Zidovudine alone or in combination with didanosine or zalcitabine in HIV-infected patients with the acquired immunodeficiency syndrome or fewer than 200 CD4 cells per cubic millimeter. Investigators for the Terry Beirn Community Programs for Clinical Research on AIDS.

BACKGROUND: We compared two combinations of nucleosides with zidovudine alone in patients with advanced human immunodeficiency virus (HIV) infection. METHODS: A total of 1102 patients with the acquired immunodeficiency syndrome or fewer than 200 CD4 cells per cubic millimeter were randomly assigned to receive zidovudine alone or zidovudine combined with either didanosine or zalcitabine. Disease progression, survival, toxic effects, and the CD4 cell response were assessed. RESULTS: After a median follow-up of 35 months, disease progression or death occurred in 62 percent of the 363 patients assigned to zidovudine plus didanosine, 63 percent of the 367 assigned to zidovudine plus zalcitabine, and 66 percent of the 372 assigned to zidovudine only (P=0.24). As compared with zidovudine therapy, treatment with zidovudine plus didanosine was associated with a relative risk of disease progression or death of 0.86 (95 percent confidence interval, 0.71 to 1.03), and treatment with zidovudine plus zalcitabine was associated with a relative risk of 0.92 (95 percent confidence interval, 0.76 to 1.10). Survival was similar in the three groups. In a subgroup analysis, combination therapy delayed disease progression or death in patients who had previously received zidovudine for 12 months or less. Therapy with zidovudine plus didanosine resulted in more gastrointestinal adverse effects, and treatment with zidovudine plus zalcitabine, more neuropathy. The mean increases in CD4 cell counts at two months were higher with combination therapy than with zidovudine alone. CONCLUSIONS: In patients with advanced HIV infection, combination therapy with zidovudine and either didanosine or zalcitabine is not superior to zidovudine therapy alone. However, these combinations may be more effective than zidovudine monotherapy in patients with little or no previous zidovudine treatment.

Selection conditions affect the evolution of specific mutations in the reverse transcriptase gene associated with resistance to DMP 266.

OBJECTIVE: To monitor the appearance of HIV-1 variants resistant to inhibition by DMP 266, a benzoxazinone non-nucleoside reverse transcriptase inhibitor using two different protocols for applying drug selective pressure in tissue culture. To compare the phenotype and genotype of viral isolates selected by each method. METHODS: MT-2 cells and fresh donor peripheral blood mononuclear cells (PBMC) were infected with HIV-1 strain RF. The MT-2 cells were infected in the presence of a 50% inhibitory concentration (IC50) of DMP 266 and the concentration was slowly increased during the selection period. The PBMC were infected for 1 week in the absence of inhibitor and then a single concentration was maintained throughout the selection period. Both cultures were passaged for approximately 4 months. Virus and cell pellets were harvested over this in vitro selection period, the RT genes amplified by polymerase chain reaction from the cell pellets, and the proviral DNAs sequenced. Isolated virus was tested for DMP 266 susceptibility in either the AIDS Clinical Trials Group/Department of Defense consensus assay or MT-2 yield reduction assay. RESULTS: Passage in MT-2 cells resulted in accumulation of three substitutions in RT (V179D, L1001, Y181C) after 24 passages associated with 1000-fold reduced susceptibility to DMP 266. In PBMC cultures treated with 0.96 microM DMP 266, virus replication was completely suppressed after 2 weeks; no regrowth occurred in the presence of compound after 10 weeks or in the absence of compound for 3 additional weeks. The 0.096 microM treated cultures had an initial 2.5-log reduction in infectious virus titre followed by rapid regrowth. Virus obtained at week 6 displayed a 28-fold reduction in susceptibility with an L1001 substitution in RT, and by week 11 displayed a 1000-fold reduction in susceptibility with an additional V1081 substitution. CONCLUSIONS: High-level resistance to DMP 266 may develop by at least two pathways and experimental conditions influence the genotype selected. The continued absence of detectable virus in the PBMC cultures grown at 0.96 microM is supportive evidence that maintaining trough plasma levels of DMP 266 which result in sustained antiviral activity in vivo may delay emergence of highly resistant viral variants. Confirmation of this hypothesis will require clinical trials.

