Androgen Receptor Protein Degradation Research Articles

The design, synthesis and bioactivity evaluation of novel androgen receptor degraders based on hydrophobic tagging

Prostate Cancer (PCa) easily progress to metastatic Castration-Resistant Prostate Cancer (mCRPC) that remains a significant cause of cancer-related death. Androgen receptor (AR)-dependent transcription is a major driver of prostate tumor cell proliferation. Proteolysis-targeting chimaera (PROTAC) technology based on Hydrophobic Tagging (HyT) represents an intriguing strategy to regulate the function of therapeutically androgen receptor proteins. In the present study, we have designed, synthesized, and evaluated a series of PROTAC-HyT AR degraders using AR antagonists, RU59063, which were connected with adamantane-based hydrophobic moieties by different alkyl chains. Compound D-4–6 exhibited significant AR protein degradation activity, with a degradation rate of 57 % at 5 μM and nearly 90 % at 20 μM in 24 h, and inhibited the proliferation of LNCaP cells significantly with an IC50 value of 4.77 ± 0.26 μM in a time-concentration-dependent manner. In conclusion, the present study lays the foundation for the development of a completely new class of therapeutic agents for the treatment of mCRPC, and further design and synthesis of AR-targeting degraders are currently in progress for better degradation rate.

THU573 Paxillin Regulates Androgen Receptor In Granulosa Cells

Abstract Disclosure: A. Weidner: None. A. Roy: None. K. Vann: None. O. Astapova: None. Paxillin is a ubiquitously-expressed adaptor protein that is integral in focal adhesions and plays an active role in the regulation of cell motility and apoptosis. Recently, paxillin was shown to mediate pro-tumorigenic androgen signaling in prostate cancer cells, where it is necessary for rapid cytoplasmic kinase signaling triggered by activation of membrane-bound androgen receptor. We sought to investigate the relationship between paxillin and androgen receptor (AR) in granulosa cells, where androgen actions, apoptosis and focal adhesions are of known importance, but the role of paxillin is understudied. When paxillin expression was silenced using siRNA in human granulosa-derived KGN cells, AR protein expression was significantly reduced, while its RNA expression was unaffected. Similarly, in granulosa cell-specific paxillin knockout mice, AR protein expression in granulosa cells was reduced. Further, we found that AR and paxillin co-localize in focal adhesions in mouse primary granulosa cells and in KGN cells, and their interaction requires the activity of focal adhesion kinase. Disruption of focal adhesion with a focal adhesion kinase inhibitor also leads to reduced AR protein levels. To further explore the mechanisms by which paxillin regulates AR expression, we created paxillin-null KGN cell lines using CRISPR-Cas9 gene editing. While paxillin loss resulted in reduced AR protein expression early (days) in the gene-editing process, this effect disappeared after weeks of clonal expansion from selected single cells. Expanded paxillin-null KGN clones showed normal AR protein expression, but increased AR mRNA expression, suggesting an adaptive increase in AR gene transcription to compensate for reduced AR protein levels in cells that survived paxillin deletion. Studies of AR protein degradation using cycloheximide to block protein synthesis showed that the half-life of AR was reduced from 6.7 to 4.5 hours (approximately 33%) by paxillin deletion, indicating accelerated AR protein degradation in cells lacking paxillin. Based on our results, we hypothesize that paxillin brings AR into focal adhesions in granulosa cells, thereby sequestering it from proteasomal degradation in the cytoplasm. Thus, paxillin may be a novel target in the management of androgen-related disorders in women, such as polycystic ovary syndrome. Presentation Date: Thursday, June 15, 2023

