Castration therapy results in decreased Ku70 levels in prostate cancer

Repurposing Niclosamide as a plausible neurotherapeutic in autism spectrum disorders, targeting mitochondrial dysfunction: a strong hypothesis

Autism Spectrum Disorders (ASD) are a complex set of neurodevelopmental manifestations which present in the form of social and communication deficits. Affecting a growing proportion of children worldwide, the exact pathogenesis of this disorder is not very well understood, and multiple signaling pathways have been implicated. Among them, the ERK/MAPK pathway is critical in a number of cellular processes, and the normal functioning of neuronal cells also depends on this cascade. As such, recent studies have increasingly focused on the impact this pathway has on the development of autistic symptoms. Improper ERK signaling is suspected to be involved in neurotoxicity, and the same might be implicated in autism spectrum disorders (ASD), through a variety of effects including mitochondrial dysfunction and oxidative stress. Niclosamide, an antihelminthic and anti-inflammatory agent, has shown potential in inhibiting this pathway, and countering the effects shown by its overactivity in inflammation. While it has previously been evaluated in other neurological disorders like Alzheimer's Disease and Parkinson's Disease, as well as various cancers by targeting ERK/MAPK, it's efficacy in autism has not yet been evaluated. In this article, we attempt to discuss the potential role of the ERK/MAPK pathway in the pathogenesis of ASD, specifically through mitochondrial damage, before moving to the therapeutic potential of niclosamide in the disorder, mediated by the inhibition of this pathway and its detrimental effects of neuronal development.

Intratumoral androgen biosynthesis associated with 3β-hydroxysteroid dehydrogenase 1 promotes resistance to radiotherapy in prostate cancer

Half of all men with advanced prostate cancer (PCa) inherit at least 1 copy of an adrenal-permissive HSD3B1 (1245C) allele, which increases levels of 3β-hydroxysteroid dehydrogenase 1 (3βHSD1) and promotes intracellular androgen biosynthesis. Germline inheritance of the adrenally permissive allele confers worse outcomes in men with advanced PCa. We investigated whether HSD3B1 (1245C) drives resistance to combined androgen deprivation and radiotherapy. Adrenally permissive 3βHSD1 enhanced resistance to radiotherapy in PCa cell lines and xenograft models engineered to mimic the human adrenal/gonadal axis during androgen deprivation. The allele-specific effects on radiosensitivity were dependent on availability of DHEA, the substrate for 3βHSD1. In lines expressing the HSD3B1 (1245C) allele, enhanced expression of DNA damage response (DDR) genes and more rapid DNA double-strand break (DSB) resolution were observed. A correlation between androgen receptor (AR) expression and increased DDR gene expression was confirmed in 680 radical prostatectomy specimens. Treatment with the nonsteroidal antiandrogen enzalutamide reversed the resistant phenotype of HSD3B1 (1245C) PCa in vitro and in vivo. In conclusion, 3βHSD1 promotes prostate cancer resistance to combined androgen deprivation and radiotherapy by upregulating DNA DSB repair. This work supports prospective validation of early combined androgen blockade for high-risk men harboring the HSD3B1 (1245C) allele.

Uncovering the Secrets of Prostate Cancer's Radiotherapy Resistance: Advances in Mechanism Research

Prostate cancer (PCa) is a critical global public health issue with its incidence on the rise. Radiation therapy holds a primary role in PCa treatment; however, radiation resistance has become increasingly challenging as we uncover more about PCa's pathogenesis. Our review aims to investigate the multifaceted mechanisms underlying radiation therapy resistance in PCa. Specifically, we will examine how various factors, such as cell cycle regulation, DNA damage repair, hypoxic conditions, oxidative stress, testosterone levels, epithelial-mesenchymal transition, and tumor stem cells, contribute to radiation therapy resistance. By exploring these mechanisms, we hope to offer new insights and directions towards overcoming the challenges of radiation therapy resistance in PCa. This can also provide a theoretical basis for the clinical application of novel ultra-high-dose-rate (FLASH) radiotherapy in the era of PCa.

Recent Research Advances in Double-Strand Break and Mismatch Repair Defects in Prostate Cancer and Potential Clinical Applications

Prostate cancer remains a leading cause of cancer-related death in men worldwide. Recent research advances have emphasized the critical roles of mismatch repair (MMR) and double-strand break (DSB) in prostate cancer development and progression. Here, we provide a comprehensive review of the molecular mechanisms underlying DSB and MMR defects in prostate cancer, as well as their clinical implications. Furthermore, we discuss the promising therapeutic potential of immune checkpoint inhibitors and PARP inhibitors in targeting these defects, particularly in the context of personalized medicine and further perspectives. Recent clinical trials have demonstrated the efficacy of these novel treatments, including Food and Drugs Association (FDA) drug approvals, offering hope for improved patient outcomes. Overall, this review emphasizes the importance of understanding the interplay between MMR and DSB defects in prostate cancer to develop innovative and effective therapeutic strategies for patients.

hSSB1 (NABP2/OBFC2B) modulates the DNA damage and androgen-induced transcriptional response in prostate cancer

BACKGROUND

Activation and regulation of androgen receptor (AR) signaling and the DNA damage response impact the prostate cancer (PCa) treatment modalities of androgen deprivation therapy (ADT) and radiotherapy. Here, we have evaluated a role for human single-strand binding protein 1 (hSSB1/NABP2) in modulation of the cellular response to androgens and ionizing radiation (IR). hSSB1 has defined roles in transcription and maintenance of genome stability, yet little is known about this protein in PCa.

METHODS

We correlated hSSB1 with measures of genomic instability across available PCa cases from The Cancer Genome Atlas (TCGA). Microarray and subsequent pathway and transcription factor enrichment analysis were performed on LNCaP and DU145 prostate cancer cells.

RESULTS

Our data demonstrate that hSSB1 expression in PCa correlates with measures of genomic instability including multigene signatures and genomic scars that are reflective of defects in the repair of DNA double-strand breaks via homologous recombination. In response to IR-induced DNA damage, we demonstrate that hSSB1 regulates cellular pathways that control cell cycle progression and the associated checkpoints. In keeping with a role for hSSB1 in transcription, our analysis revealed that hSSB1 negatively modulates p53 and RNA polymerase II transcription in PCa. Of relevance to PCa pathology, our findings highlight a transcriptional role for hSSB1 in regulating the androgen response. We identified that AR function is predicted to be impacted by hSSB1 depletion, whereby this protein is required to modulate AR gene activity in PCa.

CONCLUSIONS

Our findings point to a key role for hSSB1 in mediating the cellular response to androgen and DNA damage via modulation of transcription. Exploiting hSSB1 in PCa might yield benefits as a strategy to ensure a durable response to ADT and/or radiotherapy and improved patient outcomes.

