E. A. Graham

Mosquito larvicidal activity of polyacetylenes from species in the Asteraceae

Twenty-four polyacetylenes isolated from species in the Asteraceae were screened for their near-UV-mediated larvicidal properties to the mosquito, Aedes aegypti. Dosage resonse lines for three of the most active compounds were prepared. One of these, σ-terthienyl from Tagetes was more toxic than DDT when near-UV radiation was provided. A scaled up trial with this compound in a simulated field situation demonstrated its potential as a larvicide. The effects of the radiation dose on larval survival were studied and the action spectra for the phototoxic effects of three compounds on larvae were obtained with narrowband interference filters. Because of the close agreement between the action and absorption spectra, it appears most probable that the polyacetylene is the primary absorbing compound. The potential of polyacetylenes as larvicides and their role in plant herbivore relations are discussed.

Photosensitization of invertebrates by natural polyacetylenes

Fourteen polyacetylenes or their thiophene derivatives, isolated from species in the Asteraceae were screened for their biological activity to mosquito larvae (Aedes aegypti), blackfly larvae (Simulium vittatum) and adult nematodes (Caenorhabditis elegans). Toxicity of the compounds was found to be enhanced greatly by irradiation with near-UV radiation or natural sunlight. Only wavelengths less than 400 nm were effective in promoting photosensitization. The results are discussed in relation to herbivore-plant interactions.

Structure-activity studies of photoactivated antiviral and cytotoxic tricyclic thiophenes

The photoactivated antiviral and cytotoxic activities of the naturally occurring thiophene, α‐terthienyl (1), and 15 synthetic analogues were evaluated against murine cytomegalovirus and Sindbis virus, and murine mastocytoma cells. After irradiation with near UV light, α‐terthienyl and most of its analogues had significant toxicity, with minimum inhibitory concentrations in the range of 0.02–40 μM. In the absence of near UV irradiation, only one analogue had antiviral activity and five were cytotoxic. The most active analogues were those containing carboxylic acid, hydroxyl, or cyano substituents. Quantitative structure‐activity relationship analysis of thiophene phototoxicity suggested that the rate of singlet oxygen production is the primary determinant of antiviral and cytotoxic activities. For phototoxicity against murine cytomegalovirus, a significant role for hydrophobicity was also demonstrated. Tricyclic thiophenes show significant potential for photochemotherapy of viral infections and cancer. and further evaluation in animal models is recommended.

ANTIVIRAL EFFECT OF HARMINE, A PHOTOACTIVE β-CARBOLINE ALKALOID

Abstract— Harmine, a β‐carboline alkaloid, was found to be an efficient photoactive agent against the DNA‐containing murine cytomegalovirus (MCMV) and the RNA containing Sindbis virus, a togavirus, both of which contain membranes. In contrast the host cells themselves were relatively resistant. The MCMV was investigated in more detail. Virus which had been inactivated by harmine plus UVA retained its structural integrity and was fully capable of penetrating host cells, following which the viral genome entered the cell nucleus. The viral genes which normally code for the switch‐off in thymidine kinase activity arid for the normal cytopathic effects were not expressed; however the viral geneis responsible for the cytotoxic effect due to high multiplicities of infection was still expressed, indicating that there may be a differential block of some viral genes

Phototoxic polyacetylenes and their thiophene derivatives [Effects on human skin]

Polyacetylenes and their thiophene derivatives were tested for their effects on human skin. Topically applied α‐terthienyl evoked bi‐phasic phototoxic dermatitis and the appearance of ‘sunburn’ cells in human epidermis. None of 11 polyacetylenes had the same effect although they mimicked α‐terthienyl in their phototoxic effects on Candida albicans and certain pathogenic microorganisms. The UV‐mediated antibiotic activity of the compounds and their apparent lack of phototoxicity towards the skin suggest a potential topical therapeutic role for them in yeast, fungal and bacterial infections and light‐responsive dermatoses. Their topical sensitizing capacity, however, has not yet been studied.

