RESUMEN
The androgen receptor (AR) is a modular transcription factor which functions as a master regulator of gene expression. AR protein is composed of three functional domains; the ligand-binding domain (LBD); DNA-binding domain (DBD); and the intrinsically disordered N-terminal transactivation domain (TAD). AR is transactivated upon binding to the male sex hormone testosterone and other androgens. While the AR may tolerate loss of its LBD, the TAD contains activation function-1 (AF-1) that is essential for all AR transcriptional activity. AR is frequently over-expressed in most prostate cancer. Currently, androgen deprivation therapy (ADT) in the form of surgical or chemical castration remains the standard of care for patients with high risk localized disease, advanced and metastatic disease, and those patients that experience biochemical relapse following definitive primary treatment. Patients with recurrent disease that receive ADT will ultimately progress to lethal metastatic castration-resistant prostate cancer. In addition to ADT not providing a cure, it is associated with numerous adverse effects including cardiovascular disease, osteoporosis and sexual dysfunction. Recently there has been a renewed interest in investigating the possibility of using antiandrogens which competitively bind the AR-LBD without ADT for patients with hormone sensitive, non-metastatic prostate cancer. Here we describe a class of compounds termed AR transactivation domain inhibitors (ARTADI) and their mechanism of action. These compounds bind to the AR-TAD to inhibit AR transcriptional activity in the absence and presence of androgens. Thus these inhibitors may have utility in preventing prostate cancer growth in the non-castrate setting.
Asunto(s)
Neoplasias de la Próstata , Receptores Androgénicos , Activación Transcripcional , Masculino , Humanos , Receptores Androgénicos/metabolismo , Receptores Androgénicos/química , Neoplasias de la Próstata/tratamiento farmacológico , Neoplasias de la Próstata/metabolismo , Neoplasias de la Próstata/patología , Activación Transcripcional/efectos de los fármacos , Antagonistas de Receptores Androgénicos/farmacología , Antagonistas de Receptores Androgénicos/química , Animales , Dominios ProteicosRESUMEN
Hybrid genome-mining/15N-NMR was used to target compounds containing piperazate (Piz) residues, leading to the discovery of caveamides A (1) and B (2) from Streptomyces sp. strain BE230, isolated from New Rankin Cave (Missouri). Caveamides are highly dynamic molecules containing an unprecedented ß-ketoamide polyketide fragment, two Piz residues, and a new N-methyl-cyclohexenylalanine residue. Caveamide B (2) exhibited nanomolar cytotoxicity against several cancer cell lines and nanomolar antimicrobial activity against MRSA and E. coli.
Asunto(s)
Escherichia coli , Staphylococcus aureus Resistente a Meticilina , Streptomyces , Humanos , Estructura Molecular , Streptomyces/química , Escherichia coli/efectos de los fármacos , Staphylococcus aureus Resistente a Meticilina/efectos de los fármacos , Antibacterianos/farmacología , Antibacterianos/química , Antibacterianos/aislamiento & purificación , Pruebas de Sensibilidad Microbiana , Antineoplásicos/farmacología , Antineoplásicos/química , Antineoplásicos/aislamiento & purificación , Alanina/química , Alanina/farmacología , Alanina/análogos & derivados , Ensayos de Selección de Medicamentos Antitumorales , Péptidos/química , Péptidos/farmacología , Péptidos/aislamiento & purificación , Línea Celular Tumoral , PiridazinasRESUMEN
Breast cancer is a major cause of death worldwide. The complexity of endocrine regulation in breast cancer may allow the cancer cells to escape from a particular treatment and result in resistant and aggressive disease. These breast cancers usually have fewer treatment options. Targeted therapies for cancer patients may offer fewer adverse side effects because of specificity compared to conventional chemotherapy. Signaling pathways of nuclear receptors, such as the estrogen receptor (ER), have been intensively studied and used as therapeutic targets. Recently, the role of the androgen receptor (AR) in breast cancer is gaining greater attention as a therapeutic target and as a prognostic biomarker. The expression of constitutively active truncated AR splice variants in breast cancer is a possible mechanism contributing to treatment resistance. Therefore, targeting both the full-length AR and AR variants, either through the activation or suppression of AR function, depending on the status of the ER, progesterone receptor, or human epidermal growth factor receptor 2, may provide additional treatment options. Studies targeting AR in combination with other treatment strategies are ongoing in clinical trials. The determination of the status of nuclear receptors to classify and identify patient subgroups will facilitate optimized and targeted combination therapies.
