Preclinical pharmacology of ecteinascidin 729, a marine natural product with potent antitumor activity.

Ecteinascidins are marine natural products with potent antiproliferative activity under evaluation as chemotherapeutic agents by the National Cancer Institute. Ecteinascidins bind the minor groove of DNA and may form covalent adducts with DNA by binding the N-2 of guanine in a fashion similar to saframycin antibiotics. The most potent ecteinascidin is ET-729 with antitumor activity observed following administration of 3.8 and 10 micrograms/kg to mice bearing P388 leukemia and B16 melanoma, respectively. A reverse-phase high-performance liquid chromatography (HPLC) assay and an L1210 cell bioassay were developed for ET-729 and utilized for stability and murine pharmacokinetic studies. HPLC analysis showed that ET-729 was stable in organic solvents, mobile phase and acidic buffer (t1/2 > 100 h). Stability was diminished under neutral and basic conditions (t1/2 < 14 h). Following a 48-h incubation with L1210 cells in growth medium in the absence and presence of 2.5% murine plasma, the 50% growth inhibitory concentrations (IC50) of ET-729 were 37 and 72 pM, respectively. Following intravenous administration of ET-729 to male CD2F1 mice, the disappearance of antiproliferative activity determined by the bioassay was described by a two-compartment open model. The mean values of the elimination half-life and plasma clearance were 28 min and 39.7 ml/min per kg, respectively. Following intraperitoneal administration, peak plasma concentrations of antiproliferative activity were observed 6-15 min after injection and antiproliferative concentrations remained above 1 nM for longer than 1 h. Intraperitoneal bioavailability varied over a wide range (20-91%). Antiproliferative activity was detected in every urine sample following intravenous and intraperitoneal administration, but the total 48-h urinary recovery was less than 0.1%.

Melanin-related metabolites in urine of B16 melanoma-bearing mice.

5-S-Cysteinyldopa (5-S-CD), a pheomelanin precursor, has been used as a biochemical marker of melanoma metastasis. Recently, 5-hydroxy-6-methoxyindole-2-carboxylic acid (5H6MI2C), a eumelanin-related metabolite, was shown to reflect well the degree of skin pigmentation. We measured the urinary excretion of 5H6MI2C and 5-S-CD in mice bearing B16 melanoma to determine which of the two markers better reflects the progression of melanoma. The urinary excretion of both 5H6MI2C and 5-S-CD increased rapidly in parallel with the tumour volume. The highest values for the two metabolites in melanoma-bearing mice were three orders of magnitude higher than those in control mice. However, 5H6MI2C had a higher excretion level at the early stage of melanoma progression, while 5-S-CD had a higher excretion level at the later stage.