Transcription networks rewire gene repertoire to coordinate cellular reprograming in prostate cancer

Transcription factors (TFs) represent the most commonly deregulated DNA-binding class of proteins associated with multiple human cancers. They can act as transcriptional activators or repressors that rewire the cistrome, resulting in cellular reprogramming during cancer progression. Deregulation of TFs is associated with the onset and maintenance of various cancer types including prostate cancer. An emerging subset of TFs has been implicated in the regulation of multiple cancer hallmarks during tumorigenesis. Here, we discuss the role of key TFs which modulate transcriptional cicuitries involved in the development and progression of prostate cancer. We further highlight the role of TFs associated with key cancer hallmarks, including, chromatin remodeling, genome instability, DNA repair, invasion, and metastasis. We also discuss the pluripotent function of TFs in conferring lineage plasticity, that aids in disease progression to neuroendocrine prostate cancer. At the end, we summarize the current understanding and approaches employed for the therapeutic targeting of TFs and their cofactors in the clinical setups to prevent disease progression.

Androgen Receptor Splice Variants Contribute to the Upregulation of DNA Repair in Prostate Cancer

Background: Canonical androgen receptor (AR) signaling regulates a network of DNA repair genes in prostate cancer (PCA). Experimental and clinical evidence indicates that androgen deprivation not only suppresses DNA repair activity but is often synthetically lethal in combination with PARP inhibition. The present study aimed to elucidate the impact of AR splice variants (AR-Vs), occurring in advanced or late-stage PCA, on DNA repair machinery. Methods: Two hundred and seventy-three tissue samples were analyzed, including primary hormone-naïve PCA, primary metastases, hormone-sensitive PCA on androgen deprivation therapy (ADT) and castration refractory PCA (CRPC group). The transcript levels of the target genes were profiled using the nCounter platform. Experimental support for the findings was gained in AR/AR-V7-expressing LNCaP cells subjected to ionizing radiation. Results: AR-Vs were present in half of hormone-sensitive PCAs on androgen deprivation therapy (ADT) and two-thirds of CRPC samples. The presence of AR-Vs is highly correlated with increased activity in the AR pathway and DNA repair gene expression. In AR-V-expressing CRPC, the DNA repair score increased by 2.5-fold as compared to AR-V-negative samples. Enhanced DNA repair and the deregulation of DNA repair genes by AR-V7 supported the clinical data in a cell line model. Conclusions: The expression of AR splice variants such as AR-V7 in PCA patients following ADT might be a reason for reduced or absent therapy effects in patients on additional PARP inhibition due to the modulation of DNA repair gene expression. Consequently, AR-Vs should be further studied as predictive biomarkers for therapy response in this setting.

Bystander effect in photosensitized prostate cancer cells with a different grade of malignancy: The role of nitric oxide

Photodynamic therapy (PDT) is a therapeutic modality based on the simultaneous action of three elements: photosensitizer, light and oxygen. This triad generates singlet oxygen and reactive oxygen species that can reduce the mass of a tumor. PDT is also able to stimulate iNOS, the enzyme that generates nitric oxide (NO). The role of NO in PDT-treated cancer cells has been investigated in several studies. They showed that low iNOS/NO levels stimulate signaling pathways that promote tumor survival, while high iNOS/NO levels arrest tumor growth. There is increasing evidence that ROS/RNS control both proliferation and migration of cells in the vicinity of PDT-treated tumor cells (so-called bystander cells). In this work, we addressed the question of how NO, which is generated by weak PDT, affects bystander cells. We used a conditioned medium: medium of PDT-treated tumor cells containing the stressors produced by the cells was added to untreated cells mimicking the neighboring bystander cells to investigate whether the conditioned medium affects cell proliferation. We found that low-level NO in prostate cancer cells affects the bystander tumor cells in a manner that depends on their malignancy grade.

Tousled-like kinase 1: a novel factor with multifaceted role in mCRPC progression and development of therapy resistance

Standard treatment for advanced Prostate Cancer (PCa) consists of androgen deprivation therapy (ADT), but ultimately fails, resulting in the incurable phase of the disease: metastatic castration-resistant prostate cancer (mCRPC). Targeting PCa cells before their progression to mCRPC would greatly improve the outcome, if strategies could be devised selectively targeting androgen receptor (AR)-dependent and/or independent compensatory pathways which promote mCRPC development. Combination therapy by targeting the DNA damage response (DDR) along with ADT has been limited by general toxicity, and a goal of clinical trials is how to target the DDR more specifically. In recent years, our lab has identified a key role for the DDR kinase, TLK1, in mediating key aspects of adaptation to ADT, first by promoting a cell cycle arrest (through the TLK1>NEK1>ATR>Chk1 kinase cascade) under the unfavorable growth conditions (androgen deprivation), and then by reprogramming the PCa cells to adapt to androgen-independent growth via the NEK1>YAP/AR>CRPC conversion. In addition, TLK1 plays a key anti-apoptotic role via the NEK1>VDAC1 regulation on the intrinsic mitochondrial apoptotic pathway when the DDR is activated. Finally, TLK1 was recently identified as having an important role in motility and metastasis via regulation of the kinases MK5/PRAK and AKT (indirectly via AKTIP).

Co-Inhibition of Androgen Receptor and PARP as a Novel Treatment Paradigm in Prostate Cancer-Where Are We Now?

Metastatic prostate cancer remains lethal with a 5-year survival rate of about 30%, indicating the need for better treatment options. Novel antiandrogens (NAA)-enzalutamide and abiraterone-have been the mainstay of treatment for advanced disease since 2011. In patients who progress on the first NAA, responses to the second NAA are infrequent (25-30%) and short-lasting (median PFS ~3 months). With the growing adoption of NAA therapy in pre-metastatic castration-resistant settings, finding better treatment options for first-line mCRPC has become an urgent clinical need. The regulatory approval of two PARP inhibitors in 2020-rucaparib and olaparib-has provided the first targeted therapy option for patients harboring defects in selected DNA damage response and repair (DDR) pathway genes. However, a growing body of preclinical and clinical data shows that co-inhibition of AR and PARP induces synthetic lethality and could be a promising therapy for patients without any DDR alterations. In this review article, we will investigate the limitations of NAA monotherapy, the mechanistic rationale for synthetic lethality induced by co-inhibition of AR and PARP, the clinical data that have led to the global development of a number of these AR and PARP combination therapies, and how this may impact patient care in the next 2-10 years.

Advances with androgen deprivation therapy for prostate cancer

INTRODUCTION

Androgen deprivation therapy (ADT) has been a treatment of choice for prostate cancer in almost all phases, particularly in the locally advanced, metastatic setting in both hormone-sensitive and castration-resistant diseaseand in those who are unfit for any local therapy. Different ways of administering ADT comes in the form of surgical or chemical castration with the use of gonadotropin-releasing hormone (GnRH-agonists) being the foremost way of delivering ADT.

AREAS COVERED

This review encompasses ADT history, use of leuprolide, degarelix, and relugolix, with contextual use of ADT in combination with androgen-signaling inhibitors and potential mechanisms of resistance. Novel approaches with regard to hormone therapy are also discussed.

