Rationale for bipolar androgen therapy (BAT) for metastatic prostate cancer

Bipolar Androgen Therapy: When Excess Fuel Extinguishes the Fire

Androgen deprivation therapy (ADT) remains the cornerstone of advanced prostate cancer treatment. However, the progression towards castration-resistant prostate cancer is inevitable, as the cancer cells reactivate androgen receptor signaling and adapt to the castrate state through autoregulation of the androgen receptor. Additionally, the upfront use of novel hormonal agents such as enzalutamide and abiraterone acetate may result in long-term toxicities and may trigger the selection of AR-independent cells through "Darwinian" treatment-induced pressure. Therefore, it is crucial to develop new strategies to overcome these challenges. Bipolar androgen therapy (BAT) is one such approach that has been devised based on studies demonstrating the paradoxical inhibitory effects of supraphysiologic testosterone on prostate cancer growth, achieved through a variety of mechanisms acting in concert. BAT involves rapidly alternating testosterone levels between supraphysiological and near-castrate levels over a period of a month, achieved through monthly intramuscular injections of testosterone plus concurrent ADT. BAT is effective and well-tolerated, improving quality of life and potentially re-sensitizing patients to previous hormonal therapies after progression. By exploring the mechanisms and clinical evidence for BAT, this review seeks to shed light on its potential as a promising new approach to prostate cancer treatment.

ORC6, a novel prognostic biomarker, correlates with T regulatory cell infiltration in prostate adenocarcinoma: a pan-cancer analysis

BACKGROUND

The origin recognition complex (ORC), a six-subunit DNA-binding complex, participates in DNA replication in cancer cells. Specifically in prostate cancers, ORC participates the androgen receptor (AR) regulated genomic amplification and tumor proliferation throughout the entire cell cycle. Of note, ORC6, the smallest subunit of ORC, has been reported to be dysregulated in some types of cancers (including prostate cancer), however, its prognostic and immunological significances remain yet to be elucidated.

METHODS

In the current study, we comprehensively investigated the potential prognostic and immunological role of ORC6 in 33 human tumors using multiple databases, such as TCGA, Genotype-Tissue Expression, CCLE, UCSC Xena, cBioPortal, Human Protein Atlas, GeneCards, STRING, MSigDB, TISIDB, and TIMER2 databases.

RESULTS

ORC6 expression was significantly upregulated in 29 types of cancers compared to the corresponding normal adjacent tissues. ORC6 overexpression correlated with higher stage and worse prognostic outcomes in most cancer types analyzed. Additionally, ORC6 was involved in the cell cycle pathway, DNA replication, and mismatch repair pathways in most tumor types. A negative correlation was observed between the tumor endothelial cell infiltration and ORC6 expression in almost all tumors, whereas the immune infiltration of T regulatory cell was noted to be statistically positively correlated with the expression of ORC6 in prostate cancer tissues. Furthermore, in most tumor types, immunosuppression-related genes, especially TGFBR1 and PD-L1 (CD274), exhibited a specific correlation with the expression of ORC6.

CONCLUSIONS

This comprehensive pan-cancer analysis revealed that ORC6 expression serves as a prognostic biomarker and that ORC6 is involved in the regulation of various biological pathways, the tumor microenvironment, and the immunosuppression status in several human cancers, suggesting its potential diagnostic, prognostic, and therapeutic value in pan-cancer, especially in prostate adenocarcinoma.

Experience of bipolar androgen therapy (BAT) in Argentinian oncology centres

Background

Previous studies with bipolar androgen therapy (BAT) have shown clinical activity in metastatic Castration Resistant Prostate Cancer (mCRPC) as well as the potential to re-sensitise prostate cancer cells to prior androgen receptor-targeted agents. None of these studies had tested BAT after chemotherapy. In this study, we gathered real-world evidence from three centres in Argentina where BAT is being used in castration-resistant prostate cancer (CRPC), not only prior to chemotherapy but also after several lines of treatment.

Materials and methods

This retro-prospective nonrandomised multicentre cohort study included patients with mCRPC, who received BAT in different scenarios defined by the treating physician at three centres in Argentina.

