The Ultrastructural Analysis of Human Colorectal Cancer Stem Cell-Derived Spheroids and Their Mouse Xenograft Shows That the Same Cells Types Have Different Ratios

SIMPLE SUMMARY: A comparative ultrastructural and flow cytometric analysis of colorectal cancer-derived spheroids and their mouse xenografts showed that they both contain the same cell types but with different ratios, reflecting the interaction of cancer cells, respectively, with the in vitro and in vivo microenvironment. ABSTRACT: Spheroids from primary colorectal cancer cells and their mice xenografts have emerged as useful preclinical models for cancer research as they replicate tumor features more faithfully as compared to cell lines. While 3D models provide a reliable system for drug discovery and testing, their structural complexity represents a challenge and their structure-function relationships are only partly understood. Here, we present a comparative ultrastructural and flow citometric analysis of patient colorectal cancer-derived spheroids and their mice xenografts. Ultrastructural observations highlighted that multicellular spheroids and their xenografts contain the same cancer cell types but with different ratios, specifically multicellular spheroids were enriched in cells with a stem-like phenotype, while xenografts had an increased amount of lipid droplets-containing cells. The flow cytometric analysis for stem cell marker and activity showed enrichment of stem-like cells presence and activity in spheroids while xenografts had the inverse response. Our results evidence the effects on cancer cells of different in vitro and in vivo microenvironments. Those differences have to be paid into account in designing innovative experimental models for personalized drug testing.