The MLL-partial tandem duplication (PTD) associates with high-risk cytogenetically normal acute myeloid leukemia (AML). Concurrent presence of FLT3-internal tandem duplication (ITD) is observed in 25% of patients with MLL-PTD AML. However, mice expressing either Mll-PTD or Flt3-ITD do not develop AML, suggesting that 2 mutations are necessary for the AML phenotype. Thus, we generated a mouse expressing both Mll-PTD and IntroductionAcute myeloid leukemia (AML) is a genetically heterogeneous disease. Recurrent cytogenetic and molecular gene aberrations have been used to classify AML patients into distinct subsets that differ in biologic, clinical, and prognostic characteristics. The MLL gene, located at chromosome band 11q23, encodes for a protein involved in epigenetic regulation of gene expression. 1 In AML, this gene is frequently involved in chromosome translocations at 11q23 and, at the molecular level, is fused with one of more than 50 different partners. 2 We first reported an internal duplication of MLL, an in-frame repeat producing an elongated protein retaining all functional domains, in cytogenetically normal (CN)-AML. 3 Approximately 5% to 7% of CN-AML patients have a MLL-partial tandem duplication (PTD) mutation, which is associated with unfavorable prognosis, 3-5 but if and how it contributes to myeloid leukemogenesis remain to be elucidated. Approximately 25% of CN-AML patients with the MLL-PTD had constitutive activation of FLT3, a tyrosine kinase receptor regulating proliferation and survival of hematopoietic cells, via an internal tandem duplication (FLT3-ITD), and have a very poor prognosis. 6 This suggests that both MLL-PTD and FLT3-ITD mutations are necessary for an AML phenotype, as supported by the broadly accepted 2-hit model. 7 Indeed, a Mll-PTD mouse, created by knocking in exons 5 to 11 in-frame and driven off of the endogenous Mll promoter, did not develop AML. 8 8,9 This model, which develops AML, is the first that requires the MLL-PTD. In this model, the 2 mutated genes are regulated by their respective endogenous promoters to recapitulate the Mll PTD/WT :Flt3 ITD/WT AML found in humans. This differs from some other doublemutant mouse models of human AML that carry one mutation driven by the endogenous promoter and the other mutation driven by transgenes, 10 or introduced via viral transduction, 11 or 2 mutations driven off 2 endogenous promoters but requiring BM transplantation. 12 Methods Mouse strainsThe Mll PTD/WT , Flt3 ITD/WT , and Flt3 ITD/ITD mice were generated and genotyped as previously described. 8,9 Male Flt3 ITD/WT Balb/c mice were backcrossed onto the C57Bl/6J strain to purity and then bred with Mll PTD/WT mice to generate Mll PTD/WT :Flt3 ITD/WT double knock-in offspring. Genotyping was performed as previously described. 8,9 All animals studied were compared within litters and/or age-and sex-matched. All experiments were conducted under an approved The Ohio State University Institutional Submitted March 2, 2012; accepted May 17, 2012. Prepublished online as Blood Firs...

