In-vitro and in-vivo imaging of prostate tumor using NaYF4: Yb, Er up-converting nanoparticles

The aim of this study was to investigate the feasibility of prostate tumor bioimaging both in vitro and in vivo using an upconversion fluorophore, NaYF4: Yb, Er nanoparticles. Luminescent signals of human prostate cancer cells (CWR22R and LNCaP) labeled with NaYF4: Yb, Er nanoparticles were detected by laser scanning confocal microscope, while Cy3 or FITC was used as control probe. Mouse-human prostate cancer model was developed by subcutaneously injecting the CWR22R cells into BALB/c nude mice to investigate the in-vivo imaging properties of NaYF4:Yb, Er nanoparticles. Both CWR22R and LNCaP cells could phagocytose NaYF4:Yb, Er nanoparticles in vitro, and the cellular uptake of CWR22R cells was much higher than that of LNCaP cells (95.42 ± 3.47 % vs. 51.63 ± 6.43 %), which made us choose the former for the further study. CWR22R cells pre-labeled with NaYF4:Yb, Er nanoparticles showed no obvious decrease of fluorescence intensity (P > 0.05) after light exposure, while the fluorescence intensity of Cy3 or FITC labeled cells decreased rapidly with prolonged bleaching (P < 0.05). Furthermore, the in-vivo results showed that the prostate cancer cells pre-labeled with or without NaYF4:Yb, Er nanoparticles formed tumors 4 weeks after injection, and the tumor length-diameter of the nanoparticle group and the control group was (10.3 ± 2.0) mm and (9.8 ± 2.5) mm, respectively. Significant upconversion fluorescence signals were observed in the tumors of the nanoparticle group when being excited at 980 nm by a NIR laser. In summary, the results suggest that as an intensive fluorescence imaging label agent, NaYF4:Yb, Er nanoparticles possess unique features and can be used for imaging prostate tumor cells both in vitro and in vivo by phagocytosis.