Why tyrosinase for treatment of melanoma

Microwave enhanced synthesis of halogenated derivatives of L-tyrosine labeled with deuterium in aromatic ring

Three halogenated derivatives of L-tyrosine, selectively labeled with deuterium in aromatic ring, i.e., 3′-fluoro-[5′-2H]-, 3′-chloro-[5′-2H]-, and 3′-iodo-[2′,5′-2H2]-L-tyrosine, were synthesized using microwave assisted acid-catalyzed isotope exchange between 3′-fluoro-, 3′-chloro- and 3′-iodo-L-tyrosine and heavy water. The degree of deuterium incorporation was confirmed by 1H NMR spectroscopy. The spectroscopic data indicate that isotope exchange depends on the method of heating and the power of microwaves. The deuterium enrichment of 3′-fluoro-[5′-2H]- and 3′-chloro-[5′-2H]-L-tyrosine amounted to 70% and 60%, respectively, while for 3′-iodo-[2′,5′-2H2]-L-tyrosine this value was about 50% and 95% for the 2′- and 5′-position. The isotopomers were obtained in good chemical yields of 50–70%.

Isotope effects in the tyrosinase catalysed hydroxylation of l-tyrosine methyl derivatives

To investigate isotope effects in the hydroxylation of [3',5'-²H₂]-α-methyl- and [3',5'-²H₂]-N-methyl-l-tyrosine, they were synthesised using acid catalysed isotope exchange at high temperature. The kinetic and solvent deuterium isotope effects on V_max and V_max/K_m parameters of tyrosinase in its action on methylated derivatives of l-tyrosine were determined using the non-competitive spectrophotometric method. Lineweaver-Burk plots were used to consider the inhibition type of O-methyl-l-tyrosine, revealing that it is an uncompetitive inhibitor of tyrosinase.

Isotope effects in mechanistic studies of l-tyrosine halogen derivatives hydroxylation catalyzed by tyrosinase

The kinetic (KIE) and solvent (SIE) isotope effect methods were used to investigate the mechanism of enzymatic hydroxylation of halogenated derivatives of l-tyrosine to l-DOPA catalyzed by the enzyme tyrosinase (EC 1.14.18.1). The values of deuterium KIE and SIE were obtained using the non-competitive method with spectrophotometric measurements. The Lineweaver–Burk plots were used for determination of the inhibition mode of 3′-iodo-l-tyrosine. Based upon kinetic effects values the mechanism of action of enzyme tyrosinase was proposed.

Syntheses of halogen derivatives of L-tryptophan, L-tyrosine and L-phenylalanine labeled with hydrogen isotopes

Halogenated, labeled with tritium and doubly with deuterium and tritium, derivatives of L-tryptophan, i.e. 5'-bromo-[2-(3)H]-, 5'-bromo-[2-(2)H/(3)H]-, 5'-fluoro-[2-(3)H]-5'-fluoro-[2-(2)H/(3)H]-, 6'-fluoro-[2-(3)H]-, 6'-fluoro-[2-(2)H/(3)H]-L-tryptophan, as well as, L-tyrosine, i.e. 3'-fluoro-[2-(3)H]-, 3'-fluoro-[2-(2)H/(3)H]-, 3'-chloro-[2-(3)H]-, and 3'-chloro-[2-(2)H/(3)H]-L-tyrosine, and also L-phenylalanine, i.e. 2'-fluoro-[(3S)-(3)H]-, 2'-fluoro-[(3S)-(2)H/(3) H]-, 2'-chloro-[(3S)-(3)H]-, 2'-chloro-[(3S)-(2)H/(3)H]-, 4'-chloro-[(3S)-(3)H]-, and 4'-chloro-[(3S)-(2)H/(3)H]-L-phenylalanine were synthesized using enzymatic methods. Isotopomers of L-tryptophan were synthesized by coupling of halogenated indoles with S-methyl-L-cysteine carried out in deuteriated or tritiated incubation media. Labeled halogenated derivatives of L-tyrosine were obtained by the enzymatically supported exchange between halogenated L-tyrosine and isotopic water. Labeled halogenated isotopologues of L-Phe were synthesized by the enzymatic addition of ammonia to halogenated cinnamic acid. As a source of hydrogen tritiated water (HTO) and heavy water (D2O) with addition of HTO were used.