EXPERT OPINION

The use of GnRH-agonists and GnRH-antagonists yields efficacy that is likely equivalent in resulting in testosterone suppression. While the side-effect profile with ADT are generally equivalent, effects on cardiovascular morbidity may be improved with the use of oral relugolix though this is noted with caution since the cardiovascular side-effects were a result of secondary subgroup analyses. The choice of ADT hinges upon cost, availability, ease of administration, and preference amongst physicians and patients alike.

The spectrum of sex differences in cancer

Sex differences in cellular and systems biology have been evolutionarily selected to optimize reproductive success in all species with little (sperm) and big (ova) gamete producers. They are evident from the time of fertilization and accrue throughout development through genetic, epigenetic, and circulating sex hormone-dependent mechanisms. Among other effects, they significantly impact on chromatin organization, metabolism, cell cycle regulation, immunity, longevity, and cancer risk and survival. Sex differences in cancer should be expected and accounted for in basic, translational, and clinical oncology research.

Platinum Complexes as Inhibitors of DNA Repair Protein Ku70 and Topoisomerase IIα in Cancer Cells

Ku70 protein and topoisomerase IIα (Topo IIα) are promising targets of anticancer drugs, which play critical roles in DNA repair and replication processes. Three platinum(II) complexes, [PtCl(NH3)2(9-(pyridin-2-ylmethyl)-9H-carbazole)]NO3 (OPPC), [PtCl(NH3)2(9-(pyridin-3-ylmethyl)-9H-carbazole)]NO3 (MPPC),...

Mechanisms, Challenges, and Opportunities in Combined Radiation and Hormonal Therapies

Androgen receptor signaling blockade is perhaps the first example of targeted therapy in the treatment of cancer. Since the initial observations that prostate cancers depend on hormone signaling, hormonal therapies remain a cornerstone in the treatment of metastatic prostate cancer. Androgen deprivation therapy has been shown to improve outcomes involving treatment of prostate cancers with radiotherapy, though a mechanistic understanding into the optimal sequencing of androgen deprivation therapy and radiotherapy remains incomplete. In this review we highlight key clinical trials designed to study combinations of hormonal and radiotherapies and introduce recent discoveries into the complex biology of androgen receptor signaling and DNA damage and repair. These emerging mechanistic and translational studies may have profound implications on both our understanding of hormonal therapy and radiotherapy combinations and the development of novel treatment strategies for locally-advanced and metastatic castrate resistant prostate cancer.

Resistance to Antiandrogens in Prostate Cancer: Is It Inevitable, Intrinsic or Induced?

Increasingly sophisticated therapies for chemical castration dominate first-line treatments for locally advanced prostate cancer. However, androgen deprivation therapy (ADT) offers little prospect of a cure, as resistant tumors emerge rather rapidly, normally within 30 months. Cells have multiple mechanisms of resistance to even the most sophisticated drug regimes, and both tumor cell heterogeneity in prostate cancer and the multiple salvage pathways result in castration-resistant disease related genetically to the original hormone-naive cancer. The timing and mechanisms of cell death after ADT for prostate cancer are not well understood, and off-target effects after long-term ADT due to functional extra-prostatic expression of the androgen receptor protein are now increasingly being recorded. Our knowledge of how these widely used treatments fail at a biological level in patients is deficient. In this review, I will discuss whether there are pre-existing drug-resistant cells in a tumor mass, or whether resistance is induced/selected by the ADT. Equally, what is the cell of origin of this resistance, and does it differ from the treatment-naïve tumor cells by differentiation or dedifferentiation? Conflicting evidence also emerges from studies in the range of biological systems and species employed to answer this key question. It is only by improving our understanding of this aspect of treatment and not simply devising another new means of androgen inhibition that we can improve patient outcomes.

The circadian cryptochrome, CRY1, is a pro-tumorigenic factor that rhythmically modulates DNA repair

Mechanisms regulating DNA repair processes remain incompletely defined. Here, the circadian factor CRY1, an evolutionally conserved transcriptional coregulator, is identified as a tumor specific regulator of DNA repair. Key findings demonstrate that CRY1 expression is androgen-responsive and associates with poor outcome in prostate cancer. Functional studies and first-in-field mapping of the CRY1 cistrome and transcriptome reveal that CRY1 regulates DNA repair and the G2/M transition. DNA damage stabilizes CRY1 in cancer (in vitro, in vivo, and human tumors ex vivo), which proves critical for efficient DNA repair. Further mechanistic investigation shows that stabilized CRY1 temporally regulates expression of genes required for homologous recombination. Collectively, these findings reveal that CRY1 is hormone-induced in tumors, is further stabilized by genomic insult, and promotes DNA repair and cell survival through temporal transcriptional regulation. These studies identify the circadian factor CRY1 as pro-tumorigenic and nominate CRY1 as a new therapeutic target.

Cryptochrome 1 (CRY1) is a transcriptional coregulator associated with the circadian clock. Here the authors reveal that CRY1 is hormone-regulated, stabilized by genomic insult, and promotes DNA repair and cell survival through temporal transcriptional regulation.

The Nexus of Endocrine Signaling and Cancer: How Steroid Hormones Influence Genomic Stability

Endocrine-driven malignancies, including breast and prostate cancer, are among the most common human cancers. The relationship between sex steroid hormones (eg, androgen, estrogen, and progesterone), their cognate receptors, and genomic stability lie at the center of endocrine-driven cancer development, progression, and therapeutic resistance. A variety of direct and indirect mechanisms have been described that link steroid hormone signaling to the loss of genomic integrity that drives early carcinogenesis. These effects are often enriched within endocrine receptor cistromes, accounting for the high proportion of mutations and rearrangements in the region of hormone response elements. In other cases, the effects are generalized and rely on a complex array of genetic, epigenetic, and metabolic interactions. Both androgen and estrogen receptors directly modulate the DNA damage response by trans-activating DNA damage response genes and redirecting the cellular repair machinery in the wake of genotoxic stress. Here we review the key mechanistic underpinnings of the relationship between sex steroid hormone receptors and genomic stability. In addition, we summarize emerging research in this area and discuss important implications for cancer prevention and treatment.

