Androgen Receptor N-terminal Domain Research Articles

In silico study of androgen receptor N-terminal domain and exploration of its modulators

The androgen receptor (AR, Uniprot: P10275) signaling plays a key role in the progression of prostate cancer, various AR-related ligands have been reported to treat prostate cancer. However, some resistance mechanisms limited the treating effect of these ligands. Since DBD binding or the allosteric binding sites in LBD of AR may allow the circumvention of some drug resistance mechanisms, anti-resistance is expected especially through the NTD (N-terminal domain) targeting. What’s more, studies have shown that compounds including EPI-001 and its derivatives which bind to the Tau-5 region on NTD could be promising molecules for AR-based therapeutics. Herein, we employed aMD (accelerated molecular dynamics) simulation to fold Tau-5 unit proteins into native structure correctly. Subsequently, based on the predicted structural features of Tau-5, the virtual screening was conducted to discover new compounds targeting AR-NTD. We picked up 8 compounds (according to their docking scores and partly similar structural consists as known AR ligands) and analyzed their interaction with Tau-5, compared with the positive control EPI-001, four of the pick-up compounds showed better glide scores. Interestingly, although compound 8 had a lower docking score, it consisted of a similar component as the ligand EIQPN and the amide derivatives, this predicts that compound 8 has also the potential to be modified into an excellent AR-NTD binding molecule. These 8 compounds were all commercially available and could be tested to check whether there was a hit compound to bind the AR-NTD and to regulate its bio-activities. Together, this study described an in silico VLS approach to discover AR-NTD ligands and provided more choices for developing AR-targeted therapies. Communicated by Ramaswamy H. Sarma

SC912 inhibits AR-V7 activity in castration-resistant prostate cancer by targeting the androgen receptor N-terminal domain.

Androgen deprivation therapies (ADT) are the mainstay treatments for castration-resistant prostate cancer (CRPC). ADT suppresses the androgen receptor (AR) signaling by blocking androgen biosynthesis or inhibiting AR with antiandrogens that target AR's ligand-binding domain (LBD). However, the ADT's effect is short-lived, as the AR signaling inevitably arises again, which is frequently coupled with AR-V7 overexpression. AR-V7 is a truncated form of AR that lacks the LBD, thus being constitutively active in the absence of androgens and irresponsive to AR-LBD-targeting inhibitors. Though compelling evidence has tied AR-V7 to drug resistance in CRPC, pharmacological inhibition of AR-V7 is still an unmet need. Here, we discovered a small molecule, SC912, which binds to full-length AR as well as AR-V7 through AR N-terminal domain (AR-NTD). This pan-AR targeting relies on the amino acids 507-531 in the AR-NTD. SC912 also disrupted AR-V7 transcriptional activity, impaired AR-V7 nuclear localization and DNA binding. In the AR-V7 positive CRPC cells, SC912 suppressed proliferation, induced cell-cycle arrest, and apoptosis. In the AR-V7 expressing CRPC xenografts, SC912 attenuated tumor growth and antagonized intratumoral AR signaling. Together, these results suggested the therapeutic potential of SC912 for CRPC.

Abstract 6059: Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor

Abstract Patients with advanced prostate cancer inevitably acquire resistance to anti-androgen therapies, and progress to lethal castration-resistant prostate cancer (CRPC). The resistance mechanisms involve AR gene amplification and overexpression, constitutively active ligand-independent splice variants such as AR-V7, and the mutations in the AR ligand-binding domain (LBD). Our previous study has shown that the AR N-terminal domain (NTD) is responsible for AR liquid-liquid phase separation (LLPS) capability, which is essential for AR/AR-V7 transcriptional activity. We conducted a compound library screening using an AR LLPS phenotypic assay and identified ET0516 as a hit to specifically inhibit AR LLPS and its downstream gene expression, indicating that inhibition of AR. LLPS through targeting its NTD is a feasible approach to overcome the resistance to current anti-androgens therapy. Here we report the identification of a novel AR degrader, ETS-007 which is originated and evolved from internal LLPS phenotypic screening, that effectively degrades both AR and AR-V7 proteins with DC50 of single-digit nM by inducing a protein-protein interaction between AR NTD and an E3 ligase complex. ETS-007 induced AR and AR-V7 polyubiquitination, followed by degradation which could be blocked by the protease inhibitor MG132. ETS-007 significantly inhibited cell proliferation in AR and/or AR-V7 positive cell lines, e.g. LNCaP and 22RV1, and downregulated the androgen responsive genes such as PSA and TMPRSS2. Compared with enzalutamide and ARV-110, ETS-007 could block transcriptional activities of AR-V7, and AR mutants in luciferase report assay. Oral administration of ETS-007 in an enzalutamide-resistant 22RV1 xenograft model led to intratumoral AR-V7 degradation and concomitant decrease in PSA protein levels, resulting in a remarkable tumor regression. Taken together, our findings provide preclinical evidence that ETS-007 as a potent AR-NTD degrader derived from our LLPS platform can effectively block the transcriptional activities of both AR and AR-V7 for the treatment of metastatic CRPC. Citation Format: Yingjie Li, Mingyue Fei, Yingke Miao, Lijian Feng, Xiaofei Fan, Jinping Li, Yaozhong Chen, Ming Xu, Wenqi Cui, Qiangang Zheng, Jidong Zhu. Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6059.

