R 75251, a new inhibitor of steroid biosynthesis

In silico and in vitro assessment of drugs potentially causing adverse effects by inhibiting CYP17A1

Cytochrome P450 enzymes (CYPs) play a crucial role in the metabolism and synthesis of various compound classes. While drug-metabolizing CYP enzymes are frequently investigated as anti-targets, the inhibition of CYP enzymes involved in adrenal steroidogenesis is not well studied. The steroidogenic enzyme CYP17A1 is a dual-function enzyme catalyzing hydroxylase and lyase reactions relevant for the biosynthesis of adrenal glucocorticoids and androgens. Inhibition of CYP17A1-hydroxylase leads to pseudohyperaldosteronism with subsequent excessive mineralocorticoid receptor activation, hypertension and hypokalemia. In contrast, specific inhibition of the lyase function might be beneficial for the treatment of prostate cancer by decreasing adrenal androgen levels. This study combined in silico and in vitro methods to identify drugs inhibiting CYP17A1. The most potent CYP17A1 inhibitors identified are serdemetan, mocetinostat, nolatrexed, liarozole, and talarozole. While some of these drugs are currently under investigation for the treatment of various cancers, their potential for the treatment of prostate cancer is yet to be explored. The DrugBank database was screened for CYP17A1 inhibitors, to increase the awareness for the risk of drug-induced pseudohyperaldosteronism and to highlight drugs so far unknown for their potential to cause side effects resulting from CYP17A1 inhibition.

Virtual screening and biological evaluation to identify pharmaceuticals potentially causing hypertension and hypokalemia by inhibiting steroid 11β-hydroxylase

Several drugs were found after their market approval to unexpectedly inhibit adrenal 11β-hydroxylase (CYP11B1)-dependent cortisol synthesis. Known side-effects of CYP11B1 inhibition include hypertension and hypokalemia, due to a feedback activation of adrenal steroidogenesis, leading to supraphysiological concentrations of 11-deoxycortisol and 11-deoxycorticosterone that can activate the mineralocorticoid receptor. This results in potassium excretion and sodium and water retention, ultimately causing hypertension. With the risk known but usually not addressed in preclinical evaluation, this study aimed to identify drugs and drug candidates inhibiting CYP11B1. Two conceptually different virtual screening methods were combined, a pharmacophore based and an induced fit docking approach. Cell-free and cell-based CYP11B1 activity measurements revealed several inhibitors with IC50 values in the nanomolar range. Inhibitors include retinoic acid metabolism blocking agents (RAMBAs), azole antifungals, α2-adrenoceptor ligands, and a farnesyltransferase inhibitor. The active compounds share a nitrogen atom embedded in an aromatic ring system. Structure activity analysis identified the free electron pair of the nitrogen atom as a prerequisite for the drug-enzyme interaction, with its pKa value as an indicator of inhibitory potency. Another important parameter is drug lipophilicity, exemplified by etomidate. Changing its ethyl ester moiety to a more hydrophilic carboxylic acid group dramatically decreased the inhibitory potential, most likely due to less efficient cellular uptake. The presented work successfully combined different in silico and in vitro methods to identify several previously unknown CYP11B1 inhibitors. This workflow facilitates the identification of compounds that inhibit CYP11B1 and therefore pose a risk for inducing hypertension and hypokalemia.

Non-steroidal CYP17A1 Inhibitors: Discovery and Assessment

CYP17A1 is an enzyme that plays a major role in steroidogenesis and is critically involved in the biosynthesis of steroid hormones. Therefore, it remains an attractive target in several serious hormone-dependent cancer diseases, such as prostate cancer and breast cancer. The medicinal chemistry community has been committed to the discovery and development of CYP17A1 inhibitors for many years, particularly for the treatment of castration-resistant prostate cancer. The current Perspective reflects upon the discovery and evaluation of non-steroidal CYP17A1 inhibitors from a medicinal chemistry angle. Emphasis is placed on the structural aspects of the target, key learnings from the presented chemotypes, and design guidelines for future inhibitors.

Retinoids as Chemo-Preventive and Molecular-Targeted Anti-Cancer Therapies

Retinoic acid (RA) agents possess anti-tumor activity through their ability to induce cellular differentiation. However, retinoids have not yet been translated into effective systemic treatments for most solid tumors. RA signaling is mediated by the following two nuclear retinoic receptor subtypes: the retinoic acid receptor (RAR) and the retinoic X receptor (RXR), and their isoforms. The identification of mutations in retinoid receptors and other RA signaling pathway genes in human cancers offers opportunities for target discovery, drug design, and personalized medicine for distinct molecular retinoid subtypes. For example, chromosomal translocation involving RARA occurs in acute promyelocytic leukemia (APL), and all-trans retinoic acid (ATRA) is a highly effective and even curative therapeutic for APL patients. Thus, retinoid-based target discovery presents an important line of attack toward designing new, more effective strategies for treating other cancer types. Here, we review retinoid signaling, provide an update on retinoid agents and the current clinical research on retinoids in cancer, and discuss how the retinoid pathway genotype affects the ability of retinoid agents to inhibit the growth of colorectal cancer (CRC) cells. We also deliberate on why retinoid agents have not shown clinical efficacy against solid tumors and discuss alternative strategies that could overcome the lack of efficacy.

