Fig. 2

5-FU-resistant colorectal cancer cell lines normally grow in a high concentration of 5-fluorouracil. A Protocol for induction of a 5-FU-chemoresistance in CRC cell lines. DLD-1, HCT-116 and HT-29 were treated with increasing doses of 5-FU (culture medium is changed every two days). Cells underwent three passages in each dose of 5-FU. 5-FU treatments were started at 2 μM up to 50 μM by increasing the dose by 5 μM at each stage. B Morphological changes observed after induction of a 5-FU chemoresistance. Cells visualized under 10X magnification with Cell Discoverer 7 microscope. 5-FU-resistant DLD-1, HCT-116 and HT-29 CRC cell lines have a more fibroblastic appearance and demonstrate reduced intercellular contacts compare to the 5-FU-sensitive corresponding cell lines. Additionally, drug resistant cells extend pseudopodia. C Cell proliferation assays. 5-FU-sensitive (solid line) and -resistant (dotted line) DLD-1, HCT-116 and HT-29 CRC cell lines were seeded at D0 in six-well plates. They were treated at D + 2 for 24 h with 10 μM uracil (pink, circle) or 10 μM (blue, square) or 50 μM (red, triangle) 5-FU. They were counted at D + 2, D + 4 and D + 7 (three parallel samples in three independent experiments) in order to obtain these cell viability curves (GraphPad Prism 8.1.2). 5-FU: 5-fluorouracil; CRC: colorectal cancer