Inhibition of HIV replication in cell culture by the specific aspartic protease inhibitor pepstatin A

Hybrid 2D/3D-quantitative structure-activity relationship and modeling studies perspectives of pepstatin A analogs as cathepsin D inhibitors

AIM

Cathepsin D, one of the attractive targets in the treatment of breast cancer, has been implicated in HIV neuropathogenesis with potential proteolytic effects on chemokines. Methodology/result: Diverse modeling tools were used to reveal the key structural features affecting the inhibitory activities of 78 pepstatin A analogs. Analyses were performed to investigate the stability, rationality and fluctuation of the analogs. Results showed a clear correlation between the experimental and predicted activities of the analogs as well as the variation in their activities relative to structural modifications.

CONCLUSION

The insight gained from this study offers theoretical references for understanding the mechanism of action of cathepsin D and will aid in the design of more potent and clinically-relevant drugs. Graphical abstract [Formula: see text].

HIV-1 Aspartic Proteinase: High-Level Production and Automated Fluorometric Screening Assay of Inhibitors

The 99-amino-acid HIV-1 aspartic proteinase was expressed to high levels in Escherichia coli using a T7 expression system. About 50% of the insoluble material after sonication of the bacteria was composed of aggregated proteinase. Subsequent renaturation and purification yielded large quantities of a homogeneous enzyme able to cleave various heptapeptidic substrates in vitro with a Km around 2.5 mM. A fluorometric assay has been devised to allow automated screening of HIV proteinase inhibitors based on an analogous renin assay. We used the synthetic intramolecularly quenched fluorogenic substrate Suc-TLNFPIS-4MCA based on the heptapeptide TLNFPIS, which encompasses the proteinase/reverse transcriptase junction, coupled to the fluorophore 7-amino-4-methylcoumarin and blocked at the amino-terminus by a succinyl group. The enzyme cleaves the substrate between phenylalanine and proline, and conditions were optimized for liberation of 7AMC from the generated PIS-4MCA with aminopeptidase M as secondary enzyme. 7AMC was monitored with a microplate fluorescence scanner. The known aspartic proteinase inhibitor pepstatin A consistently gave Ki = 2 × 10−6M. Other synthetic and natural compounds are currently being tested.

An assay to monitor HIV-1 protease activity for the identification of novel inhibitors in T-cells

The emergence of resistant HIV strains, together with the severe side-effects of existing drugs and lack of development of effective anti-HIV vaccines highlight the need for novel antivirals, as well as innovative methods to facilitate their discovery. Here, we have developed an assay in T-cells to monitor the proteolytic activity of the HIV-1 protease (PR). The assay is based on the inducible expression of HIV-1 PR fused within the Gal4 DNA-binding and transactivation domains. The fusion protein binds to the Gal4 responsive element and activates the downstream reporter, enhanced green fluorescent protein (eGFP) gene only in the presence of an effective PR Inhibitor (PI). Thus, in this assay, eGFP acts as a biosensor of PR activity, making it ideal for flow cytometry based screening. Furthermore, the assay was developed using retroviral technology in T-cells, thus providing an ideal environment for the screening of potential novel PIs in a cell-type that represents the natural milieu of HIV infection. Clones with the highest sensitivity, and robust, reliable and reproducible reporter activity, were selected. The assay is easily adaptable to other PR variants, a multiplex platform, as well as to high-throughput plate reader based assays and will greatly facilitate the search for novel peptide and chemical compound based PIs in T-cells.

Inhibition of 1,4-beta-D-xylan xylanohydrolase by the specific aspartic protease inhibitor pepstatin: probing the two-step inhibition mechanism

