Vascular endothelial growth factor (VEGF) is a potent angiogenic peptide with biologic effects that include regulation of hematopoietic stem cell development, extracellular matrix remodeling, and inflammatory cytokine generation. The importance of angiogenic factors such as VEGF, while clearly established in solid tumors, has not been fully elucidated in human hematopoietic neoplasms. Human hematopoietic tumor cell lines, representing multiple lineages and diseases, produce and secrete VEGF and express at least one of its two receptors. Exposure of human vascular endothelial cells to VEGF increased the expression of several hematopoietic growth factors known to be involved in myeloma including interleukin-6 (IL-6). Bone marrow samples from patients diagnosed with multiple myeloma were examined for expression of VEGF and its receptors. VEGF protein production was detected in malignant plasma cells from 78% of the myeloma patients studied. While expression of the Flt-1 and KDR receptors was not observed in the malignant plasma cells, both were markedly elevated in the normal marrow myeloid and monocytic cells surrounding the tumor. In bone marrow clot sections from normal allogeneic donors, low-intensity cytoplasmic VEGF expression was detected infrequently in isolated myelocytes, macrophages, and megakaryocytes. In vitro colony-forming assays using patient-derived material revealed that antibody neutralization of VEGF resulted in an inhibition of colony growth, whereas the addition of recombinant human VEGF stimulated colony formation. Neutralization of VEGF activity also suppressed the generation of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) from bone marrow mononuclear cells. These data raise the possibility that VEGF may play a role in the growth of hematopoietic neoplasms such as multiple myeloma through paracrine and perhaps autocrine mechanisms.
Copyright 2001 by W.B. Saunders Company.