Molecular mechanisms and classification of castration-resistant prostate cancer: Insights into androgen receptor, cancer stem cells, and neuroendocrine features

Decision letter: Selective androgen receptor degrader (SARD) to overcome antiandrogen resistance in castration-resistant prostate cancer

Editor's evaluation: Selective androgen receptor degrader (SARD) to overcome antiandrogen resistance in castration-resistant prostate cancer

Author response: Selective androgen receptor degrader (SARD) to overcome antiandrogen resistance in castration-resistant prostate cancer

PSA-negative/low prostate cancer cells: the true villains of CRPC?

PAGE4 Positivity Is Associated with Attenuated AR Signaling and Predicts Patient Survival in Hormone-Naive Prostate Cancer

Background The androgen receptor (AR) signaling pathway drives prostate cancer development and progression, making it a major target for drug development. However, resistance to AR targeted therapies invariably develops and eventually leads to an aggressive, castrate-resistant prostate cancer (CRPC). Although CRPC often remains dependent on AR signaling, anti-androgen therapies can lead to the development of AR independent disease and metastatic CRPC. Understanding the molecular basis of this transition and resistance to current anti-androgen therapy will provide important insight and reveal novel therapeutic strategies for both AR-positive and -negative disease pathways. Methods and Results We analyzed in silico data of AR (signaling)-positive or -negative human CRPC tissue samples and discovered that MET expression is specifically increased only in AR-negative CRPC samples. When AR-positive CRPC models are subjected to AR signaling inhibition (by the AR antagonist enzalutamide or androgen deprivation), MET is increased and susceptible to activation by its ligand HGF. Therefore, we postulate that dual targeting of AR and MET signaling pathways may be a better approach to prevent and overcome resistance-related disease progression. Our preliminary AR ChIP-seq data suggested that MET transcription is not affected by AR directly rather, MET protein is modulated by AR signaling at the post-translational level. Therefore, we hypothesize that a combination therapy of a proteasome inhibitor and MET inhibitor may have potential therapeutic benefit for some CRPC patients. By using in vitro and in vivo models of AR-dependent CRPC, we have showed that combination of the dual MET/VEGFR2 inhibitor cabozantinib and enzalutamide treatment is more efficacious than either inhibitor alone. In addition, Bortezomib, an FDA-approved proteasome inhibitor, showed significant synergistic effect when paired with cabozantinib in our preliminary data using in vitro and in vivo CRPC models. In vitro results suggest that triple combination of anti-androgen, MET inhibitor and proteasome inhibitor therapies will maximize inhibition in CRPC. Conclusion MET is a compensatory survival pathway in AR+ CRPC upon anti-androgen therapy. The rational for triple combination of anti-androgen, MET inhibitor and proteasome inhibitor therapies is a feasible approach to maximize inhibition in CRPC while minimizing development of drug resistance to any single agent. Citation Format: Yuanyuan Qiao, Todd M. Morgan, Arul M. Chinnaiyan. Development of a rational triple combination therapy for castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2068. doi:10.1158/1538-7445.AM2017-2068

