CoMFA, HQSAR and molecular docking studies of butitaxel analogues with beta-tubulin

Results from biochemical analyses for a series of 20 butitaxel analogues, paclitaxel and docetaxel were used to build two- and three-dimensional quantitative structure-activity relationship (QSAR) models in order to investigate the properties associated with microtubule assembly and stabilization. A comparative molecular field analysis (CoMFA) model was built using steric and electrostatic fields. The CoMFA model yielded an r2 of 0.943 and a cross-validated r2 (i.e. q2) of 0.376. Hologram quantitative structure-activity relationship (HQSAR) modeling of these same data generated an r2 of 0.919 and a q2 of 0.471. Contour maps used to visualize the steric and electrostatic contributions associated with activity or lack thereof were, as expected, localized to the varied position of the taxane system. Each analogue was docked successfully into a model of beta-tubulin derived from previously determined cryoelectron microscopy analyses of the tubulin alpha/beta heterodimer. All analogues superimposed well with paclitaxel bound to the protein, as well as with each other. Defining the variable region of each structure as the ligand and docking it separately into the paclitaxel site revealed a modest correlation (r2 = 0.53) between activity and docking energy of all the compounds in the dataset. When only the butitaxel derivatives were considered, the correlation increased to 0.61. The mathematical models derived here provide information for the future development of taxanes.