Synergistic drug interactions of an HIV-1 protease inhibitor with AZT in different in vitro models of HIV-1 infection.

Synthetic peptide mimetic inhibitors of HIV-1 protease effectively block spread of infectious virus in acutely infected T-cells. These compounds also inhibit production of infectious virions from chronically infected T-cell lines. In order to determine the potential for drug interaction effects on antiviral activity, an HIV-1 protease inhibitor (SK&F 108922) and AZT were studied in three different in vitro models of HIV-1 infection of T-cell lines, specifically, (1) acutely infected cells infected at low multiplicity, (2) HIV-1 chronically-infected cells and (3) co-cultivations of chronically infected with non-infected cells. Upon co-treatment, these compounds demonstrated synergy in Molt4 or H9 cells acutely infected with HIV-1 strain IIIB. Either compound alone was a potent inhibitor of HIV-1 in co-cultivations of uninfected and chronically infected cells. In combination treatments of co-cultures, SK&F 108922 demonstrated strong synergy with AZT. Treatment of H9/IIIB chronically infected cells demonstrated no inhibitory effect by AZT treatment (EC50 = > 100 microM) whereas SK&F 108922 was inhibitory (EC50 = 3 microM). Upon co-treatment of H9/IIIB chronically infected cultures with both compounds, the antiviral activity was similar to that of the protease inhibitor alone suggesting no drug interaction. In the co-cultivation experiments, AZT's antiviral effect was most likely due to blocking spread of acute infection to uninfected cells in the culture. No antagonistic effects were observed with AZT and SK&F 108922 co-treatments. These results clearly demonstrate that an HIV-1 protease inhibitor can exert a potent antiviral effect on chronically infected T-cells in contrast to AZT and is capable of potent synergy with AZT in acute and co-culture in vitro infection models.

A replication-efficient mutant of West Nile virus is insensitive to DI particle interference.

A previous report described the isolation of a mutant of West Nile virus (WNV) from culture fluid obtained from persistently infected genetically resistant C3H/RV mouse cells that replicates significantly more efficiently in cultures of C3H/RV cells than does the parental virus. This replication-efficient mutant, designated RE-WNV, has now been found to be insensitive to interference by WNV defective interfering (DI) particles. This characteristic was demonstrated by several means. The RE-WNV mutant was able to superinfect persistently infected cultures that were no longer producing detectable parental virus, while the parental virus was not. Good yields of the mutant virus were produced during six serial undiluted passages of RE-WNV in both resistant C3H/RV and congenic susceptible C3H/HE cells. In contrast, during passage of parental virus in C3H/RV cells, progeny virus could not be detected after the third passage, due to an enhanced interference by WNV DI particles with standard virus replication in these cells. The RE-WNV was also insensitive to interference by a pool of parental virus enriched for DI particles. Analysis of the mutant genome by oligonucleotide fingerprinting indicated that the genome RNA of the mutant differs by two unique spots from the parental RNA. The relevance of this mutant to the eventual understanding of the mechanism by which C3H/RV and C3H/HE cells manifest their flavivirus-specific difference in the efficiency of progeny virus production is discussed.

The 3'-nucleotides of flavivirus genomic RNA form a conserved secondary structure.

The terminal noncoding regions of viral RNA genomes are presumed to contain signal sequences and sometimes also secondary structures involved in regulating viral RNA synthesis. Such signals would be expected to be highly conserved among related viruses. In order to identify replication signal features for flaviviruses we have compared the 3'-terminal nucleotide sequences of West Nile virus (WNV), Saint Louis encephalitis (SLE) virus, and yellow fever virus (YFV) genome RNAs. The existence of a stable 3'-terminal secondary structure was previously predicted by a cDNA sequence obtained from YFV genome RNA. We have confirmed the existence of this structure by direct RNA sequencing methods. Even though the size and shape of the 3'-terminal secondary structure is highly conserved, sequence conservation is restricted to the loop regions of the secondary structure and to 27 nucleotides immediately adjacent to the 5' side of the structure. The regions of conserved sequence represent likely signals for viral polymerase recognition and binding. However, the preservation of the configuration of the secondary structure by a means other than sequence conservation indicate that this structure is important for the survival of the virus. A WNV mutant, which replicates progeny genome RNA more efficiently than parental WNV, was found to have a 3'-genomic sequence identical to that of its parent virus. The sequence change conferring the phenotype of this mutant is therefore located in another region of the genome.

