PARP Inhibitors in Prostate and Urothelial Cancers

Predictive and Prognostic Biomarkers and Tumor Antigens for Targeted Therapy in Urothelial Carcinoma

Urothelial carcinoma (UC) is the fourth most prevalent cancer amongst males worldwide. While patients with non-muscle-invasive disease have a favorable prognosis, 25% of UC patients present with locally advanced disease which is associated with a 10-15% 5-year survival rate and poor overall prognosis. Muscle-invasive bladder cancer (MIBC) is associated with about 50% 5 year survival when treated by radical cystectomy or trimodality therapy; stage IV disease is associated with 10-15% 5 year survival. Current therapeutic modalities for MIBC include neoadjuvant chemotherapy, surgery and/or chemoradiation, although patients with relapsed or refractory disease have a poor prognosis. However, the rapid success of immuno-oncology in various hematologic and solid malignancies offers new targets with tremendous therapeutic potential in UC. Historically, there were no predictive biomarkers to guide the clinical management and treatment of UC, and biomarker development was an unmet need. However, recent and ongoing clinical trials have identified several promising tumor biomarkers that have the potential to serve as predictive or prognostic tools in UC. This review provides a comprehensive summary of emerging biomarkers and molecular tumor targets including programmed death ligand 1 (PD-L1), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), fibroblast growth factor receptor (FGFR), DNA damage response and repair (DDR) mutations, poly (ADP-ribose) polymerase (PARP) expression and circulating tumor DNA (ctDNA), as well as their clinical utility in UC. We also evaluate recent advancements in precision oncology in UC, while illustrating limiting factors and challenges related to the clinical application of these biomarkers in clinical practice.

Poly (ADP-Ribose) Polymerase Inhibitors in Patients With Urothelial Cancer

Poly ADP-ribose polymerase inhibitors (PARPis) have clinical activity in several cancers. The rationale of their therapeutic use in urothelial cancer (UC) resides in the high homologous-recombination repair (HRR) deficiency (HRD) prevalence and potential cross-sensitivity with platinum-based chemotherapy (PBCT). This review aims to summarize and analyze trials exploring the activity of PARPis in UC, focusing on patients who may benefit from those agents, the best clinical setting for the treatment and the benefit of the association with immune-checkpoint inhibitors (ICIs). We included all the available trials analyzing the activity of PARPis in UC in neoadjuvant, adjuvant, first or subsequent lines, and maintenance setting. We included PARPis in monotherapy and in association with other agents. The results in the maintenance setting are intriguing: ATLANTIS trial showed signals of improved progression-free survival in patients with known HRR aberrations, although the Meet-URO12 trial, with its negative results, suggested the failure of clinical selection based on platinum sensitivity only. Single-agent PARPis in pretreated patients showed discouraging results in an unselected population of chemo-refractory patients. Concerning the association of PARPis with ICIs, several trials are exploring their role in platinum-naïve setting; the results in the advanced setting were globally negative. Prior selection of HRD status is essential to identify patients who might benefit from PARPis. The ideal clinical settings seem to be the maintenance treatment and the combination with ICIs in platinum-naïve patients. Definitive results of ongoing and further trials will delineate the position for PARPis, if any, in UC therapy.

Current and Future Landscape of Perioperative Treatment for Muscle-Invasive Bladder Cancer

Cisplatin-based neoadjuvant chemotherapy followed by radical cystectomy is the current standard of care for muscle-invasive bladder cancer (MIBC). However, less than half of patients are candidates for this treatment, and 50% will develop metastatic disease. Adjuvant chemotherapy could be offered if neoadjuvant treatment has not been administered for suitable patients. It is important to reduce the risk of systemic recurrence and improve the prognosis of localized MIBC. Systemic therapy for metastatic urothelial carcinoma has evolved in recent years. Immune checkpoint inhibitors and targeted agents, such as antibody-drug conjugates or FGFR inhibitors, are new therapeutic alternatives and have shown their benefit in advanced disease. Currently, several clinical trials are investigating the role of these drugs, as monotherapy and in combination with chemotherapy, in the neoadjuvant and adjuvant settings with promising outcomes. In addition, the development of predictive biomarkers could predict responses to neoadjuvant therapies.

