RU 58841, a new specific topical antiandrogen: a candidate of choice for the treatment of acne, androgenetic alopecia and hirsutism

Synthesis and application of clinically approved small-molecule drugs targeting androgen receptor

Androgen receptor (AR) plays a crucial role in various physiological processes. Dysregulation of AR signaling has been implicated in several diseases, such as prostate cancer and androgenetic alopecia. Therefore, the development of drugs that specifically target AR has gained significant attention in the field of drug discovery. This review provides an overview of the synthetic routes of clinically approved small molecule drugs targeting AR and discusses the clinical applications of these drugs in the treatment of AR-related diseases. The review also highlights the challenges and future perspectives in this field, including the need for improved drug design and the exploration of novel therapeutic targets. Through an integrated analysis of the therapeutic applications, synthetic methodologies, and mechanisms of action associated with these approved drugs, this review facilitates a holistic understanding of the versatile roles and therapeutic potential of AR-targeted interventions. Overall, this comprehensive review serves as a valuable resource for medicinal chemists interested in the development of small-molecule drugs targeting AR.

Synthesis and clinical application of small-molecule drugs approved to treat prostatic cancer

Prostate cancer is a prevalent form of cancer that primarily affects men, with a high incidence and mortality rate. It is the second most common cancer among males, following lung cancer. Typically occurring in individuals aged 50 and above, this malignant tumor originates from abnormal cells in the prostate tissue. If left untreated, it can spread to nearby tissues, lymph nodes, and even bones. Current treatment methods include surgery, radiotherapy, and chemotherapy. However, these treatments have certain limitations and side effects. Therefore, researching and developing new small-molecule drugs to treat prostate cancer is of great significance. In recent years, many small-molecule drugs have been proven to have therapeutic effects on prostate cancer. The purpose of this review is to give a comprehensive look at the clinical uses and synthetic methods of various significant small-molecule drugs that have been approved to treat prostate cancer, to facilitate the development of more powerful and innovative drugs for the effective control of prostate cancer.

Therapeutic Strategies to Target the Androgen Receptor

The androgen receptor (AR) plays a key role in the maintenance of muscle and bone and the support of male sexual-related functions, as well as in the progression of prostate cancer. Accordingly, AR-targeted therapies have been developed for the treatment of related human diseases and conditions. AR agonists are an important class of drugs in the treatment of bone loss and muscle atrophy. AR antagonists have also been developed for the treatment of prostate cancer, including metastatic castration-resistant prostate cancer (mCRPC). Additionally, selective AR degraders (SARDs) have been reported. More recently, heterobifunctional degrader molecules of AR have been developed, and four such compounds are now in clinical development for the treatment of human prostate cancer. This review attempts to summarize the different types of compounds designed to target AR and the current frontiers of research on this important therapeutic target.

Synthesis of flutamide-conjugates

In this paper, we designed and extended modification basing on the flutamide structure. A series of flutamide-conjugates were obtained with methyl bromoacetate and ethylenediamine. Through the synthesis of two conjugates with 3,5-bis(dodecyloxy)benzoate derivatives, these flutamide conjugates were tested for anticancer activity. Among the compounds tested, the flutamide-conjugates showed good inhibition activity against cancer cell lines U-251, PC-3 and K-562. The conjugates showed a better inhibitory effect than free flutamide and did not show activity against normal COS-7 monkey kidney fibroblast cells. It was also observed that the flutamide conjugates had an inhibitory effect against human colorectal adenocarcinoma HCT-15.

Recent discoveries and developments of androgen receptor based therapy for prostate cancer

The main focus of this review is to discuss the discoveries and developments of various therapies for prostate cancer.

Potential targets in the discovery of new hair growth promoters for androgenic alopecia

INTRODUCTION

Androgenic alopecia (AGA) is the major type of scalp hair loss affecting 60 - 70% of the population worldwide. It is caused by two potent androgens, namely testosterone (T) and 5α-dihydrotestosterone (5α-DHT). Till date, only two FDA-approved synthetic drugs, minoxidil and finasteride, are used to cure AGA with only 35 and 48% success, respectively; therefore, a search for new drug based on the mechanism of androgens action is still needed.

