Synergistic targeting of PI3K/AKT pathway and androgen receptor axis significantly delays castration-resistant prostate cancer progression in vivo

GPCR-Gα13 Involvement in Mitochondrial Function, Oxidative Stress, and Prostate Cancer

Gα13 and Gα12, encoded by the GNA13 and GNA12 genes, respectively, are members of the G12 family of Gα proteins that, along with their associated Gβγ subunits, mediate signaling from specific G protein-coupled receptors (GPCRs). Advanced prostate cancers have increased expression of GPCRs such as CXC Motif Chemokine Receptor 4 (CXCR4), lysophosphatidic acid receptor (LPAR), and protease activated receptor 1 (PAR-1). These GPCRs signal through either the G12 family, or through Gα13 exclusively, often in addition to other G proteins. The effect of Gα13 can be distinct from that of Gα12, and the role of Gα13 in prostate cancer initiation and progression is largely unexplored. The oncogenic effect of Gα13 on cell migration and invasion in prostate cancer has been characterized, but little is known about other biological processes such as mitochondrial function and oxidative stress. Current knowledge on the link between Gα13 and oxidative stress is based on animal studies in which GPCR-Gα13 signaling decreased superoxide levels, and the overexpression of constitutively active Gα13 promoted antioxidant gene activation. In human samples, mitochondrial superoxide dismutase 2 (SOD2) correlates with prostate cancer risk and prognostic Gleason grade. However, overexpression of SOD2 in prostate cancer cells yielded conflicting results on cell growth and survival under basal versus oxidative stress conditions. Hence, it is necessary to explore the effect of Gα13 on prostate cancer tumorigenesis, as well as the effect of Gα13 on SOD2 in prostate cancer cell growth under oxidative stress conditions.

New target therapies in prostate cancer: from radioligand therapy, to PARP-inhibitors and immunotherapy

Prostate cancer (PCa) remains a significant global health challenge, particularly in its advanced stages. Despite progress in early detection and treatment, PCa is the second most common cancer diagnosis among men. This review aims to provide an overview of current therapeutic approaches and innovations in PCa management, focusing on the latest advancements and ongoing challenges. We conducted a narrative review of clinical trials and research studies, focusing on PARP inhibitors (PARPis), phosphoinositide 3 kinase-protein kinase B inhibitors, immunotherapy, and radioligand therapies (RLTs). Data was sourced from major clinical trial databases and peer-reviewed journals. Androgen deprivation therapy and androgen-receptor pathway inhibitors remain foundational in managing castration-sensitive and early-stage castration-resistant PCa (CRPC). PARPi's, such as olaparib and rucaparib, have emerged as vital treatments for metastatic CRPC with homologous recombination repair gene mutations, highlighting the importance of personalized medicine. Immune checkpoint inhibitors (ICIs) have shown clinical benefit limited to specific subgroups of PCa, demonstrating significant improvement in efficacy in patients with microsatellite instability/mismatch repair or cyclin-dependent kinase 12 alteration, highlighting the importance of focusing ongoing research on identifying and characterizing these subgroups to maximize the clinical benefits of ICIs. RLTs have shown effectiveness in treating mCRPC. Different alpha emitters (like [225Ac]PSMA) and beta emitters compounds (like [177Lu]PSMA) impact treatment differently due to their energy transfer characteristics. Clinical trials like VISION and TheraP have demonstrated positive outcomes with RLT, particularly [177Lu]PSMA-617, leading to FDA approval. Ongoing trials and future perspectives explore the potential of [225Ac]PSMA, aiming to improve outcomes for patients with mCRPC. The landscape of PCa treatment is evolving, with significant advancements in both established and novel therapies. The combination of hormonal therapies, chemotherapy, PARPis, immunotherapy, and RLTs, guided by genetic and molecular insights, opens new possibilities for personalized treatment.

Capivasertib combines with docetaxel to enhance anti-tumour activity through inhibition of AKT-mediated survival mechanisms in prostate cancer

BACKGROUND/OBJECTIVE

To explore the anti-tumour activity of combining AKT inhibition and docetaxel in PTEN protein null and WT prostate tumours.

METHODS

Mechanisms associated with docetaxel capivasertib treatment activity in prostate cancer were examined using a panel of in vivo tumour models and cell lines.

RESULTS

Combining docetaxel and capivasertib had increased activity in PTEN null and WT prostate tumour models in vivo. In vitro short-term docetaxel treatment caused cell cycle arrest in the majority of cells. However, a sub-population of docetaxel-persister cells did not undergo G2/M arrest but upregulated phosphorylation of PI3K/AKT pathway effectors GSK3β, p70S6K, 4E-BP1, but to a lesser extent AKT. In vivo acute docetaxel treatment induced p70S6K and 4E-BP1 phosphorylation. Treating PTEN null and WT docetaxel-persister cells with capivasertib reduced PI3K/AKT pathway activation and cell cycle progression. In vitro and in vivo it reduced proliferation and increased apoptosis or DNA damage though effects were more marked in PTEN null cells. Docetaxel-persister cells were partly reliant on GSK3β as a GSK3β inhibitor AZD2858 reversed capivasertib-induced apoptosis and DNA damage.

CONCLUSION

Capivasertib can enhance anti-tumour effects of docetaxel by targeting residual docetaxel-persister cells, independent of PTEN status, to induce apoptosis and DNA damage in part through GSK3β.

Dual targeting of the androgen receptor and PI3K/AKT/mTOR pathways in prostate cancer models improves antitumor efficacy and promotes cell apoptosis

Prostate cancer is a frequent malignancy in older men and has a very high 5-year survival rate if diagnosed early. The prognosis is much less promising if the tumor has already spread outside the prostate gland. Targeted treatments mainly aim at blocking androgen receptor (AR) signaling and initially show good efficacy. However, tumor progression due to AR-dependent and AR-independent mechanisms is often observed after some time, and novel treatment strategies are urgently needed. Dysregulation of the PI3K/AKT/mTOR pathway in advanced prostate cancer and its implication in treatment resistance has been reported. We compared the impact of PI3K/AKT/mTOR pathway inhibitors with different selectivity profiles on in vitro cell proliferation and on caspase 3/7 activation as a marker for apoptosis induction, and observed the strongest effects in the androgen-sensitive prostate cancer cell lines VCaP and LNCaP. Combination treatment with the AR inhibitor darolutamide led to enhanced apoptosis in these cell lines, the effects being most pronounced upon cotreatment with the pan-PI3K inhibitor copanlisib. A subsequent transcriptomic analysis performed in VCaP cells revealed that combining darolutamide with copanlisib impacted gene expression much more than individual treatment. A comprehensive reversal of the androgen response and the mTORC1 transcriptional programs as well as a marked induction of DNA damage was observed. Next, an in vivo efficacy study was performed using the androgen-sensitive patient-derived prostate cancer (PDX) model LuCaP 35 and a superior efficacy was observed after the combined treatment with copanlisib and darolutamide. Importantly, immunohistochemistry analysis of these treated tumors showed increased apoptosis, as revealed by elevated levels of cleaved caspase 3 and Bcl-2-binding component 3 (BBC3). In conclusion, these data demonstrate that concurrent blockade of the PI3K/AKT/mTOR and AR pathways has superior antitumor efficacy and induces apoptosis in androgen-sensitive prostate cancer cell lines and PDX models.

AR antagonists develop drug resistance through TOMM20 autophagic degradation-promoted transformation to neuroendocrine prostate cancer

BACKGROUND

Prostate cancer(PCa) is the most commonly occurring male cancer in the USA. Abiraterone or Enzalutamide have been approved for the treatment of metastatic castration-resistant prostate cancer (CRPC). However, the treatment-emergent neuroendocrine PCa (t-NEPC) may develop, resulting in drug resistance in about 10-17% CRPC patients. The detailed mechanisms remain unclear..

METHODS

The expression correlation of TOMM20 and AR in PCa was determined by analyzing publicly available datasets, or by IHC staining in tumor specimens. The protein interaction of TOMM20 and AR was validated by co-immunoprecipitation or GST pull-down assay. The impact of TOMM20 depletion on drug sensitivity were elucidated by assays of cell proliferation, invasion, sphere formation, xenograft growth and intravenous metastasis. The intracellular ROS level was measured by flow cytometry, and the NEPC transdifferentiation and characteristics of cancer stem-like cells were validated by RNA-seq, RT-PCR and western blotting.

RESULTS

The protein level of TOMM20 is positively correlated with AR in PCa cells and specimens. TOMM20 protein physically interacts with AR. AR antagonists induced the protein degradation of TOMM20 through autophagy-lysosomal pathway, thereby elevating the intracellular ROS level and activating PI3K/AKT signaling pathway. When TOMM20 was depleted, PCa cells underwent EMT, acquired the characteristics of cancer stem-like cells, and developed resistance to AR antagonists. The stable depletion of TOMM20 promoted the transdifferentiation of PCa adenocarcinoma into NEPC and metastasis. Conversely, the rescue of TOMM20 re-sensitized the resistant PCa cells to AR antagonists.

