Therapeutic Targeting of Poly(ADP-Ribose) Polymerase-1 (PARP1) in Cancer: Current Developments, Therapeutic Strategies, and Future Opportunities

Transcriptional regulation mechanism of PARP1 and its application in disease treatment

Poly (ADP-ribose) polymerase 1 (PARP1) is a multifunctional nuclear enzyme that catalyzes poly-ADP ribosylation in eukaryotic cells. In addition to maintaining genomic integrity, this nuclear enzyme is also involved in transcriptional regulation. PARP1 can trigger and maintain changes in the chromatin structure and directly recruit transcription factors. PARP1 also prevents DNA methylation. However, most previous reviews on PARP1 have focused on its involvement in maintaining genome integrity, with less focus on its transcriptional regulatory function. This article comprehensively reviews the transcriptional regulatory function of PARP1 and its application in disease treatment, providing new ideas for targeting PARP1 for the treatment of diseases other than cancer.

Poly (ADP-ribose) polymerase (PARP) inhibitors as anticancer agents: An outlook on clinical progress, synthetic strategies, biological activity, and structure-activity relationship

Poly (ADP-ribose) polymerase (PARP) is considered an essential component in case of DNA (Deoxyribonucleic acid) damage, response by sensing DNA damage and engaging DNA repair proteins. Those proteins repair the damaged DNA via an aspect of posttranslational modification, known as poly (ADP-Ribosyl)ation (PARylation). Specifically, PARP inhibitors (PARPi) have shown better results when administered alone in a variety of cancer types with BRCA (Breast Cancer gene) mutation. The clinical therapeutic benefits of PARP inhibitors have been diminished by their cytotoxicity, progression of drug resistance, and limitation of indication, regardless of their tremendous clinical effectiveness. A growing number of PARP-1 inhibitors, particularly those associated with BRCA-1/2 mutations, have been identified as potential cancer treatments. Recently, several researchers have identified various promising scaffolds, which have resulted in the resuscitation of the faith in PARP inhibitors as cancer therapies. This review provided a comprehensive update on the anatomy and physiology of the PARP enzyme, the profile of FDA (Food and Drug Administration) and CFDA (China Food and Drug Administration)-approved drugs, and small-molecule inhibitors of PARP, including their synthetic routes, biological evaluation, selectivity, and structure-activity relationship.

Loss of cytidine deaminase expression as a potential attempt to counteract the process of carcinogenesis by reducing basal PARP-1 activity and increasing tau levels

Cytidine deaminase (CDA) is a pyrimidine salvage pathway enzyme that catalyzes the hydrolytic deamination of free cytidine and deoxycytidine to uridine and deoxyuridine, respectively. Our team discovered that CDA deficiency is associated with several aspects of genetic instability, such as increased sister chromatid exchange and ultrafine anaphase bridge frequencies. Based on these results, we sought (1) to determine how CDA deficiency contributes to genetic instability, (2) to explore the possible relationships between CDA deficiency and carcinogenesis, and (3) to develop a new anticancer treatment targeting CDA-deficient tumors. This review summarizes our major findings indicating that CDA deficiency is associated with a genetic instability that does not confer an increased cancer risk. In light of our results and published data, I propose a novel hypothesis that loss of CDA, by reducing basal PARP-1 activity and increasing Tau levels, may reflect an attempt to prevent, slow or reverse the process of carcinogenesis.

Integrated single-cell sequencing, spatial transcriptome sequencing and bulk RNA sequencing highlights the molecular characteristics of parthanatos in gastric cancer

BACKGROUND

Parthanatos is a novel programmatic form of cell death based on DNA damage and PARP-1 dependency. Nevertheless, its specific role in the context of gastric cancer (GC) remains uncertain.

METHODS

In this study, we integrated multi-omics algorithms to investigate the molecular characteristics of parthanatos in GC. A series of bioinformatics algorithms were utilized to explore clinical heterogeneity of GC and further predict the clinical outcomes.

RESULTS

Firstly, we conducted a comprehensive analysis of the omics features of parthanatos in various human tumors, including genomic mutations, transcriptome expression, and prognostic relevance. We successfully identified 7 cell types within the GC microenvironment: myeloid cell, epithelial cell, T cell, stromal cell, proliferative cell, B cell, and NK cell. When compared to adjacent non-tumor tissues, single-cell sequencing results from GC tissues revealed elevated scores for the parthanatos pathway across multiple cell types. Spatial transcriptomics, for the first time, unveiled the spatial distribution characteristics of parthanatos signaling. GC patients with different parthanatos signals often exhibited distinct immune microenvironment and metabolic reprogramming features, leading to different clinical outcomes. The integration of parthanatos signaling and clinical indicators enabled the creation of novel survival curves that accurately assess patients' survival times and statuses.

CONCLUSIONS

In this study, the molecular characteristics of parthanatos' unicellular and spatial transcriptomics in GC were revealed for the first time. Our model based on parthanatos signals can be used to distinguish individual heterogeneity and predict clinical outcomes in patients with GC.

Collagen I-induced VCAN/ERK signaling and PARP1/ZEB1-mediated metastasis facilitate OSBPL2 defect to promote colorectal cancer progression

The global burden of colorectal cancer (CRC) has rapidly increased in recent years. Dysregulated cholesterol homeostasis facilitated by extracellular matrix (ECM) remodeling transforms the tumor microenvironment. Collagen I, a major with ECM component is highly expressed in colorectal tumors with infiltrative growth. Although oxysterol binding protein (OSBP)-related proteins accommodate tumorigenesis, OSBPL2, which is usually involved in deafness, is not associated with CRC progression. Therefore, we aimed to investigate the pathological function of OSBPL2 and identify the molecular link between ECM-Collagen I and OSBPL2 in CRC to facilitate the development of new treatments for CRC. OSBPL2 predicted a favorable prognosis in stage IV CRC and substantially repressed Collagen I-induced focal adhesion, migration, and invasion. The reduction of OSBPL2 activated ERK signaling through the VCAN/AREG/EREG axis during CRC growth, while relying on PARP1 via ZEB1 in CRC metastasis. OSBPL2 defect supported colorectal tumor growth and metastasis, which were suppressed by the ERK and PARP1 inhibitors SCH772984 and AG14361, respectively. Overall, our findings revealed that the Collagen I-induced loss of OSBPL2 aggravates CRC progression through VCAN-mediated ERK signaling and the PARP1/ZEB1 axis. This demonstrates that SCH772984 and AG14361 are reciprocally connective therapies for OSBPL2Low CRC, which could contribute to further development of targeted CRC treatment.

The functions and mechanisms of post-translational modification in protein regulators of RNA methylation: Current status and future perspectives

RNA methylation, an epigenetic modification that does not alter gene sequence, may be important to diverse biological processes. Protein regulators of RNA methylation include "writers," "erasers," and "readers," which respectively deposit, remove, and recognize methylated RNA. RNA methylation, particularly N6-methyladenosine (m6A), 5-methylcytosine (m5C), N3-methylcytosine (m3C), N1-methyladenosine (m1A) and N7-methylguanosine (m7G), has been suggested as disease therapeutic targets. Despite advances in the structure and pharmacology of RNA methylation regulators that have improved drug discovery, regulating these proteins by various post-translational modifications (PTMs) has received little attention. PTM modifies protein structure and function, affecting all aspects of normal biology and pathogenesis, including immunology, cell differentiation, DNA damage repair, and tumors. It is becoming evident that RNA methylation regulators are also regulated by diverse PTMs. PTM of RNA methylation regulators induces their covalent linkage to new functional groups, hence modifying their activity and function. Mass spectrometry has identified many PTMs on protein regulators of RNA methylation. In this review, we describe the functions and PTM of protein regulators of RNA methylation and summarize the recent advances in the regulatory mode of human disease and its underlying mechanisms.

