Androgen Receptor Degradation Research Articles

An Autophagy-Targeting Chimera Induces Degradation of Androgen Receptor Mutants and AR-v7 in Castration-Resistant Prostate Cancer.

Genetic alterations play a pivotal role in various human diseases, particularly cancer. The androgen receptor (AR) is a crucial transcription factor driving prostate cancer (PCa) progression across all stages. Current AR-targeting therapies utilize competitive AR antagonists or pathway suppressors. However, therapy resistance often emerges due to AR mutations and AR splice variants, such as AR-v7. To overcome this, we developed ATC-324, an AR degrader using the innovative protein degradation technology platform AUTOphagy-TArgeting Chimera (AUTOTAC). ATC-324 was designed to comprise enzalutamide, an AR inhibitor, as a target-binding ligand and YT 6-2, a ligand of the autophagy receptor p62/SQSTM1, as an autophagy-targeting ligand. ATC-324 induces the formation of the AR/p62 complex, leading to autophagy-lysosomal degradation of AR. Importantly, ATC-324 effectively degrades AR mutants frequently detected in PCa and co-degrades AR-v7 as a heterodimer with full-length AR. ATC-324 reduces nuclear AR levels and downregulates the target gene expression of AR and AR-v7, leading to cytotoxicity in AR-positive PCa cells. We also provide evidence of the therapeutic potential of ATC-324 in vivo as well as ex vivo bone organ culture. Moreover, ATC-324 remains potent in enzalutamide-resistant PCa cells. These results demonstrate the potential of the AUTOTAC platform to target previously considered undruggable proteins and overcome certain drug resistance mechanisms.

PROTACs as Therapeutic Modalities for Drug Discovery in Castration-Resistant Prostate Cancer.

Castration-resistant prostate cancer (CRPC) presents significant challenges in clinical management due to its resistance to conventional androgen receptor (AR)-targeting therapies. The advent of proteolysis targeting chimeras (PROTACs) has revolutionized cancer therapy by enabling the targeted degradation of key molecular players implicated in CRPC progression. In this review we discuss the developments of PROTACs for CRPC treatment, focusing on AR and other CRPC-associated regulators. We provide an overview of the strategic trends in AR PROTAC development from the aspect of targeting site selection and preclinical antitumor evaluation, as well as updates on AR degraders in clinical applications. Additionally, we briefly address the current status of selective AR degrader development. Furthermore, we review new developments in PROTACs as potential CRPC treatment paradigms, highlighting those targeting chromatin modulators BRD4, EZH2, and SWI/SNF; transcription regulator SMAD3; and kinases CDK9 and PIM1. Given the molecular targets shared between CRPC and neuroendocrine prostate cancer (NEPC), we also discuss the potential of PROTACs in addressing NEPC.

Discovery of a Series of Orally Bioavailable Androgen Receptor Degraders for the Treatment of Prostate Cancer.

Androgen receptor (AR) signaling plays a key role in the progression of prostate cancer. This study describes the discovery and optimization of a novel series of AR PROTAC degraders that recruit the Cereblon (CRBN) E3 ligase. Having identified a series of AR ligands based on 4-(4-phenyl-1-piperidyl)-2-(trifluoromethyl)benzonitrile, our PROTAC optimization strategy focused on linker connectivity and CRBN ligand SAR to deliver potent degradation of AR in LNCaP cells. This work culminated in compounds 11 and 16 which demonstrated good rodent oral bioavailability. Subsequent SAR around the AR binding region brought in an additional desirable feature, degradation of the important treatment resistance mutation L702H. Compound 22 (AZ'3137) possessed an attractive profile showing degradation of AR and L702H mutant AR with good oral bioavailability across species. The compound also inhibited AR signaling in vitro and tumor growth in vivo in a mouse prostate cancer xenograft model.

UBX-390: A Novel Androgen Receptor Degrader for Therapeutic Intervention in Prostate Cancer.