CONCLUSIONS

TOMM20 protein degradation induced by AR antagonists promoted the transdifferentiation of PCa to NEPC, thereby revealing a novel molecular mechanism by which AR antagonists develop drug resistance through mitochondrial outer membrane-mediated signaling pathway. These findings suggested that the decreasing or loss of TOMM20 expression in PCa tissues might become a useful predictor of PCa resistance to AR antagonists.

hsa_circ_0000417 downregulation suppresses androgen receptor expression and apoptotic signals in human foreskin fibroblasts via sponging miR-6756-5p

BACKGROUND

Dysregulated apoptosis of penile mesenchymal cells during male urethragenesis has been previously demonstrated to underly hypospadiac urethral closure failure, and androgen receptor (AR) has been shown to play a central role in regulating penile mesenchyme cell proliferation and survival. However, the regulatory mechanisms upstream and downstream of AR remain poorly understood. Our clinical data and bioinformatics analysis previously indicated that hsa_circ_0000417, a circRNA significantly downregulated in hypospadias preputial specimens, may act as a ceRNA for AR via sequestering hsa_miR-6756-5p, and that the biological functions of hsa_circ_0000417 may significantly involve the PI3K/AKT pathway. In this study, we employed human foreskin fibroblasts (HFF-1) to experimentally validate this putative hsa_circ_0000417/miR-6756-5p/AR axis and its impact on penile mesenchymal cell proliferation and apoptosis.

METHOD AND RESULTS

We showed that hsa_circ_0000417 knockdown significantly promoted proliferation and suppressed apoptosis of HFF-1 cells. Mechanistically, hsa_circ_0000417 functioned as a molecular sponge for miR-6756-5p in HFF-1 cells and relieved the latter's translational repression on AR mRNA, leading to decreased AKT activation and increased expression of pro-apoptotic proteins BAX and cleaved-caspase 9. Conversely, elevated levels of miR-6756-5p resulted in diminished AR expression concomitant with enhanced AKT activation and HFF-1 cell proliferation.

CONCLUSIONS

Collectively, our data describe for the first time a circRNA-mediated post-transcriptional regulatory mechanism of AR and its functional consequences in penile mesenchymal cells in the context of hypospadias. These findings may contribute to advancing our current understanding of the roles of AR and mesenchymal cell fate decisions during penile morphogenesis.

Mechanistic Insights into Harmine-Mediated Inhibition of Human DNA Methyltransferases and Prostate Cancer Cell Growth

Mammalian DNA methyltransferases (DNMTs), including DNMT1, DNMT3A, and DNMT3B, are key DNA methylation enzymes and play important roles in gene expression regulation. Dysregulation of DNMTs is linked to various diseases and carcinogenesis, and therefore except for the two approved anticancer azanucleoside drugs, various non-nucleoside DNMT inhibitors have been identified and reported. However, the underlying mechanisms for the inhibitory activity of these non-nucleoside inhibitors still remain largely unknown. Here, we systematically tested and compared the inhibition activities of five non-nucleoside inhibitors toward the three human DNMTs. We found that harmine and nanaomycin A blocked the methyltransferase activity of DNMT3A and DNMT3B more efficiently than resveratrol, EGCG, and RG108. We further determined the crystal structure of harmine in complex with the catalytic domain of the DNMT3B-DNMT3L tetramer revealing that harmine binds at the adenine cavity of the SAM-binding pocket in DNMT3B. Our kinetics assays confirm that harmine competes with SAM to competitively inhibit DNMT3B-3L activity with a Ki of 6.6 μM. Cell-based studies further show that harmine treatment inhibits castration-resistant prostate cancer cell (CRPC) proliferation with an IC50 of ∼14 μM. The CPRC cells treated with harmine resulted in reactivating silenced hypermethylated genes compared to the untreated cells, and harmine cooperated with an androgen antagonist, bicalutamide, to effectively inhibit the proliferation of CRPC cells. Our study thus reveals, for the first time, the inhibitory mechanism of harmine on DNMTs and highlights new strategies for developing novel DNMT inhibitors for cancer treatment.

Strategies to Re-Sensitize Castration-Resistant Prostate Cancer to Antiandrogen Therapy

Since prostate cancer (PCa) was described as androgen-dependent, the androgen receptor (AR) has become the mainstay of its systemic treatment: androgen deprivation therapy (ADT). Although, through recent years, more potent drugs have been incorporated, this chronic AR signaling inhibition inevitably led the tumor to an incurable phase of castration resistance. However, in the castration-resistant status, PCa cells remain highly dependent on the AR signaling axis, and proof of it is that many men with castration-resistant prostate cancer (CRPC) still respond to newer-generation AR signaling inhibitors (ARSis). Nevertheless, this response is limited in time, and soon, the tumor develops adaptive mechanisms that make it again nonresponsive to these treatments. For this reason, researchers are focused on searching for new alternatives to control these nonresponsive tumors, such as: (1) drugs with a different mechanism of action, (2) combination therapies to boost synergies, and (3) agents or strategies to resensitize tumors to previously addressed targets. Taking advantage of the wide variety of mechanisms that promote persistent or reactivated AR signaling in CRPC, many drugs explore this last interesting behavior. In this article, we will review those strategies and drugs that are able to resensitize cancer cells to previously used treatments through the use of "hinge" treatments with the objective of obtaining an oncological benefit. Some examples are: bipolar androgen therapy (BAT) and drugs such as indomethacin, niclosamide, lapatinib, panobinostat, clomipramine, metformin, and antisense oligonucleotides. All of them have shown, in addition to an inhibitory effect on PCa, the rewarding ability to overcome acquired resistance to antiandrogenic agents in CRPC, resensitizing the tumor cells to previously used ARSis.

Combination treatment in metastatic prostate cancer: is the bar too high or have we fallen short?

Androgen deprivation therapy (ADT) alone has been the cornerstone of treatment for patients with newly diagnosed metastatic prostate cancer for the past century. Based on results from landmark trials in the past decade, combination approaches of ADT with chemotherapy or novel hormonal agents have established a new standard of care for these patients. This paradigm shift in treatment has been reflected in the updates to guideline recommendations of major professional associations. However, real-world data from around the world have highlighted the dismal adoption of combination therapy, despite evidence-based recommendations. The disparity between evidence and practice is concerning, especially with emerging evidence of survival benefit with further treatment intensification using triplet combinations (ADT, docetaxel and novel hormonal agents). Thus, a pressing need to raise awareness and call the uro-oncology community to action exists to deliver evidence-based care for these patients.

Addressing the Reciprocal Crosstalk between the AR and the PI3K/AKT/mTOR Signaling Pathways for Prostate Cancer Treatment

The reduction in androgen synthesis and the blockade of the androgen receptor (AR) function by chemical castration and AR signaling inhibitors represent the main treatment lines for the initial stages of prostate cancer. Unfortunately, resistance mechanisms ultimately develop due to alterations in the AR pathway, such as gene amplification or mutations, and also the emergence of alternative pathways that render the tumor less or, more rarely, completely independent of androgen activation. An essential oncogenic axis activated in prostate cancer is the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, as evidenced by the frequent alterations of the negative regulator phosphatase and tensin homolog (PTEN) and by the activating mutations in PI3K subunits. Additionally, crosstalk and reciprocal feedback loops between androgen signaling and the PI3K/AKT/mTOR signaling cascade that activate pro-survival signals and play an essential role in disease recurrence and progression have been evidenced. Inhibitors addressing different players of the PI3K/AKT/mTOR pathway have been evaluated in the clinic. Only a limited benefit has been reported in prostate cancer up to now due to the associated side effects, so novel combination approaches and biomarkers predictive of patient response are urgently needed. Here, we reviewed recent data on the crosstalk between AR signaling and the PI3K/AKT/mTOR pathway, the selective inhibitors identified, and the most advanced clinical studies, with a focus on combination treatments. A deeper understanding of the complex molecular mechanisms involved in disease progression and treatment resistance is essential to further guide therapeutic approaches with improved outcomes.