Indirubin derivatives as bifunctional molecules inducing DNA damage and targeting PARP for the treatment of cancer

Based on the facts that significant synergistic effect existed between PARP inhibitors and DNA damage agents and the DNA damage caused by indirubin's derivatives, we herein adopted the strategy to combine the pharmacophores of PARP inhibitors and the unique scaffold of indirubin to design a series of bifunctional molecules inducing DNA damage and targeting PARP. After SAR studies, the most potent compound 12a, encoded as KWWS-12a, exhibited improved inhibitory effect against PARP1 compared with PARP1 inhibitor Olaparib (IC50 = 1.89 nM vs 7.48 nM) and enhanced antiproliferative activities than the combination of Olaparib and indirubin-3'-monoxime towards HCT-116 cells (IC50 = 0.31 μM vs 1.37 μM). In the normal NCM-460 cells, 12a showed low toxicity (IC50 > 60 μM). The mechanism research indicated that 12a could increase the levels of γH2AX concentration dependently, arrest the cell cycle in S phase and induce apoptosis in HCT-116 cells. In vivo experiments showed that 12a displayed more significant antitumor potential than that of the positive controls. Our studies demonstrated that 12a could be a promising candidate for cancer therapy.

Advances of antitumor drug discovery in traditional Chinese medicine and natural active products by using multi-active components combination

The antitumor efficacy of Chinese herbal medicines has been widely recognized. Leading compounds such as sterols, glycosides, flavonoids, alkaloids, terpenoids, phenylpropanoids, and polyketides constitute their complex active components. The antitumor monomers derived from Chinese medicine possess an attractive anticancer activity. However, their use was limited by low bioavailability, significant toxicity, and side effects, hindering their clinical applications. Recently, new chemical entities have been designed and synthesized by combining natural drugs with other small drug molecules or active moieties to improve the antitumor activity and selectivity, and reduce side effects. Such a novel conjugated drug that can interact with several vital biological targets in cells may have a more significant or synergistic anticancer activity than a single-molecule drug. In addition, antitumor conjugates could be obtained by combining pharmacophores containing two or more known drugs or leading compounds. Based on these studies, the new drug research and development could be greatly shortened. This study reviews the research progress of conjugates with antitumor activity based on Chinese herbal medicine. It is expected to serve as a valuable reference to antitumor drug research and clinical application of traditional Chinese medicine.

PARP-1: a critical regulator in radioprotection and radiotherapy-mechanisms, challenges, and therapeutic opportunities

Background: Since its discovery, poly (ADP-ribose) polymerase 1 (PARP-1) has been extensively studied due to its regulatory role in numerous biologically crucial pathways. PARP inhibitors have opened new therapeutic avenues for cancer patients and have gained approval as standalone treatments for certain types of cancer. With continued advancements in the research of PARP inhibitors, we can fully realize their potential as therapeutic targets for various diseases. Purpose: To assess the current understanding of PARP-1 mechanisms in radioprotection and radiotherapy based on the literature. Methods: We searched the PubMed database and summarized information on PARP inhibitors, the interaction of PARP-1 with DNA, and the relationships between PARP-1 and p53/ROS, NF-κB/DNA-PK, and caspase3/AIF, respectively. Results: The enzyme PARP-1 plays a crucial role in repairing DNA damage and modifying proteins. Cells exposed to radiation can experience DNA damage, such as single-, intra-, or inter-strand damage. This damage, associated with replication fork stagnation, triggers DNA repair mechanisms, including those involving PARP-1. The activity of PARP-1 increases 500-fold on DNA binding. Studies on PARP-1-knockdown mice have shown that the protein regulates the response to radiation. A lack of PARP-1 also increases the organism's sensitivity to radiation injury. PARP-1 has been found positively or negatively regulate the expression of specific genes through its modulation of key transcription factors and other molecules, including NF-κB, p53, Caspase 3, reactive oxygen species (ROS), and apoptosis-inducing factor (AIF). Conclusion: This review provides a comprehensive analysis of the physiological and pathological roles of PARP-1 and examines the impact of PARP-1 inhibitors under conditions of ionizing radiation exposure. The review also emphasizes the challenges and opportunities for developing PARP-1 inhibitors to improve the clinical outcomes of ionizing radiation damage.

PARP inhibitor olaparib induced differential protein expression in cervical cancer cells

PARP inhibitors are a potential class of chemotherapeutic drugs but PARP inhibitor response has not been explored systematically. We lack a specific understanding of the subset of the proteome preferentially modified in various cancers by PARP inhibitors. Implications of PARP inhibitor and PARP1 in cervical cancer treatment and resistance are not fully elucidated. We conducted a mass spectrometry-based proteomic analysis of cervical cancer Hela cells treated with olaparib. We aimed to identify the alteration in the protein signaling pathway induced by PARP inhibitors beyond the DNA damage response pathway. Our data demonstrate a significant reduction in PARP activity and enhanced cell death after olaparib treatment. We further observed articulated proteomic changes with a significant enrichment of proteins in diverse cellular processes. The differentially expressed proteins were predominantly associated with RNA metabolism, mRNA splicing, processing, and RNA binding. Our data also identified proteins that could probably contribute to survival mechanisms resulting in resistance to PARP inhibitors. Hence, we put forth the overview of proteomic changes induced by PARP inhibitor olaparib in cervical cancer cells. This study highlights the significant proteins modified during PARP inhibition and thus could be a probable target for combination therapies with PARP inhibitors in cervical cancer. SIGNIFICANCE.

A Double-Edged Sword: The Two Faces of PARylation

Poly ADP-ribosylation (PARylation) is a post-translational modification process. Following the discovery of PARP-1, numerous studies have demonstrated the role of PARylation in the DNA damage and repair responses for cellular stress and DNA damage. Originally, studies on PARylation were confined to PARP-1 activation in the DNA repair pathway. However, the interplay between PARylation and DNA repair suggests that PARylation is important for the efficiency and accuracy of DNA repair. PARylation has contradicting roles; however, recent evidence implicates its importance in inflammation, metabolism, and cell death. These differences might be dependent on specific cellular conditions or experimental models used, and suggest that PARylation may play two opposing roles in cellular homeostasis. Understanding the role of PARylation in cellular function is not only important for identifying novel therapeutic approaches; it is also essential for gaining insight into the mechanisms of unexplored diseases. In this review, we discuss recent reports on the role of PARylation in mediating diverse cellular functions and homeostasis, such as DNA repair, inflammation, metabolism, and cell death.

Poly (ADP-ribose) polymerase 1-mediated defective mitophagy contributes to painful diabetic neuropathy in the db/db model

Studies have shown that poly (ADP-ribose) polymerase 1 (PARP1) was involved in the pathological process of diabetes. Mitophagy is widely acknowledged to be a key regulatory process in maintaining reactive oxygen species homeostasis via lysosome degradation of damaged mitochondria. However, the regulatory role of PARP1 in mitophagy-related mitochondrial oxidative injury and progression of painful diabetic neuropathy (PDN) is unclear. In this study, we studied the in vitro and in vivo mechanisms of PARP1-mediated mitophagy blockade in a leptin gene-mutation (db/db) mouse model of PDN. Db/db mice models of PDN were established by assessing the sciatic nerve conduction velocity (SNCV), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL). The results showed that PARP1 activity and mitochondrial injury of dorsal root ganglion (DRG) neurons were increased, and mitophagy was impaired in PDN mice. PARP1 was found to mediate the impairment of mitophagy in DRG neurons isolated from PDN mice. PARP1 inhibitors (PJ34 or AG14361) attenuated diabetes-induced peripheral nerve hyperalgesia, restored DRG neuron mitophagy function and decreased mitochondrial oxidative injury. Mitophagy impairment induced by lysosome deacidificant (DC661) aggravated diabetes-induced DRG neuron mitochondrial oxidative stress and injury. Taken together, our data revealed that PARP1 induced defective mitophagy of DRG neurons is a key mechanism in diabetes-induced peripheral neuropathic injury. Inhibition of PARP1 and restoration of mitophagy function are potential therapeutic targets for PDN.