This is the first report that describes the inhibition mechanism of xylanase from Thermomonospora sp. by pepstatin A, a specific inhibitor toward aspartic proteases. The kinetic analysis revealed competitive inhibition of xylanase by pepstatin A with an IC50 value 3.6 +/- 0.5 microm. The progress curves were time-depended, consistent with a two-step slow tight binding inhibition. The inhibition followed a rapid equilibrium step to form a reversible enzyme-inhibitor complex (EI), which isomerizes to the second enzyme-inhibitor complex (EI*), which dissociated at a very slow rate. The rate constants determined for the isomerization of EI to EI* and the dissociation of EI* were 15 +/- 1 x 10(-5) and 3.0 +/- 1 x 10(-8) s(-1), respectively. The Ki value for the formation of EI complex was 1.5 +/- 0.5 microm, whereas the overall inhibition constant Ki* was 28.0 +/- 1 nm. The conformational changes induced in Xyl I by pepstatin A were monitored by fluorescence spectroscopy, and the rate constants derived were in agreement with the kinetic data. Thus, the conformational alterations were correlated to the isomerization of EI to EI*. Pepstatin A binds to the active site of the enzyme and disturbs the native interaction between the histidine and lysine, as demonstrated by the abolished isoindole fluorescence of o-phthalaldehyde-labeled xylanase. Our results revealed that the inactivation of xylanase is due to the interference in the electronic microenvironment and disruption of the hydrogen-bonding network between the essential histidine and other residues involved in catalysis, and a model depicting the probable interaction between pepstatin A with xylanase has been proposed.

Clinical pharmacology and pharmacokinetics of amprenavir

OBJECTIVE

To review the pharmacokinetics, pharmacodynamics, drug interactions, and dosage and administration information of amprenavir.

DATA SOURCE

An extensive review of the literature (MEDLINE search from 1994 to April 2001) relating to the clinical pharmacology of the HIV protease inhibitors was conducted. Meeting abstracts or full presentations and data submitted to the Food and Drug Administration were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

The data on pharmacokinetics, pharmacodynamics, drug interactions, and drug resistance were obtained from in vitro studies and open-label and controlled clinical trials.

DATA SYNTHESIS

Like all HIV protease inhibitors, amprenavir interrupts the maturation phase of the HIV replicative cycle by forming an inhibitor-enzyme complex, which prevents HIV protease from binding with its normal substrates (biologically inactive viral polyproteins). Amprenavir has an enzyme inhibition constant (Ki = 0.6 nM) that falls within the Ki range of the other protease inhibitors. Amprenavir's in vitro 50% inhibitory concentration (IC50) against wild-type clinical HIV isolates is 14.6 +/- 12.5 ng/mL (mean +/- SD). Pharmacodynamic modeling indicates that, as is the case with other protease inhibitors, the concentration-response curve for amprenavir plateaus at amprenavir trough values above the IC50 for these isolates. This exposure-activity relationship, plus such favorable pharmacokinetic parameters as a long terminal elimination half-life (7-10 h), makes amprenavir an attractive drug of choice when considering potent antiretrovirals. The higher trough exposure obtained with amprenavir coadministered with ritonavir may allow effective treatment of patients with decreased susceptibility viral isolates and once-daily dosing. Amprenavir has been approved for adults and children; the recommended capsule doses are 1200 mg twice daily for adults and 20 mg/kg twice daily or 15 mg/kg 3 times daily for children < 13 years of age or adolescents < 50 kg. The recommended dose for amprenavir oral solution is 1.5 mL/kg twice daily or 1.1 mL/kg 3 times daily.

CONCLUSIONS

The clinical pharmacology, exposure-activity relationship, and drug resistance profile of amprenavir support the use of this potent HIV protease inhibitor in combination antiretroviral regimens, especially for persons who have experienced virologic failure while on protease inhibitor-containing regimens.

Localization of pepstatin's inhibitory action during Fc-mediated antibody internalization: possible implications for antibody-mediated viral transmission

Antibody internalization via Fc receptors is an important cellular mechanism, possibly facilitating the entry of antigenic peptides or viral particles into cells when specific antibodies are present at the periphery. Using an experimental model of trophoblast cells, we have shown that anti-p21(ras) monoclonal antibodies can use IFN-gamma-induced surface Fcgamma receptors to enter the cell. This entry of anti-p21(ras) antibodies ultimately inhibits IFN-gamma-mediated class II antigen induction. Since there may be obvious and inevitable harmful aspects of this mechanism, during which Fc-mediated viral particle or autoantigen transport may occur, we concentrated efforts on defining a potent inhibitor able to eliminate such uptake. The results presented here show that the protease inhibitor pepstatin A efficiently inhibits Fcgamma receptor induction by IFN-gamma and also blocks the endocytic pathway followed by an antibody when it enters the cell at the level of early endosomal compartments. We thus postulate that the use of pepstatin A, because of its inhibition of autoantigen presentation or viral transmission, including that of HIV, may find important applications in therapeutic protocols.

