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Pharmacology and pharmacokinetics of flutamide
PHARMACOLOGY
AND PHARMACOKINETICS
OF FLUTAMIDE RUDOLPH
NERI,
PH.D.
From the Department of Oncology, Clinical Research, Schering Plough Research, Kenilworth, New Jersey
ABSTlZACT-Flutamide is rapidly metabolized by hydroxylation of the side chain to SCH 16423 (alpha, alpha, alpha-tri~luoro-2-methyl-4’-nitro-m-lactotoluidide), the major metabolic product in all species studied, which is biologically active in vivo and in vitro studies. Flutamide exhibits its antiandrogenic activity by inhibiting androgen uptake and/or inhibition of nuclear binding of the androgens in the target tissues. At daily doses from 1 to 50 mg/kg body weight, flutamide reduced seminal vesicle and ventral prostate weights of intact male rats without affecting sexual potency. In addition, flutamide reduced the rate of DNA synthesis in the prostate of rats to a greater degree than other steroidal antiandrogens. The antiandrogenic activity was corroborated by the inhibition of ana!rogen-induced prostate hypertrophy in orchiectomized rats through the use of testosterone, testosterone propionate, dihydrotestosterone, androstenedione, and dehydroepiandrosterone. Flutamidle, given orally, reduced prostatic size in aged dogs with benign prostate hyperplasia after six weeks and one year. The baboon prostate was also reduced in size whenflutamide was administered three times a week for four weeks.
The potential clinical applications of antiandrogens in prostatic hyperplasias, acne, and hirsutism have prompted an intensive search for such agents by various laboratories. Several antiandrogenic agents have been reported, most of which have other hormonal properties, particularly progestational activity. One of the more potent antiandrogenic agents described thus far is cyproterone acetate (CPA), a steroidal agent synthesized by Schering A.G., West Berlin, Germany. Since these antiandrogenic agents possess other hormonal properties, which may negate their usefulness in prostatic hyperplasias, our efforts were directed toward finding an antiandrogen devoid of other hormonal activity. This article will extend the findings previously described for the potent antiandrogenic agent, flutamide (alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-m-propiontoluidide) (SCH 13521’1 . I.* Studies in Intact Rats To *assess the ability of flutamide to inhibit endogenous androgen, the compound was given at 50 mgidaly which is 10 times the minimum effective antiandrogen dose of 5 mg/kg body weight orally
once daily for sixty days. Prior to autopsy, the control and flutamide-treated rats were placed with female rats in estrus to determine the effect on sexual potency. The rats were then sacrificed, and the seminal vesicles, ventral prostate, and testes were removed and weighed. Seminal vesicle and ventral prostate weights were markedly reduced when compared with controls, whereas testes weights were not altered. Despite these decreases, sexual. potency remained intact since all the flutamide-treated rats sired a normal complement of pups sirnilar to control-animals.3 Studies in Orchiectomized
Inhibition
o.f
Rats
rate of DNA synthesis
Flutamide reduced the rate of DNA. synthesis in the prostate to a greater degree than a number of steroidal antiandrogens when given concomitantly with testosterone propionate.4
Inhibition of androgen-induced prostatr hypertrophy In orchiectomized rats, flutamide (5-25 mglkg) inhibited hypertrophy of the prostate induced by
SUPPLEMENTTO UROLOGY / OCTOBER 1989 / VOLUME XXXIV. NUMBER4
19
TABLE
I.
Effect of flutamide
on canine prostatic hyperplasia * Post-treatment
Pretreatment Epithelial Cell Height
Prostate Volume (Cm”)
Daily Dose (mgjkg) 0 1 5 10 25
(pm)
Prostate Volume (Cm3)
33.4 31.9 30.3 41.1 27.4
36.0 23.4 6.01 13.31 3.41
35.2 29.6 29.3 70.5 26.1
‘Two animals/group. ISignificantly different
from pretreatment
Epithelial Cell Height (pm) 34.2 28.5 4.11 5.0t 4.27
p < 0.01.
androgens such as testosterone, testosterone propionate, dihydrotestosterone, androstenedione, and dehydroepiandrosterone.5
tamide was decreased by 66 percent, whereas estramustine phosphate and diethylstilbestrol reduced prostate weight 32 percent and 42 percent, respectively.
