Avoid the trap: Targeting PARP1 beyond human malignancy

Impact of a Cancer-Associated Mutation on Poly(ADP-ribose) Polymerase1 Inhibition

Poly(ADP-ribose) polymerase1 (PARP1) plays a vital role in DNA repair, and its inhibition in cancer cells may cause cell apoptosis. In this study, we investigated the effects of a PARP1 variant, V762A, which is strongly associated with several cancers in humans, on the inhibition of PARP1 by three FDA-approved inhibitors: niraparib, rucaparib, and talazoparib. Specifically, we compared the inhibition of the mutant to that of wild-type (WT) PARP1. Additionally, we investigated how the mutation influences the binding of these inhibitors to PARP1. Our work suggests that while mutant PARP1 exhibits only minor differences in residual fluctuations, backbone deviations, and residue motion correlations compared to the WT under niraparib and rucaparib inhibitions, it shows significant and distinct differences in these features when inhibited by talazoparib. Among the three inhibitions, talazoparib inhibition uniquely lowers the average residue fluctuations in the mutant than the WT including lower fluctuations of mutant's N- and C-terminal residues in the catalytic domain, conserved H-Y-E traid residues, and donor loop (D-loop) residues which are important for catalysis more effectively than other inhibitions. However, talazoparib also significantly enhances destabilizing interactions between the mutation site in the HD domain in the mutant than WT. Further, among the three inhibitions, talazoparib inhibition uniquely and significantly disrupts the functional fluctuations of terminal regions in the mutant, which are otherwise present in the WT. The mutation and inhibition do not significantly affect PARP1's essential dynamics. Lastly, these inhibitors bind to the V762A mutant more effectively than to the WT, with similar binding free energies between them.

Medroxyprogesterone promotes neuronal survival after cerebral ischemic stroke by inhibiting PARthanatos

Introduction

Cerebral ischemic stroke (CIS) is caused by the interruption of cerebral blood circulation due to thrombosis or embolism and is the second-leading cause of mortality worldwide. The neuronal death and motor dysfunction resulting from CIS are primarily attributed to the induction of PARthanatos in neurons at the site of ischemia. Blocking parthanatos is a promising treatment for CIS.

Methods

The effect of medroxyprogesterone treatment on PARthanatos in vitro was examined by CCK8 assay and flow cytometry and the target protein of medroxyprogesterone was then identified by a series of assays, including western blotting, immunofluorescence, cell thermal shift assay and molecular docking. Subsequently, the efficacy of medroxyprogesterone in the treatment of ischemic stroke was evaluated by FJC staining.

Results

In our study, medroxyprogesterone was able to block the occurrence of PARthanatos in Hela cells induced by MNNG. PARP-1 activity did not change after medroxyprogesterone treatment but prevented MNNG-induced apoptosis inducing factor (AIF) release from mitochondria by improving the stability of phosphorylated extracellular signal-regulated kinase (ERK). In vivo, medroxyprogesterone significantly reduces neuronal death in mouse models of CIS by inhibiting PARthanatos.

Conclusion

Our findings indicate that medroxyprogesterone effectively inhibits PARthanatos not by affecting the activity of PARP-1, but by directly binding to ERK and stabilizes the active phosphorylated ERK, thereby inhibiting AIF translocation. Furthermore, medroxyprogesterone shows potential as a neuroprotective agent for patients with CIS, potentially enhancing post-stroke recovery and reducing societal burdens.

