Discovery of 4-{4-[(3R)-3-Methylmorpholin-4-yl]-6-[1-(methylsulfonyl)cyclopropyl]pyrimidin-2-yl}-1H-indole (AZ20): a potent and selective inhibitor of ATR protein kinase with monotherapy in vivo antitumor activity

Metal- and additive-free β-C(sp2)-H decarboxylative alkylsulfonylation of enamides from phenyliodine(III) dicarboxylates and sulfur dioxide

A green process for the direct C(sp2)-H decarboxylative alkylsulfonylation of enamides under metal- and additive-free conditions is reported. This reaction employs phenyliodine(III) dicarboxylates as the alkyl radical precursors and DABCO·(SO2)2 as the sulfur dioxide surrogate. Diverse (E)-alkylsulfonyl enamides are generated in moderate to good yields with high stereoselectivity under extremely mild conditions via a radical process. A broad substrate scope and excellent functional group tolerance are presented. Moreover, a cascade alkylsulfonylation/cyclization reaction of N-methacryloyl enamides occurs smoothly, giving rise to various alkylsulfonylated pyrrolidones.

New Horizons of Synthetic Lethality in Cancer: Current Development and Future Perspectives

In recent years, synthetic lethality has been recognized as a solid paradigm for anticancer therapies. The discovery of a growing number of synthetic lethal targets has led to a significant expansion in the use of synthetic lethality, far beyond poly(ADP-ribose) polymerase inhibitors used to treat BRCA1/2-defective tumors. In particular, molecular targets within DNA damage response have provided a source of inhibitors that have rapidly reached clinical trials. This Perspective focuses on the most recent progress in synthetic lethal targets and their inhibitors, within and beyond the DNA damage response, describing their design and associated therapeutic strategies. We will conclude by discussing the current challenges and new opportunities for this promising field of research, to stimulate discussion in the medicinal chemistry community, allowing the investigation of synthetic lethality to reach its full potential.

Discovery of Preclinical Candidate AD1058 as a Highly Potent, Selective, and Brain-Penetrant ATR Inhibitor for the Treatment of Advanced Malignancies

The ataxia telangiectasia-mutated and Rad3-related protein (ATR) plays a crucial role in regulating the cellular DNA-damage response (DDR), making it a promising target for antitumor drug development through synthetic lethality. In this study, we present the discovery and detailed characterization of AD1058, a highly potent and selective ATR inhibitor, with good preclinical pharmacokinetic profiles. AD1058 exhibits superior efficacy in inhibiting cell proliferation, disrupting the cell cycle, and inducing apoptosis compared to AZD6738. AD1058 displays potent antitumor effects as a single agent or in combination with clinically approved tumor therapies such as PARP inhibitors, ionizing radiotherapy, or chemotherapy in vivo. Considering its enhanced ability to permeate the blood-brain barrier, AD1058 is a promising clinical candidate for the treatment of brain metastases and leptomeningeal metastases in solid tumors. Additionally, among reported ATR inhibitors, AD1058 features the shortest synthesis route and the highest efficiency to date.

Inhibition of the ATR-DNAPKcs-RB axis drives G1/S-phase transition and sensitizes triple-negative breast cancer (TNBC) to DNA holliday junctions

Targeting the DNA damage response (DDR) is a promising strategy in oncotherapy, as most tumor cells are sensitive to excess damage due to their repair defects. Ataxia telangiectasia mutated and RAD3-related protein (ATR) is a damage response signal transduction sensor, and its therapeutic potential in tumor cells needs to be precisely investigated. Herein, we identified a new axis that could be targeted by ATR inhibitors to decrease the DNA-dependent protein kinase catalytic subunit (DNAPKcs), downregulate the expression of the retinoblastoma (RB), and drive G1/S-phase transition. Four-way DNA Holliday junctions (FJs) assembled in this process could trigger S-phase arrest and induce lethal chromosome damage in RB-positive triple-negative breast cancer (TNBC) cells. Furthermore, these unrepaired junctions also exerted toxic effects to RB-deficient TNBC cells when the homologous recombination repair (HRR) was inhibited. This study proposes a precise strategy for treating TNBC by targeting the DDR and extends our understanding of ATR and HJ in tumor treatment.

