Pseudorabies virus usurps non-muscle myosin heavy chain IIA to dampen viral DNA recognition by cGAS for antagonism of host antiviral innate immunity.

Alphaherpesvirus pseudorabies virus (PRV) causes severe economic losses to the global pig industry and has garnered increasing attention due to its broad host range including humans. PRV has developed a variety of strategies to antagonize host antiviral innate immunity. However, the underlying mechanisms have not been fully elucidated. In our previous work, we demonstrated that non-muscle myosin heavy chain IIA (NMHC-IIA), a multifunctional cytoskeleton protein, attenuates innate immune responses triggered by RNA viruses. In the current study, we reported a previously unrecognized role of NMHC-IIA in counteracting PRV-induced cyclic GMP-AMP synthase (cGAS)-dependent type I interferon (IFN-I) production. Mechanistically, PRV infection led to an elevation of NMHC-IIA, strengthening the interaction between poly (ADP-ribose) polymerase 1 (PARP1) and cGAS. This interaction impeded cGAS recognition of PRV DNA and hindered downstream signaling activation. Conversely, inhibition of NMHC-IIA by Blebbistatin triggered innate immune responses and enhanced resistance to PRV proliferation both in vitro and in vivo. Taken together, our findings unveil that PRV utilizes NMHC-IIA to antagonize host antiviral immune responses via impairing DNA sensing by cGAS. This in-depth understanding of PRV immunosuppression not only provides insights for potential PRV treatment strategies but also highlights NMHC-IIA as a versatile immunosuppressive regulator usurped by both DNA and RNA viruses. Consequently, NMHC-IIA holds promise as a target for the development of broad-spectrum antiviral drugs.IMPORTANCECyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) axis plays a vital role in counteracting alphaherpesvirus infections. Alphaherpesviruses exploit various strategies for antagonizing cGAS-STING-mediated antiviral immune responses. However, limited examples of pseudorabies virus (PRV)-caused immunosuppression have been documented. Our findings reveal a novel role of non-muscle myosin heavy chain IIA (NMHC-IIA) in suppressing PRV-triggered innate immune responses to facilitate viral propagation both in vitro and in vivo. In detail, NMHC-IIA recruits poly (ADP-ribose) polymerase 1 (PARP1) to augment its interaction with cGAS, which impairs cGAS recognition of PRV DNA. Building on our previous demonstration of NMHC-IIA's immunosuppressive role during RNA virus infections, these findings indicate that NMHC-IIA acts as a broad-spectrum suppressor of host antiviral innate immunity in response to both DNA and RNA viruses. Therefore, NMHC-IIA will be a promising target for the development of comprehensive antiviral strategies.

High affinity and low PARP-trapping benzimidazole derivatives as a potential warhead for PARP1 degraders.

PARPi have been explored and applied in the treatment of various cancers with remarkable efficacy, especially BRCA1/2 mutated ovarian, breast, prostate, and pancreatic cancers. However, PARPi renders inevitable drug resistance and showed high toxicity because of PARP-Trapping with long-term clinic tracking. To overcome the drug resistance and the high toxicity of PARPi, many novel methods have been developed including PROTACs. Being an event-driven technology, PROTACs needs a high affinity, low toxicity warhead with no steric hindrance in binding process. Veliparib shows the lowest PARP-Trapping effect but could hardly to be the warhead of PROTACs because of the strong steric hindrance. Other PARP1 inhibitors showed less steric hindrance but owns high PARP-Trapping effect. Thus, the development of novel warhead with high PARP1 affinity, low PARP1-Trapping, and no steric hindrance would be valuable. In this work, we reserved benzimidazole as the motif to reserve the low PARP1-Trapping effect and substituted the pyrrole by aromatic ring to avoiding the steric hindrance in PARP1 binding cave. Thus, a series of benzimidazole derivates were designed and synthesized, and some biological activities in vitro were evaluated including the inhibition for PARP1 enzyme and the PARP-Trapping effect using MDA-MB-436 cell line. Results showed that the compound 19A10 has higher PARP1 affinity(IC50 = 4.62 nM)) and similar low PARP-Trapping effect compared with Veliparib(IC50 (MDA-MB-436) >100 µM). Docking study showed that the compound 19A10 could avoiding the steric hindrance which was much better than Veliparib. So, the compound 19A10 could potentially be a perfect warhead for PARP1 degraders. Besides, because of the depletion of the PARP1 and the decreasing of the binding capability, we suppose that the PROTACs using 19A10 as the warhead would be no-PARP-Trapping effect. Furthermore, QSAR study showed that to develop novel compounds with high PARP1 binding affinity and low PARP-Trapping, we can choose the skeleton with substituent R1H, R2 = piperiazine, and R3 with large tPSA. And, if we want to develop the compounds with high PARP1 binding affinity and high PARP-Trapping which can possibly improve the lethality against tumor cells, we can choose the skeleton with substituent R1F, R2 = 3-methy-piperiazine, and R3 with large tPSA.

