Synthesis and Biological Evaluation of Methoxypolyethylene-Glycol-Substituted Abiraterone Derivatives as Potential Antiprostate Cancer Agents.

Globally, prostate cancer is the most commonly diagnosed tumor and a cause of death in older men. Abiraterone, an orally administered irreversible CYP17 inhibitor, is employed to treat prostate cancer. However, abiraterone has several clinical limitations, such as poor water solubility, low dissolution rate, low bioavailability, and toxic side effects in the liver and kidney. Therefore, there is a need to identify high-efficiency and low-toxicity water-soluble abiraterone derivatives. In this work, we aimed to design and synthesize a series of abiraterone derivatives by methoxypoly(ethylene glycol) (mPEG) modification. Their antitumor activities and toxicology were analyzed in vitro and in vivo. The most potent compound, 2e, retained the principle of action on the CYP17 enzyme target and significantly improved the abiraterone water solubility, cell permeability, and blood safety. No significant abnormalities were observed in toxicology. mPEG-modification significantly improved abiraterone's antitumor activity and efficiency while reducing the associated toxic effects. The finding will provide a theoretical basis for future clinical application of mPEG-modified abiraterone.

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.

Exploring the Chemical Space of CYP17A1 Inhibitors Using Cheminformatics and Machine Learning.

Cytochrome P450 17A1 (CYP17A1) is one of the key enzymes in steroidogenesis that produces dehydroepiandrosterone (DHEA) from cholesterol. Abnormal DHEA production may lead to the progression of severe diseases, such as prostatic and breast cancers. Thus, CYP17A1 is a druggable target for anti-cancer molecule development. In this study, cheminformatic analyses and quantitative structure-activity relationship (QSAR) modeling were applied on a set of 962 CYP17A1 inhibitors (i.e., consisting of 279 steroidal and 683 nonsteroidal inhibitors) compiled from the ChEMBL database. For steroidal inhibitors, a QSAR classification model built using the PubChem fingerprint along with the extra trees algorithm achieved the best performance, reflected by the accuracy values of 0.933, 0.818, and 0.833 for the training, cross-validation, and test sets, respectively. For nonsteroidal inhibitors, a systematic cheminformatic analysis was applied for exploring the chemical space, Murcko scaffolds, and structure-activity relationships (SARs) for visualizing distributions, patterns, and representative scaffolds for drug discoveries. Furthermore, seven total QSAR classification models were established based on the nonsteroidal scaffolds, and two activity cliff (AC) generators were identified. The best performing model out of these seven was model VIII, which is built upon the PubChem fingerprint along with the random forest algorithm. It achieved a robust accuracy across the training set, the cross-validation set, and the test set, i.e., 0.96, 0.92, and 0.913, respectively. It is anticipated that the results presented herein would be instrumental for further CYP17A1 inhibitor drug discovery efforts.

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.

Antiproliferative, proapoptotic, and tumor-suppressing effects of the novel anticancer agent alsevirone in prostate cancer cells and xenografts.

The aim of this study was to explore the mechanisms of action of alsevirone in prostate cancer (PC) in vitro and in vivo: CYP17A1 inhibition, cytotoxic, apoptotic, and antitumor effects in comparison with abiraterone. The CYP17A1-inhibitory activity was investigated in rat testicular microsomes using high-performance liquid chromatography. Testosterone levels were evaluated using enzyme-linked immunoassay. IC50 values were calculated for PC3, DU-145, LNCaP, and 22Rv1 cells using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test. The antitumor effect in vivo was studied in DU-145 and 22Rv1 subcutaneous xenografts in Balb/c nude mice. Alsevirone reduced the CYP17A1-inhibitory activity by 98% ± 0.2%. A statistically significant reduction in the testosterone concentration in murine blood was recorded after the 7th administration of 300 mg/kg alsevirone at 0.31 ± 0.03 ng/ml (p < .001) versus 0.98 ± 0.22 ng/ml (p = .392) after abiraterone administration and 1.52 ± 0.49 ng/ml in control animals. Alsevirone was more cytotoxic than abiraterone in DU-145, LNCaP, and 22Rv1 cells, with IC50 values of 23.80 ± 1.18 versus 151.43 ± 23.70 µM, 22.87 ± 0.54 versus 28.80 ± 1.61 µM, and 35.86 ± 5.63 versus 109.87 ± 35.15 µM, respectively. Alsevirone and abiraterone significantly increased annexin V-positive, caspase 3/7-positive, and activated Bcl-2-positive cells. In 22Rv1 xenografts, alsevirone 300 mg/kg × 10/24 h per os inhibited tumor growth: on Day 9 of treatment, tumor growth inhibition = 59% (p = .022). Thus, alsevirone demonstrated significant antitumor activity associated with CYP17A1 inhibition, apoptosis in PC cells, and testosterone reduction.

