Figure 1.

A, structure of the FN3-scaffold with the corresponding amino acid sequence of FN3_VEGFR2 binder backbone and loop sequences BC (red), DE (green), and FG (blue) with a C-terminal 6xHis-tag (purple). Source: protein data bank (http://www.rcsb.org/pdb/home/home.do); search option with ID: 1TTG. B-D, overview of the overall study design. MB-FN3_VEGFR2 was generated by covalently attaching the FN3-scaffold on the surface of MB. C, molecularly-targeted MBs were tested both in vitro and D, in vivo in a transgenic mouse model of breast cancer followed by ex vivo quantitative immunofluorescence of VEGFR2 expression on the tumor neovasculature. USMI signal was measured using the destruction-replenishment technique.