Mechanism of inhibition of Epstein-Barr virus replication by phosphonoformic acid

Abstract

The trisodium salt of phosphonoformic acid (PFA) inhibits Epstein-Barr virus (EBV) replication in lymphoblastoid cells at concentrations nontoxic to cellular growth. The synthesis of early antigen (EA) in the infected cells is not affected by the drug under conditions when viral capsid antigen (VCA) and viral DNA synthesis are inhibited to the extent of 75 and 90%, respectively. In vitro studies with partially purified DNA polymerases show that PFA inhibits EBV-associated DNA polymerase to a greater extent than it inhibits α- and β-polymerases. Enzyme kinetic analysis reveals a linear noncompetitive inhibition with four deoxytriphosphates and a typical uncompetitive inhibition with variable concentrations of DNA as substrate at saturating deoxytriphosphate concentrations. The apparent inhibition constant for EBV-associated polymerase was in the range of 2-3 μM. The inhibitory effect is exerted at the pyrophosphate binding site of DNA polymerase. Although productive viral DNA synthesis is completely arrested by the drug, the virus-associated DNA polymerase activity is expressed normally in super-infected Raji cells even in the presence of the drug. We propose that in addition to potential therapeutic value, the compound could be used as a tool to study some of the restricted early functions of virus in the absence of productive viral DNA synthesis. Induction of viral DNA polymerase can also be used as an additional marker for expression of early viral functions.