Insulin-like growth factor binding protein-3 is overexpressed in endothelial cells of mouse breast tumor vessels

Angiogenesis is a key process in a variety of human diseases, including cancer. The ability to target selectively the tumor vasculature is potentially useful for the diagnosis and treatment of cancer. Still, little information is available regarding markers that are restricted to the ECs of tumor vessels. cDNA array technology allows simultaneous analysis of relative expression levels of a broad spectrum of genes in 2 related cell populations. We used this technology with the aim of identifying markers specific for TECs. TECs were isolated by CD31-mediated immunomagnetic separation from tumors induced by s.c. injection of NF9006 breast carcinoma cells into syngeneic mice. NECs were isolated from lactating mammary glands. The endothelial nature of isolated cells was confirmed by RT-PCR using CD31-specific primers and by uptake of DiI-Ac-LDL. Macrophage contamination in the EC isolations could be reasonably ruled out by assessing the expression of the macrophage marker c-fms. (32)P-labeled cDNA probes generated by reverse transcription from total RNA were hybridized to mouse-specific gene arrays. Several genes consistently showed differential expression between TECs and NECs. However, expression of only 1 of these genes, IGFBP-3, was restricted exclusively to ECs. Semiquantitative RT-PCR revealed 22- to 33-fold differential expression of IGFBP-3 in the TEC fraction. IGFBP-3 was overexpressed by a factor of 5 in an additional mouse model of breast carcinoma induced by 4T1.2 tumor cells. These results indicate that IGFBP-3 is a potential novel marker of angiogenesis. Elucidation of its role in tumor neovascularization may open the possibility of IGFBP-3 as a therapeutic target for antiangiogenesis.