Reconsidering the mechanisms of action of PARP inhibitors based on clinical outcomes

DNA damage response mutations enhance the antitumor efficacy of ATR and PARP inhibitors in cholangiocarcinoma cell lines

Cholangiocarcinoma (CCA) is a biliary tract carcinoma that is challenging to treat due to its heterogeneity and limited treatment options. Genetic alterations in DNA damage response (DDR) pathways and homologous recombination (HR) defects are common in CCA. This has prompted interest in the use of ataxia telangiectasia and Rad3-related protein (ATR) and poly(ADP-ribose) polymerase (PARP) inhibitors to treat CCA. The present study investigated the impact of an ATR inhibitor and various PARP inhibitors, individually and in combination, on CCA cell lines with different DDR mutation profiles. DDR gene alterations in these cell lines were analyzed, and the responses of the cells to treatment with the PARP inhibitors olaparib, veliparib and talazoparib and/or the ATR inhibitor AZD6738 were evaluated. Assessments focused on cellular viability, clonogenic survival and the combination index, alongside changes in DNA damage assessed via the formation of micronuclei and γ-H2A histone family member X foci. The results revealed that the CCA cell lines with more DDR mutations exhibited greater sensitivity to single and combination treatments. Talazoparib was found to be the most potent PARP inhibitor in the CCA cell lines. The combination of AZD6738 and talazoparib demonstrated varying synergistic effects depending on the genetic background of the CCA cells, with greater efficacy in the cell lines less sensitive to single drug treatments. Mechanistically, this combination promoted the accumulation of DNA damage, including DNA double-strand breaks. Overall, the study underscores the importance of HR in CCA. It reveals an association between the extent of DDR mutations and the response to AZD6738 and PARP inhibitors in CCA, both as single agents and in combination. These findings highlight that the number of mutated genes influences variability in the drug response.

PARP1 inhibitor niraparib exerts synergistic antimyeloma effect with bortezomib through inducing DNA damage and inhibiting DNA repair

Despite the improvements in outcomes for patients with multiple myeloma (MM) over the past decade, the disease remains incurable, and even those patients who initially respond favorably to induction therapy eventually suffer from relapse. Consequently, there is an urgent need for the development of novel therapeutic agents and strategies to enhance the treatment outcomes for patients with MM. The proteasome inhibitor bortezomib (BTZ) elicits endoplasmic reticulum (ER) stress and oxidative stress in MM cells, subsequent DNA damage, ultimately inducing cell apoptosis. Poly (ADP-ribose) polymerase 1 (PARP1) acts as a pivotal enzyme for DNA repair and thus deficient PARP1 renders cells more susceptible to DNA-damaging agents. Conceivably, targeting PARP1 may enhance BTZ-induced DNA damage and cell death in MM cells. In this study, Colony formation, CCK-8, and EdU-labeling assays were conducted to evaluate the effects on MM cell proliferation. The ZIP score was used to assess synergy. Apoptosis and intercellular ROS levels were analyzed using flow cytometry and fluorescence microscopy, respectively. Immunofluorescence and Western blot analyses were used to assess protein expression. The correlation between PARP1 expression levels and the clinical prognosis was examined by tumor-related databases and bioinformatics. The results show that PARP1 is overexpressed in patient MM cells and is associated with a poor prognosis. PARP1 inhibitor niraparib decreases MM cell growth and arrests cell cycle progression at the G2/M phase. When combined with BTZ, it synergistically increases DNA damage, inhibits proliferation, and induces apoptosis. Mechanistically, Niraparib facilitates BTZ-induced ROS elevation, causing DNA double-strand breaks (DSBs), and simultaneously inhibits lesion repair by impeding the expression of repair proteins XRCC1 (X-ray repair cross-complementing protein 1) and POLβ (DNA polymerase beta). Overall, Niraparib plus bortezomib represent a promising approach for treatment of MM.

Hematopoietic adverse events associated with PARP inhibitors: A FAERS database study

OBJECTIVES

Analyze hematopoietic ADR signals of PARP inhibitors (Olaparib, Niraparib, Rucaparib, Talazoparib) using FAERS data to inform clinical practice.

METHODS

Extracted ASCII data for these drugs from Q1 2019 to Q2 2024. Employed SMQ and PT for standardization. Screened ADR signals via ROR, PRR, and MHRA method, comparing SMQ ratios.

RESULTS

Hematopoietic ADRs peaked within 30 days post-treatment, with cytopenia and leukopenia most prevalent. Niraparib showed the highest adverse event count and signal intensity. Olaparib and Talazoparib also indicated strong hematotoxicity.

