Discovery of orteronel (TAK-700), a naphthylmethylimidazole derivative, as a highly selective 17,20-lyase inhibitor with potential utility in the treatment of prostate cancer

Phase III, randomized, double-blind, multicenter trial comparing orteronel (TAK-700) plus prednisone with placebo plus prednisone in patients with metastatic castration-resistant prostate cancer that has progressed during or after docetaxel-based therapy: ELM-PC 5

PURPOSE

Orteronel (TAK-700) is an investigational, nonsteroidal, reversible, selective 17,20-lyase inhibitor. This study examined orteronel in patients with metastatic castration-resistant prostate cancer that progressed after docetaxel therapy.

PATIENTS AND METHODS

In our study, 1,099 men were randomly assigned in a 2:1 schedule to receive orteronel 400 mg plus prednisone 5 mg twice daily or placebo plus prednisone 5 mg twice daily, stratified by region (Europe, North America [NA], and non-Europe/NA) and Brief Pain Inventory-Short Form worst pain score. Primary end point was overall survival (OS). Key secondary end points (radiographic progression-free survival [rPFS], ≥ 50% decrease of prostate-specific antigen [PSA50], and pain response at 12 weeks) were to undergo statistical testing only if the primary end point analysis was significant.

RESULTS

The study was unblinded after crossing a prespecified OS futility boundary. The median OS was 17.0 months versus 15.2 months with orteronel-prednisone versus placebo-prednisone (hazard ratio [HR], 0.886; 95% CI, 0.739 to 1.062; P = .190). Improved rPFS was observed with orteronel-prednisone (median, 8.3 v 5.7 months; HR, 0.760; 95% CI, 0.653 to 0.885; P < .001). Orteronel-prednisone showed advantages over placebo-prednisone in PSA50 rate (25% v 10%, P < .001) and time to PSA progression (median, 5.5 v 2.9 months, P < .001) but not pain response rate (12% v 9%; P = .128). Adverse events (all grades) were generally more frequent with orteronel-prednisone, including nausea (42% v 26%), vomiting (36% v 17%), fatigue (29% v 23%), and increased amylase (14% v 2%).

CONCLUSION

Our study did not meet the primary end point of OS. Longer rPFS and a higher PSA50 rate with orteronel-prednisone indicate antitumor activity.

A phase 1 multiple-dose study of orteronel in Japanese patients with castration-resistant prostate cancer

Purpose

Orteronel (TAK-700) is a non-steroidal, selective, reversible inhibitor of 17,20-lyase. We evaluated the safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor effect of orteronel with or without prednisolone in Japanese patients with castration-resistant prostate cancer (CRPC).

Methods

We conducted a phase 1 study in men with progressive and chemotherapy-naïve CRPC. Patients received orteronel orally at doses of 200–400 mg twice daily (BID) with or without oral prednisolone (5 mg BID). Dose-limiting toxicity (DLT) was assessed during Cycle 1 (28 days). Patients could continue study treatment until any of criteria for treatment discontinuation were met. Gonadotropin-releasing hormone therapy was continued in patients without prior orchidectomy.

Results

Fifteen patients were enrolled and administered at least one dose of orteronel. No DLTs were reported during Cycle 1 in this study. Adverse events (AEs) were reported in all 15 patients. Most common AEs (>30 %) were hyperlipasemia (47 %), hyperamylasemia (40 %), and constipation (33 %). Acute pancreatitis (Grades 2 and 3) and pancreatitis (Grade 1) were complicated in three patients during the study. Dose-dependent increase in plasma orteronel concentrations was indicated over the 200–400 mg BID dose range. Prednisolone coadministered did not alter PK of orteronel. Serum testosterone was rapidly suppressed below the lower limit of quantification across all doses. Of 15 subjects, 13 achieved at least a 50 % reduction from baseline in prostate-specific antigen.

Conclusions

Orteronel at doses up to 400 mg BID was tolerable in Japanese CRPC patients. The present results support further evaluation of orteronel with or without prednisolone.

Structural and kinetic basis of steroid 17α,20-lyase activity in teleost fish cytochrome P450 17A1 and its absence in cytochrome P450 17A2

Cytochrome P450 (P450) 17A enzymes play a critical role in the oxidation of the steroids progesterone (Prog) and pregnenolone (Preg) to glucocorticoids and androgens. In mammals, a single enzyme, P450 17A1, catalyzes both 17α-hydroxylation and a subsequent 17α,20-lyase reaction with both Prog and Preg. Teleost fish contain two 17A P450s; zebrafish P450 17A1 catalyzes both 17α-hydroxylation and lyase reactions with Prog and Preg, and P450 17A2 is more efficient in pregnenolone 17α-hydroxylation but does not catalyze the lyase reaction, even in the presence of cytochrome b5. P450 17A2 binds all substrates and products, although more loosely than P450 17A1. Pulse-chase and kinetic spectral experiments and modeling established that the two-step P450 17A1 Prog oxidation is more distributive than the Preg reaction, i.e. 17α-OH product dissociates more prior to the lyase step. The drug orteronel selectively blocked the lyase reaction of P450 17A1 but only in the case of Prog. X-ray crystal structures of zebrafish P450 17A1 and 17A2 were obtained with the ligand abiraterone and with Prog for P450 17A2. Comparison of the two fish P450 17A-abiraterone structures with human P450 17A1 (DeVore, N. M., and Scott, E. E. (2013) Nature 482, 116-119) showed only a few differences near the active site, despite only ∼50% identity among the three proteins. The P450 17A2 structure differed in four residues near the heme periphery. These residues may allow the proposed alternative ferric peroxide mechanism for the lyase reaction, or residues removed from the active site may allow conformations that lead to the lyase activity.