4'-O-methylbavachalcone alleviates ischemic stroke injury by inhibiting parthanatos and promoting SIRT3.

Cerebral ischemia-reperfusion injury (CIRI) can induce massive death of ischemic penumbra neurons via oxygen burst, exacerbating brain damage. Parthanatos is a form of caspase-independent cell death involving excessive activation of PARP-1, closely associated with intense oxidative stress following CIRI. 4'-O-methylbavachalcone (MeBavaC), an isoprenylated chalcone component in Fructus Psoraleae, has potential neuroprotective effects. This study primarily investigates whether MeBavaC can act on SIRT3 to alleviate parthanatos of ischemic penumbra neurons induced by CIRI. MeBavaC was oral gavaged to the middle cerebral artery occlusion-reperfusion (MCAO/R) rats after occlusion. The effects of MeBavaC on cerebral injury were detected by the neurological deficit score and cerebral infarct volume. In vitro, PC-12 cells were subjected to oxygen and glucose deprivation/reoxygenation (OGD/R), and assessed cell viability and cell injury. Also, the levels of ROS, mitochondrial membrane potential (MMP), and intracellular Ca2+ levels were detected to reflect mitochondrial function. We conducted western blotting analyses of proteins involved in parthanatos and related signaling pathways. Finally, the exact mechanism between the neuroprotection of MeBavaC and parthanatos was explored. Our results indicate that MeBavaC reduces the cerebral infarct volume and neurological deficit scores in MCAO/R rats, and inhibits the decreased viability of PC-12 cells induced by OGD/R. MeBavaC also downregulates the expression of parthanatos-related death proteins PARP-1, PAR, and AIF. However, this inhibitory effect is weakened after the use of a SIRT3 inhibitor. In conclusion, the protective effect of MeBavaC against CIRI may be achieved by inhibiting parthanatos of ischemic penumbra neurons through the SIRT3-PARP-1 axis.

Leveraging shape screening and molecular dynamics simulations to optimize PARP1-Specific chemo/radio-potentiators for antitumor drug design.

PARP1 plays a pivotal role in DNA repair within the base excision pathway, making it a promising therapeutic target for cancers involving BRCA mutations. Current study is focused on the discovery of PARP inhibitors with enhanced selectivity for PARP1. Concurrent inhibition of PARP1 with PARP2 and PARP3 affects cellular functions, potentially causing DNA damage accumulation and disrupting immune responses. In step 1, a virtual library of 593 million compounds has been screened using a shape-based screening approach to narrow down the promising scaffolds. In step 2, hierarchical docking approach embedded in Schrödinger suite was employed to select compounds with good dock score, drug-likeness and MMGBSA score. Analysis supplemented with decomposition energy, molecular dynamics (MD) simulations and hydrogen bond frequency analysis, pinpointed that active site residues; H862, G863, R878, M890, Y896 and F897 are crucial for specific binding of ZINC001258189808 and ZINC000092332196 with PARP1 as compared to PARP2 and PARP3. The binding of ZINC000656130962, ZINC000762230673, ZINC001332491123, and ZINC000579446675 also revealed interaction involving two additional active site residues of PARP1, namely N767 and E988. Weaker or no interaction was observed for these residues with PARP2 and PARP3. This approach advances our understanding of PARP-1 specific inhibitors and their mechanisms of action, facilitating the development of targeted therapeutics.

High-throughput screening assay for PARP-HPF1 interaction inhibitors to affect DNA damage repair.

