Registration Dossier
Registration Dossier
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EC number: 814-560-6 | CAS number: 1429755-57-6
Endpoint summary
Administrative data
Description of key information
Key value for chemical safety assessment
Skin sensitisation
Link to relevant study records
- Endpoint:
- skin sensitisation: in vitro
- Type of information:
- experimental study
- Adequacy of study:
- weight of evidence
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 442D (In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method)
- Deviations:
- no
- GLP compliance:
- yes (incl. QA statement)
- Type of study:
- activation of keratinocytes
- Key result
- Remarks on result:
- no indication of skin sensitisation
- Interpretation of results:
- study cannot be used for classification
- Conclusions:
- After 48h exposure of cells with 12 concentrations of the test item, Luciferase measurements and MTT viability testing were performed.
The test item was classified as Positive according to the KeratinoSens prediction model. - Endpoint:
- skin sensitisation, other
- Type of information:
- (Q)SAR
- Adequacy of study:
- weight of evidence
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
- Justification for type of information:
- DEREK (skin sensitisation)
1 Substance
1.1 CAS number 1429755-57-6
1.2 EC number 814-560-6
1.3 Chemical name
IUPAC E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine
Other
Other
1.4 Structural formula
1.5 Structure codes
SMILES N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S
InChI 1S/C15H21N5OS/c1-15(2,9-21)19-14(22)18-12-5-6-13(11(7-12)8-16)17-10-20(3)4/h5-7,10,21H,9H2,1-4H3,(H2,18,19,22)/b17-10+
Other
Stereochemical features Not applicable
2 General Information
2.1 Date of QPRF 30 September 2020
2.2 Author and contact details Covance Laboratories Limited, London Road, Shardlow, Derbyshire, DE72 2GD
3 Prediction
3.1 Endpoint (OECD Principle 1)
Endpoint Skin Sensitisation
Dependent variable Not applicable
3.2 Algorithm (OECD Principle 2)
Model or submodel name Skin sensitisation in mammal
Model version DEREK Nexus 6.0.1, Nexus: 2.2.1.
Knowledge Base: Derek KB 2018 1.1, Version 434 from 23/11/2017
Reference to QMRF The QMRF with the identifier Q13-34-36-315 is available from the JRC QMRF inventory (http://qsardb.jrc.it/qmrf/).
Predicted values (model result) Alert matched: 836 Thiourea
Alert matched: 432 Thiol or thiol exchange agent
Alert matched: 432 Thiol or thiol exchange agent
Predicted values (comments) Skin sensitisation in mammal is at least Equivocal (There is an equal weight of evidence for and against the proposition)
Input for prediction Smiles
Calculated descriptor values Descriptor Value
LogP 0.69
LogKp -4.18
3.3 Applicability domain (OECD Principle 3)
Domains Alert: 432 Thiol or thiol exchange agent
Alert Description image
Match with query compound:
Structural analogues Examples structure provided for the alert are:
2-mercaptobenzothiazole which has been reported to be strong sensitiser in the GPMT.
3-mercaptopropane-1,2-diol reported as a skin sensitiser in GPMT
4,4'-dithiodimorpholine reported as a skin sensitiser in GPMT
morpholinyl-mercaptobenzothiazole reported as a skin sensitiser in GPMT
Domains Alert:836 Thiourea
Alert Description image
Match with query compound
Structural analogues Examples structure provided for the alert are:
diphenylthiourea reported as a skin sensitiser in GPMT
N,N'-diethylthiourea reported as a skin sensitiser in GPMT
Consideration on structural analogues Alert: 432 Thiol or thiol exchange agent and Alert:836 Thiourea. Results of test data are in concordance with predicted results
3.4 The uncertainty of the prediction (OECD principle 4)
Skin sensitisation in mammal is at least EQUIVOCAL, i.e. There is an equal weight of evidence for and against the proposition.
3.5 The chemical and biological mechanisms according to the model underpinning the predicted result (OECD principle 5)
Alert: 432 Thiol or thiol exchange agent.
This alert describes the skin sensitisation of aromatic amines and their N-protonated forms according to the toxicophore shown.
In order to elicit a sensitisation response aromatic amines require transformation to a species capable of reacting with a skin protein nucleophilic group. Two key mechanisms through which this could be achieved have been postulated, both of which may have a role to play.
Mechanism 1:
By analogy with the generally accepted mechanism for Ames test mutagenicity, it has been suggested that N-hydroxylation occurs, possibly mediated by cytochrome P450 enzymes [Westphal et al]. Subsequent O-esterification is thought to involve two principal processes; acetylation mediated by N-acetyltransferase, or sulphation mediated by sulphotransferase. Non-enzymatic cleavage can then give rise to a reactive nitrenium ion. The bioactivation of aromatic amines to the hydroxylamine has been confirmed within human keratinocytes [Reilly et al], while O-acetylation has been demonstrated in rodent skin [Kawakubo et al]. Sulphotransferases have been detected in human and rodent skin, although O-sulphation of the hydroxylamine has not been confirmed [Smith and Hotchkiss].
