Abstract 1694: Over expression of MN1 induces therapy resistance in a murine model of AML

Abstract

Abstract Acute myeloid leukemia (AML) is an accumulation of immature myeloid precursors that leads to marrow failure and death. This disease affects approximately 12,000 people per year in the United States, causing 9,000 deaths. Despite decades of active research the overall 5 year survival remains a dismal 30-40%. The backbone of initial therapy for the last 30 years is combination chemotherapy containing cytarabine (Ara-C) and an anthracycline. Resistance is a major problem and most patients diagnosed with AML will ultimately die from resistant disease. The MN1 gene encodes a transcription co-factor that has been found over-expressed in multiple AML patient samples. There are several reports that over-expression of MN1 confers a worse prognosis in AML. High MN1 expressers are less likely to achieve a remission and have lower 3 year survival rates. Additionally, over expression of MN1 in murine bone marrow leads to AML in transplanted recipients and predicts for resistance to ATRA in elderly AML patients. However, the effect of MN1 over expression on response to standard chemotherapy is currently unknown. To answer this question we used a murine model of AML driven by MLL-ENL. Blasts were infected with retroviral vectors that contained MN1 and a GFP reporter. Partially infected blast populations were then exposed to various concentrations of either Ara-C or doxorubicin and the ratio of GFP positive and negative cells was compared to untreated controls. When blasts were exposed to 150 nM Ara-C the GFP+ percentage went from 21.10 (+/- 0.5302) in the control samples to 35.68 (+/-1.230) in the treated samples. This result was even more profound when cells were treated with 15 ng/ml doxorubicin where the percentage went from 21.10 (+/- 0.5302) to 80.27 (+/-1.615). Bother results were highly statistically significant by two tailed student's t test with p values of 0.004 and < 0.0001 respectively. Consistent with these data purified blast populations over expressing MN1 showed resistance to both doxorubicin and Ara-C. This effect was the result of reduced induction of apoptosis as MN1 over expressing blasts showed decreased levels of annexin V staining after exposure to vary amounts of Ara-C or doxorubicin. In order to determine if MN1 conferred resistance to Ara-C and doxorubicin in vivo we injected sublethally irradiated recipients with a partially infected population of blasts. Eight days after injection of blasts animals were treated with 100 mg/kg Ara-C plus 3 mg/kg doxorubicin daily for 5 days or observed. Animals treated with Ara-C plus doxorubicin had 90.58% (+/-0.6638) GFP+ blasts compared to 55.38% (+/-5.245) in control animals. This result was highly statistically significant with a p value of < 0.0001 by two tailed student's t test. These data suggest that over expression of MN1 in this model confers resistance to Ara-C and doxorubicin in vitro and in vivo and provides a biological explanation for the clinical observation that it confers a worse prognosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1694. doi:10.1158/1538-7445.AM2011-1694