Competitive inhibition of human immunodeficiency virus type-1 protease by the Gag-Pol transframe protein

The human immunodeficiency virus type-1 (HIV-1) transframe protein p6* is located between the structural and enzymatic domains of the Gag-Pol polyprotein, flanked by the nucleocapsid (NC) and the protease (PR) domain at its amino and carboxyl termini, respectively. Here, we report that recombinant highly purified HIV-1 p6* specifically inhibits mature HIV-1 PR activity. Kinetic analyses and cross-linking experiments revealed a competitive mechanism for PR inhibition by p6*. We further demonstrate that the four carboxyl-terminal residues of p6* are essential but not sufficient for p6*-mediated inhibition of PR activity. Based on these results, we suggest a role of the transframe protein p6* in regulating HIV-1 PR activity during viral replication.

Gag protein from human immunodeficiency virus type 1 assembles in the absence of cyclophilin A

Human immunodeficiency virus type 1 (HIV-1) replication requires coordinated activities of host and viral factors. We reported previously that interactions of the host factor cyclophilin A with HIV-1 Gag polyproteins affected Gag processing and maturation of virus particles (Streblow et al., 1998. Virology 245, 197-202). We now use in vitro translation and physical analysis of Gag structures to refine our understanding of how cyclophilin A affects HIV-1 replication. Gag assembled into oligomeric structures in vitro in the presence or absence of cyclophilin A, and proteins synthesized under the two conditions were equally susceptible to cleavage by exogenous HIV-1 protease. These and previous data show that Cyclophilin A is required at a step between Gag assembly and Gag processing/virion morphogenesis. Cyclophilin A may be required for Gag conformational changes subsequent to assembly, that are required for efficient dimerization and activation of the viral protease.

Human immunodeficiency virus type 1 proteinase resistance to symmetric cyclic urea inhibitor analogs

Resistant virus was isolated from virus propagated in cell culture in the presence of the human immunodeficiency virus type 1 (HIV-1) proteinase inhibitor DMP 323, Ro 31-8959, or A-75925. The proteinase gene of resistant virus was sequenced, and key mutations (G48V, V82A, I84V, L90M, and G48V/L90M) were introduced into clones used for the expression, purification, and further characterization of the enzyme. The mutant enzymes were all less active than the wild-type enzyme, as judged by k(cat) and k(cat)/Km values. L90M had a lower Km than the wild type, whereas the G48V/L90M double mutant had an increased Km compared with that of the wild type, contributing to a 10-fold reduction in the k(cat)/Km. Vitality values were used to show that the enzyme of the I84V mutant is the enzyme most resistant to the two cyclic urea inhibitors DMP 323 and AHA 008. Virus with the same mutation is also resistant, although the double mutation L10F/I84V confers even greater resistance. All of these mutants are more resistant to DMP 323 than to AHA 008. The resistance of the I84V mutant may be attributed to a loss of van der Waals interactions with the inhibitor, since the larger amino acid side chain involved in the interaction is replaced by a smaller side chain. This is supported by the lower level of resistance to AHA 008 that was observed. The phenyl groups of AHA 008 should protrude deeper into the S1 and S1' subsites than those of the smaller compound DMP 323, reducing the loss of interaction energy. These results reveal that small structural modifications of inhibitors that do not affect the inhibitory effect on wild-type virus can influence the inhibition of resistant strains. This is of importance for optimizing drugs with respect to their potency and resistance.