Review of novel therapeutic medicines targeting androgen signaling in castration-resistant prostate cancer

Prostate cancer is the most common male malignant neoplasm. Androgens and the androgen receptor (AR) play a key role in the onset and progression of prostate cancer. The expression of the AR is still preserved in the majority of patients with castration-resistant prostate cancer (CRPC). CRPC is considered to be induced by the following mechanisms: (1) sustained AR activation by enhancing intracellular conversion of adrenal androgens to dehydrotestosterone via a de novo route; (2) AR hypersensitivity; (3) promiscuous activation of AR signaling; and (4) outlaw pathways. Recent advances in the treatment of CRPC include novel medicines targeting AR signaling pathways. In addition, functional molecular studies have shown that some of the AR-regulated genes and AR coregulators are prognostic markers and potential therapeutic targets for prostate cancer, particularly in the castration-resistant state. Therefore, identification of the AR signaling pathways responsible for establishment of CRPC is critical for developing new strategies for the treatment of CRPC.

Quo vadis: advanced prostate cancer-clinical care and clinical research in the era of multiple androgen receptor-directed therapies

The novel androgen receptor-directed therapies abiraterone acetate and enzalutamide, having demonstrated improved survival in randomized phase 3 studies of men with metastatic castration-resistant prostate cancer, have ushered in a new era in the treatment of this disease. Additional novel androgen receptor-directed therapies, such as ARN-509 and orteronel, are in various phases of clinical trials and development. However, the emergence of therapeutic resistance and clinical disease progression is inevitable. Although advances in genomic technologies have led to unprecedented understanding of the biology of castration-resistant prostate cancer, efforts only now are underway to elucidate the mechanisms of resistance associated with abiraterone and enzalutamide. A tremendous challenge in the near future will be to determine the optimal sequence or combination of therapies to overcome resistance mechanisms. In this review, the current landscape of androgen receptor-directed therapies and future directions necessary to enhance their clinical efficacy for the maximal benefit of patients are discussed.

The role of epithelial plasticity in prostate cancer dissemination and treatment resistance

Nearly 30,000 men die annually in the USA of prostate cancer, nearly uniformly from metastatic dissemination. Despite recent advances in hormonal, immunologic, bone-targeted, and cytotoxic chemotherapies, treatment resistance and further dissemination are inevitable in men with metastatic disease. Emerging data suggests that the phenomenon of epithelial plasticity, encompassing both reversible mesenchymal transitions and acquisition of stemness traits, may underlie this lethal biology of dissemination and treatment resistance. Understanding the molecular underpinnings of this cellular plasticity from preclinical models of prostate cancer and from biomarker studies of human metastatic prostate cancer has provided clues to novel therapeutic approaches that may delay or prevent metastatic disease and lethality over time. This review will discuss the preclinical and clinical evidence for epithelial plasticity in this rapidly changing field and relate this to clinical phenotype and resistance in prostate cancer while suggesting novel therapeutic approaches.

Concept and viability of androgen annihilation for advanced prostate cancer

There remains no standard of care for patients with a rising prostate-specific antigen level after radical prostatectomy or radiotherapy but who have no radiographic metastases, even though this is the second largest group of patients with prostate cancer (CaP) in the United States. Androgen deprivation therapy (ADT) may cure some men with advanced CaP based on single-institution series and a randomized clinical trial of immediate versus delayed ADT for men found to have pelvic lymph node metastasis at the time of radical prostatectomy. ADT may be more effective when initiated for minimal disease burden, which can be detected using PSA after radical prostatectomy or radiotherapy, and if more complete disruption of the androgen axis using newer agents decreases the chance that androgen-sensitive cells survive to adapt to a low-androgen environment. Androgens may be "annihilated" simultaneously using a luteinizing hormone-releasing hormone antagonist or agonist to inhibit testicular production of testosterone, a P45017A1 (CYP17A1) inhibitor to diminish metabolism of testosterone via the adrenal pathway and dihydrotestosterone (DHT) via the backdoor pathway, a 5α-reductase (SRD5A) inhibitor to diminish testosterone reduction to DHT and backdoor metabolism of progesterone substrates to DHT, and a newer antiandrogen to compete better with DHT for the androgen receptor ligand-binding domain. Early initiation of androgen annihilation for induction as part of planned intermittent ADT should be safe, may reduce tumor burden below a threshold that allows eradication by the immune system, and may cure many men who have failed definitive local therapy.

Intratumoral steroidogenesis in castration-resistant prostate cancer: a target for therapy

Development of castration-resistant prostate cancer (CRPC) in a low androgen environment, arising from androgen deprivation therapy (ADT), is a major problem in patients with advanced prostate cancer (PCa). Several mechanisms have been hypothesized to explain the progression of PCa to CRPC during ADT, one of them is so called persistent intratumoral steroidogenesis. The existence of intratumoral steroidogenesis was hinted based on the residual levels of intraprostatic testosterone (T) and dihydrotestosterone (DHT) after ADT. Accumulating evidence has shown that the intraprostatic androgen levels after ADT are sufficient to induce cancer progression. Several studies now have demonstrated that PCa cells are able to produce T and DHT from different androgen precursors, such as cholesterol and the adrenal androgen, dehydroepiandrosterone (DHEA). Furthermore, up-regulation of genes encoding key steroidogenic enzymes in PCa cells seems to be an indicator for active intratumoral steroidogenesis in CRPC cells. Currently, several drugs are being developed targeting those steroidogenic enzymes, some of which are now in clinical trials or are being used as standard care for CRPC patients. In the future, novel agents that target steroidogenesis may add to the arsenal of drugs for CRPC therapy.

Strategies for targeting the androgen receptor axis in prostate cancer

Androgen receptor (AR) signaling plays a critical role in prostate cancer cell proliferation, survival, and differentiation. Therapeutic strategies targeting the androgen receptor have been developed for the treatment of metastatic hormone-naïve prostate cancer; however, despite effective targeting recent studies have demonstrated that during progression to a castrate-resistant phenotype there is restoration of AR target gene expression. On the basis of this observation, second-generation therapeutics have been developed to target AR in the castrate-resistant setting resulting in a survival benefit. In this review we will discuss the mechanisms promoting AR signaling and the development of second-generation therapeutics targeting AR in castrate-resistant prostate cancer.