Screening of inhibitors for mushroom tyrosinase using surface plasmon resonance

Tyrosinase inhibitors have been used as whitening or antihyperpigment agents because of their ability to suppress dermal-melanin production. In the present study, screening and kinetic evaluation of various small molecules were performed on mushroom tyrosinase (MT) using surface plasmon resonance. The binding constant KD (M) values obtained for tannic acid, phloroglucinol, saffron, catechol, and pyrogallol are 1.213 × 10(-4), 7.136 × 10(-5), 3.111 × 10(-5), 1.557 × 10(-5), and 7.981 × 10(-6) M, respectively. Pyrogallol has been found to display high affinity for MT, whereas catechol, saffron, and phloroglucinol have been found to bind with low affinity. MT shows considerable changes in the secondary structure in the presence of inhibitors. The study reveals the Biacore/SPR sensor's ability in the rapid identification and characterization of inhibitors for MT. The methodology described here can be used to rapidly screen and optimize various lead compounds for other enzymes and elucidate structure function inter-relationships between various enzymes.

Evaluation of crocin and curcumin affinity on mushroom tyrosinase using surface plasmon resonance

Tyrosinase inhibitors have potential applications in the cosmetics and food industries for preventing browning reactions and also as therapeutic drugs for neurodegenerative diseases such as Parkinson's. In this article, crocin and curcumin were evaluated as mushroom tyrosinase inhibitors. Results showed that, both compounds strongly inhibited the diphenolase activity than monophenolase. The IC50 values for diphenolase activity were estimated to be 0.11 mM and 0.18 mM for crocin and curcumin respectively. The binding kinetics of crocin and curcumin was studied with mushroom tyrosinase using surface plasmon resonance (SPR). Tyrosinase was immobilized on the gold surface of a Biacore sensor chip through amine coupling. Binding of inhibitors was analyzed by SPR without the need to further modify the surface or the use of other reagents. The binding constant KD (M) for mushroom tyrosinase obtained was 1.21×10(-4) M for crocin and 1.64×10(-4) M for curcumin, while showing a higher affinity for L-DOPA 1.95×10(-8) M, a substrate for tyrosinase (positive control). The study reveals the SPR sensor's ability to detect binding of the inhibitors.

Vitiligo: interplay between oxidative stress and immune system

Vitiligo is a multifactorial polygenic disorder with a complex pathogenesis, linked with both genetic and non-genetic factors. The precise modus operandi for vitiligo pathogenesis has remained elusive. Theories regarding loss of melanocytes are based on autoimmune, cytotoxic, oxidant-antioxidant and neural mechanisms. Reactive oxygen species (ROS) in excess have been documented in active vitiligo skin. Numerous proteins in addition to tyrosinase are affected. It is possible that oxidative stress is one among the main principal causes of vitiligo. However, there also exists ample evidence for altered immunological processes in vitiligo, particularly in chronic and progressive conditions. Both innate and adaptive arms of the immune system appear to be involved as a primary event or as a secondary promotive consequence. There is speculation on the interplay, if any, between ROS and the immune system in the pathogenesis of vitiligo. The article focuses on the scientific evidences linking oxidative stress and immune system to vitiligo pathogenesis giving credence to a convergent terminal pathway of oxidative stress-autoimmunity-mediated melanocyte loss.

Neuro-Immuno-Endocrine Processes in Vitiligo Pathogenesis

Vitiligo is a cutaneous disorder of depigmentation, clinically characterized by well-demarcated, white macules of varying size and distribution. It can affect up to 2% of the population, especially younger ages. In spite of recent findings implicating genetic, immune and oxidative stress factors, the exact pathogenesis of vitiligo remains obscure. Here, we briefly discuss the prevailing theories, and offer new suggestions that could explain in part the damage of melanocyte in the vitiliginous lesions. Our emerging hypothesis is that neuropeptides released from peripheral nerve endings could synergize with new cytokines to adversely affect melanocyte function and viability. These may include corticotropin-releasing hormone (CRH) and neurotensin (NT), as well as interleukin 33 (IL-33) and thymic stromal lymphopoietin (TSLP). Such interactions could serve the basis for further research, possibly leading to new treatments.

