Sequential use of the androgen synthesis inhibitors ketoconazole and abiraterone acetate in castration-resistant prostate cancer and the predictive value of circulating androgens

Progression-free survival, disease-free survival and other composite end points in oncology: improved reporting is needed

Composite outcome measures such as progression-free survival and disease-free survival are increasingly used as surrogate end points in oncology research, frequently serving as the primary end point of pivotal trials that form the basis for FDA and EMA approvals. Such outcome measures combine two or more distinct events (for example, tumour (re)growth, new lesions and/or death) into a single, time-to-event end point. The use of a composite end point can increase the statistical power of a clinical trial and decrease the follow-up period required to demonstrate efficacy, thus lowering costs; however, these end points have a number of limitations. Composite outcomes are often vaguely defined, with definitions that vary greatly between studies, complicating comparisons of results across trials. Altering the makeup of events included in a composite outcome can alter study conclusions, including whether treatment effects are statistically significant. Moreover, the events included in a composite outcome often vary in clinical significance, reflect distinct biological pathways and/or are affected differently by treatment. Therefore, knowing the precise breakdown of the component events is essential to accurately interpret trial results and gauge the true benefit of an intervention. In oncology clinical trials, however, such information is rarely provided. In this Perspective, we emphasize this deficiency through a review of 50 studies with progression-free survival as an outcome published in five top oncology journals, discuss the advantages and challenges of using composite end points, and highlight the need for transparent reporting of the component events.

Repurposing antifungal drugs for cancer therapy

BACKGROUND

Repurposing antifungal drugs in cancer therapy has attracted unprecedented attention in both preclinical and clinical research due to specific advantages, such as safety, high-cost effectiveness and time savings compared with cancer drug discovery. The surprising and encouraging efficacy of antifungal drugs in cancer therapy, mechanistically, is attributed to the overlapping targets or molecular pathways between fungal and cancer pathogenesis. Advancements in omics, informatics and analytical technology have led to the discovery of increasing "off-site" targets from antifungal drugs involved in cancerogenesis, such as smoothened (D477G) inhibition from itraconazole in basal cell carcinoma.

AIM OF REVIEW

This review illustrates several antifungal drugs repurposed for cancer therapy and reveals the underlying mechanism based on their original target and "off-site" target. Furthermore, the challenges and perspectives for the future development and clinical applications of antifungal drugs for cancer therapy are also discussed, providing a refresh understanding of drug repurposing.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review may provide a basic understanding of repurposed antifungal drugs for clinical cancer management, thereby helping antifungal drugs broaden new indications and promote clinical translation.

Testosterone analysis in prostate cancer patients

Testosterone is an essential steroid hormone associated with a wide variety of biological processes in humans. In prostate cancer, androgen signaling is an important driver of tumor cell growth. Depletion of gonadal testosterone, achieved by surgical or chemical castration, prevents androgenic signaling and temporally reduces, stops or reverses tumor growth before inevitable progression to castration-resistant prostate cancer occurs. Additional treatment strategies targeting androgenic signaling have become available, although these are without curative intent. While circulating testosterone is also associated with disease risk and potential clinical utility, the main use in the clinical lab is monitoring adequate castration and subsequent resistance to therapy. Adequate castrate testosterone concentrations are currently based on over 50 year-old double-isotope derivative assays that are disputed in automated immunoassay (IA) analysis. The debate has been further fueled with the introduction of mass spectrometry-based assays for testosterone, offering a substantial increase in sensitivity and specificity. In this review, we discuss testosterone regulation and androgen deprivation therapy in prostate cancer. We provide an overview of the developments in testosterone analysis for monitoring adequate castration and resistance to therapy. Current clinical practice and future clinical utility will be discussed. Finally, clinical and research recommendations will be presented.

Circulating and Intratumoral Adrenal Androgens Correlate with Response to Abiraterone in Men with Castration-Resistant Prostate Cancer

PURPOSE

In metastatic castration-resistant prostate cancer (mCRPC) low serum androgens prior to starting abiraterone acetate (AA) is associated with more rapid progression. We evaluated the effect of AA on androgens in castration-resistant prostate cancer (CRPC) metastases and associations of intratumoral androgens with response.

EXPERIMENTAL DESIGN

We performed a phase II study of AA plus prednisone in mCRPC. The primary outcome was tissue testosterone at 4 weeks. Exploratory outcomes were association of steroid levels and genomic alterations with response, and escalating AA to 2,000 mg at progression.

