Antitumor Agents. 199. † Three-Dimensional Quantitative Structure−Activity Relationship Study of the Colchicine Binding Site Ligands Using Comparative Molecular Field Analysis

Inhibitors of tubulin polymerization interacting at the colchicine binding site are potential anticancer agents. We have been involved in the synthesis of a number of colchicine site agents, such as thiocolchicinoids and allocolchicinoids, which are colchicine analogues, and 2-phenyl-quinolones and 2-aryl-naphthyridinones, which are the amino analogues of cytotoxic antimitotic flavonoids. The most cytotoxic of the latter compounds strongly inhibit binding of radiolabeled colchicine to tubulin, and these agents therefore probably bind in the colchicine site of tubulin. We have applied conventional CoMFA and q2-GRS CoMFA to identify the essential structural requirements for increasing the ability of these compounds to form tubulin complexes. The CoMFA model for the training set of 51 compounds yielded cross-validated R 2 (q 2) values of 0.637 for conventional CoMFA and 0.692 for q2-GRS CoMFA. The predictive power of this model was confirmed by successful activity prediction for a test set of 53 compounds with known potencies as inhibitors of tubulin polymerization. The activities of 88% of the compounds were predicted with absolute value of residuals of less than 0.5. The predictive q 2 values were 0.546 for conventional CoMFA and 0.426 for q2-GRS CoMFA. The conventional CoMFA model with the highest predictive q 2 (0.546) was analyzed in detail in terms of underlying structure−activity relationships.