Alternate therapeutic pathways for PARP inhibitors and potential mechanisms of resistance

Olaparib reverses prostate cancer resistance to Rapamycin by promoting macrophage polarization towards the M1 phenotype

Prostate cancer (PCa) is the most common non-cutaneous malignancy and the second leading cause of cancer-related death in men. Despite its prevalence, treatment outcomes are often unsatisfactory, necessitating the search for more effective therapeutic approaches. mTOR inhibitor Rapamycin (RAPA) has shown promise in managing PCa, but the emergence of resistance often undermines its long-term effectiveness. Recent studies suggest that poly ADP-ribose polymerase (PARP) inhibitor Olaparib (OLP) may overcome drug resistance in various tumor types. This study aims to assess the efficacy of OLP in treating RAPA-resistant PCa, with a specific focus on elucidating its underlying molecular mechanisms. This study utilized drug exposure and concentration escalation experiments to establish human RAPA-resistant PCa cell line (PC-3R) based on the human PCa cell line (PC-3). PC-3R cell lines were screened through a cloning assay. The efficacy of OLP in RAPA-resistant PCa, as well as its regulatory impact on tumor-associated macrophages (TAMs), was evaluated through a combination of real-time PCR, ELISA, immunohistochemistry, and fluorescence experiments. This study unveiled that the combination of OLP and RAPA effectively suppressed the proliferation, stemness, invasion, angiogenesis, apoptosis resistance, and anti-oxidative stress capacity of RAPA-resistant PCa. Additionally, it demonstrated the capacity of OLP to regulate macrophage polarization within the tumor microenvironment and reverse drug resistance to RAPA in PCa. The findings of this study lay a theoretical foundation for the potential utilization of OLP in the treatment of RAPA-resistant PCa, offering substantial academic significance and promising application prospects.

Heterogeneity of the Treatment Effect with PARP Inhibitors in Metastatic Castration-resistant Prostate Cancer: A Living Interactive Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE

Selection of patients harboring mutations in homologous recombination repair (HRR) genes for treatment with a PARP inhibitor (PARPi) is challenging in metastatic castration-resistant prostate cancer (mCRPC). To gain further insight, we quantitatively assessed the differential efficacy of PARPi therapy among patients with mCRPC and different HRR gene mutations.

METHODS

This living meta-analysis (LMA) was conducted using the Living Interactive Evidence synthesis framework. We included clinical trials assessing PARPi as monotherapy in pretreated mCRPC or in combination with an androgen receptor pathway inhibitor (ARPI) in treatment-naïve patients. Random-effects meta-analyses were performed for a priori subgroups stratified by HRR status, BRCA status, and each gene.

KEY FINDINGS AND LIMITATIONS

This first report for our LMA includes 13 trials (4278 patients). Among patients with pretreated mCRPC receiving PARPi monotherapy, the tumor response rate per 100 person-months was numerically higher for patients with BRCA2 (50% prostate-specific antigen response [PSA50%] 3.3; objective response rate [ORR] 3.3), BRCA1 (PSA50% 1.2; ORR 2.0), or PALB2 (PSA50% 3.3; ORR 1.4) alterations than for patients with ATM (PSA50% 0.4; ORR 0.3), CDK12 (PSA50% 0.2; ORR 0.2), or CHEK2 (PSA50% 1.0; ORR 0.7) alterations. Among patients receiving PARPi + ARPI, a significant radiographic progression-free survival benefit was observed in those with BRCA (hazard ratio [HR] 0.28, 95% confidence interval [CI] 0.13-0.62) or CDK12 (HR 0.58, 95% CI 0.35-0.95) alterations, but not in patients with PALB2 (HR 0.53, 95% CI 0.21-1.32), ATM (HR 0.93, 95% CI 0.57-1.53), or CHEK2 (HR 0.92, 95% CI 0.53-1.61) alterations. An overall survival benefit was observed for patients with BRCA alterations (HR 0.47, 95% CI 0.31-0.71) after adjustment for crossover and subsequent therapy, but not for patients with PALB2 (HR 0.33, 95% CI 0.10-1.16), ATM (HR 0.97, 95% CI 0.57-1.67), CDK12 (HR 0.80, 95% CI 0.36-1.78), or CHEK2 (HR 0.81, 95% CI 0.37-1.75) alterations.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Our LMA delivers information on the effect of PARPi therapy in relation to specific gene alterations in mCRPC via an interactive web platform. The evidence suggests the greatest PARPi benefit in patients with BRCA alterations, a strong signal of benefit in patients with PALB2 or CDK12 alterations, and no benefit in patients with ATM or CHEK2 alterations.

The complex universe of inactive PARP1

Poly(ADP-ribose) polymerase 1 (PARP1) is a crucial member of the PARP family, which modifies targets through ADP-ribosylation and plays key roles in a variety of biological processes. PARP inhibitors (PARPis) hinder ADP-ribosylation and lead to the retention of PARP1 at the DNA lesion (also known as trapping), which underlies their toxicity. However, inhibitors and mutations that make PARP1 inactive do not necessarily correlate with trapping potency, challenging the current understanding of inactivation-caused trapping. Recent studies on mouse models indicate that both trapping and non-trapping inactivating mutations of PARP1 lead to embryonic lethality, suggesting the unexpected toxicity of the current inhibition strategy. The allosteric model, complicated automodification, and various biological functions of PARP1 all contribute to the complexity of PARP1 inactivation.

Poly-ADP-ribosylation dynamics, signaling, and analysis

ADP-ribosylation is a reversible post-translational modification that plays a role as a signaling mechanism in various cellular processes. This modification is characterized by its structural diversity, highly dynamic nature, and short half-life. Hence, it is tightly regulated at many levels by cellular factors that fine-tune its formation, downstream signaling, and degradation that together impacts cellular outcomes. Poly-ADP-ribosylation is an essential signaling mechanism in the DNA damage response that mediates the recruitment of DNA repair factors to sites of DNA damage via their poly-ADP-ribose (PAR)-binding domains (PBDs). PAR readers, encoding PBDs, convey the PAR signal to mediate cellular outcomes that in some cases can be dictated by PAR structural diversity. Several PBD families have been identified, each with variable PAR-binding affinity and specificity, that also recognize and bind to distinct parts of the PAR chain. PARylation signaling has emerged as an attractive target for the treatment of specific cancer types, as the inhibition of PAR formation or degradation can selectively eliminate cancer cells with specific DNA repair defects and can enhance radiation or chemotherapy response. In this review, we summarize the key players of poly-ADP-ribosylation and its regulation and highlight PBDs as tools for studying PARylation dynamics and the expanding potential to target PARylation signaling in cancer treatment.

Pharmacological USP2 targeting suppresses ovarian cancer growth by potentiating apoptosis and ferroptosis

Ovarian cancer is a frequently observed type of gynaecologic malignancy generally associated with poor prognosis around the world. Ubiquitin-specific proteases (USPs) form the largest subfamily of deubiquitylating enzymes and have emerged as potential therapeutic targets against human cancers. Through a systematic analysis of the prognostic significance of USP expression, USP2 was found to be inversely correlated with patient survival in ovarian cancer. Accordingly, we investigated the effects of pharmacological inhibition of USP2 on ovarian cancer by exploiting its small molecule inhibitor ML364. Our findings show that ML364 effectively hindered ovarian cancer growth and migration using a series of in vitro assays. In addition to apoptosis induction, ML364 also sensitized ovarian cancer cells to ferroptosis. Mechanistically, ML364 treatment resulted in cyclin D1 downregulation, increased poly (ADP-ribose) polymerase (PARP) cleavage, and elevated ROS levels in ovarian cancer cells. Collectively, our findings suggest USP2 as a potential therapeutic target in ovarian cancer, and hence, its pharmacological inhibition warrants further investigation.