AR and PI3K/AKT in Prostate Cancer: A Tale of Two Interconnected Pathways

Prostate cancer (PCa) is the most common cancer in men. The androgen receptor (AR) has a pivotal role in the pathogenesis and progression of PCa. Many therapies targeting AR signaling have been developed over the years. AR signaling inhibitors (ARSIs), including androgen synthesis inhibitors and AR antagonists, have proven to be effective in castration-sensitive PCa (CSPC) and improve survival, but men with castration-resistant PCa (CRPC) continue to have a poor prognosis. Despite a good initial response, drug resistance develops in almost all patients with metastatic CRPC, and ARSIs are no longer effective. Several mechanisms confer resistance to ARSI and include AR mutations but also hyperactivation of other pathways, such as PI3K/AKT/mTOR. This pathway controls key cellular processes, including proliferation and tumor progression, and it is the most frequently deregulated pathway in human cancers. A significant interaction between AR and the PI3K/AKT/mTOR signaling pathway has been shown in PCa. This review centers on the current scene of different AR and PI3K signaling pathway inhibitors, either as monotherapy or in combination treatments in PCa, and the treatment outcomes involved in both preclinical and clinical trials. A PubMed-based literature search was conducted up to November 2022. The most relevant and recent articles were selected to provide essential information and current evidence on the crosstalk between AR and the PI3K signaling pathways. The ClinicalTrials.gov registry was used to report information about clinical studies and their results using the Advanced research tool, filtering for disease and target.

Prostate cancer small extracellular vesicles participate in androgen-independent transformation of prostate cancer by transferring let-7a-5p

Objectives

Androgen deprivation therapy (ADT) is a standard treatment for advanced prostate cancer (PCa). However, after 2-3 years ADT treatment, prostate cancer inevitably transits from androgen-dependent PCa (ADPC) to androgen-independent PCa (AIPC), which has a poor prognosis owing to its unclear mechanism and lack of effective therapeutic targets. Small extracellular vesicles (sEVs) play a vital role in the development of cancer. However, the role of PCa sEVs in the transformation of AIPC remains poorly understood.

Materials and methods

Two different cell models were employed and compared. sEVs from ADPC cells (LNCaP) and AIPC cells (LNCaP-AI + F cells) were isolated and characterized. After co-culture of LNCaP-AI + F sEVs with LNCaP cells and of LNCaP sEVs with LNCaP-AI + F cells, androgen-independent transformation was determined respectively. Mechanically, small RNA sequencing was performed. Androgen-independent transformation was examined by the upregulation and downregulation of miRNA and downstream pathways were analyzed.

Results

LNCaP-AI + F sEVs promoted the androgen-independent transformation of LNCaP cells. Interestingly, LNCaP sEVs exhibited a capacity to reverse the process.Let-7a-5p transfer was demonstrated. Furthermore, let-7a-5p overexpression promotes the androgen-independent transformation and let-7a-5p down-regulation reverses the process. Androgen receptor (AR) and PI3K/Akt pathways were identified and demonstrated by both let-7a-5p regulation and PCa sEVs coculture.

Conclusions

PCa sEVs are intimately involved in the regulation of androgen-independent transformation of prostate cancer by transferring the key sEVs molecular let-7a-5p and then activating the AR and PI3K/Akt signaling pathways. Our results provide new perspectives for the development of sEVs and sEVs molecular targeted treatment approaches for AIPC patients.

Pharmacological Optimization of PSMA-Based Radioligand Therapy

Prostate cancer (PCa) is the most common malignancy in men of middle and older age. The standard treatment strategy for PCa ranges from active surveillance in low-grade, localized PCa to radical prostatectomy, external beam radiation therapy, hormonal treatment and chemotherapy. Recently, the use of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) for metastatic castration-resistant PCa has been approved. PSMA is predominantly, but not exclusively, expressed on PCa cells. Because of its high expression in PCa, PSMA is a promising target for diagnostics and therapy. To understand the currently used RLT, knowledge about pharmacokinetics (PK) and pharmacodynamics (PD) of the PSMA ligand and the PSMA protein itself is crucial. PK and PD properties of the ligand and its target determine the duration and extent of the effect. Knowledge on the concentration-time profile, the target affinity and target abundance may help to predict the effect of RLT. Increased specific binding of radioligands to PSMA on PCa cells may be associated with better treatment response, where nonspecific binding may increase the risk of toxicity in healthy organs. Optimization of the radioligand, as well as synergistic effects of concomitant agents and an improved dosing strategy, may lead to more individualized treatment and better overall survival.

Co-Targeting ErbB Receptors and the PI3K/AKT Axis in Androgen-Independent Taxane-Sensitive and Taxane-Resistant Human Prostate Cancer Cells

Simple Summary

Advanced prostate cancer that has progressed after standard therapies such as hormone therapy and taxane-based chemotherapies is an invariably lethal disease state with limited treatment options. There remains an important need to continue to identify new treatment approaches for such patients. We used two cell culture models of prostate cancer that are resistant to hormonal therapy and chemotherapy, and which also manifest some characteristics that are often associated with advanced prostate cancer, such as neuroendocrine differentiation, to evaluate the potential anti-cancer effects of targeting the key molecules, ErbB receptors and AKT. Using several complementary approaches, we found that the concurrent targeting of ErbB receptors and AKT with specific inhibitors was more effective than targeting each of them individually, independent of the underlying molecular characteristics or relative degrees of resistance to the taxanes that defined the prostate cancer models that were studied. Enhanced anti-tumor responses occurred both in vitro and in vivo with dual targeting, with the consistent inhibition particularly of AKT occurring in both settings. These studies provide a framework to evaluate the role of signal pathway modulation as a potential therapeutic strategy in treatment-refractory prostate cancer.

Abstract

Using two representative models of androgen-independent prostate cancer (PCa), PC3 and DU145, and their respective paclitaxel- and docetaxel-resistant derivatives, we explored the anti-tumor activity of targeting the ErbB receptors and AKT using small-molecule kinase inhibitors. These cells manifest varying degrees of neuroendocrine differentiation characteristics and differ in their expression of functional PTEN. Although the specific downstream signaling events post the ErbB receptor and AKT co-targeting varied between the PC3- and DU145-lineage cells, synergistic anti-proliferative and enhanced pro-apoptotic responses occurred across the wild-type and the taxane-resistant cells, independent of their basal AKT activation state, their degree of paclitaxel- or docetaxel-resistance, or whether this resistance was mediated by the ATP Binding Cassette transport proteins. Dual targeting also led to enhanced anti-tumor responses in vivo, although there was pharmacodynamic discordance between the PCa cells in culture versus the tumor xenografts in terms of the relative activation and inhibition states of AKT and ERK under basal conditions and upon AKT and/or ErbB targeting. The consistent inhibition, particularly of AKT, occurred both in vitro and in vivo, independent of the underlying PTEN status. Thus, co-targeting AKT with ErbB, and possibly other partners, may be a useful strategy to explore further for potential therapeutic effect in advanced PCa.

Advances in the Current Understanding of the Mechanisms Governing the Acquisition of Castration-Resistant Prostate Cancer

Despite aggressive treatment and androgen-deprivation therapy, most prostate cancer patients ultimately develop castration-resistant prostate cancer (CRPC), which is associated with high mortality rates. However, the mechanisms governing the development of CRPC are poorly understood, and androgen receptor (AR) signaling has been shown to be important in CRPC through AR gene mutations, gene overexpression, co-regulatory factors, AR shear variants, and androgen resynthesis. A growing number of non-AR pathways have also been shown to influence the CRPC progression, including the Wnt and Hh pathways. Moreover, non-coding RNAs have been identified as important regulators of the CRPC pathogenesis. The present review provides an overview of the relevant literature pertaining to the mechanisms governing the molecular acquisition of castration resistance in prostate cancer, providing a foundation for future, targeted therapeutic efforts.

Functional roles of E3 ubiquitin ligases in prostate cancer

Prostate cancer (PCa) is a malignant epithelial tumor of the prostate gland with a high male cancer incidence. Numerous studies indicate that abnormal function of ubiquitin-proteasome system (UPS) is associated with the progression and metastasis of PCa. E3 ubiquitin ligases, key components of UPS, determine the specificity of substrates, and substantial advances of E3 ubiquitin ligases have been reached recently. Herein, we introduce the structures and functions of E3 ubiquitin ligases and summarize the mechanisms of E3 ubiquitin ligases-related PCa signaling pathways. In addition, some progresses in the development of inhibitors targeting E3 ubiquitin ligases are also included.

From Therapy Resistance to Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second most common malignancy among men worldwide. Although early-stage disease is curable, advanced stage PCa is mostly incurable and eventually becomes resistant to standard therapeutic options. Different genetic and epigenetic alterations are associated with the development of therapy resistant PCa, with specific players being particularly involved in this process. Therefore, identification and targeting of these molecules with selective inhibitors might result in anti-tumoral effects. Herein, we describe the mechanisms underlying therapy resistance in PCa, focusing on the most relevant molecules, aiming to enlighten the current state of targeted therapies in PCa. We suggest that selective drug targeting, either alone or in combination with standard treatment options, might improve therapeutic sensitivity of resistant PCa. Moreover, an individualized analysis of tumor biology in each PCa patient might improve treatment selection and therapeutic response, enabling better disease management.

