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A new extrapolation method from animals to man: Application to a metabolized compound, mofarotene
Life Sciences, Vol. 56, No. 26 pp. PL 4?3-478,1995 Cqyriat 0 1995 ELsevia Science Ltd Printed in the USA. All rights reserved oo?A-320519s $950 t .oo
Pergamon
0024-3205(95)00234-O
PhXRhfACOLOGY LETTERS Accelerated Communication
A NEW EXTRAPOLATION METHOD FROM ANIMALS TO MAN : APPLICATION METABOLIZED COMPOUND, MOFAROTENE
T. Lavet, A.H. Schmitt-Hoffmann, Chou
Pharmaceutical
P. Coassolo,
B. Valles, G. Ubeaud,
Research, F. Hoffmann-La
TO A
B. Ba, R. Brandt, R.C.
Roche Ltd, Basel, Switzerland
(Submitted March 13, 1995; accepted March 21, 1995; received in final form March 24, 1995)
ABSTRACT : Allometric scaling (a technique which uses data obtained in laboratory animals to predict human pharmacokinetics) works well for drugs that are cleared intact, but is less successful with extensively metabolised compounds. This paper describes a new method to improve the accuracy of such projections, by integrating metabolic data obtained in vitro (e.g. with liver microsomes or hepatocytes) into these calculations. The approach was used prospectively, to predict the clearance of mofarotene (Ro 40-8757) in humans from in vivo kinetic data obtained in mouse, rat and dog. This compound was selected to illustrate this approach because it is exclusively eliminated through metabolism. Without the metabolic correction or using empirical correcting factors, the values predicted for man were 2.7 and 0.6 ml/mm/kg. This fell outside the range subsequently obtained in healthy volunteers dosed orally with 300 mg of mofarotene (7.5 & 4.0 ml/mm/kg, n=12). However, inclusion of the microsomal or hepatocyte data gave values of 5.1 and 4.2 ml/mm/kg, respectively, illustrating that the integration of in vitro metabolic data improves the accuracy of kinetic extrapolations. In contrast to the existing empirical techniques, this approach offers a rational basis to predict clearance of metabolized compounds in human. Key Words: pharmacokinetics, extrapolation, mofarotene, allometric scaling oductiaa Mofarotene (Ro 40-8757) is a novel anticancer arotinoid which shows anti-proliferative activity against rat mammary carcinomas (1, 2) and human cancer cell lines (3). The in vivo pharmacokinetics were investigated in rat, mouse and dog following a single oral and intravenous administration. Since mofarotene is exclusively eliminated through liver metabolism, in vitro models, such as liver microsomes and hepatocytes, were also used to assess the metabolic clearance of mofarotene in the same animal species. These data were combined, to predict the in vivo pharmacokinetics of mofarotene in man, and the projections were then compared with the results from the first human study. Metho& All doses of Ro 40-8757 were administered as solutions of the free base in mixed micelles, using the 14C labelled compound (specific activity 144 pCi/mg) in rat and dog and the unlabelled drug in mouse. 1 To whom correspondence
should be addressed.