The androgen receptor (AR) is an attractive target for treating prostate cancer, considering its role in the development and progression of localized and metastatic prostate cancer. The high global mortality burden of prostate cancer, despite medical treatments such as androgen deprivation or AR antagonist therapy, highlights the need to explore alternative strategies. One strategy involves the use of heterobifunctional degraders, also known as proteolysis-targeting chimeras, which are novel small-molecule therapeutics that inhibit amplified or mutated targets. Here, the study reports a novel cereblon-based AR degrader, UBX-390, and demonstrates its superior activity over established AR degraders, such as ARV-110 or ARCC-4, in prostate cancer cells under short- and long-term treatment conditions. UBX-390 suppresses chromatin binding and gene expression of AR and demonstrates substantial efficacy in the degradation of AR mutants in patients with treatment-resistant prostate cancer. UBX-390 is presented as an optimized AR degrader with remarkable potential for treating castration-resistant prostate cancer.

ARV-766, a proteolysis targeting chimera (PROTAC) androgen receptor (AR) degrader, in metastatic castration-resistant prostate cancer (mCRPC): Initial results of a phase 1/2 study.

5011 Background: Patients with mCRPC inevitably develop resistance to available therapies, eg, novel hormonal agents (NHAs), and experience disease progression. Certain mutations that can develop in the ligand-binding domain (LBD; amino acids 671–920) of the AR gene during mCRPC treatment have been associated with poor outcomes. ARV-766 is a novel, potent, orally administered PROTAC AR degrader that targets wild-type AR and clinically relevant AR LBD mutants, including the most prevalent AR L702H, H875Y, and T878A mutations. We report initial results from a phase 1/2 study (NCT05067140) of ARV-766 in men with mCRPC and disease progression on prior NHA therapy. Methods: Eligible patients had progressive mCRPC and ongoing androgen deprivation therapy. The phase 1 dose escalation portion evaluated the safety and tolerability of escalating doses of ARV-766 (20–500 mg once daily [QD]) in patients who had progressed on ≥2 prior systemic therapies (including ≥1 NHA). The phase 2 cohort expansion portion is evaluating the clinical activity and safety of 2 doses of ARV-766 (100 or 300 mg QD) in patients who had received 1–3 prior NHAs and ≤2 prior chemotherapy regimens. Here we report safety in all patients treated with ARV-766 across the phase 1/2 study and clinical activity (proportion of patients with best prostate-specific antigen [PSA] declines of ≥50% [PSA50] after ≥1 month of PSA follow-up) in the subgroup of patients with AR LBD mutations. Results: As of December 15, 2023, 103 patients received ARV-766 (34 in phase 1 and 69 in phase 2). Patients had received a median of 4 prior therapies (range: 1–9), including 56% with ≥1 prior taxane and 46% with ≥2 prior NHAs. Patients with AR LBD mutations (n=30) had received a median of 4 prior therapies (range: 1–9), including 60% with ≥1 prior taxane and 57% with ≥2 prior NHAs. In phase 1, there were no dose-limiting toxicities, and a maximum tolerated dose was not reached. Across 103 phase 1/2 patients, treatment-emergent adverse events led to dose reduction and treatment discontinuation, respectively, in 7 (7%) and 10 (10%). Any grade treatment-related adverse events (TRAEs) reported in ≥10% of patients were fatigue (36%; 3% grade 3), nausea (19%; 1% grade 3), diarrhea (15%; 1% grade 3), alopecia (14%), increased blood creatinine (13%; 0 grade 3), and decreased appetite (11%; 0 grade 3); there were no grade 4 TRAEs. In 28 PSA-evaluable patients with AR LBD mutations, PSA50 was 50.0%. Preliminary pharmacokinetics indicated dose-dependent increases in ARV-766 exposure up to 320 mg QD, with exposure accumulation ranging from ≈5- to 8-fold at steady state. Conclusions: In this phase 1/2 study of pretreated patients with mCRPC, ARV-766 was well tolerated and showed promising clinical activity in those with tumors harboring AR LBD mutations. ARV-766 warrants further development in advanced prostate cancer. Clinical trial information: NCT05067140 .

