Receptor-mediated cytotoxicity of alpha-MSH fragments containing melphalan in a human melanoma cell line.
Four alpha-MSH drug conjugates have been synthesized, 2 C-terminal (Pep 3 and 4) and 2 central fragments (Pep 1 and 2), the latter being the 4-10 sequence known to be the main alpha-MSH-receptor-recognition site. Melphalan was introduced into each sequence at different locations. Their ability to recognize alpha-MSH receptors as well as their cytotoxic effects were compared in 3 cell lines: melanoma, carcinoma and fibroblast cells. Pep 1 and 2 were able to specifically bind to MSH receptors on melanoma cells by displacing labelled alpha-MSH from its binding sites at concentrations similar to the 4-10 heptapeptide sequence known to contain the main receptor-recognition site. They subsequently penetrate the cell, most probably by a receptor internalization mechanism, since about half of their effect could be inhibited by competition at the receptor level. Significant and selective cytotoxic effects to melanoma cells could be observed after only 2 hr exposure to the drug conjugates. Interestingly, these 2 conjugates, differing only in melphalan position, showed completely different cytotoxicity in terms of IC50 values, Pep 1 being 24 times more toxic to all cells; but the 2 were equally specific to melanoma cells. However, they both were less toxic to all cells than melphalan itself. Furthermore, Pep 1 and 2 were able to block the receptor and, unlike Pep 3 and 4, their cytotoxic effect could be significantly inhibited by an alpha-MSH agonist. Pep 3 and 4 were 5 to 10 times less toxic than melphalan to melanoma and carcinoma cells and 50 times less to fibroblast cells, and did not show any cell-type selectivity. They were less toxic than Pep 1 to melanoma and carcinoma cells by a factor of 2, but equally toxic to fibroblasts. In contrast, they were more toxic than Pep 2 to fibroblasts, melanoma and carcinoma by a factor of 3, 10 and 24 respectively. Our data strongly suggest a receptor-mediated cytotoxicity mechanism occurring with alpha-MSH central fragments in human melanoma cells due to the presence of alpha-MSH-specific receptors. This mechanism appeared to be both peptide- and cell-type-specific.
Morandini
R
R
L.O.C.E.-Campus Erasme, Free University of Brussels, Belgium.
Süli-Vargha
H
H
Libert
A
A
Loir
B
B
Botyánszki
J
J
Medzihradszky
K
K
Ghanem
G
G
D002294:Carcinoma, Squamous Cell / Q000188:drug therapy; D002478:Cells, Cultured / Q000187:drug effects; D004338:Drug Combinations; D004354:Drug Screening Assays, Antitumor; D005347:Fibroblasts / Q000187:drug effects; D006801:Humans; D008545:Melanoma / Q000188:drug therapy*; D008558:Melphalan / Q000627:therapeutic use* / Q000633:toxicity; D008969:Molecular Sequence Data; D011979:Receptors, Pituitary Hormone / Q000187:drug effects*; D012878:Skin Neoplasms / Q000188:drug therapy*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured / Q000187:drug effects; D000521:alpha-MSH / Q000627:therapeutic use* / Q000633:toxicity
D004338:Drug Combinations; D011979:Receptors, Pituitary Hormone; D000521:alpha-MSH; C029446:MSH receptor; D008558:Melphalan