PL-474
Mofarotene Extrapolation
Vol. 56, No. 26, 1995
Male MoRo mice and RoRo rats (body weight of ca 40 and 300 g, respectively), obtained from Biological Research laboratory (Fullinsdorf, Switzerland) were dosed intravenously at 3.5 mg/kg or orally by gavage at 20 mg/kg (rat n=2, mouse n=12 per route). Three mice were used per time point. Male Swiss beagle dogs were dosed by injection into the cephalic vein of the left leg at 0.5 m&g (n=l) or orally by gavage at 1.5- 3.3 mg/kg (n=5). Blood samples were collected for up to 240 hrs after administration, with EDTA as anticoagulant. Following deproteinisation with ethanol, plasma samples were analysed by an automated columnswitching HPLC-UV method (limit of quantification 10 ng/ml) (R. Wyss, Hoffmann La Roche Ltd, data on file). Liver microsomes were prepared according to a modified method from Von Bahr et al (4). The total cytochrome P-450 and protein content of the microsomal fractions were estimated according to the method of Omura and Sato (5) and the BCA assay (6), respectively. Hepatocytes were obtained by a two step collagenase perfusion (7, 8). The recovery of mofarotene from the incubation medium was always higher than 80 %. The rates of metabolism with mouse, rat, dog and human liver microsomes were determined, by incubating mofarotene at 2 to 40 PM for 10 min in presence of a NADPH regenerating system. The metabolic turnover was also measured at various time points during its incubation with mouse, rat, dog and human hepatocytes in primary culture. The incubation medium (microsomes) and the intra- and extra-cellular medium (hepatocytes) were analysed by radio HPLC, using gradient elution and on-line radiometric detection (liquid scintillation). The metabolic clearances were then calculated, for the microsomes from the ratio of maximal velocity (Vm) and the Michaelis-Menten constant (Km) and, for the hepatocytes, from the initial amount of mofarotene added divided by the AUC(O-t) value. The in vivo clearance value of Ro 40-8757 obtained in each animal species was normalized by the ratio of the in vitro clearance values, in the corresponding animal species and man. For example, the in vivo clearance in rat was multiplied by the ratio (CLhuman hepatocytes / CLrat hepatocytes). These normalized clearance values in animals were extrapolated to humans using allometric scaling (9). The clearances predicted for humans were then compared to the values predicted by conventional allometric scaling, and also by normalising for brain weight, which has been suggested as an empirical correction factor for metabolised compounds (10). All of these predictions assume linearity of the pharmacokinetics with dose. The use of hepatocytes and/or microsomes also assumes that the liver is the major site of metabolism in all species. Since protein binding was higher than 99.9 % in man, a sufficiently precise determination of the free fractions of mofarotene in the plasma of the different animal species was not possible due to technical limitations. Thus, protein binding of mofarotene in plasma was assumed to be similar in the different animal species.
Results The main pharmacokinetic parameters obtained in the different animal species are summarised in Table I. The plasma concentration versus time profiles were biphasic in mouse, rat and dog with apparent terminal half lives of 14, 22 and 44 hours, respectively. Mofarotene exhibited a low systemic plasma clearance corresponding exchrsively to liver metabolism and representing approximately 15% (after correction for blood/plasma partitioning) of hepatic blood flow in the three species studied. The volumes of distribution at steady state were large (4 to 7 l/kg) indicating extensive uptake into organs and tissues. Following oral administration, the absorption was
Vol. 56, No. 26,19!3
Mofarotene Extrapolation
PL475
relatively fast, with peak concentrations being achieved at 2-5 hrs after administration. The absolute bioavailability was high, in the range of 50 (mouse, rat) to 100% (dog). This indicates that mofarotene is well absorbed by laboratory animals, with rather limited first-pass metabolism both the liver and intestine). TABLE I: Pharmacokinetic Parameters of Mofarotene Following Administration to Mouse, Rat and Dog.
Systemic Cl (ml/min/kg) Cl/F (mVminikg) Vdss (l/kg)
Intravenous
Mouse
Rat
Dog
9.0
7.1
3.9
18.4
11.4
4.0 +1 .o
(6.3) *
3.8
7.1
and Oral
apparent terminal t1/2 (hrs) Cmax (&ml)
14
22
ND
1650.t
1007 + 357#
Tmax (hrs)
ND
2-5t
l-2#
F(%)
49t
62t
- lOO#
44f
(by
10
