Orteronel (TAK-700), a novel non-steroidal 17,20-lyase inhibitor: effects on steroid synthesis in human and monkey adrenal cells and serum steroid levels in cynomolgus monkeys

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.

Effect of Essential Oil Components on the Activity of Steroidogenic Cytochrome P450

Endocrine-disrupting chemicals (EDCs) may impact the development of prostate cancer (PCa) by altering the steroid metabolism. Although their exact mechanism of action in controlling tumor growth is not known, EDCs may inhibit steroidogenic enzymes such as CYP17A1 or CYP19A1 which are involved in the production of androgens or estrogens. High levels of circulating androgens are linked to PCa in men and Polycystic Ovary Syndrome (PCOS) in women. Essential oils or their metabolites, like lavender oil and tea tree oil, have been reported to act as potential EDCs and contribute towards sex steroid imbalance in cases of prepubertal gynecomastia in boys and premature thelarche in girls due to the exposure to lavender-based fragrances. We screened a range of EO components to determine their effects on CYP17A1 and CYP19A1. Computational docking was performed to predict the binding of essential oils with CYP17A1 and CYP19A1. Functional assays were performed using the radiolabeled substrates or Liquid Chromatography-High-Resolution Mass Spectrometry and cell viability assays were carried out in LNCaP cells. Many of the tested compounds bind close to the active site of CYP17A1, and (+)-Cedrol had the best binding with CYP17A1 and CYP19A1. Eucalyptol, Dihydro-β-Ionone, and (-)-α-pinene showed 20% to 40% inhibition of dehydroepiandrosterone production; and some compounds also effected CYP19A1. Extensive use of these essential oils in various beauty and hygiene products is common, but only limited knowledge about their potential detrimental side effects exists. Our results suggest that prolonged exposure to some of these essential oils may result in steroid imbalances. On the other hand, due to their effect on lowering androgen output and ability to bind at the active site of steroidogenic cytochrome P450s, these compounds may provide design ideas for novel compounds against hyperandrogenic disorders such as PCa and PCOS.

Steroid 17α-hydroxylase/17, 20-lyase (cytochrome P450 17A1)

Cytochrome P450 (P450) 17A1 plays a key role in steroidogenesis, in that this enzyme catalyzes the 17α-hydroxylation of both pregnenolone and progesterone, followed by a lyase reaction to cleave the C-20 land C-21 carbons from each steroid. The reactions are important in the production of both glucocorticoids and androgens. The enzyme is critical in humans but is also a drug target in treatment of prostate cancer. Detailed methods are described for the heterologous expression of human P450 17A1 in bacteria, purification of the recombinant enzyme, reconstitution of the enzyme system in the presence of cytochrome b5, and chromatographic procedures for sensitive analyses of reaction products. Historic assay approaches are reviewed. Some information is also provided about outstanding questions in the research field, including catalytic mechanisms and searches for selective inhibitors.

The Discovery of BMS-737 as a Potent, CYP17 Lyase-Selective Inhibitor for the Treatment of Castration-Resistant Prostate Cancer

We report herein, the discovery of BMS-737 (compound 33) as a potent, non-steroidal, reversible small molecule inhibitor demonstrating 11-fold selectivity for CYP17 lyase over CYP17 hydroxylase, as well as a clean xenobiotic CYP profile for the treatment of castration-resistant prostate cancer (CRPC). Extensive SAR studies on the initial lead 1 at three different regions of the molecule resulted in the identification of BMS-737, which demonstrated a robust 83% lowering of testosterone without any significant perturbation of the mineralocorticoid and glucocorticoid levels in cynomologous monkeys in a 1-day PK/PD study.

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Abiraterone, Orteronel, Enzalutamide and Docetaxel: Sequential or Combined Therapy?

Objective: To summarize the current therapeutic status using chemotherapeutic agent docetaxel and endocrine therapeutic agents (ARAT, abiraterone, orteronel or enzalutamide) for the treatment of metastatic castration-resistant prostate cancer (mCRPC), including sequential therapy and combined therapy, to promote the consensus on the optimal regimen for achieving superior treatment efficacy.

Methods: Through literature search in PubMed, articles with the following relevant keywords were collected and anlyzed: CRPC, abiraterone, orteronel and enzalutamide, median survival, overall survival, prostate specific antigen (PSA), PSA response rate and median radiologic progression-free survival.

Results: Fifty-eight articles were obtained and analyzed in this review. These articles included androgen axis-targeting agents after docetaxel, docetaxel after androgen axis-targeting agents, Triple sequential and combination therapy, covering four current drugs for mCRPC treatment: docetaxel, abiraterone, orteronel, and enzalutamide. It was found that there may be some cross-resistance between androgen axis-targeting agents, which will reduce the efficacy of subsequent drug treatment. Although neither of the studies of using combination therapy showed serious drug toxicity, the efficacy of sequential therapy was not as good as expected. Most adverse reactions after treatment were reported to be level 1–2.

Conclusion: Based on the results of the current studies, abiraterone followed by enzalutamide treatment is the best sequential treatment for most docetaxel-naïve patients. This treatment achieves not only good OS, but also PFS and PSA response rates. In addition, for patients who have previously failed docetaxel treatment, enzalutamide is the best choice as the subsequent treatment.

Synthesis and Structure–Activity Relationships of Novel Non-Steroidal CYP17A1 Inhibitors as Potential Prostate Cancer Agents

Twenty new compounds, targeting CYP17A1, were synthesized, based on our previous work on a benzimidazole scaffold, and their biological activity evaluated. Inhibition of CYP17A1 is an important modality in the treatment of prostate cancer, which remains the most abundant cancer type in men. The biological assessment included CYP17A1 hydroxylase and lyase inhibition, CYP3A4 and P450 oxidoreductase (POR) inhibition, as well as antiproliferative activity in PC3 prostate cancer cells. The most potent compounds were selected for further analyses including in silico modeling. This combined effort resulted in a compound (comp 2, IC₅₀ 1.2 µM, in CYP17A1) with a potency comparable to abiraterone and selectivity towards the other targets tested. In addition, the data provided an understanding of the structure–activity relationship of this novel non-steroidal compound class.

Cyp17a1 is Required for Female Sex Determination and Male Fertility by Regulating Sex Steroid Biosynthesis in Fish

In teleost fish, sex steroids are involved in sex determination, sex differentiation, and fertility. Cyp17a1 (Cytochrome P450 family 17 subfamily A member 1) is thought to play essential roles in fish steroidogenesis. Therefore, to further understand its roles in steroidogenesis, sex determination, and fertility in fish, we constructed a cyp17a1 gene mutant in Nile tilapia (Oreochromis niloticus). In XX fish, mutation of the cyp17a1 gene led to a female-to-male sex reversal with a significant decline in 17β-estradiol (E2) and testosterone (T) production, and ectopic expression of male-biased markers (Dmrt1 and Gsdf) in gonads from the critical window of sex determination. Sex reversal was successfully rescued via T or E2 administration, and ovarian characteristics were maintained after termination of E2 supplementation in the absence of endogenous estrogen production in cyp17a1-/- XX fish. Likewise, deficiencies in T and 11-ketotestosterone (11-KT) production in both cyp17a1-/- XX sex-reversed males and cyp17a1-/- XY mutants resulted in meiotic initiation delays, vas deferens obstruction and sterility due to excessive apoptosis and abnormal mitochondrial morphology. However, 11-KT treatment successfully rescued the dysspermia to produce normal sperm in cyp17a1-/- male fish. Significant increases in gonadotropic hormone (gth) and gth receptors in cyp17a1-/- mutants may excessively upregulate steroidogenic gene expression in Leydig cells through a feedback loop. Taken together, our findings demonstrate that Cyp17a1 is indispensable for E2 production, which is fundamental for female sex determination and differentiation in XX tilapia. Additionally, Cyp17a1 is essential for T and 11-KT production, which further promotes spermatogenesis and fertility in XY males.