Decoding NAD+ Metabolism in COVID-19: Implications for Immune Modulation and Therapy

The persistent threat of COVID-19, particularly with the emergence of new variants, underscores the urgency for innovative therapeutic strategies beyond conventional antiviral treatments. Current immunotherapies, including IL-6/IL-6R monoclonal antibodies and JAK inhibitors, exhibit suboptimal efficacy, necessitating alternative approaches. Our review delves into the significance of NAD+ metabolism in COVID-19 pathology, marked by decreased NAD+ levels and upregulated NAD+-consuming enzymes such as CD38 and poly (ADP-ribose) polymerases (PARPs). Recognizing NAD+'s pivotal role in energy metabolism and immune modulation, we propose modulating NAD+ homeostasis could bolster the host's defensive capabilities against the virus. The article reviews the scientific rationale behind targeting NAD+ pathways for therapeutic benefit, utilizing strategies such as NAD+ precursor supplementation and enzyme inhibition to modulate immune function. While preliminary data are encouraging, the challenge lies in optimizing these interventions for clinical use. Future research should aim to unravel the intricate roles of key metabolites and enzymes in NAD+ metabolism and to elucidate their specific mechanisms of action. This will be essential for developing targeted NAD+ therapies, potentially transforming the management of COVID-19 and setting a precedent for addressing other infectious diseases.

CRISPR/Cas9 Technology Providing the Therapeutic Landscape of Metastatic Prostate Cancer

Prostate cancer (PCa) is the most prevalent malignancy and the second leading cause of cancer-related death in men. Although current therapies can effectively manage the primary tumor, most patients with late-stage disease manifest with metastasis in different organs. From surgery to treatment intensification (TI), several combinations of therapies are administered to improve the prognosis of patients with metastatic PCa. Due to the high frequency of the mutation during the metastatic phase, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease 9 (Cas9) genetic engineering tool can accelerate the effects of TI by enhancing targeted gene therapy or immunotherapy. This review describes the genetic background of metastatic PCa and how CRISPR/Cas9 technology can contribute to the field of PCa treatment development. It also discusses the current limitations of conventional PCa therapy and the potential of CRISPR-based PCa therapy.

Impact of a Cancer-Associated Mutation on Poly(ADP-ribose) Polymerase1 Inhibition

Poly(ADP-ribose) polymerase1 (PARP1) plays a vital role in DNA repair and its inhibition in cancer cells may cause cell apoptosis. In this study, we investigated the effects of a PARP1 variant, V762A, which is strongly associated with several cancers in humans, on the inhibition of PARP1 by three FDA approved inhibitors: niraparib, rucaparib and talazoparib. Our work suggests that these inhibitors bind to the V762A mutant more effectively than to the wild-type (WT), with similar binding free energies between them. Talazoparib inhibition uniquely lowers the average residue fluctuations in the mutant than the WT including lower fluctuations of mutant's N- and C-terminal residues, conserved H-Y-E traid residues and donor loop (D-loop) residues which important for catalysis more effectively than other inhibitions. However, talazoparib also enhances destabilizing interactions between the mutation site in the HD domain in the mutant than WT. Further, talazoparib inhibition significantly disrupts the functional fluctuations of terminal regions in the mutant, which are otherwise present in the WT. Lastly, the mutation and inhibition do not significantly affect PARP1's essential dynamics.

Parthanatos: Mechanisms, modulation, and therapeutic prospects in neurodegenerative disease and stroke

Parthanatos is a cell death signaling pathway that has emerged as a compelling target for pharmaceutical intervention. It plays a pivotal role in the neuron loss and neuroinflammation that occurs in Parkinson's Disease (PD), Alzheimer's Disease (AD), Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS), and stroke. There are currently no treatments available to humans to prevent cell death in any of these diseases. This review provides an in-depth examination of the current understanding of the Parthanatos mechanism, with a particular focus on its implications in neuroinflammation and various diseases discussed herein. Furthermore, we thoroughly review potential intervention targets within the Parthanatos pathway. We dissect recent progress in inhibitory strategies, complimented by a detailed structural analysis of key Parthanatos executioners, PARP-1, AIF, and MIF, along with an assessment of their established inhibitors. We hope to introduce a new perspective on the feasibility of targeting components within the Parthanatos pathway, emphasizing its potential to bring about transformative outcomes in therapeutic interventions. By delineating therapeutic opportunities and known targets, we seek to emphasize the imperative of blocking Parthanatos as a precursor to developing disease-modifying treatments. This comprehensive exploration aims to catalyze a paradigm shift in our understanding of potential neurodegenerative disease therapeutics, advocating for the pursuit of effective interventions centered around Parthanatos inhibition.

