Synthesis and anti-HIV Activity of Some Novel Phosphorodiamidate Derivatives of 3′-azido-3′-deoxythymidine (AZT)

The reaction of 3′-azido-3′-deoxythymidine (AZT) with phosphoryl chloride followed by amino acid methyl esters gave novel diamidate derivatives of AZT 5′-monophosphate (AZTMP). It was hoped that the 5′-phosphorodiamidates might act as membrane-soluble prodrugs of the bio-active free nucleotides of AZT. Five different amino acids were employed, covering a range of structures and polarities. The reaction was also conducted with propylamine, and with diethylamine. The derivatives were tested for their inhibitory effect on human immunodeficiency virus type 1 (HIV-1) proliferation in a human lymphoblastoid cell line. The amino acid derivatives were potent inhibitors of viral proliferation, small changes in structure leading to marked changes in activity.

Fluorinated Analogues of the p17/p24 Sequence Incorporating 3-fluoro and 3,3-difluoro Phenylalanines as Potential Inhibitors of HIV Protease

The synthesis and activity of a series of fluorinated peptide analogues of the p17/p24 sequence incorporating 3-fluoro and 3,3-difluoro phenylananines at the P1 position of the scissile bond are described. It was hoped that these might act as potent inhibitors of HIV protease. In fact, none of the compounds studied displayed any anti-HIV activity in vitro. This may be attributed to poor cell penetration of the compounds and metabolic cleavage of their peptide bonds.

Determination of L-756 423, a novel HIV protease inhibitor, in human plasma and urine using high-performance liquid chromatography with fluorescence detection

A method for the determination of L-756 423, a novel HIV protease inhibitor, in human plasma and urine is described. Plasma and urine samples were extracted using 3M Empore extraction disk cartridges in the C18 and MPC (mixed-phase cation-exchange) formats, respectively. The extract was analyzed using HPLC with fluorescence detection (ex 248 nm, em 300 nm), and included a column switching procedure to reduce run-time. The assay was linear in the concentration range 5 to 1000 ng/ml when 1-ml aliquots of plasma and urine were extracted. Recoveries of L-756 423 were greater than 84% over the calibration curve range using the described sample preparation procedures. Intra-day precision and accuracy for this assay was less than 9% RSD and within 7%, respectively. Inter-day variabilities for the plasma (n=17) and urine (n= 10) were less than 5% and 3% for low (15 ng/ml) and high (750 ng/ml) quality control samples. Bovine serum albumin (0.5%) was used as an additive to urine to prevent precipitation of L-756 423 during the storage of clinical samples. The assay was used in support of human clinical trials.

Escape mutants of HIV-1 proteinase: enzymic efficiency and susceptibility to inhibition

Genes encoding a number of mutants of HIV-1 proteinase were sub-cloned and expressed in E. coli. The proteinases containing mutations of single residues (e.g., G48V, V82F, I84V and L90M) were purified and their catalytic efficiencies relative to that of wild-type proteinase were examined using a polyprotein (recombinant HIV-1 gag) substrate and several series of synthetic peptides based on the -Hydrophobic * Hydrophobic-, -Aromatic * Pro- and pseudo-symmetrical types of cleavage junction. The L90M proteinase showed only small changes, whereas the activity of the other mutant enzymes was compromised more severely, particularly towards substrates of the -Aromatic * Pro- and pseudo-symmetrical types. The susceptibility of the mutants and the wild-type proteinase to inhibition by eleven different compounds was compared. The L90M proteinase again showed only marginal changes in its susceptibility to all except one of the inhibitors examined. The K(i) values determined for one inhibitor (Ro31-8959) showed that its potency towards the V82F, L90M, I84V and G48V mutant proteinases respectively was 2-, 3-, 17- and 27-fold less than against the wild-type proteinase. Several of the other inhibitors examined form a systematic series with Ro31-8959. The inhibition constants derived with these and a number of other inhibitors, including ABT-538 and L-735,524, are used in conjunction with the data on enzymic efficiency to assess whether each mutation in the proteinase confers an advantage for viral replication in the presence of any given inhibitor.

Determination of L-735 524, an human immunodeficiency virus protease inhibitor, in human plasma and urine via high-performance liquid chromatography with column switching

A method for the determination of an HIV protease inhibitor, L-735 524, in human plasma and urine is described. Isolation of the analyte and the internal standard from the matrices was achieved via multiple liquid-liquid extractions with methyl tert.-butyl ether. The analyte lacks significant UV absorption at wavelengths greater than 220 nm, hence a column switching system using a cyano and C18 column was used to further purify the extracts prior to UV detection at 210 nm. The assay has been found to be linear and has been validated over the concentration range of 5 to 500 ng/ml, when 1-ml aliquots of plasma or urine were extracted. The assay has been utilized to support human pharmacokinetic studies.

