Antiangiogenic activity of sterically stabilized liposomes containing paclitaxel (SSL-PTX): in vitro and in vivo

Abstract

The purpose of this present study was to evaluate the antiangiogenic activity of sterically stabilized liposomes containing paclitaxel (SSL-PTX). The SSL-PTX was prepared by the thin-film method. The release of paclitaxel from SSL-PTX was analyzed using a dialysis method. The effect of SSL-PTX on endothelial cell proliferation and migration was investigated in vitro. The antitumor and antiangiogenic activity of SSL-PTX was evaluated in MDA-MB-231 tumor xenograft growth in BALB/c nude mice. The release of paclitaxel from SSL-PTX was 22% within 24 h. Our in vitro results indicated that SSL-PTX could effectively inhibit the endothelial cell proliferation and migration at a concentration-dependent manner. We also observed that metronomic SSL-PTX induced marked tumor growth inhibition in MDA-MB-231 xenograft model via the antiangiogenic mechanism, unlike that in paclitaxel injection (Taxol) formulated in Cremophor EL (CrEL). Overall, our results suggested that metronomic chemotherapy with low-dose, CrEL-free SSL-PTX should be feasible and effective.

Fig. 1

The release of paclitaxel from SSL-PTX or Taxol at room temperature. The release medium was PBS (pH 7.4) containing 0.1% (v/v) of Tween 80. Each data represent the mean ± standard deviation (n = 3)

Fig. 2

Effects of SSL-PTX on HUVEC proliferation. The HUVEC were incubated in the absence or in the presence of SSL-PTX at different concentrations and harvested 48 h later. The proliferation of HUVEC was assessed by SRB method to calculate the proliferation variability rate (%). Values present the mean ± SD (n = 6). ** p < 0.01, vs vehicle as control

Fig. 3

Migration assay. Wound assay was done to determine whether SSL-PTX inhibits HUVEC migration. After treatment with various concentrations of SSL-PTX, HUVEC were allowed to migrate into the denuded area for 24 h. HUVEC migration was visualized by light microscopy. a Typical photomicrographs (final magnification, ×25) were shown in unwounded, untreated in 0 hour, untreated in 24 h, and SSL-PTX treated in 24 h at the concentration of 10 nM. b Percentage of wound width which is measured in denuded areas at 24 h compared with the untreated wound width at 0-h time point versus SSL-PTX concentration. **, p < 0.01, vs untreated as control

Fig. 4

Tumor growth inhibition with MTD and metronomic paclitaxel formulations. MDA-MB-231 cells were implanted in the nude mice on the zeroth day, and the treatment was started on the 11th day when the tumor volume reached 150–200 mm³. The regimen of MTD treatment was administering Taxol or SSL-PTX (15 mg/kg) on the 11th, 15th, 19th, and 23 rd day, respectively. For metronomic treatment, Taxol or SSL-PTX (6 mg/kg) was administered from the 11th to 15th days and from the 22nd to 26th days, respectively. On the 32nd day, one of five mice in the control group began to seem moribund; thus, all nude mice were sacrificed, and the tumor was harvested. Data (change ratio for tumor volume (%)) are presented as the mean ± SD per group measured at indicated days after treatment (n = 5). **, p < 0.01, vs control treatment group at the 32nd day; ††, p < 0.01, vs metronomic Taxol treatment group at the 32nd day

Fig. 5

Effect of SSL-PTX on MVD in xenograft MDA-MB-231 tumors. a Representative micrographs of immunohistochemical detection of CD31⁺ microvessel in xenograft MDA-MB-231 tumors in control group, MTD treatment groups of Taxol or SSL-PTX, and metronomic treatment groups of Taxol or SSL-PTX (final magnification, ×400). b Mean CD31⁺ microvessel count in xenograft MDA-MB-231 tumors in control group, MTD treatment groups of Taxol or SSL-PTX, and metronomic treatment groups of Taxol or SSL-PTX. Data are presented as the means ± SD (n = 5). **, p < 0.01, vs control treatment group; †, p < 0.05, vs MTD SSL-PTX treatment group. ††, p < 0.01, vs MTD Taxol and metronomic Taxol treatment group