A Bright, Hydrophilic, and Robust Phospha-Rhodamine Near-Infrared Dye Platform for Antibody Labeling toward Tumor Imaging

In this work, we present a near-infrared (NIR) phospha-rhodamine dye POR-1, featuring a thiomorpholine 1,1-dioxide auxochrome and a carboxyl handle for constructing dye–antibody conjugates for tumor imaging. The unique auxochrome endows the dye not only with markedly improved quantum yields due to the strong inhibition of nonradiative decay, but also with high hydrophilicity without introduction of the multiple charged groups. Moreover, the dye exhibits high photostability and chemical stability alongside strong resistance to self-aggregation in aqueous solution. All of these properties are highly advantageous for achieving the high-performance dye–antibody conjugates for imaging tumors. Utilizing the carboxyl handle, we developed a fluorescence labeling agent, POR-1-NHS, for antibody conjugation. With this agent, we prepared a dye-panitumumab (Pan) conjugate, (POR-1)3-Pan, for in vivo imaging of epidermal growth factor receptor (EGFR)-positive tumors. Post intravenous injection, the conjugate achieves a high tumor-to-normal tissue ratio of 3.2 in mouse models, with negligible nonspecific liver uptake. Moreover, it enables small tumor nodules (<3 mm) to be visualized clearly. Overall, this study establishes a high-performance NIR dye platform for the development of dye–antibody conjugates for applications in fluorescence image-guided surgery.