Results

A total of 21 asymptomatic patients with mCRPC were included. There was a median of two lines before BAT, with nine patients (42.8%) receiving three or more lines, and 13 patients (61.9%) receiving chemotherapy previously. Previous lines included next-generation hormonal agents (NHA) in 100% (abiraterone 33.3% and enzalutamide 71.4%), chemotherapy in 61.9%, Radium-223 in 47.6% and others in 4.8%. The progression free survival (PFS) after BAT was 3.5 months (95% CI: 3.06-7.97). PSA50 response rate (RR) was 28.5% and the overall RR was 14.3%. Of the 17 patients who had disease progression, 9 had a rechallenge to NHA, achieving a 55% RR, 6 received other treatment (chemotherapy in 5 and ¹⁷⁷Lu-PSMA in 1) with a 66% RR and 2 best supportive care. The PFS2, calculated after the initiation of BAT in the 15 patients who received further therapy, was 7.93 months (95% CI: 6.73-NR). Treatment was overall well tolerated, with only two patients requiring hospitalisation and treatment interruption due to worsening pain.

Conclusion

To the authors' knowledge, this is the first publication of BAT in later lines of therapy in mCRPC. BAT showed clinical activity in this scenario. Our data supports that BAT may play a role in CRPC re-sensitisation after multiple treatment lines.

Maintenance of androgen deprivation therapy or testosterone supplementation in the management of castration-resistant prostate cancer: that is the question

PURPOSE

Whether or not androgen receptor (AR) axis could still be targetable in castration resistant prostate cancer (CRPC) patients with disease progression to next generation hormonal agents (NGHAs) is a controversial issue.

RESULTS

Serum testosterone in CRPC patients has a positive prognostic role and increasing testosterone levels after androgen deprivation therapy (ADT) withdrawal or testosterone supplementation, as part of a bipolar androgen therapy (BAT) strategy, has been shown to potentially restore sensitivity to previous lines of NGHAs.

CONCLUSION

These data suggest that maintenance of ADT in CRPC patients receiving further lines of treatment, as recommended by current international guidelines, could be questionable. Conversely, testosterone supplementation aimed to re-sensitize CRPC to further hormonal manipulation is a strategy worth to be explored in future clinical trials.

The androgen receptor-lncRNASAT1-AKT-p15 axis mediates androgen-induced cellular senescence in prostate cancer cells

The bipolar androgen therapy (BAT) to treat prostate cancer (PCa) includes cycles of supraphysiological androgen levels (SAL) under androgen-deprivation therapy (ADT). We showed previously that SAL induces cellular senescence in androgen-sensitive PCa cells and in ex vivo-treated patient PCa tumor samples. Here, we analyzed the underlying molecular pathway and reveal that SAL induces cellular senescence in both, castration-sensitive (CSPC) LNCaP and castration-resistant PCa (CRPC) C4-2 cells through the cell cycle inhibitor p15^INK4b and increased phosphorylation of AKT. Treatment with the AKT inhibitor (AKTi) potently inhibited SAL-induced expression of p15^INK4b and cellular senescence in both cell lines. Proximity-ligation assays (PLA) combined with high-resolution laser-scanning microscopy indicate that SAL promotes interaction of endogenous androgen receptor (AR) with AKT in the cytoplasm as well as in the nucleus detectable after three days. Transcriptome sequencing (RNA-seq) comparing the SAL-induced transcriptomes of LNCaP with C4-2 cells as well as with AKTi-treated cell transcriptomes revealed landscapes for cell senescence. Interestingly, one of the identified genes is the lncRNASAT1. SAL treatment of native patient tumor samples ex vivo upregulates lncRNASAT1. In PCa tumor tissues, lncRNASAT1 is downregulated compared with nontumor tissues of the same patients. Knockdown indicates that the lncRNASAT1 is crucial for SAL-induced cancer-cell senescence as an upstream factor for pAKT and for p15^INK4b. Further, knockdown of lncRNASAT1 enhances cell proliferation by SAL, suggesting that lncRNASAT1 serves as a tumor suppressor at SAL. Interestingly, immunoprecipitation of AR detected lncRNASAT1 as an AR-interacting partner that regulates AR target-gene expression. Similarly, RNA-ChIP experiments revealed the interaction of AR with lncRNASAT1 on chromatin. Thus, we identified a novel AR-lncRNASAT1-AKT-p15^INK4b signaling axis to mediate SAL-induced cellular senescence.

Phenotypic characterization of two novel cell line models of castration-resistant prostate cancer

BACKGROUND

Resistance to androgen deprivation therapies is a major driver of mortality in advanced prostate cancer. Therefore, there is a need to develop new preclinical models that allow the investigation of resistance mechanisms and the assessment of drugs for the treatment of castration-resistant prostate cancer.