150 Background. The Mll PTD and Flt3 ITD are co-present in a subset of adult patients (pts) with cytogenetically normal (CN) acute myeloid leukemia (AML) and poor clinical outcomes. While the single mutant knock-in (KI) mice (Mll PTD or Flt3 ITD) exhibit enhanced myeloid progenitor self-renewal or reduced apoptosis, respectively, neither model develops acute leukemia. We hypothesized that with mutant expression driven via the endogenous promoters, the two mutations may cooperate in vivo to induce an acute leukemia that mimics the human counterpart. Methods. Single mutant heterozygous KI mice were crossed to produce the PTD/ITD double KI. PTD/ITD mice were bred with the homozygous Flt3 ITD to generate the PTD/ITD2 genotype. An AML diagnosis was based on blood differentials, immunophenotyping, tissue pathology and transplantability. Real time RT-PCR and 5'-methylcytosine LC/MS assays measured gene expression and global DNA methylation levels, respectively. Results. PTD/ITD and PTD/ITD2 mice developed transplantable, CN-AML/undifferentiated leukemia exhibiting expansion of monocytic/myelomonocytic Gr1±/Mac1+ and/or immature CD3−/CD19−/CD117+/Mac1−/B220lo cell populations, splenomegaly, leukocytosis, anemia and thrombocytopenia. PTD/ITD mice had significantly reduced lifespans compared to mice with single mutant PTD and ITD KIs and wild-type (Wt) controls (medians: 50, 99, 88, 94 weeks, respectively; P<0.001) (Figure 1). Increased ITD gene dosage (PTD/ITD2) was associated with an even shorter lifespan (median: 16 weeks) (Figure 1). This is consistent with the poor prognosis conferred by high FLT3 ITD-to-FLT3 wild-type (WT) gene ratio in diagnostic leukemia blasts from AML pts treated with intensive chemotherapy. As in human MLL PTD AML, the Mll WT allele was downregulated in the murine model. Mll WT expression was >2-fold lower in bone marrow (BM) of leukemic PTD/ITD mice compared to age-matched single mutant KIs or Wt controls. HoxA9 and its cofactor Meis1 were upregulated 15- and 5-fold, respectively, in PTD/ITD mice with leukemia versus Wt BM. Yet, compared to Wt BM, single PTD KI exhibited increased HoxA9 (∼6-fold) but not Meis1, implicating an expression threshold for HoxA9 and a crucial role for Meis1 for the development of acute leukemia in the double KI. Consistent with Flt3 being a downstream transcriptional target of Meis1, total Flt3 mRNA (WT and ITD) levels increased 3-fold in the leukemic PTD/ITD mice relative to either single mutant KIs or Wt controls. Furthermore, one consequence of constitutive Flt3 ITD kinase activity is the upregulation of the anti-apoptotic kinase, Pim1, in human AML. Compared to Wt BM, a 2-fold increase in Pim-1 expression was observed in single ITD KI and a 6-fold increase was observed in leukemic PTD/ITD BM, while expression was unchanged in the single PTD KI BM. Finally, MLL PTD presence in human AML associates with increased global DNA methylation and silencing of tumor suppressor genes. We observed 3-fold higher transcript levels of a de novo methyltransferase, DNA methyltransferase 3b (DNMT3b), increased global DNA methylation and ≥2-fold decrease in the expression of tumor suppressors Id4, Shp1 and Cdkn1b in BM of leukemia PTD/ITD mice compared to age-matched single mutant KIs and Wt controls. Conclusion. The Flt3 ITD and Mll PTD, expressed via their endogenous promoters, cooperate in vivo to give rise to AML and acute undifferentiated leukemia. Elevations of Meis1 and DNMT3b solely in PTD/ITD animals appear to be critical points of dysregulation leading to development of acute leukemia. This novel murine model phenotypically, molecularly, and epigenetically mimics the human AML counterpart, thus making it highly relevant for examining critical pathways in acute myeloid leukemogenesis, investigating leukemia stem/initiating cell biology and microenvironment contributions, and testing novel targeting therapeutics. Disclosures: No relevant conflicts of interest to declare.

Despite cancer being the leading cause of death across most racial/ethnic groups, Hispanic women have the second highest mortality rate attributed to diabetes (4.7%) according to the Centers for Disease Control and Prevention (CDC). While cancer and diabetes are two distinct diseases, previous studies have demonstrated that diabetic women have a poor chance of breast cancer survival when compared to nondiabetic women. Well-known key drivers of hyperinsulinemia and insulin resistance, such as insulin and AMPK, are also those involved in breast cancer. This link could possibly contribute to the increased mitogenic effects and risk for aggressive breast cancers in Hispanic women. Based on these findings, metformin, a drug standardly used to treat and prevent hyperglycemia, may be a possible alternative (other than tamoxifen) for breast cancer prevention. Eat, Move, Live (EML), a 5-week community-based program, focuses on targeting possible treatments of chronic diseases and risk reduction through attitude and lifestyle modifications. Exercise, nutritional and health awareness classes were implemented to change participants' perspectives regarding chronic diseases and their susceptibility to other morbidities. Questionnaires were given to the participants at baseline and at two follow-ups (5 weeks and 12 weeks) to assess any changes in their attitudes, behaviors, nutrition, lifestyle and beliefs around taking medication for preventative treatments. A total of 56 participants' pretreatment responses were collected via a five-point Likert scale (1-strongly disagree, 5-strongly agree). Demographic data showed that 69% of the respondents were Hispanic women, of whom 46% completed an education level of high school or less. A majority of the responses averaged a “neutral” response to taking medication for management and prevention of diabetes. We infer that their inability to select a stance in their responses may be associated with the lack of knowledge that the community has regarding chronic diseases and risk-prevention methods. Therefore, we anticipate that availability of proper education tools and resources is essential to potentially prevent future morbidities and mortalities. Ultimately, we aim to establish a pilot study that emphasizes the necessity and importance of interventional programs, like EML, to enhance chemoprevention using metformin and improve health outcomes in high-risk breast cancer populations. Citation Format: Mayra Serrano, Angelica Sanchez, Christine Thai, Katty Nerio, Cristal Resto, Marisela Garcia, Tanya A. Chavez, Laura L. Kruper, Veronica C. Jones, Lisa D. Yee, Alan Nuñez, Ellen J. Rippberger, Angela K. Wong, Noé R. Chávez, Karen Herold, Chidimma M.K. Kalu, Jackelyn A. Alva-Ornelas, Jerneja Tomsic, Krista M. Round, Regina Agulto, Margarita Robles, Ombeni M. Idassi, Kendall J. Kennedy, Christopher Sistrunk, Victoria L. Seewaldt. Receptiveness of metformin as a breast cancer prevention drug within the Hispanic community [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr B119.

