Relative potency of bicalutamide (Casodex) and flutamide (Eulexin)
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Androgen Antagonists↗
Biomedical subjects
B J Furr
Publications and source records attributed to B J Furr.
Casodex (bicalutamide): overview of a new antiandrogen developed for the treatment of prostate cancer.
Casodex (bicalutamide, Zeneca Ltd), has been developed for prostate cancer therapy. Its preclinical, pharmacokinetic, pharmacodynamic, clinical efficacy and tolerability data are described. Casodex is a potent and specific non-steroidal antiandrogen. Clinical studies indicated that Casodex is orally bioavailable and well absorbed, with a plasma half-life of around 1 week. A Casodex dose of 50 mg daily decreased prostatic acid phosphatase comparable with castration. This dose was, therefore, evaluated initially as monotherapy and later as a component of maximal androgen blockade. Using prostate specific antigen as an end point, Casodex 150 mg daily was well-tolerated with demonstrable evidence of activity. Casodex 150 mg monotherapy was less effective than castration in terms of efficacy in patients with metastatic disease at entry. However, in patients non-metastatic at entry, Casodex 150 mg monotherapy appeared to be equivalent to castration in terms of time to death (data immature). Casodex was well-tolerated. In combination treatment, Casodex at 50 mg daily was at least as effective as 750 mg flutamide (Eulexin, Schering-Plough International) with respect to time to treatment failure, equivalent in terms of survival, and better tolerated with respect to diarrhoea. In conclusion, Casodex is a good option for the antiandrogen component of maximal androgen blockade.
Androgen Antagonists↗
The preclinical development of bicalutamide: pharmacodynamics and mechanism of action.
OBJECTIVES. To describe the preclinical development of bicalutamide and clarify its pharmacodynamics and mechanisms of action. Bicalutamide was developed from a series of nonsteroidal compounds related to flutamide that showed a range of pharmacologic activity from full androgen agonist to pure antiandrogen, including progestational and antiprogestational properties. METHODS AND RESULTS. Bicalutamide is a pure antiandrogen that binds to rat, dog, and human prostate; the affinity compared with the natural ligand 5 alpha-dihydrotestosterone is low, but bicalutamide has an affinity for the rat androgen receptor approximately four times higher than hydroxyflutamide, the active metabolite of flutamide. Bicalutamide also binds to androgen receptors found in the LNCaP human prostate tumor and the Shionogi S115 mouse mammary tumor cell line, as well as androgen receptors transfected into CV-1 and HeLa cells. In all cases, bicalutamide behaves as a pure antiandrogen and inhibits gene expression and cell growth stimulated by androgen. Studies with the LNCaP cell line are particularly interesting, as these cells contain a mutated androgen receptor (codon 868, Thr-->Ala), which behaves idiosyncratically with other antiandrogens (cyproterone acetate and flutamide): both these antiandrogens act as agonists in this cell line and stimulate proliferation. Studies in vivo show that bicalutamide is a potent antiandrogen in the rat. In immature, castrated male rats treated daily with testosterone propionate, bicalutamide produces a profound inhibition of accessory sex organ (ventral prostate and seminal vesicles) growth at oral doses as low as 0.25 mg/kg; it is more active in this test than flutamide or cyproterone acetate. In mature male rats, daily oral doses of bicalutamide produce a dose-related reduction in weights of the ventral prostate glands and seminal vesicles: in this test, bicalutamide is around five times as potent as flutamide. In contrast to flutamide, which produces dose-related, marked increases in serum luteinizing hormone (LH) and testosterone as a consequence of the central inhibition of the negative feedback effects of androgens on the hypothalamic-pituitary-tests axis, bicalutamide has little effect on serum LH and testosterone; i.e., it is peripherally selective. The peripheral selectivity of bicalutamide in the rat is not due to differences between the prostate versus hypothalamic or pituitary receptors, as bicalutamide reverses the suppressive effect of testosterone on luteinizing hormone-releasing hormone (LHRH) secretion from hypothalamic slices in vitro and is as effective as flutamide at sensitizing the pituitary gland to secrete LH in response to administered LHRH. The peripheral selectivity of bicalutamide has now been shown to be due to poor penetration across the blood-brain barrier: tissue distribution studies with [3H]bicalutamide show that although it is concentrated in the organs of metabolism and secretion as well as in the prostate, the pituitary glands, and the seminal vesicles, levels in the hypothalamus and the central nervous system (CNS) are much lower than in blood. Indeed, it is probable that levels found in the CNS reflect levels of blood contamination. In dogs, bicalutamide has exquisite potency and causes dose-related atrophy of the prostate gland and epididymides; with an oral ED50 of 0.1 mg/kg, it is around 50 times as potent as flutamide in this species and also more potent than the steroidal antiandrogen WIN49596 and the 5 alpha-reductase inhibitor MK-906. Even at substantial multiples of the active dose (up to 100 mg/kg orally), bicalutamide failed to increase serum testosterone, so it is also peripherally selective in the dog.
