Resistance of New Zealand Provenance Leptospermum scoparium, Kunzea robusta, Kunzea linearis, and Metrosideros excelsa to Austropuccinia psidii

Resistance to the pandemic strain of Austropuccinia psidii was identified in New Zealand provenance Leptospermum scoparium, Kunzea robusta, and K. linearis plants. Only 1 Metrosideros excelsa-resistant plant was found (of the 570 tested) and no resistant plants of either Lophomyrtus bullata or L. obcordata were found. Three types of resistance were identified in Leptospermum scoparium. The first two, a putative immune response and a hypersensitive response, are leaf resistance mechanisms found in other myrtaceous species while on the lateral and main stems a putative immune stem resistance was also observed. Both leaf and stem infection were found on K. robusta and K. linearis plants as well as branch tip dieback that developed on almost 50% of the plants. L. scoparium, K. robusta, and K. linearis are the first myrtaceous species where consistent infection of stems has been observed in artificial inoculation trials. This new finding and the first observation of significant branch tip dieback of plants of the two Kunzea spp. resulted in the development of two new myrtle rust disease severity assessment scales. Significant seed family and provenance effects were found in L. scoparium, K. robusta, and K. linearis: some families produced significantly more plants with leaf, stem, and (in Kunzea spp.) branch tip dieback resistance, and provenances provided different percentages of resistant families and plants. The distribution of the disease symptoms on plants from the same seed family, and between plants from different seed families, suggested that the leaf, stem, and branch tip dieback resistances were the result of independent disease resistance mechanisms.

Novel antiviral activity of l-dideoxy bicyclic nucleoside analogues versus vaccinia and measles viruses in vitro

Dideoxy bicyclic pyrimidine nucleoside analogues (ddBCNAs) with d-chirality have previously been described by us to inhibit replication of human cytomegalovirus. We herein report for the first time that activity against vaccinia virus (VACV) was achieved using novel l-analogues. A structure-activity relationship was established: Antiviral activity versus VACV was highest with an ether side chain with an optimum of n-C(9)H(18)-O-n-C(5)H(11). This gave an IC(50) of 190 nM, a 60-fold enhancement over the FDA-approved antiviral cidofovir. Interestingly, l-ddBCNAs also inhibit wild type measles virus syncytia formation with a TCID(50) of 7.5 μM for the lead compound. We propose that l-ddBCNAs represent significant innovative antiviral candidates versus measles and poxviruses, and we suggest a mechanism of action versus one or more cellular targets that are essential for viral replication.

Preclinical development of bicyclic nucleoside analogues as potent and selective inhibitors of varicella zoster virus

OBJECTIVES

To progress the anti-varicella-zoster-virus (VZV) aryl bicyclic nucleoside analogues (BCNAs) to the point of Phase 1 clinical trial for herpes zoster.

METHODS

A new chromatography-free synthetic access to the lead anti-VZV aryl BCNAs is reported. The anti-VZV activity of lead Cf1743 was evaluated in monolayer cell cultures and organotypic epithelial raft cultures of primary human keratinocytes. Oral dosing in rodents and preliminary pharmacokinetics assessment was made, followed by an exploration of alternative formulations and the preparation of pro-drugs. We also studied uptake into cells of both parent drug and pro-drug using fluorescent microscopy and biological assays.

RESULTS

Cf1743 proved to be significantly more potent than all reference anti-VZV compounds as measured either by inhibition of infectious virus particles and/or by viral DNA load. However, the very low water solubility of this compound gave poor oral bioavailability (approximately 14%). A Captisol admixture and the 5'-monophosphate pro-drug of Cf1743 greatly boosted water solubility but did not significantly improve oral bioavailability. The most promising pro-drug to emerge was the HCl salt of the 5'-valyl ester, designated as FV-100. Its uptake into cells studied using fluorescent microscopy and biological assays indicated that the compound is taken up by the cells after a short period of incubation and limited exposure to drug in vivo may have beneficial effects.

CONCLUSIONS

On the basis of its favourable antiviral and pharmacokinetic properties, FV-100 is now being pursued as the clinical BCNA candidate for the treatment of VZV shingles.

Discovery of a New Family of Inhibitors of Human Cytomegalovirus (HCMV) Based upon Lipophilic Alkyl Furano Pyrimidine Dideoxy Nucleosides: Action via a Novel Non-Nucleosidic Mechanism

Following our discovery of the potent anti-varicella zoster virus action of lipophilic alkyl furano pyrimidine 2'-deoxynucleosides, we now report that 2',3'-dideoxy sugar analogues are devoid of anti-VZV activity but are potent and selective inhibitors of human cytomegalovirus (HCMV). The present compounds are active in vitro at ca. 1 microM with cytotoxicity only above 200 microM. Importantly, we have discovered that the new agents do not act as nucleoside analogues, despite their nucleosidic structure, and time of addition studies revealed that the compounds may inhibit HCMV at an event in the replication cycle of the virus that precedes DNA synthesis. They represent new leads in the discovery of improved therapies for HCMV, particularly in view of their novel mechanism of action.

Anti-varicella-zoster virus bicyclic nucleosides: replacement of furo by pyrro base reduces antiviral potency

We have recently reported the discovery of an entirely new category of potent antiviral agents based on novel deoxynucleoside analogues with unusual fluorescent bicyclic furo base moieties. To probe structure-activity relationships and to seek to optimize the properties of the lead compounds, we prepared pyrro analogues of the furo systems. We herein report the synthesis, characterization and antiviral evaluation of these novel compounds.

Intracellular delivery of bioactive AZT nucleotides by aryl phosphate derivatives of AZT

Novel aryl phosphate derivatives of the anti-HIV nucleoside analogue AZT have been prepared by phosphorochloridate chemistry. These materials were designed to act as membrane-soluble prodrugs of the bioactive free nucleotides. In vitro evaluation revealed the compounds to have a pronounced, selective anti-HIV activity in CEM cells; the magnitude of the biological effect varied considerably depending on the nature of the phosphate blocking group. Moreover, several of the compounds retain marked antiviral activity in TK- (thymidine kinase-deficient) mutant CEM cells in which AZT was virtually inactive. These data strongly support the hypothesis that the AZT phosphate derivatives exert their biological effects via intracellular release of AZT nucleotide forms and suggest that the potential of nucleoside drugs in antiviral chemotherapy may be enhanced by suitable nucleotide delivery strategies.

Aryl phosphate derivatives of AZT retain activity against HIV1 in cell lines which are resistant to the action of AZT

Novel aryl phosphate derivatives of the anti-HIV nucleoside analogue AZT have been prepared by phosphorochloridate chemistry. These materials are designed to act as membrane-soluble pro-drugs of the bio-active free nucleotides. In vitro evaluation revealed the compounds to have a pronounced, selective antiviral activity, which, in one case, was more potent than the parent nucleoside AZT. The magnitude of the biological effect varied considerably with the nature of the phosphate-blocking group. Moreover, one of the compounds, a phosphoramidate, is particularly active in a cell line restrictive to the activity of AZT, due to poor phosphorylation therein. These data support the suggestion that the phosphate derivatives exert their biological effects via intracellular release of the nucleotide forms.