Drug costs in the management of metastatic castration-resistant prostate cancer in Canada

BACKGROUND

For Canadian men, prostate cancer (PCa) is the most common cancer and the 3rd leading cause of cancer mortality. Men dying of PCa do so after failing castration. The management of metastatic castration-resistant prostate cancer (mCRPC) is complex and the associated drug treatments are increasingly costly. The objective of this study was to estimate the cost of drug treatments over the mCRPC period, in the context of the latest evidence-based approaches.

METHODS

Two Markov models with Monte-Carlo microsimulations were developed in order to simulate the management of the disease and to estimate the cost of drug treatments in mCRPC, as per Quebec's public healthcare system. The models include recently approved additional lines of treatment after or before docetaxel (i.e. abiraterone and cabazitaxel). Drug exposure and survival were based on clinical trial results and clinical practice guidelines found in a literature review. All costs were assigned in 2013 Canadian dollars ($). Only direct drug costs were estimated.

RESULTS

The mean cost of mCRPC drug treatments over an average period of 28.1 months was estimated at $48,428 per patient (95% Confidence Interval: $47,624 to $49,232). The mean cost increased to $104,071 (95% CI: $102,373 - $105,770) per patient when one includes abiraterone initiation prior to docetaxel therapy. Over the mCRPC period, luteinizing hormone-releasing hormone agonists (LHRHa) prescribed to maintain castrate testosterone levels accounted for 20.4% of the total medication cost, whereas denosumab prescribed to decrease bone-related events accounted for 30.5% of costs. When patients received cabazitaxel in sequence after abiraterone and docetaxel, the mCRPC medications cost per patient per month increased by 60.2%. The total cost of medications for the treatment of each annual Canadian cohort of 4,000 mCRPC patients was estimated at $ 193.6 million to $416.3 million.

CONCLUSIONS

Our study estimates the direct drug costs associated with mCRPC treatments in the Canadian healthcare system. Recently identified effective yet not approved therapies will become part of the spectrum of mCRPC treatments, and may potentially increase the cost.

Androgen synthesis inhibitors in the treatment of castration-resistant prostate cancer

Suppression of gonadal testosterone synthesis represents the standard first line therapy for treatment of metastatic prostate cancer. However, in the majority of patients who develop castration-resistant prostate cancer (CRPC), it is possible to detect persistent activation of the androgen receptor (AR) through androgens produced in the adrenal gland or within the tumor itself. Abiraterone acetate was developed as an irreversible inhibitor of the dual functional cytochrome P450 enzyme CYP17 with activity as a 17α-hydroxylase and 17,20-lyase. CYP17 is necessary for production of nongonadal androgens from cholesterol. Regulatory approval of abiraterone in 2011, based on a phase III trial showing a significant improvement in overall survival (OS) with abiraterone and prednisone versus prednisone, represented proof of principle that targeting AR is essential for improving outcomes in men with CRPC. Inhibition of 17α-hydroxylase by abiraterone results in accumulation of upstream mineralocorticoids due to loss of cortisol-mediated suppression of pituitary adrenocorticotropic hormone (ACTH), providing a rationale for development of CYP17 inhibitors with increased specificity for 17,20-lyase (orteronel, galeterone and VT-464) that can potentially be administered without exogenous corticosteroids. In this article, we review the development of abiraterone and other CYP17 inhibitors; recent studies with abiraterone that inform our understanding of clinical parameters such as drug effects on quality-of-life, potential early predictors of response, and optimal sequencing of abiraterone with respect to other agents; and results of translational studies providing insights into resistance mechanisms to CYP17 inhibitors leading to clinical trials with drug combinations designed to prolong abiraterone benefit or restore abiraterone activity.

Orteronel for the treatment of prostate cancer

Orteronel (also known as TAK-700) is a novel hormonal therapy that is currently in testing for the treatment of prostate cancer. Orteronel inhibits the 17,20 lyase activity of the enzyme CYP17A1, which is important for androgen synthesis in the testes, adrenal glands and prostate cancer cells. Preclinical studies demonstrate that orteronel treatment suppresses androgen levels and causes shrinkage of androgen-dependent organs, such as the prostate gland. Early reports of clinical studies demonstrate that orteronel treatment leads to reduced prostate-specific antigen levels, a marker of prostate cancer tumor burden, and more complete suppression of androgen synthesis than conventional androgen deprivation therapies that act in the testes alone. Treatment with single-agent orteronel has been well tolerated with fatigue as the most common adverse event, while febrile neutropenia was the dose-limiting toxicity in a combination study of orteronel with docetaxel. Recently, the ELM-PC5 Phase III clinical trial in patients with advanced-stage prostate cancer who had received prior docetaxel was unblinded as the overall survival primary end point was not achieved. However, additional Phase III orteronel trials are ongoing in men with earlier stages of prostate cancer.

Ligand-independent and tissue-selective androgen receptor inhibition by pyrvinium

Pyrvinium pamoate (PP) is a potent noncompetitive inhibitor of the androgen receptor (AR). Using a novel method of target identification, we demonstrate that AR is a direct target of PP in prostate cancer cells. We demonstrate that PP inhibits AR activity via the highly conserved DNA binding domain (DBD), the only AR inhibitor that functions via this domain. Furthermore, computational modeling predicts that pyrvinium binds at the interface of the DBD dimer and the minor groove of the AR response element. Because PP acts through the DBD, PP is able to inhibit the constitutive activity of AR splice variants, which are thought to contribute to the growth of castration resistant prostate cancer (CRPC). PP also inhibits androgen-independent AR activation by HER2 kinase. The antiandrogen activity of pyrvinium manifests in the ability to inhibit the in vivo growth of CRPC xenografts that express AR splice variants. Interestingly, PP was most potent in cells with endogenous AR expression derived from prostate or bone. PP was able to inhibit several other hormone nuclear receptors (NRs) but not structurally unrelated transcription factors. PP inhibition of other NRs was similarly cell-type selective. Using dual-energy X-ray absorptiometry, we demonstrate that the cell-type specificity of PP manifests in tissue-selective inhibition of AR activity in mice, as PP decreases prostate weight and bone mineral density but does not affect lean body mass. Our results suggest that the noncompetitive AR inhibitor pyrvinium has significant potential to treat CRPC, including cancers driven by ligand-independent AR signaling.