ADP-ribosyltransferases PARP1 and PARP2 play a major role in DNA repair mechanism by detecting the DNA damage and inducing poly-ADP-ribosylation dependent chromatin relaxation and recruitment of repair proteins. Catalytic PARP inhibitors are used as anticancer drugs especially in the case of tumors arising from sensitizing mutations. Recently, a study showed that Histone PARylation Factor (HPF1) forms a joint active site with PARP1/2. The interaction of HPF1 with PARP1/2 alters the modification site from Aspartate/Glutamate to Serine, which has been shown to be a key ADP-ribosylation event in the context of DNA damage. Therefore, disruption of PARP1/2-HPF1 interaction could be an alternative strategy for drug development to block the PARP1/2 activity. In this study, we describe a FRET based high-throughput screening assay to screen inhibitor libraries against PARP-HPF1 interaction. We optimized the conditions for FRET signal and verified the interaction by competing the FRET pair in multiple ways. The assay is robust and easy to automate. Validatory screening showed the robust performance of the assay, and we discovered two compounds Dimethylacrylshikonin and Alkannin, with µM inhibition potency against PARP1/2-HPF1 interaction. The assay will facilitate the discovery of inhibitors against HPF1-PARP1/2 complex and to develop potentially new effective anticancer agents.

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

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

Synthetically accessible de novo design using reaction vectors: Application to PARP1 inhibitors.

De novo design has been a hotly pursued topic for many years. Most recent developments have involved the use of deep learning methods for generative molecular design. Despite increasing levels of algorithmic sophistication, the design of molecules that are synthetically accessible remains a major challenge. Reaction-based de novo design takes a conceptually simpler approach and aims to address synthesisability directly by mimicking synthetic chemistry and driving structural transformations by known reactions that are applied in a stepwise manner. However, the use of a small number of hand-coded transformations restricts the chemical space that can be accessed and there are few examples in the literature where molecules and their synthetic routes have been designed and executed successfully. Here we describe the application of reaction-based de novo design to the design of synthetically accessible and biologically active compounds as proof-of-concept of our reaction vector-based software. Reaction vectors are derived automatically from known reactions and allow access to a wide region of synthetically accessible chemical space. The design was aimed at producing molecules that are active against PARP1 and which have improved brain penetration properties compared to existing PARP1 inhibitors. We synthesised a selection of the designed molecules according to the provided synthetic routes and tested them experimentally. The results demonstrate that reaction vectors can be applied to the design of novel molecules of biological relevance that are also synthetically accessible.

Design and synthesis of benzodiazepines as brain penetrating PARP-1 inhibitors.

The poly (ADP-ribose) polymerase (PARP) inhibitors play a crucial role in cancer therapy. However, most approved PARP inhibitors cannot cross the blood-brain barrier, thus limiting their application in the central nervous system. Here, 55 benzodiazepines were designed and synthesised to screen brain penetrating PARP-1 inhibitors. All target compounds were evaluated for their PARP-1 inhibition activity, and compounds with better activity were selected for further assays in vitro. Among them, compounds H34, H42, H48, and H52 displayed acceptable inhibition effects on breast cancer cells. Also, computational prediction together with the permeability assays in vitro and in vivo proved that the benzodiazepine PARP-1 inhibitors we synthesised were brain permeable. Compound H52 exhibited a B/P ratio of 40 times higher than that of Rucaparib and would be selected to develop its potential use in neurodegenerative diseases. Our study provided potential lead compounds and design strategies for the development of brain penetrating PARP-1 inhibitors.HIGHLIGHTSStructural fusion was used to screen brain penetrating PARP-1 inhibitors.55 benzodiazepines were evaluated for their PARP-1 inhibition activity.Four compounds displayed acceptable inhibition effects on breast cancer cells.The benzodiazepine PARP-1 inhibitors were proved to be brain permeable.

Design, synthesis and mechanism studies of novel dual PARP1/BRD4 inhibitors against pancreatic cancer.

Inducing the deficiency of homologous recombination (HR) repair is an effective strategy to broaden the indication of PARP inhibitors in pancreatic cancer treatment. Repression of BRD4 has been reported to significantly elevate HR deficiency and sensitize cancer cells to PARP1/2 inhibitors. Inspired by the concept of synthetic lethality, we designed, synthetized and optimized a dual PARP1/BRD4 inhibitor III-7, with a completely new structure and high selectivity against both targets. III-7 repressed the expression and activity of PARP1 and BRD4 to synergistically inhibit the malignant growth of pancreatic cancer cells in vitro and in vivo. Based on the results of bioinformatic analysis, we found that Olaparib induced the acceleration of mitosis and recovery of DNA repair to cause the generation of drug resistance. III-7 reversed Olaparib-induced adaptive resistance and induced cell cycle arrest and DNA damage by perturbing PARP1 and BRD4-involved signaling pathways. We believe that the PARP1/BRD4 dual inhibitors are novel and promising antitumor agents, which provide an efficient strategy for pancreatic cancer treatment.