Reliable Target Prediction of Bioactive Molecules Based on Chemical Similarity Without Employing Statistical Methods

The prediction of biological targets of bioactive molecules from machine-readable materials can be routinely performed by computational target prediction tools (CTPTs). However, the prediction of biological targets of bioactive molecules from non-digital materials (e.g., printed or handwritten documents) has not been possible due to the complex nature of bioactive molecules and impossibility of employing computations. Improving the target prediction accuracy is the most important challenge for computational target prediction. A minimum structure is identified for each group of neighbor molecules in the proposed method. Each group of neighbor molecules represents a distinct structural class of molecules with the same function in relation to the target. The minimum structure is employed as a query to search for molecules that perfectly satisfy the minimum structure of what is guessed crucial for the targeted activity. The proposed method is based on chemical similarity, but only molecules that perfectly satisfy the minimum structure are considered. Structurally related bioactive molecules found with the same minimum structure were considered as neighbor molecules of the query molecule. The known target of the neighbor molecule is used as a reference for predicting the target of the neighbor molecule with an unknown target. A lot of information is needed to identify the minimum structure, because it is necessary to know which part(s) of the bioactive molecule determines the precise target or targets responsible for the observed phenotype. Therefore, the predicted target based on the minimum structure without employing the statistical significance is considered as a reliable prediction. Since only molecules that perfectly (and not partly) satisfy the minimum structure are considered, the minimum structure can be used without similarity calculations in non-digital materials and with similarity calculations (perfect similarity) in machine-readable materials. Nine tools (PASS online, PPB, SEA, TargetHunter, PharmMapper, ChemProt, HitPick, SuperPred, and SPiDER), which can be used for computational target prediction, are compared with the proposed method for 550 target predictions. The proposed method, SEA, PPB, and PASS online, showed the best quality and quantity for the accurate predictions.

Serine Threonine Kinase Receptor-Associated Protein Deficiency Impairs Mouse Embryonic Stem Cells Lineage Commitment Through CYP26A1-Mediated Retinoic Acid Homeostasis

Retinoic acid (RA) signaling is essential for the differentiation of embryonic stem cells (ESCs) and vertebrate development. RA biosynthesis and metabolism are controlled by a series of enzymes, but the molecular regulators of these enzymes remain largely obscure. In this study, we investigated the functional role of the WD-domain protein STRAP (serine threonine kinase receptor-associated protein) in the pluripotency and lineage commitment of murine ESCs. We generated Strap knockout (KO) mouse ESCs and subjected them to spontaneous differentiation. We observed that, despite the unchanged characteristics of ESCs, Strap KO ESCs exhibited defects for lineage differentiation. Signature gene expression analyses revealed that Strap deletion attenuated intracellular RA signaling in embryoid bodies (EBs), and exogenous RA significantly rescued this deficiency. Moreover, loss of Strap selectively induced Cyp26A1 expression in mouse EBs, suggesting a potential role of STRAP in RA signaling. Mechanistically, we identified putative Krüppel-like factor 9 (KLF9) binding motifs to be critical in the enhancement of non-canonical RA-induced transactivation of Cyp26A1. Increased KLF9 expression in the absence of STRAP is partially responsible for Cyp26A1 induction. Interestingly, STRAP knockdown in Xenopus embryos influenced anterior-posterior neural patterning and impaired the body axis and eye development during early Xenopus embryogenesis. Taken together, our study reveals an intrinsic role for STRAP in the regulation of RA signaling and provides new molecular insights for ESC fate determination. Stem Cells 2018;36:1368-1379.

R75251 in Prostate Cancer Patients in Progression after First-Line Hormonal Treatment

Introduction

The therapeutic potential of R75251, a ketoconazole derivative which has shown marked antitumor activity in animals and in men, was investigated in 16 patients with advanced prostatic cancer progressing after one or more lines of hormone therapy.

Patients and methods

Patients were given the drug at 150 mg/b.i.d. for one month. After the first month of treatment, the dose was increased to 300 mg/b.i.d. In all patients, treatment was continued until disease progression or the development of severe toxicity. Clinical and biochemical assessments were performed on days 0, 14 and 28 and then repeated on a monthly basis.

Results

Of the 13 evaluable patients, 12 showed stable disease by strictly employing US-NPCP criteria. However, in 3 patients a clear effect was observed on the volume of their measurable lesions. In addition, 2 of them showed a more than 50% decrease of prostate-specific antigens (PSA). Overall, 50% of patients showed some decrease in PSA baseline levels. Overall tolerance to treatment was good.

Conclusions

Our results, although achieved in a small number of patients, suggest that R75251 has a moderate but definite activity in patients with hormone-refractory prostate cancer and that the value of this drug as second-line treatment in these patients should be further investigated.

Therapeutic potential of the inhibition of the retinoic acid hydroxylases CYP26A1 and CYP26B1 by xenobiotics

Retinoic acid (RA), the active metabolite of vitamin A, is an important endogenous signaling molecule regulating cell cycle and maintenance of epithelia. RA isomers are also used as drugs to treat various cancers and dermatological diseases. However, the therapeutic uses of RA isomers are limited due to side effects such as teratogenicity and resistance to treatment emerging mainly from autoinduction of RA metabolism. To improve the therapeutic usefulness of retinoids, RA metabolism blocking agents (RAMBAs) have been developed. These inhibitors generally target the cytochrome P450 (CYP) enzymes because RA clearance is predominantly mediated by P450s. Since the initial identification of inhibitors of RA metabolism, CYP26 enzymes have been characterized as the main enzymes responsible for RA clearance. This makes CYP26 enzymes an attractive target for the development of novel therapeutics for cancer and dermatological conditions. The basic principle of development of CYP26 inhibitors is that endogenous RA concentrations will be increased in the presence of a CYP26 inhibitor, thus, potentiating the activity of endogenous RA in a cell-type specific manner. This will reduce side effects compared to administration of RA and allow for more targeted therapy. In clinical trials, inhibitors of RA metabolism have been effective in treatment of psoriasis and other dermatological conditions as well as in some cancers. However, no CYP26 inhibitor has yet been approved for clinical use. This review summarizes the history of development of RAMBAs, the clinical and preclinical studies with the various structural series and the available knowledge of structure activity relationships of CYP26 inhibitors.

Cyp26b1 regulates retinoic acid-dependent signals in T cells and its expression is inhibited by transforming growth factor-β

Background

The vitamin A metabolite, retinoic acid (RA), plays important roles in the regulation of lymphocyte properties. Dendritic cells in gut-related lymphoid organs can produce RA, thereby imprinting gut-homing specificity on T cells and enhancing transforming growth factor (TGF)-β-dependent induction of Foxp3⁺ regulatory T cells upon antigen presentation. In general, RA concentrations in cells and tissues are regulated by its degradation as well. However, it remained unclear if T cells could actively catabolize RA.

