Exploiting the tumor-suppressive activity of the androgen receptor by CDK4/6 inhibition in castration-resistant prostate cancer

Synergistic targeting strategies for prostate cancer

Prostate cancer is the second most commonly diagnosed cancer and the fifth leading cause of death among men worldwide. Androgen deprivation therapy is a common prostate cancer treatment, but its efficacy is often hindered by the development of resistance, which results in reducing survival benefits. Immunotherapy showed great promise in treating solid tumours; however, clinically significant improvements have not been demonstrated for patients with prostate cancer, highlighting specific drawbacks of this therapeutic modality. Hence, exploring novel strategies to synergistically enhance the efficacy of prostate cancer immunotherapy is imperative. Clinical investigations have focused on the combined use of targeted or gene therapy and immunotherapy for prostate cancer. Notably, tumour-specific antigens and inflammatory mediators are released from tumour cells after targeted or gene therapy, and the recruitment and infiltration of immune cells, including CD8+ T cells and natural killer cells activated by immunotherapy, are further augmented, markedly improving the efficacy and prognosis of prostate cancer. Thus, immunotherapy, targeted therapy and gene therapy could have reciprocal synergistic effects in prostate cancer in combination, resulting in a proposed synergistic model encompassing these three therapeutic modalities, presenting novel potential treatment strategies for prostate cancer.

Induction of cellular senescence by androgen receptor agonist or antagonist is mediated via two novel common DYRK1A-DREAM and cyclin G2 signaling pathways in castration-resistant prostate cancer

BACKGROUND

Castration-resistant prostate cancer (CRPC) is a deadly disease that in addition to being resistant to androgen deprivation often exhibits also resistant to androgen receptor (AR)-antagonists. Supraphysiological androgen levels (SAL) are used in the bipolar androgen therapy in clinical phase trials to inhibit CRPC.

METHODS

Co-immunoprecipitation, immunofluorescence, growth and cell senescence assays, mouse xenografted CRPC, AR target gene analyses of organs, analyses of RNA-seq, ChIP-seq and patient-derived xenografts, qRT-PCR, 3D tumor spheroids, knockdown experiments.

RESULTS

Both AR-antagonists and -agonist at SAL induce cellular senescence despite acting oppositely on AR transcriptional activity. Here, we identified two common growth inhibitory pathways induced by SAL and AR-antagonists. Using the novel AR-antagonist compound 28 (C28), that inhibits also those AR mutants mediating therapy resistance, represses growth including CRPC tumor spheroids and mouse xenografted tumors. Mechanistically, C28 reduces phosphorylation of AR at serine 81 and HSP27 required for AR transcriptional activity and enhances AR-p130 interaction. Notably, increased p130 levels were also detected by SAL treatment leading to activation of DREAM complex signaling and induction of cellular senescence indicating that both AR-agonist and -antagonist use the same pathway for growth repression. Inhibition of DYRK1A, a key kinase to activate DREAM complex, blocks C28- and SAL-induced cellular senescence. Both C28 and SAL also induces the atypical cyclin G2 (CCNG2), which also mediates cellular senescence. Induction of CCNG2 is confirmed in CRPC tumor spheroids and xenograft tumors of treated mice. The second-generation AR-antagonist Darolutamide (Dar) also activates DREAM complex and CCNG2.

CONCLUSION

Taken together, these findings suggest the identification of two common and independently acting pathways induced by AR-antagonists and SAL, used in bipolar androgen therapy, to mediate growth inhibition and induction of cellular senescence in CRPC.

Heterogeneous Responses to High-Dose Testosterone in Castration-Resistant Prostate Cancer Tumors with Mixed Rb-Proficient and Rb-Deficient Cells

Androgen deprivation therapy remains a cornerstone in managing prostate cancer. However, its recurrence often leads to the more aggressive castration-resistant prostate cancer (CRPC). Although second-line androgen receptor signaling inhibition treatments such as enzalutamide and abiraterone are available, their effectiveness against CRPC is only transient. High-dose testosterone (Hi-T) has recently emerged as a promising treatment for CRPC, primarily through the suppression of E2F and MYC signaling. However, the roles of Rb family proteins in influencing this therapeutic response remain debated. In this study, we utilized a CRPC patient-derived xenograft model that includes both Rb pathway-proficient and -deficient cell populations based on the positive or negative expression of RB family genes. Single-cell RNA sequencing analysis revealed that Rb-proficient cells displayed a robust response to Hi-T, whereas Rb-deficient cells exhibited significant resistance. Notably, our analysis indicated increased enrichment of the hypoxia signature in the Rb-deficient cell population. Further studies in RB1-silenced CRPC cell lines showed that treatment with a hypoxia-inducible factor-1α inhibitor can restore the sensitivity of Rb-deficient cells to high-dose dihydrotestosterone treatment. In conclusion, our research provides new molecular insights into CRPC tumor cell responses to Hi-T and proposes a new strategy to resensitize Rb-deficient CRPC cells to Hi-T treatment.

The lncRNAs PART1 and ADAMTS9-AS2 act in an antithetic manner on AR signaling and induction of cellular senescence in prostate cancer cells

BACKGROUND

Prostate cancer (PCa) is initially a hormone-dependent disease and the development and spread of PCa are tightly linked to the androgen receptor (AR) signaling activity. Therapy that targets the AR pathway is a standard approach for treating PCa including AR antagonists and supraphysiological androgen levels (SAL) used in bipolar androgen therapy. Here, we identified that the two lncRNAs PART1 and ADAMTS9-AS2 mediate in part androgen signaling in PCa cells by examining PCa specimen and response to AR antagonists or SAL as well as functionally by knockdown.