Ataxia-Telangiectasia Mutated Loss-of-Function Displays Variant and Tissue-Specific Differences across Tumor Types

PURPOSE

Mutations in the ATM gene are common in multiple cancers, but clinical studies of therapies targeting ATM-aberrant cancers have yielded mixed results. Refinement of ATM loss of function (LOF) as a predictive biomarker of response is urgently needed.

EXPERIMENTAL DESIGN

We present the first disclosure and preclinical development of a novel, selective ATR inhibitor, ART0380, and test its antitumor activity in multiple preclinical cancer models. To refine ATM LOF as a predictive biomarker, we performed a comprehensive pan-cancer analysis of ATM variants in patient tumors and then assessed the ATM variant-to-protein relationship. Finally, we assessed a novel ATM LOF biomarker approach in retrospective clinical data sets of patients treated with platinum-based chemotherapy or ATR inhibition.

RESULTS

ART0380 had potent, selective antitumor activity in a range of preclinical cancer models with differing degrees of ATM LOF. Pan-cancer analysis identified 10,609 ATM variants in 8,587 patient tumors. Cancer lineage-specific differences were seen in the prevalence of deleterious (Tier 1) versus unknown/benign (Tier 2) variants, selective pressure for loss of heterozygosity, and concordance between a deleterious variant and ATM loss of protein (LOP). A novel ATM LOF biomarker approach that accounts for variant classification, relationship to ATM LOP, and tissue-specific penetrance significantly enriched for patients who benefited from platinum-based chemotherapy or ATR inhibition.

CONCLUSIONS

These data help to better define ATM LOF across tumor types in order to optimize patient selection and improve molecularly targeted therapeutic approaches for patients with ATM LOF cancers.

Photocatalytic O- to S-Rearrangement of Tertiary Cyclopropanols

Despite the importance of heteroatom-substituted cyclopropane derivatives in drug design and organic synthesis, cyclopropanethiols remain critically underexplored. Inspired by the wide use of the Newman-Kwart rearrangement to access valuable thiophenols from phenol feedstocks, we report the development of a photocatalytic approach for efficient ambient temperature aliphatic O- to S-rearrangement on tertiary cyclopropanol derivatives. After demonstrating that a range of cyclopropanethiols-that are difficult to access by other methods-can be obtained with this strategy, we show that these rearranged products can be easily hydrolyzed and further derivatized. We conclude this study with mechanistic findings that enabled an initial extension of this approach toward other classes of aliphatic alcohols.

Discovery of the Potent and Selective ATR Inhibitor Camonsertib (RP-3500)

ATR is a key kinase in the DNA-damage response (DDR) that is synthetic lethal with several other DDR proteins, making it an attractive target for the treatment of genetically selected solid tumors. Herein we describe the discovery of a novel ATR inhibitor guided by a pharmacophore model to position a key hydrogen bond. Optimization was driven by potency and selectivity over the related kinase mTOR, resulting in the identification of camonsertib (RP-3500) with high potency and excellent ADME properties. Preclinical evaluation focused on the impact of camonsertib on myelosuppression, and an exploration of intermittent dosing schedules to allow recovery of the erythroid compartment and mitigate anemia. Camonsertib is currently undergoing clinical evaluation both as a single agent and in combination with talazoparib, olaparib, niraparib, lunresertib, or gemcitabine (NCT04497116, NCT04972110, NCT04855656). A preliminary recommended phase 2 dose for monotherapy was identified as 160 mg QD given 3 days/week.