Comparison of Homologous Recombination Repair Gene Next-Generation Sequencing Analysis in Patients With Metastatic Castration-Resistant Prostate Cancer Between Local and Central Laboratories in Korea

Background

Following success of the phase III PROfound trial, the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib was approved by the US Food and Drug Administration in May 2020 for adult patients with deleterious homologous recombination repair (HRR) gene-mutated metastatic castration-resistant prostate cancer (mCRPC). As locally adopted multigene panel next-generation sequencing (NGS) assays for selecting PARP inhibitor candidates have not been thoroughly evaluated, we compared the analytical performance of the FoundationOne CDx (Foundation Medicine, Inc., Cambridge, MA, USA) (central laboratory) and other NGS assays (local laboratory) with samples from the PROfound trial in Korea.

Methods

One hundred PROfound samples (60 HRR mutation [HRRm] cases and 40 non-HRRm cases) were analyzed. The results of HRR gene mutation analysis were compared between the FoundationOne CDx and two other NGS assays [SureSelect Custom Design assay (Agilent Technologies, Inc., Santa Clara, CA, USA) and Oncomine Comprehensive assay (Thermo Fisher Scientific, Inc., Waltham, MA, USA)].

Results

The positive percent agreement for single nucleotide variants (SNVs) and insertion/deletions (indels) between the central laboratory and local laboratory was 98.7%-100.0%. The negative percent agreement and overall percent agreement (OPA) for SNVs and indels between central and local laboratories were both 100%. Compared with that of the FoundationOne CDx assay, the OPA for copy number variations of the Oncomine Comprehensive and SureSelect Custom assays reached 99.8%-100%. Most mCRPC patients harboring a deleterious genetic variant were successfully identified with both local laboratory assays.

Conclusions

The NGS approach at a local laboratory showed comparable analytical performance for identifying HRRm status to the FoundationOne CDx assay used at the central laboratory.

Implications of targeted next-generation sequencing for bladder cancer: report of four cases

BACKGROUND

Bladder cancer is considered heterogeneous diseases with two major subgroups: non-muscle- invasive bladder cancer (NMIBC) and muscle invasive bladder cancer (MIBC). It is a major healthcare problem, and it is one of the leading causes of mortality worldwide. Genetic mutations are not only a cause for carcinogenesis but are also a way for treatment strategy. The present study aimed to investigate breast cancer (BRCA genes) tumor suppressor gene mutations in bladder cancer tissue and combined blood samples for patients who developed secondary tumor after or during trimodal therapy. Fresh tissue samples and their matched blood samples were collected from four patients with bladder cancer. The objective regions for the examined genes (BRCA1 and BRCA2) were sequenced using next-generation sequencing (NGS); generated BAM files were uploaded to the cloud-based Ionreporter server, and the Oncomine BRCA-specific plugin was used to analyze the paired normal and tumor sample for each patient using the default plugin parameters.

RESULTS

Intronic BRCA1 mutation c.5050-104 C >T was reported among the four investigated bladder cancer patients, and three somatic mutations were reported as follows: two of them were found to be benign rs1064793056 and rs28897679 on the Clinivar database and one nonsense pathogenic variant rs80357006. BRCA 2 gene mutation reported an exonic synonymous mutation rs397507876 in the tissue and germline DNA. Patients were treated with trimodal; however, three bladder cancer patients who reported BRCA mutations developed secondary tumors.

CONCLUSION

Identification of mutational BRCA changes in bladder cancer is a promising marker for better treatment strategy. Further studies are encouraged on a large cohort of bladder cancer patients to confirm our findings.

