The hypothesis that the antitumor prodrug temozolomide is ring-opened to MTIC which then further breaks down to a reactive diazonium ion at guanine-rich sequences in DNA has been probed by NMR spectroscopy and computational techniques. Temozolomide is stable at acid pH but decomposes to MTIC at pH > 7; in contrast, MTIC is stable at alkaline pH values but rapidly fragments in a methylating mode at pH < 7. The proximate methylating agent is the reactive methyldiazonium species. Runs of guanine residues represent an accessible nucleophilic microenvironment in DNA site-specific conversion of the prodrug temozolomide to MTIC possibly via an activated water molecule in the major groove. Molecular modeling of the structure of temozolomide indicates that the prodrug can make a favorable noncovalent encounter with DNA. The known structure-activity relationships as well as the biological and clinical properties of temozolomide can be interpreted in terms of this model.

A series of new imidazo[5,1-d]-1,2,3,5-tetrazinones with additional hydrogen-bonding or ionic substituents at the 8-carboxamide position of the antitumor drugs temozolomide (1) and mitozolomide (2) has been prepared. None of these compounds were significantly more cytotoxic in vitro against the mouse TLX5 lymphoma than the lead structures. Molecular modeling techniques have been used to design benzo- and pyrazolo[4,3-d]-1,2,3-triazinones bearing carboxamide groups in appropriate positions which are isosteric with temozolomide and mitozolamide but which cannot ring open to alkylating species. As predicted, these compounds have no inhibitory properties against human GM892A or Raji cell lines in vitro. Temozolomide and the spermidine-temozolomide conjugate 28 preferentially methylate guanines within guanine-rich sequences in DNA, but no experimental evidence has been found to support the hypothesis that such regions are involved in catalyzing the ring opening of the imidazotetrazinone prodrugs to their active forms.

Dendrotoxin (DTX), an Mr 7000 convulsant polypeptide from the venom of Dendroaspis angusticeps, or its facilitatory homologues act through blockade of certain voltage-sensitive K+ currents in a variety of neurons. High-affinity acceptors for DTX have been demonstrated in synaptic plasma membranes of rat or chick brain, and a fraction of these avidly bind beta-bungarotoxin (beta-BuTX), a presynaptically active protein whose lighter B polypeptide is homologous to this toxin. Extraction of rat synaptic plasma membranes using Triton X-100 in K+-containing buffer yielded binding sites with KD values of approximately 0.5 and 0.7 nM for 125I-labeled DTX and beta-BuTX, respectively. The content of high-affinity sites obtained for beta-BuTX, including the contribution of a lower affinity component, approximates to the Bmax (approximately 1.3 pmol/mg of protein) obtained for the apparent single set of DTX acceptors. On solubilization, the pharmacological specificity of the acceptor for neurotoxic DTX congeners was retained. 125I-beta-BuTX binding (2.1 nM) was blocked efficaciously by DTX (IC50 = 1.6 nM) while the binding of 2.1 nM 125I-DTX was inhibited completely by beta-BuTX (IC50 = 25 nM); the lower potency of the latter could relate to the noncompetitive nature of the mutual competition and to the presence of high- and low-affinity sites for beta-BuTX. On gel filtration, or sedimentation analysis in H2O/sucrose and 2H2O/sucrose gradients, one peak of DTX binding activity was observed, and this was inhibitable by beta-BuTX. From the hydrodynamic properties of the acceptor/detergent/lipid complex (s20,w = 13.2 S; Stokes radius = 8.6 nm), a molecular weight of 405,000-465,000 was estimated.(ABSTRACT TRUNCATED AT 250 WORDS)

Objective: To test a series of 1-alkyl-2-(4-pyridyl)pyridinium bromides with alkyl chains containing between 9 and 16 carbons against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Stenotrophomonas maltophilia, Acinetobacter baumannii and Pseudomonas aeruginosa) bacteria. Materials and Methods: Chemical synthesis was based on the reaction of 2,4′-bipyridyl with alkyl bromide. Antimicrobial activity of the bipyridyls was measured by growing bacterial cultures on Mueller-Hinton agar in the presence and absence of inhibitors. Results:The compounds were most active against S. aureus. The most active compounds had alkyl chain lengths of between 11 and 16 carbons. Methicillin-sensitive S. aureus was more susceptible to the inhibitors than methicillin-resistant S. aureus (MRSA). Two subclasses of MRSA existed which differed in their susceptibility to the inhibitors. The susceptibility of MRSA strains to the compounds was increased in the presence of the efflux pump inhibitor reserpine. The activity of the compounds against Gram-negative organisms was increased when the membrane-permeabilizing agent sodium citrate was introduced. Critical micelle concentrations of the compounds were much higher than minimum inhibitory concentrations of the inhibitors. Conclusion: The mechanism of action of the compounds may involve perturbing bacterial membranes. The resistance of some MRSA strains to the compounds may be related to efflux pumps.

Flavonoids are a group of polyphenolic plant compounds with a range of biological activities. This study shows that the flavonoids hesperetin and naringenin have antibacterial activity against methicillin-sensitive and methicillin-resistant Staphylococcus aureus isolates. Minimum inhibitory concentrations for hesperetin were 250 and 500 microg/mL, respectively, and for naringenin were 125 and 250 microg/mL, respectively. This effect was reversed by the beta-lactam antibiotics methicillin, penicillin and oxacillin, but not by cefoxitin. For bacteria growing in the presence of these antibiotics, the flavonoids had no effect on the levels of beta-lactamase enzymes and PBP-2' compared to controls. Electron microscopy showed abnormal morphology in bacteria treated with subinhibitory concentrations of flavonoids. These results are interesting because previous studies have reported synergistic interactions between flavonoids and beta-lactam antibiotics. It is suggested that an interaction removes both inhibitors from the bacterial growth milieu.