METHODS

This study utilized expression analysis of tumor tissues (TT) samples in comparison to their corresponding normal tissue adjacent to the tumor (NTAT) counterparts of 50 patients. RNA-seq and treatment of patient prostatectomy samples ex-vivo confirmed regulation of lncRNAs by SAL. Knockdown of both lncRNAs were used to analyze androgen signaling of AR target genes by qRT-PCR and in PCa senescence pathway by analyzing senescence markers. Correlation analyses of patient tumor samples confirmed co-expression. RNA immunoprecipitation (RIP) used in both LNCaP and C4-2 cells detect AR-lncRNA interaction. Bioinformatic analyses were employed to identify ligand-specific lncRNAs and miRNA interactions with PART1 and ADAMTS9-AS2 and confirmed by treatment of patient prostatectomy samples ex-vivo .

RESULTS

PART1 and ERVH48-1 were significantly overexpressed in TT samples, ADAMTS9-AS2 expression is lower in TT samples compared to NTAT samples. SAL treatment indicates opposite regulation in two human PCa cell lines and patient tumor samples. While ADAMTS9-AS2 is upregulated, PART1 is repressed by SAL. Furthermore, the obtained data suggest that ADAMTS9-AS2 may act as a co-activator and PART1 as a co-repressor of AR signaling. Interestingly, the knockdown indicates that both lncRNAs ADAMTS9-AS2 and PART1 regulate AR activity and protein level as well as SAL-mediated induction of cellular senescence. Thus, the data suggest that ADAMTS9-AS2 and PART1 control AR signaling at SAL.

CONCLUSION

In summary, we identified novel AR signaling pathways that involve lncRNAs oppositely regulated by SAL and in PCa tumorigenesis.

H2AJ Is a Direct Androgen Receptor Target Gene That Regulates Androgen-Induced Cellular Senescence and Inhibits Mesenchymal Markers in Prostate Cancer Cells

Background: Prostate cancer (PCa) is a significant public health issue, particularly in developed countries. The androgen receptor (AR) plays a key role in regulating both the normal development and the proliferation of PCa. Bipolar androgen therapy, which involves treatment with supraphysiological androgen levels (SALs), has been shown to inhibit PCa growth. SAL induces cellular senescence in AR-positive PCa cell lines, human tumor samples, and xenografted mouse models. Methods: Transcriptome and chromatin immunoprecipitation (ChIP)-seq analysis, ChIP-qPCR, knockdown (KD), overexpression (OE), qRT-PCR, immunodetection, in situ histochemistry. Results: Here, we show using ChIP-seq and RNA-seq that H2AJ, a variant of the canonical histone H2A, is a direct target gene of AR that regulates cellular senescence and the formation of senescence-associated heterochromatin foci (SAHF). Accordingly, bioinformatic analyses reveal a large overlap of the H2AJ transcriptome with the cellular senescence score of PCa. Analyzing a large cohort of patient samples, the expression of H2AJ is higher in tumor samples compared to normal samples suggesting growth-promoting activity. Interestingly, however, the expression is diminished in metastatic tumor samples, indicating that H2AJ inhibits the mesenchymal transition in PCa cells. Functionally, the KD of H2AJ inhibits growth, whereas the H2AJ overexpression promotes cell growth. Furthermore, these data suggest that H2AJ inhibits the expression of mesenchymal markers, in agreement with the low expression of H2AJ in metastatic forms of tumors from patient cohorts. Conclusion:H2AJ is a direct positively AR-regulated target gene induced by SALs that regulates cellular senescence, promotes growth, and inhibits the expression of mesenchymal markers.

Cyclin-Dependent Kinase Inhibition in Prostate Cancer: Past, Present, and Future

BACKGROUND

Despite significant progress, prostate cancer remains a leading cause of death. Cyclin-dependent kinase (CDK) 4/6 inhibitors, which are already approved for the treatment of hormone receptor-positive breast cancer, are undergoing extensive testing as monotherapy and in various combinations as a potentially valuable treatment modality in prostate cancer patients. Thus far, a limited number of these studies have published results, which have been largely disappointing.

AREAS COVERED

In this review, we describe the biologic rationale for the use of CDK4/6 inhibitors in prostate cancer, the existing clinical data describing their use in prostate cancer, and ongoing clinical trials of CDK4/6 inhibitors as monotherapy and in combination for the treatment of prostate cancer. In particular, we focus on possible resistance mechanisms that may be particularly relevant in prostate cancer patients, leading to de novo and acquired resistance, and we highlight novel strategies that can overcome this resistance.

CONCLUSIONS

Current clinical trials are actively working to (1) refine the role of CDK4/6 inhibitors in prostate cancer patients; (2) develop new inhibitors of other cell-cycle targets, such as CDK2 and CDK7; and (3) explore novel combination therapies with inhibitors of other relevant pathways, such as PI3K or MAPK. Further genomic subtyping of advanced prostate cancer will likely shed light on the subsets of patients most likely to benefit from cell-cycle-targeted agents.

