Metabolism-Guided Selective Androgen Receptor Antagonists: Design, Synthesis, and Biological Evaluation for Activity against Enzalutamide-Resistant Prostate Cancer.

A major challenge for new drug discovery in the area of androgen receptor (AR) antagonists lies in predicting the druggable properties that will enable small molecules to retain their potency and stability during further studies in vitro and in vivo. Indole (compound 8) is a first-in-class AR antagonist with very high potency (IC50 = 0.085 µM) but is metabolically unstable. During the metabolic studies described herein, we synthesized new small molecules that exhibit significantly improved stability while retaining potent antagonistic activity for an AR. This structure-activity relationship (SAR) study of more than 50 compounds classified with three classes (Class I, II, and III) and discovered two compounds (32c and 35i) that are potent AR antagonists (e.g., IC50 = 0.021 µM, T1/2 = 120 min for compound 35i). The new antagonists exhibited improved in vivo pharmacokinetics (PK) with high efficacy antiandrogen activity in Hershberger and antiandrogen Enz-Res tumor xenograft models that overexpress AR (LNCaP-AR).

Exploration and Biological Evaluation of Basic Heteromonocyclic Propanamide Derivatives as SARDs for the Treatment of Enzalutamide-Resistant Prostate Cancer.

A series of propanamide derivatives were designed, synthesized, and pharmacologically characterized as selective androgen receptor degraders (SARDs) and pan-antagonists that exert a broad-scope androgen receptor (AR) antagonism. Incorporating different basic heteromonocyclic B-ring structural elements in the common A-ring-linkage-B-ring nonsteroidal antiandrogen general pharmacophore contributed to a novel scaffold of small molecules with SARD and pan-antagonist activities even compared to our recently published AF-1 binding SARDs such as UT-69 (11), UT-155 (12), and UT-34 (13). Compound 26f exhibited inhibitory and degradation effects in vitro in a wide array of wtAR, point mutant, and truncation mutant-driven prostate cancers (PCs). Further, 26f inhibited tumor cell growth in a xenograft model composed of enzalutamide-resistant (EnzR) LNCaP cells. These results demonstrate an advancement toward the development of novel SARDs and pan-antagonists with efficacy against EnzR prostate cancers.

An Overview of Next-Generation Androgen Receptor-Targeted Therapeutics in Development for the Treatment of Prostate Cancer.

Traditional endocrine therapy for prostate cancer (PCa) has been directed at suppression of the androgen receptor (AR) signaling axis since Huggins et al. discovered that diethylstilbestrol (DES; an estrogen) produced chemical castration and PCa tumor regression. Androgen deprivation therapy (ADT) still remains the first-line PCa therapy. Insufficiency of ADT over time leads to castration-resistant PCa (CRPC) in which the AR axis is still active, despite castrate levels of circulating androgens. Despite the approval and use of multiple generations of competitive AR antagonists (antiandrogens), antiandrogen resistance emerges rapidly in CRPC due to several mechanisms, mostly converging in the AR axis. Recent evidence from multiple groups have defined noncompetitive or noncanonical direct binding sites on AR that can be targeted to inhibit the AR axis. This review discusses new developments in the PCa treatment paradigm that includes the next-generation molecules to noncanonical sites, proteolysis targeting chimera (PROTAC), or noncanonical N-terminal domain (NTD)-binding of selective AR degraders (SARDs). A few lead compounds targeting each of these novel noncanonical sites or with SARD activity are discussed. Many of these ligands are still in preclinical development, and a few early clinical leads have emerged, but successful late-stage clinical data are still lacking. The breadth and diversity of targets provide hope that optimized noncanonical inhibitors and/or SARDs will be able to overcome antiandrogen-resistant CRPC.

Pyrazol-1-yl-propanamides as SARD and Pan-Antagonists for the Treatment of Enzalutamide-Resistant Prostate Cancer.