Abstract 1231: First-in-class AR-V7/AR-fl small molecule molecular glue degrader for prostate cancer treatment

Abstract Metastatic castration resistance prostate cancer (mCRPC) is a lethal disease due to the development of treatment to androgen receptor (AR) signaling inhibitors (ARSi) and taxane chemotherapy. Treatment resistance occurs partly due to the expression of AR splice variants that lack the ligand binding domain (LBD) and are constitutively active in the nucleus. AR-V7 is the most prevalent variant conferring clinical resistance to both ARSi and taxanes. Currently, there is no selective AR-V7 inhibitor leaving patients with limited therapeutic options. Thus, the development of selective AR-V7 inhibitors is a high priority, clinically unmet need. To identify AR-V7 pharmacologic inhibitors, we performed a high throughput small molecule phenotypic screen using enzymatic complementation and nuclear AR-V7 as the assay endpoint. Our primary screen of ~170K compounds (z score = 0.8), followed by a cell-toxicity counter screen and a secondary GFP screen identified hit compound 7907, as a dual AR-V7/AR-fl protein degrader, with unique chemotype compared to all known AR modulators. Hit to lead optimization by medicinal chemistry/SAR studies identified lead compound 15, with increased potency compared to 7907. Mechanistically, we showed that compound 15 shortened AR-V7 protein half-life by activating the ubiquitin-proteasome pathway and inducing proteasomal degradation of both AR-V7/AR-fl, without affecting their transcription. Importantly, compound 15 induced degradation occurred within 3hr of treatment and was blocked by the clinically approved proteasome inhibitor, bortezomib. TurboID proximity ligation assay identified distinct E3 ligases, uniquely interacting with AR-V7 or AR-fl. Using AR-V7/AR-fl deletion mutants we further showed that compound 15 activity is mediated by the N-terminal domain of AR, present in both proteins. Remarkably, compound 15 sensitized LNCaP95 cells (endogenous AR-V7/AR-fl expression) to enzalutamide suggesting potential therapeutic synergism and ability to reverse enzalutamide resistance. Ongoing studies aim to narrow down the binding site of compound 15 as well as identify the E3 ligases mediating its activity. Together, these data support a molecular glue degrader mechanism of action, consistent with published studies showing that molecular glue degraders are ideal for targeting classically “undruggable” proteins lacking an LBD or containing intrinsically disordered domains, as is the case for AR-V7. Currently, all AR-directed therapies target the LBD of AR-fl, inhibiting AR signaling. AR-V7 expression is a direct outcome of this inhibition, leading to AR-fl and AR-V7 co-expression in patient tumors. We posit that our drug candidate, by offering dual AR-V7/AR-fl inhibition in a single treatment, has the potential to not only benefit patients with mCRPC but also patients with hormone-sensitive disease, and delay AR-V7 expression. Citation Format: CheukMan C. Au, Catrina Estrella, Prerna Vatsa, Michelle Naidoo, Michael Miller, Peter T. Meinke, David M. Nanus, Paraskevi Giannakakou. First-in-class AR-V7/AR-fl small molecule molecular glue degrader for prostate cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1231.

Abstract 4102: Treatment with androgen receptor targeting vaccines provides an overall survival benefit in AR-V7 expressing tumor models

Abstract Background: Androgen receptor (AR) signaling inhibition is part of the mechanism behind many effective prostate cancer therapies, including androgen deprivation and next generation anti-androgens. However in castration resistant prostate cancer up to 50% of treatment resistance has been linked to AR amplification or expression of the constitutively active RNA splice variant, AR-V7. Although the use of immune checkpoint blockade has failed to demonstrate clinical success, immunotherapeutic interventions remain attractive as prostate cancer’s relatively slow progression provides time for anti-tumor immune responses to develop. Cancer specific vaccines have the potential to enable and enhance tumor specific immune responses by stimulating and directing T cell immunity to important oncologic targets. We hypothesized that a cancer vaccine designed to induce a T cell response against cells expressing high levels of AR would result in an anti-tumor effect and potentially prevent or delay the development of therapeutic resistance. Methods: Adenoviral vaccines against AR (Ad-AR) or AR splice variant 7 (Ad-AR-V7) were used to evaluate the potential of AR targeting vaccination in mouse models. We evaluated AR and AR variant specific adaptive responses produced by our vaccines with naïve and tumor-bearing mice by ex vivo peptide restimulation. We challenged vaccinated mice with multiple syngeneic subcutaneous tumor models that we engineered to express AR-V7, including a PTEN-/- p53-/- prostate tumor cell line. Finally we tested our vaccines in a therapeutic regimen, vaccinating mice after implanting our subcutaneous AR-V7 expressing models. Results: Across multiple strains of mice, AR or AR-V7 targeting adenoviral vaccination induced robust adaptive immune responses against the N-terminal domain of AR. Vaccination with either Ad-AR or Ad-AR-V7 resulted in significant anti-tumor responses, providing a significant overall survival benefit and complete tumor rejection by the majority of mice vaccinated against AR or AR-V7. Similarly tumor bearing mice treated with Ad-AR or Ad-AR-V7 vaccination displayed tumor growth inhibition or complete tumor regression resulting in an overall survival benefit. Additionally, we found that vaccine responses were unaffected by the use of the approved antiandrogen drug enzalutamide, suggesting that vaccinations could be deployed in tandem with standard-of-care therapies. Conclusions: Vaccination against AR and AR splice variants can induce AR specific adaptive immune responses capable of inhibiting the growth of AR-V7 expressing tumor models, illustrating the potential of AR and its splice variants as immunologic targets in prostate cancer. Citation Format: Robert D. Marek, Junping Wei, Tao Wang, Xiao-Yi Yang, Gangjun Lei, Zachary C. Hartman. Treatment with androgen receptor targeting vaccines provides an overall survival benefit in AR-V7 expressing tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4102.