The cross-talk between PARylation and SUMOylation in C/EBPß at K134 site participates in pathological cardiac hypertrophy.

Poly(ADP-ribosyl)ation (PARylation) and SUMO modification (SUMOylation) are novel post-translational modifications (PTMs) mainly induced by PARP1 and SUMO1. Growing evidence has revealed that C/EBPß plays multiple roles in biological processes and participates in cardiovascular diseases. However, the cross-talk between C/EBPß PARylation and SUMOylation during cardiovascular diseases is unknown. This study aims to investigate the effects of C/EBPß PTMs on cardiac hypertrophy and its underlying mechanism. Abdominal aortic constriction (AAC) and phenylephrine (PE) were conducted to induce cardiac hypertrophy. Intramyocardial delivery of recombinant adenovirus (Ad-PARP1) was taken to induce PARP1 overexpression. In this study, we found C/EBPß participates in PARP1-induced cardiac hypertrophy. C/EBPß K134 residue could be both PARylated and SUMOylated individually by PARP1 and SUMO1. Moreover, the accumulation of PARylation on C/EBPß at K134 site exhibits downregulation of C/EBPß SUMOylation at the same site. Importantly, C/EBPß K134 site SUMOylation could decrease C/EBPß protein stability and participates in PARP1-induced cardiac hypertrophy. Taken together, these findings highlight the importance of the cross-talk between C/EBPß PTMs at K134 site in determining its protein level and function, suggesting that multi-target pharmacological strategies inhibiting PARP1 and activating C/EBPß SUMOylation would be potential for treating pathological cardiac hypertrophy.

The ubiquitin-dependent ATPase p97 removes cytotoxic trapped PARP1 from chromatin.

Poly (ADP-ribose) polymerase (PARP) inhibitors elicit antitumour activity in homologous recombination-defective cancers by trapping PARP1 in a chromatin-bound state. How cells process trapped PARP1 remains unclear. Using wild-type and a trapping-deficient PARP1 mutant combined with rapid immunoprecipitation mass spectrometry of endogenous proteins and Apex2 proximity labelling, we delineated mass spectrometry-based interactomes of trapped and non-trapped PARP1. These analyses identified an interaction between trapped PARP1 and the ubiquitin-regulated p97 ATPase/segregase. We found that following trapping, PARP1 is SUMOylated by PIAS4 and subsequently ubiquitylated by the SUMO-targeted E3 ubiquitin ligase RNF4, events that promote recruitment of p97 and removal of trapped PARP1 from chromatin. Small-molecule p97-complex inhibitors, including a metabolite of the clinically used drug disulfiram (CuET), prolonged PARP1 trapping and enhanced PARP inhibitor-induced cytotoxicity in homologous recombination-defective tumour cells and patient-derived tumour organoids. Together, these results suggest that p97 ATPase plays a key role in the processing of trapped PARP1 and the response of tumour cells to PARP inhibitors.

Structure-based design, synthesis, and evaluation of inhibitors with high selectivity for PARP-1 over PARP-2.

The poly (ADP-ribose) polymerase (PARP) inhibitors play a crucial role in cancer therapy. However, most approved PARP inhibitors have lower selectivity to PARP-1 than to PARP-2, so they will inevitably have side effects. Based on the different catalytic domains of PARP-1 and PARP-2, we developed a strategy to design and synthesize highly selective PARP-1 inhibitors. Compounds Y17, Y29, Y31 and Y49 showed excellent PARP-1 inhibition, and their IC50 values were 0.61, 0.66, 0.41 and 0.96 nM, respectively. Then, Y49 (PARP-1 IC50 = 0.96 nM, PARP-2 IC50 = 61.90 nM, selectivity PARP-2/PARP-1 = 64.5) was proved to be the most selective inhibitor of PARP-1. Compounds Y29 and Y49 showed stronger inhibitory effect on proliferation in BRCA1 mutant MX-1 cells than in other cancer cells. In the MDA-MB-436 xenotransplantation model, Y49 was well tolerated and showed remarkable single dose activity. The design strategy proposed in this paper is of far-reaching significance for the further construction of the next generation of selective PARP-1 inhibitors.

Inhibiting Src-mediated PARP1 tyrosine phosphorylation confers synthetic lethality to PARP1 inhibition in HCC.

