Trilostane and the normal hypothalamic-pituitary-adrenocortical axis

Trilostane in dogs

Over the last 10 years, trilostane, a competitive inhibitor of steroid synthesis, is being widely used for the treatment of canine hyperadrenocorticism. Trilostane causes a significant but reversible decrease in cortisol production and a concomitant improvement in clinical signs in most dogs with this common condition. Side effects, though infrequent, can be serious: dogs treated with this drug require regular monitoring. This review summarizes current knowledge of the use of this drug with particular emphasis on its efficacy, safety, adverse reactions, and effects on endocrine parameters. Brief mention is made of its other uses in dogs and other species.

Regulation of hepatic steroid receptors and enzymes by the 3beta-hydroxysteroid dehydrogenase inhibitor trilostane

Therapies designed to treat hypercortisolism have usually sought to reduce circulating glucocorticoid concentrations, however the local tissue endocrine environment could be an alternative target. The 3beta-hydroxysteroid dehydrogenase Delta5-4 isomerase (3beta-HSD) inhibitor trilostane is of interest, since, although it is only moderately and transiently effective in reducing circulating steroid, it is remarkably effective in alleviating Cushing's symptoms in veterinary applications. To seek alternative modes of action, male Wistar rats were treated with trilostane. Although final circulating corticosteroid concentrations were unaffected, liver 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) transcription and translation was significantly increased, whereas 3beta-HSD was not affected either in liver or adrenal. Glucocorticoid receptor (GR) mRNA was down-regulated, and mineralocorticoid receptor (MR) up-regulated by trilostane treatment: no changes in 11beta-HSD1 mRNA were observed. Trilostane also had no direct effect on GR response element-mediated gene transcription. The results show that the tissue endocrine environment is affected by trilostane treatment in the absence of sustained changes in circulating corticosteroid. The combination of increased 11beta-HSD2 and reduced GR expression in target organs could be expected to ameliorate the effects of excess glucocorticoid, suggesting new therapeutic approaches.

Endocrine effects of Trilostane: in vitro and in vivo studies

Trilostane (4-alpha-5-epoxy-17 beta-hydroxy-3-oxo-5-alpha-androstan-2-carbonitrile) is a modified steroidal molecule. In vitro and in vivo studies in rats have shown that it inhibits adrenal, ovarian and placental steroid synthesis. It seems to act by exerting a selective blockade on 3 beta-hydroxysteroid dehydrogenase. In this study, we investigated whether this molecule interacts with hormone receptors for estrogen, androgen or progesterone. We also tried to demonstrate the effect which Trilostane may have on cellular cultures of human mammary carcinoma (MCF-7 Evsa-T). We also studied hormonal modifications in a series of 12 patients treated with different doses of Trilostane, since this drug is supposed to inhibit the production by the adrenal glands of mineralocorticoids, of glucocorticoids and of the precursors of estrogens. Our results indicate that Trilostane does not react with any of the main hormonal sex steroid receptors, nor does it interfere with cultures of human mammary cancer cells either containing estrogen receptors and therefore allegedly hormone-dependent (MCF-7 line), or estrogen receptor-negative cells, presumably independent of hormonal manipulations (Evsa-T cell line). Finally, endocrine studies on postmenopausal women with advanced breast cancer show that Trilostane significantly reduces the plasma levels of estrone and of its major androgen precursor (androstenedione). However, the latter inhibition is no different from that exerted by hydrocortisone acetate administered alone at a dose of 40 mg/day. The results of clinical trials comparing hydrocortisone alone with hydrocortisone plus Trilostane are awaited.

Hormonal changes in postmenopausal women with breast cancer treated with trilostane and dexamethasone

Postmenopausal women with metastatic breast cancer were treated with trilostane, initially 240 mg daily increasing after 3 days to 480 mg daily and after a further three days to 960 mg daily. After 3 days at this dose dexamethasone 1 mg daily was added and this combination was continued until disease progression occurred. Partial remission was seen in 26% and stabilization of previously progressive disease in a further 13% of the first twenty-three patients studied. During therapy with trilostane alone significant increases in DHEAS, androstenedione, 17-hydroxypregnenolone, progesterone, testosterone and oestradiol were seen. A significant fall in oestrone concentration occurred at the same time. After dexamethasone was added the elevated steroid concentrations fell back to the baseline while oestrone remained depressed below this and testosterone was also significantly lowered. No change was seen in cortisol or ACTH concentration while patients were on trilostane alone but cortisol levels were undetectable after dexamethasone was added though, in most patients, ACTH remained detectable. There was no change in the ratio of delta 5:delta 4 steroids at any stage of therapy but a highly significant increase in the androstenedione: oestrone ratio was seen. We conclude that in long-term use in vivo it is difficult to demonstrate that trilostane inhibits 3 beta-hydroxysteroid dehydrogenase but it may produce inhibition of aromatase.

Effect of nivazol on ACTH secretion by human pituitary corticotrophic tumours in cell culture

The effects of nivazol, a novel steroid which lacks glucocorticoid activity, on ACTH secretion by cell cultures of human pituitary corticotrophic tumours has been investigated. Nivazol (0.002-20 mumol/l) inhibited ACTH secretion by 50-80%, after 4 and 24 h of incubation. (Trilostane (0.3-30 mumol/l) did not affect basal or stimulated ACTH secretion.) The potency of nivazol was comparable with that of hydrocortisone, and less than dexamethasone. The stimulatory effects of oCRF and AVP were reduced or completely blocked by nivazol in a similar manner to that previously described for hydrocortisone. It is concluded that nivazol may be of benefit in the direct treatment of Cushing's disease, particularly since it lacks glucocorticoid activity.