Integrating PARP Inhibitors in mCRPC Therapy: Current Strategies and Emerging Trends

Metastatic castrate-resistant prostate cancer (mCRPC) is associated with poor prognosis. DNA damage response (DDR) genes are commonly altered in mCRPC rendering them as promising therapeutic targets. Poly (ADP ribose) polymerase inhibitors (PARPi) demonstrated antitumor activity in mCRPC patients with DDR gene mutations through synthetic lethality. Multiple clinical trials with PARPi monotherapy exhibited encouraging clinical outcomes in selected patients with mCRPC. More recently, three Phase III randomized clinical trials (RCTs) combining PARPi with androgen receptor signaling inhibitors (ARSIs) demonstrated improved antitumor activity compared to ARSI monotherapy in mCRPC patients as the first-line therapy. Clinical benefit was more pronounced in patients harboring DDR alterations, specifically BRCA1/2. Interestingly, antitumor activity was also observed irrespective of DDR gene mutations, highlighting BRCAness phenotype with androgen receptor blockade resulting in synergistic activity between ARSIs and PARPi. In this review, we discuss the clinical efficacy and safety data of the combination of PARPi plus ARSI in all Phase 3 randomized controlled trials (RCTs), emphasizing strategies for patient selection and highlighting emerging trends based on clinical trial data.

PINX1 loss confers susceptibility to PARP inhibition in pan-cancer cells

PARP1 is crucial in DNA damage repair, chromatin remodeling, and transcriptional regulation. The principle of synthetic lethality has effectively guided the application of PARP inhibitors in treating tumors carrying BRCA1/2 mutations. Meanwhile, PARP inhibitors have exhibited efficacy in BRCA-proficient patients, further highlighting the necessity for a deeper understanding of PARP1 function and its inhibition in cancer therapy. Here, we unveil PIN2/TRF1-interacting telomerase inhibitor 1 (PINX1) as an uncharacterized PARP1-interacting protein that synergizes with PARP inhibitors upon its depletion across various cancer cell lines. Loss of PINX1 compromises DNA damage repair capacity upon etoposide treatment. The vulnerability of PINX1-deficient cells to etoposide and PARP inhibitors could be effectively restored by introducing either a full-length or a mutant form of PINX1 lacking telomerase inhibitory activity. Mechanistically, PINX1 is recruited to DNA lesions through binding to the ZnF3-BRCT domain of PARP1, facilitating the downstream recruitment of the DNA repair factor XRCC1. In the absence of DNA damage, PINX1 constitutively binds to PARP1, promoting PARP1-chromatin association and transcription of specific DNA damage repair proteins, including XRCC1, and transcriptional regulators, including GLIS3. Collectively, our findings identify PINX1 as a multifaceted partner of PARP1, crucial for safeguarding cells against genotoxic stress and emerging as a potential candidate for targeted tumor therapy.

Role of the PARP1/NF-κB Pathway in DNA Damage and Apoptosis of TK6 Cells Induced by Hydroquinone