Asunto(s)
Neoplasias de la Mama , Neoplasias de la Próstata Resistentes a la Castración , Humanos , Masculino , Receptores Androgénicos/metabolismo , Neoplasias de la Mama/tratamiento farmacológico , Neoplasias de la Mama/genética , Neoplasias de la Mama/metabolismo , Antagonistas de Receptores Androgénicos/farmacología , Antagonistas de Receptores Androgénicos/uso terapéutico , Neoplasias de la Próstata Resistentes a la Castración/tratamiento farmacológicoRESUMEN
Transcription factors are among the most attractive therapeutic targets but are considered largely 'undruggable' in part due to the intrinsically disordered nature of their activation domains. Here we show that the aromatic character of the activation domain of the androgen receptor, a therapeutic target for castration-resistant prostate cancer, is key for its activity as transcription factor, allowing it to translocate to the nucleus and partition into transcriptional condensates upon activation by androgens. On the basis of our understanding of the interactions stabilizing such condensates and of the structure that the domain adopts upon condensation, we optimized the structure of a small-molecule inhibitor previously identified by phenotypic screening. The optimized compounds had more affinity for their target, inhibited androgen-receptor-dependent transcriptional programs, and had an antitumorigenic effect in models of castration-resistant prostate cancer in cells and in vivo. These results suggest that it is possible to rationally optimize, and potentially even to design, small molecules that target the activation domains of oncogenic transcription factors.
Asunto(s)
Neoplasias de la Próstata Resistentes a la Castración , Neoplasias de la Próstata , Masculino , Humanos , Neoplasias de la Próstata Resistentes a la Castración/tratamiento farmacológico , Neoplasias de la Próstata Resistentes a la Castración/genética , Receptores Androgénicos/genética , Receptores Androgénicos/química , Andrógenos/uso terapéutico , Neoplasias de la Próstata/tratamiento farmacológico , Neoplasias de la Próstata/genética , Dominios Proteicos , Factores de Transcripción , Línea Celular TumoralRESUMEN
This chapter focuses on the development of drugs targeting the N-terminal domain of nuclear hormone receptors, using progress with the androgen receptor as an example. Historically, development of therapies targeting nuclear hormone receptors has focused on the folded C-terminal ligand-binding domain. Therapies were traditionally not developed to target the intrinsically disordered N-terminal domain as it was considered "undruggable". Recent developments have now shown it is possible to direct therapies to the N-terminal domain. This chapter will provide an introduction of the structure and function of the domains of nuclear hormone receptors, followed by a discussion of the rationale supporting the development of N-terminal domain inhibitors. Chemistry and mechanisms of action of small molecule inhibitors will be described with emphasis on N-terminal domain inhibitors developed to the androgen receptor including those in clinical trials.
Asunto(s)
Receptores Androgénicos , Ligandos , Receptores Androgénicos/genéticaRESUMEN
Hormonal therapies for prostate cancer target the androgen receptor (AR) ligand-binding domain (LBD). Clinical development for inhibitors that bind to the N-terminal domain (NTD) of AR has yielded ralaniten and its analogues. Ralaniten acetate is well tolerated in patients at 3600 mgs/day. Clinical trials are ongoing with a second-generation analogue of ralaniten. Binding sites on different AR domains could result in differential effects on AR-regulated gene expression. Here, we provide the first comparison between AR-NTD inhibitors and AR-LBD inhibitors on androgen-regulated gene expression in prostate cancer cells using cDNA arrays, GSEA, and RT-PCR. LBD inhibitors and NTD inhibitors largely overlapped in the profile of androgen-induced genes that they each inhibited. However, androgen also represses gene expression by various mechanisms, many of which involve protein-protein interactions. De-repression of the transcriptome of androgen-repressed genes showed profound variance between these two classes of inhibitors. In addition, these studies revealed a unique and strong induction of expression of the metallothionein family of genes by ralaniten by a mechanism independent of AR and dependent on MTF1, thereby suggesting this may be an off-target. Due to the relatively high doses that may be encountered clinically with AR-NTD inhibitors, identification of off-targets may provide insight into potential adverse events, contraindications, or poor efficacy.