Androgen Antagonists↗
The development of Casodex (bicalutamide): preclinical studies.
Casodex (bicalutamide, Zeneca Limited) was developed for the treatment of prostate cancer from a series of nonsteroidal compounds related to flutamide. Casodex is a selective antiandrogen that binds to rat, dog and human prostate androgen receptors, and has approximately a 4-fold higher affinity for the rat androgen receptor than hydroxyflutamide, the active metabolite of flutamide. Casodex also binds to androgen receptors found in the LNCaP human prostate tumour and the Shionogi S115 mouse mammary tumour cell line, as well as androgen receptors transfected into CV-1 and HeLa cells. In all cases, Casodex behaves as a 'pure' antiandrogen and inhibits gene expression and cell growth stimulated by androgens. Studies in vivo show that Casodex is a potent antiandrogen in the rat. In contrast to flutamide, which produces dose-related, marked increases in serum luteinising hormone (LH) and testosterone, Casodex has little effect on serum LH and testosterone; that is, it is peripherally selective. The peripheral selectivity of Casodex has now been shown to be due to poor penetration across the blood-brain barrier. In dogs, Casodex has exquisite potency and causes dose-related atrophy of the prostate gland and epididymis; with an oral ED50 of 0.1 mg/kg, it is about 50 times as potent as flutamide in this species. Casodex is also peripherally selective in the dog. In addition, magnetic resonance imaging studies have shown that Casodex is a potent antiandrogen in the monkey. Casodex, at a daily oral dose of 25 mg/kg effected a highly significant reduction in the growth of Dunning R3327H transplantable rat prostate tumours that was equivalent to that achieved by either surgical or medical castration with the LH-releasing hormone agonist Zoladex (goserelin). In a comparative study, flutamide was shown to be both less potent and less active than Casodex. In these preclinical studies, Casodex was well tolerated. The preclinical properties of Casodex give it advantages, with respect to potency, tolerability and the maintenance of effective antiandrogen serum concentrations, over other available antiandrogens. Moreover, it has a half-life that is compatible with once-daily administration.
Androgen Antagonists↗
Casodex: preclinical studies and controversies.
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Effects of the gonadotrophin-releasing hormone agonist 'Zoladex' upon pituitary and gonadal function in hypogonadal (hpg) male mice: a comparison with normal male and testicular feminized (tfm) mice.
Hypogonadal (hpg) mutant mice, with a congenital deficiency of hypothalamic gonadotrophin-releasing hormone (GnRH), and testicular feminized (tfm) mice, which lack a functional androgen receptor, were used to study the effects of the potent GnRH agonist 'Zoladex' (ICI 118630; D-Ser (Bu(t))6, Azgly10-GnRH) on pituitary and gonadal function. Zoladex (0.5 mg) in a sustained-release lactide-glycolide copolymer depot was administered subcutaneously under anaesthesia and was left in place for 7 days, after which time the effects of the drug upon pituitary and serum gonadotrophin concentrations, glycoprotein hormone subunit mRNAs and testicular morphology were investigated. At the pituitary level, Zoladex treatment resulted in a substantial reduction in LH content in normal males, and LH content was depressed in hpg mice even below the basal levels normally found in these mutants. Pituitary LH content in the Zoladex-treated animals was depressed in the tfm groups, but not to the same levels as those found in the normal and castrated normal mice. Zoladex treatment at the time of castration prevented the post-operative elevation in serum LH associated with castration alone. In the androgen-deficient tfm mouse, Zoladex did not depress the normally elevated serum LH levels. Serum LH in the hpg animals was, in all cases, below the limit of detection of the assay. Pituitary FSH content was depressed into the hpg range in both the normal and castrated animals, but there was no further depression in the hpg mice. The pituitary content was reduced in the tfm mice, again the effects not being as dramatic as in the normal and castrated animals. Serum FSH content, as measured by radioimmunoassay, was depressed by 50% in normal mice; there was no reduction in the hpg mice, however. With regard to pituitary gonadotrophic hormone gene expression, Zoladex administration to normal mice caused a dramatic reduction in LH beta mRNA content, to a level approximating that found in untreated hpg mice. The drug also depressed LH beta mRNA in the castrated group to the hpg range when given at the time of castration, whereas in untreated castrated mice there was a significant increase in LH beta mRNA. In the tfm mouse, which can be considered as a model for long-term failure of androgen feedback, Zoladex again induced a fall in LH beta mRNA, but not to the same extent as in the normal and normal castrated group. Zoladex had no effect on the already low levels of LH beta mRNA found in hpg mice.(ABSTRACT TRUNCATED AT 400 WORDS)
Androgens↗
Use of the nonsteroidal anti-androgen Casodex in advanced prostatic carcinoma.
