Nuclease stability as dominant factor in the antiviral activity of oligonucleotides directed against HSV-1 IE110.

The anti-herpes simplex virus type 1 (anti-HSV-1) efficacy of a series of oligonucleotides was determined as a function of their chemical structure. All oligonucleotides consisted of the same sequence directed against the translation initiation codon of the HSV-1 immediate early gene. The oligonucleotides were modified with phosphorothioate linkage patterns according to various protection strategies against nucleolytic degradation. We show that nuclease resistance is the dominant factor that determines the antiviral efficacy in this series. A minimal protection strategy, consisting of end-capping and pyrimidine protection, has proven to be particularly useful, because it not only yields nuclease-resistant oligonucleotides but also minimizes non-sequence-specific effects.

Evaluation of retinal toxicity and efficacy of the anticytomegalovirus compound 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine.

Compound 2242, also known as 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine, is the first known antivirally active nucleoside analog with the side chain substituted at the N-7 position of the purine ring system. Our purpose was to evaluate its retinal toxicity and assess the efficacy of its highest nontoxic concentration in a rabbit model of herpes simplex retinitis. Concentrations of the drug from 0.5 to 2,000 microM were injected intravitreally in twelve New Zealand White rabbits. Fundoscopic, histologic, and electrophysiologic data revealed no evidence of toxicity even at the highest dose of the compound. Dutch pigmented rabbits (n = 34) had their left eyes injected with herpes simplex virus type 1 3 days after, concurrently, or 3 days before intravitreal injection of either 2,000 microM compound 2242 or 480 microM ganciclovir (final concentration in the eye). Both compound 2242 and ganciclovir were equally effective compared with saline when administered simultaneously with the virus (P < 0.0001). In the 3-day pretreatment paradigm, compound 2242 was superior to ganciclovir (P < 0.04), but there was no clear difference between the two with regard to their effects on an established infection. The pharmacokinetics of compound 2242 in 10 rabbits injected intravitreally with 30 microM showed an intravitreal half-life of 8 h. This compound, which may be orally active in its pro form, has a very high therapeutic index in the eye and is more efficient than ganciclovir in this animal model of herpes retinitis.

Inhibition of viral growth by antisense oligonucleotides directed against the IE110 and the UL30 mRNA of herpes simplex virus type-1.

In the present work we elucidate that the identification of active sequences for a given target is one of the principle hurdles of antisense oligonucleotide therapeutics. A number of 100 oligonucleotides directed against different target genes of HSV-1 and different locations within those genes were screened for antiviral activity. To facilitate comparison, the same length and the same chemical modification were used for all oligonucleotides: 20mers with two phosphorothioate linkages at both the 5'- and the 3'-end. No sequence-independent effects were observed with this type of modification. Surprisingly, only six oligonucleotides did show significant antiviral activity, the most active one (#6) being directed against the translation initiation site of IE 110.

The N-7-substituted acyclic nucleoside analog 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine is a potent and selective inhibitor of herpesvirus replication.

2-Amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (compound S2242) represents the first antivirally active nucleoside analog with the side chain attached to the N-7 position of the purine ring. Compound S2242 strongly inhibits the in vitro replication of both herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) (50% effective concentration [EC50], 0.1 to 0.2 microgram/ml), varicella-zoster virus (EC50, 0.01 to 0.02 microgram/ml) and thymidine kinase (TK)-deficient strains of HSV (EC50, 0.4 microgram/ml) and varicella-zoster virus (EC50, 0.2 to 0.5 microgram/ml). Potent activity was also observed against murine cytomegalovirus (EC50, 1 microgram/ml), human cytomegalovirus (HCMV) (EC50, 0.04 to 0.1 microgram/ml), and human herpesvirus 6 (EC50, 0.0005 microgram/ml). Compound S2242 (i) was not cytotoxic to confluent Vero, HeLa, or human fibroblast cells at concentrations of > 100 micrograms/ml, (ii) proved somewhat more cytostatic to Vero, HEL, HeLa, and C127I cells than ganciclovir, and (iii) was markedly more cytostatic than ganciclovir to the growth of the human lymphocytic cell lines HSB-2 and CEM degrees. In contrast to ganciclovir, (i) compound S2242 proved not to be cytocidal to murine mammary carcinoma (FM3A) cells transfected with the HSV-1 or HSV-2 TK gene, (ii) exogenously added thymidine had only a limited effect on its anti-HSV-1 activity, and (iii) the compound was not phosphorylated by HSV-1-encoded TK derived from HSV-1 TK-transfected FM3A cells, indicating that the compound is not activated by a virally encoded TK. Compound S2242 inhibited (i) the expression of late HCHV antigens at an EC50 of 0.07 microgram/ml (0.6 microgram/ml for ganciclovir) and (ii) HCMV DNA synthesis at an EC50 of 0.1 microgram/ml (0.32 microgram/ml for ganciclovir), i.e., values that are close to the EC50S for inhibition of HCMV-induced cytopathogenicity. Neither ganciclovir nor S2242 had any effect on the expression of immediate-early HCMV antigens, which occurs before viral DNA synthesis. In time-of-addition experiments, S2242 behaved like ganciclovir and acyclovir; i.e., the addition of the drugs could be delayed until the onset of viral DNA synthesis.