RESUMEN
Androgen receptor (AR) has essential roles in the growth of prostate cancer and some breast cancers. Inhibition of AR transcriptional activity by targeting its N-terminal domain with ralaniten or an analog such as EPI-7170 causes accumulation of cells in the G1-phase of the cell cycle. Inhibition of cyclin-dependent kinases 4/6 with palbociclib also leads to accumulation of cells in the G1-phase. Here, a combination of EPI-7170 with palbociclib attenuated the in vivo growth of human castration-resistant prostate cancer xenografts that are resistant to antiandrogens. Cell-cycle tracing experiments in cultured cells revealed that EPI-7170 targeted cells in the S-phase, possibly through inducing DNA damage or impairing the DNA damage response, whereas palbociclib targeted the G1-S transition to delay the cell cycle. Combination treatment prevented cells in G1 and G2-M from progressing in the cell cycle and caused a portion of cells in the S-phase to arrest, which contributed to a twofold increase in doubling time to >63 hours compared with 25 hours in control cells. Importantly, sequential combination treatments with palbociclib administered first then followed by EPI-7170, resulted in more cells accumulating in G1 and less cells in the S-phase than concomitant combination which was presumably because each inhibitor has a unique mechanism in modulating the cell cycle in cancer cells. Together, these data support that the combination therapy was more effective than individual monotherapies to reduce tumor growth by targeting different phases of the cell cycle.
Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias de la Mama/tratamiento farmacológico , Quinasa 4 Dependiente de la Ciclina/antagonistas & inhibidores , Quinasa 6 Dependiente de la Ciclina/antagonistas & inhibidores , Piperazinas/uso terapéutico , Neoplasias de la Próstata/tratamiento farmacológico , Piridinas/uso terapéutico , Receptores Androgénicos/uso terapéutico , Animales , Protocolos de Quimioterapia Combinada Antineoplásica/farmacología , Neoplasias de la Mama/patología , Ciclo Celular , Línea Celular Tumoral , Proliferación Celular , Femenino , Humanos , Masculino , Ratones , Piperazinas/farmacología , Neoplasias de la Próstata/patología , Piridinas/farmacologíaRESUMEN
Therapies for lethal castration-resistant prostate cancer (CRPC) are an unmet medical need. One mechanism underlying CRPC and resistance to hormonal therapies is the expression of constitutively active splice variant(s) of androgen receptor (AR-Vs) that lack its C-terminus ligand-binding domain. Transcriptional activities of AR-Vs and full-length AR reside in its N-terminal domain (NTD). Ralaniten is the only drug proven to bind AR NTD, and it showed promise of efficacy in Phase 1 trials. The peptidyl-prolyl isomerase Pin1 is frequently overexpressed in prostate cancer. Here we show that Pin1 interacted with AR NTD. The inhibition of Pin1 expression or its activity selectively reduced the transcriptional activities of full-length AR and AR-V7. Combination of Pin1 inhibitor with ralaniten promoted cell cycle arrest and had improved antitumor activity against CRPC xenografts in vivo compared to individual monotherapies. These findings support the rationale for therapy that combines a Pin1 inhibitor with ralaniten for treating CRPC.
Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/farmacología , Inhibidores Enzimáticos/farmacología , Peptidilprolil Isomerasa de Interacción con NIMA/antagonistas & inhibidores , Naftoquinonas/farmacología , Neoplasias de la Próstata Resistentes a la Castración/tratamiento farmacológico , Receptores Androgénicos/efectos de los fármacos , Tretinoina/farmacología , Animales , Puntos de Control del Ciclo Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Resistencia a Antineoplásicos , Humanos , Masculino , Ratones Endogámicos NOD , Ratones SCID , Peptidilprolil Isomerasa de Interacción con NIMA/genética , Peptidilprolil Isomerasa de Interacción con NIMA/metabolismo , Células PC-3 , Neoplasias de la Próstata Resistentes a la Castración/metabolismo , Neoplasias de la Próstata Resistentes a la Castración/patología , Dominios Proteicos , Receptores Androgénicos/genética , Receptores Androgénicos/metabolismo , Transducción de Señal , Carga Tumoral/efectos de los fármacos , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
The androgen receptor (AR) is a validated therapeutic target for prostate cancer and has been a focus for drug development for more than six decades. Currently approved therapies that inhibit AR signaling, such as enzalutamide, rely solely on targeting the AR ligand-binding domain and, therefore, have limited efficacy on prostate cancer cells that express truncated, constitutively active AR splice variants (AR-Vs). The LNCaP95 cell line is a human prostate cancer cell line that expresses both functional full-length AR and AR-V7. LNCaP95 is a heterogeneous cell population that is resistant to enzalutamide, with its proliferation dependent on transcriptionally active AR-V7. The purpose of this study was to identify a LNCaP95 clone that would be useful for evaluating therapies for their effectiveness against enzalutamide-resistant prostate cancer cells. Seven clones from the LNCaP95 cell line were isolated and characterized using morphology, in vitro growth rate, and response to ralaniten (AR N-terminal domain inhibitor) and enzalutamide (antiandrogen). In vivo growth of the clones as subcutaneous xenografts was evaluated in castrated immunodeficient mice. All of the clones maintained the expression of full-length AR and AR-V7. Cell proliferation of the clones was insensitive to androgen and enzalutamide but importantly was inhibited by ralaniten, which is consistent with AR-Vs driving the proliferation of parental LNCaP95 cells. In castrated immunodeficient animals, the growth of subcutaneous xenografts of the D3 clone was the most reproducible compared to the parental cell line and other clones. These data support that the enzalutamide-resistant LNCaP95-D3 subline may be suitable as a xenograft tumor model for preclinical drug development with improved reproducibility.
Asunto(s)
Antagonistas de Andrógenos/uso terapéutico , Antineoplásicos/uso terapéutico , Benzamidas/uso terapéutico , Células Clonales/metabolismo , Células Clonales/patología , Nitrilos/uso terapéutico , Feniltiohidantoína/uso terapéutico , Neoplasias de la Próstata/genética , Antagonistas de Andrógenos/farmacología , Animales , Benzamidas/farmacología , Castración , Línea Celular Tumoral , Modelos Animales de Enfermedad , Resistencia a Antineoplásicos , Xenoinjertos , Humanos , Masculino , Ratones , Ratones Endogámicos NOD , Trasplante de Neoplasias , Nitrilos/farmacología , Feniltiohidantoína/farmacología , Neoplasias de la Próstata/tratamiento farmacológico , Neoplasias de la Próstata/metabolismo , Receptores Androgénicos/metabolismoRESUMEN
Synthetic analogues of the marine natural product sintokamides have been prepared in order to investigate the structure-activity relationships for the androgen receptor N-terminal domain (AR NTD) antagonist activity of the sintokamide scaffold. An in vitro LNCaP cell-based transcriptional activity assay with an androgen-driven luciferase (Luc) reporter was used to monitor the potency of analogues. The data have shown that the chlorine atoms on the leucine side chains are essential for potent activity. Analogues missing the nonchlorinated methyl groups of the leucine side chains (C-1 and C-17) are just as active and in some cases more active than the natural products. Analogues with the natural R configuration at C-10 and the unnatural R configuration at C-4 are most potent. Replacing the natural propionamide N-terminus cap with the more sterically hindered pivaloylamide N-terminus cap leads to enhanced potency. The tetramic acid fragment and the methyl ether on the tetramic acid fragment are essential for activity. The SAR optimized analogue 76 is more selective, easier to synthesize, more potent, and presumed to be more resistant to proteolysis than the natural sintokamides.