Key Proteins of Replication Stress Response and Cell Cycle Control as Cancer Therapy Targets

Replication stress (RS) is a characteristic state of cancer cells as they tend to exchange precision of replication for fast proliferation and increased genomic instability. To overcome the consequences of improper replication control, malignant cells frequently inactivate parts of their DNA damage response (DDR) pathways (the ATM-CHK2-p53 pathway), while relying on other pathways which help to maintain replication fork stability (ATR-CHK1). This creates a dependency on the remaining DDR pathways, vulnerability to further destabilization of replication and synthetic lethality of DDR inhibitors with common oncogenic alterations such as mutations of TP53, RB1, ATM, amplifications of MYC, CCNE1 and others. The response to RS is normally limited by coordination of cell cycle, transcription and replication. Inhibition of WEE1 and PKMYT1 kinases, which prevent unscheduled mitosis entry, leads to fragility of under-replicated sites. Recent evidence also shows that inhibition of Cyclin-dependent kinases (CDKs), such as CDK4/6, CDK2, CDK8/19 and CDK12/13 can contribute to RS through disruption of DNA repair and replication control. Here, we review the main causes of RS in cancers as well as main therapeutic targets-ATR, CHK1, PARP and their inhibitors.

Interstrand crosslinking of homologous repair template DNA enhances gene editing in human cells

We describe a strategy to boost the efficiency of gene editing via homology-directed repair (HDR) by covalently modifying the template DNA with interstrand crosslinks. Crosslinked templates (xHDRTs) increase Cas9-mediated editing efficiencies by up to fivefold in K562, HEK293T, U2OS, iPS and primary T cells. Increased editing from xHDRTs is driven by events on the template molecule and requires ataxia telangiectasia and Rad3-related (ATR) kinase and components of the Fanconi anemia pathway.

Simultaneous inhibition of DNA-PK and Polϴ improves integration efficiency and precision of genome editing

Genome editing, specifically CRISPR/Cas9 technology, has revolutionized biomedical research and offers potential cures for genetic diseases. Despite rapid progress, low efficiency of targeted DNA integration and generation of unintended mutations represent major limitations for genome editing applications caused by the interplay with DNA double-strand break repair pathways. To address this, we conduct a large-scale compound library screen to identify targets for enhancing targeted genome insertions. Our study reveals DNA-dependent protein kinase (DNA-PK) as the most effective target to improve CRISPR/Cas9-mediated insertions, confirming previous findings. We extensively characterize AZD7648, a selective DNA-PK inhibitor, and find it to significantly enhance precise gene editing. We further improve integration efficiency and precision by inhibiting DNA polymerase theta (Polϴ). The combined treatment, named 2iHDR, boosts templated insertions to 80% efficiency with minimal unintended insertions and deletions. Notably, 2iHDR also reduces off-target effects of Cas9, greatly enhancing the fidelity and performance of CRISPR/Cas9 gene editing.

Novel Cellular Functions of ATR for Therapeutic Targeting: Embryogenesis to Tumorigenesis

The DNA damage response (DDR) is recognized as having an important role in cancer growth and treatment. ATR (ataxia telangiectasia mutated and Rad3-related) kinase, a major regulator of DDR, has shown significant therapeutic potential in cancer treatment. ATR inhibitors have shown anti-tumor effectiveness, not just as monotherapies but also in enhancing the effects of standard chemotherapy, radiation, and immunotherapy. The biological basis of ATR is examined in this review, as well as its functional significance in the development and therapy of cancer, and the justification for inhibiting this target as a therapeutic approach, including an assessment of the progress and status of previous decades' development of effective and selective ATR inhibitors. The current applications of these inhibitors in preclinical and clinical investigations as single medicines or in combination with chemotherapy, radiation, and immunotherapy are also fully reviewed. This review concludes with some insights into the many concerns highlighted or identified with ATR inhibitors in both the preclinical and clinical contexts, as well as potential remedies proposed.

Design, synthesis, and biological evaluation of pyrido[3,2-d]pyrimidine derivatives as novel ATR inhibitors

Targeting ataxia telangiectasia mutated and Rad3-related (ATR) kinase is being pursued as a new therapeutic strategy for the treatment of advanced solid tumor with specific DNA damage response deficiency. Herein, we report a series of pyrido[3,2-d]pyrimidine derivatives with potent ATR inhibitory activity through structure-based drug design. Among them, the representative compound 10q exhibited excellent potency against ATR in both biochemical and cellular assays. More importantly, 10q exhibited good liver microsomes stability in different species and also showed moderate inhibitory activity against HT-29 cells in combination treatment with the ATM inhibitor AZD1390. Thus, this work provides a promising lead compound against ATR for further study.

