Poly ADP-ribose Polymerase Family Research Articles

Poly(ADP-Ribose) Polymerase (PARP) Inhibitors for Cancer Therapy: Advances, Challenges, and Future Directions.

Poly(ADP-ribose) polymerases (PARPs) are crucial nuclear proteins that play important roles in various cellular processes, including DNA repair, gene transcription, and cell death. Among the 17 identified PARP family members, PARP1 is the most abundant enzyme, with approximately 1-2 million molecules per cell, acting primarily as a DNA damage sensor. It has become a promising biological target for anticancer drug studies. Enhanced PARP expression is present in several types of tumors, such as melanomas, lung cancers, and breast tumors, correlating with low survival outcomes and resistance to treatment. PARP inhibitors, especially newly developed third-generation inhibitors currently undergoing Phase II clinical trials, have shown efficacy as anticancer agents both as single drugs and as sensitizers for chemo- and radiotherapy. This review explores the properties, characteristics, and challenges of PARP inhibitors, discussing their development from first-generation to third-generation compounds, more sustainable synthesis methods for discovery of new anti-cancer agents, their mechanisms of therapeutic action, and their potential for targeting additional biological targets beyond the catalytic active site of PARP proteins. Perspectives on green chemistry methods in the synthesis of new anticancer agents are also discussed.

Patents on PARP-1 Inhibitors for the Management of Cancer from 2017-2023.

There are eighteen members of the Poly (ADP-ribose) polymerases (PARPs) family, which oversee various cellular processes such as maintaining the integrity of the genome, regulating transcription, cell cycle progression, initiating the DNA damage response, and apoptosis. PARP1 is an essential member of the PARP family and plays a crucial role in repairing single-strand breaks in eukaryotic cells through a process called BER (base excision repair). It is the most extensively studied and commonly found member of this family. This article discusses the advancements in developing PARP inhibitors for human cancers. It covers the discovery of new PARP1 inhibitors with chemical classification that selectively target multiple areas using cancer models in vitro and in vivo and evaluates them critically. The focus is on patents that have been published from 2017 to 2023, except tankyrase inhibitors. PARP1 inhibitors were developed by various companies and academic groups from the 1990s to enhance the effectiveness of chemo and radiotherapy. However, their progress was hindered due to their severe toxicity when combined with these treatments. Therefore, on finding PARP1 inhibitors that can amplify the ability of chemotherapy agents to kill tumors while causing minimal toxicity, these substances can either be used alone as part of the synthetic lethality approach or in conjunction with radiotherapy or chemotherapy, resulting in a mutually beneficial outcome.

Abstract 4698: Measuring cellular PARylation to gain insight in PARP/PARG-targeted drug discovery

Abstract Inhibitors of poly (ADP-ribose) polymerases (PARPs) have revolutionized cancer therapy by highlighting the potential of synthetic lethal drugs to target the DNA damage response (DDR) network. More recently, the development of PARG inhibitors was spurred by the discovery that inhibiting PARG (poly (ADP-ribose) glycohydrolase) results in the accumulation of poly ADP-ribose on DDR proteins and induces cell death. Adding PARG or PARP inhibitors to a cell of interest and quantifying the resulting levels of PARylation can provide valuable insight on compound membrane permeability and target engagement in a cellular context. Nevertheless, assessing PARylation (poly-ADP-ribosylation in which multiple ribose units are added in linear or branched forms) in cells is difficult compared to biochemical assays, impeding the progress of candidate drug development. A sandwich ELISA-based assay was developed to analyze the total protein PARylation present in cellular extracts. Experimental protocols were optimized to discern differences in cellular PARylation levels resulting from activating the DDR and from exposure to PARP inhibitors and/or PARG inhibitors. It is worth noting that our assay specifically detects PARylation, measuring the effects associated with PARP family members 1 to 5, as other family members primarily catalyze MARylation (mono-ADP ribosylation in which a single ADP-ribose unit is added). Titration of known PARP inhibitors and PARG inhibitors was performed to validate the assay. 1) PARG inhibitor PDD00017273, used in combination with DNA damaging agent H2O2, increased the level of cellular PARylation, exhibiting a similar IC50 value across the four cell lines tested. This is consistent with the notion that PARG is the major de-PARylating enzyme in most cells. The potency of other known PARG inhibitors PDD00017272 and PDD00017238 ranked the compounds as expected from published results (PDD00017272< PDD00017273< PDD00017238). 2) Titration of the three PARP1/2 inhibitors Talazoparib, Olaparib and AZD5305, in combination with a DNA damage agent and PDD00017273 inhibitor, shows a dose-dependent reduction in cellular PARylation in HEK293 cells, as expected since PARP1 is activated in response to DNA damage and this activation is blocked by the inhibitors (IC50 values, Olaparib = 0.013 µM, AZD5305 = 0.0024 µM, Talazoparib = 0.0016 µM). These IC50 are consistent with published values and underscore the usefulness of the assay in measuring dose response effects, allowing accurate determination of compound IC50 in living cells. In summary, our optimized experimental cell treatment protocols and ELISA-based assay allow quantification of total cellular PARylation and accurately rank candidate drugs targeting PAR erasers or PAR writers in a high-throughput format, using living cells. Citation Format: Caila Pilo, Mohammad Awad, Veronique T. Baron, Fernando Martins, Jonathan Mikolosko, Steven Plouffe, Zhihua Tao, Katarzyna Zientara-Rytter, Henry Zhu, Pavel Shashkin. Measuring cellular PARylation to gain insight in PARP/PARG-targeted drug discovery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4698.

