(E)-N'-(2-cyano-4-(3-(1-hydroxy-2-methylpropan-2-yl)thioureido)phenyl)-N,N-dimethylformimidamide

Skin irritation / corrosion

Administrative data

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Experimental start date 04 February 2020 Experimental completion date 07 February 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2020

Report date:

2020

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.40 (In Vitro Skin Corrosion: Transcutaneous Electrical Resistance Test (TER))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine

Cas Number:

1429755-57-6

Molecular formula:

C15H12N5OS

IUPAC Name:

E-N'-{2-cyano-4-[3-(2-hydroxy-1,1-dimethylethyl)-thioureido]-phenyl}-N,N-dimethylformamidine

Specific details on test material used for the study:

Identification: SPS 5290 (Stage 3)
Batch: 80034242B
CAS Number: Unknown
Chemical Name: (E)-N'-(2-Cyano-4-(3-(1-hydroxy-2-methylpropan-2-yl)thioureido)phenyl)-N,Ndimethylformimidamide
Empirical Formula: C15H21N5OS
Molecular Weight: 319.43
Purity: 99.5%
Physical state/Appearance: Yellow crystalline powder
Expiry Date: 05 July 2020
Storage Conditions: Room temperature in the dark

In vitro test system

Test system:

human skin model

Source species:

human

Cell type:

non-transformed keratinocytes

Vehicle:

unchanged (no vehicle)

Details on test system:

EpiDerm™ Reconstructed Human Epidermis Model Kit
Supplier: MatTek In Vitro Life Sciences Laboratories
Date received: 04 February 2020
EpiDermTM Tissues (0.63cm2) lot number: 30846
Assay Medium lot number: 013020MSC
Upon receipt of the EpidermTM tissues, the sealed 24-well plate was stored in a refrigerator until use.

Main Test
Pre-Incubation
The assay medium was brought to room temperature before use. 0.9 mL of this assay medium was pipetted into the appropriate wells of two pre-labeled 6-well plates for both the 3-Minute and 60-Minute exposure periods. EpiDerm™ tissues were transferred into the 6-well plates containing the assay medium. The 6-well plates containing the EpiDerm™ samples were pre-incubated (37 °C, 5% CO2) for approximately 1 hour before dosing.

Application of Test Item and Rinsing
Before pre-incubation was complete, a 24-well plate was prepared for use as a “holding plate” for both the 3-Minute and 60-Minute exposure periods. This plate was used to maintain the viability of the tissue inserts between rinsing following chemical exposure and MTT-loading. Another 24-well plate was prepared for the MTT-loading. 300 μL of either pre-warmed assay medium (holding plate) or MTT medium (MTT-loading plate) was dispensed into each well. The two plates were placed into the incubator until required.
After pre-incubation of the EpiDerm™ tissues, the medium was aspirated and replaced with 0.9 mL of fresh assay medium. The 6-well plate for the 3-Minute exposure period was returned to the incubator, while the other was being dosed for the 60-Minute exposure. For the 60-Minute exposure period, 50 μL of sterile distilled water (negative control) was added to the first two tissues. The tissues were dosed at regular intervals to allow for the time taken to rinse each tissue following exposure and to ensure that each tissue gets an equal exposure time. 25 mg of the test item and 50 μL of 8.0 N Potassium Hydroxide (positive control) were also applied to the corresponding tissues in turn. 25 μL of sterile water was added for wetting of the test item to increase tissue surface contact. The plate was returned to the incubator (37 °C, 5% CO2) for the 60-Minute exposure period.
When dosing for the 60-Minute exposure period was complete, the same procedure was repeated for the 3-Minute exposure period. Because the exposure time was so short, the tissues were dosed at regular intervals to ensure that each tissue received an equal exposure time and to allow for the time taken to rinse each tissue following exposure. Rinsing was achieved by filling and emptying each tissue under a constant soft stream of Dulbecco’s Phosphate Buffered Saline (DPBS) (without Ca++ Mg++) for approximately 40 seconds, to gently remove any residual test item. Excess DPBS was removed by blotting the bottom of the tissue insert with tissue paper. Each tissue was placed into the prepared holding plate until all tissues were rinsed. They were then blotted and transferred to the 24-well plate prepared for MTT-loading. The plate was incubated (37 °C, 5% CO2) for 3 hours. Once the
60-Minute exposure period was complete, the same rinsing and MTT-loading procedure was repeated.
After the 3-Hour MTT incubation was complete, the tissue inserts were blotted and transferred to 24-well plates for formazan (reduced MTT) extraction. The formazan was extracted from the top and bottom of the tissue by completely immersing the tissue insert in 2 mL of isopropanol. The plate was covered with plate sealer, to prevent isopropanol evaporation, and stood overnight at room temperature, to allow extraction to proceed.
Absorbance/Optical Density Measurements
After extraction, each tissue was pierced with a pipette fitted with a 1000 μL tip and the extraction solution was forced vigorously up and down to form a homogenous solution. 3 x 200 μL aliquots of the extract were transferred to the appropriate wells of a pre-labeled 96-well plate. 200 μL of isopropanol alone was added to the three wells designated as blanks. Absorbency at 570 nm (OD570) of each well was measured using the Labtech LT-4500 microplate reader and LT-com analysis software.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