CONCLUSION

PARP inhibitors vary in ADR incidence and duration, necessitating personalized treatment plans for optimized safety and rational use.

HMGB1 promotes chemoresistance in small cell lung cancer by inducing PARP1-related nucleophagy

INTRODUCTION

Small cell lung cancer (SCLC) is prone to chemoresistance, which is closely related to genome homeostasis-related processes, such as DNA damage and repair. Nucleophagy is the elimination of specific nuclear substances by cells themselves and is responsible for maintaining genome and chromosome stability. However, the roles of nucleophagy in tumour chemoresistance have not been investigated.

OBJECTIVES

The aim of this work was to elucidate the mechanism of chemoresistance in SCLC and reverse this chemoresistance.

METHODS

RNA-seq data from SCLC cohorts, chemosensitive SCLC cells and the corresponding chemoresistant cells were used to discover genes associated with chemoresistance and patient prognosis. In vitro and in vivo experiments were performed to verify the effect of high-mobility group box 1 (HMGB1) knockdown or overexpression on the chemotherapeutic response in SCLC. The regulatory effect of HMGB1 on nucleophagy was then investigated by coimmunoprecipitation (co-IP) and mass spectrometry (MS), and the underlying mechanism was explored using pharmacological inhibitors and mutant proteins.

RESULTS

HMGB1 is a factor indicating poor prognosis and promotes chemoresistance in SCLC. Mechanistically, HMGB1 significantly increases PARP1-LC3 binding to promote nucleophagy via PARP1 PARylation, which leads to PARP1 turnover from DNA lesions and chemoresistance. Furthermore, chemoresistance in SCLC can be attenuated by blockade of the PARP1-LC3 interaction or PARP1 inhibitor (PARPi) treatment.

CONCLUSIONS

HMGB1 can induce PARP1 self-modification, which promotes the interaction of PARP1 with LC3 to promote nucleophagy and thus chemoresistance in SCLC. HMGB1 could be a predictive biomarker for the PARPi response in patients with SCLC. Combining chemotherapy with PARPi treatment is an effective therapeutic strategy for overcoming SCLC chemoresistance.

Exploration of organoids in ovarian cancer: From basic research to clinical translation

Ovarian cancer is a highly heterogeneous tumor with a poor prognosis. The lack of reliable and efficient research models that can accurately mimic heterogeneity has impeded in-depth investigations and hindered the clinical translation of research findings in ovarian cancer. Organoid models have emerged as a promising in vitro approach, demonstrating remarkable fidelity to the histological, molecular, genomic, and transcriptomic features of their tissues of origin. In recent years, organoids have contributed to advancing our understanding of ovarian cancer initiation, metastasis, and drug resistance mechanisms, as well as facilitating clinical screening of effective therapeutic agents. The establishment of high-throughput organoid culture systems, coupled with cutting-edge technologies such as organ-on-a-chip, genetic engineering, and 3D printing, has tremendous potential for accelerating ovarian cancer research translation. In this review, we present a comprehensive overview of the latest exploration of organoids in basic ovarian cancer research and clinical translation. Furthermore, we discuss the prospects and challenges associated with the use of organoids and related novel technologies in the context of ovarian cancer. This review provides insights into the application of organoids in ovarian cancer.

Targeting DNA damage response in pancreatic ductal adenocarcinoma: A review of preclinical and clinical evidence

Pancreatic ductal adenocarcinoma (PDAC) is associated with one of the most unfavorable prognoses across all malignancies. In this review, we investigate the role of inhibitors targeting crucial regulators of DNA damage response (DDR) pathways, either as single treatments or in combination with chemotherapeutic agents and targeted therapies in PDAC. The most prominent clinical benefit of PARP inhibitors' monotherapy is related to the principle of synthetic lethality in individuals harboring BRCA1/2 and other DDR gene mutations as predictive biomarkers. Moreover, induction of BRCAness with inhibitors of RTKs, including VEGFR and c-MET and their downstream signaling pathways, RAS/RAF/MEK/ERK and PI3K/AKT/mTOR in order to expand the application of PARP inhibitors in patients without DDR mutations, has also been addressed. Other DDR-targeting agents beyond PARP inhibitors, including inhibitors of ATM, ATR, CHEK1/2, and WEE1 have also demonstrated their potential in preclinical models of PDAC and may hold promise in future studies.