Abstract 7114: Exploring the landscape of PARP and PARG inhibitor selectivity in live cells using NanoBRET™ target engagement assays

Abstract The 17-member poly(ADP-ribose) polymerase (PARP) family of proteins mediate a number of cellular processes including gene transcription, cell-division and DNA-repair. PARPs catalyze the addition of poly- or mono- ADP-ribose chains on target proteins, modifying their function and/or recruitment in various pathways. Poly(ADP-ribose) Glycohydrolase (PARG) catabolizes PAR units and facilitates the recycling of PARP and other modified effector proteins. A number of PARPS are implicated in human disease, and PARP inhibitors (PARPi’s) have seen major clinical success, however, many PARPs (especially mono PARPs) are understudied and chemical tools for understanding cellular PARPi selectivity and potency across the entire family are lacking. Similarly, several PARG inhibitors have been developed to date, but tools for directly assessing target engagement in a cellular context are sorely needed. Here we describe the development and application of target engagement assays for characterizing PARP and PARG inhibitor selectivity and affinity in live cells. This method is based on the NanoBRET™ assay platform, which is a proximity-based probe displacement assay that operates in live cells. Using NanoBRET™ technology, we have developed a single probe that covers 12 out of 17 PARP family members. We explored the family-wide selectivity of a diverse panel of clinical and preclinical PARP inhibitors in live cells, representing the first family-wide, cell-based method for profiling PARP selectivity. We also describe the development of a second probe that reports on PARG target engagement. Target engagement of PARG was observed for three out of five tested inhibitors, suggesting a potential indirect mode of action for certain inhibitors on PARG glycohydrolase activity. These assays offer a complementary approach for studying target engagement within the PARylation cycle. Citation Format: Ani Michaud, Kelly Teske, Jennifer Wilkinson, Chad Zimprich, James Vasta, Cesear Corona, Min Zhou, Elizabeth Dominguez, Kaitlin Dunn-Hoffman, Matthew Robers. Exploring the landscape of PARP and PARG inhibitor selectivity in live cells using NanoBRET™ target engagement assays [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7114.

Poly-(ADP-ribose)polymerases inhibitionby olaparib attenuates activities of the NLRP3 inflammasome and of NF-κB in THP-1 monocytes.

Poly-(ADP-ribose) polymerases (PARPs) are a protein family that make ADP-ribose modifications on target genes and proteins. PARP family members contribute to the pathogenesis of chronic inflammatory diseases, including atherosclerosis, in which monocytes/macrophages play important roles. PARP inhibition is protective against atherosclerosis. However, the mechanisms by which PARP inhibition exerts this beneficial effect are not well understood. Here we show that in THP-1 monocytes, inhibition of PARP by olaparib attenuated oxidized low-density lipoprotein (oxLDL)-induced protein expressions of nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing-3 (NLRP3) inflammasome components: NLRP3, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), and caspase-1. Consistent with this effect, olaparib decreased oxLDL-enhanced interleukin (IL)-1β and IL-18 protein expression. Olaparib also decreased the oxLDL-mediated increase in mitochondrial reactive oxygen species. Similar to the effects of the NLRP3 inhibitor, MCC950, olaparib attenuated oxLDL-induced adhesion of monocytes to cultured human umbilical vein endothelial cells and reduced foam cell formation. Furthermore, olaparib attenuated the oxLDL-mediated activation of nuclear factor (NF)-κB through the oxLDL-mediated increase in IκBα phosphorylation and assembly of NF-κB subunits, demonstrated by co-immunoprecipitation of IκBα with RelA/p50 and RelB/p52 subunits. Moreover, PARP inhibition decreased oxLDL-mediated protein expression of a NF-κB target gene, VCAM1, encoding vascular cell adhesion molecule-1. This finding indicates an important role for NF-κB activity in PARP-mediated activation of the NLRP3 inflammasome. Thus, PARP inhibition by olaparib attenuates NF-κB and NLRP3 inflammasome activities, lessening monocyte cell adhesion and macrophage foam cell formation. These inhibitory effects of olaparib on NLRP3 activity potentially protect against atherosclerosis.

