Novel agents for castration-resistant prostate cancer: Early experience and beyond

The utility of the [-2]pro-prostate-specific antigen level as a prognostic marker in patients with castration-resistant prostate cancer treated with enzalutamide

BACKGROUND

The prostate health index (phi) derived using [-2]pro-prostate-specific antigen (p2PSA), a precursor of PSA, has been shown to predict cancer in the gray zone. However, the utility of p2PSA in predicting outcomes for castration-resistant prostate cancer (CRPC) patients remains unknown. Therefore, in this study, we aimed to evaluate the usefulness of p2PSA in predicting the efficacy and prognosis of enzalutamide treatment in CRPC patients.

METHODS

We conducted a prospective study of CRPC patients treated with enzalutamide at our institution, measuring p2PSA levels in 98 pre-treatment serum samples. All patients were divided into two groups based on the median values of each parameter. The PSA progression-free survival (PSA-PFS) and overall survival (OS) were compared using the Kaplan-Meier method. This study was approved by the Institutional Review Board of Gunma University Hospital (IRB No. 2021-092, 1983).

RESULTS

The median PSA level before enzalutamide treatment was 25.59 ng/mL, the median p2PSA level was 208.75 pg/mL, and the median phi was 187.95. PSA, p2PSA, and phi were not all predictors of PSA-PFS. However, the OS was significantly better in the low-value groups (log-rank p-values of PSA, p2PSA, and phi were 0.024, 0.034, and 0.018, respectively). In the docetaxel (DOC)-naive group (n = 58), PSA was not a predictor of OS, but p2PSA and phi were significantly associated with better OS in the low group. This relationship was not observed in the DOC-treated group.

CONCLUSIONS

Our study elucidates the usefulness of p2PSA in predicting outcomes for CRPC patients treated with enzalutamide. It suggests that p2PSA and phi may be prognostic markers after enzalutamide administration in CRPC patients.

Aldo-Keto Reductase 1C3 Inhibitor Prodrug Improves Pharmacokinetic Profile and Demonstrates In Vivo Efficacy in a Prostate Cancer Xenograft Model

Aldo-keto reductase 1C3 (AKR1C3) is overexpressed in castration-resistant prostate cancer where it acts to drive proliferation and aggressiveness by producing androgens. The reductive action of the enzyme leads to chemoresistance development against various clinical antineoplastics across a range of cancers. Herein, we report the continued optimization of selective AKR1C3 inhibitors and the identification of 5r, a potent AKR1C3 inhibitor (IC50 = 51 nM) with >1216-fold selectivity for AKR1C3 over closely related isoforms. Due to the cognizance of the poor pharmacokinetics associated with free carboxylic acids, a methyl ester prodrug strategy was pursued. The prodrug 4r was converted to free acid 5r in vitro in mouse plasma and in vivo. The in vivo pharmacokinetic evaluation revealed an increase in systemic exposure and increased the maximum 5r concentration compared to direct administration of the free acid. The prodrug 4r demonstrated a dose-dependent effect to reduce the tumor volume of 22Rv1 prostate cancer xenografts without observed toxicity.

A prospective study of the relationship between CRPC patient's quality of life after enzalutamide and serum testosterone levels measured via LC-MS/MS

BACKGROUND

Enzalutamide (ENZ) is used in the treatment of patients with castration-resistant prostate cancer (CRPC). The quality of life (QoL) of CRPC patients during ENZ treatment is very important, but predictive markers of QoL have not been identified. We investigated the relationship between the serum testosterone (T) level before ENZ treatment and QoL changes in CRPC patients.

PATIENTS AND METHODS

This prospective study was conducted between 2014 and 2018 at Gunma University Hospital and related facilities. We analyzed 95 patients in whom QoL could be evaluated using the Functional Assessment of Cancer Therapy-Prostate (FACT-P) questionnaire at baseline, and after 4 and 12 weeks of ENZ treatment. Serum T levels were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

The study population of 95 patients had a median age of 72 years and median prostate-specific antigen level of 21.6 ng/mL. The median overall survival from the commencement of ENZ treatment was 26.8 months. The median serum T level before ENZ treatment was 50.0 pg/mL. The mean total FACT-P scores at baseline, and after 4 and 12 weeks of ENZ treatment, were 95.8, 91.7, and 90.1, respectively. Differences in FACT-P scores between the high T level (High-T) group and low T level (Low-T) group (distinguished based on median split of the T level) were examined. The mean FACT-P scores were significantly higher in the High-T than Low-T group after both 4 and 12 weeks of ENZ treatment (98.5 vs. 84.6 and 96.4 vs. 82.2, respectively, both p < 0.05). The mean FACT-P score was significantly lower in the Low-T group after 12 weeks than before ENZ treatment (p < 0.05).

