Resistance to CYP17A1 inhibition with abiraterone in castration-resistant prostate cancer: induction of steroidogenesis and androgen receptor splice variants

Perineural Invasion as a Risk Factor For Soft Tissue Progression in Patients With Metastatic Castration-Resistant Prostate Cancer After Abiraterone Resistance

BACKGROUND

Prostate cancer presents with soft tissue progression (STP) is highly aggressive. We analyzed the risk factor for STP in patients with metastatic castration-resistant prostate cancer (mCRPC) who developed abiraterone acetate (AA) resistance.

METHODS

This retrospective study included patients with mCRPC who received AA between February 2018 and July 2022. STP was defined as recurrent lesions in situ, multiple regional lymph node metastases (mLNM), or visceral metastases. Clinical features of patients with STP were analyzed, and risk factors for STP were further investigated.

RESULTS

Sixty-three patients (mean age, 75.0 years; median follow-up time, 22.3 months) were included in this study. Twenty-three patients (36.5%) presented STP during follow up, the overall survival (OS) after STP was 4.6 months. The serum neuron-specific enolase (NSE) were significantly elevated in patients with STP. Biopsies for 8 patients with STP showed neuroendocrine prostate cancer (NEPC, n = 5) was the major pathological types. Further analysis showed that perineural invasion (PNI) in primary tumor were the independent risk factors (HR = 3.145, P = 0.020) for STP, and PNI was related to the aggressiveness of tumor. Patients with PNI showed shorter castration-resistant progression free survival (median, 23.73 months vs. 25.59 months) and STP progression free survival (median, 19.7 months vs. not reached) compared with patients without PNI.

CONCLUSIONS

STP showed extremely poor prognoses in patients with mCRPC after AA resistance, NEPC is the main pathological type of STP, and PNI in primary tumor was an independent risk factor for STP and indicated poor prognosis of prostate cancer.

Clinical value of molecular subtypes identification based on anoikis-related lncRNAs in castration-resistant prostate cancer

BACKGROUND

Anoikis is a distinctive type of apoptosis. It is involved in tumor progression and metastasis. But its function in castration-resistant prostate cancer (CRPC) remains veiled. We aimed to develop a prognostic indicator based on anoikis-related long non-coding RNAs (arlncRNAs) and to investigate their biological function in CRPC.

MATERIAL AND METHOD

Differentially expressed anoikis-related genes were extracted from two CRPC datasets, GSE51873, and GSE78201. Four lncRNAs associated with the anoikis-related genes were selected. A risk model based on these lncRNAs was developed and validated in The Cancer Genome Atlas (TCGA) and the Memorial Sloan-Kettering Cancer Center (MSKCC) prostate cancer cohorts. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, immune infiltration, immune checkpoints expression, and drug susceptibility were performed based on the model. To identify the biofunction of anoikis-related lncRNA, CCK-8 assays, colony formation assays, and flow cytometry were used.

RESULT

Twenty-nine anoikis-related genes were differentially expressed in the CRPC datasets. And 36 prognostic arlncRNAs were selected for the LASSO Cox analysis. Patients were subsequently classified into two subtypes by constructing an anoikis-related lncRNA based prognostic index (ARPI). The accuracy of this index was validated. KEGG enrichment analysis revealed that the high-ARPI group was enriched in cancer-related and immune-related pathways. Immune infiltration analysis has indicated a positive association between high-ARPI groups and increased immune infiltration. Fulvestrant, OSI-027, Lapatinib, Dabrafenib, and Palbociclib were identified as potential sensitive drugs for high-ARPI patients. In vitro experiments exhibited that silencing LINC01138 dampened the proliferation, migration and enzalutamide resistance in CRPC. Furthermore, it stimulated apoptosis and inhibited the eithelial-mesenchymal transition process.

CONCLUSION

Four arlncRNAs were identified and a risk model was established to predict the prognosis of patients with prostate cancer. Immune infiltration and drug susceptibility analysis revealed a potential therapeutic strategy for patients with castration-resistant prostate cancer.

Treatments Targeting the Androgen Receptor and Its Splice Variants in Breast Cancer

Breast cancer is a major cause of death worldwide. The complexity of endocrine regulation in breast cancer may allow the cancer cells to escape from a particular treatment and result in resistant and aggressive disease. These breast cancers usually have fewer treatment options. Targeted therapies for cancer patients may offer fewer adverse side effects because of specificity compared to conventional chemotherapy. Signaling pathways of nuclear receptors, such as the estrogen receptor (ER), have been intensively studied and used as therapeutic targets. Recently, the role of the androgen receptor (AR) in breast cancer is gaining greater attention as a therapeutic target and as a prognostic biomarker. The expression of constitutively active truncated AR splice variants in breast cancer is a possible mechanism contributing to treatment resistance. Therefore, targeting both the full-length AR and AR variants, either through the activation or suppression of AR function, depending on the status of the ER, progesterone receptor, or human epidermal growth factor receptor 2, may provide additional treatment options. Studies targeting AR in combination with other treatment strategies are ongoing in clinical trials. The determination of the status of nuclear receptors to classify and identify patient subgroups will facilitate optimized and targeted combination therapies.

Experimental treatment efficacy of dmrFABP5 on prostate cancer singly or in combination with drugs in use

Enzalutamide is a drug used to treat prostate cancer (PC) and docetaxel is a drug for chemotherapeutic treatment of diverse cancer types, including PC. The effectiveness of these drugs in treating castration-resistant prostate cancer (CRPC) is poor and therefore CRPC is still largely incurable. However, the bio-inhibitor of fatty acid-binding protein 5 (FABP5), dmrFABP5, which is a mutant form of FABP5 incapable of binding to fatty acids, has been shown recently to be able to suppress the tumorigenicity and metastasis of cultured CRPC cells. The present study investigated the possible synergistic effect of dmrFABP5 combined with either enzalutamide or docetaxel on suppressing the tumorigenic properties of PC cells, including cell viability, migration, invasion and colony proliferation in soft agar. A highly significant synergistic inhibitory effect on these properties was observed when dmrFABP5 was used in combination with enzalutamide on androgen-responsive PC 22RV1 cells. Moreover, a highly significant synergistic inhibitory effect was also observed when dmrFABP5 was combined with docetaxel, and added to 22RV1 cells and to the highly malignant, androgen-receptor (AR)-negative Du145 cells. DmrFABP5 alone failed to produce any suppressive effect when added to the FABP5-negative cell line LNCaP, although enzalutamide could significantly suppress LNCaP cells when used as a single agent. These synergistic inhibitory effects of dmrFABP5 were produced by interrupting the FABP5-related signal transduction pathway in PC cells. Thus, dmrFABP5 appears to be not only a potential single therapeutic agent, but it may also be used in combination with existing drugs to suppress both AR-positive and AR-negative PC.