Phthalimide-tethered isatins as novel poly(ADP-ribose) polymerase inhibitors: Design, synthesis, biological evaluations, and molecular modeling investigations.

Humanity is currently facing various diseases with significant mortality rates, particularly those associated with malignancies. Numerous enzymes and proteins have been identified as highly promising targets for the treatment of cancer. The poly(ADP-ribose) polymerases (PARPs) family comprises 17 members which are essential in DNA damage repair, allowing the survival of cancer cells. Unlike other PARP family members, PARP-1 and, to a lesser extent, PARP-2 show more than 90% activity in response to DNA damage. PARP-1 levels were shown to be elevated in various tumor cells, including breast, lung, ovarian, and prostate cancer and melanomas. Accordingly, novel series of phthalimide-tethered isatins (6a-n, 10a-e, and 11a-e) were synthesized as potential PARP-1 inhibitors endowed with anticancer activity. All the synthesized molecules were assessed against PARP-1, where compounds 6f and 10d showed nanomolar activities with IC50 = 15.56 ± 2.85 and 13.65 ± 1.42 nM, respectively. Also, the assessment of the antiproliferative effects of the synthesized isatins was conducted on four cancer cell lines: leukemia (K-562), liver (HepG2), and breast (MCF-7 and HCC1937) cancers. Superiorly, compounds 6f and 10d demonstrated submicromolar IC50 values against breast cancer MCF-7 (IC50 = 0.92 ± 0.18 and 0.67 ± 0.12 µM, respectively) and HCC1937 (IC50 = 0.88 ± 0.52 and 0.53 ± 0.11 µM, respectively) cell lines. In addition, compounds 6f and 10d induced arrest in the G2/M phase of the cell cycle as compared to untreated cells. Finally, in silico studies, including docking and molecular dynamic simulations, were performed to justify the biological results.

RBIO-04. INHIBITING THE SHH PATHWAY AND PARP1 IN COMBINATION ENHANCES THE RADIATION SENSITIVITY OF PEDIATRIC SONIC HEDGEHOG MEDULLOBLASTOMA

Abstract Medulloblastoma accounts for 20-25% of all pediatric brain tumors. These patients undergo craniospinal and focal radiation therapy during their treatment, resulting in negative long-term consequences such as bone and tissue hypoplasia and decreased neurocognitive functioning. One of the most concerning effects is the significantly increased risk for secondary radiation induced cancers later in life. Thus, there is a critical need for novel approaches to radiation therapy that can effectively target and kill tumor cells while minimizing long lasting toxic effects. Here, we investigate a novel approach to radiation therapy that relies on the combination of two classes of therapeutic agents, Sonic Hedgehog (SHH) inhibitors and Poly (ADP-ribose) Polymerase (PARP) inhibitors. The SHH pathway plays a key role in medulloblastoma tumorigenesis and affects the radiation sensitivity of various cancer types such as basal cell carcinoma. The PARP family, specifically PARP1, plays a key role in DNA damage repair and affects the radiation sensitivity of pediatric brain cancers such as high-grade glioma and medulloblastoma. We hypothesize that combining these approaches by inhibiting Smo and Gli1 in the SHH pathway, and PARP1 simultaneously, will enhance medulloblastoma tumor cell killing following radiation therapy. We found that in vitro treatment with Sonidegib, GANT61, and Veliparib alone and in combination with was sufficient to significantly decrease tumor cell viability and self-renewal as measured by clonogenic survival assays (p < 0.01). 24 hours following these targeted treatments, 2 Gy of radiation was administered which resulted in a greater degree of decreased cell viability and self-renewal (p < 0.01), as well as in increased cell death. Together, this data suggests that inhibition of Smo, Gli1, and PARP1 either alone as single agents, or in combination is a promising therapeutic strategy for increasing the radiation sensitivity of pediatric SHH medulloblastoma.

A Review of PARP-1 Inhibitors: Assessing Emerging Prospects and Tailoring Therapeutic Strategies.

