The CXCR4-SDF-1 axis plays a central role in the trafficking and retention of normal and malignant stem cells in the bone marrow (BM) microenvironment. Here, we utilized a mouse model of acute promyelocytic leukemia (APL) and a small molecule competitive antagonist of CXCR4, AMD3100, to examine the interaction of mouse APL cells with the BM microenvironment. APL cells from a murine cathepsin G-PML-RARα knock-in mouse were genetically modified with firefly luciferase (APLluc) to allow tracking by bioluminescence imaging. Coculture of APLluc cells with M2-10B4 stromal cells protected the leukemia cells from chemotherapy-induced apoptosis in vitro. Upon injection into syngeneic recipients, APLluc cells rapidly migrated to the BM followed by egress to the spleen then to the peripheral blood with death due to leukostasis by day 15. Administration of AMD3100 to leukemic mice induced a 1.6-fold increase in total leukocytes and a 9-fold increase of circulating APL blast counts which peak at 3 hours and return to baseline by 12 hours. Treatment of leukemic mice with chemotherapy plus AMD3100 resulted in decreased tumor burden and improved overall survival compared to mice treated with chemotherapy alone. These studies provide a proof-of-principle for directing therapy to the critical tethers that promote AML-niche interactions.
Murine APL model. Kinetics of APLluc engraftment and expansion. Genetically compatible B6129F1 recipients were injected with 106 APLluc cells. Tumor trafficking and growth was assessed at various time intervals by bioluminescence imaging. Images of a representative mouse are shown. Photon flux is indicated in the color scale bar. WBC counts were determined by automated counting and the percentage of leukemic blasts in the blood, spleen and bone marrow by flow cytometry.
AMD3100 sensitization of APL to Ara-C. (A-C) Syngeneic B6129F1 recipient mice (n = 29) were intravenously injected with 106 APLluc cells. Twelve days after APL injection, mice were left untreated (control; n = 6) or treated with AMD3100 alone (n = 7), Ara-C alone (n = 8), or the combination of AMD3100 and Ara-C (n = 8). Mice treated with chemotherapy received a single subcutaneous injection of Ara-C (500 mg/kg) on days 12 and 13 after APL injection. Mice treated with AMD3100 received subcutaneous injections of AMD3100 (5mg/kg) 1 hour before and 3 hours after each Ara-C injection. (A)In vivo bioluminescent imaging of APLluc cells. One representative animal for each group is shown over time. Photon flux is indicated in the color scale bar. Red arrow indicates initiation of treatment with AMD3100 and/or Ara-C. (B) Expansion of APLluc cells was quantified in emitted photons over total body area (ventral view). BLI signal intensity at days 15, 19, and 23 after APL injection was significantly reduced in mice receiving the combination of AMD3100 and Ara-C compared to mice receiving Ara-C alone. (C) Kaplan-Meier plot of overall survival of mice. Overall survival of leukemic mice is significantly prolonged when mice are treated with the combination of AMD3100 and Ara-C (P < 0.0006 between AraC versus AraC + AMD3100 cohorts).
Nervi B, Ramirez P, Rettig MP, Uy GL, Holt MS, Ritchey JK, Prior JL, Piwnica-Worms D, Bridger G, Ley TL, DiPersio JF. Chemosensitization of AML following mobilization by the CXCR4 antagonist AMD3100. Blood 2009; in press.