Prostate cancer (Pca) remains the second leading cause of cancer-related deaths in men in the United States. Although advanced Pca usually responds to therapies that suppress androgen-axis signaling, resistance inevitably develops, leading to the emergence of castration-resistant prostate cancer (CRPC). Importantly, the clinical efficacy of novel therapies targeting androgen receptor (AR) signaling, such as abiraterone and enzalutamide, has confirmed that most CRPC cases demonstrate intact AR signaling. Since resistance to these therapies inevitably develops, approaches that improve the response duration and address the key pathways of resistance are warranted. Mechanisms underlying androgen deprivation therapy (ADT) resistance remain poorly defined, but may depend on epigenetic reprogramming. Our group previously showed that EZH2 is overexpressed and associates with Pca progression and poor prognosis. We substantiated this finding by screening a library of epigenetic inhibitors for their ability to render ADT-resistant CRPC cells sensitive to enzalutamide. Of these compounds, the EZH2 inhibitors facilitated a substantial increase in enzalutamide-mediated growth inhibition. Given these data, we hypothesized that EZH2-mediated epigenetic reprogramming might be crucial for the development and maintenance of ADT resistance, and targeting EZH2 might sensitize resistant CRPC cells to ADT. To test this hypothesis, we performed loss-of-function of EZH2 experiments on multiple CRPC cell lines, and determined that loss-of-function of EZH2 significantly sensitized Pca cells to ADT. Interestingly, by employing RNA-seq and ChIP-seq approaches to dissect the regulatory role of EZH2, we found that EZH2 inhibition significantly up-regulates AR signaling by changing the AR cistrome. Further experimentation confirmed that the loss-of-function of EZH2-mediated deregulation of AR signaling strengthens the AR-dependency of Pca, thus increasing the sensitivity of Pca to ADT. To co-target EZH2 and AR with greater efficiency, we employed antisense oligonucleotides (ASOs) directed against EZH2 and AR at the mRNA level. We determined that co-targeting EZH2 and AR by ASOs constitutes a novel, viable therapy for CRPC in vitro and in vivo. In conclusion, we have identified EZH2 as a critical epigenetic regulator for ADT resistance and have shown that co-targeting EZH2 and AR by ASOs to be a promising, potential strategy for preventing and treating CRPC. Citation Format: Lanbo Xiao, Jean Ching-Yi Tien, Josh Vo, Abhijit Parolia, Lisha Wang, Mengyao Tan, Yuanyuan Qiao, Sudhanshu Shukla, Xiaoju Wang, Heng Zheng, Fengyun Su, Xuhong Cao, Arul Chinnaiyan. Epigenetic re-programming sensitizes prostate cancer cells to anti-androgen therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5834.

Prostate cancer is one of the most frequently diagnosed cancers and the second leading cause of cancer-related deaths in male population. While localized prostate cancer can be successfully treated with surgery or radiation therapy, the metastatic disease has no curable options. Metastasis can be developed as a result of failed therapy of localized cancer or present at initial diagnosis. As metastasis is the most common cause of prostate cancer-related death, developing novel approaches and improving the efficiency of existing therapies for the metastatic prostate cancer treatment will significantly improve patients’ survival. The first-line treatment option for metastatic prostate cancer and localized prostate cancer with high risk of recurrence is androgen deprivation therapy (ADT) that decreases androgen receptor (AR) signaling. However, targeting AR signaling inevitably leads to AR reactivation and cancer progression to the castration-resistant prostate cancer (CRPC) that has no curable treatment options. Moreover, about 30% of CRPC cases progress to neuroendocrine prostate cancer (NEPC), highly aggressive and lethal type of prostate cancer. Recently my group has shown that protein arginine methyltransferase 5 (PRMT5) functions as an activator of AR expression in hormone-naive prostate cancer (HNPC). In this dissertation, I demonstrate that PRMT5 also functions as an epigenetic activator of AR transcription in CRPC via symmetric dimethylation of H4R3 at the AR promoter. This epigenetic activation is dependent on pICln, a PRMT5 interaction partner involved in spliceosome assembly, and independent of MEP50, the canonical cofactor of PRMT5. PRMT5 and pICln, but not MEP50, were required for the expression of AR signaling pathway genes. In clinical samples of both HNPC and CRPC, nuclear PRMT5 and pICln protein expressions were highly positively correlated with nuclear AR protein expression. In xenograft tumors, targeting PRMT5 or pICln significantly decreased tumor growth and AR expression. Overall, this work identifies PRMT5/pICln as a therapeutic target for HNPC and CRPC treatment that needs to be further evaluated in clinical setting.

