Pyrimido[5,4-g]pteridine-2,4,6,8-tetramine, 4-methylbenzenesulfonate (1:1)

Endpoint summary

Additional information

Reasons for read across

The substance was not tested for genotoxicity. The test item is a mixture which consist mainly of the end product (app. 50 %) and a by product (app. 30 %) as well as of different impurities and isomers of the end product. Therefore, information about mutagenicity and chromosome aberrations are derived from studies with the end product and the by product. Moreover, one toxicological relevant impurity exceeds 1 % and is also taken into account for this summary.

 

Performance and observations

There are two reliable in vitro studies available to assess the potential of the end product for gene mutations in bacteria and cytogenicity in mammalian cells.

In a GLP conform study according to OECD guideline 471, the potential of the test substance (purity: 94.8 %) to induce gene mutations using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, and TA 100, and the Escherichia coli strain WP2 uvrA was investigated in two independent experiments.

In the first mutation assay, the test substance was tested up to concentrations of 5000 µg/plate in the absence and presence of S9-mix. The test substance precipitated on the plates at dose levels of 1000 µg/plate and upwards. The bacterial background lawn was not reduced at all concentrations tested and no biologically significant decrease in the number of revertants was observed.

In the second mutation assay, the test substance was tested up to concentrations of 1000 µg/plate in the absence and presence of S9-mix. The test item precipitated on the plates at the dose level of 1000 µg/plate. The bacterial background lawn was not reduced at all concentrations tested and no decrease in the number of revertants was observed.

In a GLP conform study according to OECD guideline 473 the substance was assessed for its potential to induce structural chromosome aberrations in cultured peripheral human lymphocytes in vitro. The possible clastogenicity of the test substance (purity: 94.8 %) was tested in two independent experiments. In the first cytogenetic assay, the test substance was tested up to 3 µg/ml for a 3 h exposure time with a 24 h fixation time in the absence and presence of S9-mix. The test substance precipitated in the culture medium at this dose level.

In the second cytogenetic assay, the test substance was tested up to 3 µg/ml for a 24h or 48h continuous exposure time with 24h or 48h fixation time in the absence of S9-mix. In the presence of 1.8 % (v/v) S9-fraction the test substance was tested up to 3 µg/ml for a 3 h exposure time with a 48 h fixation time.

The test substance did not induce an increase in the number of cells with chromosome aberrations in the absence and in the presence of S9-mix.

 

The ability of the by productto induce point mutations in bacteria was investigated by a GLP-conform Ames test using five Salmonella typhimurium strains TA 1535, TA 1537, TA 1538, TA 98 and TA 100. The plate incorporation method was used. Microsomes of rat livers (S-9) induced with Aroclor 1254 were added as a source of metabolic activation. The test substance dissolved in distilled water was tested at 10, 100, 500, 1000 and 5000 µg/plate on two separate occasions. Identical results are obtained: no mutagenic effect occurs with and without metabolic activation in any of the five strains.

The by product was examined for mutagenic activity in V79 Chinese hamster cells. The induction of chromosome aberrations after in vitro treatment was investigated in the presence and absence of a fraction liver homogenate for metabolic activation (S9-mix). A preliminary cytotoxicity experiment was performed in order to select appropriate dose levels for the mutagenicity study. The test substance produced no significant cytotoxic effect without metabolic activation up to a concentration of 1902 ug/ml (= 10 mM, which is the highest dose level tolerated for the test system). No cytotoxic effect was also observed with metabolic activation up to the limit of solubility. For mutagenicity testing two independent cell cultures with and without metabolic activation (S9-mix) up to a concentration of 10 mM were used. For the main experiment dose levels of 200, 600 and 1902 ug/ml were used, in the absence and in the presence of S9-mix metabolic activation.

The test compound did not induce a significant increase in the number of chromosome aberrations at any preparation time and dose level of the test substance. No relevant cytotoxic effect of the compound was observed in the main experiments.

 

Discussion

Based on the results of the performed studies it is concluded that the end product is not mutagenic in Salmonella and E. coli and not clastogenic in cultured human peripheral blood lymphocytes.

 

Under the experimental conditions of the decribed studies, the by product is not mutagenic in the Ames test and the substance does not induce chromosome aberrations in V79 Chinese hamster cells.

 

Mutagenicity data to the impurity is not available. The substance bears some structural similarity to the pyrimidine nucleobases. Such analogues have cytostatic or cytotoxic properties. However, no effects related to nucleic acid turnover have been reported for the substance itself.

 

Short description of key information:
Genotoxicity of this mixture is derived from toxicological information about the endproduct, the main by product and one toxicological relevant impurity. GLP-conform Ames tests (according OECD guideline 471) and tests of chromosome aberrations in vitro (according OECD guideline 473) are available for the end product and the by product. None of the substances induced mutations or chromosome aberrations in presence or absence of S9-mix.

Endpoint Conclusion: