Abiraterone in the treatment of metastatic castration-resistant prostate cancer

Metastatic Castration-Resistant Prostate Cancer: Advances in Treatment and Symptom Management

OPINION STATEMENT

The management of metastatic castrate-resistant prostate cancer (mCRPC) has evolved in the past decade due to substantial advances in understanding the genomic landscape and biology underpinning this form of prostate cancer. The implementation of various therapeutic agents has improved overall survival but despite the promising advances in therapeutic options, mCRPC remains incurable. The focus of treatment should be not only to improve survival but also to preserve the patient's quality of life (QoL) and ameliorate cancer-related symptoms such as pain. The choice and sequence of therapy for mCRPC patients are complex and influenced by various factors, such as side effects, disease burden, treatment history, comorbidities, patient preference and, more recently, the presence of actionable genomic alterations or biomarkers. Docetaxel is the first-line treatment for chemo-naïve patients with good performance status and those who have yet to progress on docetaxel in the castration-sensitive setting. Novel androgen agents (NHAs), such as abiraterone and enzalutamide, are effective treatment options that are utilized as second-line options. These medications can be considered upfront in frail patients or patients who are NHA naïve. Current guidelines recommend genetic testing in mCRPC for mutations in DNA repair deficiency genes to inform treatment decisions, as for example in breast cancer gene mutation testing. Other potential biomarkers being investigated include phosphatase and tensin homologues and homologous recombination repair genes. Despite a growing number of studies incorporating biomarkers in their trial designs, to date, only olaparib in the PROFOUND study and lutetium-177 in the VISION trial have improved survival. This is an unmet need, and future trials should focus on biomarker-guided treatment strategies. The advent of novel noncytotoxic agents has enhanced targeted drug delivery and improved treatment responses with favourable toxicity profiling. Trials should continue to incorporate and report health-related QoL scores and functional assessments into their trial designs.

Dysregulated microRNAs in prostate cancer: In silico prediction and in vitro validation

Objectives

MicroRNAs, which are micro-coordinators of gene expression, have been recently investigated as a potential treatment for cancer. The study used computational techniques to identify microRNAs that could target a set of genes simultaneously. Due to their multi-target-directed nature, microRNAs have the potential to impact multiple key pathways and their pathogenic cross-talk.

Materials and Methods

We identified microRNAs that target a prostate cancer-associated gene set using integrated bioinformatics analyses and experimental validation. The candidate gene set included genes targeted by clinically approved prostate cancer medications. We used STRING, GO, and KEGG web tools to confirm gene-gene interactions and their clinical significance. Then, we employed integrated predicted and validated bioinformatics approaches to retrieve hsa-miR-124-3p, 16-5p, and 27a-3p as the top three relevant microRNAs. KEGG and DIANA-miRPath showed the related pathways for the candidate genes and microRNAs.

Results

The Real-time PCR results showed that miR-16-5p simultaneously down-regulated all genes significantly except for PIK3CA/CB in LNCaP; miR-27a-3p simultaneously down-regulated all genes significantly, excluding MET in LNCaP and PIK3CA in PC-3; and miR-124-3p could not down-regulate significantly PIK3CB, MET, and FGFR4 in LNCaP and FGFR4 in PC-3. Finally, we used a cell cycle assay to show significant G0/G1 arrest by transfecting miR-124-3p in LNCaP and miR-16-5p in both cell lines.

Conclusion

Our findings suggest that this novel approach may have therapeutic benefits and these predicted microRNAs could effectively target the candidate genes.

TFE-Facilitated Synthesis of Tetrahydropyridino[2,3-d]pyrimidine via Cascade [1,5]-Hydride Transfer/Cyclization

An efficient fluorinated alcohol-driven cascade [1,5]-hydride transfer/cyclization between o-amino pyridyl aldehydes and primary amines has been developed. This unique transformation enabled an array of tetrahydropyridino[2,3-d]pyrimidine construction. Furthermore, the encouraging antifungal activity of Thanatephorus cucumeris was demonstrated by this tetrahydropyridino[2,3-d]pyrimidine core structure.

BLM promotes malignancy in PCa by inducing KRAS expression and RhoA suppression via its interaction with HDGF and activation of MAPK/ERK pathway

Prostate cancer (PCa) has long been the leading cause of cancer-associated deaths among male worldwide. Our previous studies have shown that Bloom syndrome protein (BLM) plays a vital role in PCa proliferation, yet the underlying molecular mechanism remains largely obscure. Mechanistically, BLM directly interacted with hepatoma-derived growth factor (HDGF). Functionally, BLM and HDGF knockdown resulted in the higher impairment of PC3 proliferation, clonogenicity, migration and invasion than that their counterpart with either BLM or HDGF knockdown exclusively. Of note, HDGF overexpression expedited, whereas its knockdown suppressed, PC3 proliferation, clonogenicity, migration and invasion. Additionally, the potentiation or attenuation was partially antagonized upon BLM depletion or overexpression. In line with the vitro data, the impact of BLM and HDGF on tumor growth was investigated in mouse xenograft models. ChIP-seq, dual-luciferase reporter and western blotting assays were employed to expound the regulatory network in PC3 cells. The results unveiled that HDGF activated KRAS and suppressed RhoA transcription, and that the function of HDGF was mediated, in part, by interaction with BLM. Accordingly, the MAPK/ERK pathway was activated. Moreover, the regulation of HDGF on KRAS and RhoA had a signal crosstalk. To recapitulate, BLM and HDGF may serve as novel prognostic markers and potential therapeutic targets in PCa.

Mechanisms of Prostate Cancer Cells Survival and Their Therapeutic Targeting

Prostate cancer (PCa) is today the second most common cancer in the world, with almost 400,000 deaths annually. Multiple factors are involved in the etiology of PCa, such as older age, genetic mutations, ethnicity, diet, or inflammation. Modern treatment of PCa involves radical surgical treatment or radiation therapy in the stages when the tumor is limited to the prostate. When metastases develop, the standard procedure is androgen deprivation therapy, which aims to reduce the level of circulating testosterone, which is achieved by surgical or medical castration. However, when the level of testosterone decreases to the castration level, the tumor cells adapt to the new conditions through different mechanisms, which enable their unhindered growth and survival, despite the therapy. New knowledge about the biology of the so-called of castration-resistant PCa and the way it adapts to therapy will enable the development of new drugs, whose goal is to prolong the survival of patients with this stage of the disease, which will be discussed in this review.

Molecular Mechanisms of Noncoding RNA in the Occurrence of Castration-Resistant Prostate Cancer

Although several therapeutic options have been shown to improve survival of most patients with prostate cancer, progression to castration-refractory state continues to present challenges in clinics and scientific research. As a highly heterogeneous disease entity, the mechanisms of castration-resistant prostate cancer (CRPC) are complicated and arise from multiple factors. Among them, noncoding RNAs (ncRNAs), the untranslated part of the human transcriptome, are closely related to almost all biological regulation, including tumor metabolisms, epigenetic modifications and immune escape, which has encouraged scientists to investigate their role in CRPC. In clinical practice, ncRNAs, especially miRNAs and lncRNAs, may function as potential biomarkers for diagnosis and prognosis of CRPC. Therefore, understanding the molecular biology of CRPC will help boost a shift in the treatment of CRPC patients. In this review, we summarize the recent findings of miRNAs and lncRNAs, discuss their potential functional mechanisms and highlight their clinical application prospects in CRPC.

Comprehensive Characterization of Androgen-Responsive circRNAs in Prostate Cancer

The androgen receptor (AR) signaling pathway plays an important role in the initiation and progression of prostate cancer. Circular RNAs (circRNAs), the novel noncoding RNAs without 5′ to 3′ polarity or 3′ poly (A), play an important role in multiple diseases. However, the potential roles of androgen-responsive circRNAs in prostate cancer remain unclear. In this study, we identified 3237 androgen-responsive circRNAs and 1954 androgen-responsive mRNAs after dihydrotestosterone (DHT) stimulation using microarray. Among them, the expression of 1296 androgen-responsive circRNAs was consistent with that of their parent genes, and we thought AR might regulate the expression of these circRNAs at the transcriptional level. In addition, 1941 circRNAs expression was not consistent with their parent genes, and we speculated that AR may regulate the expression of those circRNAs at the posttranscriptional level through affecting alternative splicing. Analyzing the androgen-responsive circRNAs regulated at the posttranscriptional level, we identified two key RNA binding proteins (RBPs), WTAP and TNRC6, using the circInteractome database, which may play important role in the biogenesis of androgen-responsive circRNAs. Furthermore, we explored the potential biological functions and predicted the molecular mechanisms of two dysregulated circRNAs (circNFIA and circZNF561) in prostate cancer. In this study, we revealed that circNFIA was upregulated in prostate cancer tissues and plasma samples from patients with prostate cancer; circNFIA may play an oncogenic role in prostate cancer. In contrast, circZNF561 was downregulated and may act as a tumor suppressor in prostate cancer. Our results suggest that androgen-responsive circRNAs might regulate the progression of prostate cancer and could be novel diagnostic biomarkers.

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.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

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.

Discovery and development of ODM-204: A Novel nonsteroidal compound for the treatment of castration-resistant prostate cancer by blocking the androgen receptor and inhibiting CYP17A1

We report the discovery of a novel nonsteroidal dual-action compound, ODM-204, that holds promise for treating patients with castration-resistant prostate cancer (CRPC), an advanced form of prostate cancer characterised by high androgen receptor (AR) expression and persistent activation of the AR signaling axis by residual tissue androgens. For ODM-204, has a dual mechanism of action. The compound is anticipated to efficiently dampen androgenic stimuli in the body by inhibiting CYP17A1, the prerequisite enzyme for the formation of dihydrotestosterone (DHT) and testosterone (T), and by blocking AR with high affinity and specificity. In our study, ODM-204 inhibited the proliferation of androgen-dependent VCaP and LNCaP cells in vitro and reduced significantly tumour growth in a murine VCaP xenograft model in vivo. Intriguingly, after a single oral dose of 10-30 mg/kg, ODM-204 dose-dependently inhibited adrenal and testicular steroid production in sexually mature male cynomolgus monkeys. Similar results were obtained in human chorionic gonadotropin-treated male rats. In rats, leuprolide acetate-mediated (LHRH agonist) suppression of the circulating testosterone levels and decrease in weights of androgen-sensitive organs was significantly and dose-dependently potentiated by the co-administration of ODM-204. ODM-204 was well tolerated in both rodents and primates. Based on our data, ODM-204 could provide an effective therapeutic option for men with CRPC.

