Characterizing prostate tumor mouse xenografts with CEST and MT-MRI and redox scanning

The main goal of this study was to use multimodality imaging methods to reveal the heterogeneity in prostate cancer and seek the correlation between the characteristic heterogeneity and tumor aggressiveness. Here we report the preliminary data on chemical exchange saturation transfer (CEST) and magnetization transfer (MT) magnetic resonance imaging (MRI) and redox scanning [cryogenic NADH/Fp (reduced nicotinamide adenine dinucleotide/oxidized flavoproteins) fluorescence imaging] of two aggressive human prostate tumor lines (DU-145 and PC-3) xenografted in athymic nude mice. The results obtained by these methods appeared to be consistent, with all showing a higher level of heterogeneity in DU-145 tumors than in PC-3 tumors. DU-145 tumors showed CEST maps with both positive and negative areas while PC-3 CEST maps were relatively homogeneous. The mean CEST value for PC-3, 23.0 ± 2.1 %, is at a significantly higher level (p < 0.05) than DU-145 (1.9 ± 6.7 %) at the peak of the CEST asymmetric curve (+2 ppm). Fp redox ratio (Fp/(NADH + Fp)) images exhibited localized highly oxidized regions in DU-145 tumors, whereas PC-3 tumors appeared to be less heterogeneous. These results suggest a possible role of metabolism in tumor progression. More studies, including an indolent prostate tumor line and with larger sample size, will be performed in the future to identify the biomarkers for prostate tumor aggressiveness.