Reporter gene expression from LTR-circles as tool to identify HIV-1 integrase inhibitors

Early HIV-1 integrase inhibitors, such as compounds containing a β-diketo acid moiety, were identified by extensive high-throughput screening campaigns. Traditionally, in vitro biochemical assays, measuring the catalytic activities of integrase, have been used for this purpose. However, these assays are confounded by the absence of cellular processes or cofactors that play a role in the integration of HIV-1 DNA in the cellular genome. In contrast to regular cell-based virus inhibition assays, which targets all steps of the viral replication cycle, a novel cellular screening assays was developed to enable the specific identification of integrase inhibitors, employing a readout that is linked with the inhibition of integrase activity. Therefore, a HIV-1 lentiviral vector equipped with the enhanced green fluorescent protein (eGFP) reporter gene was used to detect expression from extrachromosomal viral DNA (1- or 2-long terminal repeat circles), formed when integration of vector DNA into the cellular genome is prevented by an integrase inhibitor. In this assay, eGFP expression from the low residual level of transcriptional activity of extrachromosomal DNA was measured via high-throughput flow cytometry. An algorithm for analysis of eGFP expression histograms enabled the specific identification of integrase inhibitors. This assay is amenable for high throughput screening to identify inhibitors of HIV-1 integrase.

A novel high-throughput cellular screening assay for the discovery of HIV-1 integrase inhibitors

The discovery of HIV-1 integrase inhibitors has been enabled by high-throughput screening and rational design of novel chemotypes. Traditionally, biochemical assays focusing on the strand transfer activity of integrase have been used to screen compound libraries for identification of novel inhibitors. In contrast, cellular screening assays enable a phenotypic or multi-target approach, and may result in identification of compounds inhibiting integrase in its natural context, the pre-integration complex. Furthermore, a cellular assay encompassing 3' processing, strand transfer and nuclear import may lead to the identification of compounds with novel mechanisms of action targeting cellular and viral factors. Therefore, a cellular screening assay was developed, which focused on integrase activity, where infection of MT4 cells with an HIV-1 based lentiviral vector was synchronized by temporary arrest at the reverse transcriptase step and subsequent release to enable integration. The assay was validated using a panel of antivirals and proved to be a robust cellular screening assay for the identification of novel integrase inhibitors.

Age and microdistribution of 210Pb at caribou bone surfaces measured by repeated alpha spectroscopy of 210Po

PURPOSE

To measure microdistibution and age of 210Pb in Canadian caribou bone, and assess the accuracy of ICRP biokinetic and dosimetric models for 210Pb-supported 210Po at bone surfaces.

MATERIALS AND METHODS

The previously described use of alpha spectroscopy to study 210Pb microdistribution at bone surfaces was expanded in a study of femora from 23 caribou. A new technique for measuring the age in vivo of Pb in bone, on the basis of the ratio of 210Po/210Pb activity, was carried out on eight caribou femora.

RESULTS

The measured thickness p of the layer containing elevated concentration of 210Pb at femoral endosteal surfaces was 0.79 +/- 0.52 microm (SD). This thickness increased linearly with age in caribou aged 2-11 years. The surface/volume concentration ratio of 210Pb (As/Av) varied from 1 to 18, geometric mean 3.8. No trend in As/Av with caribou age was observed. In the upper 1 microm/210Pb was 17 +/- 22 days old, and at depths of 1-22 microm the age was 146 +/- 17 days. Thus Pb at the bone surface was about nine times younger than in underlying bone.

CONCLUSIONS

Modifications to the ICRP 67 biokinetic model for Pb are proposed. The alpha dose to tissue above endosteal surfaces is reduced three times due to the low ingrowth ratio of 210Po.

Speciation of plutonium in potato and the gastrointestinal transfer of plutonium and americium from potato

Complexation of Pu(IV) and Am(III) by naturally occurring agents such as citrate and phytate might enhance their uptake from the digestive tract. However, the extent to which they enhance the gastrointestinal uptake of actinides from foodstuffs is far from resolved, as this study shows. Investigations of the chemical forms of Pu(IV) and Am(III), by gel permeation chromatography, in simulated digests of potato tubers naturally radiolabelled with 239Pu(IV) and 241Am(III) have shown that neither citrate nor phytate appear to determine their chemical forms. Therefore, it is possible that these are not the complexing anions which determine the gastrointestinal transfer of these radioelements from potato meal. Isotachophoretic analyses of the juices pressed from tubers and solutions prepared by simulated digestion of potato tubers have demonstrated the presence of several low molecular weight anions. These anions might be complexing agents because they possess an isotachophoretic mobility similar to that of citrate; some of these anions remain unidentified. Whereas 239Pu and 241Am were used in the foregoing studies, 238Pu and 241Am were used to produce either in vitro or naturally radiolabelled potatoes for gastrointestinal transfer measurements using rats and hamsters. Gastrointestinal transfer values of 0.13 +/- 0.05% (mean +/- standard error of mean) and 0.16 +/- 0.06% were determined with rats for the uptake of 238Pu and 241Am, respectively, from naturally labelled potato meal. Higher gastrointestinal transfer values were obtained for hamsters: for 238Pu and 241Am the transfer values from naturally labelled meal were 0.25 +/- 0.08% and 0.33 +/- 0.07%, respectively. Similar values were observed for uptake from in vitro labelled potato meal. On the basis of the similarity of the values for the naturally labelled potato meal and for the 'spiked' potato meal it would appear that biological incorporation is not necessary for the binding of the actinides to the ligands which will determine gastrointestinal transfer.