Stability of the Arginine–Ornithine–Citrulline Cycle Maintained by Tumor–Stroma Interactions in Cell Coculture Hydrogel Microspheres

Tumor–stroma interaction is the core process of tumor metastasis. Therefore, building a model of tumor–stromal cell communication is crucial for understanding the tumor metastasis process and curing cancer completely. In this research, a controllable three-dimensional (3D) tumor–stroma coculture microsphere model based on droplet microfluidic technology was developed to culture human lung cancer cells (A549 cell) and fibroblast cells (NIH-3T3 cell) using core–shell hydrogel microspheres to partition different kinds of cells. In our coculture model, tumor cells show a trend of epithelial–mesenchymal transition (EMT): a decrease in the number of surface E-cadherin and an increase in the number of N-cadherin. At the same time, fibroblasts are activated into cancer-associated fibroblasts (CAFs) as the level of interleukin-6 (IL-6) released is increased. In addition, an interesting phenomenon was discovered; in the absence of fibroblasts, the metabolism of the tumor cell culture alone leads to arginine depletion and citrulline accumulation, whereas a coculture can maintain the arginine–ornithine–citrulline cycle to reach equilibrium after 72 h, and the balance increases the stress resistance of tumor cells. This discovery may provide a new direction for understanding tumor resistance.