Persistence of ligand-mediated androgen receptor signaling has been documented in castration-resistant prostate cancers (CRPCs). Abiraterone acetate (AA) is a potent and selective inhibitor of CYP17, which is required for androgen biosynthesis in the testes, adrenal glands, and prostate tissue. This trial evaluated the efficacy and safety of AA in combination with prednisone to reduce the symptoms of secondary hyperaldosteronism that can occur with AA monotherapy.
Patients and Methods
Fifty-eight men with progressive metastatic CRPC who experienced treatment failure with docetaxel-based chemotherapy received AA (1,000 mg daily) with prednisone (5 mg twice daily). Twenty-seven (47%) patients had received prior ketoconazole. The primary outcome was ≥ 50% prostate-specific antigen (PSA) decline, with objective response by Response Evaluation Criteria in Solid Tumors (RECIST) criteria, and changes in Eastern Cooperative Oncology Group (ECOG) performance status (PS) and circulating tumor cell (CTC) numbers. Safety was also evaluated.
A ≥ 50% decline in PSA was confirmed in 22 (36%) patients, including 14 (45%) of 31 ketoconazole-naïve and seven (26%) of 27 ketoconazole-pretreated patients. Partial responses were seen in four (18%) of 22 patients with RECIST-evaluable target lesions. Improved ECOG PS was seen in 28% of patients. Median time to PSA progression was 169 days (95% CI, 82 to 200 days). CTC conversions with treatment from ≥ 5 to < 5 were noted in 10 (34%) of 29 patients. The majority of AA-related adverse events were grade 1 to 2, and no AA-related grade 4 events were seen.
AA plus prednisone was well tolerated, with encouraging antitumor activity in heavily pretreated CRPC patients. The incidence of mineralocorticoid-related toxicities (hypertension or hypokalemia) was reduced by adding low-dose prednisone. The combination of AA plus prednisone is recommended for phase III investigations.
Preliminary data suggests a potential decreased benefit of docetaxel in metastatic castration-resistant prostate cancer (mCRPC) patients previously treated with abiraterone acetate, a novel androgen synthesis inhibitor (ASI). CALGB 90401 (Alliance), a phase 3 trial of mCRPC patients treated with docetaxel-based chemotherapy, offered the opportunity to evaluate effect of prior ketoconazole, an earlier generation ASI, on clinical outcomes following docetaxel.
CALGB 90401 randomized 1050 men with chemotherapy-naïve, mCRPC to treatment with docetaxel and prednisone with either bevacizumab or placebo. 1005 men (96%) had data available regarding prior ketoconazole therapy. The effect of prior ketoconazole on overall survival (OS), progression-free survival (PFS), PSA decline, and objective response rate (ORR) observed was assessed using proportional hazards and Poisson regression method adjusted for validated prognostic factors and treatment arm.
Baseline characteristics between patients with (N=277) and without (N=728) prior ketoconazole therapy were similar. There were no statistically significant differences between patients with and without prior ketoconazole therapy with respect to OS (median OS 21.1 vs. 22.3 months, stratified log-rank p-value=0.635); PFS (median PFS 8.1 vs. 8.6 months, stratified log-rank p-value=0.342); ≥50% PSA decline (61% vs. 66%, relative risk=1.09, adjusted p-value=0.129); or ORR (39% vs. 43%, relative risk=1.11, adjusted p-value=0.366).
As measured by OS, PFS, PSA and ORR, there is no evidence that prior treatment with ketoconazole impacts clinical outcomes in mCRPC patients treated with subsequent docetaxel-based therapy. Prospective studies are needed to assess for potential cross-resistance with novel ASIs and to define the optimal sequence of therapy in mCRPC.
Adrenal/intratumoral androgen biosynthesis contributes to ligand-dependent androgen receptor activation in metastatic castration-resistant prostate cancer (mCRCP). Compounds targeting CYP-17 hydroxylase and lyase, as ketoconazole and abiraterone, block adrenal/intratumoral androgen biosynthesis, and are used as sequential endocrine approaches in mCRCP. We aimed to describe contemporary experience and association of clinical factors with Prostate specific antigen (PSA) response and disease progression, in mCRPC progressing on GnRH-agonist, antiandrogen, antiandrogen withdrawal, and treated with ketoconazole.
Data were retrospectively analyzed in all mCRPC patients treated with ketoconazole. Patients continued GnRH-agonist, and treated with ketoconazole 200–400 mg 3× a day until dose-limiting toxicity or disease progression. A multivariate cox regression model was used to identify clinical factors associated with PSA response and disease progression.
From 1999 to 2010, 114 mCRPC patients were treated with ketoconazole. With a median follow-up time of 31 months (range 5–129), 25 patients (22%) had grade 3/4 toxicity, most commonly fatigue, abdominal discomfort, nausea, and dizziness. Sixty-one patients (54%) had ≥50% PSA decline. Median time to progression was 8 months (range 1–129). Factors associated with PSA response and disease progression were response to prior antiandrogen (≥6 vs. <6 months), pre-treatment PSADT (≥3 vs. <3 months) and extent of disease (limited-axial skeleton and/or nodal vs. extensive-appendicular skeleton and/or visceral).