Mechanism 2:
In an alternative proposal, the protein-reactive species is a nitroso compound, formed by non-enzymatic autoxidation of a hydroxylamine [Naisbitt et al 2001]. Nitroso compounds have been shown to be highly reactive with thiol groups (glutathione), but unreactive towards amine groups (lysine, aniline) [Naisbitt et al 1996].
Alert:836 Thiourea
This alert covers the skin sensitisation potential of thioureas. While thiourea itself gave negative results in the GPMT [ECHA 1981], positive results have been reported for several substituted derivatives, including diethylthiourea (N,N'-diethylthiourea, DETU), diphenylthiourea (DPTU), dibutylthiourea (DBTU) and dilaurylthiourea (DLTU) [Nakamura et al, Momma et al]. Ethylene thiourea (ETU) has also produced a weakly positive response in the GPMT [Matsushita et al]. Despite activity in the GPMT, DETU, DBTU and DPTU gave negative results when tested in the LLNA [Momma et al, Samuelsson et al]. These compounds are believed to exhibit low skin penetration and as such the GPMT may be a more sensitive test than the LLNA since the former test uses intradermal, rather than topical, application. This is supported by positive results reported for DBTU, DPTU and DLTU in the sensitive LLNA, a variant of the LLNA which employs intradermal delivery [Ikarashi et al]. Human patch tests have identified several thioureas, including thiourea itself [Geier and Fuchs], DETU [Kroft and van der Valk, Liippo et al 2011], DBTU and DPTU, as potential human contact sensitisers [Liippo et al 2010].
It has been suggested that these compounds act as prohaptens rather than reacting with skin proteins directly. Metabolic oxidation of the thionocarbonyl group of thioureas may yield sulphenic (S-OH), sulphinic (-SO2H) or sulphonic acids (-SO3H) [Bergstrom et al, Kalgutkar et al]. These electrophilic metabolites are capable of reacting with nucleophilic groups in proteins. This mechanism is supported by in vitro trapping experiments using a skin-like P450 cocktail of the most common enzymes present in skin [Samuelsson et al]. Alternatively, thioureas may decompose to give electrophilic isothiocyanate compounds, although studies suggest that this is less important than metabolic activation [Samuelsson et al].
The scope of the alert is limited to thioureas where these compounds can undergo the mechanism discussed above. Both alkyl and aryl substituents are permitted based on the activity of compounds such as DETU and DPTU. Thioureas eliciting skin sensitisation in their thiol tautomeric form are covered elsewhere in the knowledge base.
4 Adequacy (Optional)
4.1 Regulatory purpose Skin sensitisation endpoint for assessing the skin sensitisation potential with in vitro and in silico methods according to ECHA Guidance, Chapter R.7a, 2016.
4.2 Approach for regulatory interpretation of the model result
Result is directly applicable since no conversion of the result is required.
4.3 Outcome Skin sensitisation in mammal is at least EQUIVOCAL. The predictive performance of this alert is considered to be high (for details, see software printout).
4.4 Conclusion The prediction is considered reliable and the result will used together with other predictions in an argument for a weight of evidence conclusion. - Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- - Principle of test: QSAR for skin sensitisation
- Short description of test conditions: n/a
- Parameters analysed / observed: QSAR for skin sensitisation - Remarks on result:
- positive indication of skin sensitisation
- Interpretation of results:
- Category 1 (skin sensitising) based on GHS criteria
- Conclusions:
- Skin sensitisation in mammal is at least EQUIVOCAL. The predictive performance of this alert is considered to be high.
