MULTIVALENT MELANOTROPIC PEPTIDE AND FLUORESCENT MACROMOLECULAR CONJUGATES - NEW REAGENTS FOR CHARACTERIZATION OF MELANOTROPIN RECEPTORS

Radioreceptor binding studies have documented the presence of melanotr opin receptors on some but not all of the various human melanoma cell lines that have been studied. Using a newly developed class of multiva lent fluorescent melanotropin-macromolecular conjugates, we have demon strated for the first time the presence of specific melanotropin recep tors on all of the melanoma cell lines, both mouse and human, melanoti c as well as amelanotic, that were investigated. The conjugates develo ped by us consisted of multiple copies of both a potent melanotropin a nalogue and a fluorophore, both arranged in a pendent; fashion on a bi ologically inert macromolecule. While the multivalency of these conjug ates may have established stronger binding with the melanotropin recep tors on the cell surface (perhaps by establishing simultaneous multipl e interactions), the presence of multiple copies of the fluorophore al so greatly increased the level of detection in fluorescence labeling e xperiments. Membrane receptor-hormone-associated phenomena, such as ca pping and internalization of the receptor-ligand complex, also were ob served. The details of these methods are described using B-16 mouse me lanoma cells as a model system. The demonstration of MSH receptors as a common marker for melanoma suggests that this methodology might be e mployed for early clinical detection and anatomical localization of me lanoma. These results also offer the possibility that substitution of the fluorophore in these conjugates by a chemical agent of (chemo-)the rapeutic relevance may provide a powerful tool for site specific (tumo r) targeting and cytotoxicity.