SELECTIVE INVIVO AND INVITRO INCORPORATION AND ACCUMULATION OF PHENOLIC THIOETHER AMINE INTO MALIGNANT-MELANOMA AND IDENTIFICATION OF A (58 KD) BINDING GLYCOPROTEIN

Our previous in vivo studies indicated that a phenolic thioether amine (PTEA), 4-S-cysteaminylphenol (CAP), selectively disintegrates melanocytes of black hair and skin, and inhibits the growth of murine and human malignant melanomas. To elucidate the mechanism of the in vivo melanocytotoxicity and anti-melanoma effect, this study examined the selectivity and specificity of PTEA incorporation into malignant melanoma cells using [C-14]4(2)-S-CAP, and then identified a PTEA-binding protein through a ligand binding assay using [I-125]-labelled cell lysates. Whole body autoradiography showed that [C-14]4-S-CAP is selectively incorporated and accumulated into the eye and tumours of a B16 melanoma-bearing mouse. SK MEL 23 human melanoma cells also showed a steady accumulation of [C-14]4-S-CAP (threefold at least up to 5 min) and of [C-14]2-S-CAP (sevenfold up to 20 min), compared with that of HeLa cells and fibroblasts, which plateau at 5 min. Chromatography of 4-S-CAP on an affinity column (both CH- and CNBr-activated Sepharose 4B) identified a 58 kD protein in melanoma cells, which was present at very low levels in HeLa cells; this 58 kD protein was retained by both 4-S- and 2-S-CAP affinity columns, but not by columns of a phenolic thioether (cysteinylphenol: CP) or a phenolic thioether amide (N-acetyl-4-S-CAP), and could be retrieved by either 4-S or 2-S-CAP but not by CP and N-acetyl-4-S-CAP. This protein was glycosylated, and contained mannose residues. Our findings clearly indicate that a 58 kD CAP-binding glycoprotein is highly expressed in melanoma cells and is probably responsible for the selective accumulation of PTEA into melanoma, and may even account for its melanocytotoxicity.