25 mg of the test item
50 μL of 8.0 N Potassium Hydroxide (positive control)
50 μL of sterile distilled water (negative control)

Duration of treatment / exposure:

3 minutes
60 minutes

Duration of post-treatment incubation (if applicable):

3 hours

Number of replicates:

Duplicate

Results and discussion

In vitro

Results

Results 1

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

3 minute mean

Value:

108.3

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Results 2

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

60 minute mean

Value:

89.7

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Other effects / acceptance of results:

Direct MTT Reduction
An assessment found the test item was able to directly reduce MTT. Therefore, an additional procedure using freeze-killed tissues was performed. However, the results obtained showed that no interference due to direct reduction of MTT occurred. It was therefore considered unnecessary to use the results of the freeze-killed tissues for quantitative correction of results or for reporting purposes.
Assessment of Color Interference with the MTT endpoint
The solution containing the test item was a yellow color, therefore additional color correction tissues were incorporated into the testing procedure. However, the results obtained showed that no color interference occurred. It was therefore considered unnecessary to use the results of the color correction tissues for quantitative correction of results or for reporting purposes.
Double Correction Check
The results of the third set of control tissues were not used to adjust the calculated correction factors derived from the color interference and MTT direct reduction controls due to no interference occurring, therefore the correction was unnecessary.
Acceptance Criteria
The mean OD570 for the negative control treated tissues was 1.416 for the 3-Minute exposure period and 1.606 for the 60-Minute exposure period. The negative control acceptance criteria were therefore satisfied.
The relative mean tissue viability for the positive control treated tissues was 4.2 % relative to the negative control following the 60-Minute exposure period. The positive control acceptance criterion was therefore satisfied.
In the range 20 to 100% viability the Coefficient of Variation between the two tissue replicates of each treatment group did not exceed 30%. The acceptance criterion was therefore satisfied.

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

In this study and under the experimental conditions reported:
The test item was considered to be non-corrosive to the skin.

Executive summary:

Introduction

The purpose of this test was to evaluate the corrosivity potential of the test item using the EpiDerm™ Human Skin Model after treatment periods of 3 and 60 minutes.

Corrosion is directly related to cytotoxicity in the EpiDerm™ tissue. Cytotoxicity is determined by the reduction of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) to formazan by viable cells in the test item treated tissues relative to the corresponding negative control. Viable cells are able to reduce MTT to formazan whereas non-viable cells cannot. The results are used to make a prediction of the corrosivity potential of the test item (increased cytotoxicity is indicative of corrosion potential).

Methods

Duplicate tissues were treated with the test item for exposure periods of 3 and 60 minutes. Negative and positive control groups were treated for each exposure period. The test item was found to have the potential to cause color interference and therefore additional tissues were incorporated for color correction purposes. An assessment of the test item’s capability to directly reduce MTT was found to directly reduce MTT and therefore, an additional procedure using freeze-killed tissues was performed. A third set of controls was included, comprising freeze-killed tissues, in order to prevent a double correction from a colored test item that also reduces MTT. At the end of the exposure period the test item was rinsed from each tissue before each tissue was taken for MTT-loading. After MTT-loading each tissue was placed in 2 mL of isopropanol for MTT extraction.

At the end of the formazan extraction period each well was mixed thoroughly and triplicate 200 μL samples were transferred to the appropriate wells of a pre-labeled 96-well plate. The optical density (OD) was measured at 570 nm (OD570).

Data are presented in the form of percentage viability (MTT reduction in the test item treated tissues relative to negative control tissues).

Results

The relative mean viabilities for each treatment group were as follows:

Exposure Period	Percentage Viability
	Negative Control	Positive Control	Test Item
3 minute	100*	5.9	108.3
60 minute	100*	4.2	89.7

*The mean viability of the negative control tissues is set at 100%

Acceptance criteria: The criteria required for acceptance of results in the test were satisfied.

Conclusion

In this study and under the experimental conditions reported:

The test item was considered to be non-corrosive to the skin.