Inhibition kinetics of chlorobenzaldehyde thiosemicarbazones on mushroom tyrosinase

2-Chlorobenzaldehyde thiosemicarbazone (2-Cl-BT) and 4-chlorobenzaldehyde thiosemicarbazone (4-Cl-BT) were synthesized, and their inhibitory kinetics on the activity of mushroom tyrosinase were investigated. Results showed that these compounds exhibited significant inhibitory potency on both monophenolase activity and diphenolase activity of tyrosinase. For the monophenolase activity, both compounds could decrease the steady-state activity of the enzyme sharply, without any influence on the lag period. The IC50 values of them were estimated to be 15.4 μM and 6.7 μM, respectively. For the diphenolase activity, both compounds belonged to reversible inhibitors, but their mechanisms were different: 2-Cl-BT was a noncompetitive type inhibitor, while 4-Cl-BT was a mixed-type inhibitor. Their inhibition constants were determined and compared.

Vitiligo-like primary melanoma

Depigmented or hypopigmented macules and patches have been described in association to primary and metastatic melanoma. Primary melanoma presenting at the onset as a vitiliginous patch without histopathological evidence of regression seems to be a rare event. We report 2 patients with melanoma in situ that expressed clinically as vitiligo-like patches and review the possible immunologic mechanisms responsible for this unusual presentation.

Neurogenic dysregulation, oxidative stress, autoimmunity, and melanocytorrhagy in vitiligo: can they be interconnected?

Several hypotheses have been proposed to explain vitiligo, including the neural theory, impaired redux status, autoimmunity, and more recently melanocytorrhagy arising from defective cell-cell adhesion. It is most likely that the loss of melanocytes in vitiligo arises through a combination of pathogenic mechanisms that act in concert. Here, we discuss the potential interconnection of several mechanisms that are likely to operate. These include the alteration of melanocyte-specific factors by reactive oxygen species to produce neo-antigens and the role of hypoxia and oxidative stress in antigen presentation and the auto-immune destruction of melanocytes.

Vitiligo puzzle: the pieces fall in place

Over the years, the role of biochemical, immunological, genetic, and other biological aspects in the pathogenesis of vitiligo has been studied. So far, no convincing model describing the interplay of these contributing factors has been formulated. Based on existing research, we propose that vitiligo has a multi-factorial etiology, characterized by multiple steps, but always involving an increase of external or internal phenol/catechol concentration, serving as a preferred surrogate substrate of tyrosinase, competing with its physiological substrate tyrosine. The conversion of these substrates into reactive quinones is reinforced by a disturbed redox balance (increasing hydrogen peroxide). Such reactive quinones can be covalently bound to the catalytic centre of tyrosinase (haptenation). This could give rise to a new antigen, carried by Langerhans cells to the regional lymph node, stimulating the proliferation of cytotoxic T cells. However, the activation of such cytotoxic cells is only a first step in skin melanocyte killing, which also depends on a shift in the balance between immune defence and tolerance, e.g. resulting from a decrease in properly functioning T-regulatory cells. With this new model, based on a synthesis of several of the existing theories, in mind, the external and internal factors involved in the etiopathogenesis of vitiligo are reviewed, against the background of reported clinical data, experimental studies and existing and potential new therapies. A similar complex mechanism may also lead to some other autoimmune diseases.

The course of melanoma-associated vitiligo: report of a case

The appearance of vitiligo-like lesions in patients with malignant melanoma is a well-known yet uncommon phenomenon. This finding is especially reported in patients undergoing immunotherapy with or without chemotherapy for malignant melanoma and is generally believed to be associated with a better prognosis. We report a case of preexisting vitiligo in a 48-year-old man, aggravated after chemo-immunotherapy of pulmonary metastatic melanoma with interferon-alpha, vinblastine and dacarbazine. Skin lesions remained stable after discontinuation of the treatment, and repigmentation heralded the recurrence of metastatic disease. These findings were in favor of vitiligo being a marker of the immunity against melanoma cells and its favorable impact on the prognosis of melanoma patients.

