Novel receptor-targeted fluorescent contrast agents for in vivo tumor imaging

RATIONALE AND OBJECTIVES. TO evaluate the efficacy of a novel tumor recepto r-specific small-peptide-near-infrared dye conjugate for tumor detection by optical imaging. METHODS. A novel, near-infrared dye-peptide conjugate was synthesized and e valuated for tumor-targeting efficacy in a well-characterized rat tumor mod el (CA20948) known to express receptors for the chosen peptide. A simple co ntinuous-wave optical imaging system, consisting of a near-infrared laser d iode, a tooled CCD camera, and an interference filter, was used in this stu dy. RESULTS. Tumor retention of two non-tumor-specific dyes, indocyanine green and its derivatized analogue, bis-propanoic acid cyanine dye (cypate), was negligible. In contrast, the receptor-specific peptide-cypate conjugate (cy tate) was retained in the CA20948 tumor, with an excellent tumor-to-normal- tissue ratio in the six rats examined, CONCLUSIONS. Optical detection of tumors with a receptor-targeted fluoresce nt contrast agent has been demonstrated. This result represents a new direc tion in cancer diagnosis and patient management.