AREAS COVERED

Relevant literature was reviewed to identify current therapeutic targets and treatments for AGA. The potential targets are classified into three categories: i) 5α-reductase; ii) androgen receptor and iii) growth-factor-producing genes related to hair growth.

EXPERT OPINION

Relevant assay systems using the right targets are required in order to obtain specific and effective drugs for AGA treatment. It is unlikely that single targeted agents will be sufficient for treating AGA, and therefore, it would be a challenge to obtain compounds with multiple activities.

Antischistosomal versus antiandrogenic properties of aryl hydantoin Ro 13-3978

In the early 1980s, the antischistosomal aryl hydantoin Ro 13-3978 (AH01), a close structural analogue of the androgen receptor antagonist nilutamide, was discovered. Administration of 100 mg/kg oral doses of AH01 to mice infected with adult and juvenile Schistosoma mansoni produced 95% and 64% total worm burden reductions, confirming its high activity against adult worms, and showing that AH01 is also effective against juvenile infections. AH01 had no measureable interaction with the androgen receptor in a ligand competition assay, but it did block dihydrotestosterone-induced cell proliferation in an androgen-dependent human prostate cancer cell line. For AH01, nilutamide, and three closely related aryl hydantoin derivatives, there was no correlation between antischistosomal activity and androgen receptor interaction.

Alternative synthesis of the anti-baldness compound RU58841

A bromine-nitro substitution at tertiary carbon and using 2-nitropropane as leaving group enable a short phosgene-free synthesis of RU58841.

Synthesis and structure-activity relationships of the first ferrocenyl-aryl-hydantoin derivatives of the nonsteroidal antiandrogen nilutamide

We present here the first synthesis of organometallic complexes derived from the nonsteroidal antiandrogen nilutamide, bearing a ferrocenyl substituent at position N(1) or at C(5) of the hydantoin ring; for comparison, we also describe the C(5) p-anisyl organic analogue. All of these complexes retain a modest affinity for the androgen receptor. The N-substituted complexes show a weak or moderate antiproliferative effect (IC 50 around 68 microM) on hormone-dependent and -independent prostate cancer cells, while the C(5)-substituted compounds exhibit toxicity levels 10 times higher (IC 50 around 5.4 microM). This strong antiproliferative effect is probably due to a structural effect linked to the aromatic character of the ferrocene rather than to its organometallic feature. In addition, it seems connected to a cytotoxic effect rather than an antihormonal one. These results open the way toward a new family of molecules that are active against both hormone-dependent and hormone-independent prostate cancer cells.

Glucocorticoid and Sex Hormone Receptors: Clinical Implications and Therapeutic Relevance

In general, steroid hormones exert their effects through intracellular receptors, the glucocorticoid (GR), mineralocorticoid (MR), androgen (AR), estrogen (ER), and progesterone (PR) receptors. In this brief review, we will focus on glucocorticoid and sex hormone actions in the skin through their distinct receptors and discuss their clinical relevance.

Pharmacokinetics and pharmacodynamics of nonsteroidal androgen receptor ligands

Testosterone and structurally related anabolic steroids have been used to treat hypogonadism, muscle wasting, osteoporosis, male contraception, cancer cachexia, anemia, and hormone replacement therapy in aging men or age-related frailty; while antiandrogens may be useful for treatment of conditions like acne, alopecia (male-pattern baldness), hirsutism, benign prostatic hyperplasia (BPH) and prostate cancer. However, the undesirable physicochemical and pharmacokinetic properties of steroidal androgen receptor (AR) ligands limited their clinical use. Nonsteroidal AR ligands with improved pharmacological and pharmacokinetic properties have been developed to overcome these problems. This review focuses on the pharmacokinetics, metabolism, and pharmacology of clinically used and emerging nonsteroidal AR ligands, including antagonists, agonists, and selective androgen receptor modulators.

