Fluorescence imaging-guided photothermal therapy of asymmetric water-soluble pentamethine cyanine for colorectal cancer

The combination of advanced optical technology and tumor treatment has developed into a selectively targeted tumor therapy strategy. Near-infrared (NIR) cyanine derivative has recently received increasing attention in photothermal therapy (PTT) because of its excellent biocompatibility, non-immunogenicity, high fluorescence and photothermal conversion efficiency, photostability, and tumor-homing. In this study, an asymmetric and water-soluble pentamethine cyanine was designed and synthesized to investigate the photosensitive activity and to explore its potential applications as a NIR photosensitizer for the diagnosis and therapy of colorectal cancer (CRC). The results of fluorescence imaging analysis showed that CY5-664 preferentially accumulated in the tumor as time elapsed, and the maximum fluorescence intensity was obtained at 24 h. Cell viability and animal xenograft model experiments showed that CY5-664 significantly inhibited tumor growth in vivo with 0.8 W/cm2 of 660 nm red laser pointer for 2 min, and in vitro with 0.5 W/cm2 of 660 nm red laser pointer for 2 min. In vitro and in vivo photothermal conversion experiments showed that CY5-664 exhibited an anti-CRC activity mainly through the PTT effect. Therefore, this work provides experimental evidence that CY5-664 is a drug candidate for CRC treatment mainly through the PTT effect and an alternative treatment strategy to develop a pentamethine cyanine-based CRC theranostic photosensitizer for synergistic CRC targeting, imaging, and therapy.