Hepatocellular carcinoma (HCC), a heterogeneous cancer with high mortality, is resistant to single targeted therapy; thus, combination therapy based on synthetic lethality is a promising therapeutic strategy for HCC. Poly (adenosine diphosphate [ADP]-ribose) polymerase 1 (PARP1) is the most recognized target for synthetic lethality; however, the therapeutic effect of PARP1 inhibition on HCC is disappointing. Therefore, exploring new synthetic lethal partners for the efficient manipulation of HCC is urgently required. In this study, we identified Src and PARP1 as novel synthetic lethal partners, and the combination therapy produced significant anti-tumor effects without causing obvious side effects. Mechanistically, Src interacted with PARP1 and phosphorylated PARP1 at the Y992 residue, which further mediated resistance to PARP1 inhibition. Overall, this study revealed that Src-mediated PARP1 phosphorylation induced HCC resistance to PARP1 inhibitors and indicated a therapeutic window of the Y992 phosphorylation of PARP1 for HCC patients. Moreover, synthetic lethal therapy by co-targeting PARP1 and Src have the potential to broaden the strategies for HCC and might benefit HCC patients with high Src activation and resistance to PARP1 inhibitors alone.

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.

Evaluation of amentoflavone metabolites on PARP-1 inhibition and the potentiation on anti-proliferative effects of carboplatin in A549 cells.

The present study aims to determine the major metabolites of amentoflavone (AMF) and further evaluate their inhibitory effects on PARP-1. First, different fractions (Frs. 1-9), which were collected according to retention time of AMF metabolites based on UHPLC-QTOF-MS/MS qualitative analysis, were evaluated on their inhibitory effects against PARP-1. Then, two mono-sulfate metabolites in the fractions with potent PARP-1 inhibitory effect were targetedly semi-synthesized. Moreover, three mono-sulfate conjugates (compound 8, 9 and 10), including one disulfate conjugate (compound 10), were isolated and their structures were fully elucidated by UHPLC-QTOF-MS/MS and NMR. Finally, the binding mode of compound 8 (amentoflavone-4‴-O-sulfate) toward PARP-1 and its potentiation on carboplatin (CBP) in A549 cells were investigated. This study was the first report on bioactivity evaluation of AMF metabolites in rat bile on PARP-1 and the potentiation of compound 8 on carboplatin (CBP) in A549 cells in vitro. This paper also provided scientific basis for the AMF metabolites on PARP-1 inhibition and chemosensitization.

Evolution of a histone variant involved in compartmental regulation of NAD metabolism.

NAD metabolism is essential for all forms of life. Compartmental regulation of NAD+ consumption, especially between the nucleus and the mitochondria, is required for energy homeostasis. However, how compartmental regulation evolved remains unclear. In the present study, we investigated the evolution of the macrodomain-containing histone variant macroH2A1.1, an integral chromatin component that limits nuclear NAD+ consumption by inhibiting poly(ADP-ribose) polymerase 1 in vertebrate cells. We found that macroH2A originated in premetazoan protists. The crystal structure of the macroH2A macrodomain from the protist Capsaspora owczarzaki allowed us to identify highly conserved principles of ligand binding and pinpoint key residue substitutions, selected for during the evolution of the vertebrate stem lineage. Metabolic characterization of the Capsaspora lifecycle suggested that the metabolic function of macroH2A was associated with nonproliferative stages. Taken together, we provide insight into the evolution of a chromatin element involved in compartmental NAD regulation, relevant for understanding its metabolism and potential therapeutic applications.

New Synthetic Lethality Re-Sensitizing Platinum-Refractory Cancer Cells to Cisplatin In Vitro: The Rationale to Co-Use PARP and ATM Inhibitors.

The pro-apoptotic tumor suppressor BIN1 inhibits the activities of the neoplastic transcription factor MYC, poly (ADP-ribose) polymerase-1 (PARP1), and ATM Ser/Thr kinase (ATM) by separate mechanisms. Although BIN1 deficits increase cancer-cell resistance to DNA-damaging chemotherapeutics, such as cisplatin, it is not fully understood when BIN1 deficiency occurs and how it provokes cisplatin resistance. Here, we report that the coordinated actions of MYC, PARP1, and ATM assist cancer cells in acquiring cisplatin resistance by BIN1 deficits. Forced BIN1 depletion compromised cisplatin sensitivity irrespective of Ser15-phosphorylated, pro-apoptotic TP53 tumor suppressor. The BIN1 deficit facilitated ATM to phosphorylate the DNA-damage-response (DDR) effectors, including MDC1. Consequently, another DDR protein, RNF8, bound to ATM-phosphorylated MDC1 and protected MDC1 from caspase-3-dependent proteolytic cleavage to hinder cisplatin sensitivity. Of note, long-term and repeated exposure to cisplatin naturally recapitulated the BIN1 loss and accompanying RNF8-dependent cisplatin resistance. Simultaneously, endogenous MYC was remarkably activated by PARP1, thereby repressing the BIN1 promoter, whereas PARP inhibition abolished the hyperactivated MYC-dependent BIN1 suppression and restored cisplatin sensitivity. Since the BIN1 gene rarely mutates in human cancers, our results suggest that simultaneous inhibition of PARP1 and ATM provokes a new BRCAness-independent synthetic lethal effect and ultimately re-establishes cisplatin sensitivity even in platinum-refractory cancer cells.