Asunto(s)
Antagonistas de Receptores Androgénicos/farmacología , Pirrolidinonas/farmacología , Antagonistas de Receptores Androgénicos/química , Animales , Productos Biológicos/química , Productos Biológicos/farmacología , Línea Celular Tumoral , Dysidea/química , Humanos , Masculino , Estructura Molecular , Neoplasias de la Próstata Resistentes a la Castración/tratamiento farmacológico , Pirrolidinonas/química , Relación Estructura-ActividadRESUMEN
Resistance of castration-resistant prostate cancer (CRPC) to enzalutamide and abiraterone involves the expression of constitutively active, truncated androgen receptor (AR) splice variants (AR-Vs) that lack a C-terminal ligand-binding domain (LBD). Both full-length AR and truncated AR-Vs require a functional N-terminal domain (NTD) for transcriptional activity thereby providing rationale for the development of ralaniten (EPI-002) as a first-in-class antagonist of the AR-NTD. Here, we evaluated the antitumor effect of a next-generation analog of ralaniten (EPI-7170) as a monotherapy or in combination with enzalutamide in prostate cancer cells that express AR-V7 that were resistant to enzalutamide. EPI-7170 had 8-9 times improved potency compared to ralaniten. Enzalutamide increased levels of AR-V7 and expression of its target genes. Knockdown of AR-V7 restored sensitivity to enzalutamide, indicating a role for AR-V7 in the mechanism of resistance. EPI-7170 inhibited expression of genes transcriptionally regulated by full-length AR and AR-V7. A combination of EPI-7170 and enzalutamide resulted in synergistic inhibition of proliferation of enzalutamide-resistant cells that was consistent with results from cell cycle and clonogenic assays. In addition, this drug enhanced the antitumor effect of enzalutamide in enzalutamide-resistant CRPC preclinical models. Thus, a combination therapy targeting both the NTD and LBD of AR, and thereby blocking both full-length AR and AR-Vs, has potential for the treatment of enzalutamide-resistant CRPC.
Asunto(s)
Antagonistas de Receptores Androgénicos/uso terapéutico , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Benzamidas/uso terapéutico , Nitrilos/uso terapéutico , Feniltiohidantoína/uso terapéutico , Neoplasias de la Próstata/tratamiento farmacológico , Receptores Androgénicos/química , Antagonistas de Receptores Androgénicos/farmacología , Animales , Benzamidas/farmacología , Ciclo Celular/efectos de los fármacos , Puntos de Control del Ciclo Celular/efectos de los fármacos , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Resistencia a Antineoplásicos/efectos de los fármacos , Sinergismo Farmacológico , Humanos , Masculino , Ratones Endogámicos NOD , Ratones SCID , Nitrilos/farmacología , Feniltiohidantoína/farmacología , Dominios Proteicos , Transcripción Genética/efectos de los fármacos , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Blocking androgen receptor (AR) transcriptional activity by androgen deprivation therapy (ADT) improves the response to radiotherapy for intermediate and high risk prostate cancer. Unfortunately, ADT, antiandrogens, and abiraterone increase expression of constitutively active splice variants of AR (AR-Vs) which regulate DNA damage repair leading to resistance to radiotherapy. Here we investigate whether blocking the transcriptional activities of full-length AR and AR-Vs with ralaniten leads to enhanced sensitivity to radiotherapy. Combination therapies using ralaniten with ionizing radiation were evaluated for effects on proliferation, colony formation, cell cycle, DNA damage, and Western blot analyses in human prostate cancer cells that express both full-length AR and AR-Vs. Ralaniten and a potent next-generation analog (EPI-7170) decreased expression of DNA repair genes whereas enzalutamide had no effect. FACS analysis revealed a dose-dependent decrease of BrdU incorporation with increased accumulation of γH2AX with a combination of ionizing radiation with ralaniten. An additive inhibitory effect on proliferation of enzalutamide-resistant cells was achieved with a combination of ralaniten compounds with ionizing radiation. Ralaniten and EPI-7170 sensitized prostate cancer cells that express full-length AR and AR-Vs to radiotherapy whereas enzalutamide had no added benefit.