RESULTS

Twenty-nine of 30 men were evaluable. Testosterone in metastatic biopsies became undetectable at 4 weeks (P < 0.001). Serum and tissue dehydroepiandrosterone sulfate (DHEAS) remained detectable in many patients and was not increased at progression. Serum and tissue DHEAS in the lowest quartile (pretreatment), serum DHEAS in the lowest quartile (4 weeks), and undetectable tissue DHEAS (on-therapy) associated with rapid progression (20 vs. 48 weeks, P = 0.0018; 20 vs. 52 weeks, P = 0.0003; 14 vs. 40 weeks, P = 0.0001; 20 vs. 56 weeks, P = 0.02, respectively). One of 16 men escalating to 2,000 mg had a 30% PSA decline; 13 developed radiographic progression by 12 weeks. Among patients with high serum DHEAS at baseline, wild-type (WT) PTEN status associated with longer response (61 vs. 33 weeks, P = 0.02).

CONCLUSIONS

Low-circulating adrenal androgen levels are strongly associated with an androgen-poor tumor microenvironment and with poor response to AA. Patients with CRPC with higher serum DHEAS levels may benefit from dual androgen receptor (AR)-pathway inhibition, while those in the lowest quartile may require combinations with non-AR-directed therapy.

Somatic Alterations Impact AR Transcriptional Activity and Efficacy of AR-Targeting Therapies in Prostate Cancer

Simple Summary

For patients whose prostate cancer spreads beyond the confines of the prostate, treatment options continue to increase. However, we are missing the information that is needed to choose for each patient the best treatment at each step of his cancer progression so we can ensure that maximal remissions and prolonged survival are achieved. In this review, we examine whether a better understanding of how the activity of the target for the default first treatment, the androgen receptor, is regulated in prostate cancer tissues can improve prostate cancer treatment plans. We consider the evidence for variability of androgen receptor activity among patients and examine the molecular basis for this variable action. We summarize clinical evidence supporting that information on a prostate cancer’s genomic composition may inform on its level of androgen receptor action, which may facilitate choice for the most effective first-line therapy and ultimately improve prostate cancer treatment plans overall.

Abstract

Inhibiting the activity of the ligand-activated transcription factor androgen receptor (AR) is the default first-line treatment for metastatic prostate cancer (CaP). Androgen deprivation therapy (ADT) induces remissions, however, their duration varies widely among patients. The reason for this heterogeneity is not known. A better understanding of its molecular basis may improve treatment plans and patient survival. AR’s transcriptional activity is regulated in a context-dependent manner and relies on an interplay between its associated transcriptional regulators, DNA recognition motifs, and ligands. Alterations in one or more of these factors induce shifts in the AR cistrome and transcriptional output. Significant variability in AR activity is seen in both castration-sensitive (CS) and castration-resistant CaP (CRPC). Several AR transcriptional regulators undergo somatic alterations that impact their function in clinical CaPs. Some alterations occur in a significant fraction of cases, resulting in CaP subtypes, while others affect only a few percent of CaPs. Evidence is emerging that these alterations may impact the response to CaP treatments such as ADT, radiation therapy, and chemotherapy. Here, we review the contribution of recurring somatic alterations on AR cistrome and transcriptional output and the efficacy of CaP treatments and explore strategies to use these insights to improve treatment plans and outcomes for CaP patients.

Molecular tracing of prostate cancer lethality

Prostate cancer is diagnosed mostly in men over the age of 50 years, and has favorable 5-year survival rates due to early cancer detection and availability of curative surgical management. However, progression to metastasis and emergence of therapeutic resistance are responsible for the majority of prostate cancer mortalities. Recent advancement in sequencing technologies and computational capabilities have improved the ability to organize and analyze large data, thus enabling the identification of novel biomarkers for survival, metastatic progression and patient prognosis. Large-scale sequencing studies have also uncovered genetic and epigenetic signatures associated with prostate cancer molecular subtypes, supporting the development of personalized targeted-therapies. However, the current state of mainstream prostate cancer management does not take full advantage of the personalized diagnostic and treatment modalities available. This review focuses on interrogating biomarkers of prostate cancer progression, including gene signatures that correspond to the acquisition of tumor lethality and those of predictive and prognostic value in progression to advanced disease, and suggest how we can use our knowledge of biomarkers and molecular subtypes to improve patient treatment and survival outcomes.

Emerging promising biomarkers for treatment decision in metastatic castration-resistant prostate cancer

Prostate cancer is one of the most common causes of death in males. Even if treatment is often of curative intent in early stages of the disease, up to 50% of patients relapse after primary therapy. Moreover, 10% to 15% of patients present in a primary metastatic stage of disease. In the past years the treatment landscape of metastatic castration-resistant prostate cancer expanded due to the development of second-generation antiandrogens (abiraterone acetate, enzalutamide), chemotherapeutic agents and radium-223. With the availability of several therapeutic lines, we are now confronted with the problem of choosing the most suitable therapy in each state of disease. As often observed in clinical routine, prostate specific antigen is not sufficient for early prediction of a therapy response. Furthermore, biomarkers for prediction of the optimal first-line therapy are badly needed in order to avoid primary resistance. Therefore, the present short review article gives an overview of currently available clinical and preclinical biomarkers for treatment response to metastatic castration-resistant prostate cancer therapeutic agents with the aim of providing support for a personalized decision-making process in everyday use.