Targeting DNA Damage Response in Prostate and Breast Cancer

Steroid hormone signaling induces vast gene expression programs which necessitate the local formation of transcription factories at regulatory regions and large-scale alterations of the genome architecture to allow communication among distantly related cis-acting regions. This involves major stress at the genomic DNA level. Transcriptionally active regions are generally instable and prone to breakage due to the torsional stress and local depletion of nucleosomes that make DNA more accessible to damaging agents. A dedicated DNA damage response (DDR) is therefore essential to maintain genome integrity at these exposed regions. The DDR is a complex network involving DNA damage sensor proteins, such as the poly(ADP-ribose) polymerase 1 (PARP-1), the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), the ataxia-telangiectasia-mutated (ATM) kinase and the ATM and Rad3-related (ATR) kinase, as central regulators. The tight interplay between the DDR and steroid hormone receptors has been unraveled recently. Several DNA repair factors interact with the androgen and estrogen receptors and support their transcriptional functions. Conversely, both receptors directly control the expression of agents involved in the DDR. Impaired DDR is also exploited by tumors to acquire advantageous mutations. Cancer cells often harbor germline or somatic alterations in DDR genes, and their association with disease outcome and treatment response led to intensive efforts towards identifying selective inhibitors targeting the major players in this process. The PARP-1 inhibitors are now approved for ovarian, breast, and prostate cancer with specific genomic alterations. Additional DDR-targeting agents are being evaluated in clinical studies either as single agents or in combination with treatments eliciting DNA damage (e.g., radiation therapy, including targeted radiotherapy, and chemotherapy) or addressing targets involved in maintenance of genome integrity. Recent preclinical and clinical findings made in addressing DNA repair dysfunction in hormone-dependent and -independent prostate and breast tumors are presented. Importantly, the combination of anti-hormonal therapy with DDR inhibition or with radiation has the potential to enhance efficacy but still needs further investigation.

ARe we there yet? Understanding androgen receptor signaling in breast cancer

The role of androgen receptor (AR) activation and expression is well understood in prostate cancer. In breast cancer, expression and activation of AR is increasingly recognized for its role in cancer development and its importance in promoting cell growth in the presence or absence of estrogen. As both prostate and breast cancers often share a reliance on nuclear hormone signaling, there is increasing appreciation of the overlap between activated cellular pathways in these cancers in response to androgen signaling. Targeting of the androgen receptor as a monotherapy or in combination with other conventional therapies has proven to be an effective clinical strategy for the treatment of patients with prostate cancer, and these therapeutic strategies are increasingly being investigated in breast cancer. This overlap suggests that targeting androgens and AR signaling in other cancer types may also be effective. This manuscript will review the role of AR in various cellular processes that promote tumorigenesis and metastasis, first in prostate cancer and then in breast cancer, as well as discuss ongoing efforts to target AR for the more effective treatment and prevention of cancer, especially breast cancer.

Second-Generation Antiandrogen Therapy Radiosensitizes Prostate Cancer Regardless of Castration State through Inhibition of DNA Double Strand Break Repair

(1) Background: The combination of the first-generation antiandrogens and radiotherapy (RT) has been studied extensively in the clinical setting of prostate cancer (PCa). Here, we evaluated the potential radiosensitizing effect of the second-generation antiandrogens abiraterone acetate, apalutamide and enzalutamide. (2) Methods: Cell proliferation and agarose-colony forming assay were used to measure the effect on survival. Double strand break repair efficiency was monitored using immunofluorescence staining of γH2AX/53BP1. (3) Results: We report retrospectively a minor benefit for PCa patients received first-generation androgen blockers and RT compared to patients treated with RT alone. Combining either of the second-generation antiandrogens and 2Gy suppressed cell growth and increased doubling time significantly more than 2Gy alone, in both hormone-responsive LNCaP and castration-resistant C4-2B cells. These findings were recapitulated in resistant sub-clones to (i) hormone ablation (LNCaP-abl), (ii) abiraterone acetate (LNCaP-abi), (iii) apalutamide (LNCaP-ARN509), (iv) enzalutamide (C4-2B-ENZA), and in castration-resistant 22-RV1 cells. This radiosensitization effect was not observable using the first-generation antiandrogen bicalutamide. Inhibition of DNA DSB repair was found to contribute to the radiosensitization effect of second-generation antiandrogens, as demonstrated by a significant increase in residual γH2AX and 53BP1 foci numbers at 24h post-IR. DSB repair inhibition was further demonstrated in 22 patient-derived tumor slice cultures treated with abiraterone acetate before ex-vivo irradiation with 2Gy. (4) Conclusion: Together, these data show that second-generation antiandrogens can enhance radiosensitivity in PCa through DSB repair inhibition, regardless of their hormonal status. Translated into clinical practice, our results may help to find additional strategies to improve the effectiveness of RT in localized PCa, paving the way for a clinical trial.

DNA-PK in human malignant disorders: Mechanisms and implications for pharmacological interventions

The DNA-PK holoenzyme is a fundamental element of the DNA damage response machinery (DDR), which is responsible for cellular genomic stability. Consequently, and predictably, over the last decades since its identification and characterization, numerous pre-clinical and clinical studies reported observations correlating aberrant DNA-PK status and activity with cancer onset, progression and responses to therapeutic modalities. Notably, various studies have established in recent years the role of DNA-PK outside the DDR network, corroborating its role as a pleiotropic complex involved in transcriptional programs that operate biologic processes as epithelial to mesenchymal transition (EMT), hypoxia, metabolism, nuclear receptors signaling and inflammatory responses. In particular tumor entities as prostate cancer, immense research efforts assisted mapping and describing the overall signaling networks regulated by DNA-PK that control metastasis and tumor progression. Correspondingly, DNA-PK emerges as an obvious therapeutic target in cancer and data pertaining to various pharmacological approaches have been published, largely in context of combination with DNA-damaging agents (DDAs) that act by inflicting DNA double strand breaks (DSBs). Currently, new generation inhibitors are tested in clinical trials. Several excellent reviews have been published in recent years covering the biology of DNA-PK and its role in cancer. In the current article we are aiming to systematically describe the main findings on DNA-PK signaling in major cancer types, focusing on both preclinical and clinical reports and present a detailed current status of the DNA-PK inhibitors repertoire.

Role of the DNA damage response in prostate cancer formation, progression and treatment

BACKGROUND

Clinical and preclinical studies have revealed that alterations in DNA damage response (DDR) pathways may play an important role in prostate cancer (PCa) etiology and progression. These alterations can influence PCa responses to radiotherapy and anti-androgen treatment. The identification of DNA repair gene aberrations in PCa has driven the interest for further evaluation whether these genetic changes may serve as biomarkers for patient stratification.

METHODS

In this review, we summarize the current knowledge on DDR alterations in PCa, their potential impact on clinical interventions and prospects for improved management of PCa. We particularly focus on the influence of DDR gene mutations on PCa initiation and progression and describe the underlying mechanisms.

RESULTS AND CONCLUSIONS

A better understanding of these mechanisms, will contribute to better disease management as treatment strategies can be chosen based on the specific disease properties, since a growing number of treatments are targeting DDR pathway alterations (such as Poly(ADP-ribose) polymerase inhibitors). Furthermore, the recently discovered crosstalk between the DDR and androgen receptor signaling opens a new array of possible strategies to optimize treatment combinations. We discuss how these recent and ongoing studies will help to improve diagnostic, prognostic and therapeutic approaches for PCa management.