Discovery of novel biphenyl derivatives as androgen receptor degraders for the treatment of enzalutamide-resistant prostate cancer

Second-generation AR antagonists, such as enzalutamide, are the primary therapeutic agents for advanced prostate cancer. However, the development of both primary and secondary drug resistance leads to treatment failures and patient mortality. Bifunctional agents that simultaneously antagonize and degrade AR block the AR signaling pathway more completely and exhibit excellent antiproliferative activity against wild-type and drug-resistant prostate cancer cells. Here, we reported the discovery and optimization of a series of biphenyl derivatives as androgen receptor antagonists and degraders. These biphenyl derivatives exhibited potent antiproliferative activity against LNCaP and 22Rv1 cells. Our discoveries enrich the diversity of small molecule AR degraders and offer insights for the development of novel AR degraders for the treatment of enzalutamide-resistant prostate cancer.

Abstract LB027: Identifying natural inhibitors of androgen receptor (AR) and its variants from NCI Natural Product Repository

Abstract Second-generation androgen ablation therapies (ADT), enzalutamide, and abiraterone are initially effective on metastatic castration-resistant prostate cancer (mCRPC). However, nearly 30-40% of patients eventually become resistant to these treatments due to the presence of androgen-receptor variants (AR-V), which lack a ligand-binding domain. The grim reality that metastatic CRPC is virtually incurable for most patients poses a significant challenge for clinicians striving to enhance these individuals' quality of life and lifespan. Considering drug discovery efforts, we partnered with the National Cancer Institute's (NCI) Natural Product Repository, which possesses a diverse collection of natural product extracts derived from plant, marine, and microbial organisms. We developed high-throughput phenotypic screening assays to screen the crude natural product extract libraries on AR and AR-variants CRPC cell lines (C4-2B and 22Rv1). Several extracts inhibited the growth of both CRPC cell lines and were further confirmed for dose-dependent cell viability inhibition assays. Once we determined the IC50 dose, we performed a Western blot analysis that confirmed the inhibition of AR and AR-V7 expression in CRPC cells.In subsequent studies, we narrowed down by fractionating the most potent extracts and confirmed their ability to inhibit AR expression and signaling on CRPC cell lines. Currently, we are characterizing the potent compounds and their inhibitory activity on AR and AR-variants, in vitro and in vivo CRPC models. Many nutraceuticals have been shown to target AR signaling, synthesis, or degradation which effectively inhibited the growth of CRPC. Our collaborative efforts with NCI will permit us find N-terminal AR degrading molecules (AF-1), which are essential for the AR transcriptional activities of CRPC. In sum, discovery of ovel small molecules from our drug development program have the potential to translate these effective natural products into drugs with clinical benefits to treat CRPC. Citation Format: Neha Tyagi, Sepideh Hosseiniporgham, Ashish Tyagi, Balaji Chandrasekaran, Katherine Bonilla, Inna Kriger, James Saccchettini, Chendil Damodaran. Identifying natural inhibitors of androgen receptor (AR) and its variants from NCI Natural Product Repository [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB027.

