Citations

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 We have previously proposed the dysregulation of the D type cyclins by chromosome translocations to the IgH locus or by not fully characterized mechanisms in hyperdyploid patients as a unifying genetic event in the pathogenesis of Monoclonal Gammopathy of Uncertain Significance (MGUS) and multiple myeloma (MM). However, no experimental data are available to evaluate the direct consequences of cyclin Ds overexpression in plasma cells. Similarly, activating mutations of KRAS have been identified in 15% of MM patients, but never in MGUS, and have been proposed to contribute to the progression of MGUS to MM, but this hypothesis has never been experimentally validated. We evaluated the contribution of CyclinD1 and KRAS to the development and progression of monoclonal gammopathy (MG) that develops spontaneously in C57BL/6 mice. We aged a cohort of EuCCND1 mice, and lslKRASV12 mice crossed to three different CRE expressing mice: IgG1CRE, CD19CRE or Vk* CRE (KRAS/CRE). A cohort of Vk* MYC mice, Vk* MYC x EuCCND1 (MYC/CD1) and triple transgenic mice (CD1/KRAS/CRE) was also analyzed. Mice were bled every 10 weeks beginning at 30 weeks, and the presence of MG was evaluated by serum protein electrophoresis. The median Time To M-Spike (mTTS) detection was 97 weeks in C57Bl/6, 63w in EuCCND1, 54w in KRAS/CRE, 54w in Vk* MYC, 38w in CD1/KRAS/CRE and 36w in MYC/CD1 mice. This indicates that acceleration of the development of MG occurs in all these strain of mice. However, we noticed that the spontaneous MG in C57BL/6 wt, EuCCND1 or KRAS/CRE rarely progresses (as determined by detection of a M-spike >7 g/L), while in the other mouse strains it frequently progresses, with a mTTS >7 g/L around 65w. A clear progression of MGUS to MM was observed only in Vk* MYC mice, and was further accelerated in MYC/CD1 mice, which are characterized by extra-medullary disease and shorter overall survival. In conclusion, these data support our hypothesis that Cyclin Ds dysregulation in plasma cells is the initial transformation step leading to MGUS. Further oncogenic events, like activating mutations of KRAS are required to expand the monoclonal plasma cells. Among the oncogenes examined MYC provides the greatest acceleration of the MG in wildtype and EuCCND1 mice, and results in a disease with the malignant features of MM. Disclosures: No relevant conflicts of interest to declare.

Introduction Allogeneic hematopoietic stem cell transplant (HCT) patients are at risk for having a low Vitamin D (VD) level. VD level has been correlated with cancer incidence, pulmonary disease and infection. VD also has immunomodulatory properties and reports suggest that a low VD level increases the incidence of chronic GVHD and may impact mortality in HCT. HCT morbidity and mortality is attributed to infection, organ system toxicity, GVHD and recurrent disease. Identifying a correctable factor that would reduce the occurrence or severity of these complications would be beneficial. It is possible that VD may have significant effect on outcome after HCT due to its described properties. Normal VD level may infer better outcome for HCT patients by improving response in or preventing infection, protecting organ function, decreasing risk of relapse and/or decrease incidence or severity of GVHD. We hypothesize that there is a relationship between VD level and morbidity and mortality after HCT. We therefore studied VD levels pre- and post-HCT to determine if there was an impact of VD level on these outcomes. Patients and Methods Two hundred and fifty patients underwent myeloblative or non-myeloablative HCT between 3/12/2009 and 10/29/2012 at our institution. Baseline demographic data, disease characteristics, transplant variables and outcomes data were obtained from the transplant database. These data were supplemented by retrospective chart review for VD levels prior to transplant, at day 100 and 1 year post-HCT. Data were collected through day 100 for occurrence of infection and admissions to the ICU. Categories for VD level included normal (≥30 ng/ml) or abnormal (<30 ng/ml). Patient characteristics were compared using the Chi-square test or Wilcoxon rank sum test. The logrank test was used to compare the survival curves between groups, and the Cox proportional hazard model was used to measure the association between outcomes (mortality, relapse, acute or chronic GVHD) and VD level. Results Of the 250 patients undergoing HCT VD level was performed