Proxalutamide reduces SARS-CoV-2 infection and associated inflammatory response

Early in the COVID-19 pandemic, data suggested that males had a higher risk of developing severe disease and that androgen deprivation therapy might be associated with protection. Combined with the fact that TMPRSS2 (transmembrane serine protease 2), a host entry factor for the SARS-CoV-2 virus, was a well-known androgen-regulated gene, this led to an upsurge of research investigating androgen receptor (AR)-targeting drugs. Proxalutamide, an AR antagonist, was shown in initial clinical studies to benefit COVID-19 patients; however, further validation is needed as one study was retracted. Due to continued interest in proxalutamide, which is in phase 3 trials, we examined its ability to impact SARS-CoV-2 infection and downstream inflammatory responses. Proxalutamide exerted similar effects as enzalutamide, an AR antagonist prescribed for advanced prostate cancer, in decreasing AR signaling and expression of TMPRSS2 and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 receptor. However, proxalutamide led to degradation of AR protein, which was not observed with enzalutamide. Proxalutamide inhibited SARS-CoV-2 infection with an IC50 value of 97 nM, compared to 281 nM for enzalutamide. Importantly, proxalutamide inhibited infection by multiple SARS-CoV-2 variants and synergized with remdesivir. Proxalutamide protected against cell death in response to tumor necrosis factor alpha and interferon gamma, and overall survival of mice was increased with proxalutamide treatment prior to cytokine exposure. Mechanistically, we found that proxalutamide increased levels of NRF2, an essential transcription factor that mediates antioxidant responses, and decreased lung inflammation. These data provide compelling evidence that proxalutamide can prevent SARS-CoV-2 infection and cytokine-induced lung damage, suggesting that promising clinical data may emerge from ongoing phase 3 trials.

Discovery of ARD-2051 as a Potent and Orally Efficacious Proteolysis Targeting Chimera (PROTAC) Degrader of Androgen Receptor for the Treatment of Advanced Prostate Cancer.

We report the discovery of ARD-2051 as a potent and orally efficacious androgen receptor (AR) proteolysis-targeting chimera degrader. ARD-2051 achieves DC50 values of 0.6 nM and Dmax >90% in inducing AR protein degradation in both the LNCaP and VCaP prostate cancer cell lines, potently and effectively suppresses AR-regulated genes, and inhibits cancer cell growth. ARD-2051 achieves a good oral bioavailability and pharmacokinetic profile in mouse, rat, and dog. A single oral dose of ARD-2051 strongly reduces AR protein and suppresses AR-regulated gene expression in the VCaP xenograft tumor tissue in mice. Oral administration of ARD-2051 effectively inhibits VCaP tumor growth and causes no signs of toxicity in mice. ARD-2051 is a promising AR degrader for advanced preclinical development for the treatment of AR+ human cancers.

Impacts of androgen pathway manipulation on patients with lung cancer.

e21010 Background: Sex hormone may play a role in lung cancer pathophysiology. We aimed to evaluate if androgen pathway manipulation (APM) is associated with better survival in patients with lung cancer, and how finasteride, a 5-alpha reductase inhibitor, impacts androgen receptor (AR) activation and growth of lung cancer cells. Methods: In this retrospective hospital-based cohort study, we screened all men with lung cancer diagnosed during the period from January 2006 to December 2021. APM exposure was defined as using antiandrogens, 5-alpha reductase inhibitors, or gonadotropin-releasing hormone agonists for > 30 days after lung cancer diagnosis. The in vitro study was conducted on A549 lung cancer cells; while the tumor xenograft model was conducted on BALB/c nude mice. Results: Among 4744 men with lung cancer, 98 (2.1%) were identified as having APM exposure. The majority of patients (73.5%) received 5-alpha reductase inhibitors. The patients with APM exposure were older (71.5 vs. 67.0, p < 0.001), had a higher proportion of having prostate cancer (27.6% vs. 1.4%, p < 0.001), and had a smaller proportion of having metastatic lung cancer (41.8% vs. 54.0%, p = 0.003), compared to those without APM exposure. In multivariable Cox proportional hazards analysis, patients with APM exposure experienced better OS compared to those without exposure (Hazard ratio 0.57; 95% CI, 0.44–0.73, p < 0.001). In in vitro study, we illustrated that AR protein stimulated the cell proliferation of A549 cells. Finasteride reduced the AR protein expression and inhibited A549 cell growth. Finasteride promoted ubiquitination and degradation of AR protein and therefore interfered the stability of AR protein. Furthermore, finasteride inhibited cell cycle progression and promoted apoptosis of A549 cells. The in vivo results also supported the inhibition effect of finasteride on lung cancer growth. Conclusions: APM was associated with better OS in male patients with lung cancer. Finasteride interfered with the stability of AR and inhibited A549 lung cancer cell growth. Our findings indicated an oncogenic role of AR on lung cancer which may provide potential therapeutic and targets for lung cancer. The inhibition effect of finasteride on lung cancer might be of benefit for future treatment strategies, prevention and control.[Table: see text]