PARP inhibitors in prostate cancer: clinical applications

Despite recent advancements in the treatment of metastatic castrate-resistant prostate cancer (mCRPC), this disease remains lethal. A novel family of targeted pharmaceuticals known as poly-ADP-ribose polymerase (PARP) inhibitors has been developed to treat mCRPC patients with homologous recombination repair (HRR) gene alterations. The FDA recently approved olaparib and rucaparib for treating mCRPC patients with HRR gene alterations. Ongoing trials are investigating combination therapies involving PARP inhibitors combined with radiation, chemotherapy, immunotherapy, and androgen receptor signaling inhibitors (ARSIs) to improve the effectiveness of PARP inhibitors and broaden the range of patients who can benefit from the treatment. This review provides an overview of the development of PARP inhibitors in prostate cancer and analyzes the mechanisms underlying their resistance.

Ecological and evolutionary dynamics to design and improve ovarian cancer treatment

Ovarian cancer ecosystems are exceedingly complex, consisting of a high heterogeneity of cancer cells. Development of drugs such as poly ADP-ribose polymerase (PARP) inhibitors, targeted therapies and immunotherapies offer more options for sequential or combined treatments. Nevertheless, mortality in metastatic ovarian cancer patients remains high because cancer cells consistently develop resistance to single and combination therapies, urging a need for treatment designs that target the evolvability of cancer cells. The evolutionary dynamics that lead to resistance emerge from the complex tumour microenvironment, the heterogeneous populations, and the individual cancer cell's plasticity. We propose that successful management of ovarian cancer requires consideration of the ecological and evolutionary dynamics of the disease. Here, we review current options and challenges in ovarian cancer treatment and discuss principles of tumour evolution. We conclude by proposing evolutionarily designed strategies for ovarian cancer, with the goal of integrating such principles with longitudinal, quantitative data to improve the treatment design and management of drug resistance. KEY POINTS/HIGHLIGHTS: Tumours are ecosystems in which cancer and non-cancer cells interact and evolve in complex and dynamic ways. Conventional therapies for ovarian cancer inevitably lead to the development of resistance because they fail to consider tumours' heterogeneity and cellular plasticity. Eco-evolutionarily designed therapies should consider cancer cell plasticity and patient-specific characteristics to improve clinical outcome and prevent relapse.

NLRP4 renders pancreatic cancer resistant to olaparib through promotion of the DNA damage response and ROS-induced autophagy

Olaparib has been approved as a therapeutic option for metastatic pancreatic ductal adenocarcinoma patients with BRCA1/2 mutations. However, a significant majority of pancreatic cancer patients have inherent resistance or develop tolerance to olaparib. It is crucial to comprehend the molecular mechanism underlying olaparib resistance to facilitate the development of targeted therapies for pancreatic cancer. In this study, we conducted an analysis of the DepMap database to investigate gene expression variations associated with olaparib sensitivity. Our findings revealed that NLRP4 upregulation contributes to increased resistance to olaparib in pancreatic cancer cells, both in vitro and in vivo. RNA sequencing and Co-IP MS analysis revealed that NLRP4 is involved in the DNA damage response and autophagy pathway. Our findings confirmed that NLRP4 enhances the capacity for DNA repair and induces the production of significant levels of reactive oxygen species (ROS) and autophagy in response to treatment with olaparib. Specifically, NLRP4-generated mitochondrial ROS promote autophagy in pancreatic cancer cells upon exposure to olaparib. However, NLRP4-induced ROS do not affect DNA damage. The inhibition of mitochondrial ROS using MitoQ and autophagy using chloroquine (CQ) may render cells more susceptible to the effects of olaparib. Taken together, our findings highlight the significant roles played by NLRP4 in the processes of autophagy and DNA repair when pancreatic cancer cells are treated with olaparib, thereby suggesting the potential therapeutic utility of olaparib in pancreatic cancer patients with low NLRP4 expression.

Promising therapy for neuroendocrine prostate cancer: current status and future directions

Neuroendocrine prostate cancer (NEPC) is a highly aggressive variant of castration-resistant prostate cancer. It is characterized by low or no expression of the androgen receptor (AR), activation of AR-independent signaling, and increased neuroendocrine phenotype. Most of NEPC is induced by treatment of androgen deprivation therapy and androgen receptor pathway inhibitors (ARPIs). Currently, the treatment of NEPC follows the treatment strategy for small-cell lung cancer, lacking effective drugs and specific treatment options. This review summarizes potential novel targets and therapies for NEPC treatment, including epigenetic regulators (zeste homolog 2 inhibitors, lysine-specific demethylase 1 inhibitors), aurora kinase A inhibitors, poly-ADP-ribose polymerase inhibitors, delta-like ligand 3 targeted therapies, a combination of immunotherapies, etc. Other promising targets and future directions are also discussed in this review. These novel targets and therapies may provide new opportunities for the treatment of NEPC.

Nucleolytic processing of abasic sites underlies PARP inhibitor hypersensitivity in ALC1-deficient BRCA mutant cancer cells

Clinical success with poly (ADP-ribose) polymerase inhibitors (PARPi) is impeded by inevitable resistance and associated cytotoxicity. Depletion of Amplified in Liver Cancer 1 (ALC1), a chromatin-remodeling enzyme, can overcome these limitations by hypersensitizing BReast CAncer genes 1/2 (BRCA1/2) mutant cells to PARPi. Here, we demonstrate that PARPi hypersensitivity upon ALC1 loss is reliant on its role in promoting the repair of chromatin buried abasic sites. We show that ALC1 enhances the ability of the abasic site processing enzyme, Apurinic/Apyrimidinic endonuclease 1 (APE1) to cleave nucleosome-occluded abasic sites. However, unrepaired abasic sites in ALC1-deficient cells are readily accessed by APE1 at the nucleosome-free replication forks. APE1 cleavage leads to fork breakage and trapping of PARP1/2 upon PARPi treatment, resulting in hypersensitivity. Collectively, our studies reveal how cells overcome the chromatin barrier to repair abasic lesions and uncover cleavage of abasic sites as a mechanism to overcome limitations of PARPi.

Expanding the Perspective on PARP1 and Its Inhibitors in Cancer Therapy: From DNA Damage Repair to Immunomodulation

The emergence of PARP inhibitors as a therapeutic strategy for tumors with high genomic instability, particularly those harboring BRCA mutations, has advanced cancer treatment. However, recent advances have illuminated a multifaceted role of PARP1 beyond its canonical function in DNA damage repair. This review explores the expanding roles of PARP1, highlighting its crucial interplay with the immune system during tumorigenesis. We discuss PARP1's immunomodulatory effects in macrophages and T cells, with a particular focus on cytokine expression. Understanding these immunomodulatory roles of PARP1 not only holds promise for enhancing the efficacy of PARP inhibitors in cancer therapy but also paves the way for novel treatment regimens targeting immune-mediated inflammatory diseases.

Suppression of CTC1 inhibits hepatocellular carcinoma cell growth and enhances RHPS4 cytotoxicity

BACKGROUND

Although DNA repair mechanisms function to maintain genomic integrity, in cancer cells these mechanisms may negatively affect treatment efficiency. The strategy of targeting cancer cells via inhibiting DNA damage repair has been successfully used in breast and ovarian cancer using PARP inhibitors. Unfortunately, such strategies have not yet yielded results in liver cancer. Hepatocellular carcinoma (HCC), the most common type of liver cancer, is a treatment-resistant malignancy. Despite the development of guided therapies, treatment regimens for advanced HCC patients still fall short of the current need and significant problems such as cancer relapse with resistance still exist. In this paper, we targeted telomeric replication protein CTC1, which is responsible for telomere maintenance.

