A new tubulin-binding site and pharmacophore for microtubule-destabilizing anticancer drugs

Abstract

The recent success of antibody-drug conjugates (ADCs) in the treatment of cancer has led to a revived interest in microtubuledestabilizing agents. Here, we determined the high-resolution crystal structure of the complex between tubulin and maytansine, which is part of an ADC that is approved by the US Food and Drug Administration (FDA) for the treatment of advanced breast cancer. We found that the drug binds to a site on β-tubulin that is distinct from the vinca domain and that blocks the formation of longitudinal tubulin interactions in microtubules. We also solved crystal structures of tubulin in complex with both a variant of rhizoxin and the phase 1 drug PM060184. Consistent with biochemical and mutagenesis data, we found that the two compounds bound to the same site as maytansine and that the structures revealed a common pharmacophore for the three ligands. Our results delineate a distinct molecular mechanism of action for the inhibition of microtubule assembly by clinically relevant agents. They further provide a structural basis for the rational design of potent microtubuledestabilizing agents, thus opening opportunities for the development of next-generation ADCs for the treatment of cancer.drug mechanism | microtubule-targeting agents | X-ray crystallography

Biological Characterization of an Improved Pyrrole-Based Colchicine Site Agent Identified through Structure-Based Design

“…In contrast, microtubule depolymerizers inhibit tubulin polymerization and cause a loss of cellular microtubules. Three microtubule destabilizer binding sites have been identified: the vinca domain (Hamel, 2002), the maytansine site (Prota et al, 2014), and the colchicine site (Hamel, 2003). Vinblastine binds within a deep pocket formed between two adjacent ab tubulin heterodimers; occupancy within this site disrupts both the longitudinal and lateral interactions between tubulin heterodimers (Gigant et al, 2005).…”

“…Multiple clinically useful MTAs bind within the vinca domain. The maytansine site is close to, but not overlapping with, the vinca domain, and binding prevents the formation of longitudinal associations of microtubule protofilaments (Prota et al, 2014). Maytansine analogs have recently found utility as antibody-drug conjugates (Verma et al, 2012).…”

Termination of Protofilament Elongation by Eribulin Induces Lattice Defects that Promote Microtubule Catastrophes

“…Notably, the mechanism of action of Eribulin is different from that of Vinblastine, which induces tubulin ringlike oligomer formation due to the binding of the drug to the full vinca domain that is shaped by residues stemming from both a-and b-tubulin subunits [10,12]. The mode of action of Eribulin is, however, similar to the clinically relevant microtubule-destabilizing agent Maytansine that binds to a site on b-tubulin that is distinct from the vinca domain but also located at the longitudinal interface between tubulin dimers in microtubules [18]. In addition, the binding site of Eribulin overlaps with the one of DARPin D1, a designed ankyrin-repeat protein that caps microtubule plus ends and induces their disassembly [16].…”

A previously undescribed tubulin binder

“…Understanding how the drugs bind to tubulin has proven invaluable not only in elucidating how they function, but also for designing new lead agents. In PNAS, Prota et al add significant new insights into this field by defining a site within tubulin that is able to bind clinically relevant anticancer drugs in a manner that has not been previously described (5).…”