The interconnection between androgen receptor and DNA damage response pathways in prostate cancer

Abstract

The androgen receptor (AR) plays a critical role in the development and progression of prostate cancer by regulating key cellular processes such as cell proliferation and apoptosis. Although traditional AR-targeted therapies have shown initial success, acquired resistance remains a significant clinical challenge, often driven by AR alterations and somatic gene mutations associated with homologous recombination deficiency (HRD). Approximately 20% of advanced prostate cancer cases exhibit HRD, resulting in substantial genomic instability and complicating treatment. Fortunately, Food and Drug Administration–approved poly(ADP-ribose) polymerase inhibitors, including olaparib and rucaparib, exploit synthetic lethality to target prostate cancer with HRD, and additional drugs targeting DNA damage response (DDR) proteins are under development. Emerging evidence suggests that AR activity enhances DDR gene expression, with multiple DDR proteins localized near androgen-regulated regions, highlighting a close interaction between AR and DDR pathways. Consequently, recent preclinical and clinical studies have investigated combining AR-targeted therapies with treatments that induce DNA damage, such as radiation therapy, or inhibit DNA repair mechanisms. This review discusses AR's role in cellular processes, the interplay between AR and DDR, and recent advances in prostate cancer treatment strategies.

1. Introduction

Prostate cancer is the most common malignancy and the second leading cause of cancer-related deaths in men in the United States.^[1] Because of the critical role of the androgen receptor (AR) in prostate cancer growth and progression, patients are treated with androgen deprivation therapy (ADT) through either surgical or medical interventions to suppress serum testosterone levels, the main fuel for AR activation.^[2] Despite its initial effectiveness, the disease in most patients will progress to a much more lethal stage termed metastatic castration-resistant prostate cancer (mCRPC). Resistance to ADT is mainly due to the residual androgens that remain after castration and the amplification of AR.^[3] This has led to the advent of second-generation antiandrogens, such as abiraterone and enzalutamide, which can further prevent AR activation. Unfortunately, although patients initially respond to these treatments, almost all will develop treatment-resistant disease through various mechanisms, such as AR overexpression, point mutations, intrinsically activated variants, AR bypass, and the emergence of somatic mutations in critical genes.^[4–10]

DNA is a stable molecule, but it is susceptible to damage by various endogenous and exogenous agents, such as reactive oxygen species (ROS), ionizing radiation, ultraviolet radiation, and mutagenic chemicals.^[11] To maintain DNA integrity, cells have evolved a complex DNA damage response (DDR) network composed of multiple repair pathways, such as base excision repair (BER), mismatch repair (MMR), non-homologous end joining (NHEJ), and homologous recombination (HR). Dysregulation or mutations in key DDR genes can impair these pathways, leading to incomplete or inaccurate repair and allowing cells with DNA damage to evade apoptosis.^[12] This results in genomic instability, a defining hallmark of cancer. In prostate cancer, DDR deficiencies become increasingly common as the disease progresses, particularly during the transition to mCRPC, where they contribute to therapeutic resistance and poor clinical outcomes.^[13–15]

In this review, we summarize the role of AR in various cellular processes and how it contributes to prostate cancer development and progression, discuss the relationship between the AR signaling pathway and the DDR pathway, and finally highlight recent advances in prostate cancer therapeutics and how they are being explored to further improve patient outcomes.

2. Androgen receptor signaling in prostate cancer

The AR is a ligand-dependent nuclear transcription factor and a member of the steroid hormone receptor superfamily, which includes the estrogen receptor, progesterone receptor, glucocorticoid receptor, and mineralocorticoid receptor.^[16] These receptors share structural homology but are functionally distinct based on their preferred ligands and downstream transcriptional programs.^[17] The structure of nuclear hormone receptors includes a highly variable and intrinsically disordered N-terminal domain responsible for transcriptional regulation, a centrally located DNA-binding domain, a flexible hinge region containing a nuclear localization signal, and a highly conserved C-terminal ligand-binding domain (LBD).^[18]

Androgen receptor is activated by binding to its ligands, testosterone, or the more potent androgen, 5α-dihydrotestosterone.^[19] In the absence of androgens, AR typically resides in the cytoplasm, bound by chaperone heat shock proteins (such as HSP90). Androgen binding triggers a cascade of events, first inducing conformational changes that promote homodimerization. The homodimer then translocates to the nucleus and acts as a transcription factor by binding to androgen response elements (AREs) located in the enhancer and/or promoter regions of specific target genes, such as those involved in regulating the cell cycle, apoptosis, DDR, and others^[20] (Fig. 1).

Figure 1.

AR activation and function. Inactive AR resides in the cytoplasm bound to HSP90, but in the presence of androgens, the proteins dissociate. DHT binding to AR enables phosphorylation, homodimerization, and nuclear translocation. AR then functions as a transcription factor by binding to AREs located in the enhancer and/or promoter regions of target genes. ARVs are truncated versions of AR; however, they retain the transcription factor function of full-length AR, as the variants are still able to dimerize, translocate, and bind AREs. Specific genes upregulated by AR are implicated in cell proliferation, cell survival (eg., cFLIP), and DNA damage response pathways such as HR and NHEJ. Activated AR also contributes to cell proliferation by modulating mTOR-dependent translation of cyclin D. AR = androgen receptor; AREs = androgen response elements; ARV = androgen receptor variant; DHT = dihydrotestosterone; HR = homologous recombination; NHEJ = non-homologous end joining; mTOR = mammalian target of rapamycin. (Created in BioRender. Sands, M. (2025) https://BioRender.com/s7nglas)

The primary function of androgens and AR is to support the development and maintenance of prostate tissues.^[21] However, AR is also implicated in bone and cardiac growth,^[22,23] increasing skeletal and perineal muscle mass,^[24,25] and attenuating the inflammatory process.^[26] In prostate cancer, the AR pathway becomes overactive and drives tumor growth and disease progression.