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.

OR06-2 Paxillin and Androgen Receptor Interact to Modulate Female Fertility

Abstract While androgens are traditionally associated with male physiology, recently it has become more apparent that balanced levels of androgens are crucial to maintaining female health and fertility as well. Specifically, androgens are necessary for granulosa cell proliferation and follicle survival and growth. Excess androgen levels in females are a hallmark in polycystic ovary syndrome (PCOS), whereas insufficient androgen signaling due to androgen receptor (AR) knockout leads to diminished ovarian reserve (DOR) – with both extremes resulting in anovulatory infertility. However, little is known about the factors regulating AR in granulosa cells. Our previous findings demonstrate that paxillin, a cytoplasmic adaptor protein, mediates AR signaling in prostate cancer cells. However, our current interest is whether this interaction is also found in granulosa cells. As such, our results show that paxillin indeed enhances AR protein expression in granulosa cells. We have also demonstrated through immunofluorescence and proximity ligation assays that paxillin colocalizes with AR, notably in membrane-bound complexes. Moreover, paxillin-null KGN and mouse granulosa cells express lower levels of AR, as demonstrated through Western blotting and immunofluorescence imaging. We then conducted mRNA and protein degradation experiments in paxillin-null KGN cells in order to determine the mechanism by which paxillin increases AR expression. These results suggest that paxillin acts by preventing AR mRNA and protein degradation, possibly by trafficking AR to focal adhesions, where it may be sequestered from degradation. Finally, to investigate the role of paxillin in female fertility, we developed a novel granulosa cell-specific paxillin knockout mouse model using an Amhr2-driven Cre/lox system. These knockout mice experience altered estrous cycles compared to controls, spending fewer days in estrus and more days in metestrus/diestrus. When bred continuously through 6 months of age, the paxillin KO mice produced significantly more litters compared to their littermate controls. Taken together, these results suggest that paxillin acts as a regulator of androgen-mediated female fertility in granulosa cells, and may serve as a potential target for therapeutics in fertility-related diseases such as PCOS and DOR. Presentation: Saturday, June 11, 2022 11:45 a.m. - 12:00 p.m.

296 (PB076) - Cellular hormone metabolism is critical for canonical androgen receptor antagonist activity

Background: Second-generation androgen receptor (AR) antagonists and an androgen synthesizing enzyme inhibitor have become the standard of care for advanced prostate cancer (PCa). Clinically-approved AR antagonists bind to the AR ligand binding domain (LBD) and competitively inhibit AR function. Dual action AR inhibitors (DAARIs), which bind to the N-terminal domain (NTD) of the AR inhibit AR signaling and lead AR protein degradation, have been identified by our group as potential therapeutics for PCa.

Seleno-aspirin compound AS-10 promotes histone acetylation ahead of suppressing androgen receptor transcription, G1 arrest, and apoptosis of prostate cancer cells.

