Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The oral administration of alpha-difluoromethylornithine (DFMO), an enzyme-activated inhibitor of ornithine decarboxylase (ODC), produced a marked decrease in the rate of growth of amelanotic Harding-Passey melanoma transplanted in mice. The half-life of this compound in Harding-Pasey melanoma was 30 min. A combined treatment of DFMO and hyperthermia did not show any synergistic effect on the inhibition of tumor growth, and no differences in the levels of tumor ODC, S-Adenosylmethionine decarboxylase (SAMDC) and polyamines were observed between single and combination treatments. DFMO-treatment alone produced a decrease of about 80% in spermidine concentration in melanoma, while in other tissues such as kidney, the diminution of spermidine was only moderate. ODC activity was reduced greatly in the kidney and moderately in melanoma. However, the activity of SAMDC increased up to 30-fold in DFMO-treated melanoma, while only a moderate increase was observed in the renal enzyme. Melanoma tyrosinase activity did not increase with the treatment with DFMO. These results indicate that the inhibition of amelanotic Harding-Passey melanoma growth by DFMO is not caused by the stimulation of cell differentiation, and that in this system polyamine depletion caused by this drug does not produce an enhancement in the heat-induced cytotoxicity.
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PMID:Effects of treatments with alpha-difluoromethylornithine and hyperthermia on the growth and polyamine metabolism of Harding-Passey murine melanoma. 190 4

Both 2-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), and methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), strikingly stimulated melanotic expression of murine Cloudman S91 melanoma cells. The stimulation of tyrosinase (EC 1.10.3.1) activity and melanin formation by DFMO was closely associated with intracellular depletion of putrescine and spermidine developed in response to the drug. However, little or no evidence was obtained indicating that enhanced melanogenesis in response to MGBG was mediated through an inhibition of polyamine biosynthesis. Indirect inhibitors of ornithine decarboxylase, such as 1,3-diaminopropane and 1,3-diaminopropan-2-ol, but not putrescine, likewise inhibited the growth of the melanoma cells and stimulated their melanin production. The stimulation of melanogenesis by polyamine antimetabolites was not mediated by cyclic adenosine 3':5'-monophosphate, in contrast to the effect elicited by alpha-melanotropin. It is also unlikely that MGBG or the diamines acted as lysosomotropic agents capable of stimulating tyrosinase activity in situ, since the enzyme activity was stimulated by the drugs irrespective of whether assayed in cultured cells or using cell-free homogenates. None of the agents stimulated tyrosinase activity in vitro. The effect of DFMO and MGBG on melanoma cell proliferation was reversible, but the restoration of normal growth and melanin formation, especially in cells exposed to DFMO, was remarkably slow. The present results represent a further experimental model, in which the inhibition of polyamine accumulation is accompanied by signs of terminal differentiation.
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PMID:Effects of inhibitors of polyamine biosynthesis on the growth and melanogenesis of murine melanoma cells. 391 40

Continuous exposure for 96 hr of B16 melanoma cells in culture to 2.5 mM alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase, resulted in a marked increase in the activity of the enzyme tyrosinase, and also 20% cell kill as assessed by clonogenic assay. A 4-hr exposure to 0.4 mM 3,4-dihydroxybenzylamine (DHBA), a compound which is melanolytic due to its conversion to a cytotoxic quinone by the tumor specific enzyme tyrosinase, was found to be approximately equitoxic to 2.5 mM DMFO. However, a combination of DFMO (2.5 mM) and DHBA (0.4 mM) produced greater than 95% cell kill. This observed cytotoxicity with the combination suggests that induction of tyrosinase by DFMO sensitizes B16 melanoma cells to the melanolytic activity of DHBA. Oral administration of DFMO to mice bearing subcutaneous B16 melanomas also resulted in marked increases in the activity of tyrosinase in the tumor tissue. In mice inoculated intraperitoneally with 10(5) B16 melanoma cells, administration of DFMO via the drinking water (2%) increased the survival time by 8.5 days, whereas intraperitoneal administration of 300 mg/kg of DHBA for 14 days resulted in an increase in life span of 4.5 days compared to untreated controls. A combination of DFMO and DHBA prolonged the survival time by 14.6 days. These results indicate that DFMO in combination with an appropriate tyrosinase-dependent melanolytic agent might be useful in the chemotherapy of malignant melanomas.
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PMID:Potentiation by alpha-difluoromethylornithine of the activity of 3,4-dihydroxybenzylamine, a tyrosinase-dependent melanolytic agent, against B16 melanoma. 392 51

