Androgen Receptor Nuclear Translocation Research Articles

Dual androgen receptor (AR) and STAT3 inhibition by a compound targeting the AR amino-terminal domain.

Prostate cancer (PCa) often recurs as incurable castration‐resistant prostate cancer (CRPC) after the failure of androgen deprivation therapy. CRPC development relies on androgen receptor (AR) signaling. The IL6/STAT3 pathway is also a key driver of CRPC. The crosstalk between IL6/STAT3 and the AR pathways provides opportunities to explore next‐generation agents to treat PCa. Through screening of around 600 natural compounds in our newly established prostate tumorigenesis model, potential STAT3 signaling inhibitors were found and additionally examined for effects on AR signaling. The small molecular compound 154 exhibited dual effects on IL6/STAT3 and AR pathways. We show here that compound 154 inhibits AR and STAT3 transcriptional activity, reduces the expression of phosphorylation of STAT3 (Y705) and downregulates the mRNA levels of AR target genes. Compound 154 also inhibits protein expression of AR and AR splice variants (ARv567es and AR‐V7) without altering AR mRNA levels. Compound 154 binds to AR directly, but not to STAT3 and is identified as an antagonist of the AR amino‐terminal domain (NTD) by disrupting protein‐protein interactions between STAT3 and the AR NTD. Moreover, compound 154 does not reduce AR nuclear translocation. Compound 154 possesses the potential to become a leading compound in novel therapies against CRPC.

Abstract B001: CYP3A5 promotes AR downstream signaling and contributes to therapeutic resistance

Abstract Purpose: Androgen receptor (AR) plays a major role in promoting growth and progression of prostate cancer and thus has been successfully targeted therapeutically. Therapeutic resistance to androgen deprivation therapy (ADT) accounts for much of the morbidity and mortality attributable to prostate cancer. Therapeutic resistance is typically accompanied by insufficient blockade of AR activation, whose initial step involves translocation of AR to the nucleus. In recent studies we demonstrated that CYP3A5 facilitates the nuclear translocation of AR, promoting prostate cancer growth. This work focuses on understanding the role of CYP3A5 in regulating AR nuclear translocation and therapeutic resistance. Method: To understand how CYP3A5 effects AR downstream signaling, we used RT2 profiler PCR arrays to help identify set of genes in AR signaling pathway that are affected by CYP3A5 inhibition. Confocal microscopy and cell fractionation experiments were used to further confirm the effect of CYP3A5 modulation of AR signaling. As concomitant CYP3A5 inducer/inhibitor medications can affect intratumoral CYP3A5 activity and thus may modify AR downstream signaling, we utilized cell fractionation and confocal microscopy to analyze the effect of these medications on AR nuclear translocation. Further, to decipher the role of CYP3A5 in the AR translocation process we performed a series of co-immunoprecipitation (co-IP) experiments with CYP3A5 and components of HSP90-AR complex. We used extracts of LNCaP transfected with a CYP3A5-Flag-tagged construct for IP, with either Flag-agarose or HSP90 and AR antibodies with A/G beads. Finally, to decipher CYP3A5’s role in therapeutic resistance we analyzed cDNA after CYP3A5 siRNA treatment using drug resistance RT2 profiler PCR array. Results: The q-PCR based profiler assay revealed a set of nine AR regulated genes (SCL45A3, FKBP5, NCAPD3, MYC, MME, ELL2, PIK3R3, HPRT1, and SPDEF) downregulated with CYP3A5 siRNA treatment with a p value of ≤0.005. MYC and PIK3R3 are known to be involved in regulating cell growth by either affecting cell cycle progression and/or apoptosis. PSA, known to aid in the cell growth, is regulated by SPDEF, a transcription factor. Downregulation of these genes with CYP3A5 siRNA treatment indicates that CYP3A5 modifier medications can alter AR downstream signaling regulating growth. Concomitantly prescribed CYP3A inhibitors amiodarone and ritonavir blocked AR nuclear migration and decreased PSA expression whereas inducers phenytoin and rifampicin promoted increased AR nuclear migration and increased PSA production, supporting our hypothesis. Co-immunoprecipitation experiments revealed that CYP3A5 is a part of the HSP90-AR complex. Both Flag-immunoprecipitation and indirect immunoprecipitation revealed that CYP3A5 associates with the HSP90-AR complex. The CYP3A5 siRNA also downregulated 11 genes (TOP2A, BRCA1/2, CCNE1, CDK2/4, DHFR, MVP, MYC, RARB, and HPRT1) known to confer drug resistance, with a p value of ≤0.005. The role of TOP2A, MYC, and BRCA is well known in prostate cancer drug resistance; thus, their downregulation with CYP3A5 siRNA treatment may predict better outcome. Conclusion: Our results indicate that CYP3A5 is a part of the HSP90-AR complex and positively regulates AR nuclear translocation promoting AR downstream signaling and therapeutic resistance. Therefore, targeting CYP3A5 to block AR nuclear translocation may be a therapeutic adjunctive approach in advanced prostate cancer. As CYP3A5 siRNA also downregulates drug-resistance genes, targeting CYP3A5 may also help overcome therapeutic resistance. As many concomitant medications can alter CYP3A5 activity, thus they can modify AR signaling. We hypothesize that AR directed therapeutic efficacy can be optimized by proper drug selection through minimizing the use of AR inducers while maximizing the use of AR inhibitors. These observations may play a significant role in African Americans who express high level of wild-type CYP3A5 and often have aggressive prostate cancer. Citation Format: Priyatham Gorjala, Oscar B. Goodman Jr., Ranjana Mitra. CYP3A5 promotes AR downstream signaling and contributes to therapeutic resistance [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B001.

