Vascular endothelial growth factor-A is widely regarded as the principal stimulator of angiogenesis required for tumour growth. VEGF is generated as multiple isoforms of two families, the pro-angiogenic family generated by proximal splice site selection in the terminal exon, termed VEGF xxx , and the anti-angiogenic family formed by distal splice site selection in the terminal exon, termed VEGF xxx b, where xxx is the amino acid number. The most studied isoforms, VEGF 165 and VEGF 165 b have been shown to be present in tumour and normal tissues respectively. VEGF 165 b has been shown to inhibit VEGF- and hypoxia-induced angiogenesis, and VEGF-induced cell migration and proliferation in vitro . Here we show that overexpression of VEGF 165 b by tumour cells inhibits the growth of prostate carcinoma, Ewing's sarcoma and renal cell carcinoma in xenografted mouse tumour models. Moreover, VEGF 165 b overexpression inhibited tumour cell-mediated migration and proliferation of endothelial cells. These data show that overexpression of VEGF 165 b can inhibit growth of multiple tumour types in vivo indicating that VEGF 165 b has potential as an anti-angiogenic, anti-tumour strategy in a number of different tumour types, either by control of VEGF 165 b expression by regulation of splicing, overexpression of VEGF 165 b, or therapeutic delivery of VEGF 165 b to tumours.

Tumour growth is dependent on angiogenesis, the key mediator of which is vascular endothelial growth factor-A (VEGF-A). VEGF-A exists as two families of alternatively spliced isoforms - pro-angiogenic VEGF(xxx) generated by proximal, and anti-angiogenic VEGF(xxx)b by distal splicing of exon 8. VEGF(165)b inhibits angiogenesis and is downregulated in tumours. Here, we show for the first time that administration of recombinant human VEGF(165)b inhibits colon carcinoma tumour growth and tumour vessel density in nude mice, with a terminal plasma half-life of 6.2h and directly inhibited angiogenic parameters (endothelial sprouting, orientation and structure formation) in vitro. Intravenous injection of (125)I-VEGF(165)b demonstrated significant tumour uptake lasting at least 24h. No adverse effects on liver function or haemodynamics were observed. These results indicate that injected VEGF(165)b was taken up into the tumour as an effective anti-angiogenic cancer therapy, and provide proof of principle for the development of this anti-angiogenic growth factor splice isoform as a novel cancer therapy.

Renal cell carcinoma (RCC) frequently metastasizes to the bone marrow. These metastases are characterized by extensive osteolytic lesions. The mechanism, however, by which RCC cells metastasize to bone marrow remains poorly understood. To unravel the role of bone marrow cells in this context, we performed cell adhesion and migration assays using human RCC cell lines to analyze the influence of resident bone marrow cells on renal tumor cells. The strongest adhesion of RCC cells was observed to osteoblasts. Moreover, conditioned medium of osteoblasts (OB-CM) significantly increased RCC cell migration. By gene expression analysis dysadherin was identified as a transcript whose expression could be elevated more than twofold in RCC cells when exposed to OB-CM. Suppression of dysadherin expression in RCC cells by siRNA reduced their ability to migrate in the presence of OB-CM. Furthermore, the RCC cells secreted high amounts of the chemokine CCL2 when tumor cells migrated under the influence of osteoblast-secreted factors. CCL2 neutralization strongly reduced the migratory ability of the RCC cells. Silencing the expression of dysadherin in RCC cells resulted in a twofold reduction of CCL2 protein expression indicating a dysadherin-dependent expression of the chemokine. Taken together, our data show that osteoblasts are the major cell type of the bone marrow that affect RCC cells by secreting factors that increase the expression of dysadherin and CCL2 in the tumor cells leading to enhanced cell migration. These data suggest an osteoblast-induced autocrine mechanism for a facilitated homing of RCC cells to the bone marrow.