David J. Swaine

Comparative preclinical pharmacokinetic and metabolic studies of the Combretastatin prodrugs Combretastatin A4 phosphate and A1 phosphate

Purpose: Combretastatin A4 phosphate (CA4P) and its structural analog, combretastatin A1 phosphate (CA1P), are soluble prodrugs capable of interacting with tubulin and causing rapid vascular shutdown within tumors. CA4P has completed Phase I clinical trials, but recent preclinical studies have shown that CA1P displays a greater antitumor effect than the combretastatin A4 (CA4) analog at equal doses. The aim of this study, therefore, is to compare pharmacokinetics and metabolism of the two compounds to determine whether pharmacokinetics plays a role in their differential activity. Experimental Design: NMRI mice bearing MAC29 tumors received injection with either CA4P or CA1P at a therapeutic dose of 150 mg·kg−1, and profiles of both compounds and their metabolites analyzed by a sensitive and specific liquid chromatography/mass spectroscopy method. Results: The metabolic profile of both compounds is complex, with up to 14 metabolites being detected for combretastatin A1 (CA1) in the plasma. Many of these metabolites have been identified by liquid chromatography/mass spectroscopy. Initial studies, however, focused on the active components CA4 and CA1, where plasma and tumor areas under the curve were 18.4 and 60.1 μg·h·ml−1 for CA4, and 10.4 and 13.1 μg·h·ml−1 for CA1, respectively. In vitro metabolic comparisons of the two compounds strongly suggest that CA1 is metabolized to a more reactive species than the CA4. Conclusions: Although in vitro studies suggest that variable rates of tumor-specific prodrug dephosphorylation may explain these differences in pharmacokinetics profiles, the improved antitumor activity and altered pharmacokinetic profile of CA1 may be due to the formation of a more reactive metabolite.

Characterization of the Hollow Fiber Assay for the Determination of Microtubule Disruption In vivo

Purpose: The hollow fiber assay is used successfully as a routine in vivo screening model to quantitatively define anticancer activity by the National Cancer Institute. This study investigates whether the hollow fiber assay can be used as a short-term in vivo model to demonstrate specific pharmacodynamic end points, namely microtubule and cell cycle disruption. Experimental Design: The growth of A549 cells was characterized within hollow fibers over 5 days in vivo at both subcutaneous (s.c.) and intraperitoneal (i.p.) sites. Drugs were administered on day 4 (i.p.). Results: At 24 hours, cells were retrieved from fibers at both i.p. and s.c. sites of paclitaxel-treated (20 mg/kg) and combretastatin A1 phosphate–treated (150 mg/kg) mice. Cell cycle analysis after paclitaxel treatment revealed a mean G2-M phase population of 48.04% (i.p.) and 25.76% (s.c.) compared with vehicle group mice (6.78 and 5.56%, respectively; P = <0.001 and 0.005, respectively). Tumor cells retrieved from combretastatin A1 phosphate–treated mice had a mean G2-M phase population of 36.3% (i.p.) and 29.36% (s.c.) compared with cells retrieved from vehicle group mice (5.58 and 5.49%, respectively; P = <0.001). Using fluorescence and laser-confocal microscopy, paclitaxel was revealed to induce the formation of spindle asters and tubulin polymerization. Combretastatin A1 phosphate was shown to hold cells in mitosis. Changes in nuclear morphology were also observed. Conclusion: These data demonstrate that the hollow fiber assay can be used as a short-term in vivo model for studying the pharmacodynamic effects of both standard and novel compounds on microtubules. Evidence has also been provided to support the routine use of the in vivo hollow fiber assay for demonstrating the mechanism of action of a drug.

High-performance liquid chromatographic analysis of AQ4N, an alkylaminoanthraquinone N-oxide.

A simple, highly selective and reproducible reversed-phase high-performance liquid chromatography method has been developed for the analysis of the new anti-cancer pro-drug AQ4N. The sample pre-treatment involves a simple protein precipitation protocol, using methanol. Chromatographic separations were performed using a HiChrom HIRPB (25 cmX4.6 mm I.D.) column, with mobile phase of acetonitrile-ammonium formate buffer (0.05 M) (22:78, v/v), with final pH adjusted to 3.6 with formic acid. The flow-rate was maintained at 1.2 ml min(-1). Detection was via photodiode array performed in the UV range at 242 nm and, since the compounds are an intense blue colour, in the visible range at 612 nm. The structurally related compound mitoxantrone was used as internal standard. The validated quantification range of the method was 0.05-10.0 microg ml(-1) in mouse plasma. The inter-day relative standard deviations (RSDs) (n=5) ranged from 18.4% and 12.1% at 0.05 microg ml(-1) to 2.9% and 3.3% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The intra-day RSDs for supplemented mouse plasma (n=6) ranged from 8.2% and 14.2% at 0.05 microg ml(-1) to 7.6% and 11.5% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The overall recovery of the procedure for AQ4N was 89.4 +/- 1.77% and 76.1 +/- 7.26% for AQ4. The limit of detection was 50 ng ml(-1) with a 100 microl sample volume. The method described provides a suitable technique for the future analysis of low levels of AQ4N and AQ4 in clinical samples.