Abstract P056: Polθ inhibitors elicit BRCA-gene synthetic lethality and target PARP inhibitor resistance

The use of PARP inhibitors (PARPi) is growing widely as FDA approvals have shifted its use from the recurrence setting to the frontline setting. In parallel, the population developing PARPi resistance is increasing. Here we review the role of PARP, DNA damage repair, and synthetic lethality. We discuss mechanisms of resistance to PARP inhibition and how this informs on novel combinations to re-sensitize cancer cells to PARPi.

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Polθ inhibitors elicit BRCA-gene synthetic lethality and target PARP inhibitor resistance

Nature Communications ◽

10.1038/s41467-021-23463-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Diana Zatreanu ◽

Helen M. R. Robinson ◽

Omar Alkhatib ◽

Marie Boursier ◽

Harry Finch ◽

...

Keyword(s):

Dna Repair ◽

Synthetic Lethality ◽

Parp Inhibitor ◽

Repair Process ◽

End Joining ◽

Synthetic Lethal ◽

Non Homologous End Joining ◽

Inhibitor Resistance

AbstractTo identify approaches to target DNA repair vulnerabilities in cancer, we discovered nanomolar potent, selective, low molecular weight (MW), allosteric inhibitors of the polymerase function of DNA polymerase Polθ, including ART558. ART558 inhibits the major Polθ-mediated DNA repair process, Theta-Mediated End Joining, without targeting Non-Homologous End Joining. In addition, ART558 elicits DNA damage and synthetic lethality in BRCA1- or BRCA2-mutant tumour cells and enhances the effects of a PARP inhibitor. Genetic perturbation screening revealed that defects in the 53BP1/Shieldin complex, which cause PARP inhibitor resistance, result in in vitro and in vivo sensitivity to small molecule Polθ polymerase inhibitors. Mechanistically, ART558 increases biomarkers of single-stranded DNA and synthetic lethality in 53BP1-defective cells whilst the inhibition of DNA nucleases that promote end-resection reversed these effects, implicating these in the synthetic lethal mechanism-of-action. Taken together, these observations describe a drug class that elicits BRCA-gene synthetic lethality and PARP inhibitor synergy, as well as targeting a biomarker-defined mechanism of PARPi-resistance.

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In silico discovery of novel flavonoids as poly ADP ribose polymerase (PARP) inhibitors

Current Computer - Aided Drug Design ◽

10.2174/1573409916666200408082858 ◽

2020 ◽

Vol 16 ◽

Author(s):

Ashish Shah ◽

Ghanshyam Parmar ◽

Avinash Kumar Seth

Keyword(s):

Virtual Screening ◽

In Silico ◽

Synthetic Lethality ◽

Parp Inhibitor ◽

Parp Inhibitors ◽

Docking Studies ◽

Docking Score ◽

Docking Method ◽

Anti Cancer ◽

In Silico Toxicity

Background: The concept of synthetic lethality is emerging field in the treatment of cancer and can be applied for new drug development of cancer as it has been already represented by Poly (ADP-ribose) polymerase (PARPs) inhibitors. Objectives: In this study we performed virtual screening of 329 flavonoids obtained from Naturally Occurring Plant-based Anti-cancer Compound-Activity-Target (NPACT) database to identify novel PARP inhibitors. Materials and methods: Virtual screening carried out using different In Silico methods which includes molecular docking studies, prediction of druglikeness and In Silico toxicity studies. Results: Fifteen out of 329 flavonoids achieved better docking score as compared to rucaparib which is an FDA approved PARP inhibitor. These 15 hits were again rescored using accurate docking mode and drug-likeliness properties were evaluated. Accuracy of docking method was checked using re-docking. Finally NPACT00183 and NPACT00280 were identified as potential PARP inhibitors with docking score of -139.237 and -129.36 respectively. These two flavonoids were also showed no AMES toxicity and no carcinogenicity which was predicted using admetSAR. Conclusion: Our finding suggests that NPACT00183 and NPACT00280 have promising potential to be further explored as PARP inhibitors.