Abstract 2105: Targeting the “Achilles Heel” of androgen receptor activity in castration resistant prostate cancer

Abstract Background: Each year, millions of men are diagnosed with prostate cancer (CaP). The unchecked activation of the Androgen Receptor (AR) spurs CaP development and progression. Mutations or the presence of AR splice variants can add complexity to tumor ecology, leading to chemoresistance. This study aims to develop novel inhibitors targeting the “Achilles Heel” of AR activity: the N-terminal domain (NTD). This would circumvent the limitations of LBD (Ligand Binding Domain) therapies and offer a superior treatment option for patients. Though the AR-NTD is an intrinsically disordered protein, which complicates structure-based drug design, we have developed a unique small molecule inhibitor, ASR600, which specifically targets AR-NTD and promotes AR and AR- variants degradation by ubiquitination at previously unknown sites. Methods: Mass-spec analysis was performed to identify distinct ubiquitination sites in AR's NTD. To perform spatial transcriptome analysis, CytAssist Visium (10X genomics) was used. Furthermore, we used western blotting, immunofluorescence, immunoprecipitation, and PDX mice studies in CRPC mouse models to examine the impact of ASR600 on CRPC. Results: Four AR ubiquitination sites: K845, K847, and K913 (LBD) and K311 (NTD) are already identified. Interestingly, ASR600 continued to inhibit AR expression even with mutated ubiquitination sites. Mass spectrometry analysis of ASR-mediated mono-ubiquitinated N-terminal AR identified K16 as a unique ubiquitin acceptor. Altering this ubiquitination site rescues AR expression from ASR600-mediated degradation, emphasizing AR N-terminus as an ASR600 target. To discern the role of the K16 ubiquitination site in AR protein turnover, we evaluated AR protein stability in LNCaP cells that stably expressed ARWT or AR-K16R constructs. Our data indicates the pivotal importance of K16 for AR transcriptional activity. Invivo, ASR600, when used as a sole agent, exhibited inhibitory responses in PDX of clinically aggressive, AR-expressing tumors. Spatial gene expression analysis revealed marked expression differences in AR signature genes between control and ASR600-treated PDX tissues. Crucially, AR signaling, and related markers mainly aligned with epithelial markers rather than stromal ones. In contrast, the ASR600-treated PDX tumor showcased reduced AR signaling within epithelial cells. Conclusion: Targeting AR-NTD has received a lot of attention, but its innately disordered structure has hindered progress. ASR600 targets AR-NTD specifically by ubiquitinating the protein at a novel location, K16. Our in vivo, PDX studies, combined with the spatial analysis, lay a strong foundation for initiating IND-enabling TOX studies, followed by a phase-I clinical trial for ASR-600 in CRPC patients. Citation Format: Ashish Tyagi, Balaji Chandrasekaran, Arun K. Sharma, Chendil Damoadaran. Targeting the “Achilles Heel” of androgen receptor activity in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2105.

Two somatic mutations in the androgen receptor N-terminal domain are oncogenic drivers in hepatocellular carcinoma

The androgen receptor (AR) plays an important role in male-dominant hepatocellular carcinoma, and specific acquired somatic mutations of AR have been observed in HCC patients. Our previous research have established the role of AR wild type as one of the key oncogenes in hepatocarcinogenesis. However, the role of hepatic acquired somatic mutations of AR remains unknown. In this study, we identify two crucial acquired somatic mutations, Q62L and E81Q, situated close to the N-terminal activation function domain-1 of AR. These mutations lead to constitutive activation of AR, both independently and synergistically with androgens, making them potent driver oncogene mutations. Mechanistically, these N-terminal AR somatic mutations enhance de novo lipogenesis by activating sterol regulatory element-binding protein-1 and promote glycogen accumulation through glycogen phosphorylase, brain form, thereby disrupting the AMPK pathway and contributing to tumorigenesis. Moreover, the AR mutations show sensitivity to the AMPK activator A769662. Overall, this study establishes the role of these N- terminal hepatic mutations of AR as highly malignant oncogenic drivers in hepatocarcinogenesis and highlights their potential as therapeutic targets for patients harboring these somatic mutations.

