Analysis of the Crosstalk Between TGF-β–VEGF-Angiogenesis in an In Vivo Model of Acute Promyelocytic Leukemia

Abstract 1845 Acute Promyelocytic Leukemia (APL) patients present increased bone marrow microvascular density (MVD) compared to normal bone marrow, which has been associated with the aberrant secretion of the proangiogenic factor VEGF by leukemic cells. The APL associated fusion protein PML-RARα is thought to deregulate the TGF-β pathway, through its dominant negative action on cytoplasmic PML, thus down regulating SMAD2/3 signaling, and VEGF transcription. However, PML-RARα expression was associated with increased TGF-β gene transcription and secretion. We used the low molecular weight quinazolinone alkaloid Halofuginone (HF), which has been shown to be a potent TGF-β inhibitor, to test the association between TGF-β/VEGF/angiogenesis. HF inhibited the VEGF secretion by NB4 (an APL cell lineage) and cell proliferation. To determine the effects of HF in vivo , irradiated NOD/SCID mice were transplanted with leukemic cell from hCG-PML-RARα transgenic mice. Twenty-four hours after transplantation, mice were treated with 150μg/kg of HF by intraperitoneal injections for 21 days. All recipients developed leukemia, however the leukemic infiltration of bone marrow and WBC were significantly lower in animals treated HF (4.2 ± 3.89 vs. 20.6 ± 21.9, p TgfB , Smad3 , Smad4 , Myc , Vegf and Egf and the immunohistochemistry analysis of BM sections revealed a significant decrease of VEGF staining (30 vs. 80%, p =0.0227), but there was no decrease in the microvascular density. Taken together, these results showed that angiogenesis is an important therapeutic target in APL, and despite the toxicity, HF has antileukemic potential due to its antiproliferative and proangiogenic factors inhibitory capabilities. Disclosures: Assis: FAPESP: Research Funding; CNPq: Research Funding.