Residual Disease in a Novel Xenograft Model of RUNX1-Mutated, Cytogenetically Normal Acute Myeloid Leukemia.

Cytogenetically normal acute myeloid leukemia (CN-AML) patients harboring RUNX1 mutations have a dismal prognosis with anthracycline/cytarabine-based chemotherapy. We aimed to develop an in vivo model of RUNX1-mutated, CN-AML in which the nature of residual disease in this molecular disease subset could be explored. We utilized a well-characterized patient-derived, RUNX1-mutated CN-AML line (CG-SH). Tail vein injection of CG-SH into NOD scid gamma mice led to leukemic engraftment in the bone marrow, spleen, and peripheral blood within 6 weeks. Treatment of leukemic mice with anthracycline/cytarabine-based chemotherapy resulted in clearance of disease from the spleen and peripheral blood, but persistence of disease in the bone marrow as assessed by flow cytometry and secondary transplantation. Whole exome sequencing of CG-SH revealed mutations in ASXL1, CEBPA, GATA2, and SETBP1, not previously reported. We conclude that CG-SH xenografts are a robust, reproducible in vivo model of CN-AML in which to explore mechanisms of chemotherapy resistance and novel therapeutic approaches

Engraftment Properties of CG-SH cells.

<p><b>(A)</b> Sequencing chromatogram demonstrating the <i>RUNX1</i> mutation in CG-SH. <b>(B)</b> Percent hCD45+ engraftment achieved in the bone marrow (BM), peripheral blood (PB), and spleen of non-irradiated NSG mice receiving 1e6 CG-SH cells directly from cell culture via tail vein injection. Each symbol represents a single animal analyzed 6 weeks after transplantation. The horizontal black bars indicate mean engraftment. <b>(C)</b> Limiting dilution analysis of CG-SH and M9-ENL cells to determine the lowest cell dose necessary to achieve engraftment in each cell population. 1e1 – 1e6 cells were injected into non-irradiated NSG mice (5 mice per cell dose) and engraftment levels analyzed 10 weeks post- transplantation.</p

Residual Disease in CG-SH Xenografts Treated with a 5-day regimen of Anthracycline/Cytarabine-Based Chemotherapy.

<p><b>A and B.</b> Flow cytometric plots demonstrating the level of CG-SH engraftment in the bone marrow, peripheral blood, and spleen of a representative saline-treated control mouse <b>(A)</b> and a representative chemotherapy-treated mouse <b>(B)</b>. Treatment was initiated five weeks after tail vein injection of 1e6 CG-SH cells into non-irradiated NSG mice. Mice were analyzed four days after the completion of chemotherapy. <b>(C)</b> Quantification of the impact of chemotherapy in a cohort of CG-SH- xenografted mice. Each symbol represents a single mouse analyzed four days after the completion of treatment. Control mice were treated with saline. <b>(D)</b> Bone marrow histology four days after the completion of chemotherapy in CG-SH xenografts. Magnification is at 20x (left panels) and 40x (right panels), respectively. <b>(E)</b> Chemotherapy fails to eradicate leukemia-initiating cells in CG-SH xenografts. Leukemic cells were harvested from the bone marrow of chemotherapy-treated CG-SH xenografts or saline-treated controls and tested for their ability to engraft secondary NSG recipients. Non-irradiated secondary recipients were transplanted with unsorted cell populations containing 5e4 CG-SH cells and engraftment was determined 6 weeks later. All data were analyzed by the comparison of means using unpaired t-test. ***p = 0.0001, ****p<0.0001, ns = not significant.</p