Drugging ATR: progress in the development of specific inhibitors for the treatment of cancer

Update on Emerging Therapies for Advanced Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignancy worldwide. It is projected to increase by 3.2 million new cases and account for 1.6 million deaths by 2040. Mortality is largely due to limited treatment options for patients who present with advanced disease. Thus, the development of effective and tolerable therapies is crucial. Chemotherapy has been the backbone of systemic treatment of advanced CRC, but utility has been limited because of invariable resistance to therapy, narrow mechanisms of action, and unfavorable toxicity profile. Tumors that are mismatch repair-deficient have demonstrated remarkable response to immune checkpoint inhibitor therapy. However, most CRC tumors are mismatch repair-proficient and represent an unmet medical need. Although ERBB2 amplification occurs only in a few cases, it is associated with left-sided tumors and a higher incidence of brain metastasis. Numerous combinations of HER2 inhibitors have demonstrated efficacy, and antibody-drug conjugates against HER2 represent innovative strategies in this area. The KRAS protein has been classically considered undruggable. Fortunately, new agents targeting KRAS G12C mutation represent a paradigm shift in the management of affected patients and could lead the advancement in drug development for the more common KRAS mutations. Furthermore, aberrant DNA damage response is present in 15%-20% of CRCs, and emerging innovative combinations with poly (ADP-ribose) polymerase (PARP) inhibitors could improve the current therapeutic landscape. Multiple novel biomarker-driven approaches in the management of patients with advanced CRC tumors are reviewed in this article.

Discovery of Thieno[3,2-d]pyrimidine derivatives as potent and selective inhibitors of ataxia telangiectasia mutated and Rad3 related (ATR) kinase

The ataxia telangiectasia mutated and rad3-related (ATR) kinase regulates the DNA damage response (DDR), which plays a critical role in the ATR-Chk1 signaling pathway. ATR inhibition can induce synthetic lethality (SL) with several DDR deficiencies, making it an attractive drug target for cancers with DDR defects. In this study, we developed a series of selective and potent ATR inhibitors with a thieno[3,2-d]pyrimidine scaffold using a hybrid design. We identified compound 34 as a representative molecule that inhibited ATR kinase with an IC₅₀ value of 1.5 nM and showed reduced potency against other kinases tested. Compound 34 also exhibited potent antiproliferative effects against LoVo cells and SL effects against HT-29 cells. Moreover, compound 34 demonstrated good pharmacokinetic properties, in vivo antitumor efficacy, and no obvious toxicity in the LoVo xenograft tumor model. Therefore, compound 34 is a promising lead compound for drug development to combat specific DDR deficiencies in cancer patients.

Therapeutic targeting of ATR in alveolar rhabdomyosarcoma

Despite advances in multi-modal treatment approaches, clinical outcomes of patients suffering from PAX3-FOXO1 fusion oncogene-expressing alveolar rhabdomyosarcoma (ARMS) remain dismal. Here we show that PAX3-FOXO1-expressing ARMS cells are sensitive to pharmacological ataxia telangiectasia and Rad3 related protein (ATR) inhibition. Expression of PAX3-FOXO1 in muscle progenitor cells is not only sufficient to increase sensitivity to ATR inhibition, but PAX3-FOXO1-expressing rhabdomyosarcoma cells also exhibit increased sensitivity to structurally diverse inhibitors of ATR. Mechanistically, ATR inhibition leads to replication stress exacerbation, decreased BRCA1 phosphorylation and reduced homologous recombination-mediated DNA repair pathway activity. Consequently, ATR inhibitor treatment increases sensitivity of ARMS cells to PARP1 inhibition in vitro, and combined treatment with ATR and PARP1 inhibitors induces complete regression of primary patient-derived ARMS xenografts in vivo. Lastly, a genome-wide CRISPR activation screen (CRISPRa) in combination with transcriptional analyses of ATR inhibitor resistant ARMS cells identifies the RAS-MAPK pathway and its targets, the FOS gene family, as inducers of resistance to ATR inhibition. Our findings provide a rationale for upcoming biomarker-driven clinical trials of ATR inhibitors in patients suffering from ARMS.

ATR Inhibitor AZD6738 (Ceralasertib) Exerts Antitumor Activity as a Monotherapy and in Combination with Chemotherapy and the PARP Inhibitor Olaparib

AZD6738 (ceralasertib) is a potent and selective orally bioavailable inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase. ATR is activated in response to stalled DNA replication forks to promote G2-M cell-cycle checkpoints and fork restart. Here, we found AZD6738 modulated CHK1 phosphorylation and induced ATM-dependent signaling (pRAD50) and the DNA damage marker γH2AX. AZD6738 inhibited break-induced replication and homologous recombination repair. In vitro sensitivity to AZD6738 was elevated in, but not exclusive to, cells with defects in the ATM pathway or that harbor putative drivers of replication stress such as CCNE1 amplification. This translated to in vivo antitumor activity, with tumor control requiring continuous dosing and free plasma exposures, which correlated with induction of pCHK1, pRAD50, and γH2AX. AZD6738 showed combinatorial efficacy with agents associated with replication fork stalling and collapse such as carboplatin and irinotecan and the PARP inhibitor olaparib. These combinations required optimization of dose and schedules in vivo and showed superior antitumor activity at lower doses compared with that required for monotherapy. Tumor regressions required at least 2 days of daily dosing of AZD6738 concurrent with carboplatin, while twice daily dosing was required following irinotecan. In a BRCA2-mutant patient-derived triple-negative breast cancer (TNBC) xenograft model, complete tumor regression was achieved with 3 to5 days of daily AZD6738 per week concurrent with olaparib. Increasing olaparib dosage or AZD6738 dosing to twice daily allowed complete tumor regression even in a BRCA wild-type TNBC xenograft model. These preclinical data provide rationale for clinical evaluation of AZD6738 as a monotherapy or combinatorial agent.

SIGNIFICANCE

This detailed preclinical investigation, including pharmacokinetics/pharmacodynamics and dose-schedule optimizations, of AZD6738/ceralasertib alone and in combination with chemotherapy or PARP inhibitors can inform ongoing clinical efforts to treat cancer with ATR inhibitors.