Eukaryotic organisms contain an enzyme family called poly (ADP-ribose) polymerases (PARPs), which is responsible for the poly (ADP-ribosylation) of DNA-binding proteins. PARPs are members of the cell signaling enzyme class. PARP-1, the most common isoform of the PARP family, is responsible for more than 90% of the tasks carried out by the PARP family as a whole. A superfamily consisting of 18 PARPs has been found. In order to synthesize polymers of ADP-ribose (PAR) and nicotinamide, the DNA damage nick monitor PARP-1 requires NAD+ as a substrate. The capability of PARP-1 activation to boost the transcription of proinflammatory genes, its ability to deplete cellular energy pools, which leads to cell malfunction and necrosis, and its involvement as a component in the process of DNA repair are the three consequences of PARP-1 activation that are of particular significance in the process of developing new drugs. As a result, the pharmacological reduction of PARP-1 may result in an increase in the cytotoxicity toward cancer cells.

Poly(ADP-ribose) polymerase-1 affects vasopressin-mediated AQP2 expression in collecting duct cells of the kidney.

Poly(ADP-ribosyl)ation (PARylation), as a posttranslational modification mediated by poly(ADP-ribose) polymerases (PARPs) catalyzing the transfer of ADP-ribose from NAD+ molecules to acceptor proteins, involves a number of cellular processes. As mice lacking the PARP-1 gene (Parp1) produce more urine, we investigated the role of PARP-1, the most prevalent member of the PARP family, in the vasopressin-responsive expression of aquaporin-2 (AQP2). In biotin-conjugated nicotinamide adenine dinucleotide (biotin-NAD+) pulldown and immunoprecipitation assays of poly(ADP)-ribose in mpkCCDc14 cells, immunoblots demonstrated that 1-deamino-8-D-arginine vasopressin (dDAVP) induced the PARylation of total proteins, associated with an increase in the cleavage of PARP-1 and cleaved caspase-3 expression. By inhibiting PARP-1 with siRNA, the abundance of dDAVP-induced AQP2 mRNA and protein was significantly diminished. In contrast, despite a substantial decrease in PARylation, the PARP-1 inhibitor (PJ34) had no effect on the dDAVP-induced regulation of AQP2 expression. The findings suggest that PARP-1 protein expression itself, and not PARP-1-mediated PARylation, is necessary for dDAVP-regulated AQP2 expression. Bioinformatic analysis revealed that 408 proteins interact with PARP-1 in the collecting duct (CD) cells of the kidney. Among them, the signaling pathway of the vasopressin V2 receptor was identified for 49 proteins. In particular, β-catenin, which is phosphorylated at Ser552 by dDAVP, was identified as the PARP-1-interacting protein. A significant decrease of β-catenin phosphorylation (Ser552) in response to dDAVP was associated with siRNA-mediated PARP-1 knockdown. Taken together, PARP-1 is likely to play a role in vasopressin-induced AQP2 expression by interacting with β-catenin in renal CD cells.NEW & NOTEWORTHY The poly(ADP-ribose) polymerase (PARP) family catalyzes poly(ADP-ribosylation) (PARylation), which is one of the posttranslational modifications of largely undetermined physiological significance. This study investigated the role of PARP-1, the most prevalent member of the PARP family, in the vasopressin-responsive expression of aquaporin-2 (AQP2). The results demonstrated that PARP-1 protein expression itself, and not PARP-1-mediated PARylation, is necessary for dDAVP-regulated AQP2 expression. β-Catenin, which is phosphorylated at Ser552 by dDAVP, was identified as the PARP-1-interacting protein.

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

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

Synthetic PARP-1 Inhibitors Reported During the Last Decade

Background: Cancer is the world's second largest cause of death and is responsible for an estimated 9.6 million mortalities in 2018. Poly-ADP-ribose polymerases (PARPs) are enzymes and family of proteins, involved in many cellular processes, including DNA repair, gene regulation, chromatin remodeling, and apoptosis. The first characterized and best known member of the PARP family is poly(ADP-ribose) polymerase 1 (PARP-1). PARP-1 is a major protein for DNA single-strand breaks in the BER pathway (base excision repair) (SSBs). Objective: The objective of this article was to compile synthetic PARP-1 inhibitors reported in the last decade Methods: In the present manuscript, bibliographic investigation was carried out by scrutinizing peerreviewed articles from online/offline databases. The inclusion criteria consisted of the most relevant studies indicating the relationship between PARP-1 and cancer in textbooks/edited books and peer-reviewed papers from scientific databases, like SCOPUS, PUBMED, NISCAIR, and Google Scholar since 2010 to 2020. Only the studies published in English language were searched/considered. The exclusion criteria consisted of the studies on other PARP isoforms than PARP-1. The studies thus obtained were classified according to the heterocyclic moieties, year of publication, etc. The data compiled in this article is a systematic review of the reported studies. Results: The literature reports indicated that a number of PARP-1 inhibitors reported have IC50 value in nanomolar concentration. Conclusion: PARP-1 is an essential target for anti-cancer drug discovery. Further, research for more effective and safe PARP-1 inhibitors is carried out and we may discover some novel PARP-1 inhibitors in the near future.