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.

Discovery of novel 7,7-dimethyl-6,7-dihydro-5H-pyrrolo[3,4-d]pyrimidines as ATR inhibitors based on structure-based drug design

ATR kinase is essential to the viability of replicating cells responding to the accumulation of single-strand breaks in DNA, which is an attractive anticancer drug target based on synthetic lethality. Herein we design, synthesize, and evaluate a novel series of fused pyrimidine derivatives as ATR inhibitors. As a result, compound 48f, with an IC₅₀ value of 0.0030 μM against ATR, displayed strong monotherapy efficacy in ataxia-telangiectasia mutated (ATM) kinase-deficient tumor cells LoVo, SW620, OVCAR-3 cell lines with IC₅₀ values of 0.040 μM, 0.095 μM, 0.098 μM, respectively. More importantly, the combination of 48f with AZD-1390, cisplatin, oxaliplatin, and olaparib respectively resulted in synergistic activity against HT-29, HCT116, A549, MCF-7, MDA-MB-231 cells. Moreover, 48f showed a favorable pharmacokinetic profile with a bioavailability of 30.0% in SD rats, acceptable PPB, high permeability (P_app A to B = 8.23 cm s^-1 × 10^-6), and low risk of drug-drug interactions. Collectively, compound 48f could be a promising compound for further investigation.

Active DNA damage response signaling initiates and maintains meiotic sex chromosome inactivation

Meiotic sex chromosome inactivation (MSCI) is an essential process in the male germline. While genetic experiments have established that the DNA damage response (DDR) pathway directs MSCI, due to limitations to the experimental systems available, mechanisms underlying MSCI remain largely unknown. Here we establish a system to study MSCI ex vivo, based on a short-term culture method, and demonstrate that active DDR signaling is required both to initiate and maintain MSCI via a dynamic and reversible process. DDR-directed MSCI follows two layers of modifications: active DDR-dependent reversible processes and irreversible histone post-translational modifications. Further, the DDR initiates MSCI independent of the downstream repressive histone mark H3K9 trimethylation (H3K9me3), thereby demonstrating that active DDR signaling is the primary mechanism of silencing in MSCI. By unveiling the dynamic nature of MSCI, and its governance by active DDR signals, our study highlights the sex chromosomes as an active signaling hub in meiosis.

Synthesis and Anticancer Evaluation of Novel Indole Based Arylsulfonylhydrazides against Human Breast Cancer Cells

A series of novel indole based sulfonohydrazide derivatives (5a-k) containing morpholine heterocyclic ring were synthesized through multistep chemical reactions. The target compounds (5a-k) were prepared by the reaction of substituted phenyl sulfonylhydrazides (2a-k) with morpholine derivative of indole 3-carboxaldehyde. All the target compounds were screened for their anticancer activity in vitro against the estrogen receptor-positive breast cancer line MCF-7 and triple-negative breast cancer cell line, MDA-MB-468. It was found that among all the evaluated compounds, the chemotype 4-chloro-N'-((1-(2-morpholinoethyl)-1H-indol-3-yl)methylene)benzenesulfonohydrazide (5f) showed promising inhibition of both MCF-7 and MDA-MB-468 cancer cells with the respective IC₅₀ values of 13.2 μM and 8.2 μM. Compound 5f was found to be nontoxic against HEK 293 noncancerous cells in the studied concentration range, therefore indicating that such chemotypes inhibit the proliferation of cancerous cells selectively and significantly.