Methodology/Principal Findings

We assessed the expression of known RA-catabolizing enzymes in T cells from mouse lymphoid tissues. Antigen-experienced CD44⁺ T cells in gut-related lymphoid organs selectively expressed Cyp26b1, a member of the cytochrome P450 family 26. However, T cells in the spleen or skin-draining lymph nodes did not significantly express Cyp26b1. Accordingly, physiological levels of RA (1–10 nM) could induce Cyp26b1 expression in naïve T cells upon activation in vitro, but could not do so in the presence of TGF-β. Overexpression of Cyp26b1 significantly suppressed the RA effect to induce expression of the gut-homing receptor CCR9 on T cells. On the other hand, knocking down Cyp26b1 gene expression with small interfering RNA or inhibiting CYP26 enzymatic activity led to enhancement of the RA-induced CCR9 expression.

Conclusions/Significance

Our data demonstrate a role for CYP26B1 in regulating RA-dependent signals in activated T cells but not during TGF-β-dependent differentiation to Foxp3⁺ regulatory T cells. Aberrant expression of CYP26B1 may disturb T cell trafficking and differentiation in the gut and its related lymphoid organs.

Targeting cytochrome P450 enzymes: a new approach in anti-cancer drug development

Cytochrome P450s (CYPs) represent a large class of heme-containing enzymes that catalyze the metabolism of multitudes of substrates both endogenous and exogenous. Until recently, however, CYPs have been largely overlooked in cancer drug development, acknowledged only for their role in phase I metabolism of chemotherapeutics. The first successful strategy targeting CYP enzymes in cancer therapy was the development of potent inhibitors of CYP19 (aromatase) for the treatment of breast cancer. Aromatase inhibitors ushered in a new era in hormone ablation therapy for estrogen dependent cancers, and have paved the way for similar strategies (i.e., inhibition of CYP17) that combat androgen dependent prostate cancer. Identification of CYPs involved in the inactivation of anti-cancer metabolites of vitamin D(3) and vitamin A has triggered development of agents that target these enzymes as well. The discovery of the over-expression of exogenous metabolizing CYPs, such as CYP1B1, in cancer cells has roused interest in the development of inhibitors for chemoprevention and of prodrugs designed to be activated by CYPs only in cancer cells. Finally, the expression of CYPs within tumors has been utilized in the development of bioreductive molecules that are activated by CYPs only under hypoxic conditions. This review offers the first comprehensive analysis of strategies in drug development that either inhibit or exploit CYP enzymes for the treatment of cancer.

Effects of liarozole fumarate (R85246) in combination with tamoxifen on N-methyl-N-nitrosourea (MNU)-induced mammary carcinoma and uterus in the rat model

Background

Liarozole fumarate (liarozole – R85246) is a novel compound with characteristics of both aromatase inhibitor (AI) and a retinoic acid metabolism blocking agent (RAMBA). Our objective was to determine the effects of liarozole alone or in combination with tamoxifen on the N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinoma model, as well as on the uterus in ovariectomized immature rats.

Methods

(1) Tumor burden experiments: Animals bearing one or more tumors greater than 10 mm in diameter were treated for 56 consecutive days with 20 mg/kg or 80 mg/kg of liarozole by oral gavage, tamoxifen 100 μg/kg by subcutaneous injection, or a combination of liarozole and tamoxifen. At the end of the treatment period, total cumulative tumor volume as well as retinoic acid levels were measured. (2) Uterotrophic assay and proliferation experiments: 21-day-old ovariectomized (OVX) Sprague-Dawley rats were treated with 20 mg/kg or 80 mg/kg of liarozole by oral gavage, tamoxifen 1 mg/kg by subcutaneous injection, and combination of both for 4 consecutive days. At the end of the treatment period, uterine weight, epithelial lining cell height and indices of proliferation cell nuclear antigen (PCNA) were measured.

Results

The tumor burden experiments in rats bearing estrogen receptor (ER) positive mammary tumours showed that liarozole has a marked anti-tumour effect. In combination with tamoxifen, liarozole had neither an additive nor an antagonistic effect. However, liarozole markedly reduced the uterotrophic effects induced by tamoxifen.

Conclusion

Liarozole's antitumor effects on ER positive mammary tumors and its protective effect on the uterus merit further studies to confirm its clinical value in combination with tamoxifen in ER positive postmenopausal breast cancer. Liarozole and other retinomimetics might also be suitable chemoprevention drugs in combination with tamoxifen because of their favorable toxicity profile.

Oral liarozole vs. acitretin in the treatment of ichthyosis: a phase II/III multicentre, double-blind, randomized, active-controlled study

BACKGROUND

Liarozole, a retinoic acid metabolism blocking agent, has been granted orphan drug status for congenital ichthyosis by the European Commission and the U.S. Food and Drug Administration.

OBJECTIVES

The purpose of this trial was to investigate the efficacy, tolerability and safety of oral liarozole vs. acitretin in patients with ichthyosis.

METHODS

In this double-blind comparative trial of liarozole vs. acitretin, 32 patients with ichthyosis were randomized to be treated with either oral liarozole 75 mg in the morning and 75 mg in the evening or with acitretin 10 mg in the morning and 25 mg in the evening for 12 weeks. Clinical efficacy, tolerability and safety were monitored.

RESULTS

Between-group comparisons for efficacy and tolerability revealed no statistically significant differences except for scaling on the trunk at baseline which was significantly worse in the liarozole group (P = 0.024) and showed a more pronounced improvement in this group than in the acitretin-treated patients (P = 0.047). Based on the overall evaluation of the response to treatment at endpoint, 10 of 15 patients in the liarozole group and 13 of 16 patients in the acitretin group were considered by the investigator to be at least markedly improved. The expected retinoic acid-related adverse events were mostly mild to moderate and tended to occur less frequently in the liarozole group. No serious adverse events related to the drugs occurred.