Identification of Novel Biomarkers of Homologous Recombination Defect in DNA Repair to Predict Sensitivity of Prostate Cancer Cells to PARP-Inhibitors

One of the most common malignancies in men is prostate cancer, for which androgen deprivation is the standard therapy. However, prostate cancer cells become insensitive to anti-androgen treatment and proceed to a castration-resistant state with limited therapeutic options. Therefore, besides the androgen deprivation approach, novel biomarkers are urgently required for specific targeting in this deadly disease. Recently, germline or somatic mutations in the homologous recombination (HR) DNA repair genes have been identified in at least 20–25% of metastatic castration-resistant prostate cancers (mCRPC). Defects in genes involved in HR DNA repair can sensitize cancer cells to poly(ADP-ribose) polymerase (PARP) inhibitors, a class of drugs already approved by the Food and Drug Administration (FDA) for breast and ovarian cancer carrying germline mutations in BRCA1/2 genes. For advanced prostate cancer carrying Breast cancer1/2 (BRCA1/2) or ataxia telengiectasia mutated (ATM) mutations, preclinical studies and clinical trials support the use of PARP-inhibitors, which received breakthrough therapy designation by the FDA. Based on these assumptions, several trials including DNA damage response and repair (DDR) targeting have been launched and are ongoing for prostate cancer. Here, we review the state-of-the-art potential biomarkers that could be predictive of cancer cell synthetic lethality with PARP inhibitors. The identification of key molecules that are affected in prostate cancer could be assayed in future clinical studies to better stratify prostate cancer patients who might benefit from target therapy.

Canonical and Noncanonical Androgen Metabolism and Activity

Androgens are critical drivers of prostate cancer. In this chapter we first discuss the canonical pathways of androgen metabolism and their alterations in prostate cancer progression, including the classical, backdoor and 5α-dione pathways, the role of pre-receptor DHT metabolism, and recent findings on oncogenic splicing of steroidogenic enzymes. Next, we discuss the activity and metabolism of non-canonical 11-oxygenated androgens that can activate wild-type AR and are less susceptible to glucuronidation and inactivation than the canonical androgens, thereby serving as an under-recognized reservoir of active ligands. We then discuss an emerging literature on the potential non-canonical role of androgen metabolizing enzymes in driving prostate cancer. We conclude by discussing the potential implications of these findings for prostate cancer progression, particularly in context of new agents such as abiraterone and enzalutamide, which target the AR-axis for prostate cancer therapy, including mechanisms of response and resistance and implications of these findings for future therapy.

Corticosteroid switch in heavily pre-treated castration-resistant prostate cancer patients progressed on abiraterone acetate plus prednisone

The aim of this retrospective study is to evaluate the activity and safety of a steroidal switch from prednisone to dexamethasone in patients with advanced, heavily pre-treated, castration-resistant prostate cancer (CRPC) who progressed on abiraterone acetate. Treatment consisted of oral daily abiraterone plus dexamethasone (0.5 mg once daily) administered until disease progression or unacceptable toxicity. Thirty-six patients were evaluated: all men underwent a prior treatment with enzalutamide. A PSA decrease ≥50% was observed in 11% of patients; median progression-free survival was 10.8 weeks (95% CI: 9.2-16), and median survival was 17.6 weeks (95% CI: 15.8-28.8). Better efficacy and survival were observed in the subgroup of patients treated with abiraterone acetate prior for a period >3 months; treatment was well tolerated, and no grade 3-4 toxicities were observed. Our findings did not suggest the use of steroid switch in all CRPC who were heavily pre-treated. However, the switch could be an option for patients who responded well to prior abiraterone acetate treatment.

Contribution of Adrenal Glands to Intratumor Androgens and Growth of Castration-Resistant Prostate Cancer

PURPOSE

Tumor androgens in castration-resistant prostate cancer (CRPC) reflect de novo intratumoral synthesis or adrenal androgens. We used C.B.-17 SCID mice in which we observed adrenal CYP17A activity to isolate the impact of adrenal steroids on CRPC tumors in vivo.

EXPERIMENTAL DESIGN

We evaluated tumor growth and androgens in LuCaP35CR and LuCaP96CR xenografts in response to adrenalectomy (ADX). We assessed protein expression of key steroidogenic enzymes in 185 CRPC metastases from 42 patients.

RESULTS

Adrenal glands of intact and castrated mice expressed CYP17A. Serum DHEA, androstenedione (AED), and testosterone (T) in castrated mice became undetectable after ADX (all P < 0.05). ADX prolonged median survival (days) in both CRPC models (33 vs. 179; 25 vs. 301) and suppressed tumor steroids versus castration alone (T 0.64 pg/mg vs. 0.03 pg/mg; DHT 2.3 pg/mg vs. 0.23 pg/mg; and T 0.81 pg/mg vs. 0.03 pg/mg, DHT 1.3 pg/mg vs. 0.04 pg/mg; all P ≤ 0.001). A subset of tumors recurred with increased steroid levels, and/or induction of androgen receptor (AR), truncated AR variants, and glucocorticoid receptor (GR). Metastases from 19 of 35 patients with AR positive tumors concurrently expressed enzymes for adrenal androgen utilization and nine expressed enzymes for de novo steroidogenesis (HSD3B1, CYP17A, AKR1C3, and HSD17B3).

CONCLUSIONS

Mice are appropriate for evaluating adrenal impact of steroidogenesis inhibitors. A subset of ADX-resistant CRPC tumors demonstrate de novo androgen synthesis. Tumor growth and androgens were suppressed more strongly by surgical ADX than prior studies using abiraterone, suggesting reduction in adrenally-derived androgens beyond that achieved by abiraterone may have clinical benefit. Proof-of-concept studies with agents capable of achieving true "nonsurgical ADX" are warranted.

Alkaline phosphatase in metastatic castration-resistant prostate cancer: reassessment of an older biomarker

Since most patients with metastatic castration-resistant prostate cancer (mCRPC) have bone metastases, it is important to understand the potential impact of therapies on prognostic biomarkers, such as ALP. Clinical studies involving mCRPC life-prolonging agents (i.e., sipuleucel-T, abiraterone, enzalutamide, docetaxel, cabazitaxel, and radium-223) have shown that baseline ALP level is prognostic for overall survival, and may be a better prognostic marker for overall survival than prostate-specific antigen in patients with bone-dominant mCRPC. Mechanism of action differences between therapies may partly explain ALP dynamics during treatment. ALP changes can be interpreted within the context of other parameters while monitoring disease activity to better understand the underlying pathology. This review evaluates the current role of ALP in mCRPC.

