Phase I and pharmacology study of flavone acetic acid administered two or three times weekly without alkalinization

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.

Identification of New Flavone-8-Acetic Acid Metabolites Using Mouse Microsomes and Comparison with Human Microsomes

Flavone-8-acetic acid (FAA) is a potent anticancer agent in mouse but has not shown activity in humans. Because FAA metabolism could play a role in this interspecies difference, our aim was to identify the metabolites formed in vitro using mouse microsomes compared with those in human microsomes. Mouse microsomes produced six metabolites as detected by reversed-phase high-performance liquid chromatography-mass spectrometry (MS). Three metabolites were identified as the 3'-, 4'-, or 6-hydroxy-FAA, by comparison with retention times and UV and MS spectra of standards. Two metabolites presented a molecular weight of 296 (FAA = 280) indicating the presence of one oxygen but did not correspond to any monohydroxylated FAA derivative. These two metabolites were identified as epoxides because they were sensitive to epoxide hydrolase. The position of the oxygen was determined by the formation of the corresponding phenols under soft acidic conditions: one epoxide yielded the 3'- and 4'-hydroxy-FAA, thus corresponding to the 3',4'-epoxy-FAA, whereas the other epoxide yielded 5- and 6-hydroxy-FAA, thus identifying the 5,6-epoxy-FAA. The last metabolite was assigned to the 3',4'-dihydrodiol-FAA because of its molecular weight (314) and sulfuric acid dehydration that indicated that the 3'- and 4'-positions were involved. Compared with mouse microsomes, human microsomes (2 pools and 15 individual microsomes) were unable to metabolize FAA to a significant extent. In conclusion, we have identified six new FAA metabolites formed by mouse microsomes, whereas human microsomes could not metabolize this flavonoid to a significant extent. The biological importance of the new metabolites identified herein remains to be evaluated.

Characterization of monohydroxylated derivatives of the anticancer agent flavone-8-acetic acid by liquid chromatography with on-line UV and mass spectrometry

The experimental anticancer agent flavone-8-acetic acid (FAA) is metabolized into several monohydroxylated derivatives using mouse microsomes. Because these metabolites could be involved in the biological effects of FAA, the aim of this study was to characterize all its possible monohydroxylated derivatives. To do so, we have developed a methodology using reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with ultraviolet (UV) detection and mass spectrometry (MS) to analyze and identify FAA derivatives hydroxylated at the 2', 3', 4', 3, 5, 6, or 7 position. In RP-HPLC, 4'-, 3'-, 2'-, 6-, and 7-OH-FAA eluted before FAA, whereas 3- and 5-OH-FAA eluted after FAA. UV spectra showed a bathochromic shift of band I for all derivatives and of band II for 5- and 6-OH-FAA. In addition, the position of the OH group could be determined by the presence of certain product ions in MS. Ions at m/z 133 and 151 were specific for 2'-, 3'-, 4'-, and 3-OH-FAA, whereas the ion at m/z 177 was specific for 3-OH-FAA only. The ions m/z 133, 151 and 167 were specific for 2'-OH-FAA. Ions at m/z 149 were specific for the presence of the OH group on cycle A only (i.e., 5-, 6- or 7-OH-FAA). The presence of both product ions m/z 149 and 179 were specific for 7-OH-FAA. Finally, ions at m/z 149 and several product ions of even m/z values were specific for 5-OH-FAA. In conclusion, the methodology described can be used to identify all possible monohydroxylated FAA derivatives.

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.

A phase I study of monohydroxyethylrutoside in healthy volunteers

The flavonol monohydroxyethylrutoside (monoHER) has demonstrated protection against doxorubicin-induced cardiotoxicity in in vitro and in vivo studies without affecting the antitumor effect. In the present phase I study, the possible side effects and the pharmacokinetics of monoHER were evaluated in healthy volunteers with the aim to develop a safe and feasible dose to be evaluated in cancer patients treated with doxorubicin. The study was performed as a single blind, randomized trial in healthy volunteers (age between 19 and 56 years). At each dose level, six subjects received monoHER and three placebo. MonoHER was solubilized in 100 ml dextrose 5% and administered as an i.v. infusion in 10 min. The placebo consisted of 100 ml dextrose 5%. The starting dose of monoHER was 100 mg/m(2). Dose escalation by 100% of the preceding dose took place after finishing each dose level until the protecting pharmacokinetic values for C (max) and AUC(infinity) (as observed in mice after 500 mg/kg monoHER i.p.) were reached and/or serious side effects were observed. The dose was escalated up to 1,500 mg/m(2). The mean values of C (max) and AUC(infinity) were 360+/-69.3 microM and 6.8+/-2.1 micromol min/ml, respectively. These values were comparable to the C (max) and AUC(infinity) observed under the protecting conditions in mice. No serious side effects occurred during the entire study. Thus, 1,500 mg/m(2) is a feasible and safe dose to be evaluated in a phase II study to investigate the protective properties of monoHER against doxorubicin-induced cardiotoxicity in cancer patients.

Recent advances in the discovery and development of flavonoids and their analogues as antitumor and anti-HIV agents

Antitumor and anti-HIV flavonoids and their analogues will be reviewed with emphasis on those discovered in our laboratory. The active antitumor compounds include the antileukemic tricin (1) and kaempferol-3-O-beta-D-glucopyranoside (2) from Wikstroemia indica, the cytotoxic hinokiflavone (3) from Rhus succedanea, the cytotoxic isoflavone (8) from Amorpha fruticosa, two dihydroxypentamethoxyflavones (9, 10) from Polanisia dodencandra. The development of synthetic 2-phenyl-4-quinolones as potent cytotoxic antimitotic flavonoid analogues and 2-phenylthiochromen-4-ones as potent antitumor flavonoid analogues will be presented. Selected results from other laboratories and antitumor-related biological studies also will be discussed. Flavonoids have also been investigated as potential anti-HIV agents. In our laboratory, acacetin-7-O-beta-D-galactopyranoside (131) from Chrysanthemum morifolium and chrysin (102), as well as apigenin-7-O-beta-D-glucopyranoside (130), from Kummerowia striata, have been found to exhibit anti-HIV activity. In other studies, some flavonoids and related compounds have been investigated as inhibitors of HIV-1 reverse transcriptase, protease, and integrase. The isolation and structural modification of such plant-derived active principles provide a continuing source of potential antitumor and anti-HIV agents.