Roland De Coster

Pharmacokinetics of the novel antipsychotic agent risperidone and the prolactin response in healthy subjects

The pharmacokinetics of a novel antipsychotic agent, risperidone, and the prolactin response were studied in 12 dextromethorphan‐phenotyped healthy men after administration of 1 mg risperidone intravenously, intramuscularly, and orally. The formation of the equipotent major metabolite, 9‐hydroxyrisperidone, exhibited CYP2D6‐related polymorphism. The plasma area under the concentration—time curve from time zero to infinity ratio of 9‐hydroxyrisperidone to risperidone averaged 3 (intravenous and intramuscular) and 6 (oral administration) in the extensive metabolizers and 0.2 in the poor metabolizers. Risperidone half‐life was about 3 hours in extensive metabolizers and 22 hours in poor metabolizers. Risperidone absolute oral bioavailability was 66%. The pharmacokinetics of the active moiety (risperidone plus 9‐hydroxyrisperidone) varied little among subjects (mean terminal half‐life, 20 ± 21/2 hours; absolute oral and intramuscular bioavailability, 100%). The prolactin response correlated best with the plasma active moiety, which showed little hysteresis. It is concluded that risperidone metabolic polymorphism on increased plasma prolactin is minimal and that the active moiety is clinically relevant.

EFFECTS OF HIGH DOSE KETOCONAZOLE THERAPY ON THE MAIN PLASMA TESTICULAR AND ADRENAL STEROIDS IN PREVIOUSLY UNTREATED PROSTATIC CANCER PATIENTS

In vitro, ketoconazole has been shown to block testicular and adrenal 17,20‐lyase, which converts progestins to androgens. At higher concentrations, it also inhibits 11β‐hydroxylase, 20,22‐desmolase and 17α‐hydroxylase. To determine the differential hormonal effects of a 2‐week ketoconazole high‐dose therapy, the plasma levels of 10 major androgens, gluco‐ and mineralocorticoids were measured in 14 previously untreated patients with metastatic prostate cancer. Within 24 h, plasma testosterone fell from 14·6 ± 1·4 nmol/l (mean ± SEM) to 3·7 ± 0·7 nmol/l. Thereafter, it decreased to about 2·5 nmol/l and remained at that level. Plasma androstenedione and dehydroepiandrosterone decreased more gradually, respectively from 3·1 ± 0·4 nmol/l to 0·64 ± 0·17 nmol/l and from 6·6 ± 1·0 nmol/l to 2·82 ± 0·55 nmol/l (on day 14). In contrast, 17α‐hydroxyprogesterone and progesterone rose respectively 2‐ and 5‐fold. Plasma cortisol and aldosterone levels remained unchanged whereas 11‐deoxycorticosterone and 11‐deoxycortisol rose by factors of 14 and 6·7 respectively. Plasma corticosterone also increased, but to a much lesser extent (3‐fold). These results demonstrate that ketoconazole high dose therapy blocks mainly the 17,20‐lyase of both adrenal and testis. In addition it inhibits mitochondrial 11β‐hydroxylase to a lesser extent. The inhibition of 20,22‐desmolase also seems to be of little clinical relevance. However, since clinical or laboratory symptoms suggestive of hypo‐adrenalism have been reported in a small minority of patients, replacement therapy should be considered in such cases.

Vorozole, a specific non-steroidal aromatase inhibitor

SummaryVorozole, the (+)-(S)-isomer of a new triazole compound, is a potent and selective aromatase inhibitor.In vitro, the compound is over a thousandfold more active than aminoglutethimide.In vivo, the compound very potently inhibits ovarian, peripheral, and tumoral aromatase. Vorozole shows anin vitro selectivity margin of 10,000-fold for aromatase inhibition as compared to inhibition of other P450- and non-P450-dependent reactions. This selectivity was confirmed in the ratin vivo. Vorozole, like ovariectomy, almost completely reduces tumor growth in the DMBA-induced mammary carcinoma model in the rat.In postmenopausal women, vorozole very potently inhibits peripheral conversion of androstenedione to estrone. After chronic administration, plasma estradiol levels are reduced while the levels of adrenal gluco- and mineralo-corticoids remain unchanged. Vorozole has excellent oral bioavailability and exerts linear, dose-proportional pharmacokinetics.