We report herein the design, synthesis, and pharmacological characterization of a library of novel aryl pyrazol-1-yl-propanamides as selective androgen receptor degraders (SARDs) and pan-antagonists that exert broad-scope AR antagonism. Pharmacological evaluation demonstrated that introducing a pyrazole moiety as the B-ring structural element in the common A-ring-linkage-B-ring nonsteroidal antiandrogens' general pharmacophore allowed the development of a new scaffold of small molecules with unique SARD and pan-antagonist activities even compared to our recently published AF-1 binding SARDs such as UT-155 (9) and UT-34 (10). Novel B-ring pyrazoles exhibited potent AR antagonist activities, including promising distribution, metabolism, and pharmacokinetic properties, and broad-spectrum AR antagonist properties, including potent in vivo antitumor activity. 26a was able to induce an 80% tumor growth inhibition of xenografts derived from the enzalutamide-resistant (Enz-R) VCaP cell line. These results represent an advancement toward the development of novel AR antagonists for the treatment of Enz-R prostate cancer.

New Generation of Selective Androgen Receptor Degraders: Our Initial Design, Synthesis, and Biological Evaluation of New Compounds with Enzalutamide-Resistant Prostate Cancer Activity.

In our effort to find small-molecule treatments of advanced prostate cancers (PCs), a novel series of indolyl and indolinyl propanamides (series II and III) were discovered as selective androgen receptor degraders (SARDs). Initial studies of androgen receptor (AR) antagonist (1) and agonist (2) propanamides yielded a tertiary aniline (3) with novel SARD activity but poor metabolic stability. Cyclization to II and III produced submicromolar AR antagonism and protein degradation selective to AR and AR splice variant (AR SV). II and III maintained potency against enzalutamide-resistant (Enz-R) mutant ARs and PC cells and were efficacious in Enz-R xenografts, suggesting their potential to treat advanced PCs. Design, synthesis, and biological activity of novel SARDs that could potentially be used for the treatment of a wide spectrum of PCs including castration-resistant, Enz-R, and/or AR SV-dependent advanced PCs that are often untreatable with known hormone therapies are discussed.

Selective androgen receptor modulators for the prevention and treatment of muscle wasting associated with cancer.

PURPOSE OF REVIEW: This review highlights selective androgen receptor modulators (SARMs) as emerging agents in late-stage clinical development for the prevention and treatment of muscle wasting associated with cancer. RECENT FINDINGS: Muscle wasting, including a loss of skeletal muscle, is a cancer-related symptom that begins early in the progression of cancer and affects a patient's quality of life, ability to tolerate chemotherapy, and survival. SARMs increase muscle mass and improve physical function in healthy and diseased individuals, and potentially may provide a new therapy for muscle wasting and cancer cachexia. SARMs modulate the same anabolic pathways targeted with classical steroidal androgens, but within the dose range in which expected effects on muscle mass and function are seen androgenic side-effects on prostate, skin, and hair have not been observed. Unlike testosterone, SARMs are orally active, nonaromatizable, nonvirilizing, and tissue-selective anabolic agents. SUMMARY: Recent clinical efficacy data for LGD-4033, MK-0773, MK-3984, and enobosarm (GTx-024, ostarine, and S-22) are reviewed. Enobosarm, a nonsteroidal SARM, is the most well characterized clinically, and has consistently demonstrated increases in lean body mass and better physical function across several populations along with a lower hazard ratio for survival in cancer patients. Completed in May 2013, results for the Phase III clinical trials entitled Prevention and treatment Of muscle Wasting in patiEnts with Cancer1 (POWER1) and POWER2 evaluating enobosarm for the prevention and treatment of muscle wasting in patients with nonsmall cell lung cancer will be available soon, and will potentially establish a SARM, enobosarm, as the first drug for the prevention and treatment of muscle wasting in cancer patients.

Role and pharmacologic significance of cytochrome P-450 2D6 in oxidative metabolism of toremifene and tamoxifen.

We investigated the in vitro metabolism and estrogenic and antiestrogenic activity of toremifene (TOR), tamoxifen (TAM) and their metabolites to better understand the potential effects of cytochrome P-450 2D6 (CYP2D6) status on the activity of these drugs in women with breast cancer. The plasma concentrations of TOR and its N-desmethyl (NDM) and 4-hydroxy (4-OH) metabolites during steady-state dosing with TOR were also determined. Unlike TOR, TAM and its NDM metabolite were extensively oxidized to 4-OH TAM and 4-OH-NDM TAM by CYP2D6, and the rate of metabolism was affected by CYP2D6 status. 4-OH-NDM TOR concentrations were not measurable at steady state in plasma of subjects taking 80 mg of TOR. Molecular modeling provided insight into the lack of 4-hydroxylation of TOR by CYP2D6. The 4-OH and 4-OH-NDM metabolites of TOR and TAM bound to estrogen receptor (ER) subtypes with fourfold to 30-fold greater affinity were 35- to 187-fold more efficient at antagonizing ER transactivation and had antiestrogenic potency that was up to 360-fold greater than their parent drugs. Our findings suggest that variations in CYP2D6 metabolic capacity may cause significant differences in plasma concentrations of active TAM metabolites (i.e., 4-OH TAM and 4-OH-NDM TAM) and contribute to variable pharmacologic activity. Unlike TAM, the clinical benefits in subjects taking TOR to treat metastatic breast cancer would not likely be subject to allelic variation in CYP2D6 status or affected by coadministration of CYP2D6-inhibiting medications.

