Dual In Vivo Quantification of Integrin-targeted and Protease-activated Agents in Cancer Using Fluorescence Molecular Tomography (FMT)

Purpose Integrins, especially α v β 3 and α v β 5 , are upregulated in tumor cells and activated endothelial cells and as such, serve as cancer biomarkers. We developed a novel near-infrared-labeled optical agent for the in vivo detection and quantification of α v β 3 /α v β 5 . Procedures A small peptidomimetic α v β 3 antagonist was synthesized, coupled to a near-infrared fluorescent (NIRF) dye, and tested for binding specificity using integrin-overexpressing cells, inhibition of vitronectin-mediated cell attachment, binding to tumor and endothelial cells in vitro , and competition studies. Pharmacokinetics, biodistribution, specificity of tumor targeting, and the effect of an antiangiogenic treatment were assessed in vivo . Results The integrin NIRF agent showed strong selectivity towards α v β 3/ α v β 5 in vitro and predominant tumor distribution in vivo , allowing noninvasive and real-time quantification of integrin signal in tumors. Antiangiogenic treatment significantly inhibited integrin signal in vivo but had no effect on a cathepsin-cleavable NIR agent. Simultaneous imaging revealed different patterns of distribution reflecting the underlying differences in integrin and cathepsin biology during tumor progression. Conclusions NIRF-labeled integrin antagonists allow noninvasive molecular fluorescent imaging and quantification of tumors in vivo , improving and providing more refined approaches for cancer detection and treatment monitoring.