A Phase II Study Evaluating Orteronel, an Inhibitor of Androgen Biosynthesis, in Patients With Androgen Receptor (AR)-Expressing Metastatic Breast Cancer (MBC)

BACKGROUND

AR is a targetable pathway with AR modulation inhibiting estrogen- and androgen-mediated cell proliferation. Orteronel is an oral, selective, nonsteroidal inhibitor of 17, 20-lyase, a key enzyme in androgen biosynthesis. This study evaluated single-agent orteronel in AR+ metastatic breast cancer (MBC).

METHODS

Male/female patients with AR+ MBC were grouped in Cohort 1: AR+ TNBC with l-3 prior chemotherapy regimens or Cohort 2: AR+ HR+ (estrogen [ER+]/ progesterone receptor [PR+] positive) HER2+/- with 1 to 3 prior hormonal and at least 1 prior chemotherapy regimen. Patients with HER2+ MBC must have received at least 2 lines of HER2-targeted therapy. Orteronel was administered at 300 mg BID; response rate was the primary endpoint.

RESULTS

Seventy patients were enrolled (Cohort 1, n = 26 and Cohort 2, n = 44). Median treatment duration was 7.1 weeks. Seven patients were on treatment for ≥6 months. One of the 21 evaluated patients in Cohort 1 (4.8%) had an objective response. In Cohort 2, none of the first 23 patients to be evaluated had a response and accrual was stopped. Median progression-free and overall survival were 1.8 and 8.3 months, respectively. Toxicities were predominantly Grade 1 or 2 nausea/vomiting (36%) and fatigue (31%). Grade 3 or 4 events in ≥5% of patients included increased amylase/lipase (10%) and hypertension (6%).

CONCLUSIONS

Orteronel demonstrated limited clinical activity in heavily pre-treated AR+ MBC. Further development of orteronel in MBC is not recommended. Further efforts to validate the AR as a therapeutic target should focus on identifying new markers predictive of sensitivity to AR-targeted agents.

Stepwise binding of inhibitors to human cytochrome P450 17A1 and rapid kinetics of inhibition of androgen biosynthesis

Cytochrome P450 (P450) 17A1 catalyzes the 17α-hydroxylation of progesterone and pregnenolone as well as the subsequent lyase cleavage of both products to generate androgens. However, the selective inhibition of the lyase reactions, particularly with 17α-hydroxy pregnenolone, remains a challenge for the treatment of prostate cancer. Here, we considered the mechanisms of inhibition of drugs that have been developed to inhibit P450 17A1, including ketoconazole, seviteronel, orteronel, and abiraterone, the only approved inhibitor used for prostate cancer therapy, as well as clotrimazole, known to inhibit P450 17A1. All five compounds bound to P450 17A1 in a multistep process, as observed spectrally, over a period of 10 to 30 s. However, no lags were observed for the onset of inhibition in rapid-quench experiments with any of these five compounds. Furthermore, the addition of substrate to inhibitor–P450 17A1 complexes led to an immediate formation of product, without a lag that could be attributed to conformational changes. Although abiraterone has been previously described as showing slow-onset inhibition (t_1/2 = 30 min), we observed rapid and strong inhibition. These results are in contrast to inhibitors of P450 3A4, an enzyme with a larger active site in which complete inhibition is not observed with ketoconazole and clotrimazole until the changes are completed. Overall, our results indicate that both P450 17A1 reactions—17α-hydroxylation and lyase activity—are inhibited by the initial binding of any of these inhibitors, even though subsequent conformational changes occur.

Androgen receptor expression in breast cancer: Implications on prognosis and treatment, a brief review

Approximately 70%-85% of breast cancers express androgen receptors (ARs). The role of AR in breast cancer pathogenesis is currently in exploration. Both androgens and anti-androgens have demonstrated variable inhibitory and stimulatory effects in AR-positive breast cancer depending on estrogen receptor and HER2 co-expression. Androgen signaling pathways interact with other critical cellular pathways, such as the PI3K/AKT/mTOR, Ras/Raf/MAPK/ERK, Wnt/β-catenin, and estrogen signaling pathways. Therapeutic exploitation of AR has been the crux of management of prostate cancer for decades. In recent years there has been increasing interest in AR as a novel therapeutic target in breast cancer. There have been many early phase clinical trials evaluating the safety and efficacy of various AR-targeted agents in breast cancer. Some of these studies have shown promising clinical benefits. Studies of biomarkers to identify the patients likely to benefit from AR-targeted therapies are currently in progress. Besides, AR expression may be an important prognostic and predictive marker for breast cancer, which needs to be defined better in future studies.

Steroidogenic cytochrome P450 17A1 structure and function

Cytochrome P450 17A1 (CYP17A1) is a critical steroidogenic enzyme, essential for producing glucocorticoids and sex hormones. This review discusses the complex activity of CYP17A1, looking at its role in both the classical and backdoor steroidogenic pathways and the complex chemistry it carries out to perform both a hydroxylation reaction and a carbon-carbon cleavage, or lyase reaction. Functional and structural investigations have informed our knowledge of these two reactions. This review focuses on a few specific aspects of this discussion: the identities of reaction intermediates, the coordination of hydroxylation and lyase reactions, the effects of cytochrome b5, and conformational selection. These discussions improve understanding of CYP17A1 in a physiological setting, where CYP17A1 is implicated in a variety of steroidogenic diseases. This information can be used to improve ways in which CYP17A1 can be effectively modulated to treat diseases such as prostate and breast cancer, Cushing's syndrome, and glioblastoma.

Gonadotropin-Releasing Hormone Receptors in Prostate Cancer: Molecular Aspects and Biological Functions

Pituitary Gonadotropin-Releasing Hormone receptors (GnRH-R) mediate the activity of the hypothalamic decapeptide GnRH, thus playing a key role in the regulation of the reproductive axis. Early-stage prostate cancer (PCa) is dependent on serum androgen levels, and androgen-deprivation therapy (ADT), based on GnRH agonists and antagonists, represents the standard therapeutic approach for PCa patients. Unfortunately, the tumor often progresses towards the more aggressive castration-resistant prostate cancer (CRPC) stage. GnRH receptors are also expressed in CRPC tissues, where their binding to both GnRH agonists and antagonists is associated with significant antiproliferative/proapoptotic, antimetastatic and antiangiogenic effects, mediated by the Gαi/cAMP signaling cascade. GnRH agonists and antagonists are now considered as an effective therapeutic strategy for CRPC patients with many clinical trials demonstrating that the combined use of these drugs with standard therapies (i.e., docetaxel, enzalutamide, abiraterone) significantly improves disease-free survival. In this context, GnRH-based bioconjugates (cytotoxic drugs covalently linked to a GnRH-based decapeptide) have been recently developed. The rationale of this treatment is that the GnRH peptide selectively binds to its receptors, delivering the cytotoxic drug to CRPC cells while sparing nontumor cells. Some of these compounds have already entered clinical trials.