Ketoconazole is effective and safe in mCRPC. Prior response to antiandrogen, pre-treatment PSADT, and disease extent are associated with PSA response and disease progression, and further supports a therapeutic role in suppressing adrenal androgens in mCRPC.
disease progression; ketoconazole; metastatic castration-resistant prostate cancer; PSA response
Abiraterone is an oral inhibitor of CYP17, essential for androgen biosynthesis. This multicenter study assessed its efficacy in patients with CRPC without prior exposure to chemotherapy or CYP17 targeted therapy, and assessed the frequency of interpretation of bone scans discordant with PSA and clinical response.
Patients and Methods
33 patients received abiraterone acetate 1000 mg daily with prednisone 5 mg twice daily in continuous 28-day cycles. Patients were evaluated monthly for efficacy and safety. Bone scan flare was defined as the combination, after 3 months of therapy, of an interpreting radiologist's report indicating “disease progression” in the context of a ≥50% decline in PSA, with scan improvement 3 months later.
A ≥ 50% PSA decline at week 12 was confirmed in 22/33 (67%) patients. PSA declines of ≥ 50% were seen in 26 (79%) patients. Undetectable PSA levels (≤ 0.1 ng/mL) occurred in 2 patients. Median time on therapy and time to PSA progression are 63 and 71 weeks, respectively. Twenty three patients were evaluable for bone scan flare. Progression was indicated in the radiologist's report in 12/23 (52 %), and 10/12 subsequently showed improvement. As prospectively defined, bone scan flare was observed in 10/23 (43.5%) evaluable patients or 10/33 (30%) enrolled patients. Adverse events were typically grade 1/2 and consistent with prior published abiraterone reports.
Clinical response to abiraterone acetate plus prednisone was frequent and durable in men with metastatic CRPC progressing on hormonal therapy with over half of patients on therapy > 1 year. Further investigation is needed to clarify the potential confounding effect of the frequently occurring bone scan flare phenomena on patient management and interpretation of clinical trial results.
abiraterone acetate; castration-resistant prostate cancer; CRPC; hormone-resistant prostate cancer; therapy; efficacy
It has been postulated that castration-resistant prostate cancer (CRPC) commonly remains hormone dependent. Abiraterone acetate is a potent, selective, and orally available inhibitor of CYP17, the key enzyme in androgen and estrogen biosynthesis.
Patients and Methods
This was a phase I/II study of abiraterone acetate in castrate, chemotherapy-naive CRPC patients (n = 54) with phase II expansion at 1,000 mg (n = 42) using a two-stage design to reject the null hypothesis if more than seven patients had a prostate-specific antigen (PSA) decline of ≥ 50% (null hypothesis = 0.1; alternative hypothesis = 0.3; α = .05; β = .14). Computed tomography scans every 12 weeks and circulating tumor cell (CTC) enumeration were performed. Prospective reversal of resistance at progression by adding dexamethasone 0.5 mg/d to suppress adrenocorticotropic hormone and upstream steroids was pursued.
A decline in PSA of ≥ 50% was observed in 28 (67%) of 42 phase II patients, and declines of ≥ 90% were observed in eight (19%) of 42 patients. Independent radiologic evaluation reported partial responses (Response Evaluation Criteria in Solid Tumors) in nine (37.5%) of 24 phase II patients with measurable disease. Decreases in CTC counts were also documented. The median time to PSA progression (TTPP) on abiraterone acetate alone for all phase II patients was 225 days (95% CI, 162 to 287 days). Exploratory analyses were performed on all 54 phase I/II patients; the addition of dexamethasone at disease progression reversed resistance in 33% of patients regardless of prior treatment with dexamethasone, and pretreatment serum androgen and estradiol levels were associated with a probability of ≥ 50% PSA decline and TTPP on abiraterone acetate and dexamethasone.
CYP17 blockade by abiraterone acetate results in declines in PSA and CTC counts and radiologic responses, confirming that CRPC commonly remains hormone driven.
High-dose ketoconazole and docetaxel have shown activity as single agents against castration-resistant prostate cancer (CRPC). The goal of this phase I study was to determine the maximum tolerated doses, side effects, and pharmacokinetic interaction of coadministered docetaxel and ketoconazole.
Patients with metastatic CRPC received weekly docetaxel for 3 of every 4 weeks, plus daily ketoconazole. Pharmacokinetic studies were performed on day 1 (docetaxel alone) and day 16 (after ketoconazole).
The study enrolled 42 patients at 9 different dose levels. The combination regimens investigated included docetaxel weekly for three weeks out of four escalating from 5 to 43 mg/m2, with starting doses of ketoconazole of 600, 800, or 1200 mg/day. Declines in prostate-specific antigen of ≥ 50% were seen in 62% of patients. Of 25 patients with soft tissue disease, 7 (28%) had partial response. Median overall survival was 22.8 months, and was significantly greater in docetaxel-naïve patients than in patients pretreated with docetaxel (36.8 vs. 10.3 months; P = 0.0001). The most frequently observed adverse events were anemia, edema, fatigue, diarrhea, nausea, sensory neuropathy, and elevated liver function tests. The fractional change in docetaxel clearance correlated significantly with ketoconazole exposure (P < 0.01). Concomitant ketoconazole increased docetaxel exposure 2.6-fold with 1200 mg/day, 1.6-fold with 800 mg/day, and 1.3- to 1.5-fold with 600 mg/day.