Discovery of Dual TAF1-ATR Inhibitors and Ligand-Induced Structural Changes of the TAF1 Tandem Bromodomain

Bromodomains regulate chromatin remodeling and gene transcription through recognition of acetylated lysines on histones and other proteins. Bromodomain-containing protein TAF1, a subunit of general transcription factor TFIID, initiates preinitiation complex formation and cellular transcription. TAF1 serves as a cofactor for certain oncogenic transcription factors and is implicated in regulating the p53 tumor suppressor. Therefore, TAF1 is a potential target to develop small molecule therapeutics for diseases arising from dysregulated transcription, such as cancer. Here, we report the ATR kinase inhibitor AZD6738 (Ceralasertib) and analogues thereof as bona fide inhibitors of TAF1. Crystallographic and small-angle X-ray scattering studies established that newly identified and previously reported inhibitors stabilize distinct structural states of the TAF1 tandem bromodomain through "open-closed" transitions and dimerization. Combined with functional studies on p53 signaling in cancer cell lines, the data provide new insights into the feasibility and challenges of TAF1 inhibitors as chemical probes and therapeutics.

ATR inhibitor AZD6738 increases the sensitivity of colorectal cancer cells to 5‑fluorouracil by inhibiting repair of DNA damage

The repair of DNA damage caused by chemotherapy in cancer cells occurs mainly at two cell cycle checkpoints (G₁ and G₂) and is a factor contributing to chemoresistance. Most colorectal cancers harbor mutations in p53, the main pathway involved in the G₁ checkpoint, and thus, are particularly dependent on the G₂ checkpoint for DNA repair. The present study examined the effect of AZD6738, a specific inhibitor of ataxia telangiectasia mutated and rad3-related (ATR) involved in the G₂ checkpoint, combined with 5-fluorouracil (5-FU), a central chemotherapeutic agent, on colorectal cancer cells. Since 5-FU has a DNA-damaging effect, its combination with AZD6738 is likely to enhance the therapeutic effect. The effects of the AZD6738/5-FU combination were evaluated in various colorectal cancer cells (HT29, SW480, HCT116 and DLD-1 cells) by flow cytometry (HT29 cells), western blotting (HT29 cells) and water-soluble tetrazolium 1 assays (HT29, SW480, HCT116 and DLD-1 cells), as well as in an experimental animal model (HT29 cells). In vitro, the AZD6738/5-FU combination increased the number of mitotic cells according to flow cytometry, decreased the checkpoint kinase 1 phosphorylation levels and increased cleaved caspase-3 and phosphorylated form of H2A.X variant histone levels according to western blotting, and decreased the proliferation rate of four colon cancer cell lines according to cell viability experiments. In vivo, xenografted colorectal cancer cells treated with the AZD6738/5-FU combination exhibited a marked decrease in proliferation compared with the 5-FU alone group. The present results suggested that AZD6738 enhanced the effect of 5-FU in p53-mutated colorectal cancer.

Emerging Novel Therapeutic Approaches for Treatment of Advanced Cutaneous Melanoma

The prognosis of patients with advanced cutaneous melanoma has radically changed in the past decade. Nevertheless, primary or acquired resistance to systemic treatment occurs in many cases, highlighting the need for novel treatment strategies. This review has the purpose of summarizing the current area of interest for the treatment of metastatic or unresectable advanced cutaneous melanoma, including data from recently completed or ongoing clinical trials. The main fields of investigation include the identification of new immune checkpoint inhibitors (anti-LAG3, GITR agonist and anti-TIGIT), adoptive cell therapy, vaccines, engineered TCR therapy, IL-2 agonists, novel targets for targeted therapy (new MEK or RAF inhibitors, HDAC, IDO, ERK, Axl, ATR and PARP inhibitors), or combination strategies (antiangiogenetic agents plus immune checkpoint inhibitors, intra-tumoral immunotherapy in combination with systemic therapy). In many cases, only preliminary efficacy data from early phase trials are available, which require confirmation in larger patient cohorts. A more in-depth knowledge of the biological effects of the molecules and identifying predictive biomarkers remain crucial for selecting patient populations most likely to benefit from novel emerging treatment strategies.

Synthesis and Transformations of NH-Sulfoximines

Recent years have seen a marked increase in the occurrence of sulfoximines in the chemical sciences, often presented as valuable motifs for medicinal chemistry. This has been prompted by both pioneering works taking sulfoximine containing compounds into clinical trials and the concurrent development of powerful synthetic methods. This review covers recent developments in the synthesis of sulfoximines concentrating on developments since 2015. This includes extensive developments in both S-N and S-C bond formations. Flow chemistry processes for sulfoximine synthesis are also covered. Finally, subsequent transformations of sulfoximines, particularly in N-functionalization are reviewed, including N-S, N-P, N-C bond forming processes and cyclization reactions.

Phase II study of ceralasertib (AZD6738) in combination with durvalumab in patients with advanced/metastatic melanoma who have failed prior anti-PD-1 therapy

BACKGROUND

Modulating the DNA damage response and repair (DDR) pathways is a promising strategy for boosting cancer immunotherapy. Ceralasertib (AZD6738) is an oral inhibitor of the serine/threonine protein kinase ataxia telangiectasia and Rad3-related protein, which is crucial for DDR.

PATIENTS AND METHODS

This phase II trial evaluated ceralasertib plus durvalumab for the treatment of patients with metastatic melanoma who had failed anti-programmed cell death protein 1 therapy.

RESULTS

Among the 30 patients, we observed an overall response rate of 31.0% and a disease control rate of 63.3%. Responses were evident across patients with acral, mucosal, and cutaneous melanoma. The median duration of response was 8.8 months (range, 3.8-11.7 months). The median progression-free survival was 7.1 months (95% confidence interval, 3.6-10.6 months), and the median overall survival was 14.2 months (95% confidence interval, 9.3-19.1 months). Common adverse events were largely hematologic and manageable with dose interruptions and reductions. Exploratory biomarker analysis suggested that tumors with an immune-enriched microenvironment or alterations in the DDR pathway were more likely to respond to the study treatment.

CONCLUSION

We conclude that ceralasertib in combination with durvalumab has promising antitumor activity among patients with metastatic melanoma who have failed anti-programmed cell death protein 1 therapy, and constitute a population with unmet needs.

Ceralasertib (AZD6738), an Oral ATR Kinase Inhibitor, in Combination with Carboplatin in Patients with Advanced Solid Tumors: A Phase I Study

PURPOSE

This study reports the safety, tolerability, MTD, recommended phase II dose (RP2D), pharmacokinetic/pharmacodynamic profile, and preliminary antitumor activity of ceralasertib combined with carboplatin in patients with advanced solid tumors. It also examined exploratory predictive and pharmacodynamic biomarkers.

