Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones

High-throughput screening of a National Cancer Institute library of pure natural products identified the hydroxylated tropolone derivatives β-thujaplicinol (2,7-dihydroxy-4-1(methylethyl)-2,4,6-cycloheptatrien-1-one) and manicol (1,2,3,4-tetrahydro-5-7-dihydroxy-9-methyl-2-(1-methylethenyl)-6H-benzocyclohepten-6-one) as potent and selective inhibitors of the ribonuclease H (RNase H) activity of human immunodeficiency virus-type 1 reverse transcriptase (HIV-1 RT). β-Thujaplicinol inhibited HIV-1 RNase H in vitro with an IC(50) of 0.2 μM, while the IC(50) for Escherichia coli and human RNases H was 50 μM and 5.7 μM, respectively. In contrast, the related tropolone analog β-thujaplicin (2-hydroxy-4-(methylethyl)-2,4,6-cycloheptatrien-1-one), which lacks the 7-OH group of the heptatriene ring, was inactive, while manicol, which possesses a 7-OH group, inhibited HIV-1 and E.coli RNases H with IC(50) = 1.5 μM and 40 μM, respectively. Such a result highlights the importance of the 2,7-dihydroxy function of these tropolone analogs, possibly through a role in metal chelation at the RNase H active site. Inhibition of HIV-2 RT-associated RNase H indirectly indicates that these compounds do not occupy the nonnucleoside inhibitor-binding pocket in the vicinity of the DNA polymerase domain. Both β-thujaplicinol and manicol failed to inhibit DNA-dependent DNA polymerase activity of HIV-1 RT at a concentration of 50 μM, suggesting that they are specific for the C-terminal RNase H domain, while surface plasmon resonance studies indicated that the inhibition was not due to intercalation of the analog into the nucleic acid substrate. Finally, we have demonstrated synergy between β-thujaplicinol and calanolide A, a nonnucleoside inhibitor of HIV-1 RT, raising the possibility that both enzymatic activities of HIV-1 RT can be simultaneously targeted

Technology for Medical Education, Research, and Disease Screening by Exploitation of Biomarkers in a Large Collection of Uterine Cervix Images

The Communications Engineering Branch of the National Library of Medicine is collaborating with the National Cancer Institute (NCI) in developing applications for medical education, research, and disease screening for precancer detection in the uterine cervix. These applications include (1) expert marking/labeling of tissue regions, (2) Web viewing/ interpretation of histology images, (3) image database/retrieval, and (4) training/testing in clinical image interpretation. Initial NCI studies have been conducted in expert cervicography marking and histology evaluation. We are working toward making cervix images searchable by content-based image retrieval (CBIR). Image pre-processing to remove specular reflection artifacts has achieved 90% success (120 images). Similar results have been obtained for automated location of cervix regions, using Gaussian Mixture Modeling (GMM) with Lab color and one geometric feature. We describe initial classification experiments to discriminate clinically significant tissue, using RGB, HSV, Lab, and YCbCr color models, texture measures, and GMM, Fuzzy C-means, and deterministic annealing algorithms

Yonetani–Theorell plot for the inhibition of HIV-1 RT in the presence of the NNRTI calanolide A and β-thujaplicinol

<p><b>Copyright information:</b></p><p>Taken from "Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones"</p><p>Nucleic Acids Research 2005;33(4):1249-1256.</p><p>Published online 1 Mar 2005</p><p>PMCID:PMC552956.</p><p>© The Author 2005. Published by Oxford University Press. All rights reserved</p> The inverse of the rate of RNase H cleavage was plotted as a function of β-thujaplicinol concentration at calanolide A concentrations of 12.5 μM (open square), 0.78 μM (filled square), 0.39 μM (open circle) and DMSO (filled circle). The convergent best-fit lines indicate mutually exclusive binding sites for calanolide A and β-thujaplicinol