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

GL-V9 inhibits the activation of AR-AKT-HK2 signaling networks and induces prostate cancer cell apoptosis through mitochondria-mediated mechanism

Prostate cancer (PCa) is a serious health concern for men due to its high incidence and mortality rate. The first therapy typically adopted is androgen deprivation therapy (ADT). However, patient response to ADT varies, and 20-30% of PCa cases develop into castration-resistant prostate cancer (CRPC). This article investigates the anti-PCa effect of a drug candidate named GL-V9 and highlights the significant mechanism involving the AKT-hexokinase II (HKII) pathway. In both androgen receptor (AR)-expressing 22RV1 cells and AR-negative PC3 cells, GL-V9 suppressed phosphorylated AKT and mitochondrial location of HKII. This led to glycolytic inhibition and mitochondrial pathway-mediated apoptosis. Additionally, GL-V9 inhibited AR activity in 22RV1 cells and disrupted the feedback activation of AKT signaling in condition of AR inhibition. This disruption greatly increased the anti-PCa efficacy of the AR antagonist bicalutamide. In conclusion, we present a novel anti-PCa candidate and combination drug strategies to combat CRPC by intervening in the AR-AKT-HKII signaling network.

Glucocorticoid Receptor Regulates and Interacts with LEDGF/p75 to Promote Docetaxel Resistance in Prostate Cancer Cells

Patients with advanced prostate cancer (PCa) invariably develop resistance to anti-androgen therapy and taxane-based chemotherapy. Glucocorticoid receptor (GR) has been implicated in PCa therapy resistance; however, the mechanisms underlying GR-mediated chemoresistance remain unclear. Lens epithelium-derived growth factor p75 (LEDGF/p75, also known as PSIP1 and DFS70) is a glucocorticoid-induced transcription co-activator implicated in cancer chemoresistance. We investigated the contribution of the GR-LEDGF/p75 axis to docetaxel (DTX)-resistance in PCa cells. GR silencing in DTX-sensitive and -resistant PCa cells decreased LEDGF/p75 expression, and GR upregulation in enzalutamide-resistant cells correlated with increased LEDGF/p75 expression. ChIP-sequencing revealed GR binding sites in the LEDGF/p75 promoter. STRING protein-protein interaction analysis indicated that GR and LEDGF/p75 belong to the same transcriptional network, and immunochemical studies demonstrated their co-immunoprecipitation and co-localization in DTX-resistant cells. The GR modulators exicorilant and relacorilant increased the sensitivity of chemoresistant PCa cells to DTX-induced cell death, and this effect was more pronounced upon LEDGF/p75 silencing. RNA-sequencing of DTX-resistant cells with GR or LEDGF/p75 knockdown revealed a transcriptomic overlap targeting signaling pathways associated with cell survival and proliferation, cancer, and therapy resistance. These studies implicate the GR-LEDGF/p75 axis in PCa therapy resistance and provide a pre-clinical rationale for developing novel therapeutic strategies for advanced PCa.

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.

The future of patient-derived xenografts in prostate cancer research

Patient-derived xenografts (PDXs) are generated by engrafting human tumours into mice. Serially transplantable PDXs are used to study tumour biology and test therapeutics, linking the laboratory to the clinic. Although few prostate cancer PDXs are available in large repositories, over 330 prostate cancer PDXs have been established, spanning broad clinical stages, genotypes and phenotypes. Nevertheless, more PDXs are needed to reflect patient diversity, and to study new treatments and emerging mechanisms of resistance. We can maximize the use of PDXs by exchanging models and datasets, and by depositing PDXs into biorepositories, but we must address the impediments to accessing PDXs, such as institutional, ethical and legal agreements. Through collaboration, researchers will gain greater access to PDXs representing diverse features of prostate cancer.

Glucocorticoid Receptor and β-Catenin Interact in Prostate Cancer Cells and Their Co-Inhibition Attenuates Tumorsphere Formation, Stemness, and Docetaxel Resistance

Therapy resistance hinders the efficacy of anti-androgen therapies and taxane-based chemotherapy for advanced prostate cancer (PCa). Glucocorticoid receptor (GR) signaling mediates resistance to androgen receptor signaling inhibitors (ARSI) and has also been recently implicated in PCa resistance to docetaxel (DTX), suggesting a role in therapy cross-resistance. Like GR, β-catenin is upregulated in metastatic and therapy-resistant tumors and is a crucial regulator of cancer stemness and ARSI resistance. β-catenin interacts with AR to promote PCa progression. Given the structural and functional similarities between AR and GR, we hypothesized that β-catenin also interacts with GR to influence PCa stemness and chemoresistance. As expected, we observed that treatment with the glucocorticoid dexamethasone promotednuclear accumulation of GR and active β-catenin in PCa cells. Co-immunoprecipitation studies showed that GR and β-catenin interact in DTX-resistant and DTX-sensitive PCa cells. Pharmacological co-inhibition of GR and β-catenin, using the GR modulator CORT-108297 and the selective β-catenin inhibitor MSAB, enhanced cytotoxicity in DTX-resistant PCa cells grown in adherent and spheroid cultures and decreased CD44+/CD24- cell populations in tumorspheres. These results indicate that GR and β-catenin influence cell survival, stemness, and tumorsphere formation in DTX-resistant cells. Their co-inhibition could be a promising therapeutic strategy to overcome PCa therapy cross-resistance.