New benzothieno[2,3-c]pyridines as non-steroidal CYP17 inhibitors: design, synthesis, anticancer screening, apoptosis induction, and in silico ADME profile studies.

A series of [1]benzothieno[2,3-c]pyridines was synthesised. Most compounds were chosen by NCI-USA to evaluate their anticancer activity. Compounds 5a-c showed prominent growth inhibition against most cell lines. 5c was selected at five dose concentration levels. It exhibited potent broad-spectrum anticancer activity with a GI50 of 4 nM-37 µM. Cytotoxicity of 5a-c was further evaluated against prostate, renal, and breast cancer cell lines. 5c showed double and quadruple the activity of staurosporine and abiraterone, respectively, against the PC-3 cell line with IC50 2.08 µM. The possible mechanism of anti-prostate cancer was explored via measuring the CYP17 enzyme activity in mice prostate cancer models compared to abiraterone. The results revealed that 5c suppressed the CYP17 enzyme to 15.80 nM. Moreover, it was found to be equipotent to abiraterone in testosterone production. Cell cycle analysis and apoptosis were performed. Additionally, the ADME profile of compound 5c demonstrated both good oral bioavailability and metabolic stability.

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 (t1/2 = 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.

Ameliorative effects of fisetin in letrozole-induced rat model of polycystic ovary syndrome.

BACKGROUND: The present study was conducted to investigate the therapeutic effects of a potent polyphenol, fisetin, on the letrozole-induced rat model of polycystic ovary syndrome (PCOS). METHODOLOGY: Twenty-four female Wistar rats (42 days old) were divided into four groups: control group (received carboxy methylcellulose (CMC 0.5 %)), PCOS group treated with letrozole (1 mg/kg), fisetin group received same dose of letrozole + fisetin (10 mg/kg), and metformin group received same dose of letrozole + metformin (300 mg/kg). At the end of the experiment, biochemical (glucose, lipid profile) and hormonal (insulin, testosterone, estradiol, and progesterone) parameters were analyzed. Histological examinations of ovaries were also conducted by hematoxylin and eosin (H&E) staining. Real-time polymerase chain reaction (PCR) and western blotting were carried out for cytochrome P450 17A1 (CYP17A1), sirtuin-1 (SIRT1), and 5' AMP-activated protein kinase (AMPK) gene expression in the ovaries. Furthermore, enzymatic activities of antioxidants including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) in the ovaries were analyzed by colorimetric method. RESULTS: Letrozole administration resulted in a remarkable abnormality in biochemical and hormonal parameters. Fisetin normalized levels of glucose, lipid profile, homeostatic model assessment for insulin resistance (HOMA-IR), testosterone, estradiol, and progesterone. Moreover, fisetin increased expression levels of SIRT1 and AMPK, and decreased expression level of CYP17A1 in the ovaries. Additionally, fisetin showed protective effect by enhancing antioxidant activities of CAT, SOD, and GPx depleted secondary to induction of PCOS. Fisetin effects were comparable to metformin, as the standard drug used for treatment of PCOS. CONCLUSION: Our results showed that, fisetin treatment caused significant alleviating effects by restoring PCOS-induced alterations in the key genes involved in energy homeostasis and antioxidant enzymes, suggesting that it may have a key role in combating with PCOS.

Impact of pretreatment anemia on upfront abiraterone acetate therapy for metastatic hormone-sensitive prostate cancer: a multicenter retrospective study.

