Date of Award

8-29-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biochemistry Program

Abstract

Bleaching agents 4-tertiary butyl phenol (4-TBP) and monobenzyl ether of hydroquinone (MBEH) have been known to cause occupational vitiligo This project answers whether agents 4-TBP and MBEH can be used for prophylactic treatment of familial melanoma by being specifically toxic to melanocytes and activating an immune response against distant pigment cells. Cytotoxic experiments reveal that similar to 4-TBP, MBEH induces specific melanocyte death. To compare death pathways initiated by 4-TBP and MBEH, classical apoptotic hallmarks were evaluated in treated melanocytes. MBEH induced cell death without activating the caspase cascade or DNA fragmentation, showing that the death pathway is non-apoptotic. Release of High Mobility Group Box-1 protein by MBEH-treated melanocytes and ultrastructural features further confirmed a necrotic death pathway mediated by MBEH. A negative correlation between MBEH-induced cell death and cellular melanin content supports a cytoprotective role for melanin. Moreover, MBEH exposure upregulated the levels of melanogenic enzymes in cultured melanocytes whereas 4-TBP reduced the expression of the same. Insensitivity of melanoma cell lines to either agent in comparison with melanocytes further supported the need for prophylactic therapy. Successful prophylaxis will likely require a systemic immune response in order to eradicate all melanocytes; therefore, immune infiltrates in response to these agents was assessed in vivo. C57BL/6 wild type as well as k14-SCF transgenic, mice were topically treated with either agent. MBEH induced significant skin depigmentation in both strains, not observed upon 4-TBP treatment. A significant increase in the migration of Langerhans cells towards the dermis in human skin explants, upon MBEH treatment, suggested selective elicitation of an immune response. Cytokine expression patterns in skin treated with MBEH supported activation of a Th1-mediated immune response corresponding to an influx of T cells and macrophages. Importantly, despite insensitivity of tumor cells to MBEH-induced cytotoxicity, significantly retarded tumor growth was observed in B16 challenged k14-SCF mice pretreated with MBEH, likely due to an abundance of cytotoxic T cells accompanied by an increased expression of Th1 and Th17 cytokines. . In conclusion topical application of MBEH and not 4-TBP generates a two tierd response that constitutes a candidate prophylactic treatment of familial melanoma.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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