Screening of inhibitors of HIV-1 protease using an Escherichia coli cell assay

To evaluate the available peptidic and pseudopeptidic inhibitors of HIV protease for their possible in vivo activity, a screening test using Escherichia coli was established. E. coli cells carrying the plasmid pET9c-PR containing the gene for HIV-1 protease under the control of a T7-promotor are grown in the absence and in the presence of inhibitors. The action of the toxic protease produced by the cells is counteracted by the inhibitors. Provided sufficient membrane permeability of the inhibitors exists, this results in accelerated cell growth. From the peptides known to be active in an in-vitro enzyme test, most compounds inhibit HIV protease only to a limited degree in this test. However, two short peptides (Ac-Ser-Tyr-Glu-Leu and Lys-Ile-Ser-Tyr-Asp-Tyr) protect cell growth to an considerabe extent, thus indicating that they reach the E. coli cytosol and there block HIV protease. Two pseudopeptides known to be very potent in the enzyme test (SDZ PRI 053 and CIBA 61755) also inhibit HIV-1 protease strongly in this cell growth test.

Pepstatin A: polymerization of an oligopeptide

Pepstatin A, a pentapeptide with the molecular weight of 686, is a naturally occurring inhibitor of aspartyl proteases secreted by Streptomyces species. Above a critical concentration of 0.1 mM at low ionic strength and neutral pH, it can polymerize into filaments which may extend over several micrometers. After negative staining, these filaments show a helical substructure with characteristic diameters ranging from 6 to 12 nm. Selected images at higher magnification suggest the filaments are composed of two intertwined 6 nm strands. This is in agreement with the optical diffraction analysis which additionally established a periodic pitch of 25 nm for the helical intertwining. Rotary shadowing of the pepstatin A filaments clearly demonstrated the right-handedness of the helical twist. In physiological salt solution or at higher concentrations of pepstatin A, a variety of higher order structures were observed, including ribbons, sheets and cylinders with both regular and twisted or irregular geometries. Pepstatin A can interact with intermediate filament subunit proteins. These proteins possess a long, alpha-helical rod domain that forms coiled-coil dimers, which through both hydrophobic and ionic interactions form tetramers which, in turn, in the presence of physiological salt concentrations, polymerize into the 10 nm intermediate filaments. In the absence of salt, pepstatin A and intermediate filament proteins polymerize into long filaments with a rough surface and a diameter of 15-17 nm. This polymerization appears to be primarily driven by nonionic interactions between pepstatin A and polymerization-competent forms of intermediate filament proteins, resulting in a composite filament. Polymerization-incompetent proteolytic fragments of vimentin, lacking portions of the head and/or tail domain, failed to copolymerize with pepstatin A into long filaments under these conditions. These peptides, as well as bovine serum albumin, were found to stick to the surface of pepstatin A filaments, ribbons and sheets. Independent evidence for direct association of pepstatin A with intermediate filament subunit proteins was provided not only by electron microscopy but also by UV difference spectra. Pepstatin A loses its ability to inhibit the aspartyl protease of the human immunodeficiency virus type 1 following polymerization into the higher order structures described here. The amazing fact that pepstatin A can spontaneously self-associate to form very large polymers seems to be a more rare event for such small peptides. The other examples of synthetic or naturally occurring oligopeptides discussed in this review which are able to polymerize into higher order structures possess a common property, their hydrophobicity, often manifested by clusters of valine or isoleucine residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Bryodin, a single-chain ribosome-inactivating protein, selectively inhibits the growth of HIV-1-infected cells and reduces HIV-1 production

Bryodin, a single-chain ribosome-inactivating protein (RIP) isolated from Bryonia cretica ssp dioica (cucurbitaceae), was found to selectively inhibit the growth of persistently HIV-1-infected T lymphoma cells (KE37/1) and human lung fibroblast when used in concentrations from 2-20 micrograms/ml. Uninfected KE37/1 cells remained unaffected at the same doses of bryodin. In addition, bryodin reduced HIV production in the surviving infected cells. Two isoforms of bryodin were purified by dye ligand chromatography. Both isoforms exerted the growth-inhibiting influence and reduced HIV production. Trichosanthin, another member of the RIP family, had similar inhibitory effects on the growth of HIV-1 infected cells and on HIV-1 production. Bryodin and trichosanthin were effective in about the same dose range. No selective effects for HIV-infected cells were observed with the RIPs gelonin and ricin.