The prediction is considered reliable and the result will used together with other predictions in an argument for a weight of evidence conclusion. - Endpoint:
- skin sensitisation, other
- Type of information:
- (Q)SAR
- Adequacy of study:
- weight of evidence
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
- Justification for type of information:
- DEREK (EC3, potency)
1 Substance
1.1 CAS number 1429755-57-6
1.2 EC number 814-560-6
1.3 Chemical name
IUPAC E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine
Other
Other
1.4 Structural formula
1.5 Structure codes
SMILES N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S
InChI 1S/C15H21N5OS/c1-15(2,9-21)19-14(22)18-12-5-6-13(11(7-12)8-16)17-10-20(3)4/h5-7,10,21H,9H2,1-4H3,(H2,18,19,22)/b17-10+
Other
Stereochemical features Not applicable
2 General Information General Information
2.1 Date of QPRF 30 September 2020
2.2 Author and contact details Covance Laboratories Limited, London Road, Shardlow, Derbyshire, DE72 2GD
3 Prediction
3.1 Endpoint (OECD Principle 1)
Endpoint EC3
Dependent variable Not applicable
3.2 Algorithm (OECD Principle 2)
Model or submodel name Derek EC3 Model
Model version 1.2.0
Reference to QMRF The QMRF for skin sensitisation alert with the identifier Q13-34-36-315 is available from the JRC QMRF inventory (http://qsardb.jrc.it/qmrf/). No QMRF for the EC3 model available. Further details can be obtained from https://www.lhasalimited.org/products/EC3-predictions-for-skin-sensitisation.htm
Predicted values (model result) 3.0% (moderate sensitiser)
Predicted values (comments) Based on structures triggering 432 Thiol or thiol exchange agent
Input for prediction Smiles
Calculated descriptor values Alert and fingerprints used for selecting analogues
3.3 Applicability domain (OECD Principle 3)
Domains Tautomer 2
Based on structures triggering 432 Thiol or thiol exchange agent 11/17 compounds used in calculation.
Structural analogues i. LLNA EC3 % Median: 2.9% (moderate sensitiser), Similarity: 26%
CAS 2495-37-6 Saflufenacil, CAS: 372137-35-4
ii. LLNA EC3 % Median: 0.8% (strong sensitiser) Similarity: 26%
CAS 140-11-4 Budesonide, CAS: 51333-22-3
iii. LLNA EC3 % Median: 4.3% (strong sensitiser), Similarity: 35%
iv. LLNA EC3 % Median: 15% (weak sensitiser), Similarity: 33%
Domains Tautomer 3
Based on structures triggering 432 Thiol or thiol exchange agent 10/17 compounds used in calculation.
Structural analogues i. LLNA EC3 % Median: 0.80% (stong sensitiser), Similarity: 24%
CAS 2495-37-6 Saflufenacil, CAS: 372137-35-4
ii. LLNA EC3 % Median: 2.9% (moderate sensitiser) Similarity: 22%
CAS 140-11-4 Budesonide, CAS: 51333-22-3
iii. LLNA EC3 % Median: 4.3% (strong sensitiser), Similarity: 35%
iv. LLNA EC3 % Median: 15% (weak sensitiser), Similarity: 33%
Consideration on structural analogues Alert: 432 Thiol or thiol exchange agent. (tautomer 2) Results of test data have high concordance with predicted result. There mean structural similarity is 22 % and is therefore considered low.
Alert: 432 Thiol or thiol exchange agent. (tautomer 3) Results of test data have high concordance with predicted result. There mean structural similarity is 20 % and is therefore considered low.
3.4 The uncertainty of the prediction (OECD principle 4)
DEREK assessment: Skin sensitisation in mammal is at least Equivocal, i.e. There is an equal weight of evidence for and against the proposition.
3.5 The chemical and biological mechanisms according to the model underpinning the predicted result (OECD principle 5)
Alert: 432 Thiol or thiol exchange agent.
This alert describes the skin sensitisation of aromatic amines and their N-protonated forms according to the toxicophore shown.
In order to elicit a sensitisation response aromatic amines require transformation to a species capable of reacting with a skin protein nucleophilic group. Two key mechanisms through which this could be achieved have been postulated, both of which may have a role to play.
Mechanism 1:
By analogy with the generally accepted mechanism for Ames test mutagenicity, it has been suggested that N-hydroxylation occurs, possibly mediated by cytochrome P450 enzymes [Westphal et al]. Subsequent O-esterification is thought to involve two principal processes; acetylation mediated by N-acetyltransferase, or sulphation mediated by sulphotransferase. Non-enzymatic cleavage can then give rise to a reactive nitrenium ion. The bioactivation of aromatic amines to the hydroxylamine has been confirmed within human keratinocytes [Reilly et al], while O-acetylation has been demonstrated in rodent skin [Kawakubo et al]. Sulphotransferases have been detected in human and rodent skin, although O-sulphation of the hydroxylamine has not been confirmed [Smith and Hotchkiss].
Mechanism 2:
In an alternative proposal, the protein-reactive species is a nitroso compound, formed by non-enzymatic autoxidation of a hydroxylamine [Naisbitt et al 2001]. Nitroso compounds have been shown to be highly reactive with thiol groups (glutathione), but unreactive towards amine groups (lysine, aniline) [Naisbitt et al 1996].
4 Adequacy (Optional)
4.1 Regulatory purpose Skin sensitisation endpoint for assessing the skin sensitisation potency with in silico methods according to ECHA Guidance, Chapter R.7a, 2016.