Intra versus Inter Cross-resistance Determines Treatment Sequence between Taxane and AR-Targeting Therapies in Advanced Prostate Cancer

Current treatments for castration resistant prostate cancer (CRPC) largely fall into two classes: androgen receptor (AR)-targeted therapies such as the next-generation antiandrogen therapies (NGAT), enzalutamide and abiraterone, and taxanes such as docetaxel and cabazitaxel. Despite improvements in outcomes, patients still succumb to the disease due to the development of resistance. Further complicating the situation is lack of a well-defined treatment sequence and potential for cross-resistance between therapies. We have developed several models representing CRPC with acquired therapeutic resistance. Here, we utilized these models to assess putative cross-resistance between treatments. We find that resistance to enzalutamide induces resistance to abiraterone and vice versa, but resistance to neither alters sensitivity to taxanes. Acquired resistance to docetaxel induces cross-resistance to cabazitaxel but not to enzalutamide or abiraterone. Correlating responses with known mechanisms of resistance indicates that AR variants are associated with resistance to NGATs, whereas the membrane efflux protein ABCB1 is associated with taxane resistance. Mechanistic studies show that AR variant-7 (AR-v7) is involved in NGAT resistance but not resistance to taxanes. Our findings suggest the existence of intra cross-resistance within a drug class (i.e., within NGATs or within taxanes), whereas inter cross-resistance between drug classes does not develop. Furthermore, our data suggest that resistance mechanisms differ between drug classes. These results may have clinical implications by showing that treatments of one class can be sequenced with those of another, but caution should be taken when sequencing similar classed drugs. In addition, the development and use of biomarkers indicating resistance will improve patient stratification for treatment. Mol Cancer Ther; 17(10); 2197-205. ©2018 AACR.

Current and potential targets for drug design in the androgen receptor pathway for prostate cancer

INTRODUCTION

Modulating the androgen axis by different agents has been one of the most successful therapeutic interventions in the field of prostate cancer therapy. Newer agents such as abiraterone and enzalutamide have been widely adapted and have contributed to an increase in the overall survival of prostate cancer patients. However, most of these patients will develop resistance to these agents and will need chemotherapy. Areas covered: In this review, this author discusses current agents which modulate the androgen axis, the mechanisms of resistance to these agents and investigative agents which are designed to bypass these mechanisms of resistance. Potential targets in the androgen axis and related biochemical pathways are, furthermore, identified. Expert opinion: Understanding the mechanism of resistance to these agents is crucial in developing third generation anti-androgen agents which can potentially contribute to the longevity of prostate cancer patients to a greater extent. Besides developing more potent agents, it is also important to formulate new strategies to resensitize patients to current anti-androgen agents by carefully sequencing chemotherapy regimens and abrogating genetic changes which are known to cause resistance to anti-androgens. Combinatorial approach with immunotherapy offers prospects which may yield better results and need to be thoroughly explored.

Dual targeting of androgen receptor and mTORC1 by salinomycin in prostate cancer

Androgen receptor (AR) and PI3K/AKT/mTORC1 are major survival signals that drive prostate cancer to a lethal disease. Reciprocal activation of these oncogenic pathways from negative cross talks contributes to low/limited success of pathway-selective inhibitors in curbing prostate cancer progression. We report that the antibiotic salinomycin, a cancer stem cell blocker, is a dual-acting AR and mTORC1 inhibitor, inhibiting PTEN-deficient castration-sensitive and castration-resistant prostate cancer in culture and xenograft tumors. AR expression, its transcriptional activity, and androgen biosynthesis regulating enzymes CYP17A1, HSD3β1 were reduced by sub-micro molar salinomycin. Estrogen receptor-α expression was unchanged. Loss of phosphorylated AR at serine-81, which is an index for nuclear AR activity, preceded total AR reduction. Rapamycin enhanced the AR protein level without altering phosphoAR-Ser81 and CYP17A1. Inactivation of mTORC1, evident from reduced phosphorylation of mTOR and downstream effectors, as well as AMPK activation led to robust autophagy induction. Apoptosis increased modestly, albeit significantly, by sub-micro molar salinomycin. Enhanced stimulatory TSC2 phosphorylation at Ser-1387 by AMPK, and reduced inhibitory TSC2 phosphorylation at Ser-939/Thr-1462 catalyzed by AKT augmented TSC2/TSC1 activity, which led to mTORC1 inhibition. AMPK-mediated raptor phosphorylation further reduced mTOR's kinase function and mTORC1 activity. Our novel finding on dual inhibition of AR and mTORC1 suggests that salinomycin is potentially active as monotherapy against advanced prostate cancer.

[Antihormonal therapy in prostate cancer : Side effects]

Androgen deprivation is still standard therapy for prostate cancer, either as primary androgen deprivation therapy or with the use of secondary hormonal drugs including abiraterone and enzalutamide. However, especially the clinically occult side effects like metabolic changes or cardiovascular complications and effects on the psyche of the patient are often not recognized in daily practice. Active monitoring of such side effects is essential for prevention and early intervention. In addition, the efficacy of androgen deprivation therapies is limited by primary and secondary resistance. The underlying molecular mechanism including splice variants of the androgen receptor in contrast to mutations are usually reversible and should be regarded as a sign of efficacy of the current treatment. Therefore, the clever, timely use of androgen deprivation or even the use of a bipolar androgen therapy should enable reversal of resistance to again render tumor cells sensitive to androgen-deprivation therapy.

