| Protracted low dose administration of conventional chemotherapeutic agents ("metronomic dosing"), including the taxanes paclitaxel and docetaxel, has been shown to inhibit tumor growth by an anti-angiogenic mechanism. The feasibility of these two clinical agents for protracted scheduling is limited, however, by host toxicity and poor oral bioavailibility. IDN-5390 is a novel secotaxane derivative with improved oral bioavailability and a toxicity profile suitable for daily administration, rendering it an excellent candidate for metronomic dosing in vivo to achieve an anti-angiogenic effect.; While the mechanism of anti-angiogenic effect of taxanes has been primarily attributed to endothelial cell cytotoxicity, studies on HUVEC (human umbilical vein endothelial cells) also demonstrate potent inhibition of endothelial motility. Furthermore, inhibition of cellular motility is observed at non-cytotoxic concentrations of IDN 5390, suggesting a selectivity in mechanism of action of this taxane analog. Multiple techniques for the evaluation of endothelial cell migration were employed to test this hypothesis. In a modified Boyden chamber migration assay, IDN-5390 inhibited HUVEC chemotaxis in a dose-dependent manner at concentrations that did not compromise cell viability. A HUVEC monolayer "wounding" assay, in which cell migration into a denuded area of a cell monolayer was monitored by time-lapse video microscopy, also demonstrated inhibition of endothelial cell motility at non-toxic doses. Although more potent inhibitors of cell growth, paclitaxel and docetaxel did not exhibit selectivity for inhibition of cell migration in these studies.; Further evaluation of these agents revealed that paclitaxel, docetaxel and IDN 5390 all potently polymerize purified tubulin in vitro, but IDN 5390 did not stabilize microtubules against depolymerization as potently as paclitaxel or docetaxel, suggesting that the dynamic instability of microtubules may be differentially regulated in a cellular context. Indeed, treatment of HUVEC with IDN 5390, even at high concentrations, causes an arrest of the cells in G2/M that is transient; in contrast, paclitaxel and docetaxel induced G2/M arrest to an overall greater extent than IDN 5390 and this arrest was sustained. An increase in apoptosis was also correlated with cell cycle arrest, with paclitaxel and docetaxel treatment resulting in an increase in HUVEC apoptosis, while significantly less apoptosis was observed with IDN 5390 treatment. (Abstract shortened by UMI.)... |