[Salvage therapy for castration-refractory prostate cancer resistant to docetaxel]

OBJECTIVES

To evaluate the treatment for castration-refractory prostate cancer (CRPC) resistant to docetaxel

MATERIALS AND METHODS

Among 45 patients with CRPC treated with docetaxel (70-75 mg/m2) every 3 to 4 weeks at Hamamatsu University Hospital from January 2004 to July 2012, 19 patients underwent salvage treatments. We retrospectively analyzed the medical records of 14 patients except for 5 patients who were enrolled in clinical trials.

RESULTS

The median age and serum prostate-specific antigen (PSA) level at starting salvage treatments was 71 years (range 45 to 79) and 241.1 ng/mL (range 3.06 to 1,643.0), respectively. All patients maintained castration status. Salvage treatments include DTX (30 mg/m2) + cisplatin (CDDP) (70 mg/m2)/carboplatin (Area under the curve = 4), etoposide + CDDP, paclitaxel + CDDP, cyclophosphamide, S-l, tegaful-uracil. The reasons why 14 patients moved to salvage treatments after DTX were progressive disease in 12 patients and adverse events in 2. Eight patients had a PSA response, 3 patients>50% and 5 patients<50%. Six patients had a PSA progression. The median overall survival was 10.4 months (range 4.1 to 27.3). All patients died of cancer, 13 patients with prostate cancer and one patient with lung adenocarcinoma. Most adverse events were mild. Transitory grade 3 leukopenia was observed in 2 patients, and grade 3 anemia in 2. No grade 4 toxicities were noted.

CONCLUSIONS

All salvage treatments without grade 4 toxicities described in this study may be acceptable in the patients with CRPC progressing after docetaxel although the effect would be limited.

Beyond abiraterone: new hormonal therapies for metastatic castration-resistant prostate cancer

Prostate cancer is a heterogeneous disease where the previous concept of "hormone resistance" has been changed by a new generation of hormonal therapies that have proven efficacy in the castration-resistant setting. The fact is that androgens play a crucial role in the whole clinical course of prostate cancer, even when a patient meets castration-resistance criteria. The development of abiraterone showed how important and clinically meaningful can be to achieve the lowest possible levels of testosterone, and androgen receptor overexpression, mutation, or enhanced crosstalk with other pathways, which can also be targeted with new agents tested in the last few years. New androgen biosynthesis inhibitors have been developed, such as orteronel (TAK-700), but also new antiandrogens (enzalutamide, ARN-509, ODM-201) or even agents with a dual mechanism of action (galeterone). In this review the development of new hormonal therapies following the arrival of abiraterone for the treatment of prostate cancer will be summarized.

Phase I/II trial of orteronel (TAK-700)--an investigational 17,20-lyase inhibitor--in patients with metastatic castration-resistant prostate cancer

PURPOSE

The androgen receptor pathway remains active in men with prostate cancer whose disease has progressed following surgical or medical castration. Orteronel (TAK-700) is an investigational, oral, nonsteroidal, selective, reversible inhibitor of 17,20-lyase, a key enzyme in the production of androgenic hormones.

EXPERIMENTAL DESIGN

We conducted a phase I/II study in men with progressive, chemotherapy-naïve, metastatic castration-resistant prostate cancer, and serum testosterone <50 ng/dL. In the phase I part, patients received orteronel 100 to 600 mg twice daily or 400 mg twice a day plus prednisone 5 mg twice a day. In phase II, patients received orteronel 300 mg twice a day, 400 mg twice a day plus prednisone, 600 mg twice a day plus prednisone, or 600 mg once a day without prednisone.

RESULTS

In phase I (n = 26), no dose-limiting toxicities were observed and 13 of 20 evaluable patients (65%) achieved ≥50% prostate-specific antigen (PSA) decline from baseline at 12 weeks. In phase II (n = 97), 45 of 84 evaluable patients (54%) achieved a ≥50% decline in PSA and at 12 weeks, substantial mean reductions from baseline in testosterone (-7.5 ng/dL) and dehydroepiandrosterone-sulfate (-45.3 μg/dL) were observed. Unconfirmed partial responses were reported in 10 of 51 evaluable phase II patients (20%). Decreases in circulating tumor cells were documented. Fifty-three percent of phase II patients experienced grade ≥3 adverse events irrespective of causality; most common were fatigue, hypokalemia, hyperglycemia, and diarrhea.

CONCLUSIONS

17,20-Lyase inhibition by orteronel was tolerable and results in declines in PSA and testosterone, with evidence of radiographic responses.

CYP17 inhibitors--abiraterone, C17,20-lyase inhibitors and multi-targeting agents

As the first in class steroid 17α-hydroxylase/C17,20-lyase (CYP17) inhibitor, abiraterone acetate (of which the active metabolite is abiraterone) has been shown to improve overall survival in patients with castration-resistant prostate cancer (CRPC)--in those who are chemotherapy-naive and those previously treated with docetaxel. Furthermore, the clinical success of abiraterone demonstrated that CRPC, which has previously been regarded as an androgen-independent disease, is still driven, at least in part, by androgens. More importantly, abiraterone is a 'promiscuous' drug that interacts with a number of targets, which dictate its clinical benefits and adverse effects profile. Besides CYP17 inhibition, abiraterone acts as an antagonist to the androgen receptor and inhibits 3β-hydroxysteroid dehydrogenase--two effects that potentially contribute to its antitumour effects. However, the inhibition of the 17α-hydroxylase activity of CYP17, CYP11B1 and a panel of hepatic CYP enzymes leads to adverse effects and toxicities that include secondary mineralocorticoid excess. Abiraterone is also associated with increased incidence of cardiac disorders. Under such circumstances, development of new CYP17 inhibitors as an additional line of defence is urgently needed. To achieve enhanced clinical benefits, new strategies are being explored that include selective inhibition of the C17,20-lyase activity of CYP17 and multi-targeting strategies that affect androgen synthesis and signalling at different points. Some of these strategies-including the drugs orteronel, VT-464 and galeterone--are supported by preclinical data and are being explored in the clinic.

