Inhibition of neuroblastoma-induced angiogenesis by fenretinide

Retinoids are a class of natural or synthetic compounds that participate in the control of cell proliferation, differentiation and fetal development. The synthetic retinoid fenretinide (HPR) inhibits carcinogenesis in various animal models. Retinoids have also been suggested to be effective inhibito rs of angiogenesis. The effects of HPR on certain endothelial cell function s were investigated in vitro, and its effects on angiogenesis was studied i n vivo, by using the chorioallantoic membrane (CAM) assay. HPR inhibited va scular endothelial growth factor- (VEGF-) and fibroblast growth factor-2- ( FGF-2)-induced endothelial cell proliferation without affecting endothelial motility; moreover, HPR inhibited growth factor-induced angiogenesis in th e CAM assay. Furthermore, a significant antiangiogenic potential of HPR has also been observed in neuroblastoma (NB) biopsy-induced angiogenesis in vi vo. We previously demonstrated that supernatants derived from NB cell lines stimulated endothelial cell proliferation. In the present study, we found that this effect was abolished when NB cells were incubated in the presence of HPR. VEGF- and FGF-2-specific ELISA assays, performed on both NB cells derived from conditioned medium and cellular extracts, indicated no consist ent effect of HPR on the level of these angiogenic cytokines. Moreover, RT- PCR analysis of VEGF- and FGF-2 gene expression confirmed the above lack of effect. HPR was also able to significantly repress the spontaneous growth of endothelial cells, requiring at least 48-72 hr of treatment with HPR, fo llowed by a progressive accumulation of cells in G, at subsequent time poin ts. Finally, immunohistochemistry experiments performed in the CAM assay de monstrated that endothelial staining of both VEGF receptor 2 and FGF-2 rece ptor-2 was reduced after implantation of HPR-loaded sponges, as compared to control CAMs. These data suggest that HPR exerts its antiangiogenic activi ty through both a direct effect on endothelial cell proliferative activity and an inhibitory effect on the responsivity of the endothelial cells to th e proliferative stimuli mediated by angiogenic growth factors. (C) 2001 Wil ey-Liss, Inc.