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Review
. 2024 Sep 18:15:1451957.
doi: 10.3389/fphar.2024.1451957. eCollection 2024.

N-terminal domain of androgen receptor is a major therapeutic barrier and potential pharmacological target for treating castration resistant prostate cancer: a comprehensive review

Affiliations
Review

N-terminal domain of androgen receptor is a major therapeutic barrier and potential pharmacological target for treating castration resistant prostate cancer: a comprehensive review

Ye Chen et al. Front Pharmacol. .

Abstract

The incidence rate of prostate cancer (PCa) has risen by 3% per year from 2014 through 2019 in the United States. An estimated 34,700 people will die from PCa in 2023, corresponding to 95 deaths per day. Castration resistant prostate cancer (CRPC) is the leading cause of deaths among men with PCa. Androgen receptor (AR) plays a critical role in the development of CRPC. N-terminal domain (NTD) is the essential functional domain for AR transcriptional activation, in which modular activation function-1 (AF-1) is important for gene regulation and protein interactions. Over last 2 decades drug discovery against NTD has attracted interest for CRPC treatment. However, NTD is an intrinsically disordered domain without stable three-dimensional structure, which has so far hampered the development of drugs targeting this highly dynamic structure. Employing high throughput cell-based assays, small-molecule NTD inhibitors exhibit a variety of unexpected properties, ranging from specific binding to NTD, blocking AR transactivation, and suppressing oncogenic proliferation, which prompts its evaluation in clinical trials. Furthermore, molecular dynamics simulations reveal that compounds can induce the formation of collapsed helical states. Nevertheless, our knowledge of NTD structure has been limited to the primary sequence of amino acid chain and a few secondary structure motif, acting as a barrier for computational and pharmaceutical analysis to decipher dynamic conformation and drug-target interaction. In this review, we provide an overview on the sequence-structure-function relationships of NTD, including the polymorphism of mono-amino acid repeats, functional elements for transcription regulation, and modeled tertiary structure of NTD. Moreover, we summarize the activities and therapeutic potential of current NTD-targeting inhibitors and outline different experimental methods contributing to screening novel compounds. Finally, we discuss current directions for structure-based drug design and potential breakthroughs for exploring pharmacological motifs and pockets in NTD, which could contribute to the discovery of new NTD inhibitors.

Keywords: ARsplice variants; N-Terminal domain; androgen receptor; castration resistant prostate cancer; drug target.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Amino acid sequence of full length androgen receptor protein. Full-length androgen receptor (920aa) is comprised of an intrinsically disordered N-terminal domain (1-537aa), a folded DNA binding domain (538-625aa), a variable hinge region (626-669aa), and folded C-terminal ligand binding domain (670-920aa) that contains the ligand-binding pocket. The sequence of N-terminal domain lacks order-promoting amino acids, such as Ile (I, <1%), Leu (L, 8.7%), Asn (N, 1.1%), Val (V, 1.6%), Phe (F, 1.3%), Cys (C, 2.0%), Tyr (Y, 1.3%), Trp (W, <1%), most of which are hydrophobic, whereas N-terminal domain are rich in amino acids that are either polar or charged. Moreover, N-terminal domain harbors several repeat regions of glutamine (aa 58–80/86–91/195–199), proline (aa 374–381), alanine (aa 331–333/356–358/400–404), and glycine (aa 451–473), of which polyQ1 and polyG are polymorphic. (AR: androgen receptor, DBD: DNA binding domain, Ex: exon, LBD: ligand binding domain, NTD: N-terminal domain).
FIGURE 2
FIGURE 2
(A) Functional domain and motif in full length androgen receptor protein. (B) 3D structure of androgen receptor from AlphaFold Protein Structure Database. N-terminal domain harbors several repeat regions for glutamine (polyQ, aa 58–80), and proline (ployP, aa 374–381). Meanwhile, N-terminal domain contains at least three distinct regions proposed to generate amphipathic-helices, including 23FxxLF27, 181LKDIL185, and 435WxxLF439, which can interact with the hydrophobic groove in ligand binding domain. DNA binding domain has a compact, globular structure in which three substructures can be distinguished: two zinc clusters and a more loosely structured carboxy terminal extension. Hinge region can be defined as the fragment between the last α-helix of the DNA-binding domain and the first α-helix of the ligand binding domain. The 630RKLKKL635 motif, plays a central role in controlling AR activity, not only because it acts as the main part of the nuclear translocation signal, but also because it regulates the transactivation potential and intranuclear mobility of the receptor. ligand binding domain is comprised of 11 α-helices which encompass a ligand-binding pocket. When androgen binds, there is a shift in conformation to reposition helix 12 over the ligand-binding pocket to create the activation function-2 surface for interaction with coactivators. Alpha Fold produces a per-residue model confidence score (pLDDT) between 0 and 100 (Dark Blue >90, Blue >70, Yellow >50, Orange <50). Some regions below 50 pLDDT may be unstructured in isolation (https://alphafold.ebi.ac.uk/entry/D3YPP9) (Varadi et al., 2024) (AF-1: the activation function-1, AF-2: activation function-2, DBD: DNA binding domain, H: Hinge region, LBD: ligand binding domain, NDS: nuclear degration sequence, NLS: nuclear localization sequence, NTD: N-terminal domain, Tau-1: transcriptional activation unit-1, Tau-5: transcriptional activation unit-5).
FIGURE 3
FIGURE 3
Summary of current and experimental inhibitors that target the androgen receptor signalling axis via different mechanisms. Abiraterone acetate inhibit the production of DHT. First-generation (Bicalutamide, Flutamide) and second-generation (enzalutamide, apalutamide, and darolutamide) LBD-targeting ARIs competitively inhibit the DHT binding to ligand binding domain. VPC-17005 Binds L594-S613 of AR-DNA binding domain D-box to inhibit dimerization of androgen receptor. Emerging small molecules (EPIs, Niphatenone, Sintokamide, IMTPPE, QW07, ASR-600, VPC-220010, UT-143, SC428) have been able to bind the N-terminal domain of the androgen receptor and thus suppress transactivation of androgen receptor target genes. VPC com-pounds, Pyrivinium, Hairprin polyamides bind the DNA binding domain thus preventing interaction with DNA, inhibit androgen receptor dimerization so that it cannot interact with DNA. Niclosamide, ASC-J9, UT-34, PROTACs, Dimethylcurcumin upregulate AR protein degradation to reduce the abundance of the androgen receptor protein. (AR: androgen receptor, ARI: androgen receptor inhibitor, CHKA: choline kinase alpha, DBD: DNA binding domain, DHT: dihydrotestosterone, Hsp: heat shock protein, LBD: ligand binding domain, NTD: N-terminal domain, PROTAC: proteolysis-targeting chimera, SRCs: steroid receptor co-activator proteins).
FIGURE 4
FIGURE 4
Schematic of mRNA of wild type androgen receptor/androgen receptor variants. Over 20 androgen receptor variants have been identified. Truncated androgen receptor variants form due to alternative splicing and/or structural gene rearrangements of the androgen receptor gene. (AR-V: androgen receptor variant, Ex: exon).
FIGURE 5
FIGURE 5
Chemical structures of small molecules directly targeting N-terminal domain of androgen receptor.

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Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. Qinchuangyuan Foundation Project of Shaanxi province (QCYRCXM-2022-83), China.

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