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

Discovery and Optimization of a Covalent AKR1C3 Inhibitor

Aldo-keto reductase family 1 member C3 (AKR1C3) is a member of the AKR superfamily of enzymes that metabolize androgen, estrogen, and prostaglandin substrates that drive proliferation in hormone-dependent cancers. Interest in developing selective inhibitors has produced tool compounds for the inactivation or degradation of AKR1C3 with varying degrees of selectivity among the 14 known AKR proteins. Selectivity of AKR1C3 inhibitors across the AKR family is critical since a clinical candidate failed due to hepatotoxicity from off-target inhibition of AKR1D1. Here, we report development of a sulfonyl-triazole (SuTEx) covalent AKR1C3 inhibitor (RJG-2051) that selectively engages a noncatalytic tyrosine residue (Y24) on AKR1C3. Importantly, RJG-2051 exhibited negligible cross-reactivity with AKRs or other proteins across 1800+ tyrosine and lysine sites quantified by chemical proteomics. Our disclosure of a covalent inhibitor for potent AKR1C3 inactivation with proteome-wide selectivity in cells will expedite cell biological studies for testing the therapeutic potential of this metabolic target.

Blockade of neutral sphingomyelinase 2 exerts antitumor effect on metastatic castration resistant prostate cancer cells and promotes tumor regression when combined with Enzalutamide

Prostate cancer (PCa) is the second leading cause of cancer-related deaths among American men. The development of metastatic castration resistant PCa (mCRPC) is the current clinical challenge. Antiandrogens such as Enzalutamide (ENZ) are commonly used for CRPC treatment. However, patients with androgen receptor (AR)-negative tumors do not respond to ENZ, while AR-positive tumors frequently develop resistance, limiting the long-term efficacy of this therapy. This study investigates the efficacy of neutral sphingomyelinase 2 (n-SMase2) inhibition by DPTIP, both alone and in combination with ENZ, as a therapeutic strategy for mCRPC. In vitro assays were conducted to determine the half-maximal inhibitory concentration (IC50) of DPTIP and ENZ in mCRPC cells. The effect of these treatments on cell proliferation, migration, and colony formation was assessed. The antitumor effect of DPTIP was also evaluated in a preclinical PCa mouse model. Elevated n-SMase2 expression was observed in PCa patients compared to normal subjects at both mRNA and protein levels. In CWR-R1ca and PC-3 cells, DPTIP had IC50 values of 10.31 and 14.57 µM, while ENZ had IC50 values of 33.7 and 81 µM, respectively. Combined treatment significantly suppressed cell proliferation, colony formation, and migration of mCRPC cells. Mechanistically, the ERK1/2 activity and the expression of nSMase2 and NF-kB p65 were inhibited by DPTIP. The in vivo combination of DPTIP and ENZ reduced tumor size and weight more effectively than either drug alone, without significant changes in body weight. This study highlights the therapeutic potential of targeting n-SMase2 for mCRPC. Inhibition of n-SMase2 using DPTIP, both as a standalone treatment and in combination with ENZ, effectively suppressed the growth and migration of mCRPC cells. These findings suggest a promising novel approach to treating mCRPC and warrant further investigation in clinical settings.

Coumarin-Based Aldo-Keto Reductase Family 1C (AKR1C) 2 and 3 Inhibitors

A series of 7-substituted coumarin derivatives have been characterized as pan-aldo-keto reductase family 1C (AKR1C) inhibitors. The AKR1C family of enzymes are overexpressed in numerous cancers where they are involved in drug resistance development. 7-hydroxy coumarin ethyl esters and their corresponding amides have high potency for AKR1C3 and AKR1C2 inhibition. Coumarin amide 3 a possessed IC50 values of 50 nM and 90 nM for AKR1C3 and AKR1C2, respectively, and exhibits 'drug-like' metabolic stability and half-life in human and mouse liver microsomes and plasma. Compound 3 a was employed as a chemical tool to determine pan-AKR1C2/3 inhibition effects both as a radiation sensitizer and as a potentiator of chemotherapy cytotoxicity. In contrast to previously reported pan-AKR1C inhibitors, 3 a demonstrated no radiation sensitization effect in a radiation-resistant prostate cancer cell line model. Pan-AKR1C inhibition also did not potentiate the in vitro cytotoxicity of ABT-737, daunorubicin or dexamethasone, in two patient-derived T-cell ALL and pre-B-cell ALL cell lines. In contrast, a highly selective AKR1C3 inhibitor, compound K90, enhanced the cytotoxicity of both ABT-737 and daunorubicin in the T-cell ALL cell line model. Thus, the inhibitory profile required to enhance chemotherapeutic cytotoxicity in leukemia may be AKR1C isoform and drug specific.

MYO6 contributes to tumor progression and enzalutamide resistance in castration-resistant prostate cancer by activating the focal adhesion signaling pathway

BACKGROUND

Enzalutamide (Enz) resistance is a poor prognostic factor for patients with castration-resistant prostate cancer (CRPC), which often involves aberrant expression of the androgen receptor (AR). Myosin VI (MYO6), one member of the myosin family, plays an important role in regulating cell survival and is highly expressed in prostate cancer (PCa). However, whether MYO6 is involved in Enz resistance in CRPC and its mechanism remain unclear.

METHODS

Multiple open-access databases were utilized to examine the relationship between MYO6 expression and PCa progression, and to screen differentially expressed genes (DEGs) and potential signaling pathways associated with the MYO6-regulated Enz resistance. Both in vitro and in vivo tumorigenesis assays were employed to examine the impact of MYO6 on the growth and Enz resistance of PCa cells. Human PCa tissues and related clinical biochemical data were utilized to identify the role of MYO6 in promoting PCa progression and Enz resistance. The molecular mechanisms underlying the regulation of gene expression, PCa progression, and Enz resistance in CRPC by MYO6 were investigated.