CONCLUSIONS

The present study indicates that liarozole at a daily dose of 150 mg is equally effective as a treatment for ichthyosis as acitretin but shows a trend towards a more favourable tolerability profile. The results of this trial warrant further clinical trials to confirm efficacy and safety of liarozole as an orphan drug in ichthyosis.

Retinoic acid metabolism blocking agents (RAMBAs) for treatment of cancer and dermatological diseases

The naturally occurring retinoids and their synthetic analogs play a key role in differentiation, proliferation, and apoptosis, and their use/potential in oncology, dermatology and a variety of diseases are well documented. This review focuses on the role of all-trans-retinoic acid (ATRA), the principal endogenous metabolite of vitamin A (retinol) and its metabolism in oncology and dermatology. ATRA has been used successfully in differentiated therapy of acute promyelocytic leukemia, skin cancer, Kaposi's sarcoma, and cutaneous T-cell lymphoma, and also in the treatment of acne and psoriasis. However, its usefulness is limited by the rapid emergence of acquired ATRA resistance involving multifactoral mechanisms. A key mechanism of resistance involves ATRA-induced catabolism of ATRA. Thus, a novel strategy to overcome the limitation associated with exogenous ATRA therapy has been to modulate and/or increase the levels of endogenous ATRA by inhibiting the cytochrome P450-dependent ATRA-4-hydroxylase enzymes (particularly CYP26s) responsible for ATRA metabolism. These inhibitors are also referred to as retinoic acid metabolism blocking agents (RAMBAs). This review highlights development in the design, synthesis, and evaluation of RAMBAs. Major emphasis is given to liarozole, the most studied and only RAMBA in clinical use and also the new RAMBAs in development and with clinical potential.

Inhibition of all-TRANS-retinoic acid metabolism by R116010 induces antitumour activity

All-trans-retinoic acid is a potent inhibitor of cell proliferation and inducer of differentiation. However, the clinical use of all-trans-retinoic acid in the treatment of cancer is significantly hampered by its toxicity and the prompt emergence of resistance, believed to be caused by increased all-trans-retinoic acid metabolism. Inhibitors of all-trans-retinoic acid metabolism may therefore prove valuable in the treatment of cancer. In this study, we characterize R116010 as a new anticancer drug that is a potent inhibitor of all-trans-retinoic acid metabolism. In vitro, R116010 potently inhibits all-trans-retinoic acid metabolism in intact T47D cells with an IC(50)-value of 8.7 nM. In addition, R116010 is a selective inhibitor as indicated by its inhibition profile for several other cytochrome P450-mediated reactions. In T47D cell proliferation assays, R116010 by itself has no effect on cell proliferation. However, in combination with all-trans-retinoic acid, R116010 enhances the all-trans-retinoic acid-mediated antiproliferative activity in a concentration-dependent manner. In vivo, the growth of murine oestrogen-independent TA3-Ha mammary tumours is significantly inhibited by R116010 at doses as low as 0.16 mg kg(-1). In conclusion, R116010 is a highly potent and selective inhibitor of all-trans-retinoic acid metabolism, which is able to enhance the biological activity of all-trans-retinoic acid, thereby exhibiting antitumour activity. R116010 represents a novel and promising anticancer drug with an unique mechanism of action.

Oral liarozole in the treatment of palmoplantar pustular psoriasis: a randomized, double-blind, placebo-controlled study

BACKGROUND

Palmoplantar pustular psoriasis (PPP) is a chronic, relapsing condition often recalcitrant to therapy. Synthetic retinoids have been found to be efficacious in the treatment of PPP, but their use is limited by side-effects. Liarozole is an imidazole-like compound that inhibits the retinoic acid (RA) 4-hydroxylase-mediated breakdown of all-trans RA, causing elevation of plasma and cutaneous levels of RA. Thus liarozole acts as a retinoid-mimetic drug. Liarozole has already been found to be effective in the treatment of retinoid-responsive conditions such as chronic plaque psoriasis and ichthyoses.

OBJECTIVES

To assess the efficacy and side-effect profile of liarozole in the treatment of PPP.

METHODS

We performed a double-blind, randomized, placebo-controlled trial of oral liarozole 75 mg twice daily for 12 weeks in the treatment of PPP. The trial was conducted at two centres and involved 15 patients.

RESULTS

Using the PPP Area and Severity Index we found a statistically significant (P = 0.02) improvement in PPP in subjects on liarozole (median 3, range 1.8-14.1) as compared with placebo (median 12.1, range 5-18) by the end of the treatment phase. There was also a statistically significant difference (P = 0.006) in the number of fresh pustules after treatment for the two study groups (liarozole median 2, range 0-18; placebo median 38, range 2-75). The severity of disease (on a scale of 0-8) between the two groups was significantly different at the end of treatment (liarozole median 1, range 1-5; placebo median 3, range 2-6; P = 0.04). No patients withdrew from the trial because of adverse events. The most commonly reported side-effects were pruritus, cheilitis and xerosis but these were rarely severe and resolved rapidly on discontinuation of treatment. Laboratory results, including haematology, liver function tests and serum cholesterol and triglycerides were not significantly different between the liarozole and placebo groups.

CONCLUSIONS

The results of this pilot study suggest that liarozole 75 mg twice daily is an effective and well-tolerated therapy for PPP. In addition, the pharmacokinetics of liarozole may help to circumvent side-effects associated with synthetic retinoids and allow its use in premenopausal women.