DNA Damage Response in Prostate Cancer

Prostatic adenocarcinoma (PCa) remains a significant health concern. Although localized PCa can be effectively treated, disseminated disease remains uniformly fatal. PCa is reliant on androgen receptor (AR); as such, first-line therapy for metastatic PCa entails suppression of AR signaling. Although initially effective, recurrent tumors reactivate AR function, leading to a lethal stage of disease termed castration-resistant PCa (CRPC). Recent findings implicate AR signaling in control of DNA repair and show that alterations in DNA damage repair pathways are strongly associated with disease progression and poor outcome. This review will address the DNA repair alterations observed in the clinical setting, explore the anticipated molecular and cellular consequence of DNA repair dysfunction, and consider clinical strategies for targeting tumors with altered DNA repair.

Sensitization of prostate cancer to radiation therapy: Molecules and pathways to target

Radiation therapy is used to treat cancer by radiation-induced DNA damage. Despite the best efforts to eliminate cancer, some cancer cells survive irradiation, resulting in cancer progression or recurrence. Alteration in DNA damage repair pathways is common in cancers, resulting in modulation of their response to radiation. This article focuses on the recent findings about molecules and pathways that potentially can be targeted to sensitize prostate cancer cells to ionizing radiation, thereby achieving an improved therapeutic outcome.

Applying Precision Oncology Principles in Radiation Oncology

Radiation therapy is a critical component in the curative management of many solid tumor types, and advances in radiation delivery techniques during the past decade have led to improved disease control and quality of life for patients. During the same period, remarkable advances have also been made in understanding the genomic landscape of tumors; however, treatment decisions in radiation oncology continue to depend primarily on clinical and histopathologic characteristics rather than on the genetic features of the tumor or the patient. With the development of novel genomic techniques and their increasing use in clinical practice, radiation oncology is uniquely positioned to leverage these advances to identify novel biomarkers that could inform radiation dose, field, and the use of concurrent systemic agents. Here, we summarize efforts to use genomic techniques to guide radiation decisions, and we highlight some of the current opportunities and challenges that exist in attempting to apply precision oncology principles in radiation oncology.

Delineation of the androgen-regulated signaling pathways in prostate cancer facilitates the development of novel therapeutic approaches

Although androgen deprivation therapy (ADT) is initially effective for the treatment of progressive prostate cancer, it inevitably fails due to the onset of diverse resistance mechanisms that restore androgen receptor (AR) signaling. Thus, AR remains a desired therapeutic target even in the relapsed stages of the disease. Given the difficulties in stopping all AR reactivation mechanisms, we propose that the identification of the driver signaling events downstream of the receptor offer viable, alternative therapeutic targets. Here, we summarize recently described, AR-regulated processes that have been demonstrated to promote prostate cancer. By highlighting these signaling events and describing some of the ongoing efforts to pharmacologically modulate these pathways, our goal is to advocate potential new therapeutic targets that would represent an alternative approach for blocking AR actions.

CHD1 loss sensitizes prostate cancer to DNA damaging therapy by promoting error-prone double-strand break repair

Background

Deletion of the chromatin remodeler chromodomain helicase DNA-binding protein 1 (CHD1) is a common genomic alteration found in human prostate cancers (PCas). CHD1 loss represents a distinct PCa subtype characterized by SPOP mutation and higher genomic instability. However, the role of CHD1 in PCa development in vivo and its clinical utility remain unclear.

Patients and methods

To study the role of CHD1 in PCa development and its loss in clinical management, we generated a genetically engineered mouse model with prostate-specific deletion of murine Chd1 as well as isogenic CHD1 wild-type and homozygous deleted human benign and PCa lines. We also developed patient-derived organoid cultures and screened patients with metastatic PCa for CHD1 loss.

Results

We demonstrate that CHD1 loss sensitizes cells to DNA damage and causes a synthetic lethal response to DNA damaging therapy in vitro, in vivo, ex vivo, in patient-derived organoid cultures and in a patient with metastatic PCa. Mechanistically, CHD1 regulates 53BP1 stability and CHD1 loss leads to decreased error-free homologous recombination (HR) repair, which is compensated by increased error-prone non-homologous end joining (NHEJ) repair for DNA double-strand break (DSB) repair.

Conclusions

Our study provides the first in vivo and in patient evidence supporting the role of CHD1 in DSB repair and in response to DNA damaging therapy. We uncover mechanistic insights that CHD1 modulates the choice between HR and NHEJ DSB repair and suggest that CHD1 loss may contribute to the genomic instability seen in this subset of PCas.

Enhanced radiosensitization of enzalutamide via schedule dependent administration to androgen-sensitive prostate cancer cells

BACKGROUND

Prostate cancer (PCa) is a progressive disease and the most diagnosed cancer in men. The current standard of care for high-risk localized PCa is a combination of androgen deprivation therapy (ADT) and radiation (XRT). The majority of these patients however become resistant due to incomplete responses to ADT as a result of selective cells maintaining androgen receptor (AR) activity. Improvement can be made if increasing radiosensitivity is realized. Therefore, the aim of this study is to investigate the efficacy of the next-generation PCa drug Enzalutamide (ENZA), as a radiosensitizer in XRT therapy.

METHODS

Using a number of androgen-dependent (LNCaP, PC3-T877A) and androgen-independent (C4-2, 22RV1, PC3, PC3-AR V7) cell lines, the effect of ENZA as a radiosensitizer was studied alone or in combination with ADT and/or XRT. Cell viability and cell survival were assessed, along with determination of cell cycle arrest, DNA damage response and repair, apoptosis and senescence.

RESULTS

Our results indicated that either ENZA alone (in AR positive, androgen-dependent PCa cells) or in combination with ADT (in AR positive, hormone-insensitive PCa cells) potentiates radiation response [Dose enhancement factor (DEF) of 1.75 in LNCAP and 1.35 in C4-2] stronger than ADT + XRT conditions. Additionally, ENZA sensitized androgen dependent PCa cells to XRT in a schedule-dependent manner, where concurrent administration of ENZA and radiation lead to a maximal radiosensitization when compared to either drug administration prior or after XRT. In LNCaP cells, ENZA treatment significantly prolonged the presence of XRT-induced phospho-γH2AX up to 24 h after treatment; suggesting enhanced DNA damage. It also significantly increased XRT-induced apoptosis and senescence.

CONCLUSIONS

Our data indicates that ENZA acts as a much stronger radiosensitizer compared to ADT. We have also observed that its efficacy is schedule dependent and related to increased levels of DNA damage and a delay of DNA repair processes. Finally, the initial abrogation of DNA-PKcs activity by AR inhibition and its subsequent recovery might represent an important mechanism by which PCa cells acquire resistance to combined anti-androgen and XRT treatment. This work suggests a new use of ENZA in combination with XRT that could be applicable in clinical trial settings for patients with early and intermediate hormone responsive disease.