2.1. Androgen receptor promotes cell cycle progression and cell survival

It is well established that AR contributes to cell proliferation by regulating cell cycle progression. A major contributing factor to cell cycle transitions is the activation of cyclins and cyclin-dependent kinase (CDK) complexes. Although CDK expression remains relatively consistent throughout the cell cycle, the expression of various cyclins fluctuates during different phases. Initiation of the G1 phase is controlled by activation of CDK4/6 and cyclin D complexes. Androgen-dependent prostate cancer cell lines under androgen deprivation conditions exit the cell cycle to G0 and exhibit decreased expression of D-type cyclins (cyclins D1 and D3).^[27] Upon androgen stimulation, mammalian target of rapamycin-dependent translation of D-cyclins occurs, increasing protein accumulation and leading to the activation of CDK4/6 complexes^[28] (Fig. 1).

Another important cell cycle regulator is the retinoblastoma tumor suppressor (RB1), which plays a role in the G1 to S transition and DNA synthesis. In its dephosphorylated state, RB1 inhibits the cell cycle by binding to E2F transcription factors. Phosphorylation by CDK4/6–cyclin D complexes activates RB1, causing it to dissociate from E2F, which then activates downstream gene targets responsible for cellular proliferation and DNA replication.^[29] Androgen ablation has been linked to RB1 activation, whereas androgen stimulation results in RB1 deactivation and G1 progression, further demonstrating additional mechanisms of AR and cell cycle control.^[30] Retinoblastoma tumor suppressor (RB1) is frequently lost or inactivated in patients with mCRPC; in contrast, this is rarely observed in localized prostate cancer, supporting its role in disease progression.^{[13,14,28,30,31]}

Cyclindependent kinase 2 regulates completion of the G1 phase and entry into the S phase, first by forming a complex with cyclin E1 and later with cyclin A2. Under androgen deprivation, CDK2 and cyclin E activity is reduced despite stable expression levels.^[30] This effect is likely due to androgens' regulation of the CDK2 inhibitor p27^Kip1. Increased p27^Kip1 expression is observed during androgen ablation, whereas androgen stimulation promotes its degradation.^[30] Androgen depletion has also been shown to decrease the levels of cyclin A,^[30] which may result from RB1-mediated suppression of cyclin A1 transcription. In conclusion, AR influences the G1 to S transition by modulating CDK activity, inducing phosphorylation and inactivation of RB1, and promoting p27^Kip1 degradation.

Another key component of cell cycle regulation is DNA licensing, which ensures that DNA is replicated only once during each cell cycle. Androgen receptor has been identified as a licensing factor for this process, as it is observed in complexes with other known licensing proteins at DNA replication origins.^[32] Supporting this observation, AR protein levels mirror the expression patterns of licensing factors—being detectable in G1, S, and G2 phases, and degraded during mitosis to restart the cycle.^[32] Another study found that AR-mediated transcription is highest during the G1 phase, decreases in S phase, and is nearly abolished during G2 and M phases.^[33] Together, these findings suggest that AR activity fluctuates throughout the cell cycle to support phase-specific cellular functions.

In addition to cell cycle involvement, AR plays a crucial role in regulating apoptosis. Understanding how AR influences apoptotic pathways is essential for understanding the complexities of prostate cancer progression and treatment resistance. Androgen receptor regulates apoptosis through the modulation of anti-apoptotic proteins. Androgen activation leads to activation of the MAPK signaling pathway, increasing phosphorylation of ERK-1 and ERK-2 and inhibiting Bad, the Bcl-2–associated death protein.^[34] Bad inactivation prevents the release of cytochrome c from mitochondria, thereby suppressing apoptosis. Androgen receptor activation also modulates the anti-apoptotic protein survivin, which blocks caspase activation.^[35]

Another mechanism by which AR influences apoptosis is through regulation of the anti-apoptotic protein c-FLIP,^[36] a potent inhibitor of Fas/FasL-mediated apoptosis.^[37] After androgen stimulation, c-FLIP is upregulated due to AR binding to its promoter, which contains AREs (Fig. 1). c-FLIP protects against cell death by forming an apoptotic inhibitory complex with caspase-8 and other proteins.^[38] c-FLIP expression is increased in castration-resistant prostate cancer (CRPC) compared with normal tissue, further implicating it in prostate cancer progression.^[39] Furthermore, in prostate cancer xenograft models, c-FLIP overexpression has been found to accelerate tumor progression to androgen independence by inhibiting apoptotic pathways.^[40]

2.2. AR activation contributes to CRPC development and progression

Because AR contributes to prostate cancer cell proliferation, therapies have been developed to target AR signaling directly. Although ADT and anti-androgen treatments benefit many patients, resistance to these therapies is largely AR-dependent and remains a major clinical challenge. Even though ADT achieves castrate levels of circulating androgens, residual androgens persist in the tumor microenvironment (TME). As a result, a subset of cells can develop sensitivity to these low androgen levels, through either AR gene amplification or mutation.^[3] In mCRPC, AR gene amplifications are observed in 20%–60% of patients.^[41] Amplification results in AR overexpression, allowing cells to remain responsive to residual androgens after castration.^[4]

Androgen receptor gene alterations typically arise only after resistance to AR-targeting therapies develops and are not observed in treatment-naive prostate cancer.^[13–15,31] Gain-of-function mutations generally occur in the AR LBD, broadening ligand specificity. Certain AR mutations (eg, T878A, H875Y, L702H) allow activation by other steroid hormones, such as progesterone and glucocorticoids, as well as mutated AR that utilizes anti-androgens as activators, overriding the intended inhibitory function (eg., T878A, W742C, H875Y, F877L).^[10]

In mCRPC, alternative AR splicing variants also emerge, posing additional clinical challenges. These AR variants (AR-Vs) typically lack an LBD, rendering them androgen-independent and constitutively active. As a result, they undermine the effectiveness of traditional therapies targeting the LBD. Among these variants, AR-V7 is the most frequently observed clinically, detected in 20%–40% of circulating tumor cells from patients with mCRPC.^[42] Although AR-Vs are truncated, they retain the ability to dimerize—as either homodimers or heterodimers with full-length AR—and continue to function as transcription factors. They upregulate canonical AR target genes and also control AR-V-specific target genes involved in epithelial-to-mesenchymal transition, cell cycle regulation, and DNA damage repair, contributing to a more aggressive form of the disease^[43–47] (Fig. 1).

