rac-(1R,4S,4aR,8R,8aS)-9-(dichloromethylidene)-8-hydroxyoctahydro-1,4-methanonaphthalen-5(1H)-one

Endpoint summary

Link to relevant study record(s)

Reference

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

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:

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

Radiolabelling:

no

Preliminary studies:

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

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.

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) 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.

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

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 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 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.

Description of key information

Absorption: The test substance is predicted to have a high fraction absorbed across the gastrointestinal tract.

Distribution: The free fraction in plasma was approximately 16 % in male rats and approximately 11 % in female rats and together with the predicted volume of distribution, it is expected that the test substance would distribute into tissues.

Metabolism: 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 in the model is via metabolism.

Excretion: Low percentage renal excretion of the test substance was predicted.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

79

Additional information

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 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 used in the model and simulation.

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 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. 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%.

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.