Identification of a targetable JAK-STAT enriched androgen receptor and androgen receptor splice variant positive triple-negative breast cancer subtype

Triple-negative breast cancer (TNBC) is an aggressive subtype with no targeted therapeutics. The luminal androgen receptor (LAR) subtype constitutes 15% of TNBC and is enriched for androgen receptor (AR) and AR target genes. Here, we show that a cohort of TNBC not only expresses AR at a much higher rate (∼80%) but also expresses AR splice variants (AR-SVs) (∼20%), further subclassifying LAR-TNBC. Higher AR and AR-SV expression and corresponding aggressive phenotypes are observed predominantly in specimens obtained from African American women. LAR TNBC specimens are enriched for interferon, Janus kinase (JAK)-signal activator and transducer (STAT), and androgen signaling pathways, which are exclusive to AR-expressing epithelial cancer cells. AR- and AR-SV-expressing TNBC cell proliferation and xenograft and patient-tumor explant growth are inhibited by AR N-terminal domain-binding selective AR degrader or by a JAK inhibitor. Biochemical analysis suggests that STAT1 is an AR coactivator. Collectively, our work identifies pharmacologically targetable TNBC subtypes and identifies growth-promoting interaction between AR and JAK-STAT signaling.

Genomic Portraits: Reflections into a Tumor's Response to Therapy

Well-annotated matched tissue specimens both before and after initiation of androgen receptor signaling inhibitors (ARSI) have revealed activation of unique signaling pathways and genomic signatures that identify a profile to guide therapy. A recent study represents the largest prospective biospecimen banking protocol to study mechanisms of resistance to ARSIs. See related article by Menssouri et al., p. 4504.

Friedelin, a novel inhibitor of CYP17A1 in prostate cancer from Cassia tora

In prostate cancer (PC), drugs targeting CYP17A1 have shown great success in regulating PC progression. However, successful drug molecules show adverse side effects and therapeutic resistance in PC. Therefore, we proposed to discover the potent phytochemical-based inhibitor against CYP17A1 using virtual screening. In this study, a phytochemicals library of ∼13800 molecules was selected to screen the best possible inhibitors against CYP17A1. A molecular modelling approach investigated detailed intermolecular interactions, their structural stability, and binding affinity. Further, in vitro and in vivo studies were performed to confirm the anticancer activity of identified potential inhibitor against CYP17A1. Friedelin from Cassia tora (CT) is identified as the best possible inhibitor from the screened library. MD simulation study reveals stable binding of Friedelin to conserved binding pocket of CYP17A1 with higher binding affinity than studied control, that is, Orteronel. Friedelin was tested on hormone-sensitive (22Rv1) and insensitive (DU145) cell lines and the IC50 value was found to be 72.025 and 81.766 µg/ml, respectively. CT extract showed a 25.28% IC50 value against 22Rv1, ∼92.6% increase in late Apoptosis/Necrosis, and three folds decrease in early apoptosis in treated cells compared to untreated cells. Further, animal studies show a marked decrease in prostate weight by 39.6% and prostate index by 36.5%, along with a reduction in serum PSA level by 71.7% and testosterone level by 92.4% compared to the testosterone group, which was further validated with histopathological studies. Thus, we propose Friedelin and CT extract as potential leads, which could be taken further for drug development in PC.[Figure: see text]Communicated by Ramaswamy H. Sarma.

The heterogeneity and clonal evolution analysis of the advanced prostate cancer with castration resistance

BACKGROUND

Nowadays, the incidence rate of advanced and metastatic prostate cancer at the first time of diagnosis grows higher in China yearly. At present, androgen deprivation therapy (ADT) is the primary treatment of advanced prostate cancer. However, after several years of ADT, most patients will ultimately progress to castration-resistant prostate cancer (CRPC). Previous studies mainly focus on Caucasian and very few on East Asian patients.

METHODS

In this study, the pre- and post-ADT tumor samples were collected from five Chinese patients with advanced prostate cancer. The whole-exome sequencing, tumor heterogeneity, and clonal evolution pattern were analyzed.

RESULTS

The results showed that the gene mutation pattern and heterogeneity changed significantly after androgen deprivation therapy. Tumor Mutational Burden (TMB) and Copy Number Alteration (CNA) were substantially reduced in the post-treatment group, but the Mutant-allele tumor heterogeneity (MATH), Socio-Demographic Index (SDI), Intratumor heterogeneity (ITH), and weighted Genome Instability Index (wGII) had no significant difference. According to the clone types and characteristics, the presence of main clones in five pre-and post-treatment samples, the clonal evolution pattern can be further classified into two sub-groups (the Homogeneous origin clonal model or the Heterogeneous origin clonal model). The Progression-free survival (PFS) of the patients with the "Homogeneous origin clonal model" was shorter than the "Heterogeneous origin clonal model". The longer PFS might relate to MUC7 and MUC5B mutations repaired. ZNF91 mutation might be responsible for resistance to ADT resistance.

CONCLUSION

Our findings revealed potential genetic regulators to predict the castration resistance and provide insights into the castration resistance processes in advanced prostate cancer. The crosstalk between clonal evolution patterns and tumor microenvironment may also play a role in castration resistance. A multicenter-research including larger populations with different background are needed to confirm our conclusion in the future.

Histone H2A Lys130 acetylation epigenetically regulates androgen production in prostate cancer

The testicular androgen biosynthesis is well understood, however, how cancer cells gauge dwindling androgen to dexterously initiate its de novo synthesis remained elusive. We uncover dual-phosphorylated form of sterol regulatory element-binding protein 1 (SREBF1), pY673/951-SREBF1 that acts as an androgen sensor, and dissociates from androgen receptor (AR) in androgen deficient environment, followed by nuclear translocation. SREBF1 recruits KAT2A/GCN5 to deposit epigenetic marks, histone H2A Lys130-acetylation (H2A-K130ac) in SREBF1, reigniting de novo lipogenesis & steroidogenesis. Androgen prevents SREBF1 nuclear translocation, promoting T cell exhaustion. Nuclear SREBF1 and H2A-K130ac levels are significantly increased and directly correlated with late-stage prostate cancer, reversal of which sensitizes castration-resistant prostate cancer (CRPC) to androgen synthesis inhibitor, Abiraterone. Further, we identify a distinct CRPC lipid signature resembling lipid profile of prostate cancer in African American (AA) men. Overall, pY-SREBF1/H2A-K130ac signaling explains cancer sex bias and reveal synchronous inhibition of KAT2A and Tyr-kinases as an effective therapeutic strategy.

Design, Synthesis, and Evaluation of Niclosamide Analogs as Therapeutic Agents for Enzalutamide-Resistant Prostate Cancer

Niclosamide effectively downregulates androgen receptor variants (AR-Vs) for treating enzalutamide and abiraterone-resistant prostate cancer. However, the poor pharmaceutical properties of niclosamide due to its solubility and metabolic instability have limited its clinical utility as a systemic treatment for cancer. A novel series of niclosamide analogs was prepared to systematically explore the structure-activity relationship and identify active AR-Vs inhibitors with improved pharmaceutical properties based on the backbone chemical structure of niclosamide. Compounds were characterized using 1H NMR, 13C NMR, MS, and elemental analysis. The synthesized compounds were evaluated for antiproliferative activity and downregulation of AR and AR-V7 in two enzalutamide-resistant cell lines, LNCaP95 and 22RV1. Several of the niclosamide analogs exhibited equivalent or improved anti-proliferation effects in LNCaP95 and 22RV1 cell lines (B9, IC50 LNCaP95 and 22RV1 = 0.130 and 0.0997 μM, respectively), potent AR-V7 down-regulating activity, and improved metabolic stability. In addition, both a traditional structure-activity relationship (SAR) and 3D-QSAR analysis were performed to guide further structural optimization. The presence of two -CF3 groups of the most active B9 in the sterically favorable field and the presence of the -CN group of the least active B7 in the sterically unfavorable field seem to make B9 more potent than B7 in the antiproliferative activity.