BACKGROUND: Anemia has been a known prognostic factor in metastatic hormone-sensitive prostate cancer (mHSPC). We therefore examined the effect of anemia on the efficacy of upfront abiraterone acetate (ABI) in patients with mHSPC. METHODS: We retrospectively evaluated 66 mHSPC patients with high tumor burden who received upfront ABI between 2018 and 2020 (upfront ABI group). We divided these patients into two groups: the anemia-ABI group (hemoglobin < 13.0 g/dL, n = 20) and the non-anemia-ABI group (n = 46). The primary objective was to examine the impact of anemia on the progression-free survival (PFS; clinical progression or PC death before development of castration resistant PC) of patients in the upfront ABI group. Secondary objectives included an evaluation of the prognostic significance of upfront ABI and a comparison with a historical cohort (131 mHSPC patients with high tumor burden who received androgen deprivation therapy (ADT/complete androgen blockade [CAB] group) between 2014 and 2019). RESULTS: We found that the anemia-ABI group had a significantly shorter PFS than the non-anemia-ABI group. A multivariate Cox regression analysis showed that anemia was an independent prognostic factor of PFS in the upfront ABI group (hazard ratio, 4.66; P = 0.014). Patients in the non-anemia-ABI group were determined to have a significantly longer PFS than those in the non-anemia-ADT/CAB group (n = 68) (P < 0.001). However, no significant difference was observed in the PFS between patients in the anemia-ABI and the anemia-ADT/CAB groups (n = 63). Multivariate analyses showed that upfront ABI could significantly prolong the PFS of patients without anemia (hazard ratio, 0.17; P < 0.001), whereas ABI did not prolong the PFS of patients with anemia. CONCLUSION: Pretreatment anemia was a prognostic factor among mHSPC patients who received upfront ABI. Although the upfront ABI significantly improved the PFS of mHSPC patients without anemia, its efficacy in patients with anemia might be limited.

A Population-based Study Comparing Outcomes for Patients With Metastatic Castrate Resistant Prostate Cancer Treated by Urologists or Medical Oncologists With First Line Abiraterone Acetate or Enzalutamide.

OBJECTIVES: To compare toxicity and all-cause mortality for mCRPC patients receiving first line oral systemic therapy prescribed by medical oncologists and urologists. METHODS: Population-based retrospective cohort study of chemotherapy-naïve men aged ≥66 years treated for mCRPC with first-line abiraterone or enzalutamide based on administrative health data (Ontario, Canada, 2012-2017). Primary outcomes were hospitalizations/ER visits for any cause or treatment-related toxicity during first-line mCRPC treatment. Secondary outcome was all-cause mortality. We calculated hazard ratios (HRs) comparing outcomes for different medical specialties using multivariable Cox proportional hazards models. RESULTS: Among 3405 mCRPC patients, 2407 (70.7%) received abiraterone and 998 (29.3%) received enzalutamide. 1786 (52.5%) patients visited the ER or were hospitalized. Men treated by medical oncologists had an increased risk of hospitalization/ER visits (HR1.16, 95%CI 1.03-1.31; P = .02), toxicity-related visits (HR1.34, 95%CI 1.08-1.69; P = .01), and mortality (HR1.16, 95%CI 1.02-1.33; P = .02) compared to urologists. Limited information was available, beyond PSA adjustment and prior treatment, on patient disease burden. CONCLUSION: We observed fewer hospital visits overall and for treatment-related toxicity for mCRPC patients who were prescribed first line abiraterone or enzalutamide by urologists compared to medical oncologists. These differences may result from higher prostate cancer disease burden in patients managed by medical oncologists, and/or other unmeasured differences in patient management between specialties.

HSD3B1 variant and androgen-deprivation therapy outcome in prostate cancer.

OBJECTIVE: Rate-limiting enzyme 3b-hydroxysteroid dehydrogenase type 1 (3ßHSD1) encoded by HSD3B1 catalyzes the transition of dehydroepiandrosterone (DHEA) to dihydrotestosterone (DHT). The HSD3B1 (1245C) variant renders 3bHSD1 of resistant to ubiquitination and degradation, leading to a large amount of protein accumulation in the cell. Multiple clinical studies have shown that this mutation was correlated with resistance to androgen-deprivation therapy in prostate cancer. However, the results were not consistent depending on different treatment strategy and in some researches, the number of observed cases was relatively small. METHODS: To determine the effects of HSD3B1 (1245C) variant on resistance to androgen-deprivation therapy in prostate cancer, we performed a meta-analysis of the available literature. Electronic database searches identified appropriately designed studies that detected HSD3B1 in prostate cancer. We conducted a systematic search of studies in the following databases: PubMed, and EMBASE published until August 10, 2020 using the following search terms: (HSD3B1 AND ((((prostate cancer) OR prostatic neoplasm) OR prostatic carcinoma) OR prostatic cancer). RESULTS: Eight researches were included in this research. The result validated that the HSD3B1 (1245C) variant allele was associated with a shorter PFS (HR, 1.97; 95% CI, 1.39-2.79; P = 0.0001) (homozygous wild-type group) in men with prostate cancer when treated with ADT, however, a higher PFS (HR, 0.68; 95% CI, 0.48-0.96; P = 0.03) when treated with ADT and CYP17A1 inhibitor. CONCLUSION: The HSD3B1 (1245C) variant is a predictor of ADT plus CYP17A1 inhibitor response in prostate cancer.

