Common Genetic Variation in CYP17A1 and Response to Abiraterone Acetate in Patients with Metastatic Castration-Resistant Prostate Cancer

Treatment with abiraterone acetate and prednisone (AA/P) prolongs survival in metastatic castration-resistant prostate cancer (mCRPC) patients. We evaluated the genetic variation in CYP17A1 as predictive of response to AA/P. A prospective collection of germline DNA prior to AA/P initiation and follow-up of a mCRPC cohort was performed. Five common single-nucleotide polymorphisms (SNPs) in CYP17A1 identified using a haplotype-based tagging algorithm were genotyped. Clinical outcomes included biochemical response and time to biochemical progression on AA/P. Logistic regression was used to assess the association between tag SNPs and biochemical response. Proportional hazards regression was used to assess the association between tag SNPs and time to biochemical progression. Odds or hazard ratio per minor allele were estimated and p-values below 0.05 were considered statistically significant. Germline DNA was successfully genotyped for four tag SNPs in 87 patients. The median age was 73 years (54-90); the median prostate-specific antigen was 66 ng/dL (0.1-99.9). A single SNP, rs2486758, was associated with lower odds of experiencing a biochemical response (Odds ratio 0.22, 95% confidence interval 0.07-0.63, p = 0.005) and a shorter time to biochemical progression (Hazard ratio 2.23, 95% confidence interval 1.39-3.56, p < 0.001). This tag SNP located in the promoter region of CYP17A1 will need further validation as a predictive biomarker for AA/P therapy.

Safety of long-term exposure to abiraterone acetate in patients with castration-resistant prostate cancer and concomitant cardiovascular risk factors

BACKGROUND

We aimed to evaluate the long-term safety profile of abiraterone in patients with metastatic castration-resistant prostate cancer (mCRPC) with controlled cardiovascular comorbidities or risk factors.

METHODS

We retrospectively analysed the clinical charts of consecutive mCRPC patients with cardiac disorders/risk factors who had been treated with abiraterone 1000 mg once daily plus prednisone 5 mg twice daily for a median duration of 16 months at an oncology referral centre between April 2011 and July 2015. Patients underwent an electrocardiogram (ECG) and echocardiographic assessments, including measurement of left ventricular ejection fraction (LVEF) at baseline and at the end of treatment. Blood pressure (BP) was measured daily at home. During follow up (median 24 months), all adverse events were recorded. Cardiac events (CEs) were defined, according to Common Terminology Criteria for Adverse Events version 4.0, as the appearance of a symptomatic CE that required medical intervention.

RESULTS

A total of 51 patients (median age 71 years) were evaluated. Pre-existing cardiovascular conditions included hypertension (41%), cardiac ischaemia (12%), stroke (9%), dyslipidaemia (18%) and type 2 diabetes mellitus (12%). No CEs were recorded and no changes in LVEF were observed. The most frequently reported adverse events were Grade 1-2 fluid retention (18%), hypertension (16%) and asthenia (16%). No patients permanently discontinued abiraterone due to cardiac events.

CONCLUSIONS

Long-term abiraterone treatment was well tolerated in mCRPC patients with controlled cardiovascular comorbidities/risk factors, with no apparent worsening of cardiovascular conditions from baseline over an extended observation period.

Current advances in intratumoral androgen metabolism in castration-resistant prostate cancer

PURPOSE OF REVIEW

Androgen deprivation therapy is a cornerstone in the treatment of advanced prostate cancer and has extended the lives of countless patients. Unfortunately, many of these patients eventually succumb to metastatic castration-resistant prostate cancer (mCRPC). The efficacy of abiraterone acetate (AA, Zytiga) and enzalutamide (Enza, Xtandi) in the mCRPC setting prove that these tumors remain androgen-driven. We review recent studies that have shown that intratumoral androgen biosynthesis plays a significant role in the ever-evolving mCRPC tumor and we discuss the therapeutic implications of these findings.

RECENT FINDINGS

A novel abiraterone metabolite, 17-(pyridin-3-yl)androsta-4,16-dien-3-one (D4A), possesses robust antitumor activity in rodent models via the inhibition of androgen biosynthetic enzymes and antagonism of the androgen receptor. The TMPRSS2 : ERG fusion drives aldo-keto reductase 1C3 (AKR1C3) expression and activity to facilitate androgen biosynthesis and activate the androgen receptor in prostate cancer. Intracrine androgen formation and AKR1C3 expression and activity have been found to confer resistance to enzalutamide.

