AKR1C3 Converts Castrate and Post-Abiraterone DHEA-S into Testosterone to Stimulate Growth of Prostate Cancer Cells via 5-Androstene-3β,17β-Diol

Androgen receptor signaling inhibitors (ARSI) are used to treat castration-resistant prostate cancer (CRPC) to stop a resurgence of androgen receptor (AR) signaling. Despite early success, patients on ARSIs eventually relapse, develop drug resistance, and succumb to the disease. Resistance may occur through intratumoral steroidogenesis mediated by upregulation of aldo-keto reductase family 1C member 3 (AKR1C3). Patients treated with leuprolide (castrate) and those treated with leuprolide plus abiraterone (post-Abi) harbor a reservoir of DHEA-S which could fuel testosterone (T) biosynthesis via AKR1C3 to cause a resurgence of prostate cancer cell growth. We demonstrate that concentrations of DHEA-S found in castrate and post-Abi patients are (i) converted to T in an AKR1C3-dependent manner in prostate cancer cells, and (ii) in amounts sufficient to stimulate AKR1C3-dependent cell growth. We observed this in primary and metastatic prostate cancer cell lines, CWR22PC and DuCaP, respectively. Androgen measurements were made by stable isotope dilution LC-MS/MS. We demonstrate AKR1C3 dependence using stable short hairpin RNA knockdown and pharmacologic inhibitors. We also demonstrate that free DHEA is reduced to 5-androstene-3β,17β-diol (5-Adiol) by AKR1C3 and that this is a major metabolite, suggesting that in our cell lines 5-Adiol is a predominant precursor of T. We have identified a mechanism of ARSI resistance common to both primary and metastatic cell lines that is dependent on the conversion of DHEA to 5-Adiol on route to T catalyzed by AKR1C3.

SIGNIFICANCE

We show that reservoirs of DHEA-S that remain after ARSI treatment are converted into T in primary and metastatic prostate cancer cells in amounts sufficient to stimulate cell growth. Pharmacologic and genetic approaches demonstrate that AKR1C3 is required for these effects. Furthermore, the route to T proceeds through 5-Adiol. We propose that this is a mechanism of ARSI drug resistance.

High sensitivity LC-MS methods for quantitation of hydroxy- and keto-androgens

The quantitation of androgens is necessary to diagnose and monitor the development of diseases such as prostate cancer and polycystic ovary syndrome. Androgen measurements also support the laboratory-based study of androgen metabolism in cellular and animal models. The methods described in this chapter combine chemical derivatization of hydroxy- and keto-androgens with stable isotope dilution liquid chromatography mass spectrometry (SID-LC-MS). Chemical derivatization of hydroxy-androgens by picolinic acid and keto-androgens by Girard P enhances the ionization and detection sensitivity of androgens, while chromatographic separation and [13C]-labeled internal standards add specificity that allow for simultaneous quantitation of multiple androgens. This chapter describes the materials and protocols necessary for chemical derivatization, enzymatic synthesis of internal standards, and LC-MS detection of keto- and hydroxy-androgens.

Aldo keto-reductase family 1C members 1 through 4 recombinant enzyme purification and enzyme assay

Aldo-keto reductase family 1C (AKR1C) members transform steroids via their 3-, 17-, and 20-ketosteroid reductase activities. The biochemical study of these enzymes can help to inform their roles in hormone-dependent diseases and develop therapeutic inhibitors. This work describes a protocol to purify AKR1C1-4 members from a bacterial expression system using two chromatography steps. It also describes the basis of discontinuous assays to measure steroid conversion.

Germline Mutations in Steroid Metabolizing Enzymes: A Focus on Steroid Transforming Aldo-Keto Reductases

Steroid hormones synchronize a variety of functions throughout all stages of life. Importantly, steroid hormone-transforming enzymes are ultimately responsible for the regulation of these potent signaling molecules. Germline mutations that cause dysfunction in these enzymes cause a variety of endocrine disorders. Mutations in SRD5A2, HSD17B3, and HSD3B2 genes that lead to disordered sexual development, salt wasting, and other severe disorders provide a glimpse of the impacts of mutations in steroid hormone transforming enzymes. In a departure from these established examples, this review examines disease-associated germline coding mutations in steroid-transforming members of the human aldo-keto reductase (AKR) superfamily. We consider two main categories of missense mutations: those resulting from nonsynonymous single nucleotide polymorphisms (nsSNPs) and cases resulting from familial inherited base pair substitutions. We found mutations in human AKR1C genes that disrupt androgen metabolism, which can affect male sexual development and exacerbate prostate cancer and polycystic ovary syndrome (PCOS). Others may be disease causal in the AKR1D1 gene that is responsible for bile acid deficiency. However, given the extensive roles of AKRs in steroid metabolism, we predict that with expanding publicly available data and analysis tools, there is still much to be uncovered regarding germline AKR mutations in disease.

Reconstitution of human adrenocortical specification and steroidogenesis using induced pluripotent stem cells

The mechanisms leading to adrenal cortex development and steroid synthesis in humans remain poorly understood due to the paucity of model systems. Herein, we recapitulate human fetal adrenal cortex specification processes through stepwise induction of human-induced pluripotent stem cells through posterior intermediate mesoderm-like and adrenocortical progenitor-like states to ultimately generate fetal zone adrenal-cortex-like cells (FZLCs), as evidenced by histomorphological, ultrastructural, and transcriptome features and adrenocorticotropic hormone (ACTH)-independent Δ5 steroid biosynthesis. Furthermore, FZLC generation is promoted by SHH and inhibited by NOTCH, ACTIVIN, and WNT signaling, and steroid synthesis is amplified by ACTH/PKA signaling and blocked by inhibitors of Δ5 steroid synthesis enzymes. Finally, NR5A1 promotes FZLC survival and steroidogenesis. Together, these findings provide a framework for understanding and reconstituting human adrenocortical development in vitro, paving the way for cell-based therapies of adrenal insufficiency.

