Understanding and overcoming the mechanisms of primary and acquired resistance to abiraterone and enzalutamide in castration resistant prostate cancer

Learning From Evidence: Changes in Real-World Use of Second Androgen Receptor Targeted Treatments in Metastatic Castration-Resistant Prostate Cancer (mCRPC)

BACKGROUND

Androgen receptor targeted therapies (ART) play a major role in the treatment of metastatic castration-resistant prostate cancer (mCRPC). In recent years consensus has been reached that treatment with a second ART should be avoided due to low response rates. The aim of this study was to investigate if new scientific insights led to changes in clinical daily practice in the Netherlands.

METHODS

Patients included in the Dutch CAPRI-3 prostate cancer registry, currently encompassing 19 hospitals, and treated with at least 1 ART (ie, abiraterone or enzalutamide) were included. Patients were stratified based on start date of first ART (ART1) according to standard of care between 2016-2017, 2018-2019 and 2020-2021. Second ART (ART2) was defined as either direct (ART1>ART2) or at any given time (any ART2).

RESULTS

Between the first and last ART1 group, the prevalence of ART1>ART2 declined from 14.3% to 6.5% (P = .001) and the prevalence of any ART2 from 27.6% to 10.7% (P < .001). The decline was observed before recommendations were included in European guidelines. The use of other life-prolonging drugs (LPDs) after ART1 (ART1>LPD) increased. Patients who were selected for ART1>ART2 instead of ART1>LPD were older, less frequently treated with taxane-based chemotherapy for mHSPC and had a longer time to development of mCRPC.

CONCLUSIONS

New scientific insights were incorporated into clinical daily practice, with a significant decline in in the prevalence of sequential ART treatment, even before recommendations were included in European guidelines.

Urolithins: Emerging natural compound targeting castration-resistant prostate cancer (CRPC)

Castration-resistant prostate cancer (CRPC) presents a significant challenge due to its resistance to conventional androgen deprivation therapies. Urolithins, bioactive metabolites derived from ellagitannins, have recently emerged as promising therapeutic agents for CRPC. Urolithins not only inhibit androgen receptor (AR) signaling, a crucial factor in the progression of CRPC, but also play a key role in regulating oxidative stress by their antioxidant properties, thereby inhibiting increased reactive oxygen species, a common feature of the aggressive nature of CRPC. Research has shown that urolithins induce apoptosis and diminish pro-survival signaling, leading to tumor inhibition. This review delves into the intricate mechanisms through which urolithins exert their therapeutic effects, focusing on both AR-dependent and AR-independent pathways. It also explores the exciting potential of combining urolithins with androgen ablation therapy, opening new avenues for CRPC treatment.

The role of radium-223 in the evolving treatment landscape of metastatic castration-resistant prostate cancer: A narrative review

The treatment of metastatic castration-resistant prostate cancer (mCRPC) has been rapidly evolving over the last two decades. The advent of new androgen receptor pathway inhibitors (ARPIs) such as abiraterone acetate or enzalutamide marks a great advance for treating mCRPC patientd in the pre- and post-docetaxel settings. The subsequent approval of ARPIs in early stages-i.e., metastatic hormone-sensitive (mHSPC) or nonmetastatic CRPC-led to a realignment of subsequent treatment choices upon progression to mCRPC, given the possibility of cross-resistance between ARPIs. Therapies with mechanisms of action different from those of ARPIs are now the focus of new treatment developments. Also, this anomalous situation brings the focus back to well-known treatments currently used later in the treatment sequence. This is the case of radium-223 which, when administered with enzalutamide, has recently been shown to prolong radiographic progression-free survival vs. enzalutamide alone in the first line in asymptomatic or mildly symptomatic patients with no known visceral metastases. In this narrative review, we summarize the treatment landscape for mCRPC, both from a historical and practical point of view, to understand the new potential of radium-223 as a treatment option in this setting.

An expanded metabolic pathway for androgen production by commensal bacteria

Commensal bacteria have been implicated in the modulation of steroid hormones, including circulating androgen levels in the host. However, the microbial genetic pathways involved in androgen production have not been fully characterized. Here we identify a microbial gene encoding an enzyme that catalyses the conversion of androstenedione to epitestosterone in the gut microbiome member Clostridium scindens and named this gene desF. We demonstrate that epitestosterone impacts androgen receptor-dependent prostate cancer cell proliferation in vitro. We also demonstrate that stool desF levels are elevated in patients with prostate cancer who are unresponsive to abiraterone/prednisone therapy. Bacterial isolates from urine or prostatectomy tissue produced androgens, and 17β-hydroxysteroid dehydrogenase activity encoded by the desG gene was detected in strains of the urinary tract bacterium Propionimicrobium lymphophilum. Furthermore, we demonstrate that urinary androgen-producing bacterial strains can promote prostate cancer cell growth through metabolism of cortisol and prednisone. Abiraterone, which targets host desmolase (CYP17A1), a rate-limiting enzyme in adrenal steroidogenesis, does not inhibit bacterial desmolase (DesAB), whereas the conversion of prednisone to androgens by DesAB, DesF and DesG drives androgen-receptor-dependent prostate cancer cell line proliferation in vitro. Our results are a significant advance in steroid microbiology and highlight a potentially important role for gut and urinary tract bacteria in host endocrine function and drug metabolism.

Deep targeted sequencing of circulating tumor DNA to inform treatment in patients with metastatic castration-resistant prostate cancer

BACKGROUND

Intrinsic and acquired resistance to second-generation anti-androgens pose a significant clinical challenge in the treatment of metastatic castration-resistant prostate cancer (mCRPC). Novel biomarkers to predict treatment response and inform alternative treatment options are urgently needed.

METHODS

Deep targeted sequencing, with a prostate cancer-specific gene panel, was performed on circulating tumor DNA (ctDNA) and germline DNA from blood of mCRPC patients recruited in Denmark (n = 53), prior to starting first-line treatment with enzalutamide or abiraterone acetate, and for a subset of patients also at progression (n = 18). Likely clonal hematopoietic variants were filtered out. Genomic findings were correlated to clinical outcomes (PSA progression-free survival (PFS), overall survival (OS)). Intrinsic resistance candidate biomarkers were considered by enrichment analysis of nonresponders vs. responders. Genomic alterations at progression were considered as possible drivers of acquired resistance. Clinical actionability was assessed based on OncoKB and ESCAT.

RESULTS

Somatic alterations in PTEN, cell cycle regulators (CCND1, CDKN1B, CDKN2A, and RB1) and chromatin modulators (CHD1, ARID1A) were associated with significantly shorter PFS and OS, also after adjusting for ctDNA% in multivariate Cox regression analysis. The associations with poorer outcomes for alterations in PTEN and chromatin modulators were validated in an external dataset. Patients with primary resistance to enzalutamide/abiraterone had enrichment for BRAF amplification and CHD1 loss, while responders had enrichment for TMPRSS2 fusions. AR resistance mutations emerged in 22% of patients at progression. These were mutually exclusive with other alterations that may confer resistance (i.e., activating CTNNB1 mutations, combined TP53/RB1 loss). Clinically actionable alterations, primarily in homologous recombination repair genes, were found in 54.7% and 49.0% of patients (OncoKB and ESCAT, respectively), with few additional alterations detected at progression. Level I alterations were identified in 41.5% of patients employing OncoKB, however only in 13.2% based on ESCAT.

CONCLUSIONS

Our study identifies known and novel prognostic and predictive biomarker candidates in patients with mCRPC undergoing first-line treatment with enzalutamide or abiraterone acetate. It further provides real-world evidence of the significant potential of genomic profiling of ctDNA to inform treatment in this setting. Clinical trials are warranted to advance the implementation of ctDNA-based biomarkers into clinical practice.