4.2 Approach for regulatory interpretation of the model result
Result is directly applicable since no conversion of the result is required.
4.3 Outcome Using the result identified from the target compound, the conclusion is an EC3 value of 3.0%.
4.4 Conclusion The prediction is considered reliable and will be used together with predictions from other models in a weight of evidence conclusion. - Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- - Principle of test: QSAR for skin sensitisation
- Short description of test conditions: n/a
- Parameters analysed / observed: QSAR for skin sensitisation - Remarks on result:
- positive indication of skin sensitisation
- Interpretation of results:
- Category 1B (indication of skin sensitising potential) based on GHS criteria
- Conclusions:
- Using the result identified from the target compound, the conclusion is an EC3 value of 3.0%.
The prediction is considered reliable and will be used together with predictions from other models in a weight of evidence conclusion. - Endpoint:
- skin sensitisation, other
- Type of information:
- (Q)SAR
- Adequacy of study:
- weight of evidence
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
- Justification for type of information:
- 1. SOFTWARE
QSAR Toolbox 4.4
2. MODEL (incl. version number)
QSAR Toolbox 4.4
Database version: 4.4
TPRF v4.4
3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S
4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
[Explain how the model fulfils the OECD principles for (Q)SAR model validation. Consider attaching the QMRF or providing a link]
see attached justificaiton
5. APPLICABILITY DOMAIN
[Explain how the substance falls within the applicability domain of the model]
see attached justification
6. ADEQUACY OF THE RESULT
[Explain how the prediction fits the purpose of classification and labelling and/or risk assessment]
Profiling with OECD Toolbox indicates that while no protein binding alert for skin sensitisation was triggered for the compound itself, Times metabolism simulator suggest SPS 5290 stage 3 to act as a pro hapten via Schiff base formation with carbonyl compounds. There is uncertainty in the model due to many category members and neighbors used for the read across being non sensitisers. - Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- - Principle of test: QSAR for skin sensitisation
- Short description of test conditions: n/a
- Parameters analysed / observed: QSAR for skin sensitisation - Remarks on result:
- positive indication of skin sensitisation
- Interpretation of results:
- Category 1 (skin sensitising) based on GHS criteria
- Conclusions:
- Profiling with OECD Toolbox indicates that while no protein binding alert for skin sensitisation was triggered for the compound itself, Times metabolism simulator suggest SPS 5290 stage 3 to act as a pro hapten via Schiff base formation with carbonyl compounds. There is uncertainty in the model due to many category members and neighbors used for the read across being non sensitisers.
- Endpoint:
- skin sensitisation, other
- Type of information:
- (Q)SAR
- Adequacy of study:
- weight of evidence
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
- Justification for type of information:
- 1. SOFTWARE
QSAR Toolbox 4.4
2. MODEL (incl. version number)
QSAR Toolbox 4.4
Database version: 4.4
TPRF v4.4
3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S
4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
[Explain how the model fulfils the OECD principles for (Q)SAR model validation. Consider attaching the QMRF or providing a link]
see attached justificaiton
5. APPLICABILITY DOMAIN
[Explain how the substance falls within the applicability domain of the model]
see attached justification
6. ADEQUACY OF THE RESULT
[Explain how the prediction fits the purpose of classification and labelling and/or risk assessment]
The positive/negative prediction with toolbox concluded the substance to be sensitising. Using the same methodology to reach this conclusion, a prediction of EC3 was also carried out. The predicted EC3 suggests the compound to be a weak sensitiser. However, it is noteworthy that two of the 5 nearest compounds to the target structure are strong and moderate sensitisers, suggesting some uncertainty in the prediction. - Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- - Principle of test: QSAR for skin sensitisation
- Short description of test conditions: n/a
- Parameters analysed / observed: QSAR for skin sensitisation - Remarks on result:
- positive indication of skin sensitisation
- Interpretation of results:
- Category 1B (indication of skin sensitising potential) based on GHS criteria
- Conclusions:
- Profiling with OECD Toolbox indicates that while no protein binding alert for skin sensitisation was triggered for the compound itself, Times metabolism simulator suggest SPS 5290 stage 3 to act as a pro hapten via Schiff base formation with carbonyl compounds. There is uncertainty in the model due to many category members and neighbors used for the read across being non sensitisers. Further to this, using the same methodology it was possible to derive a predicted EC3 value for the compound, suggesting it to be a weak sensitizer, though this prediction is similarly mared by the nearest neighbors, some of which were strong and moderate sensitisers, suggesting some uncertainty.
