Rational design of peptide-based HIV proteinase inhibitors.

A series of peptide derivatives based on the transition-state mimetic concept has been designed that inhibit the proteinase from the human immunodeficiency virus (HIV). The more active compounds inhibit both HIV-1 and HIV-2 proteinases in the nanomolar range with little effect at 10 micromolar against the structurally related human aspartic proteinases. Proteolytic cleavage of the HIV-1 gag polyprotein (p55) to the viral structural protein p24 was inhibited in chronically infected CEM cells. Antiviral activity was observed in the nanomolar range (with one compound active below 10 nanomolar) in three different cell systems, as assessed by p24 antigen and syncytium formation. Cytotoxicity was not detected at 10 and 5 micromolar in C8166 and JM cells, respectively, indicating a high therapeutic index for this new class of HIV proteinase inhibitors.

Comparison of antigen capture assays against HIV-1 in evaluating antiviral compounds.

Five antigen capture enzyme-linked immunosorbent assays (ELISAs) have been assessed for detecting HIV-1 in tissue culture supernatants of cell cultures used routinely to investigate antiviral activity. Although all the ELISAs are very sensitive to low levels of antigens they have different characteristics when used for titrating virus antigens.

Lithium gamma-linolenate-induced cytotoxicity against cells chronically infected with HIV-1.

Lithium gamma-linolenate (Li-GLA), was evaluated for its activity in selectively killing H9 cells chronically infected with HIV-1RF. After 4 days incubation with Li-GLA approximately 90% of the H9RF cells were non-viable compared to 20% of uninfected H9 cells. The efficacy of the Li-GLA, in preferentially killing HIV infected cells also correlates with lipid peroxidation, as measured by the intracellular thiobarbituric acid-reactive material content. The addition of an antioxidant (vitamin E) to the culture medium reduced the toxicity of Li-GLA. These data indicate that this selective killing effect of cells chronically infected with HIV may be due to the enhanced extent of lipid peroxidation of the added Li-GLA.

Syncytia formation in HIV-1 infected cells is associated with an increase in cellular oleic acid.

Infection of cells with the human immunodeficiency virus type-1 (HIV-1) usually results in the formation of giant multinuclear cells (syncytia) [(1986) Nature 322, 470-474; (1986) Nature 322, 725-728; (1985) Hum. Pathol. 18, 760-765; (1987) Ann. Neurol. 21, 490-496]. The appearance of syncytia is associated with an increase in the monounsaturated oleic acid content. This report describes experiments which compare the activity of known antiviral agents with that of saturated fatty acid derivatives in inhibiting oleic acid and syncytia formation. A concept is introduced which proposes that infection of cells with the human immunodeficiency virus causes a rise in cellular oleic acid which leads to increased membrane fluidity.

Nucleoside analogues previously found to be inactive against HIV may be activated by simple chemical phosphorylation.

Nucleoside analogues previously found to be inactive against the human immunodeficiency virus (HIV) may be activated by simple chemical derivatisation. As part of our effort to deliver masked phosphates inside living cells we have discovered that certain phosphate triester derivatives of inactive nucleoside analogues become inhibitors of HIV replication. This discovery underlies the importance of the masked phosphate approach, and has significant implications for the future design of chemotherapeutic nucleoside analogues. If highly modified nucleoside analogues may be active without the intervention of nucleoside kinase enzymes, major advantage may accrue in terms of low toxicity and enhanced selectivity. Moreover, the increased structural freedom may have implications for dealing with the emergence of resistance. The concept herein described as 'kinase bypass' may thus stimulate the discovery of a new generation of antiviral agents.

The detection of subtle differences between different orthopoxvirus genomes by heteroduplex analysis.

Corresponding DNA fragments from variola (Harvey) and monkeypox (Denmark) viruses which had been cloned into different plasmid vectors were subjected to heteroduplex analysis. Characteristic deletion loops corresponding to differences between the cloning vectors served as internal markers to identify and to orientate the heteroduplexed molecules. Partial denaturation of the resulting heteroduplexes was used as a primary screen to locate regions of heterogeneity between the poxvirus inserts. The denaturation threshold for homoduplexes was consistently higher than that for heteroduplexes. However, significant sequence divergence between corresponding fragments was indicated by larger than usual differences in thresholds between corresponding homo- and heteroduplexes. Denaturation bubbles of 0.1-0.5 kb were detected and hence small regions of heterogeneity between the genomes (180 kb) of variola and monkeypox viruses were localised. This procedure has a general application in comparative studies on large, complex but closely related DNA molecules.