Modified bile acids and androstanes-Novel promising inhibitors of human cytochrome P450 17A1.

Cytochromes P450 are key enzymes for steroid hormone biosynthesis in human body. They are considered as targets for the screening of novel high efficient drugs. The results of screening of bile acids and androstane derivatives toward human recombinant steroid 17α-hydroxylase/17,20-lyase (CYP17A1) are presented in this paper. A group of steroids, binding with micromolar or submicromolar affinity (in a range from 9 µM - less than 0.1 µM), was identified. Results presented here showed that these steroidal compounds are able to decrease rate of hydroxylation of essential CYP17A1 substrate - progesterone, while some compounds completely inhibited enzyme activity. Structure-activity relationship (SAR) analysis based on in vitro and in silico studies showed that high affinity of the enzyme to bile acids derivatives is correlated with side chain hydrophobicity and presence of hydroxyl or keto group at C3 position. From the other side, bile acid-derived compounds with more polar side chain or substituents at C7 and C12 positions possess higher Kd values. Among androstane-derived steroids couple of Δ5-steroids with hydroxyl group at C3 position, as well as 16,17-secosteroids, were found to be high affinity ligands of this enzyme. The data obtained could be useful for the design of novel highly efficient inhibitors of CYP17A1, since the bile acids-derived compounds are for first time recognized as effective CYP17A1 inhibitors.

CYP17 inhibitors improve the prognosis of metastatic castration-resistant prostate cancer patients: A meta-analysis of published trials.

BACKGROUND AND AIMS: CYP17 inhibitors can block androgen production both intratumorally and systemically, thus attenuating the progression of prostate cancer (PCa). Many randomized controlled trials (RCTs) showed promising results that men with metastatic castration-resistant PCa (mCRPC) might benefit from treatment with CYP17 inhibitors such as abiraterone acetate and orteronel. The goal of this study was to evaluate the efficacy of CYP17 inhibitors for the prognosis in patients with mCRPC. MATERIALS AND METHODS: Studies were identified in PubMed/MEDLINE, the Cochrane Library, and the Web of Science. The RCTs with mCRPC patients focusing on the efficacy of CYP17 inhibitors were involved. Then, we analyzed the patients' prognosis such as overall survival (OS) and radiographic progression-free survival (RPFS). RESULTS: A meta-analysis of the pooled data from seven randomized Phase III clinical trials was performed to compare 5516 mCRPC patients with CYP17 inhibitors versus that with placebo. Compared to placebo, the CYP17 inhibitors significantly increased the OS (pooled hazard ratios [HR]: 0.816, 95% confidence interval [CI]: 0.750-0.887), RPFS (pooled HR: 0.647, 95% CI: 0.557-0.752), and time to prostate-specific antigen (PSA) progression (pooled HR: 0.599, 95% CI: 0.517-0.693). Additional endpoints such as PSA response rate, objective response assessed by Response Evaluation Criteria in Solid Tumors, and time to initiation of chemotherapy were included in this study and were found having significant improvement with CYP17 inhibitors compared to placebo. CONCLUSION: This research showed that CYP17 inhibitors had a significant improvement on prognosis of patients with mCRPC within a relative safety profile both in pre- and post-chemotherapy trials. These expected results provide evidence for the use of CYP17 inhibitors to treat mCRPCs.

Discovery of Novel Non-Steroidal Cytochrome P450 17A1 Inhibitors as Potential Prostate Cancer Agents.