Instrumental and transcriptome analysis reveals the chemotherapeutic effects of doxorubicin-loaded black phosphate nanosheets on abiraterone-resistant prostate cancer

Prostate cancer is the second most common cause of cancer-related deaths in men and is common in most developed countries. Androgen deprivation therapy (ADT) that uses abiraterone acetate (AA) is an effective second-line treatment for prostate cancer. However, approximately 20-40% of patients develop primary resistance to abiraterone post-treatment. In this study, we aimed to understand the molecular mechanisms underlying the development of abiraterone resistance in prostate cancer cells and the potential use of black phosphorus nanosheets (BPNS) for treating abiraterone-resistant prostate cancer. We first established abiraterone-resistant prostate cancer PC-3 cells and found that these cells have higher migration ability than normal prostate cancer cells. Using comparative transcriptomic and bioinformatics analyses between abiraterone-sensitive PC-3 and abiraterone-resistant PC-3 cells, we highlighted the differentially expressed genes (DEGs) involved in the biological processes related to prostate gland morphogenesis, drug response, immune response, angiogenesis. We further studied the therapeutic effects of BPNS. Our results show that BPNS reduced the proliferation and migration of abiraterone-resistant PC-3 cells. Bioinformatics analysis, including gene ontology, Kyoto encyclopedia of genes and genomes enrichment analysis, and ingenuity pathway analysis (IPA) of the DEGs, suggested that BPNS treatment controlled cancer cell proliferation, metastasis, and oncogenic signaling pathways. Furthermore, the IPA gene network highlighted the involvement of the MMP family, ATF, and notch families in the anti-prostate cancer function of BPNS. Our findings suggest that BPNS may have a chemotherapeutic function in treating abiraterone-resistant prostate cancer.

Adapting to hormone-therapy resistance for adopting the right therapeutic strategy in advanced prostate cancer

INTRODUCTION

The androgen/androgen receptor (AR) axis represents a key driver of treatment resistance in prostate cancer (PCa) patients receiving androgen deprivation therapy (ADT) and targeted agents, and a deeper comprehension of resistance mechanisms is fundamental to adopt effective therapeutic strategies.

AREAS COVERED

We review the mechanisms of primary or secondary resistance to hormone therapy (HT) in PCa, especially focusing on available data and emerging evidence.

EXPERT OPINION

First- and second-generation HT resistance has been associated with several AR-dependent and AR-independent mechanisms, ranging from the amplification of the AR gene locus to somatic AR mutations and the intratumoral synthesis of androgens from adrenal steroids and cholesterol. As reported in the current review, the development of novel and effective treatments is needed to personalize anticancer therapies in this setting and to finally improve clinical outcomes in patients with HT resistant disease.

A Phase II Trial of Abiraterone With Dutasteride for Second-Generation Antiandrogen- and Chemotherapy-Naïve Patients With Castration-Resistant Prostate Cancer

The development of a novel therapy to overcome primary and acquired resistance to abiraterone is an unmet need. This study aimed to evaluate the efficacy and safety of adding 5α-reductase inhibitor dutasteride to abiraterone, explore proof of concept, and identify candidates suitable for combination therapy. This phase II, single-arm, and open-label study enrolled second-generation antiandrogen- and chemotherapy-naïve patients with castration-resistant prostate cancer. Patients received abiraterone and prednisolone for 4 weeks, followed by adding dutasteride. The primary end point was a 50% prostate-specific antigen response rate. Serum concentrations of abiraterone and its metabolites as well as HSD3B1 and SRD5A2 genotypes were measured. The association between drug metabolism and genotypes and their impact on the efficacy of combination therapy were assessed. Among 21 patients, 18 (85.7%) achieved ≥50% PSA reduction. Median time to treatment failure was not reached during the median follow-up of 15.4 months. No patients experienced grade ≥3 adverse events. Although dutasteride reduced serum 3-keto-5α-abiraterone concentrations, higher serum 3-keto-5α-abiraterone concentrations on combination therapy were associated with a shorter time to treatment failure. HSD3B1 and SRD5A2 genotypes were associated with serum Δ4-abiraterone and 3-keto-5α-abiraterone concentrations before adding dutasteride, respectively. Time to treatment failure was longer in patients with homozygous wild-type HSD3B1, but comparable between those with the SRD5A2 genotype. The promising outcomes of this study warrant further investigation of combination therapy in a randomized trial. Stratification by HSD3B1 and SRD5A2 genetic profiles might identify patients suitable for combination therapy.

Murine toxicology and pharmacokinetics of lead next generation galeterone analog, VNPP433-3β

VNPP433-3β (compound 2, (3β-(1H-imidazole-1-yl)-17-(1H-benzimidazole-1-yl)-androsta-5,16-diene), a multitarget anticancer agent has emerged as our lead next generation galeterone analogs (NGGA). Compound 2 is currently in development as potential new therapeutic for prostate and pancreatic cancers. The preliminary toxicity study reveals that the compound 2 was better tolerated by the normal male CD-1 mice than the male Nude mice. The maximum tolerated dose (MTD) in the Nude mice was estimated to be between 25 < 50 mg/kg. After oral dosing of compound 2 to male and female rats, the plasma concentration versus time curves were very consistent between animals and the AUClast increased with dose. Many plasmas concentration versus time curves profiles were nearly flat over 24 hr., suggesting extended absorption from the GI tract. Consequently, reliable values for half-life and AUCinf were not determined. Calculated oral bioavailability (using oral AUClast and excluding the outlier IV animal) ranged from 32 to 47 %. This should be considered a minimum value since the contribution to true AUC beyond 24 hr. is clearly not zero. Clearly, these toxicology and pharmacokinetics parameters pave the way for understanding the anticancer pharmacological actions and provide a meaningful basis for further preclinical development and eventual clinical development.

Pseurotin A Validation as a Metastatic Castration-Resistant Prostate Cancer Recurrence-Suppressing Lead via PCSK9-LDLR Axis Modulation

Metastatic castration-resistant prostate cancer (mCRPC) cells can de novo biosynthesize their own cholesterol and overexpress proprotein convertase subtilisin/kexin type 9 (PCSK9). PCSK9 proved to contribute to mCRPC cell motility since PCSK9 knockdown (KD) in mCRPC CWR-R1ca cells led to notable reductions in cell migration and colony formation. Human tissue microarray results proved a higher immunohistoscore in patients ≥ 65 years old, and PCSK9 proved to be expressed higher at an early Gleason score of ≤7. The fermentation product pseurotin A (PS) suppressed PCSK9 expression, protein-protein interactions with LDLR, and breast and prostate cancer recurrences. PS suppressed migration and colony formation of the CWR-R1ca cells. The progression and metastasis of the CWR-R1ca-Luc cells subcutaneously (sc) xenografted into male nude mice fed a high-fat diet (HFD, 11% fat content) showed nearly 2-fold tumor volume, metastasis, serum cholesterol, low-density lipoprotein cholesterol (LDL-C), prostate-specific antigen (PSA), and PCSK9 levels versus mice fed a regular chow diet. Daily oral PS 10 mg/kg treatments prevented the locoregional and distant tumor recurrence of CWR-R1ca-Luc engrafted into nude mice after primary tumor surgical excision. PS-treated mice showed a significant reduction in serum cholesterol, LDL-C, PCSK9, and PSA levels. These results comprehensively validate PS as an mCRPC recurrence-suppressive lead by modulating the PCSK9-LDLR axis.