RESULTS

MYO6 expression increases in patients with PCa and is positively correlated with AR expression in PCa cell lines and tissues. Overexpression of AR increases MYO6 expression to promote PCa cell proliferation, migration and invasion, and to inhibit PCa cell apoptosis; whereas knockdown of MYO6 expression reverses these outcomes and enhances Enz function in suppressing the proliferation of the Enz- sensitive and resistant PCa cells both in vitro and in vivo. Mechanistically, AR binds directly to the promoter region (residues - 503 to - 283 base pairs) of MYO6 gene and promotes its transcription. Furthermore, MYO6 activates focal adhesion kinase (FAK) phosphorylation at tyrosine-397 through integrin beta 8 (ITGB8) modulation to promote PCa progression and Enz resistance. Notably, inhibition of FAK activity by Y15, an inhibitor of FAK, can resensitize CRPC cells to Enz treatment in cell lines and mouse xenograft models.

CONCLUSIONS

MYO6 has pro-tumor and Enz-resistant effects in CRPC, suggesting that targeting MYO6 may be beneficial for ENZ-resistant CRPC therapy through the AR/MYO6/FAK signaling pathway.

Discovery of an Aldo-Keto reductase 1C3 (AKR1C3) degrader

Aldo-keto reductase 1C3 (AKR1C3) is a protein upregulated in prostate cancer, hematological malignancies, and other cancers where it contributes to proliferation and chemotherapeutic resistance. Androgen receptor splice variant 7 (ARv7) is the most common mutation of the AR receptor that confers resistance to clinical androgen receptor signalling inhibitors in castration-resistant prostate cancer. AKR1C3 interacts with ARv7 promoting stabilization. Herein we report the discovery of the first-in-class AKR1C3 Proteolysis-Targeting Chimera (PROTAC) degrader. This first-generation degrader potently reduced AKR1C3 expression in 22Rv1 prostate cancer cells with a half-maximal degradation concentration (DC50) of 52 nM. Gratifyingly, concomitant degradation of ARv7 was observed with a DC50 = 70 nM, along with degradation of the AKR1C3 isoforms AKR1C1 and AKR1C2 to a lesser extent. This compound represents a highly useful chemical tool and a promising strategy for prostate cancer intervention.

Structure-guided optimization of 3-hydroxybenzoisoxazole derivatives as inhibitors of Aldo-keto reductase 1C3 (AKR1C3) to target prostate cancer

AKR1C3 is an enzyme that is overexpressed in several types of radiotherapy- and chemotherapy-resistant cancers. Despite AKR1C3 is a validated target for drug development, no inhibitor has been approved for clinical use. In this manuscript, we describe our study of a new series of potent AKR1C3-targeting 3-hydroxybenzoisoxazole based inhibitors that display high selectivity over the AKR1C2 isoform and low micromolar activity in inhibiting 22Rv1 prostate cancer cell proliferation. In silico studies suggested proper substituents to increase compound potency and provided with a mechanistic explanation that could clarify their different activity, later confirmed by X-ray crystallography. Both the in-silico studies and the crystallographic data highlight the importance of 90° rotation around the single bond of the biphenyl group, in ensuring that the inhibitor can adopt the optimal binding mode within the active pocket. The p-biphenyls that bear the meta-methoxy, and the ortho- and meta-trifluoromethyl substituents (in compounds 6a, 6e and 6f respectively) proved to be the best contributors to cellular potency as they provided the best IC50 values in series (2.3, 2.0 and 2.4 μM respectively) and showed no toxicity towards human MRC-5 cells. Co-treatment with scalar dilutions of either compound 6 or 6e and the clinically used drug abiraterone led to a significant reduction in cell proliferation, and thus confirmed that treatment with both CYP171A1-and AKR1C3-targeting compounds possess the potential to intervene in key steps in the steroidogenic pathway. Taken together, the novel compounds display desirable biochemical potency and cellular target inhibition as well as good in-vitro ADME properties, which highlight their potential for further preclinical studies.

AKR1C3 in carcinomas: from multifaceted roles to therapeutic strategies

Aldo-Keto Reductase Family 1 Member C3 (AKR1C3), also known as type 5 17β-hydroxysteroid dehydrogenase (17β-HSD5) or prostaglandin F (PGF) synthase, functions as a pivotal enzyme in androgen biosynthesis. It catalyzes the conversion of weak androgens, estrone (a weak estrogen), and PGD2 into potent androgens (testosterone and 5α-dihydrotestosterone), 17β-estradiol (a potent estrogen), and 11β-PGF2α, respectively. Elevated levels of AKR1C3 activate androgen receptor (AR) signaling pathway, contributing to tumor recurrence and imparting resistance to cancer therapies. The overexpression of AKR1C3 serves as an oncogenic factor, promoting carcinoma cell proliferation, invasion, and metastasis, and is correlated with unfavorable prognosis and overall survival in carcinoma patients. Inhibiting AKR1C3 has demonstrated potent efficacy in suppressing tumor progression and overcoming treatment resistance. As a result, the development and design of AKR1C3 inhibitors have garnered increasing interest among researchers, with significant progress witnessed in recent years. Novel AKR1C3 inhibitors, including natural products and analogues of existing drugs designed based on their structures and frameworks, continue to be discovered and developed in laboratories worldwide. The AKR1C3 enzyme has emerged as a key player in carcinoma progression and therapeutic resistance, posing challenges in cancer treatment. This review aims to provide a comprehensive analysis of AKR1C3's role in carcinoma development, its implications in therapeutic resistance, and recent advancements in the development of AKR1C3 inhibitors for tumor therapies.

Proguanil Suppresses Breast Tumor Growth In Vitro and In Vivo by Inducing Apoptosis via Mitochondrial Dysfunction

Breast cancer, ranking as the second leading cause of female cancer-related deaths in the U.S., demands the exploration of innovative treatments. Repurposing FDA-approved drugs emerges as an expedited and cost-effective strategy. Our study centered on proguanil, an antimalarial drug, reveals notable anti-proliferative effects on diverse breast cancer cell lines, including those derived from patients. Proguanil-induced apoptosis was associated with a substantial increase in reactive oxygen species (ROS) production, leading to reduced mitochondrial membrane potential, respiration, and ATP production. Proguanil treatment upregulated apoptotic markers (Bax, p-H2AX, cleaved-caspase 3, 9, cleaved PARP) and downregulated anti-apoptotic proteins (bcl-2, survivin) in breast cancer cell lines. In female Balb/c mice implanted with 4T1 breast tumors, daily oral administration of 20 mg/kg proguanil suppressed tumor enlargement by 55%. Western blot analyses of proguanil-treated tumors supported the in vitro findings, demonstrating increased levels of p-H2AX, Bax, c-PARP, and c-caspase3 as compared to controls. Our results collectively highlight proguanil's anticancer efficacy in vitro and in vivo in breast cancer, prompting further consideration for clinical investigations.

