Printed in Great Britain Phosphonoformate Inhibits Reverse Transcriptase

The new antiviral substance phosphonoformate (PFA) has been tested in a cell-free system for its effect on reverse transcriptases from an avian retrovirus (avian myeloblastosis virus, AMV) and from mammalian retroviruses (Rauscher leukaemia virus, RMuLV; bovine leukaemia virus; baboon endogenous virus; simian sarcoma virus; visna virus). The observed inhibitory effect of PFA has been compared with that of a structurally related substance, phosphonoacetate (PAA). Phosphonoformate, at a concentration of IOO #M, reduced the activities of all the above mentioned polymerases by 90 ~o when (rA)n.(dT)10 was used as a template/primer. The dose-response curves for AMV and RMuLV poly-merases primed with (rA)n.(dT)lo showed PFA to be a lOOO-fold more active than PAA; the RMuEV polymerase activity was reduced to 5o ~ after incubation with o'7/zM-PFA and o. 7 mM-PAA, respectively. There was no difference in PFA inhibition of virus-associated and purified reverse transcriptase activity. Results with various synthetic templates showed that both the RNA- and the DNA-dependent polymerase activities of reverse transcriptase were inhibited by PFA. The endogenous polymerase activity of AMV was inhibited to 5o ~ at Ioo/tM-PFA, while PAA had no effect. The PFA inhibition was dependent on whether Mg ~+ or Mn ~+ was used as divalent cation in the assay. Phosphonoformate arrested DNA synthesis immediately after being added to the assay system. The mechanism of inhibition of the AMV polymerase was non-competitive with respect o substrate and template and the apparent inhibition constants were 16 #M and 9/~M, respectively