Drug Metabolism Reviews
ISSN: 0360-2532 (Print) 1097-9883 (Online) Journal homepage: http://www.tandfonline.com/loi/idmr20
Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics Frederick J. Di Carlo To cite this article: Frederick J. Di Carlo (1979) Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics, Drug Metabolism Reviews, 10:2, 225-237, DOI: 10.3109/03602537908997470 To link to this article: http://dx.doi.org/10.3109/03602537908997470
Published online: 22 Sep 2008.
Submit your article to this journal
Article views: 4
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=idmr20 Download by: [University of California, San Diego]
Date: 06 November 2015, At: 11:44
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
DRUG METABOLISM REVIEWS, 10(2), 225-237 (1979)
Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics* FREDERICK J. DI CARL0 Office of Pesticides and Toxic Substances (TS-792) United States Environmental Protection Agency Washington, D. C. 20460
I. 11.
111,
....................,......... ..,.... .. - -.-.... PROPERTIES OF OXISURAN .-. ..... A. Structure, Synthesis, and Physical Properties .. B. Pharmacologic Properties ............... .. ....... C. Toxicologic Properties .. ........... .. .. .......... METABOLISM AND PHARMACOKINETICS O F OXISURAN .......................................... A . Purpose and Scope of Studies .... .. .. . . . . . ... . . . B. Biotransformation Schema .. ... ......... ..... ... C. Immunologic Activities of Oxisuran Metabolites . . D. Interspecies Comparisons of Oxisuran Metabolism ........ . ...... . .............. .. ..... E. Immunologic Significance of Interspecies Differences in Oxisuran Metabolism . . . .. . .. . . . . ... F. Interspecies Comparisons of Oxisuran Pharmacokinetics ............................... INTRODUCTION
*
G. H.
Immunologic Significance of Interspecies Differences in Oxisuran Pharmacokinetics Overall Evaluation of Lower Species as Models for Oxisuran Immunologic Activity in Man
..........
226 227
227 228 229
229 229 230 231 231 232 234 235
235
*Presented at Third Annual Symposium on "Drug Metabolism Today and Tomorrow, I' held in Fort Washington, Pennsylvania, May 2 and 3, 1979, under the auspices of the Drug Metabolism Discussion Group. 225 Copyright 0 1980 by Marcel Dekker. Inc. All Rights Reserved. Neither this work n o r a n y part m a y he reproduced or t r a n s m i t t e d in any f o r m o r by a n y means, electronic or mechanical. including p h o t o c o p y i n g , microfilming, a n d recording, or by a n y i n f o r m a t i o n storage a n d retrieval s y s t e m , w i t h o u t permission in writing f r o m t h e publisher.
DI CARL0
226
................................... Dedication ......................................... References .........................................
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Acknowledgments
236 236 236
I. INTRODUCTION "The California s e a lion (Zalophus californianus) is a prime example of an animal in ample supply, but one requiring special environment for maintenance," wrote Schroeder [l ] in his contribution to the International Symposium on Comparative Pharmacology which was held in 1967. Less provocative, but memorable, was a presentation by Schmidt-Nielsen [2] at the same symposium. Entitled "The unusual animal, o r to expect the unexpected," Reference 11 reads, "Fleming, I. You only live twice ( P a r t 11). Playboy 11:78, May 1964. I T Other interesting papers appear in the symposium proceedings which were published a s an entire issue of Federation Proceedings, but the most outstanding was the course-setting contribution on "Comparative patterns of drug metabolism" by Williams [3]. H e cited the discovery of species differences in metabolism a century ago [4], and stressed the importance of understanding "how close the test animal is to man" with regard to metabolism a s well as biological response to pharmacologically and toxicologically active compounds. It is my view that the effort being expended to relate metabolism and pharmacokinetics to biological activity on an interspecies basis is appallingly minor, considering the possibilities of gaining clinically applicable knowledge in the short term. By regrettable contrast, mutagenicity work is reputed to be ongoing in more than 2 , 0 0 0 laboratories despite the view that the data a r e not expected to be applicable to human situations for decades. Furthermore, it i s eminently clear that simply performing more mutagenicity studies will not yield desirable quantitative clarification until investigations a r e performed in basic a r e a s which were discussed previously [5]. In 1977, Smith and Caldwell [ 61 evaluated subhuman primates versus nonprimates as metabolic models for man. The fact that their data base included only 2 3 compounds indicates the extent to which this research a r e a has been neglected. One of the compounds used in their interspecies comparison was oxisuran. When they considered both the biotransformation and excretion kinetics of
INTERSPE CIES METABOLISM/PHARMACOKINE TICS
227
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
0
OX ISU RAN
FIG. 1. Structure of oxisuran.
oxisuran, Smith and Caldwell stated, "On balance, therefore, taking into account both metabolic pattern and pharmacokinetics, the rhesus monkey provides a better model for the human situation than either the rat o r the dog. ' I However, later in the paper, these authors concluded in Table 12 that the rat was a Igood" model for oxisuran metabolism in man, while the dog and monkey were "fair" models. This ambivalence would be less unfortunate if the summary table were not so prominent and more apt to be cited than the earlier statement in the text. Additionally, there is question about the validity of the evaluation of the other 22 compounds because their interspecies pharmacokinetics appears to have been discounted. In any case, the purpose of the present document i s to examine oxisuran metabolism and pharmacokinetics in different species (rat, dog, pig, rhesus monkey, and man) in the light of the biological activities of its metabolites, and to attempt to determine which lower species may best reflect the human situation.
11. PROPERTIES O F OXISURAN
A . Structure, Synthesis, and Physical Properties Oxisuran is the generic name f o r 2-( [methylsulfinyl]acetyl) pyridine (Fig. 1). The compound was synthesized easily from ethyl picolinate and the anion of diinethylsulfoxide [TI. It is a low-melting white solid which, like dimethylsulfoxide, is very soluble in wat e r and in many organic solvents. It is noteworthy that oxisuran contains an asymmetric sulfur atom, but has not been resolved into i t s stereoisomers. ''C-Oxisuran was synthesized by Merrill and Vernice [a] for metabolism studies. Their method involved treating 2-bromopyridine with n-butyl lithium to produce a lithio derivative. Carbonation with
DI CARL0
228
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
14C0, converted the lithio compounds to carboxyl-labeled picolinic acid, which was then esterified with ethanol. The ester was converted to ''C-oxisuran by treatment with the dimethylsulfoxide anion generated with sodium hydride. B.
Pharmacologic Properties
A team of immunologists and chemists a t the Warner-Lambert Res e a r c h Institute worked collaboratively in an effort to discover a supp e r i o r immunosuppressive compound for use in organ and tissue transplantation. Their objective was to identify compounds which would distinguish the two limbs of the immune response. Specifically, they sought agents which would suppress cell-mediated immune mechanisms to promote graft acceptance by the host, but which would not inhibit humoral antibody formation and thereby endanger the patient by increasing susceptibility to infection. In 1972, Freedman and his colleagues [7] reported their s u c c e s s ; a compound which they called oxisuran was found to selectively s u p p r e s s cellmediated immunity, as measured by prolongation of skin allograft survival, without inhibiting humoral immunity in rodents. In companion experiments, 6-mercaptopurine suppressed antibody formation in both intact and graft-bearing animals. Further studies [ 91 showed that oxisuran prolonged the survival of fetal heart allografts in mice, mammary gland grafts a c r o s s a s e x b a r r i e r in r a t s , and skin allografts in dogs, without the concomitant suppression of hum o r a l antibody production which was observed to be induced by 6mercaptopurine o r azathioprine. Oxisuran was also found to prolong the functional survival time of heterotopic cardiac allografts in r a t s [ 103, and to inhibit expressions of other immunologic responses in several species [ l l ] . The latter inhibitory effects were on hypersensitivity to bacterial endotoxin in rabbits and mice, delayed hypersensitivity to ovalbumin in guinea pigs and to tuberculin in r a t s , and to contact hypersensitivity to dinitrochlorobenzene and dinitrofluorobenzene in guinea pigs [ l l ] . One hypothesis proposed for the mechanism of oxisuran action is that the compound "may influence thymusderived lymphocytes responsible for immunologic memory and cellmediated immunity, diverting differentiation from the latter toward the former" r111. Some effects of oxisuran on human immunologic responses were studied by Pirofsky e t al. [12] in nine patients with systemic lupus erythematosus o r dermatopolymyositis. They reported that the s u r vival of skin grafts donated by ABO-compatible nonrelatives was
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
IN TE RSPE CIE S META BOLISM/PHAR MACOKINETIC S
229
prolonged to a mean of 31 days in their oxisuran-treated patients, and that only two of the nine patients became sensitized to dinitrochlorobenzene. A variety of assays indicated that humoral immunologic reactions were unaffected by oxisuran while primary cellular immune reactivity was suppressed considerably, Oxisuran is not h o w n to possess other pharmacologic properties. A s examples, it is not anti-inflammatory [9] and does not prolong pentobarbital sleeping time o r accelerate phagocytosis unless administered in massive doses [IS]. C.
Toxicologic Properties
Briziarelli et al. [14] tenaciously performed acute, subacute, and subchronic toxicity studies of oxisuran, and detailed their rather unremarkable findings. However, the discussion section of their paper is interesting because it presents some of the toxic effects produced by immunosuppressants in current clinical use. Clearly, oxisuran is relatively innocuous, and is probably unique among immunosuppressive agents because it demonstrated no cytotoxicity in studies performed in vitro [g], in r a t s and dogs given daily doses up to 2 gm/ kg for 13 weeks [9], and in nine patients with lupus erythematosus o r dermatomyositis [12]. Further, oxisuran caused no teratogenic effects in mice and r a t s [ 71.
111. METABOLISM AND PHARMACOKINETICS OF OXISURAN A.
Purpose and Scope of Studies
One objective of these investigations may be described more precisely as an aspiration. It was to identify a mammalian species which resembled man with regard to oxisuran biotransformation and pharmacokinetics, and in which it would be possible to conduct organ transplantation studies. To this end, the fate of ''C-oxisuran was determined after oral administration to mice (unpublished), r a t s [Is], dogs [16], pigs [17], rhesus monkeys [18], baboons (unpublished), and humans [19]. Additional investigations were performed in vitro by our group [20] and by Bachur and Felsted [21] in o r d e r to clarify biotransformation pathways and some of the enzymic reactions involved.
DI C A R L 0
"30
~ C O C + S C H 3
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
OXISURAN SULFIDE
~ C H O H C H ~ S C H 3
1
OXISURAN ALCOHOL SULFIDE
i
b C O C H + H 3
(H)
.0
i
CHOHCH2SCH3 SULFATE
lo)
OX ISU RAN
OXISURAN ALCOHOL SULFOXIDES
0 c 0 c H 2 s 0 2 c H 3 OXISURAN SULFONE
FIG. 2.
(H)
(HI
N oCHOHCH2S02CH3 --.)SULFATE
OX ISU RAN ALCOHOL SULFONE
Pathways of oxisuran biotransformation.
B.
Biotransformation Schema
Figure 2 illustrates all of the metabolic conversions thought to lie involved in the biotransformation of oxisuran. Oxisuran undergoes three primary attacks; two a r e reductive and the third is oxidative. Sulfoxide reduction yields oxisuran sulfide, and carbonyl reduction forms oxisuran alcohol sulfoxide. Sulfoxide oxidation produces oxisuran sulfone. Two of these metabolites a r e subsequently reduced; oxisuran sulfide to oxisuran alcohol sulfide, and oxisuran sulfone to oxisuran alcohol sulfone. Oxisuran alcohol sulfoxide is oxidized to the corresponding sulfone, but there is no evidence to support its reduction to oxisuran alcohol sulfide [20]. T w o of the three alcohol metabolites undergo conjugation with sulfate; the sulfate of oxisuran alcohol sulfide w a s not detected. None of the three alcohols was observed to undergo glucuronidation. A s stated earlier, oxisuran contains an asymmetric sulfur atom. Reduction of the carhonyl group in oxisuran produced a second asynimetric center in the form of a secondary alcohol. Actually isolated
INTERSPECJE S ME TA BOLISM/PHARMACOKINETICS
231
from in vivo and in vitro experiments were two optically inactive diasterioisomers of oxisuran alcohol sulfoxide, which were resolved by TLC and GLC.
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
C. Immunologic Activities of Oxisuran Metabolites Chemists at the Warner-Lambert Research Institute synthesized both diasterioisomeric oxisuran alcohol sulfoxides, oxisuran sulfone and oxisuran alcohol sulfone, for immunological evaluation by Fox and Freedman [22]. Each oxisuran alcohol sulfoxide showed the same immunosuppressive activity and approximately the same potency a s oxisuran. Oxisuran sulfone was observed to have activities significantly different from those of -0xisuran; i. e . , it enhanced both allograft rejection and humoral antibody formation. While oxisuran alcohol sulfone did not affect either allograft rejection o r antibody formation, it was found to potentiate the selective activity of oxisuran when coadministered. Oxisuran sulfide was synthesized but its activity w a s not studied. D.
Interspecies Comparisons of Oxisuran Metabolism
Table 1 shows the quantities of oxisuran and i t s metabolites which were excreted into the urine of five species over time periods when the extents of 14C excretion were comparable. 14C-Oxisuran had been administered orally in all cases; the doses were 17 mg/kg for humans, 45 mg/kg for rhesus monkeys, and 50 mg/kg for pigs, dogs, and rats. The urine collection periods were 0 to 24 h r for monkeys, dogs, and rats, and 0 to 48 h r for humans and pigs. Plasma assays and the data in Table 1 demonstrate that oxisuran was metabolized very rapidly and extensively in all species. Low levels of the unchanged compound were found i n the urine of all species except the monkey. Two qualitatively notable points are evident; i.e., l ) oxisuran sulfone w a s absent from human urine, but was measurable in urine of the other species; and 2) dogs converted oxisuran to such large quantities of unidentified metabolites that i t seems highly probable that the metabolic pathways followed were additional to those identified for the other species, o r a t least for humans and rats. Carbonyl reduction was the predominant route of oxisuran biotransformation in man. Since oxisuran sulfone w a s not found, the excreted oxisuran alcohol sulfone and corresponding sulfate are considered to be derivatives of the initial reductive pathway, indicating
DI CARL0
"3"
TABLE 1 Urinary Composition over Periods of Comparable 14C Excretion after Oxisuran Administration
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
?h of doseC
Oxisuran
Mana
Monkeyb
0.8
0
Piga 0.8
Dogb Ratb 1
3
Oxisuran alcohol sulfoxides
38
18
7
15
26
Oxisuran alcohol sulfone
12
15
7
8
27
Oxisuran alcohol sulfide
3
-
5
-
-
Oxisuran sulfone
0
0.1
0.1
0
0.6
4
-
-
18
-
-
Oxisuran alcohol sulfoxide. SO, Oxisuran alcohol sulfone.SO, Unidentified metabolites Total
1 )
22
3 2 -
12 -
19 -
34 -
-1
60
67
61
58
58
"Data for urine collected 0 to 48 hr after dosing. bData for urine collected 0 to 24 h r after dosing. C A dash indicates no data available. that about 9270 (100 X 54/59) of all of the oxisuran metabolism proceeded through the oxisuran alcohol sulfoxides. A similar estimation suggests that only 40% (100 X 23/57) of the oxisuran administered to dogs was converted to this metabolite. In the absence of information on the relative kinetics of oxisuran sulfone reduction and oxisuran alcohol sulfide oxidation in monkeys, pigs, and dogs, it is possible to assign only minimum and maximum values for the extent of oxisuran reduction a t its carbonyl a s the first metabolic step. These minimum/maximum estimates a r e 27%/82% for monkeys, 18%/6OY0for pigs, and 47%/96'% for r a t s (Table 2). E
. ImmunologicinSignificance of Interspecies Differences Oxisuran Metabolism
In view of the facts that 1) oxisuran alcohol sulfoxides share the immunologic activities of the parent compound and 2) these sulfoxides
INTERSPE CIE S META BOLISM/PHARMACOKINETICS
233
TABLE 2 Derived Estimates of Extent of Oxisuran Conversion to Equipotent Oxisuran Alcohol Sulfoxides
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
% conversion Species
Observed
Minimum
Maxi mum
Man
96
Dog
40
-
-
Monkey
-
27
82
Pig
-
18
60
47
96
Rat
a r e formed in very significant quantities in all five species, i t appears very probable that oxisuran would express selective activity in all of these species. Further, i t would appear that the compound would best express its activity in man because metabolism by initial carbonyl reduction is so predominant in this species. The considerations developed in the preceding section allow direct comparisons of only man vs dog, and monkey vs pig vs rat. The first comparison leads to the clear conclusion that oxisuran should be f a r more effective in man (92%carbonyl reduction) than in the dog (40% carbonyl reduction). The second interspecies comparison is difficult to interpret; if one were to rely solely upon the numbers generated, oxisuran effectiveness would be expected to decrease in the sequence: rat, monkey, pig. However, there is comparative immunologic information which needs to be considered; namely, that oxisuran showed considerably higher potency in the rat than in the dog [91. This experimental finding can be accommodated by several metabolic interpretations. One is that the estimated maximum conversion of oxisuran to i t s sulfoxide alcohols (96%, Table 2) may more closely represent actuality than does the minimum value (47%) which would imply that the potency of oxisuran wa s comparable in the r a t and dog. Another possibility is that the extremely high quantity of unidentified metabolites produced in the dog may well represent the formation of compound(s) antagonistic to oxisuran activity [l8, 231.
DI CARL0
'34
TABLE 3 Half-Life Values of Oxisuran and Metabolites
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Man Total radioactivity Oxisuran
56 1
Half-life (hr) Monkey Pig Dog
HAt
21
21
12
10
-
-
-
-
Oxisuran alcohol sulfoxides
15
5
10
4a
3"
Oxisuran alcohol sulfone
56
21
I6
-
Oxisuran alcohol sulfide
54
17
27
-
-
aApproximated from t 1/2 for total radioactivity in this species and from mean t 1/2 values of oxisuran alcohol sulfoxides relative to t 1/2 values for total radioactivity, oxisuran alcohol sulfone, and oxisuran alcohol sulfide in humans, monkeys, and pigs,
F. Interspecies Comparisons of Oxisuran Pharmacokinetics
The elimination phase of oxisuran-derived radioactivity from plasma proceeded with half-life values of 56 h r in humans, 21 h r in monkeys and pigs, 12 h r in dogs, and 10 h r in rats. These data a r e useful f o r regulatory purposes, but obviously a r e less informative than the halflife values specifically for oxisuran and some of its metabolites (Table 3). Unfortunately, however, the compound-specific data w e r e obtainable in only three species (man, rhesus monkey, and pig). Unaltered oxisuran w a s not detected in monkey and pig plasma, and was briefly present in human plasma where it had a short halflife. The half-life of the immunologically active oxisuran alcohol sulfoxides decreased in the order 15 hr in humans, 1 0 h r in pigs, and 5 h r in monkeys, suggesting the expression of activity i n this sequence. Following is an effort to utilize the experimental data in Tallle 3 to develop approximations of the half-life of oxisuran alcohol sulfoxides in dogs and rats in order to extend oxisuran pharmacokinetics to cover all five species. A s shown in TalJle 3, the clearance of oxisuran alcohol sulfoxides from plasma i s much faster than the clearance of total radioactivity, oxisuran alcohol sulfone, and oxisuran alcohol sulfoxide. Therefore,
INTERSPE CIE S META BOLISM/PHARMACOKINETICS
235
TABLE 4
Evaluation of Lower Species a s Models f o r Oxisuran Immunologic Activity in Man
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Smith and Caldwell [6]
P r e s e n t review PharmacoMetabolism kinetics
Metabolism
Overall
Overall
Monkey Pig
Good
Fair
Good
Poor
Fair
-3
-a
Fair
Good
Good
Dog
Fair
Fair
Poor
Poor
Poor
Rat
Fair
Good
Good
Poor
Fair
aKot evaluated.
