Flavone acetic acid distribution in human malignant tumors

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.

Pharmacokinetics of 5,6-dimethylxanthenone-4-acetic acid (AS1404), a novel vascular disrupting agent, in phase I clinical trial

PURPOSE

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) (AS1404) is a novel antitumour agent that selectively disrupts tumour vasculature and induces cytokines. The purpose of this study was to determine the pharmacokinetics (PK) of DMXAA in cancer patients enrolled in a phase I clinical trial.

METHODS

DMXAA was administered as a 20-min i.v. infusion every 3 weeks and doses were escalated in cohorts of patients according to a predefined schema. PK samples were taken over the first 24 h of at least the first cycle.

RESULTS

DMXAA was administered to 63 patients at 19 dose levels from 6 to 4,900 mg m(-2), and 3,700 mg m(-2) was established as the maximum tolerated dose. The PK observed over the dose range showed a non-linear fall in clearance from 16.1 to 1.42 l h(-1) m(-2) and resultant increase in the area under the concentration-time curve (AUC) from 1.29 to 12,400 microM h. In contrast, the increase in peak plasma concentrations from 2.17 to 1,910 microM approximated linearity. DMXAA was highly protein-bound to albumin (>99%) until saturation occurred at higher doses, leading to a rapid increase in the free fraction (up to 20%) and greater concentrations of DMXAA bound to non-albumin proteins. However, the main determinant of the non-linearity of the PK appeared to be sequential saturation of elimination mechanisms, which include hydroxylation, glucuronidation and perhaps hepatic transport proteins. This resulted in an exaggerated non-linear increase in free DMXAA plasma concentrations and AUC compared to total drug.

CONCLUSIONS

The PK of DMXAA are well-defined, with a consistent degree of non-linearity across a very large dose range.

Flavone acetic acid (FAA) with recombinant interleukin-2 (rIL-2) in advanced malignant melanoma. IV: Pharmacokinetics and toxicity of flavone acetic acid and its metabolites

Flavone acetic acid (FAA) was administered at a dose of 4.8 g m-2 over 1 h to patients with advanced malignant disease in combination with Interleukin II. A new high performance liquid chromatography method is described to determine both the parent compound and eight drug-related products, and the conditions required to determine these components in plasma are discussed. The half-life over the first 8 h was 2.3 h, but the terminal clearance of the drug was extremely slow. Severe (WHO Grade 4) hypotension was observed in some patients. However, incidence of this did not appear to be associated with any differences in FAA plasma concentrations, nor were there differences in FAA clearance between those patients whose tumour responded to the drug combination and those who did not.