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Purpose: To highlight the importance of building a high-risk breast cancer clinic for women who do not have a BRCA 1, BRCA 2 or other highly penetrant cancer susceptibility mutation. Background: Breast cancer is the most common cancer in women and the second most prevalent cause of cancer death of women in the United States; the lifetime risk for breast cancer in women is approximately 12%. Women may be at increased risk for breast cancer for many reasons including family history, genetic alterations, age, reproductive status and menstrual history. Most women who are at increased risk of developing breast cancer do not have a BRCA 1, BRCA 2 or other mutation. The majority of breast cancer diagnoses are due to acquired somatic mutations; only 5 to 10% of breast cancer diagnoses are attributable to highly penetrant Mendelian cancer susceptibility genes. White women with Ashkenazi Jewish ancestry tend to have a higher incidence of BRCA 1 and 2 mutations; traditionally, most research efforts about highly penetrant genes have been focused on this group rather than other racial and ethnic groups. However, there is a great need to study breast cancer risk-reduction strategies in racial and ethnic minorities in the United States, particularly because most breast cancers are not caused by BRCA 1 and 2 mutations. City of Hope is located approximately 21 miles northeast of Los Angeles and operates 13 clinical practice locations including Los Angeles, Orange, Riverside, San Bernardino and Ventura counties. These five counties are home to the majority of California's multicultural and ethnic residents where San Bernardino County has the highest percentage of Hispanics (49.9%) and blacks (8.3%), Ventura County has the highest percentage of whites (48.1%), and Orange County has the highest concentration of Asians (18.2%). It has been established in the literature that the greatest benefit from breast cancer prevention strategies comes from treating women who are at high risk of the disease. While it is important to build a high-risk breast cancer clinic for women with genetic mutations, it is equally important to build a high-risk breast clinic for women who are at increased risk of breast cancer but do not have a mutation, particularly because most breast cancer is diagnosed in this population. In addition, it is crucial to educate high-risk patients that although they may have tested negative for a genetic mutation if they have a family history of breast cancer, they warrant close clinical surveillance. Methods: We are proposing a retrospective, descriptive study of data that will be collected as part of a high-risk breast cancer program implemented by City of Hope. Results/Conclusions: We expect to discuss the findings related to serving women of all races and ethnicities who do not have a mutation in a highly penetrant gene mutation. Citation Format: Karen Herold, Lisa D. Yee, Chidimma M. Kalu, Laura L. Kruper, Veronica C. Jones, Amy C. Polverini, Sharon Clancy, Tanya A. Chavez, Jackelyn A. Alva-Ornelas, Noe R Chavez, Ellen J. Rippberger, Jerneja Tomsic, Christopher Sistrunk, Ombeni Idassi, Daniel B. Schmolze, Courtney Vito, Alan Nunez, Angela K. Wong, Krista M. Round, Christine Thai, Angelica Sanchez, Margarita Robles, Kendall Kennedy, Terry Hyslop, Victoria L. Seewaldt. Architecture of increased breast cancer risk [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr B109.