 patients (15.8%) with MoR, 5 patients (26.3%) with MiR, and 5 patients (26.3%) with NR. Table 1. Peg INF2a Patient Responses RESPONSE Disease IWG-ELN response criteria: (Patient #, %) (Barosi, Blood 2013, Tefferi, Blood 2013) EUMET response criteria: (Patient #, %) (Barosi, Blood 2005) PV: N=36 CR: 3 pts (8.3%) PR: 14 pts (38.8%) CR/PR: 14 pts (38.8%) NR: 5 pts (13.8%) PD: 0 NA ET: N=20 CR: 5 pts (25%) PR: 4 pts (20%) CR/PR: 4 pts (20%) NR: 6 pts (30%) PD: 1 (5%) NA MF: N=19 IWG-ELN: PR: 2 pts (10.5%) CI: 4 pts (21.1%) SD: 12 pts (63.2%) PD: 1 pt (5.3%) EUNMET: CR: 1 pt (5.3%) MR: 5 pts (26.3%) MoR: 3 pts (15.8%) MiR: 5 pts (26.3%) NR: 5 pts (26.3%) NA: Not applicable Conclusions: Peg INF2a is active and well-tolerated when administered outside of the support of a clinical trial. Given the majority of patients had previously failed cytoreductive therapy these results substantiate prior reports of efficacy of Peg INF2a in MPNs. Disclosures Mesa: Pfizer: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; CTI Biopharma: Research Funding; Incyte Corporation: Research Funding; NS Pharma: Research Funding; Genentech: Research Funding.

Abstract Background: Hypomethylating agents (HMA) such as 5-Azacitidine (Aza) have overall responses rate of ~35-50% in acute myeloid Leukemia (AML) and higher risk myelodysplastic syndrome (MDS) patients (pts). However, eventually all pts develop resistance on therapy. To improve upfront response rates and to address HMA failure, we performed genome-scale RNAi screens targeting genes on chromosomes 5 and 7, recurrent cytogenetic abnormalities in AML/MDS. These screens identified Hedgehog pathway (Hh) genes as potentially targetable vulnerabilities with Aza. Combination experiments with smoothened (SMO) inhibitors (SMO is a central activating gene within the Hh pathway) showed pre-clinical synergy. These and additional published data support the Hh pathway as a targetable vulnerability in AML, and provide a rational for a trial. Methods: A phase I/Ib protocol of the oral SMO inhibitor LDE225 (Sonidegib) in combination with Aza in untreated and relapsed/refractory (rel/ref) AML, chronic myelomonocytic leukemia (CMML), MDS, or MDS/myeloproliferative neoplasm overlap pts. Objectives of the phase I part are to determine safety, toxicity and MTD and for the phase Ib part to assess the preliminary overall efficacy. Sonidegib was started at dose level (DL) 0 at 400mg oral daily continuously and Aza at the approved doses (75mg/m2 x 7 days or days 5-2-2) with dose adjustment per label. A classical 3+3 design was used and DLT (CTCAE v4.0) defined as > grade 3 CPK elevation or hepatic or non-hematologic adverse events (AEs) lasting > 7 days or any grade 4 event, except for hematologic toxicities. DLT was assessed after 42 days when steady-state concentrations of Sonidegib were reached. Pharmacokinetic assessments were not performed for this study. Results: Patients and Dose Levels : Between 5/22/2014 and the data cut-off date (7/20/2015), 36 pts were enrolled. Median age was 72 y (range 52-85 y) and 64% were male. Most AML pts (23 of 24) had intermediate or unfavorable cytogenetics and most MDS/CMML pts were in the int.- to high-/very high-risk group (IPSS-R). Six pts were treated at DL-0 of Sonidegib 400mg/day and one DLT of CPK elevation was observed. Another patient had grade 4 neutropenia (which at the time was included in the DLT definition, later removed). Due to overall tolerance of the combination at DL 0 and investigator assessment, despite only 1/6 pts having a formal DLT, DL -1 at Sonidegib 200mg was explored at which 0/3 pts (1 pt non-evaluable) had DLT and the phase Ib portion was opened at DL -1. To date a total of 24 AML (13 newly dx, 11 rel/ref), 11 MDS/CMML (5 newly dx, 6 rel/ref ) and 1 myelofibrosis pt have been enrolled. Safety and Tolerability: An initial safety and efficacy assessment for 25 of the 29 pts treated on the phase Ib (n=26) + the MTD cohort of 200 mg (n=3) and for who at least 2 cycles of treatment follow up was available, showed that all pts experienced at least one grade-3 or 4 hematologic AE with a lower rate in the untreated vs. treated cohort. Other, non-hematologic grade-3 and 4 AEs respectively were seen in 24 and 28% of patients-most commonly hyponatremia and fatigue, known AEs for this drug class. Treatment delays occurred in 28% of pts and Aza or Sonidegib dose reductions in 16%. 23 (79%) pts are alive and 6 have died (21%), with one death while pt was actively treated but was deemed unrelated; 11 pts remain on study, with the remainder showing disease progression (n=3) or taken-off study for other reasons (n=3 each for AEs and did not want further treatment; n=4 other). Efficacy : As of 7/20/15 with a median treatment duration of 2 cycles, 2/5 untreated MDS/CMML pts achieved CR/CRi; 1 HMA rel/ref AML had CR; 1 untreated AML pt each had PR and MLFS. 90% of pts have not progressed. Updated results will be presented at the ASH 2015 meeting; by then all 29 pts will have completed a minimum of 4-6 cycles on study and full efficacy and AE result on all pts will be reported. To date the OS at 6 mo is 77% (95% CI: 44-97%) with a median PFS of 4 mo (range: 2-NR). Many pts in the untreated cohorts have just enrolled. Conclusion: Hh pathway inhibition with the clinically well tolerated SMO inhibitor Sonidegib in combination with Aza in MDS and AML pts is well tolerated with mostly hematologic AEs as expected with early signs of clinical activity in untreated and HMA-failure pts. Full efficacy results of 29 pts and updated safety data will be reported for this first combination trial of a SMO inhibitor in combination with a HMA in MDS and AML pts. Disclosures Mesa: Gilead: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; Incyte Corporation: Research Funding; Genentech: Research Funding; Pfizer: Research Funding; Promedior: Research Funding; NS Pharma: Research Funding; CTI Biopharma: Research Funding. Al-Kali:Novartis: Research Funding.

