N2-Isobutyryl-5′-O-(4,4′-dimethoxytrityl)-2′-deoxyguanosine-3′-O-[O-(2-cyanoethyl)-N,N′-diisopropylphosphoramidite]

Endpoint summary

Description of key information

No data is available for Guanosine, 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxy-N-(2-methyl-1-oxopropyl)-, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] (target substance). Thus, available data from a suitable read-across partner was used to assess the potential to induce skin sensitisation of the target substance. The read across partner (CAS 98796-51-1), a related phosphoramidite, differs only in the nucleoside moiety (guanosine replaced by thymidine).

The skin sensitisation potential of the read across partner 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] was assessed in an in vivo LLNA study conducted according to OECD 429. Based on the results, the source substance can be considered as a non-skin sensitizer.

Furthermore, supporting information of the skin sensitisation potential of the target substance was predicted by QSAR, using the Skin Sensitisation models CAESAR 2.1.6 and IRFMN/JRC 1.0.0, which are implemented in the QSAR tool VEGA (core version 1.2.8.). Both QSAR models gave contradictory predictions. In the model CAESAR 2.1.6 the prediction was negative (non-sensitizer) and in the IRFMN/JRC 1.0.0 model the prediction was positive (sensitizer). But, in both models the substance was not within the applicability domain and thus the predictions must be considered as not reliable.

Based on the available data, the target substance is considered as not skin sensitising and no classification is warranted in accordance with CLP regulation 1272/2008.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

For details and justification of read-across please refer to the report attached in section 13 of IUCLID.

Reason / purpose for cross-reference:

read-across source

Positive control results:

α-hexyl cinnamaldehyde dissolved in acetone/olive oil (4+1 v/v) was used as a positive control. The positive control substance exceeded the stimulation index of 3 confirming the sensitivity and reliability of the experimental technique (see Table 2 in box "Any other information on results").

Key result

Parameter:

SI

Remarks:

mean of five animals

Value:

1.8

Test group / Remarks:

5%

Key result

Parameter:

SI

Remarks:

mean of five animals

Value:

1.4

Test group / Remarks:

10%

Key result

Parameter:

SI

Remarks:

mean of five animals

Value:

2

Test group / Remarks:

25%

Key result

Parameter:

SI

Remarks:

mean of five animals

Value:

1.8

Test group / Remarks:

50%

Cellular proliferation data / Observations:

DETAILS ON STIMULATION INDEX CALCULATION
- Please see Table 2 in box "Any other information on results incl. Tables".

EC3 CALCULATION
- The EC3 value could not be calculated, since all S.I.´s are below the threshold value of 3.

CLINICAL OBSERVATIONS:
- No deaths occured during the study period. No signs of systemic toxicity were observed during the study period. From day 1 to 6, the animals showed an erythema of the ear skin (Score 1 to 2). Additionally, scaly ears and fur loss was observed.

BODY WEIGHTS:
- The body weight of the animals, recorded prior to the first application and prior to treatment with 3HTdR, was within the range commonly recorded for animals of this strain and age.

Results of vehicle and dose selection:

Solubility test:

The maximum concentration of test item which could be technically used was a 50% solution in DMF.

Pre-test: Irritation and toxicity test:

Two mice were treated by (epidermal) topical application to the dorsal surface of each ear with test item concentrations of 25 and 50% once daily each on three consecutive days. At the tested concentrations the animals did not show any signs of systemic toxicity. From day 2 to 6, the animals showed an erythema of the ear skin (Score 1 to 2). Additionally, fur loss, stiffened ears, scaly ears and erythema of scalp were observed in the animal treated with the high dose of the test item. In the animal treated with the low dose, substance residuals and scaly ears were observed. A maximum increase in ear thickness of 10.4% (animal 1) and 7.5 % (animal 2) was observed. No excessive increase in ear weights was observed in both animals.

Results of the main study:

Table 2: Results of the positive control group

Test item (alpha-Hexylcinnamaldehyde) Concentration [%]	Group	Result Stimulation Index
-	background	-
-	background	-
0	1	1.00
5	2	1.68
10	3	1.78
25	4	8.19

Table 3: Results of the main experiment

						Group calculation
Test item (DMT-dT-Phosphoramidite) concentration [%]	Group Number	Animal Number	DPM values measured	DPM−BG per animal (2 lymph nodes)	Stimulation Index	Mean DPM per animal (2 lymph nodes)	standard deviation	Stimulation Index
-	-	background 1	13	-	-	-	-	-
-	-	background 2	21	-	-	-	-	-
Vehicle Control Group (DMF)	1	1	1457	1440	-	2378.0	709.0	1.0
	1	2	2352	2335	-
	1	3	2588	2571	-
	1	4	3414	3397	-
	1	5	2164	2147	-
5% DMT-dT-Phosphoramidite	2	6	3310	3293	1.4	4323.0	1598.8	1.8
	2	7	2841	2824	1.2
	2	8	3492	3475	1.5
	2	9	6526	6509	2.7
	2	10	5531	5514	2.3
10% DMT-dT-Phosphoramidite	3	11	1863	1846	0.8	3287.8	1085.6	1.4
	3	12	3225	3208	1.3
	3	13	2798	2781	1.2
	3	14	4716	4699	2.0
	3	15	3922	3905	1.6
25% DMT-dT-Phosphoramidite	4	16	2049	2032	0.9	4849.0	1867.8	2.0
	4	17	4839	4822	2.0
	4	18	4394	4377	1.8
	4	19	6138	6121	2.6
	4	20	6910	6893	2.9
50% DMT-dT-Phosphoramidite	5	21	2528	2511	1.1	4270.4	1302.9	1.8
	5	22	5766	5749	2.4
	5	23	3460	3443	1.4
	5	24	5165	5148	2.2
	5	25	4518	4501	1.9

Interpretation of results:

GHS criteria not met

Conclusions:

In conclusion, in a mouse local lymph node assay, the test item DMT-dT-Phosphoramidite is not to be considered a skin sensitizer under the test conditions of this study.

Executive summary:

In a dermal sensitization study conducted according to OECD 429, five young adult female CBA/CaOlaHsd mice per dose group were dermally exposed to DMT-dT-Phosphoramidite in DMF at concentrations of 5%, 10% and 25% and 50% (w/w) by topical application to the dorsum of each ear for three consecutive days and observed until day 6 in a local lymph node assay (LLNA). α-hexyl cinnamaldehyde dissolved in acetone/olive oil (4+1 v/v) was used as a positive control. The positive control substance exceeded the stimulation index of 3 at the highest dose tested (25%).

No signs of systemic toxicity were observed during the study period. From day 1 to 6, the animals showed an erythema of the ear skin (Score 1 to 2). Additionally, scaly ears and fur loss was observed.

No mortality or effects on body weight occurred during the study. None of the four tested concentrations exceeded a stimulation index of 3 (1.8 (5%), 1.4 (10%) and 2.0 (25%) and 1.8 (50%)). As a consequence, an EC3 value could not be calculated. In this study, DMT-dT-Phosphoramidite is not a dermal sensitizer.

This information is used in a read-across approach in the assessment of the target substance.

For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available data, the test item is considered as not skin sensitising and no classification is warranted in accordance with CLP regulation 1272/2008.