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DRUG AND CHEMICAL TOXICOLOGY, 12(1), 21-37 (1989)
TOXICITY OF 8-METHOXYPSORALEN I N CYNOMOLGOUS MONKEYS (MACACA FASCICULARIS)
* T. Rozman*", F. Leuschner', R. B r i c k l " and K. Roman # Medizinische Forschung und Entwicklung der Basotherm GmbH
7950 Biberach an der R i B (F.R.G.), Laboratorium fu r Pharmakologie und Tox iko log ie
Abte i lung Biochemie der D r . Kar l Thomae GmbH 7950 Biberach an der R i 6 (F.R.G.)
and #Department o f Pharmacology, Toxicology and Therapeutics
U n i v e r s i t y o f Kansas Medical Center Kansas City, KS 66103 (U.S.A.)
t
+t 2014 Hamburg 92 (F.R.G.),
ABSTRACT
Male and female cynomolgous monkeys were administered 0, 2, 6 o r 18 mg/kg 8-methoxypsoralen (8-MOP) 3 times a week o r a l l y f o r 26 consecutive weeks. Dose-dependent emesis was the most s e n s i t i v e i n d i c a t o r o f 8-MOP t o x i c i t y . The lowest dose t o e l i c i t emesis was 3 x 6 mg/kg/week o f &MOP. Among the h i s t o l o g i c a l f i n d i n g s p r o l i f - e r a t i o n o f Kupf fe r c e l l s was the o n l y r e c u r r i n g observat ion. However, these f i n d i n g as we l l as some hematological and serum e l e c t r o l y t e changes lacked a dose-response r e l a t i o n s h i p . I n the h ighes t dosage group one female monkey was found i n moribund cond i t i on on the 39th day o f the study and was k i l l e d . Histopatho- l o g i c a l evidence ind i ca ted beginning shock as the cause o f t he r a p i d l y d e t e r i o r a t i n g hea l th o f the monkey. S i m i l a r t o e f f e c t s i n man and ra ts , 8-MOP d isp layed non l inear pharmacokinetics i n the cynomolgous monkey, sa tu ra t i on occur r ing between 3 x 2 and 3 x 6 mg/kg/week. Increased clearance o f 8-MOP i n t h e lowest dosage group a f t e r 26 t e s t weeks was a t t r i b u t e d t o a combination o f enzyme induc t i on and sa turab le f i r s t pass e f f e c t . Since the plasma p r o f i l e o f 8-MOP a t the lowest dose (3 x 2 mg/kg/week) in cynomol-
To whom correspondence should be addressed, a t the Department o f Pharma- cology, Toxicology and Therapeutics, Un ivers i ty - o f Kansas Medical Center, 39th L Rainbow B l v d . , Kansas City, KS 66103 U.S.A.
1
21
Copyright 0 1989 by Marcel Dekker, Inc.
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22 ROZMAN ET AL.
gous monkeys closely resembles that in humans after therapeutic doses (0.4-0.6 mg/kg) arid because of other similarities (vomiting as earliest sign of toxicity, saturable first pass effect), it is reasonable to assume that chronic toxicity of 8-MOP as defined in this study is quite predictive for man.
INTRODUCTION
9-Methoxy- 7H-f u ro [ 3,2-g] benzopyran-7-one (8-met hoxypsora 1 en ) administered orally or topically has been used in combination with ultraviolet radiation (PUVA therapy) to increase skin tolerance to sunlight, to facilitate repigmentation in vitiligo and to treat various skin diseases (dermatoses) such as psoriasis, eczema and mycosis fungoides . There is a large body of data on the acute and chronic toxicity of 8-methoxypsoralen (8-MOP) and long wave ultra- violet light (320-400 nm) in clinical trials, case reports, epi- demiological studies and in animal experiments”’. However, the toxicity of 8-NOP without exposure to ultraviolet light is not well defined. Some tentative data indicate that the acute toxicity of 8-MOP in rodents ranges from about 0.2 to 4.0 g/kg body weight depending on the mode of formulation and route of administration . No adequate data exist for the subacute and chronic toxicity of 8-NOP alone in any species . Among common side (toxic) effects of oral 8-MOP therapy is nausea. Since rats cannot vomit4, a nonhuman primate species compatible with the human vomiting reflex was chosen for this study.