Aromatase inhibitors: past, present and future

For the cellular physiology of sex steroid sensitive cells, the androgen/estrogen ratio may be more important than only one hormone action per se, in both sexes. This ratio is controlled in vertebrates by aromatase; its gene expression can be inhibited in different ways, and this is crucial for the treatment of estrogen-dependent diseases such as breast cancer, or gynecomastia in males for instance. To reach this goal, new steroidal and non-steroidal inhibitors are continuously being developed, and some of them are used as first or second line agents. Aromatase inhibition is also an essential tool for studying the role of estrogens in the adult, or during development. Aromatase inhibitors have shown in particular that estrogens are essential also in males for skeletal maturation and bone mineralization, development of masculine dendritic morphology in male brain linked to mating behaviour, and testicular function. Testosterone is often the prohormone converted in situ in active estrogens, at these levels. Several strategies can be used for aromatase inhibition. The first ones employed were blind screening or deductions from in vivo observations, which led for instance to the discovery of the role of aminoglutethimide in aromatase inhibition. Subsequently, in the years 1975-1990, the molecular modeling of compounds to mimic the substrate shape of the enzyme constituted the major idea. Hundreds of chemicals were synthesized by numerous authors, ranging from the well-known and very efficient 4-OHA to complicated imidazole or indane derivatives tested by sophisticated comparative molecular field analyses. Reticulum-bound active aromatase has not as yet been X-ray analyzed. Thus, aromatase inhibitors were also used more recently to probe and understand the active site conformation of the enzyme and its modelization was obtained from comparisons with bacterial-related cytochromes. We developed a mammalian model considerably closer to human aromatase in order to study the active site shape with new potent aromatase non-steroidal inhibitors. This model is equine aromatase. This enzyme was biochemically characterized, purified, and cloned by our group. It allowed testing, by site-directed mutagenesis, predictive hypotheses in human aromatase which contributed to designing of new inhibitors. The understanding of the functioning of an essential member of the cytochrome P450 family, which is necessary for cellular detoxification, was also facilitated. Inhibition of aromatase activity has also been carried out with antibodies directed to the catalytic site and at the gene level by knock-out or by control of factor-specific promoters. This may result in different mRNA synthesized by alternative splicing. We have also obtained specific inhibition of aromatase activity in human cells with antisense stable phosphorothioate oligodeoxynucleotides directed against aromatase mRNA tertiary structures. Besides known steroidal and non-steroidal inhibitors, the antiaromatase effects of compounds found in our daily environment such as dietary flavonoids or xenobiotic pollutants have also been described. Finally, we underline that all these aromatase inhibitors, or methods of aromatase inhibition, can modulate the estrogenic balance essential not only for female, but also for male physiology, including gonadal function.

Treatment of psoriasis with oral liarozole: a dose-ranging study

BACKGROUND

Liarozole is an inhibitor of the metabolism of all-trans-retinoic acid. Systemic administration increases tissue levels of this endogenous retinoid and has been reported to improve psoriasis in an open, uncontrolled study.

OBJECTIVES

A multicentre, double-blind, placebo-controlled, dose-ranging study was therefore undertaken to determine the lowest effective oral dose of liarozole in the treatment of psoriasis vulgaris.

PATIENTS/METHODS

Adult male and postmenopausal female patients requiring systemic treatment for psoriasis were randomized to receive placebo or liarozole at total daily doses of 50 mg, 75 mg or 150 mg for 12 weeks. The daily doses were each divided into two equal (morning and evening) doses. Response was assessed using an eight-point global scale to assess improvement and by monitoring the Psoriasis Area and Severity Index (PASI). The primary end-point was the proportion of subjects in each treatment group demonstrating 'marked improvement' or better as assessed on the eight-point scale. The tolerability of the treatment was assessed by recording mucocutaneous effects of retinoids and all adverse events. Biochemical and haematological monitoring were also performed.

RESULTS

One hundred and thirty-nine subjects were randomized (118 male and 21 female) and 116 completed the study. A marked improvement or better response was observed in 6% of subjects on placebo, 18% on liarozole 50 mg, 11% on 75 mg and 38% on 150 mg. Only in the 150-mg group was the response rate significantly different to placebo (P < 0.001). Over the treatment period the mean PASI changed from 15.9 to 15.4 on placebo, from 17.4 to 13.8 on liarozole 50 mg, from 17.5 to 14.5 on 75 mg and from 15.8 to 8.8 on 150 mg. Again, only in the group receiving 150 mg was the response significantly better than placebo (P < 0.001). Liarozole was generally well tolerated. Mucocutaneous retinoid effects were generally infrequent and mild. Five subjects were withdrawn from treatment as a result of adverse events that may have been treatment related. These events were abnormalities of liver enzymes in two cases, an episode of erythema multiforme (in a patient receiving placebo), an allergic reaction in one and a rash accompanied by deterioration of the psoriasis in another. There was mild elevation of triglycerides in the groups receiving liarozole 75 mg and 150 mg daily. In males, the serum luteinizing hormone and testosterone levels rose significantly in all the active treatment groups.

CONCLUSIONS

The data confirm that liarozole is an effective treatment for psoriasis and indicate that the lowest effective dose is 75 mg twice daily. The drug seems generally to be well tolerated.

Synthesis and evaluation of 17-aliphatic heterocycle-substituted steroidal inhibitors of 17alpha-hydroxylase/C17-20-lyase (P450 17)

In the search for potent inhibitors of P450 17, the key enzyme in androgen biosynthesis, a series of steroidal inhibitors were synthesized and tested toward rat and human P450 17. Small aliphatic heterocycles (aziridine, oxirane, thiirane, diaziridine, diazirine, azetidine) were introduced into the 17beta-position of anstrost-5-en-3beta-ol. After identifying that aziridine is the most suitable functional group to coordinate with the heme iron, modifications of the steroidal skeleton were performed for further optimization. A wide range of inhibitory potencies toward P450 17 were found for the 21 test compounds. The most potent inhibitors toward the human and rat enzyme were aziridine compounds 3 (IC(50) rat: 0.21 microM, K(i) = 3 nM; IC(50) human: 0.54 microM, K(i) = 8 nM), 5 (IC(50) rat: 0.43 microM, K(i) = 7 nM; IC(50) human: 0.29 microM, K(i) = 4 nM), and 8 (21R:21S = 1:1; IC(50) rat: 0.53 microM, K(i) = 9 nM; IC(50) human: 0.40 microM, K(i) = 6 nM) which were more potent than the reference ketoconazole (IC(50) rat: 67 microM; IC(50) human: 0.74 microM). The inhibitory potency depends markedly on the stereochemistry at C20 of the inhibitors. This effect is more pronounced for the rat enzyme. Tested for selectivity, the highly potent inhibitors show poor inhibitory activity toward P450 arom, P450 scc, P450 TxA(2), and 5alpha-reductase. Tested for in vivo activity, 3 and 8 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats by 81% and 84% after 2 h.

