Inhibitors of melanogenesis increase toxicity of cyclophosphamide and lymphocytes against melanoma cells

Abstract

High mortality rate for metastatic melanoma is related to its resistant to the current methods of therapy. Melanogenesis is a metabolic pathway characteristic for normal and malignant melanocytes that can affect the behavior of melanoma cells or its surrounding environment. Human melanoma cells in which production of melanin pigment is dependent on tyrosine levels in medium were used for experiments. Peripheral blood mononuclear cells were derived from the buffy coats purchased from Lifeblood Biological Services. Cell pigmentation was evaluated macroscopically, and tyrosinase activity was measured spectrophotometrically. Cell proliferation and viability were measured using lactate dehydrogenase release MTT, [ 3 H]-thymidine incorporation and DNA content analyses, and gene expression was measured by real time RT-PCR. Pigmented melanoma cells were significantly less sensitive to cyclophosphamide and to killing action of IL-2-activated peripheral blood lymphocytes. The inhibition of melanogenesis by either blocking tyrosinase catalytic site or chelating copper ions sensitized melanoma cells towards cytotoxic action of cyclophosphamide, and amplified immunotoxic activities of IL-2 activated lymphocytes. Exogenous L-DOPA inhibited lymphocyte proliferation producing the cell cycle arrest in G1/0 and dramatically inhibited the production of IL-1beta, TNF-alpha, IL-6 and IL-10. Thus, the active melanogenesis could not only impair the cytotoxic action of cyclophosphamid but also has potent immunosuppressive properties. This resistance to a chemotherapeutic agent or immunotoxic activity of lymphocytes could be reverted by the action of tyrosinase inhibitors. Thus, the inhibition of melanogenesis might represent a valid therapeutic target for the management of advanced melanotic melanomas.

Targeting protein-trafficking pathways alters melanoma treatment sensitivity

“…The data here indicate that melanomas can be protected from apoptosis by melanosomal sequestration of treatment agents, consistent with our and other groups' previous findings that melanosome function plays a role in melanoma treatment resistance (13,(27)(28)(29)(30)(31). Gottesman and colleagues (29) have shown that chemosensitivity is independent of melanoma pigment content, consistent with a melanosome function alternative to that of melanin synthesis (e.g., sequestration) influencing chemosensitivity.…”

Oral Mucosal Melanoma: Some Pathobiological Considerations and an Illustrative Report of a Case

“…Melanocytes also have the capacity to produce melatonin and serotonin which appear to contribute to the regulation of the metabolic activities of neighbouring cells and thus to the homeostasis of skin and mucosa both under physiological conditions, and in response to noxious stimuli [30]. The functions of mucosal melanocytes in this regard are not well understood [12,31,32].…”

“…On the other hand, melatonin, IL-1, IL-6, TNFa, TGF-b, IFNc and glucocorticoids in the local microenvironment are inhibitors of melanogenesis [33]. The production of melanin is therefore regulated by complex interactions between stimulating and inhibiting biological mediators [30,33,34].…”

Evaluation of Anti-Melanogenic and Cytotoxic Activities of Phlomis caucasica on Human Melanoma SKMEL-3 Cells

“…Afterwards, tyrosinase over activity increases some toxic and mutagenic intermediates of melanogenesis as well as hyperpigmentation. Moreover, it can affect the melanoma cells' behavior through autophagy effect on tumor cells (1)(2)(3). The melanin can protect malignant melanocytes as well as normal melanocytes from numerous physical and chemical damages.…”