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PC3 Human Prostate Carcinoma Cell Holoclones Contain Self-renewing Tumor-Initiating Cells

¹ Department of Carcinogenesis, Science Park-Research Division, The University of Texas M.D. Anderson Cancer Center, Smithville, Texas; ² Division of Nutritional Science, Department of Human Ecology, The University of Texas at Austin, Austin, Texas; and ³ Program in Molecular Carcinogenesis, Graduate School of Biomedical Sciences, Houston, Texas

Requests for reprints: Dean G. Tang, The University of Texas M.D. Anderson Cancer Center, Smithville, TX 78957. Phone: 512-237-9575; Fax: 512-237-2475; E-mail: dtang{at}mdanderson.org.

Key Words: holoclones • tumor-initiating cell • cancer stem cells • prostate cancer • PC3

Primary keratinocytes exhibit three typical clonal morphologies represented by holoclones, meroclones, and paraclones, with holoclones containing self-renewing stem cells, and meroclones and paraclones containing more mature and differentiated cells. Interestingly, long-term–cultured human epithelial cancer cells in clonal cultures also form holoclones, meroclones, and paraclones, and tumor cell holoclones have been hypothesized to harbor stem-like cells or cancer stem cells. However, the key question of whether tumor cell holoclones genuinely contain tumor-initiating cells has not been directly addressed. Here, using PC3 human prostate carcinoma cells as a model, we provide direct experimental evidence that tumor cell holoclones contain stem-like cells that can initiate serially transplantable tumors. Importantly, holoclones derived from either cultured PC3 cells or holoclone-initiated tumors can be serially passaged and regenerate all three types of clones. In contrast, meroclones and paraclones cannot be continuously propagated and fail to initiate tumor development. Phenotypic characterizations reveal high levels of CD44, ₂β₁ integrin, and β-catenin expression in holoclones, whereas meroclones and paraclones show markedly reduced expression of these stem cell markers. The present results have important implications in understanding morphologic heterogeneities and tumorigenic hierarchies in human epithelial cancer cells. [Cancer Res 2008;68(6):1820–5]