Investigational medications in the treatment of alopecia

Androgenetic alopecia (hereditary thinning) is the most common cause of hair loss in both men and women. Chemotherapy-induced alopecia is another distressing cause of hair loss. With a better understanding of follicular biology and the signals responsible for hair growth and regression, targeted therapies for hair loss are being investigated. This review summarises investigational medications for androgenetic and chemotherapy-induced alopecia that are in preclinical stages or later.

Synthesis and structure–activity investigation of iodinated arylhydantoins and arylthiohydantoins for development as androgen receptor radioligands

A series of side-chain derivatives of the arylhydantoin RU 58841 and the arylthiohydantoin RU 59063, wherein the aromatic trifluoromethyl group was replaced with iodine, was synthesized for possible development as radioiodinated androgen receptor (AR) ligands. Derivatives containing the cyanomethyl, methoxyethyl and propenyl side-chains displayed moderately high affinity (K(i)=20-59nM) towards the rat AR. Side-chains containing bulky lipophilic groups such as, benzyl and phenylpropyl, were poorly tolerated (K(i)>219nM). Superior AR binding affinities (0.71nM<K(i)<11nM) were displayed by arylhydantoins and arylthiohydantoin derivatives containing hydroxybutyl or methyl side-chains. The latter compounds are potential candidates for development as radioiodinated AR ligands.

[Androgenetic alopecia]

Androgenetic alopecia is the most common form of hair loss in men and women. Although the clinical manifestations are different in men and women, the pathogenetic pathways leading to this type of hair loss are similar in both sexes. In short genetically predestined hair follicles show an increased sensitivity to androgens. In recent years, much new data concerning the pathophysiology, management and therapy of androgenetic alopecia has been gathered. This article gives a critical overview of these new findings and assesses their practical relevance.

Rational Design and Synthesis of Androgen Receptor-Targeted Nonsteroidal Anti-Androgen Ligands for the Tumor-Specific Delivery of a Doxorubicin−Formaldehyde Conjugate

The synthesis and preliminary evaluation of a doxorubicin-formaldehyde conjugate tethered to the nonsteroidal antiandrogen, cyanonilutamide (RU 56279), for the treatment of prostate cancer are reported. The relative ability of the targeting group to bind to the human androgen receptor was studied as a function of tether. The tether served to attach the antiandrogen to the doxorubicin-formaldehyde conjugate via an N-Mannich base of a salicylamide derivative. The salicylamide was selected to serve as a trigger release mechanism to separate the doxorubicin-formaldehyde conjugate from the targeting group after it has bound to the androgen receptor. The remaining part of the tether consisted of a linear group that spanned from the 5-position of the salicylamide to the 3'-position of cyanonilutamide. The structures explored for the linear region of the tether were derivatives of di(ethylene glycol), tri(ethylene glycol), N,N'-disubstituted-piperazine, and 2-butyne-1,4-diol. Relative binding affinity of the tethers bound to the targeting group for human androgen receptor were measured using a (3)H-Mibolerone competition assay and varied from 18% of nilutamide binding for the butynediol-based linear region to less than 1% for one of the piperazine derivatives. The complete targeted drug with the butynediol-based linear region has a relative binding affinity of 10%. This relative binding affinity is encouraging in light of the cocrystal structure of human androgen receptor ligand binding domain bound to the steroid Metribolone which predicts very limited space for a tether connecting the antiandrogen on the inside to the cytotoxin on the outside.