Effect of Dexamethasone on Abiraterone Pharmacokinetics in Mice: Determined by LC/MS Analysis

Background: Abiraterone acetate is a cytochrome P450 17A1 (CYP17A1) inhibitor that is indicated for use in both castration-resistant and castration-sensitive prostate cancer patients. To manage the mineralocorticoid effects of CYP17A1 inhibition, a glucocorticoid such as dexamethasone is co-administered with abiraterone. The goal of the present study was to understand the effect of dexamethasone on the disposition of abiraterone. Methods: Adult male CD-1 mice were treated with either dexamethasone (80 mg/kg/day) or vehicle for three consecutive days, followed by the administration of a single dose of abiraterone acetate (180 mg/kg) as an oral gavage. Blood samples were collected by tail bleeding at timepoints between 0 to 24 h. Subsequently, abiraterone was extracted from the mouse serum using a neutral pH condition and serum abiraterone levels were determined using a liquid chromatography–mass spectrometry assay. Results: Our results demonstrated that dexamethasone lowered the maximum plasma concentration and area under the curve parameters by approximately five- and ten-fold, respectively. Similar effects were also observed on the plasma half-life and oral clearance parameters. This is the first report of dexamethasone effect on abiraterone disposition in vivo. Conclusions: We conclude that dexamethasone has the potential to reduce the plasma abiraterone level and thus compromise its CYP17A1 inhibitory ability in the procancerous androgen biosynthesis pathway. Thus, use of a higher abiraterone dose may be warranted when used alongside dexamethasone.

Exploring the Chemical Space of CYP17A1 Inhibitors Using Cheminformatics and Machine Learning

Cytochrome P450 17A1 (CYP17A1) is one of the key enzymes in steroidogenesis that produces dehydroepiandrosterone (DHEA) from cholesterol. Abnormal DHEA production may lead to the progression of severe diseases, such as prostatic and breast cancers. Thus, CYP17A1 is a druggable target for anti-cancer molecule development. In this study, cheminformatic analyses and quantitative structure-activity relationship (QSAR) modeling were applied on a set of 962 CYP17A1 inhibitors (i.e., consisting of 279 steroidal and 683 nonsteroidal inhibitors) compiled from the ChEMBL database. For steroidal inhibitors, a QSAR classification model built using the PubChem fingerprint along with the extra trees algorithm achieved the best performance, reflected by the accuracy values of 0.933, 0.818, and 0.833 for the training, cross-validation, and test sets, respectively. For nonsteroidal inhibitors, a systematic cheminformatic analysis was applied for exploring the chemical space, Murcko scaffolds, and structure-activity relationships (SARs) for visualizing distributions, patterns, and representative scaffolds for drug discoveries. Furthermore, seven total QSAR classification models were established based on the nonsteroidal scaffolds, and two activity cliff (AC) generators were identified. The best performing model out of these seven was model VIII, which is built upon the PubChem fingerprint along with the random forest algorithm. It achieved a robust accuracy across the training set, the cross-validation set, and the test set, i.e., 0.96, 0.92, and 0.913, respectively. It is anticipated that the results presented herein would be instrumental for further CYP17A1 inhibitor drug discovery efforts.

Targeting the N-terminal domain of the androgen receptor: The effective approach in therapy of CRPC

The androgen receptor (AR) is dominant in prostate cancer (PCa) pathology. Current therapeutic agents for advanced PCa include androgen synthesis inhibitors and AR antagonists that bind to the hormone binding pocket (HBP) at the ligand binding domain (LBD). However, AR amplification, AR splice variants (AR-Vs) expression, and intra-tumoral de novo synthesis of androgens result in the reactivation of AR signalling. The AR N-terminal domain (NTD) plays an essential role in AR transcriptional activity. The AR inhibitor targeting NTD could potentially block the activation of both full-length AR and AR-Vs, thus overcoming major resistance mechanisms to current treatments. This review discusses the progress of research in various NTD inhibitors and provides new insight into the development of AR-NTD inhibitors.

Mechanisms of Prostate Cancer Cells Survival and Their Therapeutic Targeting

Prostate cancer (PCa) is today the second most common cancer in the world, with almost 400,000 deaths annually. Multiple factors are involved in the etiology of PCa, such as older age, genetic mutations, ethnicity, diet, or inflammation. Modern treatment of PCa involves radical surgical treatment or radiation therapy in the stages when the tumor is limited to the prostate. When metastases develop, the standard procedure is androgen deprivation therapy, which aims to reduce the level of circulating testosterone, which is achieved by surgical or medical castration. However, when the level of testosterone decreases to the castration level, the tumor cells adapt to the new conditions through different mechanisms, which enable their unhindered growth and survival, despite the therapy. New knowledge about the biology of the so-called of castration-resistant PCa and the way it adapts to therapy will enable the development of new drugs, whose goal is to prolong the survival of patients with this stage of the disease, which will be discussed in this review.

Novel inhibition of AKR1C3 and androgen receptor axis by PTUPB synergizes enzalutamide treatment in advanced prostate cancer

Castration-resistant prostate cancer (CRPC) is the main driving force of mortality in prostate cancer patients. Among the parameters contributing to the progression of CRPC and treatment failure, elevation of the steroidogenic enzyme AKR1C3 and androgen receptor variant 7 (AR-V7) are frequently reported. The AKR1C3/AR-V7 complex has been recognized as a major driver for drug resistance in advanced prostate cancer. Herein we report that the level of AKR1C3 is reciprocally regulated by the full-length androgen receptor (AR-FL) through binding to the distal enhancer region of the AKR1C3 gene. A novel function of PTUPB in AKR1C3 inhibition was discovered and PTUPB showed more effectiveness than indomethacin and celecoxib in suppressing AKR1C3 activity and CRPC cell growth. PTUPB synergizes with enzalutamide treatment in tumor suppression and gene signature regulation. Combination treatments with PTUPB and enzalutamide provide benefits by blocking AR/AR-V7 signaling, which inhibits the growth of castration relapsed VCaP xenograft tumors and patient-derived xenograft organoids. Targeting of the ARK1C3/AR/AR-V7 axis with PTUPB and enzalutamide may overcome drug resistance to AR signaling inhibitors in advanced prostate cancer.

Clinical and molecular significance of the RNA m6A methyltransferase complex in prostate cancer

N⁶-methyladenosine (m⁶A) is the most abundant internal mRNA modification and is dynamically regulated through distinct protein complexes that methylate, demethylate, and/or interpret the m⁶A modification. These proteins, and the m⁶A modification, are involved in the regulation of gene expression, RNA stability, splicing and translation. Given its role in these crucial processes, m⁶A has been implicated in many diseases, including in cancer development and progression. Prostate cancer (PCa) is the most commonly diagnosed non-cutaneous cancer in men and recent studies support a role for m⁶A in PCa. Despite this, the literature currently lacks an integrated analysis of the expression of key components of the m⁶A RNA methyltransferase complex, both in PCa patients and in well-established cell line models. For this reason, this study used immunohistochemistry and functional studies to investigate the mechanistic and clinical significance of the METTL3, METTL14, WTAP and CBLL1 components of the m⁶A methyltransferase complex in PCa specimens and cell lines. Expression of METTL3 and CBLL1, but not METTL14 and WTAP, was associated with poorer PCa patient outcomes. Expression of METTL3, METTL14, WTAP and CBLL1 was higher in PCa cells compared with non-malignant prostate cells, with the highest expression seen in castrate-sensitive, androgen-responsive PCa cells. Moreover, in PCa cell lines, expression of METTL3 and WTAP was found to be androgen-regulated. To investigate the mechanistic role(s) of the m⁶A methyltransferase complex in PCa cells, short hairpin RNA (shRNA)-mediated knockdown coupled with next generation sequencing was used to determine the transcriptome-wide roles of METTL3, the catalytic subunit of the m⁶A methyltransferase complex. Functional depletion of METTL3 resulted in upregulation of the androgen receptor (AR), together with 134 AR-regulated genes. METTL3 knockdown also resulted in altered splicing, and enrichment of cell cycle, DNA repair and metabolic pathways. Collectively, this study identified the functional and clinical significance of four essential m⁶A complex components in PCa patient specimens and cell lines for the first time. Further studies are now warranted to determine the potential therapeutic relevance of METTL3 inhibitors in development to treat leukaemia to benefit patients with PCa.

