A xanthene-based near-infrared fluorogenic probe for imaging Cu+ and assessing ionophores in 4T1 tumor-bearing mice

Copper is an essential micronutrient that play indispensable roles in living systems. Small-molecule based fluorescence probes for imaging cuprous (Cu+) dynamics are essential to elucidate its biology. Nonetheless, the availability of near infrared (NIR) fluorogenic probes for Cu+ imaging in vivo is still limited. Here we develop a new NIR fluorogenic probe that allows imaging of Cu+ dynamics and assessing its ionophores in live cells and in vivo. The probe is comprised of a xanthene-based fluorophore as a reporter and a thioether rich unit as a Cu+ binding and reporter-quenching moiety. We demonstrate that the fluorescence probe using xanthene-conjugated with 1-methylindole-3-carboxaldehyde exhibits fluorogenic NIR fluorescence with excitation/emission wavelengths of 640 nm/704 nm, high sensitivity with a limit of detection of 28.4 ± 0.3 nM from three replicates, high selectivity and desirable reversibility in response to Cu+. The probe is further employed to image Cu+ dynamics under different conditions and assess the efficacy of Cu+ ionophores in different cancer cell lines. Its ability to image Cu+ fluctuation and evaluate the efficacy of Cu+ ionophores in vivo is demonstrated in a 4T1 tumor-bearing mice model using bovine serum albumin as a probe carrier. Our probe could afford a valuable tool for elucidating copper biology and assessing Cu+ ionophores for treating related diseases in living systems.