Discovery and preclinical characterization of novel small molecule TRK and ROS1 tyrosine kinase inhibitors for the treatment of cancer and inflammation.

Receptor tyrosine kinases (RTKs), in response to their growth factor ligands, phosphorylate and activate downstream signals important for physiological development and pathological transformation. Increased expression, activating mutations and rearrangement fusions of RTKs lead to cancer, inflammation, pain, neurodegenerative diseases, and other disorders. Activation or over-expression of ALK, ROS1, TRK (A, B, and C), and RET are associated with oncogenic phenotypes of their respective tissues, making them attractive therapeutic targets. Cancer cDNA array studies demonstrated over-expression of TRK-A and ROS1 in a variety of cancers, compared to their respective normal tissue controls. We synthesized a library of small molecules that inhibit the above indicated RTKs with picomolar to nanomolar potency. The lead molecule GTx-186 inhibited RTK-dependent cancer cell and tumor growth. In vitro and in vivo growth of TRK-A-dependent IMR-32 neuroblastoma cells and ROS1-overexpressing NIH3T3 cells were inhibited by GTx-186. GTx-186 also inhibited inflammatory signals mediated by NFκB, AP-1, and TRK-A and potently reduced atopic dermatitis and air-pouch inflammation in mice and rats. Moreover, GTx-186 effectively inhibited ALK phosphorylation and ALK-dependent cancer cell growth. Collectively, the RTK inhibitor GTx-186 has a unique kinase profile with potential to treat cancer, inflammation, and neuropathic pain.

Androgen receptor antagonists: a patent review (2008-2011).

INTRODUCTION: Androgen receptor (AR) antagonists are predominantly used as chemical castration to treat prostate cancer (i.e., in conjunction with androgen deprivation therapy (ADT)). Unfortunately, castration-resistant prostate cancer (CRPC) typically develops that is refractory to targeted therapy. Insights into CRPC biology have led to the emergence of a promising clinical candidate MDV3100 (1) and a resurgence in this field. A pipeline of preclinical competitive (C-terminally directed) antagonists was discovered using a variety of innovative screening paradigms. Some inhibit nuclear translocation, selectively downregulate or degrade AR (SARD), antagonize wild-type and escape mutant AR (pan-antagonists) and/or antagonize AR target organs in vivo. Separately, the N-terminal domain has emerged as a promising novel target for noncompetitive antagonists. AREAS COVERED: AR antagonists whose patents published between 2008 and 2011 are reviewed. Antagonists are organized based on the screening paradigm reported as discussed above. EXPERT OPINION: Novel mechanisms provide a more informed basis for selecting a competitive antagonist; however, high potency and favorable in vivo properties remain paramount. Noncompetitive antagonists have theoretical advantages suggestive of improved clinical efficacy, but no clinical proof of concept as of yet.

Design, synthesis, and SAR studies of 4-substituted methoxylbenzoyl-aryl-thiazoles analogues as potent and orally bioavailable anticancer agents.

In a continued effort to improve upon the previously published 4-substituted methoxybenzoyl-aryl-thiazole (SMART) template, we explored chemodiverse "B" rings and "B" to "C" ring linkage. Further, to overcome the poor aqueous solubility of this series of agents, we introduced polar and ionizable hydrophilic groups to obtain water-soluble compounds. For instance, based on in vivo pharmacokinetic (PK) studies, an orally bioavailable phenyl-amino-thiazole (PAT) template was designed and synthesized in which an amino linkage was inserted between "A" and "B" rings of compound 1. The PAT template maintained nanomolar (nM) range potency against cancer cell lines via inhibiting tubulin polymerization and was not susceptible to P-glycoprotein mediated multidrug resistance in vitro, and markedly improved solubility and bioavailability compared with the SMART template (45a-c (PAT) vs 1 (SMART)).