Inhibition of Androgen Receptor Function and Level in Castration-Resistant Prostate Cancer Cells by 2-[(isoxazol-4-ylmethyl)thio]-1-(4-phenylpiperazin-1-yl)ethanone

The androgen receptor (AR) plays a critical role in the development of castration-resistant prostate cancer (CRPC) as well as in the resistance to the second-generation AR antagonist enzalutamide and the selective inhibitor of cytochrome P450 17A1 (CYP17A1) abiraterone. Novel agents targeting AR may inhibit the growth of prostate cancer cells resistant to enzalutamide and/or abiraterone. Through a high-throughput/high-content screening of a 220,000-member small molecule library, we have previously identified 2-[(isoxazol-4-ylmethyl)thio]-1-(4-phenylpiperazin-1-yl)ethanone (IMTPPE) (SID 3712502) as a novel small molecule capable of inhibiting AR transcriptional activity and protein level in C4-2 prostate cancer cells. In this study, we show that IMTPPE inhibits AR-target gene expression using real-time polymerase chain reaction, Western blot, and luciferase assays. IMTPPE inhibited proliferation of AR-positive, but not AR-negative, prostate cancer cells in culture. IMTPPE inhibited the transcriptional activity of a mutant AR lacking the ligand-binding domain (LBD), indicating that IMTPPE inhibition of AR is independent of the LBD. Furthermore, animal studies showed that IMTPPE inhibited the growth of 22Rv1 xenograft tumor, a model for enzalutamide-resistant prostate cancer. These findings suggest that IMTPPE is a potential lead compound for developing clinical candidates for the treatment of CRPC, including those resistant to enzalutamide.

Androgen Signaling in Prostate Cancer

The androgen-signaling axis plays a pivotal role in the pathogenesis of prostate cancer. Since the landmark discovery by Huggins and Hodges, gonadal depletion of androgens has remained a mainstay of therapy for advanced disease. However, progression to castration-resistant prostate cancer (CRPC) typically follows and is largely the result of restored androgen signaling. Efforts to understand the mechanisms behind CRPC have revealed new insights into dysregulated androgen signaling and intratumoral androgen synthesis, which has ultimately led to the development of several novel androgen receptor (AR)-directed therapies for CRPC. However, emergence of resistance to these newer agents has also galvanized new directions in investigations of prereceptor and postreceptor AR regulation. Here, we review our current understanding of AR signaling as it pertains to the biology and natural history of prostate cancer.

Resistance to Hormonal Therapy in Prostate Cancer

Several therapeutic strategies are actually available in the management of prostate cancer: Targeting the androgen receptor (AR) is the goal both for initial androgen deprivation therapy (ADT) and second-generation androgen ablative agents (abiraterone and enzalutamide). Chemotherapy with taxanes, administered upon progression or as first line approach in association with ADT, is another therapeutic option. Unfortunately, none of these therapies is curative and patients are destined to develop a resistant phenotype.Progression to ADT leads to the attainment of a castration resistant disease whose mechanisms remain incompletely understood. Reactivation of AR has been shown to occur and second-generation of AR targeting drugs are usually prescribed. Upon progression to these agents AR signaling still remains the primary driver although it often becomes ligand independent, since it can be either restored through mutations on the ligand binding domain and/or formation of AR splicing variants or by passed through a cross talk with other oncogenic signaling pathways.AR-independent signaling pathways may represent additional mechanisms underlying castration resistant progression. It is clear that castration resistant prostate cancer is a group of diverse diseases and new treatment paradigms need to be developed.

Study of cases of abiraterone discontinuation due to toxicity in pre-chemotherapy after 1 year’s experience

Abiraterone acetate is a potent and irreversible inhibitor of cytochrome p450 17A1 that suppresses androgen synthesis. It is approved for chemotherapy-naive and docetaxel-treated patients with metastatic castration-resistant prostate cancer. We describe the protocol for use of abiraterone in metastatic castration-resistant prostate cancer chemotherapy naive patients has been implanted in our centre and we review the cases of those patients whose adverse effects have forced the discontinuation of treatment. The side effects fit the safety profile of abiraterone, speed of their appearance and severity indicate that you should perform a thorough follow-up of these patients especially in the early phases of treatment.

Management of castrate-resistant prostate cancer in older men

Prostate cancer is the most common cancer diagnosed in men with the highest incidence in older men. Older men are more likely to present with metastatic disease compared with younger patients and eventually all will develop castrate resistant disease. In recent years, a number of new treatment options have demonstrated survival benefits for metastatic castrate resistant prostate cancer. However, the lack of randomized trials directly comparing the different available options results in some uncertainty on how best to choose and sequence therapy. In this paper, we outline the therapeutic options available to men with metastatic castrate-resistant prostate cancer, including cytotoxic therapy, hormonal agents and bone-directed therapy. We focus particularly on the evidence for specific treatment options and the challenges faced in choosing the appropriate therapy for the older patient.

Association of SLCO2B1 Genotypes With Time to Progression and Overall Survival in Patients Receiving Androgen-Deprivation Therapy for Prostate Cancer

PURPOSE

To validate the association of three previously demonstrated SLCO2B1 germline variants with time to progression (TTP) in patients receiving androgen-deprivation therapy (ADT), and to evaluate if the SLCO2B1 genetic variants impacted overall survival (OS) for prostate cancer (PC).