"The emerging role of capivasertib in breast cancer"

Over 50% of breast tumors harbor alterations in one or more genes of the phosphatidylinositol 3-kinase (PI3K) pathway including PIK3CA mutations (31%), PTEN loss (34%), PTEN mutations (5%) and AKT1 mutations (3%). While PI3K and mTOR inhibitors are already approved in advanced breast cancer, AKT inhibitors have been recently developed as a new therapeutic approach. Capivasertib (AZD5363) is a novel, selective ATP-competitive pan-AKT kinase inhibitor that exerts similar activity against the three AKT isoforms, AKT1, AKT2, and AKT3. Preclinical studies demonstrated efficacy of capivasertib in breast cancer cell lines as a single agent or in combination with anti-HER2 agents and endocrine treatment, especially in tumors with PIK3CA or MTOR alterations. Phase I/II studies demonstrated greater efficacy when capivasertib was co-administered with paclitaxel, fulvestrant in hormone receptor (HR)-positive, HER2-negative breast cancer or olaparib. The recommended phase II dose of capivasertib as monotherapy was 480 mg bid on a 4-days-on, 3-days-off dosing schedule. Toxicity profile proved to be manageable with hyperglycemia (20–24%), diarrhea (14–17%) and maculopapular rash (11–16%) being the most common grade ≥3 adverse events. Ongoing Phase III trials of capivasertib in combination with fulvestrant (CAPItello-291), CDK4/6 inhibitor palbociclib (CAPItello-292) and paclitaxel (CAPItello- 290) will better clarify the therapeutic role of capivasertib in breast cancer.

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Phosphatidylinositol-3-kinase (PI3K)/Akt (PI3K/AKT) pathway is one of the most commonly altered pathways in breast cancer.

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Capivasertib (AZD5363) is a highly potent Akt kinase inhibitor with activity against the three isoforms AKT1, AKT2, and AKT3.

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Preclinical studies demonstrated efficacy of capivasertib either alone or in combination with anti-HER2 agents, chemotherapy and endocrine treatment.

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Dose-limiting toxicities include hyperglycemia (20–24%), diarrhea (14–17%) and maculopapular rash (11–16%).

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Capivasertib increased susceptibility to paclitaxel (PAKT, BEECH), fulvestrant (NCT01226316, FAKTION) or Olaparib (ComPAKT).

The androgen receptor is a therapeutic target in desmoplastic small round cell sarcoma

Desmoplastic small round cell tumor (DSRCT) is an aggressive, usually incurable sarcoma subtype that predominantly occurs in post-pubertal young males. Recent evidence suggests that the androgen receptor (AR) can promote tumor progression in DSRCTs. However, the mechanism of AR-induced oncogenic stimulation remains undetermined. Herein, we demonstrate that enzalutamide and AR-directed antisense oligonucleotides (AR-ASO) block 5α-dihydrotestosterone (DHT)-induced DSRCT cell proliferation and reduce xenograft tumor burden. Gene expression analysis and chromatin immunoprecipitation sequencing (ChIP-seq) were performed to elucidate how AR signaling regulates cellular epigenetic programs. Remarkably, ChIP-seq revealed novel DSRCT-specific AR DNA binding sites adjacent to key oncogenic regulators, including WT1 (the C-terminal partner of the pathognomonic fusion protein) and FOXF1. Additionally, AR occupied enhancer sites that regulate the Wnt pathway, neural differentiation, and embryonic organ development, implicating AR in dysfunctional cell lineage commitment. Our findings have direct clinical implications given the widespread availability of FDA-approved androgen-targeted agents used for prostate cancer.

Androgen receptor can promote tumour progression in desmoplastic small round cell tumour (DSRCT), an aggressive paediatric malignancy that predominantly affects young males. Here, the authors show that DSRCT is an AR-driven malignancy and sensitive to androgen deprivation therapy

Phase Ib/II Study of Enzalutamide with Samotolisib (LY3023414) or Placebo in Patients with Metastatic Castration-Resistant Prostate Cancer

PURPOSE

To report efficacy and safety of samotolisib (LY3023414; PI3K/mTOR dual kinase and DNA-dependent protein kinase inhibitor) plus enzalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC) following cancer progression on abiraterone.

PATIENTS AND METHODS

In this double-blind, placebo-controlled phase Ib/II study (NCT02407054), following a lead-in segment for evaluating safety and pharmacokinetics of samotolisib and enzalutamide combination, patients with advanced castration-resistant prostate cancer with progression on prior abiraterone were randomized to receive enzalutamide (160 mg daily)/samotolisib (200 mg twice daily) or placebo. Primary endpoint was progression-free survival (PFS) assessed by Prostate Cancer Clinical Trials Working Group criteria (PCWG2). Secondary and exploratory endpoints included radiographic PFS (rPFS) and biomarkers, respectively. Log-rank tests assessed treatment group differences.

RESULTS

Overall, 13 and 129 patients were enrolled in phase Ib and II, respectively. Dose-limiting toxicity was not reported in patients during phase Ib and mean samotolisib exposures remained in the targeted range despite a 35% decrease when administered with enzalutamide. In phase II, median PCWG2-PFS and rPFS was significantly longer in the samotolisib/enzalutamide versus placebo/enzalutamide arm (3.8 vs. 2.8 months; P = 0.003 and 10.2 vs. 5.5 months; P = 0.03), respectively. Patients without androgen receptor splice variant 7 showed a significant and clinically meaningful rPFS benefit in the samotolisib/enzalutamide versus placebo/enzalutamide arm (13.2 months vs. 5.3 months; P = 0.03).

CONCLUSIONS

Samotolisib/enzalutamide has tolerable side effects and significantly improved PFS in patients with mCRPC with cancer progression on abiraterone, and this may be enriched in patients with PTEN intact and no androgen receptor splice variant 7.

Studying molecular signaling in major angiogenic diseases

The growth of blood vessels from already existing vasculature is angiogenesis and it is one of the fundamental processes in fetal development, tissue damage or repair, and the reproductive cycle. In a healthy person, angiogenesis is regulated by the balance between pro- and anti-angiogenic factors. However, when the balance is disturbed, it results in various diseases or disorders. The angiogenesis pathway is a sequential cascade and differs based on the stimuli. Therefore, targeting one of the factors involved in the process can help us find a therapeutic strategy to treat irregular angiogenesis. In the past three decades of cancer research, angiogenesis has been at its peak, where an anti-angiogenic agent inhibiting vascular endothelial growth factor acts as a promising substance to treat cancer. In addition, cancer can be assessed based on the expression of angiogenic factors and its response to therapies. Angiogenesis is important for all tissues, which might be normal or pathologically changed and occur through ages. In clinical therapeutics, target therapy focusing on discovery of novel anti-angiogenic agents like bevacizumab, cetuximab, sunitinib, imatinib, lenvatinib, thalidomide, everolimus etc., to block or inhibit the angiogenesis pathway is well explored in recent times. In this review, we will discuss about the molecular signaling pathways involved in major angiogenic diseases in detail.

RUVBL1 promotes enzalutamide resistance of prostate tumors through the PLXNA1-CRAF-MAPK pathway

Although enzalutamide improves the overall survival of patients with metastatic prostate cancers, enzalutamide resistance (ENZR) will be inevitably developed. Emerging evidence support that alternative oncogenic pathways may bypass the androgen receptor (AR) signaling to promote ENZR progression, however, the underpinning mechanisms remain poorly defined. Here, we report that the expression of RuvB like AAA ATPase 1 (RUVBL1) is upregulated in ENZR cells and xenograft models and prostate tumors in patients. Enzalutamide increases RUVBL1 accumulation in the cytoplasm, which in turn enhances the recruitment of CRAF proto-oncogene serine/threonine kinase protein to plexin A1 (PLXNA1) and the subsequent activation of the downstream MAPK pathway. Co-overexpression of RUVBL1 and PLXNA1 defines a subgroup of prostate cancer (PCa) patients with a poor prognosis. Furthermore, pharmacological inhibition of RUVBL1 by CB-6644 suppresses ENZR cell proliferation and xenograft growth and allows re-sensitization of ENZR cells and xenografts to enzalutamide, indicating that RUVBL1 may act to substitute the AR signaling to promote cancer cell survival and ENZR development. Together, these findings may lead to the identification of RUVBL1 as a potential therapeutic target for ENZR tumors.