Inhibition of androgen receptor transactivation function by adenovirus type 12 E1A undermines prostate cancer cell survival.

Mutations or truncation of the ligand-binding domain (LBD) of androgen receptor (AR) underlie treatment resistance for prostate cancer (PCa). Thus, targeting the AR N-terminal domain (NTD) could overcome such resistance. Luciferase reporter assays after transient transfection of various DNA constructs were used to assess effects of E1A proteins on AR-mediated transcription. Immunofluorescence microscopy and subcellular fractionation were applied to assess intracellular protein localization. Immunoprecipitation and mammalian two-hybrid assays were used to detect protein-protein interactions. qRT-PCR was employed to determine RNA levels. Western blotting was used to detect protein expression in cells. Effects of adenoviruses on prostate cancer cell survival were evaluated with CellTiter-Glo assays. Adenovirus 12 E1A (E1A12) binds specifically to the AR. Interestingly, the full-length E1A12 (266 aa) preferentially binds to full-length AR, while the small E1A12 variant (235 aa) interacts more strongly with AR-V7. E1A12 promotes AR nuclear translocation, likely through mediating intramolecular AR NTD-LBD interactions. In the nucleus, AR and E1A12 co-expression in AR-null PCa cells results in E1A12 redistribution from nuclear foci containing CBX4 (also known as Pc2), suggesting a preferential AR-E1A12 interaction over other E1A12 interactors. E1A12 represses AR-mediated transcription in reporter gene assays and endogenous AR target genes such as ATAD2 and MYC in AR-expressing PCa cells. AR-expressing PCa cells are more sensitive to death induced by a recombinant adenovirus expressing E1A12 (Ad-E1A12) than AR-deficient PCa cells, which could be attributed to the increased viral replication promoted by androgen stimulation. Targeting the AR by E1A12 promotes apoptosis in PCa cells that express the full-length AR or C-terminally truncated AR variants. Importantly, inhibition of mTOR signaling that blocks the expression of anti-apoptotic proteins markedly augments Ad-E1A12-induced apoptosis of AR-expressing cells. Mechanistically, Ad-E1A12 infection triggers apoptotic response while activating the PI3K-AKT-mTOR signaling axis; thus, mTOR inhibition enhances apoptosis in AR-expressing PCa cells infected by Ad-E1A12. Ad12 E1A inhibits AR-mediated transcription and suppresses PCa cell survival, suggesting that targeting the AR by E1A12 might have therapeutic potential for treating advanced PCa with heightened AR signaling.

Abstract B48: Effect of concomitant CYP3A5-modulating drugs on androgen-receptor signaling in African American men undergoing androgen deprivation therapy