Hydroquinone(HQ) is a widely used industrial raw material and is a topical lightening product found in over-the-counter products. However, inappropriate exposure to HQ can pose certain health hazards. This study aims to explore the mechanisms of DNA damage and cell apoptosis caused by HQ, with a focus on whether HQ activates the nuclear factor-κB (NF-κB) pathway to participate in this process and to investigate the correlation between the NF-κB pathway activation and poly(ADP-ribose) polymerase 1(PARP1). Through various experimental techniques, such as DNA damage detection, cell apoptosis assessment, cell survival rate analysis, immunofluorescence, and nuclear-cytoplasmic separation, the cytotoxic effects of HQ were verified, and the activation of the NF-κB pathway was observed. Simultaneously, the relationship between the NF-κB pathway and PARP1 was verified by shRNA interference experiments. The results showed that HQ could significantly activate the NF-κB pathway, leading to a decreased cell survival rate, increased DNA damage, and cell apoptosis. Inhibiting the NF-κB pathway could significantly reduce HQ-induced DNA damage and cell apoptosis and restore cell proliferation and survival rate. shRNA interference experiments further indicated that the activation of the NF-κB pathway was regulated by PARP1. This study confirmed the important role of the NF-κB pathway in HQ-induced DNA damage and cell apoptosis and revealed that the activation of the NF-κB pathway was mediated by PARP1. This research provides important clues for a deeper understanding of the toxic mechanism of HQ.

PROTAC: Novel degradable approach for different targets to treat breast cancer

The revolutionary Proteolysis Targeting Chimera (PROTACs) have the exciting potential to reshape the pharmaceutical industry landscape by leveraging the ubiquitin-proteasome system for targeted protein degradation. Breast cancer, the most prevalent cancer in women, could be treated using PROTAC therapy. Although substantial work has been conducted, there is not yet a comprehensive overview or progress update on PROTAC therapy for breast cancer. Hence, in this article, we've compiled recent research progress focusing on different breast cancer target proteins, such as estrogen receptor (ER), BET, CDK, HER2, PARP, EZH2, etc. This resource aims to serve as a guide for future PROTAC-based breast cancer treatment design.

Discovery of Potent Isoindolinone Inhibitors that Target an Active Conformation of PARP1 Using DNA-Encoded Libraries

Inhibition of poly (ADP-ribose) polymerase-1 (PARP1), a DNA repair enzyme, has proven to be a successful strategy for the treatment of various cancers. With the appropriate selection conditions and protein design, DNA-encoded library (DEL) technology provides a powerful avenue to identify small molecules with the desired mechanism of action towards a target of interest. However, DNA-binding proteins, such as PARP1, can be challenging targets for DEL screening due to non-specific protein-DNA interactions. To overcome this, we designed and screened a PARP1 catalytic domain construct without the autoinhibitory helical domain. This allowed us to interrogate an active, functionally-relevant form of the protein resulting in the discovery of novel isoindolinone PARP1 inhibitors with single-digit nanomolar potency. These inhibitors also demonstrated little to no PARP1-DNA trapping, a property that could be advantageous in the clinic.

Replication stress as a driver of cellular senescence and aging

Replication stress refers to slowing or stalling of replication fork progression during DNA synthesis that disrupts faithful copying of the genome. While long considered a nexus for DNA damage, the role of replication stress in aging is under-appreciated. The consequential role of replication stress in promotion of organismal aging phenotypes is evidenced by an extensive list of hereditary accelerated aging disorders marked by molecular defects in factors that promote replication fork progression and operate uniquely in the replication stress response. Additionally, recent studies have revealed cellular pathways and phenotypes elicited by replication stress that align with designated hallmarks of aging. Here we review recent advances demonstrating the role of replication stress as an ultimate driver of cellular senescence and aging. We discuss clinical implications of the intriguing links between cellular senescence and aging including application of senotherapeutic approaches in the context of replication stress.

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.

Blocking the Self-Destruct Program of Dopamine Neurons through Macrophage Migration Inhibitory Factor Nuclease Inhibition