RESUMEN
Methods for the focused isolation of low-abundance natural products with specific chemical substructures could expand known bioactive chemical diversity for drug discovery. Here we report the combined use of genome mining and an 15N NMR-based screening method for the targeted isolation of the low-abundance piperazic-acid-containing peptides incarnatapeptins A (1) and B (3). Incarnatapeptin B (3) shows in vitro cytotoxicity to LNCaP prostate cancer cells.
Asunto(s)
Antineoplásicos/farmacología , Productos Biológicos/farmacología , Streptomyces/química , Antineoplásicos/química , Antineoplásicos/aislamiento & purificación , Productos Biológicos/química , Productos Biológicos/aislamiento & purificación , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Ensayos de Selección de Medicamentos Antitumorales , Humanos , Espectroscopía de Resonancia Magnética , Isótopos de Nitrógeno , Protones , Streptomyces/genéticaRESUMEN
Introduction: Intrinsically disordered proteins (IDPs) and regions (IDRs) lack stable three-dimensional structure making drug discovery challenging. A validated therapeutic target for diseases such as prostate cancer is the androgen receptor (AR) which has a disordered amino-terminal domain (NTD) that contains all of its transcriptional activity. Drug discovery against the AR-NTD is of intense interest as a potential treatment for disease such as advanced prostate cancer that is driven by truncated constitutively active splice variants of AR that lack the C-terminal ligand-binding domain (LBD).Areas covered: This article presents an overview of the relevance of AR and its intrinsically disordered NTD as a drug target. AR structure and approaches to blocking AR transcriptional activity are discussed. The discovery of small molecules, including the libraries used, proven binders to the AR-NTD, and site of interaction of these small molecules in the AR-NTD are presented along with discussion of the Phase I clinical trial.Expert opinion: The lack of drugs in the clinic that directly bind IDPs/IDRs reflects the difficulty of targeting these proteins and obtaining specificity. However, it may also point to an inappropriateness of too closely borrowing concepts and resources from drug discovery to folded proteins.
Asunto(s)
Antagonistas de Receptores Androgénicos/farmacología , Neoplasias de la Próstata/tratamiento farmacológico , Receptores Androgénicos/efectos de los fármacos , Antagonistas de Receptores Androgénicos/administración & dosificación , Animales , Descubrimiento de Drogas , Humanos , Proteínas Intrínsecamente Desordenadas/química , Masculino , Terapia Molecular Dirigida , Neoplasias de la Próstata/patología , Pliegue de Proteína , Receptores Androgénicos/química , Receptores Androgénicos/metabolismo , Activación TranscripcionalRESUMEN
The androgen receptor (AR) is tightly linked to prostate cancer, but the mechanisms by which AR transactivation is dysregulated during cancer progression are not fully explored. Dagar et al. examined AR translocation to the nucleus to identify a link between heat shock protein 90 (HSP90) and protein kinase A (PKA). Their findings provide a potential mechanism of the initiation of AR transactivation and potential targets for developing and refining treatments for prostate cancer.