Synthesis and Evaluation of Small Molecule Inhibitors of the Androgen Receptor N-Terminal Domain.

The androgen receptor (AR) is central to prostate cancer pathogenesis and has been extensively validated as a drug target. However, small-molecule anti-androgen therapies remain limited due to resistance and will eventually fail to suppress tumor growth, resulting in progression to castration-resistant prostate cancer (CRPC). The intrinsically disordered N-terminal domain (NTD) is crucial for AR transactivation and has been investigated as a suitable target in the presence of ligand binding domain mutations. A screening campaign identified biaryl isoxazole compound 7 as a weak inhibitor of the AR NTD. A library of biaryl analogues were synthesized, and their biological activities were assessed in a VCaP cell-based luciferase reporter gene assay. A structure-activity relationship (SAR) study revealed that indazole analogue 16 exhibited increased potency and favorable physicochemical properties with a benchmarked pharmacokinetic profile, providing a suitable starting point for further optimization of 16 as a CRPC therapeutic in the presence of AR mutations.

SAT023 The Role Of Cysteine Residues In The Binding Of Inhibitors Of The N-Terminal Domain Of The Androgen Receptor

Abstract Disclosure: L. Deneault: None. A. Tien: None. A. Banuelos: Stock Owner; Self; ESSA. T. Tam: None. R. Andersen: Stock Owner; Self; ESSA. M.D. Sadar: Stock Owner; Self; ESSA. Background: Therapies for prostate cancer (PC) involve pharmaceutical castration by targeting the androgen receptor (AR) ligand-binding domain (LBD). These therapies are not curative with the malignancy progressing to castration-resistant PC (CRPC). Most CRPC remains driven by AR through multiple resistances, e.g. constitutively active AR splice variants that lack LBD (AR-Vs), or gain-of-function mutations in LBD. This has led to clinical development of EPI analogues (“EPI”) which target the AR N-terminal domain (NTD) to block the transcriptional activities of, AR-Vs and mutated ARs. The EPI-binding pocket involves region 341-446 amino acid residues of the NTD. AR NTD is enriched in cysteine residues with C404 suggested to be important in the binding mechanism of EPI. Free cysteine residues are able interact forming disulfide bonds, which are important in intra- and intermolecular protein-protein interactions. Here we begin to elucidate the role of cysteines in the inhibition of AR activity by EPI. Methods: Binding assays assess the role of cysteines in the covalent binding mechanism used a fluorescein-labelled EPI with fragments of recombinant AR-NTD (rNTD) with or without the addition of iodoacetamide (caps cysteines). Protein-protein interactions requiring disulfide bonds with AR examined by non-reducing SDS-PAGE and diagonal SDS-PAGE of cells treated with inhibitors. A role of specific cysteines in the activity of EPI to block AR transcriptional activity was assessed by cysteine mutants using a reporter gene construct driven by AR. Results: Capping cysteine residues on rNTD with iodoacetamide reduced the amount of covalent binding of EPI. This data suggests that cysteines are essential for covalent binding of EPI to AR-NTD. EPI bound preferentially to the oxidized form of rNTD suggesting the importance of disulfide bridges. Diagonal SDS-PAGE revealed differential alterations in intramolecular and intermolecular disulfide bonds in response to EPI compared to AR LBD inhibitors. These gels also revealed unique differences in protein-protein interactions with AR depending on the inhibitor. AR-driven reporter gene assays revealed mutations of cysteine residues in the AR- NTD did not adversely affect AR transcriptional activity in response to androgen. Conclusions: Although cysteines residing in the AR-NTD were required for covalent binding of EPI, mutation of C404 in the EPI-binding site was not essential for the efficacy of EPI to block AR transcriptional activity. There were differential patterns in protein-protein interactions with AR depending upon which domain the inhibitor targeted. Our future goal is to identify these unique proteins to provide insight into the mechanisms and develop more potent and more specific therapeutics for the treatment of CRPC. Presentation: Saturday, June 17, 2023

SAT022 A Mechanism Of Resistance To Novel Inhibitors Of The N-Terminal Domain Of Androgen Receptor