Synthesis and evaluation of novel steroidal oxime inhibitors of P450 17 (17 alpha-hydroxylase/C17-20-lyase) and 5 alpha-reductase types 1 and 2

17 alpha-Hydroxylase/C17-20-lyase (P450 17, CYP 17) and 5 alpha-reductase are the key enzymes in androgen biosynthesis and targets for the treatment of prostate cancer and benign prostatic hyperplasia. In the search of inhibitors for both enzymes, 23 pregnenolone- or progesterone-based steroids were synthesized bearing an oxime group connected directly or via a spacer to the steroidal D-ring. Tested for inhibition of human and rat P450 17, some pregnenolone (9, 11, 14) and a series of progesterone compounds (17-20) turned out to be highly active inhibitors of the human enzyme. The most active compound was Z-21-hydroxyiminopregna-5, 17(20)-dien-3 beta-ol (9) showing K(i) values of 44 and 3.4 nM for the human and rat enzymes, respectively, and a type II UV-difference spectrum indicating a coordinate bond between the oxime group and the heme iron. In contrast to the pregnenolones which showed no inhibition of 5 alpha-reductase isozymes 1 and 2, the progesterones 16, 17, 20, 21, and 23 showed marked inhibition, especially toward the type 2 enzyme. Compounds 17 and 20 were identified as potent dual inhibitors of both P450 17 and 5 alpha-reductase. Tested for selectivity, the most potent P450 17 inhibitors 9, 10, and 14 showed no or only marginal inhibition of P450 arom, P450 scc, and P450 TxA(2). Selected compounds were tested for inhibition of the target enzymes using whole-cell assays. Compounds 9-11 strongly inhibited P450 17 being coexpressed with NADPH-P450 reductase in E. coli cells, and 16, 20, and 23 markedly inhibited 5 alpha-reductase expressed in HEK 293 cells. Tested for in vivo activity, 9 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats after 2 and 6 h by 57% and 44%.

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 liarozole's mechanisms of action. Patients were postmenopausal with either: ER negative disease in first relapse (Group 1: 1n = 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 (150-300mg) 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 (9.1-1,839 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 liarozole's 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 > or = 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.

Some effects of the fungicide propiconazole on cytochrome P450 and glutathione S-transferase in brown trout (Salmo trutta)

The fungicide propiconazole (1-(2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl) -1H-1,2,4-triazole) induced the hepatic cytochrome P4501A (CYP1A) activity towards ethoxyresorufin-O-deethylase (EROD), the content of CYP1A protein as quantified by enzyme-linked immunosorbent assay (ELISA) and the glutathione S-transferase (GST) activity towards the three commonly used substrates CDNB(1-chloro-2,4-dinitrobenzene), cumene hydroperoxide (CU) and ethachrynic acid (EA) in brown trout (Salmo trutta) depending on dose and body weight. An exponential dose response relationship existed between propiconazole exposure and CYP1A activity. A 2. order polynomial regression of the propiconazole concentration (square root transformed) on the data for CDNB, EU and CU revealed a bell-shaped pattern of the GST induction. Reverse-phase HPLC of the GSH-affinity chromatography purified GST isozymes in trout exposed to respectively 8.3, 23, 93, 313 and 606 microg l(-1) propiconazole in the water indicated that the propiconazole treatment may lead to changes in the composition of the subunits compared to the controls. Thus, propiconazole exposure through the water changed the properties of the brown trout hepatic CYP1A and GST, and these changes may be used as a bioindicator on the molecular level of exposure and effect of propiconazole in controlled experiments. The use in monitoring of propiconazole exposure under natural field conditions is possible, however needs further investigation.

YM116, 2-(1H-imidazol-4-ylmethyl)-9H-carbazole, decreases adrenal androgen synthesis by inhibiting C17-20 lyase activity in NCI-H295 human adrenocortical carcinoma cells

The concentrations of androstenedione and dehydroepiandrosterone, products of C17-20 lyase, in the medium after a 6-hr incubation of NCI-H295 cells were decreased by YM116 (2-(1H-imidazol-4-ylmethyl)-9H-carbazole) (IC50: 3.6 and 2.1 nM) and ketoconazole (IC50: 54.9 and 54.2 nM). 17Alpha-hydroxyprogesterone, a product of 17alpha-hydroxylase, was increased by YM116 (1-30 nM) and by ketoconazole (10-300 nM) and then was decreased at higher concentrations of both agents (IC50: 180 nM for YM116, 906 nM for ketoconazole), indicating that YM116 and ketoconazole were 50- and 16.5-fold more specific inhibitors of C17-20 lyase, respectively, than 17alpha-hydroxylase. Compatible with these findings, progesterone, a substrate of 17alpha-hydroxylase, was increased by these agents. Cortisol production was inhibited by YM116 and ketoconazole (IC50: 50.4 and 80.9 nM, respectively). YM116 was a 14-fold more potent inhibitor of androstenedione production than cortisol production, whereas ketoconazole was a nonselective inhibitor of the production of both steroids. YM116 and ketoconazole inhibited the C17-20 lyase activity in human testicular microsomes (IC50: 4.2 and 17 nM, respectively). These results demonstrate that YM116 reduces the synthesis of adrenal androgens by preferentially inhibiting C17-20 lyase activity.

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Novel nonsteroidal inhibitor of cytochrome P450(17alpha) (17alpha-hydroxylase/C17-20 lyase), YM116, decreased prostatic weights by reducing serum concentrations of testosterone and adrenal androgens in rats

BACKGROUND

The purpose of this study was to determine the effects of a nonsteroidal C17-20 lyase inhibitor, 2-(1H-imidazol-4-ylmethyl)-9H-carbazole (YM116), on serum concentrations of androgens and ventral prostatic weight in rats.

METHODS

Serum concentrations of testosterone and of dehydroepiandrosterone sulfate and prostatic weights were measured in rats treated with YM116.

