In vitro and in vivo evaluations of the P-glycoprotein-mediated efflux of dibenzoylhydrazines.

P-glycoprotein (P-gp) is a member of the ATP-binding cassette transporter family. It actively transports a wide variety of compounds out of cells to protect humans from xenobiotics. Thus, determining whether chemicals are substrates and/or inhibitors of P-gp is important in risk assessments of pharmacokinetic interactions among chemicals because P-gp-mediated transport processes play a significant role in their absorption and disposition. We previously reported that dibenzoylhydrazines (DBHs) such as tebufenozide and methoxyfenozide (agrochemicals) stimulated P-gp ATPase activity. However, it currently remains unclear whether these derivatives are transport substrates of P-gp and inhibit transport of other chemicals by P-gp. In the present study, in order to evaluate the interactions of DBHs with other chemicals in humans, we determined whether DBHs are P-gp transport substrates using both the in vitro bidirectional transport assay and the in vivo study of rats. In the in vivo study, we investigated the influence of P-gp inhibitors on the brain to plasma ratio of methoxyfenozide in rats. We also examined the inhibitory effects of DBHs on quinidine (a P-gp substrate) transport by P-gp in order to ascertain whether these derivatives are inhibitors of P-gp. Based on the results, DBHs were concluded to be weak P-gp transport substrates and moderate P-gp inhibitors. However, the risk of DBHs caused by interaction with other chemicals including drugs was considered to be low by considering the DBHs' potential as the substrates and inhibitors of P-gp as well as their plasma concentrations as long as DBHs are properly used.

Structure-activity relationships of dibenzoylhydrazines for the inhibition of P-glycoprotein-mediated quinidine transport.

We previously demonstrated that dibenzoylhydrazines (DBHs) are not only P-glycoprotein (P-gp) substrates, but also inhibitors. In the present study, we evaluated the inhibition of P-gp-mediated quinidine transport by two series of DBHs and performed a classical QSAR analysis and docking simulation in order to investigate the mechanisms underlying P-gp substrate/inhibitor recognition. The results of the QSAR analysis identified the hydrophobic factor as the most important for inhibitory activities, while electronic and steric effects also influenced the activities. The different substituent effects observed in each series suggested the different binding modes of each series of DBHs, which was supported by the results of the docking simulation.

Convenient synthesis of N-unprotected deoxynucleoside 3'-phosphoramidite building blocks by selective deacylation of N-acylated species and their facile conversion to other N-functionalized derivatives.

[reaction: see text] A new route to N-unprotected deoxynucleoside 3'-phosphoramidite building blocks by use of highly selective N-deacylation of commercially available N-acylated deoxynucleoside 3'-phosphoramidites is described. These compounds could be readily converted to other types of N-protected species by facile N-acylations with acylating reagents.

Synthesis and triplex formation of oligonucleotides containing 8-thioxodeoxyadenosine.

For more effective DNA triplex formation under neutral conditions, we synthesized triplex-forming oligonucleotides containing 8-thioxodeoxyadenosine (s(8)dA) residues in place of the protonated deoxycytidines required for the third base pairing with DNA duplexes. Consequently, it was found that s(8)dA exhibited much stronger hybridization ability than dC under neutral conditions when four s(8)dA bases were arranged in a consecutive sequence.

Development of a colorimetric assay for determining the amount of H2O2 generated in tobacco cells in response to elicitors and its application to study of the structure-activity relationship of flagellin-derived peptides.

Plants exhibit various defense responses after recognizing elicitor molecules derived from pathogenic microorganisms and host plants. In this study, we developed an improved colorimetric assay for quantifying the generation of H2O2 in plant cells, one of the defense responses, to evaluate elicitor activity quantitatively. H2O2 is detected using a dye, N-(carboxymethylaminocarbonyl)-4,4'-bis(dimethylamino)-diphenylamine sodium salt (DA-64), which can be measured by conventional spectrometers in a highly sensitive and quantitative manner. Using this method, we successfully measured the elicitor activity of flagellin-derived peptides in cultured tobacco cells, and identified several structural features of the peptides important for the elicitor activity. The results suggest that the structural factors required for expression of the elicitor activity differ slightly among plant species. The efficient and sensitive assay developed in this study should be useful not only for studying structure-activity relationships, but also for the screening of novel compounds that can induce defense responses.