The bioavailability and metabolism of trilostane in normal subjects, a comparative study using high pressure liquid chromatographic and quantitative cytochemical assays

High pressure liquid chromatographic (HPLC) analysis of plasma taken over 8 h from ten normal male subjects medicated with 120 mg of trilostane revealed that the drug is rapidly metabolised into at least one metabolite, 17-keto trilostane. Both compounds were detected in the blood stream at concentrations greater than 2 X 10(-7) M within an hour and were cleared from the blood by 6-8 h. Approximately 3 times the concentration of metabolite was detected compared to the parent compound in most samples analysed. There were large subject to subject variations in the handling of drug. Standard curves of pure 17-keto trilostane and trilostane were parallel as assessed by cytochemical bioassay. This assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase activity in unfixed tissue sections of the dioestrous rat ovary. The relative potency of the metabolite compared to trilostane was 1.71 (95% confidence 1.5-2.0) over the dose range 0.15-1.5 microM. Thus, the metabolite may be the major active agent when trilostane is administered for clinical purposes. In a further 4 volunteers, who also received 120 mg trilostane and were sampled over an 8 h period, plasma was analysed independently by HPLC and cytochemical assays. In the majority of cases the bioactivity recorded (relative to a trilostane standard curve) was substantially higher than the molar sum of circulating trilostane and 17-keto-trilostane (as assessed by HPLC). However, if the relative potency of 17-keto-trilostane is taken into consideration, correlation between the two assays was excellent (r = 0.947, n = 18, P less than 0.001). This also suggests that no further active metabolites were present in the plasma samples. The drug profiles seen in the second study were essentially the same as described for the first 10 volunteers. The combination of a bioassay, which detects trilostane-like bioactivity, and HPLC, which reveals the type of metabolism, should aid our understanding of the clinical value of this potentially important drug.

A cytochemical section bioassay for plasma trilostane: an orally active inhibitor of 3 beta-hydroxysteroid dehydrogenase activity

Trilostane is a competitive inhibitor of 3 beta-hydroxysteroid dehydrogenase activity in vitro and an orally active inhibitor of steroidogenesis in vivo. A cytochemical section bioassay for this drug (4 alpha, 5-epoxy-17 beta-hydroxy-3-oxo-5 alpha-androstane-2 alpha-carbonitrile) in human plasma has been developed. The assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the corpus luteum of unfixed tissue sections (6 micron) of the mature dioestrous rat ovary. Trilostane is extracted from plasma by a simple chloroform procedure. The standard curve (0.15-2.5 mumol/l pure trilostane) exhibits a four-fold change in 3 beta-HSD activity and is constructed in the presence of extract from control plasma pools. The detection limit of the plasma assay is 2 mumol/l trilostane after allowing for dilution effects and recovery losses. This level gives a significantly different response from the zero quality control (P less than 0.05) and has an inter-assay coefficient of variation of less than 15%. No false positives have been recorded to date and the majority of samples from subjects receiving therapeutic doses of the drug have levels of greater than 2 mumol/l. Intra- and inter-assay coefficients of variation using both plasma quality controls and unknown samples are 4% (n = 15) and 13.9% (n = 27) respectively. Recovery is 80 +/- 9% (n = 13) and 79 +/- 10% (n = 10) for plasma quality controls containing 12 and 4.8 mumol/l trilostane respectively. Dilutions (up to 1:5) of plasma extracts are parallel to the standard curve and the assay throughput is approximately 16 samples/week technician.(ABSTRACT TRUNCATED AT 250 WORDS)

11 beta-Hydroxy-11-ketosteroids equilibrium, a source of misinterpretation in steroid synthesis: evidence through the effects of trilostane on 11 beta-hydroxysteroid dehydrogenase in sheep and human adrenals in vitro

Trilostane is known as an inhibitor of 3 beta-hydroxysteroid dehydrogenase. Conflicting data published on this drug led us to look for the effects of 0.02 to 0.5 mM of trilostane on the in vitro steroid synthesis in sheep adrenals and human adrenals (Cushing's or Conn's syndrome) in the presence of an NADPH-generating system. The synthesis of 4-androstenedione, 11 beta-hydroxyandrostenedione and 11-ketoandrostenedione were studied either from dehydroepiandrosterone or 4-androstenedione or 11 beta-hydroxyandrostenedione. The synthesis of 11-deoxycortisol, cortisol, cortisone, 4-androstenedione, 11 beta-hydroxyandrostenedione and 11-ketoandrostenedione were studied either from 17-hydroxyprogesterone or 11-deoxycortisol or cortisol. This study showed that trilostane inhibited 3 beta-hydroxysteroid dehydrogenase whereas it had no effect on 21-, 11- and 17-hydroxylase. Trilostane was responsible for an increased 11 beta-hydroxysteroid dehydrogenase activity in vitro, resulting in low yields of cortisol and 11 beta-hydroxyandrostenedione, and high yields of cortisone and 11-ketoandrostenedione. This unexpected effect of trilostane allowed us to show that erroneous conclusions (in this case: pseudo inhibition of 11 beta-hydroxylase) can be drawn if all the metabolic pathways from a determined precursor are not exhaustively documented when studying the effects of drugs on steroid synthesis in vitro. The decrease of cortisol synthesis by trilostane may thus be related to the effects of the drug on both 3 beta-hydroxysteroid-dehydrogenase (inhibitory effect) and 11 beta-hydroxysteroid-dehydrogenase (stimulatory effect). This latter effect was found to be species-dependent.