Selective inhibition of herpes simplex virus glycoprotein synthesis by a benz-amidinohydrazone derivative

5-Propyl-2-deoxyuridine induced interference with glycosylation in herpes simplex virus infected cells. Nature of PdU-induced modifications of N-linked glycans

In herpes simplex virus-infected (HSV) cells, the antiviral nucleoside analogue 5-n-propyl-2'-deoxyuridine (PdU) may, under certain circumstances, induce a pattern of interference with late steps in formation of N-linked glycans, resulting in increased availability of viral glycoproteins for neutralizing antibodies. The PdU-induced changes in N-linked glycans, released by pronase digestion of the HSV-specified glycoprotein gC-1, were investigated by using lectin affinity chromatography and Bio-Gel P6 gel filtration of glycans, radiolabelled with [3H]galactose or [3H]glucosamine. PdU-treatment of HSV-infected cells totally inhibited addition of sialic acid and reduced the amount of galactose incorporated into N-linked glycans by 70%. In addition, the PDU-treatment caused a decrease in oligosaccharides with affinity for Phaseoulus vulgaris leuco-agglutinin and erythro-agglutinin, and an increase in Lens culinaris lectin (LCA)-binding oligosaccharides, suggesting a PdU-induced shift from multi-branched to moderately branched structures. This shift was also found in HSV-infected B16 mouse melanoma cells, where the large content of multi-branched oligosaccharides contributes to the metastatic potential. The LCA-binding glycans from PdU-treated cells were smaller and contained less galactose units than corresponding structures from untreated cells. In a cell-free system, PdU 5'-monophosphate inhibited the translocation of UDP-GlcNAc, and, to a smaller extent, also the translocation of UDP-galactose into Golgi vesicles, suggesting that nucleotide sugar translocation is one important target for the PdU-induced interference with glycosylation in HSV-infected cells.

Relevance of DNA binding to the mechanism of anti-herpesvirus activity of benzhydrazone

Benzhydrazone (1H-benz(f)indene-1,3(2H)-dione bis (amidino-hydrazone) (BH) is a synthetic compound with selective anti-herpesvirus activity. Its selectivity seems to stem from the inhibition of viral protein glycosylation and several hypotheses have been formulated to explain such an effect. Data presented here demonstrate that DNA binding is a prominent feature of BH. Interaction is taking place with a relatively high affinity constant and is more efficient for GC-rich viral sequences. Experiments with the cloned DNA fragments from a BH-resistant virus strain indicate that BH-DNA complex formation is drastically reduced as compared to BH-sensitive virus. The occurrence of the resistant phenotype in HEp-2 cells but not in Vero cells could be explained by differences in BH cytotoxicity. Changes in drug uptake and accumulation by cells following infection, in addition to GC preference, may also account for the degree of antiviral selectivity shown by BH.

A herpes simplex virus type 1 mutant resistant to benzhydrazone, an inhibitor of glycoprotein synthesis in herpesvirus-infected cells. Preliminary mapping of benzhydrazone-resistance and of a novel syncytial mutation

Benzhydrazone (BH) is an inhibitor of glycoprotein biosynthesis. It acts selectively in Herpes simplex virus (HSV)-infected cells and does not significantly affect glycoprotein synthesis in uninfected cells and in cells infected with other viruses. Previously, we reported on a syncytial (syn) mutant, designated HSV-1(13)S11, resistant to BH, and showed that BH-resistance is encoded in the mutant virus DNA and therefore can be transferred into the genome of wild type HSVs. The present paper reports on a preliminary mapping in HSV-1(13)S11 genome of the loci which confer resistance to BH and of three distinct syn mutations present simultaneously in this mutant. Two of them were mapped in previously described syn loci localized in BamHI fragment L (map units 0.707-0.745) (locus syn 1) and BamHI fragment Q (map units 0.296-0.317) (locus syn 5). A third mutation not described before and mapping in BamHI fragment SP (c.a. map units 0.81-0.85) conferred the syn phenotype to both HEp-2 and Vero cells. This novel mutation has been designated herein locus syn 6. Transfer of BH-resistance could be achieved in cotransfection experiments involving two HSV-1(13)S11 fragments, BamHIL and BamHISP.