Progestogens with antiandrogenic properties

Chlormadinone acetate, cyproterone acetate and dienogest are potent, orally active progestogens, which have antiandrogenic instead of partial androgenic activity. They act mainly by blocking androgen receptors in target organs, but also reduce the activity of skin 5alpha-reductase, the enzyme responsible for converting testosterone to the more potent androgen, 5alpha-dihydrotestosterone, in sebaceous glands and hair follicles. Chlormadinone acetate and cyproterone acetate also suppress gonadotropin secretion, thereby reducing ovarian and adrenal androgen production. Combined oral contraceptives (COCs) containing antiandrogenic progestogens provide highly effective contraception (gross and adjusted Pearl indices: 0-0.7 and 0-0.3, respectively) with excellent cycle control. Furthermore, COCs containing 2mg of chlormadinone acetate or cyproterone acetate plus 30 or 35 microg of ethinylestradiol produced improvement or resolution of seborrhoea in 80% of users, acne in 59-70%, hirsutism in 36% and androgen-related alopecia in up to 86%. These COCs are generally well tolerated, the main adverse effects being nonspecific or as expected for a COC (headache, breast tenderness and nausea). They have no clinically relevant effects on metabolic or liver functions or on bodyweight. Effects on mood and libido are uncommon (<3.5% and <6% of women, respectively). COCs containing antiandrogenic progestogens are likely to be particularly valuable in women with pre-existing androgen-related disorders who require contraception. They also increase the choice of products available for women with normal skin and hair who are concerned about the possibility of developing seborrhoea or acne with other COCs.

Fluridil, a rationally designed topical agent for androgenetic alopecia: first clinical experience

BACKGROUND

Fluridil, a novel topical antiandrogen, suppresses the human androgen receptor. While highly hydrophobic and hydrolytically degradable, it is systemically nonresorbable. In animals, fluridil demonstrated high local and general tolerance.

OBJECTIVE

To evaluate the safety and efficacy of a topical anti- androgen, fluridil, in male androgenetic alopecia.

METHODS

In 20 men, for 21 days, occlusive forearm patches with 2, 4, and 6% fluridil, isopropanol, and/or vaseline were applied. In 43 men with androgenetic alopecia (AGA), Norwood grade II-Va, 2% fluridil was evaluated in a double-blind, placebo-controlled study after 3 months clinically by phototrichograms, hematology, and blood chemistry including analysis for fluridil, and at 9 months by phototrichograms.

RESULTS

Neither fluridil nor isopropanol showed sensitization/irritation potential, unlike vaseline. In all AGA subjects, baseline anagen/telogen counts were equal. After 3 months, the average anagen percentage did not change in placebo subjects, but increased in fluridil subjects from 76% to 85%, and at 9 months to 87%. In former placebo subjects, fluridil increased the anagen percentage after 6 months from 76% to 85%. Sexual functions, libido, hematology, and blood chemistry values were normal throughout, except that at 3 months, in the spring, serum testosterone increased within the normal range equally in placebo and fluridil groups. No fluridil or its decomposition product, BP-34, was detectable in the serum at 0, 3, or 90 days.

CONCLUSION

Topical fluridil is nonirritating, nonsensitizing, nonresorbable, devoid of systemic activity, and anagen promoting after daily use in most AGA males.

Synthesis and structure-activity studies of side-chain derivatized arylhydantoins for investigation as androgen receptor radioligands

A series of arylhydantoin derivatives modeled after the antiandrogen RU 58841 was generated to identify potential candidates for development as androgen receptor (AR) radioligands. Side-chain modified derivatives of RU 58841, suitable for labeling with either carbon-11 or radiohalogens (fluorine-18, iodine-123), were synthesized and tested for their AR binding affinities. The N-(iodopropenyl) derivative 13 (Ki = 13 nM) is a potential candidate for development as a radioiodinated AR ligand.

Distinguishing androgen receptor agonists and antagonists: distinct mechanisms of activation by medroxyprogesterone acetate and dihydrotestosterone