A standard treatment for prostate cancer (PCa) is androgen deprivation therapy (ADT) that suppresses androgen receptor (AR) signaling axis. Although initially responsive, most patients receiving ADT eventually develop metastatic castration-resistant prostate cancer (CRPC), with more than 90% of them exhibiting bone metastases. A mechanism by which CRPC cells evade ADT is the expression of constitutively active AR variants (AR-Vs), such as the well-characterized AR-V7. Recently we developed GH501, a flurbiprofen-modified small-molecule compound, and investigated its anti-cancer activity and mechanism of action in pre-clinical models of CRPC. At nanomolar range, GH501 effectively induces cell cycle arrest and apoptosis in CRPC cells regardless of their resistance status to enzalutamide treatment. RNA-seq analysis of GH501 combined with Western blotting analysis identified key targets implicated in CRPC progression, including the full-length AR, AR-V7 variant, and other important genes implicated in CRPC progression. Importantly, low doses of GH501 effectively inhibit the skeletal growth of CRPC in a xenograft model without obvious in vivo toxicities. These preclinical results indicate that GH501 is a promising small-molecule compound that can be further developed for the treatment of lethal prostate cancer. Citation Format: Kenza Mamouni, Lajos Gera, Xin Li, Daqing Wu. A nanomolar potency small-molecule compound against castration-resistant and bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3205. doi:10.1158/1538-7445.AM2017-3205

Prostate cancer is the second leading cause of cancer death in men in western countries. Advanced prostate cancer is often resistant to hormonal treatment and systemic chemotherapy has limited efficacy. Androgen receptor (AR), a ligand dependent transcription factor plays pivotal role in the development and progression of prostate cancer. While majority of prostate cancers are initially androgen dependent and respond to androgen ablation therapy, most patients eventually recur with more aggressive castration-resistant prostate cancer (CRPC) where AR signaling is reactivated even in the absence of androgen stimulation. Therefore developing novel chemotherapeutic agents for castrate resistant prostate cancer (CRPC) treatment is critical to improve survival in men with CRPC. Triptolide, a diterpene triepoxide isolated from a chinese herb, is extremely effective against several cancers like pancreatic cancer, colorectal cancer and liver cancer both in vivo and in vitro. The water-soluble pro-drug of triptolide, Minnelide, downregulates HSP70 via inhibition of the activity of transcription factor Sp1. Since both Sp1 and HSP70 have been reported to be critical in functionality of AR, we assessed therapeutic potential of Minnelide on androgen dependent, CRPC in vitro and in vivo. Triptolide treatment resulted in dose- and time-dependent cell death in an androgen dependent cell line LNCaP, CRPC cell line C4-2 and enzalutamide resistant CRPC tumor cell line 22RV1. Triptolide treatment decreased expression of AR full length, AR splice variants and its downstream targets (PSA, NKX3.1) at the mRNA and protein levels. Further, reporter assay with AR responsive elements showed that triptolide decreased transcriptional activity of AR. Expression levels of Sp1 and HSP70 were also reduced following treatment with triptolide these cell lines. To test the efficacy of Minnelide in vivo, male athymic nude mice were castrated 7 days prior to implantation of enzalutamide resistant CRPC (22RV1) cells subcutaneously. The animals received daily intraperitoneal injection of Minnelide and tumor volume was measured weekly until tumor size reached 2cm3.Mice receiving daily injection of Minnelide had significantly smaller tumors than controls as early as two week of treatment (p = 0.008). Triptolide therapy inhibited enzalutamide resistant CRPC growth both in vitro and in vivo. Further, our studies for the first time showed that triptolide induces prostate tumor cell death by reducing expression of both full length AR and AR splice variants in a similar manner. Citation Format: Sumit Isharwal, Shrey Modi, Usman Barlass, Vikas Dudeja, Ashok Saluja, Sulagna Banerjee, Badrinath Konety. Minnelide reduces castration-resistant and enzalutamide-resistant prostate cancer via downregulation of androgen receptor-mediated signaling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-017. doi:10.1158/1538-7445.AM2015-LB-017

Prostate cancer (PCa) is the second most frequently diagnosed cancer in men in the United States. Following androgen deprivation therapy, advanced PCa usually evolves into a refractory stage termed castration resistant prostate cancer (CRPC), which is responsible for most mortality. Importantly, androgen receptor (AR) signaling is still active in CRPC. Therefore, next-generation drugs that inhibit AR signaling such as enzalutamide and abiraterone are used for therapy for many patients with CRPC. These drugs provide a survival benefit but are not curative. In this article, we review the mechanisms through which the AR signaling axis promotes resistance to androgen-deprivation therapy and drives progression of CRPC. There are a number of pathways that allow AR to escape androgen-deprivation therapy, including activation of glucocorticoid receptors, synthesis of androgens in CRPC tissues, AR mutations, AR amplification and AR splice variants. Although the AR appears to be involved in resistance to other therapeutics such as the taxanes, which disrupt normal microtubule function, this article will focus on the role of AR in resistance to androgen-deprivation therapy.