Parkinson's disease (PD) is a progressive neurodegenerative condition that pathognomonically involves the death of dopaminergic neurons in the substantia nigra pars compacta, resulting in a myriad of motor and non-motor symptoms. Given the insurmountable burden of this disease on the population and healthcare system, significant efforts have been put forth toward generating disease modifying therapies. This class of treatments characteristically alters disease course, as opposed to current strategies that focus on managing symptoms. Previous literature has implicated the cell death pathway known as parthanatos in PD progression. Inhibition of this pathway by targeting poly (ADP)-ribose polymerase 1 (PARP1) prevents neurodegeneration in a model of idiopathic PD. However, PARP1 has a vast repertoire of functions within the body, increasing the probability of side effects with the long-term treatment likely necessary for clinically significant neuroprotection. Recent work culminated in the development of a novel agent targeting the macrophage migration inhibitory factor (MIF) nuclease domain, also named parthanatos-associated apoptosis-inducing factor nuclease (PAAN). This nuclease activity specifically executes the terminal step in parthanatos. Parthanatos-associated apoptosis-inducing factor nuclease inhibitor-1 was neuroprotective in multiple preclinical mouse models of PD. This piece will focus on contextualizing this discovery, emphasizing its significance, and discussing its potential implications for parthanatos-directed treatment. © 2024 International Parkinson and Movement Disorder Society.

Effects of food and ethnicity on the pharmacokinetics of venadaparib, a next-generation PARP inhibitor, in healthy Korean, Caucasian, and Chinese male subjects

AIM

Venadaparib is a next-generation poly(ADP-ribose) polymerase inhibitor under development for treating gastric cancer. This study aimed to evaluate the effects of food and ethnicity on the pharmacokinetics (PKs) and safety of venadaparib after a single oral administration in healthy Korean, Caucasian, and Chinese male subjects.

METHODS

In this randomized, open-label, single-dose, two-sequence, two-period, and crossover study, Korean and Caucasian subjects received venadaparib 80 mg in each period (fasted or fed state) with a seven-day washout. In an open-label, single-dose study, Chinese subjects received venadaparib 80 mg only in the fasted state. Serial blood samples were collected up to 72 h post-dosing.

RESULTS

Twelve subjects from each ethnic group completed the study. The geometric mean ratios (90% confidence intervals) of the maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from time zero to the last measurable time point (AUClast) of venadaparib for the fed to fasted state were 0.82 (0.7457-0.9094) and 1.02 (0.9088-1.1339) in Koreans, and 0.77 (0.6871-0.8609) and 0.96 (0.9017-1.0186) in Caucasians, respectively. No statistically significant differences were observed in Cmax (P-value = 0.45) or AUClast (P-value = 0.30) among the three ethnic groups. A single venadaparib dose was well-tolerated.

CONCLUSION

The overall systemic exposure of venadaparib was not affected by the high-fat meal, despite delayed absorption with a decreased Cmax in the fed state. The PK profiles were comparable among the Korean, Caucasian, and Chinese subjects. A single venadaparib 80 mg dose was safe and well-tolerated in both fasted and fed states.

Nimbolide targets RNF114 to induce the trapping of PARP1 and synthetic lethality in BRCA-mutated cancer

Recent studies have pointed to PARP1 trapping as a key determinant of the anticancer effects of PARP1 inhibitors (PARPi). We identified RNF114, as a PARylation-dependent, E3 ubiquitin ligase involved in DNA damage response. Upon sensing genotoxicity, RNF114 was recruited, in a PAR-dependent manner, to DNA lesions, where it targeted PARP1 for degradation. The blockade of this pathway interfered with the removal of PARP1 from DNA lesions, leading to profound PARP1 trapping. We showed that a natural product, nimbolide, inhibited the E3 ligase activity of RNF114 and thus caused PARP1 trapping. However, unlike conventional PARPi, nimbolide treatment induced the trapping of both PARP1 and PARylation-dependent DNA repair factors. Nimbolide showed synthetic lethality with BRCA mutations, and it overcame intrinsic and acquired resistance to PARPi, both in vitro and in vivo. These results point to the exciting possibility of targeting the RNF114-PARP1 pathway for the treatment of homologous recombination-deficient cancers.

