Docosahexaenoic acid enhances the treatment efficacy for castration-resistant prostate cancer by inhibiting autophagy through Atg4B inhibition.

Autophagy induction in cancer is involved in cancer progression and the acquisition of resistance to anticancer agents. Therefore, autophagy is considered a potential therapeutic target in cancer therapy. In this study, we found that long-chain fatty acids (LCFAs) have inhibitory effects on Atg4B, which is essential for autophagosome formation, through screening based on the pharmacophore of 21f, a recently developed Atg4B inhibitor. Among these fatty acids, docosahexaenoic acid (DHA), a polyunsaturated fatty acid, exhibited the most potent Atg4B inhibitory activity. DHA inhibited autophagy induced by androgen receptor signaling inhibitors (ARSI) in LNCaP and 22Rv1 prostate cancer cells and significantly increased apoptotic cell death. Furthermore, we investigated the effect of DHA on resistance to ARSI by establishing darolutamide-resistant prostate cancer 22Rv1 (22Rv1/Dar) cells, which had developed resistance to darolutamide, a novel ARSI. At baseline, 22Rv1/Dar cells showed a higher autophagy level than parental 22Rv1 cells. DHA significantly suppressed Dar-induced autophagy and sensitized 22Rv1/Dar cells by inducing apoptotic cell death through mitochondrial dysfunction. These results suggest that DHA supplementation may improve prostate cancer therapy with ARSI.

Artepillin C overcomes apalutamide resistance through blocking androgen signaling in prostate cancer cells.

Prostate cancer has a relatively good prognosis, but most cases develop resistance to hormone therapy, leading to castration-resistant prostate cancer (CRPC). Androgen receptor (AR) antagonists and a cytochrome P450 17A1 inhibitor have been used to treat CRPC, but cancer cells readily develop resistance to these drugs. In this study, to improve the therapy of CRPC, we searched for natural compounds which block androgen signaling. Among cinnamic acid derivatives contained in Brazilian green propolis, artepillin C (ArtC) suppressed expressions of androgen-induced prostate-specific antigen and transmembrane protease serine 2 in a dose-dependent manner. Reporter assays revealed that ArtC displayed AR antagonist activity, albeit weaker than an AR antagonist flutamide. In general, aberrant activation of the androgen signaling is involved in the resistance of prostate cancer cells to hormone therapy. Recently, apalutamide, a novel AR antagonist, has been in clinical use, but its drug-resistant cases have been already reported. To search for compounds which overcome the resistance to apalutamide, we established apalutamide-resistant prostate cancer 22Rv1 cells (22Rv1/APA). The 22Rv1/APA cells showed higher AR expression and androgen sensitivity than parental 22Rv1 cells. ArtC inhibited androgen-induced proliferation of 22Rv1/APA cells by suppressing the enhanced androgen signaling through blocking the nuclear translocation of AR. In addition, ArtC potently sensitized the resistant cells to apalutamide by inducing apoptotic cell death due to mitochondrial dysfunction. These results suggest that the intake of Brazilian green propolis containing ArtC improves prostate cancer therapy.

Antiandrogenic Effects of a Polyphenol in Carex kobomugi through Inhibition of Androgen Synthetic Pathway and Downregulation of Androgen Receptor in Prostate Cancer Cell Lines.