on 180 (72%) patients pre-HCT, 149 (60%) patients at day 100 post-HCT and 81 (32%) patients at 1 year post-HCT. The rate of acute or chronic GVHD was not significantly associated with VD level pre or post-HCT. Overall infection risk was not significant pre or post-HCT but when sorted by type of infection bacterial infection (p=0.01), radiologic evidence of pulmonary nodules/consolidation (p=0.03), and ICU admissions (p=0.0313) within the first 100 days post-transplant were significantly increased in patients who had a low VD level at day 100 post -HCT. Pre-HCT and 1 year post-HCT VD level did not impact mortality or relapse but there was a significant increase in one year mortality (p=0.02, HR = 5.99) and relapse (p = 0.03, HR=9.47) in patients who had a low VD level at day 100 post-HCT. Discussion This study shows that VD may play a significant role in bacterial infection, pulmonary infection, ICU admission, mortality and relapse after HCT. Those patients with a low VD level at day 100 post-HCT had significantly worse outcomes for relapse and mortality. Those patients with a low VD level at day 100 post-HCT had a higher incidence of lung infection, bacterial infection and admission to the ICU. In contrast to previous studies, we found no correlation between VD level and incidence of acute or chronic GVHD. This study is one of the largest reported and the first to our knowledge that reports decreased risk of certain types of infection (bacterial and lung), mortality and relapse in those with an adequate VD level receiving HCT. It is possible that supplementation of VD to keep levels ≥30 would reduce these complications of HCT. Future prospective study of VD is warranted. Finding a low cost and easy to administer therapy (such as VD replacement) that would reduce morbidity, mortality and relapse in the HCT population is needed. Disclosures: Reeder: Celgene: Research Funding; Novartis: Research Funding; Millenium: Research Funding.

Abstract Abstract 606 Multiple myeloma is a complex malignancy with multiple underlying genetic events. Our group has spent considerable effort over the last 15 years to elucidate the genetic underpinnings of myeloma. Most recently, we used array-based comparative genomic hybridization (aCGH) as a discovery tool in 62 myeloma patients and 46 myeloma cell lines. In that preliminary screen using the Agilent 44B aCGH platform (∼70kb resolution) we identified a diverse array of abnormalities, which resulted in constitutive activation of the NF-kB pathways. That initial analysis concentrated on the 43 genes we identified as potential targets of the 13 homozygous deletion events detected in the patient samples. A pathway analysis of these genes revealed a single pathway involving TRAF3, TRAF2, BIRC2, BIRC3, and CYLD. This first analysis focused exclusively on abnormalities present in the patient samples as we worried some abnormalities identified exclusively in the cell lines might not be relevant to the pathogenesis of myeloma in patients. However, several abnormalities were equally or more frequent overall but occurred exclusively in cell lines including CDKN2C (14 samples), CDKN1B (4 samples), KDM6A/UTX (4 samples), RB1 (3 samples), TP53 (3 samples). Given the fact that KDM6A/UTX deletions were as frequent as many of the best-described tumor suppressors it seemed like a good candidate but in the absence of patient events or a known function at the time it was not prioritized for further study. Recently, as part of the Multiple Myeloma Research Consortium (MMRC) Genomics Initiative, we have completed the analysis of a cohort of 250 myeloma patient samples by aCGH using the Agilent 244A aCGH platform (∼15kb resolution) and gene expression profiling using the Affymetrix U133Plus2.0 genechip. In this cohort with a significantly improved aCGH platform we identified 17 genes that are recurrently inactivated by homozygous deletions including DIAPH2 (15 samples), CDKN2C (14 samples), TRAF3 (11 samples), CYLD (8 samples), BIRC2/3 (7 samples), KDM6A/UTX (6 samples), and RB1 (5 samples). Based on the significant improvement in resolution and data quality achieved with the Agilent 244A aCGH platform we rescreen all of the cell lines on this improved platform. This significantly changed the frequency of several homozygous deletions in this population with the most frequently targeted genes now being CDKN2C (20 samples), KDM6A/UTX (13 samples), DIAPH2 (7 samples), RB1 (4 samples), TP53 (4 samples), CDKN1B (4 samples), and TRAF3 (4 samples). Moreover, as