The biotransformation of quinone containing anthracycline antitumor agents (e.g. adriamycin) by reductive glycosidase activity has been shown to produce 7-deoxyaglycone products (1,2) as well as anthracycline free radical anions. Oxygen was shown to inhibit aglycone production in this reaction. A proposed scheme for drug action, places a great deal of emphasis not only on the drug free radicals generated, but also on superoxide anion produced during aerobiosis (3). Drug and oxygen free radicals have been implicated in drug cardiotoxicity, and free radical scavangers such as alpha-tocopherol have been used to ameliorate this condition. The work proposed here is aimed at testing the proposed scheme of drug action which involves drug free radicals. We want to start by quantifying the effect of oxygen in the reaction described above and calculate the efficiency of the free radical to aglycone conversion. The experimental procedure will involve electron spin resonance (ESR) to detect and quantify the free radicals as well as thin layer chromatography (TLC) and fluorecence spectroscopy to quantify the aglycone products. These experiments will give concrete data useful in writing steps on the metabolic pathways of anthracyclines. AZQ is another quinone containing agent with two aziridine groups. It is presently undergoing phase I and phase II trials in our center. We have shown that this agent is also activated to a free radical anion by cytochrome C reductase, but the molecular nature of the free radical has not been identified. We want to identify the species by using several AZQ analogs with approrpriate substituents which can indicate which are the predominant nitrogens responsible for the hyperfine coupling, and whether the free radical is due to a metabolite, the parent compound or a combination of both. ESR, TLC, and HPLC (high pressure liquid chromatography) will be used in these experiments. The hypothesis of drug free radical involvement in the toxicity and/or antitumor effect of quinone containing agents will be further studied by correlating antitumor activity with the free radical structure of AZQ and its analogs. Knowledge of the free radical structure yields parameters such as unpaired spin density distribution among the different atoms of the molecule. The free radicals will be obtained electrochemically, their spectra will be analyzed and computer simulated. The compounds's activity will be assayed in vitro using 3H-thymidine incorporation on L1210 murine leukemia cells.
Showing the most recent 10 out of 17 publications