CONCLUSION

The serum T level before treatment may be useful for predicting QoL changes after ENZ treatment in CRPC patients.

A Prospective Study of the Relationship Between Clinical Outcomes After Enzalutamide and Serum Androgen Levels Measured via Liquid Chromatography-tandem Mass Spectrometry in Patients with Castration-resistant Prostate Cancer

Background

Enzalutamide (ENZ) is used to treat patients with castration-resistant prostate cancer (CRPC). However, the kinetics of serum androgens before and after ENZ treatment are unknown.

Objective

To elucidate the kinetics of serum androgens and explore the possibility of identifying a useful marker for predicting the effects of ENZ.

Design setting and participants

We conducted a prospective study from 2014 to 2018 at Gunma University Hospital and related facilities. Data were analyzed for 104 patients with CRPC treated with ENZ.

Outcome measurements and statistical analysis

We measured serum androgen levels using liquid chromatography-tandem mass spectrometry. Relationships with outcomes were assessed using multivariable Cox regression and log-rank analyses.

Results and limitations

The median age of the patients was 73 yr. Median serum testosterone, dihydrotestosterone (DHT), androstenedione, and dehydroepiandrosterone sulfate levels were 49.0, 5.8, 222.2, and 326.3 pg/ml, respectively. We performed multivariate analysis using Cox regression to predict prostate-specific antigen progression-free survival (PSA-PFS) and overall survival (OS). Hemoglobin level (≥12.5 vs <12.5 g/dl), docetaxel treatment history (no vs yes), and DHT level (≥5.9 vs <5.9 pg/ml) were significant predictors of PSA-PFS (p <  0.05). Eastern Cooperative Oncology Group performance status (0 vs. 1-2), hemoglobin level (≥12.5 vs <12.5 g/dl), presence of visceral metastasis (no vs yes), amount of bone metastasis (extent of disease 0-2 vs 3-4), and docetaxel treatment history (no vs yes) were significant predictors of OS (p <  0.05). Binomial logistic analysis of the predictors of any grade of anorexia, malaise, and fatigue showed that the presence of visceral metastasis and a low DHT level (<5.9 pg/ml) were significant.

Conclusions

Our results suggest that serum androgen levels before ENZ treatment may be useful for predicting efficacy, prognosis, and the incidence of adverse events.

Patient summary

We measured blood levels of testosterone and other male hormones before treatment with enzalutamide among men with prostate cancer resistant to castration. We found that the levels of these hormones may be useful for predicting the efficacy of enzalutamide treatment, prognosis, and the occurrence of adverse side effects.

Efficacy and Safety of 4-Weekly Docetaxel for Castration-Resistant Prostate Cancer

We investigated the efficacy and safety profiles of 4-weekly docetaxel for castration-resistant prostate cancer. Patients treated with ≥2 courses of docetaxel chemotherapy (median, 70 mg/m²) between 2008 and 2018 were included. Among 125 Japanese men, 40 (32.0%) and 85 (68.0%) were treated with 3-weekly and 4-weekly regimens, respectively. In the 4-weekly regimen, the risks of progression, treatment failure, and any-cause mortality were comparable to those in the 3-weekly regimen. The incidences of severe adverse events were also similar between the 3-weekly and 4-weekly regimens. These data suggest that the 4-weekly regimen may be an acceptable option for selected patients.

Prognostic significance of lactate dehydrogenase in cabazitaxel chemotherapy for castration-resistant prostate cancer: a multi-institutional study

This multi-institutional study aimed to identify prognostic factors for cabazitaxel treatment of castration-resistant prostate cancer (CRPC). This study included 74 Japanese patients with CRPC who were treated with cabazitaxel between 2014 and 2017. Associations between clinicopathological factors including serum markers and progression-free survival (PFS) and overall survival (OS) were investigated. On multivariate analysis, high Gleason score [≥9 vs. ≤7; hazard ratio (HR), 95% confidence interval (CI): 2.00 (1.01-4.34); P = 0.047], presence of pain [HR, 95% CI: 2.02 (1.14-3.58); P = 0.016], and lactate dehydrogenase (LDH) level [HR, 95% CI: 47.31 (3.79-577.49); P = 0.0019] were significantly associated with PFS. Similarly, number of docetaxel cycles [HR, 95% CI: 0.050 (0.0037-0.45); P = 0.0057], performance status [≥2 vs. 0; HR, 95% CI: 5.07 (1.57-16.24); P < 0.0001], and LDH level [HR, 95% CI: 2946 (50-420994); P = 0.0001] were significantly associated with OS. This study showed that LDH level is robustly prognostic for both PFS and OS in cabazitaxel chemotherapy for CRPC.

