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The hydroxyethylurea human immunodeficiency virus type 1 (HIV-1) protease inhibitors SC-55389A and SC-52151 were used to select drug-resistant variants in vitro. One clinical HIV-1 strain (89-959) and one laboratory HIV-1 strain (LAI) were passaged in peripheral blood mononuclear cells or CEMT4 cells in the presence of SC-55389A. Resistant isolates from both strains consistently had a mutation to serine for asparagine at amino acid 88 (N88S) in the protease gene either alone or in combination with a change to phenylalanine at position 10. The N88S mutation, recreated by oligonucleotide-mediated site-directed mutagenesis in HXB2, was sufficient to confer resistance to SC-55389A. In contrast, SC-52151-resistant variants selected from the monocytotropic strain SF162 had multiple substitutions in the protease gene (I11V, M461, F53L, A71V, and N88D), and the N88D mutation, re-created by oligonucleotide-mediated site-directed mutagenesis in HXB2, did not confer resistance to SC-52151. The potencies of L735,524 and Ro31-8959 were not reduced when these compounds were assayed against variants with either the N88S or N88D substitution. Position 88 is in a helix that lies behind the substrate binding pocket and may indirectly influence inhibitor binding through interactions with the amino acid at position 31. The selected mutations were persistent in the viral populations after more than 20 passages in the absence of drugs. Passaging of virus first in SC-55389A alone and then in combination with SC-52151 resulted in the accumulation of more mutations in the protease gene (L10F, D35E, D37M, I47V, 154L, A71V, V82I, and S88D) and in the selection of a variant that was cross-resistant to multiple protease inhibitors. These results indicate that a mutation in the HIV-1 protease at a position that is located outside of the substrate binding pocket confers resistance to a protease inhibitor and that mutations in the protease gene accumulate with increasing selection pressure and can persist in the absence of selection pressure.

Syringacin W-1, a bacteriocin produced by Pseudomonas syringae pathovar syringae strain PsW-1, is a 20 × 75 nm rod-shaped particle composed of an inner core and outer sheath. Production of syringacin W-1 in broth was induced with 0.1 μLg/mL mitomycin C. The bacteriocin was purified from culture lysates using ultrafiltration, rate zonal centrifugation in sucrose gradients, and DEAE-cellulose chromatography. Purity was evaluated by subjecting syringacin W-1 preparations to electrophoresis in polyacrylamide gels under nondenaturing and denaturing conditions. The chemical composition was principally protein (67.2%), and also comigrating nonessential carbohydrate (10–35%). The physical properties of purified syringacin W-1 were a sedimentation coefficient of 104 for rod-shaped particles, pH stability of 5.2–8.2, and temperature stability from −20 to 40 °C. The bacteriocin was resistant to proteases and to 12 of 13 surfactants tested.

The production and activity of syringacin W-1, a particulate bacteriocin made by Pseudomonas syringae PsW-1, was studied in plant tissue. The bacteriocin is rod shaped, approximately 20 nm wide and 75 nm long, and composed of an outer sheath and inner core. Both the producing strain, PsW-1, and a sensitive strain, 16, grew within red kidney bean stems. Strains PsW-1 and 16, or mutants derived from them, were injected into bean stems singly or in mixtures. All singly inoculated strains grew well. However, when the bacteriocin-producing strain was co-inoculated with the sensitive strain, the latter grew poorly, if at all. This was not due to competition for available nutrients, since the sensitive strain grew as well in the presence of a bacteriocin-nonproducing mutant as it did alone. Also, a bacteriocin-resistant mutant grew as well in the presence of a bacteriocin-nonproducing mutant as it did alone. Also, a bacteriocin-resistant mutant grew as well in the presence of the producing strain as it did alone. Bacteriocin activity and particles were recovered from infected plant tissue.

SC-52151 is a potent, selective, tight-binding human immunodeficiency virus (HIV) protease inhibitor containing the novel (R)-(hydroxyethyl) urea isostere. The mean 50% effective concentration for lymphotropic, monocytotropic strains and field isolates of HIV type 1 (HIV-1), HIV-2, and simian immunodeficiency virus is 26 ng/ml (43 nM). The combination of SC-52151 and nucleoside reverse transcriptase inhibitors synergistically inhibited HIV-1 replication without additive toxicity. An extended postantiviral effect correlates with inhibition of gag and gag-pol polyprotein processing. SC-52151 is highly protein bound (>90%) in human plasma, and the level of partitioning into erythrocytes is low. Physiological concentrations of ␣-1-acid glycoprotein, but not albumin, substantially affect the antiviral potency of SC-52151. The oral bioavailability of [ 14 C]SC-52151 is 17% when it is administered as an elixir to the rat, dog, or monkey. Oxidation of the t-butyl moiety is the major route of biotransformation, and elimination is mainly by biliary excretion. No toxicologically significant effects have been observed in animals. Pharmacokinetic and metabolism studies in multiple animal species predict 20 to 30% systemic bioavailability, an elimination half-life of 1 to 2 h, and a volume of distribution of greater than 3 liters/kg in humans.The late stage of human immunodeficiency virus (HIV) replication requires a virus-encoded aspartyl protease for maturational processing of structural proteins and replicative enzyme precursors (12). Inhibition of the protease results in immature, noninfectious virus particles and the cessation of virus propagation. Because of recent advances in peptidomimetic chemistry, novel orally bioavailable inhibitors of the HIV protease have been designed and are undergoing clinical evaluation (18).SC-52151 represents a unique class of nonnucleoside, ureabased peptidomimetic antiretroviral compounds (8) which are active alone or in combination with reverse transcriptase (RT) inhibitors. SC-52151 is orally bioavailable as an ethanol-containing solution, and the pharmacokinetic properties and metabolism in multiple animal species suggest that an antiviral concentration could be achievable in human plasma.(The antiviral properties of SC-52151 were discussed in part at the 34th Interscience Conference on Antimicrobial Agents and Chemotherapy, Orlando, Fla., 4 to 7 October 1994.) MATERIALS AND METHODSChemical description. SC-52151 was synthesized by previously reported methods (8). The structural formula of SC-52151 is given in Fig. 1, and its chemical name is given in the legend to Fig. 1. It is a white, amorphous solid with a molecular weight of 604.75 atomic mass units.Enzyme assay. HIV protease activity (enzyme concentration, 12 nM) was measured at pH 6.4 with the synthetic heptapeptide AntThrIleNlePhe (p-NO 2 ) GlnArgNH 2 by the continuous fluorometric assay developed by Toth and Marshall (22). An increase in fluorescence is generated by the removal of intramolecular fluorescence quenching followin...