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.

Plasma Exosomal AKR1C3 mRNA Expression Is a Predictive and Prognostic Biomarker in Patients with Metastatic Castration-Resistant Prostate Cancer

PURPOSE

Aldo-keto reductase family 1 member C3 (AKR1C3) is important in prostate cancer progression, being a potential biomarker in metastatic castration-resistant prostate cancer (mCRPC). Previous explorations of AKR1C3 are mainly based on tissue samples. This study investigates using plasma-based liquid biopsy to validate the prognostic and predictive value of AKR1C3 in patients with mCRPC .

MATERIALS AND METHODS

We prospectively recruited 62 patients with mCRPC. All patients received repeated prostate biopsies at the time of mCRPC diagnosis, and immunohistochemistry (IHC) staining was used to detect protein expression of AKR1C3 in the tissues. We took their blood simultaneously and performed digital droplet polymerase chain reaction (ddPCR) to measure expression levels of AKR1C3 in the exosomes. The detected plasma and tissue AKR1C3 expression levels were analyzed for patients' overall survival (OS) and progression-free survival under first-line abiraterone use (ABI-PFS).

RESULTS

All other baseline characteristics were balanced between the 2 groups. 15/62 (24.2%) and 25/62 (40.3%) patients showed AKR1C3-EXO positive (≥20 copies/20 μL) and AKR1C3-IHC positive, respectively. Positive AKR1C3-EXO expression was associated with decreased patients' survival [ABI-PFS: 3.9 vs 10.1 months, P < .001; OS: 16.2 vs 32.5 months, P < .001]. AKR1C3-IHC positivity was also correlated with ABI-PFS and OS (P = .010, P = .016). In patients with worse baseline blood tests (including higher alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) level and lower hemoglobin (HB) level), and lower ISUP/WHO group (<4), their OS was significantly worse when showing AKR1C3-EXO positive.

CONCLUSION

AKR1C3-EXO is associated with patient prognosis regarding OS and ABI-PFS and can be used as a biomarker in mCRPC.

Discovery of Novel Aldo-Keto Reductase 1C3 Inhibitors as Chemotherapeutic Potentiators for Cancer Drug Resistance

As a crucial target which is overexpressed in a variety of cancers, aldo-keto reductase 1C3 (AKR1C3) confers chemotherapeutic resistance to many clinical agents. However, a limited number of AKR1C3-selective inhibitors are applied clinically, which indicates the importance of identifying active compounds. Herein, we report the discovery, synthesis, and evaluation of novel and potent AKR1C3 inhibitors with structural diversity. Molecular dynamics simulations of these active compounds provide reasonable clarification of the interpreted biological data. Moreover, we demonstrate that AKR1C3 inhibitors have the potential to be superior therapeutic agents for re-sensitizing drug-resistant cell lines to chemotherapy, especially the pan-AKR1C inhibitor S07-2010. Our study identifies new structural classes of AKR1C3 inhibitors and enriches the structural diversity, which facilitates the future rational design of inhibitors and structural optimization. Moreover, these compounds may serve as promising therapeutic adjuvants toward new therapeutics for countering drug resistance.

Chlorinated benzothiadiazines inhibit angiogenesis through suppression of VEGFR2 phosphorylation

Angiogenesis inhibitors are a critical pharmacological tool for the treatment of solid tumors. Suppressing vascular permeability leads to inhibition of tumor growth, invasion, and metastatic potential by blocking the supply of oxygen and nutrients. Disruption of the vascular endothelial growth factor (VEGF) signaling pathway is a validated target for the design of antiangiogenic agents. Several VEGFR2 inhibitors have been clinically approved over the past years. Structural analysis of these clinical VEGFR2 inhibitors highlighted key functional group overlap with the benzothiadiazine core contained in a library of in-house compounds. Herein we ascribe anti-angiogenic activity to a series of chlorinated benzothiadiazines. Selected compounds show significant activity to completely ameliorate VEGF-induced endothelial cell proliferation by suppression of VEGFR2 phosphorylation. The scaffold is devoid of activity to inhibit carbonic anhydrases and generally lacks cytotoxicity across a range of cancer and non-malignant cell lines. Assay of activity at 468 kinases shows remarkable selectivity with only four kinases inhibited > 65% at 10 µM concentration, and with significant activity to inhibit TNK2/ACK1 and PKRD2 by > 90%. All four identified kinase targets are known modulators of angiogenesis, thus highlighting compound 17b as a novel angiogenesis inhibitor for further development.

The Effect of Nano Albumin Combined with Paclitaxel on Drug Resistance of Breast Cancer Through Regulating ATP Binding Cassette Subfamily B Member 1 (ABCB1)

The paclitaxel is a common-used chemotherapy drug and its combination with nano albumin reduces drug side effect. However, whether nab-paclitaxel affects drug resistance of breast cancer remains unclear. This study intends to discuss the mechanism of drug resistance induced by nab-paclitaxel. The drug resistance of MCF-7/nab-paclitaxel in MCF-7 cell and cell proliferation was detected by MTT along with analysis of ABCB1 expression, cell cycle, and apoptosis. There was stronger drug resistance of nab-paclitaxel in the MCF-7/nab-paclitaxel cell group through be adopted with different concentration of nab-paclitaxel at the 0th hour, 24th hour and 48th hour. There was remarkable abnormal expression of the ABCB1 in the MCF-7/nab-paclitaxel cell group. The si-ABCB1 could release the quantity of the MCF-7/nab-paclitaxel cell blocked at S period. And the si-ABCB1 could reduce the expression of cyclin D1 and CDK2 in the MCF-7/nab-paclitaxel cell notably. But the expression level of p21 was increased when there was high concentration of si-ABCB1. The si-ABCB1 could increase the quantity of the MCF-7/nab-paclitaxel cell at the later period of cell apoptosis notably. The rat’s tumor growth was delayed obviously at the MCF-7/nabpaclitaxel cell group treated by si-ABCB1. But the inhibiting effect of the MCF-7/nab-paclitaxel cell on tumor growth was less. There was stronger drug resistance of cell for the nano albumin combined with paclitaxel. The function of cell proliferation in breast cancer was restrained by the nano albumin combined with paclitaxel mainly through inducing the expression of ABCB1, adjusting the growth of cell cycle and the expression of P21/BCL-2 protein.