Using the AR-V7 biomarker to determine treatment in metastatic castrate resistant prostate cancer, a feasibility randomised control trial, conclusions from the VARIANT trial

Background

Prostate cancer is the most commonly diagnosed malignancy in the UK. Castrate resistant prostate cancer (CRPC) can be difficult to manage with response to next generation hormonal treatment variable. AR-V7 is a protein biomarker that can be used to predict response to treatment and potentially better inform management in these patients. Our aim was to establish the feasibility of conducting a definitive randomised controlled trial comparing the clinical utility of AR-V7 biomarker assay in personalising treatments for patients with metastatic CRPC within the United Kingdom (UK) National Health Service (NHS). Due to a number of issues the trial was not completed successfully, we aim to discuss and share lessons learned herein.

Methods

We conducted a randomised, open, feasibility trial, which aimed to recruit 70 adult men with metastatic CRPC within three secondary care NHS trusts in the UK to be run over an 18-month period. Participants were randomised to personalised treatment based on AR-V7 status (intervention) or standard care (control). The primary outcome was feasibility, which included: recruitment rate, retention and compliance. Additionally, a baseline prevalence of AR-V7 expression was to be estimated.

Results

Fourteen participants were screened and 12 randomised with six into each arm over a nine-month period. Reliability issues with the AR-V7 assay meant prevalence was not estimated. Due to limited recruitment the study did not complete to target.

Conclusions

Whilst the trial did not complete to target, we have ascertained that men with advanced cancer are willing to take part in trials utilising biomarker guided treatment. A number of issues were identified that serve as important learning points in future clinical trials.

Exosomes in Genitourinary Cancers: Emerging Mediators of Drug Resistance and Promising Biomarkers

Drug resistance presents a major obstacle in the treatment of genitourinary cancers. Exosomes as the medium of intercellular communication serve important biological functions and play essential roles in pathological processes, including drug response. Through the transfer of bioactive cargoes, exosomes can modulate drug resistance via multiple mechanisms. This review attempts to elucidate the mechanisms of exosomal cargoes with reference to tumor drug resistance, their role in genitourinary cancers, and their potential clinical applications as candidate biomarkers in liquid biopsy.

Acetyl-CoA Counteracts the Inhibitory Effect of Antiandrogens on Androgen Receptor Signaling in Prostate Cancer Cells

The commonly used therapeutic management of PC involves androgen deprivation therapy (ADT) followed by treatment with AR signaling inhibitors (ARSI). However, nearly all patients develop drug-resistant disease, with a median progression-free survival of less than 2 years in chemotherapy-naïve men. Acetyl-coenzyme A (acetyl-CoA) is a central metabolic signaling molecule with key roles in biosynthetic processes and cancer signaling. In signaling, acetyl-CoA serves as the acetyl donor for acetylation, a critical post-translational modification. Acetylation affects the androgen receptor (AR) both directly and indirectly increasing expression of AR dependent genes. Our studies reveal that PC cells respond to the treatment with ARSI by increasing expression of ATP-citrate lyase (ACLY), a major enzyme responsible for cytosolic acetyl-CoA synthesis, and up-regulation of acetyl-CoA intracellular levels. Inhibition of ACLY results in a significant suppression of ligand-dependent and -independent routes of AR activation. Accordingly, the addition of exogenous acetyl-CoA, or its precursor acetate, augments AR transcriptional activity and diminishes the anti-AR activity of ARSI. Taken together, our findings suggest that PC cells respond to antiandrogens by increasing activity of the acetyl-coA pathway in order to reinstate AR signaling.

Androgen Metabolism and Response in Prostate Cancer Anti-Androgen Therapy Resistance

All aspects of prostate cancer evolution are closely related to androgen levels and the status of the androgen receptor (AR). Almost all treatments target androgen metabolism pathways and AR, from castration-sensitive prostate cancer (CSPC) to castration-resistant prostate cancer (CRPC). Alterations in androgen metabolism and its response are one of the main reasons for prostate cancer drug resistance. In this review, we will introduce androgen metabolism, including how the androgen was synthesized, consumed, and responded to in healthy people and prostate cancer patients, and discuss how these alterations in androgen metabolism contribute to the resistance to anti-androgen therapy.

Steroidogenesis in castration-resistant prostate cancer

Castration resistance is in part attributable to aberrant activation of androgen receptor (AR) signaling by the intracrine activation of androgen precursors derived from adrenal glands. To overcome this, novel AR pathway inhibitors (ARPIs) that suppress androgen synthesis by CYP17 inhibition or AR activation by antiandrogen effects have been developed. However, primary or acquired resistance to these ARPIs occurs; in turn attributable, at least in part, to the maintained androgen milieu despite intensive suppression of AR signaling similar to castration resistance. In addition to the classical pathway to produce potent androgens such as testosterone and dihydrotestosterone, the alternative pathway and the backdoor pathway which bypasses testosterone to produce dihydrotestosterone have been shown to play a role in intratumor steroidogenesis. Furthermore, the 11β-hydroxyandrostenedione pathway to produce the potent oxygenated androgens 11-ketotestosterone and 11-ketodihydrotestosterone has been suggested to be functional in prostate cancer. These steroidogenesis pathways produce potent androgens that promote tumor resistance to endocrine therapy including novel ARPIs. Here, we overview the current evidence on the pathological androgen milieu by altered metabolism and transport in prostate cancer, leading to resistance to endocrine therapy.

Choice of antibody is critical for specific and sensitive detection of androgen receptor splice variant-7 in circulating tumor cells

Androgen receptor variant 7 (AR-V7) is an important biomarker to guide treatment options for castration-resistant prostate cancer (CRPC) patients. Its detectability in circulating tumour cells (CTCs) opens non-invasive diagnostic avenues. While detectable at the transcript level, AR-V7 protein detection in CTCs may add additional information and clinical relevance. The aim of this study was to compare commercially available anti-AR-V7 antibodies and establish reliable AR-V7 immunocytostaining applicable to CTCs from prostate cancer (PCa) patients. We compared seven AR-V7 antibodies by western blotting and immmunocytostaining using a set of PCa cell lines with known AR/AR-V7 status. The emerging best antibody was validated for detection of CRPC patient CTCs enriched by negative depletion of leucocytes. The anti-AR-V7 antibody, clone E308L emerged as the best antibody in regard to signal to noise ratio with a specific nuclear signal. Moreover, this antibody detects CRPC CTCs more efficiently compared to an antibody previously shown to detect AR-V7 CTCs. We have determined the best antibody for AR-V7 detection of CTCs, which will open future studies to correlate AR-V7 subcellular localization and potential co-localization with other proteins and cellular structures to patient outcomes.