Alzheimer's Disease, and Breast and Prostate Cancer Research: Translational Failures and the Importance to Monitor Outputs and Impact of Funded Research

Dementia and cancer are becoming increasingly prevalent in Western countries. In the last two decades, research focused on Alzheimer's disease (AD) and cancer, in particular, breast cancer (BC) and prostate cancer (PC), has been substantially funded both in Europe and worldwide. While scientific research outcomes have contributed to increase our understanding of the disease etiopathology, still the prevalence of these chronic degenerative conditions remains very high across the globe. By definition, no model is perfect. In particular, animal models of AD, BC, and PC have been and still are traditionally used in basic/fundamental, translational, and preclinical research to study human disease mechanisms, identify new therapeutic targets, and develop new drugs. However, animals do not adequately model some essential features of human disease; therefore, they are often unable to pave the way to the development of drugs effective in human patients. The rise of new technological tools and models in life science, and the increasing need for multidisciplinary approaches have encouraged many interdisciplinary research initiatives. With considerable funds being invested in biomedical research, it is becoming pivotal to define and apply indicators to monitor the contribution to innovation and impact of funded research. Here, we discuss some of the issues underlying translational failure in AD, BC, and PC research, and describe how indicators could be applied to retrospectively measure outputs and impact of funded biomedical research.

Multistep Binding of the Non-Steroidal Inhibitors Orteronel and Seviteronel to Human Cytochrome P450 17A1 and Relevance to Inhibition of Enzyme Activity

Orteronel (TAK-700) is a substituted imidazole that was developed for the treatment of castration-resistant prostate cancer but was dropped in phase III clinical trials. Both enantiomers of this inhibitor of cytochrome P450 (P450) 17A1 show some selectivity in differentially blocking the 17α-hydroxylation and lyase activities of the enzyme. Although both enantiomers of this compound have sub-micromolar IC₅₀ values and bind to the enzyme with a type II spectral change (indicative of nitrogen-iron bonding) and reported K_d values of 56 and 40 nM (R and S, respectively), the rates of binding to P450 17A1 were relatively slow. We considered the possibility that the drug is a slow, tight-binding inhibitor. Analysis of the kinetics of binding revealed rapid formation of an initial complex, presumably in the substrate binding site, followed by a slower change to the spectrum of a final iron complex. Similar kinetics were observed in the interaction of another inhibitor, the triazole (S)-seviteronel (VT-464), with P450 17A1. Kinetic tests and modeling indicate that the further change to the iron-complexed form of the orteronel- or seviteronel-P450 complex is not a prerequisite for enzyme inhibition. Accordingly, the inclusion of heme-binding heterocyclic nitrogen moieties in P450 17A1 inhibitors may not be necessary to achieve inhibition but may nevertheless augment the process.

Therapies Targeted to Androgen Receptor Signaling Axis in Prostate Cancer: Progress, Challenges, and Hope

Prostate cancer is the mostly commonly diagnosed non-cutaneous malignancy and the second leading cause of cancer-related death affecting men in the United States. Moreover, it disproportionately affects the men of African origin, who exhibit significantly greater incidence and mortality as compared to the men of European origin. Since androgens play an important role in the growth of normal prostate and prostate tumors, targeting of androgen signaling has remained a mainstay for the treatment of aggressive prostate cancer. Over the years, multiple approaches have been evaluated to effectively target the androgen signaling pathway that include direct targeting of the androgens, androgen receptor (AR), AR co-regulators or other alternate mechanisms that impact the outcome of androgen signaling. Several of these approaches are currently in clinical practice, while some are still pending further development and clinical evaluation. This remarkable progress has resulted from extensive laboratory, pre-clinical and clinical efforts, and mechanistic learnings from the therapeutic success and failures. In this review, we describe the importance of androgen signaling in prostate cancer biology and advances made over the years to effectively target this signaling pathway. We also discuss emerging data on the resistance pathways associated with the failure of various androgen signaling- targeted therapies and potential of this knowledge for translation into future therapies for prostate cancer.

Prospective computational design and in vitro bio-analytical tests of new chemical entities as potential selective CYP17A1 lyase inhibitors

The development and advancement of prostate cancer (PCa) into stage 4, where it metastasize, is a major problem mostly in elder males. The growth of PCa cells is stirred up by androgens and androgen receptor (AR). Therefore, therapeutic strategies such as blocking androgens synthesis and inhibiting AR binding have been explored in recent years. However, recently approved drugs (or in clinical phase) failed in improving the expected survival rates for this metastatic-castration resistant prostate cancer (mCRPC) patients. The selective CYP17A1 inhibition of 17,20-lyase route has emerged as a novel strategy. Such inhibition blocks the production of androgens everywhere they are found in the body. In this work, a three dimensional-quantitative structure activity relationship (3D-QSAR) pharmacophore model is developed on a diverse set of non-steroidal inhibitors of CYP17A1 enzyme. Highly active compounds are selected to define a six-point pharmacophore hypothesis with a unique geometrical arrangement fitting the following description: two hydrogen bond acceptors (A), two hydrogen bond donors (D) and two aromatic rings (R). The QSAR model showed adequate predictive statistics. The 3D-QSAR model is further used for database virtual screening of potential inhibitory hit structures. Density functional theory (DFT) optimization provides the electronic properties explaining the reactivity of the hits. Docking simulations discovers hydrogen bonding and hydrophobic interactions as responsible for the binding affinities of hits to the CYP17A1 Protein Data Bank structure. 13 hits from the database search (including five derivatives) are then synthesized in the laboratory as different scaffolds. Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in vitro experiments reveals three new chemical entities (NCEs) with half maximal inhibitory concentration (IC₅₀) values against the lyase route at mid-micromolar range with favorable selectivity to the lyase over the hydroxylase route (one of them with null hydroxylase inhibition). Thus, prospective computational design has enabled the design of potential lead lyase-selective inhibitors for further studies.

Diagnosis and Therapy of Triple-Negative Breast Cancer (TNBC) - Recommendations for Daily Routine Practice

The rapid increase in knowledge in tumour biology and tumour pathogenesis of triple-negative breast cancer (TNBC) has resulted in new therapeutic approaches and new therapeutic concepts for treatment. For years, TNBC has been considered to be a difficult-to-treat tumour due to its generally aggressive tumour biology and in view of limited therapeutic options. The risk of recurrence and metastasis is higher than in the case of other breast cancer subtypes of the same stage. In addition to surgery and radiation in the curative situation, systemic chemotherapy with anthracyclines and/or taxanes is still the therapy of choice. New therapeutic approaches are based on the knowledge that TNBC is a molecularly very heterogeneous disease. Research groups are working to classify TNBC better and better on a molecular level and use this molecular subtyping as the basis for new therapeutic strategies. The most promising new approaches and considerations regarding the therapy of TNBCs are shown below. In addition, the current therapeutic strategies are discussed using a fictitious case history, taking the current data and the resultant therapeutic consequence into account.

A bypass mechanism of abiraterone-resistant prostate cancer: Accumulating CYP17A1 substrates activate androgen receptor signaling

BACKGROUND

Intratumoral steroidogenesis and its potential relevance in castration-resistant prostate cancer (CRPC) and in cytochrome P450, family 17, subfamily A, polypeptide 1 (CYP17A1)-inhibitor treated hormone-naïve and patients with CRPC are not well established. In this study, we tested if substrates for de novo steroidogenesis accumulating during CYP17A1 inhibition may drive cell growth in relevant preclinical models.

METHODS

PCa cell lines and their respective CRPC sublines were used to model CRPC in vitro. Precursor steroids pregnenolone (Preg) and progesterone (Prog) served as substrate for de novo steroid synthesis. TAK700 (orteronel), abiraterone, and small interfering RNA (siRNA) against CYP17A1 were used to block CYP17A1 enzyme activity. The antiandrogen RD162 was used to assess androgen receptor (AR) involvement. Cell growth was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. AR-target gene expression was quantified by reverse transcription polymerase chain reaction (RT-PCR). Nuclear import studies using cells with green fluorescent protein (GFP)-tagged AR were performed to assess the potential of precursor steroids to directly activate AR.