Abstract Introduction: In a recent study we have established that CYP3A5 augments nuclear translocation of androgen receptor (AR) and promotes prostate cancer (PC) growth. CYP3A isoforms are responsible for metabolizing almost 50% of the commonly prescribed drugs, many of which are CYP3A5 inhibitors and inducers. PC patients are elderly with comorbidities and are often prescribed concomitant medications while undergoing androgen-deprivation therapy (ADT), the most preferred treatment for PC. CYP3A5 is polymorphic, and African Americans (AA, 73%) express higher levels of CYP3A5 due to presence of wild-type CYP3A5 (*1/*1) compared to Caucasians (95%) expressing the mutant (*3/*3) producing only 13% of the active full-length CYP3A5 protein. Due to the expression of wild-type CYP3A5 in AA, concomitant medications modulating CYP3A5 activity can drastically alter AR activity and ADT efficacy in these patients. Our current work is focused on deciphering the mechanism of how commonly used CYP3A5-modulating medications can alter AR signaling in AA carrying the wild-type CYP3A5. Method: We genotyped the androgen-responsive prostate cancer cell lines to determine their CYP3A5 status using TaqMan® Drug Metabolism assay. We used cDNA from cells treated with either nontarget or CYP3A5 siRNA in RT2 profiler PCR arrays to identify set of genes in AR signaling pathway that are affected by CYP3A5 inhibition. Confocal microscopy was used to study AR nuclear localization after exposure to commonly used CYP3A5 inducer/inhibitor drugs. Cell fractionation experiments were used to further confirm the effect of these drugs on AR signaling. Luciferase-based reporter assay was used to test effect of CYP3A5-modulating drugs on AR activity. Results: Our genotyping assay revealed that MDA PCa 2b (African American) carries *1/*3 CYP3A5 gene compared to LNCaP (Caucasian) carrying *3/*3 genotype. To compare the differences due to CYP3A5 genotype on AR signaling, we selected MDAPCa2b and LNCaP cells for further studies. Consistent with earlier observations with LNCaP, MDA PCa 2b cell lines also showed decreased nuclear translocation of AR with CYP3A5 siRNA in both confocal and cell fractionation experiments. We also observed blocking of AR nuclear localization with azamulin, a CYP3A-specific inhibitor in both cell lines. The q-PCR-based profiler assay revealed a set of nine AR-regulated genes (SCL45A3, FKBP5, NCAPD3, MYC, MME, ELL2, PIK3R3, HPRT1, and SPDEF) downregulated with CYP3A5 siRNA treatment with a p value of ≤0.005 in MDA PCa 2b cells. MYC is known to be involved in cell cycle progression and apoptosis whereas PIK3R3 codes for the regulatory subunit of PI3 kinase regulating cell growth. SPDEF codes for a transcription factor promoting PSA known to aid in the cell growth. Downregulation of these genes with CYP3A5 siRNA treatment indicates that CYP3A5 modifier medications can alter AR downstream signaling regulating growth. We tested some commonly prescribed drugs that are either CYP inhibitors (amiodarone, ritonavir) or inducers (phenytoin, rifampicin) and evaluated their ability to alter AR signaling. The results revealed that the CYP inducers promoted increased AR nuclear migration and increased PSA production whereas CYP3A5 inhibitors blocked AR nuclear migration, decreasing PSA expression in both cell lines. A luminescence-based reporter assay using androgen response elements also supported that these CYP3A inducer and inhibitor drugs alter AR signaling. Conclusion: Our results indicate that concomitant medications that can alter CYP3A5 activity can modify AR signaling and PC growth. These results suggest that these CYP-modulating drugs can alter efficacy of ADT severely in AA men predominantly expressing wild-type CYP3A5 (*1/*1). We hypothesize that AR-directed therapeutic efficacy can be optimized by proper drug selection through minimizing the use of AR inducers while maximizing the use of AR inhibitors in patients undergoing ADT. Citation Format: Priyatham Gorjala, Oscar B. Goodman Jr., Ranjana Mitra. Effect of concomitant CYP3A5-modulating drugs on androgen-receptor signaling in African American men undergoing androgen deprivation therapy [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B48.

Abstract 945: Novel role for SIRT1 in non-canonical activation of AR signaling

Abstract Metastatic castrate resistance prostate cancer (CRPC) is most challenging to treat with a 5-year survival of less than 32%. Despite improved treatment landscape including use of second-generation androgen receptor (AR)-pathway inhibitors, emergence of acquired resistance is a significant problem facing both physicians and researchers. This is in part due to incomplete understanding of the compensatory molecular networks associated with therapeutic resistance. NAD+-dependent deacetylase, Sirtuin 1 (SIRT1), was traditionally known to modulate various cellular and pathological processes by regulating both histone and non-histone proteins. Furthermore, analysis of data from multiple prostate cancer cohorts indicated association of SIRT1 genetic alterations with poor clinical outcome. These findings suggest previously uncharacterized role for SIRT1 in prostate pathogenesis including therapeutic resistance. Based on these observations, we examined the role of SIRT1 in prostate pathogenesis using in vitro cell culture and in vivo preclinical models. Levels of SIRT1 are relatively higher in hormone-sensitive (LNCaP) cells compared to castrate resistant AR-positive (22Rv1) and androgen independent AR-negative (PC-3 & DU145) cells. Notably, stably knockdown (KD) of SIRT1 in LNCaP but not 22Rv1 cells showed downregulation of AR signaling pathway as evidenced by decreased levels and expression of subset of AR target genes (PSA, FKBP5), and secreted levels of PSA. Interestingly, SIRT1 KD reduced PSA reporter activity and secreted levels even under androgen depleted conditions with no significant effect on AR protein levels and nuclear translocation. Further, the observed SIRT1-mediated repression of AR signaling changes was independent of AR activation by androgen stimulation or suppression by enzalutamide. Biologically, these changes reflected in significantly decreased cell growth and migratory ability. Importantly, SIRT1 silenced LNCaP cells were more sensitive to growth suppression under conditions of androgen deprivation. Additionally, silencing of SIRT1 markedly inhibited tumor development in nude mice. Taken together, these findings led us to believe that SIRT1 could play a regulatory role in prostate pathogenesis in part by altering AR transcriptional network, independent of canonical AR signaling. Thus, our study identified previously uncharacterized role for SIRT1 in activation of AR signaling and promoting therapeutic resistance, offering avenues to develop SIRT1 or SIRT1 regulated pathways as novel therapeutic targets for PCA management. Supported by CPRIT RP150166 (APK) & CPRIT RP170345 (SH). Citation Format: Shih-Bo Huang, Dinesh Thapa, Amanda Muñoz, Roble G. Bedolla, Ratnesh Srivastav, Rita Ghosh, Addanki P. Kumar. Novel role for SIRT1 in non-canonical activation of AR signaling [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 945.