SUMMARY

These studies highlight the significant role that intratumoral androgen biosynthesis plays in the mCRPC tumor. The therapeutic implications include the inhibition of AKR1C3 in tumors that become resistant to current drugs such as abiraterone acetate or Enza and the potential administration of D4A as an mCRPC therapeutic.

Novel treatment strategies in congenital adrenal hyperplasia

PURPOSE OF REVIEW

In recent years, important steps have been taken to improve the treatment of congenital adrenal hyperplasia (CAH), a relatively stagnant area for decades. In this review, we summarize these advances and propose future lines of investigation.

RECENT FINDINGS

The two main goals of CAH treatment are to replace the deficient hormones when necessary and to dampen the adrenocorticotropin activation and the ensuing adrenal androgen excess. Glucocorticoids have been the mainstay of CAH treatment, but available preparations only partially meet the clinical needs. Recent efforts have focused on improving the delivery of glucocorticoid replacement agents, to closer mimic the physiologic secretion pattern. Examples include modified release oral glucocorticoids and continuous subcutaneous hydrocortisone pumps. Furthermore, nonglucocorticoid approaches to address the androgen excess have emerged, such as inhibition of key androgenic enzymes and adrenocorticotropin secretion blockade by corticotropin-releasing hormone receptor antagonists.

SUMMARY

The promising recent progress made in CAH treatment brings new perspectives for individualized care in this complex disease.

A phase II trial of abiraterone acetate plus prednisone in patients with triple-negative androgen receptor positive locally advanced or metastatic breast cancer (UCBG 12-1)

BACKGROUND

Several expression array studies identified molecular apocrine breast cancer (BC) as a subtype that expresses androgen receptor (AR) but not estrogen receptor α. We carried out a multicentre single-arm phase II trial in women with AR-positive, estrogen, progesterone receptor and HER2-negative (triple-negative) metastatic or inoperable locally advanced BC to assess the efficacy and safety of abiraterone acetate (AA) plus prednisone.

PATIENTS AND METHODS

Patients with a metastatic or locally advanced, centrally reviewed, triple-negative and AR-positive (≥10% by immunohistochemistry, IHC) BC were eligible. Any number of previous lines of chemotherapy was allowed. AA (1000 mg) was administered once a day with prednisone (5 mg) twice a day until disease progression or intolerance. The primary end point was clinical benefit rate (CBR) at 6 months defined as the proportion of patients presenting a complete response (CR), partial response (PR) or stable disease (SD) ≥6 months. Secondary end points were objective response rate (ORR), progression-free survival (PFS) and safety.

RESULTS

One hundred and forty-six patients from 27 centres consented for IHC central review. Of the 138 patients with sufficient tissue available, 53 (37.6%) were AR-positive and triple-negative, and 34 of them were included from July 2013 to December 2014. Thirty patients were eligible and evaluable for the primary end point. The 6-month CBR was 20.0% [95% confidence interval (CI) 7.7%-38.6%], including 1 CR and 5 SD ≥6 months, 5 of them still being under treatment at the time of analysis (6.4+, 9.2+, 14.5+, 17.6+, 23.4+ months). The ORR was 6.7% (95% CI 0.8%-22.1%). The median PFS was 2.8 months (95% CI 1.7%-5.4%). Fatigue, hypertension, hypokalaemia and nausea were the most common drug-related adverse events; the majority of them being grade 1 or 2.

CONCLUSIONS

AA plus prednisone treatment is beneficial for some patients with molecular apocrine tumours and five patients are still on treatment.

CLINICALTRIALSGOV

NCT01842321.

Abiraterone acetate for metastatic castration-resistant prostate cancer after docetaxel failure: A randomized, double-blind, placebo-controlled phase 3 bridging study

OBJECTIVES

To evaluate the efficacy and safety of abiraterone acetate-prednisone versus placebo-prednisone in Asian metastatic castration-resistant prostate cancer patients who have failed docetaxel-based chemotherapy.

METHODS

In this double-blind, phase 3 study from China, 214 patients were randomized (2:1) to abiraterone acetate 1000 mg once daily plus prednisone 5 mg twice daily and placebo plus prednisone 5 mg twice daily in 28-day treatment cycles.

