Coculture of native human acute myelogenous leukemia blasts with fibroblasts and osteoblasts results in an increase of vascular endothelial growth factor levels

Objectives: Angiogenesis seems important in the development of acute myelogenous leukemia (AML). Proangiogenic vascular endothelial growth factor (VEGF) is constitutively secreted by the AML blasts for a subset of patients, but it can also be released by non-leukemic bone marrow cells. Methods: VEGF levels were determined after coculture of native human AML blasts with fibroblast lines, osteoblastic sarcoma cell lines, normal bone marrow stromal cells and normal osteoblasts. Cultures were prepared with leukemic and non-leukemic cells separated by a semipermeable membrane or in direct contact. Results: The non-leukemic cells usually showed higher spontaneous VEGF release than AML cell populations. Coculture of AML blasts with HFL1 fibroblasts caused a supra-additive increase of VEGF levels when the cell populations were cultured separately, and the increase was also observed when cells were cultured in direct contact. An increase was also observed when AML blasts were cultured with osteoblastic sarcoma cells, normal bone marrow stromal cells and normal osteoblasts. Coculture had divergent effects on VEGF mRNA levels both for leukemic and non-leukemic cells, but increased mRNA levels were commonly observed especially for the non-leukemic cells. Cytokine inhibition experiments suggest that IL1 is important for the VEGF-increasing crosstalk, whereas the mechanisms are probably heterogeneous for coculture with osteoblasts. Conclusion: The bi-directional crosstalk via local cytokine networks between AML blasts and non-leukemic cells results in increased local VEGF levels, an observation suggesting that VEGF-targeting antiangiogenic therapy should be considered as a general therapeutic strategy in AML.