Characteristics of BRCA1/2 pathogenic germline mutations in chinese NSCLC patients and a comparison with HBOC

Background and purposes

The pathogenic BRCA1/2 germline mutations contributed to Hereditary Breast and Ovarian Cancer (HBOC) susceptibility. The features of BRCA1/2 germline mutations in non-small cell lung cancer (NSCLC) have not been systematically studied. Here we performed the first study investigating the characteristics of pathogenic BRCA1/2 germline mutations in Chinese NSCLC patients and compared them with those from Chinese HBOC.

Methods

Information on BRCA1/2 germline mutations from 9010 Chinese NSCLC patients were collected from available studies and analyzed, and compared with the BRCA1/2 germline mutations from Chinese HBOC BRCA1/2 database (LOVD database, 20,523 patients).

Results

19 (20 carriers, 0.22 %) pathogenic BRCA1 and 60 (66 carriers, 0.73 %) pathogenic BRCA2 germline mutations from NSCLC were identified. The carrier frequency of BRCA1/2 in Chinese NSCLC patients (86/9010 = 0.95 %) was significantly lower than that in Chinese breast and ovary cancer patients (1481/20,523 = 7.2 %) (P < 0.001). We found that frameshift and nonsense mutations were the predominant types of BRCA1/2 mutation in NSCLC, with no obvious hot spot mutations. No significant difference in the ratio of frameshift and nonsense mutations was found between BRCA1 and BRCA2 in NSCLC. 5 out of 19 mutations in BRCA1 and 23 out of 60 mutations in BRCA2 were novel mutations found in NSCLC that have never been reported in Chinese HBOC. A trend of higher percentage of BRCA1 nonsense mutations in the carriers was revealed in NSCLC compared with HBOC, while no such difference was found in BRCA2 in all types of mutations.

Conclusions

BRCA1/2 germline mutations from NSCLC exhibited distinct characteristics compared with those from HBOC in Chinese population, including lower carrier frequency than HBOC, higher ratio of nonsense mutations and carriers than HBOC, and novel BRCA1/2 germline mutations never found in HBOC.

The Tumor Microenvironment and Immunotherapy in Prostate and Bladder Cancer

Bladder cancer has been successfully treated with immunotherapy, whereas prostate cancer is a cold tumor with inadequate immune-related treatment response. A greater understanding of the tumor microenvironment and methods for harnessing the immune system to address tumor growth will be needed to improve immunotherapies for both prostate and bladder cancer. Here, we provide an overview of prostate and bladder cancer, including fundamental aspects of the disease and treatment, the elaborate cellular makeup of the tumor microenvironment, and methods for exploiting relevant pathways to develop more effective treatments.

Olaparib is effective for recurrent urothelial carcinoma with BRCA2 pathogenic germline mutation: first report on olaparib response in recurrent UC

Urothelial carcinoma (UC) is a common malignancy of the lower and upper urinary tract. Recurrent UC has poor prognosis due to delayed diagnosis and a lack of clinical management guidance, especially for upper urinary tract UC. Patients with germline or somatic BRCA1/2 mutations are a special population in UC. No evidence is available so far on the effectiveness of poly ADP-ribose polymerase inhibitor (PARPi) in this population. Here, we report a 60-year-old female patient diagnosed with left ureter high-grade UC. Recurrent lesions were found 20 months after radical surgery. Computed tomography (CT) examination showed a slightly high-density soft tissue mass (3.2 × 3.1 cm) on the left posterior wall of the abdomen (waist), soft tissue mass adjacent to the left inner wall of the pelvis (3.2 × 4.2 cm), and multiple enlarged lymph nodes to the left of abdominal aorta. A next-generation sequencing (NGS)-based 605-gene panel detected a novel BRCA2 pathogenic germline mutation c.1670T>A (p.L557*), and a series of somatic insertion and deletion (INDEL) mutations of BRCA1, RB1, and JAK2, and single nucleotide variation (SNV) mutations of TP53, KMT2D, MET, ROS1, and IL7R. The above lesions were reduced significantly or disappeared (partial response, PR) after a 3-month Olaparib treatment, and the patient’s general condition remained well. In conclusion, this study proved for the first time that PARPi was effective for UC treatment in patients carrying germline BRCA2 pathogenic mutations, providing new treatment options for such patients. In addition, the circulating tumor DNA (ctDNA) test can be used for drug selection and response monitoring in UC 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.