As mCRPC progresses under the selective pressure of ADT and anti-androgen treatments, approximately 25%–30% of advanced cases undergo transdifferentiation into neuroendocrine prostate cancer (NEPC), a highly aggressive and lethal subtype.^[48] This phenotypic shift is typically characterized by a loss of dependence on AR signaling and is often accompanied by distinct morphological changes.^[49] Evidence suggests that NEPC arises from prostate adenocarcinoma precursor cells, as shown in a study of metastatic biopsies that revealed shared molecular signatures and gene copy number profiles between the 2 subtypes.^[50] Despite these insights, therapeutic options remain limited, largely due to an incomplete understanding of the molecular mechanisms driving lineage plasticity in prostate cancer.

3. DNA damage repair pathways in prostate cancer

Cells have evolved a highly regulated DDR network consisting of multiple pathways that function to protect the genome from DNA damage. Single-stranded breaks (SSBs) are the more common type of DNA lesion and are primarily caused by oxidative attacks from ROS.^[51] The pathways responsible for correcting SSBs include BER and MMR. Double-stranded breaks (DSBs), on the other hand, are much more detrimental to cellular function. Although DSBs can also be caused by ROS, they are more commonly associated with exposure to ultraviolet radiation, ionizing radiation, and chemical agents.^[52] Cells use NHEJ or HR to repair this type of damage.

Regardless of the specific repair pathway, the presence of DNA damage must first be detected to initiate downstream events such as activation of checkpoint machinery to halt the cell cycle and allow for repair, and the recruitment of proteins necessary to complete the repair process.^[52] Effective DNA repair allows cells to reenter the cell cycle, whereas improper repair should result in cell death. However, dysregulation of repair pathways or failure to induce apoptosis enables cells with damaged DNA to persist, leading to genomic instability and contributing to carcinogenesis.^[12] The following are 4 different pathways that cells use to repair damaged DNA (Fig. 2).

Figure 2.

DNA damage repair pathways. NHEJ and HR are 2 key pathways for repairing double-stranded DNA breaks. NHEJ directly ligates broken DNA ends without a homologous template, making it more prone to errors that result in mutations. In contrast, HR utilizes a sister chromatid as a template, ensuring high fidelity and preservation of the genome. BER repairs small base lesions by excising the damaged base and filling in the gap with new nucleotides. MMR corrects replication errors by recognizing and replacing mispaired bases. BER = base excision repair; HR = homologous recombination; MMR = mismatch repair; NHEJ = non-homologous end joining. (Created in BioRender. Sands, M. (2025) https://BioRender.com/1q7neaz)

3.1. Non-homologous end joining

Non-homologous end joining is one mechanism by which DSBs are repaired. Because NHEJ does not require a chromosome template to facilitate repair, it is not restricted to any specific phase of the cell cycle. However, because no template is used, NHEJ is error-prone and can lead to mutations and genomic instability.^[53] When DSBs form, the DNA ends are bound by the Ku70/80 heterodimer (Ku), which protects the DNA from nonspecific cleavage.^[54] Ku recruits the NHEJ machinery: first, DNA-PKcs binds to Ku and acts as a scaffold for other repair proteins. Next, XRCC4 and LIG4 bind to the complex, with XRCC4 directly interacting with the Ku70 subunit.^[54] LIG4 completes ligation, as it can ligate incompatible DNA ends and across gaps.^[55]

3.2. Homologous recombination repair

Homologous recombination is carried out with high fidelity because a sister chromatid is used as a template. Consequently, HR is restricted to the S and G2 phases of the cell cycle. The initial step in HR involves the recruitment of the MRN complex, composed of MRE11, RAD50, and NBS1, to the site of DSBs.^[56] This complex recruits and activates the ATM kinase, which phosphorylates the MRN complex, promoting further recruitment of MRN components (and thus assembling more MRN complexes) and activating ATM-dependent downstream targets such as CHK1, CHK2, and p53.

The activated MRN complex, in conjunction with CtIP, generates a resection nick. The Exo1 nuclease then carries out long-range resection of the 5′ ends of the DSB, producing single-stranded DNA with a 3′ overhanging tail.^[57] This resection is tightly regulated by proteins like BRCA1, which promotes resection by antagonizing 53BP1, a protein that inhibits resection and favors NHEJ. This regulation is critical for determining pathway choice between HR and NHEJ.

After resection, the single-stranded DNA-binding protein replication protein A rapidly binds to the overhang to prevent nonspecific nuclease cleavage and secondary structure formation. RAD51 is then directed to the break site and displaces replication protein A.^[57] This displacement and RAD51 loading are facilitated by the mediator protein BRCA2. RAD51 binds to the BRCT domain of BRCA2, which acts as a scaffold at the DNA. Several RAD51 monomers assemble into a nucleoprotein filament that searches for and invades a homologous DNA sequence.^[56] DNA polymerase then resynthesizes the DNA using the homologous template.

3.3. Base excision repair

Base excision repair corrects base lesions. DNA glycosylases excise the damaged base, creating a noncoding abasic site, which is processed by the endonuclease APE1.^[58] This results in a 5′-deoxyribose phosphate intermediate that is recognized and bound by poly (ADP-ribose) polymerase 1 (PARP1), which facilitates the recruitment of additional DNA repair proteins.^[59] The first protein recruited is XRCC1, which acts as a scaffold for PNKP, aprataxin, DNA polymerase beta, and LIG1 in most mammalian cells, or LIG3 in mitochondrial DNA repair. PNKP and aprataxin process the DNA ends, polymerase beta resynthesizes the DNA, and LIG1 completes the ligation.^[58]

3.4. Mismatch repair

Mismatch repair corrects spontaneous mismatches in base pairing that occur during DNA replication. Cells have protective mechanisms to check DNA polymerase fidelity after replication. The protein complex MSH2–MSH6 scans newly synthesized DNA strands and, upon detecting a mismatch, initiates repair.^[60] The MSH2–MSH6 heterodimer activates and recruits the MLH1–PMS2 complex, which has endonuclease activity that introduces a nick in the newly synthesized strand containing the mismatch. EXO1 is then recruited to excise the DNA from the mismatch site to the nick, leading to removal of the erroneous sequence. DNA polymerase delta (Pol δ) resynthesizes the strand, and LIG1 completes the ligation.^[61]

3.5. Mutations in DNA repair genes in prostate cancer

Prostate cancer becomes more lethal as it progresses and develops resistance to therapies, due in part to alterations in critical genes. In addition to AR mutations, the most prevalent alterations are found in DDR genes. Approximately 25%–40% of patients with mCRPC carry DDR gene mutations, compared with only 10%–12% of patients with primary prostate cancer. Many of these alterations affect the HR pathway, resulting in homologous recombination deficiency (HRD). Homologous recombination deficiency arises from mutation or dysfunction in key genes such as BRCA1, BRCA2, and RAD51, which are responsible for high-fidelity DNA repair using a homologous template.