The novel selenium-aspirin compound AS-10 was recently reported by us with a cancer cell killing potency three orders of magnitude greater than aspirin in pancreatic cancer cell lines with caspase-mediated apoptosis and a reasonable selectivity against malignant cells. Although we also observed its cytocidal activity against PC-3 and DU145 androgen receptor (AR)-negative and P53-null/mutant aggressive human prostate cancer (PCa) cell lines in NCI-60 screen, the potential involvement and targeting of AR and P53 pathways that are intact in early-stage prostate carcinogenesis has not been examined, nor its primary molecular signaling after exposure. Human LNCaP PCa cells with functional AR and intact P53 were used to examine their cell cycle and cell fate responses to AS-10 exposure and upstream molecular signaling events including histone acetylation as a known aspirin effect. The AR-positive 22Rv1 human PCa cells were used to validate key findings. In addition to confirming AS-10's superior cytocidal potency than aspirin against all four PCa cell lines, we report a rapid (within 5 min) promotion of histone acetylation several hours ahead of the suppression of AR and prostate-specific antigen (PSA, coded by KLK3 gene) in LNCaP and 22Rv1 cells. AS-10 decreased AR and KLK3 mRNA levels without impacting pre-existing AR protein degradation or nuclear translocation in LNCaP cells. Sustained exposure to AS-10 arrested cells predominantly in G1 , and induced caspase-mediated apoptosis without necrosis. The death induced by AS-10 in LNCaP cells was attenuated by nontranscriptional activation of P53 protein or Jun N-terminal Kinase cellular stress signaling and was mitigated modestly by glutathione-boosting antioxidant N-acetylcysteine. AS-10 synergized with histone deacetylase inhibitor SAHA to suppress AR/PSA abundance and kill LNCaP cells. RNA-seq confirmed AR suppression at the transcriptional level and suggested multiple oncogene, cyclin, and CDK/CKI transcriptional actions to contribute to the cellular consequences. AS-10 promotes histone acetylation as its probable primary mechanism of action to induce PCa cell-cycle arrest and apoptosis, regardless of AR and P53 status. Nevertheless, the inhibition of AR signaling through mechanisms distinct from canonical AR antagonists may hold promise for combinatorial use with androgen deprivation therapy regimens or AR-axis targeting drugs.

Crotonianoids A-C, Three Unusual Tigliane Diterpenoids from the Seeds of Croton tiglium and Their Anti-Prostate Cancer Activity.

Crotonianoids A-C (1-3), three unusual tigliane diterpenoids, were isolated from the seeds of Croton tiglium. Compound 1 is a 13,14:13,15-diseco-tigliane featuring a unique spiro[bicyclo[5.3.0]decane-2,5'-2'(3'H,4'H)-furanone] core; 2 is a 13,15-seco-tigliane incorporating a rare peroxide bridge between C-13 and C-15; and 3 is the first example of a phorbol ester with a 10R-configuration. Their structures were determined by spectroscopic, computational, and X-ray diffraction methods. Compounds 1 and 2 markedly inhibited the growth and survival of prostate cancer cell C4-2B at micromolar concentrations and induced cell apoptosis. Mechanistic study revealed that 1 and 2 could suppress androgen receptor (AR) signaling pathway by promoting the degradation of AR protein.

Regression of Castration-Resistant Prostate Cancer by a Novel Compound HG122.

Prostate cancer (PCa) is a common aggressive disease worldwide which usually progresses into incurable castration-resistant prostate cancer (CRPC) in most cases after 18–24 months treatment. Androgen receptor (AR) has been considered as a crucial factor involved in CRPC and the study of AR as a potential therapeutic target in CRPC may be helpful in disease control and life-cycle management. In this study, we identified a potent small molecule compound, HG122, that suppressed CRPC cells proliferation and metastasis, and inhibited tumor growth both in subcutaneous and orthotopic tumor model. In addition, HG122 reduced the mRNA expression of PSA and TMPRSS2 which are target genes of AR, resulting in cell growth inhibition and metastasis suppression of CRPC, without affecting the expression of AR mRNA level. Mechanically, HG122 promoted AR protein degradation through the proteasome pathway impairing the AR signaling pathway. In conclusion, HG122 overcomes enzalutamide (ENZ) resistance in CRPC both in vitro and in vivo, thus suggesting HG122 is a potential candidate for the clinical prevention and treatment of CRPC.

