Besides the common issue of drug-resistance, the conventional approaches for
cancer diagnostics and treatment are constantly challenged by poor selectivity and limited access to neoplastic cells, which not only lead to the dose-limiting effect on the
tumor region, but also bring side-effects to healthy cells/tissues. In recent years, a novel strategy has arisen to target the vasculature of
tumors for
drug-delivery and molecular imaging, based on the success of anti-angiogenic
therapy. In addition to being easily accessible, the endothelial cells of
tumor vasculature are also genetically stable and thus do not develop drug-resistance, making them ideal targets for chemotherapeutics and biomedical imaging. Among various
ligands identified so far, the
Asn-Gly-Arg (NGR) tripeptide can specifically target the neovasculature via interaction with the
aminopeptidase N (APN/CD13) receptor which is highly up-regulated in the membranes of endothelial
tumor cells. NGR-directed
drug delivery as well as molecular imaging have therefore been undergone development, and appear to be intriguing approaches in current
cancer research. Herein we highlight some recent developments of the
NGR peptide based
cancer therapy including
drug-delivery and imaging studies, with future perspectives. Some of these agents have been under clinical trials, indicating promising future for the NGR-based drugs.