Canine Prostatic Hyperplasia Benign prostatic hyperplasia (BPH), which occurs spontaneously in a percentage of aged dogs, has been used as a model for the development of chemotherapeutic agents for the treatment of BPH in man; although structural differences of the hypertrophied prostate in man and dog were recognized . Flutamide was administered to dogs orally once daily in gelatin capsules at doses of 1, 5, 10, and 25 mg/kg for six weeks and 5 mg/kg for one year. Verification of prostate hypertrophy was by caliper measurements (dorsal, ventral, dorsoventral widths, expressed as volume in cubic centimeters) and biopsy at laparotomy. After six weeks of treatment, the size of the prostate was reduced (Table I). Microscopic examination of the prostate revealed a marked reduction in the height of epithelial cells. The minimum effective dose was 5 mgikg. When flutamide was given orally for one year at 5 mg/kg, the reduction in prostate size was maintained, but the hyperplastic state returned two months after cessation of therapy. Libido and spermatogenesis were not adversely affected since these dogs mated and sired several litters.‘j Studies in Baboons Flutamide, diethylstilbestrol diphosphate (DES), and estramustine phosphate (Estracyt) were examined for their effects on the prostate.’ Flutamide was given intramuscularly, and estramustine phosphate and diethylstilbestrol were injected intravenously. All drugs were given at 5 mgikg three times a week for four weeks. Following treatment, all drugs produced a reduction in prostate size compared with the prostate size of normal animals. The mean prostate weight of the three baboons treated with flu-
20
SUPPLEMENT
Pharmacokinetics Flutamide administered orally to rats, cats, dogs, and rhesus monkeys at doses of 25 to 100 mg/kg was rapidly absorbed by all species. Plasma levels of flutamide and/or its metabolites were generally maximal four to six hours after dosing. When daily dosing was continued in rats and dogs, plasma samples collected prior to the daily dose showed no evidence of flutamide accumulation in rats; but flutamide doses above 35 mg/kg resulted in apparent accumulation in dogs. Excretion, when examined in rats, occurred mainly via the kidneys, and was essentially completed by three days after an oral dose.* Flutamide was rapidly metabolized by hydroxylation of the side chain to SCH 16423 (alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-m-lactotoluidide), the major metabolic product in all species. From two to six minor metabolites were observed in the various laboratory species studied. Tissue distribution of flutamide was examined in male rats given an oral dose of 14C-flutamide at 5 mg/kg. While flutamide concentration was generally low in all tissues examined, the metabolite SCH 16423 was present in concentrations up to 70 times the flutamide content by six hours after dosing. SCH 16423 was relatively concentrated in the rat ventral prostate and seminal vesicles, previously demonstrated to be the target organs of pharmacologic activity. Metabolism Single oral doses of flutamide ranging from 50 mgikg to 100 mg/kg given to dogs, rats, and cats resulted in peak plasma concentrations of the drug and its metabolites after about seven hours in the cats and four to six hours in the other species.
