N-[(1R)-2-[(Methylsulfonyl)oxy]-1-phenylethyl]carbamic acid 1,1-dimethylethyl ester

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vitro

Type of information:

experimental study

Adequacy of study:

key study

Study period:

3 October, 2018 - 9 January, 2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2019

Report date:

2019

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 442D (In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method)

GLP compliance:

not specified

Type of study:

other: KeratinoSens assay (Luciferase Test Method)

Justification for non-LLNA method:

The Induction of Antioxidant-Response-Element Dependent Gene Activity in the Keratinocyte ARE-Reporter Cell Line KeratinoSens skin sensitization assay is a high-throughput cell-based in vitro test to screen for the skin sensitization potential of chemicals.

Test material

Test material information

Constituent 1

Reference substance name:

tert-butyl N-[(1R)-2-(methanesulfonyloxy)-1-phenylethyl]carbamate

EC Number:

855-580-5

Cas Number:

102089-75-8

Molecular formula:

C14H21NO5S

IUPAC Name:

tert-butyl N-[(1R)-2-(methanesulfonyloxy)-1-phenylethyl]carbamate

Test material form:

solid: particulate/powder

In vitro test system

Details on the study design:

Receipt of Skin Sensitization Assay Reagents:
Reagents used for the skin sensitization bioassay were inspected upon receipt and stored according to the manufacturer’s instructions.

Cell Thawing Procedure:
A cryovial of the cryo preserved KeratinoSens cells was thawed in a water bath at approximately 37ºC (in a beaker containing 70% ethanol). Once thawed, the cryovial was immediately decontaminated with 70% ethanol and placed in a laminar flow hood. The cells were added to a sterile conical tube and diluted by slowly adding 9 mL pre-warmed Assay Medium. The cells were then centrifuged at approximately 200 x g for 5 minutes at room temperature. The supernatant was aspirated, the pellet was re-suspended in approximately 15 mL of fresh pre-warmed Assay Medium, and then transferred into a T75 tissue-culture flask. The flask was then incubated at 37 ± 1ºC, 90 ± 10% humidity, and 5.0 ± 1% CO2in air (standard culture conditions),until the KeratinoSens cells reached approximately 60% to 90% confluence.

Routine Culturing of the KeratinoSens Cells:
When the cultures reached approximately 60 to 90% confluence, they were removed from the flask by trypsinization. The medium was aspirated and the cell sheet rinsed twice with approximately 10mL of CMF-DPBS containing 0.05% EDTA. One mL of trypsin/EDTA was added to cover the cell sheet. The flask was then placed into the incubator and incubated at standard culture conditions for 6-8 minutes, or until the cells became dislodged. When more than 50% of the cells became dislodged, the flask was rapped sharply against the palm of the hand. Then approximately 7 mL of Maintenance Medium was added to each T75 flask to obtain a single cell suspension and cells passaged at appropriate densities. The KeratinoSens cells were routinely passaged every 2-4 days.

Subculture of KeratinoSens Cells into 96-Well Plates:
The KeratinoSens cells were subcultured into transparent Costar 96-well plates or white-walled Perkin Elmer plates when the flasks were approximately 60 to 90% confluent. The flasks were rinsed and trypsinized as previously described. The cells were resuspended in 5 mL of Assay Medium per flask. The concentration of cells in suspension was determined using a Coulter Counter. A cell suspension of 1.0 x 105 cells/mL in Assay Medium was prepared. One hundredμL of the cell suspension was added to all but one well designated as a blank well (H12). The stock cell suspension was mixed often to ensure a uniform distribution of cells into each well.

Three white-walled and one transparent plate were seeded for each test article replicate set (definitive trials).The plates were incubated for approximately 24 hours at standard culture conditions. The cultures seeded into the clear plates were examined under a phase contrast microscope and evaluated for uniform seeding and confluence prior to treating the cells with the test articles or positive control.

Solubility Determination:
The solubility of the test articles were tested in DMSO on the day of the initial definitive assay (at the highest 100X concentration of 200 mM). The 200mM dosing solutions for test articles were described as clear colorless non-viscous solutions.

MTT Direct Reduction Test:
The ability of the test articles to directly reduce MTT was assessed at the same time of test article treatment in the definitive assays. A 1.0 mg/mL MTT solution was prepared by dissolving a10 mg/mL stock solution of MTT into warm MTT Addition Medium. Approximately 100 μL of the 100X (200 mM) test article concentration in DMSO was added to 1 mL of the MTT solution and then incubated in the dark at 37ºC for one to three hours. One hundred μL of a negative control (e.g. DMSO) was tested concurrently. If the MTT solution color turned blue/purple, the test article was presumed to have reduced the MTT. None of the test articles, turned the MTT solution color blue/purple. Therefore, the test articles, do not directly reduce MTT.

Controls:
Each assay plate included a range of doses of the positive control, Cinnamic Aldehyde (Sigma). A 100X concentration of positive control was prepared by weighing an appropriate amount of Cinnamic Aldehyde into a pre-labeled conical tube and adding the necessary amount of DMSO to prepare a 64,000 μM dilution. The 64,000 μM dilution was further diluted 1:10 in DMSO to prepare a 6,400 μM 100X stock concentration. The final 1X concentrations of the positive control were 64, 32, 16, 8, and 4 μM. The solvent control for the test articles and the positive control was 1% DMSO in the dilution solvent (1% DMEM.) Each plate included a set of 6 solvent control wells.

Testing Concentrations:
The test articles had defined molecular weights provided by the Sponsor,and were diluted based on molarity. The 100 X stock dilution was prepared to a top concentration of 200 mM. The final 1X tested concentrations were 0.977, 1.95, 3.91, 7.81, 15.6, 31.3, 62.5, 125, 250, 500, 1000, and 2000 μM.

