Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Receptor-mediated cytotoxicity of alpha-MSH fragments containing melphalan in a human melanoma cell line. 826 69

A biotinylated derivative of [beta-Ala1,Lys17]-ACTH1-17-NH-(CH2)4-NH2 (ACTH1-17) was synthesized and biologically characterized. The heptadecapeptide with free N-terminus and blocked side-chains was prepared by the solid-phase method using TentaGel resin and a 4-aminobutylamide linker. Biotinyl-beta-Ala-OH was then coupled to the terminal amino group and the resulting [N alpha-(biotinyl-beta-alanyl)-beta-Ala1,Lys17]-ACTH1-17-NH-(CH2)4-N H2 (Bio-ACTH1-17) cleaved from the resin, purified and analyzed. Competition binding assays with mouse B16-F1 and human D10 and HBL melanoma cells using [125I]-alpha-MSH as radioligand gave dissociation constants for Bio-ACTH1-17 of 1.67 +/- 0.07 nM (B16-F1), 0.02 +/- 0.005 nM (D10) and 0.21 +/- 0.02 nM (HBL). The EC50 for Bio-ACTH1-17 in the B16 melanin assay was 4.15 +/- 1.0 nM. Analysis of the binding characteristics of [125I]-Bio-ACTH1-17 demonstrated that in human melanoma cells this radioligand was displaced by ACTH1-17 as well as alpha-MSH whereas in B16-F1 cells the tracer was only displaced from the binding site by ACTH1-17. Studies of Bio-ACTH1-17 with streptavidin showed that the peptide is to a large extent trapped specifically through reaction with biotin. These results demonstrate that (1) the biological characteristics of Bio-ACTH1-17 are almost identical to those of ACTH1-17, (2) Bio-ACTH1-17 is bound by avidin, and (3) Bio-ACTH1-17 may become a useful tool for MSH receptor targeting.
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PMID:Synthesis and biological properties of a biotinylated derivative of ACTH1-17 for MSH receptor studies. 838 54

We have examined the mechanism of homologous regulation of MSH receptor binding and receptor-mediated adenylate cyclase activation in three human and two mouse melanoma cell lines. Pretreatment with alpha-MSH resulted in a time- and dose-dependent up-regulation of MSH receptors in human D10 and 205 melanoma cells whereas in human HBL and in mouse B16-F1 and Cloudman S91 cells alpha-MSH induced receptor down-regulation. Up-regulation of receptors was maximal after a 24-h incubation period and an alpha-MSH concentration of 100 nM (EC50 = 2.4 nM). The increase in alpha-MSH binding was independent of adenylate cyclase activation and protein synthesis and appeared to be caused by recruitment of spare receptors. The structural requirements of the peptide for triggering this process differed from those found in receptor-binding analyses. Receptor down-regulation was maximal after 12 h and hence more rapid than up-regulation. In B16-F1 cells, 10 nM alpha-MSH caused the disappearance of 85-90% of the MSH receptors, the EC50 of 0.23 nM lying exactly between that for alpha-MSH-induced melanogenesis (0.027 nM) and the dissociation constant of receptor binding (1.31 nM). Down-regulation in B16-F1 cells appears to be the consequence of receptor internalization following MSH binding and seems to be initiated during an early step in MSH signalling, preceding the activation of adenylate cyclase and the cAMP signal. Receptor up- and down-regulation were not accompanied by an alteration in affinity to alpha-MSH, as demonstrated by Scatchard analysis of the binding curves.
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PMID:Homologous regulation of the MSH receptor in melanoma cells. 838 55

Investigation of physiological effects of alpha-MSH and its analog (NLe4, D-Phe7)-alpha-MSH on human melanoma cells with different phenotypes has shown that these peptides have a growth-modulating activity. The effect of inhibition or activation of the growth of melanoma cells depended on their phenotypes. (NLe4, D-Phe7)-alpha-MSH activated 1.5-2.5-fold the growth of amelanotic BRO cells at concentrations of 10(-6)-10(-12) M, but inhibited the growth of melanin-producing MS cells under the same conditions not affecting the growth of human lung fibroblasts.
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PMID:[The effect of alpha-melanocyte-stimulating hormone and its analog on the growth of human melanoma cell lines with different phenotypes]. 838 7