Referenceopen allclose all
ARE-Nrf2 Luciferase Test (KeratinoSens™) – Results summary
Study Number: SQ46WL
Test Date: 13 August 2020
SPS 5290 Stage 3 Results
Test item conc. (µM) |
0.98 |
1.95 |
3.91 |
7.81 |
15.63 |
31.25 |
62.5 |
125 |
250 |
500 |
1000 |
2000 |
Mean fold induction |
0.78 |
0.81 |
3.76 |
1.02 |
1.02 |
0.92 |
1.08 |
1.19 |
1.63 |
2.21 |
3.40 |
9.24 |
Statistically significant |
N/A |
N/A |
Yes |
N/A |
N/A |
N/A |
N/A |
N/A |
Yes |
Yes |
Yes |
Yes |
Viability (%) |
115.80 |
105.40 |
108.22 |
99.99 |
99.27 |
101.07 |
93.85 |
90.68 |
104.03 |
93.78 |
91.76 |
38.41 |
Imax |
9.24 |
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EC1.5(µM) |
214.03 |
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IC30(µM) |
1407.83 |
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IC50(µM) |
1782.70 |
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Determination criteria for the skin sensitisation potential of the test item |
Result |
Is the Imax≥1.5 fold and statistically significant |
Yes |
Is the cellular viability >70% at the EC1.5determining concentration |
Yes |
Is the EC1.5value <1000 µM |
Yes |
Is there a dose-response increase for luciferase induction |
Yes |
KeratinoSens™ prediction |
Positive |
Positive Control (cinnamic aldehyde) Results
Positive control conc. (µM) |
4 |
8 |
16 |
32 |
64 |
Mean fold induction |
1.15 |
4.79 |
2.66 |
2.79 |
7.67 |
Statistically significant |
N/A |
Yes |
Yes |
Yes |
Yes |
Viability (%) |
90.60 |
104.18 |
85.48 |
95.66 |
44.90 |
Imax |
7.67 |
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EC1.5(µM) |
4.39 |
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IC30(µM) |
N/A |
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IC50(µM) |
N/A |
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Test Acceptance Criteria |
Result |
|
Luciferase activity induction obtained with the positive control statistically significant above the threshold of 1.5 in at least one of the test concentrations |
Yes |
Pass |
Average induction of positive control at 64 µM between 2 – 8 |
Yes (7.67) |
Pass |
EC1.5of positive control within two standard deviations of the historical mean (‑2.36 to 28.67) |
Yes (4.39) |
Pass |
CV% of blank values < 20% |
No (32.3%) |
Fail |
DEREK (skin sensitisation) |
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Substance |
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1.1 |
CAS number |
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1429755-57-6 |
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EC number |
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814-560-6 |
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1.3 |
Chemical name |
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IUPAC |
E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine |
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Other |
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Other |
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1.4 |
Structural formula |
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1.5 |
Structure codes |
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SMILES |
N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S |
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InChI |
1S/C15H21N5OS/c1-15(2,9-21)19-14(22)18-12-5-6-13(11(7-12)8-16)17-10-20(3)4/h5-7,10,21H,9H2,1-4H3,(H2,18,19,22)/b17-10+ |
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Other |
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Stereochemical features |
Not applicable |
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2 |
General Information |
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2.1 |
Date of QPRF |
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30 September 2020 |
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2.2 |
Author and contact details |
Covance Laboratories Limited, London Road, Shardlow, Derbyshire, DE72 2GD |
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3 |
Prediction |
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3.1 |
Endpoint (OECD Principle 1) |
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Endpoint |
Skin Sensitisation |
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Dependent variable |
Not applicable |
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3.2 |
Algorithm (OECD Principle 2) |
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Model or submodel name |
Skin sensitisation in mammal |
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Model version |
DEREK Nexus 6.0.1, Nexus: 2.2.1. |
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Reference to QMRF |
The QMRF with the identifier Q13-34-36-315 is available from the JRC QMRF inventory (http://qsardb.jrc.it/qmrf/). |
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Predicted values (model result) |
Alert matched: 836 Thiourea Alert matched: 432 Thiol or thiol exchange agent Alert matched: 432 Thiol or thiol exchange agent |
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Predicted values (comments) |
Skin sensitisation in mammal is at least Equivocal (There is an equal weight of evidence for and against the proposition) |
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Input for prediction |
Smiles |
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Calculated descriptor values |
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3.3 |
Applicability domain (OECD Principle 3) |
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Domains |
Alert: 432 Thiol or thiol exchange agent Alert Description image Match with query compound:
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Structural analogues |
Examples structure provided for the alert are: 2-mercaptobenzothiazole which has been reported to be strong sensitiser in the GPMT. 3-mercaptopropane-1,2-diol reported as a skin sensitiser in GPMT 4,4'-dithiodimorpholine reported as a skin sensitiser in GPMT morpholinyl-mercaptobenzothiazole reported as a skin sensitiser in GPMT |
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Domains |
Alert:836 Thiourea Alert Description image Match with query compound
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Structural analogues |
Examples structure provided for the alert are: diphenylthioureareported as a skin sensitiser in GPMT N,N'-diethylthioureareported as a skin sensitiser in GPMT |
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Consideration on structural analogues |
Alert: 432 Thiol or thiol exchange agent and Alert:836 Thiourea. Results of test data are in concordance with predicted results |
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3.4 |
The uncertainty of the prediction (OECD principle 4) |
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Skin sensitisation in mammal is at least EQUIVOCAL, i.e. There is an equal weight of evidence for and against the proposition. |
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3.5 |
The chemical and biological mechanisms according to the model underpinning the predicted result (OECD principle 5) |
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Alert: 432 Thiol or thiol exchange agent. This alert describes the skin sensitisation of aromatic amines and their N-protonated forms according to the toxicophore shown.