PATIENTS AND METHODS

Eligible patients (n = 36) received a fixed dose of carboplatin (AUC5) with escalating doses of ceralasertib (20 mg twice daily to 60 mg once daily) in 21-day cycles. Sequential and concurrent combination dosing schedules were assessed.

RESULTS

Two ceralasertib MTD dose schedules, 20 mg twice daily on days 4-13 and 40 mg once daily on days 1-2, were tolerated with carboplatin AUC5; the latter was declared the RP2D. The most common treatment-emergent adverse events (Common Terminology Criteria for Adverse Events grade ≥3) were anemia (39%), thrombocytopenia (36%), and neutropenia (25%). Dose-limiting toxicities of grade 4 thrombocytopenia (n = 2; including one grade 4 platelet count decreased) and a combination of grade 4 thrombocytopenia and grade 3 neutropenia occurred in 3 patients. Ceralasertib was quickly absorbed (tmax ∼1 hour), with a terminal plasma half-life of 8-11 hours. Upregulation of pRAD50, indicative of ataxia telangiectasia mutated (ATM) activation, was observed in tumor biopsies during ceralasertib treatment. Two patients with absent or low ATM or SLFN11 protein expression achieved confirmed RECIST v1.1 partial responses. Eighteen of 34 (53%) response-evaluable patients had RECIST v1.1 stable disease.

CONCLUSIONS

The RP2D for ceralasertib plus carboplatin was established as ceralasertib 40 mg once daily on days 1-2 administered with carboplatin AUC5 every 3 weeks, with pharmacokinetic and pharmacodynamic studies confirming pharmacodynamic modulation and preliminary evidence of antitumor activity observed.

Phase I Study of Ceralasertib (AZD6738), a Novel DNA Damage Repair Agent, in Combination with Weekly Paclitaxel in Refractory Cancer

PURPOSE

Ceralasertib is a potent and selective oral inhibitor of the serine/threonine protein kinase ataxia telangiectasia and Rad3-related (ATR) protein.

PATIENTS AND METHODS

Eligible patients with solid tumors, enriched for melanoma, received ceralasertib in combination with a fixed dose of paclitaxel (80 mg/m² on D1, D8, D15) in 28-day cycles. The dose of ceralasertib was escalated to reach an MTD in a rolling 6 design. The starting dose of ceralasertib was 40 mg QD. Fifty-seven patients (33 patients with melanoma who failed prior PD1/L1 treatment) were enrolled in 7 dose cohorts ranging from 40 mg QD to 240 mg BD plus weekly paclitaxel.

RESULTS

The RP2D was established as ceralasertib 240 mg BD days 1-14 plus paclitaxel 80 mg/m² on D1, D8, D15 every 28 days. The most common toxicities were neutropenia (n = 39, 68%), anemia (n = 25, 44%), and thrombocytopenia (n = 21, 37%). In the full analysis set of 57 patients, the overall response rate (ORR) was 22.6% (95% CI, 12.5-35.3). In 33 patients with melanoma, resistant to prior anti-PD1 therapy, the ORR was 33.3% (95% CI, 18.0-51.8). In the melanoma subset, the mPFS was 3.6 months (95% CI, 2.0-5.8), the median duration of response was 9.9 months (95% CI, 3.7-23.2), and the mOS was 7.4 months (95% CI, 5.7-11.9).

CONCLUSIONS

Ceralasertib in combination with paclitaxel was well tolerated in patients with advanced malignancies and showed evidence of antitumor activity. Durable responses were observed in patients with advanced cutaneous, acral, and mucosal melanoma resistant to anti-PD1/L1 treatment.See related commentary by Ashworth, p. 4667.

Pd-Catalyzed double carbopalladation/syn-insertion cascade reactions toward medium-size sulfoximine heterocycles

With the assistance of Ac in sulfoximine as a protecting group (PG) and MeOH as a de-PG agent, Pd-catalyzed multicomponent reactions were developed to access indene-fused medium-size sulfoximine heterocycles. The reactions proceeded smoothly under exceptionally mild conditions to produce polyheterocyclic sulfoximines with regiospecificity and good functional group tolerance. A double carbopalladation/syn-insertion of triple bond sequences was proposed tothis transformation.

One-pot multi-step cascade protocols toward β-indolyl sulfoximidoyl amides via intermolecular trapping of an α-indolylpalladium complex by CO

Various β-indolyl sulfoximidoyl amides were efficiently prepared from ortho-iodoanilines, propargyl bromides, 1 atm of CO, and substituted NH-sulfoximines, through a palladium-catalyzed indole annulation/carbonyl insertion/C-N bond formation cascade. Mostly good to high yields of the products were obtained through this multi-step, one-pot reaction protocol under very gentle reaction conditions. The obtained β-indolyl sulfoximidoyl amides could be converted into biologically interesting sulfoximine analogues that contain a tryptamine moiety.

Progress towards a clinically-successful ATR inhibitor for cancer therapy

The DNA damage response (DDR) is now known to play an important role in both cancer development and its treatment. Targeting proteins such as ATR (Ataxia telangiectasia mutated and Rad3-related) kinase, a major regulator of DDR, has demonstrated significant therapeutic potential in cancer treatment, with ATR inhibitors having shown anti-tumour activity not just as monotherapies, but also in potentiating the effects of conventional chemotherapy, radiotherapy, and immunotherapy. This review focuses on the biology of ATR, its functional role in cancer development and treatment, and the rationale behind inhibition of this target as a therapeutic approach, including evaluation of the progress and current status of development of potent and specific ATR inhibitors that have emerged in recent decades. The current applications of these inhibitors both in preclinical and clinical studies either as single agents or in combinations with chemotherapy, radiotherapy and immunotherapy are also extensively discussed. This review concludes with some insights into the various concerns raised or observed with ATR inhibition in both the preclinical and clinical settings, with some suggested solutions.

