Microtubule Interactions with Chemically Diverse Stabilizing Agents: Thermodynamics of Binding to the Paclitaxel Site Predicts Cytotoxicity

Abstract

The interactions of microtubules with most compounds described as stabilizing agents have been studied. Several of them (lonafarnib, dicumarol, lutein, and jatrophane polyesters) did not show any stabilizing effect on microtubules. Taccalonolides A and E show paclitaxel-like effects in cells, but they were not able to modulate in vitro tubulin assembly or to bind microtubules, which suggests that other factors are involved in their cellular effects. The binding constants of epothilones, eleutherobin, discodermolide, sarcodictyins, 3,17beta-diacetoxy-2-ethoxy-6-oxo-B-homo-estra-1,3,5(10)-triene, and dictyostatin to the paclitaxel site; the critical concentrations of ligand-induced assembly; and their cytotoxicity in carcinoma cells have been measured, and correlations between these parameters have been determined. The inhibition of cell proliferation correlates better with the binding enthalpy change than with the binding constants, suggesting that large, favorable enthalpic contribution to the binding is desired to design paclitaxel site drugs with higher cytotoxicity.

Synthesis and biological evaluation of truncated α-tubulin-binding pironetin analogues lacking alkyl pendants in the side chain or the dihydropyrone ring

“…Standard work-up (CH 2 Cl 2 ) and column chromatography on silica gel (hexanes-EtOAc mixtures) afforded the desired silylated derivative. Compounds 16,34,42, 50 and 52 were prepared in this way (yields are indicated in the corresponding Schemes).…”

“…The cells were fixed with 70% ethanol, treated with RNase and stained with propidium iodide as previously described. 42 The analysis was performed with a Coulter Epics XL flow cytometer.…”

Targeting the Cytoskeleton with Plant-Bioactive Compounds in Cancer Therapy

“…They act as microtubule stabilizers by binding to another microtubule site than taxol resulting in the formation of microtubule bundles and leading to cell cycle arrest and apoptosis. It is also reported that taccalonolides bind to β-tubulin near the lumen of microtubule, which is diferent from the taxol-binding site stabilizers which bind to α-tubulin protoilaments [46][47][48][49].…”

The Binding Mode of Side Chain‐ and C3‐Modified Epothilones to Tubulin

“…Binding constants of epothilone analogues 2, 3, 6-8 for glutaraldehyde-stabilized microtubules (MTs) were determined at 35 8C by the method previously described by Buey et al, [30] which is based on the displacement of Flutax-2. Binding constants were calculated using Equigra v. 5.…”

“…To address this issue, we also determined the MT binding constants of compounds 2 and 3 using methodology that was developed previously in one of our laboratories and involves the displacement of the fluorescent paclitaxel derivative Flutax-2 from stabilized MTs. [30] …”