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

Background:

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

Objective:

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

Methods:

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

Results:

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

Conclusions:

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

Level of evidence:

Not applicable

Choosing Kinase Inhibitors for Androgen Deprivation Therapy-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) is a systemic therapy for advanced prostate cancer (PCa). Although most patients initially respond to ADT, almost all cancers eventually develop castration resistance. Castration-resistant PCa (CRPC) is associated with a very poor prognosis, and the treatment of which is a serious clinical challenge. Accumulating evidence suggests that abnormal expression and activation of various kinases are associated with the emergence and maintenance of CRPC. Many efforts have been made to develop small molecule inhibitors to target the key kinases in CRPC. These inhibitors are designed to suppress the kinase activity or interrupt kinase-mediated signal pathways that are associated with PCa androgen-independent (AI) growth and CRPC development. In this review, we briefly summarize the roles of the kinases that are abnormally expressed and/or activated in CRPC and the recent advances in the development of small molecule inhibitors that target kinases for the treatment of CRPC.

Systemic Triple Therapy in Metastatic Hormone-Sensitive Prostate Cancer (mHSPC): Ready for Prime Time or Still to Be Explored?

For decades, mono androgen deprivation therapy (ADT) has been the gold standard for metastatic hormone-sensitive prostate cancer (mHSPC) treatment. Several studies have been published within the last seven years demonstrating a significant survival advantage by combination treatment with standard ADT plus docetaxel or androgen receptor-axis-targeted therapy (ARAT) compared to ADT monotherapy. As a result, overall survival can be prolonged by at least 18 months. Recently published congress data of the PEACE-1 study suggests that in the future, triple therapy might be the new gold standard. In addition to this study, which has shown that triple treatment with standard ADT plus docetaxel plus abiraterone is superior to standard ADT plus docetaxel, several other phase III triple therapy studies are currently ongoing. The different modes of action that are investigated reach from AR-targeting over mitotic inhibition and immunotherapy to PARP and AKT inhibition. In this review we will explore if triple therapy has the potential to be the new standard for mHSPC treatment in the near future.

Androgen Receptor Signaling in Prostate Cancer and Therapeutic Strategies

Understanding of the molecular mechanisms of prostate cancer has led to development of therapeutic strategies targeting androgen receptor (AR). These androgen-receptor signaling inhibitors (ARSI) include androgen synthesis inhibitor-abiraterone and androgen receptor antagonists-enzalutamide, apalutamide, and darolutamide. Although these medications provide significant improvement in survival among men with prostate cancer, drug resistance develops in nearly all patients with time. This could be through androgen-dependent or androgen-independent mechanisms. Even weaker signals and non-canonical steroid ligands can activate AR in the presence of truncated AR-splice variants, AR overexpression, or activating mutations in AR. AR splice variant, AR-V7 is the most studied among these and is not targeted by available ARSIs. Non-androgen receptor dependent resistance mechanisms are mediated by activation of an alternative signaling pathway when AR is inhibited. DNA repair pathway, PI3K/AKT/mTOR pathway, BRAF-MAPK and Wnt signaling pathway and activation by glucocorticoid receptors can restore downstream signaling in prostate cancer by alternative proteins. Multiple clinical trials are underway exploring therapeutic strategies to overcome these resistance mechanisms.

Role of PI3K-AKT-mTOR Pathway as a Pro-Survival Signaling and Resistance-Mediating Mechanism to Therapy of Prostate Cancer

Androgen deprivation therapy (ADT) and androgen receptor (AR)-targeted therapy are the gold standard options for treating prostate cancer (PCa). These are initially effective, as localized and the early stage of metastatic disease are androgen- and castration-sensitive. The tumor strongly relies on systemic/circulating androgens for activating AR signaling to stimulate growth and progression. However, after a certain point, the tumor will eventually develop a resistant stage, where ADT and AR antagonists are no longer effective. Mechanistically, it seems that the tumor becomes more aggressive through adaptive responses, relies more on alternative activated pathways, and is less dependent on AR signaling. This includes hyperactivation of PI3K-AKT-mTOR pathway, which is a central signal that regulates cell pro-survival/anti-apoptotic pathways, thus, compensating the blockade of AR signaling. The PI3K-AKT-mTOR pathway is well-documented for its crosstalk between genomic and non-genomic AR signaling, as well as other signaling cascades. Such a reciprocal feedback loop makes it more complicated to target individual factor/signaling for treating PCa. Here, we highlight the role of PI3K-AKT-mTOR signaling as a resistance mechanism for PCa therapy and illustrate the transition of prostate tumor from AR signaling-dependent to PI3K-AKT-mTOR pathway-dependent. Moreover, therapeutic strategies with inhibitors targeting the PI3K-AKT-mTOR signal used in clinic and ongoing clinical trials are discussed.

Undesirable Status of Prostate Cancer Cells after Intensive Inhibition of AR Signaling: Post-AR Era of CRPC Treatment

Recent advances in prostate cancer (PC) research unveiled real androgen receptor (AR) functions in castration-resistant PC (CRPC). Moreover, AR still accelerates PC cell proliferation via the activation of several mechanisms (e.g., mutation, variants, and amplifications in CRPC). New-generation AR signaling-targeted agents, inhibiting extremely the activity of AR, were developed based on these incontrovertible mechanisms of AR-induced CRPC progression. However, long-term administration of AR signaling-targeted agents subsequently induces the major problem that AR (complete)-independent CRPC cells present neither AR nor prostate-specific antigen, including neuroendocrine differentiation as a subtype of AR-independent CRPC. Moreover, there are few treatments effective for AR-independent CRPC with solid evidence. This study focuses on the transformation mechanisms of AR-independent from AR-dependent CRPC cells and potential treatment strategy for AR-independent CRPC and discusses them based on a review of basic and clinical literature.

Targeting Feedforward Loops Formed by Nuclear Receptor RORγ and Kinase PBK in mCRPC with Hyperactive AR Signaling

Metastatic castration-resistant prostate cancer (mCRPC) is a highly aggressive disease with few therapeutic options. Hyperactive androgen receptor (AR) signaling plays a key role in CRPC progression. Previously, we identified RAR-related orphan receptor gamma (RORγ) as a novel key driver of AR gene overexpression and increased AR signaling. We report here that several RORγ antagonists/inverse agonists including XY018 and compound 31 were orally effective in potent inhibition of the growth of tumor models including patient-derived xenograft (PDX) tumors. RORγ controls the expression of multiple aggressive-tumor gene programs including those of epithelial-mesenchymal transition (EMT) and invasion. We found that PDZ binding kinase (PBK), a serine/threonine kinase, is a downstream target of RORγ that exerts the cellular effects. Alterations of RORγ expression or function significantly downregulated the mRNA and protein level of PBK. Our further analyses demonstrated that elevated PBK associates with and stabilizes RORγ and AR proteins, thus constituting novel, interlocked feed-forward loops in hyperactive AR and RORγ signaling. Indeed, dual inhibition of RORγ and PBK synergistically inhibited the expression and function of RORγ, AR, and AR-V7, and the growth and survival of CRPC cells. Therefore, our study provided a promising, new strategy for treatment of advanced forms of prostate cancer.

Androgen Receptor-Dependent Mechanisms Mediating Drug Resistance in Prostate Cancer

Androgen receptor (AR) is a main driver of prostate cancer (PCa) growth and progression as well as the key drug target. Appropriate PCa treatments differ depending on the stage of cancer at diagnosis. Although androgen deprivation therapy (ADT) of PCa is initially effective, eventually tumors develop resistance to the drug within 2-3 years of treatment onset leading to castration resistant PCa (CRPC). Castration resistance is usually mediated by reactivation of AR signaling. Eventually, PCa develops additional resistance towards treatment with AR antagonists that occur regularly, also mostly due to bypass mechanisms that activate AR signaling. This tumor evolution with selection upon therapy is presumably based on a high degree of tumor heterogenicity and plasticity that allows PCa cells to proliferate and develop adaptive signaling to the treatment and evolve pathways in therapy resistance, including resistance to chemotherapy. The therapy-resistant PCa phenotype is associated with more aggressiveness and increased metastatic ability. By far, drug resistance remains a major cause of PCa treatment failure and lethality. In this review, various acquired and intrinsic mechanisms that are AR‑dependent and contribute to PCa drug resistance will be discussed.

Optimal treatment sequencing of abiraterone acetate plus prednisone and enzalutamide in patients with castration-resistant metastatic prostate cancer: A systematic review and meta-analysis

PURPOSE

To evaluate the impact of the hormonal treatment sequencing including abiraterone acetate plus prednisone (AAP) and enzalutamide (ENZ) in mCRPC, and determine which sequence provides more benefits for patients.

METHODS

Studies published in English between 1 January 2013 and 30 September 2017 were identified in PubMed and EMBASE electronic databases. Studies assessing the efficacy of treatment sequences, based on AAP and ENZ, in mCRPC patients, were eligible for analysis.

