Methotrexate-induced senescence in human adenocarcinoma cells is accompanied by induction of p21waf1/cip1 expression and lack of polyploidy

Human colorectal adenocarcinoma C85 cells, treated with high dose methotrexate (1 μM; IC50 = 51 nM), undergo accelerated senescence, as the cells (i) are growth arrested at the G1 and S phases of the cell cycle, (ii) are SA-β-galactosidase-positive, (iii) show induced expression of p21waf1/cip1 and decreased expression of p16INK4a, and (iv) show DNA synthesis continued at the reduced level. The fraction of C85 cells with DNA content higher than 4 N is maintained at the same level (14%) in cells untreated, as well as regrown after the treatment. Multinucleation is found as the main karyotypic abnormality.