Cyclic HIV protease inhibitors: synthesis, conformational analysis, P2/P2' structure-activity relationship, and molecular recognition of cyclic ureas.

High-resolution X-ray structures of the complexes of HIV-1 protease (HIV-1PR) with peptidomimetic inhibitors reveal the presence of a structural water molecule which is hydrogen bonded to both the mobile flaps of the enzyme and the two carbonyls flanking the transition-state mimic of the inhibitors. Using the structure-activity relationships of C2-symmetric diol inhibitors, computed-aided drug design tools, and first principles, we designed and synthesized a novel class of cyclic ureas that incorporates this structural water and preorganizes the side chain residues into optimum binding conformations. Conformational analysis suggested a preference for pseudodiaxial benzylic and pseudodiequatorial hydroxyl substituents and an enantiomeric preference for the RSSR stereochemistry. The X-ray and solution NMR structure of the complex of HIV-1PR and one such cyclic urea, DMP323, confirmed the displacement of the structural water. Additionally, the bound and "unbound" (small-molecule X-ray) ligands have similar conformations. The high degree of preorganization, the complementarity, and the entropic gain of water displacement are proposed to explain the high affinity of these small molecules for the enzyme. The small size probably contributes to the observed good oral bioavailability in animals. Extensive structure-based optimization of the side chains that fill the S2 and S2' pockets of the enzyme resulted in DMP323, which was studied in phase I clinical trials but found to suffer from variable pharmacokinetics in man. This report details the synthesis, conformational analysis, structure-activity relationships, and molecular recognition of this series of C2-symmetry HIV-1PR inhibitors. An initial series of cyclic ureas containing nonsymmetric P2/P2' is also discussed.

Improved cyclic urea inhibitors of the HIV-1 protease: synthesis, potency, resistance profile, human pharmacokinetics and X-ray crystal structure of DMP 450.

BACKGROUND: Effective HIV protease inhibitors must combine potency towards wild-type and mutant variants of HIV with oral bioavailability such that drug levels in relevant tissues continuously exceed that required for inhibition of virus replication. Computer-aided design led to the discovery of cyclic urea inhibitors of the HIV protease. We set out to improve the physical properties and oral bioavailability of these compounds. RESULTS: We have synthesized DMP 450 (bis-methanesulfonic acid salt), a water-soluble cyclic urea compound and a potent inhibitor of HIV replication in cell culture that also inhibits variants of HIV with single amino acid substitutions in the protease. DMP 450 is highly selective for HIV protease, consistent with displacement of the retrovirus-specific structural water molecule. Single doses of 10 mg kg-1 DMP 450 result in plasma levels in man in excess of that required to inhibit wild-type and several mutant HIVs. A plasmid-based, in vivo assay model suggests that maintenance of plasma levels of DMP 450 near the antiviral IC90 suppresses HIV protease activity in the animal. We did identify mutants that are resistant to DMP 450, however; multiple mutations within the protease gene caused a significant reduction in the antiviral response. CONCLUSIONS: DMP 450 is a significant advance within the cyclic urea class of HIV protease inhibitors due to its exceptional oral bioavailability. The data presented here suggest that an optimal cyclic urea will provide clinical benefit in treating AIDS if it combines favorable pharmacokinetics with potent activity against not only single mutants of HIV, but also multiply-mutant variants.

Identification of a clinical isolate of HIV-1 with an isoleucine at position 82 of the protease which retains susceptibility to protease inhibitors.

The HIV-1 protease (PR) is essential for the production of mature virions. As such, it has become a target for the development of anti-HIV chemotherapeutics. Multiple passages of virus in cell culture in the presence of PR inhibitors have resulted in the selection of variants with decreased sensitivity to inhibitors of the PR. The most common alteration observed is a single amino acid change at position 82. This particular position has been well characterized by several laboratories as being important for the susceptibility of the virus to inhibitors of PR function. Mutations which result in the substitution of the wild-type valine with alanine, phenylalanine, threonine or isoleucine at position 82 of the PR have been associated with decreased sensitivity to several PR inhibitors. We describe here a clinical strain of HIV-1 that contains an isoleucine at position 82 of the PR instead of the usual valine. This strain is unique in that it was isolated from a patient that was anti-retroviral naive, and in the past, variants at position 82 of the PR have only been found after treatment of patients or cell culture with PR inhibitors. Moreover, this virus remains sensitive to PR inhibitors of the cyclic urea and C-2 symmetrical diol classes.

