Interaction between cyclic nucleotides and herpes simplex viruses: productive infection

Evaluation of novel acyclic nucleoside phosphonates against human and animal gammaherpesviruses revealed an altered metabolism of cyclic prodrugs upon Epstein-Barr virus reactivation in P3HR-1 cells

Acyclic nucleoside phosphonates (ANPs), such as (S)-1-[(3-hydroxy-2-phosphonomethoxy)propyl)]cytosine (HPMPC), are an important group of broad-spectrum antiviral agents with activity against DNA viruses. In this report, we present the in vitro potencies of novel ANPs against gammaherpesviruses, including Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus (EBV), and three animal gammaherpesviruses. 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC), (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine (3-deaza-HPMPA), and their cyclic derivatives have emerged as highly potent antigammaherpesvirus agents. Interestingly, cyclic prodrugs of ANPs exhibited reduced activities against EBV strain P3HR-1, but not against EBV strain Akata. Cell culture metabolism studies with HPMPC and cyclic HPMPC revealed that these differences were attributable to an altered drug metabolism in P3HR-1 cells after EBV reactivation and, more specifically, to a reduced hydrolysis of cyclic HPMPC by cyclic CMP phosphodiesterase. We did not correlate this effect with phosphodiesterase downregulation, or to functional mutations. Instead, altered cyclic AMP levels in P3HR-1 cells indicated a competitive inhibition of the phosphodiesterase by this cyclic nucleotide. Finally, both HPMPC and HPMP-5-azaC emerged as highly effective inhibitors in vivo through significant inhibition of murine gammaherpesvirus replication and dissemination. With the current need for potent antigammaherpesvirus agents, our findings underline the requirement of appropriate surrogate viruses for antiviral susceptibility testing and highlight HPMP-5-azaC as a promising compound for future clinical development.

Inhibition of virus multiplication and alteration of cyclic AMP level in cell cultures by flavonoids

The inhibitory effect of four flavonoid compounds on virus multiplication and their influence on the intracellular cyclic AMP (cAMP) level were studied in cell cultures. Quercetin and quercitrin reduced the yields of Human (alpha) herpesvirus 1 (HSV-1) and Suid (alpha) herpesvirus 1 (pseudorabies virus), but hesperidin and rutin had no effect. Further, quercetin and quercitrin elevated the intracellular level of cAMP, whereas hesperidin and rutin did not alter the cAMP level. Both antiviral activity and cAMP-enhancing effect were dependent on the concentrations of the flavonoids, and these effects turned out to be parallel. This study suggests that a relation exists between the antiviral effect and the cAMP-enhancing activity of flavonoids.

Effect of cyclic AMP and cyclic GMP on the activity of interferon against herpes simplex virus types 1 and 2, and vesicular stomatitis virus

The antiviral action of interferon (IFN) on herpes simplex virus (HSV) types 1 and 2, and vesicular stomatitis virus (VSV) was examined with respect to the intracellular levels of cyclic adenosine monophosphate (CAMP) and cyclic guanosine monophosphate (CGMP) in human fibroblast (HF) cultures. Interferon by itself increased the intracellular levels of CAMP, but had no effect on the CGMP levels. Inoculation of HF with HSV, however, decreased the CAMP levels. Also, HSV inoculation elevated the CGMP levels, but VSV did not alter the CGMP levels. When HSV and IFN were added to the HF cultures in various combinations, HSV inhibited the IFN-induced elevation of CAMP and increased the CGMP levels to that characteristically observed with HSV inoculation in the absence of IFN. In contrast, IFN antagonized the VSV-associated decrease in CAMP levels. Although the yields of VSV were unaltered by the presence of CAMP- or CGMP-enhancing compounds, the yields of HSV were decreased with CAMP enhancers and increased with CGMP enhancers. the combination of IFN and CAMP enhancers had an additive effect in reducing the yields of HSV. Neither the CAMP or CGMP enhancers affected the action of IFN on VSV. These studies suggest that the interactions observed between HSV and cyclic nucleotides might account for the relatively refractive nature of HSV, as compared to VSV, toward the antiviral activity of IFN.

Reversible repression and activation of measles virus infection in neural cells

Conversion of acute measles virus infection to an indolent state has been achieved by treatment of infected cells of neural origin with agents that affect cyclic nucleotide metabolism. Striking results were obtained with papaverine, an inhibitor of cAMP phosphodiesterase that is capable of enhancing neural differentiation. In papaverine-treated cultures, decreased production of infectious virus was accompanied by selective disappearance of intracellular matrix proton, as detected by immunofluorescence. Viral nucleocapsid protein was enhanced in the cytoplasm while three other structural proteins--polymerase, hemagglutinin, and fusion protein--showed little change in distribution or intensity of staining. These results were specific for cells of neural origin and not observed in CV-1 or Vero cultures. cAMP, dibutyryl cAMP, 8-bromo-cAMP, and isobutylmethylxanthine all inhibited replication of virus but less so than did papaverine. Inhibition of virus replication by any of these agents was rapidly reversible, either by removal of the agent or by addition of cGMP to the culture medium and was accompanied by reappearance of the matrix protein. These results suggest that measles virus replication in neural cells depends on host factors, particularly those affecting endogenous cAMP and cGMP. Viral persistence may thus be related to the state of neural differentiation. This model system may yield information on mechanisms of recrudescence observed in some chronic diseases of the nervous system.

Differential effect of prostaglandins and other products of arachidonic acid metabolism on measles virus replication in Vero cells

The influence of cyclic adenosine 3', 5'-monophosphate (cAMP) and prostaglandin (PG), E1, E2, F2 alpha, A2 and thromboxane B2 (TxB2) and measles virus infection was investigated. Addition of PGE1, E2 and cAMP (10(-3)-10(-)8M) inhibited measles virus replication in Vero cells. TxB2 and PGA2 enhanced replication. Cytotoxic effects were not observed. Inhibition of infectious titers (98%) was most pronounced when agents were present throughout replication. Treated cells exhibited hemadsorbing antigen, but the size and number of cytoplasmic inclusions was decreased by cAMP. Pre-treatment of cells with PGE1 or presence of PGE1 during virus adsorption enhanced infectious titers (30%). Results suggest that cAMP and PGE1 inhibit measles virus production infection. That both enhancing and inhibiting effects of PGs were seen suggest that measles virus may require PG at specific times during the replicative cycle.

Effect of prostaglandins and cyclic adenosine 3',5'-monophosphate modulators on herpes simplex virus growth and interferon response in human cells

Mechanisms whereby prostaglandins and other cyclic adenosine 3',5'-monophosphate (cAMP) modulators might enhance the growth of herpes simplex virus (HSV) in human skin fibroblasts were explored. Prostaglandins A1, B1, E1, E2, and F2 alpha, as well as isoproterenol, imidazole, carbamylcholine, and dibutyryl cAMP had no effect on HSV growth. On the other hand, the phosphodiesterase inhibitors 1-methyl-3-isobutylxanthine and theophylline delayed the growth, suppressed the cell-to-cell spread, but inhibited neither the adsorption nor the penetration of the virus. Although none of the cAMP-elevating reagents directly enhanced HSV growth, they were found to inhibit dose dependently the antiviral action of both type I and HSV antigen-induced human interferon preparations. Furthermore, these reagents suppressed the production of HSV antigen-induced interferon by immune human mononuclear leukocytes. These data support the hypothesis that prostaglandin elaboration in vivo could contribute to exacerbations of HSV infections by compromising the host's interferon defense system.