NATURE OF THE INTERACTION BETWEEN THE PHOTOACTIVE COMPOUND PHENYLHEPTATRIYNE AND ANIMAL VIRUSES

Abstract The mechanism of action of the phototoxic polyacetylene phenylheptatriyne (PHT) against viruses was investigated. For this purpose the membrane containing mouse cytomegalovirus (MCMV) was treated with PHT in long wave UV light, and several functions of the virus were then examined. Following this treatment MCMV retained its structural integrity, as revealed by electron microscopy, resistance to exogenous deoxyribonuclease, and sedimentation‐velocity. The treated virus was also normal in its ability to penetrate into the nuclei of susceptible mouse cells. Replication of the virus was defective, however, in that infectious centers could not be established and no infectious progeny resulted. Two RNA‐containing viruses, Sindbis and infectious hematopoietic necrosis virus (IHNV, a fish virus), both of which contain membranes, were inactivated by PHT in long wave UV as efficiently as MCMV. In contrast, the fish virus IPNV (infectious pancreatic necrosis virus), which does not possess a membrane, was resistant to PHT. Thus, it appears that PHT, in the presence of long wave UV, exerts its action via the viral membrane and as a consequence the viral genome, DNA or RNA, is unable to replicate.

THE UNUSUAL UVA‐DEPENDENT ANTIVIRAL PROPERTIES OF THE FUROISOCOUMARIN, CORIANDRIN

The novel furoisocoumarin, coriandrin, which was found recently to possess an interesting combination of photobiological properties, was investigated for antiviral activity in the presence and absence of UVA (long‐wavelength ultraviolet radiation). In contrast to results obtained with other antiviral furocoumarins, such as 8‐MOP (8‐methoxypsoralen), coriandrin was much more phototoxic to the RNA‐virus Sindbis virus than to the DNA‐virus murine cytomegalovirus, although both viruses were substantially more sensitive to this compound than they were to 8‐MOP. Human immunodeficiency virus, HIV‐1, was also susceptible to coriandrin + UVA.

ANTIVIRAL ACTIVITY OF THE PHOTOACTIVE THIOPHENE α-TERTHIENYL

The naturally occurring thiophene, α‐terthienyl, was investigated for phototoxicity against several viruses and a line of mouse cells. The compound was extremely phototoxic to the two‐membrane‐containing animal viruses, murine cytomegalovirus (MCMV) and Sindbis virus (SV). Antiviral activity was detected at 105μg/m in the presence of UVA. However, no effect was seen in the absence of UV‐A, even at 0.1 μg/m of αT. Mouse cells were much more resistant to αT, as was the bacterial virus T4, which does not contain a membrane. Murine CMV, which had been inactivated by αT and UVA, penetrated mouse cells efficiently; but the viral DNA could not replicate, and late viral proteins were not made. Thus viral gene expression was inhibited in the photoinactivated virus. In order to account for all these data we suggest that αT may interact with viral proteins in addition to membrane lipids.

INVESTIGATION OF THE ANTIVIRAL ACTION OF THE PHOTOACTIVE COMPOUND PHENYLHEPTATRIYNE

Abstract— Murine cytomegalovirus, a herpes virus, was used as a model virus to investigate the mechanism of the anti‐viral action of phenylheptatriyne in long wave ultraviolet light. The genome and proteins of the inactivated virus penetrated the nuclei of susceptible cells normally. Furthermore, the viral genome did not contain extra single strand breaks or cross‐links. However, cells infected with the treated virus did not synthesize late viral proteins, as determined by polyacrylamide gel electrophoresis. nor did they synthesize late viral RNA and viral DNA according to nucleic acid hybridization tests. Thus the compound may interfere with an early viral function so that the replication cycle cannot proceed.

FURTHER STUDIES ON THE ANTIVIRAL ACTIVITY OF HARMINE, A PHOTOACTIVE β-CARBOLINE ALKALOID

The UV‐A mediated antiviral effect of harmine was investigated using murine cytomegalovirus (MCMV) as the target. Virus, which had been inactivated by harmine + UVA, was used to infect cultured mouse cells, and various stages in the viral replication cycle were examined. No viral protein synthesis or RNA synthesis (as measured by polyacrylamide gel electrophoresis or DNA‐RNA hybridization) could be detected, and the viral DNA did not replicate (measured by DNA‐DNA hybridization). In contrast virus which had been treated with harmine in the dark promoted a complete growth cycle in mouse cells.