Further characterization of virus obtained from herpes simplex virus type 1 recurrences and primary infections. Influence of the temperature of incubation upon glycoprotein synthesis and virus release. Brief report

The virus contained in clinical isolates of herpes simplex virus type 1 (HSV-1) which have not undergone previous in vitro passages (new isolates) differs from HSV-1 prototype strains with respect to infected cell glycoprotein pattern, and, most probably efficiency of virus egress at 37 degrees C. The differences can be abolished by lowering the temperature of incubation to 33 degrees C. A few tissue culture passages cause the conversion of the original virus to a virus undistinguishable from HSV-1 prototype strains with respect to the parameters mentioned above.

Study of herpes simplex virus type 1 populations obtained from recurrences and primary infections

The analysis of 23 clinical isolates of herpes simplex virus type 1 (HSV-1) showed that 15 of 15 isolates that had undergone a few passages in tissue culture (fresh isolates) and two of eight isolates that had never been passaged (new isolates) were composed of a mixed population with respect to plaque morphology in Vero cells. Cloning and characterization of 10 large plaque viruses (L variants) and nine small plaque viruses (S variants), obtained from seven different isolates, showed the following. BamHI DNA restriction patterns of the L and the S variants from a single isolate differed only with respect to the electrophoretic mobility of the fragments that contain reiteration of specific sequences; they did not differ regarding the presence or the absence of restriction endonuclease cleavage sites. The L and S variants differed with respect to the electrophoretic profiles of infected cell glycoproteins, thermosensitivity of growth and plaquing efficiency at 39 degrees C, and, at least in the case of the two couples of variants that we tested, pathogenicity for the mouse. The hypothesis that the L variants might arise from the S variant during in vivo replication is discussed.

Characterization of a herpes simplex virus type 1 mutant resistant to benzhydrazone, a selective inhibitor of herpesvirus glycosylation

Benzhydrazone [BH; 1H-benz[f]indene-1,3(2H) -dionebis(amidinohydrazone)] significantly inhibits glycosylation of proteins, but only in cells infected with herpes simplex virus. We report on a herpes simplex virus type 1 (HSV-1) mutant resistant to BH. A syncytium-inducing mutant designated HSV-1(13)S11 was found to be biochemically resistant to BH in that [14C]glucosamine incorporation was not inhibited in infected HEp-2 cells exposed to the drug. Intertypic recombinants were obtained which showed that BH resistance is encoded in the DNA of the mutant virus and may be transferred into the genome of BH-sensitive HSV. In the recombinants the biochemical resistance marker segregated from the syncytial marker, suggesting that the two markers probably map in different loci. The BH-resistant mutant did not complement wild-type BH-sensitive HSV-1 and -2. Furthermore, resistance was apparent in HEp-2 but not in Vero cells. The paper discusses the hypothesis that inhibition of glycosylation of HSV proteins is the consequence of modification or selective transport of BH involving a HSV gene product.

Anti-gD monoclonal antibodies inhibit cell fusion induced by herpes simplex virus type 1

Monoclonal antibodies directed against glycoprotein D of herpes simplex virus completely inhibited fusion of Vero cells infected with type 1 virus. In contrast, several monoclonal antibodies directed against other viral glycoproteins, including B, were ineffective or were only minimally inhibitory at the highest concentrations tested.

Inhibition of glycosylation of herpes simplex virus glycoproteins: identification of antigenic and immunogenic partially glycosylated glycopeptides on the cell surface membrane