Results suggest that the combination of weekly docetaxel and ketoconazole has significant antitumor activity in CRPC with manageable toxicities. The extremely long survival in the docetaxel-naïve cohort (36.8 months) warrants additional larger trials of docetaxel with ketoconazole or possibly CYP17A1 inhibitors such as abiraterone.
castration-resistant prostate cancer; docetaxel; ketoconazole; drug-drug interaction; CYP3A4
The COU-AA-301 trial showed that abiraterone acetate (abiraterone), an oral cytochrome p450 CYP17 inhibitor, improved survival for men with metastatic castration-resistant prostate cancer (mCRPC) progressing after docetaxel. To better understand the non-clinical trial experience with abiraterone, we undertook a multicentre retrospective analysis of Canadian mCRPC patients treated with abiraterone.
Consecutive patients with mCRPC who received abiraterone post-docetaxel were identified using centralized pharmacy records. These patients came from 5 Canadian tertiary cancer centres. Patients who received abiraterone for approved indications were included. Demographics, prognostic factors, treatment outcomes and adverse events were abstracted.
We included 187 patients who initiated abiraterone between January 2011 and June 2012. The median age at diagnosis and abiraterone start was 65 and 73 years, respectively. Seventy-three (39%) patients had metastatic disease at diagnosis. The Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, 2 and 3 was noted in 17, 96, 39 and 8 patients, respectively. The median prostate-specific antigen (PSA) at abiraterone start was 132, with a median PSA doubling time of 2.8 months. The median follow-up of patients still on active follow-up was 13 months. The proportion of patients achieving a ≥50% PSA reduction was 64/177 (36%). PSA progression-free survival was 3.5 months (95% confidence interval [CI], 3.0, 4.0). Median overall survival from start of abiraterone was 11 months (95% CI, 8.0, 13) and 38 months (95% CI, 31, 41) from date of mCRPC. Anemia and fatigue were the most commonly reported adverse events.
This study carries the inherent limitations of a retrospective chart review. The outcomes in this series of men treated with abiraterone in a non-trial setting were expected, considering previous clinical trials. Our results, therefore, support the generalizability of the COU-AA-301 study results.
Androgen deprivation therapy remains the single most effective treatment for the initial therapy of advanced prostate cancer, but is uniformly marked by progression to castration-resistant prostate cancer (CRPC). Residual tumor androgens and androgen axis activation are now recognized to play a prominent role in mediating CRPC progression. Despite suppression of circulating testosterone to castrate levels, castration does not eliminate androgens from the prostate tumor microenvironment and residual androgen levels are well within the range capable of activating the androgen receptor (AR) and AR-mediated gene expression. Accordingly, therapeutic strategies that more effectively target production of intratumoral androgens are necessary. The introduction of abiraterone, a potent suppressor of cytochrome P450 17 α-hydroxysteroid dehydrogenase-mediated androgen production, has heralded a new era in the hormonal treatment of men with metastatic CRPC. Herein, the androgen and AR-mediated mechanisms that contribute to CRPC progression and establish cytochrome P450 17 α-hydroxysteroid dehydrogenase as a critical therapeutic target are briefly reviewed. The mechanism of action and pharmacokinetics of abiraterone are reviewed and its recently described activity against AR and 3-β-hydroxysteroid dehydrogenase is discussed. The Phase I and II data initially demonstrating the efficacy of abiraterone and Phase III data supporting its approval for patients with metastatic CRPC are reviewed. The safety and tolerability of abiraterone, including the incidence and management of side effects and potential drug interactions, are discussed. The current place of abiraterone in CRPC therapy is reviewed and early evidence regarding cross-resistance of abiraterone with taxane therapy, mechanisms of resistance to abiraterone, and observations of an abiraterone withdrawal response are presented. Future directions in the use of abiraterone, including optimal dosing strategies, the role of abiraterone in earlier disease settings, including castration sensitive, biochemically recurrent, or localized disease, and the rationale for combinatorial treatment strategies of abiraterone with enzalutamide and other targeted agents are also discussed.
castration-resistant; abiraterone; CYP17A; androgen; intracrine
Abiraterone acetate, an androgen biosynthesis inhibitor, improves overall survival (OS) in metastatic castration-resistant prostate cancer (mCRPC) post-chemotherapy. Many mCRPC patients never receive chemotherapy and thus cannot benefit from abiraterone acetate; we evaluated this agent in mCRPC patients who had not received chemotherapy.
In this double-blind study, 1088 patients were randomized 1:1 to abiraterone acetate (1000 mg) plus prednisone (5 mg twice daily) or placebo plus prednisone. Co-primary end points were radiographic progression-free survival (rPFS) and OS. Secondary end points measured clinically relevant landmarks of mCRPC progression. Patient-reported outcomes included pain progression and quality of life.
The study was unblinded after a planned interim analysis (IA) at 43% of OS events. Treatment with abiraterone acetate-prednisone resulted in a 57% reduction in the risk of radiographic progression or death (hazard ratio [HR], 0.43; 95% confidence interval [CI]: 0.35 to 0.52; P<0.001; 13% OS events IA) and an estimated 25% decrease in the risk of death (HR, 0.75; 95% CI: 0.61 to 0.93; P=0.009; 43% OS events IA). Secondary end points supported superiority of abiraterone acetate-prednisone: time to cytotoxic chemotherapy initiation, opiate use for cancer-related pain, prostate-specific antigen progression (all P<0.001) and performance status deterioration (P=0.005). Self-reported time to pain progression and patient functional status degradation favored abiraterone acetate-prednisone (P=0.05 and P=0.003). Grade 3/4 mineralocorticoid-related adverse events and liver function test abnormalities were more common with abiraterone acetate-prednisone.