Apalutamide: the established and emerging roles in the treatment of advanced prostate cancer

ABSTRACTIntroduction: Prostate cancer (PCa) is the most common cancer in elderly males. Androgen deprivation therapy (ADT) is still the cornerstone of initial treatment; however, the vast majority of patients develop castration-resistant prostate cancer (CRPC). Several studies with numerous androgen receptor (AR)-directed agents have emerged since the approval of abiraterone acetate and enzalutamide. One of these agents is apalutamide, which seems to be a promising AR antagonist for the treatment of CRPC.Areas covered: The authors review Phase I, II, and III studies for apalutamide, in a large spectrum of PCa (from low-risk to metastatic CRPC [mCRPC]) patients as sole treatment or in the setting of combined therapy.Expert opinion: Apalutamide is an oral, investigational, AR antagonist that targets the AR ligand-binding domain and prevents AR nuclear translocation, DNA binding, and transcription of AR gene targets. It has shown favorable safety profile and therapeutic index in Phase I studies, good tolerance and efficacy in patients with high-risk CRPC in Phase II studies. Also, results were promising in a recent phase III study in patients with non-mCRPC who were at high risk for the development of metastasis. These data may offer potential advantages over the second-generation antiandrogens.

Androgen receptor modulation following combination exposure to brominated flame-retardants

Endocrine disrupting compounds can interfere with androgen receptor (AR) signaling and disrupt steroidogenesis leading to reproductive failure. The brominated flame-retardant (BFR) 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane (TBECH), is an agonist to human, chicken and zebrafish AR. Recently another group of alternative BFRs, allyl 2, 4, 6-tribromophenyl ether (ATE), and 2, 3-dibromopropyl 2, 4, 6-tribromophenyl ether (DPTE) along with its metabolite 2-bromoallyl 2, 4, 6-tribromophenyl ether (BATE) were identified as potent human AR antagonists. These alternative BFRs are present in the environment. The aim of the present study was to determine the effect of mixed exposures to the AR agonist and the AR antagonists at environmentally relevant concentrations. In vitro reporter luciferase assay showed that the AR antagonists, when present at concentration higher than TBECH, were able to inhibit TBECH-mediated AR activity. These AR antagonists also promoted AR nuclear translocation. In vitro gene expression analysis in the non-tumorigenic human prostate epithelial cell RWPE1 showed that TBECH induced AR target genes whereas DPTE repressed these genes. Further analysis of steroidogenic genes showed that TBECH up-regulated most of the genes while DPTE down-regulated the same genes. The results indicate that when TBECH and DPTE are present together they will antagonize each other, thereby reducing their individual effects.

Mycophenolate Mofetil induces c-Jun-N-terminal kinase expression in 22Rv1 cells: an impact on androgen receptor signaling.

Mycophenolate Mofetil (MYC) is a transplant drug used to prevent rejection in heart and kidneys transplant patients. Inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in de novo synthesis of guanosine nucleotides, was considered as a primary target for MYC. Recently, we described that MYC was activates aryl hydrocarbon receptor and it antagonizes glucocorticoid receptor. Here we describe an androgen receptor (AR) as another off-target for MYC.We found that MYC increased basal and dihydrotestosterone (DHT)-inducible AR-dependent luciferase activity in AIZ-AR cells. In the same manner it induced or augmented mRNA level of KLK3 (prostate specific antigen; PSA) in 22Rv1 cells. Herein it displayed a hormetic effect on proliferation activity, since it significantly stimulated proliferation in lower concentrations but inhibited in higher (>1 µg/ml) concentrations in the presence of DHT. In contrast, MYC suppressed DHT-inducible KLK3 mRNA expression and cell proliferation in androgen-dependent LNCaP cells. MYC augmented DHT-inducible nuclear translocation of AR and increased the expression of MAPK8/9 (JNK46/54) resulting in the drop of their phosphorylation status. Moreover, MYC sensitized DHT-treated 22Rv1 cells to JNK-IN-8 mediated growth inhibition with the drop of IC50 from 1425 nM to 84 nM within 24 hrs. In conclusion, we suggest that, castrate-resistant prostate cancers progression might be retarded with the combination of MYC and chemical JNK inhibitors, involving AR-dependent mechanism.

Differential regulation of the androgen receptor by protein phosphatase regulatory subunits.

