Evaluation of DNA crosslinks and monoadducts in mouse embryo fibroblasts after treatment with mono- and bifunctional furocoumarins and 365 nm (UVA) irradiation. possible relationship to carcinogenicity

Detection of pyrimidine dimers and monoadducts induced by 7-methylpyrido(3,4-c) psoralen and UVA in Chinese hamster V79 cells by enzymatic cleavage and high-pressure liquid chromatography

The photochemotherapeutically active psoralen derivative 7-methylpyrido(3,4-c) psoralen (MePyPs) has been recently shown to be able to photoinduce monoadducts of the C4-cycloaddition type as well as pyrimidine dimers in DNA in vitro. In the present study, we report on the induction of these two types of photolesions in mammalian cells in culture. The MePyPs photocycloadducts were quantified in V79 Chinese hamster cells after treatment with MePyPs plus UVA following enzymatic hydrolysis of the DNA by DNase I, S1 nuclease and acidic phosphatase treatments. Concomitantly induced pyrimidine dimers were determined by two methods, high-pressure liquid chromatography and alkaline gel electrophoresis after dimer-specific endonucleolytic cleavage. The results show that, in Chinese hamster cells treated with MePyPs plus UVA, the yield of pyrimidine dimers is approximately 5-10% that of MePyPs-DNA photocycloadducts. Because psoralen monoadditions to DNA alone are generally not considered as being very phototoxic, a synergistic interaction of monoadditions with pyrimidine dimers may be expected to occur in order to explain the high photobiological effectiveness of this psoralen derivative.

Structure and carcinogenicity of dibenzo(c,g)carbazole derivatives

The carcinogenicity of several groups of carcinogens is evoked with particular reference to Dibenzo(c,g)carbazole derivatives. The activity of these derivatives is discussed with respect to their species and organ specificity. The enzymatic equipment is decisive as to whether the compounds formed can react with DNA or are simply detoxified and eliminated. All these carcinogens are complete carcinogens, i.e. they have the property of both initiation and promotion.

Unusual alkaline elution pattern induced in mammalian cell DNA by fast neutrons p(34) + Be

Syrian hamster fibroblasts (cell line BHK 21/13) were exposed to p(34) + Be fast neutron irradiation and their DNA analysed by the alkaline elution technique. The elution profiles showed an unusual tailing off, characteristic of neutron-irradiated samples, suggesting the presence of a modification in DNA induced by the neutrons. This was not seen with 60Co gamma-irradiation. In neutron-irradiated samples the alteration of DNA appeared to persist even after 2 h of post-treatment incubation (37 degrees C) indicating the absence of repair. The modification of DNA induced by neutrons provides a possible explanation for the reduction of the shoulders in survival curves obtained with neutrons, and the high RBE of neutrons.

Aspects of psoralen phototumorigenesis with emphasis on the possible role of tumour promotion

8-Methoxypsoralen in combination with UVA radiation (PUVA) is carcinogenic in mice and probably so in man. PUVA is genotoxic and so has tumour initiation potential. Some evidence suggests that PUVA has other biological effects which may be equated with tumour promotion. Thus, the use of a two-stage model, similar to that of chemical carcinogenesis, may be a useful experimental approach for the further understanding of PUVA carcinogenesis.