RESULTS

Abiraterone acetate-prednisone treatment significantly decreased prostate-specific antigen progression risk by 49%, with longer median time to prostate-specific antigen progression of 5.55 months versus 2.76 months in the placebo-prednisone group (hazard ratio 0.506, P = 0.0001, primary end-point). There was a strong trend for improved overall survival in the abiraterone acetate-prednisone group, with a 40% decrease in the risk of death (hazard ratio 0.604, P = 0.0597); however, median survival was not reached in either group because of the short follow-up period (12.9 months) and limited number of observed death events. The prostate-specific antigen response rate was higher in the abiraterone-prednisone group (49.7%) than in the placebo-prednisone group (14.1%). A total of 37.1% patients in this group had pain progression events compared with 50.7% in the placebo-prednisone group. Abiraterone-prednisone significantly decreased the risk of pain progression by 50% (hazard ratio 0.496, P = 0.0014). The incidence of adverse events was similar between the two groups; the most common adverse events being anemia (25.9% for abiraterone-prednisone vs 22.5% for placebo-prednisone), hypokalemia (25.9% and 11.3%), bone pain (23.8% and 21.1%), hypertension (16.1% and 12.7%) and increased aspartate aminotransferase (14.7% and 15.5%), respectively.

CONCLUSIONS

Abiraterone-prednisone significantly delays disease and pain progression, and prostate-specific antigen, with a favorable benefit-risk ratio in Asian metastatic castration-resistant prostate cancer patients in the post-docetaxel setting.

[Concomitant use of abiraterone acetate and triptorelin in patients with castration-resistant prostate cancer]

The relevance of drug treatment for prostate cancer increases with the number of patients who develop castration resistance. Currently, no unified treatment regimen for castration-resistant prostate cancer exists, but the standard treatment for these patients is continuous androgen deprivation therapy. This paper presents the experience of concomitant use of abiraterone acetate and triptorelin in patients with castration-resistant prostate cancer. Ten patients with disease duration of 1.5 to 18 years and established castration resistance are currently being followed up. Nine of ten patients have long-term bone metastases, one patient has visceral metastases. The combination therapy produced a significant PSA decrease in nine patients and regression of bone lesions in two patients.

A prognostic index model for predicting overall survival in patients with metastatic castration-resistant prostate cancer treated with abiraterone acetate after docetaxel

A prognostic index model was developed, composed of six readily available and assessable factors and categorizing patients with metastatic castration-resistant prostate cancer treated with abiraterone–prednisone into distinct prognostic risk groups. This model could be useful for determining patient prognosis for follow-up, monitoring and patient stratification for clinical trials.

Background

Few prognostic models for overall survival (OS) are available for patients with metastatic castration-resistant prostate cancer (mCRPC) treated with recently approved agents. We developed a prognostic index model using readily available clinical and laboratory factors from a phase III trial of abiraterone acetate (hereafter abiraterone) in combination with prednisone in post-docetaxel mCRPC.

Patients and methods

Baseline data were available from 762 patients treated with abiraterone–prednisone. Factors were assessed for association with OS through a univariate Cox model and used in a multivariate Cox model with a stepwise procedure to identify those of significance. Data were validated using an independent, external, population-based cohort.

Results

Six risk factors individually associated with poor prognosis were included in the final model: lactate dehydrogenase > upper limit of normal (ULN) [hazard ratio (HR) = 2.31], Eastern Cooperative Oncology Group performance status of 2 (HR = 2.19), presence of liver metastases (HR = 2.00), albumin ≤4 g/dl (HR = 1.54), alkaline phosphatase > ULN (HR = 1.38) and time from start of initial androgen-deprivation therapy to start of treatment ≤36 months (HR = 1.30). Patients were categorized into good (n = 369, 46%), intermediate (n = 321, 40%) and poor (n = 107, 13%) prognosis groups based on the number of risk factors and relative HRs. The C-index was 0.70 ± 0.014. The model was validated by the external dataset (n = 286).

Conclusion

This analysis identified six factors used to model survival in mCRPC and categorized patients into three distinct risk groups. Prognostic stratification with this model could assist clinical practice decisions for follow-up and monitoring, and may aid in clinical trial design.

Trial registration numbers

NCT00638690.

Does Gleason score at initial diagnosis predict efficacy of abiraterone acetate therapy in patients with metastatic castration-resistant prostate cancer? An analysis of abiraterone acetate phase III trials

BACKGROUND

The usefulness of Gleason score (<8 or ≥8) at initial diagnosis as a predictive marker of response to abiraterone acetate (AA) plus prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC) was explored retrospectively.

PATIENTS AND METHODS

Initial diagnosis Gleason score was obtained in 1048 of 1195 (COU-AA-301, post-docetaxel) and 996 of 1088 (COU-AA-302, chemotherapy-naïve) patients treated with AA 1 g plus prednisone 5 mg twice daily by mouth or placebo plus prednisone. Efficacy end points included radiographic progression-free survival (rPFS) and overall survival (OS). Distributions and medians were estimated by Kaplan-Meier method and hazard ratio (HR) and 95% confidence interval (CI) by Cox model.