RESULTS

Seventeen studies met the inclusion criteria. Two assessed both treatment sequences AAP → ENZ and ENZ → AAP; it was found that sequence of AAP → ENZ showed a statistically significantly longer PSA-PFS than the observed in ENZ → AAP (pooled HR: 0,54; 95% CI; 0,36-0,82; p < 0,05). The nine studies analysing Doc → AAP → ENZ sequence, revealed favourable results in terms of PFS. The 5 studies which analysed AAP → ENZ sequence, show a decrease in PSA levels ≥ 50% in 11-41% of patients treated with enzalutamide after previous treatment with AAP. In the two studies that analysed the Doc → ENZ → AAP sequence, PSA response rates were much lower than those reported with Doc → AAP → ENZ, with decreases in PSA ≥ 30 of 3-18% and PSA ≥ 50 of 8-11%.

CONCLUSION

Significant clinical efficacy of AAP administered as the first-line treatment in mCRPC patients followed by enzalutamide, delaying disease progression, compared with the ENZ → AAP sequence. However, more studies and randomized trials are needed, to validate the best treatment sequencing.

Revisiting prostate cancer metabolism: From metabolites to disease and therapy

Prostate cancer (PCa), one of the most commonly diagnosed cancers worldwide, still presents important unmet clinical needs concerning treatment. In the last years, the metabolic reprogramming and the specificities of tumor cells emerged as an exciting field for cancer therapy. The unique features of PCa cells metabolism, and the activation of specific metabolic pathways, propelled the use of metabolic inhibitors for treatment. The present work revises the knowledge of PCa metabolism and the metabolic alterations that underlie the development and progression of the disease. A focus is given to the role of bioenergetic sources, namely, glucose, lipids, and glutamine sustaining PCa cell survival and growth. Moreover, it is described as the action of oncogenes/tumor suppressors and sex steroid hormones in the metabolic reprogramming of PCa. Finally, the status of PCa treatment based on the inhibition of metabolic pathways is presented. Globally, this review updates the landscape of PCa metabolism, highlighting the critical metabolic alterations that could have a clinical and therapeutic interest.

Imipramine Inhibits Migration and Invasion in Metastatic Castration-Resistant Prostate Cancer PC-3 Cells via AKT-Mediated NF-κB Signaling Pathway

Imipramine (IMI) is a tricyclic synthetic antidepressant that is used to treat chronic psychiatric disorders, including depression and neuropathic pain. IMI also has inhibitory effects against various cancer types, including prostate cancer; however, the mechanism of its anticancer activity is not well understood. In the present study, we investigated the antimetastatic and anti-invasive effects of IMI in metastatic castration-resistant prostate cancer PC-3 cells, with an emphasis on the serine/threonine protein kinase AKT-mediated nuclear factor kappa B (NF-κB) signaling pathway. While IMI did not induce cell death, it attenuated PC-3 cell proliferation. According to the wound healing assay and invasion assay, migration and invasion in PC-3 cells were significantly inhibited by IMI in a dose-dependent manner. IMI significantly downregulated p-AKT protein expression but upregulated phospho-extracellular signal-regulated kinase (ERK1)/2 protein expression levels. Furthermore, IMI treatment resulted in decreased AKT-mediated downstream signaling, including p-inhibitor of κB kinase (IKK)α/β, p-inhibitor of κB (IκBα), and p-p65. Inhibited NF-κB signaling reduced the secretion of several proinflammatory cytokines and chemokine by PC-3 cells. Overall, our study explored the negative correlation between the use of antidepressants and prostate cancer progression, showing that IMI attenuated cell viability, migration, and invasion of PC-3 cells by suppressing the expression of AKT and NF-κB-related signaling proteins and secretion of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and monocyte chemoattractant protein-1 (MCP-1).

Brassicasterol from Edible Aquacultural Hippocampus abdominalis Exerts an Anti-Cancer Effect by Dual-Targeting AKT and AR Signaling in Prostate Cancer

In the Compendium of Materia Medica, seahorse (Hippocampus) is considered effective for the reinforcement of kidney and men’s health. However, the role of seahorse on human health lacks scientific evidence. Therefore, we evaluated the effect of seahorse on human prostate cancer using various in vitro methods and identified bioactive compound. Seahorse lipid extract (SHL) decreased androgen receptor (AR) and prostate-specific antigen (PSA) expression in dihydrotestosterone (DHT)-induced LNCaP cells of prostate cancer. Gas Chromatography (GC)-mass spectrometry data showed that brassicasterol was present in H. abdominalis. Brassicasterol downregulated the expression of AR and PSA in DHT-induced LNCaP cells. Brassicasterol induced apoptosis accompanied by sub-G1 phase arrest and inhibited migration in LNCaP cells. We confirmed that AKT and AR mediated the anti-cancer effect of brassicasterol using siRNA transfection. Brassicasterol exerts an anti-cancer effect in AR-independent cancer as well as in AR-dependent cells by AKT inhibiting. Our findings suggest that SHL has the anticancer potential via inhibition of AR and demonstrated that brassicasterol from H. abdominalis exerted an anti-cancer effect by dual-targeting AKT and AR signaling in prostate cancer.

Resistance to second generation antiandrogens in prostate cancer: pathways and mechanisms

Androgen deprivation therapy targeting the androgens/androgen receptor (AR) signaling continues to be the mainstay treatment of advanced-stage prostate cancer. The use of second-generation antiandrogens, such as abiraterone acetate and enzalutamide, has improved the survival of prostate cancer patients; however, a majority of these patients progress to castration-resistant prostate cancer (CRPC). The mechanisms of resistance to antiandrogen treatments are complex, including specific mutations, alternative splicing, and amplification of oncogenic proteins resulting in dysregulation of various signaling pathways. In this review, we focus on the major mechanisms of acquired resistance to second generation antiandrogens, including AR-dependent and AR-independent resistance mechanisms as well as other resistance mechanisms leading to CRPC emergence. Evolving knowledge of resistance mechanisms to AR targeted treatments will lead to additional research on designing more effective therapies for advanced-stage prostate cancer.

Overcoming the mechanisms of primary and acquired resistance to new generation hormonal therapies in advanced prostate cancer: focus on androgen receptor independent pathways

In recent years, many therapeutic advances have been made in the management of castration-resistant prostate cancer, with the development and approval of many new drugs. The androgen receptor (AR) is the main driver in prostate cancer growth and progression and the most effective therapeutic agents are still directed against this pathway. Among these, new generation hormonal agents (NHA) including enzalutamide, abiraterone acetate, apalutamide, and darolutamide have shown to improve overall survival and quality of life of prostate cancer patients. Unfortunately, despite the demonstrated benefit, not all patients respond to treatment and almost all are destined to develop a resistant phenotype. Although the resistance mechanisms are not fully understood, the most studied ones include the activation of both dependent and independent AR signalling pathways. Recent findings about multiple growth-promoting and survival pathways in advanced prostate cancer suggest the presence of alternative mechanisms involved in disease progression, and an interplay between these pathways and AR signalling. In this review we discuss the possible mechanisms of primary and acquired resistance to NHA with a focus on AR independent pathways.

Dual targeting of EZH2 and androgen receptor as a novel therapy for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) emerges after androgen withdrawal therapy and remains incurable due to the lack of effective treatment protocols. Treatment with enzalutamide, a second generation androgen receptor (AR) antagonist, offers an initial response followed by drug resistance and tumor relapse. Enhancer of zeste homolog 2 (EZH2), a member of PRC2 complex, is an important target that acts as a coactivator of AR-mediated gene suppression whose oncogenic activity increases during castration. We hypothesize that dual targeting of EZH2 and AR could be highly effective in CRPC treatment. The present study aimed to examine the effectiveness of combination using EZH2 inhibitor GSK126 with antiandrogen enzalutamide in the treatment of CRPC cells. Treatment of 22Rv1 and C42B CRPC cells with a combination of GSK126 and enzalutamide led to synergistic inhibition of cell proliferation, cell cycle arrest and marked increase in cell death. Mechanistically, this combination treatment significantly reduced expression of AR and AR-v7, decrease in PSA and Akt activity, diminution of EZH2 and other members of PCR2 complex including SUZ12 and EED, with simultaneous loss of H3K27 trimethylation and dissociation between AR and PRC2 complex members compared to individual treatment. This study provides preclinical proof-of-concept that combined treatment of EZH2 inhibitor with AR antagonist results in synergistic anticancer effects opening new possibilities for treatment of CRPC tumors.

