Multicolor in vivo targeted imaging to guide real‐time surgery of HER2‐positive micrometastases in a two‐tumor coincident model of ovarian cancer

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Abstract
One of the primary goals of oncological molecular imaging is to accurately identify and characterize malignant tissues in vivo. Currently, molecular imaging relies on targeting a single molecule that while overexpressed in malignancy, is often also expressed at lower levels in normal tissue, resulting in reduced tumor to background ratios. One approach to increasing the specificity of molecular imaging in cancer is to use multiple probes each with distinct fluorescence to target several surface antigens simultaneously, in order to identify tissue expression profiles, rather than relying on the expression of a single target. This next step forward in molecular imaging will rely on characterization of tissue based on fluorescence and therefore will require the ability to simultaneously identify several optical probes each attached to different targeting ligands. We created a novel ‘coincident’ ovarian cancer mouse model by coinjecting each animal with two distinct cell lines, HER2+/red fluorescent protein (RFP)− SKOV3 and HER2−/RFP+ SHIN3-RFP, in order to establish a model of disease in which animals simultaneously bore tumors with two distinct phenotypes (HER2+/RFP−, HER2−/RFP+), which could be utilized for multicolor imaging. The HER2 receptor of the SKOV3 cell line was targeted with a trastuzumab–rhodamine green conjugate to create green tumor implants, whereas the RFP plasmid of the SHIN3 cells created red tumor implants. We demonstrate that real-time in vivo multicolor imaging is feasible and that fluorescence characteristics can then serve to guide the surgical removal of disease. (Cancer Sci 2009; 100: 1099–1104)