A highly sensitive and specific rapid assay for 5-fluorouracil (5-FU) in plasma samples at concentrations as low as 1 ng/ml was developed using mass fragmentography. Highly enriched C14-5-FU was empolyed as an internal standard. A two-compartmental open model for the disposition of free 5-FU in plasma is proposed. The beta-phase of 5-FU plasma elimination describes the pool size of anabolic metabolites, assuming this model is correct. Injections of 5-fu at 15, 40, and 90 mg/kg in rats resulted in an alpha-phase of elimination from plasma with a half-life of 10-18 minutes. The beta-phase could only be measured after the injection of 90 mg/kg of 5-FU and amounted to about 20 hours in two rats. Higher doses resulted in an unproportional increase in 5-FU plasma concentrations in the beta-phase, thus establishing nonlinear kinetics, presumably of the degradative metabolism. Plasma concentrations of 5-FU in man were measured after oral and intravenous administration of 15 mg/kg of 5-FU. Plasma elimination half-lives after intravenous doses were 12 minutes and dropped below measurable levels 2 hours after administration in three patients. After oral administration, peak plasma levels of 5-FU varied between 0.8 and 60 mug/ml of 5-FU in three patients after 10 minutes to 2 hours. Two of these patients showed rapid absorption and a measurable beta-phase of 5-FU plasma elimination possibly indicating a larger anabolic pool size of 5-FU-derived nucleosides and nucleotides when compared to patients receiving intravenous doses. This study may provide a pharmacokinetic rationale to monitor patients receiving 5-FU treatment.

Administration, Oral↗

PubMedDate not supplied

Inhibition of mouse melanoma cell proliferation by corticotropin-releasing hormone and its analogs.

BACKGROUND: Observations that epidermal cells release both corticotropin-releasing hormone (CRH) and proopiome lanocortin (POMC) peptides has raised questions about the physiological relevance of this hypothalamo-pituitary-like system in mammalian skin. As CRH has shown anti-proliferative effects on cultured keratinocytes, we tested whether CRH can also regulate growth of melanoma cells. MATERIALS AND METHODS: CRH, [D-Glu20]-CRH, [D-Pro5]-CRH, acetyl-cyclo(30-33)[D-Phe12,D-Glu20,Nle21,D-His32,Lys33,D-Nle38]-CRH(4-41), acetyl-cyclo(30-33)[D-Phe12,Nle18,D-Glu20,Nle21,D-Ala32]-urotensin I(4-41), urocortin, and sauvagine were tested on Cloudman melanoma cell proliferation in culture and B16 melanoma tumor growth in C57B1/6 mice. Calcium-sensitive fluorescence measurements were used to examine the effect of CRH on intracellular Ca2+ signaling. The effects of CRH and [D-Glu20]-CRH on blood pressure were compared by measuring mean arterial pressure in anesthetized rats. RESULTS: CRH and six analogs were tested, and all demonstrated exceptional potency in inhibiting Cloudman cell proliferation in culture, with half-maximal effective concentrations ranging between 0.2 and 100 pM. The amplitude of ionomycin-induced Ca2+ influx into Cloudman cells grown in suspension was reduced by 50% after 48-hr exposure to CRH. Daily injections of CRH or [D-Glu20]-CRH, 100 micrograms/kg.day s.c., for 5 days, reduced net B16 tumor volume in mice by 30-60% compared to control animals. [D-Glu20]-CRH was less hypotensive compared to CRH, despite having similar anti-proliferative potency. CONCLUSION: CRH, and various analogs thereof, inhibit proliferation of Cloudman cells in culture, and inhibit B16 tumor growth rate in vivo, most likely by activation of endogenous CRH1 receptors and subsequent altered intracellular Ca2+ signaling. CRH analogs, such as [D-Glu20]-CRH, with less hypotensive activity may provide new directions of therapy for melanoma.

Amino Acid Substitution↗