Effect of an investigational CYP17A1 inhibitor, orteronel (TAK-700), on estrogen- and corticoid-synthesis pathways in hypophysectomized female rats and on the serum estradiol levels in female cynomolgus monkeys

Orteronel (TAK-700) is an investigational, non-steroidal inhibitor of CYP17A1 with preferential inhibition of 17,20-lyase in NCI-H295 cells. Estrogen is synthesized from androgen by aromatase activity, and the effect of orteronel on estrogen synthesis was therefore evaluated. First, it was confirmed that orteronel does not directly inhibit aromatase activity. Second, the specific decline of serum estradiol and androgen levels in hypophysectomized female rats by orteronel in comparison with aromatase inhibitor anastrozole was evaluated; orteronel at doses ≥3mg/kg significantly suppressed serum estradiol, testosterone, androstenedione and 17-hydroxyprogesterone levels, and increased progesterone levels in the estrogen-synthesis pathway. Orteronel, at a dose of 300mg/kg, suppressed serum estradiol concentrations to a similar degree as 0.1mg/kg anastrozole. In contrast, in the corticoid-synthesis pathway, serum aldosterone, corticosterone, and progesterone levels did not change significantly following administration of 300mg/kg of orteronel. Third, the effect of multiple oral administration of orteronel on serum estradiol levels in regularly cycling female cynomolgus monkeys was evaluated. Orteronel at 15mg/kg/day (7.5mg/kg/treatment, twice daily [bid]) continued to suppress the estradiol surge prior to the start of luteal phase for 1.5-times the average duration of three consecutive, pre-treatment menstrual cycles, while serum progesterone was maintained at levels almost equal to those in the luteal phase although a certain portion of this increased level of progesterone could be of adrenal-origin. This suppressive effect on estradiol surge was thought to be reversible since serum estradiol levels started to rise immediately after the discontinuation of orteronel. Estradiol surge was not abrogated by treatment with anastrozole 0.2mg/kg/day (0.1mg/kg/treatment, bid). In summary, orteronel can suppress serum estradiol concentrations in hypophysectomized female rats and monkeys through selective inhibition of CYP17A1 activity, suggesting that orteronel might be effective for hormone-dependent breast cancers and estrogen-dependent diseases.

Lessons from in-vivo models of castration-resistant prostate cancer

PURPOSE OF REVIEW

Although the treatment of castration-resistant prostate cancer (CRPC) has benefited from the use of increasingly potent androgen synthesis inhibitors and androgen receptor (AR) antagonists, it is only marginally effective. There is therefore a critical need for a better understanding of the mechanisms underlying the CRPC development and more effective therapeutic approaches. Here, we focus on the advancements reported in the last 18 months, particularly with regard to the mechanisms of castration resistance and potential therapeutic targets emerging from the studies with in-vivo models.

RECENT FINDINGS

Recent findings indicate that AR-dependent mechanisms, for example, increased expression of CYP17A1 and AR splice variants, play important roles in in-vivo castration resistance to new antiandrogens and androgen synthesis inhibitors. Whereas current therapeutic approaches focus on AR-dependent CRPC, studies based on genetically engineered mouse models indicate that castration resistance can develop in the absence of robust AR signaling. Furthermore, increasing evidence suggests that cellular plasticity of prostate adenocarcinoma allows AR-independent CRPC development via various adaptive mechanisms.

SUMMARY

Significant progress has been made in the understanding of AR-dependent and AR-independent mechanisms involved in the development of CRPC. This may lead to identification of new therapeutic targets and improved therapy.

Management of hormone-sensitive metastatic prostate cancer

Targeting gonadal androgen synthesis (often in conjunction with blockade of androgen receptor) is the cornerstone of treatment of hormone-sensitive metastatic prostate cancer (HSPC). Despite the failure of androgen deprivation therapy, most tumors maintain some dependence on androgen or androgen receptor signaling for proliferation. This article reviews the current standard of care for metastatic HSPC, mechanisms of treatment resistance, novel drugs targeting the androgen signaling pathway, biomarkers predicting response to treatment and survival, future directions, and ongoing clinical trials in HSPC.

Targeting the adrenal gland in castration-resistant prostate cancer: a case for orteronel, a selective CYP-17 17,20-lyase inhibitor

Androgen and the androgen receptor (AR) pathway remain the key targets for emerging new therapies against castration-resistant prostate cancer (CRPC). Adrenal androgens and intratumoral testosterone production appear to be sufficient to activate AR in the castration-resistant setting. This process re-engages AR and allows it to continue to be the primary target responsible for prostate cancer progression. Adrenal androgen production can be blocked by inhibiting cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17), a key enzyme for androgen synthesis in adrenal glands and peripheral tissues. Therapeutic CYP17 inhibition by ketoconazole or by the recently approved adrenal inhibitor abiraterone acetate is the only available choice to target this pathway in CRPC. A new CYP17 inhibitor, with more selective inhibition of 17,20-lyase over 17α-hydroxylase, orteronel (TAK-700), is currently undergoing phase III clinical trials in pre- and postchemotherapy CRPC. In a completed phase II trial in CRPC patients, orteronel demonstrated its efficacy by lowering the levels of circulating androgens, reducing prostate-specific antigen (PSA) levels, and decreasing the levels of circulating tumor cells. Ongoing studies evaluating orteronel in CRPC will further define its safety and role in the management of this disease.