RESULTS

Preg and Prog stimulated cell proliferation and AR target gene expression in VCaP, DuCaP, LNCaP, and their respective CRPC sublines. The antiandrogen RD162, but not CYP17A1 inhibition with TAK700, abiraterone or siRNA, was able to block Preg- and Prog-induced proliferation. In contrast to TAK700, abiraterone also affected dihydrotestosterone-induced cell growth, indicating direct AR binding. Furthermore, Prog-induced AR translocation was not affected by treatment with TAK700 or abiraterone, while it was effectively blocked by the AR antagonist enzalutamide, further demonstrating the direct AR activation by Prog.

CONCLUSION

Activation of the AR by clinically relevant levels of Preg and Prog accumulating in abiraterone-treated patients may act as a driver for CRPC. These data provide a scientific rationale for combining CYP17A1 inhibitors with antiandrogens, particularly in patients with overexpressed or mutated-AR.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Conformational selection dominates binding of steroids to human cytochrome P450 17A1

Cytochrome P450 (P450, CYP) enzymes are the major catalysts involved in the oxidation of steroids as well as many other compounds. Their versatility has been explained in part by flexibility of the proteins and complexity of the binding mechanisms. However, whether these proteins bind their substrates via induced fit or conformational selection is not understood. P450 17A1 has a major role in steroidogenesis, catalyzing the two-step oxidations of progesterone and pregnenolone to androstenedione and dehydroepiandrosterone, respectively, via 17α-hydroxy (OH) intermediates. We examined the interaction of P450 17A1 with its steroid substrates by analyzing progress curves (UV-visible spectroscopy), revealing that the rates of binding of any of these substrates decreased with increasing substrate concentration, a hallmark of conformational selection. Further, when the concentration of 17α-OH pregnenolone was held constant and the P450 concentration increased, the binding rate increased, and such opposite patterns are also diagnostic of conformational selection. Kinetic simulation modeling was also more consistent with conformational selection than with an induced-fit mechanism. Cytochrome b ₅ partially enhances P450 17A1 lyase activity by altering the P450 17A1 conformation but did not measurably alter the binding of 17α-OH pregnenolone or 17α-OH progesterone, as judged by the apparent K_d and binding kinetics. The P450 17A1 inhibitor abiraterone also bound to P450 17A1 in a multistep manner, and modeling indicated that the selective inhibition of the two P450 17A1 steps by the drug orteronel can be rationalized only by a multiple-conformation model. In conclusion, P450 17A1 binds its steroid substrates via conformational selection.

Long non-coding RNAs: implications in targeted diagnoses, prognosis, and improved therapeutic strategies in human non- and triple-negative breast cancer

Triple-negative breast cancer (TNBC) has been clinically difficult to manage because of tumor aggressiveness, cellular and histological heterogeneity, and molecular mechanisms’ complexity. All this in turn leads us to evaluate that tumor biological behavior is not yet fully understood. Additionally, the heterogeneity of tumor cells represents a great biomedicine challenge in terms of the complex molecular—genetical-transcriptional and epigenetical—mechanisms, which have not been fully elucidated on human solid tumors.

Recently, human breast cancer, but specifically TNBC is under basic and clinical-oncology research in the discovery of new molecular biomarkers and/or therapeutic targets to improve treatment responses, as well as for seeking algorithms for patient stratification, seeking a positive impact in clinical-oncology outcomes and life quality on breast cancer patients.

In this sense, important knowledge is emerging regarding several cancer molecular aberrations, including higher genetic mutational rates, LOH, CNV, chromosomal, and epigenetic alterations, as well as transcriptome aberrations in terms of the total gene-coding ribonucleic acids (RNAs), known as mRNAs, as well as non-coding RNA (ncRNA) sequences. In this regard, novel investigation fields have included microRNAs (miRNAs), as well as long ncRNAs (lncRNAs), which have been importantly related and are likely involved in the induction, promotion, progression, and/or clinical therapeutic response trackers of TNBC. Based on this, in general terms according with the five functional archetype classification, the lncRNAs may be involved in the regulation of several molecular mechanisms which include genetic expression, epigenetic, transcriptional, and/or post-transcriptional mechanisms, which are nowadays not totally understood.

Here, we have reviewed the main dis-regulated and functionally non- and well-characterized lncRNAs and their likely involvement, from a molecular enrichment and mechanistic point of view, as tumor biomarkers for breast cancer and its specific histological subtype, TNBC. In reference to the abovementioned, it has been described that some lncRNA expression profiles correspond or are associated with the TNBC histological subtype, potentially granting their use for TNBC malignant progression, diagnosis, tumor clinical stage, and likely therapy. Based on this, lncRNAs have been proposed as potential biomarkers which might represent potential predictive tools in the differentiated breast carcinomas versus TNBC malignant disease. Finally, elucidation of the specific or multi-functional archetypal of lncRNAs in breast cancer and TNBC could be fundamental, as these molecular intermediary-regulator “lncRNAs” are widely involved in the genome expression, epigenome regulation, and transcriptional and post-transcriptional tumor biology, which in turn will probably represent a new prospect in clinical and/or therapeutic molecular targets for the oncological management of breast carcinomas in general and also for TNBC patients.

Structure-Based Design of Inhibitors with Improved Selectivity for Steroidogenic Cytochrome P450 17A1 over Cytochrome P450 21A2

Inhibition of androgen biosynthesis is clinically effective for treating androgen-responsive prostate cancer. Abiraterone is a clinical first-in-class inhibitor of cytochrome P450 17A1 (CYP17A1) required for androgen biosynthesis. However, abiraterone also causes hypertension, hypokalemia, and edema, likely due in part to off-target inhibition of another steroidogenic cytochrome P450, CYP21A2. Abiraterone analogs were designed based on structural evidence that B-ring substituents may favorably interact with polar residues in binding CYP17A1 and sterically clash with residues in the CYP21A2 active site. The best analogs increased selectivity of CYP17A1 inhibition up to 84-fold compared with 6.6-fold for abiraterone. Cocrystallization with CYP17A1 validated the intended new contacts with CYP17A1 active site residues. Docking these analogs into CYP21A2 identified steric clashes that likely underlie decreased binding and CYP21A2 inhibition. Overall, these analogs may offer a clinical advantage in the form of reduced side effects.

Metastatic Castration-Sensitive Prostate Cancer: Optimizing Patient Selection and Treatment

The treatment landscape for metastatic castration-sensitive prostate cancer (mCSPC) has rapidly evolved over the past 5 years. Although androgen-deprivation therapy (ADT) is still the backbone of treatment, the addition of docetaxel or abiraterone acetate has improved outcomes for patients with mCSPC and become standard of care. With multiple treatment options available for patients with mCSPC, treatment selection to optimize patient outcomes has become increasingly difficult. Here, we review the clinical trials involving ADT plus docetaxel or abiraterone and provide clinicians with guidelines for treatment. Although surgery and/or radiation are standard of care for localized, intermediate- and high-risk prostate cancer, these treatments are not routinely used as part of initial treatment plans for patients with de novo mCSPC. Recent clinical data are challenging that dogma, and we review the literature on the addition of surgery and radiation to systemic therapy for mCSPC. Finally, the standard of care for oligometastatic prostate cancer (a subset of mCSPC with limited metastases) has not been established compared with that for some other cancers. We discuss the recent studies on metastasis-directed therapy for treatment of oligometastatic prostate cancer.