In order to elicit a sensitisation response aromatic amines require transformation to a species capable of reacting with a skin protein nucleophilic group. Two key mechanisms through which this could be achieved have been postulated, both of which may have a role to play.
Mechanism 1: By analogy with the generally accepted mechanism for Ames test mutagenicity, it has been suggested that N-hydroxylation occurs, possibly mediated by cytochrome P450 enzymes [Westphal et al]. Subsequent O-esterification is thought to involve two principal processes; acetylation mediated by N-acetyltransferase, or sulphation mediated by sulphotransferase. Non-enzymatic cleavage can then give rise to a reactive nitrenium ion. The bioactivation of aromatic amines to the hydroxylamine has been confirmed within human keratinocytes [Reilly et al], while O-acetylation has been demonstrated in rodent skin [Kawakubo et al]. Sulphotransferases have been detected in human and rodent skin, although O-sulphation of the hydroxylamine has not been confirmed [Smith and Hotchkiss].
Mechanism 2: In an alternative proposal, the protein-reactive species is a nitroso compound, formed by non-enzymatic autoxidation of a hydroxylamine [Naisbitt et al 2001]. Nitroso compounds have been shown to be highly reactive with thiol groups (glutathione), but unreactive towards amine groups (lysine, aniline) [Naisbitt et al 1996].
Alert:836 Thiourea This alert covers the skin sensitisation potential of thioureas. While thiourea itself gave negative results in the GPMT [ECHA 1981], positive results have been reported for several substituted derivatives, including diethylthiourea (N,N'-diethylthiourea, DETU), diphenylthiourea (DPTU), dibutylthiourea (DBTU) and dilaurylthiourea (DLTU) [Nakamura et al, Momma et al]. Ethylene thiourea (ETU) has also produced a weakly positive response in the GPMT [Matsushita et al]. Despite activity in the GPMT, DETU, DBTU and DPTU gave negative results when tested in the LLNA [Momma et al, Samuelsson et al]. These compounds are believed to exhibit low skin penetration and as such the GPMT may be a more sensitive test than the LLNA since the former test uses intradermal, rather than topical, application. This is supported by positive results reported for DBTU, DPTU and DLTU in the sensitive LLNA, a variant of the LLNA which employs intradermal delivery [Ikarashi et al]. Human patch tests have identified several thioureas, including thiourea itself [Geier and Fuchs], DETU [Kroft and van der Valk, Liippo et al 2011], DBTU and DPTU, as potential human contact sensitisers [Liippo et al 2010].
It has been suggested that these compounds act as prohaptens rather than reacting with skin proteins directly. Metabolic oxidation of the thionocarbonyl group of thioureas may yield sulphenic (S-OH), sulphinic (-SO2H) or sulphonic acids (-SO3H) [Bergstrom et al, Kalgutkar et al]. These electrophilic metabolites are capable of reacting with nucleophilic groups in proteins. This mechanism is supported by in vitro trapping experiments using a skin-like P450 cocktail of the most common enzymes present in skin [Samuelsson et al]. Alternatively, thioureas may decompose to give electrophilic isothiocyanate compounds, although studies suggest that this is less important than metabolic activation [Samuelsson et al].
