Flavone acetic acid induced changes in human endothelial permeability: potentiation by tumour-conditioned medium

Not flavone-8-acetic acid (FAA) but its murine metabolite 6-OH-FAA exhibits remarkable antivascular activities in vitro

Flavone-8-acetic acid (FAA) has been proved to be a potent vascular-disrupting agent in mice. Unfortunately, FAA did not produce any anticancer activity in clinical trials. Previously, we had reported that FAA is metabolized by mouse microsomes into six metabolites, whereas it was poorly metabolized by human microsomes, with fewer metabolites formed in lesser amounts. Especially, 6-OH-FAA was not formed by human microsomes. In this work, two major available metabolites, 4'-OH-FAA and 6-OH-FAA, were tested and compared with the parent compound FAA for their potential antivascular activities in vitro. The ability of the products to induce morphological changes, disrupt preformed capillaries of EA.hy926 endothelial cells and inhibit tubulin polymerization in vitro was assessed. The action mechanism was determined using the RhoA and Rac1 inhibitors. At 25 µg/ml, 6-OH-FAA induced morphological changes and membrane blebbing, whereas 300 µg/ml of FAA and 4'-OH-FAA slightly changed the morphology without inducing membrane blebbing. At 300 µg/ml, 6-OH-FAA produced morphological changes that were 2.1-6.9-fold greater than that produced by FAA and 4'-OH-FAA, an effect that was consistent with its much greater inhibitory effect on tubulin polymerization compared with FAA and 4'-OH-FAA. 6-OH-FAA significantly disrupted the EA.hy926 cell capillaries. 6-OH-FAA activities were prevented in EA.hy926 cells pretreated with RhoA, but not Rac1, inhibitor. In this short communication we report for the first time that, in vitro, 6-OH-FAA, a mouse-specific FAA metabolite, exhibits significantly stronger antivascular activities compared with FAA and 4'-OH-FAA, which are mediated through the RhoA kinase pathway.

Differential inhibition of invasion and proliferation by bisphosphonates: anti-metastatic potential of Zoledronic acid in prostate cancer

OBJECTIVES

To determine the mode of action of Zoledronic acid in the inhibition of metastasis in prostate cancer and the reduction of prostate cancer bone metastases.

METHODS

Benign and malignant primary prostatic epithelial cells (PEC) and the PC-3 prostate cancer cell line were studied in co-culture using human bone marrow stroma in the presence of escalating doses of EDTA, Clodronate, Pamidronate and Zoledronic acid. PEC binding and colony growth in bone marrow stroma was measured using standardised quantitative techniques. PEC cellular invasion through Matrigel and an endothelial monolayer was measured either in invasion chambers or by the measurement of endothelial monolayer permeability to fluorescent dextran. Co-culture supernatants were assayed for specific cytokine levels. Bone marrow cellular toxicity was assessed using a standard Mix assay.

RESULTS

Treatment of PEC with up to 100 microM bisphosphonate did not affect their ability to bind to bone marrow endothelium or stroma. Bone marrow endothelial permeability was reduced by 100 microM Zoledronic acid by 3.8% (p = 0.03856). Both Pamidronate (40% at 100 microM, p < or = 0.05) and Zoledronic acid inhibited PEC invasion, with Zoledronic acid being the most potent (40% at 10 microM, p < or = 0.05 rising to 91% at 100 microM, p < or = 0.001). Zoledronic acid inhibits malignant PEC proliferation in bone marrow stroma co-culture (26.5% at 10 microM rising to 66.5% at 40 microM). This was accompanied by changes within the cytokine milieu with a >800% rise in TIMP-2.

CONCLUSION

Zoledronic acid is a potent inhibitor of PEC invasion across bone marrow endothelium and colony formation with the bone marrow stroma, affecting the MMP: TIMP-2 balance to favour MMP inhibition.

Relationship between tumour endothelial cell apoptosis and tumour blood flow shutdown following treatment with the antivascular agent DMXAA in mice

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is currently undergoing clinical evaluation as an antivascular agent for the treatment of cancer. We have previously demonstrated that DMXAA induces apoptosis of vascular endothelial cells in murine tumour sections and in a breast carcinoma biopsy from one patient in a Phase I trial. We wished to determine the tissue selectivity of this effect and its relationship to induced blood flow changes. Mice with Colon 38 tumours were treated with DMXAA and tissues were examined for apoptosis by TdT-mediated dUTP nick-end labelling (TUNEL). Hoechst 33342 was used to stain functional vessels, with the loss of stained vessels used as a measure of tumour vascular collapse. Treatment with DMXAA at 25 mg kg⁻¹, its maximum tolerated dose (MTD), showed, after 3 h, a 12-fold increase in TUNEL staining of tumour vascular endothelial cells. In contrast, tissue from the heart, brain, liver and spleen showed no increase. Induction of apoptosis in tumour tissue was both dose-dependent, observable at doses as low as 5 mg kg⁻¹, and time-dependent. Apoptosis was significantly lower in Colon 38 tumours of mice, with a targeted disruption in the TNF gene (TNF^−/−), or in the TNF receptor 1 gene (TNFR^−/−), as compared with that in wild-type mice. Increasing the DMXAA dose to 50 mg kg⁻¹ in these knockout mice raised tumour apoptosis to a level comparable to that induced in wild-type mice given DMXAA at the MTD. For all the data, a significant correlation (r=0.94; P<0.001) was found between logarithmic percentage apoptosis induction and the logarithmic density of Hoechst-stained vessels. These results suggest that blood flow inhibition caused by DMXAA is tumour tissue-specific and is a consequence of induction of apoptosis in tumour vascular endothelial cells.

Structural requirements for the interaction of combretastatins with tubulin: how important is the trimethoxy unit?

A series of combretastatins possessing both a trimethoxy unit and other substituents on ring A has been synthesised and tested for cytotoxicity and their ability to interact with the protein tubulin. All previous studies have indicated that the trimethoxy unit is essential for interaction with tubulin. The studies herein show that molecules possessing functionalities other than trimethoxy can also interact with tubulin. Importantly a trimethyl substituted agent 52a has shown reduced cytotoxicity, but increased potency in its ability to inhibit the assembly of tubulin.