Abiraterone acetate produces OS and rPFS benefits, as well as significant delays in clinical deterioration and initiation of chemotherapy, in mCRPC.
Abiraterone acetate; prednisone; metastatic castration-resistant prostate cancer; androgen; CYP17
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.
androgen synthesis; castration-resistant prostate cancer; treatment
We analyzed the potential of abiraterone acetate (henceforth abiraterone) to reduce androgen levels below lower limits of quantification (LLOQ) and explored the association with changes in PSA decline in metastatic castration-resistant prostate cancer (mCRPC) patients.
COU-AA-301 is a 2:1 randomized, double-blind, placebo-controlled study comparing abiraterone (1000 mg q.d.) plus low-dose prednisone (5 mg b.i.d.) with placebo plus prednisone in mCRPC patients post docetaxel. Serum testosterone, androstenedione and dehydroepiandrosterone sulfate from baseline to week 12 were measured by novel ultrasensitive two-dimensional liquid chromatography coupled to tandem mass spectrometry assays in a subset of subjects in each arm (abiraterone plus prednisone, n=80; prednisone, n=38). The association between PSA response (⩽50% baseline) and undetectable androgens (week 12 androgen level below LLOQ) was analyzed using logistic regression.
A significantly greater reduction in serum androgens was observed with abiraterone plus prednisone versus prednisone (all P⩽0.0003), reaching undetectable levels for testosterone (47.2% versus 0%, respectively). A positive association was observed between achieving undetectable serum androgens and PSA decline (testosterone: odds ratio=1.54; 95% confidence interval: 0.546–4.347). Reduction of androgens to undetectable levels did not occur in all patients achieving a PSA response, and a PSA response did not occur in all patients achieving undetectable androgen levels.
Abiraterone plus prednisone significantly reduced serum androgens, as measured by ultrasensitive assays and was generally associated with PSA response. However, androgen decline did not uniformly predict PSA decline suggesting ligand-independent or other mechanisms for mCRPC progression.
The principal objective of this trial was to evaluate the antitumor activity of abiraterone acetate, an oral, specific, irreversible inhibitor of CYP17 in docetaxel-treated patients with castration-resistant prostate cancer (CRPC).
Patients and Methods
In this multicenter, two-stage, phase II study, abiraterone acetate 1,000 mg was administered once daily continuously. The primary end point was achievement of a prostate-specific antigen (PSA) decline of ≥ 50% in at least seven of 35 patients. Per an attained phase II design, more than 35 patients could be enrolled if the primary end point was met. Secondary objectives included: PSA declines of ≥ 30% and ≥ 90%; rate of RECIST (Response Evaluation Criteria in Solid Tumors) responses and duration on study; time to PSA progression; safety and tolerability; and circulating tumor cell (CTC) enumeration.
Docetaxel-treated patients with CRPC (N = 47) were enrolled. PSA declines of ≥ 30%, ≥ 50% and ≥ 90% were seen in 68% (32 of 47), 51% (24 of 47), and 15% (seven of 47) of patients, respectively. Partial responses (by RECIST) were reported in eight (27%) of 30 patients with measurable disease. Median time to PSA progression was 169 days (95% CI, 113 to 281 days). The median number of weeks on study was 24, and 12 (25.5%) of 47 patients remained on study ≥ 48 weeks. CTCs were enumerated in 34 patients; 27 (79%) of 34 patients had at least five CTCs at baseline. Eleven (41%) of 27 patients had a decline from at least five to less than 5 CTCs, and 18 (67%) of 27 had a ≥ 30% decline in CTCs after starting treatment with abiraterone acetate. Abiraterone acetate was well tolerated.
Abiraterone acetate has significant antitumor activity in post-docetaxel patients with CRPC. Randomized, phase III trials of abiraterone acetate are underway to define the future role of this agent.
Abiraterone is approved in the European Union in combination with prednisone or prednisolone for the treatment of metastatic castration-resistant prostate cancer. It has been shown to improve survival in selected patients and is most commonly associated with adverse reactions resulting from increased or excessive mineralocorticoid activity. These reactions are generally manageable with basic medical interventions.
Describe the EU regulatory considerations on the benefits of abiraterone in the treatment of prostate cancer.Describe the EU regulatory considerations on the risks of abiraterone in the treatment of prostate cancer and their management.Describe the EU regulatory basis for approving abiraterone for use in the treatment of prostate cancer.
On September 5, 2011, abiraterone was approved in the European Union in combination with prednisone or prednisolone for the treatment of metastatic castration-resistant prostate cancer (CRPC) in adult men whose disease has progressed on or after a docetaxel-based chemotherapy regimen. On December 18, 2012, the therapeutic indication was extended to include the use of abiraterone in combination with prednisone or prednisolone for the treatment of metastatic CRPC in adult men who are asymptomatic or mildly symptomatic after failure of androgen deprivation therapy in whom chemotherapy is not yet clinically indicated. Abiraterone is a selective, irreversible inhibitor of cytochrome P450 17α, an enzyme that is key in the production of androgens. Inhibition of androgen biosynthesis deprives prostate cancer cells from important signals for growth, even in cases of resistance to castration. At the time of European Union approval and in a phase III trial in CRPC patients who had failed at least one docetaxel-based chemotherapy regimen, median overall survival for patients treated with abiraterone was 14.8 months versus 10.9 months for those receiving placebo (hazard ratio, 0.65; 95% confidence interval 0.54–0.77; p < .0001). In a subsequent phase III trial in a similar but chemotherapy-naïve patient population, median radiographic progression-free survival was 16.5 months for patients in the abiraterone treatment arm versus 8.3 months for patients in the placebo arm (hazard ratio, 0.53; 95% confidence interval, 0.45–0.62; p < .0001). Abiraterone was most commonly associated with adverse reactions resulting from increased or excessive mineralocorticoid activity. These were generally manageable with basic medical interventions. The most common side effects (affecting more than 10% of patients) were urinary tract infection, hypokalemia, hypertension, and peripheral edema.