Privileged Scaffolds for Potent and Specific Inhibitors of Mono-ADP-Ribosylating PARPs

The identification of new targets to address unmet medical needs, better in a personalized way, is an urgent necessity. The introduction of PARP1 inhibitors into therapy, almost ten years ago, has represented a step forward this need being an innovate cancer treatment through a precision medicine approach. The PARP family consists of 17 members of which PARP1 that works by poly-ADP ribosylating the substrate is the sole enzyme so far exploited as therapeutic target. Most of the other members are mono-ADP-ribosylating (mono-ARTs) enzymes, and recent studies have deciphered their pathophysiological roles which appear to be very extensive with various potential therapeutic applications. In parallel, a handful of mono-ARTs inhibitors emerged that have been collected in a perspective on 2022. After that, additional very interesting compounds were identified highlighting the hot-topic nature of this research field and prompting an update. From the present review, where we have reported only mono-ARTs inhibitors endowed with the appropriate profile of pharmacological tools or drug candidate, four privileged scaffolds clearly stood out that constitute the basis for further drug discovery campaigns.

Poly(ADP-ribose) polymerase-1 and its ambiguous role in cellular life and death

The deletion of the gene coding for poly(ADP-ribose) polymerase-1 (PARP1) or its pharmacological inhibition protects mice against cerebral ischemia and Parkinson's disease. In sharp contrast, PARP1 inhibitors are in clinical use for the eradication of vulnerable cancer cells. It appears that excessive PARP1 activation is involved in a specific cell death pathway called parthanatos, while inhibition of PARP1 in cancer cells amplifies DNA damage to a lethal level. Hence, PARP1 plays a context-dependent role in cell fate decisions. In addition, it appears that PARP1 plays an ambiguous role in organismal aging.

A PARP1 PROTAC as a novel strategy against PARP inhibitor resistance via promotion of ferroptosis in p53-positive breast cancer

Therapeutic targeting of the nuclear enzyme poly (ADP-ribose) polymerase 1 (PARP1) with PARP inhibitors (PARPis) in patients with a homologous recombination (HR)- deficient phenotype based on the mechanism of synthetic lethality has been shown tremendous success in cancer therapy. With the clinical use of various PARPis, emerging evidence has shown that some PARPis offer hope for breakthroughs in triple-negative breast cancer (TNBC) therapy, regardless of HR status. However, similar to other conventional cytotoxic drugs, PARPis are also subject to the intractable problem of drug resistance. Notably, acquired resistance to PARPis caused by point mutations in the PARP1 protein is hard to overcome with current strategies. To explore modalities to overcome resistance and identify patients who are most likely to benefit from PARP1-targeted therapy, we developed a proteolysis-targeted chimaera (PROTAC) to degrade mutant PARP1 in TNBC. Here, we investigated a PARP1 PROTAC termed "NN3″, which triggered ubiquitination and proteasome-mediated degradation of PARP1. Moreover, NN3 degraded PARP1 with resistance-related mutations. Interestingly, compared with other reported PARP1 degraders, NN3 exhibited a unique antitumor mechanism in p53-positive breast cancer cells that effectively promoted ferroptosis by downregulating the SLC7A11 pathway. Furthermore, NN3 showed potent activity and low toxicity in vivo. In conclusion, we propose PROTAC-mediated degradation of PARP1 as a novel strategy against mutation-related PARPi resistance and a paradigm for targeting breast cancer with functional p53 via ferroptosis induction.

The role of E3 ubiquitin ligase WWP2 and the regulation of PARP1 by ubiquitinated degradation in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) has been a huge threat for people's health and finding effective target therapy is urgent and important. WWP2, as one of E3 ubiquitin ligase, is involved in many biological processes by specifically binding to substrates. PARP1 plays a role in cell apoptosis and is considered as a therapeutic target of certain cancers. In this study, we firstly found that WWP2 expressed higher in newly diagnosed ALL patients comparing with complete remission (CR) ALL patients and normal control people, and WWP2 in relapse ALL patients expressed higher than normal control people. WWP2 expression was related with the FAB subtype of ALL and the proportion of blast cells in bone marrow blood tested by flow cytometry. We demonstrated knockout WWP2 inhibited the ALL growth and enhanced apoptosis induced by Dox in vitro and vivo for the first time. WWP2 negatively regulated and interacted with PARP1 and WWP2 mechanically degraded PARP1 through polyubiquitin-proteasome pathway in ALL. These findings suggested WWP2 played a role in ALL development as well as growth and apoptosis, and also displayed a regulatory pathway of PARP1, which provided a new potential therapeutic target for the treatment of ALL.