Roles of CDK12 mutations in PCa development and treatment

Prostate cancer (PCa) is one of the most common cancers in men, and cyclin-dependent kinase 12 (CDK12) is emerging as a novel star player in the PCa tumorigenesis and progression to castration-resistant prostate cancer (CRPC). In PCa, CDK12 alterations are mostly loss-of-function mutations featuring intronic polyadenylation (IPA), focal tandem duplications (FTDs), and R-loops formation and transcription-replication conflicts (TRCs). The occurrence of IPA can result in homologous recombination deficiency (HRD) and androgen receptor (AR) variation. FTDs induce neoantigens and increase the expression of the AR, MYC, and other hotspot- associated genes. R-loops lead to TRCs and influence various cellular processes, including gene expression and genome stability. Due to the poor prognosis of CDK12-mutant PCa patients and the mediocre response to classic standard therapies, HRD and increased neoantigen levels have provided clinicians with new insights into alternative systematic treatments for this novel PCa phenotype. In this review, we summarize the roles of CDK12 mutations in PCa and discuss their clinical value, suggesting that CDK12 potentially represents a target for further research and the development of clinical strategies for PCa.

Dysregulated LINC01133 expression in laryngeal carcinoma: Prognostic implications and predicted ceRNA interactome

Long non-coding RNAs (lncRNAs) have recently emerged as critical regulators of oncogenic or tumor-suppressive pathways in human cancers. LINC01133 is a lncRNA that has exhibited dichotomous roles in various malignancies but to the best of our knowledge, the role of LINC01133 in laryngeal squamous cell carcinoma (LSCC) has not been previously investigated. This study aimed to investigate the expression, clinical significance, and potential functions of the LINC01133 in LSCC. Integrative bioinformatics analysis of sequencing data obtained from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets revealed LINC01133 as a differentially expressed lncRNA in head and neck/laryngeal cancers. Experimental validation via quantitative real-time PCR in 41 pairs of stage III and IV LSCC tissues and normal tissues adjacent to the tumor (NAT) demonstrated significant downregulation of LINC01133 in tumors (p<0.0001). Decreased LINC01133 expression associated with advanced tumor stage (p=0.0206) and lymph node metastasis (p=0.0203). The receiver operating characteristic analysis indicated potential diagnostic utility (AUC=0.7115, p=0.001). Bioinformatic predictions and literature mining suggested two potential competing endogenous RNA (ceRNA) mechanisms whereby LINC01133 may act as a tumor suppressor by sponging miR-205-5p to derepress the leucine-rich repeat kinase 2 (LRRK2) and androgen receptor, leading to dysregulation of cancer-related signaling cascades. This study provides initial evidence that loss of lncRNA LINC01133 expression may promote LSCC tumorigenesis, possibly by dysregulating microRNA interactions. Further verification of its regulatory mechanisms and diagnostic value is warranted.

Canonical androgen response element motifs are tumor suppressive regulatory elements in the prostate

The androgen receptor (AR) is central in prostate tissue identity and differentiation, and controls normal growth-suppressive, prostate-specific gene expression. It also drives prostate tumorigenesis when hijacked for oncogenic transcription. The execution of growth-suppressive AR transcriptional programs in prostate cancer (PCa) and the potential for reactivation remain unclear. Here, we use a genome-wide approach to modulate canonical androgen response element (ARE) motifs-the classic DNA binding elements for AR-to delineate distinct AR transcriptional programs. We find that activating these AREs promotes differentiation and growth-suppressive transcription, potentially leading to AR+ PCa cell death, while ARE repression is tolerated by PCa cells but deleterious to normal prostate cells. Gene signatures driven by ARE activity correlate with improved prognosis and luminal phenotypes in PCa patients. Canonical AREs maintain a normal, lineage-specific transcriptional program that can be reengaged in PCa cells, offering therapeutic potential and clinical relevance.

Functional circuits of LYL1 controlled by supraphysiological androgen in prostate cancer cells to regulate cell senescence

BACKGROUND

Prostate cancer (PCa) is a public health problem mostly reported in developed countries. The androgen receptor (AR) regulates the development and physiological function of normal prostate as well as the proliferation of cancerous prostate tissue. Treatment with supraphysiological androgen levels (SAL) is used in bipolar androgen therapy and inhibits PCa growth, suggesting SAL induces a tumor suppressive program. It was shown that SAL induces cellular senescence, in PCa cell lines, human tumor samples and in xenografted mouse tumor model.

METHODS

Transcriptome and ChIP-seq analysis, PCa spheroids, knockdown (KD), co-immunoprecipitation, qRT-PCR, immune detection, in situ histochemistry.

RESULTS

Here we show that LYL1 is upregulated by the clock gene BHLHE40 in both C4-2 and LNCaP cells and mediates SAL-induced cellular senescence. LYL1 is a transcriptional co-factor with oncogenic activity in leukemia. However, analysis of a large cohort of PCa patients shows that LYL1 expression is reduced during PCa development and reduced expression is significantly associated with reduced overall survival. SAL induces the expression of LYL1 through upregulation of BHLHE40. On the other hand, the KD of LYL1 enhances BHLHE40 expression via a negative feedback loop including p27kip1. Regulatory feedback loops were identified by rescue experiments. Functional analysis revealed that KD of BHLHE40 reduces whereas LYL1 KD enhances p27kip1 levels. The KD of p27kip1 suggests that this cell cycle inhibitor is a mediator of cellular senescence by the BHLHE40 - LYL1 regulatory loop. Interestingly, ChIP-seq data revealed recruitment of both AR and BHLHE40 to the LYL1 gene indicating that LYL1 is a novel direct target of both factors. Furthermore, RNA-seq data from C4-2 cells suggests that LYL1 and BHLHE40 encompass a large overlap of genes by SAL suggesting a co-regulatory activity controlled by androgens. In line with this, co-immunoprecipitation suggests LYL1 is in a complex with BHLHE40 and the AR.