Therapeutic advances in metastatic pancreatic cancer: a focus on targeted therapies

Mortality from pancreatic ductal adenocarcinoma (PDAC) is increasing worldwide and effective new treatments are urgently needed. The current treatment of metastatic PDAC in fit patients is based on two chemotherapy combinations (FOLFIRINOX and gemcitabine plus nab-paclitaxel) which were validated more than 8 years ago. Although almost all treatments targeting specific molecular alterations have failed so far when administered to unselected patients, encouraging results were observed in the small subpopulations of patients with germline BRCA 1/2 mutations, and somatic gene fusions (neurotrophic tyrosine receptor kinase, Neuregulin 1, which are enriched in KRAS wild-type PDAC), KRAS G12C mutations, or microsatellite instability. While targeted tumor metabolism therapies and immunotherapy have been disappointing, they are still under investigation in combination with other drugs. Optimizing pharmacokinetics and adapting available chemotherapies based on molecular signatures are other promising avenues of research. This review evaluates the current expectations and limits of available treatments and analyses the existing trials. A permanent search for actionable vulnerabilities in PDAC tumor cells and microenvironments will probably result in a more personalized therapeutic approach, keeping in mind that supportive care must also play a major role if real clinical efficacy is to be achieved in these patients.

Determining the Potential of DNA Damage Response (DDR) Inhibitors in Cervical Cancer Therapy

Cisplatin-based chemo-radiotherapy (CRT) is the standard treatment for advanced cervical cancer (CC) but the response rate is poor (46-72%) and cisplatin is nephrotoxic. Therefore, better treatment of CC is urgently needed. We have directly compared, for the first time, the cytotoxicity of four DDR inhibitors (rucaparib/PARPi, VE-821/ATRi, PF-477736/CHK1i and MK-1775/WEE1i) as single agents, and in combination with cisplatin and radiotherapy (RT) in a panel of CC cells. All inhibitors alone caused concentration-dependent cytotoxicity. Low ATM and DNA-PKcs levels were associated with greater VE-821 cytotoxicity. Cisplatin induced ATR, CHK1 and WEE1 activity in all of the cell lines. Cisplatin only activated PARP in S-phase cells, but RT activated PARP in the entire population. Rucaparib was the most potent radiosensitiser and VE-821 was the most potent chemosensitiser. VE-821, PF-47736 and MK-1775 attenuated cisplatin-induced S-phase arrest but tended to increase G2 phase accumulation. In mice, cisplatin-induced acute kidney injury was associated with oxidative stress and PARP activation and was prevented by rucaparib. Therefore, while all inhibitors investigated may increase the efficacy of CRT, the greatest clinical potential of rucaparib may be in limiting kidney damage, which is dose-limiting.

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

Nucleotide imbalance decouples cell growth from cell proliferation

Nucleotide metabolism supports RNA synthesis and DNA replication to enable cell growth and division. Nucleotide depletion can inhibit cell growth and proliferation, but how cells sense and respond to changes in the relative levels of individual nucleotides is unclear. Moreover, the nucleotide requirement for biomass production changes over the course of the cell cycle, and how cells coordinate differential nucleotide demands with cell cycle progression is not well understood. Here we find that excess levels of individual nucleotides can inhibit proliferation by disrupting the relative levels of nucleotide bases needed for DNA replication and impeding DNA replication. The resulting purine and pyrimidine imbalances are not sensed by canonical growth regulatory pathways like mTORC1, Akt and AMPK signalling cascades, causing excessive cell growth despite inhibited proliferation. Instead, cells rely on replication stress signalling to survive during, and recover from, nucleotide imbalance during S phase. We find that ATR-dependent replication stress signalling is activated during unperturbed S phases and promotes nucleotide availability to support DNA replication. Together, these data reveal that imbalanced nucleotide levels are not detected until S phase, rendering cells reliant on replication stress signalling to cope with this metabolic problem and disrupting the coordination of cell growth and division.

Surprising lipophilicity observations identify unexpected conformational effects

Contrary to expectation N-aryl pyrrolidinones (and isosteric imidazolinones and oxazolinones) are more lipophilic and less soluble than the corresponding piperidinones (tetrahydropyrimidinones and oxazinones). Exploration of the basis for these results uncovered a subtle interplay of steric and electronic effects that result in different conformations for the two classes of compounds which drive the observed effects.