PARP Inhibitors and Radiometabolic Approaches in Metastatic Castration-Resistant Prostate Cancer: What’s Now, What’s New, and What’s Coming?

Simple Summary

Prostate cancer still represents an important health problem in men, considering its high frequency. Over the last decade, novel treatment options have emerged, leading to notable clinical benefits. These recent scientific acquisitions are creating the basis to widen the treatment scenario of this tumor, evolving from targeting the androgen receptor axis or the traditional chemotherapy approach.

Abstract

In recent years, the advances in the knowledge on the molecular characteristics of prostate cancer is allowing to explore novel treatment scenarios. Furthermore, technological discoveries are widening diagnostic and treatment weapons at the clinician disposal. Among these, great relevance is being gained by PARP inhibitors and radiometabolic approaches. The result is that DNA repair genes need to be altered in a high percentage of patients with metastatic prostate cancer, making these patients optimal candidates for PARP inhibitors. These compounds have already been proved to be active in pretreated patients and are currently being investigated in other settings. Radiometabolic approaches combine specific prostate cancer cell ligands to radioactive particles, thus allowing to deliver cytotoxic radiations in cancer cells. Among these, radium-223 and lutetium-177 have shown promising activity in metastatic pretreated prostate cancer patients and further studies are ongoing to expand the applications of this therapeutic approach. In addition, nuclear medicine techniques also have an important diagnostic role in prostate cancer. Herein, we report the state of the art on the knowledge on PARP inhibitors and radiometabolic approaches in advanced prostate cancer and present ongoing clinical trials that will hopefully expand these two treatment fields.

PARP1 as a therapeutic target in acute myeloid leukemia and myelodysplastic syndrome

Poly(ADP-ribose) polymerase 1 (PARP1) is a key mediator of various forms of DNA damage repair and plays an important role in the progression of several cancer types. The enzyme is activated by binding to DNA single-strand and double-strand breaks. Its contribution to chromatin remodeling makes PARP1 crucial for gene expression regulation. Inhibition of its activity with small molecules leads to the synthetic lethal effect by impeding DNA repair in the treatment of cancer cells. At first, PARP1 inhibitors (PARPis) were developed to target breast cancer mutated cancer cells. Currently, PARPis are being studied to be used in a broader variety of patients either as single agents or in combination with chemotherapy, antiangiogenic agents, ionizing radiation, and immune checkpoint inhibitors. Ongoing clinical trials on olaparib, rucaparib, niraparib, veliparib, and the recent talazoparib show the advantage of these agents in overcoming PARPi resistance and underline their efficacy in targeted treatment of several hematologic malignancies. In this review, focusing on the crucial role of PARP1 in physiological and pathological effects in myelodysplastic syndrome and acute myeloid leukemia, we give an outline of the enzyme's mechanisms of action and its role in the pathophysiology and prognosis of myelodysplastic syndrome/acute myeloid leukemia and we analyze the available data on the use of PARPis, highlighting their promising advances in clinical application.

MicroRNA-550a-3-5p controls the brain metastasis of lung cancer by directly targeting YAP1

Background

This study aimed to explore the potential regulatory mechanisms of brain metastasis and to identify novel underlying targets of lung cancer with brain metastasis.

Methods

Exosomes were isolated from the plasma of lung cancer patients with or without brain metastasis and low or high metastatic lung cancer cells, and small RNA from plasma-derived exosomes were sequenced. Differentially expressed miRNAs (DE-miRNAs) were identified. Human brain microvascular endothelial cells (HBMECs) were transfected with miR-550a-3-5p mimics or inhibitors and exosomes. Cell viability, migration, and apoptosis/cycle were determined using Cell Counting Kit-8 (CCK-8), Transwell, and flow cytometry, respectively. Western blotting was used to measure the expression of the associated proteins. Finally, a dual-luciferase reporter gene assay was performed to confirm the miR-550a-3-5p target.

Results

Transmission electron microscopy, NanoSight, and western blotting showed that exosomes were successfully isolated and cell-derived exosomes could be taken up by HBMECs. Sequencing identified 22 DE-miRNAs which were enriched in the MAPK, chemokine, PPAR, and Wnt signaling pathways. MiR-550a-3-5p was significantly enriched in brain metastatic exosomes. Cellular experiments showed that miR-550a-3-5p and exosome enrichment significantly inhibited cell viability and migration, promoted apoptosis, and regulated the cell cycle of HBMECs compared with the controls (P  <  0.05). Compared with the controls, high levels of both miR-550a-3-5p and exosomes markedly upregulated cleaved-PARP expression, but downregulated the expression of pRB, CDK6, YAP1, CTGF, and CYR61 (P  <  0.05). Finally, YAP1 was confirmed to bind directly to miR-550a-3-5p.

Conclusion

Our results indicate that miR-550a-3-5p and YAP1 may be novel potential targets for controlling brain metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02197-z.

Research progress on the association between environmental pollutants and the resistance mechanism of PARP inhibitors in ovarian cancer

The occurrence and progression of ovarian cancer are closely related to genetics and environmental pollutants. Poly(ADP-ribose) polymerase (PARP) inhibitors have been a major breakthrough in the history of ovarian cancer treatment. PARP is an enzyme responsible for post-translational modification of proteins and repair of single-stranded DNA damage. PARP inhibitors can selectively inhibit PARP function, resulting in a synthetic lethal effect on tumor cells defective in homologous recombination repair. However, with large-scale application, drug resistance also inevitably appears. For PARP inhibitors, the diversity and complexity of drug resistance mechanisms have always been difficult problems in clinical treatment. Herein, we mainly summarized the research progress of DNA damage repair and drug resistance mechanisms related to PARP inhibitors and the impact of environmental pollutants on DNA damage repair to aid the development prospects and highlight urgent problems to be solved.

Calycosin stimulates the proliferation of endothelial cells, but not breast cancer cells, via a feedback loop involving RP11-65M17.3, BRIP1 and ERα

It is widely accepted that estrogen can be replaced by phytoestrogens to treat postmenopausal cardiovascular disease and possibly decrease the risk of breast cancer. However, few studies have investigated the effects of phytoestrogens on vascular endothelial cells (ECs). In the present study, we show that the phytoestrogen calycosin (20 μM) stimulated the proliferation of ECs (HUVECs and HMEC-1) but inhibited the growth of breast cancer cells (BCCs) expressing ERα (MCF-7 and T47D). Here we provide evidence for the presence of a positive feedback loop between ERα and long noncoding RNA RP11-65M17.3 in both normal and cancer cells, and calycosin stimulated this feedback loop in ECs but decreased RP11-65M17.3 expression in BCCs. Subsequently, the calycosin-induced activation of this loop decreased the expression of the target of BRIP1 (BRCA1 interacting protein C-terminal helicase 1), increased the phosphorylation of Akt and ERK1/2, and finally inhibited the cleavage of PARP-1 in ECs. In nude mice bearing MCF-7 xenografts, calycosin did not stimulate tumor growth as strongly as 17β-estradiol. Together, these results suggest that calycosin promotes the proliferation of ECs, and notable inhibits the growth of BCCs. A possible reason for these results is the involvement of a feedback loop between ERα and RP11-65M17.3.