Natural and pharmacological androgen receptor (AR) ligands were tested for their ability to induce the AR NH2-terminal and carboxyl-terminal (N/C) interaction in a two-hybrid protein assay to determine whether N/C complex formation distinguishes in vivo AR agonists from antagonists. High-affinity agonists such as dihydrotestosterone, mibolerone, testosterone, and methyltrienolone at concentrations between 0.1 and 1 nM induce the N/C interaction more than 40-fold. The lower affinity anabolic steroids, oxandrolone and fluoxymesterone, require concentrations of 10-100 nM for up to 23-fold induction of the N/C interaction. However no N/C interaction was detected in the presence of the antagonists, hydroxyflutamide, cyproterone acetate, or RU56187, at concentrations up to 1 microM, or with 1 microM estradiol, progesterone, or medroxyprogesterone acetate; each of these steroids at 1-500 nM inhibited the dihydrotestosterone-induced N/C interaction, with medroxyprogesterone acetate being the most effective. In transient and stable cotransfection assays using the mouse mammary tumor virus reporter vector, all ligands displayed concentration-dependent AR agonist activity that paralleled induction of the N/C interaction, with antagonists and weaker agonists failing to induce the N/C interaction. AR dimerization and DNA binding in mobility shift assays and AR stabilization reflected, but were not dependent on, the N/C interaction. The results indicate that the N/C interaction facilitates agonist potency at low physiological ligand concentrations as detected in transcription, dimerization/DNA binding, and stabilization assays. However the N/C interaction is not required for agonist activity at sufficiently high ligand concentrations, nor does its inhibition imply antagonist activity.

Evaluation of RU58841 as an anti-androgen in prostate PC3 cells and a topical anti-alopecia agent in the bald scalp of stumptailed macaques

The effect of androgen receptor transcriptional activation by RU58841, a nonsteroidal anti-androgen, was studied in the human prostate cancer PC3 cell line by cotransfection with wild-type androgen receptor (wt AR) and an androgen-responsive reporter (MMTV-ARE-CAT) construct. Anti-and rogens, hydroxyflutamide, and Casodex, and the antiestrogen, genistein, were studied in parallel for comparison with RU58841. The wt AR was activated only by the androgen dihydrotestosterone (DHT). Neither the anti-androgens nor antiestrogen can enhance AR transcriptional activity at 10(-11)-10(-7)M in PC3 cells. Hydroxyflutamide, RU58841, and Casodex, but not genistein, displayed competitively suppressive effects on DHT activation of wt AR. The potency of RU58841 was comparable to that of hydroxyflutamide. From this result, topical application of RU58841, which is considered to be a potential therapy for skin diseases, may induce systemic side effects. However, RU58841, on topical application, revealed a potent increase in density, thickening, and length of hair in the macaque model of androgenetic alopecia, whereas no systemic effects were detected. Together our results suggest that RU58841 may have potent antagonism to the wt AR and could be considered as a topically applied active anti-androgen for the treatment of androgen-dependent skin disorders, such as acne, androgenetic alopecia, and hirsutism.

Promotion of agonist activity of antiandrogens by the androgen receptor coactivator, ARA70, in human prostate cancer DU145 cells

Although hormone therapy with antiandrogens has been widely used for the treatment of prostate cancer, some antiandrogens may act as androgen receptor (AR) agonists that may result in antiandrogen withdrawal syndrome. The molecular mechanism of this agonist response, however, remains unclear. Using mammalian two-hybrid assay, we report that antiandrogens, hydroxyflutamide, bicalutamide (casodex), cyproterone acetate, and RU58841, and other compounds such as genistein and RU486, can promote the interaction between AR and its coactivator, ARA70, in a dose-dependent manner. The chloramphenicol acetyltransferase assay further demonstrates that these antiandrogens and related compounds significantly enhance the AR transcriptional activity by cotransfection of AR and ARA70 in a 1:3 ratio into human prostate cancer DU145 cells. Our results suggest that the agonist activity of antiandrogens might occur with the proper interaction of AR and ARA70 in DU145 cells. These findings may provide a good model to develop better antiandrogens without agonist activity.

Pharmacological profile of RU 58642, a potent systemic antiandrogen for the treatment of androgen-dependent disorders

The pharmacological profile of RU 58642, a new non-steroidal antiandrogen was investigated both in vitro and in vivo. In vitro, the compound displays a strong and specific affinity for androgen receptor. In vivo, its antiandrogenic activity was evaluated in castrated rat supplemented with testosterone propionate and in intact animals on prostate, seminal vesicles weight and serum levels of testosterone by oral and subcutaneous route. In castrated rats RU 58642 induced a significant decrease in prostate weight at a dose as low as 0.3 mg/kg whatever the route of administration. In intact rats its activity was compared to that of other non-steroidal antiandrogens such as flutamide, nilutamide and bicalutamide. RU 58642 proved to be significantly more potent than the reference compounds in reducing prostate weight: 3-30 times orally and 3-100 times subcutaneously, and thus the most potent antiandrogen to date to our knowledge. These results suggest that this compound may be very useful in the treatment of systemic androgen-dependent diseases.