Deep Modeling of Gain-of-Function Mutations on Androgen Receptor

The efficiency of Androgen Receptor (AR) pathway inhibitors for prostate cancer (PCa) is on decline due to resistance mechanisms including the occurrence of gain-of-function mutations on human androgen receptor (AR). Hence, understanding and predicting such mutations is crucial for developing effective PCa treatment strategies. Leveraging accu- mulated data on clinically relevant AR mutants with recent advances in deep modeling techniques, this study aims to unveil and quantify critical AR mutation-drug relation- ships. By incorporating molecular descriptors for drugs and mutated genes sequences, this work represented these features as single vectors and demonstrates their effective- ness in modeling AR mutant responses to conventional antiandrogens. The developed approach achieves above 80% accuracy in predicting the gain-of-function behavior of AR mutants and therefore can potentially uncover unknown agonist/antagonist relationships among mutant-drug pairs.

Dual inhibition of ATR and DNA-PKcs radiosensitizes ATM-mutant prostate cancer

In advanced castration resistant prostate cancer (CRPC), mutations in the DNA damage response (DDR) gene ataxia telangiectasia mutated (ATM) are common. While poly(ADP-ribose) polymerase inhibitors are approved in this context, their clinical efficacy remains limited. Thus, there is a compelling need to identify alternative therapeutic avenues for ATM mutant prostate cancer patients. Here, we generated matched ATM-proficient and ATM-deficient CRPC lines to elucidate the impact of ATM loss on DDR in response to DNA damage via irradiation. Through unbiased phosphoproteomic screening, we unveiled that ATM-deficient CRPC lines maintain dependence on downstream ATM targets through activation of ATR and DNA-PKcs kinases. Dual inhibition of ATR and DNA-PKcs effectively inhibited downstream γH2AX foci formation in response to irradiation and radiosensitized ATM-deficient lines to a greater extent than either ATM-proficient controls or single drug treatment. Further, dual inhibition abrogated residual downstream ATM pathway signaling and impaired replication fork dynamics. To circumvent potential toxicity, we leveraged the RUVBL1/2 ATPase inhibitor Compound B, which leads to the degradation of both ATR and DNA-PKcs kinases. Compound B effectively radiosensitized ATM-deficient CRPC in vitro and in vivo, and impacted replication fork dynamics. Overall, dual targeting of both ATR and DNA-PKcs is necessary to block DDR in ATM-deficient CRPC, and Compound B could be utilized as a novel therapy in combination with irradiation in these patients.

Cabazitaxel versus abiraterone or enzalutamide for metastatic castration-resistant prostate cancer following docetaxel failure: a systematic review and meta-analysis

PURPOSE

Treatment for metastatic castration-resistant prostate cancer (mCRPC) includes chemotherapy and inhibition of the androgen receptor pathway. However, the optimal treatment sequence in this scenario is not yet fully understood. Therefore, we conducted a systematic review and meta-analysis comparing cabazitaxel versus abiraterone or enzalutamide for efficacy and safety outcomes as second-line therapy in mCRPC patients after docetaxel failure.

METHODS

We searched PubMed, Embase, and Cochrane databases for interventional studies comparing cabazitaxel versus abiraterone or enzalutamide for patients with mCRPC who have experienced treatment failure with docetaxel as their first-line therapy. We computed hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs).

RESULTS

Eight studies, comprising 1,897 patients were included, of whom 548 (28.8%) received cabazitaxel. Mean follow-up time ranged from 3 to 16.4 months. Median age ranged from 68.1 to 73.9 years in the cabazitaxel group, and 68.0 to 73.1 years in the abiraterone or enzalutamide group. In our meta-analysis, cabazitaxel significantly improved progression-free survival (PFS) rates (HR 0.60; 95% CI 0.47-0.78; p < 0.001) compared to abiraterone or enzalutamide. There were no differences between groups in overall survival (HR 0.76; 95% CI 0.46-1.24; p = 0.27), therapy-related grade ≥ 3 adverse events (AEs) (OR 3.00; 95% CI 0.72-12.40; p = 0.12), and PSA decline ≥ 50% (OR 1.20; 95% CI 0.51-2.80; p = 0.67).

CONCLUSIONS

In this systematic review and meta-analysis of men with mCRPC after docetaxel failure, second-line therapy with cabazitaxel was associated with a longer PFS compared with abiraterone or enzalutamide, though without a significant difference in OS.

Identification of selective SWI/SNF dependencies in enzalutamide-resistant prostate cancer

Enzalutamide is a potent second-generation antiandrogen commonly used to treat hormone-sensitive and castration-resistant prostate cancer (CRPC) patients. While initially effective, the disease almost always develops resistance. Given that many enzalutamide-resistant tumors lack specific somatic mutations, there is strong evidence that epigenetic factors can cause enzalutamide resistance. To explore how resistance arises, we systematically test all epigenetic modifiers in several models of castration-resistant and enzalutamide-resistant prostate cancer with a custom epigenetic CRISPR library. From this, we identify and validate SMARCC2, a core component of the SWI/SNF complex, that is selectivity essential in enzalutamide-resistant models. We show that the chromatin occupancy of SMARCC2 and BRG1 is expanded in enzalutamide resistance at regions that overlap with CRPC-associated transcription factors that are accessible in CRPC clinical samples. Overall, our study reveals a regulatory role for SMARCC2 in enzalutamide-resistant prostate cancer and supports the feasibility of targeting the SWI/SNF complex in late-stage PCa.

Synergistic antitumor effect of MK-1775 and CUDC-907 against prostate cancer

Due to the emergence of drug resistance, androgen receptor (AR)-targeted drugs still pose great challenges in the treatment of prostate cancer, and it is urgent to explore an innovative therapeutic strategy. MK-1775, a highly selective WEE1 inhibitor, is shown to have favorable therapeutic benefits in several solid tumor models. Recent evidence suggests that the combination of MK-1775 with DNA-damaging agents could lead to enhanced antitumor efficacy. Here, our results demonstrate that MK-1775 alone could indeed inhibit proliferation and induce apoptosis in prostate cancer. Moreover, the combination of MK-1775 and a dual PI3K and HDAC inhibitor, CUDC-907, can synergistically inhibit cell proliferation and dramatically induces apoptosis in prostate cancer cells. This effect is partially mediated by DNA damage, resulting from the downregulation of DNA damage response (DDR) proteins such as CDK, CHK, and RRM1/2. Notably, the combination of MK-1775 and CUDC-907 leads to significant antitumor effects in vivo. Our findings provide a strong basis for a promising combination strategy against prostate cancer.

Discovery of a Potent and Selective GSPT1 Molecular Glue Degrader for the Treatment of Castration-Resistant Prostate Cancer

The treatment of castration-resistant prostate cancer (CRPC) remains a significant challenge, necessitating the development of new and promising therapeutic strategies. Utilizing molecular glue to degrade previously intractable cancer drivers represents an emerging and promising therapeutic approach to cancer treatment. In this study, we developed a novel CRBN-interacting molecular glue, 7d (XYD049), which exhibits potent and selective degradation of G1 to S phase transition 1 (GSPT1), a well-known untargetable cancer driver in diverse cancer cells. Importantly, 7d exhibits superior efficacy compared to 1 (CC-90009) in degrading GSPT1 in 22Rv1 cells with a DC50 value of 19 nM. It effectively suppresses the growth of 22Rv1 cells with an IC50 value of 0.007 ± 0.004 μM and demonstrates efficacy in inhibiting 22Rv1 tumor growth in mice. Mechanistically, via degradation of GSPT1, 7d downregulates CRPC-related oncogenes in 22Rv1 cells, including AR, AR-V7, PSA, and c-Myc. Thus, our work provides a novel GSPT1 selective degrader with potent effectiveness in targeting Myc-driven CRPC.

