Proliferation and weak aerotaxis changes the cancer cell distribution in oxygen gradients at physiological level

The migration and proliferation of cancer cells within the extracellular matrix play a critical role in cancer metastasis, enabling cancer cells to move between the blood and lymph vessels and surrounding tissues and form tumors. The heterogeneous oxygen conditions in the tumor microenvironment (TME) also affect cancer cell behaviors. However, the behaviors of cancer cells in the extremely low oxygen concentration gradients in the TME are poorly understood. The present study evaluated the behaviors of cultured cancer cells using microfluidic devices capable of precise oxygen concentration control. MDA-MB-231 cells mixed within a collagen gel were placed in the device and observed for 24 h under various oxygen concentration gradients with different oxygen levels and slopes. The cell distribution changed depending on the oxygen concentration gradient, with cell proliferation being the primary factor, with some contribution of aerotaxis. Aerotaxis directed the migration of MDA-MB-231 cells toward higher oxygen concentrations within the 2–6% O₂ range and lower oxygen concentrations within the 7–12% O₂ range. These results demonstrate the utility of microfluidic devices for analyzing cancer cell behaviors under oxygen concentration gradients at oxygen levels similar to those in the TME and show that cancer cells exhibit different aerotactic behaviors at specific oxygen concentrations.