In vitro and in vivo production of vascular endothelial growth factor by chronic lymphocytic leukemia cells

Expansion of primary solid tumors and their malignant dissemination are ang iogenesis-dependent, Vascular endothelial growth factor (VEGF) is the key f actor playing a pivotal role in solid tumor-induced angiogenesis. Recent st udies indicate that angiogenesis may also be involved in the pathogenesis o f certain hemic malignancies, including B-cell chronic lymphocytic leukemia (B-CLL). Mechanisms underlying angiogenesis in B-CLL and the role of VEGF in this process are incompletely understood. In this study, it was examined whether angiogenically functional VEGF is produced by B-CLL cells. Immunoh istochemical staining with antibodies against VEGF and CD34, an endothelial cell marker, demonstrated the presence of VEGF protein and abundant blood vessels in infiltrated lymphoreticular tissues. Low levels of VEGF were det ected by ELISA in the culture media of unstimulated cells; this was enhance d up to 7-fold by hypoxic stimulation. SDS-PAGE and Western blot analysis o f the concentrated culture media showed 2 isoforms of VEGF protein with mol ecular weights of 28 and 42 kd, respectively. RNA hybridization showed that these cells expressed VEGF mRNA, Reverse transcription-polymerase chain re action, combined with nucleotide sequence analysis, revealed that the predo minantly expressed isoforms were VEGF121 and VEGF165, Moreover, H-3-thymidi ne incorporation and an in vivo angiogenic assay demonstrated that the VEGF produced by CLL cells can induce angiogenesis by stimulating endothelial c ell proliferation. In conclusion, this study shows that B-CLL cells produce VEGF and demonstrates the angiogenic effects of this growth factor, which may be relevant for the tissue phase of the disease. (C) 2000 by The Americ an Society of Hematology.