C80

Microenvironment-Driven Polarity Switches Determine Chemoresistance via ABCB1 Localization

Colonic epithelial polarity is critical for function and prognosis, yet how the tumor microenvironment regulates this in 3D remains unclear. Ashley et al. investigated how extracellular matrix (ECM) and serum dynamically regulate polarity and the localization of the multidrug transporter ABCB1 in colon cancer spheroids.

Using Matrigel-embedded cultures, they observed that lumen-forming cell lines (C80, OXCO2, SW1222) actively pumped the ABCB1 substrate Rhodamine 123 (R123) into their lumens, whereas non-lumen-forming lines (HCT116, HT29, DLD1) did not (Fig. 1C). This polarized efflux was confirmed using the ABCB1 substrates TMRE and doxorubicin, which accumulated within the lumens of ECM/serum-grown C80 and primary C105251 colonies (Fig. 1D, Fig. 2). Specific ABCB1 inhibitors (verapamil, CP-100356) blocked this luminal accumulation (Fig. 2). Notably, ABCB1 expression levels were unchanged between ECM/serum and serum-free suspension cultures. Instead, polarity dictated drug distribution: ECM/serum attachment induced apical-in polarity, sequestering drugs within lumens, while serum-free suspension cultures exhibited apical-out polarity, expelling drugs outward. This differential localization provides a structural basis for microenvironment-dependent chemoresistance.