Comparative kinetic analyses of interaction of inhibitors with Rauscher murine leukemia virus and human immunodeficiency virus reverse transcriptases.

The inhibitory effects of several nucleoside triphosphate analogs on Rauscher murine leukemia virus (RMuLV) and human immunodeficiency virus (HIV) type 1 reverse transcriptases (RTs) were studied. With RNA as the template, the apparent K(m) and apparent K(i) values of HIV RT toward its substrates and inhibitors are 12 to 500 times lower than the corresponding values for RMuLV RT. However, the k(i)/k(m) ratios (inhibition efficiencies) for HIV and RMuLV RTs'are similar for AZTTP (zidovudine triphosphate), d4TTP [3'-deoxythymidine-2'-ene-(3'-deoxy-2',3'-didehydrothymidine) triphosphate], PMEADP [9-(2-phosphonylmethoxyethyl)adenine diphosphate], FIAUTP [1-(2-fluoro-2-deoxy-beta-D-arabinofuranosyl)-5-iodouracil triphosphate], and HPMPCDP [(S)-1-(3-hydroxy-2-phosphylmethoxypropyl) cytosine diphosphate]. With DNA as the template, the K(m) values are similar for HIV and RMuLV RTs. However, the K(i)/K(m) values of HIV and RMuLV RTs are significantly different for ddCTP, ddATP, and 3TCTP (2',3'-dideoxy-3'-thiacytidine). The RTs of RMuLV and HIV are sufficiently different from one another that the kinetic inhibition constants for a particular antiviral compounds should be determined to indicate whether anti-RMuLV activity is likely to be predictive for the anti-HIV activity of the compound. This information, in conjunction with species-specific drug metabolism differences and tissue culture antiviral activity, is important in determining the suitability of a particular animal model.

Protection against murine cytomegalovirus infection in aged mice and mice with severe combined immunodeficiency disease with the biological response modifiers polyribosinic-polycytidylic acid stabilized with L-lysine and carboxymethylcellulose, maleic anhydride divinyl ether and colony stimulating factor 1.

A variety of biological response modifiers (BRMs) have provided antiviral protection to immunocompetent mice, and this prompted us to determine their efficacy against murine cytomegalovirus (MCMV) infection in immunocompromised mice-including the profoundly immunocompromised SCID mice and C57Bl/6 and B6D2F1 aged mice. SCID mice showed a marked decrease (> 20-fold) in resistance to MCMV, while there was a slight decrease (3-fold) in aged mice. In BRM antiviral protection studies, SCID mice were almost completely protected against MCMV infection by the pleiotropic immunomodulators, MVE-2 and pICLC, but much less by the more selective CSF-1. pICLC-induced IFN and NK cell cytotoxicity were maintained in SCID mice, suggesting that pleiotropic immunomodulatory effects may be required for antiviral protection in such a profoundly immunocompromised model. pICLC also effectively protected aged mice against lethal MCMV infection and effectively induced IFN. These results emphasize the potential for BRM treatment in immunocompromised hosts.

Biological response modifier-mediated resistance to herpesvirus infections requires induction of alpha/beta interferon.

The role of interferon alpha/beta (IFN) induction by the immunomodulators pICLC and CL246,738 was investigated in CD-1 mice infected with murine cytomegalovirus (MCMV) or herpes simplex virus type 2 (HSV-2). Mice were treated with either normal sheep serum or anti-alpha/beta IFN antiserum, inoculated with the immunomodulators, and infected with virus. Because anti-IFN treatment also decreased natural resistance to HSV-2 and MCMV, two viral challenge doses were used to ensure that the mice with control serum or anti-IFN antiserum received biologically equivalent infections. Antiviral protection of pICLC and CL246,738 against HSV-2 infection was completely abrogated by treatment with anti-alpha/beta interferon antiserum. Mice treated with pICLC also lost antiviral protection against MCMV when interferon alpha/beta was depleted. These results indicate that induction of interferon alpha/beta appears to be a major mechanism for both natural resistance and pICLC-induced antiviral protection against MCMV and HSV-2 herpesvirus infections.

Role of NK cells in immunomodulator-mediated resistance to herpesvirus infection.

Seven chemically diverse biological response modifiers (BRM) were compared for antiviral activity in intact and NK cell-depleted CD-1 mice. Both spontaneous and BRM-induced splenic NK cell cytotoxicity were depleted for at least 5 days following treatment with the monoclonal antibody NK1.1. Antiviral protection of standard doses of MVE-2, pIC, pICLC, rmIFN-tau and CL246,738 against lethal MCMV or HSV-2 infections was not abrogated by NK cell depletion, demonstrating that NK cells are not required for BRM-induced antiviral activity against these herpesviruses. When mice were treated with 100,000 U of rHuIFN-alpha B/D, NK cells were not required for activity against MCMV, while at a dose of 25,000 U, NK cells appeared to be partially required against MCMV. At lower doses, the activity of rHuIFN-alpha B/D against MCMV appeared dependent upon the presence of NK cells. A similar dose-related requirement for NK cells was observed for activity of OK-432. Thus, at higher doses of rHuIFN-alpha B/D and OK-432, elements of the natural immune system in addition to or other than NK cells are apparently involved, while at lower doses NK cells appear to play a more important role in antiviral protection against MCMV infection.