PATIENTS AND METHODS

Three single nucleotide polymorphisms (SNPs), exonic SNP rs12422149 and intronic SNPs rs1789693 and rs1077858, were genotyped in an independent validation cohort of 616 patients with PC who were treated with ADT at the Dana-Farber Cancer Institute from 1996 to 2013. Multivariable Cox proportional hazards regression adjusting for known prognostic factors estimated the association of these genetic variants with TTP and OS in patients receiving ADT. The expression of SLCO2B1 was examined in prostatectomy samples, and the impact of SLCO2B1 expression level on DHEAS (dehydroepiandrosterone sulfate) uptake was evaluated in cell lines.

RESULTS

The association between exonic SNP rs12422149 and TTP in patients treated with ADT was confirmed in univariable (P = .019) and multivariable analyses (adjusted hazard ratio, 1.31; 95% CI, 1.00 to 1.72 for GG v AA/AG; P = .049). Because OS had not been previously evaluated, we examined the association in the combined initial and validation cohorts (N = 1,094). The intronic SNP rs1077858 was associated with OS in both univariable (P = .009; Bonferroni's method adjusted P = .027) and multivariable analyses (adjusted hazard ratio, 1.35; 95% CI, 1.07 to 1.71 for GG v AA/AG; P = .012). SLCO2B1 expression in normal prostate tissue and in 22RV1 cells carrying the major allele of SNP rs1077858 was significantly lower than in cells carrying the risk allele. We show in vitro that SLCO2B1 expression levels correlated with DHEAS uptake by PC cells.

CONCLUSION

The association of SNP rs1077858 with OS may be a result of differential SLCO2B1 expression and the consequent increased uptake of DHEAS and subsequent resistance to ADT, which, in turn, may contribute to decreased OS.

Mechanisms of resistance in castration-resistant prostate cancer (CRPC)

Despite advances in prostate cancer diagnosis and management, morbidity from prostate cancer remains high. Approximately 20% of men present with advanced or metastatic disease, while 29,000 men continue to die of prostate cancer each year. Androgen deprivation therapy (ADT) has been the standard of care for initial management of advanced or metastatic prostate cancer since Huggins and Hodges first introduced the concept of androgen-dependence in 1972, but progression to castration-resistant prostate cancer (CRPC) occurs within 2-3 years of initiation of ADT. CRPC, previously defined as hormone-refractory prostate cancer, is now understood to still be androgen dependent. Multiple mechanisms of resistance help contribute to the progression to castration resistant disease, and the androgen receptor (AR) remains an important driver in this progression. These mechanisms include AR amplification and hypersensitivity, AR mutations leading to promiscuity, mutations in coactivators/corepressors, androgen-independent AR activation, and intratumoral and alternative androgen production. More recently, identification of AR variants (ARVs) has been established as another mechanism of progression to CRPC. Docetaxel chemotherapy has historically been the first-line treatment for CRPC, but in recent years, newer agents have been introduced that target some of these mechanisms of resistance, thereby providing additional survival benefit. These include AR signaling inhibitors such as enzalutamide (Xtandi, ENZA, MDV-3100) and CYP17A1 inhibitors such as abiraterone acetate (Zytiga). Ultimately, these agents will also fail to suppress CRPC. While some of the mechanisms by which these agents fail are unique, many share similarities to the mechanisms contributing to CRPC progression. Understanding these mechanisms of resistance to ADT and currently approved CRPC treatments will help guide future research into targeted therapies.

Vitamin D in Prostate Cancer

Metastatic castration-resistant prostate cancer (mCRPC) is a progressive, noncurable disease induced by androgen receptor (AR) upon its activation by tumor tissue androgen, which is generated from adrenal steroid dehydroepiandrosterone (DHEA) through intracrine androgen biosynthesis. Inhibition of mCRPC and early-stage, androgen-dependent prostate cancer by calcitriol, the bioactive vitamin D3 metabolite, is amply documented in cell culture and animal studies. However, clinical trials of calcitriol or synthetic analogs are inconclusive, although encouraging results have recently emerged from pilot studies showing efficacy of a safe-dose vitamin D3 supplementation in reducing tumor tissue inflammation and progression of low-grade prostate cancer. Vitamin D-mediated inhibition of normal and malignant prostate cells is caused by diverse mechanisms including G1/S cell cycle arrest, apoptosis, prodifferentiation gene expression changes, and suppressed angiogenesis and cell migration. Biological effects of vitamin D are mediated by altered expression of a gene network regulated by the vitamin D receptor (VDR), which is a multidomain, ligand-inducible transcription factor similar to AR and other nuclear receptors. AR-VDR cross talk modulates androgen metabolism in prostate cancer cells. Androgen inhibits vitamin D-mediated induction of CYP24A1, the calcitriol-degrading enzyme, while vitamin D promotes androgen inactivation by inducing phase I monooxygenases (e.g., CYP3A4) and phase II transferases (e.g., SULT2B1b, a DHEA-sulfotransferase). CYP3A4 and SULT2B1b levels are markedly reduced and CYP24A1 is overexpressed in advanced prostate cancer. In future trials, combining low-calcemic, potent next-generation calcitriol analogs with CYP24A1 inhibition or androgen supplementation, or cancer stem cell suppression by a phytonutrient such as sulfarophane, may prove fruitful in prostate cancer prevention and treatment.