Access to Highly Strained Tricyclic Ketals Derived from Coumarins

Synthesis of highly strained fused substituted dihydrobenzopyran cyclopropyl lactones derived from coumarin carboxylates are reported. The substrate scope tolerates a variety of 6- and 8-substituents on the coumarin ring. Substitution at the 5- or 7-position is resistant to tricyclic lactone formation except with 7-methyl substitution. Benzamide-containing coumarins afford the tricyclic ketal. A plausible mechanism is proposed for the formation of the fused lactone: intramolecular rearrangement of trans cyclopropyl methyl ketones with phenolic acetate via the formation of a hemiacetal.

Validation of Cell-Free RNA and Circulating Tumor Cells for Molecular Marker Analysis in Metastatic Prostate Cancer

Since tissue material is often lacking in metastatic prostate cancer (mPCa), there is increasing interest in using liquid biopsies for treatment decision and monitoring therapy responses. The purpose of this study was to validate the usefulness of circulating tumor cells (CTCs) and plasma-derived cell-free (cf) RNA as starting material for gene expression analysis through qPCR. CTCs were identified upon prostate-specific membrane antigen and/or cytokeratin positivity after enrichment with ScreenCell (Westford, Massachusetts, USA) filters or the microfluidic Parsortix^TM (Guildford, Surrey, United Kingdom) system. Overall, 50% (28/56) of the patients had ≥5 CTCs/7.5 mL of blood. However, CTC count did not correlate with Gleason score, serum PSA, or gene expression. Notably, we observed high expression of CD45 in CTC samples after enrichment, which could be successfully eliminated through picking of single cells. Gene expression in picked CTCs was, however, rather low. In cfRNA from plasma, on the other hand, gene expression levels were higher compared to those found in CTCs. Moreover, we found that PSA was significantly increased in plasma-derived cfRNA of mPCa patients compared to healthy controls. High PSA expression was also associated with poor overall survival, indicating that using cfRNA from plasma could be used as a valuable tool for molecular expression analysis.

Hydralazine and Enzalutamide: Synergistic Partners against Prostate Cancer

Advanced prostate cancers frequently develop resistance to androgen-deprivation therapy with serious implications for patient survival. Considering their importance in this type of neoplasia, epigenetic modifications have drawn attention as alternative treatment strategies. The aim of this study was to assess the antitumoral effects of the combination of hydralazine, a DNA methylation inhibitor, with enzalutamide, an antagonist of the androgen receptor, in prostate cancer cell lines. Several biological parameters, such as cell viability, proliferation, DNA damage, and apoptosis, as well as clonogenic and invasive potential, were evaluated. The individual treatments with hydralazine and enzalutamide exerted growth-inhibitory effects in prostate cancer cells and their combined treatment displayed synergistic effects. The combination of these two drugs was very effective in decreasing malignant features of prostate cancer and may become an alternative therapeutic option for prostate cancer patient management.

Aldo-Keto Reductases and Cancer Drug Resistance

Human aldo-keto reductases (AKRs) catalyze the NADPH-dependent reduction of carbonyl groups to alcohols for conjugation reactions to proceed. They are implicated in resistance to cancer chemotherapeutic agents either because they are directly involved in their metabolism or help eradicate the cellular stress created by these agents (e.g., reactive oxygen species and lipid peroxides). Furthermore, this cellular stress activates the Nuclear factor-erythroid 2 p45-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 pathway. As many human AKR genes are upregulated by the NRF2 transcription factor, this leads to a feed-forward mechanism to enhance drug resistance. Resistance to major classes of chemotherapeutic agents (anthracyclines, mitomycin, cis-platin, antitubulin agents, vinca alkaloids, and cyclophosphamide) occurs by this mechanism. Human AKRs also catalyze the synthesis of androgens and estrogens and the elimination of progestogens and are involved in hormonal-dependent malignancies. They are upregulated by antihormonal therapy providing a second mechanism for cancer drug resistance. Inhibitors of the NRF2 system or pan-AKR1C inhibitors offer promise to surmount cancer drug resistance and/or synergize the effects of existing drugs. SIGNIFICANCE STATEMENT: Aldo-keto  reductases (AKRs) are overexpressed in a large number of human tumors and mediate resistance to cancer chemotherapeutics and antihormonal therapies. Existing drugs and new agents in development may surmount this resistance by acting as specific AKR isoforms or AKR pan-inhibitors to improve clinical outcome.

Atovaquone Suppresses the Growth of Metastatic Triple-Negative Breast Tumors in Lungs and Brain by Inhibiting Integrin/FAK Signaling Axis

Triple-negative breast cancer (TNBC) is considered to be the most aggressive and malignant neoplasm and is highly metastatic in nature. In the current study, we investigated the anti-metastatic potential of atovaquone, a protozoal drug prescribed for Pneumocystis pneumonia. We showed that atovaquone induced apoptosis and reduced the survival of several aggressive metastatic TNBC cell lines including metastatic patient-derived cells by reducing the expression of integrin α6, integrin β4, FAK, Src, and Vimentin. In order to study the efficacy of atovaquone in suppressing metastasized breast tumor cells in brain and lungs, we performed three in vivo experiments. We demonstrated that oral administration of 50 mg/kg of atovaquone suppressed MDA-MB-231 breast tumor growth by 90% in lungs in an intravenous metastatic tumor model. Anti-metastatic effect of atovaquone was further determined by intracardiac injection of 4T1-luc breast tumor cells into the left ventricle of mouse heart. Our results showed that atovaquone treatment suppressed the growth of metastatic tumors in lungs, liver and brain by 70%, 50% and 30% respectively. In an intracranial model, the growth of HCC1806-luc brain tumors in atovaquone treated mice was about 55% less than that of control. Taken together, our results indicate the anti-metastatic effects of atovaquone in vitro and in vivo in various breast tumor metastasis models.