In prostate cancer, BRCA2 accounts for the largest proportion of HRD-related mutations (11%–13%), followed by ATM (4%–6%), CHEK2 (1.4%–2%), CHEK1 (0.9%–2%), and BRCA1 (0.7%–1%).^[62] Alterations in other DDR pathways, such as MMR, have also been observed. About 3%–5% of CRPC patients have mutations in genes such as MLH1, MSH2, MSH6, and PMS2.^[62]

3.6. Alterations in DNA repair genes in NEPC

A defining feature of NEPC is lineage reprogramming, marked by AR loss and driven by amplification or overexpression of the proto-oncogene MYCN and its stabilizing cofactor AURKA.^[48] MYCN amplifications have been identified in 40% of NEPC tumor samples and in 20% of mCRPC samples without NEPC morphology.^[48] N-MYC, the protein encoded by MYCN, is a transcription factor that regulates multiple biological pathways associated with cancer hallmarks, including genomic instability. N-MYC activation promotes DNA replication and can override or transcriptionally suppress cell cycle checkpoints, enabling unchecked cell proliferation.^[63]

Moreover, chromatin immunoprecipitation, followed by PCR (ChIP-PCR) analysis of N-MYC–expressing CRPC and NEPC cell lines, has shown that N-MYC directly binds to the promoters of DDR genes, including PARP1, PARP2, BRCA1, RMI2, and TOPBP1.^[64] These findings support a model in which N-MYC simultaneously upregulates DDR gene expression and downregulates cell cycle checkpoints, thereby enabling abnormal cell cycle progression and promoting genomic instability.

4. The interconnection between AR and DNA damage repair pathways

4.1. AR regulates DNA damage repair pathways

Androgen receptor activation and inhibition have been shown to modulate DDR genes, but findings have been conflicting. Upon androgen stimulation in LNCaP cells, 74 DDR genes were upregulated, and among these, 32 genes also contained AR binding sites in their enhancers or promoters.^[65] Some of these genes include ATR, MRE11A, RAD51C, RAD21, and RAD54B, which are required for HR, as well as genes involved in NHEJ, such as LIG3 and XRCC5 (which encodes the Ku80 subunit; Fig. 1). Another study used a qPCR array to identify XRCC2, XRCC3, and PRKDC as genes induced after AR activation.^[66] Additional evidence supports that AR is required for downstream ATM signaling in response to DNA damage.^[67] Inhibition of AR has also been shown to downregulate DDR pathways and genes such as MRE11, RAD21, RAD50, RAD51, and RAD54.^[65,67,68] However, another group demonstrated that AR does not directly regulate the transcription of DDR genes. They identified 16 genes that were both repressed by the AR antagonist enzalutamide and activated by radiation, but gene enrichment revealed that all were canonical AR targets and not DDR genes.^[69]

The influence of AR signaling on DDR gene regulation remains a subject of ongoing debate, largely due to conflicting experimental findings. Although several studies have identified upregulation of key DDR genes after AR activation,^[65,66] others have not observed direct transcriptional regulation by AR.^[67] A key factor contributing to these discrepancies is variability in experimental conditions, particularly the duration of androgen or antagonist treatment before gene expression analysis. Short- versus long-term exposure may capture different phases of gene regulation, potentially distinguishing between primary and secondary transcriptional effects. In addition, differences in cell lines, AR ligands, and analytical platforms may further complicate comparisons across studies. These inconsistencies highlight the need for standardized methodologies to resolve the current ambiguities and advance our understanding of the interplay between AR signaling and DDR mechanisms.

4.2. DNA damage repair proteins regulate AR activity

Transcriptionally active regions, promoters, and enhancers are susceptible to DNA damage.^[70] Androgen receptor and other nuclear receptors have been associated with the generation of DNA breaks to relieve torsional strain and facilitate gene expression.^[71,72] Specifically, DNA topoisomerase I (TOP1) and TOP II β (TOP2β) have been implicated in AR transcriptional activation (Fig. 3).^[73] Evidence supports the recruitment of TOP1 with AR to the enhancer regions of target genes, where TOP1 is thought to generate single-stranded nicks that contribute to AR transcriptional activity.^[74] After androgen stimulation, AR and TOP1 are recruited concurrently after ~15 minutes. Subsequently, various DDR proteins associated with BER are also recruited.^[74] Other studies have observed that after androgen stimulation, AR, TOP1, RNA polymerase, DNA-PKcs, Ku, and PARP1 are detected in a complex associated with AR regulatory regions, suggesting a collective role in supporting AR activity.^[72]

Figure 3.

DDR proteins facilitate AR transcriptional activity. Upon androgen binding, activated AR recruits multiple coregulators (eg., CBP, ARA55, ARA70) as well as DDR proteins (eg., BRCA1, KU, DNA-PKcs, PARP1, PARP2). These proteins enhance AR-mediated transcription and are found in proximity to AREs. Notably, these regions of high transcriptional activity are also prone to DNA damage, which helps relieve torsional strain on the DNA helix during transcription. Based on published studies, 2 models have been proposed to explain the requirement of DNA damage for AR transcription: (Left) TOP1 is recruited alongside AR to induce single-strand nicks, and (Right) TOP2β is recruited alongside AR to generate DSBs. Collectively, these mechanisms highlight how DDR proteins may regulate AR signaling. AR = androgen receptor; AREs = androgen response elements; DDR = DNA damage response; DSB = double-stranded break. (Created in BioRender. Sands, M. (2025) https://BioRender.com/uq7v423)

DNA topoisomerase2β has also been implicated in the induction of DSBs at AR target gene promoters, which are required for AR activity.^[71] After androgen activation, recruitment of AR, TOP2β, RNA polymerase, DNA-PKcs, Ku, and PARP1 has been observed at these promoter regions.^[71] Although normal prostate cells do not express TOP2β, AR and TOP2β colocalize in prostatic neoplastic lesions.^[75] These findings implicate TOP2β in oncogenic AR activity and potential genomic instability.