CONCLUSIONS

Three novel feed-back loops and a novel AR- BHLHE40 / LYL1 -p27kip1 axis has been identified mediating cellular senescence in PCa cells.

The Novel Direct AR Target Gene Annexin A2 Mediates Androgen-Induced Cellular Senescence in Prostate Cancer Cells

Clinical trials for prostate cancer (PCa) patients have implemented the bipolar androgen therapy (BAT) that includes the treatment with supraphysiological androgen level (SAL). SAL treatment induces cellular senescence in tumor samples of PCa patients and in various PCa cell lines, including castration-resistant PCa (CRPC), and is associated with enhanced phospho-AKT levels. Using an AKT inhibitor (AKTi), the SAL-mediated cell senescence is inhibited. Here, we show by RNA-seq analyses of two human PCa cell lines, that annexin A2 (ANXA2) expression is induced by SAL and repressed by co-treatment with AKTi. Higher ANXA2 expression is associated with better survival of PCa patients and suggests that ANXA2 is part of SAL-mediated tumor suppressive activity. ChIP-seq revealed that AR is recruited to the intronic regions of ANXA2 gene suggesting that ANXA2 is a novel direct AR target gene. Knockdown of ANXA2 shows that SAL-induced cellular senescence is mediated by ANXA2 and enhances the levels of phospho-AKT indicating an interaction between the AR, ANXA2 and AKT. Notably, we found that the level of heat shock protein HSP27, known to interact with ANXA2, is associated with cellular senescence. HSP27 level is induced by SAL but the induction is blunted by knockdown of ANXA2 suggesting a novel ANXA2-HSP27 pathway in PCa. This was confirmed using an HSP27 inhibitor that reduced the SAL-induced cellular senescence levels suggesting that ANXA2 upregulates HSP27 to mediate AR-signaling in SAL-induced cellular senescence. Thus, the data indicate ANXA2-HSP27 cross-talk as novel factors in the signaling by the AR-AKT pathway to mediate cellular senescence.

The Decreased Proliferation Capacity of Cardiomyocytes Induced By Androsterone Is Mediated By the Interactions Between Androgen Receptor and Retinoblastoma Protein

Our previous study has demonstrated that the decline in cardiomyocytes proliferation capacity induced by maternal androgen excess was mainly attributed to the accumulation of androsterone in the heart. However, the underlying mechanism by which androsterone inhibits cardiomyocytes proliferation remains unknown. In this study, pregnant mice were injected subcutaneously daily with dihydrotestosterone (DHT) from gestational day (GD) 16.5 to GD18.5. On GD18.5, fetal heart tissue was dissected and used for analyzing androgen receptor (AR) levels. H9c2 cells and primary cardiomyocytes, isolated from fetal hearts, were applied to investigate the mechanism. H9c2 cells under androsterone treatment were subjected to RNA sequencing analysis and the results showed that genes were primarily enriched in cell cycle and DNA replication pathways. Elevated AR levels were observed in fetal cardiac tissue in the maternal DHT-treated group. Androsterone treatment increased the ratio of nuclear AR and cytoplasmic AR both in H9c2 cells and primary cardiomyocytes. The ablation and overexpression of AR can mildly reverse and aggravate cell cycle arrest induced by androsterone, respectively. ChIP-qPCR analysis suggested that AR can directly repress cell cycle and DNA replication-related gene expression, which was mediated by the recruitment of retinoblastoma protein (Rb). The repression of cell proliferation in response to androsterone was alleviated partly through the downregulation of Rb by siRNA transfection. In conclusion, AR repression to cell cycle and DNA replication-related gene expression, mediated by recruitment of Rb, may be one of the potential mechanisms of cell cycle arrest in cardiomyocytes induced by androsterone.

CDK4/6 Alters TBK1 Phosphorylation to Inhibit the STING Signaling Pathway in Prostate Cancer

The efficacy of immunotherapy in patients with prostate cancer is limited due to the "cold" tumor microenvironment and the paucity of neoantigens. The STING-TBK1-IRF3 signaling axis is involved in innate immunity and has been increasingly recognized as a candidate target for cancer immunotherapy. Here, we found that treatment with CDK4/6 inhibitors stimulates the STING pathway and enhances the antitumor effect of STING agonists in prostate cancer. Mechanistically, CDK4/6 phosphorylated TBK1 at S527 to inactivate the STING signaling pathway independent of RB1 in prostate cancer cells. CDK4/6-mediated phosphorylation of RB1 at S249/T252 also induced the interaction of RB1 with TBK1 to diminish the phosphorylation of TBK1 at S172, which suppressed STING pathway activation. Overall, this study showed that CDK4/6 suppresses the STING pathway through RB1-dependent and RB1-independent pathways, indicating that CDK4/6 inhibition could be a potential strategy to overcome immunosuppression in prostate cancer. Significance: Inhibiting CDK4/6 activates STING-TBK1-IRF3 signaling in prostate cancer by regulating TBK1 phosphorylation, suggesting that the combination of CDK4/6 inhibitors and STING agonists could be an effective approach to stimulate innate immunity.