ODP440 Characterization of the Major Single Nucleotide Polymorphic Variants of Aldo-Keto Reductase 1c3 (Type 5 17β-Hydroxysteroid Dehydrogenase)

Background

Aldo-keto-reductase (AKR) 1C3, also known as type 517β-hydroxysteroid dehydrogenase and prostaglandin F synthase,is a member of the AKR superfamily that reduces aldehydes and ketones to primary and secondary alcohols. It plays an essential role in the peripheral formation of androgens and is associated with several steroid hormone dependent diseases including prostate cancer (PC), breast cancer, and polycystic ovarian syndrome (PCOS). Furthermore, AKR1C3 is implicated in castration resistant prostate cancer (CRPC) drug resistance on the basis that it is upregulated in CRPC tumors and metastases and overexpressed in cell culture & xenograft models of Abiraterone and Enzalutamide resistance, where resistance is surmounted by AKR1C3 knockdown or treatment with the AKR1C3 inhibitor indomethacin. AKR1C3 has 14 nonsynonymous single nucleotide polymorphisms (nsSNPs) with different global frequencies and ethnic distributions. Association studies support their role in PC and other diseases, but detailed functional genomic studies of these variants are lacking. One study examined5 AKR1C3 nsSNPs for their ability to reduce exemestane, an aromatase inhibitor used to treat breast cancer, to 17β-dihydroexemestane, and reported a 17-250-fold reduction in catalytic efficiency of H5Q, E77G, K104D, and R258C variants compared to WT. This observation provided the impetus to examine impact of these variants on AKR1C3 function in the context of PC. We purified AKR1C3 WT, and the top four most frequently occurring nsSNPs, H5Q, E77G, K104D, and R258C, from E. coli to expand upon their characterization and illuminate functional differences that could affect disease outcome and treatment. METHODS: Kinetic measurements were made using either a continuous spectrophotometric assay monitoring the appearance of the reduced cofactor NADH, or a discontinuous RP UV-HPLC assay based on chromatographic separation of substrate and product. Inhibitor sensitivity studies were conducted with a fluorescence-based plate-reader assay monitoring enzyme activity via oxidation of a standard substrate in the presence of increasing inhibitor. Stability was assessed by monitoring the percent of maximum activity remaining via oxidation of a standard substrate over a range of increasing temperatures for each variant.

Results

We report no major deviations in kinetics in the top four most frequently occurring AKR1C3 variants compared to WT. Additionally, variants did not display differences in inhibitor sensitivity to competitive inhibitor indomethacin. However, the K104D variant lost activity at a lower temperature than WT, suggesting that this mutation results in a decrease in stability.

Conclusions

Altogether, these findings contrast with previous claims that AKR1C3 variants, mainly H5Q, give rise to significant advantage or disadvantage over WT in PC and other diseases, and suggests that patients with AKR1C3 dependent diseases would likely be overall unaffected by variant status.

Presentation: No date and time listed

Characterization of the major single nucleotide polymorphic variants of aldo-keto reductase 1C3 (type 5 17β-hydroxysteroid dehydrogenase)

Aldo-keto reductase (AKR) 1C3, also known as type 5 17β-hydroxysteroid dehydrogenase and prostaglandin F synthase, is a member of the AKR superfamily that reduces aldehydes and ketones to primary and secondary alcohols. It plays an essential role in the peripheral formation of androgens and is implicated in several steroid hormone dependent diseases including prostate cancer, breast cancer, and polycystic ovary syndrome (PCOS). AKR1C3 has 14 nonsynonymous single nucleotide polymorphisms (nsSNPs) with different global frequencies and ethnic distributions. Association studies support their role in disease, but a detailed functional genomic analysis of these variants is lacking. One study examined five AKR1C3 nsSNPs for their ability to reduce exemestane, an aromatase inhibitor used to treat breast cancer, to 17β-dihydroexemestane, and reported a 17-250-fold reduction in catalytic efficiency of H5Q, E77G, K104D, and R258C variants compared to wild type (WT). This observation provided the impetus to examine the impact of these variants on AKR1C3 function. Here, we purified AKR1C3 WT, and the top four most frequently occurring nsSNPs, H5Q, E77G, K104D, and R258C, from E. coli to expand upon their characterization and illuminate functional differences that could affect disease outcome and treatment. While we found negligible deviations in steady state kinetics, the K104D variant showed reduced thermal stability compared to WT. The presence of NAD(P)⁺ restored the stability of the variant. As it is unlikely that the apoenzyme will exist within the cell without cofactor bound the K104D is not expected to manifest a phenotype.

Intracrinology-revisited and prostate cancer

The formation of steroid hormones in peripheral target tissues is referred to as their intracrine formation. This process occurs in hormone dependent malignancies such as prostate and breast cancer in which the disease can be either castrate resistant or occur post-menopausally, respectively. In these instances, the major precursor steroid of androgens and estrogens is dehydroepiandrosterone (DHEA) and DHEA-SO₄. This article reviews the major pathways by which adrenal steroids are converted to the potent male sex hormones, testosterone (T) and 5α-dihydrotestosterone (5α-DHT) and the discrete enzyme isoforms involved in castration resistant prostate cancer. Previous studies have mainly utilized radiotracers to investigate these pathways but have not used prevailing concentrations of precursors found in castrate male human serum. In addition, the full power of stable-isotope dilution liquid chromatography tandem mass spectrometry has not been applied routinely. Furthermore, it is clear that adaptive responses occur in the transporters and enzyme isoforms involved in response to androgen deprivation therapy that need to be considered.