As mentioned previously, AR regulates the expression and activity of DNA-PKcs, Ku70, and Ku80, thereby promoting both NHEJ and AR-directed transcription. Non-homologous end joining proteins have also been detected in complexes with AR at regulatory regions, suggesting that they may regulate AR activity directly (Fig. 3).^[71,75,76] Moreover, NU7441, a selective DNA-PKcs inhibitor, suppresses androgen-induced target gene expression, suggesting that DNA-PKcs is required for AR activity.^[66] Similar to AR, DNA-PKcs can also interact with AR-Vs, helping to maintain their transcriptional activity and modulate downstream targets that promote metastatic phenotypes—indicating a role for DNA-PKcs in mCRPC.^[77]

Interestingly, the role of DSBs in AR-directed transcription has also been implicated in the development of the TMPRSS2:ERG fusion gene, frequently observed in prostate cancer.^[75,78] This rearrangement involves the fusion of TMPRSS2, which contains an androgen-responsive promoter, with ERG, an oncogenic ETS transcription factor that promotes proliferation. Androgen receptor binds to multiple intergenic regions near DNA break sites of neighboring genes, such as TMPRSS2 and ERG, juxtaposing the breaks for subsequent recombination.^[75] Data suggest that the NHEJ repair pathway is the primary mechanism facilitating this fusion event, as knockdown of NHEJ genes attenuated fusion, whereas knockdown of HR genes enhanced it. TMPRSS2:ERG fusion events are present in approximately 50% of mCRPC patients,^{[13,15,31,79]} and they also occur at high frequency in localized prostate cancer, implicating a role in proliferation.^[13]

Other DNA damage-sensing proteins, PARP1 and PARP2, have also been identified as facilitators of AR-mediated gene expression due to their proximity to AREs (Fig. 3).^[80,81] Both proteins have been shown to enhance AR-V transcriptional activity. Moreover, PARP inhibitors reduce AR target gene expression, further underscoring the importance of these proteins in AR regulation.^[80,81] Recently, a study that investigated the AR chromatin-bound proteome after androgen treatment identified PARP1 as one of AR's interacting partners,^[76] supporting earlier findings.

Another essential HR protein, BRCA1, has also been identified as a coregulator of androgen-dependent AR activity by enhancing transactivation (Fig. 3). It directly interacts with AR via the DNA-binding domain and cooperates with other AR coregulators such as CBP, ARA55, and ARA70 to facilitate gene expression.^[82] Collectively, these findings suggest that DNA repair proteins act in concert to support AR-driven transcription.

5. Therapeutic implications of AR and DNA damage repair pathway interplay

5.1. Current treatments and emerging therapies for prostate cancer

The standard of care for localized prostate cancer includes surgery, radiation, and active surveillance. Because of the established role of androgens and AR in prostate cancer, metastatic disease is treated with ADT to achieve castration levels of circulating androgens.^[83] Although ADT is initially effective, almost all patients eventually develop mCRPC and succumb to the disease. To overcome this resistance, next-generation anti-androgens—abiraterone, enzalutamide, apalutamide, and darolutamide—were developed to directly target the AR signaling pathway. Abiraterone inhibits a critical cytochrome P450 enzyme, CYP17A1, in the androgen biosynthesis pathway, whereas enzalutamide, apalutamide, and darolutamide compete with androgens for binding to AR, thereby preventing its activation and downstream transcription.^[84]

The development of drug resistance remains a major clinical challenge. Resistance often occurs through AR amplification, mutations, and variants, as well as AR bypass mechanisms. Clinical evidence also indicates that other mutations and genomic alterations in critical DDR pathway genes contribute significantly, such as BRCA2 mutations.^[4–10] At this stage of disease progression, PARP inhibitors (olaparib, rucaparib, talazoparib) are used because of the principle of synthetic lethality, particularly in tumors with HR deficiencies.

Poly(ADP-ribose) polymerase 1 and PARP2 are involved in the repair of SSBs in DNA by sensing damage and recruiting repair proteins to the site. These proteins catalyze the addition of poly(ADP-ribose) chains to themselves and other proteins in a process known as PARylation.^[59] Poly(ADP-ribose) polymerase inhibitors (PARPi) target this process by binding to the active sites of PARP1 or PARP2. These drugs are effective in mCRPC tumors with HRD due to mutations in BRCA2, BRCA1, or ATM.^[13–15,31] Poly(ADP-ribose) polymerase inhibitors function by preventing PARP self-PARylation, thereby trapping PARP proteins at SSB sites, leading to replication fork collapse, the formation of DSBs, and ultimately cell death.^[85]

Other therapies targeting DDR genes are in development for various cancers and may benefit prostate cancer as well. Targets of these emerging inhibitors include POLQ, DNA-PKcs, ATM, ATR, CHK1, and RAD51, among others.^[86] These proteins have been selected based on clinical observations that their expression is increased in drug-resistant cancers. Inhibition of these proteins may result in synthetic lethality in patients with BRCA1/2 or other DDR gene deficiencies.