Abiraterone; Prostate cancer; EMA; European Medicines Agency
Abiraterone is a standard treatment for men with castration-resistant prostate cancer (CRPC). We evaluated the antitumour activity of abiraterone following the synthetic oestrogen diethylstilboestrol (DES).
Castration-resistant prostate cancer patients treated with abiraterone were identified. Demographics, response variables and survival data were recorded.
Two-hundred and seventy-four patients received abiraterone, 114 (41.6%) after DES. Pre-chemotherapy abiraterone resulted in ⩾50% PSA declines in 35/41 (85.4%) DES-naïve and 20/27 (74.1%) DES-treated patients. Post-docetaxel abiraterone resulted in ⩾50% PSA declines in 40/113 (35.4%) DES-naïve and 23/81 (28.4%) DES-treated patients. Time to PSA progression was similar regardless of prior DES.
Abiraterone has important antitumour activity in men with CRPC even after DES exposure.
castration-resistant prostate cancer; abiraterone; treatment sequencing; diethylstilboestrol
Persistent androgen signaling is implicated in castrate-resistant prostate cancer (CRPC) progression. This study aimed to evaluate androgen signaling in bone marrow–infiltrating cancer and testosterone in blood and bone marrow and to correlate with clinical observations.
Patients and Methods
This was an open-label, observational study of 57 patients with bone-metastatic CRPC who underwent transiliac bone marrow biopsy between October 2007 and March 2010. Patients received oral abiraterone acetate (1 g) once daily and prednisone (5 mg) twice daily. Androgen receptor (AR) and CYP17 expression were assessed by immunohistochemistry, testosterone concentration by mass spectrometry, AR copy number by polymerase chain reaction, and TMPRSS2-ERG status by fluorescent in situ hybridization in available tissues.
Median overall survival was 555 days (95% CI, 440 to 965+ days). Maximal prostate-specific antigen decline ≥ 50% occurred in 28 (50%) of 56 patients. Homogeneous, intense nuclear expression of AR, combined with ≥ 10% CYP17 tumor expression, was correlated with longer time to treatment discontinuation (> 4 months) in 25 patients with tumor-infiltrated bone marrow samples. Pretreatment CYP17 tumor expression ≥ 10% was correlated with increased bone marrow aspirate testosterone. Blood and bone marrow aspirate testosterone concentrations declined to less than picograms-per-milliliter levels and remained suppressed at progression.
The observed pretreatment androgen-signaling signature is consistent with persistent androgen signaling in CRPC bone metastases. This is the first evidence that abiraterone acetate achieves sustained suppression of testosterone in both blood and bone marrow aspirate to less than picograms-per-milliliter levels. Potential admixture of blood with bone marrow aspirate limits our ability to determine the origin of measured testosterone.
Abiraterone acetate (AA) is an androgen biosynthesis inhibitor shown to prolong life in patients with castration-resistant prostate cancer (CRPC) already treated with chemotherapy. AA treatment results in dramatic declines in prostate-specific antigen (PSA) in some patients and no declines in others, suggesting the presence of molecular determinants of sensitivity in tumors.
To study the role of transmembrane protease, serine 2 (TMPRSS2)–v-ets erythroblastosis virus E26 oncogene homolog (ERG) fusion, an androgen-dependent growth factor, in circulating tumor cells (CTCs) as a biomarker of sensitivity to AA.
Design, setting, and participants
The predictive value of TMPRSS2-ERG status was studied in 41 of 48 men with postchemotherapy-treated CRPC enrolled in sequential phase 2 AA trials.
Patients received AA 1000 mg daily and continuously.
TMPRSS2-ERG status was characterized by a sensitive, analytically valid reverse transcription polymerase chain reaction assay in CTCs enriched from ethylene-diaminetetraacetic acid anticoagulated blood obtained prior to AA treatment. Outcomes were measured by PSA Working Group 1 criteria.
Results and limitations
Standard procedures for specimen acquisition, processing, and testing using the validated TMPRSS2-ERG assay on a multiplex platform gave intra-assay and interassay coefficients of variation <7%. TMPRSS2-ERG fusion was present in 15 of 41 patients (37%), who had a median baseline CTC count of 17 (interquartile range: 7–103 cells per 7.5 ml). A PSA decline ≥50% was observed in 7 of 15 patients (47%) with the fusion and in 10 of 26 patients (38%) without the fusion. Although limited by the low number of patients, a posttherapy CTC count of less than five per 7.5 ml was prognostic for longer survival relative to a CTC count five or more. TMPRSS2-ERG status did not predict a decline in PSA or other clinical outcomes.
Molecular profiles of CTCs with an analytically valid assay identified the presence of the prostate cancer–specific TMPRSS2-ERG fusion but did not predict for response to AA treatment. This finding demonstrates the role of CTCs as surrogate tissue that can be obtained in a routine practice setting.