1
3
1
METHODS
Fifteen male (5.5 f 0.2 kg) and 15 female (3.7 f 0.1 kg) cynomolgous monkeys (macaca fascicularis) obtained from Primaten Import und Export Viersen, F.R.G., were housed individually in metabolism cages (12 hr dark/light cycle, 22 ? 1°C room tempera- ture, 55 f 5% humidity) with free access to water and 60 g/kg food (Altromin 6024, Lage/Lippe, F.R.G.) per day supplemented by fruit. Groups of 3 male and 3 female monkeys received for 26 consecutive
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TOXICITY OF 8-METHOXYPSORALEN 23
weeks 0, 2, 6 o r 18 mg/kg 8-MOP (Basotherm GmbH, Biberach, F.R.G.) 3 times a week (Monday, Wednesday and Fr iday) i n hydroxypropyl-
methy l -ce l lu lose ge l (1 ml/kg) by stomach tube. Three a d d i t i o n a l male (4.6 f 0.1 kg) and 3 female (2.8 k 0.1 kg) monkeys designated
f o r an 8 week post dosage recovery pe r iod were maintained i d e n t i - c a l l y and received the h ighes t dosage (18 mg/kg) o f 8-MOP. Behavior and ex terna l appearance as w e l l as the presence o f vomitus
were observed and recorded d a i l y . Food and water i n t a k e were determined d a i l y , body weight weekly.
Venous blood (10 ml ) was withdrawn from each monkey ( f a s t e d f o r 24 h r ) the day before admin i s t ra t i on o f t he f i r s t dose o f 8-MOP and a t 1, 6, 13, 18 and 26 weeks i n t o dosing as w e l l as a t week 34 i n the animals designated f o r recovery. Hematology (hemoglobin,
e ry th rocy tes , leucocytes, d i f f e r e n t i a l b lood count, hematocr i t , tomboplast in and prothrombin time, e ry th rocy te sedimentat ion ra te , p l a t e l e t s and r e t i c u l o c y t e s ) , c l i n i c a l chemistry ( a l a n i n amino- t ransferase, aspar ta te aminotransferase, a l k a l i n e phosphatase, l a c t a t e dehydrogenase, blood urea, glucose, t o t a l p ro te in , u r i c ac id , t o t a l b i l i r u b i n , albumin, g lobu l i n , c rea t i n ine , t o t a l choles- t e r o l , ch lo r ide , sodium, potassium and calc ium as w e l l as l i v e r f unc t i on t e s t w i t h bromosulphthalein) and immunological s ta tus
( q u a n t i t a t i v e es t imat ion of p r o t e i n by e lec t rophores is i n agarosegel con ta in ing an t ibod ies) o f each blood sample was de te r - ,
mined according t o standard c l i n i c a l l abo ra to ry t e s t s . I n add i t i on , 3 m l o f b lood was c o l l e c t e d i n hepar in ized tubes
from each monkey dosed w i t h 2, 6 o r 18 mg/kg 8-MOP 3 t imes a week
(except the animals designated f o r recovery) a t 1, 2, 4 and 8 h r a f t e r dosing w i t h 8-MOP on the f i r s t day and a f t e r the 13th t e s t week, whereas a f t e r the 26th t e s t week blood samples were procured a t 1, 2, 4, 8 and 24 h r a f t e r the 8-MOP dosage. A f t e r cen t r i f uga - t i o n , plasma was harvested and s to red a t -18°C u n t i l processed. Plasma l e v e l s o f 8-MOP were determined by h igh performance l i q u i d chromatography (HPLC) us ing spec ia l equipment w i t h precolumn enrichment . HPLC ana lys is was c a r r i e d ou t by w a t e r / a c e t o n i t r i l e 60/40 as mobi le phase on a hypers i l ODS ( 5 p ) column w i t h 4.6 mn
5
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24 ROZMAN ET AL.
diameter and a length of 125 mn with a flow rate of 1.5 ml/min. 8-MOP was detected by fluorescence spectrometry with 310 nm
excitation and 490 nm emission. The detection limit of thi's system was 10 ng/ml with a coefficient of variation of 4.2%.