Discovery of A031 as effective proteolysis targeting chimera (PROTAC) androgen receptor (AR) degrader for the treatment of prostate cancer.

Androgen receptor (AR) is an effective therapeutic target for the treatment of prostate cancer. We report herein the design, synthesis, and biological evaluation of highly effective proteolysis targeting chimeras (PROTAC) androgen receptor (AR) degraders, such as compound A031. It could induce the degradation of AR protein in VCaP cell lines in a time-dependent manner, achieving the IC 50 value of less than 0.25μM. The A031 is 5 times less toxic than EZLA and works with an appropriate half-life (t 1/2) or clearance rate (Cl). Also, it has a significant inhibitory effect on tumor growth in zebrafish transplanted with human prostate cancer (VCaP). Therefore, A031 provides a further idea of developing novel drugs for prostate cancer.

Design and characterization of cereblon-mediated androgen receptor proteolysis-targeting chimeras.

Proteolysis-targeting chimera (PROTAC)-mediated protein degradation is a rapidly emerging therapeutic intervention that induces the degradation of targeted proteins. Herein, we report the design and biological evaluation of a series of androgen receptor (AR) PROTAC degraders for the treatment of metastatic castration-resistant prostate cancer. Predominantly, instead of thalidomide, we utilized the TD-106 scaffold, a novel cereblon (CRBN) binder that was identified in our previous study. Our results suggest that the linker position in the TD-106 CRBN binder is critical for the efficiency of AR degradation. The compounds attached to the 6-position of TD-106 promoted better degradation of AR than those at the 5- and 7-positions. Among the synthesized AR PROTACs, the representative degrader 33c (TD-802) effectively induced AR protein degradation, with a degradation concentration 50% of 12.5nM and a maximum degradation of 93% in LNCaP prostate cancer cells. Additionally, most AR PROTAC degraders, including TD-802, displayed good liver microsomal stability and invivo pharmacokinetic properties. Finally, we showed that TD-802 effectively inhibited tumor growth in an invivo xenograft study.

Abstract 1960: Targeted androgen receptor (AR) protein degradation for the treatment of metastatic castration-resistant prostate cancer (mCRPC)

Abstract Androgen receptor (AR) and its downstream signaling play a critical role in the development and progression of both localized and metastatic prostate cancer. As a validated therapeutic target for the treatment of metastatic castration-resistant prostate cancer (mCRPC), previous strategies that successfully target AR signaling have focused on blocking androgen synthesis by drugs such as abiraterone and inhibition of AR function by AR antagonists such as enzalutamide and apalutamide (ARN-509). However, such agents become ineffective in advanced prostate cancer with AR gene amplification, mutation and alternate splicing. It is very clear however that in most patients with CRPC, the AR protein continues to be expressed and tumors are still dependent upon AR signaling. Here we describe our design, synthesis and evaluation of small-molecule AR degraders based on the proteolysis targeting chimera (PROTAC) concept and our investigation of their therapeutic potential and mechanism of action in vitro and in vivo. In vitro, our potent AR degraders effectively induce degradation of AR protein in AR+ LNCaP, VCaP and 22Rv1 prostate cancer cell lines with DC50 values as low as 1 nM. AR degraders are capable of reducing the AR protein level by >95% in these AR+ cancer cell lines and effectively reduces AR-regulated gene expression suppression. In vivo, our AR degrader showed potent AR degradation effects and anti-tumor activities in multiple murine xenograft models of prostate cancer at well-tolerated dosing schedules. Our data provides clear evidence that targeting AR for degradation by the PROTAC methodology is a novel and very exciting therapeutic approach for the treatment of mCRPC. Citation Format: Xin Han, Lijie Zhao, Weiguo Xiang, Chong Qin, Bukeyan Miao, Tianfeng Xu, Jianfeng Lu, Mi Wang, Shaomeng Wang. Targeted androgen receptor (AR) protein degradation for the treatment of metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1960.