The role of adrenal derived androgens in castration resistant prostate cancer

Castration resistant prostate cancer (CRPC) remains androgen dependant despite castrate levels of circulating testosterone following androgen deprivation therapy, the first line of treatment for advanced metstatic prostate cancer. CRPC is characterized by alterations in the expression levels of steroidgenic enzymes that enable the tumour to derive potent androgens from circulating adrenal androgen precursors. Intratumoral androgen biosynthesis leads to the localized production of both canonical androgens such as 5α-dihydrotestosterone (DHT) as well as less well characterized 11-oxygenated androgens, which until recently have been overlooked in the context of CRPC. In this review we discuss the contribution of both canonical and 11-oxygenated androgen precursors to the intratumoral androgen pool in CRPC. We present evidence that CRPC remains androgen dependent and discuss the alterations in steroidogenic enzyme expression and how these affect the various pathways to intratumoral androgen biosynthesis. Finally we summarize the current treatment strategies for targeting adrenal derived androgen biosynthesis.

Androgens and Overall Survival in Patients With Metastatic Castration-resistant Prostate Cancer Treated With Docetaxel

BACKGROUND

Pre-treatment androgen levels are associated with overall survival (OS) in patients with metastatic castration-resistant prostate cancer (CRPC) treated with androgen synthesis inhibitors. The current study sought to determine whether pre-treatment serum androgens predict clinical outcome among patients with metastatic CRPC treated with docetaxel chemotherapy.

MATERIALS AND METHODS

Data were obtained from 1050 men who were chemotherapy-naive prior to treatment with docetaxel, prednisone, and either bevacizumab or placebo (CALGB 90401). Pretreatment serum assays for testosterone, androstenedione, and dehydroepiandrosterone (DHEA) were performed with tandem liquid chromatography-mass spectrometry.

RESULTS

Median values for testosterone, androstenedione, and DHEA were 1.00, 13.50, and 8.12 ng/dL, respectively. The median was used to define the midpoint between low and high values. In univariate analysis, median OS for low versus high levels was 21.4 and 24.2 months for testosterone, 23.8 and 21.9 months for androstenedione, and 20.2 and 25.2 months for DHEA (P = NS). In multivariable analysis of all androgens, baseline DHEA was prognostic of ≥ 50% PSA decline from baseline (P = .008). In multivariable analysis adjusting for 10 known prognostic values and prior ketoconazole use for metastatic CRPC, a 10-unit increase in baseline testosterone increased risk of death (hazard ratio, 1.11; 95% confidence interval, 1.01-1.23; P = .039), whereas a 10-unit increase in androstenedione lowered risk of death (hazard ratio, 0.92; 95% confidence interval, 0.88-0.97; P = .001).

CONCLUSION

Consistent with prior studies, higher androstenedione levels in patients with metastatic CRPC treated with docetaxel are associated with improved survival. However pretreatment levels of other androgen levels are associated with varied effects on clinical outcome in chemotherapy-treated patients.

The role of ketoconazole in current prostate cancer care

Ketoconazole is a nonselective steroid 17α-hydroxylase/17,20 lyase (CYP17A1) inhibitor that has been used, off-label, as a second-line therapy for castration-resistant prostate cancer (CRPC). The drug has shown clinical efficacy without survival benefit. Despite not improving survival, ketoconazole has beneficial characteristics, such as its low cost, a relatively favourable toxicity profile compared with chemotherapy, and its efficacy both before and after chemotherapy. The approval of several new, highly effective treatments, including abiraterone acetate, enzalutamide, and apalutamide, warrants re-evaluation of the role of ketoconazole and other classic agents in achieving the optimal timing and sequencing of available agents to prolong survival and maintain patients' quality of life. In the current CRPC treatment landscape, we believe that ketoconazole can be considered in patients with nonmetastatic CRPC and in those with metastatic CRPC who do not respond to, tolerate, or have access to chemotherapy and other standard therapeutic options.

Canonical and Noncanonical Androgen Metabolism and Activity

Androgens are critical drivers of prostate cancer. In this chapter we first discuss the canonical pathways of androgen metabolism and their alterations in prostate cancer progression, including the classical, backdoor and 5α-dione pathways, the role of pre-receptor DHT metabolism, and recent findings on oncogenic splicing of steroidogenic enzymes. Next, we discuss the activity and metabolism of non-canonical 11-oxygenated androgens that can activate wild-type AR and are less susceptible to glucuronidation and inactivation than the canonical androgens, thereby serving as an under-recognized reservoir of active ligands. We then discuss an emerging literature on the potential non-canonical role of androgen metabolizing enzymes in driving prostate cancer. We conclude by discussing the potential implications of these findings for prostate cancer progression, particularly in context of new agents such as abiraterone and enzalutamide, which target the AR-axis for prostate cancer therapy, including mechanisms of response and resistance and implications of these findings for future therapy.