RAD51-Mediated DNA Homologous Recombination Is Independent of PTEN Mutational Status

Simple Summary

PTEN is an important tumor suppressor that is frequently mutated in malignancy. PTEN mutational loss has been associated with reduced RAD51 expression and homologous recombination deficiency (HRD), however; recent studies have failed to recapitulate these findings. Here, we show that RAD51 expression, foci formation and homologous recombination repair activity are unaltered in normal and tumorigenic PTEN-deficient cells and patient samples. Furthermore, we show that PTEN-deficient tumor cell lines do not synergize with the clinical PARP inhibitor olaparib, underscoring a need to discontinue its use in treating patients with PTEN-deficient tumors that do not otherwise exhibit HRD.

Abstract

PTEN mutation occurs in a variety of aggressive cancers and is associated with poor patient outcomes. Recent studies have linked mutational loss of PTEN to reduced RAD51 expression and function, a key factor involved in the homologous recombination (HR) pathway. However, these studies remain controversial, as they fail to establish a definitive causal link to RAD51 expression that is PTEN-dependent, while other studies have not been able to recapitulate the relationship between the PTEN expression and the RAD51/HR function. Resolution of this apparent conundrum is essential due to the clinically-significant implication that PTEN-deficient tumors may be sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) commonly used in the clinical management of BRCA-mutated and other HR-deficient (HRD) tumors. Methods: Primary Pten-deficient (and corresponding wild-type) mouse embryonic fibroblasts (MEFs) and astrocytes and PTEN-null human tumor cell lines and primary cells were assessed for RAD51 expression (via the Western blot analysis) and DNA damage repair analyses (via alkali comet and γH2AX foci assays). RAD51 foci analysis was used to measure HR-dependent DNA repair. Xrcc2-deficient MEFs served as an HR-deficient control, while the stable knockdown of RAD51 (shRAD51) served to control for the relative RAD51/HR-mediated repair and the phospho-53BP1 foci analysis served to confirm and measure non-homologous end joining (NHEJ) activity in PTEN-deficient and shRAD51-expressing (HRD) lines. Cell proliferation studies were used to measure any potential added sensitivity of PTEN-null cells to the clinically-relevant PARPi, olaparib. RAD51 levels and DNA damage response signaling were assessed in PTEN-mutant brain tumor initiating cells (BTICs) derived from primary and recurrent glioblastoma multiforme (GBM) patients, while expression of RAD51 and its paralogs were examined as a function of the PTEN status in the RNA expression datasets isolated from primary GBM tumor specimens and BTICs. Results: Pten knockout primary murine cells display unaltered RAD51 expression, endogenous and DNA strand break-induced RAD51 foci and robust DNA repair activity. Defective HR was only observed in the cells lacking Xrcc2. Likewise, human glioblastoma multiforme (GBM) cell lines with known PTEN deficiency (U87, PTEN-mutated; U251 and U373, PTEN-null) show apparent expression of RAD51 and display efficient DNA repair activity. Only GBM cells stably expressing shRNAs against RAD51 (shRAD51) display dysfunctional DNA repair activity and reduced proliferative capacity, which is exacerbated by PARPi treatment. Furthermore, GBM patient-derived BTICs displayed robust RAD51 expression and intact DNA damage response signaling in spite of PTEN-inactivating mutations. RNA expression analysis of primary GBM tissue specimens and BTICs demonstrate stable levels of RAD51 and its paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3, and DMC1), regardless of the PTEN mutational status. Conclusions: Our findings demonstrate definitively that PTEN loss does not alter the RAD51 expression, its paralogs, or the HR activity. Furthermore, deficiency in PTEN alone is not sufficient to impart enhanced sensitivity to PARPi associated with HRD. This study is the first to unequivocally demonstrate that PTEN deficiency is not linked to the RAD51 expression or the HR activity amongst primary neural and non-neural Pten-null cells, PTEN-deficient tumor cell lines, and primary PTEN-mutant GBM patient-derived tissue specimens and BTICs.