part of the genomic characterization of a spontaneous myeloma mouse model that we have developed, Vk*-Myc, we have identified recurrent (∼50%) homozygous deletions of Kdm6a/Utx. Therefore, one of the genes most commonly targeted by a homozygous deletion in human and mouse myeloma is KDM6A/UTX. In late 2007 after we had identified the first patients with KDM6A/UTX deletions it was shown that UTX is a functional histone demethylase that removes methyl groups from histone H3 lysine 27 (H3K27me). Given the high incidence of deletions and the fact that MMSET, the overexpressed target gene of t(4;14) in myeloma, is predicted to methylate H3K27, H3K36, and/or H4K20 by evolutionary conservation we developed the hypothesis that myeloma is characterized by abnormalities that result in excessive H3K27me (typically a repressive chromatin mark). Given the extensive whole genome sequencing occurring in the MMRC genomics initiative we elected to focus our resequencing efforts on the cell lines exclusively. These studies identified an additional 4 samples with LOH and an inactivating mutation bringing the total percentage of inactivated cell lines to 33%. Clearly, in the expanded patient and cell line cohorts the inactivation of KDM6A/UTX is not independent of MMSET overexpression suggesting they may act independently or synergistically. We are currently attempting to identify the genes controlled by KDM6A/UTX inactivation to better understand the functional consequences of this highly recurrent event. However, in the mouse model unlike the patient or cell lines, the gene expression profiling has identified a gene expression signature that differentiates UTX inactivated and functional samples suggesting an oncogenic function of inactivation. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Patients with CLL have a variable clinical course. Current novel prognostic indicators (ZAP-70, CD38, IgVH gene mutation status, FISH) are able to identify early-stage CLL patients at high risk of rapid disease progression. These prognostic factors focus on characteristics of the malignant B cell clone and are not currently changeable factors. Identification of modifiable characteristics of the host unrelated to the leukemic B-cell but that relate to CLL-specific survival may provide opportunities for therapeutic intervention. Since the immune system is likely to modulate disease progression in CLL patients, we evaluated critical features of that system in relation to the size of the circulating clonal B-cell population in a CLL cohort. Methods: 186 consecutive patients with CLL who were evaluated at Mayo Clinic within 2 months of diagnosis between 2000 and 2002 were identified. The primary end-point of the study was to assess if host immunity affected time to treatment (TTT). Baseline flow cytometry analysis was available for 166 patients (88%) and was used to calculate the absolute number of T-cell and natural kill (NK)-cells present at diagnosis. The size of the T-cell/NK-cell compartment relative to the size of the malignant monoclonal B-cell (MBC) compartment was then evaluated by calculating the NK:MBC ratio and T:MBC ratio. Relationships with other prognostic parameters and with TTT were evaluated. Results: Patients exhibited substantial variation in the absolute number of T-cells and NK cells as well as T:MBC and NK:MBC ratios at the time of diagnosis. Higher T:MBC and NK:MBC ratios were observed among patients with early Rai stage and mutated IgVH genes (all P≤0.0002). As continuous variables, both the T:MBC ratio (p value=0.03) and NK:MBC ratio (p value=0.02) were associated with TTT. Since they correlated with TTT as continuous variables, thresholds to classify MBC, T:MBC ratio, and NK:MBC were identified using the method of Contal and O’Quigly. On multivariate Cox modeling including stage, CD38, absolute MBC count, T:MB ratio, and NK:MB ratio, the independent predictors of TTT were disease stage, T:MB ratio, and NK:MB ratio (Table 1). Conclusion: Measurable characteristics of the host immune system appear to relate to the rate of disease progression in patients with newly diagnosed CLL. These characteristics can be modified and continued evaluation of immunomodulatory drugs, vaccination strategies, and cellular therapies to delay/prevent disease progression are warranted. Additional studies exploring how interactions between the host immune system and the leukemic clone influence clinical outcomes are needed.

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.