METHODS

CTC expression was analyzed using tumor and matched-tissue RNA-sequencing data from TCGA and GTEx. In HCC cell lines, q-RT-PCR and Western blotting were used to detect CTC1 expression. The knock-down of CTC1 was achieved using lentiviral plasmids. The effects of CTC1 silencing on HCC cells were analyzed by flow cytometry, MTT, spheroid and colony formation assays.

RESULTS

CTC1 is significantly downregulated in HCC tumor samples. However, CTC1 protein levels were higher in sorafenib-resistant cell lines compared to the parental groups. CTC1 inhibition reduced cell proliferation in sorafenib-resistant HCC cell lines and diminished their spheroid and colony forming capacities. Moreover, these cells were more sensitive to single and combined drug treatment with G4 stabilizer RHPS4 and sorafenib.

CONCLUSION

Our results suggest that targeting CTC1 might be a viable option for combinational therapies designed for sorafenib resistant HCC patients.

Functional Characterization of the Human BRCA1 ∆11 Splicing Isoforms in Yeast

BRCA1, a crucial tumor suppressor gene, has several splicing isoforms, including Δ9-11, Δ11, and Δ11q, which lack exon 11, coding for significant portions of the protein. These isoforms are naturally present in both normal and cancerous cells, exhibiting altered activity compared to the full-length BRCA1. Despite this, the impact on cancer risk of the germline intronic variants promoting the exclusive expression of these Δ11 isoforms remains uncertain. Consequently, they are classified as variants of uncertain significance (VUS), posing challenges for traditional genetic classification methods due to their rarity and complexity. Our research utilizes a yeast-based functional assay, previously validated for assessing missense BRCA1 variants, to compare the activity of the Δ11 splicing isoforms with known pathogenic missense variants. This approach allows us to elucidate the functional implications of these isoforms and determine whether their exclusive expression could contribute to increased cancer risk. By doing so, we aim to provide insights into the pathogenic potential of intronic VUS-generating BRCA1 splicing isoforms and improve the classification of BRCA1 variants.

PARP inhibition leads to synthetic lethality with key splicing-factor mutations in myelodysplastic syndromes

BACKGROUND

Splicing factors are frequently mutated in patients with myelodysplastic syndromes and acute myeloid leukaemia. Recent studies have revealed convergent molecular defects caused by splicing factor mutations, among which R-loop dysregulation and resultant genome instability are suggested as contributing factors to disease progression. On the other hand, understanding how mutant cells survive upon aberrant R-loop formation and genome instability is essential for developing novel therapeutics.

METHODS

The immunoprecipitation was performed to identify R-loops in association with PARP1/poly-ADP-ribosylation. The western blot, immunofluorescence, and flow cytometry assays were used to test the cell viability, cell cycle arrest, apoptosis, and ATM activation in mutant cells following the treatment of the PARP inhibitor. The Srsf2(P95H) knock-in murine hematopoietic cells and MLL-AF9 transformed leukaemia model were generated to investigate the potential of the PARP inhibitor as a therapy for haematological malignancies.

RESULTS

The disease-causing mutations in SRSF2 activate PARP and elevate the overall poly-ADP-ribosylation levels of proteins in response to R-loop dysregulation. In accordance, mutant cells are more vulnerable to the PARP inhibitors in comparison to the wild-type counterpart. Notably, the synthetic lethality was further validated in the Srsf2(P95H) knock-in murine hematopoietic cell and MLL-AF9 leukaemia model.

CONCLUSIONS

Our findings suggest that mutant cells antagonise the genome threat caused by R-loop disruption by PARP activation, thus making PARP targeting a promising therapeutic strategy for myeloid cancers with mutations in SRSF2.

Tumor Treating Fields (TTFields) induce homologous recombination deficiency in ovarian cancer cells, thus mitigating drug resistance

Background

Ovarian cancer is the leading cause of mortality among gynecological malignancies. Carboplatin and poly (ADP-ribose) polymerase inhibitors (PARPi) are often implemented in the treatment of ovarian cancer. Homologous recombination deficient (HRD) tumors demonstrate increased sensitivity to these treatments; however, many ovarian cancer patients are homologous recombination proficient (HRP). TTFields are non-invasive electric fields that induce an HRD-like phenotype in various cancer types. The current study aimed to investigate the impact of TTFields applied together with carboplatin or PARPi (olaparib or niraparib) in preclinical ovarian cancer models.

Methods

A2780 (HRP), OVCAR3 (HRD), and A2780cis (platinum-resistant) human ovarian cancer cells were treated in vitro with TTFields (1 V/cm RMS, 200 kHz, 72 h), alone or with various drug concentrations. Treated cells were measured for cell count, colony formation, apoptosis, DNA damage, expression of DNA repair proteins, and cell cycle. In vivo, ID8-fLuc (HRP) ovarian cancer cells were inoculated intraperitoneally to C57BL/6 mice, which were then treated with either sham, TTFields (200 kHz), olaparib (50 mg/kg), or TTFields plus olaparib; over a period of four weeks. Tumor growth was analyzed using bioluminescent imaging at treatment cessation; and survival analysis was performed.

Results

The nature of TTFields-drug interaction was dependent on the drug's underlying mechanism of action and on the genetic background of the cells, with synergistic interactions between TTFields and carboplatin or PARPi seen in HRP and resistant cells. Treated cells demonstrated elevated levels of DNA damage, accompanied by G2/M arrest, and induction of an HRD-like phenotype. In the tumor-bearing mice, TTFields and olaparib co-treatment resulted in reduced tumor volume and a survival benefit relative to olaparib monotherapy and to control.

Conclusion

By inducing an HRD-like phenotype, TTFields sensitize HRP and resistant ovarian cancer cells to treatment with carboplatin or PARPi, potentially mitigating a-priori and de novo drug resistance, a major limitation in ovarian cancer treatment.

Nucleolar Localization of the RNA Helicase DDX21 Predicts Survival Outcomes in Gynecologic Cancers

Cancer cells with DNA repair defects (e.g., BRCA1/2 mutant cells) are vulnerable to PARP inhibitors (PARPi) due to induction of synthetic lethality. However, recent clinical evidence has shown that PARPi can prevent the growth of some cancers irrespective of their BRCA1/2 status, suggesting alternative mechanisms of action. We previously discovered one such mechanism in breast cancer involving DDX21, an RNA helicase that localizes to the nucleoli of cells and is a target of PARP1. We have now extended this observation in endometrial and ovarian cancers and provided links to patient outcomes. When PARP1-mediated ADPRylation of DDX21 is inhibited by niraparib, DDX21 is mislocalized to the nucleoplasm resulting in decreased rDNA transcription, which leads to a reduction in ribosome biogenesis, protein translation, and ultimately endometrial and ovarian cancer cell growth. High PARP1 expression was associated with high nucleolar localization of DDX21 in both cancers. High nucleolar DDX21 negatively correlated with calculated IC50s for niraparib. By studying endometrial cancer patient samples, we were able to show that high DDX21 nucleolar localization was significantly associated with decreased survival. Our study suggests that the use of PARPi as a cancer therapeutic can be expanded to further types of cancers and that DDX21 localization can potentially be used as a prognostic factor and as a biomarker for response to PARPi.

SIGNIFICANCE

Currently, there are no reliable biomarkers for response to PARPi outside of homologous recombination deficiency. Herein we present a unique potential biomarker, with clear functional understanding of the molecular mechanism by which DDX21 nucleolar localization can predict response to PARPi.