Urine was sampled from each monkey the day prior to dosing and after the lst, 6th, 13th and 26th week and from the monkeys desig- nated for the 8 week recovery period after the 34th week. On the day of urine collection each animal received 25 ml tap water by stomach tube between 7:30 and 9:00 A.M. Urine was collected in a metabolism cage for the following 5 hr. Urine specimens were monitored for the usual parameters.
Electrocardiograms were registered in each animal after the lst, 6th, 13th, 18th and 26th test week and in the monkeys desig- nated for the 8 week recovery period after the 34th week. Extrem- ity leads 1-111 were used for evaluation by a qualified cardiol- ogist. "Normal" versus "abnormal" EKG pattern was determined based on textbook knowledge about EKG evaluation in combination with background data obtained i n conscious restraint cynomolgous mon- keys.
Blood pressure was measured in each monkey after the 26th week, and in animals designated for the recovery period, after the 34th week. Contrary to the conventional oscultatory and palpatory measurements, the oscillations produced by motions of the arterial walls transmitted by the cuff were used for evaluation.
Examinations of sight, hearing and dentition were conducted in all animals after 26 test weeks, and after 34 test weeks in monkeys designated for the recovery period. The eyes were examined with a HEINE-MAY ophthalmoscope (including slit lamp). Sight was evalu- ated daily be examining the capability of each monkey to follow with the eyes a silent move of the hand from the left to the right edge of the cage. Hearing was checked daily by the reaction of the monkeys to a click of the tongue.
One female animal (3 x 18 mg/kg/week; intended for recovery) was found in moribund condition on the 39th test day and was killed
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TOXICITY OF 8-METHOXYPSORALEN 25
and necropsied. A f t e r 26 weeks, 12 male and 12 female monkeys were anesthet ized w i t h 0.3 mg T 61/kg and k i l l e d by exsanguinat ion a f t e r
d i ssec t i on o f the ca ro t i d . Three male and 2 female monkeys desig- nated f o r the 8 week recovery per iod were k i l l e d i d e n t i c a l l y a f t e r t he 34th t e s t week. Complete necropsy was performed on each monkey. A f t e r macroscopic inspec t ion the f o l l o w i n g organ weights were determined: heart , l i v e r , lungs, kidneys, spleen, adrenals,
thymus, p i t u i t a r y gonads, t h y r o i d and b ra in . Tissues (hear t , lung, l i v e r , spleen, kidney, adrenal, thymus, p i t u i t a r y , gonads, t hy ro id , b ra in , p ros t ra te /u te rus , stomach, duodenum, jejunum, ileum, colon, rectum, s a l i v a r y gland, eye w i t h o p t i c nerve, u r i n a r y bladder, bone
marrow, bone, trachea, aorta, esophagus, pancreas, mesenteric lymph node, per ipehra l nerve, s k e l e t a l muscle, sk in , tongue, sp ina l cord, g a l l bladder and mammary gland) were f i x e d i n 10% n e u t r a l fo rmal in , imbedded i n p a r a f f i n , sect ioned and s ta ined w i t h hematoxyl in /eos in f o r microscopic evaluat ion. Furthermore, f rozen sec t ions o f hear t , l i v e r and kidney were s ta ined w i t h Sudan 111.
S t a t i s t i c a l eva lua t ion o f body weight, food consumption, hematology, c l i n i c a l chemistry, e lec t rophores is , u r i n e ana lys is ,
e lectrocardiography, blood pressure and organ weights was performed by Student 's t - t e s t ( p < 0.01) whereas t h a t o f h i s t o l o g y was by Fishers exact t e s t ( p < 0.05). The c r i t e r i o n p < 0.01 was chosen t o d imin ish chance s ign i f i cance i n a small number o f animals captured i n the w i l d w i t h known la rge i n d i v i d u a l v a r i a b i l i t y o f t he parameters measured.
RESULTS
Body weight o f male and female monkeys rece iv ing 3 x (0, 2, 6 o r 18) mg/kg 8-MOP f o r 26 weeks i s depicted i n Fig. 1. There was no s i g n i f i c a n t d i f f e rence between the var ious groups and the con t ro l s among male o r female monkeys, al though a t rend towards reduced body weight was apparent i n bo th males and females a t the h ighes t dose l e v e l . Monkeys designated f o r the 8 week post-dosage recovery showed l i t t l e o r no change du r ing t h i s pe r iod (da ta no t shown).
