Synergistic antiviral activities of oligonucleoside methylphosphonates complementary to herpes simplex virus type 1 immediate-early mRNAs 4, 5, and 1.

An oligonucleoside methylphosphonate (ONMP) complementary to the splice acceptor site of immediate-early (IE) pre-mRNAs 4 and 5 (IE4,5SA) inhibits herpes simplex virus type 1 (HSV-1) growth in vitro and in infected animals. The antiviral effect appears to be due to inhibition of IE pre-mRNA 4 and 5 splicing and/or IE4 gene expression (M. Kulka, M. Wachsman, S. Miura, R. Fishelevich, P. S. Miller, P. O. P. Ts'o, and L. Aurelian, Antiviral Res. 20:115-130, 1993). We describe the potentiation of antiviral activity when we targeted two IE genes with different ONMPs. A psoralen derivative of an ONMP complementary to the IE mRNA 1 (IE1) translation initiation site (IE1TI) covalently bound a 2.8-kb transcript that hybridized with a 20-base oligonucleotide complementary to the 5' leader sequence of IE1 but not a 20-base oligonucleotide complementary to the first intron of IE1. IE1TI inhibited IE1 gene expression and virus replication in cells infected with HSV-1 in vitro. Inhibition was specific because it was not observed with oligomers mutated in two (IE1TImu1) or four (IE1TImu2) central residues or in cells infected with an IE1 deletion mutant (HSV-1 dl1403). IE1TI potentiated the antiviral activity of IE4,5SA (synergistic effect), while potentiation was not observed when IE4,5SA was mixed with IE1TImu1. A similar synergistic effect was seen when IE1TI was mixed with an ONMP complementary to the translation initiation site of IE mRNA 4 but not with an ONMP complementary to the translation initiation site of IE mRNA 5. These findings suggest that synergistic antiviral activity is mediated by targeting at least two IE genes (IE1 and IE4).