The Role of the Tumor Microenvironment in CSC Enrichment and Chemoresistance: 3D Co-culture Methods.

Cancer stem-like cells (CSC) are responsible for tumor progression, chemoresistance, recurrence, and poor outcomes in many cancers, making them critical research and therapeutic targets. One of the critical components potentiating CSC chemoresistance is the interactions between CSC and the surrounding cells in the tumor microenvironment. Our lab has developed several 3D co-culture models to study ovarian CSC interactions with stromal or immune cells found in ovarian tumor microenvironments. In this chapter, we use ovarian cancer as a model to describe the methodologies developed in our lab; however, these techniques are applicable to a wide range of cancers. First, we discuss our method for isolating CSC from heterogeneous tumors and for creating 3D self-assembled tumoroids in hanging drop plates, in either monoculture or co-culture with mesenchymal stem cells or monocytes/macrophages. We then discuss methods for analyzing these models with a focus on isolating cell-type-specific changes and mechanism investigation. Specifically, we describe lentiviral transduction and flow cytometry as established and robust methods to identify and separate each cell type for downstream analysis. We then describe methods to examine CSC functionality with transwell migration assays and colorimetric MTS-based proliferation assays. Finally, we demonstrate enzyme-linked immunosorbent assays (ELISA ) and quantitative polymerase chain reaction (qPCR) methods as mechanistic investigation tools to decouple paracrine and juxtacrine interactions. These methods have wide-reaching applications in cancer research from basic biological investigations, to drug discovery, and personalized drug screening for precision medicine.