Promising anti- cervical carcinoma and inflammatory agent, Resveratrol targets poly (ADP-ribose) polymerase 1 (PARP-1) induced premature ovarian failure with a potent enzymatic modulatory activity

Radioprotective effects of Resveratrol is well known in normal cells exposed to the damaging effects of ionizing radiation however, its potential radioprotective effect on ovarian follicle formation and development is still uncertain. Astonishingly, it has been reported that PARP contributed to the pathogenesis of immune-mediated ovarian injury. In this paper, Resveratrol was tested for its inflammatory, anti-cervical carcinoma activity, and checked its targets poly (ADP-ribose) polymerase 1 (PARP-1) induced premature ovarian failure with a potent enzymatic modulatory activity. Through high-throughput virtual screening method, Resveratrol was screened to find its target. That the compound strongly inhibited cervical carcinoma HT-3 cell. The cell proliferation was evaluated by an CCK-8 assay, and the cell apoptosis was assessed by a flow cytometry. Rat model of premature ovarian failure was used to introduce resveratrol preparation and rtPCR was done to measure expression of apoptosis related markers. We report resveratrol as a potential target for PARP-1 and its modulator from a high-throughput virtual screening method. Resveratrol was measured its anti-cervical carcinoma activity by using an CCK-8 assay, which suggested that the compound strongly inhibited HT-3 cell proliferation, the IC₅₀ value is 0.65 μM. In addition, the compound induced HT-3 cell apoptosis in a dose-response manner. Resveratrol preserves the entire ovarian follicle pool manifested by increasing serum anti-Müllerian hormone (AMH) levels. Study suggest that resveratrol restored ovarian function through increasing AMH levels, and diminishing ovarian inflammation, predominantly modulation of PPAR-1 and inhibition of inflammatory cytokines. Resveratrol was identified targets for PARP-1 from a high-throughput virtual screening method, strongly inhibited PARP-1 protein and HT-3 cell proliferation. Resveratrol is a promising PARP-1 modulator with anti-cervical carcinoma activity, which deserves further investigation.

PARP Inhibition Increases the Reliance on ATR/CHK1 Checkpoint Signaling Leading to Synthetic Lethality-An Alternative Treatment Strategy for Epithelial Ovarian Cancer Cells Independent from HR Effectiveness

Poly (ADP-ribose) polymerase inhibitor (PARPi, olaparib) impairs the repair of DNA single-strand breaks (SSBs), resulting in double-strand breaks (DSBs) that cannot be repaired efficiently in homologous recombination repair (HRR)-deficient cancers such as BRCA1/2-mutant cancers, leading to synthetic lethality. Despite the efficacy of olaparib in the treatment of BRCA1/2 deficient tumors, PARPi resistance is common. We hypothesized that the combination of olaparib with anticancer agents that disrupt HRR by targeting ataxia telangiectasia and Rad3-related protein (ATR) or checkpoint kinase 1 (CHK1) may be an effective strategy to reverse ovarian cancer resistance to olaparib. Here, we evaluated the effect of olaparib, the ATR inhibitor AZD6738, and the CHK1 inhibitor MK8776 alone and in combination on cell survival, colony formation, replication stress response (RSR) protein expression, DNA damage, and apoptotic changes in BRCA2 mutated (PEO-1) and HRR-proficient BRCA wild-type (SKOV-3 and OV-90) cells. Combined treatment caused the accumulation of DNA DSBs. PARP expression was associated with sensitivity to olaparib or inhibitors of RSR. Synergistic effects were weaker when olaparib was combined with CHK1i and occurred regardless of the BRCA2 status of tumor cells. Because PARPi increases the reliance on ATR/CHK1 for genome stability, the combination of PARPi with ATR inhibition suppressed ovarian cancer cell growth independently of the efficacy of HRR. The present results were obtained at sub-lethal doses, suggesting the potential of these inhibitors as monotherapy as well as in combination with olaparib.

Parthanatos and its associated components: Promising therapeutic targets for cancer

Parthanatos is a PARP1-dependent, caspase-independent, cell-death pathway that is distinct from apoptosis, necrosis, or other known forms of cell death. Parthanatos is a multistep pathway that plays a pivotal role in tumorigenesis. There are many molecules in the parthanatos cascade that can be exploited to create therapeutic interventions for cancer management, including PARP1, PARG, ARH3, AIF, and MIF. These critical molecules are involved in tumor cell proliferation, progression, invasion, and metastasis. Therefore, these molecular signals in the parthanatos cascade represent promising therapeutic targets for cancer therapy. In addition, intimate interactions occur between parthanatos and other forms of cancer cell death, such as apoptosis and autophagy. Thus, co-targeting a combination of parthanatos and other death pathways may further provide a new avenue for cancer precision treatment. In this review, we elaborate on the signaling pathways of canonical parthanatos and briefly introduce the non-canonical parthanatos. We also shed light on the role parthanatos and its associated components play in tumorigenesis, particularly with respect to the aforementioned five molecules, and discuss the promise targeted therapy of parthanatos and its associated components holds for cancer therapy.

Flavonoids from Rosaroxburghii Tratt prevent reactive oxygen species-mediated DNA damage in thymus cells both combined with and without PARP-1 expression after exposure to radiation in vivo

This study aimed to evaluate the role of FRT in ROS/DNA regulation with or without PARP-1 in radiation-injured thymus cells. The administration of FRT to PARP-1-/- (KO) mice demonstrated that FRT significantly increased the viability of thymus cells and decreased their rate of apoptosis through PARP-1. Radiation increased the levels of ROS, γ-H2AX and 53BP1, and induced DNA double strand breaks. Compared with wild type (WT) mice, levels of ROS, γ-H2AX and 53BP1 in KO mice were much less elevated. The FRT treatment groups also showed little reduction in these indicators in KO mice compared with WT mice. The results of the KO mice study indicated that FRT reduced ROS activation through inhibition of PARP-1. Furthermore, FRT reduced the concentrations of γ-H2AX by decreasing ROS activation. However, we found that FRT did not regulate 53BP1, a marker of DNA damage, because of its elimination of ROS. Levels of apoptosis-inducing factor (AIF), exhibited no significant difference after irradiation in KO mice. To summarize, ROS suppression by PARP-1 knockout in KO mice highlights potential therapeutic target either by PARP-1 inhibition combined with radiation or by treatment with a drug therapy alone. AIF-induced apoptosis could not be activated in KO mice.

Biomarkers in Triple-Negative Breast Cancer: State-of-the-Art and Future Perspectives

Triple-negative breast cancer (TNBC) is a heterogeneous group of tumors characterized by aggressive behavior, high risk of distant recurrence, and poor survival. Chemotherapy is still the main therapeutic approach for this subgroup of patients, therefore, progress in the treatment of TNBC remains an important challenge. Data derived from molecular technologies have identified TNBCs with different gene expression and mutation profiles that may help developing targeted therapies. So far, however, only a few of these have shown to improve the prognosis and outcomes of TNBC patients. Robust predictive biomarkers to accelerate clinical progress are needed. Herein, we review prognostic and predictive biomarkers in TNBC, discuss the current evidence supporting their use, and look at the future of this research field.