Abstract Disclosure: J. Setiawan: None. N.R. Mawji: None. A.H. Tien: None. R.J. Andersen: Stock Owner; Self; ESSA Pharma. M.D. Sadar: Stock Owner; Self; ESSA Pharma. Background: Androgen receptor (AR) is a steroid hormone receptor and a major therapeutic target in prostate cancer. Antiandrogen therapies directed at the AR C-terminal ligand-binding domain (LBD) provide initial benefit to patients with advanced prostate cancer, but they eventually progress to lethal metastatic castration-resistant prostate cancer (CRPC). AR N-terminal domain (NTD) inhibitors are a novel class of antagonists that were developed to overcome resistance mechanisms related to the AR-LBD, including splice variants lacking the LBD (AR-V7). While mutations in the AR-LBD have been well-characterized, the impact of NTD mutations on AR transcriptional activity and drug efficacy remains unclear. The mutation W435L was discovered from clinical samples of prostate cancer from patients treated with antiandrogens. This mutation stabilizes interaction between the AR’s NTD and LBD (N/C interaction) to increase AR transcriptional activity. Tryptophan residues W435 and W397 in AR NTD are essential in the binding site for the AR-NTD inhibitor EPI-7386 that is currently in clinical trials. We hypothesize that tryptophan mutations within the EPI-7386 binding site of AR are a potential mechanism of resistance. Methods: Site-directed mutagenesis was used to create expression vectors with W435 and W397 point mutations in AR. Plasmids were transfected into AR-negative CV-1 cells to compare the transcriptional activity of wild-type (WT) versus mutant ARs. IC50s for each inhibitor were generated for androgen-induced reporter gene constructs. A mammalian two-hybrid system assay was used to assess the impact of inhibitors and AR mutations on N/C interaction. Results: The AR-W435L mutation led to higher IC50s to inhibit androgen-induced MMTV-luciferase activity by NTD inhibitors and antiandrogens. Differences in N/C interaction were observed between WT and mutant ARs treated with EPI-7386. Importantly, the ability of another EPI analog, EPI-7170, to decrease AR-N/C interaction was not significantly impacted by W435L. These data support that loss of efficacy with EPI-7386 is not across the entire class of EPI analogs and may be specific to EPI-7386. Conclusion: Tryptophan mutations in the EPI-7386 binding site are predictive of resistance to this specific antagonist and do not broadly apply to the entire class of EPI analogs. Key differences were revealed between AR-LBD and AR-NTD inhibitors that support the recruitment of different tau regions in the NTD. Presentation: Saturday, June 17, 2023

Discovery of BWA-522, a First-in-Class and Orally Bioavailable PROTAC Degrader of the Androgen Receptor Targeting N-Terminal Domain for the Treatment of Prostate Cancer.

We report small molecular PROTAC compounds targeting the androgen receptor N-terminal domain (AR-NTD), which were obtained by tethering AR-NTD antagonists and different classes of E3 ligase ligands through chemical linkers. A representative compound, BWA-522, effectively induces degradation of both AR-FL and AR-V7 and is more potent than the corresponding antagonist against prostate cancer (PC) cells in vitro. We have shown that the degradation of AR-FL and AR-V7 proteins by BWA-522 can suppress the expression of AR downstream proteins and induce PC cell apoptosis. BWA-522 achieves 40.5% oral bioavailability in mice and 69.3% in beagle dogs. In a LNCaP xenograft model study, BWA-522 was also proved to be an efficacious PROTAC degrader, resulting in 76% tumor growth inhibition after oral administration of a dose of 60 mg/kg. This study indicates that BWA-522 is a promising AR-NTD PROTAC for the treatment of AR-FL- and AR-V7-dependent tumors.

Selected Articles from This Issue

Highlights| May 04 2023 Selected Articles from This Issue Author & Article Information Online ISSN: 1538-8514 Print ISSN: 1535-7163 ©2023 American Association for Cancer Research2023American Association for Cancer Research Mol Cancer Ther (2023) 22 (5): 553. https://doi.org/10.1158/1535-7163.MCT-22-5-HI Related Content A commentary has been published: Discovery of a Small-Molecule Inhibitor Targeting the Androgen Receptor N-Terminal Domain for Castration-Resistant Prostate Cancer A commentary has been published: Novel Arginase Inhibitor, AZD0011, Demonstrates Immune Cell Stimulation and Antitumor Efficacy with Diverse Combination Partners A commentary has been published: Preclinical Evaluation of ON203, A Novel Bioengineered mAb Targeting Oxidized Macrophage Migration Inhibitory Factor as an Anticancer Therapeutic Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record May 4 2023 Citation Selected Articles from This Issue. Mol Cancer Ther 1 May 2023; 22 (5): 553. https://doi.org/10.1158/1535-7163.MCT-22-5-HI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search The oxidized macrophage migration inhibitory factor (oxMIF) is an emerging therapeutic target for many cancers due to oxMIF's selective occurrence in tumor lesions. Here, Rossmueller and colleagues describe ON203, a novel anti-oxMIF antibody with optimized physicochemical characteristics, in-vitro safety, and enhanced ADCC and ADCP effector functions. ON203 significantly reduced tumor growth and tumor cell proliferation as well as tumor cell intravasation and neo-angiogenesis in xenograft models. These findings highlight the potential of ON203 as a standalone immunotherapy or for enhancing efficacy in combination with angiogenesis and immune checkpoint-inhibitors in patients with solid tumors. Current mainstay treatment for prostate cancer is to suppress the androgen receptor (AR) signaling by castration and antiandrogens that target the ligand-binding domain (LBD). However, emergence of AR variants, such as AR-V7 lacking the LBD, have conferred severe drug resistance to all LBD-targeting AR inhibitors. AR-V7 has been established as a driver for the sustained AR signaling... You do not currently have access to this content.

