PT  - JOURNAL ARTICLE
AU  - Henry R. Wolfe
AU  - Marivi Mendizabal
AU  - Elinor Lleong
AU  - Alan Cuthbertson
AU  - Vinay Desai
AU  - Shirley Pullan
AU  - Dennis K. Fujii
AU  - Matthew Morrison
AU  - Richard Pither
AU  - Scott A. Waldman
TI  - In Vivo Imaging of Human Colon Cancer Xenografts in Immunodeficient Mice Using a Guanylyl Cyclase C–Specific Ligand
DP  - 2002 Mar 01
TA  - Journal of Nuclear Medicine
PG  - 392--399
VI  - 43
IP  - 3
4099  - http://jnm.snmjournals.org/content/43/3/392.short
4100  - http://jnm.snmjournals.org/content/43/3/392.full
SO  - J Nucl Med2002 Mar 01; 43
AB  - Guanylyl cyclase C (GC-C) is a transmembrane receptor expressed by human intestinal cells and primary and metastatic colorectal adenocarcinomas but not by extraintestinal tissues or tumors. The Escherichia coli heat-stable enterotoxin analog, STa (5–18), is a 14–amino acid peptide that selectively binds to the extracellular domain of GC-C with subnanomolar affinity. This study examined the utility of a radiolabeled conjugate of STa (5–18) to selectively target and image extraintestinal human colon cancer xenografts in vivo in nude mice. Methods: The STa conjugate, ethoxyethyl-mercaptoacetamidoadipoylglycylglycine-STa (5–18) (NC100586), was synthesized and labeled with 99mTc to produce 99mTc-NC100586. This compound was intravenously administered to nude mice bearing human colon cancer xenografts, and specific targeting was evaluated by biodistribution and gamma camera imaging. Results: In CD-1 nude mice, biodistribution and scintigraphic imaging analyses showed selective uptake of 99mTc-NC100586 into human colon cancer xenografts that express GC-C but not into normal tissues that do not express GC-C. Similarly, 99mTc-NC100586 injected intravenously into CD-1 nude mice with human colon cancer hepatic metastases selectively accumulated in those metastases, and ∼5-mm foci of tumor cells were visualized after ex vivo imaging of excised livers. Accumulation of 99mTc-NC100586 in human colon cancer xenografts reflected binding to GC-C because 99mTc-NC100588, an inactive analog that does not bind to GC-C, did not selectively accumulate in cancer xenografts compared with normal tissues. Also, coadministration of excess unlabeled STa (5–18) prevented accumulation of 99mTc-NC100586 in human colon cancer xenografts. Furthermore, 99mTc-NC100586 did not selectively accumulate in Lewis lung tumor xenografts, which do not express GC-C. Conclusion: This study showed that intravenously administered STa (5–18) selectively recognizes and binds to GC-C expressed by human colon cancer cells in vivo. Also shown was the ability to exploit this selective interaction to target imaging agents to extraintestinal human colon tumors in nude mice. These results suggest the utility of STa and GC-C for the development of novel targeted imaging and therapeutic agents with high specificity for metastatic colorectal tumors in humans.