The current study presents the design, synthesis, and evaluation of novel cytochrome P450 17A1 (CYP17A1) ligands. CYP17A1 is a key enzyme in the steroidogenic pathway that produces androgens among other steroids, and it is implicated in prostate cancer. The obtained compounds are potent enzyme inhibitors (sub µM) with antiproliferative activity in prostate cancer cell lines. The binding mode of these compounds is also discussed.

Slow-, Tight-Binding Inhibition of CYP17A1 by Abiraterone Redefines Its Kinetic Selectivity and Dosing Regimen.

Substantial evidence underscores the clinical efficacy of inhibiting CYP17A1-mediated androgen biosynthesis by abiraterone for treatment of prostate oncology. Previous structural analysis and in vitro assays revealed inconsistencies surrounding the nature and potency of CYP17A1 inhibition by abiraterone. Here, we establish that abiraterone is a slow-, tight-binding inhibitor of CYP17A1, with initial weak binding preceding the subsequent slow isomerization to a high-affinity CYP17A1-abiraterone complex. The in vitro inhibition constant of the final high-affinity CYP17A1-abiraterone complex ( ( K i * = 0.39 nM )yielded a binding free energy of -12.8 kcal/mol that was quantitatively consistent with the in silico prediction of -14.5 kcal/mol. Prolonged suppression of dehydroepiandrosterone (DHEA) concentrations observed in VCaP cells after abiraterone washout corroborated its protracted CYP17A1 engagement. Molecular dynamics simulations illuminated potential structural determinants underlying the rapid reversible binding characterizing the two-step induced-fit model. Given the extended residence time (42 hours) of abiraterone within the CYP17A1 active site, in silico simulations demonstrated sustained target engagement even when most abiraterone has been eliminated systemically. Subsequent pharmacokinetic-pharmacodynamic (PK-PD) modeling linking time-dependent CYP17A1 occupancy to in vitro steroidogenic dynamics predicted comparable suppression of downstream DHEA-sulfate at both 1000- and 500-mg doses of abiraterone acetate. This enabled mechanistic rationalization of a clinically reported PK-PD disconnect, in which equipotent reduction of downstream plasma DHEA-sulfate levels was achieved despite a lower systemic exposure of abiraterone. Our novel findings provide the impetus for re-evaluating the current dosing paradigm of abiraterone with the aim of preserving PD efficacy while mitigating its dose-dependent adverse effects and financial burden. SIGNIFICANCE STATEMENT: With the advent of novel molecularly targeted anticancer modalities, it is becoming increasingly evident that optimal dose selection must necessarily be predicated on mechanistic characterization of the relationships between target exposure, drug-target interactions, and pharmacodynamic endpoints. Nevertheless, efficacy has always been perceived as being exclusively synonymous with affinity-based measurements of drug-target binding. This work demonstrates how elucidating the slow-, tight-binding inhibition of CYP17A1 by abiraterone via in vitro and in silico analyses was pivotal in establishing the role of kinetic selectivity in mediating time-dependent CYP17A1 engagement and eventually downstream efficacy outcomes.

Molecular underpinnings of systemic treatment resistance in metastatic castration-resistant prostate cancer / [Az áttétes kasztrációrezisztens prosztatarák gyógyszer-rezisztenciájának molekuláris vonatkozásai]

In the last few years, several new drugs with various mechanisms of action have been approved for the treatment of castration-resistant prostate cancer. Due to this development, therapeutic decision-making has become increasingly complex. Therefore, therapy selection as well as timing and sequence of treatments need to be optimized in an individual manner. In addition, also for these novel therapies, baseline and acquired as well as cross-resistance have been observed. Underlying mechanisms become increasingly clear, resulting in a shift from empiric-based towards rational-based therapeutic decision-making. In the present review, we provide an overview on the resistance mechanisms against the most frequently applied systemic treatments of metastatic castration-resistant prostate cancer such as docetaxel, abiraterone and enzalutamide. We summarize - among others - the mechanisms by MDR (multidrug-resistant) protein expression, alterations of androgen receptor, Wnt, p53 and DNA-repair pathways (BRCA/ATM) as well as resistance through therapy-induced neuroendocrine differentiation of the tumour. Orv Hetil. 2020; 161(20): 813-820.

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 Kd 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.

Seviteronel, a Novel CYP17 Lyase Inhibitor and Androgen Receptor Antagonist, Radiosensitizes AR-Positive Triple Negative Breast Cancer Cells.