Androgen-glucocorticoid interactions in the era of novel prostate cancer therapy

Great strides have been made in the treatment of castration-resistant prostate cancer (CRPC) with the development of new antiandrogens (enzalutamide) and more potent androgen synthesis inhibitors (abiraterone) that have both improved patient outcomes. These new drugs have also helped unravel the complex biology of androgen-androgen receptor driven prostate cancer and brought into prominence various mechanisms triggering the development of drug resistance and tumour cell survival despite use of androgen deprivation therapy (ADT). The complex role of glucocorticoids in the treatment, management and progression of patients with CRPC is integral to these advances. Historically, glucocorticoid treatment has resulted in both subjective and objective responses in patients with advanced-stage prostate cancer. With the use of these new therapeutic agents, however, unexpected glucocorticoid-related mechanisms that can cause iatrogenic stimulation of prostate cancer growth have emerged, which might contribute to drug resistance and disease progression despite optimal ADT. For example, the upregulation of glucocorticoid receptors (GRs) during enzalutamide therapy results in glucocorticoid-GR-mediated regulation of androgen target genes, leading to escape from enzalutamide blockade. Thus, understanding the biological role of glucocorticoids in patients with prostate cancer is of major importance in the era of new and evolving antiandrogen therapies.

Cabozantinib Inhibits Abiraterone's Upregulation of IGFIR Phosphorylation and Enhances Its Anti-Prostate Cancer Activity

PURPOSE

Abiraterone improves the overall survival of men with metastatic castration-resistant prostate cancer. However, de novo or adaptive resistance to abiraterone limits its activity. Rational combinations of drugs with different mechanisms of action that overcome resistance mechanisms may improve the efficacy of therapy. To that end, we studied the molecular and phenotypic effects of the combination of cabozantinib plus abiraterone.

EXPERIMENTAL DESIGN

Three prostate cancer cell lines were used to interrogate the in vitro molecular and antiproliferative effects of the single agents and combination of cabozantinib and abiraterone. The in vivo impact of the combination was assessed using the LAPC4-CR xenograft mouse model.

RESULTS

In vitro proliferation studies demonstrated single-agent doses between 2 μmol/L and 10 μmol/L for abiraterone and cabozantinib inhibit prostate cancer cell proliferation in a dose-dependent manner, and the anticancer activity of abiraterone is enhanced when combined with cabozantinib. In vivo LAPC4-CR xenograft mouse studies also showed that cabozantinib can improve the antitumor activity of abiraterone. Cabozantinib, a multiple receptor tyrosine kinase inhibitor, enhances the ability of abiraterone to inhibit AR activity in a cell line-dependent manner. In addition, our cell line studies demonstrate abiraterone-stimulated insulin-like growth factor I receptor (IGFIR) phosphorylation with downstream activation of MEK1/2 and ERK1/2, and that this potential adaptive resistance mechanism was inhibited by cabozantinib.

CONCLUSIONS

Cabozantinib can enhance the efficacy of abiraterone by blocking multiple compensatory survival mechanisms, including IGFIR activation, and supports the assessment of the combination in a clinical trial.

Hormonal therapy in oncology: a primer for the radiologist

OBJECTIVE

The purpose of this article is to provide a comprehensive imaging review of the common hormonal therapies used in oncology and the side effects associated with them.

CONCLUSION

Commonly used hormones in oncology include corticosteroids, somatostatin analogues, progestins, gonadotropin-releasing hormone agonists and antagonists, antiandrogens, aromatase inhibitors, and selective estrogen receptor modulators. Familiarity with these hormones and their side effects can help radiologists to be vigilant for the side effects and complications of these agents.

Shifting paradigms in the estimation of survival for castration-resistant prostate cancer: A tertiary academic center experience

OBJECTIVES

Castration-resistant prostate cancer (CRPC) has retained a guarded prognosis, with historical survival estimates of 18 to 24 months. However, the landscape of available therapy has changed, and the emphasis has altered from supportive to active treatment. Few large series from real-world populations exist in the contemporary era with fully mature survival data to confirm the indication based on clinical trials that patients with CRPC are surviving far longer than the historical estimates. We aim to review a large patient cohort with CRPC and provide mature survival data.

METHODS AND MATERIALS

Using the electronic histopathology database at Queen Elizabeth Hospital, Birmingham, UK, all prostate-specific antigentest results between April 2006 and September 2007 were extracted, and patients satisfying the American Society for Radiation Oncology (ASTRO) definition of hormone failure were identified. Electronic records were reviewed and variables were collected, including survival, treatment, biochemistry, histopathology, and demographics. Probability of survival, and of developing metastasis or CRPC, was determined using the Kaplan-Meier method. Patients were stratified into 3 groups, namely, D0--no metastasis at diagnosis but later appearance, D1--no metastasis at diagnosis or at last follow-up, and D2--metastasis at diagnosis.

RESULTS

From 8,062 patient-prostate-specific antigen episodes, we identified 447 patients meeting the criteria. A notes review revealed 147 patients with CRPC. Median overall survival (OS) from diagnosis was 84.7 months (95% CI: 73-89), and 129 deaths had occurred (88%). Median OS from diagnosis for D0, D1, and D2 patients was 100.4, 180.1, and 58.9 months, respectively (P< 0.0001), and median OS from CRPC was 40 months (95% CI: 31-58), 82.9 (95% CI: 72-94; P = 0.0125), and 38.7 months (95% CI: 33-46), respectively. One-quarter of patients survived 6 years after development of CRPC. Metastasis is the key prognostic event.

CONCLUSIONS

Some current international guidelines quote ≤19 months as a survival figure for patients with metastatic CRPC. In our study, median survival is more than double this. We have shown survival more than previously reported figures and believe that these data benefit clinicians and patients in understanding prognosis and treatment choices. Importantly, our patients were diagnosed before the current wave of novel therapeutics for CRPC, so survival for men diagnosed today may be more than our findings.

Preclinical evaluation of investigational radiopharmaceutical RISAD-P intended for use as a diagnostic and molecular radiotherapy agent for prostate cancer

BACKGROUND

The androgen receptor (AR) plays a dominant role in the pathogenesis of prostate cancer. 5-Radioiodo-3'-O-(17β-succinyl-5α-androstan-3-one)-2'-deoxyuridin-5'-yl phosphate (RISAD-P) is an AR-targeting reagent developed for noninvasive assessment of AR and proliferative status of the AR-expressing tumors, and for molecular radiotherapy with Auger electron-emitting radionuclides. In this study, the preclinical toxicity and targeting potential of RISAD-P was evaluated.