Atovaquone Suppresses Triple-Negative Breast Tumor Growth by Reducing Immune-Suppressive Cells

A major contributing factor in triple-negative breast cancer progression is its ability to evade immune surveillance. One mechanism for this immunosuppression is through ribosomal protein S19 (RPS19), which facilitates myeloid-derived suppressor cells (MDSCs) recruitment in tumors, which generate cytokines TGF-β and IL-10 and induce regulatory T cells (Tregs), all of which are immunosuppressive and enhance tumor progression. Hence, enhancing the immune system in breast tumors could be a strategy for anticancer therapeutics. The present study evaluated the immune response of atovaquone, an antiprotozoal drug, in three independent breast-tumor models. Our results demonstrated that oral administration of atovaquone reduced HCC1806, CI66 and 4T1 paclitaxel-resistant (4T1-PR) breast-tumor growth by 45%, 70% and 42%, respectively. MDSCs, TGF-β, IL-10 and Tregs of blood and tumors were analyzed from all of these in vivo models. Our results demonstrated that atovaquone treatment in mice bearing HCC1806 tumors reduced MDSCs from tumor and blood by 70% and 30%, respectively. We also observed a 25% reduction in tumor MDSCs in atovaquone-treated mice bearing CI66 and 4T1-PR tumors. In addition, a decrease in TGF-β and IL-10 in tumor lysates was observed in atovaquone-treated mice with a reduction in tumor Tregs. Moreover, a significant reduction in the expression of RPS19 was found in tumors treated with atovaquone.

Discovery of Halogenated Benzothiadiazine Derivatives with Anticancer Activity*

Mitochondrial respiratory complex II (CII), also known as succinate dehydrogenase, plays a critical role in mitochondrial metabolism. Known but low potency CII inhibitors are selectively cytotoxic to cancer cells including the benzothiadiazine-based anti-hypoglycemic diazoxide. Herein, we study the structure-activity relationship of benzothiadiazine derivatives for CII inhibition and their effect on cancer cells for the first time. A 15-fold increase in CII inhibition was achieved over diazoxide, albeit with micromolar IC₅₀ values. Cytotoxicity evaluation of the novel derivatives resulted in the identification of compounds with much greater antineoplastic effect than diazoxide, the most potent of which possesses an IC₅₀ of 2.93±0.07 μM in a cellular model of triple-negative breast cancer, with high selectivity over nonmalignant cells and more than double the potency of the clinical agent 5-fluorouracil. No correlation between cytotoxicity and CII inhibition was found, thus indicating an as-yet-undefined mechanism of action of this scaffold. The derivatives described herein represent valuable hit compounds for therapeutic discovery in triple-negative breast cancer.

AKR1C3 is a biomarker and druggable target for oropharyngeal tumors

PURPOSE

Oropharynx squamous cell carcinoma (OPSCC) is a subtype of head and neck squamous cell carcinoma (HNSCC) arising from the base of the tongue, lingual tonsils, tonsils, oropharynx or pharynx. The majority of HPV-positive OPSCCs has a good prognosis, but a fraction of them has a poor prognosis, similar to HPV-negative OPSCCs. An in-depth understanding of the molecular mechanisms underlying OPSCC is mandatory for the identification of novel prognostic biomarkers and/or novel therapeutic targets.

METHODS

14 HPV-positive and 15 HPV-negative OPSCCs with 5-year follow-up information were subjected to gene expression profiling and, subsequently, compared to three extensive published OPSCC cohorts to define robust biomarkers for HPV-negative lesions. Validation of Aldo-keto-reductases 1C3 (AKR1C3) by qRT-PCR was carried out on an independent cohort (n = 111) of OPSCC cases. In addition, OPSCC cell lines Fadu and Cal-27 were treated with Cisplatin and/or specific AKR1C3 inhibitors to assess their (combined) therapeutic effects.

RESULTS

Gene set enrichment analysis (GSEA) on the four datasets revealed that the genes down-regulated in HPV-negative samples were mainly involved in immune system, whereas those up-regulated mainly in glutathione derivative biosynthetic and xenobiotic metabolic processes. A panel of 30 robust HPV-associated transcripts was identified, with AKR1C3 as top-overexpressed transcript in HPV-negative samples. AKR1C3 expression in 111 independent OPSCC cases positively correlated with a worse survival, both in the entire cohort and in HPV-positive samples. Pretreatment with a selective AKR1C3 inhibitor potentiated the effect of Cisplatin in OPSCC cells exhibiting higher basal AKR1C3 expression levels.

CONCLUSIONS

We identified AKR1C3 as a potential prognostic biomarker in OPSCC and as a potential drug target whose inhibition can potentiate the effect of Cisplatin.

Intracrine androgen biosynthesis and drug resistance

Castration-resistant prostate cancer is the lethal form of prostate cancer and most commonly remains dependent on androgen receptor (AR) signaling. Current therapies use AR signaling inhibitors (ARSI) exemplified by abiraterone acetate, a P450c17 inhibitor, and enzalutamide, a potent AR antagonist. However, drug resistance to these agents occurs within 12-18 months and they only prolong overall survival by 3-4 months. Multiple mechanisms can contribute to ARSI drug resistance. These mechanisms can include but are not limited to germline mutations in the AR, post-transcriptional alterations in AR structure, and adaptive expression of genes involved in the intracrine biosynthesis and metabolism of androgens within the tumor. This review focuses on intracrine androgen biosynthesis, how this can contribute to ARSI drug resistance, and therapeutic strategies that can be used to surmount these resistance mechanisms.

AKR1C3 mediates pan-AR antagonist resistance in castration-resistant prostate cancer

BACKGROUND

Antiandrogens are effective therapies that block androgen receptor (AR) transactivation and signaling in over 50% of castration-resistant prostate cancer (CRPC) patients. However, an estimated 30% of responders will develop resistance to these therapies within 2 years. JNJ-pan-AR is a broad-spectrum AR antagonist that inhibits wild-type AR as well as several mutated versions of AR that have emerged in patients on chronic antiandrogen treatment. In this work, we aimed to identify the potential underlying mechanisms of resistance that may result from chronic JNJ-pan-AR treatment.

METHODS

The LNCaP JNJR prostate cancer subline was developed by chronically exposing LNCaP parental cells to JNJ-pan-AR. Transcriptomic and proteomic profiling was performed to identify potential drivers and/or biomarkers of the resistant phenotype.