The objective of the present study was to investigate the effect of polyamine depletion by alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, on the growth and differentiation of B16 melanoma cells grown in culture and also as solid tumors in mice. Polyamine depletion by DFMO (2.5 mM) resulted in a complete inhibition of cell growth in culture and a 90% inhibition of viability of melanoma cells as determined by clonogenic assay at the end of 7 days after DFMO treatment. These results indicate that polyamine depletion induced by DFMO is cytotoxic to B16 melanoma cells in culture. Furthermore a 2- to 5-fold increase in tyrosinase activity and 10-fold accumulation of melanine were observed in polyamine depleted cells compared to control cultures. These effects of DFMO could easily be reversed by the addition of putrescine simultaneously with DFMO. Administration of different doses of DFMO in drinking water to B16 melanoma tumor bearing mice also resulted in an increase in tyrosinase activity and a dose dependent inhibition (86-90%) of tumor growth. Although one cannot rule out the possibility of induction of differentiated phenotype as a result of antiproliferative activity of DFMO, the data presented indicate that the unique sensitivity of melanoma to DFMO may be due to a combination of cell growth inhibition and concomitant induction of differentiation upon polyamine depletion. The results of the present study indicate that polyamines play an important role in growth and differentiation of melanoma and also provide an example of inhibition of tumor cell growth by induction of cellular differentiation.
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PMID:Effect of inhibition of polyamine biosynthesis by DL-alpha-difluoromethylornithine on the growth and melanogenesis of B16 melanoma in vitro and in vivo. 392 49

1. Intermediates in the process of melanin synthesis formed through oxidation of catechols by tyrosinase produced the inactivation of ornithine decarboxylase (ODC), a key enzyme in the polyamine biosynthesis pathway. 2. The inactivation was dependent on the substrate used (dihydroxybenzylamine > L-3,4-dihydroxyphenylalanine > L-tyrosine) and on the concentration of intermediate produced rather than on the rate of formation. 3. Sulfhydryl compounds (dithiothreitol and glutathione) or quinone-reducing agents (ascorbic acid) prevented the inactivation of ODC; L-ornithine, but not other amino acids, also protected partially ODC. The results suggest that different cysteine residues in ODC molecule are implicated in the inactivatory event. 4. When 14C-labeled catechols were used, numerous polypeptides resulted labeled, showing that the reactive quinones formed as intermediates in the process of melanin biosynthesis bind covalently to many cellular proteins.
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PMID:Inactivation of ornithine decarboxylase by intermediates of tyrosinase-catalyzed reaction. 846 26

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in the biosynthesis of polyamines, a family of cationic compounds required for optimal cell proliferation and differentiation. Within mammalian melanocytes, the expression of genes regulating cell growth and/or differentiation can be controlled by alpha-melanocyte-stimulating hormone (alphaMSH) and other melanogenesis modulating agents. In the B16 mouse melanoma model, alphaMSH stimulates melanogenesis by upmodulation of tyrosinase (tyr) activity, whereas the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) inhibits melanin synthesis. Therefore, we analyzed the regulation of ODC by these agents, as related to changes in the melanogenic pathway. Treatment of B16 cells with TPA or alphaMSH rapidly stimulated ODC activity. The effect was stronger for TPA and appeared mainly posttranslational. Irreversible inhibition of ODC with the active site-directed inhibitor alpha-difluoromethylornithine (DFMO) did not block TPA-mediated inhibition of tyr. Conversely, prolonged treatment of B16 cells with DFMO stimulated tyr activity by a posttranslational mechanism, probably requiring polyamine depletion. Combination treatment with alphaMSH and DFMO synergistically activated tyr. Therefore, ODC induction is not involved in the melanogenic response of B16 cells to alphaMSH. Rather, increased intracellular concentrations of polyamines following ODC induction might constitute a feedback mechanism to limit melanogenesis activation by alphaMSH.
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PMID:Regulation of ornithine decarboxylase in B16 mouse melanoma cells: synergistic activation of melanogenesis by alphaMSH and ornithine decarboxylase inhibition. 1185 79