Prostate cancer (PC) represents the most common cancer disease in men. Since high levels of androgens increase the risk of PC, androgen deprivation therapy is the primary treatment; however this leads to castration-resistant PC (CRPC) with a poor prognosis. The progression to CRPC involves ectopic androgen production in the adrenal glands and abnormal activation of androgen signaling due to mutations and/or amplification of the androgen receptor (AR) as well as activation of androgen-independent proliferative pathways. Recent studies have shown that adrenal-derived 11-oxygenated androgens (11-ketotestosterone and 11-ketodihydrotestosterone) with potencies equivalent to those of traditional androgens (testosterone and dihydrotestosterone) are biomarkers of CRPC. Additionally, dehydrogenase/reductase SDR family member 11 (DHRS11) has been reported to be a 17ß-hydroxysteroid dehydrogenase that catalyzes the production of the 11-oxygenated and traditional androgens. This study was conducted to evaluate the pathophysiological roles of DHRS11 in PC using three LNCaP, C4-2 and 22Rv1 cell lines. DHRS11 silencing and inhibition resulted in suppression of the androgen-induced expression of AR downstream genes and decreases in the expression of nuclear AR and the proliferation marker Ki67, suggesting that DHRS11 is involved in androgen-dependent PC cell proliferation. We found that 5,7-dihydroxy-8-methyl-2-[2-(4-hydroxyphenyl)ethenyl]-4H-1-benzopyran-4-one (Kobochromone A, KC-A), an ingredient in the flowers of Carex kobomugi, is a novel potent DHRS11 inhibitor (IC50 = 0.35 µM). Additionally, KC-A itself decreased the AR expression in PC cells. Therefore, KC-A suppresses the androgen signaling in PC cells through both DHRS11 inhibition and AR downregulation. Furthermore, KC-A enhanced the anticancer activity of abiraterone, a CRPC drug, suggesting that it may be a potential candidate for the development of drugs for the prevention and treatment of CRPC.

Vacuum Ultraviolet Absorption Spectroscopy Analysis of Breath Acetone Using a Hollow Optical Fiber Gas Cell.

Human breath is a biomarker of body fat metabolism and can be used to diagnose various diseases, such as diabetes. As such, in this paper, a vacuum ultraviolet (VUV) spectroscopy system is proposed to measure the acetone in exhaled human breath. A strong absorption acetone peak at 195 nm is detected using a simple system consisting of a deuterium lamp source, a hollow-core fiber gas cell, and a fiber-coupled compact spectrometer corresponding to the VUV region. The hollow-core fiber functions both as a long-path and an extremely small-volume gas cell; it enables us to sensitively measure the trace components of exhaled breath. For breath analysis, we apply multiple regression analysis using the absorption spectra of oxygen, water, and acetone standard gas as explanatory variables to quantitate the concentration of acetone in breath. Based on human breath, we apply the standard addition method to obtain the measurement accuracy. The results suggest that the standard deviation is 0.074 ppm for healthy human breath with an acetone concentration of around 0.8 ppm and a precision of 0.026 ppm. We also monitor body fat burn based on breath acetone and confirm that breath acetone increases after exercise because it is a volatile byproduct of lipolysis.

Inhibition of aldo-keto reductase 1C3 overcomes gemcitabine/cisplatin resistance in bladder cancer.

Systemic chemotherapy with gemcitabine and cisplatin (GC) has been used for the treatment of bladder cancer in which androgen receptor (AR) signaling is suggested to play a critical role. However, its efficacy is often limited, and the prognosis of patients who develop resistance is extremely poor. Aldo-keto reductase 1C3 (AKR1C3), which is responsible for the production of a potent androgen, 5α-dihydrotestosterone (DHT), by the reduction of 5α-androstane-3α,17ß-dione (5α-Adione), has been attracting attention as a therapeutic target for prostate cancer that shows androgen-dependent growth. By contrast, the role of AKR1C3 in bladder cancer remains unclear. In this study, we examined the effect of an AKR1C3 inhibitor on androgen-dependent proliferation and GC sensitivity in bladder cancer cells. 5α-Adione treatment induced the expression of AR and its downstream factor ETS-domain transcription factor (ELK1) in both T24 cells and newly established GC-resistant T24GC cells, while it did not alter AKR1C3 expression. AKR1C3 inhibitor 2j significantly suppressed 5α-Adione-induced AR and ELK1 upregulation, as did an AR antagonist apalutamide. Moreover, the combination of GC and 2j in T24GC significantly induced apoptotic cell death, suggesting that 2j could enhance GC sensitivity. Immunohistochemical staining in surgical specimens further revealed that strong expression of AKR1C3 was associated with significantly higher risks of tumor progression and cancer-specific mortality in patients with muscle-invasive bladder cancer. These results suggest that AKR1C3 inhibitors as adjunctive agents enhance the efficacy of GC therapy for bladder cancer.

