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Acute myeloid leukemia (AML) is a conglomerate of hematologic malignancies characterized by recurrent genetic and/or chromosomal aberrations. Recent development of targeted agents has bolstered our armamentarium of therapeutic options and improved outcomes for many patients. Acquiring deeper mechanistic understanding of myeloid leukemogenesis will provide a basis for development of even more therapeutic strategies and further improve patient outcomes. Our clinical data have revealed that overexpression of HNRNPK is a recurrent abnormality that occurs in upwards of 20% of AML cases at both the RNA and protein levels. Using bone marrow samples from a similar proportion of patients, we have recently discovered a supernumerary marker chromosome containing an extra copy of the HNRNPK locus that is not detectable with routine cytogenetic testing. We have further associated high hnRNP K protein levels with decreased overall survival in de novo AML, emphasizing the need to understand the role of hnRNP K in myeloid malignancy. To directly evaluate the oncogenic capacity of hnRNP K, we have overexpressed hnRNP K in murine fetal liver cells (FLCs). Using CyTOF and colony formation assays, we demonstrated that hnRNP K-overexpressing FLCs have altered differentiation potential and self-renewal capacity compared to empty vector controls in vitro. These findings are recapitulated in vivo, as murine recipients of hnRNP K-overexpressing FLCs develop myeloid lineage disease, often manifesting as fatal megakaryocytic leukemia. To elucidate a mechanism by which hnRNP K causes myeloid disease, we performed hnRNP K immunoprecipitation followed by mass spectrometry in an AML cell line and identified that hnRNP K preferentially interacts with translational machinery, ribosomal subunits, and proteins involved in RNA processing. In conjunction with data from our hnRNP K overexpression models that indicate overexpression of hnRNP K occurs primarily in the cytoplasm, we then performed hnRNP K-RNA immunoprecipitation followed by sequencing (RIP-Seq). We determined that hnRNP K interacts with the transcript of RUNX1-a master regulator of hematopoiesis and a critical player in a myriad of leukemias-including megakaryocytic leukemias like those observed in our mouse models. Using biochemical assays, we have demonstrated that hnRNP K directly binds to consensus sequences in the RUNX1 transcript, and ultimately alters RUNX1 translation. Indeed, mice exhibiting hnRNP K overexpression have increased protein levels of Runx1 in hematopoietic tissues. Our data demonstrate that hnRNP K overexpression drives myeloid malignancy. Currently, we are screening compounds that will disrupt the interaction between hnRNP K and RUNX1 in our efforts to further understand myeloid biology and ultimately improve outcomes for patients with these diseases. Disclosures No relevant conflicts of interest to declare.

INTRODUCTION The TET2 (Ten‐Eleven Translocation 2) gene, located at chromosome 4q24.1, belongs to TET family of proteins that possesses the capacity of catalyzing the conversion of 5‐methylcytosine into 5‐hydroxymethylcytosine. It is considered to be a putative tumor suppressor gene during cancer initiation and development. TET2 mutations are extensively studied and reported in a variety of human hematological malignancies including acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), suggesting a crucial role of TET2 in the pathogenesis of blood cancers. The landscape of rare TET2 variants which may be of potential clinical relevance is not fully described. The landscape of TET2 variants from a large cohort of MDS and AML patients was explored. METHODS We analyzed data from bone marrow samples of 2634 patients with AML or MDS who presented at MD Anderson between the years 2012-2016. Seven hundred seventy seven patients were found to have TET2 variants that were not classifiable as known mutations. Two hundred sixty-three patients were diagnosed with MDS, 144 with secondary AML transformed from MDS, and 370 with AML without prior history of MDS. The coding regions of TET2 gene was analyzed by next-generation sequencing in the molecular diagnostics laboratory. Non-mutation variants were classified into 2 groups: 1) those reported as germline polymorphisms (GP) in population studies, literature or matched tumor-normal analysis on patients at MDACC; and 2) variants for which a germline versus somatic origin could not be determined unequivocally (variants of uncertain origin, VUO). Very common GP variants (defined as those with a population frequency of over 20% in laboratory sample cohort) were not evaluated. Variants' predicted frequency in the population according to gnomAD Exomes 2.0.2, and classification according to American College of Medical Genetics and Genomics (ACMG) guidelines for interpretation of sequence variants, were assessed using the VarSome platform by Saphetor. RESULTS Two-hundred and twenty-eight unique variants were identified. The amino acid substitutions from missense variants were widely distributed throughout TET2. Fifty-four unique variants were classified as GP and several