Discovery of Highly Potent and Efficient PROTAC Degraders of Androgen Receptor (AR) by Employing Weak Binding Affinity VHL E3 Ligase Ligands.

Androgen receptor (AR) is a validated therapeutic target for the treatment of metastatic castration-resistant prostate cancer (mCRPC). We report herein our design, synthesis, and biological characterization of highly potent small-molecule proteolysis targeting chimera (PROTAC) AR degraders using a potent AR antagonist and E3 ligase ligands with weak binding affinities to VHL protein. Our study resulted in the discovery of 11 (ARD-266), which effectively induces degradation of AR protein in AR-positive (AR+) LNCaP, VCaP, and 22Rv1 prostate cancer cell lines with DC50 values of 0.2-1 nM. ARD-266 is capable of reducing the AR protein level by >95% in these AR+ prostate cancer cell lines and effectively reduces AR-regulated gene expression suppression. For the first time, we demonstrated that an E3 ligand with micromolar binding affinity to its E3 ligase complex can be successfully employed for the design of highly potent and efficient PROTAC degraders and this finding may have a significant implication for the field of PROTAC research.

Androgen Receptor Modulation Optimized for Response—Splice Variant: A Phase 3, Randomized Trial of Galeterone Versus Enzalutamide in Androgen Receptor Splice Variant-7–expressing Metastatic Castration-resistant Prostate Cancer

Background: Detection of androgen receptor (AR) splice variant-7 (AR-V7) messenger RNA (mRNA) in circulating tumor cells (CTCs) is associated with a suboptimal response to abiraterone and enzalutamide in metastatic castration-resistant prostate cancer (mCRPC). Galeterone inhibits CYP17 and AR, and induces AR protein degradation. We hypothesized that galeterone would be clinically superior to enzalutamide in AR-V7–positive (AR-V7+) mCRPC. Objective: To screen and characterize AR-V7+ mCRPC, and evaluate galeterone compared with enzalutamide. Design, setting, and participants: This was a multicenter randomized phase 3 trial; enzalutamide-, abiraterone-, and chemotherapy-naïve mCRPC patients had AR-V7 prescreening using a CTC-based mRNA assay. Intervention: AR-V7+ patients were randomized (1:1) to open-label galeterone or enzalutamide; planned sample size was 148. Outcome measurements and statistical analysis: The primary endpoint was radiographic progression-free survival (rPFS). Baseline AR-V7 status was correlated with patient characteristics. Results and limitations: Overall, 953 men were prescreened for AR-V7; 323 (34%) had detectable CTCs, and 73/323 had AR-V7 mRNA. The AR-V7+ prevalence was 8% (73/953; 95% confidence interval [CI] 6–10%). AR-V7 was associated with indicators of advanced and high-volume disease at baseline, including higher prostate-specific antigen (PSA) level (p < 0.001), more bone metastases (p < 0.001), docetaxel for hormone-sensitive disease (p < 0.001), prior first-generation androgen deprivation therapy (p < 0.001), and shorter time from diagnosis to enrollment (p < 0.001). Of 73 eligible patients, 38 were randomized to galeterone (n=19) or enzalutamide (n=19); 35 dropped out before randomization. Owing to high censorship for the rPFS events, the data monitoring committee recommended early closure based on interim evidence that the primary endpoint would not be met. The PSA50 values were 2/16 (13%) and 8/19 (42%) for galeterone and enzalutamide respectively (proportion difference=−0.278, 95% CI −0.490 to 0.097). Conclusions: The prevalence of CTC mRNA AR-V7 in first-line mCRPC was 8% (95% CI 6–10%). AR-V7+ was associated with the characteristics of aggressive and advanced disease. These men had rapid disease progression. Development of galeterone will not be pursued. Patient summary: Of men with metastatic castration-resistant prostate cancer, 8% had the androgen receptor splice variant-7 (AR-V7) blood biomarker. The AR-V7+ patients had features of aggressive disease. Thirty-eight men were treated with either galeterone or enzalutamide; the trial was stopped early prior to determining efficacy because too many patients transitioned off the trial due to advancing cancer before having required radiographs.