Comparative effects of the aromatase inhibitor R76713 and of its enantiomers R83839 and R83842 on steroid biosynthesis in vitro and in vivo.

R76713 (6-[(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-methyl-1H- benzotriazole) is a selective, non-steroidal aromatase inhibitor containing an asymmetric carbon atom. In this paper, we compare the effects of R76713 (racemate) with its enantiomers R83839 (the levo-isomer) and R83842 (the dextro-isomer) on steroid biosynthesis in rat cells in vitro and in the rat in vivo. In rat granulosa cells, aromatase activity was inhibited by 50% at concentrations of 0.93 nM of R76713, 240 nM of R83839 and 0.44 nM of R83842, revealing a 545-fold difference in activity between both enantiomers. Up to 1 microM, none of the compounds had any effect on steroid production in primary cultures of rat testicular cells. Above this concentration all three compounds showed a similar slight inhibition of androgen synthesis with a concomitant increase in the precursor progestins, indicative for some effect on the 17-hydroxylase/17,20-lyase enzyme. In rat adrenal cells none of the compounds showed any effect on corticosterone synthesis. At concentrations above 1 microM there was an increase in the levels of 11-deoxycorticosterone pointing towards an inhibition of the 11-hydroxylase enzyme. This increase was more pronounced for R83839 than for R76713 and R83842. In vivo, in PMSG-primed rats, R83842 reduced plasma estradiol by 50%. 2 h after oral administration of 0.0034 mg/kg, whereas 0.011 mg/kg of R76713 and 0.25 mg/kg of R83839 were needed to obtain the same result. Oral administration of up to 20 mg/kg of the compounds did not significantly affect plasma levels of adrenal steroids in LHRH/ACTH-injected rats. Plasma testosterone was lowered at 10 and 20 mg/kg of R83842 and at the highest dose (20 mg/kg) of R76713 and R83839. In conclusion, the present study shows that the aromatase inhibitory activity of R76713 resides almost exclusively in its dextro-isomer R83842. R83842 exhibits a specificity for aromatase as compared to other enzymes involved in steroid biosynthesis of at least a 1000-fold in vitro as well as in vivo. This confirms the extreme selectivity previously found for the racemate.

Antitumoral Effects of Liarozole in Androgen-Dependent and Independent R3327-Dunning Prostate Adenocarcinomas

We examined the in vivo antitumoral effects of liarozole against androgen-dependent and independent Dunning rat prostatic tumors. Liarozole, applied as a dietary admixture, at a dose of 120 mg./100 gm. food, equivalent to 100 mg./kg. per day, inhibited the growth of the slow growing, well-differentiated, androgen-dependent Dunning-H tumor (median tumor volume decrease of 60%). At the same dose it also significantly reduced the growth of the androgen-independent, moderately differentiated PIF-1 (-60%) and androgen-independent, anaplastic AT-6 tumors (-73%). The growth of AT-6 sq tumor showing squamous metaplasia was unaffected by liarozole. When administered by oral gavage, liarozole at 40 (-82%) mg./kg. twice a day was as effective as castration (-92%) in reducing the androgen-dependent, poorly differentiated Dunning R3327-G tumor. Liarozole, administered by gavage, twice a day, also significantly reduced median tumor volume in the androgen-independent, AT-6 sq (-90% at 60 mg./kg., twice a day). This difference between liarozole administration by gavage and food admixture will have to be taken into account in further experimental studies. Inhibition of the growth of several androgen-dependent and, chiefly, androgen-independent Dunning prostate carcinoma sublines that differ widely in their histological degree of differentiation and growth rate suggests that liarozole may be a suitable agent for evaluation in second line treatment of hormone refractory prostate carcinoma in patients who relapse after androgen ablation.