Contribution of Adrenal Glands to Intratumor Androgens and Growth of Castration-Resistant Prostate Cancer

PURPOSE

Tumor androgens in castration-resistant prostate cancer (CRPC) reflect de novo intratumoral synthesis or adrenal androgens. We used C.B.-17 SCID mice in which we observed adrenal CYP17A activity to isolate the impact of adrenal steroids on CRPC tumors in vivo.

EXPERIMENTAL DESIGN

We evaluated tumor growth and androgens in LuCaP35CR and LuCaP96CR xenografts in response to adrenalectomy (ADX). We assessed protein expression of key steroidogenic enzymes in 185 CRPC metastases from 42 patients.

RESULTS

Adrenal glands of intact and castrated mice expressed CYP17A. Serum DHEA, androstenedione (AED), and testosterone (T) in castrated mice became undetectable after ADX (all P < 0.05). ADX prolonged median survival (days) in both CRPC models (33 vs. 179; 25 vs. 301) and suppressed tumor steroids versus castration alone (T 0.64 pg/mg vs. 0.03 pg/mg; DHT 2.3 pg/mg vs. 0.23 pg/mg; and T 0.81 pg/mg vs. 0.03 pg/mg, DHT 1.3 pg/mg vs. 0.04 pg/mg; all P ≤ 0.001). A subset of tumors recurred with increased steroid levels, and/or induction of androgen receptor (AR), truncated AR variants, and glucocorticoid receptor (GR). Metastases from 19 of 35 patients with AR positive tumors concurrently expressed enzymes for adrenal androgen utilization and nine expressed enzymes for de novo steroidogenesis (HSD3B1, CYP17A, AKR1C3, and HSD17B3).

CONCLUSIONS

Mice are appropriate for evaluating adrenal impact of steroidogenesis inhibitors. A subset of ADX-resistant CRPC tumors demonstrate de novo androgen synthesis. Tumor growth and androgens were suppressed more strongly by surgical ADX than prior studies using abiraterone, suggesting reduction in adrenally-derived androgens beyond that achieved by abiraterone may have clinical benefit. Proof-of-concept studies with agents capable of achieving true "nonsurgical ADX" are warranted.

Response to flutamide, as second-line therapy after bicalutamide, predicts efficacy of abiraterone, not that of enzalutamide

OBJECTIVE

The objective of this retrospective study was to evaluate whether the effect of second-line therapy of flutamide after bicalutamide can predict the response to abiraterone.

RESULTS

Thirty-four patients received abiraterone and 32 received enzalutamide after treatment with second-line flutamide for castration-resistant prostate cancer. Prostate-specific antigen-progression-free survival during treatment with abiraterone or enzalutamide was the endpoint. The response to flutamide therapy was defined as any decrease in prostate-specific antigen compared to baseline prostate-specific antigen. Among the abiraterone-treated patients, those for whom flutamide after bicalutamide was effective showed significantly lower prostate-specific antigen changes than those for whom it was ineffective (P = 0.0175). Prostate-specific antigen-progression-free survival was significantly higher in the abiraterone patients when flutamide was effective than in the patients when it was ineffective (P = 0.027). However, in enzalutamide-treated patients, the prostate-specific antigen changes were not significantly different between those for whom flutamide after bicalutamide was effective and those for whom it was ineffective (P = 0.75). In the enzalutamide patients, prostate-specific antigen-progression-free survival was not significantly different between those for whom flutamide was effective and those for whom it was ineffective (P = 0.92). Therefore, the response to second-line flutamide predicts the efficacy of abiraterone. This information should be helpful when choosing between abiraterone and enzalutamide for patients with castration-resistant prostate cancer.