Novel androgen axis systemic therapies for metastatic hormone-sensitive prostate cancer

PURPOSE OF REVIEW

Upfront docetaxel and androgen deprivation therapy (ADT) has improved outcomes over ADT alone in men with metastatic hormone-sensitive prostate cancer (mHSPC). Here in, we review the emerging role of novel androgen axis inhibitors in the treatment of men with mHSPC.

RECENT FINDINGS

Recently two studies, LATITUDE and STAMPEDE arm G, showed improved survival with addition of abiraterone acetate with prednisone or prednisolone to ADT in men with hormone-naïve advanced prostate cancer.

SUMMARY

Upfront docetaxel in addition to ADT has been shown to improve survival outcomes in men with high-volume mHSPC. Recently, abiraterone acetate and prednisone or prednisolone and ADT have been shown to improve survival outcomes compared with ADT alone in men with mHSPC. Multiple other novel androgen axis inhibitors are being investigated in this setting, and expected to garner regulatory approval in the near future. Biomarkers predicting response to these agents are urgently needed to optimize treatment selection, not only to improve outcomes but to also minimize cost and toxicities.

Dehydroepiandrosterone (DHEA)-SO4 Depot and Castration-Resistant Prostate Cancer

Dehydroepiandrosterone (DHEA)-SO₄ of adrenal origin is the major C19 steroid in the serum. It is a precursor of intratumoral androgen biosynthesis in patients with advanced prostate cancer following chemical or surgical castration. DHEA is a product of the P450c17 (17α-hydroxylase-17,20-lyase) enzyme. Despite inhibition of P450c17 with new agents, e.g., Abiraterone acetate, Orterenol, and Galeterone, the level of enzyme inhibition rarely exceeds 90% leaving behind a significant depot for androgen biosynthesis within the tumor. For DHEA-SO₄ to be utilized there is uptake by organic anion transporter polypeptides, deconjugation catalyzed by steroid sulfatase, and adaptive upregulation of prostate steroidogenic enzymes that will convert DHEA into either testosterone or dihydrotestosterone. The depot of DHEA-SO₄ that remains after P450c17 inhibition and the adaptive responses that occur within the tumor to promote DHEA utilization contribute to mechanisms of drug resistance observed with P450c17 inhibitors. Knowledge of these mechanisms identify new targets for therapeutics that could be used to surmount drug resistance in prostate cancer.

Inherent steroid 17α,20-lyase activity in defunct cytochrome P450 17A enzymes

Cytochrome P450 (P450) 17A1 catalyzes the oxidations of progesterone and pregnenolone and is the major source of androgens. The enzyme catalyzes both 17α-hydroxylation and a subsequent 17α,20-lyase reaction, and several mechanisms have been proposed for the latter step. Zebrafish P450 17A2 catalyzes only the 17α-hydroxylations. We previously reported high similarity of the crystal structures of zebrafish P450 17A1 and 17A2 and human P450 17A1. Five residues near the heme, which differed, were changed. We also crystallized this five-residue zebrafish P450 17A1 mutant, and the active site still resembled the structure in the other proteins, with some important differences. These P450 17A1 and 17A2 mutants had catalytic profiles more similar to each other than did the wildtype proteins. Docking with these structures can explain several minor products, which require multiple enzyme conformations. The 17α-hydroperoxy (OOH) derivatives of the steroids were used as oxygen surrogates. Human P450 17A1 and zebrafish P450s 17A1 and P450 17A2 readily converted these to the lyase products in the absence of other proteins or cofactors (with catalytically competent kinetics) plus hydroxylated 17α-hydroxysteroids. The 17α-OOH results indicate that a "Compound I" (FeO³⁺) intermediate is capable of formation and can be used to rationalize the products. We conclude that zebrafish P450 17A2 is capable of lyase activity with the 17α-OOH steroids because it can achieve an appropriate conformation for lyase catalysis in this system that is precluded in the conventional reaction.

A randomized, double-blind, placebo-controlled phase II study of maintenance therapy with tasquinimod in patients with metastatic castration-resistant prostate cancer responsive to or stabilized during first-line docetaxel chemotherapy

BACKGROUND

This phase II study was conducted to assess clinical efficacy of tasquinimod maintenance therapy in patients with metastatic castrate-resistant prostate cancer not progressing during first-line docetaxel-based therapy.

PATIENTS AND METHODS

Patients were randomly assigned (1 : 1) to receive tasquinimod (0.25-1.0 mg/day orally) or placebo. The primary end point was radiologic progression-free survival (rPFS); secondary efficacy end points included: overall survival (OS); PFS on next-line therapy (PFS 2) and symptomatic PFS, assessed using the Brief Pain Inventory (BPI) questionnaire and analgesic use. Quality of life was measured by the Functional Assessment of Cancer Therapy-Prostate (FACT-P) questionnaire and by the EuroQol-5 Dimension Quality of Life Instrument (EQ-5D). Adverse events were recorded.

RESULTS

A total of 219 patients were screened and 144 patients randomized. The median duration of treatment was 18.7 weeks (range 0.6-102.7 weeks) for the tasquinimod arm and 19.2 weeks (range 0.4-80.0 weeks) for the placebo arm. Median (90% CI) rPFS was 31.7 (24.3-53.7) and 22.7 (16.1-25.9) weeks in the tasquinimod and placebo arms, respectively [HR (90% CI) 0.6 (0.4-0.9), P = 0.0162]. The median OS was not reached because only 14 deaths occurred by the cut-off date. No statistically significant differences between treatment arms were noted for symptomatic PFS, PFS 2, BPI score, FACT-P score, or EQ-5D. The incidence of any treatment emergent adverse event (TEAE) was similar in the tasquinimod and placebo arms (97.2% versus 94.3%, respectively), whereas severe TEAEs (NCI-CTC Grade 3-5) incidence was higher in the tasquinimod group (50.7% versus 27.1%).

CONCLUSIONS

Randomized trials testing new drugs as maintenance can be successfully conducted after chemotherapy in castrate-resistant prostate cancer. Maintenance tasquinimod therapy significantly reduced the risk of rPFS by 40%.

CLINICALTRIALS

gov identifier NCT01732549.

Therapeutic Implications of the Molecular and Immune Landscape of Triple-Negative Breast Cancer

Treatment and management of breast cancer imposes a heavy burden on public health care, and incidence rates continue to increase. Breast cancer is the most common female neoplasia and primary cause of death among women worldwide. The recognition of breast cancer as a complex and heterogeneous disease, comprising different molecular entities, was a landmark in our understanding of this malignancy. Valuing the impact of the molecular characteristics on tumor behavior enabled a better assessment of a patient's prognosis and increased the predictive power to therapeutic response and clinical outcome. Molecular heterogeneity is also prominent in the triple-negative breast cancer subtype, and is reflected by the distinct prognostic and patient's sensitivity to treatment, being chemotherapy the only systemic treatment currently available. From a therapeutic perspective, gene expression profiling of triple-negative tumors has notably contributed to the exploration of new druggable targets and brought to light the need to align these patients to the various therapies according to their triple-negative subtype. Additionally, the higher amount of tumor infiltrating lymphocytes, and the prevalence of an increased expression of PD-1 receptor and its ligand, PD-L1, in triple-negative tumors, created a new treatment opportunity with immune checkpoint inhibitors. This manuscript addresses the current knowledge on the molecular and immune profiles of breast cancer, and its impact on the development of targeted therapies, with a particular emphasis on the triple-negative subtype.