#4085 POLY(ADP-RIBOSE) POLYMERASE 1 AFFECTS THE VASOPRESSIN-MEDIATED AQP2 EXPRESSION VIA AN INTERACTION WITH BETA-CATENIN

Abstract Background and Aims Poly(ADP-ribosy)lation (PARylation), which is mediated by poly(ADP-ribose) polymerases (PARPs), catalyzes the transfer of ADP-ribose from NAD+ molecules to acceptor proteins, regulates diverse cellular processes. Since PARP1 gene-deficient mice revealed an increase in urine volume, we aimed to examine the role of PARP1, the most abundant type of protein in the PARPs family, in the vasopressin-mediated AQP2 regulation. Method 1) Immunoblotting for PARP1 in mpkCCDc14 cells; 2) Pulldown assay of biotin-conjugated NAD+ and immunoprecipitation (IP) assay using poly(ADP-ribose) (PAR) antibody; 3) qRT-PCR and immunoblotting for AQP2; and 4) Bioinformatics for elucidating PARP1-interacting proteins in kidney collecting duct (CD) cells. Results Immunoblots showed that dDAVP treatment (10−9 M, 2 h, 6 h, 24 h, and 48 h) induced the cleavage of PARP1 (both 89 kDa and 25 kDa) in mpkCCDc14 cells. dDAVP treatment (10−9 M, 24 h) also increased the abundance of total PARylated proteins in biotin-NAD+ pulldown and IP assay of PAR in mpkCCDc14 cells. On the other hand, siRNA-mediated PARP1 knockdown significantly attenuated the dDAVP-induced mRNA and protein abundance, suggesting a role of PARP1 in AQP2 regulation. PARP1 cleavage induced by dDAVP was not changed under PARP1 knockdown, indicating that PARP1 cleavage is unlikely to be involved in AQP2 regulation. In contrast to PARP1 knockdown, PARP1 inhibitor (PJ34) did not reduce the dDAVP-induced AQP2 abundance, despite the significant decrease in the PARylation. The results suggest that dDAVP-regulated AQP2 expression is associated with PARP1 protein per se, but not with PARP1-mediated PARylation. Bioinformatics study revealed that 408 proteins interact with PARP1 in the kidney CD cells. Among them, 49 proteins were mapped on the vasopressin V2 receptor (V2R) signaling pathway. In particular, β-catenin, which is phosphorylated (S552) by dDAVP, was identified as the PARP1-interacting protein mapped on the V2R signaling. Immunoblotting demonstrated that siRNA-mediated knockdown of PARP1 was associated with decreased dDAVP-induced phosphorylation of β-catenin at S552 in mpkCCDc14 cells. Conclusion PARP1 is likely to play a role in vasopressin-mediated AQP2 regulation via the protein interaction with β-catenin rather than PARylation of proteins and/or PARP1 cleavage in the kidney CD cells.

Poly(ADP-ribose)polymerases 1 and 2: Classical Functions and Interaction with HPF1 ‒ New Histone Poly(ADP-ribosyl)ation Factor

Poly(ADP-ribose) (PAR) is a negatively charged polymer, linear and branched, consisting of ADP-ribose monomers. This polymer is synthesized by poly(ADP-ribose)polymerase (PARP) enzymes which are activated on DNA damage and use nicotinamide adenine dinucleotide (NAD+) as a substrate. The most studied members of the PARP family, PARP1 and PARP2, are the most important nuclear proteins involved in many cellular processes, including the regulation of DNA repair. PARP1 and PARP2 catalyze both the synthesis and transfer of poly(ADP-ribose) to amino acid residues of target proteins, including autoPARylation. In view of the key role in the regulation of the DNA repair process, PARP1 and PARP2 are promising targets for chemotherapy. Recently, a novel histone PARylation factor (HPF1) has been discovered to modulate PARP1/2 activity by forming a transient joint active site with PARP1/2. In the presence of HPF1, histone modification occurs at serine residues. The general mechanism of interaction between HPF1 and PARP1/2 is only beginning to be elucidated. In this review, we consider the discovery and classical mechanism of this important process in higher eukaryotes, as well as the role of a new histone PARylation factor in this HPF1 process.

Poly(ADP-Ribose) Polymerases 1 and 2: Classical Functions and Interaction with New Histone Poly(ADP-Ribosyl)ation Factor HPF1

Poly(ADP-ribose) (PAR) is a negatively charged polymer, linear or branched, that consists of ADP-ribose monomers. PAR is synthesized by poly(ADP-ribose)polymerase (PARP) enzymes, which are activated upon DNA damage and use nicotinamide adenine dinucleotide (NAD^(+)) as a substrate. The best-studied members of the PARP family, PARP1 and PARP2, are the most important nuclear proteins involved in many cell processes, including the regulation of DNA repair. PARP1 and PARP2 catalyze PAR synthesis and transfer to amino acid residues of target proteins, including autoPARylation. PARP1 and PARP2 are promising targets for chemotherapy in view of their key role in regulating DNA repair. A novel histone PARylation factor (HPF1) was recently discovered to modulate PARP1/2 activity by forming a transient joint active site with PARP1/2. Histones are modified at serine residues in the presence of HPF1. The general mechanism of the interaction between HPF1 and PARP1/2 is a subject of intense research now. The review considers the discovery and classical mechanism of PARylation in higher eukaryotes and the role of HPF1 in the process.

Current status and future promise of next-generation poly (ADP-Ribose) polymerase 1-selective inhibitor AZD5305.

The family of poly (ADP-ribose) polymerases (PARPs) consists of 17 members, which have been demonstrated as having effects on a series of cellular processes, including DNA replication and repair. PARP inhibitors (PARPi) suppress DNA repair through "PARP trapping", thus, constitute an important treatment option for cancer nowadays. In addition, PARP inhibition and homologous recombination repair (HRR) defects are synthetically lethal, giving a promising therapeutic for homologous recombination repair deficient (HRD) tumors including BRCA mutation. However, overlapping hematologic toxicity causes PARPi to fail in combination with some first-line chemotherapies. Furthermore, recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for antitumor activity in HRD cancer models. Currently approved PARPi have shown varying levels of selectivity for the entire 17-member PARP family, hence contribute to toxicity. Together, these findings above have provided the necessity and feasibility of developing next-generation PARPi with improved selectivity for PARP1, expanding significant clinical values and wide application prospects both in monotherapy and combination with other anticancer agents. In this review, we summery the latest research of current approved PARPi, discuss the current status and future promise of next-generation PARP1-selective inhibitor AZD5305, including its reported progress up to now and anticipated impact on clinical.

Mono-ADP-ribosylation by PARP10 and PARP14 in genome stability.

ADP-ribosylation is a post-translational modification involved in a variety of processes including DNA damage repair, transcriptional regulation, and cellular proliferation. Depending on the number of ADP moieties transferred to target proteins, ADP-ribosylation can be classified either as mono-ADP-ribosylation (MARylation) or poly-ADP-ribosylation (PARylation). This post-translational modification is catalyzed by enzymes known as ADP-ribosyltransferases (ARTs), which include the poly (ADP-ribose)-polymerase (PARP) superfamily of proteins. Certain members of the PARP family including PARP1 and PARP2 have been extensively studied and assessed as therapeutic targets. However, the other members of the PARP family of protein are not as well studied but have gained attention in recent years given findings suggesting their roles in an increasing number of cellular processes. Among these other members are PARP10 and PARP14, which have gradually emerged as key players in maintenance of genomic stability and carcinogenesis. PARP10 and PARP14 catalyze the transfer of a single ADP moiety to target proteins. Here, we summarize the current knowledge on MARylation in DNA repair and cancer, focusing on PARP10 and PARP14. We highlight the roles of PARP10 and PARP14 in cancer progression and response to chemotherapeutics and briefly discuss currently known PARP10 and PARP14 inhibitors.

Synergistic Leukaemia Cell Death Induced with PARP and TiP60 Inhibitors Is a Prospective Therapeutic Strategy for AML

Background: We previously identified pharmacological inhibition of lysine demethylase 4A (KDM4A) sensitises AML cells to inhibition of poly ADP ribose polymerase (PARP), one of the major DNA damage response (DDR) mediators. We hypothesise that synergy between inhibition of PARP and histone acetyltransferase (HAT) family member, Tip60 that is involved in DSB repair, may drive effective AML leukemic cell death sparing normal cells. We aim to unravel molecular mechanisms of action of the targeted inhibitors and downstream targets of Tip60 and PARP in AML. Methods: Phenotypic changes, such as in cell viability, apoptosis, cell cycle arrest by flow cytometry, colony forming capacity, and DNA damage protein markers by western blotting, in AML cells following drug treatments were determined by standard protocols. Enrichment of biological pathways in which genes with transcriptional changes in AML cells upon the drug treatment were discovered using gene set enrichment analysis (GSEA) of RNA-seq dataset generated from treated cell lines. Downstream target genes of Tip60 and PARP together in common were identified via cross-validation using least absolute shrinkage and selection operator (LASSO) linear regression in clinical datasets. Results: Loss of PARP and Tip60 enzymatic activities was driven by pharmacological inhibition of PARP and Tip60 individually and in combination in AML cell lines. As a result, a significant synergistic effect of the combination treatment (PARPi plus Tip60i) was confirmed in THP-1 and MOLM-13 cells with combination indices (CI) < 1, which was further validated via the Bliss independent model and isobolograms. Simultaneous combination of PARPi together with Tip60i resulted in significant phenotypic changes with increased early and late apoptotic cell populations, cell cycle arrest at S phase, decreased colony forming ability, and accumulation of DNA lesion markers, γH2A.X and cleaved PARP proteins, which contributed to inhibition of cell growth and ultimately significant increase (p<0.0001) in AML leukemic cell death. GSEA revealed that combination treatment of PARPi and Tip60i induced significant enrichment of genes (adjusted p-value<0.05) involved in DDR sub-pathways, mismatch repair (MMR; NES=-1.54; FDR=0.088) and interstrand crosslink repair (ICLR; NES=-1.25; FDR=0.22), in parallel, suggesting an inhibitory role of PARPi and Tip60i in impairing DDR in AML cells. Furthermore, global GSEA further demonstrated that synergistic effect of PARPi plus Tip60i induced significant upregulation of biological pathways of hypoxia, unfolded protein response, p53 pathway, and apoptosis; and significant downregulation of oxidative phosphorylation, glycolysis, and Myc pathway. A minimum subset of 13 genes mediated by inhibition of Tip60 and PARP ('TiP13') in AML cells was constructed in relation to patient survival. Kaplan-Meier survival analysis showed that the gene signature score of each patient in four patient cohorts, calculated as the sum of the weighted gene expression for each gene in TiP13, was highly correlated with patient survival in four test clinical datasets (GSE12417, FDR=0.00091; GSE37642, FDR=0.042; GSE6891, FDR=0.044; Beat AML, FDR<0.0001). Discussion: Failure to repair DNA damage at transcriptional level by blocking of MMR and ICLR pathways led to constant accumulation of DNA lesions and thereby effective cell killing in AML cells treated with PARPi and Tip60i in combination. This study further demonstrates that transcriptional outcomes driven by synergising PARPi and Tip60i activities contribute to dysregulation of oxidative phosphorylation for oxidation of nutrients and production of ATP in glycolysis in AML cells, leading to genomic instability, accumulated global DNA damage, and increased response to stress or unfolded protein. Consequently, the accumulated DNA lesions alongside impaired capacity of AML cells to repair their damaged DNA, thereby stimulated apoptosis, facilitated with downregulation of an oncogenic Myc pathway and upregulation of tumour suppressor p53 pathway. In addition, this study has uncovered a novel TiP13 gene signature (downstream targets of PARP and Tip60) with prognostic significance in AML that successfully stratifies outcomes of AML patients.

Roles of DNA damage repair and precise targeted therapy in renal cancer (Review).

The primary subtypes of renal cell carcinoma (RCC) include clear cell, papillary and chromophobe RCC. RCC occurs often due to loss of von Hippel-Lindau (VHL) and accumulation of lipids and glycogen, and RCC cells may exhibit sensitivity to the disruption of normal metabolism or homologous recombination gene defect. Although the application of molecular-targeted drugs (tyrosine kinase inhibitors) and immune checkpoint inhibitors has been recommended for the treatment of advanced RCC, more targets of DNA damage repair (DDR) signaling pathway involved in the synthetic lethal effect have been investigated. However, although achievements has been made in the exploration of the roles of DDR genes on RCC progression, their association has not been systematically summarized. Poly (ADP-ribose) polymerase (PARP) 1 inhibitors are used in tumors with BRCA1/2 DNA repair-associated mutations. PARP family enzymes perform post-translational modification functions and participate in DDR and cell death. Inhibitors of PARP, ataxia telangiectasia mutant gene and polymerase θ serve key roles in the treatment of specific RCC subtypes. PARP1 may serve as an important biological marker to predict the therapeutic effect of immune checkpoint inhibitors and evaluate the prognosis of patients with ccRCC with polybromo 1 mutation. Therefore, the roles of DDR pathway on RCC progression or treatment may hold promises for the treatment of certain specific types of RCC.

A multi-task FP-GNN framework enables accurate prediction of selective PARP inhibitors.

PARP (poly ADP-ribose polymerase) family is a crucial DNA repair enzyme that responds to DNA damage, regulates apoptosis, and maintains genome stability; therefore, PARP inhibitors represent a promising therapeutic strategy for the treatment of various human diseases including COVID-19. In this study, a multi-task FP-GNN (Fingerprint and Graph Neural Networks) deep learning framework was proposed to predict the inhibitory activity of molecules against four PARP isoforms (PARP-1, PARP-2, PARP-5A, and PARP-5B). Compared with baseline predictive models based on four conventional machine learning methods such as RF, SVM, XGBoost, and LR as well as six deep learning algorithms such as DNN, Attentive FP, MPNN, GAT, GCN, and D-MPNN, the evaluation results indicate that the multi-task FP-GNN method achieves the best performance with the highest average BA, F1, and AUC values of 0.753 ± 0.033, 0.910 ± 0.045, and 0.888 ± 0.016 for the test set. In addition, Y-scrambling testing successfully verified that the model was not results of chance correlation. More importantly, the interpretability of the multi-task FP-GNN model enabled the identification of key structural fragments associated with the inhibition of each PARP isoform. To facilitate the use of the multi-task FP-GNN model in the field, an online webserver called PARPi-Predict and its local version software were created to predict whether compounds bear potential inhibitory activity against PARPs, thereby contributing to design and discover better selective PARP inhibitors.

92 (PB082) - RP12146, a novel, selective, and potent small molecule inhibitor of PARP 1/2, synergizes with SOC therapy in preclinical models of solid tumors

Background: Poly (ADP-ribose) polymerase (PARP) activity involves synthesis of Poly-ADP ribose (PAR) polymers that recruit host DNA repair proteins leading to correction of DNA damage and maintenance of cell viability. Several PARP inhibitors have been approved for the treatment of BRCA-mutated ovarian, breast and pancreatic cancer. In addition to BRCA-mutated cancers, therapeutic role of PARP inhibitors as monotherapy agent or in combination with established therapy can be expanded to other types of solid tumors through ‘synthetic lethality’ mechanism. Herein, we describe the efficacy of RP12146 as a single agent and in combination with approved therapies in preclinical models of solid tumors. Material & Methods: Enzymatic potency was evaluated using a PARP Chemiluminescent Activity Assay Kit (BPS biosciences). Cell growth was determined following incubation with RP12146 as a single agent or in combination with approved agents in various solid tumor cell lines. Apoptosis & Cell cycle was evaluated following incubation of cell lines with compound for 48 or 72 h, subsequent staining with Annexin-V-PE and 7-AAD or Propidium Iodide, and analysis by flow cytometry. Anti-tumor potential of RP12146 as a single agent or in combination with chemotherapeutic agents was tested in OVCAR-3 and NCI-H69 Xenografts. Expression of downstream markers were determined in cell lines and xenograft tumor samples by Western blotting. Results: RP12146 inhibited PARP1 (0.6 nM) & PARP2 (0.5 nM) with equal potency with several fold selectivity over the other members of the PARP family. In addition, RP12146 demonstrated selective PARP1-Trapping with ∼20-fold selectivity over PARP2. RP12146 caused a dose-dependent growth inhibition of both BRCA mutant and non-mutant cancer cell lines with GI50 in the range of 0.04 μM to 9.6 μM. Combination of RP12146 with Temozolomide, SN-38, Topotecan, and Lurbinectedin demonstrated either additive or synergistic effects manifested by an inhibition in growth, induction of apoptosis and cell cycle arrest in Breast, Gastric, Glioma, Lung Cancer, and Ovarian cancer cell lines. RP12146 exhibited anti-tumor potential with TGI of 28% and 21.8% as a single agent in OVCAR-3 and NCI-H69 Xenograft model respectively. In NCI-H69 xenograft model, RP12146 in combination with cisplatin exhibited TGI of 69.3%. Conclusion: Data demonstrate the therapeutic potential of RP12146 as single agent and in combination in solid tumors. RP12146 is currently being evaluated in Phase 1 clinical trials in patients with locally advanced or metastatic solid tumors (NCT05002868). No conflict of interest.