Pure anti-androgens have advantages over steroidal anti-androgens of the cyproterone acetate type in the treatment of patients with advanced prostate cancer because they do not have steroidal side effects or such a marked inhibitory effect on libido. In addition, the long half-life of a pure anti-androgen such as Casodex results in maintenance of high serum anti-androgen concentrations, which allays concern over the clinical significance of any small rise in serum testosterone concentrations. The anti-androgen of choice for the treatment of androgen-responsive diseases has yet to be defined. However, this choice should be based on extensive clinical evaluations of a drug as monotherapy. As always, the clinical efficacy and tolerability of the drug will be important factors in determining the anti-androgen of choice; however, favorable pharmacokinetics should be emphasized in the treatment of a disease in which high and sustained concentrations of antagonist must be present to prevent androgenic stimulation. Casodex, a pure anti-androgen with a relatively long half-life, produces objective and subjective responses similar to those of surgical or pharmacologic castration and is well tolerated. Its profile makes it a strong candidate for consideration as the future anti-androgen of choice in the treatment of advanced prostate cancer.
Androgen Antagonists↗
A new extra long acting depot preparation of the LHRH analogue Zoladex. First endocrinological and pharmacokinetic data in patients with advanced prostate cancer.
A new depot formulation of the LHRH analogue Zoladex (goserelin acetate) has been developed which releases the drug over a period of at least 3 months as judged by measurement of drug content in depots at intervals after insertion in male rats and by the suppression of oestrogen secretion and oestrus in female rats. This formulation is based on the lactide/glycolide polymer system used for the standard 1-month Zoladex depot, but the dose has been increased to 10.8 mg and the characteristics have been modified to enable a longer release of drug to be achieved. Thirty-eight patients with histologically proven, locally advanced (stage T3 or T4) and/or metastatic prostate cancer were treated with this new longer acting LHRH analogue depot formulation containing 10.8 mg Zoladex. After initial increase of serum testosterone in the first week of therapy, castration levels were reached in all patients after 4 weeks and this was maintained for more than 14 weeks. At the time of depot exhaustion, when escape from castration levels of androgen occurred, all patients received a single injection of a standard 1-month depot containing 3.6 mg Zoladex which restored castration levels of androgen thus showing that the pituitary gland was again suppressed. The tolerance and acceptability of the longer-acting depot is high and comparable to the 1-month depot. Taking into account social and psychological factors, patients with advanced prostate carcinoma will soon be able to be treated with a longer acting LHRH depot formulation every 3 months an alternative of the 1-month depot now widely used clinically.
Aged↗
Protection of spermatogenesis in rats from the cytotoxic procarbazine by the depot formulation of Zoladex, a gonadotropin-releasing hormone agonist.
The hypothesis that adjuvant treatment designed to produce testicular atrophy would preserve fertility in males receiving cancer chemotherapy was examined in the rat. Testicular atrophy was induced by a depot formulation of Zoladex [D-Ser(Bu(t))6-Aza-Gly10-GnRH], a gonadotropin-releasing hormone (GnRH) analogue. The experiments were conducted in albino Wistar as well as in the piebald variegated rat. Rats received the depot Zoladex formulation 2 weeks before and immediately prior to being treated with four weekly doses of procarbazine (200 mg/kg). Testicular function was evaluated 50 and 90 days after the last procarbazine dose. Procarbazine induced testicular atrophy concomitant with marked germinal cell aplasia in both strains of rat. In the Wistar rat adjuvant treatment with Zoladex caused slight but not significant alleviation of the testicular toxicity of procarbazine. The testicular toxicity of procarbazine was more extensive in the piebald variegated rat, and 50 days after the last procarbazine treatment the testes were small, sperm were absent, and the stem cell index was close to zero. Serum luteinizing hormone (LH) concentrations were raised and testicular LH receptor binding was low in the presence of normal serum and testicular testosterone concentrations, indicating compensated Leydig cell failure. Testicular weight and sperm content, as well as LH receptor binding, were still decreased in rats which received both Zoladex and procarbazine, suggesting that the analogue offered no protection. However, the stem cell index of the seminiferous tubules in the procarbazine-Zoladex-treated rats was not significantly different from vehicle-treated rats, which suggested that recovery from the effects of procarbazine was in progress. Ninety days after the end of procarbazine treatment alone the testes of rats were still atrophied and there was little evidence of active spermatogenesis. Leydig cell failure appeared to have progressed as, in addition to the low testicular LH receptor content and raised serum LH concentration, the prostate and seminal vehicle weights were decreased. The combination of Zoladex treatment with procarbazine was successful in preserving testicular function in the piebald variegated rats as virtually all the functional and morphological parameters of both the seminiferous tubule and the Leydig cell were not significantly different from those of vehicle-treated rats. This study demonstrates for the first time that effective gonadal protection from the toxic effects of procarbazine chemotherapy can be achieved by administration of the depot formulation of the gonadotropin-releasing hormone analogue Zoladex. The results show clearly that complete suppression of spermatogenesis is not a prerequisite for the successful outcome of treatments designed to protect the gonad from cytotoxic chemotherapy.