The melanocyte-stimulating hormone (alpha-MSH) used at 10(-6)-5 x 10(-8) M concentrations inhibited the growth of amelanotic cells of human malignant melanoma BRO and influenced cell morphology without any effect on melanization or tyrosinase activity. Inhibition of tumour cell growth was accompanied by marked elevation of intracellular cAMP levels but not that of cGMP. Dibutyryl-cAMP and the cAMP-dependent protein kinase A inhibitor also inhibited the cell growth. alpha-MSH increased mono-, di- and 1.4.5-myoinositol triphosphate concentrations and influenced the activities of phosphatidylinositol kinase and phosphatidylinositol-4-phosphate kinase determining phosphatidylinositol-4-phosphate kinase and phosphatidylinositol-4.5-diphosphate levels. Myoinositol phosphate concentrations changed on a second scale and levelled off by the 3rd-5th min, whereas that of cAMP increased drastically by the 30th min.
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PMID:[Melanocyte-stimulating hormone induces growth of human malignant melanoma amelanotic cells with a change in cAMP, phosphatidylinositols, and inositol phosphate concentration]. 838 47

The possible mechanisms for the reduced melanin content and poor melanogenic response to MSH was investigated in B16-F10DD differentiation deficient melanoma cells. In particular, the MSH receptor status and associated signal transduction pathway linking to tyrosinase activity in these cells was studied for evidence of any defects. F10DD cells contained high-affinity binding sites for alpha-MSH, with KD values similar to those previously reported for other variants of the B16 melanoma. SDS-PAGE analysis after radioactive ligand cross-linking showed no evidence of gross structural alterations of the receptor. The F10DD cells expressed approximately twice as many receptors as the F10 parent cell line, suggesting a possible feedback response attempting to compensate for the amelanotic condition. The functional integrity of the MSH receptors in F10DD cells was confirmed by the presence of increased levels of cAMP in response to MSH stimulation. These results, coupled with the observation that F10 and F10DD cells express similar levels of tyrosinase mRNA and protein, point to a structural defect in tyrosinase or in the post-translational control mechanisms by which the activity of this enzyme is regulated.
Melanoma Res 1993 Apr
PMID:MSH receptors and function in amelanotic B16 melanoma cells. 839 Aug 76

A human genomic clone designated MC-2 is isolated. The cloned DNA codes for a protein of 325 amino acids which possesses seven hydrophobic segments, a characteristic of G-protein coupled receptors. The MC-2 receptor is expressed in brain tissue but not in the melanoma cells. When the MC-2 DNA is expressed in COS-7 cells, it binds [125I]-labelled [Nle4, D-Phe7]- alpha melanocyte stimulating hormone (NDP-MSH) which then could be displaced by melanotropic peptides alpha-MSH, beta-MSH, gamma-MSH and adrenocorticotropic hormone, but not by non-melanotropic peptide beta-endorphin. The highest affinity of 5.18 nM was for the NDP-MSH peptide. The novel MC-2 receptor and the MC-1 receptor, described earlier by us (8) showed identical order of affinity for the melanocortin peptides, but the affinities and the fold differences in the affinities to the melanocortin peptides were different when compared to the earlier described MC-1 receptor. The results suggest that the MC-2 DNA codes for a novel melanocortin receptor.
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PMID:Molecular cloning of a novel human melanocortin receptor. 856 9