METHODS

We generated two novel cell line models (LAPC4-CR and VCaP-CR) which were derived by passaging LAPC4 and VCaP cells in vivo and in vitro under castrate conditions. We performed detailed transcriptomic (RNA-seq) and proteomic analyses (SWATH-MS) to delineate expression differences between castration-sensitive and castration-resistant cell lines. Furthermore, we characterized the in vivo and in vitro growth characteristics of these novel cell line models.

RESULTS

The two cell line derivatives LAPC4-CR and VCaP-CR showed castration-resistant growth in vitro and in vivo which was only minimally inhibited by AR antagonists, enzalutamide, and bicalutamide. High-dose androgen treatment resulted in significant growth arrest of VCaP-CR but not in LAPC4-CR cells. Both cell lines maintained AR expression, but exhibited distinct expression changes on the mRNA and protein level. Integrated analyses including data from LNCaP and the previously described castration-resistant LNCaP-abl cells revealed an expression signature of castration resistance.

CONCLUSIONS

The two novel cell line models LAPC4-CR and VCaP-CR and their comprehensive characterization on the RNA and protein level represent important resources to study the molecular mechanisms of castration resistance.

Titration of Androgen Signaling: How Basic Studies Have Informed Clinical Trials Using High-Dose Testosterone Therapy in Castrate-Resistant Prostate Cancer

Since the Nobel Prize-winning work of Huggins, androgen ablation has been a mainstay for treatment of recurrent prostate cancer. While initially effective for most patients, prostate cancers inevitably develop the ability to survive, grow, and metastasize further, despite ongoing androgen suppression. Here, we briefly review key preclinical studies over decades and include illustrative examples from our own laboratories that suggest prostate cancer cells titrate androgen signaling to optimize growth. Such laboratory-based studies argue that adaptations that allow growth in a low-androgen environment render prostate cancer sensitive to restoration of androgens, especially at supraphysiologic doses. Based on preclinical data as well as clinical observations, trials employing high-dose testosterone (HDT) therapy have now been conducted. These trials suggest a clinical benefit in cancer response and quality of life in a subset of castration-resistant prostate cancer patients. Laboratory studies also suggest that HDT may yet be optimized further to improve efficacy or durability of response. However, laboratory observations suggest that the cancer will inevitably adapt to HDT, and, as with prior androgen deprivation, disease progression follows. Nonetheless, the adaptations made to render tumors resistant to hormonal manipulations may reveal vulnerabilities that can be exploited to prolong survival and provide other clinical benefits.

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer

The androgen receptor (AR) plays a leading role in the control of prostate cancer (PCa) growth. Interestingly, structurally different AR antagonists with distinct mechanisms of antagonism induce cell senescence, a mechanism that inhibits cell cycle progression, and thus seems to be a key cellular response for the treatment of PCa. Surprisingly, while physiological levels of androgens promote growth, supraphysiological androgen levels (SAL) inhibit PCa growth in an AR-dependent manner by inducing cell senescence in cancer cells. Thus, oppositional acting ligands, AR antagonists, and agonists are able to induce cellular senescence in PCa cells, as shown in cell culture model as well as ex vivo in patient tumor samples. This suggests a dual AR-signaling dependent on androgen levels that leads to the paradox of the rational to keep the AR constantly inactivated in order to treat PCa. These observations however opened the option to treat PCa patients with AR antagonists and/or with androgens at supraphysiological levels. The latter is currently used in clinical trials in so-called bipolar androgen therapy (BAT). Notably, cellular senescence is induced by AR antagonists or agonist in both androgen-dependent and castration-resistant PCa (CRPC). Pathway analysis suggests a crosstalk between AR and the non-receptor tyrosine kinase Src-Akt/PKB and the PI3K-mTOR-autophagy signaling in mediating AR-induced cellular senescence in PCa. In this review, we summarize the current knowledge of therapeutic induction and intracellular pathways of AR-mediated cellular senescence.

Prostate cancer research: The next generation; report from the 2019 Coffey-Holden Prostate Cancer Academy Meeting

INTRODUCTION

The 2019 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, "Prostate Cancer Research: The Next Generation," was held 20 to 23 June, 2019, in Los Angeles, California.