Human T-cell leukemia virus type 1 protease protein expressed in Escherichia coli possesses aspartic proteinase activity

We amplified the human T-cell leukemia virus type 1 (HTLV-1) protease gene fragment by polymerase chain reaction (PCR) and cloned it into a pUC plasmid vector. DNA sequencing data of the protease gene fragment indicated that it contained an open reading frame capable of encoding the active HTLV-1 protease. To express a fusion protein of beta-galactosidase linked with the HTLV-1 protease in Escherichia coli, a plasmid DNA was constructed by inserting the HTLV-1 protease gene DNA into a procaryotic expression vector, pUEX2, consisting of a lacZ gene directed by a lambda phage Pr promoter and designated pUEX-pro. By Western blot analysis using anti-beta-galactosidase antibody, a bigger molecular size band than that of the control beta-galactosidase molecule was observed in E. coli cells transformed with pUEX-pro but not with control pUEX2, suggesting that the particular fusion protein was successfully expressed. This recombinant protease protein in the E. coli cell lysate was demonstrated to be able to cleave the decapeptide substrates composed of amino acid sequences containing proteolytic cleavage sites in the HTLV-1 gag precursor polyprotein. The gag precursor polyprotein expressed in the mammalian cells by the recombinant vaccinia virus system was also expectedly cleaved by this enzyme. Significant inhibition of this protease activity by pepstatin A, an aspartic proteinase-specific inhibitor, confirms that HTLV-1 protease is a member of the aspartic proteinase group as suggested previously. Since the crude lysate without purification is utilized sufficiently as a native HTLV-1 protease reagent, this protease preparation is easily applicable to the large scale screening of HTLV-1 protease inhibitors for the treatment of diseases caused by HTLV-1.

Present status and future prospects for HIV therapies

Since the discovery of human immunodeficiency virus (HIV) in 1983, significant progress has been made toward the discovery, development, and licensing of anti-HIV drugs. In vitro screens against whole virus are now being complemented by screens against specific viral targets, resulting in the development of clinical candidates acting at several critical stages of the viral life cycle. Despite these advances, clinical therapy remains largely palliative. In addition, it has recently been recognized that HIV resistance to most drugs may pose even greater obstacles. Moreover, emerging data on immunopathogenesis raise the possibility that even if virus was eliminated from an infected individual, the patient's immune system might not be capable of restoration to normal function. In the face of such obstacles, deeper insights into the pathogenic mechanisms of disease, aggressive exploitation of those mechanisms for therapeutic gain, and continued commitment of both public and private sectors to support and collaborate in this research are needed.

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.

Antiviral properties of Ro 31-8959, an inhibitor of human immunodeficiency virus (HIV) proteinase

Ro 31-8959 inhibits the spread of HIV infection and the production of cytopathic effects in cultures of acutely infected cells. IC50 values for these effects are in the range 0.5-6.0 nM and IC90 values are in the range 6.0-30.0 nM. This inhibitor is effective even when added to cultures at a late stage of infection, after syncytia have started to form. Virus antigen, virus particles and virus cytopathic effects can largely be cleared from cultures treated with compound from 3 days until 6 days post infection. In chronically-infected cells, inhibition of virus maturation can be detected after 24 hours' treatment with 10 nM Ro 31-8959. In addition, a significant reduction of the proteolytic processing of p56 to p24 can be demonstrated in these cells with compound at picomolar concentrations. These properties indicate that Ro 31-8959 is highly effective against HIV with the potential to inhibit acute, established acute and chronic infections.

Analysis of subsite preferences of HIV-1 proteinase using MA/CA junction peptides substituted at the P3-P1' positions

The residues P3, P2, P1, and P1' of a peptide corresponding to the matrix/capsid protein junction in the HIV-1 gag protein (Ser-Gln-Asn-Tyr-Pro-Ile-Val) were systematically replaced and the effect of these single amino acid substitutions on the hydrolysis of each peptide by HIV-1 proteinase was studied. Subsites S1 and S1' of the enzyme showed explicit preference for hydrophobic moieties, but beta-branched amino acids and proline are not tolerated in S1. The S2 subsite shows a preference for small polar and apolar amino acids; it may be occupied by Asn, Asp, Glu, Cys, Ala, or Val, other substitutions, especially by Gln and Ser, prevent hydrolysis of the peptides. In subsite S3 all amino acids except proline can be accommodated.

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 high throughput assay for inhibitors of HIV-1 protease. Screening of microbial metabolites

A novel method for discovery of HIV-1 protease inhibitors in complex biological samples has been developed. The assay is based on two specific reagents: a recombinant protein constituted by a portion of the HIV-1 Gag polyprotein comprising the p17-p24 cleavage site, fused to E. coli beta-galactosidase, and a monoclonal antibody which binds the fusion protein in the Gag region. Binding occurs only if the fusion protein has not been cleaved by the HIV-1 protease. The assay has been adapted for the screening of large numbers of samples in standard 96-well microtiter plates. Using this method about 12000 microbial fermentation broths have been tested and several HIV-1 protease inhibitory activities have been detected. One of these has been studied in detail.