ND data missing because of small number of points ; * approximate estimate due to limited sampling ; t data for a 20 mg!kg oral dose. ; # data for a 1.5 - 3.3 mg/kg oral dose. The enzyme kinetic parameters were determined in mouse, rat, dog and human liver microsomes. Eadie Hofstee plots clearly showed two apparent sites for all four species. The values for the intrinsic clearance were in the same range of magnitude in the different species investigated (Table II). Dog tended to exhibit the lowest intrinsic clearance (0.10 ml/min/mg protein) whereas mouse, rat and human liver preparations showed comparable values (0.15, 0.13 and 0.16 ml/min/mg protein, respectively). The intrinsic clearance determined with hepatocytes in primary culture (Table II) confirmed a lower value for dog (0.063 ml/h/million cells), with a similar value for mouse (0.065 ml/h/million cells). By contrast, the human and rat hepatocytes again showed similar but comparatively higher clearances (0.11 and 0.14 ml/h/million cells, respectively). Pharmacokinetic parameters for man were extrapolated from mouse, rat and dog data using allometric scaling (9). Combining the in vivo clearance in animals, with the corresponding in vitro data from liver microsomes and hepatocytes in animals and human gave projected oral clearance values for man of 5.1 and 4.2 mYmin/kg, respectively (Figure 1). Extrapolating the oral clearance directly, or using brain weight as a correcting factor (lo), gave lower predicted oral clearances in man of 2.7 and 0.6 ml/min/kg, respectively (Figure 2). A bioequivalence study with two different formulations were performed in healthy volunteers (B. Reigner, Hoffmann La Roche Ltd, data on file). After oral administration of 300 mg of
PL-476
Vol. 56, No. 26, 1995
Mofarotene Extrapolation
mofarotene an oral clearance of 7.5 f 4.0 ml/min/kg (n=12) was calculated. This was in good agreement with our predictions of 4.2 I 5.1 ml/mm/kg, from the interspecies scaling combined with the hepatocyte / microsomal data. Using conventional extrapolation methods for metabolised compounds (e.g. correction of clearance with brain weight) would have led to a 10 fold underestimation of the clearance in human. TABLE II: Hepatic Intrinsic Clearance of Mofarotene in Liver Microsomes Primary Culture from Different Species.
Mouse
Microsomes Clint (ml/min/mg protein) 0.151/0.162
Hepatocytes Clint (ml/h/million cells) 0.065+0.004
Rat
0.126+0.025
0.140+0.040
Dog
O.lOOfO.OO1
0.063+0.014
and Hepatocytes
in
0.120/0.098 0.164M.048 Human Mean + SD for 3 batches of microsomes and hepatocytes, except for human hepatocytes and mouse microsomes (n=2).
-2 1 -3-4 , -2
--c-
Hepatocytes,y = 0.784x + 1.024 r2 = 0.972
---~--
Microsomesy = 0.823x + 1.035 r2 = 0.999
I -1
0
1
2
Log (Body Weight) Eicl Allometric
scaling of clearance,
normalized
with in vitro data obtained
from
microsomes (- -x- -) or hepatocytes (---). Projected oral clearance values for man were 5.1 and 4.2 ml/m&kg, respectively. Open circle: observed oral clearance in man (- 7.5 ml/mm/kg).
Vol. 56, No. 26, 1995
PL477
Mofarotene Extrapolation
A
-_i
-i
i
i
i
Log (Body Weight) B 3
1y=
1.638x - 1.202 r2 = 0.994
0 MAN
Log (Body Weight) E&2 Allometric scaling of clearance (A) and of clearance normalized with brain weight (B). Projected oral clearance values for man were 2.7 and 0.6 ml/min/kg, respectively. Open circle: observed oral clearance in man (t: 7.5 ml/m&kg).
PL478
Mofarotene Extrapolation
Vol. 56, No. 24,1995
Discussion In this study, the pharmacokinetics of mofarotene were investigated after intravenous and oral administration to mice, rats and dogs. As the studies used a small number of animals, and in parallel groups rather than a cross-over design, the kinetic parameters which are presented in Table I have to be regarded as approximate values. Nevertheless, the results obtained do provide a clear insight into the disposition of mofarotene, with evidence that the drug is handled in a similar way by all three species: low clearance, large volume of distribution and high bioavailability. The intrinsic clearances obtained from liver microsomes and hepatocytes were within a two fold range for all species studied, consistent with the in vivo kinetic data. Interestingly, the intrinsic clearance for humans in both in vitro systems were close to the values found for the different animal species (metabolic rates generally tend to be lower in humans than in laboratory animals). The in vivo clearances values obtained in these studies were prospectively correlated to body weight, to predict the oral clearance for mofarotene in man, using both classical allometric scaling (9,lO) and the in vitro integrated data. Results obtained in healthy volunteers after oral administration of 300 mg of mofarotene showed a mean oral clearance of 7.5 ml/mm&g (n=12), in good agreement with the predictions from interspecies scaling combined with the microsomal or hepatocyte data. Compared to the “classical” allometric scaling, this integration of in vitro data substantially improved the accuracy of the predicted clearance value in man. The validity of the approach reported here for mofarotene, which offers a rational basis to predict clearance of metabolized compounds in human, will be confirmed with additional examples in the near future. kferences 1. 2.