Damage Incorporated: Discovery of the Potent, Highly Selective, Orally Available ATR Inhibitor BAY 1895344 with Favorable Pharmacokinetic Properties and Promising Efficacy in Monotherapy and in Combination Treatments in Preclinical Tumor Models

The ATR kinase plays a key role in the DNA damage response by activating essential signaling pathways of DNA damage repair, especially in response to replication stress. Because DNA damage and replication stress are major sources of genomic instability, selective ATR inhibition has been recognized as a promising new approach in cancer therapy. We now report the identification and preclinical evaluation of the novel, clinical ATR inhibitor BAY 1895344. Starting from quinoline 2 with weak ATR inhibitory activity, lead optimization efforts focusing on potency, selectivity, and oral bioavailability led to the discovery of the potent, highly selective, orally available ATR inhibitor BAY 1895344, which exhibited strong monotherapy efficacy in cancer xenograft models that carry certain DNA damage repair deficiencies. Moreover, combination treatment of BAY 1895344 with certain DNA damage inducing chemotherapy resulted in synergistic antitumor activity. BAY 1895344 is currently under clinical investigation in patients with advanced solid tumors and lymphomas (NCT03188965).

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.

Synthesis of NH-Sulfoximines by Using Recyclable Hypervalent Iodine(III) Reagents under Aqueous Micellar Conditions

The synthesis of NH-sulfoximines from sulfides has been first developed under mild conditions in an aqueous solution with surfactant TPGS-750-M as the catalyst at room temperature. In this newly developed process, a simple and convenient recycling strategy to regenerate the indispensable hypervalent iodine(III) is used. The resulting 1,2,3-trifluoro-5-iodobezene can be recovered almost quantitively from the mixture by liquid-liquid extraction and then oxidized to give the corresponding iodine(III) species. This optimized procedure is compatible with a broad range of functional groups and can be easily performed on a gram scale, providing a green protocol for the synthesis of sulfoximines.

Discovery of ATR kinase inhibitor berzosertib (VX-970, M6620): Clinical candidate for cancer therapy

Chemoresistance, radioresistance, and the challenge of achieving complete resection are major driving forces in the search for more robust and targeted anticancer therapies. Targeting the DNA damage response has recently attracted research interest, as these processes are enhanced in tumour cells. The major replication stress responder is ATM and Rad3-related (ATR) kinase, which is attracting attention worldwide with four drug candidates currently in phase I/II clinical trials. This review addresses a potent and selective small-molecule ATR inhibitor, which is known as VX-970 (also known as berzosertib or M6620), and summarizes the existing preclinical data to provide deep insight regarding its real potential. We also outline the transition from preclinical to clinical studies, as well as its relationships with other clinical candidates (AZD6738, VX-803 [M4344], and BAY1895344). The results suggest that VX-970 is indeed a promising anticancer drug that can be used both as monotherapy and in combination with either chemotherapy or radiotherapy strategies. Based on patient anamnesis and biomarker identification, VX-970 could become a valuable tool for oncologists in the fight against cancer.

From yeast to humans: Understanding the biology of DNA Damage Response (DDR) kinases

The DNA Damage Response (DDR) is a complex network of biological processes that protect cells from accumulating aberrant DNA structures, thereby maintaining genomic stability and, as a consequence, preventing the development of cancer and other diseases. The DDR pathway is coordinated by a signaling cascade mediated by the PI3K-like kinases (PIKK) ATM and ATR and by their downstream kinases CHK2 and CHK1, respectively. Together, these kinases regulate several aspects of the cellular program in response to genomic stress. Much of our understanding of these kinases came from studies performed in the 1990s using yeast as a model organism. The purpose of this review is to present a historical perspective on the discovery of the DDR kinases in yeast and the importance of this model for the identification and functional understanding of their mammalian orthologues.

The Novel ATR Inhibitor BAY 1895344 Is Efficacious as Monotherapy and Combined with DNA Damage-Inducing or Repair-Compromising Therapies in Preclinical Cancer Models

The DNA damage response (DDR) secures the integrity of the genome of eukaryotic cells. DDR deficiencies can promote tumorigenesis but concurrently may increase dependence on alternative repair pathways. The ataxia telangiectasia and Rad3-related (ATR) kinase plays a central role in the DDR by activating essential signaling pathways of DNA damage repair. Here, we studied the effect of the novel selective ATR kinase inhibitor BAY 1895344 on tumor cell growth and viability. Potent antiproliferative activity was demonstrated in a broad spectrum of human tumor cell lines. BAY 1895344 exhibited strong monotherapy efficacy in cancer xenograft models that carry DNA damage repair deficiencies. The combination of BAY 1895344 with DNA damage-inducing chemotherapy or external beam radiotherapy (EBRT) showed synergistic antitumor activity. Combination treatment with BAY 1895344 and DDR inhibitors achieved strong synergistic antiproliferative activity in vitro, and combined inhibition of ATR and PARP signaling using olaparib demonstrated synergistic antitumor activity in vivo Furthermore, the combination of BAY 1895344 with the novel, nonsteroidal androgen receptor antagonist darolutamide resulted in significantly improved antitumor efficacy compared with respective single-agent treatments in hormone-dependent prostate cancer, and addition of EBRT resulted in even further enhanced antitumor efficacy. Thus, the ATR inhibitor BAY 1895344 may provide new therapeutic options for the treatment of cancers with certain DDR deficiencies in monotherapy and in combination with DNA damage-inducing or DNA repair-compromising cancer therapies by improving their efficacy.

Neglected sulfur(vi) pharmacophores in drug discovery: exploration of novel chemical space by the interplay of drug design and method development

The key learnings of the utilization of sulfoximines, sulfondiimines and sulfonimidamides in drug discovery at Bayer AG are shared.

Therapeutic Targeting of the DNA Damage Response Using an ATR Inhibitor in Biliary Tract Cancer

PURPOSE

The DNA damage response (DDR) is a multi-complex network of signaling pathways involved in DNA damage repair, cell cycle checkpoints, and apoptosis. In the case of biliary tract cancer (BTC), the strategy of DDR targeting has not been evaluated, even though many patients have DNA repair pathway alterations. The purpose of this study was to test the DDR-targeting strategy in BTC using an ataxia-telangiectasia and Rad3-related (ATR) inhibitor.

MATERIALS AND METHODS

A total of nine human BTC cell lines were used for evaluating anti-tumor effect of AZD6738 (ATR inhibitor) alone or combination with cytotoxic chemotherapeutic agents through MTT assay, colony-forming assays, cell cycle analyses, and comet assays. We established SNU478-mouse model for in vivo experiments to confirm our findings.