Nuclear receptor E75/NR1D2 promotes tumor malignant transformation by integrating Hippo and Notch pathways

Hormone therapy resistance and the ensuing aggressive tumor progression present a significant clinical challenge. However, the mechanisms underlying the induction of tumor malignancy upon inhibition of steroid hormone signaling remain poorly understood. Here, we demonstrate that Drosophila malignant epithelial tumors show a similar reduction in ecdysone signaling, the main steroid hormone pathway. Our analysis of ecdysone-induced downstream targets reveals that overexpression of the nuclear receptor E75, particularly facilitates the malignant transformation of benign tumors. Genome-wide DNA binding profiles and biochemistry data reveal that E75 not only binds to the transcription factors of both Hippo and Notch pathways, but also exhibits widespread co-binding to their target genes, thus contributing to tumor malignancy. We further validated these findings by demonstrating that depletion of NR1D2, the mammalian homolog of E75, inhibits the activation of Hippo and Notch target genes, impeding glioblastoma progression. Together, our study unveils a novel mechanism by which hormone inhibition promotes tumor malignancy, and describes an evolutionarily conserved role of the oncogene E75/NR1D2 in integration of Hippo and Notch pathway activity during tumor progression.

Discovery of 5-Nitro-N-(3-(trifluoromethyl)phenyl) Pyridin-2-amine as a Novel Pure Androgen Receptor Antagonist against Antiandrogen Resistance

The transformation of clinical androgen receptor (AR) antagonists into agonists driven by AR mutations poses a significant challenge in treating prostate cancer (PCa). Novel anti-AR therapeutics combating mutation-induced resistance are required. Herein, by combining structure-based virtual screening and biological evaluation, a high-affinity agonist E10 was first discovered. Then guided by the representative conformation of State 1 at the free energy landscape, the structural optimization of E10 was performed, and pure AR antagonists EL15 (IC50 = 0.94 μM) and EF2 (IC50 = 0.30 μM) were successfully identified. Both can antagonize wild-type and variant drug-resistant ARs. Therein, EF2 demonstrated potent inhibition of the AR pathway and effectively suppressed tumor growth in a C4-2B xenograft mouse model following oral administration. Further molecular dynamics simulation and mutagenesis studies revealed atomic insights into the mode of action of EF2 which may serve as a novel lead compound for developing therapeutics against AR-driven PCa.

Long noncoding RNA mediates enzalutamide resistance and transformation in neuroendocrine prostate cancer

Prostate cancer is a malignant tumor caused by the malignant proliferation of epithelial cells, which is highly heterogeneous and drug-resistant, and neuroendocrine prostate cancer (NEPC) is an essential cause of drug resistance in its late stage. Elucidating the evolution of NEPC and the resistance process of enzalutamide, a novel antiandrogen, will be of great help in improving the prognosis of patients. As a research hotspot in the field of molecular biology in recent years, the wide range of biological functions of long noncoding RNAs (lncRNAs) has demonstrated their position in the therapeutic process of many diseases, and a large number of studies have revealed their critical roles in tumor progression and drug resistance. Therefore, elucidating the involvement of lncRNAs in the formation of NEPCs and their interrelationship with enzalutamide resistance may provide new ideas for a deeper understanding of the development of this disease and the occurrence of enzalutamide resistance and give a new direction for reversing the therapeutic dilemma of advanced prostate cancer. This article focuses on lncRNAs that regulate enzalutamide resistance and the neuroendocrine transition of prostate cancer through epigenetic, androgen receptor (AR) signaling, and non-AR pathways that act as "molecular sponges" interacting with miRNAs. Some insights into these mechanisms are used to provide some help for subsequent research in this area.

Nodularin-R Synergistically Enhances Abiraterone Against Castrate- Resistant Prostate Cancer via PPP1CA Inhibition

Clinically, most prostate cancer (PCa) patients inevitably progress to castration-resistant prostate cancer (CRPC) with poor prognosis after androgen deprivation therapy (ADT), including abiraterone, the drug of choice for ADT. Therefore, it is necessary to explore the resistance mechanism of abiraterone in depth. Genome-wide CRISPR/Cas9 knockout technology was used to screen CRPC cell line 22Rv1 for abiraterone-resistant genes. Combined with bioinformatics, a key gene with high expression and poor prognosis in CRPC patients was screened. Then, the effects of target gene on abiraterone-resistant 22Rv1 cell function were explored by silencing and overexpression. Further, a natural product with potential targeting effect was identified and validated by molecular docking and protein expression. Molecular dynamics simulations revealed potential mechanism for the natural product affecting target protein expression. Finally, the combined anti-CRPC effects of the natural product and abiraterone were validated by cellular and in vivo experiments. Five common resistance genes (KCNJ3, COL2A1, PPP1CA, MDH2 and EXOSC5) were identified successfully, among which high PPP1CA expression had the worst prognosis for disease-free survival. Moreover, PPP1CA was highly expressed in abiraterone-resistant 22Rv1 cells. Silencing PPP1CA increased cell sensitivity to abiraterone while promoting apoptosis and inhibiting clone formation. Overexpressing PPP1CA exerted the opposite effects. Molecular docking revealed the binding mode of the natural product nodularin-R to PPP1CA with a dose-dependent manner for inhibition. Mechanistically, nodularin-R attenuates the interaction between PPP1CA and USP11 (deubiquitinating enzyme), potentially promoting PPP1CA degradation. Additionally, combination of 2.72 μM nodularin-R and 54.5 μM abiraterone synergistically inhibited the resistant 22Rv1 cell function. In vivo experiments also revealed that combination therapy significantly inhibited tumour growth and reduced inducible expression of PPP1CA. PPP1CA is a key driver for abiraterone resistance, and nodularin-R enhances the anti-CRPC effects of abiraterone by inhibiting PPP1CA.

PROTACing the androgen receptor and other emerging therapeutics in prostate cancer

INTRODUCTION

The androgen receptor (AR) is a critical driver of prostate cancer progression, and the advent of androgen receptor pathway inhibitors (ARPIs) has transformed the treatment landscape of metastatic prostate cancer. However, resistance to ARPIs eventually develops via mutations in AR, AR overexpression, and alternative AR signaling which have required novel approaches to target effectively.

AREAS COVERED

The mechanism of action and early clinical results of proteolysis targeting chimera (PROTAC) agents targeting AR are reviewed. Preclinical and early clinical data for other emerging AR-targeting therapeutics, including dual-action androgen receptor inhibitors (DAARIs) and anitens that target the N-terminal domain of AR, were also identified through literature search for agents which may circumvent resistance through AR splice variants and AR ligand-binding domain mutations. The literature search utilized PubMed to identify articles that were relevant to this review from 2000 to 2024.

EXPERT OPINION

PROTACs, DAARIs, and anitens represent novel and promising AR-targeting therapeutics that may become an important part of prostate cancer treatment in the future. Elucidating mechanisms of resistance, including ability of these agents to target full length AR, may yield further insights into maximal therapeutic efficacy aimed at silencing AR signaling.