Cellular growth factors as prospective therapeutic targets for combination therapy in androgen independent prostate cancer (AIPC)

Cancer is the second leading cause of death worldwide, with prostate cancer, the second most commonly diagnosed cancer among men. Prostate cancer develops in the peripheral zone of the prostate gland, and the initial progression largely depends on androgens, the male reproductive hormone that regulates the growth and development of the prostate gland and testis. The currently available treatments for androgen dependent prostate cancer are, however, effective for a limited period, where the patients show disease relapse, and develop androgen-independent prostate cancer (AIPC). Studies have shown various intricate cellular processes such as, deregulation in multiple biochemical and signaling pathways, intra-tumoral androgen synthesis; AR over-expression and mutations and AR activation via alternative growth pathways are involved in progression of AIPC. The currently approved treatment strategies target a single cellular protein or pathway, where the cells slowly develop resistance and adapt to proliferate via other cellular pathways over a period of time. Therefore, an increased research aims to understand the efficacy of combination therapy, which targets multiple interlinked pathways responsible for acquisition of resistance and survival. The combination therapy is also shown to enhance efficacy as well as reduce toxicity of the drugs. Thus, the present review focuses on the signaling pathways involved in the progression of AIPC, comprising a heterogeneous population of cells and the advantages of combination therapy. Several clinical and pre-clinical studies on a variety of combination treatments have shown beneficial outcomes, yet further research is needed to understand the potential of combination therapy and its diverse strategies.

The PI3K-AKT-mTOR Pathway and Prostate Cancer: At the Crossroads of AR, MAPK, and WNT Signaling

Oncogenic activation of the phosphatidylinositol-3-kinase (PI3K), protein kinase B (PKB/AKT), and mammalian target of rapamycin (mTOR) pathway is a frequent event in prostate cancer that facilitates tumor formation, disease progression and therapeutic resistance. Recent discoveries indicate that the complex crosstalk between the PI3K-AKT-mTOR pathway and multiple interacting cell signaling cascades can further promote prostate cancer progression and influence the sensitivity of prostate cancer cells to PI3K-AKT-mTOR-targeted therapies being explored in the clinic, as well as standard treatment approaches such as androgen-deprivation therapy (ADT). However, the full extent of the PI3K-AKT-mTOR signaling network during prostate tumorigenesis, invasive progression and disease recurrence remains to be determined. In this review, we outline the emerging diversity of the genetic alterations that lead to activated PI3K-AKT-mTOR signaling in prostate cancer, and discuss new mechanistic insights into the interplay between the PI3K-AKT-mTOR pathway and several key interacting oncogenic signaling cascades that can cooperate to facilitate prostate cancer growth and drug-resistance, specifically the androgen receptor (AR), mitogen-activated protein kinase (MAPK), and WNT signaling cascades. Ultimately, deepening our understanding of the broader PI3K-AKT-mTOR signaling network is crucial to aid patient stratification for PI3K-AKT-mTOR pathway-directed therapies, and to discover new therapeutic approaches for prostate cancer that improve patient outcome.

Androgen receptor-induced integrin α6β1 and Bnip3 promote survival and resistance to PI3K inhibitors in castration-resistant prostate cancer

The androgen receptor (AR) is the major driver of prostate cancer growth and survival. However, almost all patients relapse with castration resistant disease (CRPC) when treated with anti-androgen therapy. In CRPC, AR is often aberrantly activated independent of androgen. Targeting survival pathways downstream of AR could be a viable strategy to overcome CRPC. Surprisingly, little is known about how AR drives prostate cancer survival. Furthermore, CRPC tumors in which Pten is lost are also resistant to eradication by PI3K inhibitors. We sought to identify the mechanism by which AR drives tumor survival in CRPC to identify ways to overcome resistance to PI3K inhibition. We found that integrin α6β1 and Bnip3 are selectively elevated in CRPC downstream of AR. While integrin α6 promotes survival and is a direct transcriptional target of AR, the ability of AR to induce Bnip3 is dependent on adhesion to laminin and integrin α6β1-dependent nuclear translocation of HIF1α. Integrin α6β1 and Bnip3 were found to promote survival of CRPC cells selectively on laminin through the induction of autophagy and mitophagy. Furthermore, blocking Bnip3 or integrin α6β1 restored sensitivity to PI3K inhibitors in Pten-negative CRPC. We identified an AR driven pathway that cooperates with laminin and hypoxia to drive resistance to PI3K inhibitors. These findings can help explain in part why PI3K inhibitors have failed in clinical trials to overcome AR-dependent CRPC.

TBCRC 032 IB/II Multicenter Study: Molecular Insights to AR Antagonist and PI3K Inhibitor Efficacy in Patients with AR+ Metastatic Triple-Negative Breast Cancer

PURPOSE

Preclinical data demonstrating androgen receptor (AR)-positive (AR+) triple-negative breast cancer (TNBC) cells are sensitive to AR antagonists, and PI3K inhibition catalyzed an investigator-initiated, multi-institutional phase Ib/II study TBCRC032. The trial investigated the safety and efficacy of the AR-antagonist enzalutamide alone or in combination with the PI3K inhibitor taselisib in patients with metastatic AR+ (≥10%) breast cancer.

PATIENTS AND METHODS

Phase Ib patients [estrogen receptor positive (ER+) or TNBC] with AR+ breast cancer received 160 mg enzalutamide in combination with taselisib to determine dose-limiting toxicities and the maximum tolerated dose (MTD). Phase II TNBC patients were randomized to receive either enzalutamide alone or in combination with 4 mg taselisib until disease progression. Primary endpoint was clinical benefit rate (CBR) at 16 weeks.

RESULTS

The combination was tolerated, and the MTD was not reached. The adverse events were hyperglycemia and skin rash. Overall, CBR for evaluable patients receiving the combination was 35.7%, and median progression-free survival (PFS) was 3.4 months. Luminal AR (LAR) TNBC subtype patients trended toward better response compared with non-LAR (75.0% vs. 12.5%, P = 0.06), and increased PFS (4.6 vs. 2.0 months, P = 0.082). Genomic analyses revealed subtype-specific treatment response, and novel FGFR2 fusions and AR splice variants.

CONCLUSIONS

The combination of enzalutamide and taselisib increased CBR in TNBC patients with AR+ tumors. Correlative analyses suggest AR protein expression alone is insufficient for identifying patients with AR-dependent tumors and knowledge of tumor LAR subtype and AR splice variants may identify patients more or less likely to benefit from AR antagonists.

Deregulated PTEN/PI3K/AKT/mTOR signaling in prostate cancer: Still a potential druggable target?

Although the prognosis of patients with localized prostate cancer is good after surgery, with a favorable response to androgen deprivation therapy, about one third of them invariably relapse, and progress to castration-resistant prostate cancer. Overall, prostate cancer therapies remain scarcely effective, thus it is mandatory to devise alternative treatments enhancing the efficacy of surgical castration and hormone administration. Dysregulation of the phosphoinositide 3-kinase pathway has attracted growing attention in prostate cancer due to the highly frequent association of epigenetic and post-translational modifications as well as to genetic alterations of both phosphoinositide 3-kinase and PTEN to onset and/or progression of this malignancy, and to resistance to canonical androgen-deprivation therapy. Here we provide a summary of the biological functions of the major players of this cascade and their deregulation in prostate cancer, summarizing the results of preclinical and clinical studies with PI3K signaling inhibitors and the reasons of failure independent from genomic changes.

Exendin-4 enhances the sensitivity of prostate cancer to enzalutamide by targeting Akt activation

BACKGROUND

Glucagon-like peptide 1 (GLP-1) and its analogs are first-line choices for the treatment of type 2 diabetes mellitus. Recent studies have shown that they exhibit antitumor properties in some tumors. We previously found that a GLP-1 analog, exendin-4 (Ex-4), inhibited the growth of prostate cancer cells through suppressing the PI3K/Akt/mTOR pathway, which is activated in response to enzalutamide treatment and reported to be closely related to resistance to enzalutamide. So we speculated that exendin-4 may enhance the sensitivity of prostate cancer to enzalutamide through inhibiting Akt activation.

METHODS

LNCap and CWR22RV1 cell lines, as well as mice bearing xenografts formed from the two cells, were used.

RESULTS

Exendin-4 in combination with enzalutamide dramatically suppressed tumor growth of prostate cancer cells compared to enzalutamide alone; exendin-4 is capable of antagonizing enzalutamide-induced invasion and migration of both prostate cancer cells (P < .05). Furthermore, the combination treatment significantly reduced Akt and mTOR levels that were triggered by enzalutamide administration, caused a further decrease in nuclear AR localization compared with the enzalutamide as a monotherapy (P < .5), though exendin-4 treatment alone showed no effect on nuclear AR.

CONCLUSION

Our study demonstrated that exendin-4 alleviated resistance to enzalutamide, and suggested that exendin-4 combined with enzalutamide may be a more efficacious treatment for patients with advanced prostate cancer.

Oncological and Postoperative Outcomes of Robot-Assisted Laparoscopic Radical Prostatectomy in Renal Transplant Recipients: A Multicenter and Comparative Study

BACKGROUND

Robot-assisted laparoscopic radical prostatectomy (RARP) has been poorly studied in men with renal graft.

OBJECTIVE

To determine the predictive factors for oncologic outcomes and complications after RARP in renal transplants recipients (RTRs).

