Note: Mice were injected with 100 μg of FITC-CPE peptide i.v. and fluorescence in tumor and normal tissues was measured using a whole-body optical imaging system at the indicated time points as described in the Methods. Data are presented as tumor-to-organ ratios calculated from the organ distribution of FITC-CPE peptide in SCID mice with OSPC-ARK-1 tumor xenografts (n = 3-5 animals). The autofluorescence background in mice that did not receive fluorescent compound was subtracted from the experimental values. Results are representative of 2 independent experiments showing similar results.