Shaping DNA damage responses: Therapeutic potential of targeting telomeric proteins and DNA repair factors in cancer

Shelterin proteins regulate genomic stability by preventing inappropriate DNA damage responses (DDRs) at telomeres. Unprotected telomeres lead to persistent DDR causing cell cycle inhibition, growth arrest, and apoptosis. Cancer cells rely on DDR to protect themselves from DNA lesions and exogenous DNA-damaging agents such as chemotherapy and radiotherapy. Therefore, targeting DDR machinery is a promising strategy to increase the sensitivity of cancer cells to existing cancer therapies. However, the success of these DDR inhibitors depends on other mutations, and over time, patients develop resistance to these therapies. This suggests the need for alternative approaches. One promising strategy is co-inhibiting shelterin proteins with DDR molecules, which would offset cellular fitness in DNA repair in a mutation-independent manner. This review highlights the associations and dependencies of the shelterin complex with the DDR proteins and discusses potential co-inhibition strategies that might improve the therapeutic potential of current inhibitors.

Quinoxaline derivatives: Recent discoveries and development strategies towards anticancer agents

Cancer is a leading cause of death and a major health problem worldwide. While many effective anticancer agents are available, most drugs currently on the market are not specific, raising issues like the common side effects of chemotherapy. However, recent research hold promises for the development of more efficient and safer anticancer drugs. Quinoxaline and its derivatives are becoming recognized as a novel class of chemotherapeutic agents with activity against different tumors. The present review compiles and discusses studies concerning the therapeutic potential of the anticancer activity of quinoxaline derivatives, covering articles published between January 2018 and January 2023.

Exploration of poly (ADP-ribose) polymerase inhibitor resistance in the treatment of BRCA1/2-mutated cancer

Breast cancer susceptibility 1/2 (BRCA1/2) genes play a crucial role in DNA damage repair, yet mutations in these genes increase the susceptibility to tumorigenesis. Exploiting the synthetic lethality mechanism between BRCA1/2 mutations and poly(ADP-ribose) polymerase (PARP) inhibition has led to the development and clinical approval of PARP inhibitor (PARPi), representing a milestone in targeted therapy for BRCA1/2 mutant tumors. This approach has paved the way for leveraging synthetic lethality in tumor treatment strategies. Despite the initial success of PARPis, resistance to these agents diminishes their efficacy in BRCA1/2-mutant tumors. Investigations into PARPi resistance have identified replication fork stability and homologous recombination repair as key factors sensitive to PARPis. Additionally, studies suggest that replication gaps may also confer sensitivity to PARPis. Moreover, emerging evidence indicates a correlation between PARPi resistance and cisplatin resistance, suggesting a potential overlap in the mechanisms underlying resistance to both agents. Given these findings, it is imperative to explore the interplay between replication gaps and PARPi resistance, particularly in the context of platinum resistance. Understanding the impact of replication gaps on PARPi resistance may offer insights into novel therapeutic strategies to overcome resistance mechanisms and enhance the efficacy of targeted therapies in BRCA1/2-mutant tumors.

EMQN best practice guidelines for genetic testing in hereditary breast and ovarian cancer

Hereditary Breast and Ovarian Cancer (HBOC) is a genetic condition associated with increased risk of cancers. The past decade has brought about significant changes to hereditary breast and ovarian cancer (HBOC) diagnostic testing with new treatments, testing methods and strategies, and evolving information on genetic associations. These best practice guidelines have been produced to assist clinical laboratories in effectively addressing the complexities of HBOC testing, while taking into account advancements since the last guidelines were published in 2007. These guidelines summarise cancer risk data from recent studies for the most commonly tested high and moderate risk HBOC genes for laboratories to refer to as a guide. Furthermore, recommendations are provided for somatic and germline testing services with regards to clinical referral, laboratory analyses, variant interpretation, and reporting. The guidelines present recommendations where 'must' is assigned to advocate that the recommendation is essential; and 'should' is assigned to advocate that the recommendation is highly advised but may not be universally applicable. Recommendations are presented in the form of shaded italicised statements throughout the document, and in the form of a table in supplementary materials (Table S4). Finally, for the purposes of encouraging standardisation and aiding implementation of recommendations, example report wording covering the essential points to be included is provided for the most common HBOC referral and reporting scenarios. These guidelines are aimed primarily at genomic scientists working in diagnostic testing laboratories.

Current trends in clinical trials and the development of small molecule epigenetic inhibitors as cancer therapeutics

Epigenetic mechanisms control and regulate normal chromatin structure and gene expression patterns, with epigenetic dysregulation observed in many different cancer types. Importantly, epigenetic modifications are reversible, offering the potential to silence oncogenes and reactivate tumor suppressors. Small molecule drugs manipulating these epigenetic mechanisms are at the leading edge of new therapeutic options for cancer treatment. The clinical use of histone deacetyltransferases inhibitors (HDACi) demonstrates the effectiveness of targeting epigenetic mechanisms for cancer treatment. Notably, the development of new classes of inhibitors, including lysine acetyltransferase inhibitors (KATi), are the future of epigenetic-based therapeutics. We outline the progress of current classes of small molecule epigenetic drugs for use against cancer (preclinical and clinical) and highlight the potential market growth in epigenetic-based therapeutics.

A review of poly(ADP-ribose)polymerase-1 (PARP1) role and its inhibitors bearing pyrazole or indazole core for cancer therapy

Cancer is a disease with a high mortality rate characterized by uncontrolled proliferation of abnormal cells. The hallmarks of cancer evidence the acquired cells characteristics that promote the growth of malignant tumours, including genomic instability and mutations, the ability to evade cellular death and the capacity of sustaining proliferative signalization. Poly(ADP-ribose) polymerase-1 (PARP1) is a protein that plays key roles in cellular regulation, namely in DNA damage repair and cell survival. The inhibition of PARP1 promotes cellular death in cells with homologous recombination deficiency, and therefore, the interest in PARP protein has been rising as a target for anticancer therapies. There are already some PARP1 inhibitors approved by Food and Drug Administration (FDA), such as Olaparib and Niraparib. The last compound presents in its structure an indazole core. In fact, pyrazoles and indazoles have been raising interest due to their various medicinal properties, namely, anticancer activity. Derivatives of these compounds have been studied as inhibitors of PARP1 and presented promising results. Therefore, this review aims to address the importance of PARP1 in cell regulation and its role in cancer. Moreover, it intends to report a comprehensive literature review of PARP1 inhibitors, containing the pyrazole and indazole scaffolds, published in the last fifteen years, focusing on structure-activity relationship aspects, thus providing important insights for the design of novel and more effective PARP1 inhibitors.

Somatic mutations in four novel genes contribute to homologous recombination deficiency in breast cancer: a real-world clinical tumor sequencing study

Breast cancers involving mutations in homologous recombination (HR) genes, most commonly BRCA1 and BRCA2 (BRCA1/2), respond well to PARP inhibitors and platinum-based chemotherapy. However, except for these specific HR genes, it is not clear which other mutations contribute to homologous recombination defects (HRD). Here, we performed next-generation sequencing of tumor tissues and matched blood samples from 119 breast cancer patients using the OncoScreen Plus panel. Genomic mutation characteristics and HRD scores were analyzed. In the HR genes, we found that BRCA1/2 and PLAB2 mutations were related to HRD. HRD was also detected in a subset of patients without germline or somatic mutations in BRCA1/2, PLAB2, or other HR-related genes. Notably, LRP1B, NOTCH3, GATA2, and CARD11 (abbreviated as LNGC) mutations were associated with high HRD scores in breast cancer patients. Furthermore, functional experiments demonstrated that silencing CARD11 and GATA2 impairs HR repair efficiency and enhances the sensitivity of tumor cells to olaparib treatment. In summary, in the absence of mutations in the HR genes, the sensitivity of tumor cells to PARP inhibitors and platinum-based chemotherapy may be enhanced in a subset of breast cancer patients with LNGC somatic mutations.