Participation of the ATR/CHK1 pathway in replicative stress targeted therapy of high-grade ovarian cancer

Ovarian cancer is one of the most lethal gynecologic malignancies reported throughout the world. The initial, standard-of-care, adjuvant chemotherapy in epithelial ovarian cancer is usually a platinum drug, such as cisplatin or carboplatin, combined with a taxane. However, despite surgical removal of the tumor and initial high response rates to first-line chemotherapy, around 80% of women will develop cancer recurrence. Effective strategies, including chemotherapy and new research models, are necessary to improve the prognosis. The replication stress response (RSR) is characteristic of the development of tumors, including ovarian cancer. Hence, RSR pathway and DNA repair proteins have emerged as a new area for anticancer drug development. Although clinical trials have shown poly (ADP-ribose) polymerase inhibitors (PARPi) response rates of around 40% in women who carry a mutation in the BRCA1/2 genes, PARPi is responsible for tumor suppression, but not for complete tumor regression. Recent reports suggest that cells with impaired homologous recombination (HR) activities due to mutations in TP53 gene or specific DNA repair proteins are specifically sensitive to ataxia telangiectasia and Rad3-related protein (ATR) inhibitors. Replication stress activates DNA repair checkpoint proteins (ATR, CHK1), which prevent further DNA damage. This review describes the use of DNA repair checkpoint inhibitors as single agents and strategies combining these inhibitors with DNA-damaging compounds for ovarian cancer therapy, as well as the new platforms used for optimizing ovarian cancer therapy.

Mitochondrial Protection by PARP Inhibition

Inhibitors of the nuclear DNA damage sensor and signalling enzyme poly(ADP-ribose) polymerase (PARP) have recently been introduced in the therapy of cancers deficient in double-strand DNA break repair systems, and ongoing clinical trials aim to extend their use from other forms of cancer non-responsive to conventional treatments. Additionally, PARP inhibitors were suggested to be repurposed for oxidative stress-associated non-oncological diseases resulting in a devastating outcome, or requiring acute treatment. Their well-documented mitochondria- and cytoprotective effects form the basis of PARP inhibitors’ therapeutic use for non-oncological diseases, yet can limit their efficacy in the treatment of cancers. A better understanding of the processes involved in their protective effects may improve the PARP inhibitors’ therapeutic potential in the non-oncological indications. To this end, we endeavoured to summarise the basic features regarding mitochondrial structure and function, review the major PARP activation-induced cellular processes leading to mitochondrial damage, and discuss the role of PARP inhibition-mediated mitochondrial protection in several oxidative stress-associated diseases.

Targeted PARP Inhibition Combined with FGFR1 Blockade is Synthetically Lethal to Malignant Cells in Patients with Pancreatic Cancer

The role and therapeutic promise of poly-ADP ribose polymerase (PARP) inhibitors in anticancer chemotherapy are increasingly being explored, particularly in adjuvant or maintenance therapy, considering their low efficacy as monotherapy agents and their potentiating effects on concurrently administered contemporary chemotherapeutics. Against the background of increasing acquired resistance to FGFR1 inhibitors and our previous work, which partially demonstrated the caspase-3/PARP-mediated antitumor and antimetastatic efficacy of PD173074, a selective FGFR1 inhibitor, against ALDH-high/FGFR1-rich pancreatic ductal adenocarcinoma (PDAC) cells, we investigated the probable synthetic lethality and therapeutic efficacy of targeted PARP inhibition combined with FGFR1 blockade in patients with PDAC. Using bioinformatics-based analyses of gene expression profiles, co-occurrence and mutual exclusivity, molecular docking, immunofluorescence staining, clonogenicity, Western blotting, cell viability or cytotoxicity screening, and tumorsphere formation assays, we demonstrated that FGFR1 and PARP co-occur, form a complex, and reduce survival in patients with PDAC. Furthermore, FGFR1 and PARP expression was upregulated in FGFR1 inhibitor (dasatinib)-resistant PDAC cell lines SU8686, MiaPaCa2, and PANC-1 compared with that in sensitive cell lines Panc0403, Panc0504, Panc1005, and SUIT-2. Compared with the limited effect of single-agent olaparib (PARP inhibitor) or PD173074 on PANC-1 and SUIT-2 cells, low-dose combination (olaparib + PD173074) treatment significantly, dose-dependently, and synergistically reduced cell viability, upregulated cleaved PARP, pro-caspase (CASP)-9, cleaved-CASP9, and cleaved-CASP3 protein expression, and downregulated Bcl-xL protein expression. Furthermore, combination treatment markedly suppressed the clonogenicity and tumorsphere formation efficiency of PDAC cells regardless of FGFR1 inhibitor-resistance status and enhanced RAD51 and γ-H2AX immunoreactivity. In vivo studies have shown that both early and late initiation of combination therapy markedly suppressed tumor xenograft growth and increase in weight, although the effect was more pronounced in the early initiation group. In conclusion, FGFR1 inhibitor-resistant PDAC cells exhibited sensitivity to PD173074 after olaparib-mediated loss of PARP signaling. The present FGFR1/PARP-mediated synthetic lethality proof-of-concept study provided preclinical evidence of the feasibility and therapeutic efficacy of combinatorial FGFR1/PARP1 inhibition in human PDAC cell lines.

Role of Akt Activation in PARP Inhibitor Resistance in Cancer

Poly(ADP-ribose) polymerase (PARP) inhibitors have recently been introduced in the therapy of several types of cancers not responding to conventional treatments. However, de novo and acquired PARP inhibitor resistance is a significant limiting factor in the clinical therapy, and the underlying mechanisms are not fully understood. Activity of the cytoprotective phosphatidylinositol-3 kinase (PI3K)-Akt pathway is often increased in human cancer that could result from mutation, expressional change, or amplification of upstream growth-related factor signaling elements or elements of the Akt pathway itself. However, PARP-inhibitor-induced activation of the cytoprotective PI3K-Akt pathway is overlooked, although it likely contributes to the development of PARP inhibitor resistance. Here, we briefly summarize the biological role of the PI3K-Akt pathway. Next, we overview the significance of the PARP-Akt interplay in shock, inflammation, cardiac and cerebral reperfusion, and cancer. We also discuss a recently discovered molecular mechanism that explains how PARP inhibition induces Akt activation and may account for apoptosis resistance and mitochondrial protection in oxidative stress and in cancer.

Design, Synthesis and Molecular Modeling Study of Conjugates of ADP and Morpholino Nucleosides as A Novel Class of Inhibitors of PARP-1, PARP-2 and PARP-3

We report on the design, synthesis and molecular modeling study of conjugates of adenosine diphosphate (ADP) and morpholino nucleosides as potential selective inhibitors of poly(ADP-ribose)polymerases-1, 2 and 3. Sixteen dinucleoside pyrophosphates containing natural heterocyclic bases as well as 5-haloganeted pyrimidines, and mimicking a main substrate of these enzymes, nicotinamide adenine dinucleotide (NAD+)-molecule, have been synthesized in a high yield. Morpholino nucleosides have been tethered to the β-phosphate of ADP via a phosphoester or phosphoramide bond. Screening of the inhibiting properties of these derivatives on the autopoly(ADP-ribosyl)ation of PARP-1 and PARP-2 has shown that the effect depends upon the type of nucleobase as well as on the linkage between ADP and morpholino nucleoside. The 5-iodination of uracil and the introduction of the P–N bond in NAD+-mimetics have shown to increase inhibition properties. Structural modeling suggested that the P–N bond can stabilize the pyrophosphate group in active conformation due to the formation of an intramolecular hydrogen bond. The most active NAD+ analog against PARP-1 contained 5-iodouracil 2ʹ-aminomethylmorpholino nucleoside with IC50 126 ± 6 μM, while in the case of PARP-2 it was adenine 2ʹ-aminomethylmorpholino nucleoside (IC50 63 ± 10 μM). In silico analysis revealed that thymine and uracil-based NAD+ analogs were recognized as the NAD+-analog that targets the nicotinamide binding site. On the contrary, the adenine 2ʹ-aminomethylmorpholino nucleoside-based NAD+ analogs were predicted to identify as PAR-analogs that target the acceptor binding site of PARP-2, representing a novel molecular mechanism for selective PARP inhibition. This discovery opens a new avenue for the rational design of PARP-1/2 specific inhibitors.