Pressure Overload Activates DNA-Damage Response in Cardiac Stromal Cells: A Novel Mechanism Behind Heart Failure With Preserved Ejection Fraction?

Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous syndrome characterized by impaired left ventricular (LV) diastolic function, with normal LV ejection fraction. Aortic valve stenosis can cause an HFpEF-like syndrome by inducing sustained pressure overload (PO) and cardiac remodeling, as cardiomyocyte (CM) hypertrophy and fibrotic matrix deposition. Recently, in vivo studies linked PO maladaptive myocardial changes and DNA damage response (DDR) activation: DDR-persistent activation contributes to mouse CM hypertrophy and inflammation, promoting tissue remodeling, and HF. Despite the wide acknowledgment of the pivotal role of the stromal compartment in the fibrotic response to PO, the possible effects of DDR-persistent activation in cardiac stromal cell (C-MSC) are still unknown. Finally, this novel mechanism was not verified in human samples. This study aims to unravel the effects of PO-induced DDR on human C-MSC phenotypes. Human LV septum samples collected from severe aortic stenosis with HFpEF-like syndrome patients undergoing aortic valve surgery and healthy controls (HCs) were used both for histological tissue analyses and C-MSC isolation. PO-induced mechanical stimuli were simulated in vitro by cyclic unidirectional stretch. Interestingly, HFpEF tissue samples revealed DNA damage both in CM and C-MSC. DDR-activation markers γH2AX, pCHK1, and pCHK2 were expressed at higher levels in HFpEF total tissue than in HC. Primary C-MSC isolated from HFpEF and HC subjects and expanded in vitro confirmed the increased γH2AX and phosphorylated checkpoint protein expression, suggesting a persistent DDR response, in parallel with a higher expression of pro-fibrotic and pro-inflammatory factors respect to HC cells, hinting to a DDR-driven remodeling of HFpEF C-MSC. Pressure overload was simulated in vitro, and persistent activation of the CHK1 axis was induced in response to in vitro mechanical stretching, which also increased C-MSC secreted pro-inflammatory and pro-fibrotic molecules. Finally, fibrosis markers were reverted by the treatment with a CHK1/ATR pathway inhibitor, confirming a cause-effect relationship. In conclusion we demonstrated that, in severe aortic stenosis with HFpEF-like syndrome patients, PO induces DDR-persistent activation not only in CM but also in C-MSC. In C-MSC, DDR activation leads to inflammation and fibrosis, which can be prevented by specific DDR targeting.

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.

BEZ235 reduction of cisplatin resistance on wild-type EGFR non-small cell lung cancer cells

Cisplatin, as a first-line chemotherapy drug for advanced wild-type epidermal growth factor receptor (wtEGFR) non-small cell lung cancer (NSCLC), often loses effectiveness because of acquired drug resistance. We found that ataxia-telangiectasia mutated (ATM), ataxia-telangiectasia and Rad3-related (ATR) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) of DNA repair kinases and signal transduction molecules, protein kinase B (AKT)/target mammalian target of rapamycin (mTOR), were significantly phosphorylated in cisplatin-resistant wtEGFR NSCLC cell lines (H358R and A549R) than in their parental cells. Also, BEZ235 (dual phosphatidylinositol-3-kinase (PI3K)/mTOR inhibitor) significantly decreased the phosphorylation levels of these kinases/proteins, as detected by Western blot analysis. In H358R and A549R cells, the results of indirect immunofluorescence, single-cell gel electrophoresis, flow cytometry, methylthiazolyldiphenyl-tetrazolium bromide, clone formation assay, and scratch healing experiment showed that BEZ235 enhanced cisplatin-induced DNA damage and cell apoptosis, and effectively inhibited cellular proliferation/migration when combined with cisplatin. The data indicated that the abnormal activation of ATM/ATR/DNA-PKcs kinases and AKT/mTOR pathway might induce wtEGFR NSCLC cell resistance to cisplatin. The effects of the combination of BEZ235 and cisplatin suggested that BEZ235 should be considered as a combination therapy for patients with cisplatin-resistant wtEGFR NSCLC.