Systematic Multi-Omics Investigation of Androgen Receptor Driven Gene Expression and Epigenetics changes in Prostate Cancer

Background

Prostate cancer, a common malignancy, is driven by androgen receptor (AR) signaling. Understanding the function of AR signaling is critical for prostate cancer research.

Methods

We performed multi-omics data analysis for the AR+, androgen-sensitive LNCaP cell line, focusing on gene expression (RNAseq), chromatin accessibility (ATACseq), and transcription factor binding (ChIPseq). High-quality datasets were curated from public repositories and processed using state-of-the-art bioinformatics tools.

Results

Our analysis identified 1004 up-regulated and 707 down-regulated genes in response to androgen deprivation therapy (ADT) which diminished AR signaling activity. Gene-set enrichment analysis revealed that AR signaling influences pathways related to neuron differentiation, cell adhesion, P53 signaling, and inflammation. ATACseq and ChIPseq data demonstrated that as a transcription factor, AR primarily binds to distal enhancers, influencing chromatin modifications without affecting proximal promoter regions. In addition, the AR-induced genes maintained higher active chromatin states than AR-inhibited genes, even under ADT conditions. Furthermore, ADT did not directly induce neuroendocrine differentiation in LNCaP cells, suggesting a complex mechanism behind neuroendocrine prostate cancer development. In addition, a publicly available online application LNCaP-ADT (https://pcatools.shinyapps.io/shinyADT/) was launched for users to visualize and browse data generated by this study.

Conclusion

This study provides a comprehensive multi-omics dataset, elucidating the role of AR signaling in prostate cancer at the transcriptomic and epigenomic levels. The reprocessed data is publicly available, offering a valuable resource for future prostate cancer research.

The clock gene BHLHE40 and atypical CCNG2 control androgen-induced cellular senescence as a novel tumor suppressive pathway in prostate cancer

BACKGROUND

The androgen receptor (AR) is a drug target used to inhibit AR and prostate cancer (PCa) growth. Surprisingly, treatment with supraphysiological androgen level (SAL), used in bipolar androgen therapy, inhibits growth of PCa suggesting a tumor-suppressive activity by SAL. SAL was shown to induce cellular senescence in PCa.

METHODS

RNA-seq and transcriptome analysis, ChIP-seq, human 3D PCa spheroids, mouse xenografted castration-resistant PCa, knockdown and overexpression, Co-immunoprecipitation (Co-IP), translocation analysis, immune detection, qRT-PCR, protein-protein interaction modelling.

RESULTS

Here, mice xenografts with castration-resistant PCa tumors show that SAL inhibits cancer growth in vivo suggesting that SAL activates a tumor-suppressive mechanism. RNA-seq and ChIP-seq revealed the clock gene BHLHE40 is a novel direct AR target. Compared to adjacent human prostate tissues, the expression of BHLHE40 is reduced in PCa tumors and associated with reduced survival. Knockdown suggests that BHLHE40 mediates SAL-induced cellular senescence including tumor spheroids. Interestingly, a large overlap of differentially expressed gene sets was identified between BHLHE40 and SAL leading to the identification of four classes of SAL-BHLHE40 transcriptome landscapes. Co-IP and modelling suggest binding of BHLHE40 to AR and their co-translocation into nucleus by SAL treatment. Further, RNA-seq and ChIP-seq analysis indicate that the atypical tumor suppressive cyclin G2 emerged as a novel downstream target of BHLHE40 and a mediator of SAL-induced cellular senescence.

CONCLUSIONS

The data provide evidence of the tumor suppressive activity of SAL and a novel signaling by the AR-BHLHE40-CCNG2 axis for androgen-induced cellular senescence, linking circadian rhythm factor to androgen signaling as a novel tumor suppressive pathway.

Retinoblastoma-associated protein is important for TRIM24-mediated activation of the mTOR signaling pathway through DUSP2 action in prostate cancer

RB transcriptional corepressor 1 (RB) deletion is the most important genomic factor associated with the prognosis of castration-resistant prostate cancer (CRPC) patients receiving androgen receptor (AR) signaling inhibitor therapy. Loss of RB could support prostate cancer cell growth in a hormone-independent manner, but the underlying mechanism by which RB regulates tumor progression extends far beyond the cell cycle pathway. A previous study indicated that RB inactivates AKT signaling but has no effect on mTOR signaling in cancer cells. Here, we found that the S249/T252 site in RB is key to regulating the transcriptional activity of the tumor-promoting factor TRIM24 in CRPC, as identified through FXXXV mapping. The RB/TRIM24 complex functions through DUSP2, which serves as an intermediate bridge, to activate the mTOR pathway and promote prostate cancer progression. Accordingly, we designed RB-linker-proteolysis-targeting chimera (PROTAC) molecules, which decreased TRIM24 protein levels and inactivated the mTOR signaling pathway, thereby inhibiting prostate cancer. Therefore, this study not only elucidates the novel function of RB but also provides a theoretical basis for the development of new drugs for treating prostate cancer.