The scope of the alert is limited to thioureas where these compounds can undergo the mechanism discussed above. Both alkyl and aryl substituents are permitted based on the activity of compounds such as DETU and DPTU. Thioureas eliciting skin sensitisation in their thiol tautomeric form are covered elsewhere in the knowledge base. |
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4 |
Adequacy (Optional) |
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4.1 |
Regulatory purpose |
Skin sensitisation endpoint for assessing the skin sensitisation potential with in vitro and in silico methods according to ECHA Guidance, Chapter R.7a, 2016. |
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4.2 |
Approach for regulatory interpretation of the model result |
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Result is directly applicable since no conversion of the result is required. |
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4.3 |
Outcome |
Skin sensitisation in mammal is at least EQUIVOCAL. The predictive performance of this alert is considered to be high (for details, see software printout). |
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4.4 |
Conclusion |
The prediction is considered reliable and the result will used together with other predictions in an argument for a weight of evidence conclusion. |
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DEREK (EC3, potency) |
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1 |
Substance |
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1.1 |
CAS number |
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1429755-57-6 |
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1.2 |
EC number |
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814-560-6 |
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1.3 |
Chemical name |
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IUPAC |
E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine |
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Other |
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Other |
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1.4 |
Structural formula |
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1.5 |
Structure codes |
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SMILES |
N#Cc1cc(ccc1(N=CN(C)C))NC(NC(C)(C)CO)=S |
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InChI |
1S/C15H21N5OS/c1-15(2,9-21)19-14(22)18-12-5-6-13(11(7-12)8-16)17-10-20(3)4/h5-7,10,21H,9H2,1-4H3,(H2,18,19,22)/b17-10+ |
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Other |
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Stereochemical features |
Not applicable |
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2 |
General Information |
General Information |
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2.1 |
Date of QPRF |
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30 September 2020 |
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2.2 |
Author and contact details |
Covance Laboratories Limited, London Road, Shardlow, Derbyshire, DE72 2GD |
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3 |
Prediction |
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3.1 |
Endpoint (OECD Principle 1) |
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Endpoint |
EC3 |
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Dependent variable |
Not applicable |
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3.2 |
Algorithm (OECD Principle 2) |
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Model or submodel name |
Derek EC3 Model |
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Model version |
1.2.0 |
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Reference to QMRF |
The QMRF for skin sensitisation alert with the identifier Q13-34-36-315 is available from the JRC QMRF inventory (http://qsardb.jrc.it/qmrf/). No QMRF for the EC3 model available. Further details can be obtained from https://www.lhasalimited.org/products/EC3-predictions-for-skin-sensitisation.htm |
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Predicted values (model result) |
3.0% (moderate sensitiser) |
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Predicted values (comments) |
Based on structures triggering 432 Thiol or thiol exchange agent |
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Input for prediction |
Smiles |
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Calculated descriptor values |
Alert and fingerprints used for selecting analogues |
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3.3 |
Applicability domain (OECD Principle 3) |
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Domains |
Tautomer 2 Based on structures triggering 432 Thiol or thiol exchange agent 11/17 compounds used in calculation. |
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Structural analogues |
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Domains |
Tautomer 3 Based on structures triggering 432 Thiol or thiol exchange agent 10/17 compounds used in calculation. |
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Structural analogues |
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Consideration on structural analogues |
Alert: 432 Thiol or thiol exchange agent. (tautomer 2) Results of test data have high concordance with predicted result. There mean structural similarity is 22 % and is therefore considered low. Alert: 432 Thiol or thiol exchange agent. (tautomer 3) Results of test data have high concordance with predicted result. There mean structural similarity is 20 % and is therefore considered low. |
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3.4 |
The uncertainty of the prediction (OECD principle 4) |
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DEREK assessment: Skin sensitisation in mammal is at least Equivocal, i.e. There is an equal weight of evidence for and against the proposition. |
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3.5 |
The chemical and biological mechanisms according to the model underpinning the predicted result (OECD principle 5) |
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Alert: 432 Thiol or thiol exchange agent. This alert describes the skin sensitisation of aromatic amines and their N-protonated forms according to the toxicophore shown.
In order to elicit a sensitisation response aromatic amines require transformation to a species capable of reacting with a skin protein nucleophilic group. Two key mechanisms through which this could be achieved have been postulated, both of which may have a role to play.
Mechanism 1: By analogy with the generally accepted mechanism for Ames test mutagenicity, it has been suggested that N-hydroxylation occurs, possibly mediated by cytochrome P450 enzymes [Westphal et al]. Subsequent O-esterification is thought to involve two principal processes; acetylation mediated by N-acetyltransferase, or sulphation mediated by sulphotransferase. Non-enzymatic cleavage can then give rise to a reactive nitrenium ion. The bioactivation of aromatic amines to the hydroxylamine has been confirmed within human keratinocytes [Reilly et al], while O-acetylation has been demonstrated in rodent skin [Kawakubo et al]. Sulphotransferases have been detected in human and rodent skin, although O-sulphation of the hydroxylamine has not been confirmed [Smith and Hotchkiss].