Prospective International Randomized Phase II Study of Low-Dose Abiraterone With Food Versus Standard Dose Abiraterone In Castration-Resistant Prostate Cancer

Purpose Abiraterone acetate (AA) is a standard of care for metastatic castration-resistant prostate cancer (CRPC). Despite a large food effect, AA was administered under fasting conditions in its pivotal trials. We sought to test the hypothesis that low-dose AA (LOW; 250 mg with a low-fat meal) would have comparable activity to standard AA (STD; 1,000 mg fasting) in patients with CRPC. Patients and Methods Patients (n = 72) with progressive CRPC from seven institutions in the United States and Singapore were randomly assigned to STD or LOW. Both arms received prednisone 5 mg twice daily. Prostate-specific antigen (PSA) was assessed monthly, and testosterone/dehydroepiandrosterone sulfate were assessed every 12 weeks with disease burden radiographic assessments. Plasma was collected for drug concentrations. Log change in PSA, as a pharmacodynamic biomarker for efficacy, was the primary end point, using a noninferiority design. Progression-free survival (PFS), PSA response (≥ 50% reduction), change in androgen levels, and pharmacokinetics were secondary end points. Results Thirty-six patients were accrued to both arms. At 12 weeks, there was a greater effect on PSA in the LOW arm (mean log change, -1.59) compared with STD (-1.19), and noninferiority of LOW was established according to predefined criteria. The PSA response rate was 58% in LOW and 50% in STD, and the median PFS was approximately 9 months in both groups. Androgen levels decreased similarly in both arms. Although there was no difference in PSA response or PFS, abiraterone concentrations were higher in STD. Conclusion Low-dose AA (with low-fat breakfast) is noninferior to standard dosing with respect to PSA metrics. Given the pharmacoeconomic implications, these data warrant consideration by prescribers, payers, and patients. Additional studies are indicated to assess the long-term efficacy of this approach.

Sex steroids in the tumor microenvironment and prostate cancer progression

Prostate cancer is uniquely dependent on androgens. Despite years of research on the relationship between androgens and prostate cancer, many questions remain as to the biological effects of androgens and other sex steroids during prostate cancer progression. This article reviews the clinical and basic research on the influence of sex steroids such as androgens, estrogens and progesterone within the prostate tumor microenvironment on the progression of prostate cancer. We review clinical studies to date evaluating serum sex steroids as prognostic biomarkers and discuss their respective biological effects within the prostate tumor microenvironment. We also review the link between genomic alterations and sex steroid levels within prostate tumors. Finally, we highlight the links between sex steroid levels and the function of the immune system within the tumor microenvironment. As the context of treatment of lethal prostate cancer evolves over time, an understanding of this underlying biology remains central to developing optimal treatment approaches.

Circulating steroid hormone variations throughout different stages of prostate cancer

Steroid hormones play a central role in the maintenance and progression of prostate cancer. The androgen receptor is the primary driver of tumor cell proliferation and is activated by the androgens testosterone and 5α-dihydrotestosterone. Inhibition of this pathway through medical or surgical castration improves survival in the majority of advanced prostate cancer patients. However, conversion of adrenal androgen precursors and alternative steroidogenic pathways have been found to contribute to tumor progression and resistance to treatment. The emergence of highly accurate detection methods allows us to study steroidogenic mechanisms in more detail, even after treatment with potent steroidogenic inhibitors such as the CYP17A1 inhibitor abiraterone. A clear overview of steroid hormone levels in patients throughout the local, metastatic and castration-resistant stages of prostate cancer and treatment modalities is key toward a better understanding of their role in tumor progression and treatment resistance. In this review, we summarize the currently available data on steroid hormones that have been implicated in the various stages of prostate cancer. Additionally, this review addresses the implications of these findings, highlights important studies in this field and identifies current gaps in literature.

Characterization of Prostate Cancer in a Functional Eunuch

BACKGROUND

Eunuchs rarely, if ever, develop prostate cancer (CaP). This article reports on a 62-year-old functional eunuch from prepubertal mumps orchitis who developed clinically localized CaP.

METHODS

Serum and CaP and benign prostate tissue androgen levels were measured using a validated liquid chromatography-tandem mass spectrometry assay. The assay measures testosterone; dihydrotestosterone (DHT); the adrenal androgens, androstenedione and dehydroepiandrosterone; and the androgen metabolites, androsterone and androstanedione. Gene and protein expression levels of androgen metabolism enzymes, and androgen receptor and androgen-regulated genes were measured using quantitative reverse-transcription polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Intracrine androgen metabolism produced tissue DHT when serum and tissue testosterone levels were castrate and undetectable, respectively. Androgen receptor, androgen-regulated, and androgen metabolism enzyme genes were expressed but at lower levels in CaP than benign tissues.

CONCLUSIONS

DHT was synthesized using the primary backdoor androgen metabolism pathway and not using androstenedione or dehydroepiandrosterone via the frontdoor or secondary backdoor pathways.

High-Dose Abiraterone Acetate in Men With Castration Resistant Prostate Cancer

BACKGROUND

Abiraterone acetate (AA) inhibits androgen biosynthesis and prolongs survival in men with metastatic castration-resistant prostate cancer (mCRPC) when combined with prednisone (P). Resistance to therapy remains incompletely understood. In this open-label, single-arm, multicenter phase II study we investigated the clinical benefit of increasing the dose of AA at the time of resistance to standard-dose therapy.