i t s e e m s reasonable to expect that the s a m e situation e x i s t s in dogs and rats. Using s i m p l e a r i t h m e t i c and combining the half-life r a t i o s f o r man, monkey, and pig, one obtains n u m b e r s ranging f r o m 3 . 1 to 3 . 3 whether one u s e s 14C/oxisuran alcohol sulfoxides, oxisuran alcohol sulfone/oxisuran alcohol sulfoxides, o r oxisuran alcohol sulfide/ oxisuran alcohol sulfoxides. T h e r e f o r e , the half-life of oxisuran alcohol sulfoxides w a s approximated as 4 h r (12/3.2) for the dog and 3 h r (10/3.2) f o r the r a t , To my knowledge, no one h a s used total radioactivity in t h i s presumptuous fashion, and many may adopt an a r t i c attitude toward this effort. G.
Immunologic Significance of I n t e r s p e c i e s Differences in Oxisuran Pharmacokinetics
F r o m the half-life values of o x i s u r a n alcohol sulfoxides which app e a r in Table 3, t h e s e d i a s t e r e o i s o m e r s may he expected to e x p r e s s t h e i r immunologic activity most effectively in humans. F u r t h e r , t h e s e compounds may be s u r m i s e d to be l e s s effective in pigs and far less effective in monkeys, d o g s , and r a t s . H.
Overall Evaluation of L o w e r Species a s Models f o r Oxisuran Immunoloeic Activitv in Man
Table 4 s u m m a r i z e s thc conclusions of an e a r l i e r r e p o r t [ 6 1 and those of the p r e s e n t analysis. Comparison of these conclusions shows
DI CARL0
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
"36
very little agreement, even with regard to interpreting the biotransformation findings alone, Reviewing the differences and their derivation would be a futile exercise. Consequently, it seems appropriate only to state that considerations of both the metabolism and pharmacokinetics of oxisuran lead this author to conclude that the pig may be the best of the four species to serve as a predictive model for the selective immunologic activity of oxisuran in man. This conclusion can be evaluated definitively only by additional investigation. Acknowledgments It is with nostalgic pleasure that I take this opportunity to thank my former colleagues for their collaboration, Dr. Malcolm ("Mike!') C r e w participated in almost all of our various efforts, working harmoniously (most of the time) with M i s s Myriam Melgar and Mrs. Rosie Gala. D r s . Franz Leinweher and Clive Greenough made our "last hurrah" on oxisuran a significant contribution to the biochemical literature. The collaboration of Drs. Felix de la Iglesia and Lorrie Mitchell assured the success of our study in rhesus monkeys, and Drs. Elliot Vesell and Tom Passananti played invaluable roles in our study in humans. Dedication This review is dedicated to the memory of Lloyd Haynes and Edward Merrill, two fine gentlemen who collaborated with me over an important segment of my professional career.
REFERENCES C. R. Schroeder, Fed. Proc., 26, 1157 (1967). K. Schmidt-Nielsen, X d . , 26, 981 (1967). R. T. Williams, I N.26, , 1029 (1967). M. Jaffe, Ber. Dtsch. Chem. Ges., Lo, 1925 (1877). F. J. Di Carlo, Drug.Metab. Rev., 2, v (1979). R. L. Smith and J. Caldwell, i n Drug Metabolism-From Microhe to Man (D. V. Parke and H. L. Smith, eds.), Taylor and Francis, London, 1977, pp. 331-356. H. H. Freedman, A. E . Fox, J. Shavel, Jr., andG. C. Morrison, Proc. SOC. Exp. Biol. Med., 139, 909 (1972). E . J. Merrill and G. G . Vernice, J. Labelled Comp., 8, 589 (1972).
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
INTE RSPE CJE S ME TABOLISM/PHARMACOKINETICS
237
A. E. Fox, D. L. Gawlak, D. L . Ballantyne, Jr., a n d H . H. F r e e d m a n , Transplantation, 2, 389 (1973). B. Husberg and I. Penn, P r o c . SOC. Exp. Biol. Med., 145, 669 (1974). A. E . Fox, J. L. Gingold, and H. H. Freedman, Infect. Imm x . , S, 549 (1973). B. Pirofsky, M. T. Nolte, a n d E . J. Bardana, Jr., T r a n s plantation, 20, 357 (1975). F. J. Di Carlo, M. D. Melgar, L. J. Haynes, and M. C. Crew, J. Reticuloendothelial SOC., l4, 387 (1973). G. B r i z i a r e l l i , D. Abrutyn, J. A. Tornaben, and E . Schwartz, Toxicol. Appl. Pharmacol,, 36, 4 9 (1976). F. J. Di Carlo, M. C. Crew, L. J. Haynes, and R . L. Gala, Xenobiotica, 2, 159 (1972). M. C. Crew, M. D. Melgar, L. J. Haynes, R. L. Gala, and F. J. Di Carlo, Ibid., 2, 431 (1972). M. C. C r e w a n d T J . Di Carlo, D r u g Metab. Dispos., 4, 147 (1976). M. C. Crew, L. Mitchell, F. d e la Iglesia, and F. J. Di Carlo, 3, 10 (1975). M. C. Crew, E . S. Vesell, G. T.Passananti, R. L. Gala, and F. J. Di Carlo, Clin. Pharmacol. Ther., 1_4, 1013 (1973). F.-J. Leinweber, R. C. Greenough, and F. J. Di Carlo, Xenobiotica, 5, 617 (1976). N. R. Bachur and R . L. Felsted, D r u g Metab. Dispos., 239 (1976). A. E . Fox and H. H. Freedman, J. Reticuloendothelial SOC., 15, 65a (1974). Russell, Murphy's Law, Celestial A r t s , Millbrae, California, 1978.
