Elsevier

Chemico-Biological Interactions

Volume 234, 5 June 2015, Pages 332-338
Chemico-Biological Interactions

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

https://doi.org/10.1016/j.cbi.2014.12.012Get rights and content

Highlights

  • Androgen deprivation therapy (ADT) is a mainstay in advanced prostate cancer treatment.

  • Total androgen pathway suppression and abiraterone neoadjuvant clinical trials were compared.

  • P450c17 inhibition reduced serum Δ4-AD, DHEA and DHEA-S, in addition to T and DHT.

  • A depot of DHEA-S remains and may facilitate intratumoral androgen conversion.

  • In CYP17A1 refractory tumors, AKR1C3 inhibitors are a promising strategy.

Abstract

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, Δ4-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 Δ4-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.

Introduction

Prostate cancer is the second leading cause of cancer mortality in men in the developed world. According to the Surveillance, Epidemiology and End Results (SEER) program registries, it is projected that there are nearly 3 million men living with prostate cancer in the United States and that 233,000 new cases will be diagnosed in 2014. Individuals diagnosed with high-risk prostate cancer are typically treated with surgery or a combination of radiation and androgen deprivation therapy (ADT). Many will inevitably relapse and ultimately develop castration-resistant prostate cancer (CRPC), which is responsible for the vast majority of prostate cancer mortalities. There is a need to improve therapies for this high risk population. The mechanisms of resistance are multi-factorial but the androgen receptor (AR) remains active in most cases, as illustrated by the initial efficacy of newer ADT agents such as abiraterone acetate (AA) and enzalutamide in the mCRPC setting. There is a body of evidence that indicates that the resistant tumor can adapt to castrate conditions imposed by ADT via the increased expression of enzymes that facilitate the intratumoral conversion of circulating adrenal androgen precursors to the active AR ligands. Further, there is evidence that AR mutations, splice variants and increased copy number represent putative mechanisms of resistance to therapy. Here, we review the data from our SID-LC/ESI/SRM/MS quantification of serum androgens in patients enrolled in the neoadjuvant TAPS and the neoadjuvant AA trials. In both trials, conventional ADT agents were effective at achieving castrate concentrations of T and DHT. In the neoadjuvant TAPS trial, drastic reductions in the adrenal androgen precursors such as DHEA-S were observed in the arm in which patients received the non-specific P450c17 inhibitor, ketoconazole. Similarly, in the neoadjuvant AA trial, DHEA-S levels were consistently reduced only in patients that received the specific P450c17 inhibitor, AA. However, despite the large reductions in adrenal androgen precursors following P450c17 inhibition, a significant depot of DHEA-S remains in the circulation. Therefore, we hypothesize that the DHEA-S depot may be utilized for intratumoral biosynthesis of T and DHT, which would present an opportunity for AKR1C3 inhibition in the ketoconazole and AA refractory mCRPC setting.

Section snippets

Prostate cancer and androgen deprivation therapy

In the 1940’s, Huggins and Hodges laid the foundation for the treatment of advanced, metastatic prostate cancer by successfully conducting surgical castration or orchiectomy to shrink prostate tumors [1]. This work extended Beatson’s pioneering efforts whereby oophorectomy was used to successfully treat select cases of advanced breast cancer [2]. The present day treatment of hormone-dependent cancers continues to build upon this legacy with the advent and development of pharmacological ADT. The

The problem – resistance to therapy

The mechanisms for CRPC include modifications in the AR via an increase in copy number [11], [12], [13], [14], mutations in the AR that may lead to ligand promiscuity [15], [16], [17], [18], [19] and the emergence of splice variants that may facilitate resistance to AR antagonists [20], [21], [22]. The primary focus of this review is the resistance that arises when castrate conditions trigger an adaptive response by up-regulating the expression of enzymes such as 5α-reductase type 1 and 2 [23],

Prostate specific antigen (PSA)

The clinical biomarker for prostate cancer is prostate specific antigen (PSA) and its implementation has facilitated early disease detection and monitoring of therapy. PSA is the primary clinical biomarker used in tracking the efficacy of ADT. It is our contention that quantification of serum and tissue androgen metabolites, both conjugated and unconjugated will greatly augment PSA measurements during the monitoring of ADT treatment and shed light on potential pre-receptor mechanisms of drug