Abstract 2626: Exquisite specificity of PMEPA1 isoforms in regulation of androgen signaling through AR protein degradation in prostate cancer

Abstract Introduction: Prostate Transmembrene Protein, androgen Induced 1 (PMEPA1) gene was defined as an androgen and TGF-β responsive gene to inhibit androgen receptor (AR) and TGF-β signaling via negative feedback loops. Our previous studies identified two functionally distinct PMEPA1 isoforms: androgen responsive PMEPA1-b and TGF-β responsive PMEPA1-a. These two isoforms share high homology within the intracellular domains including PY1 and PY2 motifs essential for binding to E3 ubiqintin ligase, NEDD4. It is still unclear which PMEPA1 isoform with distinct N-terminus regulates AR protein stability in CaP cells. Methods: An immunoprecipitation (IP) assay was used to study the protein-protein interactions between AR, PMEPA1 isoforms and NEDD4. HEK293 cells were used for co-transfection of the expression vectors harboring PMEPA1 isoforms, AR and NEDD4. RNA Seq data from TCGA datasets were utilized to analyze the correlation between transcript levels of both PMEPA1 isoforms and clinical outcomes including Gleason scores, overall survival and progression free survival of cancers of prostate, breast, lung and colon. Results: Only PMEPA1-b isoform bound to wild-type and T877A mutated AR, directly. In contrast, PMEPA1 isoforms a, b and c bound to E3 ubiquintin ligase NEDD4. As expected, only PMEPA1-b bound to AR and NEDD4 for tri-complex interactome. Interestingly, the direct binding between AR and NEDD4 was not detected, which highlighted the adaptor function of PMEPA1-b in mediating proteasome-mediated AR degradation. Furthermore, the deletion of the transmembrane domain compromised binding of PMEPA1-b with AR. The TGF-β responsive PMEPA1-a was not found to bind to AR or form AR/NEDD/PMEPA1 complex. Consistently, ectopic PMEPA1-b down-regulated AR protein, inhibited AR signaling, and suppressed cell growth of LNCaP cells. But PMEPA1-a was not detected to interfere with AR signaling in CaP cells. Clinically, a higher ratio of PMEPA1-a/b was correlated with higher Gleason scores in CaP. And higher expression of PMEPA1-a and b was associated with more aggressive lung cancer and colon cancer. All of these findings highly suggest that the biological functions of PMEPA1 isoforms on TGF-β or AR signaling are tissue specific. Conclusions: Our study highlighted PMEPA1 isoform b as an essential docking platform by interacting with AR at N-terminus and NEDD4 at C-terminus for mediating the protein degradation of AR by NEDD4. Additionally, the transmembrane domain at N-terminus of PMEPA1-b protein was essential for NEDD4 dependent AR degradation. These findings might help guide a novel anti-AR strategy in development of anti-CaP therapy. RNA seq data analysis further underscored the tissue-specificity of division of labor among PMEPA1 isoforms in tum Citation Format: Shashwat Sharad, Natashia Benjamin, Zsófia Sztupinszki, Zoltan Szallasi, Shiv Srivastava, Inger L. Rosner, Jennifer Cullen, Hua Li, Albert Dobi. Exquisite specificity of PMEPA1 isoforms in regulation of androgen signaling through AR protein degradation in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2626.