Mechanism 2: In an alternative proposal, the protein-reactive species is a nitroso compound, formed by non-enzymatic autoxidation of a hydroxylamine [Naisbitt et al 2001]. Nitroso compounds have been shown to be highly reactive with thiol groups (glutathione), but unreactive towards amine groups (lysine, aniline) [Naisbitt et al 1996]. |
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4 |
Adequacy (Optional) |
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4.1 |
Regulatory purpose |
Skin sensitisation endpoint for assessing the skin sensitisation potency with in silico methods according to ECHA Guidance, Chapter R.7a, 2016. |
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4.2 |
Approach for regulatory interpretation of the model result |
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Result is directly applicable since no conversion of the result is required. |
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4.3 |
Outcome |
Using the result identified from the target compound, the conclusion is an EC3 value of 3.0%. |
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4.4 |
Conclusion |
The prediction is considered reliable and will be used together with predictions from other models in a weight of evidence conclusion. |
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Endpoint conclusion
- Endpoint conclusion:
- adverse effect observed (sensitising)
Respiratory sensitisation
Endpoint conclusion
- Endpoint conclusion:
- no study available
Justification for classification or non-classification
Introduction
The prediction of the skin sensitising potential ofSPS 5290 stage 3was performed with BIOVIA Discovery Studio (TOPKAT) 2020, VEGA NIC 1.1.5 (CAESAR, IRFMN/JRC), OECD QSAR Toolbox 4.5, Toxtree 3.1.0 and DEREK Nexus 6.0.1. The TOPKAT model for skin sensitisation was extended by including 70 compounds from the Covance database. The model statistics are reported in section Information to Extended TOPKAT Model.
The prediction results for SPS 5290 stage 3 are detailed in the (Q)SAR prediction reporting formats (QPRFs). Reliability is assigned to each prediction by expert judgement considering similar structures in the data set, prediction statistics, the applicability domain and alerts, where applicable. For details, it is referred to the QPRFs. Toxtree is based on classification trees and does not provide such information and thus no reliability is assigned. All original model results are presented in the software printout section.
Appraisal of (Q)SAR Modelling
TOPKAT predicted SPS 5290 stage 3 not to be sensitising however considerations on structural similar compounds in the training set and prediction statistics indicate no confidence in the prediction.
CAESAR predicted SPS 5290 stage 3 to be sensitising. The query compound is however out of the applicability domain of the model and the prediction not considered reliable.
The query compound was predicted to be sensitising by the IRFMN/JRC model. The query compound is however out of the applicability domain of the model and the prediction not considered reliable.
Table1 Prediction Results
Model |
Prediction result |
Reliability |
TOPKAT |
Not sensitising |
Not reliable |
CAESAR (VEGA) |
Sensitising |
Not reliable |
IRFMN/JRC (VEGA) |
Sensitising |
Not reliable |
OECD Toolbox |
Sensitising |
Low |
OECD Toolbox (EC3) |
29.6 % (weak senitiser) |
Low |
DEREK |
Skin sensitisation in mammal is PLAUSIBLE |
Not applicable |
DEREK (EC3) |
3.0% (moderate sensitiser) |
Not applicable |
Toxtree |
Alert for Acyl Transfer agent |
Not applicable |
Profiling with OECD Toolbox indicates that while no protein binding alert for skin sensitisation was triggered for the compound itself,Times metabolism simulator suggest SPS 5290 stage 3 to act as a pro hapten via Schiff base formation with carbonyl compounds.There is uncertainty in the model due to many category members and neighbors used for the read across being non sensitisers. Further to this, using the same methodology it was possible to derive a predicted EC3 value for the compound, suggesting it to be a weak sensitizer, though this prediction is similarly mared by the nearest neighbors, some of which were strong and moderate sensitisers, suggesting some uncertainty.
Derek predicted SPS 5290 stage 3 to be sensitizing. Derek identified two alerts based on the structural features of the substance, namely the substance can tautomerise to contain a thiol or thiourea.The mechanism of skin sensitisation by thiols (R2 = H) is proposed to be nucleophilic attack of the thiol on disulphide bonds in the skin proteins to form a new disulphide bridge.Thiol compounds are proposed to act as prohaptens rather than reacting with skin proteins directly.Derek was also able to predict an EC3 value based on the thiol alert, predicting the compound to be a moderate sensitizer with the two nearest compounds being moderate and strong sensitisers, thus a similar uncertainty to that of the toolbox prediction presents itself.
Conclusion
With the models being used generally considered to be either of
low reliability, or possessing some degree of uncertainty, while there
is an argument for a weight of evidence, the discussed reliability of
the predictions leaves low confidence in the conclusions. The prediction
is therefore considered unreliable and further in vitro / in chemico testing
was recommended.
A further OECD 442D study (SQ46WL) was performed which
displayed positive results, lending some confidence to the predictions
and overall weight of evidence. A further OECD 442E study is ongoing for
further confirmation.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.
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