Androgen receptor splice variants drive castration-resistant prostate cancer metastasis by activating distinct transcriptional programs

One critical mechanism through which prostate cancer (PCa) adapts to treatments targeting androgen receptor (AR) signaling is the emergence of ligand-binding domain-truncated and constitutively active AR splice variants, particularly AR-V7. While AR-V7 has been intensively studied, its ability to activate distinct biological functions compared with the full-length AR (AR-FL), and its role in regulating the metastatic progression of castration-resistant PCa (CRPC), remain unclear. Our study found that, under castrated conditions, AR-V7 strongly induced osteoblastic bone lesions, a response not observed with AR-FL overexpression. Through combined ChIP-seq, ATAC-seq, and RNA-seq analyses, we demonstrated that AR-V7 uniquely accesses the androgen-responsive elements in compact chromatin regions, activating a distinct transcription program. This program was highly enriched for genes involved in epithelial-mesenchymal transition and metastasis. Notably, we discovered that SOX9, a critical metastasis driver gene, was a direct target and downstream effector of AR-V7. Its protein expression was dramatically upregulated in AR-V7-induced bone lesions. Moreover, we found that Ser81 phosphorylation enhanced AR-V7's pro-metastasis function by selectively altering its specific transcription program. Blocking this phosphorylation with CDK9 inhibitors impaired the AR-V7-mediated metastasis program. Overall, our study has provided molecular insights into the role of AR splice variants in driving the metastatic progression of CRPC.

Identification of Molecular Subtype and Prognostic Signature for Prostate Adenocarcinoma based on Neutrophil Extracellular Traps

Background: Prostate adenocarcinoma (PRAD) is one of the most common cancers in male. Increasing evidences pointed out that Neutrophil Extracellular Traps (NETs) play an important role in tumor angiogenesis, tumor metastasis and drug resistance. However, limited systematic studies regarding the role of NETs in PRAD have been performed. Identification of biomarkers based on NETs might facilitate risk stratification which help optimizing the clinical strategies. Methods: NETs-related genes with differential expressions were identified between PRAD and adjacent normal tissues in TCGA-PRAD dataset. Consensus cluster analysis was performed to determine the PRAD subtypes based on the different-expressed NETs-related genes. The difference of pathway enrichment, infiltrating immune cell and genomic mutation were also evaluated between subtypes. LASSO cox regression analysis was conducted to construct a NETs-related prognostic signature. Result: We identified 19 NETs related genes with differential expressions between PRAD and adjacent normal tissue in TCGA-PRAD dataset. Two significant subtypes were identified based on these 19 genes by consensus cluster analysis, namely subtype 1 and subtype 2. Significant differences in prognosis, immune infiltration and tumor mutation burden were observed in subtypes. LASSO Cox regression analysis identified a NETs-associated prognostic signature including 13 genes, and this signature had a good performance in predicting the progression-free survival of PRAD patients. Further integrated analysis indicated that MMP9 mostly expressed in Mono/Macrophage cells might play a role in regulating NETs formation via neutrophil activation in PRAD. Conclusion: To sum up, the current study identified two NETs-related molecular subtypes and based on which constructed a prognostic signature for PRAD.

Canonical AREs are tumor suppressive regulatory elements in the prostate

The androgen receptor (AR) is the central determinant of prostate tissue identity and differentiation, controlling normal, growth-suppressive prostate-specific gene expression 1 . It is also a key driver of prostate tumorigenesis, becoming "hijacked" to drive oncogenic transcription 2-5 . However, the regulatory elements determining the execution of the growth suppressive AR transcriptional program, and whether this can be reactivated in prostate cancer (PCa) cells remains unclear. Canonical androgen response element (ARE) motifs are the classic DNA binding element for AR 6 . Here, we used a genome-wide strategy to modulate regulatory elements containing AREs to define distinct AR transcriptional programs. We find that activation of these AREs is specifically associated with differentiation and growth suppressive transcription, and this can be reactivated to cause death in AR + PCa cells. In contrast, repression of AREs is well tolerated by PCa cells, but deleterious to normal prostate cells. Finally, gene expression signatures driven by ARE activity are associated with improved prognosis and luminal phenotypes in human PCa patients. This study demonstrates that canonical AREs are responsible for a normal, growth-suppressive, lineage-specific transcriptional program, that this can be reengaged in PCa cells for potential therapeutic benefit, and genes controlled by this mechanism are clinically relevant in human PCa patients.

Targeting CBX3 with a Dual BET/PLK1 Inhibitor Enhances the Antitumor Efficacy of CDK4/6 Inhibitors in Prostate Cancer

The development of castration-resistant prostate cancer (CRPC) is a significant factor that reduces life expectancy among patients with prostate cancer. Previously, it is reported that CDK4/6 inhibitors can overcome the resistance of CRPC to BET inhibitors by destabilizing BRD4, suggesting that the combination of CDK4/6 inhibitors and BET inhibitors is a promising approach for treating CRPC. In this study, candidates that affect the combined antitumor effect of CDK4/6 inhibitors and BET inhibitors on CRPC is aimed to examine. The data demonstrates that CBX3 is abnormally upregulated in CDK4/6 inhibitors-resistant cells. CBX3 is almost positively correlated with the cell cycle in multiple malignancies and is downregulated by BET inhibitors. Mechanistically, it is showed that CBX3 is transcriptionally upregulated by BRD4 in CRPC cells. Moreover, it is demonstrated that CBX3 modulated the sensitivity of CRPC to CDK4/6 inhibitors by binding with RB1 to release E2F1. Furthermore, it is revealed that PLK1 phosphorylated CBX3 to enhance the interaction between RB1 and CBX3, and desensitize CRPC cells to CDK4/6 inhibitors. Given that BRD4 regulates CBX3 expression and PLK1 affects the binding between RB1 and CBX3, it is proposed that a dual BRD4/PLK1 inhibitor can increase the sensitivity of CRPC cells to CDK4/6 inhibitors partially through CBX3.