Abstract ND02: Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer

Abstract The androgen receptor (AR) is a key driver of the cellular processes that contribute to the pathology of prostate cancers at most stages, and drugs that inhibit the activity of this receptor or interfere with androgen biosynthesis have become the cornerstone of treatments for prostate cancer. While both types of therapy have had a significant positive impact on disease progression and overall survival, de novo and acquired resistance remains an impediment to a durable clinical response in patients with metastatic castration-resistant prostate cancer (mCRPC). The mechanisms underlying drug resistance are complex and multifactorial, being attributable to AR overexpression, point mutations in the receptor that alter drug pharmacology, and to the upregulation of receptor-associated coregulators, which render AR less dependent on an activating ligand. Regardless, absolute inhibition of AR signaling remains the objective of contemporary approaches to treat prostate cancer. Recently, there has been specific interest in the development of approaches to eliminate AR proteins using drugs that enable targeted degradation of AR in cancer cells.This puts in context the significance of our discovery of BMS-986365 (also known as CC-94676), a heterobifunctional ligand-directed degrader (LDD) that enables the CRL4CRBN E3 ligase-dependent ubiquitination and degradation of AR (DC50 10 to 40 nM, Ymin 7 to 19%). BMS-986365 is a highly potent and selective AR degrader that induces rapid and deep degradation of both wildtype and mutant forms of the receptor residing in either the cytoplasmic or nuclear compartments of the cell. The drug is ~100-fold more potent than enzalutamide (ENZ) at inhibiting androgen-stimulated transcription of AR target genes, and 10 to 120-fold more potent than ENZ at inhibiting AR-dependent proliferation of multiple prostate cancer cell lines in vitro. In animal models of advanced prostate cancer, BMS-986365 demonstrates on-target activity, degrading AR, suppressing AR signaling, and inhibiting tumor growth. Indeed, tumor volume reductions of 63-92% were achieved by BMS-986365 in validated models of advanced CRPC and therapy resistant patient-derived xenografts, including those with acquired resistance to ENZ. Collectively our preclinical data suggest that the AR degrader BMS-986365 is superior to standard-of-care AR antagonists, such as ENZ, in both preclinical and disease-relevant animal models, and support its clinical development for treatment of prostate cancer. BMS-986365 has advanced into clinical studies where it has demonstrated encouraging clinical activity in patients with mCRPC. Citation Format: Shuichan Xu, Surendra Nayak, John D. Norris, Massimo Ammirante, Emyly Rychak, Suzanne E. Wardell, Toshiya Tsuji, Ken Liu, Joseph Meiring, Joseph R. Piccotti, Deepak Dalvie, Debbie Liao, Raju Kandimalla, Nadia Guerrero, Lisa Sapinoso, Jennifer G. Baker, Yeeun Bae, Joshua Baughman, Brandon Toyama, Celia Fontanillo Fontanillo, Stephen Norris, Evan J. Horn, Veronique Plantevin-Krenitsky, Deborah Mortensen, Brian Cathers, Marie Hong Nguyen, Joshua D. Hensen, Lawrence G. Hamann, Donald P. McDonnell, Rama Krishna Narla, Mark Rolfe. Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr ND02.

Blocking the dimerization of polyglutamine-expanded androgen receptor protects cells from DHT-induced toxicity by increasing AR turnover

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular degenerative disease caused by a polyglutamine expansion in the androgen receptor (AR). This mutation causes AR to misfold and aggregate, contributing to toxicity in and degeneration of motor neurons and skeletal muscle. There is currently no effective treatment or cure for this disease. The role of an interdomain interaction between the amino- and carboxyl-termini of AR, termed the N/C interaction, has been previously identified as a component of androgen receptor-induced toxicity in cell and mouse models of SBMA. However, the mechanism by which this interaction contributes to disease pathology is unclear. This work seeks to investigate this mechanism by interrogating the role of AR homodimerization- a unique form of the N/C-interaction- in SBMA. We show that, although the AR N/C-interaction is reduced by polyglutamine-expansion, homodimers of 5α-dihydrotestosterone (DHT)-bound AR are increased. Additionally, blocking homodimerization results in decreased AR aggregation and toxicity in cell models. Blocking homodimerization results in the increased degradation of AR, which likely plays a role in the protective effects of this mutation. Overall, this work identifies a novel mechanism in SBMA pathology that may represent a novel target for the development of therapeutics for this disease.

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.

Abstract 4479: Design, synthesis, and evaluation of amino acid conjugated niclosamide prodrugs as a PepT1 substrate

Abstract The anthelmintic drug, Niclosamide, has a multitude of promising anticancer properties including inhibition of key signaling pathways involved in tumorigenesis, disruption of mitochondrial function, degradation of the overexpressed androgen receptor, and more. However, a key limitation of the clinical use of Niclosamide in cancer treatment is its low solubility and cellular uptake, which result in poor pharmacokinetic properties and dose-limiting GI toxicities at concentrations lower than the therapeutic threshold of the drug. To overcome this, we hypothesized that we could use amino acid conjugated niclosamide prodrugs to improve cellular uptake by creating a substrate of the PepT1 transport protein. The overexpression of the PepT1 transport protein that is involved in many hormonal cancers is being used to our advantage. Our study involved first synthesizing a group of niclosamide and niclosamide analogs conjugated with polar or nonpolar amino acids. Next, we conducted a Glycine-Sarcosine assay measuring changes in the uptake of the dipeptide glycyl-sarcosine (Gly-Sar). Our initial step was to examine if our conjugates could disrupt the absorption of Gly-Sar. The active conjugate will be tested whether they are substrates or inhibitors of the transporter. For the future, we have plans to determine the half-maximal inhibitory concentration (IC50) of niclosamide conjugates in various cancer cell lines and to quantify cleavage of the prodrugs intracellularly. Citation Format: Alaina C. McDonough, Jeffery Y. Cheng, Shabber Mohammed, Pui-Kai Li, Yangzom Bhutia. Design, synthesis, and evaluation of amino acid conjugated niclosamide prodrugs as a PepT1 substrate [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 4479.