TO UROLOGY
/ OCTOBER
1989
/ VOLUME
XXXIV, NUMBER
4
In the monkey, the estimated half-life of an intravenous dose was forty-five to ninety minutes. Oral studies showed that flutamide was rapidly and extensively metabolized. Excretion of “H-flutamide and its metabolites occurred mainly via the kidneys, with about half of the label being recorded in urine and only 5 percent recovered in feces. The remainder of the tritium label was present as tritiated water formed through flutamide metabolism. The major urinary product was alpha, alpha, alpha-trifluoro-2-amino-5-nitrocresol. ‘The very rapid and almost complete conversion of flutamide to other compounds indicated that the biol.ogic activity shown by this substance is due to an active metabolite. SCH 16423 is the major metabolite in laboratory animals, and in man it has been shown to possess potent antiandrogenic activity.* Mechanism
TO UROL,OGY
The effects of flutamide on prostate tissue in vitro were also studied and were shown to be similar, though not as marked as those observed in vivo. The in vitro studies suggest that flutamide might achieve its results, at least in part, through an active metabolite, the hydroxylated form SCH 16423. Flutamide had no marked effect on the metabolic conversion by the rat ventral prostate of 3H-testosterone to its active metabolite 3H-dihydrotestosterone, or on any of the other metabolic products. These results are consistent with the conclusion that flutamide. or a metabolite, exerts its antiandrogenic effects on male secondary sex structures by an inhibition of androgen uptake and/or inhibition of nuclear binding of the androgens in the target tissues. 2000 Galloping Hill Road Kenilworth. New Jersey 07033
of Action
The effect of flutamide on tritiated testosterone and dihydrotestosterone uptake and metabolism in rat ventral prostate and seminal vesicle has been studied.” When testosterone-treated castrated rats were g:iven an oral dose of 15 mg/kg of either drug for three to seven days, flutamide did not suppress 3H-testosterone uptake by the tissue at sixty minutes following an intraperitoneal injection of the labeled steroid., which was given twenty-four hours after the last dose of drug. However, flutamide fully antagonized the effect of testosterone in maintaining prostate and seminal vesicle weights in these rats. In contrast, flutamide administered orally at 15 mgikg for four days, showed markedly inhibited “H-testosterone uptake and retention by prostate and prostate nuclei when labeled androgen was given three hours following the last dose of the drug. Similarly, a single dose co-administered via IP injection with either :‘H-testosterone or 3H-dihydrotestosterone inhibited uptake and retention of the labeled androgen by prostate whole tissue and nuclei. Flutamide was demonstrated to inhibit the formation of the nuclear 3S protein-3H androgen complex in addition to
SUPPLE:MENT
depressing whole tissue uptake and retention of 3Htestosterone.
/ OCTOBER
1989
ACKNO\~I.EI>GMENT. To Michelle Ewaskiew for assistance in the preparation of this manuscript.
I VOLUME
References 1. Neri RO, et al: A biological profile of a nonsteroidal antiandrogen SCH 13521, Endocrinology 91: 427 (1972). 2. Neri RO, and Peets EA: Biological aspects of antiandrogens. J Steroid Biochem 6: 815 (1975). 3. Neri RO, and Kassem N: Biological and clinical properties of antiandrogens, in Bresciani F (Ed): Progress in Cancer Research and Therapy 31, New York, Raven Press, 1984, p 507. 4. Sufrin G, and Coffey DS: A new model for studying the effect of drugs on prostatic growth, J Invest Urol 11: 45 (1973). 5. Neri RO, and Kassem N: Pharmacoloa and clinical uses of flutamide, in Furr JB, and Wakeling A (Eds): Pharmacology and Clinical Uses of Inhibitors of Hormone Secretion and Action. London, 1987, Bailliere Tindall, p 160. 6. Neri RO, and Monahan M: Effects of a no!,el nonsteroidal antiandrogen on canine prostatic hyperplasia. Invest Urol 10: 123 (1972). 7. Muntzing J, et al: Studies of antiprostatic agents in the baboon, Proc Sot Exp Biol Med 146: 849 (1974). 8. Katchen B, and Buxbaum S: Disposition of a new nonsteroid antiandrogen, alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-moroniontoluidide (flutamide). Proeress Renort No. 3867, Ken’ilworth, Schering Publication, 19ib. ’ 9. Peets EA, Henson MF, and Neri RO: On the mechanism of the antiandrogenic action of flutamide (alpha, alpha, alpha-trifluoro-2-methyl-4’.nitro-propiontoluidide) in the rat. Endocrinology 94: 532 (1974).