RESULTS

YM116 inhibited testicular C17-20 lyase competitively (Ki, 0.38 nM), and decreased the serum testosterone concentration in gonadotropin-releasing hormone-treated rats (ED50, 0.7 mg/kg), indicating that YM116 was about 21-24 times more potent than other C17-20 lyase inhibitors such as ketoconazole and liarozole, and was twice as potent as CB7630. YM116 also reduced dehydroepiandrosterone sulfate levels in ACTH-treated castrated rats (ED50, 11 mg/kg). YM116 (40 mg/kg, p.o., for 2 weeks) was almost comparable to bilateral orchiectomy with respect to the time course and magnitude of the reduction in prostatic weight. Each of these two treatments decreased the prostatic weight 3 days following the treatment. Contrarily, leuprolide transiently increased the prostatic weight and then decreased it. YM116 (100 mg/kg) had no effect on the serum cortisol level in guinea pigs, and slightly decreased the serum aldosterone level in rats.

CONCLUSIONS

YM116 is a selective C17-20 lyase inhibitor which decreases rat prostatic weight by reducing androgen production in the testes and adrenal glands.

Phase II study of liarozole in advanced non-small cell lung cancer

The aim of this phase II study was to investigate the efficacy and tolerability of liarozole, a novel benzimidazole derivative, in non-small cell lung cancer (NSCLC). Liarozole 300 mg twice daily orally was evaluated in 14 patients with stage IIIB and IV NSCLC. 8 patients had received prior treatment with chemotherapy and/or radiotherapy. WHO toxicity grading and response criteria were used. Liarozole was well tolerated. Grade 2 toxicities included alopecia (1 patient), dermatological toxicity (5 patients), dry mouth (2 patients) and nausea and vomiting (2 patients). Leukocytosis was seen in 5 patients, including 2 cases with an elevated white cell count pretreatment. Liarozole was discontinued in 1 patient who developed intolerable progressive pruritus associated with an erythematous rash. No objective tumour response was seen, all 14 patients developing progressive disease within 4 months of commencing treatment. Liarozole was well tolerated but was ineffective as single agent therapy in the management of NSCLC. The side-effect profile was compatible with inhibition of retinoic acid degradation.

P450-dependent enzymes as targets for prostate cancer therapy

Metastatic prostate adenocarcinoma is a leading cause of cancer-related deaths among men. First line treatment is primarily aimed at blocking the synthesis and action of androgens. As primary endocrine treatment, androgen deprivation is usually achieved by orchidectomy or LHRH analogues, frequently combined with androgen receptor antagonists in order to block the residual adrenal androgens. However, nearly all the patients will eventually relapse. Available or potential second line therapies include, among others, alternative endocrine manipulations and chemotherapy. Cytochrome P450-dependent enzymes are involved in the synthesis and/or degradation of many endogenous compounds, such as steroids and retinoic acid. Some of these enzymes represent suitable targets for the treatment of prostate cancer. In first line therapy, inhibitors of the P450-dependent 17,20-lyase may achieve a maximal androgen ablation with a single drug treatment. Ketoconazole at high dose blocks both testicular and adrenal androgen biosynthesis but its side-effects, mainly gastric discomfort, limit its widespread use. A series of newly synthesized, more selective, steroidal 17,20-lyase inhibitors related to 17-(3-pyridyl)androsta-5,16-dien-3beta-ol, may open new perspectives in this field. In prostate cancer patients who relapse after surgical or medical castration, therapies aiming at suppressing the remaining adrenal androgen biosynthesis (ketoconazole) or producing a medical adrenalectomy (aminoglutethimide+hydrocortisone) have been used, but are becoming obsolete with the generalization of maximal androgen blockade in first line treatment. The role of inhibition of aromatase in prostate cancer therapy, which was postulated for aminoglutethimide, could not be confirmed by the use of more selective aromatase inhibitors, such as formestane. An alternative approach is represented by liarozole fumarate (LIA), a compound that blocks the P450-dependent catabolism of retinoic acid (RA). In vitro, it enhances the antiproliferative and differentiation effects of RA in cell lines that express RA metabolism, such as F9 teratocarcinoma and MCF-7 breast carcinoma cells. In vivo, monotherapy with LIA increases RA plasma levels and, to a greater extent, endogenous tissue RA levels leading to retinoid-mimetic effects. In the rat Dunning prostate cancer models, it inhibits the growth of androgen-independent as well as androgen-dependent carcinomas relapsing after castration. Concurrently, changes in the pattern of cytokeratins characteristic of increased differentiation were observed. Early clinical trials show that LIA, in second or third line therapy in metastatic prostate cancer, induces PSA responses in about 30% of unselected patients. In some patients regression of soft tissue metastasis ha been observed. In a subgroup of patients, an important relief of metastatic bone pain was also noted.

Liarozole, an antitumor drug, modulates cytokeratin expression in the Dunning AT-6sq prostatic carcinoma through in situ accumulation of all-trans-retinoic acid

Liarozole showed antitumoral activity in the Dunning AT-6sq, an androgen-independent rat prostate carcinoma. To investigate its potential mechanism of action, the effects of the drug doses (ranging from 3.75 to 80 mg/kg b.i.d.) on endogenous plasma and tissue all-trans-retinoic acid levels and on the differentiation status of the tumor cells were evaluated. To follow modulation of differentiation, cytokeratins were localized in the (un)treated tumors by immunocytochemistry and quantitatively determined by immunoblotting. Results showed that liarozole statistically significantly reduced tumor weight from 30 mg/kg upwards and induced accumulation of all-trans-retinoic acid both in plasma and tumors. In the tumors, a statistically significant accumulation was already noted from 7.5 mg liarozole/kg upwards. Concomitantly, the differentiation status shifted from a keratinizing towards a non-keratinizing squamous carcinoma, which was further confirmed by the cytokeratin profile of the carcinoma (presence of CK 8, 10, 13, 14, 18, 19). Immunoblotting revealed an overall decrease in cytokeratin content, except for CK 8. These findings suggest that the antitumoral properties of liarozole might be related to an increase in the degree of tumor differentiation through accumulation of all-trans-retinoic acid.

