Abstract A59: Wnt, Notch, and Hedgehog pathways as potential therapeutic targets in OCT4A expressing cancer stem cells of malignant melanoma.

Recent findings have demonstrated that within tumors a small subpopulation of so called cancer stem cells (CSCs) exists, which exhibits a self-renewing capacity and seems responsible for tumor maintenance and metastasis. But today's methods of isolating CSCs from the bulk of cells are highly inefficient. The most important step in the field of CSC research is to identify markers that represent stem cell criteria like self-renewal and asymmetric cell division. We identified small subpopulations of OCT4A⁺ cells within patient-derived malignant melanoma cells providing such criteria. To enrich for putative CSCs we sorted these low-passage melanoma cells into CD133⁺ and CD133⁻ fractions and found the TGF-β signaling cascade only active in CD133⁺ cells. Furthermore, the self-renewal factor OCT4 is predominantly present in CD133⁺ but not in CD133⁻ tumor cells. Sequencing and restriction digest confirmed specific expression of OCT4A. OCT4A⁺ and OCT4A⁻ cells were then transfected with a phOCT4-EGFP reporter construct and FACS sorted into the respective subpopulations. Immunocytological staining with an anti-OCT4A-specific antibody confirmed that OCT4-EGFP⁺ melanoma cells express nuclear OCT4A. Results showed a strong nuclear staining pattern for OCT4A in OCT4-EGFP⁺ melanoma cells whereas OCT4-EGFP⁻ melanoma cells were only weakly and unspecifically stained all over the cell body. To further characterize OCT4-EGFP⁺ and OCT4-EGFP⁻ cells we performed genome-wide expression profiling. KEGG pathway analysis revealed that key developmental pathways such as Wnt, Notch and Hedgehog signaling were amongst the most up-regulated pathways in OCT4-EGFP⁺ compared to OCT4-EGFP⁻ melanoma cells, thus suggesting that OCT4 expression plays a crucial role in maintaining cancer stem-like properties in melanoma-derived cells. In embryonic stem cells processes that govern development, self-renewal and cell fate are mainly regulated by the Wnt, Notch and Hedgehog pathways. These pathways are also known to be frequently deregulated in many types of cancers. Our data provide evidence that only a small subpopulation of melanoma cells is characterized by aberrant developmental pathways. These OCT4⁺ cells comprise both, the characteristics of stem-like cells and malignant tumors, thus defining CSCs in melanoma. In conclusion, Notch, Wnt and Hedgehog pathways might be ideal targets to eradicate CSCs from the tumor, thus preventing regrowth and metastasis. In combination with classical chemotherapeutic agents this might be an effective therapeutic strategy to circumvent the failure of conventional therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A59.