Androgen Receptor and Beyond, Targeting Androgen Signaling in Castration-Resistant Prostate Cancer

The development of metastatic castration-resistant prostate cancer (mCRPC) signals the terminal disease phase. The preceding hormone-dependent disease setting is effectively managed with androgen deprivation therapy. This foundation of treatment has a high rate of biochemical and clinical response and meaningful clinical benefit but is finite in duration as most cancers will progress to castration resistance. Historically, treatment for mCRPC entailed androgen receptor (AR) inhibitors (nilutamide, flutamide, bicalutamide), nonspecific steroidal biosynthesis inhibitors (ketoconazole, itraconazole), steroids (prednisone, diethylstilbesterol, dexamethasone), or palliative chemotherapy (mitoxantrone, estramustine), but none of these strategies impacted survival. Docetaxel was the first agent to demonstrate a survival improvement in this population, and other therapies followed (cabazitaxel, sipuleucel-T and radium-223). Understanding how prostate cancer cells grow in a systemic androgen-deprived environment further changed this clinical landscape. Deciphering what steroidogenic enzymes are overactive and required for testosterone/dihydrotestosterone synthesis has yielded therapies directed toward both adrenal and tumor-derived androgens. All androgens normally act through AR, and this fact remains true in mCRPC. The cancer accomplishes this by overexpressing the receptor (by genomic copy-number gains or RNA amplification), mutating it directly to lose its selectivity for testosterone/dihydrotestosterone, or selecting for splice variants that do not require ligand at all. These resistance mechanisms result in persistent AR-mediated signaling. Through this understanding, drugs targeting non-ligand-binding aspects of AR functioning (e.g., nuclear translocation, cofactor recruitment) have been developed. Finally, how AR interacts with other signaling pathway is being explored, and new combinations of targets to test are being proposed. Multiple compounds remain in various stages of clinical development based on targeting these resistance pathways, and hopefully, they will further the armamentarium for mCRPC. This review visits these mechanisms of resistance, how they are targeted, and remaining challenges in implementing these therapies into clinical practice among the other approved treatments.

The prognostic significance of combined androgen receptor, E-Cadherin, Ki67 and CK5/6 expression in patients with triple negative breast cancer

Background

Triple Negative Breast Cancer (TNBC) represents a heterogeneous group of tumors with poor prognosis owing to aggressive tumor biology and lack of targeted therapies. No clear prognostic biomarkers have been identified to date for this subgroup.

Materials and Methods

In this retrospective study we evaluated the prognostic role of 4 different molecular determinants, including androgen receptor (AR), E-cadherin (CDH1), Ki67 index, and basal cytokeratins (CKs) 5/6, in a cohort of 99 patients with TNBC. All patients received neo/adjuvant chemotherapy (mostly anthracycline/taxane-based). Immunohistochemistry (IHC) was performed in formalin-fixed paraffin-embedded primary tumor samples. CDH1 expression was considered positive as ≥ 30% of the membrane cells staining. AR positivity was defined as > 10% of positive tumor cells. High Ki67 was defined as ≥20% positive tumor cells. CK5/6 expression was judged positive if the score was ≥1.

Results

The absence of AR expression was significantly associated with highly undifferentiated tumors. Univariate analyses showed that lack of expression of CDH1, tumor size and nodal status were significantly correlated with worse RFS and OS (p< 0.05). AR expression and low Ki67 showed a trend towards better RFS and OS. Patients with absent CK5/6 expression in univariate and multivariate analyses had poorer RFS (p=0.02 and p=0.002, respectively) and OS (p=0.05 and p=0.02, respectively). Multivariate analysis showed an independent association between CDH1 expression and better RFS and OS (p< 0.05) beyond tumor size, nodal status, and grade. The Kaplan-Meier curves showed that patients with AR and CDH1 negative expression and high Ki-67 levels have a significant correlation with poor outcome.

Conclusions

Our study supports the use of IHC expression of AR, CDH1, Ki67, and CK5/6 as prognostic markers in TNBCs and suggests a link between their expression and prognosis and may help to stratify TNBC patients in different prognostic classes.

Kinetic processivity of the two-step oxidations of progesterone and pregnenolone to androgens by human cytochrome P450 17A1

Cytochrome P450 (P450, CYP) 17A1 plays a critical role in steroid metabolism, catalyzing both the 17α-hydroxylation of pregnenolone and progesterone and the subsequent 17α,20-lyase reactions to form dehydroepiandrosterone (DHEA) and androstenedione (Andro), respectively, critical for generating glucocorticoids and androgens. Human P450 17A1 reaction rates examined are enhanced by the accessory protein cytochrome b₅ (b₅), but the exact role of b₅ in P450 17A1-catalyzed reactions is unclear as are several details of these reactions. Here, we examined in detail the processivity of the 17α-hydroxylation and lyase steps. b₅ did not enhance reaction rates by decreasing the k_off rates of any of the steroids. Steroid binding to P450 17A1 was more complex than a simple two-state system. Pre-steady-state experiments indicated lag phases for Andro production from progesterone and for DHEA from pregnenolone, indicating a distributive character of the enzyme. However, we observed processivity in pregnenolone/DHEA pulse-chase experiments. (S)-Orteronel was three times more inhibitory toward the conversion of 17α-hydroxypregnenolone to DHEA than toward the 17α-hydroxylation of pregnenolone. IC₅₀ values for (S)-orteronel were identical for blocking DHEA formation from pregnenolone and for 17α-hydroxylation, suggestive of processivity. Global kinetic modeling helped assign sets of rate constants for individual or groups of reactions, indicating that human P450 17A1 is an inherently distributive enzyme but that some processivity is present, i.e. some of the 17α-OH pregnenolone formed from pregnenolone did not dissociate from P450 17A1 before conversion to DHEA. Our results also suggest multiple conformations of P450 17A1, as previously proposed on the basis of NMR spectroscopy and X-ray crystallography.

Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1)

Cytochrome b5 (cyt b5) is a small hemoprotein that plays a significant role in the modulation of activities of an important steroidogenic enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1, CYP17A1). Located in the zona fasciculata and zona reticularis of the adrenal cortex and in the gonads, P450 17A1 catalyzes two different reactions in the steroidogenic pathway; the 17α-hydroxylation and 17,20-lyase, in the endoplasmic reticulum of these respective tissues. The activities of P450 17A1 are regulated by cyt b5 that enhances the 17,20-lyase reaction by promoting the coupling of P450 17A1 and cytochrome P450 reductase (CPR), allosterically. Cyt b5 can also act as an electron donor to enhance the 16-ene-synthase activity of human P450 17A1. In this review, we discuss the many roles of cyt b5 and focus on the modulation of CYP17A1 activities by cyt b5 and the mechanisms involved.