Detection of inhibition of HIV-1 protease activity by an enzyme-linked immunosorbent assay (ELISA)

An ELISA is described for the detection of HIV-1 protease activity using an immobilized gag-related polyprotein as substrate. Proteolytic activity was demonstrated with either bacterial lysates expressing HIV-1 protease or purified protease. No cleavage was observed with a protein preparation from control bacteria not expressing HIV-1 protease. Under these conditions the aspartyl-type protease inhibitor, pepstatin A, was found to inhibit HIV-1 protease cleavage by > 90% at a concentration of 0.1 mM. This assay may be a useful tool for the study of both synthetic and natural inhibitors of HIV-1 protease.

Plasmodium falciparum: differential sensitivity in vitro to E-64 (cysteine protease inhibitor) and Pepstatin A (aspartyl protease inhibitor)

We investigated the effect of a cysteine proteinase inhibitor (E-64) and an aspartyl proteinase inhibitor (Pepstatin A) on asexual erythrocytic stages of Plasmodium falciparum in culture. These two protease inhibitors showed different patterns of activity. E-64 acted preferentially against trophozoite and schizont stages. After 48 h incubation at high concentrations of E-64 (28, 140, 280 microM), growth was totally abolished and the parasites presented characteristic enlarged food vacuoles. Morphological alterations were also seen after shorter incubation periods (6 h at 28 microM) or 12 h at the inhibitory concentration 50% (12 microM), but an additional culture period (24 h) in inhibitor-free medium allowed normal parasite development, demonstrating a parasitostatic effect. E-64 acts on parasite multiplication; the normal merozoite maturation was altered and the normal reinvasion process partially impaired. Pepstatin A used at the inhibitory concentration 50% (4 microM) killed the parasites before trophozoite development and had a major effect on schizonts maturation. No altered parasite development occurred during an additional culture period without Pepstatin A, demonstrating a parasiticidal effect. E-64 and Pepstatin A used in combination inhibit the parasite growth with a strong synergistic effect.

Requirement of N- and C-terminal regions for enzymatic activity of human T-cell leukemia virus type I protease

The requirement of N- and C-terminal regions for the enzymatic activity of human T-cell leukemia virus type I (HTLV-I) protease was investigated using a series of deletion mutants. The activity was analyzed by autoprocessing of the protease itself or by processing of the gag p53 precursor. The deletional analyses indicated that Asp38-Gly152 with an additional Met-Pro sequence at the N-terminus was probably sufficient for the enzymatic activity, although the mature HTLV-I protease consists of Pro33-Leu157. A molecular model of HTLV-I protease, which was constructed by comparison with the structure of Rous sarcoma virus protease, predicted that Pro33-Leu37 and Gly143-Leu147 would form a beta-sheet. Our experimental results and the model structure suggest that (a) five amino acids in the N-terminal region (Pro33-Leu37), which are thought to be involved in the beta-sheet, are not crucial for the enzymatic activity; (b) Pro153-Leu157 is not necessary but Pro148-Gly152 is important for the enzymatic activity, in addition to Gly143-Leu147 involved in the beta-sheet.

Potential role of the viral protease in human immunodeficiency virus type 1 associated pathogenesis

Infection with the human immunodeficiency virus type 1 (HIV-1) results in a variety of pathological changes culminating in the acquired immune deficiency syndrome (AIDS). While most of these changes can readily be accounted for either by direct effects of HIV-1 on the immune system or by indirect effects of secondary infectious agents as a result of faulty immune surveillance, the direct cause for a number of disease states, including some neuropathies, myopathies, nephropathy, thrombocytopenia, wasting syndromes and increased incidence of cancers (primarily lymphoma) has remained an enigma. We have recently shown that the HIV-1 protease, a viral encoded enzyme necessary for virus maturation and infectivity, can cleave a variety of host cell cytoskeletal proteins in vitro. Potential substrates for the HIV-1 protease are found in all of the cell types affected in these unexplained diseases. Recent proposals suggest that elements of the cytoskeleton may play an important role in the regulation of large scale genetic regulation. We propose that some of the degenerative changes associated with infection by HIV-1 are a direct consequence of cleavage of host cell cytoskeletal proteins, which in turn may be responsible for the increased incidence of cancer in HIV-1 infected individuals as a result of the perturbation of the regulation of gene expression by cytoskeletal components.