The Androgen Receptor (AR) is a key molecule in the development, maintenance and progression of prostate cancer (PC). However, the relationship between the AR and co-regulatory proteins that facilitate AR activity in castrate resistant settings remain understudied. Here we show that protein phosphatase 1 regulatory subunits, identified from a phosphatase RNAi screen, direct PP1 catalytic subunits to a varied yet significant response in AR function. As such, we have characterised the PP1β holoenzyme, myosin phosphatase (MLCP), as a novel ligand independent regulator of the AR. Sustained MLCP activity through down-regulation of the MLCP inhibitory subunit, PPP1R14C, results in impaired AR nuclear translocation, protein stability and transcriptional activity in distinct models of PC progression, culminating in restoration of a non-malignant prostate genotype. Phenotypically, a marked reduction in cell proliferation and migration, characterised by G1 cell cycle arrest is observed, confirming PP1 holoenzyme disruption as a novel treatment approach in PC.

Selective inhibition reveals cyclin-dependent kinase 2 as another kinase that phosphorylates the androgen receptor at serine 81

Several studies have revealed that cyclin-dependent kinases (CDK) can mediate phosphorylation of steroid receptors at multiple sites, including serine 81 of the androgen receptor (AR). Phosphorylation of S81 is required for AR nuclear translocation, an association with chromatin and also regulates endogenous AR-regulated transcription in response to hormones. Up to date, S81-phosphorylation has been studied using different CDK inhibitors. Nevertheless, most inhibitors are non-selective or have unknown selectivity. We investigated the selectivity of commercially available CDK inhibitors and identified compounds that will be suitable for further studies to identify the CDKs responsible for S81-AR phosphorylation. We confirmed the positive impact of CDK1 and CDK9 on phosphorylation of S81-AR and its transcriptional activity. Although CDK1-mediated phosphorylation was previously shown to occur during mitosis, our experiments did not confirm this finding. By using chemical and genetic inhibition techniques, we identified that CDK2 contributes to S81-AR phosphorylation and transactivation while CDK4 was not shown to be involved in this process.

Fluoride Alters Klk4 Expression in Maturation Ameloblasts through Androgen and Progesterone Receptor Signaling.

Fluorosed maturation stage enamel is hypomineralized in part due to a delay in the removal of matrix proteins to inhibit final crystal growth. The delay in protein removal is likely related to reduced expression of kallikrein-related peptidase 4 (KLK4), resulting in a reduced matrix proteinase activity that found in fluorosed enamel. Klk4 transcription is known to be regulated in other cell types by androgen receptor (AR) and progesterone receptors (PR). In this study, we determined the possible role of fluoride in down-regulation of KLK4 expression through changes in AR and PR. Immunohistochemical localization showed that both AR and PR nuclear translocation was suppressed in fluoride exposed mice. However, when AR signaling was silenced in mouse ameloblast-lineage cells (ALCs), expression of both Pgr and Klk4 were increased. Similar to the effect from AR silencing, fluoride also upregulated Pgr in ALCs, but downregulated Klk4. This finding suggests that though suppression of AR transactivation by fluoride increases Prg expression, inhibition of PR transactivation by fluoride has a much greater effect, ultimately resulting in downregulation of Klk4 expression. These findings indicate that in ameloblasts, PR has a dominant role in regulating Klk4 expression. We found that when AR was retained in the cytoplasm in the presence of fluoride, that co-localized with heat shock protein 90 (HSP90), a well-known chaperone for steroid hormone receptors. HSP90 also known to regulate TGF-β signaling. Consistent with the effect of fluoride on AR and HSP90, we found evidence of reduced TGF-β signaling activity in fluorosed ameloblasts as reduced immunolocalization of TGFB1 and TGFBR-2 and a significant increase in Cyclin D1 mRNA expression, which also possibly contributes to the reduced AR signaling activity. In vitro, when serum was removed from the media, aluminum was required for fluoride to inhibit the dissociation of HSP90 from AR. In conclusion, fluoride related downregulation of Klk4 is associated with reduced nuclear translocation of AR and PR, and also reduced TGF-β signaling activity, all of which are regulated by HSP90. We suggest that a common mechanism by which fluoride affects AR, PR, and TGF-β signaling is through inhibiting ATP-dependent conformational cycling of HSP90.

PADI2-Mediated Citrullination Promotes Prostate Cancer Progression.

