Interaction of microtubule depolymerizing agent indanocine with different human aαβ tubulin isotypes

Abstract

Tubulin isotypes are known to regulate the stability and dynamics of microtubules, and are also involved in the development of resistance against microtubule-targeted cancer drugs. Indanocine, a potent microtubule depolymerizing agent, is highly active against multidrugresistant (MDR) cancer cells without affecting normal cells. It is known to disrupt microtubule dynamics in cells and induce apoptotic cell death. Indanocine is reported to bind to tubulin at the colchicine site i.e. at the interface of aαβ tubulin heterodimer. However, it's precise binding mode, involved molecular interactions and the binding affinities with different aαβ-tubulin isotypes present in MDR cells are not well understood. Here, the binding affinities of human aαβ-tubulin isotypes with indanocine were examined, employing the molecular modeling approach i.e. docking, molecular dynamics simulation and binding energy calculations. Multiple sequence analysis suggests that the amino acid sequences are different in the indanocine binding pockets of βI, βIIa, βIII and βVI isotypes. However, such differences are not observed in the amino acid sequences of βIVa, βIVb, and βV tubulin isotypes at indanocine binding pockets. Docking and molecular dynamics simulation results show that indanocine prefers the interface binding pocket of aαβIIa, aαβIII, aαβIVb, aαβV, and aαβVI tubulin isotypes; whereas it is expelled from the interface binding pocket of aαβIVa and aαβI-tubulin isotypes. Further, binding free energy calculations show that aαβVI has the highest binding affinity and aαβI has the lowest binding affinity for indanocine among all β-tubulin isotypes. The binding free energy decreases in the order of aαβVI > aαβIVb > aαβIIa > aαβIII > aαβV > aαβIVa > aαβI. Thus, our study provides a significant understanding of involved molecular interactions of indanocine with tubulin isotypes, which may help to design potent indanocine analogues for specific tubulin isotypes in MDR cells in future.