A Multicentric, Retrospective Efficacy and Safety Study of Nanosomal Docetaxel Lipid Suspension in Metastatic Castration-Resistant Prostate Cancer

Purpose

To evaluate the efficacy and safety of nanosomal docetaxel lipid suspension (NDLS, DoceAqualip) in patients with metastatic castration-resistant prostate cancer (mCRPC).

Materials and Methods

In this multicenter, retrospective study, we analyzed the medical charts of mCRPC patients, who were treated with NDLS administered as 2-weekly (50 mg/m²) or 3-weekly regimens (75 mg/m²). The study endpoints were prostate-specific antigen (PSA) response (>50% PSA decline from baseline), PSA progression (PSA increase from baseline beyond 12 weeks: ≥25% and ≥2 ng/mL), median PSA decline, and time-to-treatment failure (TTF). Overall survival (OS) and safety were also evaluated.

Results

Data of 24 patients with mCRPC were analyzed in this study. NDLS was administered as a 2-weekly regimen in 37.5% (9/24; all first-line) patients and as a 3-weekly regimen in 62.5% patients (15/24; first-line: 20% (3/15), second-line: 80% (12/15)). Overall, PSA response was reported in 66.7% (16/24) patients. The PSA response was 77.8% (7/9 patients) in the 2-weekly group and 60% (9/15 patients) in the 3-weekly group. The median decline in PSA was 96.31% in the 2-weekly group and 83.29% in the 3-weekly group; the median TTF was 6.7 and 6.5 months in the 2 weekly group and 3-weekly group, respectively. The median OS was 14.6 months (follow-up: 5.5–25.8 months) in the 2-weekly group whereas it was not reached in the 3-weekly group (follow-up: 7.9–15.6 months). The most common hematological AEs were anemia, lymphopenia, thrombocytopenia, and neutropenia whereas nausea, weakness, constipation, vomiting, and diarrhea were the most common (≥10%) nonhematological AEs. Overall, NDLS treatment was well tolerated without any new safety concerns.

Conclusions

Nanosomal docetaxel lipid suspension (2-weekly or 3-weekly) was effective and well tolerated in patients with metastatic castration-resistant prostate cancer.

Design, Synthesis and Cytotoxicity Evaluation of Novel Indole Derivatives Containing Benzoic Acid Group as Potential AKR1C3 Inhibitors

Castration-resistant prostate cancer (CRPC) is a fatal, metastatic form of prostate cancer, characterized by reactivation of the androgen axis. Aldo-keto reductase 1C3 (AKR1C3) converts androstenedione (AD) and 5α-androstanedione to testosterone (T) and 5α-dihydrotestosterone (DHT), respectively. In CRPC, AKR1C3 is upregulated and implicated in drug resistance and has been regarded as a potential therapeutic target. Here we examined a series of indole derivatives containing benzoic acid or phenylhydroxamic acid and found that 4-({3-[(3,4,5-trimethoxyphenyl)sulfanyl]-1H-indol-1-yl}methyl)benzoic acid (3e) and N-hydroxy-4-({3-[(3,4,5-trimethoxyphenyl)sulfanyl]-1H-indol-1-yl}methyl)benzamide (3q) inhibited 22Rv1 cell proliferation with IC₅₀ values of 6.37 μM and 2.72 μM, respectively. In enzymatic assay, compounds 3e and 3q exhibited potent inhibitory effect against AKR1C3 (IC₅₀ =0.26 and 2.39 μM, respectively). These results indicated that compounds 3e and 3q might be useful leads for further investigation of more potential AKR1C3 inhibitors used for CRPC.

Prognostic significance of complete blood count parameters in castration-resistant prostate cancer patients treated with androgen receptor pathway inhibitors

BACKGROUND

This study investigated the prognostic significance of complete blood count data in castration-resistant prostate cancer patients treated using androgen receptor pathway inhibitors (ARPIs).