PARP1 Inhibition Augments UVB-Mediated Mitochondrial Changes-Implications for UV-Induced DNA Repair and Photocarcinogenesis

Keratinocytes provide the first line of defense of the human body against carcinogenic ultraviolet (UV) radiation. Acute and chronic UVB-mediated cellular responses were widely studied. However, little is known about the role of mitochondrial regulation in UVB-induced DNA damage. Here, we show that poly (ADP-ribose) polymerase 1 (PARP1) and ataxia-telangiectasia-mutated (ATM) kinase, two tumor suppressors, are important regulators in mitochondrial alterations induced by UVB. Our study demonstrates that PARP inhibition by ABT-888 upon UVB treatment exacerbated cyclobutane pyrimidine dimers (CPD) accumulation, cell cycle block and cell death and reduced cell proliferation in premalignant skin keratinocytes. Furthermore, in human keratinocytes UVB enhanced oxidative phosphorylation (OXPHOS) and autophagy which were further induced upon PARP inhibition. Immunoblot analysis showed that these cellular responses to PARP inhibition upon UVB irradiation strongly alter the phosphorylation level of ATM, adenosine monophosphate-activated kinase (AMPK), p53, protein kinase B (AKT), and mammalian target of rapamycin (mTOR) proteins. Furthermore, chemical inhibition of ATM led to significant reduction in AMPK, p53, AKT, and mTOR activation suggesting the central role of ATM in the UVB-mediated mitochondrial changes. Our results suggest a possible link between UVB-induced DNA damage and metabolic adaptations of mitochondria and reveal the OXPHOS-regulating role of autophagy which is dependent on key metabolic and DNA damage regulators downstream of PARP1 and ATM.

The Enigmatic Function of PARP1: From PARylation Activity to PAR Readers

Poly(ADP-ribosyl)ation (PARylation) is catalysed by poly(ADP-ribose) polymerases (PARPs, also known as ARTDs) and then rapidly removed by degrading enzymes. Poly(ADP-ribose) (PAR) is produced from PARylation and provides a delicate and spatiotemporal interaction scaffold for numerous target proteins. The PARylation system, consisting of PAR synthesizers and erasers and PAR itself and readers, plays diverse roles in the DNA damage response (DDR), DNA repair, transcription, replication, chromatin remodeling, metabolism, and cell death. Despite great efforts by scientists in biochemistry, cell and molecular biology, genetics, and pharmacology over the last five decades, the biology of PARPs and PARylation remains enigmatic. In this review, we summarize the current understanding of the biological function of PARP1 (ARTD1), the founding member of the PARP family, focusing on the inter-dependent or -independent nature of different functional domains of the PARP1 protein. We also discuss the readers of PAR, whose function may transduce signals and coordinate the cellular processes, which has recently emerged as a new research avenue for PARP biology. We aim to provide some perspective on how future research might disentangle the biology of PARylation by dissecting the structural and functional relationship of PARP1, a major effector of the PARPs family.

Evaluation of some genes and proteins involved in apoptosis on human chronic myeloid leukemia cells (K562 cells) by datura innoxia leaves aqueous extract

Datura innoxia (D. innoxia) has an extensive usage in traditional medicine and can also be used for intervention therapy in order to treat cancer. Despite of accomplishing some researches on D. innoxia mechanism, still our knowledge is very little about exact D. innoxia apoptotic mechanism on human chronic myeloid leukemia cells (K562 cells). This study purpose was to clarify the molecular mechanism of apoptosis, which was mediated by D. innoxia leaves aqueous extract in K562 cells. MTT assay and flow cytometry was applied in order to assess the viability and apoptosis induction of K562 cells and normal human lymphoid B cells in the D. innoxia presence. Finally, the expression of the apoptotic related genes (p53, BAX, BCL2, Caspases 3, 6, 7 and 9) were evaluated using quantitative Real-Time PCR. Western blot analysis was applied for assessing the protein expression. MTT results indicated that D. innoxia could inhibit the viability of K562 cells in a dose- and time-dependent manner. In parallel, D. innoxia inhibitory effect on normal human lymphoid B cells was lower in comparison with its effect on K562 cells at the same concentrations and same incubation time. Apoptosis induction in K562 cells after D. innoxia exposure was determined by flow cytometry. Apoptosis was activated by D. innoxia in K562 cells throughout increasing the expression of P53, BAX/BCL2 ratio, caspase 9, 3, 6, 7. Western blot analysis demonstrated significant increase in cleaved PARP-1 and cleaved caspase 3 in treated K562 cells with high D. innoxia leaves aqueous extract concentration. D. innoxia leaves trigger apoptosis in K562 cells throughout intrinsic apoptotic pathway.Communicated by Ramaswamy H. Sarma.

Purpurogallin Protects Keratinocytes from Damage and Apoptosis Induced by Ultraviolet B Radiation and Particulate Matter 2.5

Purpurogallin, a natural phenol obtained from oak nutgalls, has been shown to possess antioxidant, anticancer, and anti-inflammatory effects. Recently, in addition to ultraviolet B (UVB) radiation that induces cell apoptosis via oxidative stress, particulate matter 2.5 (PM_2.5) was shown to trigger excessive production of reactive oxygen species. In this study, we observed that UVB radiation and PM_2.5 severely damaged human HaCaT keratinocytes, disrupting cellular DNA, lipids, and proteins and causing mitochondrial depolarization. Purpurogallin protected HaCaT cells from apoptosis induced by UVB radiation and/or PM_2.5. Furthermore, purpurogallin effectively modulates the pro-apoptotic and anti-apoptotic proteins under UVB irradiation via caspase signaling pathways. Additionally, purpurogallin reduced apoptosis via MAPK signaling pathways, as demonstrated using MAPK-p38, ERK, and JNK inhibitors. These results indicate that purpurogallin possesses antioxidant effects and protects cells from damage and apoptosis induced by UVB radiation and PM_2.5.

Discovery of Novel Bromophenol-Thiosemicarbazone Hybrids as Potent Selective Inhibitors of Poly(ADP-ribose) Polymerase-1 (PARP-1) for Use in Cancer

Poly(ADP-ribose) polymerase-1 (PARP-1) is a new potential target for anticancer drug discovery. A series of bromophenol-thiosemicarbazone hybrids as PARP-1 inhibitors were designed, synthesized, and evaluated for their antitumor activities. Among them, the most promising compound, 11, showed excellent selective PARP-1 inhibitory activity (IC₅₀ = 29.5 nM) over PARP-2 (IC₅₀ > 1000 nM) and potent anticancer activities toward the SK-OV-3, Bel-7402 and HepG2 cancer cell lines (IC₅₀ = 2.39, 5.45, and 4.60 μM), along with inhibition of tumor growth in an in vivo SK-OV-3 cell xenograft model. Further study demonstrated that compound 11 played an antitumor role through multiple anticancer mechanisms, including the induction of apoptosis and cell cycle arrest, cellular accumulation of DNA double-strand breaks, DNA repair alterations, inhibition of H₂O₂-triggered PARylation, antiproliferative effects via the production of cytotoxic reactive oxygen species, and autophagy. In addition, compound 11 displayed good pharmacokinetic characteristics and favorable safety. These observations demonstrate that compound 11 may serve as a lead compound for the discovery of new anticancer drugs.