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Kinase Phosphorylation-based Mechanisms of PARP Inhibitor Resistance During Synthetic Lethal Oncotherapy

Current Signal Transduction Therapy ◽

10.2174/1574362413666180724134204 ◽

2020 ◽

Vol 15 (1) ◽

pp. 12-23

Author(s):

Eriko Osaki ◽

Shinya Mizuno

Keyword(s):

Cancer Progression ◽

Catalytic Domain ◽

Synthetic Lethality ◽

Excision Repair ◽

Parp Inhibitor ◽

Clinical Importance ◽

Parp Inhibition ◽

Special Focus ◽

Driver Genes ◽

Kinase Phosphorylation

Background: Poly-(ADP-Ribose) Polymerase (PARP) plays a central role in recovery from single-strand DNA (ssDNA) damage via base excision repair. When PARP activity is inhibited by a NAD+ mimetic analog, ssDNA is converted into a Double-Strand Break (DSB) during the S-phase in a cell cycle. However, the DSB site is repaired in a process of Homologous Recombination (HR) that is derived by genes such as BRCA1/2, PALB2, and RAD51. Under conditions of HR dysfunction, including mutations of BRCA1/2 (called BRCAness), PARP inhibitor (PARPi) induces “synthetic lethality” in BRCAness-specific cancer cells. Indeed, clinical trials using forms of PARPi that include olaparib, veliparib and rucaparib, have revealed that PARP inhibition produces a dramatic effect that actually arrests cancer progression. Its clinical efficiency is limited, however, due to the acquisition of PARPi resistance during long-term use of this inhibitor. Thus, it is important to elucidate the mechanisms of PARPi resistance. Methods: We searched the scientific literature published in PubMed, with a special focus on kinase phosphorylation that is involved in acquiring PARPi resistance. We also summarized the possible molecular events for recovering HR system, a key event for acquiring PARPi resistance. Results: CDK1 is a critical kinase for 5’-3’ DNA end resection, which is important for generating ssDNA for recruiting HR-priming factors. CDK12 is necessary for the transcription of HR-driver genes, such as BRCA1, BRCA2, RAD51 and ATR via the phosphorylation of RNA Pol-II. PLK-1 participates in driving HR via the phosphorylation of RAD51. The PI3K-AKT-mTOR signaling cascade is involved in BRCA1 induction via an ETS1 transcriptional pathway. Even under ATMdeficient conditions, the ATR-CHK1 axis compensates for loss in the DNA damage response, which results in HR recovery. The HGF receptor Met tyrosine kinase is responsible for promoting DNA repair by activating the PARP catalytic domain. Conclusion: These kinase-based signaling pathways are biologically important for understanding the compensatory system of HR, whereas inactivation of these kinases has shown promise for the release of PARPi resistance. Several lines of preclinical studies have demonstrated the potential use of kinase inhibitors to enhance PARPi sensitivity. We emphasize the clinical importance of chemical inhibitors as adjuvant drugs to block critical kinase activities and prevent the possible PARPi resistance.

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Abstract 2052: TRIP13 amplification confers PARP inhibitor resistance and polymerase theta inhibitor sensitivity

10.1158/1538-7445.am2021-2052 ◽

2021 ◽

Author(s):

Jeffrey Patterson-Fortin ◽

Jia Zhou ◽

Alan D'Andrea

Keyword(s):

Parp Inhibitor ◽

Inhibitor Resistance

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Predictors and Modulators of Synthetic Lethality: An Update on PARP Inhibitors and Personalized Medicine

BioMed Research International ◽

10.1155/2016/2346585 ◽

2016 ◽

Vol 2016 ◽

pp. 1-12 ◽

Cited By ~ 18

Author(s):

Stephen Murata ◽

Catherine Zhang ◽

Nathan Finch ◽

Kevin Zhang ◽

Loredana Campo ◽

...

Keyword(s):

Synthetic Lethality ◽

Parp Inhibitor ◽

Advanced Ovarian Cancer ◽

Parp Inhibitors ◽

Damage Repair ◽

Trial Testing ◽

United States Food ◽

States Food ◽

And Personalized Medicine ◽

Inhibitor Treatment

Poly(ADP-ribose) polymerase (PARP) inhibitors have proven to be successful agents in inducing synthetic lethality in several malignancies. Several PARP inhibitors have reached clinical trial testing for treatment in different cancers, and, recently, Olaparib (AZD2281) has gained both United States Food and Drug Administration (USFDA) and the European Commission (EC) approval for use inBRCA-mutated advanced ovarian cancer treatment. The need to identify biomarkers, their interactions in DNA damage repair pathways, and their potential utility in identifying patients who are candidates for PARP inhibitor treatment is well recognized. In this review, we detail many of the biomarkers that have been investigated for their ability to predict both PARP inhibitor sensitivity and resistance in preclinical studies as well as the results of several clinical trials that have tested the safety and efficacy of different PARP inhibitor agents inBRCAand non-BRCA-mutated cancers.