The surface membranes of cells infected with herpes simplex virus type 1 (HSV-1), strain KOS, contain three principal glycoproteins, gC (apparent Mr 129k), gB (apparent Mr 120k), and gD (apparent Mr 58k). Infections carried out in the presence of the glycosylation inhibitor 2-deoxy-D-glucose result in the loss of the mature species with the concurrent appearance of lower-molecular-weight polypeptides which are presumably partially glycosylated forms of the fully processed glycoproteins. Specific immunoprecipitation of radiolabeled cytoplasmic extracts of 2-deoxy-D-glucose-inhibited infections identified partially glycosylated proteins designated DG92, DG88, and DG53, which are antigenically related to the corresponding mature forms gB, gC, and gD. Cell surface radioiodination, in combination with specific immunoprecipitation, revealed that DG88 and DG53 were the principal species transported to the cell surface in 2-deoxy-D-glucose-inhibited infections. DG92 was readily detected in the cytoplasm but not on the plasma membrane. Cells infected with the KOS mutant, syn LD70, did not synthesize glycoprotein gC. In glycosylation-inhibited syn LD70 infections, DG88 was not detected in either the cytoplasm or plasma membrane, demonstrating a genetic relationship between DG88 and gC. Polyclonal and monoclonal antibodies directed against the glycoproteins gC, gB, and gD sensitized infected cells to complement-mediated immune cytolysis. Cells infected in the presence of the inhibitor were sensitized to lysis only by antibody specific for gC and gD. The glycosylation-inhibited cells were insensitive to immunolysis by anti-gB monoclonal antibody. These findings confirm that the glycosylation-deficient forms of gC and gD, but not gB reach the cell surface in the presence of inhibitor and that the inhibitor-induced alterations in glycosylation do not cause a complete loss of antigenicity. Inoculation of mice with syngeneic 3T3 cells infected in the presence or absence of inhibitor-induced cytolytic and neutralizing antibody. A major portion of the cytolytic antibody was directed against gC, but anti-gC antibody appeared to play a minor role in virus neutralization. While the serum induced by the control infected cells contained precipitating antibodies for gC, gB, and gD, the serum derived from mice inoculated with inhibitor-treated infected cells had only weak immunoprecipitating activity against gB. Together, these findings have identified partially glycosylated forms of the major HSV glycoproteins and show that complete glycosylation is not required for transport of some of these partially glycosylated polypeptides to the cell surface. Moreover, complete glycosylation of the glycopeptides is not essential for maintenance of antigenicity or immunogenicity, indicating that at least some determinants recognized by antibodies directed against the mature glycoproteins are not affected by 2-deoxy-D-glucose-induced carbohydrate alterations.

Infectivity and glycoprotein processing of herpes simplex virus type 1 grown in a ricin-resistant cell line deficient in N-acetylglucosaminyl transferase I

We report on the replication of herpes simplex virus type 1 (HSV-1) and viral glycoprotein processing in RicR14 cells, a mutant ricin-resistant cell line defective in N-acetylglucosaminyl transferase I activity. In these cells HSV-1(MP) and (F) replicated to yields very similar to those in parental BHK cells. The kinetics of HSV-1 adsorption in mutant and in parent cells was also essentially identical. Progeny virions from ricin-resistant and wild-type cells displayed comparable specific infectivities. However, in the mutant cells the efficiency of plating of progeny virus from both RicR14 and BHK cells was reduced. HSV-1(MP) failed to induce syncytia in RicR14 cells either in a plaque assay or after a high-multiplicity infection. Moreover, the fully glycosylated forms of glycoproteins (gB, gC, and gD) were totally absent, and only the partially glycosylated precursors (pgC, pgD. and a triplet in the gB-gA region) accumulated in HSV-1-infected ricin-resistant cells and in herpesvirions made in these cells. Consistent with these results analysis of pronase glycopeptides from cells labeled with [14C]glucosamine showed a strong decrease of sialylated complex-type oligosaccharides and a dramatic accumulation of the neutral mannose-rich chains. The latter chains predominate in partially glycosylated precursors, whereas the complex acidic chains predominate in the fully processed forms of HSV glycoproteins. These results taken together indicate that (i) host-cell N-acetylglucosaminyl transferase I participates in the processing of HSV glycoproteins; and (ii) infectivity of herpesvirions does not necessarily require the mature form of gB. The absence of HSV-1(MP)-induced fusion in RicR14 cells is discussed.

Studies on benzhydrazone, a specific inhibitor of herpesvirus glycoprotein synthesis. Size distribution of glycopeptides and endo-beta-N-acetylglucosaminidase-H treatment

Benzhydrazone is a bis-amidinohydrazone derivative which specifically hinders the formation of herpes simplex virus (HSV) glycoproteins. In this study we present some structural features of the oligosaccharide chains of herpesvirus glycoproteins synthesized in cells incubated with the inhibitor. Gel filtration analysis of glycopeptides, obtained through exhaustive pronase-digestion of infected cells after a long or a short labeling with 14C-glucosamine, showed that benzhydrazone reduced the appearance of glycopeptides of all the size-classes, including the mannose-rich glycopeptide with an approximate molecular weight of 1500. The same percent of label was released from both untreated and benzhydrazone-treated cells after digestion with endo-beta-N-acetylglucosaminidase H, an enzyme which cleaves between the N-acetylglucosamine residues in large high-mannose type oligosaccharides. This indicates that the relative amount of glycoproteins sensitive to this enzyme did not differ in the two kinds of samples. PAGE analysis confirmed that the same glycoproteins were digested in both samples. They were gA, pgC, and pgD, which therefore contain high-mannose type oligosaccharides. It is concluded that benzhydrazone hinders carbohydrate addition to herpesvirus proteins at an early step.