Figure 1

Tumor-associated ECs enhance human xenograft tumor formation and demonstrate a mesenchymal phenotype in breast tumors. A) NOD/SCID mice were sacrificed 18 and 30 days after subcutaneous injection with MDA-231 cells (2 × 10⁵ cells) with or without ECs (2 × 10⁶ cells) to make an assessment on xenograft tumor burden. Injection of MDA-231 cells without ECs (shown on the right side of each image) resulted in formation of non-angiogenic small tumors. In contrast, inoculation of MDA-231 cells mixed with ECs (1:10 ratio) (shown on the left side of each image) led to the generation of bulkier angiogenic tumors. B) Quantification of xenograft tumor weights formed in NOD/SCID mice injected by MDA-231 cells with and without ECs (***p < 0.001). C) Snap-frozen angiogenic xenograft tumors sections were stained with endothelial marker CD31 as well as vascular structural and functional markers CD44 and desmin to show the existence of viable capillaries in xenograft tumors. D) The xenograft tumor sections were stained with mesenchymal markers vimentin and α-SMA to demonstrate the acquisition of mesenchymal phenotype by tumor vasculature. E) Human neoplastic breast tissues were examined for the potential occurrence of mesenchymal properties in tumor endothelium in vivo. The tumor endothelium was first detected by CD31⁺ staining, and then examined for the existence of ECs showing mesenchymal phenotype within tumor by vimentin and α-SMA staining. Scale bars represent 10 μm.