PARP Inhibitors: Clinical Limitations and Recent Attempts to Overcome Them

PARP inhibitors are the first clinically approved drugs that were developed based on synthetic lethality. PARP inhibitors have shown promising outcomes since their clinical applications and have recently been approved as maintenance treatment for cancer patients with BRCA mutations. PARP inhibitors also exhibit positive results even in patients without homologous recombination (HR) deficiency. Therapeutic effects were successfully achieved; however, the development of resistance was unavoidable. Approximately 40–70% of patients are likely to develop resistance. Here, we describe the mechanisms of action of PARP inhibitors, the causes of resistance, and the various efforts to overcome resistance. Particularly, we determined the survival probability of cancer patients according to the expression patterns of genes associated with HR restoration, which are critical for the development of PARP inhibitor resistance. Furthermore, we discuss the innovative attempts to degrade PARP proteins by chemically modifying PARP inhibitors. These efforts would enhance the efficacy of PARP inhibitors or expand the scope of their usage.

DNA Methylation Malleability and Dysregulation in Cancer Progression: Understanding the Role of PARP1

Mammalian genomic DNA methylation represents a key epigenetic modification and its dynamic regulation that fine-tunes the gene expression of multiple pathways during development. It maintains the gene expression of one generation of cells; particularly, the mitotic inheritance of gene-expression patterns makes it the key governing mechanism of epigenetic change to the next generation of cells. Convincing evidence from recent discoveries suggests that the dynamic regulation of DNA methylation is accomplished by the enzymatic action of TET dioxygenase, which oxidizes the methyl group of cytosine and activates transcription. As a result of aberrant DNA modifications, genes are improperly activated or inhibited in the inappropriate cellular context, contributing to a plethora of inheritable diseases, including cancer. We outline recent advancements in understanding how DNA modifications contribute to tumor suppressor gene silencing or oncogenic-gene stimulation, as well as dysregulation of DNA methylation in cancer progression. In addition, we emphasize the function of PARP1 enzymatic activity or inhibition in the maintenance of DNA methylation dysregulation. In the context of cancer remediation, the impact of DNA methylation and PARP1 pharmacological inhibitors, and their relevance as a combination therapy are highlighted.

Therapeutic Potentials of Poly (ADP-Ribose) Polymerase 1 (PARP1) Inhibition in Multiple Sclerosis and Animal Models: Concept Revisiting

Poly (ADP-ribose) polymerase 1 (PARP1) plays a fundamental role in DNA repair and gene expression. Excessive PARP1 hyperactivation, however, has been associated with cell death. PARP1 and/or its activity are dysregulated in the immune and central nervous system of multiple sclerosis (MS) patients and animal models. Pharmacological PARP1 inhibition is shown to be protective against immune activation and disease severity in MS animal models while genetic PARP1 deficiency studies reported discrepant results. The inconsistency suggests that the function of PARP1 and PARP1-mediated PARylation may be complex and context-dependent. The article reviews PARP1 functions, discusses experimental findings and possible interpretations of PARP1 in inflammation, neuronal/axonal degeneration, and oligodendrogliopathy, three major pathological components cooperatively determining MS disease course and neurological progression, and points out future research directions. Cell type specific PARP1 manipulations are necessary for revisiting the role of PARP1 in the three pathological components prior to moving PARP1 inhibition into clinical trials for MS therapy.