7. 8 9. 10.
J. ELIASON, K. TEELMAN and M. CRETTAZ, Retinoids in cutaneous malienancy, (Marks R. Ed), 157-170, Blakwell, Oxford (1990). D. HARTMANN, K. TEELMAN, J. ELIASON, F. KAUFMANN and M. KLAUS, Retinoids. Progress in research and clinical applications, (Livrea M.A. and Packer L. Eds), 49 l-505, Marcel Dekker Inc, New York (1993). J. ELIASON, F. KAUFMANN, T. TANAKA and T. TSUKAGUCHI, Br. J. Cancer u 1293-1298 (1993). C. VON BAHR, C.-G. GROTH, H. JANSSON, G. LUNDGREN, M. LIND and H. GLAUMANN, Clin. Pharmacol. Ther. 22 71 l-725 (1980). T. OMURA and R. SATO, J. Biol. Chem. 229.2379-2385 (1964). P.K. SMITH, R.I. KROHN, G.T. HERMANSON, A.K. MALLIA, F.H. GARTNER, M.D. PROVENZANO, E.K. FUJIMOTO, N.M. GOEKE, B.J. OLSON and D.C. KLENK, Anal. Biochem. m 76-85 (1985). G. FABRE, R. RAHMANI, M. PLACIDI, J. COMBALBERT, J. COVO, J.-P. CANO, C. COULANGE, M. DUCROS and M. RAMPAL, Biochem. Pharmacol. z 4389-4397 (1988). P.O. SEGLEN, Methods Cell Biol, (Prescott D.M. Ed), 29-83, Academic Press, New York, (1976). J. MORDENTI, J. Pharm. Sci. E 1028-1040 (1986). H. BOXENBAUM and J.B. FERTIG, Eur. J. Drug Metab. Pharmacokinet. 2 177-183 (1984).
Pergamon
0024-3205(95)00234-O
PhXRhfACOLOGY LETTERS Accelerated Communication
A NEW EXTRAPOLATION METHOD FROM ANIMALS TO MAN : APPLICATION METABOLIZED COMPOUND, MOFAROTENE
T. Lavet, A.H. Schmitt-Hoffmann, Chou
Pharmaceutical
P. Coassolo,
B. Valles, G. Ubeaud,
Research, F. Hoffmann-La
TO A
B. Ba, R. Brandt, R.C.
Roche Ltd, Basel, Switzerland
(Submitted March 13, 1995; accepted March 21, 1995; received in final form March 24, 1995)
ABSTRACT : Allometric scaling (a technique which uses data obtained in laboratory animals to predict human pharmacokinetics) works well for drugs that are cleared intact, but is less successful with extensively metabolised compounds. This paper describes a new method to improve the accuracy of such projections, by integrating metabolic data obtained in vitro (e.g. with liver microsomes or hepatocytes) into these calculations. The approach was used prospectively, to predict the clearance of mofarotene (Ro 40-8757) in humans from in vivo kinetic data obtained in mouse, rat and dog. This compound was selected to illustrate this approach because it is exclusively eliminated through metabolism. Without the metabolic correction or using empirical correcting factors, the values predicted for man were 2.7 and 0.6 ml/mm/kg. This fell outside the range subsequently obtained in healthy volunteers dosed orally with 300 mg of mofarotene (7.5 & 4.0 ml/mm/kg, n=12). However, inclusion of the microsomal or hepatocyte data gave values of 5.1 and 4.2 ml/mm/kg, respectively, illustrating that the integration of in vitro metabolic data improves the accuracy of kinetic extrapolations. In contrast to the existing empirical techniques, this approach offers a rational basis to predict clearance of metabolized compounds in human. Key Words: pharmacokinetics, extrapolation, mofarotene, allometric scaling oductiaa Mofarotene (Ro 40-8757) is a novel anticancer arotinoid which shows anti-proliferative activity against rat mammary carcinomas (1, 2) and human cancer cell lines (3). The in vivo pharmacokinetics were investigated in rat, mouse and dog following a single oral and intravenous administration. Since mofarotene is exclusively eliminated through liver metabolism, in vitro models, such as liver microsomes and hepatocytes, were also used to assess the metabolic clearance of mofarotene in the same animal species. These data were combined, to predict the in vivo pharmacokinetics of mofarotene in man, and the projections were then compared with the results from the first human study. Metho& All doses of Ro 40-8757 were administered as solutions of the free base in mixed micelles, using the 14C labelled compound (specific activity 144 pCi/mg) in rat and dog and the unlabelled drug in mouse. 1 To whom correspondence
should be addressed.