E.,
4,
ISSN: 0360-2532 (Print) 1097-9883 (Online) Journal homepage: http://www.tandfonline.com/loi/idmr20
Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics Frederick J. Di Carlo To cite this article: Frederick J. Di Carlo (1979) Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics, Drug Metabolism Reviews, 10:2, 225-237, DOI: 10.3109/03602537908997470 To link to this article: http://dx.doi.org/10.3109/03602537908997470
Published online: 22 Sep 2008.
Submit your article to this journal
Article views: 4
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=idmr20 Download by: [University of California, San Diego]
Date: 06 November 2015, At: 11:44
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
DRUG METABOLISM REVIEWS, 10(2), 225-237 (1979)
Interspecies Comparisons of Oxisuran Metabolism and Pharmacokinetics* FREDERICK J. DI CARL0 Office of Pesticides and Toxic Substances (TS-792) United States Environmental Protection Agency Washington, D. C. 20460
I. 11.
111,
....................,......... ..,.... .. - -.-.... PROPERTIES OF OXISURAN .-. ..... A. Structure, Synthesis, and Physical Properties .. B. Pharmacologic Properties ............... .. ....... C. Toxicologic Properties .. ........... .. .. .......... METABOLISM AND PHARMACOKINETICS O F OXISURAN .......................................... A . Purpose and Scope of Studies .... .. .. . . . . . ... . . . B. Biotransformation Schema .. ... ......... ..... ... C. Immunologic Activities of Oxisuran Metabolites . . D. Interspecies Comparisons of Oxisuran Metabolism ........ . ...... . .............. .. ..... E. Immunologic Significance of Interspecies Differences in Oxisuran Metabolism . . . .. . .. . . . . ... F. Interspecies Comparisons of Oxisuran Pharmacokinetics ............................... INTRODUCTION
*
G. H.
Immunologic Significance of Interspecies Differences in Oxisuran Pharmacokinetics Overall Evaluation of Lower Species as Models for Oxisuran Immunologic Activity in Man
..........
226 227
227 228 229
229 229 230 231 231 232 234 235
235
*Presented at Third Annual Symposium on "Drug Metabolism Today and Tomorrow, I' held in Fort Washington, Pennsylvania, May 2 and 3, 1979, under the auspices of the Drug Metabolism Discussion Group. 225 Copyright 0 1980 by Marcel Dekker. Inc. All Rights Reserved. Neither this work n o r a n y part m a y he reproduced or t r a n s m i t t e d in any f o r m o r by a n y means, electronic or mechanical. including p h o t o c o p y i n g , microfilming, a n d recording, or by a n y i n f o r m a t i o n storage a n d retrieval s y s t e m , w i t h o u t permission in writing f r o m t h e publisher.
DI CARL0
226
................................... Dedication ......................................... References .........................................
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Acknowledgments
236 236 236
I. INTRODUCTION "The California s e a lion (Zalophus californianus) is a prime example of an animal in ample supply, but one requiring special environment for maintenance," wrote Schroeder [l ] in his contribution to the International Symposium on Comparative Pharmacology which was held in 1967. Less provocative, but memorable, was a presentation by Schmidt-Nielsen [2] at the same symposium. Entitled "The unusual animal, o r to expect the unexpected," Reference 11 reads, "Fleming, I. You only live twice ( P a r t 11). Playboy 11:78, May 1964. I T Other interesting papers appear in the symposium proceedings which were published a s an entire issue of Federation Proceedings, but the most outstanding was the course-setting contribution on "Comparative patterns of drug metabolism" by Williams [3]. H e cited the discovery of species differences in metabolism a century ago [4], and stressed the importance of understanding "how close the test animal is to man" with regard to metabolism a s well as biological response to pharmacologically and toxicologically active compounds. It is my view that the effort being expended to relate metabolism and pharmacokinetics to biological activity on an interspecies basis is appallingly minor, considering the possibilities of gaining clinically applicable knowledge in the short term. By regrettable contrast, mutagenicity work is reputed to be ongoing in more than 2 , 0 0 0 laboratories despite the view that the data a r e not expected to be applicable to human situations for decades. Furthermore, it i s eminently clear that simply performing more mutagenicity studies will not yield desirable quantitative clarification until investigations a r e performed in basic a r e a s which were discussed previously [5]. In 1977, Smith and Caldwell [ 61 evaluated subhuman primates versus nonprimates as metabolic models for man. The fact that their data base included only 2 3 compounds indicates the extent to which this research a r e a has been neglected. One of the compounds used in their interspecies comparison was oxisuran. When they considered both the biotransformation and excretion kinetics of
INTERSPE CIES METABOLISM/PHARMACOKINE TICS
227
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
0
OX ISU RAN
FIG. 1. Structure of oxisuran.
oxisuran, Smith and Caldwell stated, "On balance, therefore, taking into account both metabolic pattern and pharmacokinetics, the rhesus monkey provides a better model for the human situation than either the rat o r the dog. ' I However, later in the paper, these authors concluded in Table 12 that the rat was a Igood" model for oxisuran metabolism in man, while the dog and monkey were "fair" models. This ambivalence would be less unfortunate if the summary table were not so prominent and more apt to be cited than the earlier statement in the text. Additionally, there is question about the validity of the evaluation of the other 22 compounds because their interspecies pharmacokinetics appears to have been discounted. In any case, the purpose of the present document i s to examine oxisuran metabolism and pharmacokinetics in different species (rat, dog, pig, rhesus monkey, and man) in the light of the biological activities of its metabolites, and to attempt to determine which lower species may best reflect the human situation.
11. PROPERTIES O F OXISURAN
A . Structure, Synthesis, and Physical Properties Oxisuran is the generic name f o r 2-( [methylsulfinyl]acetyl) pyridine (Fig. 1). The compound was synthesized easily from ethyl picolinate and the anion of diinethylsulfoxide [TI. It is a low-melting white solid which, like dimethylsulfoxide, is very soluble in wat e r and in many organic solvents. It is noteworthy that oxisuran contains an asymmetric sulfur atom, but has not been resolved into i t s stereoisomers. ''C-Oxisuran was synthesized by Merrill and Vernice [a] for metabolism studies. Their method involved treating 2-bromopyridine with n-butyl lithium to produce a lithio derivative. Carbonation with
DI CARL0
228
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
14C0, converted the lithio compounds to carboxyl-labeled picolinic acid, which was then esterified with ethanol. The ester was converted to ''C-oxisuran by treatment with the dimethylsulfoxide anion generated with sodium hydride. B.
