The signal-to-background ratio (SBR) is the key determinant of sensitivity, detectability and linearity in optical imaging. As signal strength is often constrained by fundamental limits, background reduction becomes an important approach for improving the SBR. We recently reported that a zwitterionic near-infrared (NIR) fluorophore, ZW800-1, exhibits low background. Here we show that this fluorophore provides a much-improved SBR when targeted to cancer cells or proteins by conjugation with a cyclic RGD peptide, fibrinogen or antibodies. ZW800-1 outperforms the commercially available NIR fluorophores IRDye800-CW and Cy5.5 in vitro for immunocytometry, histopathology and immunoblotting and in vivo for image-guided surgery. In tumor model systems, a tumor-to-background ratio of 17.2 is achieved at 4 h after injection of ZW800-1 conjugated to cRGD compared to ratios of 5.1 with IRDye800-CW and 2.7 with Cy5.5. Our results suggest that introducing zwitterionic properties into targeted fluorophores may be a general strategy for improving the SBR in diagnostic and therapeutic applications.
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We thank S. Gioux, R. Oketokoun and A. Stockdale for assistance with development of the FLARE (Fluorescence-Assisted Resection and Exploration) imaging system and software. We also thank D. Burrington Jr. for manuscript editing and E. Trabucchi for administrative assistance. This study was supported by the following grants from the US National Institutes of Health: National Cancer Institute Bioengineering Research Partnership grant #R01-CA-115296 (J.V.F.) and National Institute of Biomedical Imaging and Bioengineering grants #R01-EB-010022 and #R01-EB-011523 (both to H.S.C. and J.V.F.); this study was also supported by the Dana Foundation Program in Brain and Immuno-Imaging (H.S.C.). S.H.K. was supported by a WCU Program (R31-20029) from the Korea Ministry of Education, Science and Technology (KMEST).
FLARE technology is owned by Beth Israel Deaconess Medical Center, a teaching hospital of Harvard Medical School. It has been licensed to the FLARE Foundation, a nonprofit organization focused on promoting the dissemination of medical imaging technology for research and clinical use. J.V.F. is the founder and chairman of the FLARE Foundation. The Beth Israel Deaconess Medical Center will receive royalties for the sale of FLARE Technology. J.V.F. has elected to surrender post-market royalties to which he would otherwise be entitled as inventor, and has elected to donate pre-market proceeds to the FLARE Foundation. J.V.F. has started three for-profit companies, Curadel, Curadel Medical Devices and Curadel In Vivo Diagnostics, which may someday be nonexclusive sublicensees of FLARE technology.
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Choi, H., Gibbs, S., Lee, J. et al. Targeted zwitterionic near-infrared fluorophores for improved optical imaging. Nat Biotechnol 31, 148–153 (2013). https://doi.org/10.1038/nbt.2468
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