Untreated prostate cancers rely on androgen receptor (AR) signaling for growth and survival, forming the basis for the initial efficacy of androgen deprivation therapy (ADT). Yet the disease can relapse and progress to a lethal stage termed castration-resistant prostate cancer (CRPC). Reactivation of AR signaling represents the most common driver of CRPC growth, and next-generation AR signaling inhibitors (ARSIs) are now used in combination with ADT as first-line therapy. However, ARSIs can result in selective pressure, thereby generating AR-independent tumors. The transition from AR dependence frequently accompanies a change in a phenotype resembling developmental transdifferentiation or “lineage plasticity”. Neuroendocrine prostate cancer, which lacks a defined pathologic classification, is the most studied type of lineage plasticity. However, most AR-null tumors do not exhibit neuroendocrine features and are classified as “double-negative prostate cancer”, the drivers of which are poorly defined. Lineage plasticity studies in CRPC are limited by the lack of genetically defined patient-derived models that recapitulate the disease spectrum. To address this, we developed a biobank of organoids generated from patient biopsies to study the landscape of metastatic CRPC and allow for functional validation assays. Proteins called transcription factors (TFs) are drivers of tumor lineage plasticity. To identify the key TFs that drive the growth of AR-independent tumors, we integrated epigenetic and transcriptomic data generated from CRPC models. We generated ATAC-seq (assay for transposase-accessible chromatin sequencing) and RNA-seq data from 22 metastatic human prostate cancer organoids, six patient-derived xenografts (PDXs), and 12 derived or traditional cell lines. We classified the 40 models into four subtypes and predicted key TFs of each subtype. Besides the well-characterized AR-dependent (CRPC-AR) and neuroendocrine subtypes (CRPC-NE), we identified two novel AR-negative/low groups, including a Wnt-dependent subtype (CRPC-WNT), driven by TCF/LEF TFs, and a stem cell-like (SCL) subtype (CRPC-SCL), driven by the AP-1 family of TFs. To apply the subtype classification to patient samples, we derived RNA-seq signatures from the organoids and applied them to 366 patient samples from two independent CRPC cohorts. The generated signatures recapitulated the four-subtype classification and revealed that CRPC-SCL is the second most prevalent group. Patients from CRPC-SCL are also associated with shorter time under ARSI treatment compared to CRPC-AR, indicating that the ARSI treatments were less effective for CRPC-SCL patients. Additional chromatin immunoprecipitation sequencing (ChIP-seq) analysis indicated that AP-1 (FOSL1) collaboratively binds with TEAD and transcription coactivators, YAP and TAZ. Knocking down of AP-1 (FOSL1), YAP/TAZ decreased cell growth of CRPC-SCL and showed a decrease of chromatin accessibility at CRPC-SCL-specific open chromatin sites and down-regulation of YAP/TAZ target gene expression. In addition, the expression of AP-1 (FOSL1) decreased upon YAP/TAZ knockdown suggesting a positive feedback loop as well as YAP/TAZ as actional targets in CRPC-SCL. We used two small-molecule inhibitors, verteporfin and T-5224, that act on the YAP/TAZ/AP-1 pathway for their potential use as therapeutics for CRPC-SCL tumors, both inhibited the growth of samples from CRPC-SCL but not CRPC-AR. By overexpressing an AP-1 family gene (FOSL1) in AR-high cells, we observed an increase in chromatin accessibility at CRPC-SCL-specific open chromatin sites as well as significant up-regulation of CRPC-SCL signature genes, suggesting that AP-1 functions as a pioneering factor and master regulator for CRPC-SCL. All this work was recently published in Science (Tang, Xu et al. Science, 2022) where I am the co-first author. In summary, by using a diverse biobank of organoids, PDXs, and cell lines that recapitulate the heterogeneity of metastatic prostate cancer, we created a map of the chromatin accessibility and transcriptomic landscape of CRPC. We validated the CRPC-AR and CRPC-NE subtypes and report two novel subtypes of AR-negative/low samples, CRPC-SCL and CRPC-WNT, as well as their respective key TFs. Additional analysis revealed a model in which YAP, TAZ, TEAD, and AP-1 function together and drive oncogenic growth in CRPC-SCL samples. In addition, we proposed small inhibitors of YAP and TAZ that can potentially be used to treat CRPC-SCL patients. Overall, our results show how the stratification of CRPC patients into four subtypes using their transcriptomes can potentially inform appropriate clinical decisions. Citation Format: Fanying Tang, Duo Xu, Shangqian Wang, Chen Khuan Wong, Alexander Martinez-Fundichely, Cindy J. Lee, Sandra Cohen, Jane Park, Corinne E. Hill, Kenneth Eng, Rohan Bareja, Teng Han, Eric Minwei Liu, Ann Palladino, Wei Di, Dong Gao, Wassim Abida, Shaham Beg, Loredana Puca, Maximiliano Meneses, Elisa de Stanchina, Michael F. Berger, Anuradha Gopalan, Lukas E. Dow, Juan Miguel Mosquera, Himisha Beltran, Cora N. Sternberg, Ping Chi, Howard I. Scher, Andrea Sboner, Yu Chen, Ekta Khurana. Chromatin profiles classify castration-resistant prostate cancers suggesting therapeutic targets. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG10.