RESULTS

Among nine human BTC cell lines, SNU478 and SNU869 were the most sensitive to AZD6738, and showed low expression of both ataxia-telangiectasia mutated (ATM) and p53. AZD6738 blocked p-Chk1 and p-glycoprotein and increased γH2AX, a marker of DNA damage, in sensitive cells. AZD6738 significantly increased apoptosis, G2/M arrest and p21, and decreased CDC2. Combinations of AZD6738 and cytotoxic chemotherapeutic agents exerted synergistic effects in colony-forming assays, cell cycle analyses, and comet assays. In our mouse models, AZD6738 monotherapy decreased tumor growth and the combination with cisplatin showed more potent effects on growth inhibition, decreased Ki-67, and increased terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling than monotherapy with each drug.

CONCLUSION

In BTC, DDR targeting strategy using ATR inhibitor demonstrated promising antitumor activity alone or in combination with cytotoxic chemotherapeutic agents. This supports further clinical development of DDR targeting strategy in BTC.

Evaluation of Maltose Binding Protein-Tagged hATR Kinase Domain Catalytic Activity with p53 Ser-15 Phosphorylation

DNA damage response (DDR) pathways form an integral part of the body's repair machinery, and ATR (ataxia-telangiectasia and Rad3-related kinase) protein is one of the key mediators in the DDR pathway that helps in maintaining genomic integrity. A growing body of evidence suggests that inhibition of ATR can help sensitize tumor cells to combinatorial treatment. However, specific ATR kinase inhibitors have largely remained elusive until now. Despite much interest in the protein for more than a decade, there has been little characterization of only the kinase domain, an essential target site for a variety of ATR inhibitors. Here, we report our findings for the bacterial expression, purification, and biological characterization of this potentially important recombinant kinase domain, which could further be considered for structure elucidation studies. Introduction of a solubility partner, i.e., maltose binding protein (MBP), at the N-terminus of the ATR kinase domain generated a soluble form of the protein, i.e., MBP-tagged hATR kinase domain (MBP-ATR-6X His), which was found to be catalytically active, as assessed by substrate p53 Ser-15 phosphorylation (EPPLSQEAFADLWKK). Our results also highlight the prospect of utilization of the overexpressed recombinant ATR kinase domain in characterization of kinase domain specific inhibitors.

Discovery and Characterization of AZD6738, a Potent Inhibitor of Ataxia Telangiectasia Mutated and Rad3 Related (ATR) Kinase with Application as an Anticancer Agent

The kinase ataxia telangiectasia mutated and rad3 related (ATR) is a key regulator of the DNA-damage response and the apical kinase which orchestrates the cellular processes that repair stalled replication forks (replication stress) and associated DNA double-strand breaks. Inhibition of repair pathways mediated by ATR in a context where alternative pathways are less active is expected to aid clinical response by increasing replication stress. Here we describe the development of the clinical candidate 2 (AZD6738), a potent and selective sulfoximine morpholinopyrimidine ATR inhibitor with excellent preclinical physicochemical and pharmacokinetic (PK) characteristics. Compound 2 was developed improving aqueous solubility and eliminating CYP3A4 time-dependent inhibition starting from the earlier described inhibitor 1 (AZ20). The clinical candidate 2 has favorable human PK suitable for once or twice daily dosing and achieves biologically effective exposure at moderate doses. Compound 2 is currently being tested in multiple phase I/II trials as an anticancer agent.

The ATR Inhibitor AZD6738 Synergizes with Gemcitabine In Vitro and In Vivo to Induce Pancreatic Ductal Adenocarcinoma Regression

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest cancers, and overall survival rates have barely improved over the past five decades. The antimetabolite gemcitabine remains part of the standard of care but shows very limited antitumor efficacy. Ataxia telangiectasia and Rad3-related protein (ATR), the apical kinase of the intra-S-phase DNA damage response, plays a central role in safeguarding cells from replication stress and can therefore limit the efficacy of antimetabolite drug therapies. We investigated the ability of the ATR inhibitor, AZD6738, to prevent the gemcitabine-induced intra-S-phase checkpoint activation and evaluated the antitumor potential of this combination in vitro and in vivo In PDAC cell lines, AZD6738 inhibited gemcitabine-induced Chk1 activation, prevented cell-cycle arrest, and restrained RRM2 accumulation, leading to the strong induction of replication stress markers only with the combination. Moreover, synergistic growth inhibition was identified in a panel of 5 mouse and 7 human PDAC cell lines using both Bliss Independence and Loewe models. In clonogenic assays, the combination abrogated survival at concentrations for which single agents had minor effects. In vivo, AZD6738 in combination with gemcitabine was well tolerated and induced tumor regression in a subcutaneous allograft model of a KrasG12D; Trp53R172H; Pdx-Cre (KPC) mouse cancer cell line, significantly extending survival. Remarkably, the combination also induced regression of a subgroup of KPC autochthonous tumors, which generally do not respond well to conventional chemotherapy. Altogether, our data suggest that AZD6738 in combination with gemcitabine merits evaluation in a clinical trial in patients with PDAC. Mol Cancer Ther; 17(8); 1670-82. ©2018 AACR.

Therapeutic targeting of PGBD5-induced DNA repair dependency in pediatric solid tumors

Despite intense efforts, the cure rates of childhood and adult solid tumors are not satisfactory. Resistance to intensive chemotherapy is common, and targets for molecular therapies are largely undefined. We have found that the majority of childhood solid tumors, including rhabdoid tumors, neuroblastoma, medulloblastoma, and Ewing sarcoma, express an active DNA transposase, PGBD5, that can promote site-specific genomic rearrangements in human cells. Using functional genetic approaches, we discovered that mouse and human cells deficient in nonhomologous end joining (NHEJ) DNA repair cannot tolerate the expression of PGBD5. In a chemical screen of DNA damage signaling inhibitors, we identified AZD6738 as a specific sensitizer of PGBD5-dependent DNA damage and apoptosis. We found that expression of PGBD5, but not its nuclease activity-deficient mutant, was sufficient to induce sensitivity to AZD6738. Depletion of endogenous PGBD5 conferred resistance to AZD6738 in human tumor cells. PGBD5-expressing tumor cells accumulated unrepaired DNA damage in response to AZD6738 treatment and underwent apoptosis in both dividing and G₁-phase cells in the absence of immediate DNA replication stress. Accordingly, AZD6738 exhibited nanomolar potency against most neuroblastoma, medulloblastoma, Ewing sarcoma, and rhabdoid tumor cells tested while sparing nontransformed human and mouse embryonic fibroblasts in vitro. Finally, treatment with AZD6738 induced apoptosis and regression of human neuroblastoma and medulloblastoma tumors engrafted in immunodeficient mice in vivo. This effect was potentiated by combined treatment with cisplatin, including substantial antitumor activity against patient-derived primary neuroblastoma xenografts. These findings delineate a therapeutically actionable synthetic dependency induced in PGBD5-expressing solid tumors.

