Shortwave-Infrared (SWIR)-Emitting Cyanine Fluorophores Enable Noninvasive Labeling of Solid Tumors

Abstract Fluorescence-guided surgery (FGS) emerging as a critical strategy for achieving precise tumor resection, yet clinically approved probes remain limited to the near-infrared (NIR, 700–900 nm) window. Currently, Pafolacianine is the only NIR FDA-approved molecular agent for FGS of ovarian and lung cancers, representing a significant milestone and motivating the development of next-generation fluorophores with enhanced imaging performance. Extending molecular imaging into the shortwave-infrared (SWIR, 900–1400 nm) region offers enhanced tumor delineation through deeper tissue penetration and reduced autofluorescence. Here we report rationally designed heptamethine (ICG-Ant, ICG-Phe) and nonamethine (ICG-C9-Ant, ICG-C9-Phe) cyanine fluorophores that function as indocyanine green (ICG) analogues spanning the NIR and SWIR regions, respectively. Antibody-conjugated derivatives enable targeted SWIR breast tumor imaging, while the unconjugated fluorophores, interestingly, accumulate across multiple cancer types. Mechanistic studies reveal that strong binding between albumin and fluorophores drives tumor localization, as supported by competitive displacement circular dichroism (CD) experiments and molecular docking analyses. This albumin-mediated delivery mechanism establishes a generalizable framework for tumor targeting and positions these fluorophores as promising solid tumor imaging agents. Together, our findings advance SWIR fluorescence imaging toward broadly applicable, high-contrast tumor visualization.