Contrast ultrasound in imaging tumor angiogenesis

New strategies to detect tumor angiogenesis and monitor response of tumor vasculature to therapy are needed. There are a plethora of anti-angiogenic strategies being evaluated pre-clinically and in the clinical setting; however, a -significant unmet challenge is following the response of tumors to anti-angiogenic therapy. Herein we review current modalities being investigated for this purpose and highlight the utility of contrast ultrasound imaging using targeted microbubbles (MB). MB are small (1-10 μm) gas-filled intravascular tracers. MB can be targeted via antibodies, peptides or other moieties to virtually any endothelial cell surface marker and thus selectively mark specific vascular beds (e.g., tumor blood vessels). Furthermore targeted MB can be used to non-invasively evaluate the expression level of particular molecular antigens (e.g., CD105, VEGFR2) and monitor the effect of therapy on target expression. We conclude that targeted MB represent a novel and attractive tool for non-invasive, vascular-targeted molecular imaging of tumor angiogenesis and for monitoring vascular effects specific to anti-tumor therapy in vivo.