METHODS

The CHPCA Meeting is an annual conference held by the Prostate Cancer Foundation, that is uniquely structured to stimulate intense discussion surrounding topics most critical to accelerating prostate cancer research and the discovery of new life-extending treatments for patients. The 7th Annual CHPCA Meeting was attended by 86 investigators and concentrated on many of the most promising new treatment opportunities and next-generation research technologies.

RESULTS

The topics of focus at the meeting included: new treatment strategies and novel agents for targeted therapies and precision medicine, new treatment strategies that may synergize with checkpoint immunotherapy, next-generation technologies that visualize tumor microenvironment (TME) and molecular pathology in situ, multi-omics and tumor heterogeneity using single cells, 3D and TME models, and the role of extracellular vesicles in cancer and their potential as biomarkers.

DISCUSSION

This meeting report provides a comprehensive summary of the talks and discussions held at the 2019 CHPCA Meeting, for the purpose of globally disseminating this knowledge and ultimately accelerating new treatments and diagnostics for patients with prostate cancer.

Chromatin reprogramming as an adaptation mechanism in advanced prostate cancer

Tumor evolution is based on the ability to constantly mutate and activate different pathways under the selective pressure of targeted therapies. Epigenetic alterations including those of the chromatin structure are associated with tumor initiation, progression and drug resistance. Many cancers, including prostate cancer, present enlarged nuclei, and chromatin appears altered and irregular. These phenotypic changes are likely to result from epigenetic dysregulation. High-throughput sequencing applied to bulk samples and now to single cells has made it possible to study these processes in unprecedented detail. It is therefore timely to review the impact of chromatin relaxation and increased DNA accessibility on prostate cancer growth and drug resistance, and their effects on gene expression. In particular, we focus on the contribution of chromatin-associated proteins such as the bromodomain-containing proteins to chromatin relaxation. We discuss the consequence of this for androgen receptor transcriptional activity and briefly summarize wider gain-of-function effects on other oncogenic transcription factors and implications for more effective prostate cancer treatment.

Resolving the Coffey Paradox: what does the androgen receptor do in normal vs. malignant prostate epithelial cells?

Donald Straley Coffey completed his 85 year life's journey on November 9, 2017. In his wake, he left a legion of inspired and loyal students, fellows, and faculty colleagues from all over the world to carry on his passion both for life in general and his 50 year quest to conquer cancer. Early in his career, Dr. Coffey developed a series of animal models to study how androgen regulates the growth of both normal and abnormal prostatic epithelium. As part of these early studies, Dr. Coffey uncovered a paradox in that anti-androgen treatment given at the "wrong" time paradoxically enhanced, not inhibited, normal prostate growth. Advances over the last several years concerning the paracrine-dependent stem cell organization of the prostate provide a mechanistic explanation for this "Coffey Paradox". This is based upon the realization that the normal function of the Androgen Receptor (AR) in the paracrine-dependent stem cell organization of the prostate is to induce terminal differentiation of normal prostate epithelial cells while suppressing their growth, despite the presence of high levels of stromal cell-derived paracrine growth factors. Such growth suppression involves ligand-dependent AR binding to the Tcf-4/β-catenin 3'c-Myc enhancer in prostate epithelial cells, which inhibits c-Myc transcription needed for proliferation. Therefore, if anti-androgen is given at the wrong time, it prevents such AR-dependent c-Myc down regulation, and thus paradoxically enhances epithelial regrowth (i.e. the Coffey Paradox) induced by exogenous androgen replacement in the castration regressed prostate. In contrast to the normal prostate epithelium, in prostate cancer cells retaining AR expression, androgen-induced AR signaling no longer reduces c-Myc transcription but instead up-regulates c-Myc translation and protein stability to stimulate malignant growth. Thus, in these AR expressing prostate cancer cells, AR signaling is converted from a growth suppressor to an oncogene, which involves a gain of function to upregulate c-Myc protein expression. Such a gain of function "addicts" these prostate cancer cells to AR signaling for their proliferation and survival, which provides the rationale for therapy targeted at inhibiting such AR signaling. While therapies targeted at maximally decreasing the level of androgen ligand are the most commonly used, recent studies have documented that a subset of patients progressing on such androgen ablation (i.e. castration-resistant disease) due to their adaptive increase in AR protein expression respond positively to rapid cycling between pharmacologically high and castration low levels of circulating androgen. [i.e. Bipolar Androgen Therapy (BAT)].