5.2. Clinical trials of PARPi and responsive biomarkers

Clinical trials of PARPi have demonstrated success in treating prostate, breast, ovarian, and pancreatic cancers. Below is a summary of recent clinical trials evaluating PARPi in prostate cancer (Table 1). The PROfound trial evaluated olaparib in mCRPC patients with DDR gene alterations who had progressed after treatment with abiraterone or enzalutamide. Patients receiving olaparib had greater median progression-free and overall survival compared with those receiving enzalutamide or abiraterone at the physician's discretion.^[87] The TRITON2 trial examined rucaparib in mCRPC patients who had progressed after second-generation anti-androgen therapy and carried BRCA1, BRCA2, or ATM alterations. Rucaparib improved both median progression-free and overall survival compared with the control group.^[88] The TALAPRO-1 trial assessed talazoparib in mCRPC patients with DDR gene alterations who had progressed on enzalutamide and/or abiraterone and previously received taxane-based chemotherapy. Talazoparib improved median overall survival relative to the control group.^[89] The GALAHAD phase 2 trial investigated niraparib in mCRPC patients who had progressed on prior treatments and harbored DDR gene alterations. All patients received niraparib and were divided into 2 cohorts: those with BRCA alterations and those with non-BRCA alterations. The BRCA cohort showed longer median progression-free and overall survival compared with the non-BRCA cohort.^[90] These results suggest that PARPi are effective treatment options for mCRPC patients with DDR deficiencies whose disease is resistant to standard AR-targeted therapies.

Table 1.

Summary of PARP inhibitor monotherapy clinical trials in prostate cancer.

Trial	Phase	Experimental arm	Control arm	Patient selection	Key endpoints
PROfound[87] NCT02987543	3	Olaparib	ENZA or ABI + PRED	mCRCP  1. Progressed on ARSI  2. With HRR gene alterations.     Cohort A: BRCA1, BRCA2, ATM   Cohort B: Other HRR gene alterations   (BRIP1, BARD1, CDK12, CHEK2, CHEK2,   FANCL, PALB2, PPP2R2A, RAD51B, RAD51C,   RAD51D, RAD54L)	Cohort A:  rPFS 7.4 mo vs. 3.6 mo (HR, 0.34; 95% CI,  0.25–0.47; p < 0.001)  ORR 33% vs. 2% (odds ratio, 20.86; 95% CI,  4.18–379.18; p < 0.001)  mOS 19.1 mo vs. 14.7 mo (HR, 0.69; 95% CI,  0.50–0.97; p = 0.02) Cohort B:  mOS 14.1 mo vs 11.5 mo (HR, 0.96; 95% CI,  0.63–1.49)
TRITON3[88] NCT02975934	3	Rucaparib	Physician's choice (docetaxel or NHT)	mCRPC  1. Progressed on ARSI  2. With BRCA1, BRCA2 or ATM gene   alterations	BRCA1/2 subgroup:  rPFS 11.2 mo vs. 6.4 mo (HR, 0.50; 95% CI,  0.36–0.69; p < 0.001) ATM subgroup:  rPFS 8.1 mo vs. 6.9 mo (HR, 0.95; 95% CI,  0.59–1.52)
TALAPRO-1[89] NCT03148795	2	Talazoparib	No control arm	mCRPC  1. Received taxane-based chemotherapy   and progressed on ARSI  2. With HRR gene alterations. (BRCA1,   BRCA2 or other ATM, ATR, CHEK2,   FANCA, MLH1, MRE11A, NBN, PALB2,   RAD51C)	Overall:  rPFS 5.6 mo (95% CI, 3.7–8.8)  ORR 29.8% (95% CI, 21.2–39.6) BRCA1/2 subgroup:  rPFS 11.2 mo (95% CI, 7.5–19.2)  ORR 46% ATM subgroup:  rPFS 3.5 mo (95% CI, 1.7–8.3)  ORR 12%
GALAHAD[90] NCT02854436	2	Niraparib	No control arm	mCRPC  1. Received taxane-based chemotherapy   and progressed on ARSI  2. With HRR gene alterations   BRCA subgroup: BRCA1 or BRCA2   germline or somatic alterations   Non-BRCA subgroup: alterations in   other prespecified HRR genes	BRCA subgroup:  rPFS 3.71 mo (95% CI, 1.97–5.49)  ORR 34.2% (95% CI, 23.7–46.0) Non-BRCA subgroup:  rPFS 3.71 mo (95% CI, 1.97–5.49)  ORR 10.6% (95% CI, 1.97–5.49)

ABI = abiraterone acetate; ARSI = androgen receptor signaling inhibitors; CI = confidence interval; ENZA = enzalutamide; HR = hazard ratio; HRR = homologous recombination repair; mCRPC = metastatic castration-resistant prostate cancer; mOS = median overall survival; NHT = neoadjuvant hormonal therapy; ORR = objective response rate; PARP = poly(ADP-ribose) polymerase; PRED = prednisone; rPFS = radiographic progression-free survival.

The PARPi discussed—olaparib, rucaparib, talazoparib, and niraparib—are classified as pan-PARP inhibitors because they lack selectivity across the 17-member PARP protein family.^[91] This broad activity contributes to adverse effects, particularly hematologic toxicities. Poly(ADP-ribose) polymerase 2 inhibition, for example, is associated with anemia due to its role in red blood cell development and maintenance.^[92] Anemia is a major clinical concern in cancer patients as it contributes to fatigue, reduced treatment tolerance, lower quality of life, and poorer clinical outcomes.^[93]

To address these issues, investigators developed saruparib, a next-generation PARPi with selective trapping activity for PARP1.^[94] By minimizing off-target inhibition of PARP2, saruparib aims to reduce clinical side effects while preserving antitumor activity. Saruparib is currently being evaluated in the PETRA phase 1/2 clinical trial for patients with advanced breast, ovarian, prostate, or pancreatic cancers who harbor BRCA1/2, PALB2, or RAD51C/D mutations. The trial has thus far shown promising clinical activity and tolerability.^[95]

Based on the rationale for the synthetic lethality of PARPi, HRD mutations—such as mutations in BRCA1, BRCA2, ATM, and others—serve as biomarkers to identify which patients would benefit from PARPi treatment (Table 1). In addition, it is essential to understand genetic backgrounds that do not elicit a response to PARPi. For example, mutations in DDR genes such as TP53 or CHEK2 have been shown to reduce PARPi sensitivity in vitro and in vivo.^[96] The checkpoint protein CHK2 senses DNA damage and, upon recognition, phosphorylates and stabilizes the tumor suppressor p53. Stabilization of p53 can promote cell cycle arrest by upregulating the G1 phase inhibitor p21 or triggering apoptosis if the damage is too severe.^[97] Therefore, loss-of-function mutations in either of these DDR genes would decrease DNA damage detection, thereby reducing the efficacy of PARPi-induced synthetic lethality. Furthermore, loss of p53 has been shown to upregulate other DDR genes, such as BRCA2, which also counteracts the effects of synthetic lethality. Clinical trial data also demonstrate that patients with CHEK2 mutations exhibit little response to PARPi.^[87,89] TP53 mutations are observed in 30%–50% of patients with mCRPC, whereas CHEK2 mutations are much rarer at 1.4%–2%,^[13–15,62] but both must be considered when making treatment decisions.