Impact of Neuroendocrine Differentiation (NED) on Enzalutamide and Abiraterone Efficacy in Metastatic Castration-Resistant Prostate Cancer (mCRPC): A Retrospective Analysis

Neuroendocrine differentiation (NED) represents a possible androgen receptor pathway inhibitors (ARPI) resistance mechanism in metastatic castration resistance prostate cancer (mCRPC). As mCRPC with NED has been excluded from clinical trials evaluating ARPI efficacy, this study investigates the prognostic impact of NED in mCRPC patients treated with ARPIs. Methods: We retrospectively analyzed 327 mCRPC patient data treated with Enzalutamide or Abiraterone in the first and second or successive lines of treatment. NED was assessed using prostate biopsy samples through immunohistochemical staining. Results: NED was confirmed in 32/327 (9.8%) mCRPC patients. In the overall population, mCRPC with NED showed worse PFS (4.38 vs. 11.48 months HR 2.505 [1.71-3.68] p < 0.05), disease control rate (DCR), and PSA response. In the first line setting, mCRPC with NED demonstrated worse PFS (8.5 vs. 14.9 months HR 2.13 [1.18-3.88], p < 0.05). Similarly, in the second or successive lines, mCRPC with NED showed worse PFS (4.0 vs. 7.5 months HR 2.43 [1.45-4.05] p < 0.05), DCR, PSA response and OS (12.53 vs. 18.03 months HR 1.86 [1.12-3.10] p < 0.05). The adverse impact of NED on PFS was consistence across all subgroups; we also noted a trend of worse PFS in patients with high vs. low NED. Conclusions: In our study, mCRPC with NED treated with Enzalutamide or Abiraterone showed worse clinical outcomes. NED assessment should be considered to optimize treatment decisions in the mCRPC setting.

METTL3-mediated m6A modification of circGLIS3 promotes prostate cancer progression and represents a potential target for ARSI therapy

BACKGROUND

Circular RNAs (circRNAs) have been shown to be involved in tumorigenesis and progression. However, the role of circGLIS3 (hsa_circ_0002874) in prostate cancer (PCa) has yet not been reported.

METHODS

Candidate circRNA were determined through comprehensive analysis of public datasets, PCa cell lines, and tissues data. A series of cellular functional assays, including CCK-8, colony formation, wound healing, and transwell assays were performed. Subsequently, RNA sequencing, RNA immunoprecipitation, methylated RNA immunoprecipitation, microRNA pulldown, luciferase reporter assay, and western blot were used to explore the underlying molecular mechanisms. Moreover, the xenograft tumor mouse model was established to elucidate the function of circGLIS3.

RESULTS

CircGLIS3, derived from exon 2 of the parental GLIS3 gene, was identified as a novel oncogenic circRNA in PCa that was closely associated with the biochemical recurrence. Its expression levels were upregulated in PCa tissues and cell lines as well as enzalutamide high-resistant cells. The cellular functional assays revealed that circGLIS3 promoted PCa cell proliferation, migration, and invasion. METTL3-mediated N6-methyladenosine (m6A) modification maintained its upregulation by enhancing its stability. Mechanically, CircGLIS3 sponged miR-661 to upregulate MDM2, thus regulating the p53 signaling pathway to promote cell proliferation, migration, and invasion. Furthermore, in vitro and in vivo experiments, the knockdown of circGLIS3 improved the response of PCa cells to ARSI therapies such as enzalutamide.

CONCLUSIONS

METTL3-mediated m6A modification of circGLIS3 regulates the p53 signaling pathway via the miR-661/MDM2 axis, thereby facilitating PCa progression. Meanwhile, this study unveils a promising potential target for ARSI therapy for PCa.

Dual inhibition of ATR and DNA-PKcs radiosensitizes ATM-mutant prostate cancer

In advanced castration resistant prostate cancer (CRPC), mutations in the DNA damage response (DDR) gene ataxia telangiectasia mutated ( ATM ) are common. While poly(ADP-ribose) polymerase inhibitors are approved in this context, their clinical efficacy remains limited. Thus, there is a compelling need to identify alternative therapeutic avenues for ATM mutant prostate cancer patients. Here, we generated matched ATM-proficient and ATM-deficient CRPC lines to elucidate the impact of ATM loss on DDR in response to DNA damage via irradiation. Through unbiased phosphoproteomic screening, we unveiled that ATM-deficient CRPC lines maintain dependence on downstream ATM targets through activation of ATR and DNA-PKcs kinases. Dual inhibition of ATR and DNA-PKcs effectively inhibited downstream γH2AX foci formation in response to irradiation and radiosensitized ATM-deficient lines to a greater extent than either ATM-proficient controls or single drug treatment. Further, dual inhibition abrogated residual downstream ATM pathway signaling and impaired replication fork dynamics. To circumvent potential toxicity, we leveraged the RUVBL1/2 ATPase inhibitor Compound B, which leads to the degradation of both ATR and DNA-PKcs kinases. Compound B effectively radiosensitized ATM-deficient CRPC in vitro and in vivo , and impacted replication fork dynamics. Overall, dual targeting of both ATR and DNA-PKcs is necessary to block DDR in ATM-deficient CRPC, and Compound B could be utilized as a novel therapy in combination with irradiation in these patients.

Aberrant Super-Enhancer Landscape in Enzalutamide-Resistant Prostate Cancer Cells

Background: Castration-resistant prostate cancer (CRPC), which has developed resistance to next-generation antiandrogens, such as enzalutamide (Enz), is a lethal disease. Furthermore, transcriptional regulation by super enhancers (SEs) is crucial for the growth and spread of prostate cancer, as well as drug resistance. The functions of SEs, a significant class of noncoding DNA cis-regulatory elements, have been the subject of numerous recent studies in the field of cancer research. Materials and Methods: The goal of this research was to identify SEs associated with Enz resistance in C4-2B cells using chromatin immunoprecipitation sequencing and cleavage under targets and tagmentation (CUT&Tag). Using HOMER analysis to predict protein/gene-binding motifs, we identified master transcription factors (TFs) that may bind to SE sites. Using small interfering RNA, WST-1 assays, and qRT-PCR, we then confirmed the associations between TFs of SEs and Enz resistance. Results: A total of 999 SEs were screened from C4-2B EnzR cells in total. Incorporating analysis with RNA-seq data revealed 41 SEs to be strongly associated with the promotion of Enz resistance. In addition, we finally predicted that master TFs bind to SE-binding regions. Subsequently, we selected zinc finger protein 467 (ZFP467) and SMAD family member 3 to confirm the functional connections of master TFs with Enz resistance through SEs (ZNF467). Conclusions: In this study, SMAD3 and ZNF467 were found to be closely related to Enz-resistant CRPC. Our research uncovered a sizable group of SEs linked to Enz resistance in prostate cancer, dissected the mechanisms underlying SE Enz resistance, and shed light on potential clinical uses for SEs.

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.

Current Systemic Therapy in Men with Metastatic Castration-Sensitive Prostate Cancer

PURPOSE OF REVIEW

This review aims to explore the evolving landscape of treatments available for metastatic castration-sensitive prostate cancer (mCSPC) patients.

RECENT FINDINGS

In less than a decade, evidence was chronologically provided that (1) systemic treatment intensification with docetaxel improves outcomes, including survival, in men with mCSPC, (2) then that these outcomes are also improved when a second-generation androgen receptor pathway inhibitor (ARPI) is combined with androgen deprivation therapy (ADT), and (3) using a "triplet systemic therapy," which consists in the combination of ADT, an ARPI and docetaxel, further improves outcomes, including survival. Radiotherapy to the prostate combined with ADT alone is now recommended in men with low-volume mCSPC. Combining prostate radiotherapy and intensified systemic treatment including abiraterone may be synergistic as suggested in the PEACE-1 trial. Also, the role of metastases-directed local therapies (mostly stereotactic radiotherapy) is currently being assessed in phase 3 trials. Finally, the integration of biomarkers (e.g. BRCA2 gene alterations, PTEN loss, PSMA expression) for decision making is not currently established, though trials are also currently underway. Importantly, most evidence currently available was obtained in men with de novo metastases, while for those with metastatic relapse after definitive local treatment, the role of treatment intensification is less well established. Treatment intensification is nowadays the standard of care for patients with de novo mCSPC as it leads to outcomes improvement, including survival, and the standard of care is evolving almost on a yearly basis.