PATIENTS AND METHODS

Patients treated with an ARPI, abiraterone or enzalutamide, as first-line therapy for castration-resistant prostate cancer from 2014 to 2018 were included. The association between complete blood count data and prognoses including progression-free survival and overall survival (OS) was investigated.

RESULTS

High white blood cell counts (<median vs. ≥median; hazard ratio [HR], 1.82, 95% confidence interval [CI], 1.14-2.89; P = 0.012) and high neutrophil-to-lymphocyte ratios (<median vs. ≥median; HR, 1.90, 95% CI, 1.11-3.27; P = 0.020) were associated with a high risk of progression in univariate analysis. In univariate analysis, high hemoglobin (Hb) levels (<median vs. ≥median; HR, 0.41, 95% CI, 0.24-0.73; P = 0.0023) and high red cell distribution widths (<median vs. ≥median; HR, 2.41, 95% CI, 1.37-4.25; P = 0.0023) were associated with a low and a high risk of all-cause mortality, respectively. In multivariate analysis, high Hb levels (<median vs. ≥median; HR, 0.42, 95% CI, 0.22-0.79; P = 0.0076) were repeatedly associated with a low risk of all-cause mortality.

CONCLUSION

We found that white blood cell counts and neutrophil-to-lymphocyte ratios may be prognostic for progression-free survival while red cell distribution widths may be prognostic for OS. In particular, a low Hb level was a robust prognostic factor for poor OS. These findings could be useful in predicting prognosis in CRPC patients treated with ARPIs.

Safety evaluation of enzalutamide dose-escalation strategy in patients with castration-resistant prostate cancer

PURPOSE

Enzalutamide (ENZ) is an androgen receptor inhibitor used for the treatment of castration-resistant prostate cancer (CRPC). The aim of this study was to evaluate the safety of the ENZ by dose-escalation strategy in patients with CRPC.

METHODS

We retrospectively reviewed patients with CRPC who received standard ENZ (started at 160 mg) or dose-escalation ENZ (started at 80 mg followed by dose escalation) from May 2014 to June 2019 in our hospital. Safety and time to treatment failure (TTF) were evaluated. Multivariate logistic regression analysis was used to evaluate adverse events and drug discontinuation. Multivariate Cox regression analysis was used to evaluate TTF.

RESULTS

Among 107 patients, 17 patients received standard ENZ and 90 patients received dose-escalation ENZ therapy. Adverse events (any grade) were observed in 88.2% of patients in the standard group and 63.3% in the dose-escalation group (P = 0.020). Grade ≥3 adverse events were observed in 23.5% and 6.7% of the patients in the standard and dose-escalation groups, respectively, (P = 0.021). Discontinuation due to adverse events was 35.3% and 12.2% in the standard and dose-escalation groups, respectively (P = 0.070). Median TTF was 10.4 months (95% confidential interval [CI]: 2.6-31.3 months) and 18.0 months (95% CI: 11.5-22.8 months) in the standard and dose-escalation groups, respectively (Hazard ratio: 0.60, 95% CI: 0.29-1.30, P = 0.194).

CONCLUSIONS

With the ENZ dose-escalation strategy, adverse events related to ENZ of any grade and grade ≥3 were significantly decreased, and discontinuation due to adverse events also decreased. Therefore, the dose-escalation strategy could be useful in optimizing the dose of ENZ.

Impact of antiandrogen withdrawal syndrome in castration-resistant prostate cancer patients treated with abiraterone or enzalutamide

OBJECTIVES

To assess the impact of antiandrogen withdrawal syndrome after bicalutamide withdrawal in castration-resistant prostate cancer patients treated with androgen receptor-axis targeted agents.

METHODS

The study cohort comprised 94 patients treated with abiraterone (n = 34) or enzalutamide (n = 60) as a first-line androgen receptor-axis targeted agent for castration-resistant prostate cancer despite combined androgen blockade by castration with bicalutamide as the first-line therapy. The association between clinicopathological factors (including antiandrogen withdrawal syndrome) and therapeutic outcome after using abiraterone and enzalutamide was investigated.

RESULTS

The decline in the prostate-specific antigen level after use of abiraterone or enzalutamide was comparable between patients with and without antiandrogen withdrawal syndrome. Antiandrogen withdrawal syndrome (hazard ratio 3.84, 95% confidence interval 1.29-11.45; P = 0.016) was associated with a higher risk of progression on multivariate analysis, but not all-cause death after abiraterone use. Progression-free survival and overall survival after enzalutamide use did not differ between patients with and without antiandrogen withdrawal syndrome.