Supraphysiological Androgens Promote the Tumor Suppressive Activity of the Androgen Receptor through cMYC Repression and Recruitment of the DREAM Complex

The androgen receptor (AR) pathway regulates key cell survival programs in prostate epithelium. The AR represents a near-universal driver and therapeutic vulnerability in metastatic prostate cancer, and targeting AR has a remarkable therapeutic index. Though most approaches directed toward AR focus on inhibiting AR signaling, laboratory and now clinical data have shown that high dose, supraphysiological androgen treatment (SPA) results in growth repression and improved outcomes in subsets of patients with prostate cancer. A better understanding of the mechanisms contributing to SPA response and resistance could help guide patient selection and combination therapies to improve efficacy. To characterize SPA signaling, we integrated metrics of gene expression changes induced by SPA together with cistrome data and protein-interactomes. These analyses indicated that the dimerization partner, RB-like, E2F, and multivulval class B (DREAM) complex mediates growth repression and downregulation of E2F targets in response to SPA. Notably, prostate cancers with complete genomic loss of RB1 responded to SPA treatment, whereas loss of DREAM complex components such as RBL1/2 promoted resistance. Overexpression of MYC resulted in complete resistance to SPA and attenuated the SPA/AR-mediated repression of E2F target genes. These findings support a model of SPA-mediated growth repression that relies on the negative regulation of MYC by AR leading to repression of E2F1 signaling via the DREAM complex. The integrity of MYC signaling and DREAM complex assembly may consequently serve as determinants of SPA responses and as pathways mediating SPA resistance.

SIGNIFICANCE

Determining the molecular pathways by which supraphysiological androgens promote growth arrest and treatment responses in prostate cancer provides opportunities for biomarker-selected clinical trials and the development of strategies to augment responses.

LSD1 Inhibition Disrupts Super-Enhancer-Driven Oncogenic Transcriptional Programs in Castration-Resistant Prostate Cancer

The lysine demethylase LSD1 (also called KDM1A) plays important roles in promoting multiple malignancies including both hematologic cancers and solid tumors. LSD1 targets histone and nonhistone proteins and can function as a transcriptional corepressor or coactivator. LSD1 has been reported to act as a coactivator of androgen receptor (AR) in prostate cancer and to regulate the AR cistrome via demethylation of its pioneer factor FOXA1. A deeper understanding of the key oncogenic programs targeted by LSD1 could help stratify prostate cancer patients for treatment with LSD1 inhibitors, which are currently under clinical investigation. In this study, we performed transcriptomic profiling in an array of castration-resistant prostate cancer (CRPC) xenograft models that are sensitive to LSD1 inhibitor treatment. Impaired tumor growth by LSD1 inhibition was attributed to significantly decreased MYC signaling, and MYC was found to be a consistent target of LSD1. Moreover, LSD1 formed a network with BRD4 and FOXA1 and was enriched at super-enhancer regions exhibiting liquid-liquid phase separation. Combining LSD1 inhibitors with BET inhibitors exhibited strong synergy in disrupting the activities of multiple drivers in CRPC, thereby inducing significant growth repression of tumors. Importantly, the combination treatment showed superior effects than either inhibitor alone in disrupting a subset of newly identified CRPC-specific super-enhancers. These results provide mechanistic and therapeutic insights for cotargeting two key epigenetic factors and could be rapidly translated in the clinic for CRPC patients.

SIGNIFICANCE

LSD1 drives prostate cancer progression by activating super-enhancer-mediated oncogenic programs, which can be targeted with the combination of LSD1 and BRD4 inhibitors to suppress the growth of CRPC.

CHRM4/AKT/MYCN upregulates interferon alpha-17 in the tumor microenvironment to promote neuroendocrine differentiation of prostate cancer

Current treatment options for prostate cancer focus on targeting androgen receptor (AR) signaling. Inhibiting effects of AR may activate neuroendocrine differentiation and lineage plasticity pathways, thereby promoting the development of neuroendocrine prostate cancer (NEPC). Understanding the regulatory mechanisms of AR has important clinical implications for this most aggressive type of prostate cancer. Here, we demonstrated the tumor-suppressive role of the AR and found that activated AR could directly bind to the regulatory sequence of muscarinic acetylcholine receptor 4 (CHRM4) and downregulate its expression. CHRM4 was highly expressed in prostate cancer cells after androgen-deprivation therapy (ADT). CHRM4 overexpression may drive neuroendocrine differentiation of prostate cancer cells and is associated with immunosuppressive cytokine responses in the tumor microenvironment (TME) of prostate cancer. Mechanistically, CHRM4-driven AKT/MYCN signaling upregulated the interferon alpha 17 (IFNA17) cytokine in the prostate cancer TME after ADT. IFNA17 mediates a feedback mechanism in the TME by activating the CHRM4/AKT/MYCN signaling-driven immune checkpoint pathway and neuroendocrine differentiation of prostate cancer cells. We explored the therapeutic efficacy of targeting CHRM4 as a potential treatment for NEPC and evaluated IFNA17 secretion in the TME as a possible predictive prognostic biomarker for NEPC.

