A Flexible Reporter System for Direct Observation and Isolation of Cancer Stem Cells

• A fluorescent reporter was generated that reports on the presence of SOX2 and OCT4
• Breast cancer cells marked by the reporter have characteristics of cancer stem cells
• The reporter identifies a therapy-resistant subpopulation of cancer cells
• The reporter allows visualization of cancer stem cells in vivo and in real time

SummaryMany tumors are hierarchically organized with a minority cell population that has stem-like properties and enhanced ability to initiate tumorigenesis and drive therapeutic relapse. These cancer stem cells (CSCs) are typically identified by complex combinations of cell-surface markers that differ among tumor types. Here, we developed a flexible lentiviral-based reporter system that allows direct visualization of CSCs based on functional properties. The reporter responds to the core stem cell transcription factors OCT4 and SOX2, with further selectivity and kinetic resolution coming from use of a proteasome-targeting degron. Cancer cells marked by this reporter have the expected properties of self-renewal, generation of heterogeneous offspring, high tumor- and metastasis-initiating activity, and resistance to chemotherapeutics. With this approach, the spatial distribution of CSCs can be assessed in settings that retain microenvironmental and structural cues, and CSC plasticity and response to therapeutics can be monitored in real time.

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