5.3. Combination therapies and potential biomarkers

As previously discussed, AR can modulate DDR pathways, and DDR pathways facilitate AR transcriptional activity, providing the rationale for clinical treatment strategies that simultaneously combine AR-targeted therapies with treatments that induce DNA damage—such as radiation therapy—or inhibit DNA repair mechanisms.

Clinical trials combining ADT with radiation therapy significantly improve outcomes for prostate cancer patients across various stages of the disease. Key studies include the RTOG 8531 and RTOG 9202 trials, which demonstrated that adding long-term ADT to radiation therapy improved overall survival and progression-free survival in patients with locally advanced prostate cancer^[98,99] (Table 2). The EORTC 22961 trial highlighted the advantage of long-term over short-term ADT when combined with radiation therapy, emphasizing its importance in high-risk patients^[100] (Table 2). Similarly, evidence increasingly suggests that adjuvant ADT after radiation therapy significantly improves metastasis-free survival compared with neoadjuvant or concurrent ADT treatment.^[104–106] These findings establish the combination of ADT and radiation therapy as a cornerstone of treatment for localized and locally advanced prostate cancer, particularly in high-risk or advanced cases, by enhancing the therapeutic efficacy of radiation through hormonal modulation. In addition, several ongoing studies—such as the OPTIMAL, DIVINE, INNOVATE, and INDICATE trials—aim to enhance treatment outcomes for prostate cancer by leveraging the radiosensitizing effects of AR inhibitors.

Table 2.

Summary of combinatorial therapy targeting AR and inducing DNA damage in clinical trials in prostate cancer.

Trial	Phase	Experimental arm	Control arm	Patient selection	Key endpoints
RTOG 8531[98]	3	RT + adjuvant ADT	RT	Locally advanced prostate cancer  1. Regional lymphatic involvement allowed  2. No evidence of distant metastasis	After 10 yr:  OS 49% vs. 39%; p = 0.002
RTOG 9202[99]	3	RT + LTAD	RT + STAD	Primary prostate cancer No evidence of distant metastasis	After 15 yr:  DFS 16% vs. 10%  (HR, 0.71; 95% CI, 0.64–0.79; p < 0.0001)
EORTC 22961[100] NCT00003026	3	2.5 yr of ADT after RT + LTAD	No further treatment after RT + STADT	Locally advanced prostate cancer Previously received radiotherapy plus 6 mo of androgen deprivation	After 5 yr:  Prostate-specific mortality 3.2% vs. 4.7%  (HR, 1.71; 95% CI, 1.14–2.57)
PROpel[101] NCT03732820	3	Olaparib + ABI+ PRED	ABI + PRED + Placebo	mCRPC  1. No previous treatment for mCRPC  2. Unselected by HRR status	rPFS 24.8 mo vs. 16.6 mo (HR, 0.66; 95% CI, 0.54–0.81; p < 0.001)
MAGNITUDE[102] NCT03748641	3	Niraparib + ABI+ PRED	ABI + PRED + Placebo	mCRPC  1. No previous treatment for mCRPC  2. Enrolled into 2 cohorts on the basis of   HRD gene alterations  3. Previous ARSI and docetaxel treatment in   the castration-sensitive setting were allowed   Cohort 1: with HRR gene alterations (ATM,   BRAC1, BRCA2, BRIP1, CDK12, CHEK2, etc.)   Cohort 2: without HRR gene alterations	Cohort 1:  rPFS 16.5 mo vs. 13.7 mo (HR, 0.73; 95% CI,  0.56–0.96; p = 0.022) BRCA1/2 subgroup:  rPFS 16.6 mo vs. 10.9 mo (HR, 0.53; 95% CI,  0.36–0.79; p = 0.001) Cohort 2:  rPFS (HR, 1.09; 95% CI, 0.75–1.5; p = 0.66)
TALAPRO-2[103] NCT03395197	3	Talazoparib + ENZA	Placebo + ENZA	mCRPC  1. No previous treatment for mCRPC  2. Enrolled into 2 cohorts on the basis of HRR   gene alterations  3. Previous docetaxel and ABI in the castration-sensitive   setting were allowed   Cohort 1: All-comers, recruited first   Cohort 2: With HRR gene alterations (BRCA1, BRCA2,   PALB2, ATM, ATR, CHEK2, etc.)	Cohort 1:  rPFS NR vs. 21.9 mo (HR, 0.63; 95% CI,  0.51–0.78; p < 0.0001) Cohort 2:  rPFS NR vs. 16.4 mo (HR, 0.46; 95% CI,  0.30–0.70; p = 0.003)

ABI = abiraterone acetate; ADT = androgen deprivation therapy; AR = androgen receptor; ARSI = androgen receptor signaling inhibitor; CI = confidence interval; DFS = disease-free survival; ENZA = enzalutamide; HR = hazard ratio; HRD = homologous recombination deficiency; HRR = homologous recombination repair; LTAD = long-term androgen deprivation; mCRPC = metastatic castration-resistant prostate cancer; NR = not reached; OS = overall survival; PRED = prednisone; rPFS = radiographic progression-free survival; RT = radiation therapy; STAD = short-term androgen deprivation; STADT = short-term androgen deprivation therapy.