Pharmacologic Properties
A team of immunologists and chemists a t the Warner-Lambert Res e a r c h Institute worked collaboratively in an effort to discover a supp e r i o r immunosuppressive compound for use in organ and tissue transplantation. Their objective was to identify compounds which would distinguish the two limbs of the immune response. Specifically, they sought agents which would suppress cell-mediated immune mechanisms to promote graft acceptance by the host, but which would not inhibit humoral antibody formation and thereby endanger the patient by increasing susceptibility to infection. In 1972, Freedman and his colleagues [7] reported their s u c c e s s ; a compound which they called oxisuran was found to selectively s u p p r e s s cellmediated immunity, as measured by prolongation of skin allograft survival, without inhibiting humoral immunity in rodents. In companion experiments, 6-mercaptopurine suppressed antibody formation in both intact and graft-bearing animals. Further studies [ 91 showed that oxisuran prolonged the survival of fetal heart allografts in mice, mammary gland grafts a c r o s s a s e x b a r r i e r in r a t s , and skin allografts in dogs, without the concomitant suppression of hum o r a l antibody production which was observed to be induced by 6mercaptopurine o r azathioprine. Oxisuran was also found to prolong the functional survival time of heterotopic cardiac allografts in r a t s [ 103, and to inhibit expressions of other immunologic responses in several species [ l l ] . The latter inhibitory effects were on hypersensitivity to bacterial endotoxin in rabbits and mice, delayed hypersensitivity to ovalbumin in guinea pigs and to tuberculin in r a t s , and to contact hypersensitivity to dinitrochlorobenzene and dinitrofluorobenzene in guinea pigs [ l l ] . One hypothesis proposed for the mechanism of oxisuran action is that the compound "may influence thymusderived lymphocytes responsible for immunologic memory and cellmediated immunity, diverting differentiation from the latter toward the former" r111. Some effects of oxisuran on human immunologic responses were studied by Pirofsky e t al. [12] in nine patients with systemic lupus erythematosus o r dermatopolymyositis. They reported that the s u r vival of skin grafts donated by ABO-compatible nonrelatives was
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
IN TE RSPE CIE S META BOLISM/PHAR MACOKINETIC S
229
prolonged to a mean of 31 days in their oxisuran-treated patients, and that only two of the nine patients became sensitized to dinitrochlorobenzene. A variety of assays indicated that humoral immunologic reactions were unaffected by oxisuran while primary cellular immune reactivity was suppressed considerably, Oxisuran is not h o w n to possess other pharmacologic properties. A s examples, it is not anti-inflammatory [9] and does not prolong pentobarbital sleeping time o r accelerate phagocytosis unless administered in massive doses [IS]. C.
Toxicologic Properties
Briziarelli et al. [14] tenaciously performed acute, subacute, and subchronic toxicity studies of oxisuran, and detailed their rather unremarkable findings. However, the discussion section of their paper is interesting because it presents some of the toxic effects produced by immunosuppressants in current clinical use. Clearly, oxisuran is relatively innocuous, and is probably unique among immunosuppressive agents because it demonstrated no cytotoxicity in studies performed in vitro [g], in r a t s and dogs given daily doses up to 2 gm/ kg for 13 weeks [9], and in nine patients with lupus erythematosus o r dermatomyositis [12]. Further, oxisuran caused no teratogenic effects in mice and r a t s [ 71.
111. METABOLISM AND PHARMACOKINETICS OF OXISURAN A.
Purpose and Scope of Studies
One objective of these investigations may be described more precisely as an aspiration. It was to identify a mammalian species which resembled man with regard to oxisuran biotransformation and pharmacokinetics, and in which it would be possible to conduct organ transplantation studies. To this end, the fate of ''C-oxisuran was determined after oral administration to mice (unpublished), r a t s [Is], dogs [16], pigs [17], rhesus monkeys [18], baboons (unpublished), and humans [19]. Additional investigations were performed in vitro by our group [20] and by Bachur and Felsted [21] in o r d e r to clarify biotransformation pathways and some of the enzymic reactions involved.
DI C A R L 0
"30
~ C O C + S C H 3
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
OXISURAN SULFIDE
~ C H O H C H ~ S C H 3
1
OXISURAN ALCOHOL SULFIDE
i
b C O C H + H 3
(H)
.0
i
CHOHCH2SCH3 SULFATE
lo)
OX ISU RAN
OXISURAN ALCOHOL SULFOXIDES
0 c 0 c H 2 s 0 2 c H 3 OXISURAN SULFONE
FIG. 2.
(H)
(HI
N oCHOHCH2S02CH3 --.)SULFATE
OX ISU RAN ALCOHOL SULFONE
Pathways of oxisuran biotransformation.
B.
Biotransformation Schema
Figure 2 illustrates all of the metabolic conversions thought to lie involved in the biotransformation of oxisuran. Oxisuran undergoes three primary attacks; two a r e reductive and the third is oxidative. Sulfoxide reduction yields oxisuran sulfide, and carbonyl reduction forms oxisuran alcohol sulfoxide. Sulfoxide oxidation produces oxisuran sulfone. Two of these metabolites a r e subsequently reduced; oxisuran sulfide to oxisuran alcohol sulfide, and oxisuran sulfone to oxisuran alcohol sulfone. Oxisuran alcohol sulfoxide is oxidized to the corresponding sulfone, but there is no evidence to support its reduction to oxisuran alcohol sulfide [20]. T w o of the three alcohol metabolites undergo conjugation with sulfate; the sulfate of oxisuran alcohol sulfide w a s not detected. None of the three alcohols was observed to undergo glucuronidation. A s stated earlier, oxisuran contains an asymmetric sulfur atom. Reduction of the carhonyl group in oxisuran produced a second asynimetric center in the form of a secondary alcohol. Actually isolated
INTERSPECJE S ME TA BOLISM/PHARMACOKINETICS
231
from in vivo and in vitro experiments were two optically inactive diasterioisomers of oxisuran alcohol sulfoxide, which were resolved by TLC and GLC.
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
C. Immunologic Activities of Oxisuran Metabolites Chemists at the Warner-Lambert Research Institute synthesized both diasterioisomeric oxisuran alcohol sulfoxides, oxisuran sulfone and oxisuran alcohol sulfone, for immunological evaluation by Fox and Freedman [22]. Each oxisuran alcohol sulfoxide showed the same immunosuppressive activity and approximately the same potency a s oxisuran. Oxisuran sulfone was observed to have activities significantly different from those of -0xisuran; i. e . , it enhanced both allograft rejection and humoral antibody formation. While oxisuran alcohol sulfone did not affect either allograft rejection o r antibody formation, it was found to potentiate the selective activity of oxisuran when coadministered. Oxisuran sulfide was synthesized but its activity w a s not studied. D.