XXXIV. NUMBER
4
21
AND PHARMACOKINETICS
OF FLUTAMIDE RUDOLPH
NERI,
PH.D.
From the Department of Oncology, Clinical Research, Schering Plough Research, Kenilworth, New Jersey
ABSTlZACT-Flutamide is rapidly metabolized by hydroxylation of the side chain to SCH 16423 (alpha, alpha, alpha-tri~luoro-2-methyl-4’-nitro-m-lactotoluidide), the major metabolic product in all species studied, which is biologically active in vivo and in vitro studies. Flutamide exhibits its antiandrogenic activity by inhibiting androgen uptake and/or inhibition of nuclear binding of the androgens in the target tissues. At daily doses from 1 to 50 mg/kg body weight, flutamide reduced seminal vesicle and ventral prostate weights of intact male rats without affecting sexual potency. In addition, flutamide reduced the rate of DNA synthesis in the prostate of rats to a greater degree than other steroidal antiandrogens. The antiandrogenic activity was corroborated by the inhibition of ana!rogen-induced prostate hypertrophy in orchiectomized rats through the use of testosterone, testosterone propionate, dihydrotestosterone, androstenedione, and dehydroepiandrosterone. Flutamidle, given orally, reduced prostatic size in aged dogs with benign prostate hyperplasia after six weeks and one year. The baboon prostate was also reduced in size whenflutamide was administered three times a week for four weeks.
The potential clinical applications of antiandrogens in prostatic hyperplasias, acne, and hirsutism have prompted an intensive search for such agents by various laboratories. Several antiandrogenic agents have been reported, most of which have other hormonal properties, particularly progestational activity. One of the more potent antiandrogenic agents described thus far is cyproterone acetate (CPA), a steroidal agent synthesized by Schering A.G., West Berlin, Germany. Since these antiandrogenic agents possess other hormonal properties, which may negate their usefulness in prostatic hyperplasias, our efforts were directed toward finding an antiandrogen devoid of other hormonal activity. This article will extend the findings previously described for the potent antiandrogenic agent, flutamide (alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-m-propiontoluidide) (SCH 13521’1 . I.* Studies in Intact Rats To *assess the ability of flutamide to inhibit endogenous androgen, the compound was given at 50 mgidaly which is 10 times the minimum effective antiandrogen dose of 5 mg/kg body weight orally
once daily for sixty days. Prior to autopsy, the control and flutamide-treated rats were placed with female rats in estrus to determine the effect on sexual potency. The rats were then sacrificed, and the seminal vesicles, ventral prostate, and testes were removed and weighed. Seminal vesicle and ventral prostate weights were markedly reduced when compared with controls, whereas testes weights were not altered. Despite these decreases, sexual. potency remained intact since all the flutamide-treated rats sired a normal complement of pups sirnilar to control-animals.3 Studies in Orchiectomized
Inhibition
o.f
Rats
rate of DNA synthesis
Flutamide reduced the rate of DNA. synthesis in the prostate to a greater degree than a number of steroidal antiandrogens when given concomitantly with testosterone propionate.4
Inhibition of androgen-induced prostatr hypertrophy In orchiectomized rats, flutamide (5-25 mglkg) inhibited hypertrophy of the prostate induced by
SUPPLEMENTTO UROLOGY / OCTOBER 1989 / VOLUME XXXIV. NUMBER4
19
TABLE
I.
Effect of flutamide
on canine prostatic hyperplasia * Post-treatment
Pretreatment Epithelial Cell Height
Prostate Volume (Cm”)
Daily Dose (mgjkg) 0 1 5 10 25
(pm)
Prostate Volume (Cm3)
33.4 31.9 30.3 41.1 27.4
36.0 23.4 6.01 13.31 3.41
35.2 29.6 29.3 70.5 26.1
‘Two animals/group. ISignificantly different
from pretreatment
Epithelial Cell Height (pm) 34.2 28.5 4.11 5.0t 4.27
p < 0.01.
androgens such as testosterone, testosterone propionate, dihydrotestosterone, androstenedione, and dehydroepiandrosterone.5
tamide was decreased by 66 percent, whereas estramustine phosphate and diethylstilbestrol reduced prostate weight 32 percent and 42 percent, respectively.