A Phase I Study of Acapatamab, a Half-life Extended, PSMA-Targeting Bispecific T-cell Engager for Metastatic Castration-Resistant Prostate Cancer

PURPOSE

Safety and efficacy of acapatamab, a prostate-specific membrane antigen (PSMA) x CD3 bispecific T-cell engager were evaluated in a first-in-human study in metastatic castration-resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

Patients with mCRPC refractory to androgen receptor pathway inhibitor therapy and taxane-based chemotherapy received target acapatamab doses ranging from 0.003 to 0.9 mg in dose exploration (seven dose levels) and 0.3 mg (recommended phase II dose) in dose expansion intravenously every 2 weeks. Safety (primary objective), pharmacokinetics, and antitumor activity (secondary objectives) were assessed.

RESULTS

In all, 133 patients (dose exploration, n = 77; dose expansion, n = 56) received acapatamab. Cytokine release syndrome (CRS) was the most common treatment-emergent adverse event seen in 97.4% and 98.2% of patients in dose exploration and dose expansion, respectively; grade ≥ 3 was seen in 23.4% and 16.1%, respectively. Most CRS events were seen in treatment cycle 1; incidence and severity decreased at/beyond cycle 2. In dose expansion, confirmed prostate-specific antigen (PSA) responses (PSA50) were seen in 30.4% of patients and radiographic partial responses in 7.4% (Response Evaluation Criteria in Solid Tumors 1.1). Median PSA progression-free survival (PFS) was 3.3 months [95% confidence interval (CI): 3.0-4.9], radiographic PFS per Prostate Cancer Clinical Trials Working Group 3 was 3.7 months (95% CI: 2.0-5.4). Acapatamab induced T-cell activation and increased cytokine production several-fold within 24 hours of initiation. Treatment-emergent antidrug antibodies were detected in 55% and impacted serum exposures in 36% of patients in dose expansion.

CONCLUSIONS

Acapatamab was safe and tolerated and had a manageable CRS profile. Preliminary signs of efficacy with limited durable antitumor activity were observed. Acapatamab demonstrated pharmacokinetic and pharmacodynamic activity.

Discovery of the First-in-Class RORγ Covalent Inhibitors for Treatment of Castration-Resistant Prostate Cancer

Nuclear receptor receptor-related orphan receptor γ (RORγ) is a ligand-dependent transcription factor and has been established as a key player in castration-resistant prostate cancers (CRPC) by driving androgen receptor (AR) overexpression, representing a potential therapeutical target for advanced prostate cancers. Here, we report the identification of the first-in-class RORγ covalent inhibitor 29 via the structure-based drug design approach following structure-activity relationship (SAR) exploration. Mass spectrometry assay validated its covalent inhibition mechanism. Compound 29 significantly inhibited RORγ transcriptional activity and remarkably suppressed the expression levels of AR and AR-targeted genes. Compound 29 also exhibited much superior activity in inhibiting the proliferation and colony formation and inducing apoptosis of the CRPC cell lines relative to the positive control 2 and noncovalent control 33. Importantly, it markedly suppressed the tumor growth in a 22Rv1 mouse tumor xenograft model with good safety. These results clearly demonstrate that 29 is a highly potent and selective RORγ covalent inhibitor.

Systematic review and integrated analysis of prognostic gene signatures for prostate cancer patients

Prostate cancer (PC) is one of the most common cancers in men and becoming the second leading cause of cancer fatalities. At present, the lack of effective strategies for prognosis of PC patients is still a problem to be solved. Therefore, it is significant to identify potential gene signatures for PC patients' prognosis. Here, we summarized 71 different prognostic gene signatures for PC and concluded 3 strategies for signature construction after extensive investigation. In addition, 14 genes frequently appeared in 71 different gene signatures, which enriched in mitotic and cell cycle. This review provides extensive understanding and integrated analysis of current prognostic signatures of PC, which may help researchers to construct gene signatures of PC and guide future clinical treatment.

Molecular Efficacy of Gnetin C as Dual-Targeted Therapy for Castrate-Resistant Prostate Cancer

SCOPE

Resistance of castrate-resistant prostate cancer (CRPC) to enzalutamide (Enz) involves the expression of constitutively active androgen receptor splice variant (AR-V7). In addition to altered AR pathways, CRPC is characterized by "non-AR-driven" signaling, which includes an overexpression of metastasis-associated protein 1 (MTA1). Combining natural compounds with anticancer drugs may enhance drug effectiveness while reducing adverse effects. In this study, the in vitro and in vivo anticancer effects of Gnetin C (GnC) alone and in combination with Enz against CRPC are examined.

METHODS AND RESULTS

The effects of GnC alone and in combination with Enz are assessed by cell viability, clonogenic survival, cell migration, and AR and MTA1 expression using 22Rv1 cells. The tumor growth in vivo is assessed by bioluminescent imaging, western blots, RT-PCR, and IHC. GnC alone and in combined treatment inhibit cell viability, clonogenic survival and migration, and AR and MTA1 expression in 22Rv1 cells. The underlying AR- and MTA1-targeted anticancer mechanisms of treatments in vivo involve inhibition of proliferation and angiogenesis, and induction of apoptosis.

CONCLUSION

The findings demonstrate that GnC alone and GnC combined with Enz effectively inhibits AR- and MTA1-promoted tumor-progression in advanced CRPC, which indicates its potential as a novel therapeutic approach for CRPC.

Discovery of a highly potent and orally available importin-β1 inhibitor that overcomes enzalutamide-resistance in advanced prostate cancer

Nuclear transporter importin-β1 is emerging as an attractive target by virtue of its prevalence in many cancers. However, the lack of druggable inhibitors restricts its therapeutic proof of concept. In the present work, we optimized a natural importin-β1 inhibitor DD1 to afford an improved analog DD1-Br with better tolerability (>25 folds) and oral bioavailability. DD1-Br inhibited the survival of castration-resistant prostate cancer (CRPC) cells with sub-nanomolar potency and completely prevented tumor growth in resistant CRPC models both in monotherapy (0.5 mg/kg) and in enzalutamide-combination therapy. Mechanistic study revealed that by targeting importin-β1, DD1-Br markedly inhibited the nuclear accumulation of multiple CRPC drivers, particularly AR-V7, a main contributor to enzalutamide resistance, leading to the integral suppression of downstream oncogenic signaling. This study provides a promising lead for CRPC and demonstrates the potential of overcoming drug resistance in advanced CRPC via targeting importin-β1.

Downregulation of EZH2 inhibits epithelial-mesenchymal transition in enzalutamide-resistant prostate cancer

BACKGROUND

Androgen signaling inhibitors (ASI) have been approved for treatment of metastatic castration-resistant prostate cancer (mCRPC). However, the limited success of ASI in clinic justifies an urgent need to identify new targets and develop novel approaches for treatment. EZH2 significantly increases in prostate cancer (PCa). Little is understood, however, regarding the roles of EZH2 in Enzalutamide-resistant (EnzR) mCRPC.

METHODS

We firstly investigated the levels of EZH2 and the altered pathways in public database which was comprised with primary and metastatic PCa patient tumors. To elucidate the roles of EZH2 in mCRPC, we manipulated EZH2 in EnzR PCa cell lines to examine epithelial-mesenchymal transition (EMT). To dissect the underlying mechanisms, we measured the transcription levels of EMT-associated transcription factors (TFs).

RESULTS

We found that EZH2 was highly expressed in mCRPC than that of primary PCa tumors and that EnzR PCa cells gained more EMT characteristics than those of enzalutamide-sensitive counterparts. Further, loss of EZH2-induced inhibition of EMT is independent of polycomb repressive complex 2 (PRC2). Mechanistically, downregulation of EZH2 inhibits transcription of EMT-associated TFs by repressing formation of H3K4me3 to the promotor regions of the TFs.