Variation in the degree of prolonged (residual) biological activity of the melanotropin peptides alpha-MSH (alpha-melanocyte-stimulating hormone, Ac-Ser-Tyr-Met-Glu- His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2) and the superpotent analogues [Nle4,DPhe7]alpha-MSH (MT-I) and Ac-[Nle4,Asp5,DPhe7,Lys10]alpha-MSH(4-10-NH2 (MT-II) has stimulated considerable interest regarding this biological phenomena. We have examined the differences in their relative dissociation rates from the melanocortin receptor, hMC1R, to try and correlate peptide dissociation rates with the observations of prolonged biological activity. Interestingly, these studies revealed that alpha-MSH remained 25% bound, MT-I 65% bound, and MT-II 86% bound 6 h after the ligand had been removed from the assay medium. The relative dissociation rate of MT-II was 4 times slower than that for alpha-MSH and 2 times slower than that for MT-I, which was 2 times slower than that for alpha-MSH. These data suggest that slow dissociation kinetics (hours) may contribute to the prolonged biological activities observed for both MT-I and MT-II peptides in vitro and in vivo. The prolonged binding, biological activities, and enzymatic stability of MT-I and MT-II make them putative candidates for clinical uses such as external scintigraphy for the localization of tumors (i.e., melanoma).
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PMID:Characterizations of the unusual dissociation properties of melanotropin peptides from the melanocortin receptor, hMC1R. 855 11

Seventeen human melanoma cell (HMC) lines, both melanotic and amelanotic, were incubated in the continuous presence of a potent melanotropic peptide hormone analog, [Nle4,D-Phe7] alpha-MSH, for 72 hr with daily changes of medium. Only one cell line (HD, melanotic) consistently responded to the hormone analog by increased tyrosinase activity. Three (one melanotic, two amelanotic) of the HMC lines also failed to respond to the peptide by either increased or decreased enzyme activity when incubated continuously in the presence of the peptide for longer periods of time (6,15,27,43 days). The HD cell line, however, again responded with increasingly enhanced basal enzyme activity the longer the cells were incubated in the presence of the melanotropin. One amelanotic cell line (C8161) responded with enhanced enzyme activity when grown to confluency in the continuous presence of the peptide. Basal tyrosinase activity of the C8161 cell line may have increased as cell density in the flasks increased. These results suggest that under conditions of increased cell number, phenotypic expression of tyrosinase activity in so called "amelanotic" (tyrosinase-negative) cells is increased and can be enhanced further by stimulation with a melanotropic peptide. Under conditions of increased cell number, the presence of [Nle4,D-Phe7] alpha-MSH caused morphological differentiation (shape change); the cells became enlarged and very dendritic. The number of cells in monolayer (surface of the flask) and in the medium were drastically reduced in both melanotic and "amelanotic" cell lines incubated with [Nle4,D-Phe7] alpha-MSH. The data support other published reports that melanotropic peptides inhibit human melanoma cell growth (proliferation) in vitro, most likely through a cytostatic mechanism. [Nle4,D-Phe7] alpha-MSH also exhibited a prolonged (residual) inhibitory action on HD cell proliferation. In other words, inhibition of cell growth (proliferation) of the HMCs was evident even several days after removal of the melanotropic peptide from the incubation medium.
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PMID:The melanotropic peptide, [Nle4,D-Phe7] alpha-MSH, stimulates human melanoma tyrosinase activity and inhibits cell proliferation. 878 40

Stable expression of the MSH receptor in a homologous system is important for the study of the function and mechanism of signalling of this receptor. This is the first report on the stable expression of the human alpha-MSH receptor in the mouse melanoma G4F clone which lacks an endogenous MSH receptor. Several stable transfectant cell lines were obtained all of which express the human MSH receptor in high numbers. Human MSH receptor mRNA expression was detected by Northern blot analysis. Competition binding experiments showed that the MSH receptors expressed in these cells have the same affinity for [Nle4,D-Phe7]-alpha-MSH as the MSH receptors of the human HBL melanoma cell line. Several of the transfectant cell lines produced melanin constitutively, some of them secreting melanin into the medium whereas other clones did not secrete melanin. MSH and cholera toxin did not or only marginally increase melanogenesis in these clones, and forskolin had an opposite effect. These results suggest that the human MSH receptor may be constitutively active in these transfected mouse melanoma cells.
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PMID:Stable expression of the human MSH receptor in a mouse melanoma cell line. 890 30


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