Advances in P45017A1 inhibitors and AR antagonists as therapy

The emergence of mCRPC has led to the development and pursuit of additional ADT agents such as the P450c17 17α-hydroxylase/17, 20-lyase inhibitor, abiraterone acetate (AA) [29] and the latest addition to the AR antagonist family, enzalutamide [30]. AA increased the median survival of mCRPC patients by 3.9 months [31] and 4.6 months [32] and enzalutamide increased median survival of CRPC patients by 4.8 months [33], confirming that some of these tumors remained hormonally driven. However, tumors

AKR1C3 and prostate cancer

The 17β hydroxysteroid dehydrogenase type 5, also known as aldo–keto reductase 1C3 (17β-HSD5; AKR1C3) is the predominant 17β-HSD isoform expressed in the prostate [37]. AKR1C3 catalyzes the NADPH-dependent reduction of both Δ4-AD to T and 5α-androstane-3,17-dione to DHT (Scheme 1) [38]. AKR1C3 is up-regulated in prostate cancer and expression levels correlate with stage of disease [39]. In prostate cancer cell lines, natural and synthetic androgens down-regulate AKR1C3, whereas androgen

ADT clinical trials and androgen measurements

Several ADT clinical trials have monitored the reduction in a few serum androgens during the course of drug treatment [48], [49], [50], [51]. However, the clinical experience has shown that patients develop resistance to treatment in spite of castrate levels of serum T and DHT. The historic definition of castrate levels of serum androgens has been <50 ng/dL as this was the limit of quantification of previous analytical methods. The confounding factor in a number of these past analyses is that

The total androgen pathway suppression trial

The TAPS trial randomized intermediate to high-risk prostate cancer patients into one of four arms for a 12 week period prior to radical prostatectomy. Patients in arm 1 received goserelin, a leutinizing hormone releasing hormone agonist (LHRHa) and R-bicalutamide, an AR antagonist; patients in arm 2 received goserelin and dutasteride, a dual 5α-reductase type 1 and type 2 inhibitor; patients in arm 3 received, goserelin, R-bicalutamide and dutasteride; and patients in arm 4 received goserelin, R

The neo-adjuvant AA trial

Abiraterone acetate (AA) is one of the newest additions to the ADT armamentarium and acts by inhibiting P450c17, 17α-hydroxylase and 17,20-lyase activity. The primary endpoint of the neoadjuvant AA trial was to analyze the difference in prostate tissue hormones as a result of leuprolide treatment alone compared to leuprolide and AA, thus confirming an AA target effect in prostate tissue. In this trial, patients with localized high and intermediate-risk prostate cancer were randomly assigned to

Trends from the TAPS and AA trials

In arm 4 of the TAPS trial and the leuprolide and AA and prednisone arm of the neoadjuvant AA trial, castrate levels of serum T were achieved (95–99% reduction). The reduction in serum DHEA-S concentration following AA treatment was more robust (>90% reduction) than that seen with the non-specific P450c17 inhibitor, ketoconazole, used in the TAPS trial, (∼70% reduction). However, the reduction following AA treatment still left serum DHEA-S concentration in the ∼20 μg/dL range, which may serve as

Intratumoral androgen conversion and AKR1C3 inhibition

Under normal physiological conditions, circulating DHEA and DHEA-S is utilized in peripheral tissue for intracrine production of androgens and estrogens [56]. Likewise, the intratumoral conversion of circulating DHEA-S to yield potent AR ligands (T and DHT) requires the expression and activity of organic anion transporter polypeptides (OATPs) to facilitate transport of the conjugated androgen into the cell. The expression of steroid sulfatase (STS) is required to release unconjugated DHEA and

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Conflict of Interest

Dr. Tamae reports grants from National Cancer Institute during the conduct of the study. Dr. Mostaghel reports grants from National Cancer Institute during the conduct of the study; and personal fees from Janssen Pharmaceuticals outside the submitted work. Dr. Montgomery reports grants from Prostate Cancer Foundation, during the conduct of the study; and personal fees from Janssen Pharmaceuticals outside the submitted work. Dr. Nelson reports grants from National Cancer Institute, grants from

Acknowledgements

Grant support was from the following funding sources: the National Cancer Institute (NCI)/National Institutes of Health (NIH) Cancer Pharmacology Training Grant (R25 CA101871) to D.T.; Prostate Cancer Foundation Challenge Award (S.P.B. and P.N.), AA clinical trial support Janssen Pharmaceuticals, TAPS clinical trial support; the National Institute of Environmental Health Sciences/NIH Center of Excellence in Environmental Toxicology (P30-ES013508), the NCI Grant (P01-CA163227) and a Prostate

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