Abiraterone; Biomarker; Circulating tumor cells; Prostate cancer; Prostate-specific antigen; TMPRSS2-ERG fusion
Biosynthesis of extragonadal androgen may contribute to the progression of castration-resistant prostate cancer. We evaluated whether abiraterone acetate, an inhibitor of androgen biosynthesis, prolongs overall survival among patients with metastatic castration-resistant prostate cancer who have received chemotherapy.
We randomly assigned, in a 2:1 ratio, 1195 patients who had previously received docetaxel to receive 5 mg of prednisone twice daily with either 1000 mg of abiraterone acetate (797 patients) or placebo (398 patients). The primary end point was overall survival. The secondary end points included time to prostate-specific antigen (PSA) progression (elevation in the PSA level according to prespecified criteria), progression-free survival according to radiologic findings based on prespecified criteria, and the PSA response rate.
After a median follow-up of 12.8 months, overall survival was longer in the abiraterone acetate–prednisone group than in the placebo–prednisone group (14.8 months vs. 10.9 months; hazard ratio, 0.65; 95% confidence interval, 0.54 to 0.77; P<0.001). Data were unblinded at the interim analysis, since these results exceeded the preplanned criteria for study termination. All secondary end points, including time to PSA progression (10.2 vs. 6.6 months; P<0.001), progression-free survival (5.6 months vs. 3.6 months; P<0.001), and PSA response rate (29% vs. 6%, P<0.001), favored the treatment group. Mineralocorticoid-related adverse events, including fluid retention, hypertension, and hypokalemia, were more frequently reported in the abiraterone acetate–prednisone group than in the placebo–prednisone group.
The inhibition of androgen biosynthesis by abiraterone acetate prolonged overall survival among patients with metastatic castration-resistant prostate cancer who previously received chemotherapy. (Funded by Cougar Biotechnology; COU-AA-301 ClinicalTrials.gov number, NCT00638690.)
Visceral disease, non-nodal soft-tissue metastases predominantly involving the lung and liver, is a negative prognostic factor in patients with metastatic castration-resistant prostate cancer (mCRPC). An exploratory analysis of COU-AA-301 assessed whether abiraterone acetate (AA) improved overall survival (OS) in mCRPC patients with visceral disease progressing post docetaxel.
In COU-AA-301, post-docetaxel mCRPC patients were randomized 2:1 to AA 1000 mg (n=797) or placebo (n=398) once daily, each with prednisone 5 mg b.i.d. The primary end point was OS; secondary end points included radiographic progression-free survival (rPFS), PSA response rate and objective response rate (ORR). Treatment effects in visceral disease (n=352) and non-visceral disease (n=843) subsets were examined using final data (775 OS events).
AA plus prednisone produced similar absolute improvement in median OS in patients with (4.6 months) and without (4.8 months) visceral disease versus prednisone; hazard ratios (HRs) were 0.79 (95% confidence interval (CI): 0.60–1.05; P=0.102) and 0.69 (95% CI: 0.58–0.83; P<0.0001), respectively. Treatment with AA plus prednisone significantly and comparably improved secondary endpoint outcomes versus prednisone in both the subsets: the HRs for rPFS were 0.60 (95% CI: 0.46–0.78; P=0.0002) and 0.68 (95% CI: 0.58–0.80; P<0.0001) in visceral and non-visceral disease subsets, respectively. PSA response rates were 28% versus 7% in the visceral disease subsets and 30% versus 5% in the non-visceral disease subsets (both P<0.0001), and ORRs were 11% versus 0% (P=0.0058) and 19% versus 5% (P=0.0010), respectively. The incidence of grade 3/4 adverse events was similar between the subsets and between the treatment arms in each subset. Adverse events related to CYP17 blockade were increased in the AA arms and were similar in patients with or without visceral disease.
AA plus prednisone provides significant clinical benefit, including improvements in OS and secondary end points, in post-docetaxel mCRPC patients with or without baseline visceral disease. The presence of visceral disease does not preclude clinical benefit from abiraterone.
abiraterone acetate; liver metastases; metastatic prostate cancer; survival; visceral disease
While androgen-deprivation therapy can induce dramatic clinical responses in advanced and metastatic prostate cancer, refractory disease (castration-resistant prostate cancer [CRPC]) eventually emerges. In recent years, several studies have demonstrated the importance of residual intratumoral androgens in maintaining androgen receptor (AR) transcriptional activity in CRPC. The cytochrome P450 enzyme CYP17 is an obligatory step in androgen synthesis, and therefore a critical therapeutic target in CRPC. Abiraterone acetate is a selective, irreversible inhibitor of CYP17 and can suppress adrenal synthesis of androgen precursors, and possibly in situ steroidogenesis in the tumor microenvironment. In a phase III multicenter study, abiraterone in combination with prednisone improved median overall survival of men with docetaxel-refractory CRPC by 3.9 months compared to placebo plus prednisone, and also resulted in higher objective prostate-specific antigen and radiographic response rates. The study led to the FDA approval in April 2011 of abiraterone for treatment of chemotherapy-refractory CRPC patients, validating steroidogenesis and the AR axis in general as therapeutic targets in CRPC. The FDA indication for abiraterone was expanded to all CRPCs in December 2012, while evaluation in even earlier disease states is ongoing. We propose a comprehensive AR axis-targeting approach via simultaneous, frontline enzymatic blockade of several steroidogenic enzymes (eg, CYP17 and AKR1C3) in combination with gonadotropin-releasing hormone analogs and potent, second-generation AR antagonists (eg, enzalutamide) in order to improve outcomes in patients with prostate cancer.
androgen synthesis; testosterone; dihydrotestosterone; CYP17; AKR1C3; MDV3100 (enzalutamide)
Association between the pretreatment neutrophil-to-lymphocyte ratio and outcome of patients with metastatic castration-resistant prostate cancer treated with ketoconazole was assessed. The pretreatment neutrophil-to-lymphocyte ratio and prostate-specific antigen doubling time, and prior response to androgen-deprivation therapy, were associated with the progression-free survival interval in these patients.
