CMP

Endpoint summary

Additional information

1. INFORMATION BASED ON PHYSICO-CHEMICAL PROPERTIES

The substance is a white solid with a molecular weight of 144.56 g/mol. It is very soluble in water (17000 mg/litre at 25 ± 1 °C) and possesses a Log P value of 1.28 at 25 ± 1 °C. The material tested in toxicity studies had a purity value of 99.5% or 99.7% (w/w).

Based upon its structure, molecular weight and log P value, some absorption of orally administered test substance across the gastrointestinal mucosa would be expected. Its molecular weight is below the biliary exclusion limit in the rat, consequently, it would not be excreted directly in bile.

The high aqueous solubility of any absorbed test substance would allow some direct urinary excretion. In addition, the absorbed molecule could be subjected to biotransformation to promote its excretion.

The chlorine is subject to displacement by glutathione, leading to the ultimate formation of a mercapturic acid. Demethylation of the O-methyl group is feasible with subsequent conjugation of the resultant hydroxyl group as a glucuronide or sulphate. These various conjugation reactions would promote the excretion of this test substance. Ring hydroxylation is also possible, but may be hindered by the existing substitution of the pyrimidine ring.

 

2. INFORMATION BASED ON TOXICITY STUDIES

The following studies have been considered:

IUCLID Chapter 7.2.1: Fixed Dose Acute Oral Toxicity Study in Rats

IUCLID Chapter 7.2.3: Acute Dermal Toxicity Study in Rats

IUCLID Chapter 7.5.3: 28 Day Dermal Toxicity Study In Rats

IUCLID Chapter 7.4.1: Local Lymph Node Assay

IUCLID Chapter 7.3.1: Skin Irritation Study in Rabbits

IUCLID Chapter 7.3.2: Eye Irritation Study in Rabbits

IUCLID Chapter 7.6.1: Bacterial Mutation Assay in S. typhimurium and E. coli

IUCLID Chapter 7.6.1: In Vitro Cytogenetic Assay in Human Lymphocytes

 

There were various clinical observations including decreased activity, lachrymation, piloerection, salivation and upward curvature of the spine following a single oral dose of a com oil preparation of 500 mg/kg to male and female rats, but with complete recovery by day 4. All of the males and 2 of the 5 female animals showed an overall weight gain during the study. At examination post mortem, there were no treatment-related findings.

Following a single 24 hour occluded application of 500 mg/kg to male and female rat skin, applied as a paste moistened with water, there were signs of slight systemic toxicity, but with complete recovery by day 4. Slight skin irritation was seen in three males and all females, but had completely resolved by day 13. All animals showed an overall body weight gain during the study and there were no macroscopic abnormalities at examination post mortem, other than one male showing red areas in the thymus. Following a similar occluded dermal dose of 750 mg/kg, all five males were killed on days 1 or 2 and three of the females were found dead on day 2. The surviving females showed signs of slight systemic toxicity, with complete recovery by day 3, with both showing an overall weight gain during the study.

At examination post mortem, treatment-related abnormalities were observed in one male and three females, comprising eye discharge, staining of the nares and discolouration of the thymus. However, there were no macroscopic abnormalities in the surviving females.

Following a 1000 mg/kg dose, all animals were killed in extremis on day 1, with one of the males showing a discoloured thymus at examination post mortem. The acute median lethal dermal dose was estimated to be 612 mg CMP/kg for males and 709 mg/kg for females.

Following a 4 hour, occluded application of 500 mg of the test substance to rabbit skin, applied as a paste in a small volume (0.5 mL) of water, very slight erythema was observed in two of the three animals at approximately one hour after decontamination only, although this was seen in the other animal for 7 days. There was no sign of oedema in any animal. Slight thickening of the skin was observed in one animal from days 3 to 7. All signs of irritation had completely resolved by 10 days after application. Accordingly, the substance was classified as a slight irritant under the conditions of this test.