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.

Etoposide-induced DNA damage is increased in p53 mutants: identification of ATR and other genes that influence effects of p53 mutations on Top2-induced cytotoxicity

The functional status of the tumor suppressor p53 is a critical component in determining the sensitivity of cancer cells to many chemotherapeutic agents. DNA topoisomerase II (Top2) plays essential roles in DNA metabolism and is the target of FDA approved chemotherapeutic agents. Topoisomerase targeting drugs convert the enzyme into a DNA damaging agent and p53 influences cellular responses to these agents. We assessed the impact of the loss of p53 function on the formation of DNA damage induced by the Top2 poison etoposide. Using human HCT116 cells, we found resistance to etoposide in cell growth assays upon the functional loss of p53. Nonetheless, cells lacking fully functional p53 were etoposide hypersensitive in clonogenic survival assays. This complex role of p53 led us to directly examine the effects of p53 status on topoisomerase-induced DNA damage. A deficiency in functional p53 resulted in elevated levels of the Top2 covalent complexes (Top2cc) in multiple cell lines. Employing genome-wide siRNA screens, we identified a set of genes for which reduced expression resulted in enhanced synthetic lethality upon etoposide treatment of p53 defective cells. We focused on one hit from this screen, ATR, and showed that decreased expression sensitized the p53-defective cells to etoposide in all assays and generated elevated levels of Top2cc in both p53 proficient and deficient cells. Our findings suggest that a combination of etoposide treatment with functional inactivation of DNA repair in p53 defective cells could be used to enhance the therapeutic efficacy of Top2 targeting agents.

Phosphoproteomics of ATR signaling in mouse testes

The phosphatidylinositol 3' kinase (PI3K)-related kinase ATR is crucial for mammalian meiosis. ATR promotes meiotic progression by coordinating key events in DNA repair, meiotic sex chromosome inactivation (MSCI), and checkpoint-dependent quality control during meiotic prophase I. Despite its central roles in meiosis, the ATR-dependent meiotic signaling network remains largely unknown. Here, we used phosphoproteomics to define ATR signaling events in testes from mice following chemical and genetic ablation of ATR signaling. Quantitative analysis of phosphoproteomes obtained after germ cell-specific genetic ablation of the ATR activating 9-1-1 complex or treatment with ATR inhibitor identified over 14,000 phosphorylation sites from testes samples, of which 401 phosphorylation sites were found to be dependent on both the 9-1-1 complex and ATR. Our analyses identified ATR-dependent phosphorylation events in crucial DNA damage signaling and DNA repair proteins including TOPBP1, SMC3, MDC1, RAD50, and SLX4. Importantly, we identified ATR and RAD1-dependent phosphorylation events in proteins involved in mRNA regulatory processes, including SETX and RANBP3, whose localization to the sex body was lost upon ATR inhibition. In addition to identifying the expected ATR-targeted S/T-Q motif, we identified enrichment of an S/T-P-X-K motif in the set of ATR-dependent events, suggesting that ATR promotes signaling via proline-directed kinase(s) during meiosis. Indeed, we found that ATR signaling is important for the proper localization of CDK2 in spermatocytes. Overall, our analysis establishes a map of ATR signaling in mouse testes and highlights potential meiotic-specific actions of ATR during prophase I progression.

Therapeutic Targeting of DNA Damage Response in Cancer

DNA damage response (DDR) is critical to ensure genome stability, and defects in this signaling pathway are highly associated with carcinogenesis and tumor progression. Nevertheless, this also provides therapeutic opportunities, as cells with defective DDR signaling are directed to rely on compensatory survival pathways, and these vulnerabilities have been exploited for anticancer treatments. Following the impressive success of PARP inhibitors in the treatment of BRCA-mutated breast and ovarian cancers, extensive research has been conducted toward the development of pharmacologic inhibitors of the key components of the DDR signaling pathway. In this review, we discuss the key elements of the DDR pathway and how these molecular components may serve as anticancer treatment targets. We also summarize the recent promising developments in the field of DDR pathway inhibitors, focusing on novel agents beyond PARP inhibitors. Furthermore, we discuss biomarker studies to identify target patients expected to derive maximal clinical benefits as well as combination strategies with other classes of anticancer agents to synergize and optimize the clinical benefits.