Exploration of Novel Chemical Space: Synthesis and in vitro Evaluation of N-Functionalized Tertiary Sulfonimidamides

An unprecedented set of structurally diverse sulfonimidamides (47 compounds) has been prepared by various N-functionalization reactions of tertiary =NH sulfonimidamide 2 aa. These N-functionalization reactions of model compound 2 aa include arylation, alkylation, trifluoromethylation, cyanation, sulfonylation, alkoxycarbonylation (carbamate formation) and aminocarbonylation (urea formation). Small molecule X-ray analyses of selected N-functionalized products are reported. To gain further insight into the properties of sulfonimidamides relevant to medicinal chemistry, a variety of structurally diverse reaction products were tested in selected in vitro assays. The described N-functionalization reactions provide a short and efficient approach to structurally diverse sulfonimidamides which have been the subject of recent, growing interest in the life sciences.

Clinically Applicable Inhibitors Impacting Genome Stability

Advances in technology have facilitated the molecular profiling (genomic and transcriptomic) of tumours, and has led to improved stratification of patients and the individualisation of treatment regimes. To fully realize the potential of truly personalised treatment options, we need targeted therapies that precisely disrupt the compensatory pathways identified by profiling which allow tumours to survive or gain resistance to treatments. Here, we discuss recent advances in novel therapies that impact the genome (chromosomes and chromatin), pathways targeted and the stage of the pathways targeted. The current state of research will be discussed, with a focus on compounds that have advanced into trials (clinical and pre-clinical). We will discuss inhibitors of specific DNA damage responses and other genome stability pathways, including those in development, which are likely to synergistically combine with current therapeutic options. Tumour profiling data, combined with the knowledge of new treatments that affect the regulation of essential tumour signalling pathways, is revealing fundamental insights into cancer progression and resistance mechanisms. This is the forefront of the next evolution of advanced oncology medicine that will ultimately lead to improved survival and may, one day, result in many cancers becoming chronic conditions, rather than fatal diseases.

Highly Chemoselective NH- and O-Transfer to Thiols Using Hypervalent Iodine Reagents: Synthesis of Sulfonimidates and Sulfonamides

Aryl thiols can be selectively converted to sulfonimidates or sulfonamides with three new S-X connections being made selectively in one pot. Using hypervalent iodine reagents in the presence of ammonium carbamate, NH- and O-groups are transferred under mild and practical conditions. Reducing the loading of ammonium carbamate changed the product distribution, converting the sulfonimidate to the sulfonamide. Studies into the possible intermediate species are presented, suggesting that multiple pathways may be possible via sulfinate esters, or related intermediates, with each species forming the same products.

BRD4 facilitates replication stress-induced DNA damage response

Previous reports have demonstrated that select cancers depend on BRD4 to regulate oncogenic gene transcriptional programs. Here we describe a novel role for BRD4 in DNA damage response (DDR). BRD4 associates with and regulates the function of pre-replication factor CDC6 and plays an indispensable part in DNA replication checkpoint signaling. Inhibition of BRD4 by JQ1 or AZD5153 resulted in a rapid, time-dependent reduction in CHK1 phosphorylation and aberrant DNA replication re-initiation. Furthermore, BRD4 inhibition sensitized cancer cells to various replication stress-inducing agents, and synergized with ATR inhibitor AZD6738 to induce cell killing across a number of cancer cell lines. The synergistic interaction between AZD5153 and AZD6738 is translatable to in vivo ovarian cell-line and patient-derived xenograft models. Taken together, our study uncovers a new biological function of BRD4 and provides mechanistic rationale for combining BET inhibitors with DDR-targeted agents for cancer therapy.

Non-thermal plasma-induced apoptosis is modulated by ATR- and PARP1-mediated DNA damage responses and circadian clock

Non-thermal plasma (NTP) has been emerging as a potential cancer therapeutic. However, the practical use of NTP as a cancer therapy requires a better understanding of the precise mechanisms underlying NTP-induced DNA damage responses in order to achieve optimal efficacy. It has been shown that the addition of oxygen gas flow during NTP treatment (NTPO), when compared to NTP exposure alone, can induce a 2–3 fold greater generation of intracellular reactive oxygen species (ROS) in A549 cells. Here, we examined NTPO-induced DNA damage responses and found that NTPO generated a substantial number of genomic DNA lesions and breaks that activated ATR-mediated cell-cycle checkpoints. In addition, we discovered that NTPO-induced DNA lesions were primarily removed by base excision repair (BER) rather than by nucleotide excision repair (NER). Therefore, the inhibition of the BER pathway using a PARP1 inhibitor drastically induced the phosphorylation of γH2AX, and was followed by the programmed cell death of cancer cells. However, the knock-down of XPA, which inhibited the NER pathway, had no effect on NTPO-induced phosphorylation of γH2AX. Finally, in agreement with a recent report, we found a circadian rhythm of PARP1 activity in normal mouse embryonic fibroblasts that needed for cell viability upon NTPO treatment. Taken together, our findings provided an advanced NTP regimen for cancer treatment by combining NTPO treatment with chemical adjuvants for the inhibition of ATR- and PARP1-activated DNA damage responses, and circadian timing of treatment.

2-Hydroxyglutarate produced by neomorphic IDH mutations suppresses homologous recombination and induces PARP inhibitor sensitivity

2-Hydroxyglutarate (2HG) exists as two enantiomers, (R)-2HG and (S)-2HG, and both are implicated in tumor progression via their inhibitory effects on α-ketoglutarate (αKG)-dependent dioxygenases. The former is an oncometabolite that is induced by the neomorphic activity conferred by isocitrate dehydrogenase 1 (IDH1) and IDH2 mutations, whereas the latter is produced under pathologic processes such as hypoxia. We report that IDH1/2 mutations induce a homologous recombination (HR) defect that renders tumor cells exquisitely sensitive to poly(adenosine 5'-diphosphate-ribose) polymerase (PARP) inhibitors. This "BRCAness" phenotype of IDH mutant cells can be completely reversed by treatment with small-molecule inhibitors of the mutant IDH1 enzyme, and conversely, it can be entirely recapitulated by treatment with either of the 2HG enantiomers in cells with intact IDH1/2 proteins. We demonstrate mutant IDH1-dependent PARP inhibitor sensitivity in a range of clinically relevant models, including primary patient-derived glioma cells in culture and genetically matched tumor xenografts in vivo. These findings provide the basis for a possible therapeutic strategy exploiting the biological consequences of mutant IDH, rather than attempting to block 2HG production, by targeting the 2HG-dependent HR deficiency with PARP inhibition. Furthermore, our results uncover an unexpected link between oncometabolites, altered DNA repair, and genetic instability.

