Gatorbulin-1, a distinct cyclodepsipeptide chemotype, targets a seventh tubulin pharmacological site

Abstract

Tubulin-targeted chemotherapy has proven to be a successful and wide spectrum strategy against solid and liquid malignancies. Therefore, new ways to modulate this essential protein could lead to new antitumoral pharmacological approaches. Currently known tubulin agents bind to six distinct sites at α/β-tubulin either promoting microtubule stabilization or depolymerization. We have discovered a seventh binding site at the tubulin intradimer interface where a novel microtubule-destabilizing cyclodepsipeptide, termed gatorbulin-1 (GB1), binds. GB1 has a unique chemotype produced by a marine cyanobacterium. We have elucidated this dual, chemical and mechanistic, novelty through multidimensional characterization, starting with bioactivity-guided natural product isolation and multinuclei NMR-based structure determination, revealing the modified pentapeptide with a functionally critical hydroxamate group; and validation by total synthesis. We have investigated the pharmacology using isogenic cancer cell screening, cellular profiling, and complementary phenotypic assays, and unveiled the underlying molecular mechanism by in vitro biochemical studies and high-resolution structural determination of the α/β-tubulin−GB1 complex.

Lead optimization of novel quinolone chalcone compounds by a structure–activity relationship (SAR) study to increase efficacy and metabolic stability

“…3 b). CTR-21 potentially interacts with Pro175 of β-tubulin, a part of the recently identified gatorbulin binding site 10 . This site substantially overlaps the colchicine binding site and is the intramolecular equivalent of the vinblastine binding site on the intermolecular surface, but represents a potential novel and distinct binding site.…”

“…Many different molecules have been developed over the last few years as potential anti-cancer agents 1 – 9 . One common target remains the microtubule cytoskeleton 10 – 12 . Microtubules, the polymers of alpha and beta tubulin proteins, are essential for a wide range of cellular functions including proliferation, intracellular trafficking, cell signaling, cell shape and migration, and even tumor angiogenesis.…”

“…Through studying the mechanisms of natural product MTAs, seven distinct drug binding sites have been identified as described below 1 , 7 – 11 , 15 MTAs are broadly classified in two major groups: microtubule-stabilizing agents which promote microtubule polymerization while also inhibiting disassembly by binding to the tubulin polymer, and microtubule-destabilizing agents which bind to the tubulin dimers and block microtubule polymerization 10 , 11 , 17 , 18 . Two classes of compounds are considered microtubule-stabilizing agents: taxanes and laulimalide/peloruside.…”

“…In contrast, there are five distinct binding sites on the tubulin subunit for compounds that can prevent microtubule polymerization. These molecule families are the vinca alkaloids, colchicine maytansine, pironetin 1 , 7 , 8 , 11 , 15 , and the recently described gatorbulin-1 10 . Although some of these molecules have been known for decades as anti-proliferative, they often suffer from some common drawbacks that limit their effectiveness in many cases, preventing their clinical use.…”

Conformational changes in tubulin upon binding cryptophycin-52 reveal its mechanism of action

“…For a review, see Steinmetz and Prota ( 1 ). More recently, a seventh pharmacologic site has also been defined by gatorbulin-1 ( 2 ). Maytansine, a microtubule-destabilizing agent, occupies and defines a site on β-tubulin at the interdimer interface that is also the target of four other agents (rhizoxin, spongistatin, disorazole Z, and phase 1 drug PM060184) ( 3 ).…”