Estrogen receptor beta selective nonsteroidal estrogens: seeking clinical indications.

IMPORTANCE OF THE FIELD: Nonsteroidal estrogens have been known since the 1930s. However, the relatively recent (1996) discovery of estrogen receptor subtype beta (ERbeta) suggested a possible paradigm shift away from SERM-like selectivity. Selective ERbeta agonism would potentially allow expansion of estrogenic targeting into new indications (discussed herein) currently precluded by the thrombogenic and hyperproliferative effects of nonselective estrogens. AREAS COVERED IN THIS REVIEW: ERbeta agonist design has been very successful. Pharmacophores for ERbeta selective nonsteroidal estrogens are generally diphenolic compounds that achieve an inter-phenolic distance and geometry similar to 17beta-estradiol with few restraints on the nature of the element linking the phenols (or phenol mimetics). The tremendously chemodiverse ERbeta agonist patent literature is reviewed, segregating the agonists into structurally similar compounds based on their interphenolic linking elements. WHAT THE READER WILL GAIN: A comprehensive understanding of the chemotype landscape of this field and an assessment of its maturation. TAKE HOME MESSAGE: Subtype selective ERbeta agonist therapy seems very promising. However, more clinical testing is needed to firmly establish its therapeutic potential. At this point, ERbeta is a promising target in search of an indication.

Recent and emerging anti-diabetes targets.

Diabetes is a disease that affects over 150 million people worldwide for which there are multiple oral and injectable medications. Because of trends in obesity and sedentary lifestyles, diabetes rates in both developed and developing countries are increasing at an alarming rate. Current medications are not adequately effective in maintaining long-term glycemic control in most patients, even when used in combination, leaving diabetics susceptible to developing life threatening and debilitating complications such as cardiovascular disease, blindness, kidney complications, and amputations. Consequently, there is a critical need for more potent pharmacotherapies with novel mechanisms of action. A panel of 20 emerging diabetes targets is presented, and small molecule modulators for each target will be discussed.

Selective androgen receptor modulators in preclinical and clinical development.

Androgen receptor (AR) plays a critical role in the function of several organs including primary and accessory sexual organs, skeletal muscle, and bone, making it a desirable therapeutic target. Selective androgen receptor modulators (SARMs) bind to the AR and demonstrate osteo- and myo-anabolic activity; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents produce less of a growth effect on prostate and other secondary sexual organs. SARMs provide therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, or end-stage renal disease, osteoporosis, frailty, and hypogonadism. This review summarizes the current standing of research and development of SARMs, crystallography of AR with SARMs, plausible mechanisms for their action and the potential therapeutic indications for this emerging class of drugs.

Effects, in an in-vivo model system, of 1,2,3,4-tetrahydroisoquinoline on glioma.

The effects of 1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol (EDL-155) on the growth of glioma was tested in vitro and in vivo. Normal cultured rat astrocytes and C6 rat glioma were used as a differential screen to test the effects of EDL-155. The compound was preferentially cytotoxic for C6 glioma (EC50=1.5 micromol/l) relative to cultured neonatal astrocytes (EC50=27.4 micromol/l). When compared with a standard chemotherapeutic agent, carmustine (1,3-bis[2-chloroethyl]-1-nitrosourea), or temozolomide, EDL-155 was more selective and more potent in our differential tissue culture assay. The effect of EDL-155 was also tested in an animal model in which C6 glioma was transplanted into the brains of Sprague-Dawley rats. EDL-155 was delivered directly onto the tumor by an osmotic minipump directly into the brain or by intraperitoneal injection. Animals treated with EDL-155 had significantly smaller tumors than did control animals treated with carrier solution. We observed anatomical changes in cultured glioma cells treated with EDL-155 that were consistent with selective destruction of mitochondria and the induction of autophagy. These changes were not observed in normal astrocytes cultured from rat pups. The selective killing of glioma in tissue culture and in the rat brain models indicates that EDL-155 has potential therapeutic value in treating this type of brain cancer.

Effect of B-ring substitution pattern on binding mode of propionamide selective androgen receptor modulators.