The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications

The discovery of the benefits of castration for prostate cancer treatment in 1941 led to androgen deprivation therapy, which remains a mainstay of the treatment of men with advanced prostate cancer. However, as early as this original publication, the inevitable development of castration-resistant prostate cancer was recognized. Resistance first manifests as a sustained rise in the androgen-responsive gene, PSA, consistent with reactivation of the androgen receptor axis. Evaluation of clinical specimens demonstrates that castration-resistant prostate cancer cells remain addicted to androgen signalling and adapt to chronic low-testosterone states. Paradoxically, results of several studies have suggested that treatment with supraphysiological levels of testosterone can retard prostate cancer growth. Insights from these studies have been used to investigate administration of supraphysiological testosterone to patients with prostate cancer for clinical benefits, a strategy that is termed bipolar androgen therapy (BAT). BAT involves rapid cycling from supraphysiological back to near-castration testosterone levels over a 4-week cycle. Understanding how BAT works at the molecular and cellular levels might help to rationalize combining BAT with other agents to achieve increased efficacy and tumour responses.

Increased AR expression in castration-resistant prostate cancer rapidly induces AR signaling reprogramming with the collaboration of EZH2

Elevated androgen receptor (AR) expression is a hallmark of castration-resistant prostate cancer (CRPC) and contributes to the restoration of AR signaling under the conditions of androgen deprivation. However, whether overexpressed AR alone with the stimulation of castrate levels of androgens can be sufficient to induce the reprogramming of AR signaling for the adaptation of prostate cancer (PCa) cells remains unclear. In this study, we used a PCa model with inducible overexpression of AR to examine the acute effects of AR overexpression on its cistrome and transcriptome. Our results show that overexpression of AR alone in conjunction with lower androgen levels can rapidly redistribute AR chromatin binding and activates a distinct transcription program that is enriched for DNA damage repair pathways. Moreover, using a recently developed bioinformatic tool, we predicted the involvement of EZH2 in this AR reprogramming and subsequently identified a subset of AR/EZH2 co-targeting genes, which are overexpressed in CRPC and associated with worse patient outcomes. Mechanistically, we found that AR-EZH2 interaction is impaired by the pre-castration level of androgens but can be recovered by the post-castration level of androgens. Overall, our study provides new molecular insights into AR signaling reprogramming with the engagement of specific epigenetic factors.

Androgen-Induced MIG6 Regulates Phosphorylation of Retinoblastoma Protein and AKT to Counteract Non-Genomic AR Signaling in Prostate Cancer Cells

The bipolar androgen therapy (BAT) includes the treatment of prostate cancer (PCa) patients with supraphysiological androgen level (SAL). Interestingly, SAL induces cell senescence in PCa cell lines as well as ex vivo in tumor samples of patients. The SAL-mediated cell senescence was shown to be androgen receptor (AR)-dependent and mediated in part by non-genomic AKT signaling. RNA-seq analyses compared with and without SAL treatment as well as by AKT inhibition (AKTi) revealed a specific transcriptome landscape. Comparing the top 100 genes similarly regulated by SAL in two human PCa cell lines that undergo cell senescence and being counteracted by AKTi revealed 33 commonly regulated genes. One gene, ERBB receptor feedback inhibitor 1 (ERRFI1), encodes the mitogen-inducible gene 6 (MIG6) that is potently upregulated by SAL, whereas the combinatory treatment of SAL with AKTi reverses the SAL-mediated upregulation. Functionally, knockdown of ERRFI1 enhances the pro-survival AKT pathway by enhancing phosphorylation of AKT and the downstream AKT target S6, whereas the phospho-retinoblastoma (pRb) protein levels were decreased. Further, the expression of the cell cycle inhibitor p15^INK4b is enhanced by SAL and ERRFI1 knockdown. In line with this, cell senescence is induced by ERRFI1 knockdown and is enhanced slightly further by SAL. Treatment of SAL in the ERRFI1 knockdown background enhances phosphorylation of both AKT and S6 whereas pRb becomes hypophosphorylated. Interestingly, the ERRFI1 knockdown does not reduce AR protein levels or AR target gene expression, suggesting that MIG6 does not interfere with genomic signaling of AR but represses androgen-induced cell senescence and might therefore counteract SAL-induced signaling. The findings indicate that SAL treatment, used in BAT, upregulates MIG6, which inactivates both pRb and the pro-survival AKT signaling. This indicates a novel negative feedback loop integrating genomic and non-genomic AR signaling.

Current Status and Prospects of Clinical Treatment of Osteosarcoma

Osteosarcoma, one of the common malignant tumors in the skeletal system, originates in mesenchymal tissue, and the most susceptible area of occurrence is the metaphysis with its abundant blood supply. Tumors are characterized by highly malignant spindle stromal cells that can produce bone-like tissue. Most of the osteosarcoma are primary, and a few are secondary. Osteosarcoma occurs primarily in children and adolescents undergoing vigorous bone growth and development. Most cases involve rapid tumor development and early blood metastasis. In recent years, research has grown in the areas of molecular biology, imaging medicine, biological materials, applied anatomy, surgical techniques, biomechanics, and comprehensive treatment of tumors. With developments in molecular biology and tissue bioengineering, treatment methods have also made great progress, especially in comprehensive limb salvage treatment, which significantly enhances the quality of life after surgery and improves the 5-year survival rate of patients with malignant tumors. This article provides a review of limb salvage, immunotherapy, gene therapy, and targeted therapy from traditional amputation to neoadjuvant chemotherapy, providing a reference for current clinical treatments for osteosarcoma.