RESULTS

Several enzymes critical to intratumoral androgen biosynthesis, Aldo-keto reductase family 1 member C3 (AKR1C3), UGT2B15, and UGT2B17 were identified as potential upstream regulators of the JNJ-pan-AR resistant cells. While we confirmed the overexpression of all three enzymes in the resistant cells only AKR1C3 expression played a functional role in driving JNJ-pan-AR resistance. We also discovered that AKR1C3 regulates UGT2B15 and UGT2B17 expression in JNJ-pan-AR resistant cells.

CONCLUSIONS

This study supports the rationale to further investigate the benefits of AKR1C3 inhibition in combination with antiandrogens to prevent CRPC disease progression.

Development of Novel AKR1C3 Inhibitors as New Potential Treatment for Castration-Resistant Prostate Cancer

Aldo-keto reductase (AKR) 1C3 catalyzes the synthesis of active androgens that promote the progression of prostate cancer. AKR1C3 also contributes to androgen-independent cell proliferation and survival through the metabolism of prostaglandins and reactive aldehydes. Because of its elevation in castration-resistant prostate cancer (CRPC) tissues, AKR1C3 is a promising therapeutic target for CRPC. In this study, we found a novel potent AKR1C3 inhibitor, N-(4-fluorophenyl)-8-hydroxy-2-imino-2H-chromene-3-carboxamide (2d), and synthesized its derivatives with IC₅₀ values of 25-56 nM and >220-fold selectivity over other AKRs (1C1, 1C2, and 1C4). The structural factors for the inhibitory potency were elucidated by crystallographic study of AKR1C3 complexes with 2j and 2l. The inhibitors suppressed proliferation of prostate cancer 22Rv1 and PC3 cells through both androgen-dependent and androgen-independent mechanisms. Additionally, 2j and 2l prevented prostate tumor growth in a xenograft mouse model. Furthermore, the inhibitors significantly augmented apoptotic cell death induced by anti-CRPC drugs (abiraterone or enzalutamide).

Dual Inhibitory Action of a Novel AKR1C3 Inhibitor on Both Full-Length AR and the Variant AR-V7 in Enzalutamide Resistant Metastatic Castration Resistant Prostate Cancer

The expanded use of second-generation antiandrogens revolutionized the treatment landscape of progressed prostate cancer. However, resistances to these novel drugs are already the next obstacle to be solved. Various previous studies depicted an involvement of the enzyme AKR1C3 in the process of castration resistance as well as in the resistance to 2nd generation antiandrogens like enzalutamide. In our study, we examined the potential of natural AKR1C3 inhibitors in various prostate cancer cell lines and a three-dimensional co-culture spheroid model consisting of cancer cells and cancer-associated fibroblasts (CAFs) mimicking enzalutamide resistant prostate cancer. One of our compounds, named MF-15, expressed strong antineoplastic effects especially in cell culture models with significant enzalutamide resistance. Furthermore, MF-15 exhibited a strong effect on androgen receptor (AR) signaling, including significant inhibition of AR activity, downregulation of androgen-regulated genes, lower prostate specific antigen (PSA) production, and decreased AR and AKR1C3 expression, indicating a bi-functional effect. Even more important, we demonstrated a persisting inhibition of AR activity in the presence of AR-V7 and further showed that MF-15 non-competitively binds within the DNA binding domain of the AR. The data suggest MF-15 as useful drug to overcome enzalutamide resistance.

Overview of AKR1C3: Inhibitor Achievements and Disease Insights

Human aldo-keto reductase family 1 member C3 (AKR1C3) is known as a hormone activity regulator and prostaglandin F (PGF) synthase that regulates the occupancy of hormone receptors and cell proliferation. Because of the overexpression in metabolic diseases and various hormone-dependent and -independent carcinomas, as well as the emergence of clinical drug resistance, an increasing number of studies have investigated AKR1C3 inhibitors. Here, we briefly review the physiological and pathological function of AKR1C3 and then summarize the recent development of selective AKR1C3 inhibitors. We propose our viewpoints on the current problems associated with AKR1C3 inhibitors with the aim of providing a reference for future drug discovery and potential therapeutic perspectives on novel, potent, selective AKR1C3 inhibitors.

A Mansonone Derivative Coupled with Monoclonal Antibody 4D5-Modified Chitosan Inhibit AKR1C3 to Treat Castration-Resistant Prostate Cancer

Purpose

Aldo-ketoreductase (AKR) 1C3 is crucial for testosterone synthesis. Abnormally high expression/activity of AKR1C3 can promote castration-resistant prostate cancer (CRPC). A mansonone derivative and AKR1C3 inhibitor, 6e, was combined with 4D5 (extracellular fragment of the monoclonal antibody of human epidermal growth factor receptor-2)-modified chitosan to achieve a nanodrug-delivery system (CS-4D5/6e) to treat CRPC.

Materials and Methods

Morphologies/properties of CS-4D5/6e were characterized by atomic force microscopy, zeta-potential analysis, and Fourier transform-infrared spectroscopy. CS-4D5/6e uptake was measured by immunofluorescence under confocal laser scanning microscopy. Testosterone in LNCaP cells overexpressing human AKR1C3 (LNCaP-AKR1C3) and cell lysates was measured to reflect AKR1C3 activity. Androgen receptor (AR) and prostate-specific antigen (PSA) expression was measured by Western blotting. CS-4D5/6e-based inhibition of AKR1C3 was evaluated in tumor-xenografted mice.

Results

CS-4D5/6e was oblate, with a particle size of 200-300 nm and thickness of 1-5 nm. Zeta potential was 1.39±0.248 mV. 6e content in CS-4D5/6e was 7.3±1.4% and was 18±3.6% for 4D5. 6e and CS-4D5/6e inhibited testosterone production significantly in a concentration-dependent manner in LNCaP-AKR1C3 cells, and a decrease in expression of AKR1C3, PSA, and AR was noted. Half-maximal inhibitory concentration of CS-4D5/6e on LNCaP-AKR1C3 cells was significantly lower than that in LNCaP cells (P<0.05). CS-4D5/6e significantly reduced growth of 22Rv1 tumor xenografts by 57.00% compared with that in the vehicle group (P<0.01).