RESULTS

Baseline characteristics were similar across studies and treatment groups. Regardless of Gleason score, AA treatment significantly improved rPFS in post-docetaxel [Gleason score <8: median, 6.4 versus 5.5 months (HR = 0.70; 95% CI 0.56-0.86), P = 0.0009 and Gleason score ≥8: median, 5.6 versus 2.9 months (HR = 0.58; 95% CI 0.48-0.72), P < 0.0001] and chemotherapy-naïve patients [Gleason score <8: median, 16.5 versus 8.2 months (HR = 0.50; 95% CI 0.40-0.62), P < 0.0001 and Gleason score ≥8: median, 13.8 versus 8.2 months (HR = 0.61; 95% CI 0.49-0.76), P < 0.0001]. Clinical benefit of AA treatment was also observed for OS, prostate-specific antigen (PSA) response, objective response and time to PSA progression across studies and Gleason score subgroups.

CONCLUSION

OS and rPFS trends demonstrate AA treatment benefit in patients with pre- or post-chemotherapy mCRPC regardless of Gleason score at initial diagnosis. The initial diagnostic Gleason score in patients with mCRPC should not be considered in the decision to treat with AA, as tumour metastases may no longer reflect the histology at the time of diagnosis.

CLINICAL TRIALS NUMBER

COU-AA-301 (NCT00638690); COU-AA-302 (NCT00887198).

Ureteral Metastasis: Uncommon Manifestation in Prostate Cancer

Ureteral metastasis from a primary prostate cancer is a rare event in the initial diagnosis and progression of prostate cancer. We report here the case of a 72- year-old patient who was treated for castration-resistant metastatic prostate cancer involving bone, intra-abdominal lymph nodes, bilateral adrenal glands, and a small distal ureteral lesion with left hydronephrosis considered in remission, with a luteinizing hormone-releasing hormone analog plus abiraterone acetate (AA) and prednisone after initial docetaxel plus prednisone chemotherapy. After an episode of acute left flank pain, the previous left distal intraluminal ureteral mass appeared increased in volume on computed tomographic scan and was compatible with either a metastasis from prostate cancer, transitional cell carcinoma of the ureter, or a collision tumor. After left nephroureterectomy (NU), the mass was confirmed to be of prostatic origin on histopathological examination and the only site of metastatic progression of prostate cancer. Abdominal CT-scan and the operative specimen of the NU showed no direct extension of the abdominal lymph nodes into the ureteral lesion. We speculate that this unique ureteral prostate cancer metastasis was the result of hematogenic spread of prostate cancer, although microscopic spread through the lymphatic system could not be excluded. The transient anti-tumor effect of AA plus prednisone at the level of ureteral metastasis, as far as we are aware of, has never been documented before.

Abiraterone acetate, exemestane or the combination in postmenopausal patients with estrogen receptor-positive metastatic breast cancer

Resistance to nonsteroidal aromatase inhibitors is a major obstacle in the management of estrogen receptor-positive postmenopausal metastatic breast cancer. The addition of abiraterone acetate to exemestane did not improve clinical outcomes compared with exemestane alone in an androgen receptor-enriched population, potentially due to induced serum progesterone as a resistance mechanism.

Background

Androgen receptor (AR) signaling and incomplete inhibition of estrogen signaling may contribute to metastatic breast cancer (MBC) resistance to a nonsteroidal aromatase inhibitor (NSAI; letrozole or anastrozole). We assessed whether combined inhibition of androgen biosynthesis with abiraterone acetate plus prednisone and estradiol synthesis with exemestane (E) may be of clinical benefit to postmenopausal patients with NSAI-pretreated estrogen receptor-positive (ER+) MBC.

Patients and methods

Patients (N = 297) were stratified by the number of prior therapies for metastatic disease (0–1 versus 2) and by prior NSAI use (adjuvant versus metastatic), and randomized (1 : 1 : 1) to receive oral once daily 1000 mg abiraterone acetate plus 5 mg prednisone (AA) versus AA with 25 mg E (AAE) versus 25 mg E alone (E). Each treatment arm was well balanced with regard to the proportion of patients with AR-positive breast cancer. The primary end point was progression-free survival (PFS). Secondary end points included overall survival, clinical benefit rate, duration of response, and overall response rate.

Results

There was no significant difference in PFS with AA versus E (3.7 versus 3.7 months; hazard ratio [HR] = 1.1; 95% confidence interval [CI] 0.82–1.60; P = 0.437) or AAE versus E (4.5 versus 3.7 months; HR = 0.96; 95% CI 0.70–1.32; P = 0.794). Increased serum progesterone concentrations were observed in both arms receiving AA, but not with E. Grade 3 or 4 treatment-emergent adverse events associated with AA, including hypokalemia and hypertension, were less common in patients in the E (2.0% and 2.9%, respectively) and AA arms (3.4% and 1.1%, respectively) than in the AAE arm (5.8% for both).