Importance of sebaceous glands in cutaneous penetration of an antiandrogen: target effect of liposomes

The significance of the sebaceous gland pathway in the cutaneous permeation of an antiandrogen, 4-[3-(4-hydroxybutyl)-4,4-dimethyl -2,5-dioxo-1-imidazolidinyl]-2-(trifluoromethyl)benzonitrile (RU 58841), was studied with normal hairless rat skin and an induced scar hairless rat skin without sebaceous glands. RU 58841 was dissolved in an alcoholic solution and encapsulated in liposomes for comparison. After 24 h, the cumulative percentage of RU 58841 absorbed in vitro was 3-4-fold higher in the normal skin than in the scar skin; in the case of liposomes, the accumulation of the drug in the normal dermis was significantly higher than in the scar one. In the in vivo cutaneous distribution, the epidermis and dermis of the normal skin contained higher amounts of RU 58841 than the scar skin (ninefold with the solution and 16-fold with liposomes). An autoradiography study showed that with the solution, the drug was mainly localized in the stratum corneum/epidermis, and with the liposomes, the drug was mainly localized in the sebaceous glands. We concluded that the sebaceous glands constituted the main pathway for RU 58841. The alcoholic solution encouraged the localization of the drug into the stratum corneum, whereas liposomes targeted the sebaceous glands.

Local inhibition of sebaceous gland growth by topically applied RU 58841

The biological activity of a series of nonsteroidal, pure androgen receptor inhibitors was compared using the Syrian hamster ear skin sebaceous gland model. RU 58841, RU 56187, RU 38882 and cyproterone acetate were applied topically for 4 weeks on the ventral ear pinna of sexually mature male Syrian hamsters. Their order of efficacy was as follows: RU 58841 > RU 56187 > RU 38882 > cyproterone acetate. Maximal reduction of 60% in the size of the sebaceous glands was observed in hamsters treated with RU 58841 at a dose of 10 micrograms per day. This degree of inhibition occurred without any systemic side effects as shown by the absence of inhibition on the contralateral untreated ear pinna. Longer treatment did not produce greater inhibition since extending the treatment period from 4 weeks to 12 weeks showed similar data. The effect of RU 58841 was reversible since the inhibited sebaceous glands returned to normal size within 4 weeks after the cessation of the topical applications. The potent localized inhibition of sebaceous glands by RU 58841 demonstrates the excellent potential of this compound as a topical drug for the treatment of acne and other androgen-mediated disorders.

Preliminary pharmacokinetics and metabolism of novel non-steroidal antiandrogens in the rat: relation of their systemic activity to the formation of a common metabolite

The non-steroidal antiandrogens, RU 58841 and RU 56187 are amongst the most active of a new series of N-substituted aryl hydantoins or thiohydantoins. Their pharmacokinetics and principal metabolic profiles have been evaluated in rat plasma after intravenous administration of a 10 mg/kg dose. Both compounds disappear relatively rapidly from the plasma (elimination half-life of the order of 1 h), but they form a common metabolite, the N-desalkyl derivative, RU 56279, which is eliminated much more slowly. The percentage transformations of each into RU 56279, estimated from the AUCs of the metabolite compared with the AUC obtained after administration of RU 56279 itself, were respectively 1% and 77%. In parallel, their in vivo activity, as well as that of their metabolites, was determined with respect to parameters related to systemic antiandrogenic effects (prostate and seminal vesicle weights). The results showed that: (1) the common metabolite, RU 56279, is clearly antiandrogenic; (2) there appears to be a relationship between the percentage formation of this metabolite and the systemic antiandrogenic activity of the compounds. Thus, the pharmacological profile of RU 58841 which displays a potent local antiandrogenic activity without systemic effects can be related to its very low propensity to form the N-desalkyl metabolite.