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'r Males -0- Omglkg
--+- 2mglkg
-4- 6mgl kg
-..m.-i amglkg
Females -0- Omglkg
-0- 2mglkg
--.*a Gmglkg
---o--i amglkg
IMseks of Dosing
F I G . 1. x ( 0 , 2 , 6 or 18) mg/kg/week 8-methoxypsorblen f o r 26 weeks.
Body we igh t o f male and female cynomolgous monkeys dosed w i t h 3
F I G . 2. Food consumption o f male and female cynomolgous monkeys dosed w i t h 3 x (0, 2, 6 o r 18) mg/kg/week 8-methoxypsoralen f o r 26 weeks.
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TOXICITY OF 8-METHOXYPSORALEN 21
Males +Omg/kg No Emesis
-+--2mg/kg No Emesis
- 4 - 6 m g I k g
--m--l 8mglkg 8 a
r 0
Females -0-Omglkg No Emesis
--+-2mglkg No Emesis
-4.- Gmglkg
-+*- 18mgIkg
0 4 8 12 16 20 24 28
Weks of Dosing
FIG. 3. Frequency o f emesis in male and female cynomolgous monkeys dosed w i th 3 x (0, 2, 6 o r 18) mg/kg/week 8-methoxypsoralen fo r 26 weeks.
Food consumption was n o t a f f e c t e d by any dose o f 8-MOP i n
e i t h e r sex o f cynomolgous monkeys (F ig . 2 ) . Emesis was the most s e n s i t i v e s ign o f t o x i c i t y o f 8-MOP and i t
occurred i n a dose-dependent fashion (Fig. 3 ) . No emesis was observed i n any monkey a t any t ime a t the 3 x 2 mg/kg/week dosage
l e v e l ; i n t e r m i t t e n t emesis occurred a t the 3 x 6 mg/kg/week dose o f 8-MOP and monkeys a t the 3 x 18 mg/kg/week dose l e v e l vomited regu la r l y . Female monkeys seemed t o be more s e n s i t i v e t o the
emetic a c t i o n o f 8-MOP than males were (Fig. 3 ) . Elec t rophores is , u r i nanalysi s , e lec t rocard iography , b lood
pressure, s igh t , hearing, d e n t i t i o n and organ weights were n o t
d i f f e r e n t between con t ro l s and any o f the dosed groups o f any sex. Among the hematologic and c l i n i c a l chemistry parameters measured,
on l y c h l o r i d e , c a l c i um, hemogl ob i n and hema t o c r i t revealed
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Tab
le 1
N
Q
,
Dif
fere
nce
s in
Hem
atol
ogy
and
Cli
nic
al
Che
mis
try
betw
een
Co
ntr
ol
and
8-M
OP
-tre
ated
C
ynom
olgo
us
Mon
keys
His
tolo
gyl
clin
ical
T
est
chem
i str
v
wee
k 8-
MOP
(m
g/kg
/wee
k)
Co
ntr
ol s
3
x2
3
x6
3
x 18
Ch
lori
de
Cal
cium
Hem
oglo
bin
1
107.
5 f
1.4a
10
6.3 f 2
.0
105.
6 f
1.8
105.
5 f 1.
0*
6 10
6.3
f
1.8
105.
8 f
1.0
106.
4 f 0
.7
106.
0 f
1.0
13
107.
2 f 0
.8
106.
7 f 0
.8
106.
5 f 1
.2
107.
7 f 1
.4
26
107.
5 f 0
.5
107.
3 f
1.2
106.
8 f 0
.7
107.
0 f 0
.9
1
2.7
5 0.
2 2.
4 f 0.
1*
2.4
f 0
.2
2.5
f 0.
1 6
2.3
f 0
.2
2.5
f
0.1
2.4
f 0
.2
2.4
f 0
.1
2.5
f 0
.2
2.5
f 0.
1 2.
5 f
0.2
13
2.4
f 0
.1
18
2.5
f 0.
2 2.
5 f 0.
1 2.
4 f
0.1
2.5
k 0.
1 26
2.
5 i 0
.2
2.4
f 0.
2 2.