Discovery of a Small-Molecule Inhibitor Targeting the Androgen Receptor N-Terminal Domain for Castration-Resistant Prostate Cancer.

The current mainstay therapeutic strategy for advanced prostate cancer is to suppress androgen receptor (AR) signaling. However, castration-resistant prostate cancer (CRPC) invariably arises with restored AR signaling activity. To date, the AR ligand-binding domain (LBD) is the only targeted region for all clinically available AR signaling antagonists, such as enzalutamide (ENZ). Major resistance mechanisms have been uncovered to sustain the AR signaling in CRPC despite these treatments, including AR amplification, AR LBD mutants, and the emergence of AR splice variants (AR-Vs) such as AR-V7. AR-V7 is a constitutively active truncated form of AR that lacks the LBD; thus, it can not be inhibited by AR LBD-targeting drugs. Therefore, an approach to inhibit AR through the regions outside of LBD is urgently needed. In this study, we have discovered a novel small molecule SC428, which directly binds to the AR N-terminal domain (NTD) and exhibits pan-AR inhibitory effect. SC428 potently decreased the transactivation of AR-V7, ARv567es, as well as full-length AR (AR-FL) and its LBD mutants. SC428 substantially suppressed androgen-stimulated AR-FL nuclear translocation, chromatin binding, and AR-regulated gene transcription. Moreover, SC428 also significantly attenuated AR-V7-mediated AR signaling that does not rely on androgen, hampered AR-V7 nuclear localization, and disrupted AR-V7 homodimerization. SC428 inhibited in vitro proliferation and in vivo tumor growth of cells that expressed a high level of AR-V7 and were unresponsive to ENZ treatment. Together, these results indicated the potential therapeutic benefits of AR-NTD targeting for overcoming drug resistance in CRPC.

Targeting androgen receptor and the variants by an orally bioavailable Proteolysis Targeting Chimeras compound in castration resistant prostate cancer.

Despite the advent of improved therapeutic options for advanced prostate cancer, the durability of clinical benefits is limited due to inevitable development of resistance. By constitutively sustaining androgen receptor (AR) signaling, expression of ligand-binding domain truncated AR variants (AR-V(ΔLBD)) accounts for the major mechanism underlying the resistance to anti-androgen drugs. Strategies to target AR and its LBD truncated variants are needed to prevent the emergence or overcome drug resistance. We utilize Proteolysis Targeting Chimeras (PROTAC) technology to achieve induced degradation of both full-length AR (AR-FL) and AR-V(ΔLBD) proteins. In the ITRI-PROTAC design, an AR N-terminal domain (NTD) binding moiety is appended to von-Hippel-Lindau (VHL) or Cereblon (CRBN) E3 ligase binding ligand with linker. Invitro studies demonstrate that ITRI-PROTAC compounds mechanistically degrade AR-FL and AR-V(ΔLBD) proteins via ubiquitin-proteasome system, leading to impaired AR transactivation on target gene expression, and inhibited cell proliferation accompanied by apoptosis activation. The compounds also significantly inhibit enzalutamide-resistant growth of castration resistant prostate cancer (CRPC) cells. In castration-, enzalutamide-resistant CWR22Rv1 xenograft model without hormone ablation, ITRI-90 displays a pharmacokinetic profile with decent oral bioavailability and strong antitumor efficacy. AR NTD that governs the transcriptional activities of all active variants has been considered attractive therapeutic target to block AR signaling in prostate cancer cells. We demonstrated that utilizing PROTAC for induced AR protein degradation via NTD represents an efficient alternative therapeutic strategy for CRPC to overcome anti-androgen resistance. The funding detail can be found in the Acknowledgements section.

203 (PB083) - Molecular characterization of next generation AR-NTD inhibitors

Background: Inhibition of the androgen receptor (AR) is the mainstay treatment for advanced prostate cancer. While initially effective, the disease ultimately progresses to metastatic castration-resistant prostate cancer (mCRPC), which is lethal. All current AR-targeted therapies directly or indirectly target the ligand binding domain (LBD). We have developed the EPI and sintokamide (SINT) compounds which target the AR N-terminal domain (NTD), allowing for sustained inhibition in the context of constitutively active AR-splice variants and mutations which often drive resistance to current AR-targeted therapies.