Aromatase inhibition by R 76 713: a kinetic analysis in rat ovarian homogenates

Reaction kinetics of the aromatase enzyme and of a new nonsteroidal aromatase inhibitor, R 76 713 (6-[(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)-methyl]-1-methyl-1H- benzotriazole), were studied in ovarian homogenates obtained from pregnant mares serum gonadotropin (PMSG)-injected female Wistar rats. The Km (Michaelis constant) of the aromatase enzyme with androstenedione as the substrate was 47 +/- 13 nM; for testosterone as the substrate, a value of 159 +/- 10 nM was found. In the presence of increasing concentrations of R 76 713, the Km increased while the Vmax (maximal velocity of enzyme-catalyzed reaction) remained unchanged. Using androstenedione and testosterone as the substrate, Lineweaver-Burk analysis of the data showed a Ki (dissociation constant of the enzyme-inhibitor complex) for R 76 713 of 0.7 +/- 0.3 nM and 1.6 +/- 0.4 nM, respectively. R 76 713 appeared to competitively inhibit the rat ovarian aromatase.

Pharmacology of vorozole

Vorozole (R83842) is a potent and selective, non-steroidal aromatase inhibitor. It is the dextro-enantiomer of the triazole derivative R 76,713. In FSH-stimulated rat granulosa cells, vorozole inhibited aromatase activity with an IC50-value of 1.4 +/- 0.5 nM. In pregnant mare serum gonadotropin (PMSG)-primed female rats, plasma estradiol levels measured 2 h after single oral administration of vorozole were significantly reduced by drug doses of 0.001 mg/kg and higher, with an ED50-value of 0.0034 mg/kg. In ovariectomized nude mice, bearing an estrogen-producing JEG-3 choriocarcinoma, 5 days treatment with vorozole, dose-dependently reduced uterus weight and completely inhibited tumor aromatase, measured ex vivo. Vorozole showed IC50-values higher than 10 microM for inhibition of progesterone synthesis in rat granulosa cells, for inhibition of steroid biosynthesis in isolated rat testicular and adrenal cells and for inhibition of steroid binding to estrogen-, progestin-, androgen- and gluco- and mineralocorticoid-receptors. In LHRH/ACTH-injected male rats and in rats fed a sodium-deprived diet, single oral administration of up to 10 mg/kg vorozole did not affect plasma levels of testicular and adrenal steroids. The compound also had no in vivo estrogen or androgen (ant)agonistic properties. In the DMBA-induced rat mammary carcinoma model, vorozole at an oral dose of 2.5 mg/kg b.i.d. inhibited tumor growth similarly to ovariectomy.

Liarozole fumarate (R85246): in the treatment of ER negative, tamoxifen refractory or chemotherapy resistant postmenopausal metastatic breast cancer.

Three phase II studies were conducted to determine the efficacy and tolerability of liarozole fumarate (R85246; liarozole), a retinoic acid metabolism blocking agent (RAMBA) and aromatase inhibitor. Additionally, animal experiments in the MNU-induced rat mammary tumor model and in immature ovariectomized rats were conducted to further elucidate liarozoles mechanisms of action. Patients were postmenopausal with either: ER negative disease in first relapse (Group 1; n = 16); ER positive or unknown disease refractory to tamoxifen (Group 2; n = 16); ER positive, negative or unknown disease resistant or refractory to chemotherapy (Group 3; n = 27). Treatment was liarozole (150–300 mg) twice daily orally until disease progression. Response rates were: 25% in group 1 (95% CI 11.0–52.3%; median duration (MD) 20 months; range 2–36.5); 25% in group 2 (95% CI 11.0–52.3%; MD 6.5 months; range 3.5–38); 11% in group 3 (95% CI 4.2–29.2%; MD 7 months; range 3–8.5). No significant improvement in quality of life scores (FLI-C) was noted. Toxicities observed were predominantly dermatological (skin disorders: 88%; dry mouth/eyes/lips: 69%). Plasma estradiol decreased from mean pre-treatment levels of 72.7 pM (9.1–1839 pM) to below detection (9.2 pM) after 1 month. Liarozole, but not vorozole, partially inhibited estradiol induced uterine hypertrophy and demonstrated dose-dependent anti-tumor effects in the rats, only partially overcome by coadministration of estradiol. The clinical responses observed, together with our preclinical results, confirm liarozoles dual mechanism of action and provide a rationale for further evaluation of RAMBAs in the treatment of breast cancer.