CONCLUSIONS

The present data suggest a modest therapeutic efficacy of abiraterone in castration-resistant prostate cancer patients with anti-androgen withdrawal syndrome after bicalutamide withdrawal.

High-throughput screen identifies 5-HT receptor as a modulator of AR and a therapeutic target for prostate cancer

BACKGROUND

Eradication of persistent androgen receptor (AR) activity in castration-resistant prostate cancer may be a promising strategy to overcome castration resistance. We aimed to identify novel compounds that inhibit AR activity and could be potential therapeutic agents for prostate cancer.

METHODS

A high-throughput screening system involving cell lines stably expressing AR protein and AR-responsive luciferase was employed for the 1260 compound library. Molecular and antitumor effects on candidate pathways that interacted with AR signaling were examined in prostate cancer cells expressing AR.

RESULTS

The high-throughput screening identified various potential compounds that interfered with AR signaling through known and novel pathways. Among them, a 5-hydroxytryptamine 5A (5-HT5A) receptor antagonist suppressed AR activity through protein kinase A signaling, which was confirmed by 5-HT5A receptor knockdown. Consistently, 5-HT5A receptor inhibitors showed cytotoxic effects toward prostate cancer cells.

CONCLUSIONS

Taken together, this study identifies 5-HT5A receptor as a promising therapeutic target for prostate cancer via its interaction with AR signaling.

Real-world efficacy and safety of two doses of cabazitaxel (20 or 25 mg/m2) in patients with castration-resistant prostate cancer: results of a Japanese post-marketing surveillance study

Background

The recommended starting dose of cabazitaxel for castration-resistant prostate cancer (CRPC) is 25 mg/m² in Japan and Europe. Although lower doses are established alternatives based on randomized controlled trials, the safety and efficacy of 25 and 20 mg/m² in real-world settings are not well established. Therefore, we investigated the safety and efficacy of cabazitaxel at the recommended starting dose or a lower dose (20 mg/m²) in real-world clinical practice.

Methods

We compared the safety and efficacy of cabazitaxel between patients who received cabazitaxel at starting doses of 25 and 20 mg/m² (C25 and C20, respectively) in a Japanese post-marketing surveillance study of 662 patients with docetaxel-refractory CRPC. Safety was assessed in terms of adverse drug reactions (ADRs). Prostate-specific antigen (PSA) response rate, overall survival (OS), and time-to-treatment failure (TTF) were compared between the C25 and C20 groups in unmatched patients and after applying propensity score matching.

Results

The C20 and C25 groups comprised 190 and 159 patients without matching and 112 patients per group after matching. In unmatched patients, any-grade (C25 vs C20: 89.3% vs 78.4%, Fisher’s p < 0.01) and grade ≥ 3 (81.1% vs 61.1%) ADRs were more frequent in the C25 group. Neutropenia (any grade: 61.6% vs 54.2%; grade ≥ 3: 55.3% vs 42.6%) and febrile neutropenia (grade ≥ 3: 30.2% vs 14.7%) were more frequent in the C25 group. In matched patients, the PSA response rate (reduction in PSA ≥30% from a baseline ≥5 ng/mL) was 26.4 and 32.0% in the C20 and C25 groups, respectively, median OS was 291 days (95% CI 230–not reached) versus not reached (hazard ratio 0.73, 95% CI 0.50–1.08), and TTF favored C25 (hazard ratio 0.75, 95% CI 0.57–0.99).

Conclusions

Clinicians should consider the patient’s risk of clinically significant ADRs and prophylactic granulocyte colony stimulating factor when selecting the starting dose of cabazitaxel for CRPC. Some patients at high risk of ADRs or unfit patients may benefit from a lower starting dose of 20 mg/m², whereas fit patients may be candidates for a starting dose of 25 mg/m².

Trial registration

Not applicable.

Cabazitaxel in patients aged ≥80 years with castration-resistant prostate cancer: Results of a post-marketing surveillance study in Japan

OBJECTIVES

Data on the safety and efficacy of cabazitaxel in patients aged ≥80 years with castration-resistant prostate cancer (CRPC) are limited. We report the safety (adverse drug reactions [ADRs]) and efficacy (overall survival [OS], time to treatment failure [TTF], and prostate-specific antigen [PSA] response rates) in patients aged <80 or ≥80 years treated with cabazitaxel for CRPC in clinical practice.