In the rabbit eye experiment, the substance was shown to be a mild irritant, although no toxicokinetic information could be concluded from this finding.

Under the conditions of the mouse local lymph node assay, the substance did not have the capacity to cause skin sensitisation when applied as 0.1 - 10% preparations in acetone. The conclusion was drawn that this test substance was unlikely to be a moderate or strong skin sensitiser.

In the 28 day dermal toxicity study in the rat, dose levels of 0, 30, 75 and 200 mg/kg/day were used, with olive oil as the dose vehicle. Twenty daily applications were made during this 28 day study. There were no mortalities during this study, no changes in organ weights and no significant perturbations in haematological or clinical chemistry parameters at any dose level. At the top dose level, male body weights were reduced and remained lower than controls throughout the study. Female body weights and food consumption in both sexes were slightly lower than controls during just the first week of the study. There were no treatment-related changes in organ weights, macro- or micropathology. Application of the 75 mg/kg/day dose level caused transient differences in food consumption and body weight in both sexes, but these did not persist beyond the first week of the study.

 

3. ABSORPTION, DISTRIBUTION & EXCRETION

In the 28-day dermal dose study, there were a few transient clinical changes indicative of systemic toxicity, being based mainly upon changes in body weights and food consumption. There was clearer evidence of the dermal penetration of the substance in the acute dermal rat study, with deaths at dose levels of 750 mg/kg and above, whereas doses of 500 mg/kg produced symptoms of slight systemic toxicity with complete recovery by day 4. Similarly, a 500 mg/kg dermal dose to rabbits produced symptoms only of slight irritation. During these various dermal studies, the absorption of the substance would have been promoted by the occlusion of the application sites.

The local lymph node assay in the mouse showed that the substance was unlikely to be a moderate or strong sensitiser, but this study did not demonstrate any potential absorption of the substance through the skin in this species.

 

4. METABOLISM

In the bacterial mutation assays in S. typhimurium and E. coli, the substance did not induce any significant reproducible increases in the observed numbers of revertant colonies in any of the tester strains used, either in the presence or absence of S9-mix. Hence, no conclusions can be drawn about the metabolism of the substance from this study.

Using pooled cultures of lymphocytes from female human donors, the clastogenic potential of the susbtance was tested over a range of concentrations up to 10 mM, the limit concentration for this assay. It was concluded that under the conditions of the assay, the substance was not clastogenic to cultured human lymphocytes treated in vitro in both the presence and absence of S9-mix. Hence no conclusion can be drawn on the metabolism of the substance from this study.

 

5. CONCLUSION

Toxicity studies have shown some evidence for the absorption of the substance following oral administration. The potential for absorption through skin was more clearly demonstrated by severe toxicity and some deaths of animals given a single dermal dose of 750 mg/kg or higher. However, a single dermal dose of 500 mg/kg to rats or rabbits produced symptoms only of mild toxicity. At sub-lethal doses, the various toxicity studies showed limited evidence of absorption with no changes in organ weights and no marked changes in haematological or clinical chemistry parameters. The only tissue to show any change was the thymus, with observations of discolouration.

An assessment of the potential absorption of the substance is also based upon its physico-chemical properties, which suggest that the intact molecule would be subject to some absorption across the gastrointestinal mucosa following oral administration.

The high aqueous solubility suggests that some absorbed substance could be excreted directly in urine. In addition, biotransformation of any absorbed molecule is also possible. The chlorine is subject to displacement by glutathione, which would involve elimination of the conjugate via bile with reabsorption of the cysteine conjugate and its subsequent N-acetylation to produce a mercapturic acid, which would be excreted in urine. Demethylation of the O-methyl group is feasible with subsequent conjugation of the resultant hydroxyl group as a glucuronide or sulphate, which would also be readily excreted. Ring hydroxylation is also possible, but may be hindered by the existing substitution of the pyrimidine ring.