Animals↗
A new longer-acting LHRH analog depot: preliminary results of a Dutch open phase II clinical study on a 10.8 mg Zoladex 3-monthly depot.
A new longer-acting depot formulation containing 10.8 mg Zoladex was administered subcutaneously without anesthetic to 35 patients with advanced carcinoma of the prostate. Pharmacodynamic and pharmacokinetic data show that following a transient elevation in serum LH and testosterone, the levels of both hormones decrease. Serum testosterone reaches the castrate range in all patients by week 4 and remains at this level for at least 12 weeks. The serum Zoladex profile shows that castrate serum testosterone values can be sustained by very low serum concentrations of the drug of around 0.05 ng/ml. In this preliminary report, the efficacy and safety of this new longer-acting 3-month depot formulation of 10.8 mg Zoladex has been shown to be comparable to the 1-month depot formulation of 3.6 mg Zoladex, in patients with advanced carcinoma of the prostate.
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Casodex: preclinical studies.
Antiandrogens are effective drugs in the treatment of advanced prostatic cancer. The main problems associated with their use are their short half-lives, leading to fluctuating serum levels, and their non-selectivity, which leads to increases in serum LH and testosterone through centrally-mediated actions. Casodex is a pure, potent antiandrogen which, in pre-clinical studies, has been shown to have a long half-life and a high degree of peripheral selectivity. Casodex is as effective as surgical castration or medical castration with Zoladex in inhibiting the growth of a transplantable Dunning prostate tumor in rats. These properties suggest that Casodex, given once daily, would be an effective and well-tolerated monotherapy for advanced prostatic cancer.
Anilides↗
A possible explanation for the peripheral selectivity of a novel non-steroidal pure antiandrogen, Casodex (ICI 176,334).
The in vivo antiandrogenicity of Casodex has been confirmed and characterised. Androgen receptor (AR) binding assays of rat ventral prostate gland cytosols revealed a relative binding affinity (RBA) for the AR of 0.267 and a k1 of 1.25 x 10(-7) M for Casodex. In addition, the peripheral selectivity of Casodex relative to other non-steroidal antiandrogens was confirmed in that daily treatment of non-castrated rats with Casodex (25 mg kg-1) did not elicit any changes in serum LH and testosterone concentrations relative to vehicle-treated controls, whereas elevated serum LH and testosterone were observed in rats treated with flutamide (25 mg kg-1). The peripheral selectivity of Casodex in the intact male rat was related to the distribution of radiolabelled antiandrogen following intravenous injection. All tissues with the exception of the hypothalamus and cerebral cortex (CC) sequestered radioactivity such that the tissue:serum ratio (TSR) for the drug was greater than unity. In the testis, the TSR was less than unity 1 h after injection but approached unity 5 h after injection and was greater than unity 10 h after injection. This may be explained by the presence of a blood-testis barrier for the drug, resulting in delayed equilibration between the blood and testis tissue. By comparison, an order of magnitude lower amounts of radioactivity in the hypothalamus and CC were maintained for the 10 h period after injection. These data, together with known physicochemical properties of Casodex suggest that a blood-brain barrier exists for the drug which results in exclusion of this antiandrogen from central sites of androgen negative feedback and that this accounts for its peripherally selective antihormonal profile.
Androgen Antagonists↗
"Casodex" (ICI 176,334)--a new, pure, peripherally-selective anti-androgen: preclinical studies.