Prostate cancer resistance leads to a global deregulation of translation factors and unconventional translation

Emerging evidence associates translation factors and regulators to tumorigenesis. However, our understanding of translational changes in cancer resistance is still limited. Here, we generated an enzalutamide-resistant prostate cancer (PCa) model, which recapitulated key features of clinical enzalutamide-resistant PCa. Using this model and poly(ribo)some profiling, we investigated global translation changes that occur during acquisition of PCa resistance. We found that enzalutamide-resistant cells exhibit an overall decrease in mRNA translation with a specific deregulation in the abundance of proteins involved in mitochondrial processes and in translational regulation. However, several mRNAs escape this translational downregulation and are nonetheless bound to heavy polysomes in enzalutamide-resistant cells suggesting active translation. Moreover, expressing these corresponding genes in enzalutamide-sensitive cells promotes resistance to enzalutamide treatment. We also found increased association of long non-coding RNAs (lncRNAs) with heavy polysomes in enzalutamide-resistant cells, suggesting that some lncRNAs are actively translated during enzalutamide resistance. Consistent with these findings, expressing the predicted coding sequences of known lncRNAs JPX, CRNDE and LINC00467 in enzalutamide-sensitive cells drove resistance to enzalutamide. Taken together, this suggests that aberrant translation of specific mRNAs and lncRNAs is a strong indicator of PCa enzalutamide resistance, which points towards novel therapeutic avenues that may target enzalutamide-resistant PCa.

Glucocorticoid receptor and androgen receptor-targeting therapy in patients with castration-resistant prostate cancer

Objective

The glucocorticoid receptor (GR) promotes resistance to androgen receptor (AR)-targeting therapies in castration-resistant prostate cancer (CRPC) by bypassing AR blockade. However, the clinical relevance of evaluating GR expression in patients with CRPC has not been determined. The present study investigated the association of relative GR expression in CRPC tissue samples with treatment response to AR-targeting therapy.

Methods

Levels of GR, AR-FL, and AR-V7 mRNAs were measured in prostate cancer tissue from prospectively enrolled CRPC patients who were starting treatment. Patients were divided into groups with high and low AR-V7/AR-FL ratios and with high and low GR/AR-FL ratios. The primary endpoint was prostate-specific antigen (PSA) response rate to treatment.

Results

Evaluation of 38 patients treated with AR-targeting therapies showed that the PSA response rate was significantly higher in patients with low than high AR-V7/AR-FL ratios (77.8% vs. 25.0%, p=0.003) and in patients with low than high GR/AR-FL ratios (81.3% vs. 27.3%, p=0.003). Patients with low GR/AR-FL ratios had higher rates of PSA progression-free survival (46.0% vs. 22.4%, p=0.006), radiologic progression-free survival (28.9% vs. 10.0%, p=0.02), and overall survival (75.2% vs. 48.0%, p=0.037) than patients with high GR/AR-FL ratios. The association of GR/AR-FL ratio with PSA response to AR-targeting therapy remained significant in multivariable models. Evaluation of the 14 patients who received taxane chemotherapy showed that PSA response rates did not differ significantly in those with low and high AR-V7/AR-FL and GR/AR-FL ratios, although no definitive conclusions can be drawn due to the small number of patients.

Conclusion

Relative GR expression is associated with sensitivity to AR-targeting therapy and survival in patients with CRPC. Large-scale prospective validation and liquid biopsy-based studies are warranted.

Design, Synthesis, and Biological Evaluation of Androgen Receptor Degrading and Antagonizing Bifunctional Steroidal Analogs for the Treatment of Advanced Prostate Cancer

Metastatic castration-resistant prostate cancer (mCRPC) with high mortality has seriously threatened men's health. Bifunctional agents simultaneously degrade and antagonize androgen receptor (AR), display robust AR signaling pathway blockade, and show the therapeutic prospect for mCRPC. Herein, systemic structural modifications on the C-3, C-6, and C-17 positions of galeterone led to the discovery of 67-b with the dual functions of AR antagonism and degradation. In vitro, 67-b exhibited excellent antiproliferative activity and potent AR degradation activity in different PCa cells (LNCaP and 22RV1), as well as outstanding antagonistic activity against wild-type and mutant (W741L, T877A, and F876L) ARs. In vivo, 67-b effectively inhibited the growth of hormone-sensitive organs in the Hershberger assay and exhibited tumor regression in the enzalutamide-resistant (c4-2b-ENZ) xenograft model. These results confirmed 67-b to be a promising AR degrader and antagonist for the treatment of mCRPC patients.

Evolution-based mathematical models significantly prolong response to abiraterone in metastatic castrate-resistant prostate cancer and identify strategies to further improve outcomes

Background

Abiraterone acetate is an effective treatment for metastatic castrate-resistant prostate cancer (mCRPC), but evolution of resistance inevitably leads to progression. We present a pilot study in which abiraterone dosing is guided by evolution-informed mathematical models to delay onset of resistance.

Methods

In the study cohort, abiraterone was stopped when PSA was <50% of pretreatment value and resumed when PSA returned to baseline. Results are compared to a contemporaneous cohort who had >50% PSA decline after initial abiraterone administration and met trial eligibility requirements but chose standard of care (SOC) dosing.

Results

17 subjects were enrolled in the adaptive therapy group and 16 in the SOC group. All SOC subjects have progressed, but four patients in the study cohort remain stably cycling (range 53-70 months). The study cohort had significantly improved median time to progression (TTP; 33.5 months; p<0.001) and median overall survival (OS; 58.5 months; hazard ratio, 0.41, 95% confidence interval (CI), 0.20-0.83, p<0.001) compared to 14.3 and 31.3 months in the SOC cohort. On average, study subjects received no abiraterone during 46% of time on trial. Longitudinal trial data demonstrated the competition coefficient ratio (αRS/αSR) of sensitive and resistant populations, a critical factor in intratumoral evolution, was two- to threefold higher than pre-trial estimates. Computer simulations of intratumoral evolutionary dynamics in the four long-term survivors found that, due to the larger value for αRS/αSR, cycled therapy significantly decreased the resistant population. Simulations in subjects who progressed predicted further increases in OS could be achieved with prompt abiraterone withdrawal after achieving 50% PSA reduction.

Conclusions

Incorporation of evolution-based mathematical models into abiraterone monotherapy for mCRPC significantly increases TTP and OS. Computer simulations with updated parameters from longitudinal trial data can estimate intratumoral evolutionary dynamics in each subject and identify strategies to improve outcomes.

Funding

Moffitt internal grants and NIH/NCI U54CA143970-05 (Physical Science Oncology Network).

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Drug resistance in metastatic castration-resistant prostate cancer: an update on the status quo

Prostate cancer (PCa) is a leading cause of cancer-related morbidity and mortality in men globally. Despite improvements in the diagnosis and treatment of PCa, a significant proportion of patients with high-risk localized disease and all patients with advanced disease at diagnosis will experience progression to metastatic castration-resistant prostate cancer (mCRPC). Multiple drugs are now approved as the standard of care treatments for patients with mCRPC that have been shown to prolong survival. Although the majority of patients will respond initially, primary and secondary resistance to these therapies make mCRPC an incurable disease. Several molecular mechanisms underlie the development of mCRPC, with the androgen receptor (AR) axis being the main driver as well as the key drug target. Understanding resistance mechanisms is crucial for discovering novel therapeutic strategies to delay or reverse the progression of the disease. In this review, we address the diverse mechanisms of drug resistance in mCRPC. In addition, we shed light on emerging targeted therapies currently being tested in clinical trials with promising potential to overcome mCRPC-drug resistance.