of these recurrent variants were found to be present in our population at a significantly higher frequency (p CONCLUSIONS The landscape of rare TET2 variants in a large group of MDS and AML patients was frequent, diverse, and included both GP and VUO. GP variants were more likely benign by ACMG classification and found in both MDS and AML patients. A large number of singleton VUO were found among MDS patients, and many were predicted to be pathogenic or had uncertain significance. VUO's also contained many fs and nonsense variants. These result support the idea that rare pathogenic variants in TET2 are currently underrecognized as contributory, although they are likely to help drive leukemogenesis. Greater understanding of the importance of individual TET2 variants and additional classification metrics are needed. Disclosures DiNardo: Karyopharm: Honoraria; Abbvie: Honoraria; Agios: Consultancy; Medimmune: Honoraria; Celgene: Honoraria; Bayer: Honoraria. Daver:Karyopharm: Research Funding; Incyte: Consultancy; Novartis: Consultancy; ImmunoGen: Consultancy; Sunesis: Consultancy; Pfizer: Consultancy; Daiichi-Sankyo: Research Funding; Kiromic: Research Funding; Alexion: Consultancy; Otsuka: Consultancy; Sunesis: Research Funding; Incyte: Research Funding; ARIAD: Research Funding; BMS: Research Funding; Karyopharm: Consultancy; Novartis: Research Funding; Pfizer: Research Funding. Kadia:Celgene: Research Funding; Takeda: Consultancy; BMS: Research Funding; Abbvie: Consultancy; Novartis: Consultancy; Novartis: Consultancy; Amgen: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Abbvie: Consultancy; Pfizer: Consultancy, Research Funding; Takeda: Consultancy; Amgen: Consultancy, Research Funding; BMS: Research Funding; Pfizer: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Celgene: Research Funding. Konopleva:Stemline Therapeutics: Research Funding; abbvie: Research Funding; cellectis: Research Funding; Immunogen: Research Funding. Andreeff:Amgen: Consultancy, Research Funding; Astra Zeneca: Research Funding; Jazz Pharma: Consultancy; Oncolyze: Equity Ownership; Aptose: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Oncoceutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; SentiBio: Equity Ownership; United Therapeutics: Patents & Royalties: GD2 inhibition in breast cancer ; Reata: Equity Ownership; Celgene: Consultancy; Eutropics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy, Patents & Royalties: MDM2 inhibitor activity patent, Research Funding.

hnRNP K is an RNA binding protein that controls a multitude of cellular processes and is aberrantly expressed in cancers. We have previously shown that hnRNP K functions as a haploinsufficient tumor suppressor in AML patients with 9q deletions. However, overexpression of hnRNP K is the more commonly observed clinical phenomenon. We have recently discovered that hnRNP K overexpression in patients with diffuse large B-cell lymphoma correlates with dismal outcomes and directly resulted in the development of lymphomas in transgenic mice. To understand the mechanistic basis for the oncogenicity of hnRNP K overexpression and to identify therapeutic vulnerabilities, we performed RNA-sequencing, RNA immunoprecipitation following by sequencing (RIP-Seq), mass spectrometry, and polysome assays. We observed that hnRNP K regulates both global transcription and translational processes within the cell via modulation of 7SK and translation initiation proteins (such as the eIFs and PABP), respectively. Consequently, we hypothesized that aberrant hnRNP K expression primarily perturbs oncogenes with short half-lives. Mechanistically, we identified that hnRNP K binds to the RNA and regulates the expression of a plethora of critical oncogenes and tumor suppressors involved in hematologic malignancies such as c-Myc, RUNX1, and Cyclin D1. As proof of concept for clinical applications, we have demonstrated that hnRNP K-driven c-Myc overexpression renders tumors susceptible to bromodomain inhibition. Given that hnRNP K directs global transcription and translation, it is likely that hnRNP K overexpressing tumors will also be sensitive to transcriptional and translational inhibitors such as CDK9 inhibitors and omacetaxine mepesuccinate, respectively. However, since hnRNP K also regulates a plethora of additional cellular processes that extend far beyond mRNA and protein synthesis, there is a need to develop hnRNP K-specific inhibitors that will only target these activities. Thus, we have recently begun to identify small molecule compounds that can directly inhibit hnRNP K-RNA binding function on specific targets using an in vitro fluorescent binding assay. Using this assay, we are currently screening a library of 70,000 small molecule compounds to identify agents that can prevent hnRNP K-RNA interactions. In summary, we have established that hnRNP K is a bona fide oncogene that drives lymphomagenesis. Global analyses have revealed therapeutic vulnerabilities of hnRNP K overexpressing tumors. Furthermore, using our in vitro RNA binding assays, we anticipate identification of novel hnRNP K-specific inhibitors. Disclosures No relevant conflicts of interest to declare.

