Liangli Zhao

Mechanisms of tumor vascular shutdown induced by 5,6-dimethylxanthenone-4-acetic acid (DMXAA): Increased tumor vascular permeability

The novel vascular targeting agent 5,6‐dimethylxanthenone‐4‐acetic acid (DMXAA) has completed phase 1 clinical trial and has shown tumor antivascular activity in both mice and humans. We have investigated its ability to change tumor vascular permeability, relating it to tumor vascular perfusion and other responses. The murine colon 38 adenocarcinoma was grown in C57Bl wild‐type mice and mice lacking expression of either tumor necrosis factor receptor‐1 (TNFR1−/−) or TNF (TNF−/−). Tumor vascular permeability, as measured by extravasation of albumin‐Evans Blue complexes 4 hr after DMXAA treatment, was significantly increased in tumor tissue in C57Bl, TNFR1−/− and TNF−/− mice but not in normal (skin) tissue. Significant linear relationships were found between increased tumor vascular permeability, decreased functioning tumor blood vessels (measured by Hoechst 33342 staining at 4 hr), increased plasma 5‐hydroxyindole‐3‐acetic acid concentrations (as a measure of serotonin release by platelets) and the degree of induced tumor hemorrhagic necrosis. The results support the hypothesis that DMXAA increases tumor vascular permeability both directly and through the induction of other vasoactive mediators, including TNF. DMXAA might be useful clinically to potentiate the vascular permeability of other anticancer modalities such as cytotoxic drugs, antibodies, drug conjugates and gene therapy.

Measurement of plasma 5-hydroxyindoleacetic acid as a possible clinical surrogate marker for the action of antivascular agents

BACKGROUND Serotonin (5HT), a naturally occurring vasoactive substance, is released from platelets into plasma under various pathological conditions. Recently, anticancer drugs that act by selectively disrupting tumour blood flow have been found to increase plasma 5HT concentrations in mice. Two such antivascular agents, flavone acetic acid (FAA) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA), have completed Phase I clinical trial and raise the important question of whether suitable surrogate markers for antivascular effects can be identified. METHODS 5HT is unstable to storage, precluding routine clinical assay, but the 5HT metabolite, 5-hydroxyindoleacetic acid (5HIAA) accumulates in plasma following 5HT release and is a more suitable marker because of its greater stability. We have developed an automated procedure for the assay of the low concentrations of 5HIAA found in humans by combining solid-phase extraction with high-performance liquid chromatography (HPLC). RESULTS Efficient separation of 5HIAA from possible interfering substances in human plasma, including a variety of pharmaceutical agents, was achieved on C18 columns using cetyltrimethylammonium bromide (CETAB) as an organic modifier. Adequate precision, accuracy and sensitivity were achieved by electrochemical detection (ECD) at +400 mV. Analysis of plasma from two patients treated with DMXAA in a Phase I trial demonstrated DMXAA-induced elevation of plasma 5HIAA with a time course similar to that previously described in mice. CONCLUSIONS Measurement of changes in plasma 5HIAA provides a new approach to the monitoring of therapies with an antivascular effect. The assay is sensitive to dietary sources of 5HT, which should be minimised.

Modulation of the pharmacokinetics of the antitumour agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in mice by thalidomide.

Background: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), an investigative drug currently in clinical trial, acts on tumour vasculature through the induction of cytokines. Coadministration of thalidomide, a modulator of cytokine production, potentiates the antitumour activity of DMXAA against the murine Colon 38 carcinoma in mice. We wished to determine whether alteration of the pharmacokinetics of DMXAA by thalidomide could provide an explanation for this potentiation. Results: Coadministration of thalidomide to Colon 38 tumour-bearing mice significantly (P < 0.05) increased the elimination half-life (t1/2) of DMXAA in plasma (413 μmol/l), liver (132 μmol/l), and spleen (77 μmol/l), and significantly (P < 0.05) increased DMXAA concentrations in Colon 38 tumour tissue (0.25–4.5 h). l-Thalidomide had a greater effect on DMXAA elimination (P < 0.01) than did d-thalidomide or the racemate. Coadministration of thalidomide increased the area under the concentration-time curve (AUC) of DMXAA by 1.8-fold in plasma, liver and spleen, and by 3.0-fold in tumour. Bile from mice given thalidomide and DMXAA contained substantially lower amounts of the glucuronide metabolite of DMXAA (DMXAA-G) than did bile from mice given DMXAA alone. Conclusion: Glucuronidation is a major excretory pathway for DMXAA in the mouse. Thalidomide, probably as the l-form, decreases the rate of elimination of DMXAA from plasma, spleen, liver and tumour by altering the rate of glucuronidation. The reduction in the elimination of DMXAA by thalidomide may lead to a selective increase in exposure of tumour tissue to drug, providing a basis for its potentiation of antitumour activity.