Castration-resistant prostate cancer: from new pathophysiology to new treatment

CONTEXT

Until recently, the only approved agent for metastatic castration-resistant prostate cancer (mCRPC) was docetaxel chemotherapy. But over the last 5 years, significant advances in the field have led to the approval of five new agents, each with different mechanisms of action and demonstrating improved overall survival in separate randomized phase 3 trials. Many of these novel agents are now also being evaluated in earlier stages of the disease, which may ultimately lead to even better outcomes.

OBJECTIVE

To summarize the current literature on the management of mCRPC with a particular focus on novel chemotherapy approaches, hormonal approaches, immunotherapy, and radiopharmaceuticals showing survival benefits in phase 3 clinical trials. Emerging therapies in late stages of development are also discussed briefly.

EVIDENCE ACQUISITION

A comprehensive search of PubMed, identified studies pertaining to novel therapies evaluated in mCRPC since the initial approval of docetaxel in 2004. Abstracts from major international meetings were hand searched to identify studies of novel agents in late stage development in mCRPC. The Clinical Trials.gov database was used to find ongoing clinical trials in the area of mCRPC. A detailed search of each new agent was also performed to ensure that additional trials of these agents in other stages of the disease were included where relevant.

EVIDENCE SYNTHESIS

The main agents discussed are the androgen synthesis inhibitor abiraterone acetate, the androgen receptor inhibitor enzalutamide, the novel taxane chemotherapy cabazitaxel, the immunotherapy sipuleucel-T, and the radiopharmaceutical radium 223. Other emerging agents and a brief discussion of negative phase 3 results are also included.

CONCLUSIONS

It is a very exciting time in the field of mCRPC, where therapeutic advances have improved outcomes in this disease, although once metastatic overall median survival remains a dismal 2-3 years. The key now will be to understand how best to use these new agents, understand the mechanisms of resistance to them, continue to develop novel treatment strategies, and ultimately test these agents earlier in the disease when cure may be possible.

Novel therapies for the treatment of advanced prostate cancer

In recent years, great success has been achieved on many fronts in the treatment of men with metastatic castration-resistant prostate cancer (CRPC), including novel chemotherapeutics, immunotherapies, bone microenvironment-targeted agents, and hormonal therapies. Numerous agents are currently in early-phase clinical trial development for the treatment of advanced prostate cancer. These novel therapies target several areas of prostate tumor biology, including the upregulation of androgen signaling and biosynthesis, critical oncogenic intracellular pathways, epigenetic alterations, and cancer immunology. Importantly, the characterization of the prostate cancer genome offers the potential to exploit conserved genetic alterations, which may increase the efficacy of these targeted therapies. Predictive and prognostic biomarkers are urgently needed to maximize therapeutic efficacy and safety of these promising new treatments options in prostate cancer.

Systematic structure modifications of multitarget prostate cancer drug candidate galeterone to produce novel androgen receptor down-regulating agents as an approach to treatment of advanced prostate cancer

As part of our program to explore the influence of small structural modifications of our drug candidate 3β-(hydroxy)-17-(1H-benzimidazol-1-yl)androsta-5,16-diene (galeterone, 5) on the modulation of the androgen receptor (AR), we have prepared and evaluated a series of novel C-3, C-16, and C-17 analogues. Using structure activity analysis, we established that the benzimidazole moiety at C-17 is essential and optimal and also that hydrophilic and heteroaromatic groups at C-3 enhance both antiproliferative (AP) and AR degrading (ARD) activities. The most potent antiproliferative compounds were 3β-(1H-imidazole-1-carboxylate)-17-(1H-benzimidazol-1-yl)androsta-5,16-diene (47), 3-((EZ)-hydroximino)-17-(1H-benzimidazol-1-yl)androsta-4,16-diene (36), and 3β-(pyridine-4-carboxylate)-17-(1H-benzimidazol-1-yl)androsta-5,16-diene (43), with GI50 values of 0.87, 1.91, and 2.57 μM, respectively. Compared to 5, compound 47 was 4- and 8-fold more potent with respect to AP and ARD activities, respectively. Importantly, we also discovered that our compounds, including 5, 36, 43, and 47, could degrade both full-length and truncated ARs in CWR22rv1 human prostate cancer cells. With these activities, they have potential for development as new drugs for the treatment of all forms of prostate cancer.

Takeda's Oncology Discovery Strategy

Takeda's Oncology Discovery Strategy is tightly integrated and focused on first and fast-best-in-class products and product combinations. Core areas of expertise include hormones, protein homeostasis, biotherapeutics and signal transduction. Strategic imperatives for research success are understanding of unmet needs, focus on biological expertise in foundational areas of leadership and flexibility to adapt to new information.

Effect of a novel 17,20-lyase inhibitor, orteronel (TAK-700), on androgen synthesis in male rats

Endogenous androgens play a role in the development and progression of prostate cancer (PC), thus androgen suppression may offer an effective therapeutic strategy for this disease. Orteronel (TAK-700), 6-[(7S)-7-hydroxy-6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-7-yl]-N-methyl-2-naphthamide, is a novel, non-steroidal, selective inhibitor of the 17,20-lyase activity of CYP17A--a key enzyme in the production of steroidal hormones--and is being developed as a therapy for PC. The purpose of this study was to elucidate the inhibitory activity of orteronel, in particular its specificity for androgen synthesis enzymes, in male rats--an androgen-synthesis model that largely reflects this pathway in humans. Orteronel inhibited 17,20-lyase activity in rats with an IC(50) of 1200 nM but did not inhibit 17α-hydroxylase or 11β-hydroxylase (CYP11B1) activity in rats at concentrations up to 10 μM. In cellular steroidogenesis assays using rat testicular cells, orteronel suppressed testosterone and androstenedione production with an IC(50) of 640 nM and 210 nM, respectively, but did not suppress either corticosterone or aldosterone production in rat adrenal cells at concentrations up to 30 μM. In addition, serum testosterone and androstenedione levels in human chorionic gonadotropin-injected hypophysectomized rats were significantly reduced by single oral administration of orteronel at a dose of 30 mg/kg (both p ≤ 0.01); serum corticosterone and aldosterone levels in ACTH-injected hypophysectomized rats did not result in significant differences compared with controls, following orteronel administration at doses up to 300 mg/kg. Serum testosterone levels in intact male rats were significantly reduced by orteronel 4h after dosing at 100mg/kg (p ≤ 0.01); testosterone levels showed a tendency to recover afterward. In intact male rats, the weight of the prostate glands and seminal vesicles was decreased in a dose-dependent manner following multiple doses of orteronel at 37.5, 150, and 600 mg/kg, TID for 4 days. The reversibility of orteronel was further confirmed using a human adrenocortical tumor cell line. In summary, orteronel is a selective and reversible 17,20-lyase inhibitor, and decreases the weight of androgen-dependent organs in male rats. Our data suggests that orteronel would therefore be effective for androgen-dependent disorders such as PC.