Inhibition of the metabolism of endogenous retinoic acid as treatment for severe psoriasis: an open study with oral liarozole

Retinoids derived from retinol or beta-carotene are inactivated, among other ways, by enzymes belonging to the P450 cytochrome group. Liarozole, an imidazole-containing compound, is known to be a potent inhibitor of the cytochrome P450-mediated metabolism of all-trans retinoic acid. As a result, increased levels of this retinoid are found in skin and plasma. Therefore, in the treatment of psoriasis, therapeutic effects may be expected with liarozole which are similar to those observed with synthetic retinoids. In an open study, oral liarozole was given at a daily dose of 75 mg b.i.d., for 12 weeks to 31 patients with severe psoriasis. After 1 month, this dosage could be increased to 150 mg b.i.d. if there was no improvement or only moderate improvement. Initially, the effect of liarozole was mainly on scaling. A decrease in the Psoriasis Area and Severity Index (PASI) score of 45% at week 4, of 69% at week 8 and of 77% at week 12 was obtained, compared with baseline. A further decrease in the PASI score of up to 87% was observed in the 16 patients who were allowed to continue treatment for a maximum period of 12 months. An excellent or good improvement was noted in 77% of the patients within 12 weeks of starting treatment. This response rate had increased to 88% by the last follow-up visit. Nearly all patients (29 of 31) experienced adverse reactions, such as dry oral mucosa, headache and itching. These were mostly mild and transient, but four patients dropped out of the study because of an adverse event. Haematological, biochemical and cardiovascular parameters were not significantly influenced by liarozole. Six patients showed an increase in triglycerides, which normalized in three of four patients during further treatment. The results of this pilot study suggest that, at doses of 75-150 mg b.i.d., liarozole is an active antipsoriatic drug, and may be a useful addition to the existing therapeutic armamentarium. Controlled studies should be performed to compare liarozole with standard oral treatments.

P450 inhibitors of use in medical treatment: focus on mechanisms of action

A number of cytochrome P450s are targets for compounds that are clinically used or under clinical evaluation for treatment of patients with mycotic infections, such as dermatophytosis, superficial and systemic candidiasis, cryptococcosis and aspergillosis, with skin diseases, such as psoriasis or ichthyosis, and other retinoid-sensitive malignancies, e.g., neuro-ectodermal glioma. Some of the P450 inhibitors are candidates for the treatment of hirsutism or prostate cancer, others are potent inhibitors of the P450 isomerase involved in the synthesis of thromboxane A2, a potent platelet aggregation inducer and vasoconstrictor.

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.

Inhibitors of P450-dependent steroid biosynthesis: from research to medical treatment

A number of cytochrome P450-dependent enzymes are major targets for both steroidal and nonsteroidal compounds that may be of use in the treatment of a number of androgen-independent, androgen-, estrogen- and other steroid-dependent diseases. Compounds of interest are for example aminoglutethimide and derivatives; esters of 4-pyridineacetic acid; imidazole derivatives, such as ketoconazole, liarozole, fadrozole, CGS 18320 B; bis-chlorophenyl-pyrimidine analogues; triazole derivatives vorozole and CGS 20267, and steroidal aromatase inhibitors such as 4-hydroxyandrostenedione. Some of them (e.g. ketoconazole) triggered studies to find new possibilities in medical treatment. Others are of use clinically or under clinical evaluation to provide a palliative treatment and/or cure to patients with for example prostatic carcinoma, breast cancer, hypercortisolism and benign prostatic hyperplasia.

Experimental studies with liarozole (R 75,251): an antitumoral agent which inhibits retinoic acid breakdown

Liarozole reduced tumor growth in the androgen-dependent Dunning-G and the androgen-independent Dunning MatLu rat prostate carcinoma models as well as in patients with metastatic prostate cancer who had relapsed after orchiectomy. In vitro, liarozole did not have cytostatic properties, as measured by cell proliferation in breast MCF-7 and prostate DU145 and LNCaP carcinoma cell lines. It did not alter the metabolism of labeled testosterone i.e. the 5 alpha-reductase in cultured rat prostatic cells. In mouse F9 teratocarcinoma cells liarozole did not show any retinoid-like properties but enhanced the plasminogen activator production induced by retinoic acid. Furthermore, liarozole and retinoic acid similarly reduced the growth of the androgen-dependent Dunning-G tumor in nude mice and inhibited tumor promotion elicited by phorbol ester in mouse skin. These data have raised the hypothesis that the antitumoral properties of liarozole may be related to inhibition of retinoic acid degradation, catalyzed by a P-450-dependent enzyme that is blocked by the drug.

Antitumoral effects of R 75251 on the growth of transplantable R3327 prostatic adenocarcinoma in rats

The antitumoral activity of a novel imidazole derivative, R 75,251, has been studied in the androgen-dependent R3327G Dunning prostate adenocarcinoma grafted subcutaneously in syngeneic rats. Dietary application resulting approximately in dose levels of 80, 120, and 160 mg/kg reduced tumor weight by 66, 81, and 79%, respectively. This effect was not significantly different from that measured after castration (-82%). In intact animals, however, serum testosterone levels were almost not affected by R 75,251 treatment while LH levels rose two- to threefold. In castrated rats a tenfold increase in LH was observed. Moreover, prostate and seminal vesicles weights decreased much less after R 75,251 treatment than after castration. In castrated animals, treatment with R 75,251 induced a slight, non-significant reduction in tumor weight (-36%) compared with castration alone. In castrated animals, tumor growth was restored by exogenous administration of testosterone. In such animals R 75,251 also significantly reduced tumor weight by 57%. Similar results were obtained with Dunning R3327G prostate adenocarcinoma grafted beneath the renal capsule in male syngeneic rats receiving twice daily orally by gavage a dose of 80 mg/kg of R 75,251. These data suggest that R 75,251 exerts an antitumoral effect independent of its inhibition of androgen biosynthesis.