Persulfate-promoted oxidative C–N bond coupling of quinoxalinones andNH-sulfoximines

A simple approach for a direct sulfoximination of quinoxalinonesviaK₂S₂O₈-mediated oxidative coupling is reported.

A New, Practical One-Pot Synthesis of Unprotected Sulfonimidamides by Transfer of Electrophilic NH to Sulfinamides

Unprotected tertiary sulfonimidamides have been prepared in good to excellent yields in a one-pot transformation from tertiary sulfinamides through NH transfer. The reaction is mediated by commercially available (diacetoxyiodo)benzene and ammonium carbamate in methanol under convenient conditions. A wide range of functional groups are tolerated and initial results indicate that the NH transfer is stereospecific. A small molecule X-ray analysis of NH sulfonimidamide 2 a and its behavior in selected in vitro assays in comparison to the matched sulfonamide are also reported. This new reaction provides a safe, short and efficient approach to sulfonimidamides, which have been the subject of recent, growing interest in the life sciences.

Inhibition of ataxia telangiectasia related-3 (ATR) improves therapeutic index in preclinical models of non-small cell lung cancer (NSCLC) radiotherapy

BACKGROUND AND PURPOSE

To evaluate the impact of ATR inhibition using AZD6738 in combination with radiotherapy on the response of non-small cell lung cancer (NSCLC) tumour models and a murine model of radiation induced fibrosis.

MATERIALS AND METHODS

AZD6738 was evaluated as a monotherapy and in combination with radiation in vitro and in vivo using A549 and H460 NSCLC models. Radiation induced pulmonary fibrosis was evaluated by cone beam computed tomography (CBCT) and histological staining.

RESULTS

AZD6738 specifically inhibits ATR kinase and enhanced radiobiological response in NSCLC models but not in human bronchial epithelial cells (HBECs) in vitro. Significant tumour growth delay was observed in cell line derived xenografts (CDXs) of H460 cells (p<0.05) which were less significant in A549 cells. Combination of AZD6738 with radiotherapy showed no significant change in lung tissue density by CBCT (p>0.5) and histological scoring of radiation induced fibrosis (p>0.5).

CONCLUSION

Inhibition of ATR with AZD6738 in combination with radiotherapy increases tumour growth delay without observable augmentation of late radiation induced toxicity further underpinning translation towards clinical evaluation in NSCLC.

LC-MS/MS assay for the quantitation of the ATR kinase inhibitor VX-970 in human plasma

DNA damaging chemotherapy and radiation are widely used standard-of-care modalities for the treatment of cancer. Nevertheless, the outcome for many patients remains poor and this may be attributed, at least in part, to highly effective DNA repair mechanisms. Ataxia-telangiectasia mutated and Rad3-related (ATR) is a key regulator of the DNA-damage response (DDR) that orchestrates the repair of damaged replication forks. ATR is a serine/threonine protein kinase and ATR kinase inhibitors potentiate chemotherapy and radiation. The ATR kinase inhibitor VX-970 (NSC 780162) is in clinical development in combination with primary cytotoxic agents and as a monotherapy for tumors harboring specific mutations. We have developed and validated an LC-MS/MS assay for the sensitive, accurate and precise quantitation of VX-970 in human plasma. A dilute-and-shoot method was used to precipitate proteins followed by chromatographic separation with a Phenomenex Polar-RP 80Å (4μm, 50×2mm) column and a gradient acetonitrile-water mobile phase containing 0.1% formic acid from a 50μL sample volume. Detection was achieved using an API 4000 mass spectrometer using electrospray positive ionization mode. The assay was linear from 3 to 5,000ng/mL, proved to be accurate (94.6-104.2%) and precise (<8.4% CV), and fulfilled criteria from the FDA guidance for bioanalytical method validation. This LC-MS/MS assay will be a crucial tool in defining the clinical pharmacokinetics and pharmacology of VX-970 as it progresses through clinical development.

Reevaluation of ATR signaling in primary resting chronic lymphocytic leukemia cells: evidence for pro-survival or pro-apoptotic function

ATM, primarily activated by DNA double-strand breaks, and ATR, activated by single-stranded DNA, are master regulators of the cellular response to DNA damage. In primary chronic lymphocytic leukemia (CLL) cells, ATR signaling is considered to be switched off due to ATR downregulation. Here, we hypothesized that ATR, though expressed at low protein level, could play a role in primary resting CLL cells after genotoxic stress. By investigating the response of CLL cells to UV-C irradiation, a prototypical activator of ATR, we could detect phosphorylation of ATR at Thr-1989, a marker for ATR activation, and also observed that selective ATR inhibitors markedly decreased UV-C-induced phosphorylation of ATR targets, including H2AX and p53. Similar results were obtained with the purine analogs fludarabine and cladribine that were also shown to activate ATR and induce ATR-dependent phosphorylation of H2AX and p53. In addition, ATR inhibition was found to sensitize primary CLL cells to UV-C by decreasing DNA repair synthesis. Conversely, ATR inhibition rescued CLL cells against purine analogs by reducing expression of the pro-apoptotic genes PUMA and BAX. Collectively, our study indicates that ATR signaling can be activated in resting CLL cells and play a pro-survival or pro-apoptotic role, depending on the genotoxic context.

Targeting the ATR-CHK1 Axis in Cancer Therapy

Targeting the DNA damage response (DDR) is a new therapeutic approach in cancer that shows great promise for tumour selectivity. Key components of the DDR are the ataxia telangiectasia mutated and Rad3 related (ATR) and checkpoint kinase 1 (CHK1) kinases. This review article describes the role of ATR and its major downstream target, CHK1, in the DDR and why cancer cells are particularly reliant on the ATR-CHK1 pathway, providing the rationale for targeting these kinases, and validation of this hypothesis by genetic manipulation. The recent development of specific inhibitors and preclinical data using these inhibitors not only as chemosensitisers and radiosensitisers but also as single agents to exploit specific pathologies of tumour cells is described. These potent and specific inhibitors have now entered clinical trial and early results are presented.