PATIENTS AND METHODS

Eligible patients had progressive mCRPC and started AA 1000 mg daily and P 5 mg twice daily. Patients who achieved any prostate-specific antigen (PSA) decline after 12 weeks of therapy continued AA with P until PSA or radiographic progression. At progression, AA was increased to 1000 mg twice daily with unchanged P dosing. Patients were monitored for response to therapy for a minimum of 12 weeks or until PSA or radiographic progression. The primary end point was PSA decline of at least 30% after 12 weeks of therapy at the increased dose of AA.

RESULTS

Forty-one patients were enrolled from March 2013 through March 2014. Thirteen men experienced disease progression during standard-dose therapy and were subsequently treated with AA 1000 mg twice per day. Therapy was well tolerated. No PSA declines ≥ 30% nor radiographic responses were observed after 12 weeks of dose-escalated therapy. Higher baseline dehydroepiandrosterone levels, lower circulating tumor cell burden, and higher pharmacokinetic levels of abiraterone and abiraterone metabolites were associated with response to standard-dose therapy.

CONCLUSION

Increasing the dose of abiraterone at the time of resistance has limited clinical utility and cannot be recommended. Lower baseline circulating androgen levels and interpatient pharmacokinetic variance appear to be associated with primary resistance to AA with P.

Association of Tissue Abiraterone Levels and SLCO Genotype with Intraprostatic Steroids and Pathologic Response in Men with High-Risk Localized Prostate Cancer

Purpose: Germline variation in solute carrier organic anion (SLCO) genes influences cellular steroid uptake and is associated with prostate cancer outcomes. We hypothesized that, due to its steroidal structure, the CYP17A inhibitor abiraterone may undergo transport by SLCO-encoded transporters and that SLCO gene variation may influence intracellular abiraterone levels and outcomes.Experimental Design: Steroid and abiraterone levels were measured in serum and tissue from 58 men with localized prostate cancer in a clinical trial of LHRH agonist plus abiraterone acetate plus prednisone for 24 weeks prior to prostatectomy. Germline DNA was genotyped for 13 SNPs in six SLCO genes.Results: Abiraterone levels spanned a broad range (serum median 28 ng/mL, 108 nmol/L; tissue median 77 ng/mL, 271 nmol/L) and were correlated (r = 0.355, P = 0.001). Levels correlated positively with steroids upstream of CYP17A (pregnenolone, progesterone), and inversely with steroids downstream of CYP17A (DHEA, AED, testosterone). Serum PSA and tumor volumes were higher in men with undetectable versus detectable tissue abiraterone at prostatectomy (median 0.10 vs. 0.03 ng/dL, P = 0.02; 1.28 vs. 0.44 cc, P = 0.09, respectively). SNPs in SLCO2B1 associated with significant differences in tissue abiraterone (rs1789693, P = 0.0008; rs12422149, P = 0.03) and higher rates of minimal residual disease (tumor volume < 0.5 cc; rs1789693, 67% vs. 27%, P = 0.009; rs1077858, 46% vs. 0%, P = 0.03). LNCaP cells expressing SLCO2B1 showed two- to fourfold higher abiraterone levels compared with vector controls (P < 0.05).Conclusions: Intraprostatic abiraterone levels and genetic variation in SLCO genes are associated with pathologic responses in high-risk localized prostate cancer. Variation in SLCO genes may serve as predictors of response to abiraterone treatment. Clin Cancer Res; 23(16); 4592-601. ©2017 AACR.

Predictors of duration of abiraterone acetate in men with castration-resistant prostate cancer

BACKGROUND

Androgen receptor signaling remains important in castration-resistant prostate cancer (CRPC) as demonstrated by the efficacy of abiraterone acetate (henceforth abiraterone) in phase III trials. Given that heterogeneous patient responses are observed, we sought to identify clinical factors associated with duration of abiraterone.

METHODS

We retrospectively identified patients with CRPC treated with abiraterone in our database. Patient characteristics and types and duration of prostate cancer (PC) therapies were analyzed. These parameters were analyzed with duration of abiraterone in univariate and multivariable analyses.

RESULTS

We identified 161 patients who had received abiraterone. All had received primary androgen-deprivation therapy (ADT), 86% prior secondary hormone therapy (SHT) and 33% prior chemotherapy. The median duration of primary ADT was 23 months, duration of SHT (excluding abiraterone) was 17 months and duration of chemotherapy was 8 months. We demonstrated that lower PSA at abiraterone initiation, longer primary ADT duration, no prior ketoconazole, no prior chemotherapy and longer chemotherapy duration were associated with a longer duration on abiraterone in univariate analysis. In multivariable analysis, duration of primary ADT (duration of abiraterone 9 versus 13 months for ⩽12 versus >12 months, P=0.03) and no use of prior chemotherapy (duration of abiraterone 16 versus 7 months for no versus yes prior chemotherapy, P<0.01) were associated with duration of abiraterone.