Abstract 6045: Development and characterization of ATC-324: An AUTOTAC-based androgen receptor degrader for prostate cancer treatment

Abstract Prostate cancer (PCa) progression is largely driven by the androgen receptor (AR), making it a prime target for therapy. However, therapy resistance often arises due to AR mutations and splice variants, such as AR-v7. AUTOTAC (AUTOphagy-TArgeting Chimera) is a novel protein degradation platform that utilizes the autophagy-lysosomal pathway to selectively degrade disease-causing proteins. In this study, we characterize ATC-324, an AUTOTAC-based AR degrader designed for the treatment of PCa. ATC-324 comprises enzalutamide linked to YT 6-2, a small molecule activator of the autophagy receptor p62/SQSTM1. ATC-324 induces the formation of the AR/p62 complex while activating autophagic flux, leading to the autophagy-lysosomal degradation of AR. To characterize ATC-324, we employed various AR-dependent, AR-null, and enzalutamide-resistant PCa cell lines. Given that bone metastasis is a major clinical complication of castrate-resistant PCa associated with greater morbidity and mortality, we utilized the bone-in-culture array (BICA) assay, an ex vivo bones culture model, to investigate the impact of ATC-324 on PCa cell survival and growth in the bone microenvironment. We demonstrated that ATC-324 effectively degrades wild-type, mutant, and splice variants of AR. In addition, ATC-324 induces AR-dependent apoptosis and cytotoxicity. Importantly, ATC-324 maintains its potency in enzalutamide-resistant PCa cells. Utilizing the BICA assay, we showed that ATC-324 exhibits cytotoxicity against 22Rv1 bone micrometastases at even lower concentrations than in 2D cell culture. In conclusion, our study demonstrates the successful development and characterization of ATC-324 as a potent and selective degrader of various forms of AR. Furthermore, its effectiveness against enzalutamide-resistant cells indicates its capability to overcome therapy resistance. The observed cytotoxicity against bone micrometastases suggests a therapeutic potential for combating bone metastasis, a major complication of castration-resistant PCa. Our study underscores the potential of the AUTOTAC platform to selectively degrade disease-causing proteins Citation Format: Tri Pham, Tae Hyun Bae, Ki Woon Sung, Abdo Najy, Alaleh Zamiri, Hyejeong Jang, Su Ran Mun, Seongho Kim, Dongping Shi, Steven Kregel, Elizabeth Heath, Michael Cher, Yong Tae Kwon, Hyeong-Reh Kim. Development and characterization of ATC-324: An AUTOTAC-based androgen receptor 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 6045.

Tanshinone analog inhibits castration-resistant prostate cancer cell growth by inhibiting glycolysis in an AR-dependent manner

Androgen receptor (AR) is one of the key targets for the treatment of Castration-resistant prostate cancer (CRPC). Current endocrine therapy can greatly improve CRPC patients. However, with the change of pathogenic mechanism, acquired resistance often leads to the failure of treatment. Studies have shown that tanshinone IIA (TS-IIA) and its derivatives have significant antitumor activity, and have certain AR targeting effects, but the mechanism is unknown. In this study, the TS-IIA analog TB3 was found to significantly inhibit the growth of CRPC in vitro and in vivo. Molecular docking, cellular thermal shift assay and CHX experiments confirmed that AR was the target of TB3 and promoted the degradation of AR. Furthermore, TB3 can significantly inhibit glycolysis metabolism by targeting the AR/PKM2 axis..The addition of pyruvic acid could significantly alleviate the inhibitory effect of TB3 on CRPC cells. Besides, the knockdown of AR or PKM2 also could reverse the effect of TB3 on CRPC cells. Taken together, our study suggests that TS-IIA derivative TB3 inhibits glycolysis to prevent the CRPC process by targeting the AR/PKM2 axis.