Genotypic variation among six isolates of lactate dehydrogenase-elevating virus.

In the present study, six lactate dehydrogenase-elevating virus (LDV) isolates obtained independently from inbred mice were compared by RNA oligonucleotide fingerprint analysis. The genome RNAs of four of the isolates gave unique fingerprint patterns. The patterns obtained for the other two isolates were similar, but not identical to one of the four unique patterns. These results indicate that more than one genotype of LDV exists and that virus isolates can be grouped by genotype. We have also demonstrated the presence of a 3'-terminal poly(A) tract by direct sequencing of 3'-32P-labelled LDV genome RNA. The presence of a 3'-terminal poly(A) tract distinguishes LDV from the members of the family Flaviviridae, which lack a 3'-poly(A), and justifies the current classification of LDV within the family Togaviridae.

Inhibition of herpes proteases and antiviral activity of 2-substituted thieno[2,3-d]oxazinones.

Cinnamyl derivatives of thieno[2,3-d]oxazinones are mechanism-based inhibitors of the HSV-2, VZV and CMV herpes proteases which demonstrate nanomolar potency. Compounds 5 and 28 inhibit protease processing in HSV-2 infected cells with a selectivity index of at least 30.

Hydroxyethylene isostere inhibitors of human immunodeficiency virus-1 protease: structure-activity analysis using enzyme kinetics, X-ray crystallography, and infected T-cell assays.

Analogues of peptides ranging in size from three to six amino acids and containing the hydroxyethylene dipeptide isosteres Phe psi Gly, Phe psi Ala, Phe psi NorVal, Phe psi Leu, and Phe psi Phe, where psi denotes replacement of CONH by (S)-CH(OH)CH2, were synthesized and studied as HIV-1 protease inhibitors. Inhibition constants (Ki) with purified HIV-1 protease depend strongly on the isostere in the order Phe psi Gly greater than Phe psi Ala greater than Phe psi NorVal greater than Phe psi Leu greater than Phe psi Phe and decrease with increasing length of the peptide analogue, converging to a value of 0.4 nM. Ki values are progressively less dependent on inhibitor length as the size of the P1' side chain within the isostere increases. The structures of HIV-1 protease complexed with the inhibitors Ala-Ala-X-Val-Val-OMe, where X is Phe psi Gly, Phe psi Ala, Phe psi NorVal, and Phe psi Phe, have been determined by X-ray crystallography (resolution 2.3-3.2 A). The crystals exhibit symmetry consistent with space group P6(1) with strong noncrystallographic 2-fold symmetry, and the inhibitors all exhibit 2-fold disorder. The inhibitors bind in similar conformations, forming conserved hydrogen bonds with the enzyme. The Phe psi Gly inhibitor adopts an altered conformation that places its P3' valine side chain partially in the hydrophobic S1' pocket, thus suggesting an explanation for the greater dependence of the Ki value on inhibitor length in the Phe psi Gly series. From the kinetic and crystallographic data, a minimal inhibitor model for tight-binding inhibition is derived in which the enzyme subsites S2-S2' are optimally occupied. The Ki values for several compounds are compared with their potencies as inhibitors of proteolytic processing in T-cell cultures chronically infected with HIV-1 (MIC values) and as inhibitors of acute infectivity (IC50 values). There is a rank-order correspondence, but a 20-1000-fold difference, between the values of Ki and those of MIC or IC50. IC50 values can approach those of Ki but are highly dependent on the conditions of the acute infectivity assay and are influenced by physiochemical properties of the inhibitors such as solubility.