Sonja Kazmer

Distinct binding determinants for 9-cis retinoic acid are located within AF-2 of retinoic acid receptor alpha.

Retinoids exert their physiological action by interacting with two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which regulate gene expression by forming transcriptionally active heterodimeric RAR/RXR or homodimeric RXR/RXR complexes on DNA. Retinoid receptor activity resides in several regions, including the DNA and ligand binding domains, a dimerization interface, and both a ligand-independent (AF-1) and a ligand-dependent (AF-2) transactivation function. While 9-cis retinoic acid (RA) alone is the cognate ligand for the RXRs, both 9-cis RA and all-trans RA (t-RA) compete for binding with high affinity to the RARs. This latter observation suggested to us that the two isomers may interact with a common binding site. Here we report that RAR alpha has two distinct but overlapping binding sites for 9-cis RA and t-RA. Truncation of a human RAR alpha to 419 amino acids yields a receptor that binds both t-RA and 9-cis RA with high affinity, but truncation to amino acid 404 yields a mutant receptor that binds only t-RA with high affinity. Remarkably, this region also defines a C-terminal boundary for AF-2, as addition of amino acids 405 to 419 restores receptor-mediated gene activity to a truncated human RAR alpha lacking this region. It is interesting to speculate that binding of retinoid stereoisomers to unique sites within an RAR may function with AF-2 to cause differential activation of retinoid-responsive gene pathways.

The effect of methylxanthines on chromosomes of human lymphocytes in culture

The effect of caffeine (I,3,7-trimethylxanthine), theophylline (I,3-dimethylxanthine), theobromine (3,7-dimethylxanthine), paraxanthine (I,7-dimethylxanthine) I-methylxanthine, 3-methylxanthine, and 7-methylxanthine added at the 48th h on the chromosomes of human lymphocytes in 72-h cultures has been investigated. Caffeine and the dimethylxanthines cause breakage at 750 mug/ml, with caffeine the most, and paraxanthine the least clastogenic. I-Methylxanthine and dimethylxanthines with a methyl group in the I-position are the most effective in depressing mitotic indices. No chromosome damage was exhibited by the monomethylxanthines.

The effect of caffeine on chromosomes of human lymphocytes: A search for the mechanism of action

Abstract In an attempt to determine the mechanism of action of caffeine clastogenicity (chromosome breakage), substances directly or indirectly affecting the synthesis or integrity of DNA were added to caffeine-treated human lymphocyte cultures. At concentrations of 250–750 μg caffeine per ml, no evidence could be found which would indicate that caffeine was acting as a purine analogue, inhibitor of phosphodiesterase, stimulator of adenylosuccinate (S-AMP) lyase, labilizer of lysosomes, or as a clastogen which could be inhibited by an antimutagen.

Discovery and optimization of 2-phenyloxazole derivatives as diacylglycerol acyltransferase-1 inhibitors.

In a discovery effort to find safe and effective DGAT-1 inhibitors, we have identified 2-phenyloxazole 4-carboxamide 1 as a conformationally constrained analog of a hydrazide hit, which was previously identified from high-throughput screening. Further optimization of this series has led to chemically more stable 2-phenyloxazole-based DGAT-1 inhibitor 25 with improved solubility, cell-based activity, and pharmacokinetic properties. Compound 25 also demonstrated in vivo efficacy in a diet-induced obesity (DIO) rat model.