Interspecies Comparisons of Oxisuran Metabolism
Table 1 shows the quantities of oxisuran and i t s metabolites which were excreted into the urine of five species over time periods when the extents of 14C excretion were comparable. 14C-Oxisuran had been administered orally in all cases; the doses were 17 mg/kg for humans, 45 mg/kg for rhesus monkeys, and 50 mg/kg for pigs, dogs, and rats. The urine collection periods were 0 to 24 h r for monkeys, dogs, and rats, and 0 to 48 h r for humans and pigs. Plasma assays and the data in Table 1 demonstrate that oxisuran was metabolized very rapidly and extensively in all species. Low levels of the unchanged compound were found i n the urine of all species except the monkey. Two qualitatively notable points are evident; i.e., l ) oxisuran sulfone w a s absent from human urine, but was measurable in urine of the other species; and 2) dogs converted oxisuran to such large quantities of unidentified metabolites that i t seems highly probable that the metabolic pathways followed were additional to those identified for the other species, o r a t least for humans and rats. Carbonyl reduction was the predominant route of oxisuran biotransformation in man. Since oxisuran sulfone w a s not found, the excreted oxisuran alcohol sulfone and corresponding sulfate are considered to be derivatives of the initial reductive pathway, indicating
DI CARL0
"3"
TABLE 1 Urinary Composition over Periods of Comparable 14C Excretion after Oxisuran Administration
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
?h of doseC
Oxisuran
Mana
Monkeyb
0.8
0
Piga 0.8
Dogb Ratb 1
3
Oxisuran alcohol sulfoxides
38
18
7
15
26
Oxisuran alcohol sulfone
12
15
7
8
27
Oxisuran alcohol sulfide
3
-
5
-
-
Oxisuran sulfone
0
0.1
0.1
0
0.6
4
-
-
18
-
-
Oxisuran alcohol sulfoxide. SO, Oxisuran alcohol sulfone.SO, Unidentified metabolites Total
1 )
22
3 2 -
12 -
19 -
34 -
-1
60
67
61
58
58
"Data for urine collected 0 to 48 hr after dosing. bData for urine collected 0 to 24 h r after dosing. C A dash indicates no data available. that about 9270 (100 X 54/59) of all of the oxisuran metabolism proceeded through the oxisuran alcohol sulfoxides. A similar estimation suggests that only 40% (100 X 23/57) of the oxisuran administered to dogs was converted to this metabolite. In the absence of information on the relative kinetics of oxisuran sulfone reduction and oxisuran alcohol sulfide oxidation in monkeys, pigs, and dogs, it is possible to assign only minimum and maximum values for the extent of oxisuran reduction a t its carbonyl a s the first metabolic step. These minimum/maximum estimates a r e 27%/82% for monkeys, 18%/6OY0for pigs, and 47%/96'% for r a t s (Table 2). E
. ImmunologicinSignificance of Interspecies Differences Oxisuran Metabolism
In view of the facts that 1) oxisuran alcohol sulfoxides share the immunologic activities of the parent compound and 2) these sulfoxides
INTERSPE CIE S META BOLISM/PHARMACOKINETICS
233
TABLE 2 Derived Estimates of Extent of Oxisuran Conversion to Equipotent Oxisuran Alcohol Sulfoxides
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
% conversion Species
Observed
Minimum
Maxi mum
Man
96
Dog
40
-
-
Monkey
-
27
82
Pig
-
18
60
47
96
Rat
a r e formed in very significant quantities in all five species, i t appears very probable that oxisuran would express selective activity in all of these species. Further, i t would appear that the compound would best express its activity in man because metabolism by initial carbonyl reduction is so predominant in this species. The considerations developed in the preceding section allow direct comparisons of only man vs dog, and monkey vs pig vs rat. The first comparison leads to the clear conclusion that oxisuran should be f a r more effective in man (92%carbonyl reduction) than in the dog (40% carbonyl reduction). The second interspecies comparison is difficult to interpret; if one were to rely solely upon the numbers generated, oxisuran effectiveness would be expected to decrease in the sequence: rat, monkey, pig. However, there is comparative immunologic information which needs to be considered; namely, that oxisuran showed considerably higher potency in the rat than in the dog [91. This experimental finding can be accommodated by several metabolic interpretations. One is that the estimated maximum conversion of oxisuran to i t s sulfoxide alcohols (96%, Table 2) may more closely represent actuality than does the minimum value (47%) which would imply that the potency of oxisuran wa s comparable in the r a t and dog. Another possibility is that the extremely high quantity of unidentified metabolites produced in the dog may well represent the formation of compound(s) antagonistic to oxisuran activity [l8, 231.
DI CARL0
'34
TABLE 3 Half-Life Values of Oxisuran and Metabolites
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Man Total radioactivity Oxisuran
56 1
Half-life (hr) Monkey Pig Dog
HAt
21
21
12
10
-
-
-
-
Oxisuran alcohol sulfoxides
15
5
10
4a
3"
Oxisuran alcohol sulfone
56
21
I6
-
Oxisuran alcohol sulfide
54
17
27
-
-
aApproximated from t 1/2 for total radioactivity in this species and from mean t 1/2 values of oxisuran alcohol sulfoxides relative to t 1/2 values for total radioactivity, oxisuran alcohol sulfone, and oxisuran alcohol sulfide in humans, monkeys, and pigs,
F. Interspecies Comparisons of Oxisuran Pharmacokinetics
The elimination phase of oxisuran-derived radioactivity from plasma proceeded with half-life values of 56 h r in humans, 21 h r in monkeys and pigs, 12 h r in dogs, and 10 h r in rats. These data a r e useful f o r regulatory purposes, but obviously a r e less informative than the halflife values specifically for oxisuran and some of its metabolites (Table 3). Unfortunately, however, the compound-specific data w e r e obtainable in only three species (man, rhesus monkey, and pig). Unaltered oxisuran w a s not detected in monkey and pig plasma, and was briefly present in human plasma where it had a short halflife. The half-life of the immunologically active oxisuran alcohol sulfoxides decreased in the order 15 hr in humans, 1 0 h r in pigs, and 5 h r in monkeys, suggesting the expression of activity i n this sequence. Following is an effort to utilize the experimental data in Tallle 3 to develop approximations of the half-life of oxisuran alcohol sulfoxides in dogs and rats in order to extend oxisuran pharmacokinetics to cover all five species. A s shown in TalJle 3, the clearance of oxisuran alcohol sulfoxides from plasma i s much faster than the clearance of total radioactivity, oxisuran alcohol sulfone, and oxisuran alcohol sulfoxide. Therefore,
INTERSPE CIE S META BOLISM/PHARMACOKINETICS
235
TABLE 4
Evaluation of Lower Species a s Models f o r Oxisuran Immunologic Activity in Man
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
Smith and Caldwell [6]
P r e s e n t review PharmacoMetabolism kinetics
Metabolism
Overall
Overall
Monkey Pig
Good
Fair
Good
Poor
Fair
-3
-a
Fair
Good
Good
Dog
Fair
Fair
Poor
Poor
Poor
Rat
Fair
Good
Good
Poor
Fair
aKot evaluated.