Conclusions

Adding AA to E in NSAI-pretreated ER+ MBC patients did not improve PFS compared with treatment with E. An AA-induced progesterone increase may have contributed to this lack of clinical activity.

ClinicalTrials.gov

NCT01381874.

Impact of visceral metastases on outcome to abiraterone after docetaxel in castration-resistant prostate cancer patients

BACKGROUND

The objective of this study was to analyze the impact of visceral metastases in castration-resistant prostate cancer (CRPC) treated with abiraterone.

MATERIALS & METHODS

All CRPC patients received abiraterone 1000 mg daily plus prednisone 10 mg orally daily. Liver and lung metastases were considered as visceral metastases.

RESULTS

Of 265 CRPC patients, 49 had visceral metastases. Results on progression-free survival were not significantly different in patients with or without visceral metastases. Conversely, the median overall survival between the two groups was 12.4 and 18.5 months (p = 0.01), respectively, and median overall survival of patients with liver-only disease versus other sites was 10.5 versus 18.5 months (p = 0.006), respectively.

CONCLUSION

Visceral disease appears to be an important predictor of clinical outcome in CRPC patients treated with abiraterone.

Metabolic syndrome in castration-resistant prostate cancer patients treated with abiraterone

BACKGROUND

Metabolic syndrome (MS) has not yet been studied in castration-resistant prostate cancer (CRPC) men treated with novel hormonal therapies. The study aims to assess the impact of MS on outcome from time starting abiraterone.

PATIENTS AND METHODS

We retrospectively evaluated a consecutive series of metastatic CRPC patients treated with abiraterone after docetaxel failure. MS, as defined by modified Adult Treatment Panel (ATP) III criteria, was assessed at the time of initiation of abiraterone, during treatment and follow-up.

RESULTS

Sixty-seven of 178 patients evaluated (37.6%) met MS criteria at baseline, before abiraterone initiation, whereas for 11 (9.9%) without MS before treatment with abiraterone this occurred during treatment. Median PFS was equal to 4.7 months for patients with MS versus 9 months for those without MS. Patients with MS had an increased risk of 71% of progression or death for all causes than patients without MS (HR = 1.7, 95% CI [1.2-2.4], P = 0.03). Median OS was 14.7 months and 22.3 months in patients with and without MS, respectively. After adjusting for covariates, MS resulted not significantly associated to OS (HR = 1.42, 95% CI [0.91-2.22], P = 0.073).

CONCLUSIONS

The presence of MS is a significant risk factor for shorter PFS in CRPC patients treated with abiraterone, even if it does not show a significant impact on OS. A prospective evaluation is warranted.

Treatment Sequences and Pharmacy Costs of 2 New Therapies for Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

The approval of new therapies for metastatic castration-resistant prostate cancer (mCRPC), including the oral agents abiraterone acetate and enzalutamide, has altered the standard of care for patients with mCRPC. Little information exists regarding the sequences in which new therapies for mCRPC with evidence of survival benefits are used.

OBJECTIVE

To describe the sequence of medication use for patients with mCRPC as observed in 3 healthcare data sets.

METHODS

Three healthcare claims data sets were used to identify patients with mCRPC who had no previous use of and were newly initiating 1 of the 2 oral study drugs (ie, abiraterone acetate or enzalutamide). The index date was the first study drug claim after September 1, 2012. Patients were followed until the data cutoff or until being lost to follow-up. Descriptive statistics summarized the proportion of patients receiving 1 line of therapy versus ≥2 lines of therapy. The use of a corticosteroid and the mean monthly pharmacy costs of abiraterone acetate or enzalutamide during the follow-up period were compared between the cohorts.

RESULTS

A total of 3525 patients with mCRPC were identified from data set 1, 499 patients from data set 2, and 1949 patients from data set 3. The first-line use of abiraterone acetate was observed in 74%, 82%, and 80% of data sets 1, 2, and 3, respectively, and the first-line use of enzalutamide was seen in 26%, 18%, and 20%, respectively, of these same populations. The concomitant use of corticosteroids was observed in patients receiving first-line abiraterone acetate and in patients receiving first-line enzalutamide in all 3 data sets. After September 2012, abiraterone acetate was the most frequently administered therapy for mCRPC among the 2 oral agents, abiraterone acetate and enzalutamide. The monthly pharmacy costs associated with abiraterone acetate were significantly lower than those associated with enzalutamide in all 3 data sets.