Therapeutic vulnerability to PARP1,2 inhibition in RB1-mutant osteosarcoma.

Loss-of-function mutations in the RB1 tumour suppressor are key drivers in cancer, including osteosarcoma. RB1 loss-of-function compromises genome-maintenance and hence could yield vulnerability to therapeutics targeting such processes. Here we demonstrate selective hypersensitivity to clinically-approved inhibitors of Poly-ADP-Polymerase1,2 inhibitors (PARPi) in RB1-defective cancer cells, including an extended panel of osteosarcoma-derived lines. PARPi treatment results in extensive cell death in RB1-defective backgrounds and prolongs survival of mice carrying human RB1-defective osteosarcoma grafts. PARPi sensitivity is not associated with canonical homologous recombination defect (HRd) signatures that predict PARPi sensitivity in cancers with BRCA1,2 loss, but is accompanied by rapid activation of DNA replication checkpoint signalling, and active DNA replication is a prerequisite for sensitivity. Importantly, sensitivity in backgrounds with natural or engineered RB1 loss surpasses that seen in BRCA-mutated backgrounds where PARPi have established clinical benefit. Our work provides evidence that PARPi sensitivity extends beyond cancers identifiable by HRd and advocates PARP1,2 inhibition as a personalised strategy for RB1-mutated osteosarcoma and other cancers.

PARP-1-Associated Pathological Processes: Inhibition by Natural Polyphenols.

Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme involved in processes of cell cycle regulation, DNA repair, transcription, and replication. Hyperactivity of PARP-1 induced by changes in cell homeostasis promotes development of chronic pathological processes leading to cell death during various metabolic disorders, cardiovascular and neurodegenerative diseases. In contrast, tumor growth is accompanied by a moderate activation of PARP-1 that supports survival of tumor cells due to enhancement of DNA lesion repair and resistance to therapy by DNA damaging agents. That is why PARP inhibitors (PARPi) are promising agents for the therapy of tumor and metabolic diseases. A PARPi family is rapidly growing partly due to natural polyphenols discovered among plant secondary metabolites. This review describes mechanisms of PARP-1 participation in the development of various pathologies, analyzes multiple PARP-dependent pathways of cell degeneration and death, and discusses representative plant polyphenols, which can inhibit PARP-1 directly or suppress unwanted PARP-dependent cellular processes.

New Hybrid Compounds Combining Fragments of Usnic Acid and Thioether Are Inhibitors of Human Enzymes TDP1, TDP2 and PARP1.

Tyrosyl-DNA phosphodiesterase 1 (TDP1) catalyzes the cleavage of the phosphodiester bond between the tyrosine residue of topoisomerase 1 (TOP1) and the 3' phosphate of DNA in the single-strand break generated by TOP1. TDP1 promotes the cleavage of the stable DNA-TOP1 complexes with the TOP1 inhibitor topotecan, which is a clinically used anticancer drug. This article reports the synthesis and study of usnic acid thioether and sulfoxide derivatives that efficiently suppress TDP1 activity, with IC50 values in the 1.4-25.2 µM range. The structure of the heterocyclic substituent introduced into the dibenzofuran core affects the TDP1 inhibitory efficiency of the compounds. A five-membered heterocyclic fragment was shown to be most pharmacophoric among the others. Sulfoxide derivatives were less cytotoxic than their thioester analogs. We observed an uncompetitive type of inhibition for the four most effective inhibitors of TDP1. The anticancer effect of TOP1 inhibitors can be enhanced by the simultaneous inhibition of PARP1, TDP1, and TDP2. Some of the compounds inhibited not only TDP1 but also TDP2 and/or PARP1, but at significantly higher concentration ranges than TDP1. Leader compound 10a showed promising synergy on HeLa cells in conjunction with the TOP1 inhibitor topotecan.