Onset of castration-resistance prostate cancer (CRPC) after long-term androgen deprivation therapy remains a major obstacle in the treatment of prostate cancer. The peptidylarginine deiminase PADI2 has been implicated in chronic inflammatory diseases and cancer. Here we show that PADI2 is an androgen-repressed gene and is upregulated in CRPC. PADI2 expression was required for survival and cell-cycle progression of prostate cancer cells, and PADI2 promoted proliferation of prostate cancer cells under androgen-deprived or castration conditions in vitro and in vivo Cytoplasmic PADI2 protected the androgen receptor (AR) against proteasome-mediated degradation and facilitated AR binding to its target genes after nuclear translocation and citrullination of histone H3 amino acid residue R26. In contrast, mutant PADI2 D180A failed to affect AR stability, nuclear translocation, or transcriptional activity. PADI2 mediated AR control in a manner dependent on its enzymatic activity and nuclear localization, as correlated with increased histone H3 citrullination. Notably, coadministration of the PADI inhibitor Cl-Amidine and the AR signaling inhibitor enzalutamide synergized in inhibiting CRPC cell proliferation in vitro and tumor growth in vivo Overall, our results establish PADI2 as a key mediator for AR in prostate cancer progression, especially CRPC, and they suggest PADI as novel therapeutic targets in this disease setting. Cancer Res; 77(21); 5755-68. ©2017 AACR.

Moving Towards Precision Urologic Oncology: Targeting Enzalutamide-resistant Prostate Cancer and Mutated Forms of the Androgen Receptor Using the Novel Inhibitor Darolutamide (ODM-201)

Darolutamide (ODM-201) is a novel androgen receptor (AR) antagonist with a chemical structure distinctly different from currently approved AR antagonists that targets both wild-type and mutated ligand binding domain variants to inhibit AR nuclear translocation. Here, we evaluate the activity of darolutamide in enzalutamide-resistant castration resistant prostate cancer (CRPC) as well as in AR mutants detected in patients after treatment with enzalutamide, abiraterone, or bicalutamide. Darolutamide significantly inhibited cell growth and AR transcriptional activity in enzalutamide-resistant MR49F cells in vitro, and led to decreased tumor volume and serum prostate-specific antigen levels in vivo, prolonging survival in mice bearing enzalutamide-resistant MR49F xenografts. Moreover, darolutamide inhibited the transcriptional activity of AR mutants identified in the plasma of CRPC patients progressing on traditional therapies. In particular, darolutamide significantly inhibited the transcriptional activity of the F877L, H875Y/T878A, F877L/T878A, and the previously unreported T878G AR mutants, that transform enzalutamide into a partial agonist. In silico cheminformatics computer modeling provided atomic level insights confirming darolutamide antagonist effect in F877L and T878G AR mutants. In conclusion, our results provide a rationale for further clinical evaluation of darolutamide in enzalutamide-resistant CRPC, in particular in combination with circulating tumor DNA assays that detect AR mutants sensitive to darolutamide, in a precision oncology setting. Patient summaryIn this study we evaluated the novel drug darolutamide in preclinical models of prostate cancer. We found that darolutamide delays growth of enzalutamide-resistant prostate cancer, in particular in cells with mutated forms of the androgen receptor after previous treatment. Our data supports further evaluation of darolutamide in clinical trials.

Abstract 3130: CYP3A5 positively regulates androgen receptor signaling in prostate cancer cells: Potential for therapeutic targeting

Abstract Purpose: Prostate cancer is the most common malignancy and second leading cause of cancer-specific mortality in US men. The androgen receptor (AR) plays a major role in promoting growth and progression of prostate cancer and thus has been successfully targeted therapeutically. Therapeutic resistance to androgen deprivation therapy (ADT) accounts for much of the morbidity and mortality attributable to prostate cancer. Therapeutic resistance is typically accompanied by insufficient blockade of AR activation, whose initial step involves translocation of AR to the nucleus. Previously we demonstrated that CYP3A5 facilitates the nuclear translocation of AR, promoting prostate cancer growth. Targeting CYP3A5 and blocking AR nuclear translocation may override therapeutic resistance to ADT, representing a novel approach for treating men with advanced prostate cancer. This work focuses on understanding the role of CYP3A5 in regulating AR nuclear translocation process and its subsequent promotion of prostate cancer growth. Methods: AR nuclear translocation is tightly regulated through a process involving several chaperones, multiple cofactors, and kinases, including HSP90, HSP70, HSP40 and HSP27. Complexed HSP90 maintains the AR as an inactive receptor in the cytoplasm. Upon androgen binding and activation, AR associates with HSP27, then translocates to the nucleus where it activates transcription of AR regulated genes responsible for prostate cancer growth. To decipher the role of CYP3A5 in this AR translocation process we performed a series of co-immunoprecipitation experiments with CYP3A5 and components of HSP90-AR complex, at different stages of AR translocation process. We used extracts of LNCaP transfected with a CYP3A5-Flag-tagged construct with either Flag-agarose or HSP90 and AR antibodies with A/G beads for immunoprecipitation. Results: Our co-immunoprecipitation experiments using CYP3A5-Flag transfected LNCaP extracts demonstrate that CYP3A5 associates with the HSP90-AR complex that helps to maintain AR in a form that can be readily activated by androgen. Using Flag-agarose in co-immunoprecipitation experiments, we demonstrated that CYP3A5 is a component of the HSP90-AR complex, associating with AR, HSP90, HSP70 and HSP40 each which are chaperones regulating AR nuclear translocation. We further confirmed the presence of CYP3A5 in the HSP90-AR complex by co-immunoprecipitation using HSP90 and AR antibodies in combination with A/G beads instead of flag-agarose. Conclusion: Our current finding supports the notion that CYP3A5 is a part of the HSP90-AR complex and positively regulates AR nuclear translocation. Therefore, targeting CYP3A5 to block AR nuclear translocation may be a therapeutic adjunctive approach in advanced prostate cancer. Citation Format: Ranjana Mitra, Priyatham Gorjala, Oscar B. Goodman. CYP3A5 positively regulates androgen receptor signaling in prostate cancer cells: Potential for therapeutic targeting [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 3130. doi:10.1158/1538-7445.AM2017-3130