Characterization of human immunodeficiency virus type 1 mutants with decreased sensitivity to proteinase inhibitor Ro 31-8959.

A human immunodeficiency virus type 1 (HIV-1) variant with highly reduced susceptibility to Ro 31-8959, an inhibitor of the viral proteinase, has been selected by repeated passage of wild-type virus in CEM cells in the presence of increasing concentrations of the inhibitor. Peptide sequences of the proteinase of selected virus were obtained from proviral DNA. Sequence comparison to wild-type (wt) proteinase demonstrated two amino acid substitutions in the resistant virus, a Gly to Val exchange at position 48 and a Leu to Met exchange at position 90. Furthermore, sequences of intermediate passage virus suggest contributions from positions 12, 36, 57, and 63 in early steps of resistance development. The selected virus showed a ca. 40-fold increase in 50% inhibitory concentration of Ro 31-8959. Growth kinetics of resistant virus were comparable to wild-type virus and the resistant genotype proved to be stable in the absence of inhibitor. Directed mutagenesis of the HIV-1 HXB2 proteinase at positions 48 and 90 suggested that each mutation alone led to a moderate decrease in sensitivity of the recombinant virus to proteinase inhibitor. However, a recombinant virus carrying both mutations in the proteinase gene showed a significant reduction in its sensitivity to Ro 31-8959 thus proving the importance of these exchanges for the resistance phenotype.

Limited sequence diversity of the HIV type 1 protease gene from clinical isolates and in vitro susceptibility to HIV protease inhibitors.

Proviral DNAs from 3 laboratory strains and 21 clinical isolates of HIV-1 were extracted from infected cells after proteinase K digestion and the protease gene was PCR amplified and sequenced directly by the Sanger method. In vitro susceptibilities of the virus isolates to protease inhibitors were determined by the ACTG/DoD consensus assay. Four different HIV protease inhibitors were tested including P9941, a C2 symmetrical diol (Du Pont-Merck); A80987, an asymmetric mono-ol (Abbott); XM323, a cyclic urea (Du Pont-Merck); and Ro31-8959, an asymmetric hydroxyethylene isostere (Roche). Maximum sequence variation was 10% at both the nucleic and amino acid levels. Purine-purine substitutions were most common. Five noncontiguous regions were conserved across all isolates and corresponded to amino acids 1-9 (amino terminal), 21-32 (catalytic site), 47-56 ("flap" region), 78-88 (substrate-binding region), and 94-99 (carboxy terminal). All clinical isolates demonstrated in vitro susceptibility to the protease inhibitors. There was no significant difference between the susceptibility of the reference strains and the clinical isolates. These data suggest that the variable regions of protease do not contain sites that are important for interactions with the inhibitors tested.

Construction of infectious molecular clones of HIV-1 containing defined mutations in the protease gene.

A DNA clone of HIV-1 containing the full-length infectious viral sequence was cleaved at a unique Nco I restriction site within the viral genome, and DNA fragments containing the 5' and 3' portions of the HIV genome were subcloned into separate plasmid vectors. The 5' 'half-virus' construct was further modified by incorporating a class IIS restriction site, Esp3I, near the 3' end of the protease gene of HIV. This site, in combination with a natural ApaI site near the 5' end of the protease gene, creates a convenient cassette shuttle vector in which the protease coding region can be easily replaced. Recombinant viruses containing protease genes either altered by site-directed mutagenesis or amplified from clinical or laboratory isolates can be reconstructed. The DNA fragment containing the protease gene is first subcloned into the 5' half-virus shuttle vector plasmid. Infectious recombinant virus is subsequently recovered by cotransfecting 5' and 3' half-virus plasmids linearized at their common Nco I sites into mammalian cells. This method was successfully applied to constructing viruses containing various substitutions in protease.

In vitro susceptibility of clinical isolates of HIV-1 to XM323, a non-peptidyl HIV protease inhibitor.