CONCLUSION

We identified the novel roles of EZH2 in EnzR mCRPC. EnzR PCa gains more EMT properties than that of enzalutamide-sensitive PCa. Loss of EZH2-assocaited inhibition of EMT is PRC2 independent. Downregulation of EZH2 suppresses EMT by impairing formation of H3K4me3 at the promotor regions, thus repressing expression of EMT-associated TFs.

Inhibition of phosphoglycerate dehydrogenase induces ferroptosis and overcomes enzalutamide resistance in castration-resistant prostate cancer cells

Phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in the first step of the serine synthesis pathway (SSP), is overexpressed in multiple types of cancers. The androgen receptor inhibitor enzalutamide (Enza) is the primary therapeutic drug for patients with castration-resistant prostate cancer (CRPC). However, most patients eventually develop resistance to Enza. The association of SSP with Enza resistance remains unclear. In this study, we found that high expression of PHGDH was associated with Enza resistance in CRPC cells. Moreover, increased expression of PHGDH led to ferroptosis resistance by maintaining redox homeostasis in Enza-resistant CRPC cells. Knockdown of PHGDH caused significant GSH reduction, induced lipid peroxides (LipROS) increase and significant cell death, resulting in inhibiting growth of Enza-resistant CRPC cells and sensitizing Enza-resistant CRPC cells to enzalutamide treatment both in vitro and in vivo. We also found that overexpression of PHGDH promoted cell growth and Enza resistance in CRPC cells. Furthermore, pharmacological inhibition of PHGDH by NCT-503 effectively inhibited cell growth, induced ferroptosis, and overcame enzalutamide resistance in Enza-resistant CRPC cells both in vitro and in vivo. Mechanically, NCT-503 triggered ferroptosis by decreasing GSH/GSSG levels and increasing LipROS production as well as suppressing SLC7A11 expression through activation of the p53 signaling pathway. Moreover, stimulating ferroptosis by ferroptosis inducers (FINs) or NCT-503 synergistically sensitized Enza-resistant CRPC cells to enzalutamide. The synergistic effects of NCT-503 and enzalutamide were verified in a xenograft nude mouse model. NCT-503 in combination with enzalutamide effectively restricted the growth of Enza-resistant CRPC xenografts in vivo. Overall, our study highlights the essential roles of increased PHGDH in mediating enzalutamide resistance in CRPC. Therefore, the combination of ferroptosis inducer and targeted inhibition of PHGDH could be a potential therapeutic strategy for overcoming enzalutamide resistance in CRPC.

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.

PARP1 negatively regulates transcription of BLM through its interaction with HSP90AB1 in prostate cancer

BACKGROUND

Prostate cancer (PCa) is a prevalent malignant disease affecting a significant number of males globally. Elevated expression of the Bloom's syndrome protein (BLM) helicase has emerged as a promising cancer biomarker, being associated with the onset and progression of PCa. Nevertheless, the precise molecular mechanisms governing BLM regulation in PCa remain elusive.

METHODS

The expression of BLM in human specimens was analyzed using immnohistochemistry (IHC). A 5'-biotin-labeled DNA probe containing the promoter region of BLM was synthesized to pull down BLM promoter-binding proteins. Functional studies were conducted using a range of assays, including CCK-8, EdU incorporation, clone formation, wound scratch, transwell migration, alkaline comet assay, xenograft mouse model, and H&E staining. Mechanistic studies were carried out using various techniques, including streptavidin-agarose-mediated DNA pull-down, mass spectrometry (MS), immunofluorescence (IF), dual luciferase reporter assay system, RT-qPCR, ChIP-qPCR, co-immunoprecipitation (co-IP), and western blot.

RESULTS

The results revealed significant upregulation of BLM in human PCa tissues, and its overexpression was associated with an unfavorable prognosis in PCa patients. Increased BLM expression showed significant correlations with advanced clinical stage (P = 0.022) and Gleason grade (P = 0.006). In vitro experiments demonstrated that BLM knockdown exerted inhibitory effects on cell proliferation, clone formation, invasion, and migration. Furthermore, PARP1 (poly (ADP-ribose) polymerase 1) was identified as a BLM promoter-binding protein. Further investigations revealed that the downregulation of PARP1 led to increased BLM promoter activity and expression, while the overexpression of PARP1 exerted opposite effects. Through mechanistic studies, we elucidated that the interaction between PARP1 and HSP90AB1 (heat shock protein alpha family class B) enhanced the transcriptional regulation of BLM by counteracting the inhibitory influence of PARP1 on BLM. Furthermore, the combination treatment of olaparib with ML216 demonstrated enhanced inhibitory effects on cell proliferation, clone formation, invasion, and migration. It also induced more severe DNA damage in vitro and exhibited superior inhibitory effects on the proliferation of PC3 xenograft tumors in vivo.

CONCLUSIONS

The results of this study underscore the significance of BLM overexpression as a prognostic biomarker for PCa, while also demonstrating the negative regulatory impact of PARP1 on BLM transcription. The concurrent targeting of BLM and PARP1 emerges as a promising therapeutic approach for PCa treatment, holding potential clinical significance.

Novel therapies for metastatic prostate cancer

INTRODUCTION

Patients with metastatic prostate cancer, especially in the castrate-resistant setting, have a poor prognosis. Many agents have been approved for metastatic prostate cancer, such as androgen receptor pathway inhibitors, taxane-based chemotherapy, radiopharmaceuticals, and immunotherapy. However, prostate cancer remains the leading cause of cancer deaths in nonsmoking men. Fortunately, many more novel agents are under investigation.

AREAS COVERED

We provide an overview of the broad group of novel therapies for metastatic prostate cancer, with an emphasis on active and recruiting clinical trials that have been recently published and/or presented at national or international meetings.

EXPERT OPINION

The future for patients with metastatic prostate cancer is promising, with further development of novel therapies such as radiopharmaceuticals. Based on a growing understanding of prostate cancer biology, novel agents are being designed to overcome resistance to approved therapies. There are many trials using novel agents either as monotherapy or in combination with already approved agents with potential to further improve outcomes for men with advanced prostate cancer.

PRMT5 promotes chemotherapy-induced neuroendocrine differentiation in NSCLC

BACKGROUND

In response to therapeutic treatments, cancer cells can exhibit a variety of resistance phenotypes including neuroendocrine differentiation (NED). NED is a process by which cancer cells can transdifferentiate into neuroendocrine-like cells in response to treatments, and is now widely accepted as a key mechanism of acquired therapy resistance. Recent clinical evidence has suggested that non-small cell lung cancer (NSCLC) can also transform into small cell lung cancer (SCLC) in patients treated with EGFR inhibitors. However, whether chemotherapy induces NED to confer therapy resistance in NSCLC remains unknown.

METHODS

We evaluated whether NSCLC cells can undergo NED in response to chemotherapeutic agents etoposide and cisplatin. By Knock-down of PRMT5 or pharmacological inhibition of PRMT5 to identify its role in the NED process.

RESULTS

We observed that both etoposide and cisplatin can induce NED in multiple NSCLC cell lines. Mechanistically, we identified protein arginine methyltransferase 5 (PRMT5) as a critical mediator of chemotherapy-induced NED. Significantly, the knock-down of PRMT5 or pharmacological inhibition of PRMT5 suppressed the induction of NED and increased the sensitivity to chemotherapy.

CONCLUSION

Taken together, our results suggest that targeting PRMT5 may be explored as a chemosensitization approach by inhibiting chemotherapy-induced NED.

Emerging systemic treatment for metastatic castration-resistant prostate cancer: a review of recent randomized controlled trials

PURPOSE OF REVIEW

The landscape of therapy for metastatic castration-resistant prostate cancer (mCRPC) has seen an unprecedented transformation with the emergence of combination therapies. This review summarizes the current findings from randomized controlled trials (RCTs) assessing the oncologic outcomes of mCRPC.