Synthesis and anti-HIV activity of some novel lactyl and glycolyl phosphate derivatives.

Novel phosphate triester derivatives of 3'-acetylthymidine, and of the anti-HIV nucleoside analogue AZT have been prepared by phosphorochloridate chemistry. These materials are designed to act as membrane-soluble pro-drugs of the bio-active free nucleotides. In particular, novel glycolate and lactate phosphate derivatives have been prepared. In vitro evaluation revealed the AZT compounds to have a pronounced and selective antiviral effect, the magnitude of which varied considerably with the nature of the phosphate blocking group.

Synthesis and anti-HIV activity of some haloalkyl phosphoramidate derivatives of 3'-azido-3'-deoxythymidine (AZT): potent activity of the trichloroethyl methoxyalaninyl compound.

Phosphate triester derivatives of AZT have been prepared as membrane-soluble pro-drugs of the bio-active nucleotides, and have been evaluated against HIV-1 in vitro. In particular, the phosphorus centre carries a trichloro- or trifluoroethyl group and a carboxyl-protected, amino-linked amino acid. The compounds are prepared using phosphorochloridate chemistry, and are characterized by a range of techniques. They display potent anti-HIV activity and low host toxicity, but surprisingly this activity does not increase on the introduction of the haloalkyl moiety. The trichloroethyl methoxyalaninyl compound is exceptional: here the activity is enhanced 50-fold by the introduction of the trichloroethyl group.

A comparison of gag, pol and rev antisense oligodeoxynucleotides as inhibitors of HIV-1.

Sequences from the gag, pol and rev regions of the RF strain of HIV-1 (HIV-1RF) were chosen as targets for antisense phosphorothioate oligodeoxynucleotides (S-oligos). These sequences were the p18/p24 junction in gag, the active site of HIV protease in pol; a sequence from the first exon of the rev gene and S-oligodeoxycytidylic acid controls. Compounds were tested against HIV-1 in both acutely and chronically infected cells. The results show that these phosphorothioate analogues tested in acutely infected cells were active in the 0.1-2 microM range, were dependent on chain length but had no sequence specificity. To study the mechanism of action, the time of addition of S-oligos to acutely infected cells was delayed for up to 48 h post-infection. It was found that antiviral activity was lost when compounds were added to the cultures later than 10 h post-infection. With chronically infected cells only the antisense rev sequence showed activity at 30 microM and neither of the gag or pol antisense sequences has a significant effect on HIV replication at 50 microM. These results are consistent with previous in vitro studies which demonstrate that antisense S-oligodeoxynucleotides have several modes of action.

Synthesis and anti-HIV evaluation of some phosphoramidate derivatives of AZT: studies on the effect of chain elongation on biological activity.

A series of phosphoramidate derivatives of the anti-HIV drug AZT has been prepared as membrane soluble pro-drugs of the bio-active nucleotide forms and evaluated in vitro against HIV-1. Terminal substituted alkyl amines have a pronounced anti-HIV effect: this effect declines upon increasing the length of the methylene spacer. The results are consistent with a mechanism of action involving intracellular cleavage of the phosphoramidate bond, and release of the nucleotide, or a derivative thereof. Full spectroscopic data are included on the products and their phosphorochloridate precursors.

Recent advances in antiviral therapy.

In the early 1980s many institutions in Britain were seriously considering whether there was a need for specialist departments of virology. The arrival of HIV changed that perception and since then virology and antiviral chemotherapy have become two very active areas of bio-medical research. Cloning and sequencing have provided tools to identify viral enzymes and have brought the day of the "designer drug" nearer to reality. At the other end of the spectrum of drug discovery, huge numbers of compounds for screening can now be generated by combinatorial chemistry. The impetus to find drugs effective against HIV has also stimulated research into novel treatments for other virus infections including herpesvirus, respiratory infections, and hepatitis B and C viruses. The need to understand the function of the immune system during HIV infection has brought virologists and immunologists together into new partnerships. The huge increase in activity in antiviral research is reflected in the frequency with which these drugs are now being licensed: in 1985 there were two licensed antiviral drugs for systemic use. Since then approximately 20 compounds have been licensed and more are being submitted to the regulatory authorities on a regular basis.