Increased rates of locoregional recurrence (LR) have been observed in triple negative breast cancer (TNBC) despite multimodality therapy, including radiation (RT). Recent data suggest inhibiting the androgen receptor (AR) may be an effective radiosensitizing strategy, and AR is expressed in 15-35% of TNBC tumors. The aim of this study was to determine whether seviteronel (INO-464), a novel CYP17 lyase inhibitor and AR antagonist, is able to radiosensitize AR-positive (AR+) TNBC models. In cell viability assays, seviteronel and enzalutamide exhibited limited effect as a single agent (IC50 > 10 µM). Using clonogenic survival assays, however, AR knockdown and AR inhibition with seviteronel were effective at radiosensitizing cells with radiation enhancement ratios of 1.20-1.89 in models of TNBC with high AR expression. AR-negative (AR-) models, regardless of their estrogen receptor expression, were not radiosensitized with seviteronel treatment at concentrations up to 5 µM. Radiosensitization of AR+ TNBC models was at least partially dependent on impaired dsDNA break repair with significant delays in repair at 6, 16, and 24 h as measured by immunofluorescent staining of γH2AX foci. Similar effects were observed in an in vivo AR+ TNBC xenograft model where there was a significant reduction in tumor volume and a delay to tumor doubling and tripling times in mice treated with seviteronel and radiation. Following combination treatment with seviteronel and radiation, increased binding of AR occurred at DNA damage response genes, including genes involved both in homologous recombination and non-homologous end joining. This trend was not observed with combination treatment of enzalutamide and RT, suggesting that seviteronel may have a different mechanism of radiosensitization compared to other AR inhibitors. Enzalutamide and seviteronel treatment also had different effects on AR and AR target genes as measured by immunoblot and qPCR. These results implicate AR as a mediator of radioresistance in AR+ TNBC models and support the use of seviteronel as a radiosensitizing agent in AR+ TNBC.

How do we define "castration" in men on androgen deprivation therapy?

Androgen deprivation therapy (ADT) is the mainstay for the treatment of advanced prostate cancer. Since the clinical evolution from surgical orchiectomy, we have typically used ADT and orchiectomy to be synonymous terms for castration. The goal of this study is to determine if, in contemporary medical practice, surgical and chemical castration provide for similar levels of diminishment of total and free testosterone. Further, what approaches should be used to most accurately measure testosterone levels in men with advanced prostate cancer and what cutoff values, for example for total testosterone 50 ng dl-1 or 20 ng dl-1, should be utilized. Studies available in the literature have been analyzed and compiled to address these questions. Finally, evidence is provided that free testosterone, the biologically active component, should be utilized to provide clinically relevant state of castration.

Persistence and adherence to androgen deprivation therapy in men with prostate cancer: an administrative database study.

BACKGROUND: The aim of this study was to assess adherence to and persistence with androgen deprivation therapy (ADT) in a large cohort of prostate cancer (PCa) patients selected from an administrative database, with special attention to elderly patients. METHODS: Patients treated with LHRH analogues, LHRH antagonists, the novel androgen antagonist enzalutamide, and the CYP17 inhibitor abiraterone were included spanning the years 2011-2017. Descriptive statistics were used to analyze persistence and adherence in older patients stratified by age (46-55, 56-65, 66-75, 76-85, and >85 years). The effect of persistence duration on overall survival in super-elderly patients was analyzed by the Kaplan-Meier method, together with the influence of multiple prescriptions on overall survival. RESULTS: A total of 1160 male patients were treated with ADT. Of these, 1075 were given LHRH analogues, 80 LHRH antagonists, 14 novel androgen antagonists, and 109 the CYP17 inhibitor. Median adherence values were 0.93, 0.97, 0.95, and 0.99 respectively. The highest persistence was recorded for LHRH analogues/antagonists (24 months), followed enzalutamide and abiraterone (8 months). A total of 107 patients (9.2%) were classified as super-elderly (age range 85-97 years). Median persistence and OS in this group were 13 months and 29 months, respectively. The adherence was 0.92. Overall survival was significantly associated with additional prescriptions for other conditions-indications (P=0.0047) but not with differences in adherence rates (P=0.98). CONCLUSIONS: Our data showed high adherence and persistence rates in men on ADT. The overall survival in the super-elderly is not influenced by persistence and/or adherence but rather by coprescriptions.