RECENT FINDINGS

In the first-line, treatment-naïve setting, recent RCTs demonstrated the oncologic benefit of adding AKT inhibitors or poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors to abiraterone in terms of radiographical progression-free survival. Although this is a strong surrogate endpoint, these agents have not yet shown overall survival (OS) improvement. In the second- or later-line settings, olaparib improved OS in patients with at least one alteration in BRCA1 , BRCA2 , or ATM gene and lutetium-177-prostate-specific membrane antigen-617 [177-Lu-prostate-specific membrane antigen (PSMA)-617] were superior to repeat androgen receptor signaling inhibitor (ARSI) therapy. In addition, 177-Lu-PSMA-617 had better progression-free survival compared with cabazitaxel but failed to result in an OS benefit. To date, there is no evidence for effective immune checkpoint inhibitor regimens/combinations for mCRPC.

SUMMARY

According to recent RCTs, several novel agents and/or combinations exhibit promising oncologic outcomes. In the first-line setting, OS benefits compared with currently available regimens are still missing. Results from ongoing/well-designed phase 3 RCTs and real-world data regarding the sequential impact of currently available agents on outcomes of mCRPC patients after ARSI-based combination therapy for metastatic hormone-sensitive prostate cancer are awaited. Such data will improve clinical decision-making in the ever-intensifying treatment era.

An integrated in vitro/in silico approach to assess the anti-androgenic potency of isobavachin

Isobavachin is a dietary flavanone with multiple biological activities. Our previous research has confirmed the estrogenicity of isobavachin, and this work aims to assess the anti-androgenic potency of isobavachin by an integrated in vitro and in silico approach. Isobavachin can limit the proliferation of prostate cancer cells by inducing a distinct G1 cell-cycle arrest. In addition, isobavachin also significantly represses the transcription of androgen receptor (AR)-downstream targets such as prostate specific antigen. Mechanistically, we demonstrated that isobavachin can disrupt the nuclear translocation of AR and promote its proteasomal degradation. The results of computer simulations showed that isobavachin can stably bind to AR, and the amino acid residue Gln711 may play a critical role in AR binding of both AR agonists and antagonists. In conclusion, this work has identified isobavachin as a novel AR antagonist.

LOX-1 Activation by oxLDL Induces AR and AR-V7 Expression via NF-κB and STAT3 Signaling Pathways Reducing Enzalutamide Cytotoxic Effects

The oxidized low-density lipoprotein receptor 1 (LOX-1) is one of the most important receptors for modified LDLs, such as oxidated (oxLDL) and acetylated (acLDL) low-density lipoprotein. LOX-1 and oxLDL are fundamental in atherosclerosis, where oxLDL/LOX1 promotes ROS generation and NF-κB activation inducing the expression of IL-6, a STAT3 activator. Furthermore, LOX-1/oxLDL function has been associated with other diseases, such as obesity, hypertension, and cancer. In prostate cancer (CaP), LOX-1 overexpression is associated with advanced stages, and its activation by oxLDL induces an epithelial-mesenchymal transition, increasing angiogenesis and proliferation. Interestingly, enzalutamide-resistant CaP cells increase the uptake of acLDL. Enzalutamide is an androgen receptor (AR) antagonist for castration-resistant prostate cancer (CRPC) treatment, and a high percentage of patients develop a resistance to this drug. The decreased cytotoxicity is promoted in part by STAT3 and NF-κB activation that induces the secretion of the pro-inflammatory program and the expression of AR and its splicing variant AR-V7. Here, we demonstrate for the first time that oxLDL/LOX-1 increases ROS levels and activates NF-κB, inducing IL-6 secretion and the activation of STAT3 in CRPC cells. Furthermore, oxLDL/LOX1 increases AR and AR-V7 expression and decreases enzalutamide cytotoxicity in CRPC. Thus, our investigation suggests that new factors associated with cardiovascular pathologies, such as LOX-1/oxLDL, may also promote important signaling axes for the progression of CRPC and its resistance to drugs used for its treatment.

Targeting androgen receptor and the variants by an orally bioavailable Proteolysis Targeting Chimeras compound in castration resistant prostate cancer

BACKGROUND

Despite the advent of improved therapeutic options for advanced prostate cancer, the durability of clinical benefits is limited due to inevitable development of resistance. By constitutively sustaining androgen receptor (AR) signaling, expression of ligand-binding domain truncated AR variants (AR-V(ΔLBD)) accounts for the major mechanism underlying the resistance to anti-androgen drugs. Strategies to target AR and its LBD truncated variants are needed to prevent the emergence or overcome drug resistance.

METHODS

We utilize Proteolysis Targeting Chimeras (PROTAC) technology to achieve induced degradation of both full-length AR (AR-FL) and AR-V(ΔLBD) proteins. In the ITRI-PROTAC design, an AR N-terminal domain (NTD) binding moiety is appended to von-Hippel-Lindau (VHL) or Cereblon (CRBN) E3 ligase binding ligand with linker.

FINDINGS

In vitro studies demonstrate that ITRI-PROTAC compounds mechanistically degrade AR-FL and AR-V(ΔLBD) proteins via ubiquitin-proteasome system, leading to impaired AR transactivation on target gene expression, and inhibited cell proliferation accompanied by apoptosis activation. The compounds also significantly inhibit enzalutamide-resistant growth of castration resistant prostate cancer (CRPC) cells. In castration-, enzalutamide-resistant CWR22Rv1 xenograft model without hormone ablation, ITRI-90 displays a pharmacokinetic profile with decent oral bioavailability and strong antitumor efficacy.

INTERPRETATION

AR NTD that governs the transcriptional activities of all active variants has been considered attractive therapeutic target to block AR signaling in prostate cancer cells. We demonstrated that utilizing PROTAC for induced AR protein degradation via NTD represents an efficient alternative therapeutic strategy for CRPC to overcome anti-androgen resistance.

FUNDING

The funding detail can be found in the Acknowledgements section.

Elevated labile iron in castration-resistant prostate cancer is targetable with ferrous iron-activatable antiandrogen therapy

Clinical responses to second generation androgen signaling inhibitors (e.g., enzalutamide) in metastatic castration-resistant prostate cancer (mCRPC) are variable and transient, and are associated with dose limiting toxicities, including rare but severe CNS effects. We hypothesized that changes to iron metabolism coincident with more advanced disease might be leveraged for tumor-selective delivery of antiandrogen therapy. Using the recently described chemical probes SiRhoNox and 18F-TRX in mCRPC models, we found elevated Fe2+ to be a common feature of mCRPC in vitro and in vivo. We next synthesized ferrous-iron activatable drug conjugates of second and third-generation antiandrogens and found these conjugates possessed comparable or enhanced antiproliferative activity across mCRPC cell line models. Mouse pharmacokinetic studies showed that these prototype antiandrogen conjugates are stable in vivo and limited exposure to conjugate or free antiandrogen in the brain. Our results reveal elevated Fe2+ to be a feature of mCRPC that might be leveraged to improve the tolerability and efficacy of antiandrogen therapy.

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.

Selective androgen receptor degrader (SARD) to overcome antiandrogen resistance in castration-resistant prostate cancer

In patients with castration-resistant prostate cancer (CRPC), clinical resistances such as androgen receptor (AR) mutation, AR overexpression, and AR splice variants (ARVs) limit the effectiveness of second-generation antiandrogens (SGAs). Several strategies have been implemented to develop novel antiandrogens to circumvent the occurring resistance. Here, we found and identified a bifunctional small molecule Z15, which is both an effective AR antagonist and a selective AR degrader. Z15 could directly interact with the ligand-binding domain (LBD) and activation function-1 region of AR, and promote AR degradation through the proteasome pathway. In vitro and in vivo studies showed that Z15 efficiently suppressed AR, AR mutants and ARVs transcription activity, downregulated mRNA and protein levels of AR downstream target genes, thereby overcoming AR LBD mutations, AR amplification, and ARVs-induced SGAs resistance in CRPC. In conclusion, our data illustrate the synergistic importance of AR antagonism and degradation in advanced prostate cancer treatment.