Insight into Recent Advances in Degrading Androgen Receptor for Castration-Resistant Prostate Cancer

Induced protein degradation has emerged as an innovative drug discovery approach, complementary to the classical method of suppressing protein function. The androgen receptor signaling pathway has been identified as the primary driving force in the development and progression of lethal castration-resistant prostate cancer. Since androgen receptor degraders function differently from androgen receptor antagonists, they hold the promise to overcome the drug resistance challenges faced by current therapeutics. Proteolysis-targeting chimeras (PROTACs), monomeric degraders, hydrophobic tagging, molecular glues, and autophagic degradation have demonstrated their capability in downregulating intracellular androgen receptor concentrations. The potential of these androgen receptor degraders to treat castration-resistant prostate cancer is substantiated by the advancement of six PROTACs and two monomeric androgen receptor degraders into phase I or II clinical trials. Although the chemical structures, in vitro and in vivo data, and degradation mechanisms of androgen receptor degraders have been reviewed, it is crucial to stay updated on recent advances in this field as novel androgen receptor degraders and new strategies continue to emerge. This review thus provides insight into recent advancements in this paradigm, offering an overview of the progress made since 2020.

First-in-human phase 1 study of CC-94676, a first-in-class androgen receptor (AR) ligand-directed degrader (LDD), in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC).

134 Background: Androgen receptor (AR) signaling is the principal driver of PC at all stages. CC-94676 (BMS-986365) is a heterobifunctional, first-in-class, orally bioavailable AR LDD designed to induce rapid, sustained, and highly selective AR degradation in pts who progressed on standard of care therapies. We report initial results from an open-label, multicenter study, NCT04428788, evaluating CC-94676 in pts with progressive mCRPC. Methods: Pts with mCRPC who progressed on androgen deprivation therapy, ≥ 1 second generation hormonal therapy (eg, enzalutamide [enza], abiraterone [abi], darolutamide, and apalutamide) and taxane chemotherapy (chemo) (unless refused or not indicated) were enrolled to evaluate the safety, tolerability, PK/PD, and preliminary efficacy of CC-94676. Escalation doses evaluated were 100–1200 mg QD and 600–900 mg BID; expansion doses were 600 mg QD and 400–900 mg BID. Results: As of Aug 21, 2023, 95 pts received CC-94676 (median age 71 yrs) with a median of 5 (range 2–12) prior therapies, including enza (80%), abi (72%), both enza & abi (56%), and chemo (56%) (docetaxel 55%; cabazitaxel 20%). There were no ≥ Grade (G) 4 treatment-related adverse events (TRAEs) or discontinuations due to TRAEs. Of 27 pts treated in escalation, treatment (Tx) was well tolerated; 2 pts had non-serious G3 TRAEs at doses ≥ 800 mg QD, which were manageable with dose modifications. One dose-limiting toxicity of asymptomatic QTc prolongation was observed at 900 mg BID and resolved with dose interruption. The maximum tolerated dose was not reached. Of 68 pts treated in expansion, the most common TRAEs were dose-dependent: QTc prolongation (asymptomatic) (43%; G3: 9%), bradycardia (31%; ≥G3: none), and fatigue (24%; ≥G3: none). G3 TRAEs were manageable with dose modifications. The rate of pts with confirmed PSA reductions ≥ 30% (PSA30) increased dose-dependently from 400 to 900 mg BID. 23/68 (34%) pts across all dose levels achieved ≥ PSA30. At 900 mg BID, 11/20 (55%) pts showed PSA30; 7/20 (35%) and 2/20 (10%) had confirmed PSA declines of ≥50% and ≥90%, respectively. PSA responses and radiographic tumor shrinkage occurred across all dose levels, including in pts with AR wildtype (WT) , amplifications, and mutations (by cfDNA), and in heavily pretreated pts who progressed on abi, enza, and chemo. At 900 mg BID, the median duration of Tx was 182 days (range 21-448) and 9/20 (45%) pts remained free of radiographic progression with treatment ongoing at 6 months. Conclusions: CC-94676 is well tolerated with a manageable safety profile. CC-94676 shows promising and prolonged clinical activity in heavily pretreated mCRPC pts who progressed on abi, enza, and chemo with activity seen in pts with tumors expressing WT and mutant ARs. Selection of the recommended phase 2 dose is ongoing. Clinical trial information: NCT04428788 .