The neutrophil-to-lymphocyte ratio (NLR), an inflammation marker, is prognostic in several cancers. We assessed the association between the pretreatment NLR and outcome of patients with metastatic castration-resistant prostate cancer (mCRPC) treated with the CYP17 inhibitor ketoconazole.
This was an international, retrospective study of 156 mCRPC patients treated with ketoconazole. The independent effect of the pretreatment NLR and factors associated with treatment outcome were determined by multivariate analysis.
Seventy-eight patients (50%) had a ≥50% decline in prostate-specific antigen (PSA). The median progression-free survival (PFS) time was 8 months. Excluded from the analysis were 23 patients without available data on their NLR and those with a recent health event or treatment associated with a blood count change. Sixty-two patients (47%) had a pretreatment NLR >3. Risk factors associated with the PFS outcome were a pretreatment NLR >3 and PSA doubling time (PSADT) <3 months and a prior response to a gonadotropin-releasing hormone agonist of <24 months or to an antiandrogen of <6 months. The number of risk factors was used to form a predictive nomogram by patient categorization into favorable (zero or one factor), intermediate (two factors), and poor (three or four factors) risk groups.
In mCRPC patients treated with ketoconazole, the pretreatment NLR and PSADT, and prior response to androgen-deprivation therapy, may be associated with the PFS time and used to form a risk stratification predictive nomogram.
Ketoconazole treatment; Metastatic castration-resistant prostate cancer; Neutrophil-to-lymphocyte ratio; Outcome; Predictive nomogram
Abiraterone is a potent inhibitor of the steroidogenic enzyme CYP17A1 and suppresses tumor growth in patients with castration-resistant prostate cancer (CRPC). The effectiveness of abiraterone in reducing tumor androgens is not known, nor have mechanisms contributing to abiraterone resistance been established.
We treated human CRPC xenografts with abiraterone and measured tumor growth, tissue androgens, androgen receptor (AR) levels, and steroidogenic gene expression vs. controls.
Abiraterone suppressed serum PSA levels and improved survival in two distinct CRPC xenografts: median survival of LuCaP35CR improved from 17 to 39 days (HR 3.6, p=0.0014) and LuCaP23CR from 14 to 24 days (HR 2.5, p=0.0048). Abiraterone strongly suppressed tumor androgens, with testosterone (T) decreasing from 0.49 ± 0.22 to 0.03 ± 0.01 pg/mg (p<0.0001), and from 0.69 ± 0.36 to 0.03 ± 0.01 pg/mg (p=0.002) in abiraterone-treated 23CR and 35CR, respectively, with comparable decreases in tissue DHT. Treatment was associated with increased expression of full length AR (ARFL) and truncated AR variants (ARFL 2.3 fold, p=0.008 and ARdel567es 2.7 fold, p=0.036 in 23CR; ARFL 3.4 fold, p=0.001 and ARV7 3.1 fold, p=0.0003 in 35CR), and increased expression of the abiraterone target CYP17A1 (~2.1 fold, p=0.0001 and p=0.028 in 23CR and 35CR, respectively) and transcript changes in other enzymes modulating steroid metabolism.
These studies indicate that abiraterone reduces CRPC growth via suppression of intratumoral androgens and that resistance to abiraterone may occur through mechanisms that include upregulation of CYP17A1, and/or induction of AR and AR splice variants that confer ligand-independent AR transactivation.
castration resistant prostate cancer; CYP17A1; abiraterone; steroidogenesis; androgen receptor splice variant
Prostate cancer is the second leading cause of cancer death in men in the US and Europe. The treatment of advanced-stage prostate cancer has been androgen deprivation. Medical castration leads to decreased production of testosterone and dihydrotestosterone by the testes, but adrenal glands and even prostate cancer tissue continue to produce androgens, which eventually leads to continued prostate cancer growth despite castrate level of androgens. This stage is known as castrate-resistant prostate cancer (CRPC), which continues to be a challenge to treat. Addition of androgen antagonists to hormonal deprivation has been successful in lowering the prostate-specific antigen levels further, but has not actually translated into life-prolonging options. The results of several contemporary studies have continued to demonstrate activation of the androgen receptor as being the key factor in the continued growth of prostate cancer. Blockade of androgen production by nongonadal sources has led to clinical benefit in this setting. One such agent is abiraterone acetate, which significantly reduces androgen production by blocking the enzyme, cytochrome P450 17 alpha-hydroxylase (CYP17). This has provided physicians with another treatment option for patients with CRPC. The landscape for prostate cancer treatment has changed with the approval of cabazitaxel, sipuleucel-T and abiraterone. Here we provide an overview of abiraterone acetate, its mechanism of action, and its potential place for therapy in CRPC.