The changing landscape in the treatment of metastatic castration-resistant prostate cancer

The past few years have brought increasing advances in the therapeutic management of metastatic castration-resistant prostate cancer with the approval of several agents, including vaccine therapy with sipuleucel-T, second-line chemotherapy with cabazitaxel, the bone-targeted pharmaceutical denosumab, and the novel antiandrogen therapy abiraterone acetate. There are ongoing developments with other agents in the pipeline such as MDV3100 and alpharadin that have shown promising results. This review describes the clinical trials that brought about the drug approvals of various agents and offers some insights regarding a rational approach to optimal treatment sequencing for these drugs since national guidelines are currently lacking.

Current and emerging treatments in the management of castration-resistant prostate cancer

Historically, patients diagnosed with castration-resistant prostate cancer (CRPC) have had poor survival rates. In recent years there have been significant advances in the treatment of CRPC. In addition to cytotoxic chemotherapy, treating physicians and their patients now have the option of several new agents that target not only androgen- and cytotoxic-mediated pathways, but also the patient's own immune system. In this review, we discuss the existing US FDA-approved therapies, a wide range of experimental treatments that are currently in development, and also palliative options for patients with symptoms secondary to metastatic disease. We also discuss the progression-free survival, overall survival, PSA levels and other end points used in clinical trials in order to evaluate and compare novel therapeutic options for CRPC. Currently, docetaxel and sipuleucel-T are the first line treatment options for patients with CRPC; approved second-line treatments for first line treatment failure are limited to cabazitaxel and abiraterone acetate. Recently, a few experimental agents, MDV3100 and radium-223, have demonstrated efficacy in improving overall survival in patients who had previously failed chemotherapy. These agents, and possibly others introduced in this review, are positioned to change the treatment landscape for CRPC.

Moving toward personalized medicine in castration-resistant prostate cancer

Recent advances in research technologies have allowed improved molecular characterization of castration-resistant prostate cancer (CRPC). These efforts hold promise for development of therapies that target alterations unique to an individual patient's prostate cancer. Targets include androgens and the androgen receptor pathway, pathways associated with hormone-resistant disease, and the immune system. In aggregate, this will allow physicians to choose treatments based on a particular tumor profile. As these approaches are developed, CRPC treatment is becoming an example of truly personalized medicine.

New developments in castrate-resistant prostate cancer

Castrate-resistant prostate cancer (CRPC) occurs when disease progresses in the presence of castrate levels of androgens and remains sensitive to further hormonal manipulation. For many years the treatment of CRPC was limited to the use of docetaxel for metastatic disease. However, this has recently changed with the approval of several new agents. Sipuleucel-T, an immunotherapeutic vaccine, is now available in the US for patients with non-metastatic CRPC and abiraterone, an oral enzyme inhibitor of androgen biosynthesis, as well as cabazitaxel, a cytotoxic chemotherapeutic, have been approved for the treatment of metastatic CRPC. Also, denosumab, a subcutaneous antibody, is now an option for the treatment of patients with CRPC with bone metastases, in addition to zoledronic acid, an intravenous bisphosphonate. Further treatment advances for metastatic CRPC therapeutics are in late stage phase III development. These include therapies affecting the androgen receptor (MDV3100) as well as additional immune-based therapeutics, PROSTVAC and ipilimumab. A broad range of agents is also emerging under the term targeted therapies. The endothelin-A receptor antagonist zibotentan, the tyrosine kinase inhibitors dasatinib, sorafenib and cabozantinib, the anti-angiogenic agent aflibercept, and the clusterin inhibitor custirsen, are all currently being tested for efficacy in metastatic CRPC. The mechanism of action of these and other promising agents are discussed alongside current therapeutic options and their potential place in the treatment landscape for CRPC is considered.

Overcoming castration resistance in prostate cancer

PURPOSE OF REVIEW

Recent advances in our understanding of the androgen axis signaling pathway have led to the development of therapeutic strategies to overcome the state of 'castration resistance' in prostate cancer. In this review, we examine the mechanisms of castration resistance, as well as recently reported and ongoing clinical studies, which will further identify therapeutic opportunities for novel therapeutics targeting the androgen-signaling axis in advanced prostate cancer.

RECENT FINDINGS

As evidenced by recently reported positive phase III clinical trials, secondary hormonal agents such as abiraterone and MDV3100 may still be very effective in the treatment of castration-resistant prostate cancer, even after the use of docetaxel chemotherapy.

SUMMARY

Novel agents targeting this pathway have demonstrated a proof of principle that overcoming castration resistance is possible, leading to significant changes in the landscape of treatment in this disease. The optimal combination, sequence, and pattern of use in these novel therapies will be the focus of clinical research in the near future.

