Novel 2-thienyl-1,8-naphthyridin-4-ones as a new class of antimitotic antitumor agents

Two projects were carried out in this research program: (1) Synthesis and biological evaluation of disubstituted 2-phenyl or 2-thienyl-1,8-naphthyridin-4-ones to explore steric and electronic effects with regard to their effects on cytotoxicity and inhibition of tubulin polymerization (studies 1 and 2), (2) 3D QSAR study of the colchicine-binding site agents by CoMFA and Docking methods to explore the structural requirements for colchicine-binding site of tubulin (study 3).; In project 1, most 2-dimethoxyphenyl-1,8-naphthyridin-4-ones ( 17--24) were inactive in both assays. Only 3 ',5'-dichlorophenyl-1,8-naphthyridin-4-one (25) showed significant activity. However, in study 2, most 2-thienyl-1,8-naphthyridin-4-ones (46--63) showed significant activity in both assays. The most active compounds (51--53 and 60) demonstrated strong cytotoxic effects with ED50 values in the micromolar or submicromolar range in most tumor cell lines. The most cytotoxic compounds inhibited tubulin polymerization at concentrations substoichiometric to the tubulin concentration. The most potent inhibitors of polymerization (60, 62, and 63) had effects comparable to those of potent antimitotic natural products. Only compound 60 was a potent inhibitor of the binding of radiolabeled colchicine to tubulin, and it was both the most cytotoxic agent and the most effective inhibitor of polymerization among the newly synthesized compounds. Therefore, these agents probably bind in the colchicine site of tubulin.; In project 2, we explored the 3D QSAR of the colchicine-binding site agents including thiocolchicinoids, allocolchicinoids, 2-phenyl-4-quinolones, and 2-aryl-1,8-naphthyridin-4-ones, using CoMFA methods. The CoMFA model yielded cross-validated R2 (q2) values of 0.637 for conventional CoMFA and 0.692 for q2-GRS CoMFA. The predictive power of this model was confirmed by successfully predicting activities of a test set of 53 compounds with known differences in their potencies as inhibitors of tubulin polymerization. The predictive q2 values were 0.546 for conventional CoMFA and 0.426 for q2-GRS CoMFA. A computational model of the colchicine-binding site in tubulin was built by Flexidock. The steric contour plot was compared with the computational model. The comparison reveals that the CoMFA steric field is compatible with stereochemical properties of the colchicine-binding site in tubulin. The results obtained from this study shall guide our future synthetic efforts.