Conclusion

We demonstrated the antineoplastic activity of a potent AKR1C3 inhibitor (6e) and its nanodrug-delivery system (CS-4D5/6e). First, CS-4D5/6e targeted HER2-positive CRPC cells. Second, it transferred 6e (an AKR1C3 inhibitor) to achieve a reduction in intratumoral testosterone production. Compared with 6e, CS-4D5/6e showed lower systemic toxicity. CS-4D5/6e inhibited tumor growth effectively in mice implanted with tumor xenografts by downregulating testosterone production mediated by intratumoral AKR1C3. These results showed a promising strategy for treatment of the CRPC that develops invariably in prostate-cancer patients.

Reversal of Apalutamide and Darolutamide Aldo-Keto Reductase 1C3-Mediated Resistance by a Small Molecule Inhibitor

The antiandrogen therapeutics apalutamide and darolutamide entered the clinic in 2018 and 2019, respectively, for the treatment of castration-resistant prostate cancer (CRPC). Increased expression of the enzyme aldo-keto reductase 1C3 (AKR1C3) is phenotypic of CRPC. The enzyme acts to circumvent castration by producing potent androgens that drive proliferation. Furthermore, AKR1C3 mediates chemotherapeutic resistance to the standard of care, enzalutamide, a structural analogue of apalutamide. Resistance develops in almost all CRPC patients within three months of beginning treatment. Herein, we report that both apalutamide and the structurally distinct darolutamide induce AKR1C3 expression in in vitro models of prostate cancer and are susceptible to AKR1C3-mediated resistance. This effect is countered by pretreatment with a potent and highly selective AKR1C3 inhibitor, sensitizing high AKR1C3 expressing prostate cancer cell lines to the action of both chemotherapeutics with a concomitant reduction in expression of AKR1C3 and the biomarker prostate-specific antigen.

Therapeutic targeting of the androgen receptor (AR) and AR variants in prostate cancer

Prostate cancer (PCa) accounted for over 300 000 deaths world-wide in 2018. Most of the PCa deaths occurred due to the aggressive castration-resistant PCa (CRPC). Since the androgen receptor (AR) and its ligands contribute to the continued growth of androgen-dependent PCa (ADPCa) and CRPC, AR has become a well-characterized and pivotal therapeutic-target. Although AR signaling was identified as therapeutic-target in PCa over five-decades ago, there remains several practical issues such as lack of antagonist-bound AR crystal structure, stabilization of the AR in the presence of agonists due to N-terminus and C-terminus interaction, unfavorable large-molecule accommodation of the ligand-binding domain (LBD), and generation of AR splice variants that lack the LBD that impede the discovery of highly potent fail-safe drugs. This review summarizes the AR-signaling pathway targeted therapeutics currently used in PCa and the approaches that could be used in future AR-targeted drug development of potent next-generation molecules. The review also outlines the discovery of molecules that bind to domains other than the LBD and those that inhibit both the full length and splice variant of ARs.

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.

Atovaquone: An Antiprotozoal Drug Suppresses Primary and Resistant Breast Tumor Growth by Inhibiting HER2/β-Catenin Signaling

Breast cancer is the second leading cause of cancer-related mortality in women. In the current study, we evaluated the anticancer effects of an antiprotozoal drug, atovaquone, against several breast cancer cell lines. Our results showed that atovaquone treatment induced apoptosis and inhibited the growth of all the breast cancer cell lines tested, including several patient-derived cells. In addition, atovaquone treatment significantly reduced the expression of HER2, β-catenin, and its downstream molecules such as pGSK-3β, TCF-4, cyclin D1, and c-Myc in vitro Efficacy of atovaquone was further evaluated in an in vivo tumor model by orthotropic implantation of two highly aggressive 4T1 and CI66 breast cancer cells in the mammary fat pad of female mice. Our results demonstrated that oral administration of atovaquone suppressed the growth of CI66 and 4T1 tumors by 70% and 60%, respectively. Paclitaxel is the first-line chemotherapeutic agent for metastatic breast cancer. We demonstrate that atovaquone administration suppressed the growth of 4T1 paclitaxel-resistant tumors by 40%. Tumors from atovaquone-treated mice exhibited reduced HER2, β-catenin, and c-Myc levels alongside an increase in apoptosis in all the three tumor models when analyzed by Western blotting, IHC, and TUNEL assay. Taken together, our results indicate that atovaquone effectively reduces the growth of primary and paclitaxel-resistant breast tumors. Atovaquone is already in the clinics with high safety and tolerability profile. Therefore, the findings from our studies will potentially prompt further clinical investigation into repurposing atovaquone for the treatment of patients with advanced breast cancer.

Interaction between leukocyte aldo-keto reductase 1C3 activity, genotypes, biological, lifestyle and clinical features in a prostate cancer cohort from New Zealand

Introduction

Aldo-keto reductase 1C3 (AKR1C3) is known for multiple functions including its catalytic activity towards producing extra-testicular androgen. The present study is towards understanding interaction between biological, lifestyle and genetic impacts of AKR1C3 and their influence on clinical factors in a prostate cancer (PC) cohort from New Zealand (NZ).

Method

Characteristics of 516 PC patients were collected from the Auckland Regional Urology Facility, NZ. These men were genotyped for the AKR1C3 rs12529 single nucleotide polymorphism (SNP). The leukocyte AKR1C3 activity was measured in a sub-cohort. Variability of leukocyte AKR1C3 activity between biological, lifestyle and clinical features as well as correlation between biological and clinical features were assessed with and without genetic stratification.

Results

The leukocyte AKR1C3 activity was associated with age at diagnosis (0.51 vs 0.34 μM coumberol units for >69y vs ≤69y, P = 0.03); and with anatomic stage/prognostic grouping among the AKR1C3 rs12529 CC genotype carriers (0.50 vs 28 μM coumberol units among low- and high-risk groups respectively, P = 0.02). Significant correlation between leukocyte AKR1C3 activity and age at PC diagnosis was also observed (correlation coefficient 0.20 and P = 0.02). Ever- smoking impacted both age and PSA at PC diagnosis among AKR1C3 rs12529 GG and CG genotype carriers respectively. Age at diagnosis significantly correlated with PSA at diagnosis in the main (correlation coefficient 0.29, and P<0.001) and sub-cohorts (correlation coefficient 0.24, and P = 0.01); and those carrying the AKR1C3 rs12529 CG and GG genotypes in both the main (correlation coefficient 0.30, and P<0.001 and correlation coefficient 0.35, and P<0.001 respectively) and sub-cohorts (correlation coefficient 0.43, and P<0.001 and correlation coefficient 0.39, and P = 0.06 respectively); but not with those carrying the CC genotype.