Rationally Designed PI3Kα Mutants to Mimic ATR and Their Use to Understand Binding Specificity of ATR Inhibitors

ATR, a protein kinase in the PIKK family, plays a critical role in the cell DNA-damage response and is an attractive anticancer drug target. Several potent and selective inhibitors of ATR have been reported showing significant antitumor efficacy, with most advanced ones entering clinical trials. However, due to the absence of an experimental ATR structure, the determinants contributing to ATR inhibitors' potency and specificity are not well understood. Here we present the mutations in the ATP-binding site of PI3Kα to progressively transform the pocket to mimic that of ATR. The generated PI3Kα mutants exhibit significantly improved affinity for selective ATR inhibitors in multiple chemical classes. Furthermore, we obtained the X-ray structures of the PI3Kα mutants in complex with the ATR inhibitors. The crystal structures together with the analysis on the inhibitor affinity profile elucidate the roles of individual amino acid residues in the binding of ATR inhibitors, offering key insights for the binding mechanism and revealing the structure features important for the specificity of ATR inhibitors. The ability to obtain structural and binding data for these PI3Kα mutants, together with their ATR-like inhibitor binding profiles, makes these chimeric PI3Kα proteins valuable model systems for structure-based inhibitor design.

Novel Pieces for the Emerging Picture of Sulfoximines in Drug Discovery: Synthesis and Evaluation of Sulfoximine Analogues of Marketed Drugs and Advanced Clinical Candidates

Sulfoximines have gained considerable recognition as an important structural motif in drug discovery of late. In particular, the clinical kinase inhibitors for the treatment of cancer, roniciclib (pan-CDK inhibitor), BAY 1143572 (P-TEFb inhibitor), and AZD 6738 (ATR inhibitor), have recently drawn considerable attention. Whilst the interest in this underrepresented functional group in drug discovery is clearly on the rise, there remains an incomplete understanding of the medicinal-chemistry-relevant properties of sulfoximines. Herein we report the synthesis and in vitro characterization of a variety of sulfoximine analogues of marketed drugs and advanced clinical candidates to gain a better understanding of this neglected functional group and its potential in drug discovery.

Radiosensitization by the ATR Inhibitor AZD6738 through Generation of Acentric Micronuclei

AZD6738 is an orally active ATR inhibitor (ATRi) currently in phase I clinical trials. We found in vitro growth inhibitory activity of this ATRi in a panel of human cancer cell lines. We demonstrated radiosensitization by AZD6738 to single radiation fractions in multiple cancer cell lines independent of both p53 and BRCA2 status by the clonogenic assay. Radiosensitization by AZD6738 to clinically relevant doses of fractionated radiation was demonstrated in vitro using a 3D tumor spheroid model and, in vivo, AZD6738 radiosensitized by abrogating the radiation-induced G2 cell-cycle checkpoint and inhibiting homologous recombination. Mitosis with damaged DNA resulted in mitotic catastrophe as measured by micronucleus formation by live-cell fluorescent-ubiquitination cell-cycle imaging of cell-cycle progression and nuclear morphology. Induction of micronuclei was significantly more prominent for AZD6738 compared with inhibition of the downstream kinase CHK1 alone at isoeffective doses. Micronuclei were characterized as acentric chromosomal fragments, which displayed characteristics of increased DNA damage and cell-cycle dyssynchrony when compared with the primary nucleus. Mol Cancer Ther; 16(1); 25-34. ©2016 AACR.

Hsa-miR-520d-5p promotes survival in human dermal fibroblasts exposed to a lethal dose of UV irradiation

We previously reported that hsa-miR-520d-5p is functionally involved in the induction of the epithelial–mesenchymal transition and stemness-mediated processes in normal cells and cancer cells, respectively. On the basis of the synergistic effect of p53 upregulation and demethylation induced by 520d-5p, the current study investigated the effect of this miRNA on apoptotic induction by ultraviolet B (UVB) light in normal human dermal fibroblast (NHDF) cells. 520d-5p was lentivirally transfected into NHDF cells either before or after a lethal dose of UVB irradiation (302 nm) to assess its preventive or therapeutic effects, respectively. The methylation level, gene expression, production of type I collagen and cell cycle distribution were estimated in UV-irradiated cells. NHDF cells transfected with 520d-5p prior to UVB irradiation had apoptotic characteristics, and the transfection exerted no preventive effects. However, transfection with 520d-5p into NHDF cells after UVB exposure resulted in the induction of reprogramming in damaged fibroblasts, the survival of CD105-positive cells, an extended cell lifespan and prevention of cellular damage or malfunction; these outcomes were similar to the effects observed in 520d-5p-transfected NHDF cells (520d/NHDF). The gene expression of c-Abl (Abelson murine leukemia viral oncogene homolog 1), ATR (ataxia telangiectasia and Rad3-related protein), and BRCA1 (breast cancer susceptibility gene I) in transfectants was transcriptionally upregulated in order. These mechanistic findings indicate that ATR-dependent DNA damage repair was activated under this stressor. In conclusion, 520d-5p exerted a therapeutic effect on cells damaged by UVB and restored them to a normal senescent state following functional restoration via survival of CD105-positive cells through c-Abl-ATR-BRCA1 pathway activation, p53 upregulation, and demethylation.

First-in-Class Chemical Probes against Poly(ADP-ribose) Glycohydrolase (PARG) Inhibit DNA Repair with Differential Pharmacology to Olaparib

The enzyme poly(ADP-ribose) glycohydrolase (PARG) performs a critical role in the repair of DNA single strand breaks (SSBs). However, a detailed understanding of its mechanism of action has been hampered by a lack of credible, cell-active chemical probes. Herein, we demonstrate inhibition of PARG with a small molecule, leading to poly(ADP-ribose) (PAR) chain persistence in intact cells. Moreover, we describe two advanced, and chemically distinct, cell-active tool compounds with convincing on-target pharmacology and selectivity. Using one of these tool compounds, we demonstrate pharmacology consistent with PARG inhibition. Further, while the roles of PARG and poly(ADP-ribose) polymerase (PARP) are closely intertwined, we demonstrate that the pharmacology of a PARG inhibitor differs from that observed with the more thoroughly studied PARP inhibitor olaparib. We believe that these tools will facilitate a wider understanding of this important component of DNA repair and may enable the development of novel therapeutic agents exploiting the critical dependence of tumors on the DNA damage response (DDR).