ANTIVIRAL ACTIVITIES OF METHYLATED NORDIHYDROGUAIARETIC ACIDS - 2 - TARGETING HERPES-SIMPLEX VIRUS-REPLICATION BY THE MUTATION INSENSITIVE TRANSCRIPTION INHIBITOR TETRA-O-METHYL-NDGA

We had previously reported that tetramethyl-O-NGDA (M4N), a synthetic derivative of the naturally occurring nordihydroguaiaretic acid (NDGA) , is able to inhibit HIV Tat transactivation by blocking host Sp1 prot ein at the Sp1 cognate binding site on the HIV LTR promoter. The prese nt studies were undertaken to examine whether M4N is able to inhibit t he replication of herpes simplex virus (HSV), another Sp1-regulated vi rus. The results showed that in Vero cells, M4N inhibits at micromolar levels (IC50 = 43.5 mu M) the expression of the herpes immediate earl y gene (alpha-ICP4), which is essential for HSV replication. An electr ophoretic mobility shift assay, examining Spl binding to the alpha-ICP 4 promoter, showed a significant inhibition of the control bands: 88% inhibition of the fast moving band (FMB) and 45% of the slow moving ba nd (SMB), at 100 mu M of drug concentration. Comparative studies betwe en M4N and acycloguanosine (acyclovir, ACV) in cultured Vero cells rev ealed an interesting pattern in the drug sensitivity (IC50) and cytoto xicity (TC50) parameters. For M4N, the IC50 varied between 11.7 and 4 mu M in 10 passages of HSV-1 and 4 passages of HSV-2 with no indicatio n for a requirement of higher drug concentration. In contrast, for acy clovir, the IC50 increased from 7 mu M in the first passage to 444 mu M in the tenth passage of HSV-1, and > 88 mu M for the fourth passage of HSV-2, indicating a rapid build-up of drug resistance against acycl ovir. While the selective index (SI), defined as the ratio: TC50/IC50, remained relatively constant for M4N; it dropped 60-fold for acyclovi r in the endpoints of viral passages; Drug sensitivity for M4N toward the acyclovir-sensitive strain (sm44) and the acyclovir-resistant stra in (ACV-10) of HSV-1 was similar, indicating no cross-resistance betwe en M4N and acyclovir in their anti-HSV effects. These results may have an important clinical relevance since HSV has been shown to be a fact or for spreading of HIV.