PL-474
Mofarotene Extrapolation
Vol. 56, No. 26, 1995
Male MoRo mice and RoRo rats (body weight of ca 40 and 300 g, respectively), obtained from Biological Research laboratory (Fullinsdorf, Switzerland) were dosed intravenously at 3.5 mg/kg or orally by gavage at 20 mg/kg (rat n=2, mouse n=12 per route). Three mice were used per time point. Male Swiss beagle dogs were dosed by injection into the cephalic vein of the left leg at 0.5 m&g (n=l) or orally by gavage at 1.5- 3.3 mg/kg (n=5). Blood samples were collected for up to 240 hrs after administration, with EDTA as anticoagulant. Following deproteinisation with ethanol, plasma samples were analysed by an automated columnswitching HPLC-UV method (limit of quantification 10 ng/ml) (R. Wyss, Hoffmann La Roche Ltd, data on file). Liver microsomes were prepared according to a modified method from Von Bahr et al (4). The total cytochrome P-450 and protein content of the microsomal fractions were estimated according to the method of Omura and Sato (5) and the BCA assay (6), respectively. Hepatocytes were obtained by a two step collagenase perfusion (7, 8). The recovery of mofarotene from the incubation medium was always higher than 80 %. The rates of metabolism with mouse, rat, dog and human liver microsomes were determined, by incubating mofarotene at 2 to 40 PM for 10 min in presence of a NADPH regenerating system. The metabolic turnover was also measured at various time points during its incubation with mouse, rat, dog and human hepatocytes in primary culture. The incubation medium (microsomes) and the intra- and extra-cellular medium (hepatocytes) were analysed by radio HPLC, using gradient elution and on-line radiometric detection (liquid scintillation). The metabolic clearances were then calculated, for the microsomes from the ratio of maximal velocity (Vm) and the Michaelis-Menten constant (Km) and, for the hepatocytes, from the initial amount of mofarotene added divided by the AUC(O-t) value. The in vivo clearance value of Ro 40-8757 obtained in each animal species was normalized by the ratio of the in vitro clearance values, in the corresponding animal species and man. For example, the in vivo clearance in rat was multiplied by the ratio (CLhuman hepatocytes / CLrat hepatocytes). These normalized clearance values in animals were extrapolated to humans using allometric scaling (9). The clearances predicted for humans were then compared to the values predicted by conventional allometric scaling, and also by normalising for brain weight, which has been suggested as an empirical correction factor for metabolised compounds (10). All of these predictions assume linearity of the pharmacokinetics with dose. The use of hepatocytes and/or microsomes also assumes that the liver is the major site of metabolism in all species. Since protein binding was higher than 99.9 % in man, a sufficiently precise determination of the free fractions of mofarotene in the plasma of the different animal species was not possible due to technical limitations. Thus, protein binding of mofarotene in plasma was assumed to be similar in the different animal species.