Canine Prostatic Hyperplasia Benign prostatic hyperplasia (BPH), which occurs spontaneously in a percentage of aged dogs, has been used as a model for the development of chemotherapeutic agents for the treatment of BPH in man; although structural differences of the hypertrophied prostate in man and dog were recognized . Flutamide was administered to dogs orally once daily in gelatin capsules at doses of 1, 5, 10, and 25 mg/kg for six weeks and 5 mg/kg for one year. Verification of prostate hypertrophy was by caliper measurements (dorsal, ventral, dorsoventral widths, expressed as volume in cubic centimeters) and biopsy at laparotomy. After six weeks of treatment, the size of the prostate was reduced (Table I). Microscopic examination of the prostate revealed a marked reduction in the height of epithelial cells. The minimum effective dose was 5 mgikg. When flutamide was given orally for one year at 5 mg/kg, the reduction in prostate size was maintained, but the hyperplastic state returned two months after cessation of therapy. Libido and spermatogenesis were not adversely affected since these dogs mated and sired several litters.‘j Studies in Baboons Flutamide, diethylstilbestrol diphosphate (DES), and estramustine phosphate (Estracyt) were examined for their effects on the prostate.’ Flutamide was given intramuscularly, and estramustine phosphate and diethylstilbestrol were injected intravenously. All drugs were given at 5 mgikg three times a week for four weeks. Following treatment, all drugs produced a reduction in prostate size compared with the prostate size of normal animals. The mean prostate weight of the three baboons treated with flu-
20
SUPPLEMENT
Pharmacokinetics Flutamide administered orally to rats, cats, dogs, and rhesus monkeys at doses of 25 to 100 mg/kg was rapidly absorbed by all species. Plasma levels of flutamide and/or its metabolites were generally maximal four to six hours after dosing. When daily dosing was continued in rats and dogs, plasma samples collected prior to the daily dose showed no evidence of flutamide accumulation in rats; but flutamide doses above 35 mg/kg resulted in apparent accumulation in dogs. Excretion, when examined in rats, occurred mainly via the kidneys, and was essentially completed by three days after an oral dose.* Flutamide was rapidly metabolized by hydroxylation of the side chain to SCH 16423 (alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-m-lactotoluidide), the major metabolic product in all species. From two to six minor metabolites were observed in the various laboratory species studied. Tissue distribution of flutamide was examined in male rats given an oral dose of 14C-flutamide at 5 mg/kg. While flutamide concentration was generally low in all tissues examined, the metabolite SCH 16423 was present in concentrations up to 70 times the flutamide content by six hours after dosing. SCH 16423 was relatively concentrated in the rat ventral prostate and seminal vesicles, previously demonstrated to be the target organs of pharmacologic activity. Metabolism Single oral doses of flutamide ranging from 50 mgikg to 100 mg/kg given to dogs, rats, and cats resulted in peak plasma concentrations of the drug and its metabolites after about seven hours in the cats and four to six hours in the other species.