4 f
0.2
2.5
f 0
.1
18
106.
3 f 0.
5 10
6.8
f 0.
8 10
6.1
f 0
.6
106.
1 f 1.
4
1
8.0
f 0
.5
7.8
f 0
.2
7.6
f 0
.3
8.0
f 0.
6 6
8.3
5 0.
7 8.
5 f 0
.3
7.8
+ 0.
5 7.
9 * 0
.7,
13
8.6
f 1.
0 8.
0 f
0.4
7.7
f 0
.6
7.3
+ 0.
4 18
7.
8 f
0.9
7.7
f 0
.4
7.3
f 0
.6
-7.4
f 0.
4 26
8.
1 f 1.
1 8.
3 f 0
.6
7.0
f 0
.5
7.5
f 0
.6
a
Hem
otoc
ri t
1
44.2
f
1.7
42.8
f 1
.6
42.8
f 2
.7
45.0
f
3.1
0
6 45
.3
+ 4.
2 44
.5 f 3.
1 42
.0 f 4
.1
42.7
f 3
.2
13
46.0
f 3
.9
44.0
f 2
.4
43.1
f 3
.7
40.7
f
2.1
2
18
45.7
f 4
.8
44.3
f
4.6
42.9
5
3.2
43.4
f
2.7*
26
44
.7 f 6
.4
43.0
f 3.
8 40
.0 f 2
.5
41.7
f 4
.0
E n
-3 * ? a
Mea
n f
SO,
n =
3 *
Sig
nif
ica
ntl
y d
iffe
ren
t fr
om c
on
tro
ls (
p <
0.
01)
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TOXICITY OF 8-METHOXYPSORALEN 29
h W Y E 0 E tn
0 cn a
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30 ROZMAN ET A L .
scat te red d i f fe rences between con t ro l s and 8-MOP-treated monkeys !Table 1).
One female monkey from the group designated f o r the 8 week recovery per iod was found i n moribund cond i t i on and had t o be k i l l e d . Mic roscop ica l l y s igns o f beginning shock (severe conges- t i o n ) i n the lungs, l i v e r and kidney were observed. Th is animal
a l so showed severe i n v o l u t i o n o f the thymus and m u l t i p l e , g lobu la r c a l c i f i c a t i o n s of the gonads. I n add i t i on , there appeared t o be some hepatocel l u l a r degeneration and regenerat ion and Kupf fe r c e l l p r o l i f e r a t i o n (Fig. 4 ) . This l a t t e r f i n d i n g i s the o n l y
h i s topa tho log i ca l change observed a l s o i n o ther monkeys. Among a l l animals sac r i f i ced , a female con t ro l , none a t 3 x 2 mg/kg/week, 2 females and 2 males a t 3 x 6 mg/kg/week and 3 females a t 3 x 18 mg/kg/week of &MOP displayed p r o l i f e r a t i o n o f Kupf fe r c e l l s .
V a r i a b i l i t y of 8-MOP plasma l e v e l s a t the var ious doses was q u i t e l a rge and there was no apparent d i f f e r e n c e between males and females (Figs. 5-7) .
The area under the curve (AUC) was c lose t o dose l i n e a r i t y a t the 3 x 6 and the 3 x 18 mg/kg/week dose leve ls . However, t h i s was
no t the case between the 3 x 2 and the 3 x 6 mg/kg/week dosage leve ls , where the AUC increased tw ice as much as the dose (Figs. 5-7 and Table 2 ) .
Mean t ime t o peak concent ra t ion was about 1-2 h r s a t t he 2 x 2 mg/kg/week dose l e v e l and 4-8 h rs a t the 3 x ( 6 o r 18) mg/kg/week dosage regimens (Figs. 5-7).
There was no apparent d i f f e r e n c e i n the pharmacokinetics o f 8-MOP between weeks 1 and 13 b u t plasma l e v e l s o f 8-MOP were much lower a t the 3 x 2 mg/kg/week dose l e v e l a f t e r 26 weeks than a f t e r
the 1 s t o r the 13th week.
DISCUSSION
Emesis i s the most s e n s i t i v e i n d i c a t o r o f chron ic &MOP With t h i s end p o i n t o f t o x i c i t y i n cynomolgous monkeys (F ig . 3 ) .