i t s e e m s reasonable to expect that the s a m e situation e x i s t s in dogs and rats. Using s i m p l e a r i t h m e t i c and combining the half-life r a t i o s f o r man, monkey, and pig, one obtains n u m b e r s ranging f r o m 3 . 1 to 3 . 3 whether one u s e s 14C/oxisuran alcohol sulfoxides, oxisuran alcohol sulfone/oxisuran alcohol sulfoxides, o r oxisuran alcohol sulfide/ oxisuran alcohol sulfoxides. T h e r e f o r e , the half-life of oxisuran alcohol sulfoxides w a s approximated as 4 h r (12/3.2) for the dog and 3 h r (10/3.2) f o r the r a t , To my knowledge, no one h a s used total radioactivity in t h i s presumptuous fashion, and many may adopt an a r t i c attitude toward this effort. G.
Immunologic Significance of I n t e r s p e c i e s Differences in Oxisuran Pharmacokinetics
F r o m the half-life values of o x i s u r a n alcohol sulfoxides which app e a r in Table 3, t h e s e d i a s t e r e o i s o m e r s may he expected to e x p r e s s t h e i r immunologic activity most effectively in humans. F u r t h e r , t h e s e compounds may be s u r m i s e d to be l e s s effective in pigs and far less effective in monkeys, d o g s , and r a t s . H.
Overall Evaluation of L o w e r Species a s Models f o r Oxisuran Immunoloeic Activitv in Man
Table 4 s u m m a r i z e s thc conclusions of an e a r l i e r r e p o r t [ 6 1 and those of the p r e s e n t analysis. Comparison of these conclusions shows
DI CARL0
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
"36
very little agreement, even with regard to interpreting the biotransformation findings alone, Reviewing the differences and their derivation would be a futile exercise. Consequently, it seems appropriate only to state that considerations of both the metabolism and pharmacokinetics of oxisuran lead this author to conclude that the pig may be the best of the four species to serve as a predictive model for the selective immunologic activity of oxisuran in man. This conclusion can be evaluated definitively only by additional investigation. Acknowledgments It is with nostalgic pleasure that I take this opportunity to thank my former colleagues for their collaboration, Dr. Malcolm ("Mike!') C r e w participated in almost all of our various efforts, working harmoniously (most of the time) with M i s s Myriam Melgar and Mrs. Rosie Gala. D r s . Franz Leinweher and Clive Greenough made our "last hurrah" on oxisuran a significant contribution to the biochemical literature. The collaboration of Drs. Felix de la Iglesia and Lorrie Mitchell assured the success of our study in rhesus monkeys, and Drs. Elliot Vesell and Tom Passananti played invaluable roles in our study in humans. Dedication This review is dedicated to the memory of Lloyd Haynes and Edward Merrill, two fine gentlemen who collaborated with me over an important segment of my professional career.
REFERENCES C. R. Schroeder, Fed. Proc., 26, 1157 (1967). K. Schmidt-Nielsen, X d . , 26, 981 (1967). R. T. Williams, I N.26, , 1029 (1967). M. Jaffe, Ber. Dtsch. Chem. Ges., Lo, 1925 (1877). F. J. Di Carlo, Drug.Metab. Rev., 2, v (1979). R. L. Smith and J. Caldwell, i n Drug Metabolism-From Microhe to Man (D. V. Parke and H. L. Smith, eds.), Taylor and Francis, London, 1977, pp. 331-356. H. H. Freedman, A. E . Fox, J. Shavel, Jr., andG. C. Morrison, Proc. SOC. Exp. Biol. Med., 139, 909 (1972). E . J. Merrill and G. G . Vernice, J. Labelled Comp., 8, 589 (1972).
Downloaded by [University of California, San Diego] at 11:44 06 November 2015
INTE RSPE CJE S ME TABOLISM/PHARMACOKINETICS
237
A. E. Fox, D. L. Gawlak, D. L . Ballantyne, Jr., a n d H . H. F r e e d m a n , Transplantation, 2, 389 (1973). B. Husberg and I. Penn, P r o c . SOC. Exp. Biol. Med., 145, 669 (1974). A. E . Fox, J. L. Gingold, and H. H. Freedman, Infect. Imm x . , S, 549 (1973). B. Pirofsky, M. T. Nolte, a n d E . J. Bardana, Jr., T r a n s plantation, 20, 357 (1975). F. J. Di Carlo, M. D. Melgar, L. J. Haynes, and M. C. Crew, J. Reticuloendothelial SOC., l4, 387 (1973). G. B r i z i a r e l l i , D. Abrutyn, J. A. Tornaben, and E . Schwartz, Toxicol. Appl. Pharmacol,, 36, 4 9 (1976). F. J. Di Carlo, M. C. Crew, L. J. Haynes, and R . L. Gala, Xenobiotica, 2, 159 (1972). M. C. Crew, M. D. Melgar, L. J. Haynes, R. L. Gala, and F. J. Di Carlo, Ibid., 2, 431 (1972). M. C. C r e w a n d T J . Di Carlo, D r u g Metab. Dispos., 4, 147 (1976). M. C. Crew, L. Mitchell, F. d e la Iglesia, and F. J. Di Carlo, 3, 10 (1975). M. C. Crew, E . S. Vesell, G. T.Passananti, R. L. Gala, and F. J. Di Carlo, Clin. Pharmacol. Ther., 1_4, 1013 (1973). F.-J. Leinweber, R. C. Greenough, and F. J. Di Carlo, Xenobiotica, 5, 617 (1976). N. R. Bachur and R . L. Felsted, D r u g Metab. Dispos., 239 (1976). A. E . Fox and H. H. Freedman, J. Reticuloendothelial SOC., 15, 65a (1974). Russell, Murphy's Law, Celestial A r t s , Millbrae, California, 1978.
E.,
4,