CONCLUSIONS

Several clinical parameters, including type and duration of prior therapy, are predictive of responsiveness to abiraterone. These parameters are logical and correlate with smaller disease burden or less exposure to PC therapies. This information can help physicians counsel patients about the potential durability of efficacy of abiraterone. Identifying predictive biomarkers that inform patient selection for therapy is critical to optimizing treatment outcomes.

Role of OATP transporters in steroid uptake by prostate cancer cells in vivo

BACKGROUND

Epidemiologic and in vitro studies suggest that SLCO-encoded organic anion transporting polypeptide (OATP) transporters influence the response of prostate cancer (PCa) to androgen deprivation by altering intratumor androgens. We have previously shown that castration-resistant metastases express multiple SLCO transporters at significantly higher levels than primary PCa, suggesting that OATP-mediated steroid transport is biologically relevant in advanced disease. However, whether OATP-mediated steroid transport can actually modify prostate tumor androgen levels in vivo has never been demonstrated.

METHODS

We sought to determine whether OATP-mediated steroid transport can measurably alter PCa androgen levels in vivo. We evaluated the uptake of dehydroepiandrosterone (DHEAS), E1S and testosterone in LNCaP cells engineered to express OATP1B1, 1B3, 2B1 or 4A1. We measured the uptake via administration of tritiated steroids to castrate mice bearing vector control or OATP1B1-, 2B1- or 4A1-expressing xenografts. We treated tumor-bearing mice with DHEAS and testosterone at physiologically relevant levels and measured intratumor accumulation of administered steroids by mass spectrometry.

RESULTS

OATP1B1- and 2B-expressing xenografts each showed a threefold increase in tritiated-DHEAS uptake vs vector controls (P=0.002 and P=0.036, respectively). At circulating DHEAS levels similar to those in abiraterone-treated men (~15 μg dl^-1), OATP1B1- and 2B1-expressing xenografts showed a 3.9-fold (P=0.057) and 1.9-fold (P=0.048) increase in tumor accumulation of DHEAS and a 1.6-fold (P=0.057) and 2.7-fold (P=0.095) increase in DHEA, respectively. At the substantial circulating testosterone levels found in eugonadal men, a consistent effect of OATP1B1, 2B1 or 4A1 on testosterone uptake in vivo was not detected.

CONCLUSIONS

OATP transporters measurably alter DHEAS uptake and intratumor androgen levels in prostate tumors in vivo, even at circulating androgen levels achieved in abiraterone-treated patients. These novel data emphasize the continued need to inhibit ligand-mediated androgen receptor signaling in PCa tumors, and support prospective evaluation of studies designed to test inhibition of OATP-mediated DHEAS uptake and utilization.

CYP17 inhibitors in prostate cancer: latest evidence and clinical potential

Since androgen signaling plays a pivotal role in the proliferation and metastasis of prostate cancer, androgen deprivation therapy (ADT) or castration therapy is considered the backbone of treatment for newly diagnosed metastatic prostate cancer. However, almost all men experience disease progression on ADT to a state known as metastatic castration-resistant prostate cancer (mCRPC), which continues to be driven by intratumoral androgen synthesis or androgen receptor signaling. Hence, the extragonadal ablation of androgen synthesis from pregnane precursors holds much promise. An inhibitor of cytochrome P450 17α-hydroxy/17,20-lyase (CYP17) enzymes, abiraterone acetate, has already been approved for men with mCRPC. Newer CYP17 inhibitors continue to be developed which are either more selective or have concomitant inhibitory actions on AR signaling. These include VT-464, orteronel, and galeterone. Herein, we focus on the molecular mechanism of action, efficacy, latest evidence, and clinical potential of CYP17 inhibitors in prostate cancer.

Abiraterone in the management of castration-resistant prostate cancer prior to chemotherapy

The treatment armamentarium for metastatic castration-resistant prostate cancer (mCRPC) has increased significantly over the past several years. Approved drugs associated with improved survival include androgen pathway-targeted agents (abiraterone acetate and enzalutamide), chemotherapeutics (docetaxel and cabazitaxel), an autologous vaccine (sipuleucel-T) and a radiopharmaceutical (radium-223). Abiraterone acetate, a prodrug of abiraterone, inhibits the CYP17A enzyme, a critical enzyme in androgen biosynthesis. Abiraterone has regulatory approval in mCRPC in both chemotherapy-naïve patients and in the post-docetaxel setting based on results from two randomized phase III studies. In the COU-AA-302 trial, abiraterone demonstrated significant improvement in the coprimary endpoints of radiographic progression-free survival and overall survival, as well as in a number of secondary endpoints including time until initiation of chemotherapy, time until opiate use for cancer-related pain, prostate-specific antigen progression-free survival and decline in performance status. Abiraterone is well-tolerated, although adverse events associated with this agent include abnormalities in liver function testing and mineralocorticoid-associated adverse events. This review evaluates the use of abiraterone in mCRPC prior to the use of chemotherapy.