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TOXICITY OF 8-METHOXYPSORALEN 31
F I G . 5. Plasma c o n c e n t r a t i o n o f 8-methoxypsoralen i n male and female cynomolgous monkeys on a dos ing regimen o f 3 x ( 2 , 6 or 18) mg/kg/week d u r i n g 8 hours a f t e r dos ing a t t h e end o f t h e f i r s t t e s t week. D
rug
and
Che
mic
al T
oxic
olog
y D
ownl
oade
d fr
om in
form
ahea
lthca
re.c
om b
y U
nive
rsity
of
Auc
klan
d on
10/
26/1
4Fo
r pe
rson
al u
se o
nly.
32 ROZMAN ET A L .
Thirteenth Week
t
Males --*-- Imglkg
--I- 6mglkg
--m- 18mgI kg
Females --0-- Imglkg
.-As- 6mglkg
--o.-lamglkg
Hours After Dosing
FIG. 6. Plasma concentrat ion o f 8-methoxypsoralen i n male and female cynomolgous monkeys on a dosing regimen o f 3 x (2, 6, o r 18) mg/kg/week du r ing 8 hours a f t e r dosing a t t h e end o f t h e 13 th t e s t week. D
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TOXICITY OF 8-METHOXYPSORALEN 33
Hours After Dosing
F I G . 7 . Plasma concentrat ion o f 8-methoxypsoralen i n male and female cynomolgous monkeys on a dosing regimen o f 3 x (2, 6 o r 18) mg/kg/week dur ing 24 hours a f t e r dosing a t t h e end o f t h e 26th t e s t week.
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Tab le 2
ROZMAN ET AL.
AUC o f 8-MOP Plasma L e v e l s i n Cynomolgous Monkeys
Weak o f Dose AUC o f 8-MOP (pg x h/ml) t rea tmen t (mg/kg 1
Males Fema 1 es
1 2 0.85 f 0.57a 1.21 f 0.79 6 8.50 ? 3.74 5.24 f 1.47
18 18.25 f 2.23 15.92 f 3.14
2 1.11 f. 0.60 1.76 f 0.65 13 6 8.69 f 1.67 7.22 f 1.94
18 14.15 f 6.67 10.01 t 6.93
2 0.41 f 0.39 0.21 f 0.26 26 6 8.06 t 3.41 5.46 f 1.86
18 23.12 f 3.08 14.98 ? 7.83
Mean f SD, n = 3
t o x i c i t y , c h r o n i c exposure (26 weeks) t o 8-MOP does n o t cause any
adverse e f f e c t s i n cynomolgous monkeys a t t h e 3 x 2 mg/kg/week dosage l e v e l . The o n l y s i g n i f i c a n t d i f f e r e n c e between c o n t r o l s and t h i s group o f an imals was decreased c a l c i u m l e v e l s i n t e s t week one. The l a c k o f a dose-response and t h e l a c k o f r e c u r r e n c e o f
t h i s f i n d i n g i n subsequent t e s t weeks suggest t h a t t h i s sma l l change may n o t be r e l a t e d t o 8-MOP.
A t t h e 3 x ( 6 and 18) mg/kg/week dosage l e v e l s t h e r e i s an apparent dose-response t o 8-MOP w i t h r e g a r d t o emesis. Female monkeys seem t o be more s e n s i t i v e t o t h e t o x i c i t y o f 8-MOP than a r e males as i n d i c a t e d b y a g r e a t e r f requency o f emesis, a g r e a t e r a l b e i t i n c o n s i s t e n t t r e n d i n h i s t o l o g i c a l , hemato log i ca l and e l e c t r o l y t e changes and one case o f m o r t a l i t y . The cause o f dea th i n t h i s animal was cons ide red 8-MOP-related. These d a t a a l s o i n d i c a t e t h a t cynomolgous monkeys (dose: 54 mg/kg/week f o r 26
weeks) ( p a r t i c u l a r l y females) may be more s e n s i t i v e t o 8-MOP t h a n a r e mice which d i d n o t show any adverse e f f e c t s a f t e r d a i l y doses o f 12 mg/kg (dose: 84 mg/kg/week) f o r one y e a r . However, i t 6
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TOXICITY OF 8-METHOXYPSORALEN 35
should be noted t h a t perhaps a more appropr ia te comparison o f dosage based on surface area y i e l d s a dose o f 0.072 mg/cm /week
2 f o r the monkeys and 0.036 mg/cm /week f o r the mice. Thus, t he statement about species s e n s i t i v i t y ought t o be viewed w i t h caut ion.