Asunto(s)
Neoplasias de la Próstata , Receptores Androgénicos , Proteínas Quinasas Dependientes de AMP Cíclico , Proteínas HSP90 de Choque Térmico , Humanos , Masculino , FosforilaciónRESUMEN
Inhibition of the androgen receptor (AR) is the mainstay treatment for advanced prostate cancer. Ralaniten (formally EPI-002) prevents AR transcriptional activity by binding to its N-terminal domain (NTD) which is essential for transcriptional activity. Ralaniten acetate (EPI-506) the triacetate pro-drug of ralaniten, remains the only AR-NTD inhibitor to have entered clinical trials (NCT02606123). While well tolerated, the trial was ultimately terminated due to poor pharmacokinetic properties and resulting pill burden. Here we discovered that ralaniten was glucuronidated which resulted in decreased potency. Long-term treatment of prostate cancer cells with ralaniten results in upregulation of UGT2B enzymes with concomitant loss of potency. This has proven to be a useful model with which to facilitate the development of more potent second-generation AR-NTD inhibitors. Glucuronidated metabolites of ralaniten were also detected in the serum of patients in Phase 1 clinical trials. Therefore, we tested an analogue of ralaniten (EPI-045) which was resistant to glucuronidation and demonstrated superiority to ralaniten in our resistant model. These data support that analogues of ralaniten designed to mitigate glucuronidation may optimize clinical responses to AR-NTD inhibitors.
RESUMEN
Expression of androgen receptor (AR) splice variant 7 (AR-V7) has been identified as the mechanism associated with the development of castration-resistant prostate cancer (CRPC). However, a potential link between AR-V7 expression and resistance to taxanes, such as docetaxel or cabazitaxel, has not been unequivocally demonstrated. To address this, we used LNCaP95-DR cells, which express AR-V7 and exhibit resistance to enzalutamide and docetaxel. Interestingly, LNCaP95-DR cells showed cross-resistance to cabazitaxel. Furthermore, these cells had increased levels of P-glycoprotein (P-gp) and their sensitivity to both docetaxel and cabazitaxel was restored through treatment with tariquidar, a P-gp antagonist. Results generated demonstrated that P-gp mediated cross-resistance between docetaxel and cabazitaxel. Although the LNCaP95-DR cells had increased expression of AR-V7 and its target genes (UBE2C, CDC20), the knockdown of AR-V7 did not restore sensitivity to docetaxel or cabazitaxel. However, despite resistance to docetaxel and carbazitaxel, EPI-002, an antagonist of the AR amino-terminal domain (NTD), had an inhibitory effect on the proliferation of LNCaP95-DR cells, which was similar to that achieved with the parental LNCaP95 cells. On the other hand, enzalutamide had no effect on the proliferation of either cell line. In conclusion, our results suggested that EPI-002 may be an option for the treatment of AR-V7-driven CRPC, which is resistant to taxanes.
RESUMEN
Enzalutamide is a nonsteroidal antiandrogen for the treatment of metastatic castration-resistant prostate cancer (mCRPC) both before and after chemotherapy. Enzalutamide is more effective than its predecessor bicalutamide, which was analyzed in head-to-head studies of patients with CRPC. This family of nonsteroidal antiandrogens is now comprised of four drugs approved by the US Food and Drug Administration with two investigational drugs in clinical trials. Antiandrogens have been employed clinically for more than five decades to provide a rich resource of information. Steady-state concentration minimums (Cmin or trough) in the range of ~1-13 µg/mL are measured in patients at therapeutic doses. Interestingly, enzalutamide which is considered to have strong affinity for the androgen receptor (AR) requires Cmin levels >10 µg/mL. The sequence of antiandrogens and the clinical order of application in regard to other drugs that target the androgen axis remain of high interest. One novel first-in-class drug, called ralaniten, which binds to a unique region in the N-terminus domain of both the full-length and the truncated constitutively active splice variants of the AR, is currently in clinical trials for patients who previously received abiraterone, enzalutamide, or both. This highlights the trend to develop drugs with novel mechanisms of action and potentially differing mechanisms of resistance compared with antiandrogens. Better and more complete inhibition of the transcriptional activity of the AR appears to continue to provide improvements in the clinical management of mCRPC.
RESUMEN
The transcriptional activity of the androgen receptor is tightly regulated by an intrinsically disordered N-terminal transactivation domain. In this issue of Structure, De Mol et al. (2018) identify a motif in the disordered transactivation domain that can be induced to adopt a helical conformation essential for interaction with the transcriptional machinery.