2.2 Rapid generation of single tumor spheroid
To aggregate cells into a spheroid, cells in the exponential growth phase were digested with 2.5% trypsin, diluted to 10,000 cells/mL, quickly mixed with 2.5% volume fraction of Matrigel (356,237, Corning, NY, USA), and seeded into a ”U” type ultra-low attachment 96-well plate (Corning 7007, USA) at 200 μL/well. The 96-well plates were then centrifuged at 1000×g for 10 min, and incubated in a 37°C, 5% CO2 incubator.