DESIGN AND PARTICIPANTS

A retrospective multicenter controlled study identified all RTRs who had undergone RARP between 2008 and 2016 in 2 experts departments. All RTRs were matched 1:1 with patients who had also undergone RARP but with no history of renal transplant (control group).

INTERVENTION

Robot-assisted laparoscopic radical prostatectomy.

OUTCOME MEASUREMENTS

Incontinence, oncologic outcomes, and complications according to the Clavien-Dindo classification.

STATISTICAL ANALYSIS

Comparisons of the quantitative variables using Student's t tests, and comparisons of the qualitative variables using χ2 tests. Statistical analyses were performed using SAS (version 9.3). Independent risk factors of biochemical recurrence (BCR), postoperative complications, or incontinence were searched by using a multivariate linear regression.

RESULTS

Twenty-seven RTRs were included in the transplant group and compared with 27 men in the control group with similar preoperative characteristics. Univariate analysis showed a shorter BCR-free survival in RTRs, with 26.9 months vs 49.3 months in the control group (P = .018). BCR rate was similar in each group (7.4% vs 11.1%, P = .639). No difference between groups was showed for immediate postoperative complications (29.6% vs 22.2%, P = .279). Multivariate analysis showed that a renal graft history was an independent risk factor of shorter BCR-free survival (hazard ratio = 4.291; 95% confidence interval, 2.102-8.761 and P < .001). Even if it is the first comparative study on this topic, the low number of men included is the main limitation of our study.

CONCLUSIONS

These findings show the reliability of RARP in RTRs. The rate of BCR does not appear more frequently but BCR-free survival seems shorter in these patients. A prospective comparative study remains necessary with more patients to confirm our results.

Natural products targeting the PI3K-Akt-mTOR signaling pathway in cancer: A novel therapeutic strategy

The phosphatidylinositol 3-kinase (PI3K)-Akt and the mammalian target of rapamycin (mTOR) represent two vital intracellular signaling pathways, which are associated with various aspects of cellular functions. These functions play vital roles in quiescence, survival, and growth in normal physiological circumstances as well as in various pathological disorders, including cancer. These two pathways are so intimately connected to each other that in some instances these are considered as one unique pathway crucial for cell cycle regulation. The purpose of this review is to emphasize the role of PI3K-Akt-mTOR signaling pathway in different cancer conditions and the importance of natural products targeting the PI3K-Akt-mTOR signaling pathway. This review also aims to draw the attention of scientists and researchers to the assorted beneficial effects of the numerous classes of natural products for the development of new and safe drugs for possible cancer therapy. We also summarize and critically analyze various preclinical and clinical studies on bioactive compounds and constituents, which are derived from natural products, to target the PI3K-Akt-mTOR signaling pathway for cancer prevention and intervention.

Phosphorylation of DEPDC5, a component of the GATOR1 complex, releases inhibition of mTORC1 and promotes tumor growth

The Pim and AKT serine/threonine protein kinases are implicated as drivers of cancer. Their regulation of tumor growth is closely tied to the ability of these enzymes to mainly stimulate protein synthesis by activating mTORC1 (mammalian target of rapamycin complex 1) signaling, although the exact mechanism is not completely understood. mTORC1 activity is normally suppressed by amino acid starvation through a cascade of multiple regulatory protein complexes, e.g., GATOR1, GATOR2, and KICSTOR, that reduce the activity of Rag GTPases. Bioinformatic analysis revealed that DEPDC5 (DEP domain containing protein 5), a component of GATOR1 complex, contains Pim and AKT protein kinase phosphorylation consensus sequences. DEPDC5 phosphorylation by Pim and AKT kinases was confirmed in cancer cells through the use of phospho-specific antibodies and transfection of phospho-inactive DEPDC5 mutants. Consistent with these findings, during amino acid starvation the elevated expression of Pim1 overcame the amino acid inhibitory protein cascade and activated mTORC1. In contrast, the knockout of DEPDC5 partially blocked the ability of small molecule inhibitors against Pim and AKT kinases both singly and in combination to suppress tumor growth and mTORC1 activity in vitro and in vivo. In animal experiments knocking in a glutamic acid (S1530E) in DEPDC5, a phospho mimic, in tumor cells induced a significant level of resistance to Pim and the combination of Pim and AKT inhibitors. Our results indicate a phosphorylation-dependent regulatory mechanism targeting DEPDC5 through which Pim1 and AKT act as upstream effectors of mTORC1 to facilitate proliferation and survival of cancer cells.

Effect of docetaxel on the regulation of proliferation and apoptosis of human prostate cancer cells

Prostate cancer is a common type of malignancy. Given the complexity of prostate cancer and the pressing challenge of chemoresistance, the current study was conducted to investigate the effect of docetaxel (Doc) on androgen receptor (AR)‑dependent and AR‑independent prostate cancers cells. Subsequent experiments were designed to explore the mechanism underlying the Doc‑induced apoptosis. Three different human prostate cancer cell lines, namely PC‑3, LNCaP and DU‑145, were exposed to various concentrations of Doc. The cytotoxic effects of Doc were evaluated by an MTT assay, while apoptosis and cell cycle distribution were determined by flow cytometric analysis of cells stained with Annexin V‑FITC and propidium iodide. Western blot assay was also used to measure the protein levels of B‑cell lymphoma 2 (Bcl‑2), Bcl‑2‑associated death promoter (Bad), total protein kinase B (Akt), phospho‑Akt and caspase‑3/9. Doc induced cytotoxicity in all three cell lines in a dose‑dependent manner. The half maximal inhibitory concentration values for the effect of Doc on PC‑3, DU‑145 and LNCaP cells were 3.72, 4.46 and 1.13 nM, respectively. Furthermore, the results indicated a significant difference in Doc sensitivity between AR‑dependent and AR‑independent prostate cancer cells. Evaluation of key gene expression at protein levels revealed a notable decrease in antiapoptotic Bcl‑2 and p‑Akt levels, along with a significant increase in pro‑apoptotic Bad, caspase‑3 and caspase‑9 levels. Therefore, Doc may induce cell apoptosis in prostate cancer via various pathways.

Targeting AR-Beclin 1 complex-modulated growth factor signaling increases the antiandrogen Enzalutamide sensitivity to better suppress the castration-resistant prostate cancer growth

While the recently developed antiandrogen Enzalutamide (Enz) can extend survival for 4.8 months in castration-resistant prostate cancer (CRPC) patients, eventually most of these CRPC patients may develop resistance to the Enz without a clear mechanism. Here we found the expression of Beclin 1 was decreased in both Enz-resistant (EnzR) cell lines (EnzR1-C4-2 and EnzR2-C4-2B) as compared to their parental Enz-sensitive (EnzS) (EnzS1-C4-2 and EnzS2-C4-2B) cells, and targeting the Beclin 1 could lead to increase the Enz-sensitivity in these two CRPC cell lines. Mechanism dissection revealed that Enz might function via altering the interaction between Beclin 1 and the androgen receptor (AR) to decrease the activity of Beclin 1/Vps15/Vps34 complex thus increasing the ERK-mediated growth factor signaling to alter the Enz sensitivity. Interrupting the AR-Beclin 1/ERK signaling with ectopic BECN1 or ERK inhibitor led to alter the Enz sensitivity in both EnzR1-C4-2 and EnzR2-C4-2B cells compared to EnzS1-C4-2 and EnzS2-C4-2B cells, respectively. Together, these results suggest that targeting this newly identified AR-Beclin 1 complex-mediated ERK growth factor signaling with small molecule ERK inhibitor may help potentially develop new therapies to better suppress the EnzR CRPC.

Metastatic prostate cancer remains incurable, why?

Metastatic prostate cancer patients present in two ways-with already disseminated disease at the time of presentation or with disease recurrence after definitive local therapy. Androgen deprivation therapy is given as the most effective initial treatment to patients. However, after the initial response, almost all patients will eventually progress despite the low levels of testosterone. Disease at this stage is termed castration resistant prostate cancer (CRPC). Before 2010, the taxane docetaxel was the first and only life prolonging agent for metastatic CRPC (mCRPC). The last decade has witnessed robust progress in CRPC therapeutics development. Abiraterone, enzalutamide, apalutamide and sipuleucel-T have been evaluated as first- and second-line agents in mCRPC patients, while cabazitaxel was approved as a second-line treatment. Radium-223 dichloride was approved in symptomatic patients with bone metastases and no known visceral metastases pre- and post-docetaxel. However, despite significant advances, mCRPC remains a lethal disease. Both primary and acquired resistance have been observed in CRPC patients treated by these new agents. It could be solely cell intrinsic or it is possible that the clonal heterogeneity in treated tumors may result from the adaptive responses to the selective pressures within the tumor microenvironment. The aim of this review is to list current treatment agents of CRPC and summarize recent findings in therapeutic resistance mechanisms.