Design, synthesis, and biological activity evaluation of new tankyrase-2 directed inhibitors

A new series of flavonoids and quinolone derivatives were designed, synthesized and, evaluated for their biological activity. Among them, compound 14e showed better inhibition potency against TNKS2 in comparison with G007-LK, one of the most potent preclinical stage TNKS inhibitor. Molecular docking results showed that 14e occupied both the adenosine and nicotinamide pockets and formed a hydrogen bond with Met1054 of TNKS2. This study provides a lead for the design and discovery of potent and selective TNKS2 inhibitors.

Hereditary breast and ovarian cancer: from genes to molecular targeted therapies

Hereditary familial tumors constitute 10-15% of all malignancies and present opportunities for the identification of therapeutic approaches against specific germline genetic defects. Hereditary breast and ovarian cancer (HBOC) syndrome, which is linked to the pathogenic mutations of the breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) genes, is an important research model for personalized therapeutic approaches for specific germline mutations. HBOC is characterized by multiple cases of breast and ovarian carcinoma in association with other tumors (prostate, pancreas and stomach carcinoma) within the same family branch, a young age of onset (<36 years), bilaterality and an autosomal dominant pattern of inheritance. Counseling, evaluation of the clinical criteria for the diagnosis of HBOC, and the performance of genetic testing allow for the identification of subjects with BRCA1/2 mutations and provide crucial information for clinical and therapeutic management. The identification of a BRCA gene mutation has therapeutic implications for women with metastatic and non-metastatic breast cancer. In the therapeutic setting of BRCA+ breast cancer, treatment with poly (ADP-ribose) polymerase (PARP) inhibitors, which keep cancer cells from repairing their damaged DNA and cause cell death, is remarkable. This review summarizes the evidence demonstrating the value of BRCA1/2 status as a diagnostic and prognostic tool and as a predictive biomarker in the personalized approach to hereditary BRCA + cancers.

Downregulation of TAB182 promotes cancer stem-like cell properties and therapeutic resistance in triple-negative breast cancer cells

TAB182 participates in DNA damage repair and radio-/chemosensitivity regulation in various tumors, but its role in tumorigenesis and therapeutic resistance in breast cancer remains unclear. In the current paper, we observed that triple-negative Breast Cancer (TNBC), a highly aggressive type of breast cancer, exhibits a lower expression of TAB182. TAB182 knockdown stimulates the proliferation, migration, and invasion of TNBC cells. Our study first obtained RNA-seq data to explore the cellular functions mediated by TAB182 at the genome level in TNBC cells. A transcriptome analysis and in vitro experiments enabled us to identify that TAB182 downregulation drives the enhanced properties of cancer stem-like cells (CSCs) in TNBC cells. Furthermore, TAB182 deletion contributes to the resistance of cells to olaparib or cisplatin, which can be rescued by silencing GLI2, a gene downstream of cancer stemness-related signaling pathways. Our results reveal a novel function of TAB182 as a potential negative regulator of cancer stem-like properties and drug sensitivity in TNBC cells, suggesting that TAB182 may be a tumor suppressor gene and is associated with increased therapeutic benefits for TNBC patients.

The Complex Network of ADP-Ribosylation and DNA Repair: Emerging Insights and Implications for Cancer Therapy

ADP-ribosylation is a post-translational modification of proteins that plays a key role in various cellular processes, including DNA repair. Recently, significant progress has been made in understanding the mechanism and function of ADP-ribosylation in DNA repair. ADP-ribosylation can regulate the recruitment and activity of DNA repair proteins by facilitating protein-protein interactions and regulating protein conformations. Moreover, ADP-ribosylation can influence additional post-translational modifications (PTMs) of proteins involved in DNA repair, such as ubiquitination, methylation, acetylation, phosphorylation, and SUMOylation. The interaction between ADP-ribosylation and these additional PTMs can fine-tune the activity of DNA repair proteins and ensure the proper execution of the DNA repair process. In addition, PARP inhibitors have been developed as a promising cancer therapeutic strategy by exploiting the dependence of certain cancer types on the PARP-mediated DNA repair pathway. In this paper, we review the progress of ADP-ribosylation in DNA repair, discuss the crosstalk of ADP-ribosylation with additional PTMs in DNA repair, and summarize the progress of PARP inhibitors in cancer therapy.

Mechanistic insights into the dual role of CCAR2/DBC1 in cancer

Cell cycle and apoptosis regulator 2 (CCAR2), also known as deleted in breast cancer 1 (DBC1), has been recently identified as a master regulator of transcriptional processes and plays diverse roles in physiology and pathophysiology, including as a regulator of apoptosis, DNA repair, metabolism, and tumorigenesis. CCAR2 functions as a coregulator of various transcription factors and a critical regulator of numerous epigenetic modifiers. Based on its ability to stimulate apoptosis by activating and stabilizing p53, CCAR2 was initially considered to be a tumor suppressor. However, an increasing number of studies have shown that CCAR2 also functions as a tumor-promoting coregulator by activating oncogenic transcription factors and regulating the enzymatic activity of epigenetic modifiers, indicating that CCAR2 may play a dual role in cancer progression by acting as a tumor suppressor and tumor promoter. Here, we review recent progress in understanding the dual tumor-suppressing and oncogenic roles of CCAR2 in cancer. We discuss CCAR2 domain structures, its interaction partners, and the molecular mechanisms by which it regulates the activities of transcription factors and epigenetic modifiers.

Unravelling the Role of PARP1 in Homeostasis and Tumorigenesis: Implications for Anti-Cancer Therapies and Overcoming Resistance

Detailing the connection between homeostatic functions of enzymatic families and eventual progression into tumorigenesis is crucial to our understanding of anti-cancer therapies. One key enzyme group involved in this process is the Poly (ADP-ribose) polymerase (PARP) family, responsible for an expansive number of cellular functions, featuring members well established as regulators of DNA repair, genomic stability and beyond. Several PARP inhibitors (PARPi) have been approved for clinical use in a range of cancers, with many more still in trials. Unfortunately, the occurrence of resistance to PARPi therapy is growing in prevalence and requires the introduction of novel counter-resistance mechanisms to maintain efficacy. In this review, we summarize the updated understanding of the vast homeostatic functions the PARP family mediates and pin the importance of PARPi therapies as anti-cancer agents while discussing resistance mechanisms and current up-and-coming counter-strategies for countering such resistance.

Hypoxia-activated prodrugs of phenolic olaparib analogues for tumour-selective chemosensitisation

Poly(ADP-ribose)polymerase inhibitors (PARPi) are used for treatment of tumours with a defect in homologous recombination (HR) repair. Combination with radio- or chemotherapy could broaden their applicability but a major hurdle is enhancement of normal tissue toxicity. Development of hypoxia-activated prodrugs (HAPs) of PARPi has potential to restrict PARP inhibition to tumours thereby avoiding off-target toxicity. We have designed and synthesised phenolic derivatives of olaparib (termed phenolaparibs) and corresponding ether-linked HAPs. Phenolaparib cytotoxicity in HR-proficient and deficient cell lines was consistent with inhibition of PARP-1. Prodrugs were deactivated relative to phenolaparibs in biochemical PARP-1 inhibition assays, and cell culture. Prodrug 7 was selectively converted to phenolaparib 4 under hypoxia and demonstrated hypoxia-selective cytotoxicity, including chemosensitisation of HR-proficient cells in combination with temozolomide. This work demonstrates the feasibility of a HAP approach to PARPi for use in combination therapies.