Selective androgen receptor modulators (SARMs) are essentially prostate sparing androgens, which provide therapeutic potential in osteoporosis, male hormone replacement, and muscle wasting. Herein we report crystal structures of the androgen receptor (AR) ligand-binding domain (LBD) complexed to a series of potent synthetic nonsteroidal SARMs with a substituted pendant arene referred to as the B-ring. We found that hydrophilic B-ring para-substituted analogs exhibit an additional region of hydrogen bonding not seen with steroidal compounds and that multiple halogen substitutions affect the B-ring conformation and aromatic interactions with Trp741. This information elucidates interactions important for high AR binding affinity and provides new insight for structure-based drug design.

Dissociated non-steroidal glucocorticoids: tuning out untoward effects.

The endogenous glucocorticoid (GC), cortisol, is involved in maintaining homeostatic balance in glucose regulation and immune response while allowing stress adaptation. The glucocorticoid receptor (GR) is required to maintain life and is the target of numerous FDA-approved drugs. Synthetic steroidal GCs are useful in a plethora of conditions characterized by excessive inflammatory or immune responses. Unfortunately, the GCs used at present have potentially dose-limiting and debilitating side effects, some of which derive from the glucose regulatory role of GCs. Consequently, there is a great need to find agents which preserve the potent immune effects without the side effects. This manuscript reviews the existing patent literature on these intensely sought non-steroidal agents that dissociate the therapeutic from metabolic effects, or specifically retain certain GR target effects with attenuated untoward effects. The chemical classes and underlying mechanisms (when known) for these non-steroidal GCs are discussed.

Non-steroidal glucocorticoid receptor antagonists: the race to replace RU-486 for anti-glucocorticoid therapy.

The endogenous glucocorticoid, cortisol, elevates blood glucose and suppresses the immune system. Glucocorticoid (GC) levels rapidly increase in response to physiologic and mental stress, thereby allowing stress adaptation. Unfortunately, the GC response can be excessive, especially under stressful conditions for the organism. The resulting hypercortisolemia is associated with a cluster of symptoms called Cushing's syndrome, a serious and potentially fatal illness involving hyperglycemia, hypertension, osteoporosis, muscle atrophy and fat maldistribution, as well as psychoses and immunosuppresion. Several disease states, such as diabetes and Cushing's, would benefit from blocking the actions of endogenous cortisol. The only glucocorticoid receptor (GR) antagonist available in the clinic is the steroid mifepristone (RU-486), whose primary potency is antigestagenic, making its utility as a GR antagonist limited. This manuscript reviews the current patent literature on selective non-steroidal GR antagonists.

Discovery of antiglioma activity of biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues.

Cultured rat astrocytes and C6 rat glioma were used as a differential screen for a variety of 1,2,3,4-tetrahydroisoquinoline (THI) derivatives. Compound 1 [1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride] selectively blocked the growth of C6 glioma leaving normal astrocytes relatively unaffected. The potential for clinical utility of 1 was further substantiated in human gliomas and other tumor cell lines. Preliminary SAR of this activity was characterized by synthesis and testing of several THI and conformationally flexible variants.

Arylisothiocyanato selective androgen receptor modulators (SARMs) for prostate cancer.

A new series of androgen receptor targeted agents (ARTA) was prepared and tested in androgen-dependent and -independent prostate cancer cell lines. These agents were bicalutamide analogs with isothiocyanato substituted B-rings. Also, the linker sulfone of R-bicalutamide was maintained or replaced with several alternative linkages including ether, amine, N-methylamine, thioether, and methylene (in this case the product was a racemic mixture) functional groups at the X-position. To expand the structure-activity relationship (SAR) of these arylisothiocyanato AR ligands, B-ring halogenated arylisothiocyanato ligands were also prepared and tested. The arylisothiocyanato AR ligands showed strong binding affinities to AR ranging from 0.6 to 54 nM. Among them, thioether and ether linkages demonstrated high binding affinities (0.6 and 4.6 nM, respectively) and selective cell growth inhibition (approximately 3- to 6-fold) for LNCaP, an androgen-dependent prostate cancer cell line, when compared to the androgen independent prostate cell lines (DU145, PC-3, and PPC-1) and a bladder cell line (TSU-Pr1). However, the ligands were inactive (IC50>100 mM) in a normal monkey kidney cell line (CV-1) that was used as the control for non-specific toxicity.