New therapy targeting differential androgen receptor signaling in prostate cancer stem/progenitor vs. non-stem/progenitor cells

The androgen deprivation therapy (ADT) to systematically suppress/reduce androgens binding to the androgen receptor (AR) has been the standard therapy for prostate cancer (PCa); yet, most of ADT eventually fails leading to the recurrence of castration resistant PCa. Here, we found that the PCa patients who received ADT had increased PCa stem/progenitor cell population. The addition of the anti-androgen, Casodex, or AR-siRNA in various PCa cells led to increased stem/progenitor cells, whereas, in contrast, the addition of functional AR led to decreased stem/progenitor cell population but increased non-stem/progenitor cell population, suggesting that AR functions differentially in PCa stem/progenitor vs. non-stem/progenitor cells. Therefore, the current ADT might result in an undesired expansion of PCa stem/progenitor cell population, which explains why this therapy fails. Using various human PCa cell lines and three different mouse models, we concluded that targeting PCa non-stem/progenitor cells with AR degradation enhancer ASC-J9 and targeting PCa stem/progenitor cells with 5-azathioprine and γ-tocotrienol resulted in a significant suppression of the tumors at the castration resistant stage. This suggests that a combinational therapy that simultaneously targets both stem/progenitor and non-stem/progenitor cells will lead to better therapeutic efficacy and may become a new therapy to battle the PCa before and after castration resistant stages.

The evolving paradigm of second-line hormonal therapy options for castration-resistant prostate cancer

PURPOSE OF REVIEW

The review examines recent advances in second-line hormonal therapy for the treatment of castrate-resistant prostate cancer (CRPC).

RECENT FINDINGS

Recent data highlight the continued importance of androgen signaling in CRPC. These findings have spurred the development of novel inhibitors of adrenal and intra-tumoral androgen synthesis and novel androgen signaling inhibitors with activity in CRPC. In the past year abiraterone acetate, a CYP17 (17α-hydroxylase/17, 20 lyase) inhibitor, received US FDA approval for use in the treatment of metastatic CRPC in patients previously treated with docetaxel. Additionally, the novel androgen signaling inhibitor MDV3100 has been reported to confer a survival advantage compared to placebo in the same patient population. Here we review the scientific rationale for targeting androgen signaling in CRPC and the recent pivotal trials that support the use of novel second-line hormonal therapies. Additionally, we summarize ongoing preclinical and clinical efforts to ascertain and overcome mechanisms of resistance.

SUMMARY

Novel inhibitors of extra-gonadal androgen synthesis and androgen receptor function demonstrate the continued importance of androgen signaling in CRPC. These agents have improved clinical outcomes for patients with metastatic CRPC.

Development and validation of a highly sensitive LC–ESI-MS/MS method for the determination of Orteronel® (TAK-700) in rat plasma: application to a pharmacokinetic study

Background: A highly sensitive, specific and high-throughput LC–ESI-MS/MS method in the positive mode has been developed and validated for the quantitation of Orteronel® (TAK-700) in rat plasma using YM-55208 as an internal standard. Results: The assay procedure involves extraction of Orteronel and internal standard from rat plasma with liquid–liquid extraction method. Chromatographic separation was achieved using an isocratic mobile phase at a flow rate of 0.6 ml/min on an Atlantis dC18 column with a total run time of 2.5 min. The MS/MS ion transitions monitored were m/z 308.4→95.0 for Orteronel and m/z 262.3→194.2 for IS. Method validation was performed as per US FDA guidelines. The LLOQ achieved was 0.42 ng/ml and the linearity range extended from 0.42 to 814 ng/ml. Conclusion: The results met the acceptance criteria. The validated method was successfully applied to characterize the pharmacokinetic parameters of Orteronel in rat plasma.

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

Surgical or pharmacologic methods to control gonadal androgen biosynthesis are effective approaches in the treatment of a variety of non-neoplastic and neoplastic diseases. For example, androgen ablation and its consequent reduction in circulating levels of testosterone is an effective therapy for advanced prostate cancers. Unfortunately, the therapeutic effectiveness of this approach is often temporary because of disease progression to the 'castration resistant' (CRPC) state, a situation for which there are limited treatment options. One mechanism thought to be responsible for the development of CRPC is extra-gonadal androgen synthesis and the resulting impact of these residual extra-gonadal androgens on prostate tumor cell proliferation. An important enzyme responsible for the synthesis of extra-gonadal androgens is CYP17A1 which possesses both 17,20-lyase and 17-hydroxylase catalytic activities with the 17,20-lyase activity being key in the androgen biosynthetic process. Orteronel (TAK-700), a novel, selective, and potent inhibitor of 17,20-lyase is under development as a drug to inhibit androgen synthesis. In this study, we quantified the inhibitory activity and specificity of orteronel for testicular and adrenal androgen production by evaluating its effects on CYP17A1 enzymatic activity, steroid production in monkey adrenal cells and human adrenal tumor cells, and serum levels of dehydroepiandrosterone (DHEA), cortisol, and testosterone after oral dosing in castrated and intact male cynomolgus monkeys. We report that orteronel potently suppresses androgen production in monkey adrenal cells but only weakly suppresses corticosterone and aldosterone production; the IC(50) value of orteronel for cortisol was ~3-fold higher than that for DHEA. After single oral dosing, serum levels of DHEA, cortisol, and testosterone were rapidly suppressed in intact cynomolgus monkeys. In castrated monkeys treated twice daily with orteronel, suppression of DHEA and testosterone persisted throughout the treatment period. In both in vivo models and in agreement with our in vitro data, suppression of serum cortisol levels following oral dosing was less than that seen for DHEA. In terms of human CYP17A1 and human adrenal tumor cells, orteronel inhibited 17,20-lyase activity 5.4 times more potently than 17-hydroxylase activity in cell-free enzyme assays and DHEA production 27 times more potently than cortisol production in human adrenal tumor cells, suggesting greater specificity of inhibition between 17,20-lyase and 17-hydroxylase activities in humans vs monkeys. In summary, orteronel potently inhibited the 17,20-lyase activity of monkey and human CYP17A1 and reduced serum androgen levels in vivo in monkeys. These findings suggest that orteronel may be an effective therapeutic option for diseases where androgen suppression is critical, such as androgen sensitive and CRPC.