Conclusions

Age dependent PSA thresholds in PC screening could have been valid only in men carrying the AKR1C3 rs12529 CG and GG genotypes in this NZ cohort.

Consecutive Prostate Cancer Specimens Revealed Increased Aldo⁻Keto Reductase Family 1 Member C3 Expression with Progression to Castration-Resistant Prostate Cancer

Aldo-keto reductase family 1 member C3 (AKR1C3) is an enzyme in the steroidogenesis pathway, especially in formation of testosterone and dihydrotestosterone, and is believed to have a key role in promoting prostate cancer (PCa) progression, particularly in castration-resistant prostate cancer (CRPC). This study aims to compare the expression level of AKR1C3 between benign prostatic epithelium and cancer cells, and among hormone-naïve prostate cancer (HNPC) and CRPC from the same patients, to understand the role of AKR1C3 in PCa progression. Correlation of AKR1C3 immunohistochemical expression between benign and cancerous epithelia in 134 patient specimens was analyzed. Additionally, correlation between AKR1C3 expression and prostate-specific antigen (PSA) progression-free survival (PFS) after radical prostatectomy was analyzed. Furthermore, we evaluated the consecutive prostate samples derived from 11 patients both in the hormone-naïve and castration-resistant states. AKR1C3 immunostaining of cancer epithelium was significantly stronger than that of the benign epithelia in patients with localized HNPC (p < 0.0001). High AKR1C3 expression was an independent factor of poor PSA PFS (p = 0.032). Moreover, AKR1C3 immunostaining was significantly stronger in CRPC tissues than in HNPC tissues in the same patients (p = 0.0234). Our findings demonstrate that AKR1C3 is crucial in PCa progression.

Potent and Highly Selective Aldo-Keto Reductase 1C3 (AKR1C3) Inhibitors Act as Chemotherapeutic Potentiators in Acute Myeloid Leukemia and T-Cell Acute Lymphoblastic Leukemia

Aldo-keto reductase 1C3 (AKR1C3) catalyzes the synthesis of 9α,11β-prostaglandin (PG) F_2α and PGF_2α prostanoids that sustain the growth of myeloid precursors in the bone marrow. The enzyme is overexpressed in acute myeloid leukemia (AML) and T-cell acute lymphoblastic leukemia (T-ALL). Moreover, AKR1C3 confers chemotherapeutic resistance to the anthracyclines: first-line agents for the treatment of leukemias. The highly homologous isoforms AKR1C1 and AKR1C2 inactivate 5α-dihydrotestosterone, and their inhibition would be undesirable. We report herein the identification of AKR1C3 inhibitors that demonstrate exquisite isoform selectivity for AKR1C3 over the other closely related isoforms to the order of >2800-fold. Biological evaluation of our isoform-selective inhibitors revealed a high degree of synergistic drug action in combination with the clinical leukemia therapeutics daunorubicin and cytarabine in in vitro cellular models of AML and primary patient-derived T-ALL cells. Our developed compounds exhibited >100-fold dose reduction index that results in complete resensitization of a daunorubicin-resistant AML cell line to the chemotherapeutic and >100-fold dose reduction of cytarabine in both AML cell lines and primary T-ALL cells.

Penfluridol overcomes paclitaxel resistance in metastatic breast cancer

Paclitaxel is a first line chemotherapeutic agent for the patients with metastatic breast cancer. But inherited or acquired resistance to paclitaxel leads to poor response rates in a majority of these patients. To identify mechanisms of paclitaxel resistance, we developed paclitaxel resistant breast cancer cell lines, MCF-7 and 4T1 by continuous exposure to paclitaxel for several months. Western blot analysis showed increased expression of HER2 and β-catenin pathway in resistant cell lines as compared to parent cells. Hence, we hypothesized that HER2/β-catenin mediates paclitaxel resistance in breast cancer and suppression of HER2/β-catenin signaling could overcome paclitaxel resistance. Our data showed that penfluridol (PFL) treatment significantly reduced the survival of paclitaxel-resistant cells. Western blot analysis revealed that PFL treatment suppressed HER2, as well as, β-catenin pathway. In vivo data confirmed that PFL significantly potentiated tumor growth suppressive effects of paclitaxel in an orthotropic breast cancer model. In addition, tumors from paclitaxel and PFL-treated mice showed reduced HER2 and β-catenin expression, along with increased apoptosis. Taken together our results demonstrate a novel role of HER2/β-catenin in paclitaxel resistance and open up new avenues for application of PFL as a therapeutic option for overcoming paclitaxel resistance.

Characterization of a highly specific monoclonal antibody against human aldo-keto reductase AKR1C3

Human aldo-keto reductase AKR1C3 (type 2 3α-hydroxysteroid dehydrogenase/type 5 17β-hydroxysteroid dehydrogenase) is involved in testosterone and estrogen metabolism. AKR1C3 expression is relatively low in most tissues and high in prostate and mammary glands in regulating androgen and estrogen levels. However, in many cancers, overexpression of AKR1C3 was observed, thus prompting the development of therapeutics targeting AKR1C3. To facilitate the development of AKR1C3 targeting therapeutics, evaluating the expression of AKR1C3 is vital. As AKR1C3 is highly homologous with its family proteins, AKR1C1, AKR1C2, AKR1C4 and other AKR1 proteins, reagents that can unambiguously discriminate these enzymes are needed. In this report, a highly specific monoclonal antibody for AKR1C3, 10B10, was developed and characterized. Compared to other AKR1C3 antibodies, 10B10 is highly specific and sensitive to AKR1C3 in multiple assay formats. Thus, 10B10 will be a valuable tool for the clinical development of AKR1C3 targeting therapeutics and the study of AKR1C3 biology.

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.