Natural product myricetin is a pan-KDM4 inhibitor which with poly lactic-co-glycolic acid formulation effectively targets castration-resistant prostate cancer

Background

Castration-resistant prostate cancer (CRPC) with sustained androgen receptor (AR) signaling remains a critical clinical challenge, despite androgen depletion therapy. The Jumonji C-containing histone lysine demethylase family 4 (KDM4) members, KDM4A‒KDM4C, serve as critical coactivators of AR to promote tumor growth in prostate cancer and are candidate therapeutic targets to overcome AR mutations/alterations-mediated resistance in CRPC.

Methods

In this study, using a structure-based approach, we identified a natural product, myricetin, able to block the demethylation of histone 3 lysine 9 trimethylation by KDM4 members and evaluated its effects on CRPC. A structure-based screening was employed to search for a natural product that inhibited KDM4B. Inhibition kinetics of myricetin was determined. The cytotoxic effect of myricetin on various prostate cancer cells was evaluated. The combined effect of myricetin with enzalutamide, a second-generation AR inhibitor toward C4-2B, a CRPC cell line, was assessed. To improve bioavailability, myricetin encapsulated by poly lactic-co-glycolic acid (PLGA), the US food and drug administration (FDA)-approved material as drug carriers, was synthesized and its antitumor activity alone or with enzalutamide was evaluated using in vivo C4-2B xenografts.

Results

Myricetin was identified as a potent α-ketoglutarate-type inhibitor that blocks the demethylation activity by KDM4s and significantly reduced the proliferation of both androgen-dependent (LNCaP) and androgen-independent CRPC (CWR22Rv1 and C4-2B). A synergistic cytotoxic effect toward C4-2B was detected for the combination of myricetin and enzalutamide. PLGA-myricetin, enzalutamide, and the combined treatment showed significantly greater antitumor activity than that of the control group in the C4-2B xenograft model. Tumor growth was significantly lower for the combination treatment than for enzalutamide or myricetin treatment alone.

Conclusions

These results suggest that myricetin is a pan-KDM4 inhibitor and exhibited potent cell cytotoxicity toward CRPC cells. Importantly, the combination of PLGA-encapsulated myricetin with enzalutamide is potentially effective for CRPC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00812-3.

Targeting KDM1B-dependent miR-215-AR-AGR2-axis promotes sensitivity to enzalutamide-resistant prostate cancer

Post-translational modifications of histones by histone demethylases plays an important role in the regulation of gene transcription and are implicated in cancers. Castrate resistant prostate cancer (CRPC) is often driven by constitutively active androgen receptor and commonly becomes resistant to established hormonal therapy strategies such as enzalutamide as a result. However, the role of KDM1B involved in next generation anti-enzalutamide resistance and the mechanisms of KDM1B regulation are poorly defined. Here, we show that KDM1B is upregulated and correlated with prostate cancer progression and poor prognosis. Downregulation of miR-215 is correlated with overexpression of KDM1B in enzalutamide-resistant prostate cancer cells, which promotes AR-dependent AGR2 transcription and regulates the sensitivity to next generation AR-targeted therapy. Inhibition of KDM1B significantly inhibits prostate tumor growth and improves enzalutamide treatments through AGR2 suppression. Our studies demonstrate inhibition of KDM1B can offer a viable therapeutic option to overcome enzalutamide resistance in tumors with deregulated miR-215-KDM1B-AR-AGR2 signaling axis.

Mechanisms of Resistance to Second-Generation Antiandrogen Therapy for Prostate Cancer: Actual Knowledge and Perspectives

Prostate cancer therapy for locally advanced and metastatic diseases includes androgen deprivation therapy (ADT). Second-generation antiandrogens have a role in castration-resistant prostate cancer. Nevertheless, some patients do not respond to this therapy, and eventually all the patients became resistant. This is due to modifications to intracellular signaling pathways, genomic alteration, cytokines production, metabolic switches, constitutional receptor activation, overexpression of some proteins, and regulation of gene expression. The aim of this review is to define the most important mechanisms that drive this resistance and the newest discoveries in this field, specifically for enzalutamide and abiraterone, with potential implications for future therapeutic targets. Furthermore, apalutamide and darolutamide share some resistance mechanisms with abiraterone and enzalutamide and could be useful in some resistance settings.

The emerging role of cross-resistance between taxanes and AR-targeting therapy in metastatic prostate cancer

Background:

To date, the number of prostate cancer ranked first among newly diagnosed malignant tumors in men from multiple countries. Localized prostate cancer could be controlled by curative therapy. However, for patients with metastatic prostate cancer (mPC), the prognosis is poor. As among first-line treatments of systemic therapies for mPC, docetaxel and androgen receptor (AR)-targeted therapies have been widely used. However, mPC patients inevitably developed resistance to the current therapy. More importantly, there is a cross-resistance between docetaxel-based chemotherapy and AR-targeting therapy during the treatment process, which could impair the overall survival benefits without proper administration.

Objective:

Therefore, it is urgent to elucidate the mechanism of cross-resistance and explore the optimal sequential strategy.

Methods:

Here, in this review, we systematically reviewed and summarised the updated literature on clinical evidence and mechanistic research of treatment resistance in mPC.

Results:

Emerging evidence indicated that AR splice variants, AR overexpression or mutations, AR nuclear translocation, as well as AR signaling reactivation collectively contributed to the cross-resistance. With the current understanding of cross-resistance, multiple solutions are promising for improving the benefits, including refining the sequencing of available therapies for mPC, in combination with potential targeted inhibitors or immune checkpoint inhibitors. Further studies are needed to explore the combination of emerging strategies and eventually control the progression of prostate cancer.

Conclusions:

This review defined the mutual and unique resistant mechanism of these treatments, which might help to focus and accelerate therapeutic research that may ultimately improve clinical outcomes for patients with prostate cancer.

Level of evidence:

Not applicable

Abiraterone switches castration-resistant prostate cancer dependency from adrenal androgens towards androgen receptor variants and glucocorticoid receptor signalling

INTRODUCTION

Castration-resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signalling, which is largely driven by conversion of adrenal androgen precursors lasting after castration. Abiraterone, an inhibitor of the steroidogenic enzyme CYP17A1, has been demonstrated to reduce adrenal androgen synthesis and prolong CRPC patient survival. To study mechanisms of resistance to castration and abiraterone, we created coculture models using human prostate and adrenal tumours.

MATERIALS AND METHODS

Castration-naïve and CRPC clones of VCaP were incubated with steroid substrates or cocultured with human adrenal cells (H295R) and treated with abiraterone or the antiandrogen enzalutamide. Male mice bearing VCaP xenografts with and without concurrent H295R xenografts were castrated and treated with placebo or abiraterone. Response was assessed by tumour growth and PSA release. Plasma and tumour steroid levels were assessed by LC/MS-MS. Quantitative polymerase chain reaction determined steroidogenic enzyme, nuclear receptor and AR target gene expression.