Targeting Androgen Receptor and DNA Repair in Metastatic Castration-Resistant Prostate Cancer: Results From NCI 9012

Purpose To determine whether cotargeting poly (ADP-ribose) polymerase-1 plus androgen receptor is superior to androgen receptor inhibition in metastatic castration-resistant prostate cancer (mCRPC) and whether ETS fusions predict response. Patients and Methods Patients underwent metastatic site biopsy and were stratified by ETS status and randomly assigned to abiraterone plus prednisone without (arm A) or with veliparib (arm B). Primary objectives were: confirmed prostate-specific antigen (PSA) response rate (RR) and whether ETS fusions predicted response. Secondary objectives were: safety, measurable disease RR (mRR), progression-free survival (PFS), and molecular biomarker analysis. A total of 148 patients were randomly assigned to detect a 20% PSA RR improvement. Results A total of 148 patients with mCRPC were randomly assigned: arm A, n = 72; arm B, n = 76. There were no differences in PSA RR (63.9% v 72.4%; P = .27), mRR (45.0% v 52.2%; P = .51), or median PFS (10.1 v 11 months; P = .99). ETS fusions did not predict response. Exploratory analysis of tumor sequencing (80 patients) revealed: 41 patients (51%) were ETS positive, 20 (25%) had DNA-damage repair defect (DRD), 41 (51%) had AR amplification or copy gain, 34 (43%) had PTEN mutation, 33 (41%) had TP53 mutation, 39 (49%) had PIK3CA pathway activation, and 12 (15%) had WNT pathway alteration. Patients with DRD had significantly higher PSA RR (90% v 56.7%; P = .007) and mRR (87.5% v 38.6%; P = .001), PSA decline ≥ 90% (75% v 25%; P = .001), and longer median PFS (14.5 v 8.1 months; P = .025) versus those with wild-type tumors. Median PFS was longer in patients with normal PTEN (13.5 v 6.7 months; P = .02), TP53 (13.5 v 7.7 months; P = .01), and PIK3CA (13.8 v 8.3 months; P = .03) versus those with mutation or activation. In multivariable analysis adjusting for clinical covariates, DRD association with PFS remained significant. Conclusion Veliparib and ETS status did not affect response. Exploratory analysis identified a novel DRD association with mCRPC outcomes.

Synthetic lethality between androgen receptor signalling and the PARP pathway in prostate cancer

Emerging data demonstrate homologous recombination (HR) defects in castration-resistant prostate cancers, rendering these tumours sensitive to PARP inhibition. Here we demonstrate a direct requirement for the androgen receptor (AR) to maintain HR gene expression and HR activity in prostate cancer. We show that PARP-mediated repair pathways are upregulated in prostate cancer following androgen-deprivation therapy (ADT). Furthermore, upregulation of PARP activity is essential for the survival of prostate cancer cells and we demonstrate a synthetic lethality between ADT and PARP inhibition in vivo. Our data suggest that ADT can functionally impair HR prior to the development of castration resistance and that, this potentially could be exploited therapeutically using PARP inhibitors in combination with androgen-deprivation therapy upfront in advanced or high-risk prostate cancer.Tumours with homologous recombination (HR) defects become sensitive to PARPi. Here, the authors show that androgen receptor (AR) regulates HR and AR inhibition activates the PARP pathway in vivo, thus inhibition of both AR and PARP is required for effective treatment of high risk prostate cancer.

Computational analysis of androgen receptor dependent radiosensitivity in prostate cancer

In this study, we quantitatively analyze the mechanism by which androgen deprivation therapy (ADT) is enhancing radiosensitivity in prostate cancer (PCa) patients. It has been shown in laboratory experiments, as well as in patient data in the literature, that the androgen receptor (AR) reduces the effectiveness of ionizing radiation treatment by enhancing the non-homologous end joining (NHEJ) repair of radiation damage. The suppression of AR by ADT suppresses the activity of NHEJ that leads to radiosensitivity in PCa patients. In this paper, we have studied this positive interaction between AR and NHEJ using mathematical models of the NHEJ that we have developed using both the experimental and clinical data for PCa. Our results show that the biological observation of suppression of AR by ADT leading to down-regulation of the first NHEJ protein Ku and NHEJ is a plausible biological mechanism that explains both the experimental and clinical observations in the literature. The presented analysis is the first step in quantitatively analyzing possible treatment scenarios to find the optimal treatment strategies for PCa using the combination treatment with ADT, NHEJ inhibitors, and IR.

Comparison of neoadjuvant vs concurrent/adjuvant androgen deprivation in men with high-risk prostate cancer receiving definitive radiation therapy

PURPOSE

It is unknown whether there is a benefit to starting androgen deprivation therapy (ADT) prior to rather than concurrently with definitive radiation therapy in men with high-risk prostate cancer. We studied the National Cancer Data Base to determine whether the timing of ADT impacts survival.

METHODS

Men diagnosed with high-risk prostate adenocarcinoma who received external beam radiation therapy (EBRT) to a dose of 70-81 Gy along with ADT from 2004-2011 were included. Those who started ADT 42-90 days before EBRT were identified as having received neoadjuvant hormonal therapy (N-HT) and those who received ADT from 14 days before their radiation until 84 days after the start of EBRT were categorized as receiving concurrent/adjuvant treatment (C-HT). We used the log-rank test to compare Kaplan-Meier survival curves and multivariable Cox regression to assess the impact of covariables on overall survival (OS).

RESULTS

Among 11,491 included patients, those receiving N-HT were 1 year older (p<0.001) and more likely to have Gleason 8-10 disease (p = 0.01) and cT3-4 disease (p = 0.002). Men receiving N-HT had a 5-year and median OS of 80.6% and 111.4 months, respectively, compared to 78.3% and 108.9 months, respectively, in those receiving C-HT (p = 0.03). This benefit remained significant on multivariable analysis (hazard ratio 0.86, 95% confidence interval 0.77-0.96, p = 0.008). Duration of ADT was not available to report.

CONCLUSIONS

External beam radiation therapy with N-HT was associated with improved overall survival compared to C-HT. This study is hypothesis-generating and further studies are needed to best qualify the sequencing of hormone therapy with the duration of treatment.

The Role of the Core Non-Homologous End Joining Factors in Carcinogenesis and Cancer

DNA double-strand breaks (DSBs) are deleterious DNA lesions that if left unrepaired or are misrepaired, potentially result in chromosomal aberrations, known drivers of carcinogenesis. Pathways that direct the repair of DSBs are traditionally believed to be guardians of the genome as they protect cells from genomic instability. The prominent DSB repair pathway in human cells is the non-homologous end joining (NHEJ) pathway, which mediates template-independent re-ligation of the broken DNA molecule and is active in all phases of the cell cycle. Its role as a guardian of the genome is supported by the fact that defects in NHEJ lead to increased sensitivity to agents that induce DSBs and an increased frequency of chromosomal aberrations. Conversely, evidence from tumors and tumor cell lines has emerged that NHEJ also promotes chromosomal aberrations and genomic instability, particularly in cells that have a defect in one of the other DSB repair pathways. Collectively, the data present a conundrum: how can a single pathway both suppress and promote carcinogenesis? In this review, we will examine NHEJ's role as both a guardian and a disruptor of the genome and explain how underlying genetic context not only dictates whether NHEJ promotes or suppresses carcinogenesis, but also how it alters the response of tumors to conventional therapeutics.