MATERIALS AND METHODS

We performed post-hoc subgroup analyses of a Japanese post-marketing surveillance study involving 662 patients with CRPC treated with cabazitaxel between September 2014 and June 2016.

RESULTS

In patients aged <80 (n = 610) and ≥80 years (n = 49), median PSA at baseline was 168.7 and 109.0 ng/mL, and 86.7% and 83.7% of patients were previously treated with enzalutamide and/or abiraterone. ADRs (all grade) occurred in 77.2% and 79.6% of patients aged <80 and ≥80 years, with grade three/worse ADRs in 61.8% and 63.3% of patients. Hematologic toxicities were the most common grade three/worse ADRs, including neutropenia, febrile neutropenia, and anemia in both subgroups. No specific ADRs were observed in patients aged ≥80 years. The PSA response and median OS and TTF were 28.3%, 292 days, and 116 days in patients aged ≥80 years, and 29.7%, 319 days, and 125 days in patients aged <80 years.

CONCLUSION

Cabazitaxel could be a treatment option for CRPC in patients aged ≥80 years based on its safety and efficacy profiles. This is the first report to investigate the safety and efficacy of cabazitaxel in patients aged ≥80 years with CRPC.

Safety and efficacy of cabazitaxel in 660 patients with metastatic castration-resistant prostate cancer in real-world settings: results of a Japanese post-marketing surveillance study

Objective

To evaluate the real-world safety and efficacy of cabazitaxel in Japanese patients with metastatic castration-resistant prostate cancer (mCRPC) previously treated with a docetaxel-containing regimen.

Methods

This prospective multicenter observational study registered all patients with mCRPC treated with cabazitaxel following its launch in Japan in September 2014. Patient enrollment continued until at least 500 patients were enrolled. Adverse drug reactions (ADRs) were evaluated according to CTCAE ver. 4.0. Efficacy endpoints were assessed for up to 1 year, and included prostate specific antigen (PSA) response rates (defined as a decrease of ≥30% or ≥50% from baseline), overall survival (OS), and time to treatment failure (TTF).

Results

A total of 660 mCRPC patients were enrolled across 316 centers by June 2016. Frequent ADRs (any grade) were neutropenia (49.1%), febrile neutropenia (18.0%) and anemia (15.0%). Most ADRs occurred in cycle 1. Neutropenia and febrile neutropenia were significantly less frequent in patients who received prophylactic granulocyte colony-stimulating factor. The PSA response rates for decrease of ≥30% or ≥50% from baseline were 28.1% and 17.5%, respectively, in patients with baseline PSA of ≥5 ng/ml. Median OS and TTF were 319 days (95% confidence interval: 293.0–361.0) and 116 days (95% confidence interval: 108.0–135.0), respectively.

Conclusions

This study of cabazitaxel in 660 Japanese patients treated in real-world settings, the largest study of cabazitaxel to date, demonstrated a safety profile that was generally consistent with those of pivotal clinical studies. Cabazitaxel was also effective in terms of the PSA response, OS, and TTF.

An exploratory retrospective multicenter study of prognostic factors in mCRPC patients undergoing enzalutamide treatment: Focus on early PSA decline and kinetics at time of progression

BACKGROUND

Recent studies have shown that an early prostate-specific antigen (PSA) response to androgen receptor-targeting agents in metastatic castration-resistant prostate cancer (mCRPC) is associated with a better prognosis. We analyzed the early PSA response to enzalutamide (ENZ) by measuring the PSA doubling time (PSADT) and PSA velocity (PSAV) while monitoring oncologic outcomes and survival in Japanese patients.

METHODS

We analyzed a total of 241 patients with mCRPC who were treated with ENZ. The patients' median age was 75 ± 7.9 years (range, 53-93 years). There were 171 (71%) predocetaxel cases, and 70 (29%) post docetaxel cases. PSA-progression-free survival (PFS) and overall survival (OS) were assessed according to Prostate Cancer Working Group 2 criteria. This study was approved by the Institutional Review Board of Gunma University Hospital (No. 1595).