Antiviral activity and pharmacokinetics of HOE 602, an acyclic nucleoside, in animal models.

The acyclic nucleoside derivative HOE 602 (2-amino-9-[1,3-bis(isopropoxy)-2-propoxymethyl]purine) was evaluated for its antiviral activity in cell culture and for its therapeutic efficacy in mice infected with herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) or with murine cytomegalovirus (MCMV). HOE 602 was inactive in vitro against a variety of DNA- and RNA-viruses. However it prevented symptoms and mortality in mice systemically infected with HSV-1, HSV-2 or MCMV when administered intraperitoneally or orally at a dosage of 100 mumol/kg twice per day. Pharmacokinetic studies in mice and macaques revealed that HOE 602 was converted via three metabolic steps to ganciclovir, which seemed to be the antivirally active compound. The bioavailability of ganciclovir after oral administration of HOE 602 or ganciclovir was similar in mice, while in rhesus monkeys much higher serum levels of ganciclovir were reached with HOE 602. After intraperitoneal or intravenous administration higher drug levels were obtained with ganciclovir. The excellent therapeutic efficacy in animal models, the high enteral absorption in monkeys, and the favourable physical properties will hopefully lead to an orally active drug against cytomegalovirus and severe herpes infections in man.

Inhibition of HIV and virus replication by polysulphated polyxylan: HOE/BAY 946, a new antiviral compound.

Xylanpoly-(hydrogen sulphate) disodium salt with a molecular weight of about 6000 daltons (HOE/BAY 946) completely inhibited syncytium formation induced by the infection of T lymphocytes with HIV as well as viral replication at concentrations above 25 micrograms/ml. This dose was found to be inhibitory for several strains of HIV-1 and HIV-2. Low molecular weight fractions of the compound were less active against HIV, and high molecular derivatives were as active as HOE/BAY 946. A direct influence of the drug on the infectivity of the virus could not be demonstrated. The drug inhibited the reverse transcriptase of HIV. Treatment of permanently HIV-infected U937 cells resulted in a drastic reduction of virus particles released into the supernatant and points to an additional mode of action. A therapeutic effect of HOE/BAY 946 against retroviruses in vivo could be demonstrated in Friend leukaemia virus-infected mice. A clinical pilot study with the compound was started recently in Germany with AIDS patients who did not tolerate or refused to take zidovudine and with asymptomatic virus carriers.

Twelve 43-base-pair repeats map in a cis-acting region essential for partition of plasmid mini-F.

The nucleotide sequence of the DNA region involved in partitioning of plasmid mini-F has been determined. The sequence consists of 12 direct tandemly arranged repeats of 43 base pairs (the two flanking repeats, 43 plus 1 base pairs) with extensive homology to each other. Each repeat contains an additional inverted repeat of 7 base pairs.

The repeated sequences (incB) preceding the protein E gene of plasmid mini-F are essential for replication.

At the XhoI site (45.08F) of plasmid mini-F a deletion of 649 bp was generated employing exonuclease Bal31. By this deletion nucleotide sequences functioning as origin II and the four 19 bp direct repeats constituting the incB region in front of the E protein gene were removed from the plasmid. Analysis of proteins radioactively labelled in Escherichia coli mini-cells indicated that all mini-F encoded proteins are expressed. However, the plasmid carrying the deletion was not capable of replicating from the primary origin (origin I, 42.6F). Recently a smaller deletion at the XhoI site (45.08F) of about 300 bp, removing only the region functioning as origin II and replicating from origin I, was described by Tanimoto and Iino (1984, 1985). The data presented suggest that the incB repeats are essential for the initiation of replication from origin I, and possibly also from origin II, and seem not to be engaged in the autoregulation of E protein expression.

Mutations affecting replication and copy number control in plasmid mini-F both reside in the gene for the 29-kDa protein.

We have isolated and characterized cop, copts, and repam mutants of plasmid mini-F after in vitro mutagenesis with hydroxylamine. cop mutants exhibit a copy number of about 10 per cell. The copts mutants are cold-sensitive and have, at 25 degrees C, a copy number of about 30-40 copies per cell, which drops to 4 copies at 42 degrees C. The cop and repam mutations affect the 29-kDa E protein. The Copts phenotype results from the simultaneous occurrence of two mutations, a cop mutation in the E protein and a temperature-dependent mutation (termed ecp) enhancing the Cop phenotype at low temperature. The latter new type of mutation is located within the DNA region 44.1-44.85F. Complementation experiments with plasmid cointegrates show that the wild-type gene is dominant over the cop allele. The nucleotide sequences of the cop and the repam mutations have been determined.