Accumulation of pepstatin in cultured endothelial cells and its effect on endothelial processing

Aspartic acid proteases have been implicated in the processing of ET-1(1-39) to ET-1(1-21). To further understand the role of this class of enzymes in ET-1 synthesis, cultured vascular endothelial cells were incubated with pepstatin, and the accumulation of the inhibitor and its effect on the processing of ET-1(1-39) was examined. Pepstatin accumulated in the cells in a time-dependent manner, to a concentration (greater than 10(-7) M) sufficient to inhibit aspartic acid proteases. Pepstatin did not alter the ratio of ET-1(1-21) to ET-1(1-39), nor did it affect the rate of secretion of either peptide. When endothelial cells were incubated with phosphoramidon under identical conditions, the secretion of ET-1(1-21) was significantly reduced with a concomitant increase in the secretion of ET-1(1-39). These results suggest that the processing of ET-1(1-39) does not involve a pepstatin-sensitive aspartic acid protease, and that the enzyme responsible for generating ET-1(1-21) is sensitive to phosphoramidon.

Analysis of non-infectious HIV particles produced in presence of HIV proteinase inhibitor

Newly developed substrate analogue peptidomimetics are able to inhibit the human immunodeficiency virus, HIV-1 proteinase at nanomolar concentration. In HIV infected cell culture they exhibit antiviral activity. We have analyzed the non-infectious HIV particles produced in chronically HIV infected cell culture in presence of one of these inhibitors. The total production of virus particles was not substantially reduced in drug treated cultures, compared to non-inhibited control cultures, but the infectivity of these virus particles was reduced about 100 fold. The processing of gag and gag-pol protein precursor was inhibited; only borderline activity of reverse transcriptase (RT) could be detected in these particles and they contained nonprocessed gag precursor protein. Thin section electron microscopy of inhibitor-treated, HIV-infected cells revealed reduced viral cytopathogenicity and both inhibition of particle assembly and incomplete maturation of the particles formed. The HIV particles produced in the presence of the proteinase inhibitor were studded with envelope glycoprotein knobs and often comprised multiple budding regions, but were morphologically immature.

Proteases and their inhibitors: today and tomorrow

A major incentive in inhibitor research is that control of limited proteolysis constitutes a valuable pharmacological tool. Protease inhibitors have proved to be successful in influencing pathogenesis in many experimental models but a breakthrough to use in human therapy has mainly been restricted to aprotinin and angiotensin converting enzyme (ACE) inhibitors. However, the success of ACE inhibitors as pharmacological tools in hypertension has proved to be a strong stimulant for new protease inhibitor approaches to drug therapy. While emphasis in the search for next generations of ACE inhibitors may move from the circulation renin-angiotensin system to the local tissue systems, including heart, brain and genital tract, persistent and insightful design of renin inhibitors has already yielded highly specific molecules with potent activities in several in vivo models. The development of orally effective long-acting inhibitors will finally allow an evaluation to be made of their therapeutic profile with regard to the family of ACE inhibitors. The close relationship between renin and HIV-1 protease presents an exceptional opportunity for transfer of the knowledge acquired in renin inhibitor development during the past decade, to an accelerated generation of specific HIV-1 protease inhibitors as effective agents in treatment of AIDS. The self-assembly of 2 identical monomers into a symmetrical structure in HIV-1 protease is not only an elegant way to create an active enzyme while encoding a minimal amount of genetic information, but is also in concordance with the bilobular active-site found in mammalian aspartic proteases.(ABSTRACT TRUNCATED AT 250 WORDS)

The chronically infected cell as a target for the treatment of HIV infection and AIDS

Infection of the T lymphocyte with HIV results in a cytopathic effect and cell death that has been linked to a selective loss of the helper T-lymphocyte function of the immune system. In addition to acute infection, which leads to cell death, a chronic or persistent infection also occurs. The persistence of these viral reservoirs has been implicated in the progression of HIV infection and AIDS. Rational drug discovery targeted to late-stage events in HIV replication has the potential to yield antiviral agents capable of blocking virus spread by inhibiting the production of infectious virions from these chronic reservoirs. Steve Petteway and colleagues discuss antiviral strategies that target the chronically infected cell, with a focus on HIV protease inhibitors.