RESULTS

We observed 77 good response (GR; case in which PSA remained low after treatment) cases (31.9%), 125 acquired resistance (AR; decline in PSA after treatment followed by progression) cases (51.9%), and 39 primary resistance (PR; lack of decline in PSA) cases (16.2%). Predocetaxel, PSA-PFS, and OS were significantly higher compared with post docetaxel (PSA-PFS: 47.0 vs 13.4 weeks, P < .001; OS: not yet reached vs 80.7 weeks, P < .001). Multivariate analysis of prognostic factors, including PSA response at 4 weeks, was performed using Cox regression analysis. ECOG PS (0 vs 1-2), hemoglobin (Hb; ≥ 12.2 vs < 12.2 g/dL), time to CRPC ( ≥ 12 vs < 12 m), docetaxel treatment history (no vs yes), and a PSA reduction of 50% at 4 weeks were significant predictors of OS (all, P < .05). In cases of AR (n = 125), multivariate analysis showed that PSA kinetic factors, such as PSADT and PSAV (ng/mL/m), Hb, time to CRPC, PSADT ( ≥ 2 vs < 2 m), and PSAV ( < 20 vs ≥ 20 ng/mL/m), were all predictive of OS following PSA-progression (P < .05).

CONCLUSIONS

Our study has demonstrated that PSA dynamics after ENZ administration may be a useful prognostic factor for mCRPC patients.

Cigarette smoking augments androgen receptor activity and promotes resistance to antiandrogen therapy

BACKGROUND

Cigarette smoking is associated with worse outcomes in prostate cancer, whose growth is dependent on androgen receptor (AR) signaling. We aimed to elucidate the biological effect of cigarette smoking on AR signaling and its clinical influence on oncological outcome.

METHODS

Gene expression levels after exposure to tobacco smoke condensate (TSC) were evaluated by quantitative real-time polymerase chain reaction and Western blot analysis in prostate cancer cells. Cellular sensitivities to enzalutamide and docetaxel after TSC exposure were evaluated using a prostate cancer cell proliferation assay. Prognosis was compared between current smokers and nonsmokers when treated with AR-axis-targeting (ARAT) agent enzalutamide and docetaxel.

RESULTS

Expression of AR variants as well as prostate-specific antigen was augmented after TSC exposure, which occurred after Akt phosphorylation. These inductions were suppressed by Akt inhibitor LY294002 as well as antioxidant N-acetylcysteine. Consistently, TSC exposure augmented cellular resistance to enzalutamide. In clinical data, cigarette smoking was associated with worse progression-free survival and cancer-specific survival when patients with prostate cancer were treated with ARAT agents but not docetaxel.

CONCLUSIONS

It was suggested that cigarette smoking leads to detrimental oncological outcome when prostate cancer patients are treated with ARAT agents through induction of aberrant AR signaling. Accordingly, we recommend that patients with advanced prostate cancer should refrain from cigarette smoking.

Prognostic significance of antihypertensive agents in men with castration-resistant prostate cancer

PURPOSE

Comorbidity with hypertension (HTN) may affect the outcome of castration-resistant prostate cancer (CRPC). In this study, we evaluated the prognostic impact of antihypertensive agents in patients with CRPC treated with androgen receptor axis-targeting (ARAT) agents or docetaxel chemotherapy.

PATIENTS AND METHODS

This study included 156 Japanese men with CRPC who were treated with ARAT agents (n = 85) or docetaxel (n = 71) at our hospital between 2008 and 2017. Associations between clinicopathological factors, HTN status, progression-free survival (PFS) and overall survival (OS) were evaluated by univariate and multivariate analysis.

RESULTS

When adjusted for age, prostate-specific antigen levels at pretreatment, Gleason score, and clinical M-stage, comorbid HTN was significantly associated with better OS (hazards ratio, 95% confidence interval: 0.41, 0.21-0.77; P = 0.0051), but not with PFS (hazards ratio, 95% confidence interval: 0.64, 0.38-1.11; P = 0.11) in patients treated with ARAT agent. However, HTN was not associated with PFS or OS for patients treated with docetaxel.

CONCLUSIONS

Use of antihypertensive agents has prognostic significance for patients with CRPC treated with ARAT agent, but not docetaxel.

Serum testosterone level as possible predictive marker in androgen receptor axis-targeting agents and taxane chemotherapies for castration-resistant prostate cancer

PURPOSE

Currently, several therapeutic options for castration-resistant prostate cancer (CRPC) are available, for which predictive biomarkers have not been established. Therefore, we aimed to reveal the association between pretreatment serum testosterone level and antitumor outcomes when treated with androgen receptor axis-targeting agents and taxane chemotherapies for CRPC.

