Design, Synthesis and Antitumor Activity Evaluation in Vitro of Novel 1,6-Naphthyridine Derivatives

In the search for novel, highly effective antitumor agents, a series of novel 1,6-naphthyridine derivatives were designed, synthesized and evaluated for antiproliferative activity against five human cancer cell lines (HepG-2, MCF-7, NCI-H1650, U87MG and A549) using CCK-8 assay in vitro. Among them, compound (R)-N-(1-(3-(difluoromethyl)-2-fluorophenyl)ethyl)-8-(3-ethylphenyl)-7-methoxy-1,6-naphthyridin-4-amine (16f) exhibited promising broad-spectrum activity against all tested cell lines. It was particularly potent against U87MG cells, with IC₅₀ values of 3.28 ± 0.15 µM. The antitumor activity was significantly better than that of the positive control 5-fluorouracil. Preliminary mechanistic studies revealed that compound 16f inhibited the clonogenic formation and migration of U87MG cells in a concentration-dependent manner, with migration inhibition also showing time dependence. Furthermore, 16f induced apoptosis in a concentration-dependent manner by increasing the reactive oxygen species level within the cells. At a concentration of 4 µM, the apoptotic cell population increased from 3.92% (control) to 25.18%, representing a 6.4-fold increase. Nuclear damage observed via DAPI staining provided further evidence of its cytotoxic effects. The DAPI staining further confirmed the cytotoxic action of compound 16f, showing clear morphological damage to the nuclei of U87MG cells. Collectively, these findings indicate that compound 16f is a promising candidate for further development as a potent antitumor drug.