Global trends in BRCA-related breast cancer research from 2013 to 2022: A scientometric analysis

Introduction

Since the mid-2000s, breast cancer incidence among women has slowly increased at about 0.5% per year. In the last three decades, Breast Cancer Susceptibility Gene (BRCA) has been proven to be the crucial gene in encouraging the incidence and development of breast cancer. However, scientometric analysis on BRCA-related breast cancer is in shortage. Thus, to have a clear understanding of the current status and catch up with the hotspots, a scientometric analysis was conducted on specific academic publications collected from the Web of Science (WoS).

Methods

We searched the Web of Science Core Collection (WoSCC) to procure associated articles as our dataset. Bibliometric, CiteSpace, VOSviewer, and HistCite software were then applied to conduct visual analyses of countries, institutions, journals, authors, landmark articles, and keywords in this research field.

Results

A total of 7,266 articles and 1,310 review articles published between 2013 to 2022 were retrieved eventually. The annual output steadily rose year by year and peaked in 2021. The USA led the way in the number of published works, total citations, and collaboration. Breast Cancer Research and Treatment was the most favoured journal in this research field. Narod SA from the University of Toronto produced the most publications. At last, the most prominent keywords were "breast cancer" (n=1,778), "women" (n=1,369), "brca1" (n=1,276), "ovarian cancer" (n=1,259), "risk" (n=1,181), and "mutations" (n=929), which exposed the hotspots within the BRCA domain of breast cancer study.

Conclusion

The tendency in the BRCA research field over the past decade was presented by the scientometric analysis. The current research focus is the clinical trials of poly-adenosine diphosphate ribose polymerase inhibitors (PARPi) drugs and their resistance mechanisms.

PET imaging of PARP expression using 68Ga-labelled inhibitors

PURPOSE

Imaging the PARP expression using 18F probes has been approved in clinical trials. Nevertheless, hepatobiliary clearance of both 18F probes hindered their application in monitoring abdominal lesions. Our novel 68Ga-labelled probes aim for fewer abdominal signals while ensuring PARP targeting by optimizing the pharmacokinetic properties of radioactive probes.

METHODS

Three radioactive probes targeted PARP were designed, synthesized, and evaluated based on the PARP inhibitor Olaparib. These 68Ga-labelled radiotracers were assessed in vitro and in vivo.

RESULTS

Precursors that did not lose binding affinity for PARP were designed, synthesized, and then labelled with 68Ga in high radiochemical purity (> 97%). The 68Ga-labelled radiotracers were stable. Due to the increased expression of PARP-1 in SK-OV-3 cells, the uptake of the three radiotracers by SK-OV-3 cells was significantly greater than that by A549 cells. PET/CT imaging of the SK-OV-3 models indicated that the tumor uptake of 68Ga-DOTA-Olaparib (0.5 h: 2.83 ± 0.55%ID/g; 1 h: 2.37 ± 0.64%ID/g) was significantly higher than that of the other 68Ga-labelled radiotracers. There was a significant difference in the T/M (tumor-to-muscle) ratios between the unblocked and blocked groups as calculated from the PET/CT images (4.07 ± 1.01 vs. 1.79 ± 0.45, P = 0.0238 < 0.05). Tumor autoradiography revealed high accumulation in tumor tissues, further confirming the above data. PARP-1 expression in the tumor was confirmed by immunochemistry.

CONCLUSION

As the first 68Ga-labelled PARP inhibitor, 68Ga-DOTA-Olaparib displayed high stability and quick PARP imaging in a tumor model. This compound is thus a promising imaging agent that can be used in a personalized PARP inhibitor treatment regimen.

Update on poly(ADP-ribose) polymerase inhibitors resistance in ovarian cancer

Ovarian cancer is one of the most common reproductive system tumors. The incidence of ovarian cancer in China is on the rise. Poly(ADP-ribose) polymerase (PARP) inhibitor (PARPi) is a DNA repair enzyme associated with DNA damage repair. PARPi takes PARP as a target to kill tumor cells, especially for tumors with homologous recombination (HR) dysfunction. Currently, PARPi has been widely used in clinical practice, mainly for the maintenance of advanced ovarian epithelial cancer. The intrinsic or acquired drug resistance of PARPi has gradually become an important clinical problem with the wide application of PARPi. This review summarizes the mechanisms of PARPi resistance and the current progress on PARPi-based combination strategies.

Temporal recruitment of base excision DNA repair factors in living cells in response to different micro-irradiation DNA damage protocols

Laser micro-irradiation across the nucleus rapidly generates localized chromatin-associated DNA lesions permitting analysis of repair protein recruitment in living cells. Recruitment of three fluorescently-tagged base excision repair factors [DNA polymerase β (pol β), XRCC1 and PARP1], known to interact with one another, was compared in gene-deleted mouse embryonic fibroblasts and in those expressing the endogenous factor. A low energy micro-irradiation (LEMI) forming direct single-strand breaks and a moderate energy (MEMI) protocol that additionally creates oxidized bases were compared. Quantitative characterization of repair factor recruitment and sensitivity to clinical PARP inhibitors (PARPi) was dependent on the micro-irradiation protocol. PARP1 recruitment was biphasic and generally occurred prior to pol β and XRCC1. After LEMI, but not after MEMI, pol β and XRCC1 recruitment was abolished by the PARPi veliparib. Consistent with this, pol β and XRCC1 recruitment following LEMI was considerably slower in PARP1-deficient cells. Surprisingly, the recruitment half-times and amplitudes for pol β were less affected by PARPi than were XRCC1 after MEMI suggesting there is a XRCC1-independent component for pol β recruitment. After LEMI, but not MEMI, pol β dissociation was more rapid than that of XRCC1. Unexpectedly, PARP1 dissociation was slowed in the absence of XRCC1 as well with a PARPi after LEMI but not MEMI, suggesting that XRCC1 facilitates PARP1 dissociation from specific DNA lesions. XRCC1-deficient cells showed pronounced hypersensitivity to the PARPi talazoparib correlating with its known cytotoxic PARP1 trapping activity. In contrast to DNA methylating agents, PARPi only minimally sensitized pol β and XRCC1-deficient cells to oxidative DNA damage suggesting differential binding of PARP1 to alternate repair intermediates. In summary, pol β, XRCC1, and PARP1 display recruitment kinetics that exhibit correlated and unique properties that depend on the DNA lesion and PARP activity revealing that there are multiple avenues utilized in the repair of chromatin-associated DNA.

Role of PARP inhibitors beyond BRCA mutation and platinum sensitivity in epithelial ovarian cancer: a meta-analysis of hazard ratios from randomized clinical trials

BACKGROUND

PARP inhibitors (PARPi) have a well-established role in platinum-sensitive ovarian cancer (PSOC), in BRCA mutant (BRCAm), and homologous recombination deficiency (HRD) population. However, their role in wild type and homologous recombination proficient population is still not clear.

METHODS

A meta-analysis of hazard ratios (HR) of randomized control trials (RCTs) was conducted to study the role of PARPi. The published RCTs comparing the efficacy of PARP inhibitors alone or in combination with chemotherapy and/or target therapies versus placebo/chemotherapy alone/target therapy alone in primary or recurrent ovarian cancer settings were selected. Progression-free survival (PFS) and overall survival (OS) were the primary endpoints.