CONCLUSIONS

Based on the data used in this study, abiraterone acetate was more frequently administered for patients with mCRPC than enzalutamide. The concomitant use of corticosteroids was common in patients receiving first-line abiraterone acetate or first-line enzalutamide therapy. Patients receiving abiraterone acetate had significantly lower monthly pharmacy costs than patients receiving enzalutamide. These findings may facilitate the estimation of the budgetary impact of a treatment mix for population health and for managed care stakeholders.

Biological and clinical effects of abiraterone on anti-resorptive and anabolic activity in bone microenvironment

Abiraterone acetate (ABI) is associated not only with a significant survival advantage in both chemotherapy-naive and -treated patients with metastatic castration-resistant prostate cancer (mCRPC), but also with a delay in time to development of Skeletal Related Events and in radiological skeletal progression. These bone benefits may be related to a direct effect on prostate cancer cells in bone or to a specific mechanism directed to bone microenvironment. To test this hypothesis we designed an in vitro study aimed to evaluate a potential direct effect of ABI on human primary osteoclasts/osteoblasts (OCLs/OBLs). We also assessed changes in bone turnover markers, serum carboxy-terminal collagen crosslinks (CTX) and alkaline phosphatase (ALP), in 49 mCRPC patients treated with ABI.Our results showed that non-cytotoxic doses of ABI have a statistically significant inhibitory effect on OCL differentiation and activity inducing a down-modulation of OCL marker genes TRAP, cathepsin K and metalloproteinase-9. Furthermore ABI promoted OBL differentiation and bone matrix deposition up-regulating OBL specific genes, ALP and osteocalcin. Finally, we observed a significant decrease of serum CTX values and an increase of ALP in ABI-treated patients.These findings suggest a novel biological mechanism of action of ABI consisting in a direct bone anabolic and anti-resorptive activity.

A retrospective, Canadian multi-center study examining the impact of prior response to abiraterone acetate on efficacy of docetaxel in metastatic castration-resistant prostate cancer

BACKGROUND

Questions about optimal sequencing of systemic therapy in metastatic castration-resistant prostate cancer (mCRPC) and whether cross-resistance occurs between different drugs remain largely unanswered. Previous studies have produced conflicting data on the activity of docetaxel in patients who did not attain a prostate-specific antigen (PSA) response to abiraterone acetate (abiraterone). We investigated whether the biochemical response to abiraterone is associated with efficacy of subsequent docetaxel therapy.

METHODS

mCRPC patients treated with docetaxel after abiraterone were retrospectively identified at three Canadian institutions. Patients who had also received docetaxel prior to abiraterone were termed "docetaxel-experienced," while those not treated with docetaxel prior to abiraterone were termed "docetaxel-naïve." Treatment outcomes on docetaxel were stratified by prior response to abiraterone and compared using χ(2) -square test for confirmed PSA response rate (≥ 50% decline from baseline maintained for ≥ 3 weeks) and the log-rank method for progression-free survival (PFS) and overall survival (OS).

RESULTS

Eighty-six patients were treated with abiraterone, of whom 49 were docetaxel-experienced and 37 were docetaxel-naïve. Prior PSA response to abiraterone was no decline, <50% decline and ≥ 50% decline in 37%, 26%, and 37% of patients respectively. The overall PSA response rate to docetaxel was 34.9%, median PFS was 4.0 months and median OS was 11.66 months. Notably, no differences were seen in confirmed PSA response rates (38% vs. 36% vs. 31%, P = 0.86), median PFS (4.04 months vs. 3.94 months vs. 4.24 months, P = 0.43) and median OS (11.86 months vs. 15.38 months vs. 11.00 months, P = 0.56) on docetaxel for patients with no PSA decline, <50% decline and ≥ 50% decline on abiraterone respectively. Importantly, PSA response rates to docetaxel were comparable in the docetaxel-experienced and docetaxel-naïve cohorts and were not linked to prior response to abiraterone in either group.

CONCLUSION

Activity of docetaxel was not associated with the biochemical response to prior abiraterone therapy. These data suggest that prior response to abiraterone should not influence decisions on subsequent use of docetaxel in mCRPC.

A phase 2 trial of abiraterone acetate in Japanese men with metastatic castration-resistant prostate cancer and without prior chemotherapy (JPN-201 study)

Objective

Abiraterone acetate has been approved in >70 countries for chemotherapy-naïve metastatic castration-resistant prostate cancer patients. Efficacy and safety of abiraterone acetate (1000 mg/once daily) with prednisolone (5 mg/twice daily) in chemotherapy-naïve Japanese patients with metastatic castration-resistant prostate cancer was evaluated.

