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The conventional wisdom argues that DNA intercalators possess a condensed polyaromatic ring whereas DNA minor groove binders generally contain unfused aromatic heterocycles, frequently separated by amide bonds. Recently, this view has been challenged with the discovery of powerful intercalating agents formed by unfused aromatic molecules and groove binders containing a polyaromatic nucleus. Bis-amidinocarbazoles belong to this later category of drugs having a planar chromophore and capable of reading the genetic information acessible within the minor groove of AT-rich sequences [Tanious, F.A., Ding, D., Patrick, D.A., Bailly, C., Tidwell, R.R. & Wilson, W.D. (2000) Biochemistry 39, 12091–12101]. But in addition to the tight binding to AT sites, we show here that bis-amidinocarbazoles can also interact with GC sites. The extent and mode of binding of 2,7 and 3,6 substituted amidinocarbazoles to AT and GC sequences were investigated by complementary biochemical and biophysical methods. Absorption, fluorescence, melting temperature and surface plasmon resonance (SPR) measurements indicate that the position of the two amidine groups on the carbazole ring influences significantly the drug–DNA interaction. SPR and DNase I footprinting data confirm the AT-preference of the compounds and provide useful information on their additional interaction with GC sequences. The 3,6-carbazole binds approximately twice as strongly to the GC-containing hairpin oligomer than the 2,7-regioisomer. The high tendency of the 3,6 compound to intercalate into different types of DNA containing G·C base pairs is shown by electric linear dichroism. This work completes our understanding of the sequence-dependent DNA binding properties of carbazole dications. [ABSTRACT FROM AUTHOR]

This study assesses the contribution of metabolism for the disposition of pentamidine in the rat. With the use of 14C-labelled compound, the excretion of radioactivity in urine and faeces has been studied in four rats during 44 days after a single intravenous injection of the drug. The urinary and faecal excretion of the radioactivity were of equal importance; 22±2% (mean±S.D.) and 25±4% being detected in urine and faeces, respectively. The activity in organs and tissues at 44 days after drug administration was also measured and amounted to 21±5% of the administered dose. Using HPLC the proportion of metabolites in urine in relation to unchanged pentamidine increased with time after dose, being 76±15% (mean±S.D.) of the total excreted radioactivity on day 1 and 97±1% on day 6. HPLC - tandem mass spectrometry was used for identification of metabolites in urine obtained from four rats given unlabelled pentamidine. Using synthetic reference compounds and the selective MS/MS mode four oxidized metabolites of pentamidine were identified either by direct injection into the system or by analyses of extracted urine. Thus, a substantial part of pentamidine is excreted as metabolites in urine. [ABSTRACT FROM AUTHOR]