PARP Inhibitors in Biliary Tract Cancer: A New Kid on the Block?

Poly adenosine diphosphate-ribose polymerase inhibitors (PARPi) represent an effective therapeutic strategy for cancer patients harboring germline and somatic aberrations in DNA damage repair (DDR) genes. BRCA1/2 mutations occur at 1–7% across biliary tract cancers (BTCs), but a broader spectrum of DDR gene alterations is reported in 28.9–63.5% of newly diagnosed BTC patients. The open question is whether alterations in genes that are well established to have a role in DDR could be considered as emerging predictive biomarkers of response to platinum compounds and PARPi. Currently, data regarding PARPi in BTC patients harboring BRCA and DDR mutations are sparse and anecdotal; nevertheless, a variety of clinical trials are testing PARPi as monotherapy or in combination with other anticancer agents. In this review, we provide a comprehensive overview regarding the genetic landscape of DDR pathway deficiency, state of the art and future therapeutic implications of PARPi in BTC, looking at combination strategies with immune-checkpoint inhibitors and other anticancer agents in order to improve survival and quality of life in BTC patients.

Combination therapy in advanced urothelial cancer: the role of PARP, HER-2 and mTOR inhibitors

INTRODUCTION

Despite significant advances in the treatment of metastatic urothelial carcinoma, including the advent of immune checkpoint inhibitors, this disease is still challenging to treat and associated poor outcomes remain. Genomic characterization of advanced-stage urothelial carcinoma is widening the field of potential treatments due to the identification of novel biologic drivers.

AREAS COVERED

In this review, we explore the role of PARP, HER-2, and mTOR inhibitors in the therapeutic scenario of advanced urothelial carcinoma, as these pathways are frequently altered in urothelial carcinoma. We report ongoing clinical trials involving these agents, either in monotherapy or in combination with other compounds, highlighting the dynamic scenario of metastatic urothelial carcinoma treatment.

EXPERT OPINION

Several challenges need to be faced in the development of new potential therapeutic strategies, such as inter/intratumoral heterogeneity and the lack of validated biomarkers.

Current Strategies and Novel Therapeutic Approaches for Metastatic Urothelial Carcinoma

Urothelial carcinoma (UC) is a frequent cause of cancer-related deaths worldwide. Metastatic UC has been historically associated with poor prognosis, with a median overall survival of approximately 15 months and a 5-year survival rate of 18%. Although platinum-based chemotherapy remains the mainstay of medical treatment for patients with metastatic UC, chemotherapy clinical trials produced modest benefit with short-lived, disappointing responses. In recent years, the better understanding of the role of immune system in cancer control has led to the development and approval of several immunotherapeutic approaches in UC therapy, where immune checkpoint inhibitors have been revolutionizing the treatment of metastatic UC. Because of a better tumor molecular profiling, FGFR inhibitors, PARP inhibitors, anti-HER2 agents, and antibody drug conjugates targeting Nectin-4 are also emerging as new therapeutic options. Moreover, a wide number of trials is ongoing with the aim to evaluate several other alterations and pathways as new potential targets in metastatic UC. In this review, we will discuss the recent advances and highlight future directions of the medical treatment of UC, with a particular focus on recently published data and ongoing active and recruiting trials.