Replication of equine herpesvirus type 1 and type 3: resistance to hydroxyurea and thymidine.

The research investigates the replication of two types of equine herpesvirus (EHV-1 and EHV-3) and their resistance to substances commonly used to inhibit DNA synthesis. Their results show that both types of equine herpesvirus continue to replicate in cells treated with hydroxyurea or thymidine, indicating that they could potentially bypass the inhibitory mechanisms typically regulated by these compounds.

Methodology and Experiment Setup

• Three cell types were used for the experiment: equine epithelial cells, equine fibroblasts, and mouse fibroblasts.
• The DNA synthesis capacity of these cells was inhibited using hydroxyurea (HU) or thymidine (TdR).
• The experiment monitored the rate of DNA synthesis in both uninfected and equine herpesvirus-infected cells, in the presence of HU or TdR.
• The observation was made by labeling DNA precursors at different times after infection.

Findings and Results

• DNA synthesis in uninfected cultures was completely inhibited by both compounds.
• In cells infected with EHV-1 or EHV-3 and subjected to HU and TdR, an unexpected burst of DNA synthesis was observed that coincided with the time of virus-specific DNA replication in cells not treated with the inhibitors.
• The results of cesium chloride isopycnic centrifugation analysis, a technique used to separate and identify various types of DNA, confirmed that the DNA synthesis resulted from viral activities.

Conclusions and Implications

• The replication of EHV-1 and EHV-3 remained unaffected in cells whose DNA synthesis was inhibited by HU and TdR.
• The researchers suggested that a potential mechanism leading to this resistance could be the induction of a ribonucleotide reductase, an enzyme responsible for DNA component production, which resists inhibition by these compounds.
• The findings show that the equine herpesviruses possess a mechanism of resistance to these widely-used DNA synthesis inhibitors, providing vital insights into virus behavior and guiding potential future development of antiviral drugs.