Discovery of ARD-69 as a Highly Potent Proteolysis Targeting Chimera (PROTAC) Degrader of Androgen Receptor (AR) for the Treatment of Prostate Cancer.

We report herein the discovery of highly potent PROTAC degraders of androgen receptor (AR), as exemplified by compound 34 (ARD-69). ARD-69 induces degradation of AR protein in AR-positive prostate cancer cell lines in a dose- and time-dependent manner. ARD-69 achieves DC50 values of 0.86, 0.76, and 10.4 nM in LNCaP, VCaP, and 22Rv1 AR+ prostate cancer cell lines, respectively. ARD-69 is capable of reducing the AR protein level by >95% in these prostate cancer cell lines and effectively suppressing AR-regulated gene expression. ARD-69 potently inhibits cell growth in these AR-positive prostate cancer cell lines and is >100 times more potent than AR antagonists. A single dose of ARD-69 effectively reduces the level of AR protein in xenograft tumor tissue in mice. Further optimization of ARD-69 may ultimately lead to a new therapy for AR+, castration-resistant prostate cancer.

New Generation of Selective Androgen Receptor Degraders: Our Initial Design, Synthesis, and Biological Evaluation of New Compounds with Enzalutamide-Resistant Prostate Cancer Activity.

In our effort to find small-molecule treatments of advanced prostate cancers (PCs), a novel series of indolyl and indolinyl propanamides (series II and III) were discovered as selective androgen receptor degraders (SARDs). Initial studies of androgen receptor (AR) antagonist (1) and agonist (2) propanamides yielded a tertiary aniline (3) with novel SARD activity but poor metabolic stability. Cyclization to II and III produced submicromolar AR antagonism and protein degradation selective to AR and AR splice variant (AR SV). II and III maintained potency against enzalutamide-resistant (Enz-R) mutant ARs and PC cells and were efficacious in Enz-R xenografts, suggesting their potential to treat advanced PCs. Design, synthesis, and biological activity of novel SARDs that could potentially be used for the treatment of a wide spectrum of PCs including castration-resistant, Enz-R, and/or AR SV-dependent advanced PCs that are often untreatable with known hormone therapies are discussed.

Riluzole induces AR degradation via endoplasmic reticulum stress pathway in androgen-dependent and castration-resistant prostate cancer cells.

Prostate cancer (PCa) is diagnosed at the highest rate of all non-cutaneous male cancers in the United States. The androgen-dependent (AD) transcription factor, androgen receptor (AR), drives PCa-but inhibiting AR or androgen biosynthesis induces remission for only a short time. At which point, patients acquire more aggressive castration-resistant (CR) disease with re-activated AR-dependent signaling. To combat treatment resistance, down-regulating AR protein expression has been considered as a potential treatment strategy for CR-PCa. AD- and CR-PCa cell lines were treated with the well-tolerated FDA-approved oral medicine, riluzole. Expression of full-length or wild-type AR (AR-FL) and constitutively active AR-splice variant 7 (AR-V7) was assessed by immunoblotting. AR-FL/AR-V7 activity was measured using qRT-PCR of AR-target genes. Cytoplasmic [Ca2+ ] levels were measured using a fluorescent Ca2+ indicator microplate assay. Markers of the endoplasmic reticulum stress (ERS) pathway and autophagy were assessed by immunoblotting. Direct interaction between AR and selective autophagy receptor p62 was demonstrated by co-immunoprecipitation. We demonstrate that riluzole downregulates AR-FL, mutant ARs, and AR-V7 proteins expression by protein degradation through ERS pathway and selective autophagy. Riluzole also significantly inhibited AR transcription activity by decreasing its target genes expression (PSA, TMPRSS2, and KLK2). We provide key mechanistic insights by which riluzole exerts its anti-tumorigenic effects and induces AR protein degradation via ERS pathways. Our findings support the potential utility of riluzole for treatment of PCa.