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Toxicological information

Basic toxicokinetics

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Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2014-2015
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Cross-reference
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2014-2015
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Objective of study:
other: In vitro pilot studies for the determination of several parameter values used in ADME modelling
Qualifier:
no guideline followed
Principles of method if other than guideline:
In this study, in vitro microsomal metabolic stability, plasma protein binding and Caco-2 permeability were determined. This information is used in the physiologically based pharmacokinetic (PBPK) model, Cloe PK(TM), to simulate the predicted in vivo exposure in male and female rat at 30, 300 and 1000 mg/kg. Physical chemistry data including solubility, logP and pKa was also used for modelling and simulation.
GLP compliance:
no
Radiolabelling:
no
Details on study design:
See 'Any other information on materials and methods incl. tables'.
Metabolites identified:
not measured

1 Microsomal intrinsic clearance

The in vitro CLint of the test substance in male Wistar rat microsomes was 119 ± 2.34 μL/min/mg protein. This was characterised by >93 % depletion over 45 minutes. The in vitro CLint in female Wistar rat microsomes was 8.41 ± 3.16 μL/min/mg protein characterised by >22% depletion over 45 minutes.

In the absence of NADPH, there was approximately 10% depletion over 45 minutes in male microsomes and approximately 14% depletion over 45 minutes in female microsomes indicating the metabolism observed in microsomes is primarily P450-mediated.

In the absence of microsomes, there was <1% loss of the test substance over 45 minutes suggesting no potential chemical instability of the molecule in this matrix.

 

2 Plasma protein binding

The fraction of the test substance unbound in plasma (fup) was 0.160 ± 0.0370 in male plasma and in female plasma was 0.114 ± 0.0217. The recovery of the test substance in the incubations was 89.5 and 126%, respectively.

 

3 Caco-2 permeability

The apparent permeability (Papp) of the test substance across Caco-2 cell monolayers was 42.4 x 10-6 cms-1 ± 2.48 x 10-6. The recovery of the test substance from the incubation media was 74.9%.

Conclusions:
The results from these established and validated in vitro systems are used as parameter values in the commercially accepted physiologically based pharmacokinetic model (Cloe PK(TM)).
Executive summary:

In this study (non-GLP), in vitro microsomal metabolic stability, plasma protein binding and Caco-2 permeability were determined. This information is used in the physiologically based pharmacokinetic (PBPK) model, Cloe PKTM, to simulate the predicted in vivo exposure in male and female rat at 30, 300 and 1000 mg/kg.

The microsomal clearance assay indicated that the intrinsic clearance of the test substance in male microsomes was high with a major proportion being attributed to CYP-mediated metabolism. Therefore, the major clearance mechanism for the test substance in the model is via metabolism. The plasma protein binding test indicated that the free fraction in plasma was approximately 16% in male rats and approximately 11% in female rats.The Caro-2 permeability in vitro test indicated thatpermeability across the intestinal wall would be expected in the in vivo situation.

The results from these established and validated in vitro systems are used as parameter values in the commercially accepted physiologically based pharmacokinetic model (Cloe PKTM).

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2015
Report date:
2015

Materials and methods

Objective of study:
other: In vitro pilot studies for the determination of several parameter values used in ADME modelling
Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
Version / remarks:
22 July 2010
Deviations:
not specified
Principles of method if other than guideline:
In this study, in vitro microsomal metabolic stability, plasma protein binding and Caco-2 permeability parameters were used in the physiologically based pharmacokinetic (PBPK) model, Cloe PK(TM), to simulate the predicted in vivo exposure in male and female rat at 30, 300 and 1000 mg/kg. Physical chemistry data including solubility, logP and pKa was also used for modelling and simulation.
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
bis((1S,2R,6R,7S,8R)-11-(dichloromethylidene)-6-hydroxytricyclo[6.2.1.0²,⁷]undecan-3-one)
EC Number:
941-628-3
Cas Number:
1263184-87-7
Molecular formula:
C12H14Cl2O2
IUPAC Name:
bis((1S,2R,6R,7S,8R)-11-(dichloromethylidene)-6-hydroxytricyclo[6.2.1.0²,⁷]undecan-3-one)
Test material form:
solid
Radiolabelling:
no

Results and discussion

Preliminary studies:
The results from the in vitro testing are used as input in the ADME model.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
In vitro data indicates high permeability across the intestinal wall would be expected. The test substance would be expected to be similar to the control compound propranolol which has a predicted in vivo absorption in humans of 90%. In combination with a water solubility of 0.068 mg/mL and Log P of 2.5 the Cloe PK(TM) model predicted a high fraction absorbed across the gastrointestinal tract following a dose of 30 mg/kg of 100 % decreasing to 75 % at 300 mg/kg and 39 % at 1000 mg/kg.
Details on distribution in tissues:
The free fraction in plasma was approximately 16 % in male rats and approximately 11 % in female rats and the predicted volume of distribution at steady-state was 10 – 23 L/kg for male rats and 3.7 – 5.6 L/kg for female rats, indicating that the test substance would be expected to distribute into tissues.
Predicted tissue distribution was similar at all doses in males and females. Tissues showing higher predicted concentrations than plasma were brain (4326 – 16940 fold), adipose (29 - 144-fold), skin (2 - 3-fold), gonads, intestines, pancreas and stomach (~1.5 fold). Liver had a liver:plasma concentration ratio of 0.25 in males and 0.6 in females. All other tissues had concentrations below that in plasma. The predicted blood to plasma ratio was 0.9 suggesting there would be no real difference in plasma and blood concentrations. Note: these ratios were predicted ratios calculated at the end of the time course (i.e. 110 or 166 h following 30 mg/kg in male and female respectively, 129 or 167 h at 300 mg/kg in male and female respectively and 142 or 168 h at 3000 mg/kg in male and female respectively).
Details on excretion:
Cloe PK(TM) predicted a low percentage renal excretion of the test substance (0.03 – 0.08% in males, 0.48 – 1.2% in females) being higher in females due to a lower fraction metabolised. The intrinsic clearance of the test substance in male microsomes was high with a major proportion being attributed to CYP-mediated metabolism. Therefore, the major clearance mechanism for the test substance in the model is via metabolism. Following a dose of 30 mg/kg approximately 100 % metabolism would be anticipated over the time course of exposure in both males and females.
The percentage metabolism decreases at higher doses due to the reduced % absorbed at these doses.