Comparative efficacy of second-generation androgen receptor inhibitors for treating prostate cancer: A systematic review and network meta-analysis

INTRODUCTION

Second-generation androgen receptor inhibitors (SGARIs), namely enzalutamide, apalutamide, and darolutamide, are good for improving survival outcomes in prostate cancer patients, but some researchers have shown that using SGARIs increases side effects, which complicates clinicians' choice of. Therefore, we performed this network meta-analysis to assess the efficacy and toxicity of several SGARIs in the treatment of patients with metastatic hormone-sensitive prostate cancer (mHSPC), non-metastatic castration-resistant prostate cancer (nmCRPC), and metastatic castration-resistant prostate cancer (mCRPC).

METHODS

We searched PubMed, EMBASE and Cochrane Library databases from January 2000 to December 2022 to identify randomized controlled studies associated with SGARIs. We use Stata 16.0 and R 4.4.2 for data analysis, hazard ratio (HR) with 95% confidence intervals (CI) were used to assess the results.

RESULTS

This meta-analysis included 7 studies with a total of 9488 patients. In mHSPC, enzalutamide and darolutamide had a positive effect on overall survival (OS) (HR, 0.70; 95% CI, 0.59-0.82), but we did not find a difference in their efficacy to improve OS (HR, 1.19; 95% CI, 0.75-1.89). Also in nmCRPC, enzalutamide, apalutamide and darolutamide were beneficial for metastasis-free survival (MFS) (HR, 0.32; 95% CI, 0.25-0.41). Compared to darolutamide, enzalutamide (HR, 0.71; 95% CI, 0.54-0.93) and apalutamide (HR, 0.68; 95% CI, 0.51-0.91) prolonged MFS, but there was no difference in efficacy between enzalutamide and apalutamide (HR, 0.97; 95% CI, 0.73-1.28). Finally in mCRPC, there was no significant difference in indirect effects on OS between pre- and post-chemotherapy enzalutamide (HR, 0.89; 95% CI, 0.70-1.13). However, using enzalutamide before chemotherapy to improve radiographic progression-free survival (rPFS) was a better option (HR, 2.11; 95% CI, 1.62-2.73).

CONCLUSION

The SGARIs used in each trial were beneficial for the primary endpoint in the study. Firstly there was no significant difference in the effect of enzalutamide and darolutamide in improving OS in patients with mHSPC. Secondly improving MFS in patients with nmCRPC was best achieved with enzalutamide and apalutamide. In addition both pre- and post-chemotherapy use of enzalutamide was beneficial for OS in mCRPC patients, but for improving rPFS pre-chemotherapy use of enzalutamide should be preferred.The INPLASY registration number of this systematic review is INPLASY202310084.

Examining the Effect of PARP-1 Inhibitors on Transcriptional Activity of Androgen Receptor in Prostate Cancer Cells

Since the early 1940s, androgen ablation has been the cornerstone of treatment for prostate cancer (PC). Importantly, androgen receptor (AR) signaling is vital not only for the initiation of PC, which is initially androgen-dependent, but also for castration-resistant disease. Recent studies demonstrated clear promise of the poly(ADP-ribose) polymerase 1 (PARP-1) inhibitors for targeting prostate cancer cells harboring mutations in DNA damage-repair genes. In addition, it has been established that PARP-1 inhibition suppresses growth of AR-positive prostate cancer cells in cell and animal models. Thus, prostate cancer represents a particularly promising disease site for targeting PARP-1, given that both DNA repair and AR-mediated transcription depend on PARP-1 function. Here, we describe the development and use of cell-based assay to evaluate the impact of PARP-1 inhibitors on the AR signaling in prostate cancer cells.

Idarubicin combats abiraterone and enzalutamide resistance in prostate cells via targeting XPA protein

Although second-generation therapies like abiraterone (ABI) and enzalutamide (ENZ) benefit patients with castration-resistant prostate cancer (CRPC), drug resistance frequently occurs, eventually resulting in therapy failure. In this study, we used two libraries, FDA-approved drug library and CRISP/Cas9 knockout (GeCKO) library to screen for drugs that overcome treatment resistance and to identify the potential drug-resistant genes involved in treatment resistance. Our screening results showed that the DNA-damaging agent idarubicin (IDA) overcame abiraterone and enzalutamide resistance in prostate cancer cells. IDA treatment inhibited the DNA repair protein XPA expression in a transcription-independent manner. Consistently, XPA knockout sensitized prostate cancer cells to abiraterone and enzalutamide treatment. In conclusion, IDA combats abiraterone and enzalutamide resistance by reducing XPA protein level in prostate cancer.

Addition of New Androgen Receptor Pathway Inhibitors to Docetaxel and Androgen Deprivation Therapy in Metastatic Hormone-Sensitive Prostate Cancer: A Systematic Review and Metanalysis

In recent years, significant changes have occurred in metastatic hormone-sensitive prostate cancer (mHSPC) management, where docetaxel and new androgen receptor pathway inhibitors (ARPI) have been shown to improve overall survival (OS) compared to androgen deprivation therapy (ADT). Recent data could once again radically change mHSPC treatment. PEACE-1 and ARASENS trials demonstrated a survival benefit of the addition of ARPI to docetaxel and ADT combination (triplet therapy), compared to docetaxel and ADT. With multiple options to choose from, it is crucial to identify the patients who would benefit most from triplet therapy. In this meta-analysis, we evaluated the activity of the triplet therapy versus docetaxel plus ADT in mHSPC. A systematic review of PubMed/Medline, Embase, and the proceedings of major international meetings was performed. Five RCTs fulfilled the inclusion criteria. PEACE-1 and ARASENS studies reported disease-free survival (DFS) and OS. Post hoc analysis of three other trials evaluated the combination of ARPI, docetaxel and ADT. Globally, 2538 patients were included (1270 triplet therapy; 1268 docetaxel + ADT). Triplet therapy was associated with improved OS (hazard ratio (HR) 0.74; 95% confidence interval (CI), 0.66-0.83, p < 0.00001). A statistically significant benefit was shown in high-volume mHSPC patients (HR 0.76; 95% CI 0.59-0.97, p = 0.03) and in patients with de novo metastatic disease (HR 0.73; 95% CI, 0.64-0.82, p < 0.00001). The addition of ARPI to standard therapy was associated with DFS improvement (HR 0.41; 95% CI, 0.35-0.49, p < 0.00001). This metanalysis shows a significant OS benefit from concomitant administration of ARPI, docetaxel and ADT in high volume and de novo mHSPC.

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.

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.

Second generation androgen receptor antagonists and challenges in prostate cancer treatment

Prostate cancer is a hormone-dependent malignancy, whose onset and progression are closely related to the activity of the androgen receptor (AR) signaling pathway. Due to this critical role of AR signaling in driving prostate cancer, therapy targeting the AR pathway has been the mainstay strategy for metastatic prostate cancer treatment. The utility of these agents has expanded with the emergence of second-generation AR antagonists, which began with the approval of enzalutamide in 2012 by the United States Food and Drug Administration (FDA). Together with apalutamide and darolutamide, which were approved in 2018 and 2019, respectively, these agents have improved the survival of patients with prostate cancer, with applications for both androgen-dependent and castration-resistant disease. While patients receiving these drugs receive a benefit in the form of prolonged survival, they are not cured and ultimately progress to lethal neuroendocrine prostate cancer (NEPC). Here we summarize the current state of AR antagonist development and highlight the emerging challenges of their clinical application and the potential resistance mechanisms, which might be addressed by combination therapies or the development of novel AR-targeted therapies.

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.