Microtubule-targeting agents inhibit angiogenesis at subtoxic concentrations, a process associated with inhibition of Rac1 and Cdc42 activity and changes in the endothelial cytoskeleton

Abstract

Conventional anticancer agents may display antiangiogenic effects, but the underlying mechanism is poorly understood. We determined the antiangiogenic properties of cisplatin, doxorubicin, and the microtubule-targeting agents docetaxel, epothilone B, and vinblastine at concentrations not affecting cell proliferation. We also assessed tubulin and actin morphology and the activity of two key molecules in cell motility, the small Rho GTPases Cdc42 and Rac1. The highest non-toxic concentration (HNTC) of each drug was defined as the concentration inhibiting a maximum of 10% human umbilical vein endothelial cell growth on a 1-hour drug exposure, being for cisplatin 10 Mmol/L, doxorubicin 100 nmol/L, docetaxel 10 nmol/L, epothilone B 1 nmol/L, and vinblastine 10 nmol/L. Comparative endothelial cell functional assays using HNTCs for an exposure time of 1 hour indicated that endothelial cell migration in the wound assay, endothelial cell invasion in a transwell invasion system, and endothelial cell formation into tubelike structures on a layer of Matrigel were significantly inhibited by docetaxel, epothilone B, and vinblastine (P < 0.05), but not by cisplatin and doxorubicin. Docetaxel was slightly more efficient in the inhibition of endothelial cell motility than epothilone B and vinblastine. Fluorescence microscopy revealed that only the microtubule-targeting agents affected the integrity of the tubulin and F-actin cytoskeleton, which showed disturbed microtubule structures, less F-actin stress fiber formation, and appearance of nuclear F-actin rings. These observations were associated with early inhibition of Rac1 and Cdc42 activity. In conclusion, HNTCs of microtubuletargeting agents efficiently reduce endothelial cell motility by interference with microtubule dynamics preventing the activation of Rac1/Cdc42 and disorganizing the actin cytoskeleton. [Mol Cancer Ther 2006;5(9):2348 -57]

The microtubule inhibiting agent epothilone B antagonizes glioma cell motility associated with reorganization of the actin-binding protein α-actinin 4

“…The significance of the effects of epothilone B on α-actinin 4 are underscored by results from a recent study where we demonstrated that α-actinin 4 displayed significantly higher protein levels in high grade (III-IV) glioblastomas as compared to normal brain tissue (16). Furthermore, our results are consistent with studies undertaken by hayot et al (33) and Bijman et al (22), who also demonstrated that microtubule targeting agents invoked reduced endothelial cell motility as a consequence of actin-reorganization.…”

“…6B, D and F). These data parallel findings seen in endothelial (22) and breast cancer (23) cells, which also underwent filamentous actin reorganization in response to treatments with microtubule inhibiting agents. Immunoblotting experiments revealed that exposure of glioblastoma cells to epothilone B had no effect on α-actinin 4 protein levels (Fig.…”

Antiangiogenic Activity of Sterically Stabilized Liposomes Containing Paclitaxel (SSL-PTX): In Vitro and In Vivo

“…The migration assay used was a monolayer denudation assay as described by Marcel et al (25). Briefly, confluent HUVEC in 24-well plates (Costar, America) were mechanically "wounded" by scraping away a swath of cells with a pipette tip and denuding a strip of the monolayer 300 μm wide.…”

Specific reaction of α,β‐unsaturated carbonyl compounds such as 6‐shogaol with sulfhydryl groups in tubulin leading to microtubule damage

“…Thus, microtubule-interfering agents such as Vinca alkaloids and taxanes are widely used in the treatment of hematological malignancies and solid tumors. Furthermore, recent studies have indicated that microtubules regulate cell motility in close collaboration with actin fibers [4] and that microtubule-interfering agents can impair angiogenesis within a tumor by inhibiting endothelial cell motility rather than proliferation [5]. These findings suggest microtubule-interfering agents at non-toxic doses may be used to disrupt tumor vasculature and prevent tumor progression.…”