Interaction of germline variants in a family with a history of early-onset clear cell renal cell carcinoma

Background

Identification of genetic factors causing predisposition to renal cell carcinoma has helped improve screening, early detection, and patient survival.

Methods

We report the characterization of a proband with renal and thyroid cancers and a family history of renal and other cancers by whole‐exome sequencing (WES), coupled with WES analysis of germline DNA from additional affected and unaffected family members.

Results

This work identified multiple predicted protein‐damaging variants relevant to the pattern of inherited cancer risk. Among these, the proband and an affected brother each had a heterozygous Ala45Thr variant in SDHA, a component of the succinate dehydrogenase (SDH) complex. SDH defects are associated with mitochondrial disorders and risk for various cancers; immunochemical analysis indicated loss of SDHB protein expression in the patient’s tumor, compatible with SDH deficiency. Integrated analysis of public databases and structural predictions indicated that the two affected individuals also had additional variants in genes including TGFB2, TRAP1, PARP1, and EGF, each potentially relevant to cancer risk alone or in conjunction with the SDHA variant. In addition, allelic imbalances of PARP1 and TGFB2 were detected in the tumor of the proband.

Conclusion

Together, these data suggest the possibility of risk associated with interaction of two or more variants.

SUN2: A potential therapeutic target in cancer

The incidence of cancer is increasing at an alarming rate despite recent advances in prevention strategies, diagnostics and therapeutics for various types of cancer. The identification of novel biomarkers to aid in prognosis and treatment for cancer is urgently required. Uncontrolled proliferation and dysregulated apoptosis are characteristics exhibited by cancer cells in the initiation of various types of cancer. Notably, aberrant expression of crucial oncogenes or cancer suppressors is a defining event in cancer occurrence. Research has demonstrated that SAD1/UNC84 domain protein-2 (SUN2) serves a suppressive role in breast cancer, atypical teratoid/rhabdoid tumors and lung cancer progression. Furthermore, SUN2 inhibits cancer cell proliferation, migration and promotes apoptosis. Recent reports have also shown that SUN2 serves prominent roles in resistance to the excessive DNA damage that destabilizes the genome and promotes cancer development, and these functions of SUN2 are critical for evading initiation of cancer. Additionally, increasing evidence has demonstrated that SUN2 is involved in maintaining cell nuclear structure and appears to be a central component for organizing the natural nuclear architecture in cancer cells. The focus of the present review is to provide an overview on the pharmacological functions of SUN2 in cancers. These findings suggest that SUN2 may serve as a promising therapeutic target and novel predictive marker in various types of cancer.

PARP inhibition induces Akt-mediated cytoprotective effects through the formation of a mitochondria-targeted phospho-ATM-NEMO-Akt-mTOR signalosome

PURPOSE

The cytoprotective effect of poly(ADP-ribose) polymerase 1 (PARP1) inhibition is well documented in various cell types subjected to oxidative stress. Previously, we have demonstrated that PARP1 inhibition activates Akt, and showed that this response plays a critical role in the maintenance of mitochondrial integrity and in cell survival. However, it has not yet been defined how nuclear PARP1 signals to cytoplasmic Akt.

METHODS

WRL 68, HeLa and MCF7 cells were grown in culture. Oxidative stress was induced with hydrogen peroxide. PARP was inhibited with the PARP inhibitor PJ34. ATM, mTOR- and NEMO were silenced using specific siRNAs. Cell viability assays were based on the MTT assay. PARP-ATM pulldown experiments were conducted; each protein was visualized by Western blotting. Immunoprecipitation of ATM, phospho-ATM and NEMO was performed from cytoplasmic and mitochondrial cell fractions and proteins were detected by Western blotting. In some experiments, a continually active Akt construct was introduced. Nuclear to cytoplasmic and mitochondrial translocation of phospho-Akt was visualized by confocal microscopy.

RESULTS

Here we present evidence for a PARP1 mediated, PARylation-dependent interaction between ATM and NEMO, which is responsible for the cytoplasmic transport of phosphorylated (thus, activated) ATM kinase. In turn, the cytoplasmic p-ATM and NEMO forms complex with mTOR and Akt, yielding the phospho-ATM-NEMO-Akt-mTOR signalosome, which is responsible for the PARP-inhibition induced Akt activation. The phospho-ATM-NEMO-Akt-mTOR signalosome localizes to the mitochondria and is essential for the PARP-inhibition-mediated cytoprotective effects in oxidatively stressed cells. When the formation of the signalosome is prevented, the cytoprotective effects diminish, but cells can be rescued by constantly active Akt1, further confirming the critical role of Akt activation in cytoprotection.

CONCLUSIONS

Taken together, the data presented in the current paper are consistent with the hypothesis that PARP inhibition suppresses the PARylation of ATM, which, in turn, forms an ATM-NEMO complex, which exits the nucleus, and combines in the cytosol with mTOR and Act, resulting in Act phosphorylation (i.e. activation), which, in turn, produces the cytoprotective action via the induction of Akt-mediated survival pathways. This mechanism can be important in the protective effect of PARP inhibitor in various diseases associated with oxidative stress. Moreover, disruption of the formation or action of the phospho-ATM-NEMO-Akt-mTOR signalosome may offer potential future experimental therapeutic checkpoints.

The CHK1 inhibitor SRA737 synergizes with PARP1 inhibitors to kill carcinoma cells

Inhibitors of PARP1 are approved therapeutic agents in ovarian carcinomas. We determined whether the novel clinically relevant CHK1 inhibitor SRA737 interacted with PARP1 inhibitors to kill carcinoma cells. In multiple mammary and ovarian cancer lines SRA737 synergized with the PARP1 inhibitors olaparib and niraparib to cause cell death. The [SRA737 + niraparib] drug combination activated an ATM-AMPK-ULK1-mTOR pathway which resulted in the formation of autophagosomes, temporally followed by autolysosome formation. Phosphorylation of ULK1 S317 was essential for kinase activation against ATG13. The drug combination elevated eIF2α phosphorylation which was causal at increasing Beclin1 and ATG5 expression, reducing MCL-1 and BCL-XL levels, and causing CD95 activation. Knock down of CD95, eIF2α, ATM, AMPKα, ULK1, Beclin1 or ATG5 reduced drug combination lethality. Blockade of either caspase 9 function or that of AIF each partially prevented cell death. Expression of activated mTOR or of c-FLIP-s or of BCL-XL reduced cell killing. In vivo, SRA737 and niraparib interacted in an additive fashion to suppress the growth of mammary tumors. Multiplex analyses revealed that drug combination treated tumors had reduced their plasma levels of sERBB1, sERBB2, sVEGFR1, sVEGFR2, sIL-6R, HGF, PDGFAB/BB and CXCL16 and enhanced the levels of CCL26, IL-8 and MIF. Surviving tumors had activated ERK1/2 and AKT. This finding argues that IL-8/ERK/AKT signaling may be an evolutionary survival response to [SRA737 + niraparib].

Regulatory T cells increase after treatment with poly (ADP-ribose) polymerase-1 inhibitor in ischemic stroke patients

BACKGROUND

Regulatory T cells (Tregs) are thought to play a modulatory role in immune responses and to improve outcomes after ischemic stroke. Thus, various strategies for increasing Tregs in animal models of ischemic stroke have yielded successful results. The aim of this study was to examine the potential effect of poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor on Treg proportion in stroke patients.