Acute myeloid leukemia (AML) is a disease largely defined by recurrent genetic and chromosomal abnormalities. As such, The Cancer Genome Atlas' recent detailed examination of the most common genetic abnormalities that drive AML uncovered relatively few novel alterations. However, within this list of recurrently mutated genes was heterogeneous nuclear ribonucleoprotein K (HNRNPK). While previously unknown to impact AML, we recently identified HNRNPK as a haploinsufficient tumor suppressor at the 9q21.32 locus. In contrast to its tumor suppressive roles, hnRNP K is most customarily overexpressed, rather than underexpressed, in several solid tumors. In this study, we show through FISH analyses, RNA expression profiling, and reverse phase protein array analyses that the HNRNPK gene is amplified with corresponding mRNA and protein overexpression in a sizeable cohort of patients with AML that do not carry a 9q.21.32 deletion. Together, this indicates that hnRNP K may be an uncharacterized oncogene in this context. Increased hnRNP K correlated with decreased event-free and overall survival, increased WBC, and increased bone marrow and peripheral blood blast percentage. High hnRNP K levels also correlated with elevated expression of histone modifiers (e.g., ASH2L and TRIM24), regulators of ribogenesis (e.g., nucleolin and EBP1), and potent oncogenes, such as c-Myc. Together, these observations indicate that increased hnRNP K expression significantly alters the landscape of myeloid biology and may thus contribute to the etiology of AML. To directly interrogate this possibility in vivo, we generated a Vav-Cre;HnrnpkTg mouse model. In addition to significant differences in hnRNP K expression compared to Vav-Cre mice, Vav-Cre;HnrnpkTg mice exhibited reduced survival, development of transplantable myeloid malignancies, and enhanced HSPC proliferation and differentiation potential. Reflecting data from our patients, Vav-Cre;HnrnpkTg mice also exhibited elevated expression of critical oncogenic pathways such as c-Myc. Currently, we are examining pharmacologic methods to abrogate the effects of aberrant hnRNP K expression on various activated pathways. Transplant models using diseased bone marrow from Vav-Cre;HnrnpkTg mice are being utilized to evaluate the efficacy of specific pathway inhibitors (i.e., bromodomain inhibitors or bortezomib) in prolonging survival and decreasing leukemic burden. These studies will provide the rationale for potential clinical trails that employ these agents for patients with hnRNP K-overexpressing AML. Disclosures No relevant conflicts of interest to declare.

Approximately 30% of patients with acute myeloid leukemia (AML) harbor activating mutations in the fms-like tyrosine kinase receptor 3 (FLT3). Such mutations are associated with increased propensity to relapse and dramatically decreased survival. FLT3 tyrosine kinase inhibitors (TKI), such as quizartinib, have shown modest clinical effects as single agents, and resistance remains a significant clinical problem. In addition to constitutive activity of the FLT3 receptor, AML cells with an internal tandem duplication of FLT3 (FLT3-ITD) exhibit elevated levels of reactive oxygen species (ROS). Antioxidants such as heme-oxygenase 1 (HO-1) are often upregulated in conjunction with increased ROS levels. In addition to its role as an antioxidant, HO-1 also has known proliferative and anti-apoptotic functions in some cell types. A study in non-small cell lung carcinoma recently suggested that HO-1 inhibits the Notch pathway through binding the Notch receptor. As Notch signaling exerts pro-apoptotic effects in AML, targeting HO-1 may induce Notch signaling, representing a potential therapeutic approach. Our data show that HO-1 is particularly elevated in FLT3-ITD expressing AML cells. Interestingly, HO-1 protein was found to be further elevated in AML cells with acquired resistance to FLT3-directed TKI compared to TKI-sensitive cells. Importantly, knockdown of HO-1, or inhibition of HO-1 catalytic activity with zinc protoporphyrin (ZnPP), leads to decreased survival and proliferation, demonstrating a critical pro-survival role of HO-1. We have determined that expression of HO-1 is under the control of NRF2, a transcriptional regulator of the antioxidant response, in FLT3-ITD positive AML cells. Inhibition of NRF2 with brusatol resulted in increased sensitivity to quizartinib in TKI-sensitive cell lines. Further, brusatol restored sensitivity to low nanomolar concentrations of quizartinib in TKI-resistant cells. Together, our work shows that combined inhibition of FLT3 and NRF2 using quizartinib and brusatol, respectively, exhibits synergy in the context of FLT3-ITD AML. Given the reported interaction between HO-1 and Notch, we sought to determine whether this interaction occurs in AML. Using the TCGA AML database, we found significant co-occurrence of HMOX1 (HO-1) and NOTCH2 mRNA expression in 200 patient samples. In vitro immunoprecipitation of the Notch2 receptor revealed that HO-1 directly interacts with Notch2 in FLT3-ITD positive AML cells. Importantly, brusatol treatment resulted in activation of the Notch pathway as demonstrated by cleavage of the Notch receptor and increased transcript levels of HES1, a canonical downstream target of Notch signaling. Given that HO-1 interacts with Notch2 and is under NRF2 control, we propose that decreasing HO-1 levels with brusatol treatment will modulate the Notch pathway such that its anti-leukemic effects can be exerted. In conclusion, inhibition of HO-1, directly or through NRF2 inhibition, demonstrates synergistic effects with FLT3 inhibition in both TKI-sensitive and -resistant AML. Furthermore, NRF2 inhibition induces Notch activation, providing a potential mechanism for this synergistic combination. Our data suggest that antioxidant modulation is a potential therapeutic approach for FLT3-ITD positive AML. Disclosures No relevant conflicts of interest to declare.