RESULTS

A total of 14 primary studies and 5 updated studies are considered, consisting of 5363 patients. Overall, HR for PFS was 0.50 [95% CI 0.40-0.62]. HR of PFS was 0.94 [95% CI 0.76-1.15] in the PROC group, 0.41 [95% CI 0.29-0.60] was in HRD with BRCA unknown (BRCAuk), 0.38 [95% CI 0.26-0.57] in HRD with BRCAm, and 0.52 [95% CI 0.38-0.71] in HRD with BRCAwt. In the HRP group, overall HR for PFS was 0.67 [95% CI 0.56-0.80], 0.61 [95% CI 0.38-0.99] in HRD unknown with BRCA wt, and 0.40 [95% CI 0.29-0.55] in BRCAm HR for PFS. Overall, HR for OS was 0.86 [95% CI 0.73-1.031].

CONCLUSIONS

The results suggest that PARPi have a meaningful clinical benefit in PSOC, HRD, BRACm, and also in HRP and PROC; however, the evidence is not sufficient to recommend their routine use and further studies are needed to expand their role in the HRP and PROC groups.

Dual-target inhibitors of PARP1 in cancer therapy: a drug discovery perspective

Poly (ADP-ribose) polymerase 1 (PARP1), a key enzyme in DNA repair, has emerged as a promising anticancer druggable target. An increasing number of PARP1 inhibitors have been discovered to treat cancer, most notably those characterized by BRCA1/2 mutations. Although PARP1 inhibitors have achieved great clinical success, their cytotoxicity, development of drug resistance, and restriction of indication have weakened their clinical therapeutic effects. To address these issues, dual PARP1 inhibitors have been documented as a promising strategy. Here, we review recent progress in the development of dual PARP1 inhibitors, summarize the different designs of dual-target inhibitors, and introduce their antitumor pharmacology, shedding light on the discovery of dual PARP1 inhibitors for cancer treatment.

The potential of PARP as a therapeutic target across pediatric solid malignancies

BACKGROUND

Pediatric cancer is the leading cause of disease-related death in children and the need for better therapeutic options remains urgent. Due to the limited number of patients, target and drug development for pediatrics is often supplemented by data from studies focused on adult cancers. Recent evidence shows that pediatric cancers possess different vulnerabilities that should be explored independently from adult cancers.

METHODS

Using the publicly available Genomics of Drug Sensitivity in Cancer database, we explore therapeutic targets and biomarkers specific to the pediatric solid malignancies Ewing sarcoma, medulloblastoma, neuroblastoma, osteosarcoma, and rhabdomyosarcoma. Results are validated using cell viability assays and high-throughput drug screens are used to identify synergistic combinations.

RESULTS

Using published drug screening data, PARP is identified as a drug target of interest across multiple different pediatric malignancies. We validate these findings, and we show that efficacy can be improved when combined with conventional chemotherapeutics, namely topoisomerase inhibitors. Additionally, using gene set enrichment analysis, we identify ribosome biogenesis as a potential biomarker for PARP inhibition in pediatric cancer cell lines.

CONCLUSION

Collectively, our results provide evidence to support the further development of PARP inhibition and the combination with TOP1 inhibition as a therapeutic approach in solid pediatric malignancies. Additionally, we propose ribosome biogenesis as a component to PARP inhibitor sensitivity that should be further investigated to help maximize the potential utility of PARP inhibition and combinations across pediatric solid malignancies.

Therapeutic targeting of DNA damage repair pathways guided by homologous recombination deficiency scoring in ovarian cancers

The susceptibility of cells to DNA damage and their DNA repair ability are crucial for cancer therapy. Homologous recombination is one of the major repairing mechanisms for DNA double-strand breaks. Approximately half of ovarian cancer (OvCa) cells harbor homologous recombination deficiency (HRD). Considering that HRD is a major hallmark of OvCas, scholars proposed HRD scoring to evaluate the HRD degree and guide the choice of therapeutic strategies for OvCas. In the last decade, synthetic lethal strategy by targeting poly (ADP-ribose) polymerase (PARP) in HR-deficient OvCas has attracted considerable attention in view of its favorable clinical effort. We therefore suggested that the uses of other DNA damage/repair-targeted drugs in HR-deficient OvCas might also offer better clinical outcome. Here, we reviewed the current small molecule compounds that targeted DNA damage/repair pathways and discussed the HRD scoring system to guide their clinical uses.

BRCAness in biliary tract cancer: a new prognostic and predictive biomarker?

Cholangiocarcinoma (CCA) is a rare malignancy with a very poor prognosis. Considering that most cases of CCA are diagnosed at a locally advanced stage and the standard of care for advanced CCA remains suboptimal, new prognostic and predictive biomarkers must be developed to improve the management and survival of patients diagnosed with CCA regardless of disease stage. According to recent studies, 20% of biliary tract cancers exhibit the BRCAness phenotype, meaning that these tumors do not have germline mutations in BRCA but share phenotypic traits with tumors that possess hereditary BRCA mutations. Therefore, screening for these mutations in CCA patients is beneficial to predict tumor sensitivity and response to DNA-damaging chemotherapy such as platinum agents.

Olaparib-Resistant BRCA2MUT Ovarian Cancer Cells with Restored BRCA2 Abrogate Olaparib-Induced DNA Damage and G2/M Arrest Controlled by the ATR/CHK1 Pathway for Survival

The PARP inhibitor (PARPi) olaparib is currently the drug of choice for serous ovarian cancer (OC), especially in patients with homologous recombination (HR) repair deficiency associated with deleterious BRCA1/2 mutations. Unfortunately, OC patients who fail to respond to PARPi or relapse after treatment have limited therapeutic options. To elucidate olaparib resistance and enhance the efficacy of olaparib, intracellular factors exploited by OC cells to achieve decreased sensitivity to PARPi were examined. An olaparib-resistant OC cell line, PEO1-OR, was established from BRCA2MUT PEO1 cells. The anticancer activity and action of olaparib combined with inhibitors of the ATR/CHK1 pathway (ceralasertib as ATRi, MK-8776 as CHK1i) in olaparib-sensitive and -resistant OC cell lines were evaluated. Whole-exome sequencing revealed that PEO1-OR cells acquire resistance through subclonal enrichment of BRCA2 secondary mutations that restore functional full-length protein. Moreover, PEO1-OR cells upregulate HR repair-promoting factors (BRCA1, BRCA2, RAD51) and PARP1. Olaparib-inducible activation of the ATR/CHK1 pathway and G2/M arrest is abrogated in olaparib-resistant cells. Drug sensitivity assays revealed that PEO1-OR cells are less sensitive to ATRi and CHK1i agents. Combined treatment is less effective in olaparib-resistant cells considering inhibition of metabolic activity, colony formation, survival, accumulation of DNA double-strand breaks, and chromosomal aberrations. However, synergistic antitumor activity between compounds is achievable in PEO1-OR cells. Collectively, olaparib-resistant cells display co-existing HR repair-related mechanisms that confer resistance to olaparib, which may be effectively utilized to resensitize them to PARPi via combination therapy. Importantly, the addition of ATR/CHK1 pathway inhibitors to olaparib has the potential to overcome acquired resistance to PARPi.

Muscle PARP1 inhibition extends lifespan through AMPKα PARylation and activation in Drosophila

Poly(ADP-ribose) polymerase-1 (PARP1) has been reported to play an important role in longevity. Here, we showed that the knockdown of the PARP1 extended the lifespan of Drosophila, with particular emphasis on the skeletal muscle. The muscle-specific mutant Drosophila exhibited resistance to starvation and oxidative stress, as well as an increased ability to climb, with enhanced mitochondrial biogenesis and activity at an older age. Mechanistically, the inhibition of PARP1 increases the activity of AMP-activated protein kinase alpha (AMPKα) and mitochondrial turnover. PARP1 could interact with AMPKα and then regulate it via poly(ADP ribosyl)ation (PARylation) at residues E155 and E195. Double knockdown of PARP1 and AMPKα, specifically in muscle, could counteract the effects of PARP1 inhibition in Drosophila. Finally, we showed that increasing lifespan via maintaining mitochondrial network homeostasis required intact PTEN induced kinase 1 (PINK1). Taken together, these data indicate that the interplay between PARP1 and AMPKα can manipulate mitochondrial turnover, and be targeted to promote longevity.

