Ellen Stokvis

Phase I Clinical and Pharmacokinetic Study of Kahalalide F in Patients with Advanced Androgen Refractory Prostate Cancer

Purpose: The purpose is to determine the maximum tolerated dose, profile of adverse events, and dose-limiting toxicity of Kahalalide F (KF) in patients with androgen refractory prostate cancer. Furthermore, the pharmacokinetics after KF administration and preliminary antitumor activity were evaluated. KF is a dehydroaminobutyric acid–containing peptide isolated from the marine herbivorous mollusk, Elysia rufescens. Experimental Design: Adult patients with advanced or metastatic androgen refractory prostate cancer received KF as an i.v. infusion over 1 hour, during five consecutive days every 3 weeks. The starting dose was 20 μg per m2 per day. Clinical pharmacokinetics studies were done in all patients using noncompartmental analysis. Prostate-specific antigen levels were evaluated as a surrogate marker for activity against prostate cancer. Results: Thirty-two patients were treated at nine dose levels (20-930 μg per m2 per day). The maximum tolerated dose on this schedule was 930 μg per m2 per day. The dose-limiting toxicity was reversible and asymptomatic Common Toxicity Criteria grade 3 and 4 increases in transaminases. The recommended dose for phase II studies is 560 μg per m2 per day. Pharmacokinetics analysis revealed dose linearity up to the recommended dose. Thereafter, a more than proportional increase was observed. Elimination was rapid with a mean (SD) terminal half-life (t1/2) of 0.47 hour (0.11 hour). One patient at dose level 80 μg per m2 per day had a partial response with a prostate-specific antigen decline by at least 50% for ≥4 weeks. Five patients showed stable disease. Conclusions: KF can be given safely as a 1-hour i.v. infusion during five consecutive days at a dose of 560 μg per m2 per day once every 3 weeks.

Chemical and enzymatic stability of a cyclic depsipeptide, the novel, marine-derived, anti-cancer agent kahalalide F.

Kahalalide F is a cyclic depsipeptide isolated from the Hawaiian mollusk Elysia rufescens. This compound is under present phase I clinical investigations as an anti-tumor drug. The role of possible metabolic reactions of this drug in (pre-)clinical investigations has not yet been explored. The first results for kahalalide F in this field of research are given in this paper. The chemical degradation of kahalalide F was investigated under acid, neutral and alkaline conditions using high-performance liquid chromatography with ultraviolet detection. The half-lives at 80°C were 1.1, 20 and 8.6 h at pH 0, 1 and 7, respectively. At 26°C and pH 11, the half-life was 1.65 h. At pH 7 and 11, only one reaction product of kahalalide F was observed, kahalalide G, the hydrolyzed lactone product of kahalalide F. At pH 0 and 1, additional reaction products emerged. Metabolic conversion of kahalalide F was tested in vitro using three different enzyme systems based on pooled human microsomes, pooled human plasma and uridine 5′-diphosphoglucuronyl transferase, respectively. The incubated samples were analyzed using the same chromatographic technique as for the degradation samples. Biotransformations were not observed under these conditions and, therefore, it is concluded that kahalalide F is a metabolically stable drug.

DEVELOPMENT OF AN HPLC METHOD WITH UV DETECTION FOR THE PHARMACEUTICAL QUALITY CONTROL OF THE NOVEL MARINE ANTICANCER AGENT KAHALALIDE F

Kahalalide F is a cyclic depsipeptide derived from the marine mollusc Elysia rufescens, an organism living in the seas near Hawaii. On the basis of its in vitro and in vivo selectivity, kahalalide F is currently developed as a potential anticancer agent against androgen independent prostate tumors. The development and validation of a reversed-phase high performance liquid chromatography (RP-HPLC) method with ultra-violet (UV) detection for the quantification and purity determination of kahalalide F in raw drug substance and pharmaceutical dosage form is described. Linear calibration curves in the range of 0.5–12.5 μg/mL of kahalalide F with correlation coefficients > 0.999 were obtained. Within-run and between-run precisions were ≤ 3.0% and accuracy was within 100.4–103.2%. The assay proved selective, as determined by stress-testing, confirming its stability indicating capacity. Using liquid chromatography-mass spectrometry (LC-MS) analysis, kahalalide G, the hydrolyzed open-chain analog of kahalalide F, appeared upon heating and in acidic media. Furthermore, it was shown that kahalalide F remains its integrity in the freeze-dried pharmaceutical dosage form.