MDM2 regulates the stability of AR, AR-V7, and TM4SF3 proteins in prostate cancer.

Androgen receptor (AR) and its constitutively active splice variant, AR Variant 7 (AR-V7), regulate genes essential for the development and progression of prostate cancer. Degradation of AR and AR-V7 by the ubiquitination proteasomal pathway is important for the regulation of both their protein stability. Our published results demonstrate that the interaction of TM4SF3 with either AR or AR-V7 leads to mutual stabilization due to a reduction in their ubiquitination and proteasomal degradation. These results led us to search for a common E3 ligase for AR, AR-V7, and TM4SF3. Depletion by siRNA of several E3 ligases identified MDM2 as the common E3 ligase. MDM2 inhibition by siRNA depletion or using a pharmacological inhibitor (MDM2i) of its E3 ligase activity led to elevated levels of endogenous AR, AR-V7, and TM4SF3 in prostate cancer cells. MDM2 knockdown in PC-3 cells, which do not express AR, also increased TM4SF3, demonstrating that MDM2 affects the TM4SF3 protein independent of AR. We further demonstrate that MDM2i treatment reduced the ubiquitination of AR and TM4SF3, suggesting that MDM2 can induce the ubiquitination of these proteins. Increased AR and AR-V7 protein levels induced by MDM2i treatment resulted in the expected increased expression of AR-regulated genes and enhanced proliferation and migration of both LNCaP and Enzalutamide-resistant CWR-22Rv1 prostate cancer cells. Thus, our study expands the known roles of MDM2 in prostate cancer to include its potential involvement in the important mutual stabilization that TM4SF3 exhibits when interacting with either AR or AR-V7.

Traditional Scraping (Gua Sha) Combined with Copper-Curcumin Nanoparticle Oleogel for Accurate and Multi-Effective Therapy of Androgenic Alopecia.

Androgenetic alopecia (AGA) is a prevalent systemic disease caused by diverse factors, for which effective treatments are currently limited. Herein, the oleogel (OG) containing copper-curcumin (CuR) nanoparticles is developed, designated as CuRG, which is also combined with traditional naturopathic scraping (Gua Sha, SCR) as a multifunctional therapy for AGA. With the assistance of lipophilic OG and SCR, CuR can efficaciously penetrate the epidermal and dermal regions where most hair follicles (HFs) reside, thereby releasing curcumin (CR) and copper ions (Cu2+) subcutaneously to facilitate hair regeneration. Concomitantly, the mechanical stimulation induced by SCR promotes the formation of new blood vessels, which is conducive to reshaping the microenvironment of HFs. This study validates that the combination of CuRG and SCR is capable of systematically interfering with different pathological processes, ranging from improvement of perifollicular microenvironment (oxidative stress and insufficient vascularization), regulation of inflammatory responses to degradation of androgen receptor, thus potentiating hair growth. Compared with minoxidil, a widely used clinical drug for AGA therapy, the designed synergistic system displays augmented hair regeneration in the AGA mouse model.

Targeted Protein Degradation through Recruitment of the CUL4 Complex Adaptor Protein DDB1.

Targeted protein degradation has arisen as a powerful therapeutic modality for eliminating proteins. Thus far, most heterobifunctional proteolysis targeting chimeras (PROTACs) have utilized recruiters against substrate receptors of Cullin RING E3 ubiquitin ligases, such as cereblon and VHL. However, previous studies have surprisingly uncovered molecular glue degraders that exploit a CUL4 adaptor protein DDB1 to degrade neosubstrate proteins. Here, we sought to investigate whether DDB1 recruiters can be discovered that can be exploited for PROTAC applications. We utilized activity-based protein profiling and cysteine chemoproteomic screening to identify a covalent recruiter that targets C173 on DDB1 and exploited this recruiter to develop PROTACs against BRD4 and androgen receptor (AR). We demonstrated that the BRD4 PROTAC results in selective degradation of the short BRD4 isoform over the long isoform in a proteasome, NEDDylation, and DDB1-dependent manner. We also demonstrated degradation of AR with the AR PROTAC in prostate cancer cells. Our study demonstrated that covalent chemoproteomic approaches can be used to discover recruiters against Cullin RING adapter proteins and that these recruiters can be used for PROTAC applications to degrade neo-substrates.