Liarozole fumarate (R85246) : a novel imidazole in the treatment of receptor positive postmenopausal metastatic breast cancer

This phase II study of liarozole fumarate (R85246, liarozole), a novel imidazole with retinomimetic and aromatase inhibitory effects, was designed to determine the efficacy and tolerability in postmenopausal women with advanced breast cancer in progression, to correlate these effects with hormonal levels, and to evaluate quality of life. Twenty-nine women with ER-positive or unknown metastatic disease who received ≥ 2 prior hormonal therapies were treated with 150–300 mg liarozole twice daily until disease progression. All patients were evaluable for toxicity and 25 for response. Four patients (16.0%, 95% CI 5.3–37.4%) had partial remission (PR) of their disease for a median of 7.4 months (range 1.2–12.9) and 7 (28%) had disease stabilization for a median of 4.8 months (1.6–16.0). Estradiol decreased from pre-treatment levels of 9.2–52 pM (mean 17.1) to below detection (9.2 pM, p=0.0005) after 1 month. Similarly estrone levels fell from 14–307 pM (mean 92.7) to below detection (9.2 pM, p=0.0001). The most common toxicity was dermatological (96.6%) with features compatible with hypervitaminosis A syndrome such as rash, pruritus, dry skin, and brittle nails. The majority of these were mild to moderate in severity. No significant improvement in quality of life scores (FLI-C) were noted. Liarozole is an active new treatment for breast cancer in patients heavily pre-treated with hormone therapies. Further studies are needed to confirm its relative efficacy in both receptor positive and negative postmenopausal breast cancer.

Effects of chlordiazepoxide on opioid-induced antinociception and respiratory depression in restrained rats

This study investigates the influence of possible stress due to housing in Bolman cages on antinociception and on respiratory depression following opioid administration. To evaluate the functional role of this stressor and to modulate it, rats were subcutaneously pretreated with the anxiolytic chlordiazepoxide (CDP; 10 mg/kg) or saline (SAL) before the immobilization in the Bolman cages and before the intravenous administration of small doses of morphine (MOR), sufentanil (SUF), or vehicle (VEH). Antinociception, respiratory impairment and stress were evaluated by means of the tail-flick latency, blood gas analysis, and serum corticosterone (CS), adrenocorticotropic hormone (ACTH), and prolactin (PRL) determinations. The results demonstrated that 10 mg/kg CDP did not alter the antinociceptive effects of low doses of morphine and sufentanil. CDP pretreatment differentially affected the various blood gas parameters. Compared to vehicle pretreatment, there was a larger decrease in PaO2 following MOR and SUF in the CDP-pretreated rats. The effects were most pronounced at the lowest doses of both opioids. A CDP potentiation was also observed for the short-lasting raises in PaCO2 with the lowest concentrations of the opioids. At higher concentrations of the opioids, CDP was without any effect. With regard to the stress hormones, immobilization and an intravenous injection resulted in increases in CS and PRL in both CDP- and VEH-pretreated rats. ACTH did not change in these controls. SUF prevented the CS raises independent of a CDP pretreatment, while ACTH only increased in the SUF plus CDP groups, pointing to a stress-reducing effect of SUF. Also, MOR without CDP prevented the increases in CS, but the opioid intrinsically increased ACTH. These results indicate that restraint in Bolman cages in the present setup, with animals recovering for several hours in these cages after being equipped with an arterial catheter, is stressful but without any significant effect on the opioid-induced antinociception. Pretreatment with an anxiolytic benzodiazepine only minimally affected the outcome of the opioids on respiratory depression and pointed to a stress-reducing effect of low doses of the opioids, especially sufentanil.