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Cytocidal Antitumor Effects against Human Ovarian Cancer Cells Induced by B-Lactam Steroid Alkylators with Targeted Activity against Poly (ADP-Ribose) Polymerase (PARP) Enzymes in a Cell-Free Assay

Biomedicines ◽

10.3390/biomedicines9081028 ◽

2021 ◽

Vol 9 (8) ◽

pp. 1028

Author(s):

Nikolaos Nikoleousakos ◽

Panagiotis Dalezis ◽

Aikaterini Polonifi ◽

Elena G. Geromichalou ◽

Sofia Sagredou ◽

...

Keyword(s):

Ovarian Cancer ◽

Mrna Expression ◽

Cancer Cells ◽

Cell Lines ◽

Synthetic Lethality ◽

Parp Inhibitor ◽

Positive Control ◽

Ovarian Cancer Cells ◽

Antitumor Effects

We evaluated three newly synthesized B-lactam hybrid homo-aza-steroidal alkylators (ASA-A, ASA-B and ASA-C) for their PARP1/2 inhibition activity and their DNA damaging effect against human ovarian carcinoma cells. These agents are conjugated with an alkylating component (POPA), which also served as a reference molecule (positive control), and were tested against four human ovarian cell lines in vitro (UWB1.289 + BRCA1, UWB1.289, SKOV-3 and OVCAR-3). The studied compounds were thereafter compared to 3-AB, a known PARP inhibitor, as well as to Olaparib, a standard third-generation PARP inhibitor, on a PARP assay investigating their inhibitory potential. Finally, a PARP1 and PARP2 mRNA expression analysis by qRT-PCR was produced in order to measure the absolute and the relative gene expression (in mRNA transcripts) between treated and untreated cells. All the investigated hybrid steroid alkylators and POPA decreased in vitro cell growth differentially, according to the sensitivity and different gene characteristics of each cell line, while ASA-A and ASA-B presented the most significant anticancer activity. Both these compounds induced PARP1/2 enzyme inhibition, DNA damage (alkylation) and upregulation of PARP mRNA expression, for all tested cell lines. However, ASA-C underperformed on average in the above tasks, while the compound ASA-B induced synthetic lethality effects on the ovarian cancer cells. Nevertheless, the overall outcome, leading to a drug-like potential, provides strong evidence toward further evaluation.

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Genome-wide and high-density CRISPR-Cas9 screens identify point mutations in PARP1 causing PARP inhibitor resistance

10.1101/203224 ◽

2017 ◽

Author(s):

Stephen J. Pettitt ◽

Dragomir B. Krastev ◽

Inger Brandsma ◽

Amy Drean ◽

Feifei Song ◽

...

Keyword(s):

Catalytic Domain ◽

Synthetic Lethality ◽

Parp Inhibitor ◽

Point Mutations ◽

Underlying Mechanism ◽

Parp Inhibitors ◽

High Density ◽

Single Amino Acid ◽

Genome Wide ◽

Amino Acid Mutations

AbstractPARP inhibitors (PARPi) target homologous recombination defective tumour cells via synthetic lethality. Genome-wide and high-density CRISPR-Cas9 “tag, mutate and enrich” mutagenesis screens identified single amino acid mutations in PARP1 that cause profound PARPi-resistance. These included PARP1 mutations outside of the DNA interacting regions of the protein, such as mutations in solvent exposed regions of the catalytic domain and clusters of mutations around points of contact between ZnF, WGR and HD domains. These mutations altered PARP1 trapping, as did a mutation found in a clinical case of PARPi resistance. These genetic studies reinforce the importance of trapped PARP1 as a key cytotoxic DNA lesion and suggest that interactions between non-DNA binding domains of PARP1 influence cytotoxicity. Finally, different mechanisms of PARPi resistance (BRCA1 reversion, PARP1, 53BP1, REV7 mutation) had differing effects on chemotherapy sensitivity, suggesting that the underlying mechanism of PARPi resistance likely influences the success of subsequent therapies.

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