It is well established that androgen receptor (AR) signaling, is a key driver of prostate cancer (PC) growth and metastatic progression. Therefore, androgen deprivation therapy (ADT) is the first line of treatment for PC. However, most patients develop castration resistant prostate cancer (CRPC). Interestingly, AR signaling remains active in CRPC, due to the expression of transcriptionally active AR splice variants (AR-Vs), which lack the ligand binding domain (LBD) and constitutively translocate to the nucleus even in castrate conditions. AR-v7 is the most prevalent AR-V expressed in about 60% of CRPC tumors. AR-v7 expression was clinically correlated with poor prognosis of CRPC patients and with resistance to next-generation AR signaling inhibitors, which are part of standard clinical care. Therefore, inhibition of AR-v7 function is urgently needed for the treatment of CRPC. Currently, there is no therapeutic modality that can inhibit AR-v7 expression or activity. Mechanistically, AR-v7 transcriptional targets largely overlap with those of AR-fl, with the exception of a few AR-v7 unique targets. However, the exact mechanism by which transcription is activated by AR-v7 is not known. In this study we sought to investigate the mechanisms underlying the transcriptional activity of the ligand-independent AR-v7 in comparison to liganded AR-fl. We used live cell imaging to monitor the dynamics and intranuclear mobility of fluorescently-tagged AR-v7 or AR-fl. Fluorescent recovery after photobleaching (FRAP) revealed that AR-v7 intranuclear mobility was significantly faster than that of liganded AR-fl, with t1/2 3s versus several minutes, respectively. To precisely map the spatial distribution and chromatin-binding kinetics of AR-fl and AR-v7, we generated expression plasmids with AR tagged with green-to-red mEos4 photo-convertible proteins. Photoconversion of a discrete, subnuclear pool of AR-fl in the presence of its ligand (R1881) followed by 1 hr of time-lapse imaging in 5 min intervals, revealed absence of mobility indicating tight chromatin binding and active transcription. In contrast, similar photoconversion experiment for AR-v7, revealed immediate redistribution throughout the nucleus in less than 9 s, suggesting a “hit-and-run” mode of interaction with DNA with uncertain transcriptional output. QRT-PCR of endogenous target genes and ARE-mcherry reporter assays showed similar transcriptional activity of the two proteins. We are currently investigating the relationship between rates of intranuclear mobility and transcriptional activity and the mechanisms underlying the distinct mobility patterns. These data suggest that AR-v7 has a distinct mode of interaction with DNA and gene promoters, which may identify novel targetable pathways for its inhibition in CRPC. Citation Format: Seaho Kim, Mohd Azrin Jamalruddin, Paraskevi Giannakakou. High intranuclear mobility of AR-v7 reveals distinct mode of transcriptional activity in prostate cancer with important therapeutic implications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1590. doi:10.1158/1538-7445.AM2017-1590

