Idarubicin is an anthracycline antibiotic with a broad spectrum of anti-cancer activity. Idarubicin intercalates into DNA and interferes with the activity of enzyme DNA topoisomerase II, which inhibits DNA replication. The main metabolyte is idarubicinol, which also exhibits cytotoxic activity and, due to its longer half-life, prolongs efficacy of idarubicin.
In support of an in vivo clinical study at the University Clinical Center Ljubljana, which studied the relationship between exposure to idarubicin and adverse effects and therapeutic outcome in patients with hepatocellular carcinoma undergoing transarterial chemoembolization (TACE), we aimed to develop a sensitive, accurate, precise and selective method for measuring the concentrations of idarubicin and idarubicinol in patients' plasma samples. The methods published so far had a quantification limit of 0,1 μg/L, which makes it possible to monitor plasma concentrations after TACE therapy only for a period of 48 hours, which is insufficient, especially considering the half-life of idarubicinol, which ranges from 40 to 60 hours. Therefore, we aimed to develop a more sensitive method that could be used to evaluate the complete plasma profile of both cytotoxic compounds. We tested several solid-phase extraction methods and several liquid-liquid extractions with the desire for the highest possible and repeatable recovery. A liquid-liquid extraction procedure using a 9:1 mixture of tert-butyl methyl ether and isopropanol proved to be the most efficient. After chromatographic separation, we tested two detection methods: the fluorescence and the mass spectrometry detection; out of which the latter proved to be superior.
We tried to validate the developed and optimized method in accordance with the FDA and EMA guidelines for bioanalytical method validation, with some parameters adapted to the aims of our study. The selectivity, accuracy and precision were confirmed in the concentration range between 0,025 μg/L and 50 μg/L, which allowed us to quantify idarubicinol even up to 14 days after the application, which enables a comprehensive pharmacokinetic analysis and a better assessment of cytostatic exposure.
We tested the method on a large batch of samples from a clinical study and confirmed its suitability and usefulness in an actual clinical environment.
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