Discovery and Structure-Based Optimization of Novel Atg4B Inhibitors for the Treatment of Castration-Resistant Prostate Cancer.

Autophagy inhibition is an attractive target for cancer therapy. In this study, we discovered inhibitors of Atg4B essential for autophagosome formation and evaluated their potential as therapeutics for prostate cancer. Seventeen compounds were identified as candidates after in silico screening and a thermal shift assay. Among them, compound 17 showed the most potent Atg4B inhibitory activity, inhibited autophagy induced by anti-castration-resistant prostate cancer (CRPC) drugs, and significantly enhanced apoptosis. Although 17 has been known as a phospholipase A2 (PLA2) inhibitor, other PLA2 inhibitors had no effect on Atg4B and autophagy. We then performed structural optimization based on molecular modeling and succeeded in developing 21f (by shortening the alkyl chain of 17), which was a potent competitive inhibitor for Atg4B (Ki = 3.1 µM) with declining PLA2 inhibitory potency. Compound 21f enhanced the anticancer activity of anti-CRPC drugs via autophagy inhibition. These findings suggest that 21f can be used as an adjuvant drug for therapy with anti-CRPC drugs.

Human dehydrogenase/reductase SDR family member 11 (DHRS11) and aldo-keto reductase 1C isoforms in comparison: Substrate and reaction specificity in the reduction of 11-keto-C19-steroids.

Recent studies have shown that an adrenal steroid 11ß-hydroxy-4-androstene-3,17-dione serves as the precursor to androgens, 11-ketotestosterone and 11-ketodihydrotestosterone (11KDHT). The biosynthetic pathways include the reduction of 3- and 17-keto groups of the androgen precursors 11-keto-C19-steroids, which has been reported to be mediated by three human enzymes; aldo-keto reductase (AKR)1C2, AKR1C3 and 17ß-hydroxysteroid dehydrogenase (HSD) type-3. To explore the contribution of the enzymes in the reductive metabolism, we kinetically compared the substrate specificity for 11-keto-C19-steroids among purified recombinant preparations of four AKRs (1C1, 1C2,1C3 and 1C4) and DHRS11, which shows 17ß-HSD activity. Although AKR1C1 did not reduce the 11-keto-C19-steroids, AKR1C3 and DHRS11 reduced 17-keto groups of 11-keto-4-androstene-3,17-dione, 11-keto-5α-androstane-3,17-dione (11K-Adione) and 11-ketoandrosterone with Km values of 5-28 µM. The 3-keto groups of 11KDHT and 11K-Adione were reduced by AKR1C4 (Km 1 µM) more efficiently than by AKR1C2 (Km 5 and 8 µM, respectively). GC/MS analysis of the products showed that DHRS11 acts as 17ß-HSD, and that AKR1C2 and AKR1C4 are predominantly 3α-HSDs, but formed a minor 3ß-metabolite from 11KDHT. Since DHRS11 was thus newly identified as 11-keto-C19-steroid reductase, we also investigated its substrate-binding mode by molecular docking and site-directed mutagenesis of Thr163 and Val200, and found the following structural features: 1). There is a space that accommodates the 11-keto group of the 11-keto-C19-steroids in the substrate-binding site. 2) Val200 is a critical determinant for exhibiting the strict 17ß-HSD activity of the enzyme, because the Val200Leu mutation resulted in both significant impairment of the 17ß-HSD activity and emergence of 3ß-HSD activity towards 5α-androstanes including 11KDHT.