OBJECTIVE: To determine the in vitro susceptibility of primary clinical isolates and laboratory strains of HIV-1 to XM323. METHODS: The AIDS Clinical Trials Group/US Department of Defense p24 antigen-based consensus assay was used to determine in vitro susceptibility of 57 primary clinical isolates and three laboratory strains of HIV-1 to XM323, zidovudine, zalcitabine (ddC), and didanosine (ddI). RESULTS: The concentrations of compound required to inhibit viral p24 antigen production by 50% [median inhibitory concentration (IC50)] for nucleosides were as follows: zidovudine, 0.001-->5 microM; ddC, < 0.01-0.23 microM; ddI, 0.2-->25 microM). Against both nucleoside susceptible and resistant isolates XM323 exhibited potent inhibition with IC50 values of < 0.02-0.27 microM and IC90 values of 0.03-1.17 microM. CONCLUSIONS: XM323 is a potent inhibitor of diverse clinical isolates of HIV-1 in vitro and represents a novel class of non-peptidyl inhibitors of HIV-1 protease.

In vitro anti-human immunodeficiency virus (HIV) activity of XM323, a novel HIV protease inhibitor.

XM323 represents a novel class of potent inhibitors of human immunodeficiency virus (HIV) protease. In vitro studies have shown that inhibition of this enzyme translates into potent inhibition of replication of HIV type 1 (HIV-1) and HIV-2. The inhibition of virus replication was assessed with three assays designed to measure the production of infectious virus, viral RNA, or p24 antigen. The production of mature infectious virions was measured with a yield reduction assay. By this assay, several strains and isolates of HIV-1 and HIV-2 were shown to be susceptible to XM323 in two lymphoid cell lines (MT-2 and H9) and in normal peripheral blood mononuclear cells, with a concentration required for 90% inhibition (IC90) of 0.12 +/- 0.04 microM (mean +/- standard deviation). The production of HIV-1(RF) RNA was measured with an RNA hybridization-capture assay. With this assay, XM323 was shown to be a potent inhibitor of HIV-1(RF) replication, with an IC90 of 0.063 +/- 0.032 microM. A third measure of virus replication, the production of p24 viral antigen, an essential protein component of the virion, was determined with the AIDS Clinical Trial Group-Department of Defense peripheral blood mononuclear cell consensus assay. This assay was used for expanded testing of XM323 against 28 clinical isolates and laboratory strains of HIV-1. XM323 was shown to be equally effective against zidovudine-susceptible and zidovudine-resistant isolates of HIV-1, with an overall IC90 of 0.16 +/- 0.06 microM.

In vitro isolation and identification of human immunodeficiency virus (HIV) variants with reduced sensitivity to C-2 symmetrical inhibitors of HIV type 1 protease.

Protease inhibitors are another class of compounds for treatment of human immunodeficiency virus (HIV)-caused disease. The emergence of resistance to the current anti-HIV drugs makes the determination of potential resistance to protease inhibitors imperative. Here we describe the isolation of an HIV type 1 (HIV-1) resistant to an HIV-protease inhibitor. Serial passage of HIV-1 (strain RF) in the presence of the inhibitor, [2-pyridylacetylisoleucylphenylalanyl-psi (CHOH)]2 (P9941), failed to yield a stock of virus with a resistance phenotype. However, variants of the virus with 6- to 8-fold reduced sensitivity to P9941 were selected by using a combination of plaque assay and endpoint titration. Genetic analysis and computer modeling of the variant proteases revealed a single change in the codon for amino acid 82 (Val-->Ala), which resulted in a protease with lower affinity and reduced sensitivity to this inhibitor and certain, but not all, related inhibitors.

Rhodococcus equi infection in the patient with AIDS: literature review and report of an unusual case.

Rhodococcus equi is an aerobic, intracellular, gram-positive rod-coccus that is partially acid fast. The organism is primarily a pathogen in animals and has only rarely been seen in immunocompromised humans. Its most common manifestation is a slowly progressive pneumonia that may cavitate. Infections are thought to be acquired via respiratory exposure to animals or soil. R. equi infections are difficult to treat, usually requiring prolonged administration of parenteral antibiotics and often necessitating surgical drainage. A case of cavitary pneumonia and recurrent bacteremia with R. equi in a patient with AIDS is reported, and the current literature on R. equi infections in humans is reviewed.