The survival impact of neoadjuvant hormonal therapy before radical prostatectomy for treatment of high-risk prostate cancer

BACKGROUND

Several randomized controlled trials assessed the outcomes of patients treated with neoadjuvant hormonal therapy (NHT) before radical prostatectomy (RP). The majority of them included mainly low and intermediate risk prostate cancer (PCa) without specifically assessing PCa-related death (PCRD). Thus, there is a lack of knowledge regarding a possible effect of NHT on PCRD in the high-risk PCa population. We aimed to analyze the effect of NHT on PCRD in a multicenter high-risk PCa population treated with RP, using a propensity-score adjustment.

METHODS

This is a retrospective multi-institutional study including patients with high-risk PCa defined as: clinical stage T3-4, PSA >20 ng ml^-1 or biopsy Gleason score 8-10. We compared PCRD between RP and NHT+RP using competing risks analysis. Correction for group differences was performed by propensity-score adjustment.

RESULTS

After application of the inclusion/exclusion criteria, 1573 patients remained for analysis; 1170 patients received RP and 403 NHT+RP. Median follow-up was 56 months (interquartile range 29-88). Eighty-six patients died of PCa and 106 of other causes. NHT decreased the risk of PCRD (hazard ratio (HR) 0.5; 95% confidence interval (CI) 0.32-0.80; P=0.0014). An interaction effect between NHT and radiotherapy (RT) was observed (HR 0.3; 95% CI 0.21-0.43; P<0.0008). More specifically, of patients who received adjuvant RT, those who underwent NHT+RP had decreased PCRD rates (2.3% at 5 year) compared to RP (7.5% at 5 year). The retrospective design and lack of specific information about NHT are possible limitations.

CONCLUSIONS

In this propensity-score adjusted analysis from a large high-risk PCa population, NHT before surgery significantly decreased PCRD. This effect appeared to be mainly driven by the early addition of RT post-surgery. The specific sequence of NHT+RP and adjuvant RT merits further study in the high-risk PCa population.

Molecular mechanisms underlying resistance to androgen deprivation therapy in prostate cancer

Prostate cancer (PCa) is the most widely diagnosed male cancer in the Western World and while low- and intermediate-risk PCa patients have a variety of treatment options, metastatic patients are limited to androgen deprivation therapy (ADT). This treatment paradigm has been in place for 75 years due to the unique role of androgens in promoting growth of prostatic epithelial cells via the transcription factor androgen receptor (AR) and downstream signaling pathways. Within 2 to 3 years of ADT, disease recurs-at which time, patients are considered to have castration-recurrent PCa (CR-PCa). A universal mechanism by which PCa becomes resistant to ADT has yet to be discovered. In this review article, we discuss underlying molecular mechanisms by which PCa evades ADT. Several major resistance pathways center on androgen signaling, including intratumoral and adrenal androgen production, AR-overexpression and amplification, expression of AR mutants, and constitutively-active AR splice variants. Other ADT resistance mechanisms, including activation of glucocorticoid receptor and impairment of DNA repair pathways are also discussed. New therapies have been approved for treatment of CR-PCa, but increase median survival by only 2-8 months. We discuss possible mechanisms of resistance to these new ADT agents. Finally, the practicality of the application of "precision oncology" to this continuing challenge of therapy resistance in metastatic or CR-PCa is examined. Empirical validation and clinical-based evidence are definitely needed to prove the superiority of "precision" treatment in providing a more targeted approach and curative therapies over the existing practices that are based on biological "cause-and-effect" relationship.

Expression of Ku70 predicts results of radiotherapy in prostate cancer

BACKGROUND AND PURPOSE

Therapeutic strategy for prostate cancer is decided according to T stage, Gleason score, and prostate-specific antigen (PSA) level. These clinical factors are not accurate enough to predict individual risk of local failure of prostate cancer after radiotherapy. Parameters involved with radiosensitivity are required to improve the predictive capability for local relapse.

PATIENTS AND METHODS

We analyzed 58 patients with localized adenocarcinoma of the prostate between August 2007 and October 2010 treated with 76 Gy of intensity-modulated radiotherapy (IMRT) as a discovery cohort and 42 patients between March 2001 and May 2007 treated with three-dimensional conformal radiotherapy (3D-CRT) as a validation cohort. Immunohistochemical examination for proteins involved in nonhomologous end-joining was performed using biopsy specimens.

RESULTS

Ku70 expression was not correlated with various clinical parameters, such as the Gleason score and D'amico risk classification, indicating that Ku70 expression was an independent prognostic factor. The predictive value for PSA relapse was markedly improved after the combination of Gleason score and Ku70 expression, as compared with Gleason score alone. In patients treated with radiotherapy and androgen deprivation therapy (ADT), no relapses were observed in patients with Gleason score ≤7 or low Ku70 expression. In contrast, patients with Gleason score ≥8 and high Ku70 expression had high PSA relapse rates. In the validation cohort, similar results were obtained.

CONCLUSION

Treatment with 76 Gy and ADT can be effective for patients with Gleason score ≤7 or low Ku70 expression, but is not enough for patients with Gleason score ≥8 and high Ku70 expression and, thus, require other treatment approaches.

Castration radiosensitizes prostate cancer tissue by impairing DNA double-strand break repair

Chemical castration improves responses to radiotherapy in prostate cancer, but the mechanism is unknown. We hypothesized that this radiosensitization is caused by castration-mediated down-regulation of nonhomologous end joining (NHEJ) repair of DNA double-strand breaks (DSBs). To test this, we enrolled 48 patients with localized prostate cancer in two arms of the study: either radiotherapy first or radiotherapy after neoadjuvant castration treatment. We biopsied patients at diagnosis and before and after castration and radiotherapy treatments to monitor androgen receptor, NHEJ, and DSB repair in verified cancer tissue. We show that patients receiving neoadjuvant castration treatment before radiotherapy had reduced amounts of the NHEJ protein Ku70, impaired radiotherapy-induced NHEJ activity, and higher amounts of unrepaired DSBs, measured by γ-H2AX foci in cancer tissues. This study demonstrates that chemical castration impairs NHEJ activity in prostate cancer tissue, explaining the improved response of patients with prostate cancer to radiotherapy after chemical castration.

Linking DNA Damage and Hormone Signaling Pathways in Cancer

DNA damage response and repair (DDR) is a tightly controlled process that serves as a barrier to tumorigenesis. Consequently, DDR is frequently altered in human malignancy, and can be exploited for therapeutic gain either through molecularly targeted therapies or as a consequence of therapeutic agents that induce genotoxic stress. In select tumor types, steroid hormones and cognate receptors serve as major drivers of tumor development/progression, and as such are frequently targets of therapeutic intervention. Recent evidence suggests that the existence of crosstalk mechanisms linking the DDR machinery and hormone signaling pathways cooperate to influence both cancer progression and therapeutic response. These underlying mechanisms and their implications for cancer management will be discussed.

