Abstract
BACKGROUND
Prostate tumor‐initiating cells (TICs) have intrinsic resistance to current therapies. TICs are commonly isolated by cell sorting or dye exclusion, however, isolating TICs from limited primary prostate cancer (PCa) tissues is inherently inefficient. We adapted the collagen adherence feature to develop a combined immunophenotypic and time‐of‐adherence assay to identify human prostate TICs.
METHODS
PCa cells from multiple cell lines and primary tissues were allowed to adhere to several matrix molecules, and fractions of adherent cells were examined for their TIC properties.
RESULTS
Collagen I rapidly‐adherent PCa cells have significantly higher clonogenic, migration, and invasion abilities, and initiated more tumor xenografts in mice when compared to slowly‐adherent and no‐adherent cells. To determine the relative frequency of TICs among PCa cell lines and primary PCa cells, we utilized zebrafish xenografts to define the tumor initiation potential of serial dilutions of rapidly‐adherent α2β1hi/CD44hi cells compared to non‐adherent cells with α2β1low/CD44low phenotype. Tumor initiation from rapidly‐adherent α2β1hi/CD44hi TICs harboring the TMPRSS2:ERG fusion generated xenografts comprising of PCa cells expressing Erg, AMACR, and PSA. Moreover, PCa‐cell dissemination was consistently observed in the immune‐permissive zebrafish microenvironment from as‐few‐as 3 rapidly‐adherent α2β1hi/CD44hi cells. In zebrafish xenografts, self‐renewing prostate TICs comprise 0.02–0.9% of PC3 cells, 0.3–1.3% of DU145 cells, and 0.22–14.3% of primary prostate adenocarcinomas.
CONCLUSION
Zebrafish PCa xenografts were used to determine that the frequency of prostate TICs varies among PCa cell lines and primary PCa tissues. These data support a paradigm of utilizing zebrafish xenografts to evaluate novel therapies targeting TICs in prostate cancer. Prostate 74:187–200, 2014. © 2013 Wiley Periodicals, Inc.