Establish TIIC signature score based the machine learning fusion in bladder cancer

BACKGROUND

Bladder cancer is a prevalent malignant tumor with high heterogeneity. Current treatments, such as transurethral resection of bladder tumor (TURBT) and intravesical Bacillus Calmette-Guérin (BCG) therapy, still have limitations, with approximately 30% of non-muscle-invasive bladder cancer (NMIBC) progressing to muscle-invasive bladder cancer (MIBC), and a substantial number of MIBC patients experiencing recurrence after surgery. Immunotherapy has shown potential benefits, but accurate prediction of its prognostic effects remains challenging.

METHODS

We analyzed bladder cancer RNA-seq data and clinical information from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases, and used various machine learning algorithms to screen for feature RNAs related to tumor-infiltrating immune cells (TIICs) from single-cell data. Based on these RNAs, we established a TIIC signature score and evaluated its relationship with overall survival (OS) and immunotherapy response in bladder cancer patients.

RESULTS

The study identified 171 TIIC-RNAs and selected 11 TIIC-RNAs with prognostic value through survival analysis. The TIIC signature score established using a machine learning fusion method was significantly associated with OS and showed good predictive performance in different datasets. Additionally, the signature score was negatively correlated with immunotherapy response, with patients with low TIIC feature scores showing better survival outcomes after immunotherapy. Further biological functional analysis revealed a close association between the TIIC signature score and immune regulation processes, cellular metabolism, and genetic variations.

CONCLUSION

This study successfully constructed and validated an RNA signature scoring system based on tumor-infiltrating immune cell (TIIC) features, which can effectively predict OS and the effectiveness of immunotherapy in bladder cancer patients.

Leveraging PARP-1/2 to Target Distant Metastasis

Poly (ADP-Ribose) Polymerase (PARP) inhibitors have changed the outcomes and therapeutic strategy for several cancer types. As a targeted therapeutic mainly for patients with BRCA1/2 mutations, PARP inhibitors have commonly been exploited for their capacity to prevent DNA repair. In this review, we discuss the multifaceted roles of PARP-1 and PARP-2 beyond DNA repair, including the impact of PARP-1 on chemokine signalling, immune modulation, and transcriptional regulation of gene expression, particularly in the contexts of angiogenesis and epithelial-to-mesenchymal transition (EMT). We evaluate the pre-clinical role of PARP inhibitors, either as single-agent or combination therapies, to block the metastatic process. Efficacy of PARP inhibitors was demonstrated via DNA repair-dependent and independent mechanisms, including DNA damage, cell migration, invasion, initial colonization at the metastatic site, osteoclastogenesis, and micrometastasis formation. Finally, we summarize the recent clinical advancements of PARP inhibitors in the prevention and progression of distant metastases, with a particular focus on specific metastatic sites and PARP-1 selective inhibitors. Overall, PARP inhibitors have demonstrated great potential in inhibiting the metastatic process, pointing the way for greater use in early cancer settings.

Schlafen 11 further sensitizes BRCA-deficient cells to PARP inhibitors through single-strand DNA gap accumulation behind replication forks

The preferential response to PARP inhibitors (PARPis) in BRCA-deficient and Schlafen 11 (SLFN11)-expressing ovarian cancers has been documented, yet the underlying molecular mechanisms remain unclear. As the accumulation of single-strand DNA (ssDNA) gaps behind replication forks is key for the lethality effect of PARPis, we investigated the combined effects of SLFN11 expression and BRCA deficiency on PARPi sensitivity and ssDNA gap formation in human cancer cells. PARPis increased chromatin-bound RPA2 and ssDNA gaps in SLFN11-expressing cells and even more in cells with BRCA1 or BRCA2 deficiency. SLFN11 was co-localized with chromatin-bound RPA2 under PARPis treatment, with enhanced recruitment in BRCA2-deficient cells. Notably, the chromatin-bound SLFN11 under PARPis did not block replication, contrary to its function under replication stress. SLFN11 recruitment was attenuated by the inactivation of MRE11. Hence, under PARPi treatment, MRE11 expression and BRCA deficiency lead to ssDNA gaps behind replication forks, where SLFN11 binds and increases their accumulation. As ovarian cancer patients who responded (progression-free survival >2 years) to olaparib maintenance therapy had a significantly higher SLFN11-positivity than short-responders (<6 months), our findings provide a mechanistic understanding of the favorable responses to PARPis in SLFN11-expressing and BRCA-deficient tumors. It highlight the clinical implications of SLFN11.

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.