The relative merits of the steroidal anti-androgen, cyproterone acetate, and the non-steroidal anti-androgens flutamide and nilutamide, are reviewed. It is concluded that pure anti-androgens offer some advantages over cyproterone acetate but that they each have some features which merit improvement. A new compound which was a pure anti-androgen, peripherally selective, well tolerated with a long half-life would have significant advantages. Preclinical studies in rats and dogs show that Casodex (ICI 176,334) is a potent pure anti-androgen which is well tolerated and has a long half-life. Casodex induces marked regression of the prostate yet fails to cause the substantial elevation in serum LH and testosterone seen with flutamide and nilutamide; it is thus peripherally selective. Casodex is as effective as surgical or medical castration with Zoladex in limiting the growth of the transplantable androgen-responsive Dunning rat prostate tumour. Such a profile makes Casodex a strong candidate as the future anti-androgen of choice for the treatment of prostate cancer and benign prostate hypertrophy.
Androgen Antagonists↗
Pharmacology of the luteinising hormone-releasing hormone (LHRH) analogue, Zoladex.
To prevent progression of sex hormone-responsive prostate and breast tumours, anti-androgens and anti-oestrogens are commonly used to induce androgen and oestrogen withdrawal. Zoladex is a potent luteinising hormone-releasing hormone agonist analogue, which has a selective effect on pituitary gonadotrophin release, and is highly effective at inducing regression of sex hormone-responsive prostate and breast tumours. Its depot formulation, active for at least 28 days, is convenient to administer and well tolerated and for the treatment of sex hormone-responsive tumours in men and women, Zoladex is an effective alternative to surgery.
Animals↗
Biodegradable polymers for controlled release of peptides and proteins.
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Animals↗
Anti-oestrogens in the treatment of breast and gynaecological cancers.
Tamoxifen is an effective therapy for advanced breast cancer and is well tolerated. In elderly patients or in those with inoperable primary disease tamoxifen is as effective as surgery or radiotherapy. In early breast cancer tamoxifen is associated with a prolongation of disease-free and overall survival, at least in women over the age of 50 with nodal involvement. Major trials now suggest that the effectiveness of tamoxifen may, however, be independent of age, menopausal status and of nodal status, but this remains the subject of substantial controversy. These trials also suggest that longer periods of tamoxifen treatment (more than 2 years) are better than shorter treatments and, therefore, adjuvant tamoxifen until recurrence may be the final treatment of choice for such patients. Tamoxifen is also effective in the treatment of endometrial cancer; however, there seems little advantage in combining the drug with progestogens, either concurrently or sequentially. Modest clinical benefit has been seen in patients with ovarian cancer treated with tamoxifen but the majority of patients have been heavily pretreated. Clinical trials of tamoxifen as primary therapy for this disease are warranted. Tamoxifen has probably been the most widely studied endocrine therapy for breast cancer and the subject of some of the longest and best controlled studies. Although there is no doubt that tamoxifen is effective in adjuvant therapy of breast cancer, the precise position and duration of treatment remains to be defined unequivocally. Future use in the treatment of women at high risk of developing breast cancer--so-called prophylactic therapy--depends on improvements in risk factor determination and a continuing evaluation of the possible clinical relevance of findings in animals given long-term treatment with high doses of the drug.
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ICI 176,334: a novel non-steroidal, peripherally-selective antiandrogen.
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Androgen Antagonists↗
ICI 176,334: a novel non-steroidal, peripherally selective antiandrogen.
Pure antiandrogens, like flutamide, antagonize androgen action both peripherally and centrally at the hypothalamic-pituitary axis, which leads to an increase in LH and testosterone secretion. A new non-steroidal antiandrogen ICI 176,334 [2RS)-4'-cyano-3-(4-fluorophenylsulphonyl)-2-hydroxy-2-methyl-3'- trifluoromethyl)propion-anilide) has now been discovered which causes regression of the accessory sex organs but does not increase serum concentrations of LH and androgens. ICI 176,334 binds to rat prostate androgen receptors with an affinity around fourfold that of hydroxyflutamide. When administered s.c. concurrently with testosterone propionate (200 micrograms/kg) for 7 days to immature castrated rats, ICI 176,334 (10 mg/kg) significantly (P less than 0.001) inhibited growth of the seminal vesicles and ventral prostate gland. Oral administration of ICI 176,334 at doses of 1, 5 and 25 mg/kg for 14 days to adult rats caused a dose-related reduction in accessory sex organ weights but had no effect on the testes. None of these doses caused a significant increase in serum LH and testosterone. Flutamide was around fourfold less potent and significantly increased serum LH and testosterone at the higher doses. ICI 176,334 was well tolerated. ICI 176,334 should, therefore, prove useful for the treatment of androgen-responsive benign and malignant diseases.
Androgen Antagonists↗