Stem cells, biomarkers and genetic profiling: approaching future challenges in Urology

Urological research is facing future challenges, the most difficult one is the fast and meaningful transfer of the massive amount of data from research basic to clinical practice. Between the most important issues that research should focus in the next years are targeting of tumor stem cells, clinical application of biomarkers, and wide application of genetic profiling of urological neoplasms. Several clinical implications are expected, from diagnosis to selection of candidates for different treatment modalities, to modulation of sequential treatment plans, to prognosis. A number of clinical trials based on research data from the hottest issues are in the pipeline. In this review, we will focus on new insights from recent work worlwide in urological research, with particular attention to high-risk nonmuscle-invasive and muscle-invasive bladder cancer, prostate cancer, and kidney cancer. Cancer care is moving towards a personalized approach in patient management. The most important issues in urological research point strongly in this direction and show an enormous potential for the rapid landing of Urology in the era of personalized medicine.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

Androgen Deprivation Followed by Acute Androgen Stimulation Selectively Sensitizes AR-Positive Prostate Cancer Cells to Ionizing Radiation

PURPOSE

The current standard of care for patients with locally advanced prostate cancer is a combination of androgen deprivation and radiation therapy. Radiation is typically given with androgen suppression when testosterone levels are at their nadir. Recent reports have shown that androgen stimulation of androgen-deprived prostate cancer cells leads to formation of double-strand breaks (DSB). Here, we exploit this finding and investigate the extent and timing of androgen-induced DSBs and their effect on tumor growth following androgen stimulation in combination with ionizing radiation (IR).

EXPERIMENTAL DESIGN

Androgen-induced DNA damage was assessed by comet assays and γH2A.X foci formation. Effects of androgen stimulation and radiation were determined in vitro and in vivo with xenograft models.

RESULTS

We document that androgen treatment of androgen-deprived prostate cancer cell lines resulted in a dose- and time-dependent induction of widespread DSBs. Generation of these breaks was dependent on androgen receptor and topoisomerase II beta but not on cell-cycle progression. In vitro models demonstrated a synergistic interaction between IR and androgen stimulation when IR is given at a time point corresponding with high levels of androgen-induced DSB formation. Furthermore, in vivo studies showed a significant improvement in tumor growth delay when radiation was given shortly after androgen repletion in castrated mice.

CONCLUSIONS

These results suggest a potential cooperative effect and improved tumor growth delay with androgen-induced DSBs and radiation with implications for improving the therapeutic index of prostate cancer radiation therapy. Clin Cancer Res; 22(13); 3310-9. ©2016 AACRSee related commentary by Chua and Bristow, p. 3124.

In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio

BACKGROUND AND PURPOSE

Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT).

MATERIAL AND METHODS

We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay.

RESULTS

AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen.

CONCLUSIONS

This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

DNA-PKcs-Mediated Transcriptional Regulation Drives Prostate Cancer Progression and Metastasis

Emerging evidence demonstrates that the DNA repair kinase DNA-PKcs exerts divergent roles in transcriptional regulation of unsolved consequence. Here, in vitro and in vivo interrogation demonstrate that DNA-PKcs functions as a selective modulator of transcriptional networks that induce cell migration, invasion, and metastasis. Accordingly, suppression of DNA-PKcs inhibits tumor metastases. Clinical assessment revealed that DNA-PKcs is significantly elevated in advanced disease and independently predicts for metastases, recurrence, and reduced overall survival. Further investigation demonstrated that DNA-PKcs in advanced tumors is highly activated, independent of DNA damage indicators. Combined, these findings reveal unexpected DNA-PKcs functions, identify DNA-PKcs as a potent driver of tumor progression and metastases, and nominate DNA-PKcs as a therapeutic target for advanced malignancies.

Synergistic action of image-guided radiotherapy and androgen deprivation therapy

The combined use of androgen deprivation therapy (ADT) and image-guided radiotherapy (IGRT) can improve overall survival in aggressive, localized prostate cancer. However, owing to the adverse effects of prolonged ADT, it is imperative to identify the patients who would benefit from this combined-modality therapy relative to the use of IGRT alone. Opportunities exist for more personalized approaches in treating aggressive, locally advanced prostate cancer. Biomarkers--such as disseminated tumour cells, circulating tumour cells, genomic signatures and molecular imaging techniques--could identify the patients who are at greatest risk for systemic metastases and who would benefit from the addition of systemic ADT. By contrast, when biomarkers of systemic disease are not present, treatment could proceed using local IGRT alone. The choice of drug, treatment duration and timing of ADT relative to IGRT could be predicated on these personalized approaches to prostate cancer medicine. These novel treatment intensification and reduction strategies could result in improved prostate-cancer-specific survival and overall survival, without incurring the added expense of metabolic syndrome and other adverse effects of ADT in all patients.

The convergence of DNA damage checkpoint pathways and androgen receptor signaling in prostate cancer

It is increasingly clear that castration-resistant prostate cancer (PCa) is dependent on the androgen receptor (AR). This has led to the use of anti-androgen therapies that reduce endogenous steroid hormone production as well as the use of AR antagonists. However, the AR does not act in isolation and integrates with a milieu of cell-signaling proteins to affect cell biology. It is well established that cancer is a genetic disease resulting from the accumulation of mutations and chromosomal translocations that enables cancer cells to survive, proliferate, and disseminate. To maintain genomic integrity, there exists conserved checkpoint signaling pathways to facilitate cell cycle delay, DNA repair, and/or apoptosis in response to DNA damage. The AR interacts with, affects, and is affected by these DNA damage-response proteins. This review will focus on the connections between checkpoint signaling and the AR in PCa. We will describe what is known about how components of checkpoint signaling regulate AR activity and what questions still face the field.

DNA damage response and prostate cancer: defects, regulation and therapeutic implications

DNA damage response (DDR) includes the activation of numerous cellular activities that prevent duplication of DNA lesions and maintain genomic integrity, which is critical for the survival of normal and cancer cells. Specific genes involved in the DDR such as BRCA1/2 and P53 are mutated during prostate cancer progression, while various oncogenic signaling such as Akt and c-Myc are activated, enhancing the replication stress and increasing the genomic instability of cancer cells. These events may render prostate cancer cells particularly sensitive to inhibition of specific DDR pathways, such as PARP in homologous recombination (HR) DNA repair and Chk1 in cell cycle checkpoint and DNA repair, creating opportunities for synthetic lethality or synergistic cytotoxicity. Recent reports highlight the critical role of androgen receptor (AR) as a regulator of DDR genes, providing a rationale for combining DNA-damaging agents or targeted DDR inhibitors with hormonal manipulation or AR inhibition as treatment for aggressive disease. The aims of this review are to discuss specific DDR defects in prostate cancer that occur during disease progression, to summarize recent advances in understanding the regulation of DDR in prostate cancer, and to present potential therapeutic opportunities through combinational targeting of the intact components of DDR signaling pathways.