Metabolite characterisation studies

Metabolites identified:
not measured
Details on metabolites:
No metabolite identification was performed during the in vitro assessment of the test substance in this study.

Bioaccessibility (or Bioavailability)

Bioaccessibility (or Bioavailability) testing results:
Predicted oral bioavailability was 6.8 – 18 % in male rats (high to low dose) despite a high fraction absorbed at the low dose. A high metabolic clearance resulted in predicted first-pass metabolism, thereby reducing the systemic exposure to the test substance.
Predicted oral bioavailability in female rats was 31 – 79 % (high to low dose) being higher than males as metabolic intrinsic clearance was lower in females.

Any other information on results incl. tables

Tables 1 and 2 show the median pharmacokinetic parameters derived from the Cloe PK(TM) simulations for the test substance following both intravenous and oral administration, respectively.

 

Table 1. Median predicted pharmacokinetic parameters for the test substance derived using Cloe PK(TM) simulating intravenous administration at doses of 30, 300 and 1000 mg/kg in male and female rats

Parameter

30 mg/kg

300 mg/kg

1000 mg/kg

Male

Female

Male

Female

Male

Female

Cmax (µg/mL)

1900

2200

19000

22000

65000

73000

AUC

(µg.h/mL)

12

58

120

580

410

1900

T ½ (h)

6.5

7.5

6.5

7.5

6.5

7.5

Vd (L/kg)

23

5.4

23

5.4

23

5.4

Total CL (mL/min/mg)

40

8.6

40

8.6

40

8.6

MRTinf(h)

1.3

4.7

1.3

4.7

1.3

4.7

Vss (L/kg)

3

2.3

3

2.3

3

2.3

Elimination

rate (h-1)

0.11

0.093

0.11

0.093

0.11

0.093

 

Table 2. Median predicted pharmacokinetic parameters for the test substance derived using Cloe PK(TM) simulating oral administration at doses of 30, 300 and 1000 mg/kg in male and female rats

Parameter

30 mg/kg

300 mg/kg

1000 mg/kg

Male

Female

Male

Female

Male

Female

Cmax (µg/mL)

0.67

8.7

3.7

53

6

83

Tmax (h)

1.1

1.4

1.6

2

0.77

0.98

AUC

(µg.h/mL)

2.3

46

17

350

28

600

T ½ (h)

11

35

12

33

11

26

Vd (L/kg)

40

24

44

22

38

18

Elimination

rate (h-1)

0.063

0.02

0.056

0.021

0.064

0.026

Bioavailability (%)

18

79

14

59

6.8

31

Fraction absorbed

1

1

0.75

0.75

0.39

0.39

Applicant's summary and conclusion

Conclusions:
This study (non GLP, based on OECD 417) based on ADME modelling predicted to have a high fraction absorbed across the gastrointestinal tract following a dose of 30 mg/kg (approx. 100%) reducing to 39% following a dose of 1000 mg/kg. Furthermore the model indicated that the test substance would be expected to be a low (female) to moderate (male) clearance compound that distributed into tissues with a mean residence time in the body of around 1 - 5 hours in vivo. The major clearance mechanism in the model is via metabolism.
Executive summary:

This study (non GLP, based on OECD 417) was designed to assess the in vivo pharmacokinetic behaviour of the test substance via an in vitro to in vivo extrapolation (IVIVE) to help put into context the findings of toxicology studies carried out separately to this report. In vitro microsomal metabolic stability, plasma protein binding and Caco-2 permeability were determined, and the data used in the physiologically based pharmacokinetic (PBPK) model, Cloe PKTM, to simulate the predicted in vivo exposure in male and female rat at 30, 300 and 1000 mg/kg. Physical chemistry data including solubility, logP and pKa was used in the model and simulation.

The test substance, when administered in vivo to male and female rats, is predicted to have a high fraction absorbed across the gastrointestinal tract following a dose of 30 mg/kg (approx. 100%) reducing to 39% following a dose of 1000 mg/kg. However, due to a hepatic first pass effect following oral administration this translates to a systemic oral bioavailability of 6.8 – 18% in male rats over this dose range. Predicted tissue distribution was similar at all doses in males and females. Tissues showing higher predicted concentrations than plasma were brain (4326 – 16940 fold), adipose (29 - 144-fold), skin (2 - 3-fold), gonads, intestines, pancreas and stomach (~1.5 fold). Liver had a liver:plasma concentration ratio of 0.25 in males and 0.6 in females. All other tissues had concentrations below that in plasma. Due to metabolic intrinsic clearance being lower in female compared to male rats oral bioavailability in female rats was predicted to range from 31 – 79%. The major clearance mechanism in the model is via metabolism.

In general in vivo the test substance would be expected to be a low (female) to moderate (male) clearance compound that distributed into tissues with a mean residence time in the body of around 1 - 5 hours.