Results The main pharmacokinetic parameters obtained in the different animal species are summarised in Table I. The plasma concentration versus time profiles were biphasic in mouse, rat and dog with apparent terminal half lives of 14, 22 and 44 hours, respectively. Mofarotene exhibited a low systemic plasma clearance corresponding exchrsively to liver metabolism and representing approximately 15% (after correction for blood/plasma partitioning) of hepatic blood flow in the three species studied. The volumes of distribution at steady state were large (4 to 7 l/kg) indicating extensive uptake into organs and tissues. Following oral administration, the absorption was
Vol. 56, No. 26,19!3
Mofarotene Extrapolation
PL475
relatively fast, with peak concentrations being achieved at 2-5 hrs after administration. The absolute bioavailability was high, in the range of 50 (mouse, rat) to 100% (dog). This indicates that mofarotene is well absorbed by laboratory animals, with rather limited first-pass metabolism both the liver and intestine). TABLE I: Pharmacokinetic Parameters of Mofarotene Following Administration to Mouse, Rat and Dog.
Systemic Cl (ml/min/kg) Cl/F (mVminikg) Vdss (l/kg)
Intravenous
Mouse
Rat
Dog
9.0
7.1
3.9
18.4
11.4
4.0 +1 .o
(6.3) *
3.8
7.1
and Oral
apparent terminal t1/2 (hrs) Cmax (&ml)
14
22
ND
1650.t
1007 + 357#
Tmax (hrs)
ND
2-5t
l-2#
F(%)
49t
62t
- lOO#
44f
(by
10
ND data missing because of small number of points ; * approximate estimate due to limited sampling ; t data for a 20 mg!kg oral dose. ; # data for a 1.5 - 3.3 mg/kg oral dose. The enzyme kinetic parameters were determined in mouse, rat, dog and human liver microsomes. Eadie Hofstee plots clearly showed two apparent sites for all four species. The values for the intrinsic clearance were in the same range of magnitude in the different species investigated (Table II). Dog tended to exhibit the lowest intrinsic clearance (0.10 ml/min/mg protein) whereas mouse, rat and human liver preparations showed comparable values (0.15, 0.13 and 0.16 ml/min/mg protein, respectively). The intrinsic clearance determined with hepatocytes in primary culture (Table II) confirmed a lower value for dog (0.063 ml/h/million cells), with a similar value for mouse (0.065 ml/h/million cells). By contrast, the human and rat hepatocytes again showed similar but comparatively higher clearances (0.11 and 0.14 ml/h/million cells, respectively). Pharmacokinetic parameters for man were extrapolated from mouse, rat and dog data using allometric scaling (9). Combining the in vivo clearance in animals, with the corresponding in vitro data from liver microsomes and hepatocytes in animals and human gave projected oral clearance values for man of 5.1 and 4.2 mYmin/kg, respectively (Figure 1). Extrapolating the oral clearance directly, or using brain weight as a correcting factor (lo), gave lower predicted oral clearances in man of 2.7 and 0.6 ml/min/kg, respectively (Figure 2). A bioequivalence study with two different formulations were performed in healthy volunteers (B. Reigner, Hoffmann La Roche Ltd, data on file). After oral administration of 300 mg of
PL-476
Vol. 56, No. 26, 1995
Mofarotene Extrapolation
mofarotene an oral clearance of 7.5 f 4.0 ml/min/kg (n=12) was calculated. This was in good agreement with our predictions of 4.2 I 5.1 ml/mm/kg, from the interspecies scaling combined with the hepatocyte / microsomal data. Using conventional extrapolation methods for metabolised compounds (e.g. correction of clearance with brain weight) would have led to a 10 fold underestimation of the clearance in human. TABLE II: Hepatic Intrinsic Clearance of Mofarotene in Liver Microsomes Primary Culture from Different Species.
Mouse
Microsomes Clint (ml/min/mg protein) 0.151/0.162
Hepatocytes Clint (ml/h/million cells) 0.065+0.004
Rat
0.126+0.025
0.140+0.040
Dog
O.lOOfO.OO1
0.063+0.014
and Hepatocytes
in
0.120/0.098 0.164M.048 Human Mean + SD for 3 batches of microsomes and hepatocytes, except for human hepatocytes and mouse microsomes (n=2).
-2 1 -3-4 , -2
--c-
Hepatocytes,y = 0.784x + 1.024 r2 = 0.972
---~--
Microsomesy = 0.823x + 1.035 r2 = 0.999
I -1
0
1
2
Log (Body Weight) Eicl Allometric
scaling of clearance,
normalized
with in vitro data obtained
from
microsomes (- -x- -) or hepatocytes (---). Projected oral clearance values for man were 5.1 and 4.2 ml/m&kg, respectively. Open circle: observed oral clearance in man (- 7.5 ml/mm/kg).