PATIENTS AND METHODS

The present study included Japanese patients with metastatic prostate cancer whose serum testosterone levels during androgen-deprivation therapy were available. The antitumor outcomes when treated with enzalutamide, abiraterone, docetaxel, and cabazitaxel with clinicopathological parameters including serum testosterone levels during androgen-deprivation therapy, as well as prognoses including progression-free survival and overall survival, were examined.

RESULTS

Progression-free survival among men with higher serum testosterone level was superior to that among men with lower serum testosterone level when treated with enzalutamide. On the contrary, progression-free survival and overall survival among men with higher serum testosterone level were significantly inferior to those among men with lower serum testosterone level when treated with docetaxel and cabazitaxel, respectively.

CONCLUSIONS

The present study indicated distinct prognostic values of serum testosterone level when treated with androgen receptor axis-targeting agent and taxane chemotherapy for CRPC, suggesting that serum testosterone level may be useful predictive biomarker to navigate the appropriate therapy in patients with CRPC.

AKR1C3 Inhibitor KV-37 Exhibits Antineoplastic Effects and Potentiates Enzalutamide in Combination Therapy in Prostate Adenocarcinoma Cells

Aldo-keto reductase 1C3 (AKR1C3), also known as type 5 17 β-hydroxysteroid dehydrogenase, is responsible for intratumoral androgen biosynthesis, contributing to the development of castration-resistant prostate cancer (CRPC) and eventual chemotherapeutic failure. Significant upregulation of AKR1C3 is observed in CRPC patient samples and derived CRPC cell lines. As AKR1C3 is a downstream steroidogenic enzyme synthesizing intratumoral testosterone (T) and 5α-dihydrotestosterone (DHT), the enzyme represents a promising therapeutic target to manage CRPC and combat the emergence of resistance to clinically employed androgen deprivation therapy. Herein, we demonstrate the antineoplastic activity of a potent, isoform-selective and hydrolytically stable AKR1C3 inhibitor (E)-3-(4-(3-methylbut-2-en-1-yl)-3-(3-phenylpropanamido)phenyl)acrylic acid (KV-37), which reduces prostate cancer cell growth in vitro and in vivo and sensitizes CRPC cell lines (22Rv1 and LNCaP1C3) toward the antitumor effects of enzalutamide. Crucially, KV-37 does not induce toxicity in nonmalignant WPMY-1 prostate cells nor does it induce weight loss in mouse xenografts. Moreover, KV-37 reduces androgen receptor (AR) transactivation and prostate-specific antigen expression levels in CRPC cell lines indicative of a therapeutic effect in prostate cancer. Combination studies of KV-37 with enzalutamide reveal a very high degree of synergistic drug interaction that induces significant reduction in prostate cancer cell viability via apoptosis, resulting in >200-fold potentiation of enzalutamide action in drug-resistant 22Rv1 cells. These results demonstrate a promising therapeutic strategy for the treatment of drug-resistant CRPC that invariably develops in prostate cancer patients following initial treatment with AR antagonists such as enzalutamide. Mol Cancer Ther; 17(9); 1833-45. ©2018 AACR.

Androgen receptor targeted therapies in castration-resistant prostate cancer: Bench to clinic

The androgen receptor is a transcription factor and validated therapeutic target for prostate cancer. Androgen deprivation therapy remains the gold standard treatment, but it is not curative, and eventually the disease will return as lethal castration‐resistant prostate cancer. There have been improvements in the therapeutic landscape with new agents approved, such as abiraterone acetate, enzalutamide, sipuleucel‐T, cabazitaxel and Ra‐223, in the past 5 years. New insight into the mechanisms of resistance to treatments in advanced disease is being and has been elucidated. All current androgen receptor‐targeting therapies inhibit the growth of prostate cancer by blocking the ligand‐binding domain, where androgen binds to activate the receptor. Persuasive evidence supports the concept that constitutively active androgen receptor splice variants lacking the ligand‐binding domain are one of the resistant mechanisms underlying advanced disease. Transcriptional activity of the androgen receptor requires a functional AF‐1 region in its N‐terminal domain. Preclinical evidence proved that this domain is a druggable target to forecast a potential paradigm shift in the management of advanced prostate cancer. This review presents an overview of androgen receptor‐related mechanisms of resistance as well as novel therapeutic agents to overcome resistance that is linked to the expression of androgen receptor splice variants in castration‐resistant prostate cancer.