Continuous brachial plexus neural blockade in a child with intractable cancer pain.

A 6-year-old boy presented with a large, rapidly growing osteosarcoma of the upper humerus and severe neuropathic arm pain. Despite large doses of morphine (100 micrograms/kg/hr), which resulted in intermittent somnolence and respiratory depression, his pain was poorly controlled. An interscalene brachial plexus catheter was inserted, and bupivacaine was injected on ten occasions over 5 days, with markedly improved analgesia and decreased opioid requirement. Cancer pain in children can be controlled by opioids in 95% of cases; however, circumstances such as intractable neuropathic pain may require specific regional anesthetic techniques.

Separation and maintenance of primary T and B lymphocytes.

Two distinct populations of lymphocytes have been identified: T lymphocytes, which are thymus-dependent, and B cells, first observed in the Bursa Fabricus of birds. Mammals do not have an equivalent structure, and there are varying opinions as to the similarity of these cells between species. In humans, current theories are that B lymphocytes differentiate in the fetal liver and in the bone marrow of adults. Human T and B cells are most easily obtained either from peripheral blood or from biopsy of lymphoid tissues (lymph nodes, spleen, Peyer's patches from gut, tonsils, and adenoids).

Testing Compounds for Antiviral Activity in Cell Cultures Infected with HIV.

This chapter describes the procedures that can be used to determine compounds that have antiviral activity against HIV. These include: maintenance of lymphoblastoid cell lines, preparation of peripheral blood mononuclear cells (PMMCs), and determination of the infectivity of the HIV stock-supernatant and antiviral assays. The assays described use both acutely and chronically infected cells. Toxicity of compounds is assessed by measuring (14)C uptake. These protocols are used for the evaluation of compounds that can be carried out by a single individual in a Category 3 containment laboratory. The number of compounds analyzed would be about 10, which is a convenient number to fill a single 96-well p24 enzyme-linked immunosorbent assay (ELISA) plate.

The activity of candidate virucidal agents, low pH and genital secretions against HIV-1 in vitro.

The effect of low pH, normally present in the female genital tract, on HIV viability was examined. HIV is more acid stable than previously reported with no substantial reduction in infectivity occurring until pH levels are reduced below 4.5. The virucidal activity of 3 topical spermicides and chlorhexidine was assessed in vitro using previously established and newly modified assay systems. None of the agents tested had a selectivity index (SI) greater than 5.2. Semen and cervical secretions were assessed for their ability to inhibit HIV-1. While no virucidal effect was found in the latter, seminal fluid was found to have significant activity against HIV-1 and a SI of approximately 50.

Size heterogeneity of EBV and mitochondrial DNAs in Burkitt's lymphoma lines.

A simple, reproducible affinity chromatography method has been adapted for separation of high molecular weight supercoiled circular molecules from mammalian cells. Electron microscopic analysis of EB viral DNA obtained by this method, from the non-producer Burkitt's lymphoma line Raji, revealed monomer-sized viral molecules only. In contrast, the EB viral episomes from recently established human producer lines BL-8 and LY91 were very heterogeneous in size, some being considerably smaller and others much larger than the monomeric DNA. The former are probably related to defective viral species in the B-cell population, but the origin of the latter are as yet unclear. All cell lines contained both monomers and concatemers of mitochondrial DNA; among the latter, molecules apparently greater than 100 kb were observed in the population.

Characterization of Vibrio eltor typing phages: properties of the Eltor phage e4.

Biophysical characteristics of Vibrio eltor phage e4, a key phage in the Vibrio cholerae typing scheme were studied. This icosahedral phage was found to contain 12 structural polypeptides with mol. wt. ranging from 25,000 to 120,000. One of these polypeptides of mol. wt. 50,000 accounted for most of the structural proteins present and was probably the major phage capsid protein. The phage genome comprised a single linear, double-stranded DNA molecule, 69.2 kbp in length (45.6 X 10(6) mol. wt.) as determined by electron microscopy and restriction fragment analyses. The G + C content was 34.6%. Electron microscopy data indicated that unlike the DNAs of other cholera phages, phage e4 DNA is not circularly permuted. Adsorption under normal conditions was biphasic with rate constants of 1.02 X 10(-9)/ml/min up to 60% adsorption and 3 X 10(-10)/ml/min thereafter. Intracellular phage multiplication was characterized by a latent period of 27 min. The burst size was approximately 100 phage particles per infected cell.