Androgen receptor targeting drugs in castration-resistant prostate cancer and mechanisms of resistance

Reactivated androgen receptor (AR) signaling drives castration-resistant prostate cancer (CRPC). The novel AR targeting drugs abiraterone and enzalutamide have improved survival of CRPC patients. However, resistance to these agents develops and patients ultimately succumb to CRPC. Potential mechanisms of resistance include the following: 1) Expression of AR splice variants, such as the AR-V7 isoform, which lacks the ligand-binding domain; 2) AR missense mutations in the ligand-binding domain, such as F876L and T877A; and 3) Mutation or overexpression of androgen biosynthetic enzymes or glucocorticoid receptor. Several novel agents may overcome resistance mechanisms. Galeterone acts through multiple mechanisms that include degradation of AR protein and is being evaluated in CRPC patients positive for AR-V7. EPI-001 and related compounds inhibit AR splice variants by targeting the N-terminal transactivation domain of AR. Promising therapies and novel biomarkers, such as AR-V7, may lead to improved outcomes for CRPC patients.

Activation of AKR1C1/ERβ induces apoptosis by downregulation of c-FLIP in prostate cancer cells: A prospective therapeutic opportunity

We provide first-time evidence for ERβ-mediated transcriptional upregulation of c-FLIP as an underlying mechanism in the development of castrate-resistant cancer. While androgens inhibit apoptosis partly through transcriptional upregulation of the anti-apoptotic protein, c-FLIP in androgen-responsive cells, they downregulate c-FLIP in androgen-independent cells. We found that although Sp1 and p65 trans-activate c-FLIP, the combination of Sp1 and p65 has differential effects in a cellular context-dependent manner. We show that activation of the androgen metabolism enzyme, aldo-keto reductase, AKR1C1, relieves androgen independence through activation of 3β-Adiol-mediated upregulation of ERβ. ERβ competes with Sp1 and Sp3 to transcriptionally downregulate c-FLIP in the absence of consensus estrogen-response element in androgen-independent cells. Forced expression of AR in androgen-independent cells show that ERβ-mediated growth inhibition occurs under conditions of androgen independence. Reactivation of ERβ with the estrogenic metabolite, 2-methoxyestradiol, decreased enrichment ratio of Sp1/Sp3 at the c-FLIP promoter with concomitant effects on cell growth and death. Expression of Sp1 and c-FLIP are elevated while AKR1C1, ERβ and Sp3 are significantly low in human prostate tumor samples. ERβ is epigenetically silenced in prostate cancer patients, therefore our results suggest that combination of ERβ agonists with ADT would benefit men stratified on the basis of high estrogen levels.

The DHEA-sulfate depot following P450c17 inhibition supports the case for AKR1C3 inhibition in high risk localized and advanced castration resistant prostate cancer

Prostate cancer is the second leading cause of cancer death in the United States. Treatment of localized high-risk disease and de novo metastatic disease frequently leads to relapse. These metastatic castration resistant prostate cancers (mCRPC) claim a high mortality rate, despite the extended survival afforded by the growing armamentarium of androgen deprivation, radiation and immunotherapies. Here, we review two studies of neoadjuvant treatment of high-risk localized prostate cancer prior to prostatectomy, the total androgen pathway suppression (TAPS) trial and the neoadjuvant abiraterone acetate (AA) trial. These two trials assessed the efficacy of the non-specific P450c17 inhibitor, ketoconazole and the specific P450c17 inhibitor, AA, to inhibit tissue and serum androgen levels. Furthermore, a novel and validated stable isotope dilution liquid chromatography electrospray ionization selected reaction monitoring mass spectrometry assay was used to accurately quantify adrenal and gonadal androgens in circulation during the course of these trials. The adrenal androgens, Δ(4)-androstene-3,17-dione, dehydroepiandrosterone and dehydroepiandrosterone sulfate were significantly reduced in the patients receiving ketoconazole or AA compared to those who did not. However, in both trials, a significant amount of DHEA-S (∼20 μg/dL) persists and thus may serve as a depot for intratumoral conversion to the potent androgen receptor ligands, testosterone (T) and 5α-dihydrotestosterone (DHT). The final step in conversion of Δ(4)-androstene-3,17-dione and 5α-androstanedione to T and DHT, respectively, is catalyzed by AKR1C3. We therefore present the case that in the context of the DHEA-S depot, P450c17 and AKR1C3 inhibition may be an effective combinatorial treatment strategy.