METHODS

Effects of nonradioactive ISAD-P and RISAD-P labeled with (123) I, (124) I, and (125) I were evaluated in male mice. Expanded-acute single dose toxicity studies, hematologic toxicity, liver and kidney function, pharmacokinetics, biodistribution, and imaging studies were conducted. Imaging and pilot therapy studies were conducted in transgenic mice.

RESULTS

RISAD-P is not toxic at doses projected for clinical use. Its tissue distribution compares favorably with the distribution reported for (18) F-dihydrotestosterone derivatives. RISAD-P has excellent prostate cancer targeting properties. One hour after (125) IRISAD-P administration, nearly 10% of the injected dose is associated with prostate tumor. The tumor clearance is biphasic and plateaus between 24 and 48 hr post-injection. The estimated radiation doses calculated for 1 g tumor using the MIRD convention are well within the therapeutic range with values of 170, 250, 1,240 Gy × MBq(-1)  × g(-1) for (125) I-, (123) I-, and (124) I-labeled RISAD-P, respectively. The transient uptake of radioactivity is observed in the genitourinary tract and stomach. Without the potassium iodide blockade, thyroid uptake is also observed.

CONCLUSIONS

Biodistribution, toxicity, and radiation dosimetry studies suggest that RISAD-P holds characteristics of a promising candidate for imaging of AR expression and tumor proliferation, as well as molecular radiotherapy for metastatic or locally, regionally advanced prostate cancer.

Minireview: SLCO and ABC transporters: a role for steroid transport in prostate cancer progression

Androgens play a critical role in the development and progression of prostate cancer (PCa), and androgen deprivation therapy via surgical or medical castration is front-line therapy for patients with advanced PCa. However, intratumoral testosterone levels are elevated in metastases from patients with castration-resistant disease, and residual intratumoral androgens have been implicated in mediating ligand-dependent mechanisms of androgen receptor activation. The source of residual tissue androgens present despite castration has not been fully elucidated, but proposed mechanisms include uptake and conversion of adrenal androgens, such as dehdroepiandrosterone to testosterone and dihydrotestosterone, or de novo androgen synthesis from cholesterol or progesterone precursors. In this minireview, we discuss the emerging evidence that suggests a role for specific transporters in mediating transport of steroids into or out of prostate cells, thereby influencing intratumoral androgen levels and PCa development and progression. We focus on the solute carrier and ATP binding cassette gene families, which have the most published data for a role in PCa-related steroid transport, and review the potential impact of genetic variation on steroid transport activity and PCa outcomes. Continued assessment of transport activity in PCa models and human tumor tissue is needed to better delineate the different roles these transporters play in physiologic and neoplastic settings, and in order to determine whether targeting the uptake of steroid substrates by specific transporters may be a clinically feasible therapeutic strategy.

Molecular pathways and targets in prostate cancer

Prostate cancer co-opts a unique set of cellular pathways in its initiation and progression. The heterogeneity of prostate cancers is evident at earlier stages, and has led to rigorous efforts to stratify the localized prostate cancers, so that progression to advanced stages could be predicted based upon salient features of the early disease. The deregulated androgen receptor signaling is undeniably most important in the progression of the majority of prostate tumors. It is perhaps because of the primacy of the androgen receptor governed transcriptional program in prostate epithelium cells that once this program is corrupted, the consequences of the ensuing changes in activity are pleotropic and could contribute to malignancy in multiple ways. Following localized surgical and radiation therapies, 20-40% of patients will relapse and progress, and will be treated with androgen deprivation therapies. The successful development of the new agents that inhibit androgen signaling has changed the progression free survival in hormone resistant disease, but this has not changed the almost ubiquitous development of truly resistant phenotypes in advanced prostate cancer. This review summarizes the current understanding of the molecular pathways involved in localized and metastatic prostate cancer, with an emphasis on the clinical implications of the new knowledge.

Beyond T and DHT - novel steroid derivatives capable of wild type androgen receptor activation

While androgen deprivation therapy (ADT) remains the primary treatment for metastatic prostate cancer (PCa), castration does not eliminate androgens from the prostate tumor microenvironment, and residual intratumoral androgens are implicated in nearly every mechanism by which androgen receptor (AR)-mediated signaling promotes castration-resistant disease. The uptake and intratumoral (intracrine) conversion of circulating adrenal androgens such as dehydroepiandrosterone sulfate (DHEA-S) to steroids capable of activating the wild type AR is a recognized driver of castration resistant prostate cancer (CRPC). However, less well-characterized adrenal steroids, including 11-deoxcorticosterone (DOC) and 11beta-hydroxyandrostenedione (11OH-AED) may also play a previously unrecognized role in promoting AR activation. In particular, recent data demonstrate that the 5α-reduced metabolites of DOC and 11OH-AED are activators of the wild type AR. Given the well-recognized presence of SRD5A activity in CRPC tissue, these observations suggest that in the low androgen environment of CRPC, alternative sources of 5α-reduced ligands may supplement AR activation normally mediated by the canonical 5α-reduced agonist, 5α-DHT. Herein we review the emerging data that suggests a role for these alternative steroids of adrenal origin in activating the AR, and discuss the enzymatic pathways and novel downstream metabolites mediating these effects. We conclude by discussing the potential implications of these findings for CRPC progression, particularly in context of new agents such as abiraterone and enzalutamide which target the AR-axis for prostate cancer therapy.