Mechanism(s) regulating inhibition of thymidylate synthase and growth by γ-L-glutaminyl-4-hydroxy-3-iodobenzene, a novel melanin precursor, in melanogenic melanoma cells

doi:10.1016/0006-2952(93)90085-B

Biochemical Pharmacology

Volume 45, Issue 2, 26 January 1993, Pages 473-481

https://doi.org/10.1016/0006-2952(93)90085-B Get rights and content

Abstract

A proposed mechanism for the melanoma specific activity of phenolic amines is based upon the ability of the enzyme tyrosinase to oxidize these prodrugs to toxic intermediates. In this study, we synthesized an iodinated analog of γ-l-glutaminyl-4-hydroxybenzene (GHB) with increased antimelanoma activity in both human and murine melanoma cell lines. GHB and γ-l-glutaminyl-4-hydroxy-3-iodobenzene (I-GHB) were shown to be substrates for both mammalian and mushroom tyrosinase. Glutathione, a cellular antioxidant, inhibited tyrosinase mediated formation of γ-l-glutaminyl-3,4-benzoquinone (GBQ) from GHB, inhibited melanin production, and blocked the inhibition of the enzyme thymidylate synthase by oxidized GHB. Buthionine sulfoximine (BSO) depletion of cellular glutathione enhanced the growth inhibitory activity and the inhibition of in situ thymidylate synthase by phenolic amines in melanoma cells. GHB and I-GHB were shown to be approximately 5- and 10-fold more cytotoxic, respectively, in highly metastatic B16-BL6 cells than in weakly metastatic B16-F1 cells with approximately equal tyrosinase activity. B16-BL6 cells had approximately 20-fold higher γ-glutamyltranspeptidase (γ-GTPase) activity than B16-F1 cells which suggested the possible involvement of this enzyme in the activation of the cytotoxicity of the phenolic amines. 4-Aminophenol, a product of γ-GTPase reaction with GHB, was a substrate for tyrosinase and a potent inhibitor of in situ thymidylate synthase activity in melanogenic cells. In pigmented melanoma cells containing the enzyme tyrosinase, the quinone mediated mechanism of phenolic amine cytotoxicity may be uniquely important and the cellular antioxidant glutathione essential in the detoxification of these quinone-generated intermediates.

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Citation Excerpt :
The high absorbance for intracellular melanin could be ascribed to the benzoquinones found in R. melanophloeos. Gamma-l-glutaminyl-3-4-benzoquinone is a precursor in the production of melanin, therefore, the absorbance reading could have included both the melanin produced and the γ-l-glutaminyl-3-4-benzoquinone present (Prezioso et al. 1993). Consequently, the absorbance gave a false positive; possibly because γ-l-glutaminyl-3-4-benzoquinone was mostly present, there was no mature melanin which could move to the extracellular space.
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Considering both the antibacterial activity and the stimulatory effect of the treatment on melanin production, H. revolutum and W. somnifera (leaves) could be considered as potential plants for further studies for PMH.
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$Results$ : B16-F10-BL6 (BL6) melanoma cells were shown to express a 20-fold higher level of GGTP than the B16-F1 melanoma variant cells. Cultures of BL6 and B16-F1 cells depleted extracellular glutathione at rates of 2.4 and <0.1 nmol glutathione/10⁶ cells/h, respectively, and BL6 cells exported glutathione at a rate 7.2-fold higher than B16-F1 cells (710 and 98 pmol glutathione/10⁶ cells/h, respectively). BL6 melanoma cells replenished exhausted intracellular glutathione levels from an extracellular glutathione source at a rate of 1.21 nmol glutathione/h (18% basal glutathione/h); however, B16-F1 cells lacked the capacity to replenish intracellular glutathione despite the presence of exogenous glutathione in the culture medium. BL6 melanoma cells were radioresistant compared to the B16-F1 cell line, exhibiting extrapolation numbers ( $n$ ) of 14.9 and 1.0, respectively, and a lower surviving fraction to a wide range of radiation doses. The GGTP inhibitor combination of l-serine and sodium borate blocked the repletion of intracellular glutathione and in the presence or absence of buthionine sulfoximine-mediated depletion of glutathione reverses the radiation resistance in BL6 melanoma cells to near baseline levels observed with the B16-F1 parent clone. Serine-borate treatment of low-GGTP expressing B16-F1 cells had no effect on the $n$ value or the surviving fraction of cells to a range of ionizing irradiation doses.
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Mechanism(s) regulating inhibition of thymidylate synthase and growth by γ-L-glutaminyl-4-hydroxy-3-iodobenzene, a novel melanin precursor, in melanogenic melanoma cells

Abstract

J Invest Dermatol

Cancer Lett

J Biol Chem

Biochem Pharmacol

Tetrahedron Lett

Exp Cell Res

Int J Radial Oncol Biol Phys

J Biol Chem

J Biol Chem

J Invest Dermatol

J Invest Dermatol

Biochem Biophys Res Commun

The emerging epidemic of melanoma and squamous cell skin cancer

JAMA

Malignant melanoma: changing trends in factors influencing metastasis-free survival from 1964 to 1982

Cancer

Malignant melanoma

Randomized Trials in Cancer. EORTC Monogr Ser

DTIC (NSC-45388) in malignant melanoma: A perspective

Cancer Treat Rep

Human melanoma targeting with α-MSH-melphalan conjugate

Melanoma Res

Saporin 6 conjugated to monoclonal antibody selectively kills human melanoma cells

Melanoma Res

Preliminary observations of malignant melanoma therapy using radiolabeled alpha-methyltyrosine

J Surg Oncol

Melanin-affinic thioureas as selective melanoma seekers

Melanoma Res

New thermal neutron capture therapy for malignant melanoma: Melanogenesis-seeking 10B molecule-melanoma cell interaction from in vitro to first clinical trial

Pigment Cell Res

Molecular-based treatment of malignant melanoma

New thermal neutron capture therapy for malignant melanoma: Melanogenesis-seeking ¹⁰B molecule-melanoma cell interaction from in vitro to first clinical trial