New Approaches in Early-Stage NSCL Management: Potential Use of PARP Inhibitors and Immunotherapy Combination

Lung cancer is the second most common cancer in the world, being the first cause of cancer-related mortality. Surgery remains the only potentially curative treatment for Non-Small Cell Lung Cancer (NSCLC), but the recurrence risk remains high (30-55%) and Overall Survival (OS) is still lower than desirable (63% at 5 years), even with adjuvant treatment. Neoadjuvant treatment can be helpful and new therapies and pharmacologic associations are being studied. Immune Checkpoint Inhibitors (ICI) and PARP inhibitors (PARPi) are two pharmacological classes already in use to treat several cancers. Some pre-clinical studies have shown that its association can be synergic and this is being studied in different settings. Here, we review the PARPi and ICI strategies in cancer management and the information will be used to develop a clinical trial to evaluate the potential of PARPi association with ICI in early-stage neoadjuvant setting NSCLC.

WGS Data Collections: How Do Genomic Databases Transform Medicine?

As a scientific community we assumed that exome sequencing will elucidate the basis of most heritable diseases. However, it turned out it was not the case; therefore, attention has been increasingly focused on the non-coding sequences that encompass 98% of the genome and may play an important regulatory function. The first WGS-based datasets have already been released including underrepresented populations. Although many databases contain pooled data from several cohorts, recently the importance of local databases has been highlighted. Genomic databases are not only collecting data but may also contribute to better diagnostics and therapies. They may find applications in population studies, rare diseases, oncology, pharmacogenetics, and infectious and inflammatory diseases. Further data may be analysed with Al technologies and in the context of other omics data. To exemplify their utility, we put a highlight on the Polish genome database and its practical application.

Targeting tumor-stroma communication by blocking endothelin-1 receptors sensitizes high-grade serous ovarian cancer to PARP inhibition

PARP inhibitors (PARPi) have changed the treatment paradigm of high-grade serous ovarian cancer (HG-SOC). However, the impact of this class of inhibitors in HG-SOC patients with a high rate of TP53 mutations is limited, highlighting the need to develop combinatorial therapeutic strategies to improve responses to PARPi. Here, we unveil how the endothelin-1/ET-1 receptor (ET-1/ET-1R) axis, which is overexpressed in human HG-SOC and associated with poor prognosis, instructs HG-SOC/tumor microenvironment (TME) communication via key pro-malignant factors and restricts the DNA damage response induced by the PARPi olaparib. Mechanistically, the ET-1 axis promotes the p53/YAP/hypoxia inducible factor-1α (HIF-1α) transcription hub connecting HG-SOC cells, endothelial cells and activated fibroblasts, hence fueling persistent DNA damage signal escape. The ET-1R antagonist macitentan, which dismantles the ET-1R-mediated p53/YAP/HIF-1α network, interferes with HG-SOC/stroma interactions that blunt PARPi efficacy. Pharmacological ET-1R inhibition by macitentan in orthotopic HG-SOC patient-derived xenografts synergizes with olaparib to suppress metastatic progression, enhancing PARPi survival benefit. These findings reveal ET-1R as a mechanistic determinant in the regulation of HG-SOC/TME crosstalk and DNA damage response, indicating the use of macitentan in combinatorial treatments with PARPi as a promising and emerging therapy.

Novel markers in breast pathology

Breast pathology is an ever-expanding database of information which includes markers, or biomarkers, that detect or help treat the disease as prognostic or predictive information. This review focuses on these aspects of biomarkers which are grounded in immunohistochemistry, liquid biopsies and next-generation sequencing.

Tryptophan and its metabolites in normal physiology and cancer etiology

Within the growing field of amino acid metabolism, tryptophan (Trp) catabolism is an area of increasing interest. Trp is essential for protein synthesis, and its metabolism gives rise to biologically active catabolites including serotonin and numerous metabolites in the kynurenine (Kyn) pathway. In normal tissues, the production of Trp metabolites is directly regulated by the tissue-specific expression of Trp-metabolizing enzymes. Alterations of these enzymes in cancers can shift the balance and lead to an increased production of specific byproducts that can function as oncometabolites. For example, increased expression of the enzyme indoleamine 2,3-dioxygenase, which converts Trp into Kyn, leads to an increase in Kyn levels in numerous cancers. Kyn functions as an oncometabolite in cancer cells by promoting the activity of the transcription factor aryl hydrocarbon receptor, which regulates progrowth genes. Moreover, Kyn also inhibits T-cell activity and thus allows cancer cells to evade clearance by the immune system. Therefore, targeting the Kyn pathway has become a therapeutic focus as a novel means to abrogate tumor growth and immune resistance. This review summarizes the biological role and regulation of Trp metabolism and its catabolites with an emphasis on tumor cell growth and immune evasion and outlines areas for future research focus.

Human PARP1 substrates and regulators of its catalytic activity: An updated overview

Poly (ADP-ribose) polymerase 1 (PARP1) is a key DNA damage sensor that is recruited to damaged sites after DNA strand breaks to initiate DNA repair. This is achieved by catalyzing attachment of ADP-ribose moieties, which are donated from NAD⁺, on the amino acid residues of itself or other acceptor proteins. PARP inhibitors (PARPi) that inhibit PARP catalytic activity and induce PARP trapping are commonly used for treating BRCA1/2-deficient breast and ovarian cancers through synergistic lethality. Unfortunately, resistance to PARPi frequently occurs. In this review, we present the novel substrates and regulators of the PARP1-catalyzed poly (ADP-ribosyl)ation (PARylatison) that have been identified in the last 3 years. The overall aim is the presentation of protein interactions of potential therapeutic intervention for overcoming the resistance to PARPi.

Trabectedin and lurbinectedin: Mechanisms of action, clinical impact, and future perspectives in uterine and soft tissue sarcoma, ovarian carcinoma, and endometrial carcinoma

The ecteinascidins trabectedin and lurbinectedin are very interesting antineoplastic agents, with a favorable toxicity profile and peculiar mechanisms of action. These drugs form adducts in the minor groove of DNA, which produce single-strand breaks (SSBs) and double-strand breaks (DSBs) and trigger a series of events resulting in cell cycle arrest and apoptosis. Moreover, the ecteinascidins interact with the tumor microenvironment, reduce the number of tumor-associated macrophages, and inhibit the secretion of cytokines and chemokines. Trabectedin has been approved by the Federal Drug Administration (FDA) for patients with unresectable or metastatic liposarcoma or leiomyosarcoma who received a prior anthracycline-based regimen. Moreover, trabectedin in combination with pegylated liposomal doxorubicin (PLD) has been approved in the European Union for the treatment of platinum-sensitive recurrent ovarian cancer. Lurbinectedin has been approved by the FDA for patients with metastatic small cell lung cancer with disease progression on or after platinum-based chemotherapy. The review assesses in vitro and in vivo experimental studies on the antineoplastic effects of both ecteinascidins as well as the clinical trials on the activity of trabectedin in uterine sarcoma and ovarian carcinoma and of lurbinectedin in ovarian carcinoma and endometrial carcinoma.