Structural and Functional Evaluation of Clinically Relevant Inhibitors of Steroidogenic Cytochrome P450 17A1

Human steroidogenic cytochrome P450 17A1 (CYP17A1) is a bifunctional enzyme that performs both hydroxylation and lyase reactions, with the latter required to generate androgens that fuel prostate cancer proliferation. The steroid abiraterone, the active form of the only CYP17A1 inhibitor approved by the Food and Drug Administration, binds the catalytic heme iron, nonselectively impeding both reactions and ultimately causing undesirable corticosteroid imbalance. Some nonsteroidal inhibitors reportedly inhibit the lyase reaction more than the preceding hydroxylase reaction, which would be clinically advantageous, but the mechanism is not understood. Thus, the nonsteroidal inhibitors seviteronel and orteronel and the steroidal inhibitors abiraterone and galeterone were compared with respect to their binding modes and hydroxylase versus lyase inhibition. Binding studies and X-ray structures of CYP17A1 with nonsteroidal inhibitors reveal coordination to the heme iron like the steroidal inhibitors. (S)-seviteronel binds similarly to both observed CYP17A1 conformations. However, (S)-orteronel and (R)-orteronel bind to distinct CYP17A1 conformations that differ in a region implicated in ligand entry/exit and the presence of a peripheral ligand. To reconcile these binding modes with enzyme function, side-by-side enzymatic analysis was undertaken and revealed that neither the nonsteroidal seviteronel nor the (S)-orteronel inhibitors demonstrated significant lyase selectivity, but the less potent (R)-orteronel was 8- to 11-fold selective for lyase inhibition. While active-site iron coordination is consistent with competitive inhibition, conformational selection for binding of some inhibitors and the differential presence of a peripheral ligand molecule suggest the possibility of CYP17A1 functional modulation by features outside the active site.

Discovery of novel 1,2,3,4-tetrahydrobenzo[4, 5]thieno[2, 3-c]pyridine derivatives as potent and selective CYP17 inhibitors

The inhibition of CYP17 to block androgen biosynthesis is a well validated strategy for the treatment of prostate cancer. Herein we reported the design, synthesis and structure-activity relationship (SAR) study for a series of novel 1,2,3,4- tetrahydrobenzo[4,5]thieno[2,3-c]pyridine derivatives. Some analogs demonstrated a potent inhibition to both rat and human CYP17 protein and reduced testosterone production in human H295R cell line. Some analogs also showed high selectivity against other CYP enzymes such as 3A4, 1A2, 2C9, 2C19 and 2D6, which may limit side effects due to drug-drug interactions. Among these analogs, the most potent compound 9c showed 1.5 fold more potent against rat and human CYP17 protein than that of abiraterone (IC₅₀ = 16 nM and 20 nM vs. 25 nM and 36 nM respectively). In NCI-H295R cells, the inhibitory effect of compound 9c on testosterone production (52± 2%) was also more potent than that of abiraterone (74± 15%) at the concentration of 1 μM. Further, it was shown that 9c reduced plasma testosterone level in a dose-dependent manner in Sprague-Dawley rats. Thus, analog 9c maybe a potential agent used for the treatment of prostate cancer.

Structure-based optimisation of non-steroidal cytochrome P450 17A1 inhibitors

Five new non-steroidal inhibitors for cytochrome P450 17A1 were identified by structure-based optimisation.

Pushing estrogen receptor around in breast cancer

The estrogen receptor-α (herein called ER) is a nuclear sex steroid receptor (SSR) that is expressed in approximately 75% of breast cancers. Therapies that modulate ER action have substantially improved the survival of patients with ER-positive breast cancer, but resistance to treatment still remains a major clinical problem. Treating resistant breast cancer requires co-targeting of ER and alternate signalling pathways that contribute to resistance to improve the efficacy and benefit of currently available treatments. Emerging data have shown that other SSRs may regulate the sites at which ER binds to DNA in ways that can powerfully suppress the oncogenic activity of ER in breast cancer. This includes the progesterone receptor (PR) that was recently shown to reprogram the ER DNA binding landscape towards genes associated with a favourable outcome. Another attractive candidate is the androgen receptor (AR), which is expressed in the majority of breast cancers and inhibits growth of the normal breast and ER-positive tumours when activated by ligand. These findings have led to the initiation of breast cancer clinical trials evaluating therapies that selectively harness the ability of SSRs to 'push' ER towards anti-tumorigenic activity. Our review will focus on the established and emerging clinical evidence for activating PR or AR in ER-positive breast cancer to inhibit the tumour growth-promoting functions of ER.

The hunt for a selective 17,20 lyase inhibitor; learning lessons from nature

Given prostate cancer is driven, in part, by its responsiveness to androgens, treatments historically employ methods for their removal from circulation. Approaches as crude as castration, and more recently blockade of androgen synthesis or receptor binding, are still of limited use long term, since other steroids of adrenal origin or tumor origin can supersede that role as the 'castration resistant' tumor re-emerges. Broader inhibition of steroidogenesis using relatively nonselective P450 inhibitors such as ketoconazole is not an alternative since a general disruption of steroid biosynthesis is neither safe nor effective. The recent emergence of drugs more selectively targeting CYP17 have been more effective, and yet extension of life has been on the scale of months rather than years. It is now becoming clear this shortcoming arises from the adaptive capabilities of many tumors to initiate local steroid synthesis and/or become responsive to novel early pathway adrenal steroids that are synthesized when lyase activity is not selectively blocked, and ACTH rises in the face of declining cortisol feedback. Abiraterone has been described as a lyase selective inhibitor, yet its use still requires co-administration of prednisone to suppress such a rise of ACTH and fall in cortisol. So is creation of a selective lyase inhibitor even possible? Can C19 steroid production be achieved without a prominent decline in cortisol and corresponding rise in ACTH? Decades of scientific study of CYP17 in humans and nonhuman primates, as well as nature's own experiments of gene mutations in humans, reveal 'true' or 'isolated' 17,20 lyase deficiency does quite selectively prevent C19 steroid biosynthesis whereas simple 17 hydroxylase deficiency also suppresses cortisol. We propose these known outcomes of natural mutations should be used to guide analysis of clinical trials and long term outcomes of CYP17 targeted drugs. In this review, we use that framework to re-evaluate the basic and clinical outcomes of many compounds being used or in development for treatment of castration resistant prostate cancer. Specifically, we include the nonselective drug ketoconazole, and then the CYP17 targeted drugs abiraterone, orteronel (TAK-700), galaterone (TOK-001), and seviteronel (VT-464). Using this framework, we can fully discriminate the clinical outcomes for ketoconazole, a drug with broad specificity, yet clinically ineffective, from that of abiraterone, the first CYP17 targeted therapy that is limited by its need for prednisone co-therapy. We also can identify potential next generation CYP17 targeted drugs now emerging that show signs of being far more 17,20 lyase selective. We conclude that a future for improved therapy without substantial cortisol decline, thus avoiding prednisone co-administration, seems possible at long last.

Promising Tools in Prostate Cancer Research: Selective Non-Steroidal Cytochrome P450 17A1 Inhibitors

Cytochrome P450 17A1 (CYP17A1) is an important target in the treatment of prostate cancer because it produces androgens required for tumour growth. The FDA has approved only one CYP17A1 inhibitor, abiraterone, which contains a steroidal scaffold similar to the endogenous CYP17A1 substrates. Abiraterone is structurally similar to the substrates of other cytochrome P450 enzymes involved in steroidogenesis, and interference can pose a liability in terms of side effects. Using non-steroidal scaffolds is expected to enable the design of compounds that interact more selectively with CYP17A1. Therefore, we combined a structure-based virtual screening approach with density functional theory (DFT) calculations to suggest non-steroidal compounds selective for CYP17A1. In vitro assays demonstrated that two such compounds selectively inhibited CYP17A1 17α-hydroxylase and 17,20-lyase activities with IC50 values in the nanomolar range, without affinity for the major drug-metabolizing CYP2D6 and CYP3A4 enzymes and CYP21A2, with the latter result confirmed in human H295R cells.