TO UROLOGY
/ OCTOBER
1989
/ VOLUME
XXXIV, NUMBER
4
In the monkey, the estimated half-life of an intravenous dose was forty-five to ninety minutes. Oral studies showed that flutamide was rapidly and extensively metabolized. Excretion of “H-flutamide and its metabolites occurred mainly via the kidneys, with about half of the label being recorded in urine and only 5 percent recovered in feces. The remainder of the tritium label was present as tritiated water formed through flutamide metabolism. The major urinary product was alpha, alpha, alpha-trifluoro-2-amino-5-nitrocresol. ‘The very rapid and almost complete conversion of flutamide to other compounds indicated that the biol.ogic activity shown by this substance is due to an active metabolite. SCH 16423 is the major metabolite in laboratory animals, and in man it has been shown to possess potent antiandrogenic activity.* Mechanism
TO UROL,OGY
The effects of flutamide on prostate tissue in vitro were also studied and were shown to be similar, though not as marked as those observed in vivo. The in vitro studies suggest that flutamide might achieve its results, at least in part, through an active metabolite, the hydroxylated form SCH 16423. Flutamide had no marked effect on the metabolic conversion by the rat ventral prostate of 3H-testosterone to its active metabolite 3H-dihydrotestosterone, or on any of the other metabolic products. These results are consistent with the conclusion that flutamide. or a metabolite, exerts its antiandrogenic effects on male secondary sex structures by an inhibition of androgen uptake and/or inhibition of nuclear binding of the androgens in the target tissues. 2000 Galloping Hill Road Kenilworth. New Jersey 07033
of Action
The effect of flutamide on tritiated testosterone and dihydrotestosterone uptake and metabolism in rat ventral prostate and seminal vesicle has been studied.” When testosterone-treated castrated rats were g:iven an oral dose of 15 mg/kg of either drug for three to seven days, flutamide did not suppress 3H-testosterone uptake by the tissue at sixty minutes following an intraperitoneal injection of the labeled steroid., which was given twenty-four hours after the last dose of drug. However, flutamide fully antagonized the effect of testosterone in maintaining prostate and seminal vesicle weights in these rats. In contrast, flutamide administered orally at 15 mgikg for four days, showed markedly inhibited “H-testosterone uptake and retention by prostate and prostate nuclei when labeled androgen was given three hours following the last dose of the drug. Similarly, a single dose co-administered via IP injection with either :‘H-testosterone or 3H-dihydrotestosterone inhibited uptake and retention of the labeled androgen by prostate whole tissue and nuclei. Flutamide was demonstrated to inhibit the formation of the nuclear 3S protein-3H androgen complex in addition to
SUPPLE:MENT
depressing whole tissue uptake and retention of 3Htestosterone.
/ OCTOBER
1989
ACKNO\~I.EI>GMENT. To Michelle Ewaskiew for assistance in the preparation of this manuscript.
I VOLUME
References 1. Neri RO, et al: A biological profile of a nonsteroidal antiandrogen SCH 13521, Endocrinology 91: 427 (1972). 2. Neri RO, and Peets EA: Biological aspects of antiandrogens. J Steroid Biochem 6: 815 (1975). 3. Neri RO, and Kassem N: Biological and clinical properties of antiandrogens, in Bresciani F (Ed): Progress in Cancer Research and Therapy 31, New York, Raven Press, 1984, p 507. 4. Sufrin G, and Coffey DS: A new model for studying the effect of drugs on prostatic growth, J Invest Urol 11: 45 (1973). 5. Neri RO, and Kassem N: Pharmacoloa and clinical uses of flutamide, in Furr JB, and Wakeling A (Eds): Pharmacology and Clinical Uses of Inhibitors of Hormone Secretion and Action. London, 1987, Bailliere Tindall, p 160. 6. Neri RO, and Monahan M: Effects of a no!,el nonsteroidal antiandrogen on canine prostatic hyperplasia. Invest Urol 10: 123 (1972). 7. Muntzing J, et al: Studies of antiprostatic agents in the baboon, Proc Sot Exp Biol Med 146: 849 (1974). 8. Katchen B, and Buxbaum S: Disposition of a new nonsteroid antiandrogen, alpha, alpha, alpha-trifluoro-2-methyl-4’-nitro-moroniontoluidide (flutamide). Proeress Renort No. 3867, Ken’ilworth, Schering Publication, 19ib. ’ 9. Peets EA, Henson MF, and Neri RO: On the mechanism of the antiandrogenic action of flutamide (alpha, alpha, alpha-trifluoro-2-methyl-4’.nitro-propiontoluidide) in the rat. Endocrinology 94: 532 (1974).
XXXIV. NUMBER
4
21