Orthopoxvirus Replication Research Articles

Cidofovir Derivatives Demonstrate Increased Effectiveness against Orthopoxvirus Replication In Vitro and In Vivo

Cidofovir Derivatives Demonstrate Increased Effectiveness against Orthopoxvirus Replication In Vitro and In Vivo

Evaluation of nucleoside phosphonates and their analogs and prodrugs for inhibition of orthopoxvirus replication.

In the event of a bioterrorism attack using smallpox virus, there currently is no approved drug for the treatment of infections with this virus. We have reported previously that (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC) (also known as cidofovir [CDV]) has good activity against poxvirus infections; however, a major limitation is the requirement for intravenous administration. Two related acyclic nucleoside phosphonates (ANPs), adefovir (PMEA) and tenofovir (PMPA), are active against human immunodeficiency virus or hepatitis B virus but do not have activity against the orthopoxviruses. Therefore, we have evaluated a number of analogs and potential oral prodrugs of these three compounds for their ability to inhibit the replication of vaccinia virus or cowpox virus in tissue culture cells. The most-active compounds within the CDV series were (S)-HPMPA and (butyl L-alaninyl) cyclic HPMPC, with 50% effective concentrations (EC(50)s) from 4 to 8 microM, compared with 33 to 43 microM for CDV. Although PMEA itself was not active, adefovir dipivoxil [bis[(pivaloyl)oxymethyl] PMEA] and bis(butyl L-alaninyl) PMEA were active against both viruses, and bis(butyl L-alaninyl) PME-N6-(cyclopropyl)DAP and (isopropyl L-alaninyl)phenyl PME-N6-(cyclopropyl)DAP were the most active compounds tested, with EC(50)s of 0.1 to 2.6 microM. In the PMPA series, none of the analogs tested had significantly better activity than PMPA itself. These data indicate that a number of these ANP derivatives have activity against vaccinia virus and cowpox virus in vitro and should be evaluated for their efficacies in animal models.

Enhanced inhibition of orthopoxvirus replication in vitro by alkoxyalkyl esters of cidofovir and cyclic cidofovir.

The nucleotide phosphonates cidofovir (CDV) and cyclic cidofovir (cCDV) are potent antiviral compounds when administered parenterally but are not well absorbed orally. These compounds have been reported to have activity against orthopoxvirus replication in vitro and in animal models when administered parenterally or by aerosol. To obtain better oral activity, we synthesized a novel series of analogs of CDV and cCDV by esterification with two long-chain alkoxyalkanols, 3-hexadecyloxy-1-propanol (HDP-CDV; HDP-cCDV) or 3-octadecyloxy-1-ethanol (ODE-CDV; ODE-cCDV). Their activities were evaluated and compared with those of CDV and cCDV in human foreskin fibroblast (HFF) cells infected with vaccinia virus (VV) or cowpox virus (CV) using a plaque reduction assay. The 50% effective concentrations (EC(50)s) against VV in HFF cells for CDV and cCDV were 46.2 and 50.6 microM compared with 0.84 and 3.8 microM for HDP-CDV and HDP-cCDV, respectively. The EC(50)s for ODE-CDV and ODE-cCDV were 0.20 and 1.1 microM, respectively. The HDP analogs were 57- and 13-fold more active than the parent nucleotides, whereas the ODE analogs were 231- and 46-fold more active than the unmodified CDV and cCDV. Similar results were obtained using CV. Cytotoxicity studies indicated that although the analogs were more toxic than the parent nucleotides, the selective index was increased by 4- to 13-fold. These results indicate that the alkoxyalkyl esters of CDV and cCDV have enhanced activity in vitro and need to be evaluated for their oral absorption and efficacy in animal models.

Inhibitors of the lipoxygenase pathway specifically block orthopoxvirus replication

Inhibitors of arachidonic acid metabolism, 5,8,11,14-eicosatetraynoic acid (ETYA), BW755c, and nordihydroguaiaretic acid were found to specifically interfere with the replication of cowpox virus (an orthopoxvirus) both in vivo and in vitro. Further studies in vitro showed that the drugs ETYA and BW755c were effective in inhibiting the replication of two additional orthopoxviruses, ectromelia and vaccinia viruses, but not human parainfluenza virus-3. In ETYA-treated and cowpox virus-infected cells, early and late gene expression were near normal levels, whereas the assembly of virus-specific membranes was severely reduced. These results are compatible with a model of orthopoxvirus replication that has an obligate requirement for arachidonic acid or one of its metabolic forms, possibly in the assembly of virus-specific membranes.