Sigma1 Targeting to Suppress Aberrant Androgen Receptor Signaling in Prostate Cancer.

Suppression of androgen receptor (AR) activity in prostate cancer by androgen depletion or direct AR antagonist treatment, although initially effective, leads to incurable castration-resistant prostate cancer (CRPC) via compensatory mechanisms including resurgence of AR and AR splice variant (ARV) signaling. Emerging evidence suggests that Sigma1 (also known as sigma-1 receptor) is a unique chaperone or scaffolding protein that contributes to cellular protein homeostasis. We reported previously that some Sigma1-selective small molecules can be used to pharmacologically modulate protein homeostasis pathways. We hypothesized that these Sigma1-mediated responses could be exploited to suppress AR protein levels and activity. Here we demonstrate that treatment with a small-molecule Sigma1 inhibitor prevented 5α- dihydrotestosterone-mediated nuclear translocation of AR and induced proteasomal degradation of AR and ARV, suppressing the transcriptional activity and protein levels of both full-length and splice-variant AR. Consistent with these data, RNAi knockdown of Sigma1 resulted in decreased AR levels and transcriptional activity. Furthermore, Sigma1 physically associated with ARV7 and ARv567es as well as full-length AR. Treatment of mice xenografted with ARV-driven CRPC tumors with a drug-like small-molecule Sigma1 inhibitor significantly inhibited tumor growth associated with elimination of AR and ARV7 in responsive tumors. Together, our data show that Sigma1 modulators can be used to suppress AR/ARV-driven prostate cancer cells via regulation of pharmacologically responsive Sigma1-AR/ARV interactions, both in vitro and in vivoCancer Res; 77(9); 2439-52. ©2017 AACR.

Androgen receptor-positive, triple-negative breast cancer.

Androgen receptor-positive, triple-negative breast cancer.

Phase Ib study of apalutamide (APA) with abiraterone acetate (AA) and prednisone (P) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): Update on safety and efficacy.

173 Background: APA and AA target the androgenreceptor (AR) axis via different mechanisms and may have complementary activity in mCRPC. APA is an advanced AR antagonist that targets the AR ligand-binding domain with high affinity (Clegg. Cancer Res. 2012). APA prevents AR nuclear translocation, DNA binding, and transcription of AR gene targets. This phase 1b study evaluates potential PK interactions between APA and AA + P. Here we report antitumor activity and safety of APA in combination with AA + P from 57 pts versus 29 pts presented at ASCO 2015 (NCT02123758). Methods: Pts with progressive mCRPC and ECOG PS ≤ 2 received AA (1000 mg/d) + P (5 mg BID) on Cycle 1 Day 1 (C1D1) with addition of APA (240 mg/d) on C1D8 in 28-day treatment (tmt) cycles. Efficacy assessment was based on RECIST 1.1 and PCWG2 criteria. Results: 57 pts started tmt on study; median tmt duration was 17 weeks. Median age was 70 years (range, 49-89) and median baseline PSA was 111 µg/L (range, 4-2597). Bone, nodal, and visceral disease were present in 50 (88%), 31 (54%), and 17 (30%) pts, respectively. 29 (51%), 29 (51%), and 23 (40%) pts were previously treated with a taxane, AA, or enzalutamide (ENZ), respectively. 47 pts discontinued tmt: disease progression (n = 39), consent withdrawal (n = 3), physician decision (n = 1), death (n = 1), and other (n = 3). In AA- and ENZ-naïve pts (n = 18), 67% had PSA decline ≥ 50%. In AA- or ENZ-treated pts (n = 39), 15% had PSA decline ≥ 50%. Most commonly reported ( > 10% of pts) drug-related AEs: fatigue (42%), diarrhea (21%), vomiting (21%), nausea (19%), hypokalemia (19%), decreased appetite (16%), hot flush (12%), abdominal pain (12%), and dysgeusia (11%). Grade ≥ 3 drug-related AEs reported in > 1 pt: fatigue (7%), hypokalemia (3.5%), hyponatremia (3.5%), and hypertension (3.5%). 1 pt discontinued study drug for grade 3 fatigue. Conclusions: Interim data indicate that 240 mg/d of APA with 1000 mg/d of AA + P has antitumor activity and an acceptable safety profile in mCRPC. Clinical trial information: NCT02123758. [Table: see text]

The Efflux Transporter ABCG2 Maintains Prostate Stem Cells.

