A Pluripotency and Self-Renewal Program Controls the Expansion of Genetically Unstable Cancer Stem Cells in Pluripotent Stem Cell- Derived Tumors

Human germ cell tumors are often metastatic, presumably due to distal site tumor growth by cancer stem cells. To determine whether cancer stem cells can be identified in a transplantation model of testicular germ cell tumor we transplanted murine embryonic germ cells (EGCs) into the testis of adult severe combined immunodeficient (SCID) mice. Transplantation resulted in a locally invasive solid tumor, with a cellular component that generated secondary tumors upon serial transplantation. The secondary tumors were invariably metastatic, a feature not observed in the primary tumors derived from EGCs. In order to characterize the differences between EGCs and the tumor-derived stem cells, we performed karyotype and microarray analysis. Our results show that generation of cancer stem cells is associated with the acquisition of non-clonal genomic rearrangements not found in the originating population. Furthermore, pretreatment of EGCs with a potent inhibitor of selfrenewal, retinoic acid, prevented tumor formation and the emergence of these genetically unstable cancer stem cells. Microarray analysis revealed that EGCs and first and second-generation cancer stem cells were highly similar, however approximately 1,000 differentiallyexpressed transcripts could be identified corresponding to alterations in oncogenes and genes associated with motility and development. Combined, the data suggest that the activation of oncogenic pathways in a cellular background of genetic instability coupled with an inherent ability to self-renew are involved in the acquisition of metastatic behavior in the cancer stem cell population of tumors derived from pluripotent cells.