“You can observe a lot just by watching.” —Yogi Berra The androgen receptor (AR) is a resilient foe. Since the landmark studies of Huggins et al demonstrated the sensitivity of prostate cancer to androgenic hormones, androgen deprivation therapy has been the most widely used and effective treatment for metastatic disease. Although initial response rates exceed 90%, the eventual emergence of castration-resistant prostate cancer (CRPC) is nearly universal, and it represents a disease state that is usually fatal. However, a remarkable and extremely important aspect of CRPC is the near-universal reactivation of AR signaling, a finding readily substantiated through measurements of high serum concentrations prostatespecific antigen (PSA), a gene directly and exclusively regulated by the AR. Several studies have documented that most, and potentially all, genes known to be under AR transcriptional control in prostate cancer cells are re-expressed in CRPC tumors. In this context, the AR may be the earliest known example of a lineage oncogene—a master regulator to which neoplastic cells derived from prostate epithelium are addicted. AR engagement by androgenic ligands such as testosterone and dihydrotestosterone motivate AR migration from the cytoplasm to the nucleus, where AR target genes are recognized and activated through DNA binding to locations specified by nucleotide sequence and chromatin accessibility. The observation that AR-regulated genes are active in CRPC—despite undetectable levels of testosterone in blood—has prompted efforts to identify processes driving AR function in the castrate environment. Such alternative mechanisms of AR activation could represent targets for therapeutic inhibition. A key question that should influence further investment in obstructing the AR program in CRPC is whether the AR is continuing to provide the growth and survival signals for these tumors, or if the AR program is simply baggage carried along by other oncogenic drivers. Compelling evidence indicates the former is likely to be true. For example, experiments abolishing the AR itself in androgenrefractory prostate cancer cells in vitro effectively suppressed proliferation. CRPC tumors proliferating in castrate mice consistently regress after the targeted elimination of AR expression. Finally, clinical studies of secondary and tertiary methods to inhibit AR signaling in CRPC usually result in PSA and clinical responses, although they are generally of relatively short duration. Newer agents targeting androgen biosynthesis or blocking AR activation carry on this tendency. Together, these laboratory and clinical observations emphasize the continued relevance of the AR pathway as a key therapeutic node in the vast majority of patients with advanced CRPC. Unfortunately, over the past several decades, efforts to target AR signaling have blown hot and cold, with irrational exuberance followed by neglect. Insightful studies by Geller et al in the 1970s demonstrated that androgen levels within prostate cancers far exceeded concentrations found in castrate men, a finding that ushered in the era of combined androgen blockade (CAB) with steroidal and nonsteroidal androgen receptor antagonists. Despite many trials of CAB, the therapeutic advantage remains highly debated. Initial studies using either surgical or medical castration in conjunction with an antiandrogen suggested significant improvements in survival compared with historical controls. However, the benefits measured in subsequent randomized trials were not encouraging, although metaanalyses have consistently shown a statistically significant improvement in 5-year survival, on the order of 5%, in favor of CAB. Although certainly less impressive than anticipated, the trials of these early antiandrogens did not refute the hypothesis that AR is still a key driver in CRPC because of one key observation: Patients for whom these drugs failed experienced progression with a rising PSA, indicating the AR pathway remained active. Determining how the AR remained engaged awaited detailed molecular studies that identified mechanisms underlying the limited effectiveness of these AR antagonists and led to the next generation of AR inhibitors, such as MDV3100, with enhanced binding affinities and lacking agonist properties. To provide a framework for the clinical application of new agents designed to suppress androgen signaling, it is useful to consider the molecular endocrinology that underlies the maintenance of AR activity. On the basis of current knowledge of prostate cancer molecular biology, at least four discrete cellular states of prostate cancer can be defined, based solely on the status of AR program activity and the mechanism by which it is activated. Of clinical relevance, the cellular states are dynamic and evolve either through adaptation or genomic events, and each molecular state is also associated with a specific therapeutic node that generally requires effective inhibition—and JOURNAL OF CLINICAL ONCOLOGY U N D E R S T A N D I N G T H E P A T H W A Y VOLUME 30 NUMBER 6 FEBRUARY 2

What controls PTEN and what it controls (in prostate cancer)