Vol. 56, No. 26, 1995
PL477
Mofarotene Extrapolation
A
-_i
-i
i
i
i
Log (Body Weight) B 3
1y=
1.638x - 1.202 r2 = 0.994
0 MAN
Log (Body Weight) E&2 Allometric scaling of clearance (A) and of clearance normalized with brain weight (B). Projected oral clearance values for man were 2.7 and 0.6 ml/min/kg, respectively. Open circle: observed oral clearance in man (t: 7.5 ml/m&kg).
PL478
Mofarotene Extrapolation
Vol. 56, No. 24,1995
Discussion In this study, the pharmacokinetics of mofarotene were investigated after intravenous and oral administration to mice, rats and dogs. As the studies used a small number of animals, and in parallel groups rather than a cross-over design, the kinetic parameters which are presented in Table I have to be regarded as approximate values. Nevertheless, the results obtained do provide a clear insight into the disposition of mofarotene, with evidence that the drug is handled in a similar way by all three species: low clearance, large volume of distribution and high bioavailability. The intrinsic clearances obtained from liver microsomes and hepatocytes were within a two fold range for all species studied, consistent with the in vivo kinetic data. Interestingly, the intrinsic clearance for humans in both in vitro systems were close to the values found for the different animal species (metabolic rates generally tend to be lower in humans than in laboratory animals). The in vivo clearances values obtained in these studies were prospectively correlated to body weight, to predict the oral clearance for mofarotene in man, using both classical allometric scaling (9,lO) and the in vitro integrated data. Results obtained in healthy volunteers after oral administration of 300 mg of mofarotene showed a mean oral clearance of 7.5 ml/mm&g (n=12), in good agreement with the predictions from interspecies scaling combined with the microsomal or hepatocyte data. Compared to the “classical” allometric scaling, this integration of in vitro data substantially improved the accuracy of the predicted clearance value in man. The validity of the approach reported here for mofarotene, which offers a rational basis to predict clearance of metabolized compounds in human, will be confirmed with additional examples in the near future. kferences 1. 2.
7. 8 9. 10.
J. ELIASON, K. TEELMAN and M. CRETTAZ, Retinoids in cutaneous malienancy, (Marks R. Ed), 157-170, Blakwell, Oxford (1990). D. HARTMANN, K. TEELMAN, J. ELIASON, F. KAUFMANN and M. KLAUS, Retinoids. Progress in research and clinical applications, (Livrea M.A. and Packer L. Eds), 49 l-505, Marcel Dekker Inc, New York (1993). J. ELIASON, F. KAUFMANN, T. TANAKA and T. TSUKAGUCHI, Br. J. Cancer u 1293-1298 (1993). C. VON BAHR, C.-G. GROTH, H. JANSSON, G. LUNDGREN, M. LIND and H. GLAUMANN, Clin. Pharmacol. Ther. 22 71 l-725 (1980). T. OMURA and R. SATO, J. Biol. Chem. 229.2379-2385 (1964). P.K. SMITH, R.I. KROHN, G.T. HERMANSON, A.K. MALLIA, F.H. GARTNER, M.D. PROVENZANO, E.K. FUJIMOTO, N.M. GOEKE, B.J. OLSON and D.C. KLENK, Anal. Biochem. m 76-85 (1985). G. FABRE, R. RAHMANI, M. PLACIDI, J. COMBALBERT, J. COVO, J.-P. CANO, C. COULANGE, M. DUCROS and M. RAMPAL, Biochem. Pharmacol. z 4389-4397 (1988). P.O. SEGLEN, Methods Cell Biol, (Prescott D.M. Ed), 29-83, Academic Press, New York, (1976). J. MORDENTI, J. Pharm. Sci. E 1028-1040 (1986). H. BOXENBAUM and J.B. FERTIG, Eur. J. Drug Metab. Pharmacokinet. 2 177-183 (1984).