Abstract 429: Androgen receptor (AR) N-terminal domain degraders can degrade AR full length and AR splice variants in CRPC preclinical models

Abstract Introduction: Androgen receptor (AR) signaling is a main driver of prostate cancer progression and remains a crucial target for therapeutic intervention even in late stages of the disease. Current antiandrogen therapies directly or indirectly target the AR ligand binding domain (LBD) and are initially effective in prostate cancer patients. However, resistance ultimately develops, and new methods of inhibiting the AR pathway are needed. The selective targeting of the N-terminal domain (NTD) of the AR by small molecule anitens represents a novel method of blocking AR signaling that can bypass LBD-related resistance mechanisms. AR NTD is an intrinsically disordered region (IDR) which has no stable ordered structure and is generally regarded as an undruggable target due to the lack of a well-defined small-molecule binding pocket. However, we recently demonstrated that EPI-7386, an AR NTD small molecule inhibitor, inhibits AR activity by binding to Tau5 region of the NTD. By developing an aniten based bifunctional degrader (ANITAC for ANITen bAsed Chimera), our goal is to eliminate any forms of AR protein found in castration-resistant prostate cancer (CRPC), that can potentially drive disease progression, including LBD mutants and AR truncated variants. Methods: AR degradation was monitored by Western Blot or by using the HiBit assay. AR transcriptional activity was measured using different reporter assays following AR full length (FL) or truncated AR activity in in vitro models. Results: Here we report the first series of AR degraders targeting the NTD of AR, which lead to degradation of all forms of AR, including AR-V7 and AR-v567es. ANITACs eliminate AR in all cell lines tested through an E3 ligase dependent mechanism, with an observed 50% degradation concentration (DC50) < 20 nM in 22Rv1 cells for the most potent compounds. AR degradation mediated by ANITACs suppresses the expression of AR target genes and decreases the viability of prostate cancer cells. ANITACs also degrade clinically relevant AR mutants and AR splice variants and show inhibition of AR transcriptional activity in multiple cell lines expressing different forms of AR including AR FL (LNCaP, CWR-AD1), AR-V7 (22Rv1), AR-V567es (CWR-D567). In vitro and in vivo PK studies show the compounds are metabolically stable and exhibit excellent oral bioavailability in mice. Conclusion: In summary, we report preclinical data on the first generation of ANITAC molecules, that can be orally bioavailable and show activity against forms of AR expressed in late stage CRPC patients. Citation Format: Nan Hyung Hong, Berenger Biannic, Peter Virsik, Han-Jie Zhou, Ronan Le Moigne. Androgen receptor (AR) N-terminal domain degraders can degrade AR full length and AR splice variants in CRPC preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 429.

Abstract P192: Comprehensive preclinical characterization of the mechanism of action of EPI-7386, an androgen receptor N-terminal domain inhibitor

Abstract Background: Androgen receptor (AR) signaling is a main driver of prostate cancer progression and remains a crucial target for therapeutic intervention even in late stages of the disease. While current anti-androgen therapies targeting directly or indirectly the AR ligand binding domain (LBD) are initially effective, resistance ultimately develops, and new methods of inhibiting the AR pathway are needed. The selective targeting of the N-terminal domain (NTD) of the AR represents a novel method of blocking AR signaling to by-pass LBD-related resistance. EPI-7386 is a potent and metabolically stable NTD inhibitor (aniten) currently in a phase 1 dose-escalation study in mCRPC patients (NCT04421222). Here we further characterized the binding to AR NTD and the mechanism of action of EPI-7386. Methods: Target engagement was measured by Cellular Thermal Shift Assay (CETSA) and two-dimensional Nuclear Magnetic Resonance (2D NMR) spectroscopy. The potency and selectivity of EPI-7386 was determined in cellular models expressing different forms of AR using reporter and cell viability assays. qPCR, NanoString, and RNA sequencing were used to explore the activity of EPI-7386 on the AR transcriptome. To determine the effect of EPI-7386 on AR genomic occupancy, Chromatin immunoprecipitation sequencing (ChIP-seq) was performed. Results: We confirmed target engagement of EPI-7386 with an LBD truncated AR variant by CETSA using a cell line which expresses only AR-V567es, suggesting the interaction of EPI-7386 with AR NTD. In the same cell line, AR antagonist enzalutamide that binds to AR LBD showed no target engagement with AR-V567es. Furthermore, 2D NMR study results demonstrate an interaction of EPI-7386 with amino acid residues located in the transcription activation unit 5 (Tau-5) region of the AR NTD, a region which has been described to be involved in interactions with transcriptional cofactors such as CBP/p300. EPI-7386 strongly impaired the transcriptional activity and gene expression driven exclusively by LBD truncated AR variants including AR-V567es and AR-V7 and decreased cell viability. EPI-7386 has been shown to suppress the AR regulated transcriptome and the combination of EPI-7386 with lutamides resulted in broader and deeper inhibition of AR-regulated gene expression. The analysis of the AR cistrome by ChIP-seq showed that EPI-7386 displaces genome-wide androgen induced AR binding and the combination with enzalutamide completely abrogated AR binding. Conclusion: EPI-7386 is a potent AR NTD inhibitor that has the capacity to by-pass AR LBD resistance mechanisms to current anti-androgen therapies by uniquely inhibiting AR-mediated signaling. The agent has the potential for providing clinical benefit as a single agent in patients whose tumors are progressing on anti-androgens or in combination with current anti-androgens in earlier line patients. Citation Format: Nan Hyung Hong, Shihua Sun, Peter Virsik, Alessandra Cesano, Elahe A. Mostaghel, Stephen R. Plymate, Berenger Biannic, Han-Jie Zhou, Ronan Le Moigne. Comprehensive preclinical characterization of the mechanism of action of EPI-7386, an androgen receptor N-terminal domain inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P192.