Kinetic characterisation of the reaction mechanism of mushroom tyrosinase on tyramine/dopamine and L-tyrosine methyl esther/L-dopa methyl esther

Tyrosinase or polyphenol oxidase is the key enzyme in melanin biosynthesis and for the enzymatic browning of fruits and vegetables. Our research group previously proposed a kinetic reaction mechanism for tyrosinase acting on some phenolic substrates, whose reliability was demonstrated for tyrosinases from several fruits and vegetables. A kinetic analysis and an experimental design for testing the reliability of the kinetic reaction mechanism of tyrosinase are reported. The applicability of the mechanism to the oxidation of tyramine/dopamine and L-tyrosine methyl esther/L-dopa methyl esther has been checked. Some structure/activity topics are discussed. A complete kinetic characterisation of the oxidation of these phenolic substrates has been made. This will be useful for further studies about the control of depigmenting agents, antimelanome drugs and antibrowning reagents acting on tyrosinase.

Differential expression of inhibitory or activating CD94/NKG2 subtypes on MART-1-reactive T cells in vitiligo versus melanoma: a case report

Selection and activation of T cells is tightly regulated by both antigen-specific receptors and co-receptors to ensure that responses to self antigens are largely avoided. By T cell receptor clonotypic mapping and staining with tetrameric HLA-peptide complexes, we demonstrate the presence of melanocyte differentiation antigen MART-1 specific T cells in the areas of destruction of both neoplastic and normal melanocytic cells in a case of a primary melanoma and its associated hypopigmentation. These self reactive T cells expressed CD94/NKG2 major histocompatibility complex class I specific C-type lectin-like receptors. This family of receptors includes both activating and inhibitory isoforms. Thus, we performed a detailed analysis that revealed the exclusive presence of inhibitory NKG2-A/B receptors in the vitiligo-like leukoderma, whereas both the inhibitory receptors and the activating NKG2-C/E isoforms were present within the tumor. Our data suggest the differential expression of killer inhibitory receptors as a possible mechanism to regulate T cell responses to self antigens.

Self-tolerance to the murine homologue of a tyrosinase-derived melanoma antigen: implications for tumor immunotherapy

The human tyrosinase-derived peptide YMDGTMSQV is presented on the surface of human histocompatibility leukocyte antigen (HLA)-A*0201(+) melanomas and has been suggested to be a tumor antigen despite the fact that tyrosinase is also expressed in melanocytes. To gain information about immunoreactivity and self-tolerance to this antigen, we established a model using the murine tyrosinase-derived homologue of this peptide FMDGTMSQV, together with transgenic mice expressing the HLA-A*0201 recombinant molecule AAD. The murine peptide was processed and presented by AAD similarly to its human counterpart. After immunization with recombinant vaccinia virus encoding murine tyrosinase, we detected a robust AAD-restricted cytotoxic T lymphocyte (CTL) response to FMDGTMSQV in AAD transgenic mice in which the entire tyrosinase gene had been deleted by a radiation-induced mutation. A residual response was observed in the AAD(+)tyrosinase(+) mice after activation under certain conditions. At least some of these residual CTLs in AAD(+)tyrosinase(+) mice were of high avidity and induced vitiligo upon adoptive transfer into AAD(+)tyrosinase(+) hosts. Collectively, these data suggest that FMDGTMSQV is naturally processed and presented in vivo, and that this presentation leads to substantial but incomplete self-tolerance. The relevance of this model to an understanding of the human immune response to tyrosinase is discussed.

Accumulation of identical T cells in melanoma and vitiligo-like leukoderma

The cloning of genes encoding melanoma antigens has opened new possibilities for the treatment of patients with cancer; however, most tumor rejection antigens recognized by tumor infiltrating lymphocytes are the products of genes that are also expressed by normal melanocytes. Hence, a large set of antigenic determinants of the self have not induced self-tolerance and these peptide determinants furnish target structures for immune responses directed against tumors. The notion that the immunotherapeutic targets involved in cancer regression comprise normal differentiation antigens is stressed by the association between vitiligo-like leukoderma, due to destruction of normal melanocytes, and melanoma regression, due to destruction of cancer cells. Nevertheless, this is the first report to demonstrate by means of a new technique based on reverse transcription polymerase chain reaction and denaturing gradient gel electrophoresis, the presence of clonally expanded T cells with identical BV regions in areas of destruction of both normal and neoplastic cells.