Methods

Men, ≥20 years, with prostate-specific antigen levels of ≥5 ng/ml and evidence of progression were enrolled in this Phase 2, multicenter, open-label study. Primary efficacy endpoint was proportion of patients achieving a prostate-specific antigen decline of ≥50% from baseline (prostate-specific antigen response) after 12 week of treatment. Secondary efficacy endpoints and safety were assessed.

Results

A confirmed prostate-specific antigen response was observed in 29/48 (60.4%) patients by week 12; lower limit of two-sided 90% confidence interval was >35% (threshold response rate), demonstrating efficacy of abiraterone acetate. Secondary efficacy endpoints: prostate-specific antigen response rate during treatment period: 62.5%; objective radiographic response, partial response: 4/18 (22.2%) patients; complete response: none; stable disease: 11/18 (61.1%) patients; median percent change in prostate-specific antigen level from baseline at Week 12: −66.62%. Median prostate-specific antigen response duration and progression-free survival were not reached, and median radiographic progression-free survival was 253 days. Of 31/48 (64.6%) patients experienced adverse events of special interest; most common was hepatic function abnormality (37.5%, Grade 3: 10.4%). One Grade 3 hypertension was the only mineralocorticoid adverse event >Grade 1/2.

Conclusions

Efficacy of abiraterone acetate plus prednisolone was demonstrated by decline in prostate-specific antigen levels with evidence of antitumor activity by radiography in Japanese patients with chemotherapy-naïve metastatic castration-resistant prostate cancer. Abiraterone acetate plus prednisolone had an acceptable safety profile.

Clinical trial registration no

NCT01756638.

A phase 2 study of abiraterone acetate in Japanese men with metastatic castration-resistant prostate cancer who had received docetaxel-based chemotherapy

Objective

In this Phase 2 multicenter study the efficacy and safety of oral abiraterone acetate (1000 mg/once daily) plus prednisolone (5 mg/twice daily) was evaluated in metastatic castration-resistant prostate cancer patients from Japan who had previously received docetaxel-based chemotherapy.

Methods

Men (aged ≥20 years) with metastatic castration-resistant prostate cancer (prostate-specific antigen levels: ≥5 ng/ml), who had received 1 or 2 cytotoxic chemotherapies (with ≥1 regimen being docetaxel) for prostate cancer, were enrolled in this open-label, single-arm study. Primary efficacy endpoint was proportion of patients achieving a ≥50% prostate-specific antigen decline from baseline (prostate-specific antigen response rate) after 12-week treatment. Safety and pharmacokinetics were also assessed.

Results

Confirmed prostate-specific antigen response rate by Week 12 was 28.3% (90% confidence interval: 17.6%; 41.1%) or 13 out of 46 (full analysis set) treated patients. However, total prostate-specific antigen response rate including confirmed and unconfirmed responses was 34.8% (90% confidence interval: 23.2%; 47.9%). Secondary efficacy endpoints and outcomes were: improvement in Eastern Cooperative Oncology Group performance status score by ≥1 unit: 7/16 patients (43.8%); objective radiographic response: complete response, partial response and stable disease in 0, 1/22 (4.5%) and 9/22 (40.9%) patients, respectively; pain palliation response: 9/16 (56.3%) patients. The most common adverse events (>20% patients) were upper respiratory tract infection (13/47, 27.7% patients) and hepatic function abnormal (10/47, 21.3% patients, Grade 3: 8.5%). All mineralocorticoid-related toxicities were Grade 1/2.

Conclusions

Abiraterone acetate plus prednisolone showed favorable efficacy in metastatic castration-resistant prostate cancer Japanese patients who had received chemotherapy. Abiraterone acetate plus prednisolone had an acceptable safety profile.

Clinical trial registration no

NCT01795703.

Androgen metabolism in prostate cancer: from molecular mechanisms to clinical consequences

Despite our most vigorous efforts, prostate cancer remains the second leading cause of cancer death in men. Understanding the intricacies of androgen metabolism is vital to finding therapeutic targets, particularly with progression of advanced prostate cancer after initial hormone therapy, where adrenal precursors are involved. Such is the case with castration-resistant prostate cancer, where adrenal androgens, for example, dehydroepiandrosterone, are a source for intratumoural synthesis of dihydrotestosterone. As prostate cancer progresses, androgen metabolism changes due to altered expression of steroidogenic enzymes and mutations in the components of the steroidogenic machinery. These alterations sustain disease and allow progression; mechanistically, they may also enable development of hormone therapy resistance. With the development of the newer agents, abiraterone acetate and enzalutamide, efforts have been made to better define the basis for response and resistance. This work can be carried out in cell lines, animal models, as well as with ex vivo analysis of tissues obtained from patients. Efforts to further elucidate the finer details of the steroidogenic pathway are necessary to move toward a curative paradigm for patients with localised disease at high risk for recurrence.