Specificity of anti-prostate cancer CYP17A1 inhibitors on androgen biosynthesis

The orteronel, abiraterone and galeterone, which were developed to treat castration resistant prostate cancer, inhibit 17,20 lyase activity but little is known about their effects on adrenal androgen biosynthesis. We studied the effect of several inhibitors and found that orteronel was selective towards 17,20 lyase activity than abiraterone and galeterone. Gene expression analysis showed that galeterone altered the expression of HSD3B2 but orteronel did not change the expression of HSD3B2, CYP17A1 and AKR1C3. The CYP19A1 activity was not inhibited except by compound IV which lowered activity by 23%. Surprisingly abiraterone caused complete blockade of CYP21A2 activity. Analysis of steroid metabolome by gas chromatography - mass spectrometry revealed changes in steroid levels caused by different inhibitors. We can conclude that orteronel is a highly specific inhibitor of 17,20 lyase activity. The discovery of these specific drug actions on steroidogenic enzyme activities would be valuable for understanding the regulation of androgens.

Phase I and II therapies targeting the androgen receptor for the treatment of castration resistant prostate cancer

INTRODUCTION

Prostate cancer is the most common cancer in elderly males. Regardless of the initial hormonal treatment in metastatic disease, a significant proportion of patients develop castration resistant prostate cancer (CRPC). A better understanding of the molecular mechanisms behind castration resistance has led to the approval of oral medications such as abiraterone acetate and enzalutamide. Relevant research is accelerated with numerous agents being tested for the management of CRPC.

AREAS COVERED

The authors present Phase I and II studies targeting the androgen receptor for the treatment of CRPC. Three groups of agents are identified according to the mechanism of action. These include the CYP-17 modulators (Orteronel, Galeterone, VT-464 and CFG-920), novel antiandrogens (Apatorsen, ARN-509, ODM-201, EZN-4176, AZD-3514) and bipolar androgen therapy.

EXPERT OPINION

Further understanding of the mechanisms leading to castration resistance in prostate cancer can reveal potential targets for the development of novel anti-cancer agents. Except for the development of novel antiandrogens and CYP-17 modulators, bipolar androgen therapy is an interesting therapeutic approach. The combinations of the novel agents tested in Phase I and II studies with established agents is another field of interest. The real challenge is to distinguish a novel anti-cancer agent with acceptable tolerability and the best outcome.

The Metabolism, Analysis, and Targeting of Steroid Hormones in Breast and Prostate Cancer

Breast and prostate cancers are malignancies in which steroid hormones drive cellular proliferation. Over the past century, this understanding has led to successful treatment strategies aimed to inhibit hormone-mediated tumor growth. Nonetheless, disease relapse and progression still pose significant clinical problems, with recurrent and metastatic tumors often exhibiting resistance to current drug therapies. The central role of androgens and estrogens in prostate and breast cancer etiology explains not only why endocrine therapies are often initially successful but also why many tumors ultimately become resistant. It is hypothesized that reducing the concentration of active hormones in the systemic circulation may be insufficient to block cancer progression, as this action selects for tumor cells that can generate active steroids from circulating precursors. This review aims to highlight the currently known differences of steroid biosynthesis in normal physiology versus hormone-dependent cancers, modern approaches to the assessment and targeting of these pathways, and priorities for future research.

Incidence and relative risk of adverse events of special interest in patients with castration resistant prostate cancer treated with CYP-17 inhibitors: A meta-analysis of published trials

Abiraterone acetate and orteronel are two CYP-17 inhibitors that have been studied in prostate cancer. They have shown relevant toxicities, including fluid retention/oedema, hypokalaemia, hypertension, liver function test abnormalities and cardiac events. The goal of this study was to determine the risk of special adverse events related to CYP- 17 inhibitor in patients with metastatic castration-resistant prostate cancer (CRCP). Summary data from four randomized phase III trials comparing CYP-17 inhibitors and prednisone versus placebo and prednisone in metastatic CRCP patients were meta-analysed. Pooled risk ratios (RRs) for the risk of all-grade and grade 3-4 adverse events of special interest were calculated. Data from 4916 patients (2849 in the AA experimental arm; 2067 in the control arm) were analysed. The incidence of grade 3-4 adverse events was never more than 10% of the patients. However, compared with placebo, the CYP-17 inhibitor significantly increased the all-grade events of hypertension (RR=1.53; 95% CI=1.3-1.8; p<0.00001), hypokalaemia (RR=1.56; 95% CI=1.29-1.89; p<0.00001), cardiac disorders (RR=1.47; 95% CI=1.27-1.7; p<0.00001) liver function test abnormalities (RR=1.93; 95% CI=1.15-3.24; p=0.01) grade≥3 adverse events, hypokalaemia (RR=4.23; 95% CI=1.28-13.99; p=0.02) and cardiac disorders (RR=1.55; 95% CI=1.18-2.05; p=0.002). A lot of adverse events such as hypertension, hypokalaemia, cardiac disorders and liver function test abnormalities are increased during CYP-17 inhibitor based therapy. Strict monitoring of these side effects should be considered during CYP- 17 inhibitor therapy in prostate cancer patients.

New insights into the androgen biotransformation in prostate cancer: A regulatory network among androgen, androgen receptors and UGTs

Androgen, as one kind of steroid hormones, is pivotal in the hormone-sensitive cancer, such as prostate cancer (PCa). The synthesis, elimination, and bioavailability of androgen in prostate cells have been proved to be a main cause of the carcinogenesis, maintenance and deterioration of PCa. This review illustrates the outlines of androgen biotransformation, and further discusses the different enzymes, especially UDP-glucuronyltransferases (UGTs) embedded in both benign and malignant prostate cells, which catalyze the reactions. Although many inhibitors of the enzymes responsible for the synthesis of androgens have been developed into drugs to fight against PCa, the elimination procedures metabolized by the UGTs are less emphasized. Thus the regulatory network among androgen, androgen receptors (AR) and UGTs is carefully reviewed in this article, indicating the determinant effects of UGTs on prostatic androgens and the regulation of AR. Finally, the hypothesis is also put forward that the regulators of UGTs may be developed to accelerate the androgen elimination and benefit PCa therapy.

Therapeutic Rationales, Progresses, Failures, and Future Directions for Advanced Prostate Cancer

Patients with localized prostate cancer (PCa) have several therapeutic options with good prognosis. However, survival of patients with high-risk, advanced PCa is significantly less than patients with early-stage, organ-confined disease. Testosterone and other androgens have been directly linked to PCa progression since 1941. In this review, we chronicle the discoveries that led to modern therapeutic strategies for PCa. Specifically highlighted is the biology of androgen receptor (AR), the nuclear receptor transcription factor largely responsible for androgen-stimulated and castrate-recurrent (CR) PCa. Current PCa treatment paradigms can be classified into three distinct but interrelated categories: targeting AR at pre-receptor, receptor, or post-receptor signaling. The continuing challenge of disease relapse as CR and/or metastatic tumors, destined to occur within three years of the initial treatment, is also discussed. We conclude that the success of PCa therapies in the future depends on targeting molecular mechanisms underlying tumor recurrence that still may affect AR at pre-receptor, receptor, and post-receptor levels.

Discovery of the Selective CYP17A1 Lyase Inhibitor BMS-351 for the Treatment of Prostate Cancer

Efforts to identify a potent, reversible, nonsteroidal CYP17A1 lyase inhibitor with good selectivity over CYP17A1 hydroxylase and CYPs 11B1 and 21A2 for the treatment of castration-resistant prostate cancer (CRPC) culminated in the discovery of BMS-351 (compound 18), a pyridyl biaryl benzimidazole with an excellent in vivo profile. Biological evaluation of BMS-351 at a dose of 1.5 mg in castrated cynomolgus monkeys revealed a remarkable reduction in testosterone levels with minimal glucocorticoid and mineralcorticoid perturbation. Based on a favorable profile, BMS-351 was selected as a candidate for further preclinical evaluation.