RESULTS

In vitro, adrenal androgens induced castration-naïve and CRPC cell growth, while precursors steroids for de novo synthesis did not. In a coculture system, abiraterone blocked H295R-induced growth of VCaP cells. In vivo, H295R promoted castration-resistant VCaP growth. Abiraterone only inhibited VCaP growth or PSA production in the presence of H295R. Plasma steroid levels demonstrated CYP17A1 inhibition by abiraterone, whilst CRPC tumour tissue steroid levels showed no evidence of de novo intratumoural androgen production. Castration-resistant and abiraterone-resistant VCaP tumours had increased levels of AR, AR variants and glucocorticoid receptor (GR) resulting in equal AR target gene expression levels compared to noncastrate tumours.

CONCLUSIONS

In our model, ligand-dependent AR-regulated regrowth of CRPC was predominantly supported via adrenal androgen precursor production while there was no evidence for intratumoural androgen synthesis. Abiraterone-resistant tumours relied on AR overexpression, expression of ligand-independent AR variants and GR signalling.

A novel small-molecule activator of unfolded protein response suppresses castration-resistant prostate cancer growth

Androgen receptor-targeted therapy improves survival in castration-resistant prostate cancer (CRPC). However, almost all patients with CRPC eventually develop secondary resistance to these drugs. Therefore, alternative therapeutic approaches for incurable metastatic CRPC are urgently needed. Unfolded protein response (UPR) is regarded as a cytoprotective mechanism that removes misfolded proteins in rapidly proliferating tumor cells. However, acute activation of the UPR directly leads to tumor cell death. This study has shown that WJ-644A, a novel small molecule activator of UPR, potently inhibited the proliferation of prostate cancer cells and caused tumor regression with a good safety profile in multiple animal models. Mechanistically, we have identified that WJ-644A induced cell methuosis and autophagy upon UPR activation. Our study not only identifies the UPR as an actionable target for CRPC treatment, but also establishes WJ-644A as a novel UPR activator that has potential therapeutic value for CRPC.

Natural Products for the Management of Castration-Resistant Prostate Cancer: Special Focus on Nanoparticles Based Studies

Prostate cancer is the most common type of cancer among men and the second most frequent cause of cancer-related mortality around the world. The progression of advanced prostate cancer to castration-resistant prostate cancer (CRPC) plays a major role in disease-associated morbidity and mortality, posing a significant therapeutic challenge. Resistance has been associated with the activation of androgen receptors via several mechanisms, including alternative dehydroepiandrosterone biosynthetic pathways, other androgen receptor activator molecules, oncogenes, and carcinogenic signaling pathways. Tumor microenvironment plays a critical role not only in the cancer progression but also in the drug resistance. Numerous natural products have shown major potential against particular or multiple resistance pathways as shown by in vitro and in vivo studies. However, their efficacy in clinical trials has been undermined by their unfavorable pharmacological properties (hydrophobic molecules, instability, low pharmacokinetic profile, poor water solubility, and high excretion rate). Nanoparticle formulations can provide a way out of the stalemate, employing targeted drug delivery, improved pharmacokinetic drug profile, and transportation of diagnostic and therapeutic agents via otherwise impermeable biological barriers. This review compiles the available evidence regarding the use of natural products for the management of CRPC with a focus on nanoparticle formulations. PubMed and Google Scholar search engines were used for preclinical studies, while ClinicalTrials.gov and PubMed were searched for clinical studies. The results of our study suggest the efficacy of natural compounds such as curcumin, resveratrol, apigenin, quercetin, fisetin, luteolin, kaempferol, genistein, berberine, ursolic acid, eugenol, gingerol, and ellagic acid against several mechanisms leading to castration resistance in preclinical studies, but fail to set the disease under control in clinical studies. Nanoparticle formulations of curcumin and quercetin seem to increase their potential in clinical settings. Using nanoparticles based on betulinic acid, capsaicin, sintokamide A, niphatenones A and B, as well as atraric acid seems promising but needs to be verified with preclinical and clinical studies.

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.

Androprostamine A: a unique antiprostate cancer agent

The androgen receptor (AR) is an important therapeutic target for all clinical states of prostate cancer. We screened cultured broths of microorganisms for their ability to suppress androgen-dependent growth of human prostate cancer LNCaP and VCaP cells without cytotoxicity. We have already identified androprostamine A (APA) from a Streptomyces culture broth as a functional inhibitor of AR. APA repressed R1881 (the synthetic androgen methyltrienolone)-induced androgen-regulated gene expression and dramatically inhibited R1881-induced prostate-specific antigen levels. However, APA did not act as an AR antagonist and did not inhibit AR transcriptional activity. Moreover, AS2405, an APA derivative, significantly inhibited the growth of VCaP cells in SCID mice upon oral administration.

Inhibition of Scavenger Receptor Class B Type 1 (SR-B1) Expression and Activity as a Potential Novel Target to Disrupt Cholesterol Availability in Castration-Resistant Prostate Cancer

There have been several studies that have linked elevated scavenger receptor class b type 1 (SR-B1) expression and activity to the development and progression of castration-resistant prostate cancer (CRPC). SR-B1 facilitates the influx of cholesterol to the cell from lipoproteins in systemic circulation. This influx of cholesterol may be important for many cellular functions, including the synthesis of androgens. Castration-resistant prostate cancer tumors can synthesize androgens de novo to supplement the loss of exogenous sources often induced by androgen deprivation therapy. Silencing of SR-B1 may impact the ability of prostate cancer cells, particularly those of the castration-resistant state, to maintain the intracellular supply of androgens by removing a supply of cholesterol. SR-B1 expression is elevated in CRPC models and has been linked to poor survival of patients. The overarching belief has been that cholesterol modulation, through either synthesis or uptake inhibition, will impact essential signaling processes, impeding the proliferation of prostate cancer. The reduction in cellular cholesterol availability can impede prostate cancer proliferation through both decreased steroid synthesis and steroid-independent mechanisms, providing a potential therapeutic target for the treatment of prostate cancer. In this article, we discuss and highlight the work on SR-B1 as a potential novel drug target for CRPC management.

MicroRNA-1205 Regulation of FRYL in Prostate Cancer

High mortality rates of prostate cancer (PCa) are associated with metastatic castration-resistant prostate cancer (CRPC) due to the maintenance of androgen receptor (AR) signaling despite androgen deprivation therapies (ADTs). The 8q24 chromosomal locus is a region of very high PCa susceptibility that carries genetic variants associated with high risk of PCa incidence. This region also carries frequent amplifications of the PVT1 gene, a non-protein coding gene that encodes a cluster of microRNAs including, microRNA-1205 (miR-1205), which are largely understudied. Herein, we demonstrate that miR-1205 is underexpressed in PCa cells and tissues and suppresses CRPC tumors in vivo. To characterize the molecular pathway, we identified and validated fry-like (FRYL) as a direct molecular target of miR-1205 and observed its overexpression in PCa cells and tissues. FRYL is predicted to regulate dendritic branching, which led to the investigation of FRYL in neuroendocrine PCa (NEPC). Resistance toward ADT leads to the progression of treatment related NEPC often characterized by PCa neuroendocrine differentiation (NED), however, this mechanism is poorly understood. Underexpression of miR-1205 is observed when NED is induced in vitro and inhibition of miR-1205 leads to increased expression of NED markers. However, while FRYL is overexpressed during NED, FRYL knockdown did not reduce NED, therefore revealing that miR-1205 induces NED independently of FRYL.