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.

Abiraterone acetate and prednisolone for metastatic castration-resistant prostate cancer failing androgen deprivation and docetaxel-based chemotherapy: a phase II bridging study in Korean and Taiwanese patients

OBJECTIVES

To evaluate the safety and efficacy of abiraterone acetate and prednisolone in Korean and Taiwanese patients with metastatic castration-resistant prostate cancer not responding to docetaxel-based chemotherapy.

METHODS

In this single-arm study, 82 metastatic castration-resistant prostate cancer patients who failed docetaxel-based chemotherapy were treated with abiraterone (1000 mg, once daily) and prednisolone (5 mg, twice daily). Patients achieving a prostate-specific antigen decline ≥ 50% were considered as responding.

RESULTS

A total of 35 patients (43%) achieved prostate-specific antigen response (95% confidence interval 32-54). The median time to prostate-specific antigen progression was 4.7 months (95% confidence interval 3.7-8.3); the median overall survival was 11.8 months. Two (4%) of 50 patients with measurable disease achieved partial response. The median testosterone concentration was in the castration range (1.21 nmol/L) throughout the treatment period. Median dehydroepiandrosterone sulfate decreased from 0.725 μmol/L (baseline) to 0.080 μmol/L (cycle 4). The most common adverse event was bone pain (20%); grade 3/4 adverse event of special interest were hypokalemia (7%), fluid retention and liver function abnormalities (5% each), hypertension (2%), and cardiac disorders (1%).

CONCLUSIONS

A combination of abiraterone acetate and prednisolone appears to be a favorable second-line treatment in Taiwanese and Korean patients with advanced metastatic castration-resistant prostate cancer after failed docetaxel-based chemotherapy.

Challenges in the sequencing of therapies for the management of metastatic castration-resistant prostate cancer

Prior to 2010, docetaxel was the standard option for chemotherapy in men with metastatic castration-resistant prostate cancer (mCRPC). Today, the picture is vastly different: several additional therapies have each demonstrated a survival benefit such that we now have chemotherapy (cabazitaxel), androgen suppressive agents (abiraterone acetate and enzalutamide), a cellular vaccine (sipuleucel-T) and radium-233 (for symptomatic bone metastases). With several other agents in the pipeline for late-stage disease, the future looks promising for mCRPC. As the available data are not able to inform as to the optimum sequencing of therapy, this remains a challenge. This paper draws on insights from published and ongoing clinical studies to provide a practical patient-focused approach to maximize the benefits of the current therapeutic armamentarium. Preliminary sequencing suggestions are made based on clinical trial criteria. But until more data become available, clinical gestalt, experience, cost and individual patient preferences will continue to drive choices.

Hormonal Therapeutics Enzalutamide and Abiraterone Acetate in the Treatment of Metastatic Castration-Resistant Prostate Cancer (mCRPC) Post-docetaxel-an Indirect Comparison

INTRODUCTION

This study aims to make an indirect comparison between enzalutamide and abiraterone acetate for mCRPC post-docetaxel.

METHODS

A search for published phase 3 trials was performed with PubMed. Indirect comparisons of enzalutamide (AFFIRM) to abiraterone acetate (COU-AA-301) on outcomes overall survival (OS), time to prostate-specific-antigen (PSA) progression, radiographic progression-free survival (PFS), and PSA response were constructed in the context of log-linear regression models.

RESULTS

There was no statistically significant difference in OS (hazard ratio (HR) 0.85, 95% CI 0.68–1.07). However, there was some evidence that enzalutamide may outperform abiraterone acetate with respect to secondary outcomes: time to PSA progression (HR 0.40, 95% CI 0.30–0.53), radiographic PFS (HR 0.61, 95% CI 0.50–0.74), and PSA response rates (RRs) (OR 10.69, 95% CI 3.92–29.20).

CONCLUSION

While there was no statistically significant difference in OS, enzalutamide may be advantageous for secondary endpoints. Findings of this indirect comparison serve to be hypothesis-generating for future head-to-head trials.

Exploratory analysis of the visceral disease subgroup in a phase III study of abiraterone acetate in metastatic castration-resistant prostate cancer

BACKGROUND

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.

METHODS

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).

RESULTS

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.

CONCLUSIONS

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.