This study identifies the mechanism by which the prostate stem cell marker, ABCG2, plays a role in prostate stem cell maintenance and provides a rationale for targeting ABCG2 for differentiation therapy in prostate cancer. Mol Cancer Res; 15(2); 128-40. ©2016 AACR.

Highlights of This Issue

MYC is a pleiotropic transcription factor that plays an important role in promoting the development and progression of human tumors. In the current study, Posternak and colleagues expand on a global role for MYC in regulating mRNA cap methylation. MYC specifically targets genes involved in Wnt/β-catenin signaling leading to augmented translational capacity and increased Wnt signaling activity. Mechanistically, MYC promotes recruitment of RNA methyltransferase to Wnt signaling gene promoters in part through an interaction between the TRRAP/TIP60 acetyltransferase complex and TFIIH. These data provide additional avenues to pursue in the development of targeted therapies for MYC-driven cancers.Prostate stem cells and prostate cancer stem cells have low or no androgen receptor (AR) expression. The ABC transporter, ABCG2, effluxes dihydrotestosterone (DHT) and is a prostate stem cell marker. Sabnis and colleagues demonstrate that inhibition of the ABCG2-mediated DHT efflux, promotes AR nuclear translocation, activation of AR target genes, and AR-dependent luminal differentiation. ABCG2 inhibition in the presence of DHT reduced the prostate cancer stem cell population and reduced growth rates in the CWR-R1 castration recurrent prostate cancer cell line in vitro and in vivo xenografts. Thus, ABCG2 inhibition is a possible differentiation therapeutic option in prostate cancer.The estrogen receptor (ER) is well known for its ability to integrate hormonal signals that promote the expression of critical genes involved in breast cancer differentiation, proliferation, and survival. Evidence indicates that ER levels correlate with CpG methylation status suggesting that ER controls expression through pathways that involve DNA methylation. Comprehensive profiling was used to identify ER-silenced genes that could be re-activated using demethylating agents, therapeutic loss of ER, or re-suppressed by gain of ER activity. Importantly, ER-dependent DNA methylation targets were identified in key biological pathways and a subset associated with patient outcomes suggesting the potential for new biomarkers.Patients with glioblastoma multiforme (GBM), a common malignant brain tumor, display poor survival. Glioma stem-like cells (GSC) enhance GBM escape from chemotherapy and promote tumor relapse. Hu and colleagues demonstrate that astrocyte elevated gene 1 (AEG-1) plays a crucial role in glioma stem cell biology. The expression of AEG-1 is elevated in GBM neurospheres, facilitating β-catenin nuclear translocation and elevating expression of stem cell markers CD133 and SOX2 and activating downstream Wnt signaling genes. Accordingly, this study identifies a novel AEG-1 signaling axis in GSCs and establishes AEG-1 as a therapeutic target for glioblastoma multiforme.

Abstract A29: Heterogeneity of androgen receptor dynamics and drug response in prostate cancer cells

Abstract Background: Recent studies suggest that the spatio-temporal dynamics of critical signaling molecules can mediate heterogeneous response to therapeutic intervention. Here, we set out to apply live cell imaging of single cells in high throughput to correlate the dynamics of androgen receptor (AR) with response to taxane chemotherapy in heterogeneous prostate cancer (PCa) cell populations. Methods: We previously developed a 3-step high throughput imaging and data analysis workflow to improve measurements of the dynamic phenotype in heterogeneous populations. We treated PCa cells stably expressing GFP-AR with AR ligand and quantified nuclear/cytoplasmic GFP intensity to measure nuclear translocation of AR over a 30 min time course. Then we treated cells with paclitaxel and tracked cells' response for 24h. Results: Applied to PCa cell lines stably expressing GFP-AR, we measured considerable heterogeneity of AR translocation in response to ligand stimulation. We quantified populations of non-responders and classified responding cells based on the dynamics of AR. Evaluation of cell morphology revealed a fraction of relatively large cells to be exclusively slow responders to AR ligand. We measured heterogeneous response to treatment with paclitaxel that correlated with cell phenotype. Conclusion: We conclude that cell morphology features in heterogeneous PCa cell populations correlate with AR translocation dynamics and drug response. Future experiments will include expression of the constitutively active AR variant AR-v7 to analyze its effect on the dynamics of wild-type AR and on single cell response to paclitaxel chemotherapy. Note: This abstract was not presented at the conference. Citation Format: Katherin Patsch, Anjana Soundararajan, Mark Engeln, Mitchell E. Gross, Shannon M. Mumenthaler, Daniel Ruderman. Heterogeneity of androgen receptor dynamics and drug response in prostate cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A29.