SLFN11 is a BRCA Independent Biomarker for the Response to Platinum-Based Chemotherapy in High-Grade Serous Ovarian Cancer and Clear Cell Ovarian Carcinoma

BRCA1/2 mutations are robust biomarkers for platinum-based chemotherapy in epithelial ovarian cancers. However, BRCA1/2 mutations in clear cell ovarian carcinoma (CCC) are less frequent compared with high-grade serous ovarian cancer (HGSC). The discovery of biomarkers that can be applied to CCC is an unmet need in chemotherapy. Schlafen 11 (SLFN11) has attracted attention as a novel sensitizer for DNA-damaging agents including platinum. In this study, we investigated the utility of SLFN11 in HGSC and CCC for platinum-based chemotherapy. SLFN11 expression was analyzed retrospectively by IHC across 326 ovarian cancer samples. The clinicopathologic significance of SLFN11 expression was analyzed across 57 advanced HGSC as a discovery set, 96 advanced HGSC as a validation set, and 57 advanced CCC cases, all of whom received platinum-based chemotherapy. BRCA1/2 mutation was analyzed using targeted-gene sequencing. In the HGSC cohort, the SLFN11-positive and BRCA mutation group showed significantly longer whereas the SLFN11-negative and BRCA wild-type group showed significantly shorter progression-free survival and overall survival. Moreover, SLFN11-positive HGSC shrunk significantly better than SLFN11-negative HGSC after neoadjuvant chemotherapy. Comparable results were obtained with CCC but without consideration of BRCA1/2 mutation due to a small population. Multivariate analysis identified SLFN11 as an independent factor for better survival in HGSC and CCC. The SLFN11-dependent sensitivity to platinum and PARP inhibitors were validated with genetically modified non-HGSC ovarian cancer cell lines. Our study reveals that SLFN11 predicts platinum sensitivity in HGSC and CCC independently of BRCA1/2 mutation status, indicating that SLFN11 assessment can guide treatment selection in HGSC and CCC.

Selection of maintenance therapy during first-line treatment of advanced ovarian cancer based on pharmacologic characteristics

INTRODUCTION

Maintenance therapy with bevacizumab and the poly (ADP-ribose) polymerase (PARP) inhibitors olaparib and niraparib after first-line treatment of advanced ovarian cancer has been approved. However, it is not clear which one should be used for which patients.

AREAS COVERED

This paper presents a detailed analysis of data from phase 3 trials in ovarian cancer evaluating bevacizumab (ICON7, GOG-0218), olaparib (SOLO1, PAOLA-1), and niraparib (PRIMA, PRIME). We will discuss how the results of these trials relate to the 'rebound effect,' in which the risk of progression increases after discontinuation of bevacizumab in patients receiving bevacizumab, and to the significant difference in tissue permeability between olaparib and niraparib.

EXPERT OPINION

In patients with homologous recombination deficiency and no macroscopic residual disease (R0) after primary debulking surgery (PDS), the combination of bevacizumab plus olaparib seems to be the best regimen. Olaparib monotherapy is suitable for patients with BRCA mutations other than PDS R0. Bevacizumab is most useful in cases with a short duration of the rebound effect, i.e. short survival. Niraparib is useful in others but may be more useful in Asians.

The function and regulation of ADP-ribosylation in the DNA damage response

ADP-ribosylation is a post-translational modification involved in DNA damage response (DDR). In higher organisms it is synthesised by PARP 1-3, DNA strand break sensors. Recent advances have identified serine residues as the most common targets for ADP-ribosylation during DDR. To ADP-ribosylate serine, PARPs require an accessory factor, HPF1 which completes the catalytic domain. Through ADP-ribosylation, PARPs recruit a variety of factors to the break site and control their activities. However, the timely removal of ADP-ribosylation is also key for genome stability and is mostly performed by two hydrolases: PARG and ARH3. Here, we describe the key writers, readers and erasers of ADP-ribosylation and their contribution to the mounting of the DDR. We also discuss the use of PARP inhibitors in cancer therapy and the ways to tackle PARPi treatment resistance.

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.

Mechanisms of PARP1 inhibitor resistance and their implications for cancer treatment

The discovery of synthetic lethality as a result of the combined loss of PARP1 and BRCA has revolutionized the treatment of DNA repair-deficient cancers. With the development of PARP inhibitors, patients displaying germline or somatic mutations in BRCA1 or BRCA2 were presented with a novel therapeutic strategy. However, a large subset of patients do not respond to PARP inhibitors. Furthermore, many of those who do respond eventually acquire resistance. As such, combating de novo and acquired resistance to PARP inhibitors remains an obstacle in achieving durable responses in patients. In this review, we touch on some of the key mechanisms of PARP inhibitor resistance, including restoration of homologous recombination, replication fork stabilization and suppression of single-stranded DNA gap accumulation, as well as address novel approaches for overcoming PARP inhibitor resistance.