A phase 1 study to assess the safety, pharmacokinetics, and anti-tumor activity of the androgen receptor n-terminal domain inhibitor epi-506 in patients with metastatic castration-resistant prostate cancer

EPI-506 is the first of a new class of drugs targeting the N-terminal domain (NTD) of the androgen receptor (AR), potentially overcoming known resistance mechanisms to androgen receptor pathway inhibitors (ARPIs) among men with metastatic castration resistant prostate cancer (mCRPC). Patients with mCRPC who had progressed on prior ARPI were enrolled in this phase 1 open-label, adaptive 3 + 3 dose escalation study. The primary outcome was safety and tolerability of oral EPI-506. Secondary objectives included determination of the maximal tolerated dose (MTD), pharmacokinetic profile, and antitumor efficacy. 28 mCRPC patients were enrolled into 7 dose cohorts of EPI-506 ranging from 80-3600mg given once daily and 1800mg given twice daily. Six DLTs occurred in 4 patients; Grade 4 elevated amylase; Grade 3 abdominal pain; Grade 3 elevated ALT and Grade 3 elevated AST; Grade 2 nausea and Grade 1 vomiting which resulted in study drug intake of < 75% of the expected dose during the DLT assessment period. The most common drug-related adverse events included diarrhea, nausea and fatigue. Six patients had a PSA decline not meeting PSA response criteria. The study was terminated prior to reaching the MTD due to poor oral bioavailability. This phase 1 trial established the safety of EPI-506 and provides proof of concept for targeting the AR NTD. Next generation compounds with improved bioavailability and potency are in clinical development.

Development of a Benzothiazole Scaffold-Based Androgen Receptor N-Terminal Inhibitor for Treating Androgen-Responsive Prostate Cancer.

All current clinically approved androgen deprivation therapies for prostate cancer target the C-terminal ligand-binding domain of the androgen receptor (AR). However, the main transactivation function of the receptor is localized at the AR N-terminal domain (NTD). Targeting the AR NTD directly is a challenge because of its intrinsically disordered structure and the lack of pockets for drugs to bind. Here, we have taken an alternative approach using the cochaperone BAG1L, which interacts with the NTD, to develop a novel AR inhibitor. We describe the identification of 2-(4-fluorophenyl)-5-(trifluoromethyl)-1,3-benzothiazole (A4B17), a small molecule that inhibits BAG1L-AR NTD interaction, attenuates BAG1L-mediated AR NTD activity, downregulates AR target gene expression, and inhibits proliferation of AR-positive prostate cancer cells. This compound represents a prototype of AR antagonists that could be key in the development of future prostate cancer therapeutics.

Development of an Androgen Receptor Inhibitor Targeting the N-Terminal Domain of Androgen Receptor for Treatment of Castration Resistant Prostate Cancer.

Simple SummaryIn almost all patients, the proliferation and growth of prostate cancer is driven by the androgen receptor. Given this critical role, inhibiting the androgen receptor is the standard of care following surgery or radiotherapy. However, the effectiveness of current anti-androgen therapeutics is almost always temporary, with the cancer eventually developing drug resistance. There are no curative treatment options for resistant prostate cancer and these patients have an average life-expectancy of only 20 months. Currently, all clinical inhibitors of the androgen receptor act by direct binding to the hormone binding site. These drugs are therefore vulnerable to mutations which frequently arise at this region or to the emergence of truncated forms of the androgen receptor that are constitutively active without any need of hormone binding. In this study, we aim to develop small molecules inhibitors that attack the molecular functions of the androgen receptor at the N-terminal domain, distinct from steroid recruitment to evade resistance to conventional treatments.Prostate cancer patients undergoing androgen deprivation therapy almost invariably develop castration-resistant prostate cancer. Resistance can occur when mutations in the androgen receptor (AR) render anti-androgen drugs ineffective or through the expression of constitutively active splice variants lacking the androgen binding domain entirely (e.g., ARV7). In this study, we are reporting the discovery of a novel AR-NTD covalent inhibitor 1-chloro-3-[(5-([(2S)-3-chloro-2-hydroxypropyl]amino)naphthalen-1-yl)amino]propan-2-ol (VPC-220010) targeting the AR-N-terminal Domain (AR-NTD). VPC-220010 inhibits AR-mediated transcription of full length and truncated variant ARV7, downregulates AR response genes, and selectively reduces the growth of both full-length AR- and truncated AR-dependent prostate cancer cell lines. We show that VPC-220010 disrupts interactions between AR and known coactivators and coregulatory proteins, such as CHD4, FOXA1, ZMIZ1, and several SWI/SNF complex proteins. Taken together, our data suggest that VPC-220010 is a promising small molecule that can be further optimized into effective AR-NTD inhibitor for the treatment of CRPC.