Definitive Assays:
The test article was tested in three independent definitive assays. Each definitive assay included a set of 4 plates (3 for gene induction, 1 for cytotoxicity assessment). Each plate tested a range of 12 dosing concentrations for the test article. Each plate also included 5 wells designated for the positive control (tested over a range of 5 dosing concentrations), 6 wells designated as the DMSO solvent control, and 1 well which was left blank. After approximately 24 hours of incubation, the Assay Medium was removed from the cells. The plates were decanted and gently blotted on sterile paper towels. One hundred and fifty microliters of fresh pre-warmed 1% DMEM were added to all wells, including the blank. The plates were returned to the incubator until the dosing was initiated.For the test article, twelve decreasing doses were selected for the assay (test articles were diluted to a final concentration of 200 mMin DMSO). For the positive control, 5 decreasing doses were prepared. For each experiment, the positive control (5 doses), and the solvent control, a 100X DMSO master plate was made, followed by a 4X Master Plate. When added to the 150μL of 1% DMEM already in each well, the addition of the 50 μL 4X dose brought the final dose on the plates to 1X.

Visual Observations:
After approximately 48 hours of post-treatment incubation, visual observations of the cultures were performed for the cytotoxicity plate and recorded. At the highest testing concentrations, a large amount of precipitate formation precluded observation of cells dosed with the test article in the B2 trial.

Treatment Termination & Luciferase Induction Determination:
After 48 ±1 hours of exposure, each white-walled culture plate was removed from the incubator and allowed to equilibrate to room temperature for at least 30 minutes.Once at room temperature, the treatment medium was decanted from each plate. The cultures were rinsed with 250μL of CMF-DPBS (room temperature), the CMF-DPBS rinsate was decanted from the wells, and the plates were gently blotted onto paper towels.Fifty microliters of CMF-DPBS was added to each well followed by fifty microliters of ONE-Glo™ Reagent. The plates remained at room temperature in the dark for at least 5 minutes before being read by the luminometer. The plates were read within 45 minutes of addition of the ONE-Glo™ Reagent. The luminescence determination of each plate was performed by a Berthold Detection Systems luminometer initiated from an IBM-PC hosting the Windows-based Simplicity™ software. The light intensity in each well was measured at 565 nm in the form of relative light units (RLUs).

Treatment Termination:
Cytotoxicity Using the MTT Endpoint A 0.59 mg/mLMTT solution was prepared in 1% DMEM and used within 2 hours. After 48 ±1 hours, the clear 96-well plates designated for the MTT endpoint were decanted and gently blotted on paper towels. No rinsing was performed. Two hundred μL of 1% DMEM containing 0.59 mg/mL MTT was added to each well. The plate was incubated with a plate seal at standard culture conditions for approximately 4 hrs.After approximately 4 hours, the MTT solution was decanted, the plate was blotted, and 200 μL of 10% SLS was added to each well. The plate was covered with a plate seal and incubated at standard culture conditions overnight.After the overnight incubation, each plate was placed on a plate shaker and shaken for at least 20 minutes at room temperature. The absorbance at 570 nm (OD570) of each well was measured with a Molecular Devices Vmax plate reader.

Data Analysis:
For each set of up to seven test articles, a copy of the standard data file, provided by Givaudan, was made (i.e. 3 trials, each with 4 plates per trial-3 plates for the luciferase induction and 1 plate for MTT). Raw data from the luminometer was transferred directly from the luminometer software into the designated Excelspreadsheet for luminescence analyses. Raw data from the Vmax was transferred into the designated Excelspreadsheet for cytotoxicity analyses.The data file automatically calculated the gene induction and the wells with statistically significant induction over a given threshold (default value set to 1.5 = 50% enhanced gene activity). Furthermore the maximal induction (Imax), the concentration for maximal gene induction (CImax) and the EC1.5value (concentration for induction above threshold), both with linear and log-linear extrapolation, was calculated similar to the LLNA (Local Lymph Node Assay). Relative survival (viability) was obtained by comparing the amount of MTT conversion by test article treated groups compared to the associated solvent treated group on the same plate. The Givaudan Excel file calculates an IC50 value for each test article. The IC50 is determined by averaging the viability percentage of each concentration for the 3 definitive assays and then calculating by linear interpolation the IC50 concentration which results in 50% reduced cell viability using the concentration and viability percentage below and above 50% viability.A summary of the results from the 3 definitive assays was calculated. The luciferase induction and cytotoxicity data were plotted on the graphs. For the luciferase induction, the fold gene induction (as compared to the solvent controls) was plotted over the test article concentration. For the cytotoxicity, the % viability (as compared to the solvent controls) was plotted over the test article concentration.

Results and discussion

Positive control results:

The positive control cinnamic aldehyde ha a mean EC 1.5 (μM) of 9.83 and a Mean IC50 (μM) of >64 and was considered to be a sensitizer.

In vitro / in chemico

Results

Results 1

Key result

Parameter:

other: Mean CImax (μM)

Value:

2 000

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

positive indication of skin sensitisation

Results 2

Key result

Parameter:

other: Mean Imax

Value:

4.15

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

positive indication of skin sensitisation

Results 3

Key result

Parameter:

other: Mean IC50 (μM)

Value:

2 000

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

positive indication of skin sensitisation

Results 4

Key result

Parameter:

other: Mean EC 1.5 (μM)

Value:

69.71

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

positive indication of skin sensitisation

Applicant's summary and conclusion

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

According to the current prediction model, the test article was predicted to be a sensitizer.