A carboxy-terminal ubiquitylation site regulates androgen receptor activity

Degradation of unliganded androgen receptor (AR) in prostate cancer cells can be prevented by proteasome inhibition, but this is associated with only modest increases in polyubiquitylated AR. An inhibitor (VLX1570) of the deubiquitylases associated with the proteasome did not increase ubiquitylation of unliganded AR, indicating that AR is not targeted by these deubiquitylases. We then identified a series of AR ubiquitylation sites, including a not previously identified site at K911, as well as methylation sites and previously identified phosphorylation sites. Mutagenesis of K911 increases AR stability, chromatin binding, and transcriptional activity. We further found that K313, a previously reported ubiquitylation site, could also be methylated and acetylated. Mutagenesis of K313, in combination with K318, increases AR transcriptional activity, indicating that distinct posttranslational modifications at K313 differentially regulate AR activity. Together these studies expand the spectrum of AR posttranslational modifications, and indicate that the K911 site may regulate AR turnover on chromatin.

Abstract A052: Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer

Abstract Strategies targeting androgen receptor (AR) in the treatment of prostate cancer (PrCa) have shown clear clinical benefit. However, a variety of AR-signaling bypass mechanisms ultimately result in progression to metastatic castrate resistant prostate cancer (mCRPC), and therapies for these patients remain an urgent unmet need. The histone acetyltransferase paralogs p300 and CBP, key coactivators of AR, are currently under investigation as attractive therapeutic targets to abrogate aberrant AR signaling but face a challenging clinical toxicity profile in hematopoietic cells. We postulate that p300 serves as a key regulator of AR signaling, and by sparing CBP we should retain potency against AR-driven PrCa while providing a larger safety margin. We discovered potent heterobifunctional degraders with demonstrated selectivity for p300 over CBP. Our tool compound exhibits degradation of p300 within 2 hours (DC50 = 7.5nM, Dmax = 79%) with minimal impact on CBP at 48 h (DC50 >1uM, Dmax = 5%). The AR/ARv7 driven VCaP PrCa cell line demonstrated exceptional sensitivity to this p300 degrader in proliferation assays (gIC50 = 0.8 nM) comparable to the dual p300/CBP inhibitor, CCS-1477, or the AR degrader, ARV-110 and undergoes a cytotoxic response. Profiled against known AR target genes, our degrader was able to suppress KLK2, KLK3 and FKBP5 transcript levels akin to CCS-1477 in both LNCaP and VCaP PrCa cell lines, supporting the hypothesis that p300, not CBP, acts as the primary coactivator of AR signaling. In addition, our compound led to greater downregulation of full-length AR, ARv7 and cMyc compared to CCS-1477. Subsequent assessment in an in vivo model (VCaP CDX) demonstrated tumor growth inhibition at the highest dose tested (88%; p=2.6e-4). Lastly, we profiled our p300 degrader in human bone marrow derived hematopoietic progenitor colony-forming assays where we observed a significant reduction in toxicity (IC50 = 3.9uM) compared to either CCS-1477 (IC50 = 121nM) or a dual degrader tool compound (IC50 = 16nM), supporting the hypothesis that a p300-specific mechanism will offer an improved therapeutic index. Treatment with our p300-specific degrader resulted in a potent anti-tumor effect on PrCa cells both in vitro and in vivo, comparing favorably to both dual p300/CBP inhibitor or AR degrader strategies. Furthermore, selective degradation of p300 has the potential to minimize toxicity to hematopoietic cells commonly observed with dual targeting of CBP and p300. Taken together, these results support the role p300 may play in driving AR-mediated signaling in PrCa and demonstrate that a p300-specific degrader may serve as an effective therapeutic modality in this disease setting. Citation Format: Mike Russell, Cassandra L Lowenstein, Xuqing Zhang, Jeremy Roach, Jianing Song, Rakesh Nagilla, Peter Orth, Matt Tudor, Qiaolin Deng, Zhihua Sui, Corey Strickland, Larry J Jolivette, E Scott Priestley, Helai P Mohammad. Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A052.