Proton magnetic resonance spectroscopy in patients with glial tumors: a multicenter study

Budding yeast (Saccharomyces cerevisiae) Rap1p has been expressed in fission yeast (Schizosaccharomyces pombe) under the control of the regulatable fructose bisphosphatase (fbp) promoter. When the fbp promoter was derepressed, cells containing the complete RAP1 gene failed to show any significant growth, suggesting that Rap1p is toxic. A derivative of Rap1p that has a temperature-sensitive mutation in the DNA-binding domain was not toxic in cells grown at 37 degrees C, a temperature at which DNA binding by rap1p(ts) is severely inhibited. Removal of a short region downstream of the DNA-binding domain, including a region previously shown to be essential for Rap1p toxicity in budding yeast, also abolished the toxic effect. The toxic effect of Rap1p has therefore been conserved between two distantly related yeasts. In budding yeast, overexpression of Rap1p also caused changes to the lengths of the telomeric repeats. No effects on telomeres were detected in fission yeast.     

The choice of prodrugs for gene directed enzyme prodrug therapy of cancer

Prodrugs are chemicals that are pharmacodynamically and toxicologically inert but which can be converted to highly active species. In cancer chemotherapy, enzyme activated prodrugs have been effective against certain animal tumours. However, in the clinic it has been found that human tumours containing appropriately high levels of the activating enzymes were rare and not associated with any particular type of tumour. Gene directed enzyme prodrug therapy (GDEPT) attempts to overcome this problem by killing tumour cells by the activation of a prodrug after the gene encoding for an activating enzyme has been targeted to the malignant cell. Here we summarise the various enzyme/prodrug systems that have been proposed for cancer therapy and comment on their suitability for GDEPT. This is because systems developed for other applications such as antibody directed enzyme prodrug therapy (ADEPT) may not be suitable for GDEPT. What is required are nontoxic prodrugs that can be converted intracellularly to highly cytotoxic metabolites that are not cell cycle specific in their mechanism of action. The active drugs released should also be readily diffusible and exert a bystander effect. Alkylating agents best meet these criteria. An example of a suitable enzyme/prodrug system may be a bacterial nitroreductase that can convert a relatively nontoxic monofunctional alkylating agent to a difunctional alkylating agent that is some ten thousand times more cytotoxic.     

The emerging role of cytochrome P450 3A in psychopharmacology

Recent advances in molecular pharmacology have allowed the characterization of the specific isoforms that mediate the metabolism of various medications. This information can be integrated with older clinical observations to begin to develop specific mechanistic and predictive models of psychotropic drug interactions. The polymorphic cytochrome P450 2D6 has gained much attention, because competition for this isoform is responsible for serotonin reuptake inhibitor-induced increases in tricyclic antidepressant concentrations in plasma. However, the cytochrome P450 3A subfamily and the 3A3 and 3A4 isoforms (CYP3A3/4) in particular are becoming increasingly important in psychopharmacology as a result of their central involvement in the metabolism of a wide range of steroids and medications, including antidepressants, benzodiazepines, calcium channel blockers, and carbamazepine. The inhibition of CYP3A3/4 by medications such as certain newer antidepressants, calcium channel blockers, and antibiotics can increase the concentrations of CYP3A3/4 substrates, yielding toxicity. The induction of CYP3A3/4 by medications such as carbamazepine can decrease the concentrations of CYP3A3/4 substrates, yielding inefficiency. Thus, knowledge of the substrates, inhibitors, and inducers of CYP3A3/ and other cytochrome P450 isoforms may help clinicians to anticipate and avoid pharmacokinetic drug interactions and improve rational prescribing practices.     

A double-blind, randomized study of naproxen sodium, ibuprofen, and placebo in postoperative dental pain

In a double-blind, parallel, placebo-controlled study, 203 patients with post-operative dental pain following the extraction of one or two bony impacted third molars were randomized to receive a single dose of naproxen sodium 220 mg, ibuprofen 200 mg or placebo. Pain intensity and pain relief were assessed at intervals for 12 hours postdose. Both active drugs demonstrated superior analgesic efficacy over placebo. Naproxen sodium and ibuprofen were comparable both in onset of analgesic action and in pain relief. From 1 to 12 hours postdose, naproxen sodium showed a trend for superior analgesic efficacy compared with ibuprofen; this trend reached statistical significance at the 12-hour time point. Both drugs were well-tolerated and effective analgesics for postoperative dental pain.     

Crystal structures of three misacylating mutants of Escherichia coli glutaminyl-tRNA synthetase complexed with tRNA(Gln) and ATP

Three previously described mutant Escherichia coli glutaminyl-tRNA synthetase (GlnRS) proteins that incorrectly aminoacylate the amber suppressor derived from tRNATyr (supF) with glutamine were cocrystallized with wild-type tRNAGln and their structures determined. In two of the mutant enzymes studied, Asp235, which contacts base pair G3-C70 in the acceptor stem, has been changed to asparagine in GlnRS7 and to glycine in GlnRS10. These mutations result in changed interactions between Asn235 of GlnRS7 and G3-C70 of the tRNA and an altered water structure between Gly235 of GlnRS10 and base pair G3-C70. These structures suggest how the mutant enzymes can show only small changes in their ability to aminoacylate wild-type cognate tRNA on the one hand and yet show a lack of discrimination against a noncognate U3-A70 base pair on the other. In contrast, the change of Ile129 to Thr in GlnRS15 causes virtually no change in the structure of the complex, and the explanation for its ability to misacylate supF is unclear.     

A receptor subtype involved in neuropeptide-Y-induced food intake

Neuropeptide Y (NPY) is a powerful stimulant of food intake and is proposed to activate a hypothalamic 'feeding' receptor distinct from previously cloned Y-type receptors. This receptor was first suggested to explain a feeding response to NPY and related peptides, including NPY2-36, that differed from their activities at the Y1 receptor. Here we report the expression cloning of a novel Y-type receptor from rat hypothalamus, which we name Y5. The complementary DNA encodes a 456-amino-acid protein with less than 35% overall identity to known Y-type receptors. The messenger RNA is found primarily in the central nervous system, including the paraventricular nucleus of the hypothalamus. The extent to which selected peptides can inhibit adenylate cyclase through the Y5 receptor and stimulate food intake in rats correspond well. Our data support the idea that the Y5 receptor is the postulated 'feeding' receptor, and may provide a new method for the study and treatment of obesity and eating disorders.     

Beneficial effects of dextro-amphetamine in the treatment of vasodepressor syncope

Three patients with history of documented hypotension, near syncope, or syncope before or after the administration of isoproterenol during head-up tilt table are reported. Severe bradycardia was also noted in one patient. All three patients responded to the administration of 2.5 mg of oral dextroamphetamine 45 minutes prior to a repeat head-up tilt table study. The potent central and peripheral adrenergic agonist pharmacological properties of this drug permitted the prevention of severe vasodepressor syncope in these patients.