CRPC; abiraterone; CYP17; inhibitors; androgens; castration resistant prostate cancer
Abiraterone is the active metabolite of the pro-drug abiraterone acetate (AA) and a selective inhibitor of CYP17, a key enzyme in testosterone synthesis, and improves overall survival in postdocetaxel metastatic castration-resistant prostate cancer (mCRPC). This open-label, single-arm phase 1b study was conducted to assess the effect of AA and abiraterone on the QT interval.
The study was conducted in 33 patients with mCRPC. Patients received AA 1,000 mg orally once daily + prednisone 5 mg orally twice daily. Electrocardiograms (ECGs) were collected in triplicate using 12-lead Holter monitoring. Baseline ECGs were obtained on Cycle 1 Day-1. Serial ECG recordings and time-matched pharmacokinetic (PK) blood samples were collected over 24 h on Cycle 1 Day 1 and Cycle 2 Day 1. Serial PK blood samples were also collected over 24 h on Cycle 1 Day 8.
After AA administration, the upper bound of the 2-sided 90 % confidence interval (CI) for the mean baseline-adjusted QTcF change was <10 ms; no patients discontinued due to QTc prolongation or adverse events. No apparent relationship between change in QTcF and abiraterone plasma concentrations was observed [estimated slope (90 % CI): 0.0031 (−0.0040, 0.0102)].
There is no significant effect of AA plus prednisone on the QT/QTc interval in patients with mCRPC.
Abiraterone acetate; Pharmacokinetics; QT interval; Castration-resistant prostate cancer; Phase 1
Immune deficient male mice bearing human prostate cancer xenografts are used to evaluate therapeutic response to novel androgen ablation approaches and the results compared to surgical castration based upon assumption that testosterone microenvironment in intact and castrated adult male mice mimics eugonadal and castrated aging adult human males.
To test these assumptions, serum total testosterone (TT) and free testosterone (FT) were determined longitudinally in groups (n > 20) of intact versus castrated adult male nude, NOG, and immune competent C57BL/6 mice.
In adult male mice, TT and FT varies by 30- to 100-fold within the same animal providing a microenvironment that is only equivalent to hypogonadal, not eugonadal, adult human males (TT is 1.7 ± 1.2 ng/ml [5.8 ± 4.1 nM] in nude and 2.5 ± 1.3 ng/ml [8.7 ± 4.4 nM] in NOG mice versus >4.2 ng/ml [14.7 nM] in eugonadal humans). This was confirmed based upon enhanced growth of androgen dependent human prostate cancer xenografts inoculated into mice supplemented with exogenous testosterone to elevate and chronically maintain serum TT at a level (5 ng/ml [18 nM]) equivalent to a 50-year-old eugonadal human male. In castrated mice, TT and FT range from 2 to 20 pg/ml (7–70 pM) and <0.8 pg/ml (<2.6 pM), respectively, which is equivalent to castrate resistant prostate cancer (CRPC) patients treated with abiraterone. This was confirmed based upon the inability of another CYP17A1 inhibitor, ketoconazole, to inhibit the growth of CRPC xenografts in castrated mice.
Adult male mice supplemented with testosterone mimic eugonadal human males, while unsupplemented animals mimic standard androgen ablation and castrated animals mimic abiraterone treated patients. These studies confirm what is claimed in Robert Burns’ poem “To a Mouse” that “The best laid schemes of mice and men/often go awry.
serum total testosterone; free testosterone; eugonadal levels; hypogonadal levels; mice versus humans
Despite the proven success of hormonal therapy for prostate cancer using chemical or surgical castration, most patients eventually will progress to a phase of the disease that is metastatic and shows resistance to further hormonal manipulation. This has been termed metastatic castrate-resistant prostate cancer (mCRPC). Despite this designation, however, there is evidence that androgen receptor (AR)-mediated signaling and gene expression can persist in mCRPC, even in the face of castrate levels of androgen. This may be due in part to the upregulation of enzymes involved in androgen synthesis, the overexpression of AR, or the emergence of mutant ARs with promiscuous recognition of various steroidal ligands. The therapeutic options were limited and palliative in nature until trials in 2004 demonstrated that docetaxel chemotherapy could significantly improve survival. These results established first-line docetaxel as the standard of care for mCRPC. After resistance to further docetaxel therapy develops, treatment options were once again limited. Recently reported results from phase 3 trials have shown that additional therapy with the novel taxane cabazitaxel (with prednisone), or treatment with the antiandrogen abiraterone (with prednisone) could improve survival for patients with mCRPC following docetaxel therapy. Compared with mitoxantrone/prednisone, cabazitaxel/prednisone significantly improved overall survival, with a 30% reduction in rate of death, in patients with progression of mCRPC after docetaxel therapy in the TROPIC trial. Similarly, abiraterone acetate (an inhibitor of androgen biosynthesis) plus prednisone significantly decreased the rate of death by 35% compared with placebo plus prednisone in mCRPC patients progressing after prior docetaxel therapy in the COU-AA-301 trial. Results of these trials have thus established two additional treatment options for mCRPC patients in the "post-docetaxel space." In view of the continued AR-mediated signaling on mCRPC, results from additional phase 3 studies with novel antiandrogens which are directed at inhibition of the AR (e.g., MDV3100), as well as other agents, are awaited with interest and may further expand the treatment choices for this difficult-to-manage population of patients.