Polymerizing properties of pepstatin A

Pepstatin A, a pentapeptide aspartyl protease inhibitor, can spontaneously polymerize into filaments having a helical substructure and, after negative staining, characteristic diameters ranging from 6 to 12 nm. Optical diffraction analysis demonstrated that these filaments consist of a 6-nm-wide strand helically wound with a periodic pitch of 25 nm. Selected images suggest that these filaments may actually be composed of two, intertwined 6-nm-wide strands, an hypothesis not at variance with the diffraction data. These filaments may extend over several micrometers. At low ionic strength and neutral pH, the critical concentration for pepstatin A filament assembly is 0.1 mM. At higher pepstatin A concentrations or in physiological salt solutions, a variety of higher order structures were observed, including ribbons, sheets, and cylinders with both regular and twisted or irregular geometries. Pepstatin A polymerized into these higher order structures loses its ability to inhibit the aspartyl protease of the human immunodeficiency virus type 1. These results have implications not only for model studies on the polymerization of small peptides into higher order structures, but also for the practical development of soluble protease inhibitors.

Modulation of experimental systemic murine candidosis by intravenous pepstatin

The effect of intravenous pepstatin-A on systemic candidosis in NWNI mice was investigated. True solutions of the inhibitor proved ineffective due to a very fast clearance. Pepstatin was effective as a crystal suspension (0.69 mg in 0.1 ml saline) which produced serum inhibitory activity for greater than 29 h. From the intravenously applied suspension, pepstatin was taken up predominantly into the liver, no inhibitor being taken up by the kidneys. The suspension was protective if it was injected once before the mice were infected and repeatedly following infection. It was also effective if it was administered concomitantly with the infecting agent and thereafter. The suspension was ineffective if it was only given once before infection, and it proved to be detrimental if it was given only after infection. The results support previous findings (2), suggesting a role of fungal proteinase early in the adherence of Candida to host epithelia. Our results also suggest an inhibition of lysosomal cathepsin-D in vivo by pepstatin, which prohibits a parenteral therapeutic use of nonmodified pepstatin A.

A synthetic HIV-1 protease inhibitor with antiviral activity arrests HIV-like particle maturation

A synthetic peptidemimetic substrate of the human immunodeficiency virus 1 (HIV-1) protease with a nonhydrolyzable pseudodipeptidyl insert at the protease cleavage site was prepared. The peptide U-81749 inhibited recombinant HIV-1 protease in vitro (inhibition constant Ki of 70 nanomolar) and HIV-1 replication in human peripheral blood lymphocytes (inhibitory concentration IC50 of 0.1 to 1 micromolar). Moreover, 10 micromolar concentrations of U-81749 significantly inhibited proteolysis of the HIV-1 gag polyprotein (p55) to the mature viral structural proteins p24 and p17 in cells infected with a recombinant vaccinia virus expressing the HIV-1 gag-pol genes. The HIV-1 like particles released from inhibitor-treated cells contained almost exclusively p55 and other gag precursors, but not p24. Incubation of HIV-like particles recovered from drug-treated cultures in drug-free medium indicated that inhibition of p55 proteolysis was at least partially reversible, suggesting that U-81749 was present within the particles.

Inhibition of HIV replication by naphthalenemonosulfonic acid derivatives and a bis naphthalenedisulfonic acid compound

Several naphthalenemonosulfonic acid analogs and a bis naphthalenedisulfonic acid have been evaluated for anti-HIV activity in assays using H9 and MOLT-3 cells. Among the naphthalenemonosulfonic acids, a 4-amino-5-hydroxy compound and a 4,5-diamino compound showed low anti-HIV activity (upto 50% inhibition) at non-toxic doses. The bis naphthalenedisulfonic acid compound demonstrated significant suppression of HIV-1 antigen expression as measured by monoclonal antibodies to p17 (95%), p24 (94%) and syncytia inhibition (82%) at a dose of 20 micrograms/ml that was non-toxic to the host cells. The bis naphthalenedisulfonic acid analog represents a new class of compounds which may be effective in the treatment of HIV infected patients. The structure activity relationship and a probable mode of action of these compounds is discussed.