Recent preclinical investigations suggest that enzalutamide impairs NHEJ, leading to increased PAR activity, and studies have revealed synergy between AR and PARPi both in vitro and in vivo. Consequently, 3 recent phase 3 trials have explored AR-targeted therapies in combination with PARPi as first-line treatment for mCRPC (Table 2). The PROpel study analyzed the combination of olaparib with abiraterone in patients with mCRPC. Results demonstrated that the combination significantly improved radiographic progression-free survival and median overall survival compared with abiraterone alone, regardless of homologous recombination repair (HRR) gene mutation status, although aggregate biomarker subgroup analyses generally favored the combination. Patients carrying HRR gene mutations derived greater benefit than those without these mutations.^[101,107] The MAGNITUDE trial reported on the combination of niraparib and abiraterone in mCRPC. The combination significantly improved radiographic progression-free survival in patients with HRR gene mutations, particularly those with BRCA1/2 alterations, but showed no benefit in HRR-negative patients.^[102] The TALAPRO-2 study evaluated talazoparib plus enzalutamide compared with enzalutamide alone: regardless of HRR status, patients who received the combination had a lower risk of progression—34% and 37% for HRR-proficient and HRR-deficient groups, respectively.^[103] Taken together, all 3 clinical trial results demonstrate the synergistic effects of targeting AR and DDR simultaneously and suggest a new strategy for first-line treatment of mCRPC. The Food and Drug Administration has approved this approach for treating adult patients with BRCA-mutated mCRPC. Without head-to-head trials, it is difficult to determine which next-generation antiandrogen and PARPi combination is most effective. However, one group extrapolated the clinical trial data and concluded that the combination of enzalutamide and talazoparib was statistically superior when comparing both progression-free survival and overall survival.^[108]

An active phase 3 clinical trial, EvoPAR-PR01, for mCRPC is evaluating saruparib in combination with the physician's choice of second-generation antiandrogens.^[109] This ongoing study will include 2 cohorts—patients with or without HRR gene mutations—and is estimated to be completed in 2028.

Most recently, preclinical studies and clinical trial data suggest that concurrently targeting AR and PARPi limits disease progression regardless of HRD status.^{[101,103,107]} Therefore, it is important to identify biomarkers for treatment decision-making that are independent of HRD deficiencies. Retrospective analysis of patient samples from the TALAPRO-2 trial revealed that patients with AR+ signatures and high expression of AR target genes such as ALDH1A3 and CAMKK2 had longer progression-free survival when receiving enzalutamide and talazoparib combination treatment.^[110] Analyses also provided evidence that patients with the TMPRSS2:ERG fusion or RB1 may have a high response rate to enzalutamide and talazoparib combination treatment.^[111] However, this finding was based on a small subset of patients from the clinical trial and requires further investigation before it can be applied to clinical decision-making.^[111] Moreover, the mechanism by which AR signaling can serve as a biomarker to predict improved response to combination treatment still needs to be elucidated.

Although precision medicine holds significant promise for improving outcomes in prostate cancer, several technical and clinical challenges hinder its full implementation. The tendency of prostate cancer to metastasize to bone complicates the collection of high-quality tumor biopsies necessary for molecular profiling.^[112] As a result, there has been growing interest in noninvasive alternatives such as liquid biopsies, which enable the analysis of tumor-derived material such as circulating tumor DNA, circulating tumor cells, and extracellular vesicles.^[112] These approaches offer the potential for disease monitoring and real-time assessment of therapeutic responses; however, technical challenges related to sensitivity, standardization, and clinical validation remain.

6. Summary and questions for future directions

In summary, substantial evidence supports a complex and interconnected relationship between AR signaling and DDR pathways in prostate cancer. Androgen stimulation positively regulates the expression and function of key DDR components, whereas several DDR proteins are found in close association with AR near AREs. Therapeutically, this relationship has opened new avenues, particularly through the combined targeting of AR signaling and DDR pathways using AR inhibitors alongside PARPis or other DDR-targeting agents. This strategy has shown promising clinical findings, especially in mCRPC, suggesting a potential shift in first-line treatment options.

Despite these advances, several critical questions remain. A major concern is the emergence of resistance mechanisms under dual therapeutic pressures. Although resistance to AR-targeted therapies is known, resistance to PARP inhibition in prostate cancer is less well understood. It is unclear how simultaneous inhibition of AR and DDR pathways will influence resistance development and whether this could promote selection for novel escape mechanisms within the tumor. In addition, the functional redundancy within DDR networks raises the possibility that inhibition of one DDR protein could trigger compensatory activity by others, potentially undermining therapeutic efficacy. This compensatory interplay between DDR pathways remains underexplored in prostate cancer and could potentially play a pivotal role in therapy resistance.

Moreover, the impact of AR and DDR targeting on the TME warrants future investigation. The prostate cancer TME is known to be immunologically “cold,” characterized by low T-cell infiltration and the abundance of immunosuppressive cells, allowing immune system evasion.^[113] Androgen receptor signaling has been shown to modulate immune cell recruitment and inflammatory signaling,^[114] and DDR alterations can trigger an innate immune response through pathways like cGAS-STING.^[115] However, the combined influence of AR and DDR inhibition on components of the TME remains poorly understood. Dual inhibition may alter cytokine profiles, enhance immune recognition, or reinforce immunosuppressive feedback loops. Understanding these dynamics is crucial for optimizing combination therapies.

In addition to therapeutic implications and resistance mechanisms, another emerging question centers on how the interplay between AR signaling and DDR pathways influences metabolic reprogramming in prostate cancer tumors. Androgen receptor is a well-established regulator of key metabolic genes involved in glycolysis, lipogenesis, and amino acid metabolism to meet the high energy demands of cancer cells.^[116] DNA damage response alterations also increase nucleotide biosynthesis, glutamine metabolism, and redox homeostasis to support DNA repair and survival.^[117] Simultaneous targeting of AR and DDR could exacerbate stress responses, causing a shift in metabolic programming. These knowledge gaps highlight the need for integrative studies to link AR signaling, genomic instability, and metabolic programming, as this may further elucidate pathways to exploit.

Acknowledgments

Figures were created with BioRender.com.

Statement of ethics

Not applicable.

Conflict of interest statement

JL is a member of the early career editorial board of Current Urology and confirms no involvement in any stage of this article's review process, ensuring unbiased editorial decision making. The other authors declare no conflicts of interest.

Funding source

This study was supported by the Indiana CTSI Core Pilot Funding (FY24CTSIE) and the Startup Funding of JL from the University of Notre Dame (START097S).

Author contributions

MS, JL: Conception and design;

All authors: Provision of study materials, collection and assembly of data and materials, manuscript writing and final approval of the manuscript.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.