The role of 11-oxygenated androgens in prostate cancer

11-oxygenated androgens are a class of steroids capable of activating the androgen receptor (AR) at physiologically relevant concentrations. In view of the AR as a key driver of prostate cancer (PC), these steroids are potential drivers of disease and progression. The 11-oxygenated androgens are adrenal-derived, and persist after androgen deprivation therapy (ADT), the mainstay treatment for advanced PC. Consequently, these steroids are of particular interest in the castration-resistant prostate cancer (CRPC) setting. The principal androgen of the pathway, 11-ketotestosterone (11KT), is a potent AR agonist and the predominant circulating active androgen in CRPC patients. Additionally, several precursor steroids are present in the circulation which can be converted into active androgens by steroidogenic enzymes present in PC cells. In vitro evidence suggests that adaptations frequently observed in CRPC favour the intratumoral accumulation of 11-oxygenated androgens in particular. Still, apparent gaps in our understanding of the physiology and role of the 11-oxygenated androgens remain. In particular, in vivo and clinical evidence supporting these in vitro findings is limited. Despite recent advances, a comprehensive assessment of intratumoral concentrations has not yet been performed. The exact contribution of the 11-oxygenated androgens to CRPC progression therefore remains unclear. This review will focus on the current evidence linking the 11-oxygenated androgens to PC, will highlight current gaps in our knowledge, and will provide insight into the potential clinical importance of the 11-oxygenated androgens in the CRPC setting based on the current evidence.

Cell Line Characteristics Predict Subsequent Resistance to Androgen Receptor-Targeted Agents (ARTA) in Preclinical Models of Prostate Cancer

Treatment of prostate cancer (PCa) has changed considerably in the last decade due to the introduction of novel androgen receptor (AR)-targeted agents (ARTAs) for patients progressing on androgen deprivation therapy (ADT). Preclinical research however still relies heavily on AR-negative cell line models. In order to investigate potential differences in castration-resistant PCa (CRPC) growth, we set out to create a comprehensive panel of ARTA-progressive models from 4 androgen-responsive AR wild-type PCa cell lines and analyzed its androgen response as opposed to its ADT-progressive counterparts. Parallel cultures of VCaP, DuCaP, PC346C, and LAPC4 were established in their respective culture media with steroid-stripped fetal calf serum (FCS) [dextran-coated charcoal-stripped FCS (DCC)] without androgen (ADT) or in DCC plus 1 μM of the ARTAs bicalutamide, OH-flutamide, or RD162 (an enzalutamide/apalutamide analog). Cell growth was monitored and compared to those of parental cell lines. Short-term androgen response was measured using cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. qRT-PCR was performed to assess the mRNA expression of markers for AR signaling, steroidogenesis, glucocorticoid receptor (GR) signaling, epithelial-mesenchymal transition (EMT), and WNT signaling. Out of 35 parallel cultures per cell line, a total of 24, 15, 34, and 16 CRPC sublines emerged for VCaP, DuCaP, PC346C, and LAPC4, respectively. The addition of bicalutamide or OH-flutamide significantly increased CRPC growth compared to ADT or RD162. VCaP, DuCaP, and PC346C CRPC clones retained an AR-responsive phenotype. The expression of AR and subsequent androgen response were completely lost in all LAPC4 CRPC lines. Markers for EMT and WNT signaling were found to be elevated in the resilient PC346C model and CRPC derivatives of VCaP, DuCaP, and LAPC4. Although the resistant phenotype is pluriform between models, it seems consistent within models, regardless of type of ARTA. These data suggest that the progression to and the phenotype of the CRPC state might already be determined early in carcinogenesis.

Anti-Androgen Receptor Therapies in Prostate Cancer: A Brief Update and Perspective

Prostate cancer is a major health issue in western countries and is the second leading cause of cancer death in American men. Prostate cancer depends on the androgen receptor (AR), a transcriptional factor critical for prostate cancer growth and progression. Castration by surgery or medical treatment reduces androgen levels, resulting in prostatic atrophy and prostate cancer regression. Thus, metastatic prostate cancers are initially managed with androgen deprivation therapy. Unfortunately, prostate cancers rapidly relapse after castration therapy and progress to a disease stage called castration-resistant prostate cancer (CRPC). Currently, clinical treatment for CRPCs is focused on suppressing AR activity with antagonists like Enzalutamide or by reducing androgen production with Abiraterone. In clinical practice, these treatments fail to yield a curative benefit in CRPC patients in part due to AR gene mutations or splicing variations, resulting in AR reactivation. It is conceivable that eliminating the AR protein in prostate cancer cells is a promising solution to provide a potential curative outcome. Multiple strategies have emerged, and several potent agents that reduce AR protein levels were reported to eliminate xenograft tumor growth in preclinical models via distinct mechanisms, including proteasome-mediated degradation, heat-shock protein inhibition, AR splicing suppression, blockage of AR nuclear localization, AR N-terminal suppression. A few small chemical compounds are undergoing clinical trials combined with existing AR antagonists. AR protein elimination by enhanced protein or mRNA degradation is a realistic solution for avoiding AR reactivation during androgen deprivation therapy in prostate cancers.