Abstract Background: Donor cell chimerisms are tested at frequent intervals after allogeneic hematopoietic stem cell transplantation (alloHSCT). However, the predictive value of this testing in patients with myelofibrosis (MF) is not well-defined. In this study, our primary objective is to evaluate the correlation of day 30 and day 100 donor cell chimerism and overall survival (OS) in patients (pts) who undergo alloHSCT for MF. Methods: Charts were reviewed for pts who underwent alloHSCT for MF at Mayo Clinic in Arizona, Minnesota and Florida between January 2005 and December 2015. Patients who died within 30 days of alloHSCT were excluded. Chimerism studies were evaluated in the peripheral blood for CD3 and CD33 fractions at day +30 (D30) and day +100 (D100). Cut-off value of 100% and less than 100% was used because of limited variability below 100%. Standard statistical methods were used to compare continuous and categorical variables. The Kaplan-Meier method was used to provide survival curves. Results: Baseline characteristics: Sixty three consecutive patients who underwent alloHSCT for MF since January 2005 until December 2015, and had D30 and/or D100 chimerism studies available were included in the study. Of these, 24 (38%) were female. Median age at diagnosis was 56 years (range, 19 - 73 years) and median age at AHSCT was 58 years (range, 19 - 73 years). Dynamic International Prognostic Scoring System-Plus (DIPSS-Plus) risk category at the time of alloHSCT was high in 31 (49%), intermediate-2 in 30 (48%) and intermediate-1 in 2 (3%) pts. JAK2 V617F mutation status was available in 61 pts and was positive in 35 (57%) pts. Nineteen (30%) pts had been treated with a JAK2 inhibitor prior to alloHSCT. Fifty-two (83%) pts had at least grade-2 fibrosis in bone marrow at the time of HCT. Transplantation: Median time from diagnosis to AHSCT was 12.9 months (range, 2.3 - 248.2 months). Fifty-five (87%) received a reduced intensity conditioning (RIC) regimen while 8 (13%) received myeloablative conditioning regimen. Of these 55 pts, RIC regimens used were busulfan fludarabine based regimen in 15 (27%), fludarabine melphalan based regimen in 18 (33%) and fludarabine melphalan carmustine in 22 (40%) pts. Donor source was matched related in 30 (48 %), matched unrelated in 28 (44%), single-antigen mismatched related in 4 (6%) and mismatched unrelated in 1 (2%). Peripheral blood stem cells were used in all AHSCTs. Outcomes: Median follow-up was 24.4 months (range, 1.5 - 83.6 months). Amongst pts who had <100% donor chimerism at D30 in CD33 fraction, 2 had 90%, 1 had 80% and 2 had zero% donor chimerism. At D100, 1 pt had 95%, 1 had 90%, 1 had 60%, 2 had 5% and 1 had zero% donor chimerism. Eighteen out of 57 (32%) pts who had 100% donor chimerism in CD33 fraction at D30 had died at the time of analysis compared to 4 out of 5 (80%) patients with less than 100% (p=0.03). Eight out of 38 pts (21%) who had 100% donor chimerism in CD33 fraction at D100 died versus 3 out of 6 (50%) with less than 100% (p=0.12). There was no significant survival effect of CD3 chimerism (p values=0.68, 0.59). Of the 23 deaths that had occurred at the time of analysis, cause of death was disease progression or relapse in 8 (35%), graft versus host disease in 6 (26%), transplant related (sepsis / engraftment failure) in 5 (22%) and unrelated causes in 4 (17%). Survival analysis: As depicted in the Kaplan Meier curve (figure 1), median overall survival (OS) for pts with 100% donor chimerism in CD33 fraction at day 30 was not reached while for <100% donor chimerism was 16 months (p=0.04). Survival at 3 years for patients with 100% CD33 donor chimerism at D30 was 65% while it was 40% for pts with less than 100%. Also, survival at 3 years for patients with 100% CD33 donor chimerism at day 100 was 75% compared to 50% for patients with less than 100%. Conclusions: In our study, 100% donor chimerism in CD33 fraction is associated with improved survival after alloHSCT for MF compared to pts with less than 100%. Further understanding regarding the reason for this relationship is critical. Larger studies to replicate these results would be imperative to validate these findings. Disclosures Mesa: Incyte: Research Funding; Ariad: Consultancy; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Gilead: Research Funding; CTI Biopharma: Research Funding; Galena: Consultancy.