Large v a r i a b i l i t y i n plasma l e v e l s o f 8-MOP w i t h i n the groups
i s no t s u r p r i s i n g f o r a compound w i t h low s o l u b i l i t y i n water and
w i t h a sa turab le f i r s t pass e f f e c t as i t has been demonstrated f o r 8 8-MOP i n man and r a t s .
As a r e s u l t o f t h i s sa turab le f i r s t pass e f f e c t 8-MOP d isp lays
non l inear p h a r m a c o k i n e t i ~ s ~ i n man and r a t s . The f a c t t h a t the AUC of 8-MOP i n t h i s study i s l i n e a r between the 3 x (6 and 18)
mg/kg/week dosages bu t increases tw ice as f a s t as the dose between the 3 x ( 2 and 6 ) mg/kg/week dose l e v e l s i nd i ca tes , t h a t t he d i s p o s i t i o n o f 8-MOP i n the cynomolgous monkey i s a l s o sub jec t t o a sa turab le f i r s t pass e f f e c t (Figs. 5-7).
7 2
8-MOP has been shown t o be a 3-methylcholanthrene type inducer
o f cytochrome P-450 i n r a t s . Moreover, i t has a l s o been demon-
s t r a t e d t h a t t h i s enzyme induc t i on r e s u l t s i n increased b io t rans - format ion and plasma clearance o f 8-MOP . Thus, much reduced plasma l e v e l s o f 8-MOP a t the 3 x 2 mg/kg/week dosage l e v e l a f t e r 26 weeks could be due t o increased b io t rans format ion and clearance o f 8-MOP i n cynomolgous monkeys. However, no such e f fec t i s observable a t 13 weeks o f dosing w i t h the same dosage. Perhaps more impor tan t ly , such an e f f e c t i s a l s o l a c k i n g a t the h igher dosages a t a l l t ime po in ts . Therefore, an adapt ive process o the r
than enzyme induc t i on o r an u n i d e n t i f i e d e r r o r may be respons ib le f o r t h i s unexpected f i nd ing .
A l t e r n a t i v e l y , data o f t h i s study cou ld be i n t e r p r e t e d t h a t a t the 3 x 2 mg/kg/week dosage increased clearance i s due t o some adapt ive process which i s saturated a t the h igher dosages. The apparent lack o f increased 8-MOP a t t he h igher doses [3 x (6 and 18) mg/kg/week] could be the r e s u l t o f a sa tu ra t i on e f f e c t a t a low l e v e l . As a consequence the e f f e c t o f t h i s s a t u r a t i o n would be comparat ively small a t the h igher dosages and i t would remain w i t h i n the group v a r i a b i l i t y .
9
9
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36 ROZMAN ET AL.
It i s o f i n t e r e s t t o n o t e t h a t plasma p r o f i l e o f 8-MOP a t t h e
l owes t dose ( 3 x 2 mg/kg/week) i n cynomolgous monkeys c l o s e l y resembles t h a t i n humans a f t e r t h e r a p e u t i c doses (0.4-0.6 mg/kg)10s11'12. Cons ide r ing t h i s and o t h e r s i m i l a r i t i e s ( v o m i t i n g ,
s a t u r a b l e f i r s t pass e f f e c t ) , i t i s reasonable t o assume t h a t
c h r o n i c t o x i c i t y o f 8-MOP as d e f i n e d i n t h i s s t u d y i s q u i t e p r e d i c -
t i v e
1.
2 .
3.
4.
5.
6.
7.
8.
9.
f o r man.
REFERENCES
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Schmid, J., B r i c k l , R., and Zipp, H., The pharmacokinetics o f 8-methoxypsoralene, a response t o enzyme k i n e t i c s , 10 th European Drug Metabolism Workshop, Gu i l d fo rd , England, 07.-11.07.86 (1986).
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TOXICITY OF 8-METHOXYPSORALEN 37
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