Abstract 4372: Chronic myeloid leukemia (CML) exosomes promote angiogenesis in a Src-dependent fashion in vitro and in vivo

Abstract

Abstract CML is an uncontrolled proliferation of bone marrow myeloid cells driven by the constitutively active fusion product tyrosine kinase BCR/ABL. Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is newly recognized as a factor in CML progression. Exosomes, released by a broad spectrum of cells, are microvesicles that play an important role in cell-to-cell communication both in physiological and pathological conditions. The role of exosomes released by CML cells in angiogenesis is emerging; however, little is known about the mechanisms involved in this process. We first isolated and characterized exosomes released by K562 CML cells and we demonstrated their ability to stimulate human vascular endothelial cells (HUVECs) tube differentiation on Matrigel. K562 exosomes induced an increase of the cumulative tube length in a dose-dependent manner, with a maximum effect at 10ug/ml (p=0.003). Next, we evaluated the effect on exosome behavior of imatinib and dasatinib, two tyrosine kinase inhibitors in use in CML treatment. K562 CML cell treatment with either imatinib or dasatinib reduced exosome release by 58% and 56%, respectively (p<0.01). Equivalent exosome concentrations isolated from imatinib or dasatinib treated K562 cells maintained their ability to stimulate HUVEC tube formation, compared to those isolated from untreated cells. Dasatinib treatment of HUVECs strongly reduced exosome-induced vascular differentiation (p=0.0002). On the contrary, little effect was observed following treatment with imatinib. K562 exosomes stimulated vascularization when added to Matrigel plug in vivo; angiogenesis was markedly inhibited by oral administration of dasatinib (p<0.01), but not imatinib. Consistent with the differential effects of dasatinib and imatinib, exosome-induced HUVEC Src and FAK phosphorylation was only inhibited by dasatinib. Confocal images showed that both FAK and Src phosphorylation were increased at points of membrane-matrix contact. Immunoblot analysis confirmed that K562 exosomes induced a dasatinib-sensitive phosphorylation of Src and FAK and their downstream effectors, Erk and Akt. Again, imatinib was minimally active against exosome stimulation of HUVEC cell signaling. Thus, K562 CML exosomes stimulate angiogenesis in vitro and in vivo in a dasatinib-sensitive fashion. This credentials exosomes and angiogenesis as molecular targets in CML via activation of Src both in leukemia and its microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4372. doi:1538-7445.AM2012-4372