METHODS

Peripheral blood samples were collected from 12 ischemic stroke patients (within 72 h of stroke onset) and 5 healthy control subjects. Flow cytometry analyses and quantitative reverse transcription polymerase chain reactions (qRT-PCR) were performed on peripheral blood mononuclear cells (PBMCs) before and after treating them with PARP-1 inhibitor (3-AB; JPI-289 1 μm, JPI-289 10 μm) for 24 h.

RESULTS

Treg proportions were significantly higher in healthy controls (median 2.8%, IQR 2.6-5.0%) than ischemic stroke patients (median 1.6%, IQR 1.25-2.2%) (p < 0.001). In the latter, Treg proportions were positively correlated with age (r = 0.595, p = 0.041), but not with infarct volume (r = 0.367, p = 0.241). After PARP-1 inhibitor treatment, Treg proportions among PBMCs increased in response to high dose (10 μm) JPI-289 (median 2.3%, IQR 2.0-2.9%) as did Treg-associated transcription factors such as FoxP3 and CTLA-4 mRNA. PARP-1 inhibitor treatment also decreased pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-17) and increased anti-inflammatory cytokines (IL-4, IL-10, and TGF-β1).

CONCLUSION

Treg proportions are reduced in ischemic stroke patients and increased by treatment with high-dose PARP-1 inhibitor JPI-289. The PARP-1 inhibitor also had a possible anti-inflammatory effect on cytokine levels, and may ameliorate the outcome of ischemic stroke by up-regulating Tregs.

Niacin

Nicotinic acid and nicotinamide, collectively referred to as niacin, are nutritional precursors of the bioactive molecules nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD and NADP are important cofactors for most cellular redox reactions, and as such are essential to maintain cellular metabolism and respiration. NAD also serves as a cosubstrate for a large number of ADP-ribosylation enzymes with varied functions. Among the NAD-consuming enzymes identified to date are important genetic and epigenetic regulators, e.g., poly(ADP-ribose)polymerases and sirtuins. There is rapidly growing knowledge of the close connection between dietary niacin intake, NAD(P) availability, and the activity of NAD(P)-dependent epigenetic regulator enzymes. It points to an exciting role of dietary niacin intake as a central regulator of physiological processes, e.g., maintenance of genetic stability, and of epigenetic control mechanisms modulating metabolism and aging. Insight into the role of niacin and various NAD-related diseases ranging from cancer, aging, and metabolic diseases to cardiovascular problems has shifted our view of niacin as a vitamin to current views that explore its potential as a therapeutic.

[Impairment of DNA damage response and cancer]

Maintaining the genetic integrity is a key process in cell viability and is enabled by a wide network of repair pathways. When this system is defective, it generates genomic instability and results in an accumulation of chromosomal aberrations and mutations that may be responsible for various clinical phenotypes, including susceptibility to develop cancer. Indeed, these defects can promote not only the initiation of cancer, but also allow the tumor cells to rapidly acquire mutations during their evolution. Several genes are involved in these damage repair systems and particular polymorphisms are predictive of the onset of cancer, the best described of them being BRCA. In addition to its impact on carcinogenesis, the DNA damage repair system is now considered as a therapeutic target of choice for cancer treatment, as monotherapy or in combination with other cytotoxic therapies, such as chemotherapies or radiotherapy. PARP inhibitors are nowadays the best known, but other agents are emerging in the field of clinical research. The enthusiasm in this area is coupled with promising results and a successful collaboration between clinicians and biologists would allow to optimize treatment plans in order to take full advantage of the DNA repair system modulation.

Novel DNA targeted therapies for head and neck cancers: clinical potential and biomarkers

Head and neck squamous cell carcinoma is the sixth most common cancer worldwide and despite advances in treatment over the last years, there is still a relapse rate of 50%. New therapeutic agents are awaited to increase the survival of patients. DNA repair targeted agents in combination with standard DNA damaging therapies are a recent evolution in cancer treatment. These agents focus on the DNA damage repair pathways in cancer cells, which are often involved in therapeutic resistance. Interesting targets to overcome these cancer defense mechanisms are: PARP, DNA-PK, PI3K, ATM, ATR, CHK1/2, and WEE1 inhibitors. The application of DNA targeted agents in head and neck squamous cell cancer showed promising preclinical results which are translated to multiple ongoing clinical trials, although no FDA approval has emerged yet. Biomarkers are necessary to select the patients that can benefit the most from this treatment, although adequate biomarkers are limited and validation is needed to predict therapeutic response.

Candidate synthetic lethality partners to PARP inhibitors in the treatment of ovarian clear cell cancer

Inhibitors of poly(ADP-ribose) polymerase (PARP) are new types of personalized treatment of relapsed platinum-sensitive ovarian cancer harboring BRCA1/2 mutations. Ovarian clear cell cancer (CCC), a subset of ovarian cancer, often appears as low-stage disease with a higher incidence among Japanese. Advanced CCC is highly aggressive with poor patient outcome. The aim of the present study was to determine the potential synthetic lethality gene pairs for PARP inhibitions in patients with CCC through virtual and biological screenings as well as clinical studies. We conducted a literature review for putative PARP sensitivity genes that are associated with the CCC pathophysiology. Previous studies identified a variety of putative target genes from several pathways associated with DNA damage repair, chromatin remodeling complex, PI3K-AKT-mTOR signaling, Notch signaling, cell cycle checkpoint signaling, BRCA-associated complex and Fanconi's anemia susceptibility genes that could be used as biomarkers or therapeutic targets for PARP inhibition. BRCA1/2, ATM, ATR, BARD1, CCNE1, CHEK1, CKS1B, DNMT1, ERBB2, FGFR2, MRE11A, MYC, NOTCH1 and PTEN were considered as candidate genes for synthetic lethality gene partners for PARP interactions. When considering the biological background underlying PARP inhibition, we hypothesized that PARP inhibitors would be a novel synthetic lethal therapeutic approach for CCC tumors harboring homologous recombination deficiency and activating oncogene mutations. The results showed that the majority of CCC tumors appear to have indicators of DNA repair dysfunction similar to those in BRCA-mutation carriers, suggesting the possible utility of PARP inhibitors in a subset of CCC.

Inhibition of PARP1 activity enhances chemotherapeutic efficiency in cisplatin-resistant gastric cancer cells

Cisplatin (DDP) is the first line chemotherapeutic drug for several cancers, including gastric cancer (GC). Unfortunately, the rapid development of drug resistance remains a significant challenge for the clinical application of cisplatin. There is an urgent need to develop new strategies to overcome DDP resistance for cancer treatment. In this study, four types of human GC cells have been divided into naturally sensitive or naturally resistant categories according to their responses to cisplatin. PARP1 activity (poly (ADP-ribose), PAR) was found to be greatly increased in cisplatin-resistant GC cells. PARP1 inhibitors significantly enhanced cisplatin-induced DNA damage and apoptosis in the resistant GC cells via the inhibition of PAR. Mechanistically, PARP1 inhibitors suppress DNA-PKcs stability and reduce the capability of DNA double-strand break (DSB) repair via the NHEJ pathway. This was also verified in BGC823/DDP GC cells with acquired cisplatin resistance. In conclusion, we identified that PARP1 is a useful interceptive target in cisplatin-resistant GC cells. Our data provide a promising therapeutic strategy against cisplatin resistance in GC cells that has potential translational significance.