Analysis of drug-tubulin interaction by trypsin cleavage: comparison for colchicine, podophyllotoxin, griseofulvin, vinblastine and taxol

Interaction of the tumor inhibitor IKP-104, a 4(1H)-pyridinone derivative, with microtubule proteins

The effects of a mitotic arrestant, IKP-104, which has an antitumor activity, on the in vitro polymerization and depolymerization of rat brain microtubules were investigated. IKP-104 inhibited microtubule polymerization at concentrations greater than 0.71 x 10(-6) M, and its IC50 value was determined to be 1.31 x 10(-6) M by probit analysis. Fifty-two percent of pre-polymerized microtubules depolymerized at 1.31 x 10(-6) M IKP-104. Electron micrographs of microtubules taken immediately after treatment with 1 x 10(-3) M IKP-104 revealed a fraying of microtubule ends into elongated coil-like filaments, which were composed of 2 or 3 protofilaments. When microtubule protein treated with 1 x 10(-3) M IKP-104 was cleaved by trypsin, fragments of 41, 36, 34, 23, 21, 19 and 16 kilodaltons (kDa) derived from alpha-tubulin were produced. In particular, the 19, 23, and 34 kDa fragments were characteristically observed in the trypsin cleavage of microtubules tested with IKP-104, and these fragments were not observed with untreated microtubules. The effects of IKP-104 on microtubule protein mentioned above were mostly similar to those of vinblastine (VLB) and we suggest that IKP-104 bound to the site or sites near "VLB-binding site or sites" of alpha-tubulin subunit, resulting in induction of conformational changes.

Interactions of colchicine with tubulin

Colchicine exerts its biological effects through binding to the soluble tubulin heterodimer, the major component of the microtubule. The colchicine-binding abilities of tubulins from a variety of sources are summarized, and the mechanism of colchicine binding to brain tubulin is explored in depth. The relationship between colchicinoid structure and tubulin binding activity provides insight into the structural features of colchicine responsible for high affinity binding to tubulin and is reviewed for analogs in the colchicine series. The thermodynamic and kinetic aspects of the association are described and evaluated in terms of the binding mechanism. Colchicine binding to tubulin results in unusual alterations in the low energy electronic spectra of colchicine. The spectroscopic features of colchicine bound to tubulin are discussed in terms of the nature of the colchicine-tubulin complex. Attempts to locate the high affinity colchicine binding site on tubulin are presented.