Radiotherapy as a tool to elicit clinically actionable signalling pathways in cancer

A variety of targeted anticancer agents have been successfully introduced into clinical practice, largely reflecting their ability to inhibit specific molecular alterations that are required for disease progression. However, not all malignant cells rely on such alterations to survive, proliferate, disseminate and/or evade anticancer immunity, implying that many tumours are intrinsically resistant to targeted therapies. Radiotherapy is well known for its ability to activate cytotoxic signalling pathways that ultimately promote the death of cancer cells, as well as numerous cytoprotective mechanisms that are elicited by cellular damage. Importantly, many cytoprotective mechanisms elicited by radiotherapy can be abrogated by targeted anticancer agents, suggesting that radiotherapy could be harnessed to enhance the clinical efficacy of these drugs. In this Review, we discuss preclinical and clinical data that introduce radiotherapy as a tool to elicit or amplify clinically actionable signalling pathways in patients with cancer.

Discovery of small-molecule ATR inhibitors for potential cancer treatment: a patent review from 2014 to present

INTRODUCTION

Ataxia telangiectasia and RAD3-related kinase (ATR) is one of the key PIKKs family members important for DNA damage response and repair pathways. Targeting ATR kinase for potential cancer therapy has attracted a great deal of attention to both pharmaceutical industries and academic community.

AREA COVERED

This article surveys the patents published since 2014 aiming to analyze the structural features of scaffolds and the patent space. It also discusses the recent clinical developments and provides perspectives on the challenges and the future directions.

EXPERT OPINION

ATR kinase appears to be a viable drug target for anticancer therapy. Similar to DNA-PK inhibitors, the clinical investigation of an ATRi employs both monotherapy and combination strategy. In the combination strategy, an ATRi is typically combined with a radiation or a targeted drug such as chemotherapy agent poly (ADP-ribose) polymerase (PARP) inhibitor, etc. Diverse structures comprising different scaffolds from mono-heteroaryl to bicyclic heteroaryl to tricyclic heteroaryl to macrocycle are capable to achieve good ATR inhibitory activity and good ATR selectivity over other closely related enzymes. There are eight ATR inhibitors currently being evaluated in clinics, with the hope to get approval in the near future.

Transition-metal-free insertion of alkynes into the C–C σ-bond of cyclic β-keto sulfones: an atom-economical way to medium-size-ring sulfonyl derivatives

A novel base-promoted and highly efficient strategy for the preparation of medium-size-ring sulfonyl derivatives has been developed.

Genomic Instability and Replicative Stress in Multiple Myeloma: The Final Curtain?

Simple Summary

Genomic instability is recognized as a driving force in most cancers as well as in the haematological cancer multiple myeloma and remains among the leading cause of drug resistance. Several evidences suggest that replicative stress exerts a fundamental role in fuelling genomic instability. Notably, cancer cells rely on a single protein, ATR, to cope with the ensuing DNA damage. In this perspective, we provide an overview depicting how replicative stress represents an Achilles heel for multiple myeloma, which could be therapeutically exploited either alone or in combinatorial regimens to preferentially ablate tumor cells.

Abstract

Multiple Myeloma (MM) is a genetically complex and heterogeneous hematological cancer that remains incurable despite the introduction of novel therapies in the clinic. Sadly, despite efforts spanning several decades, genomic analysis has failed to identify shared genetic aberrations that could be targeted in this disease. Seeking alternative strategies, various efforts have attempted to target and exploit non-oncogene addictions of MM cells, including, for example, proteasome inhibitors. The surprising finding that MM cells present rampant genomic instability has ignited concerted efforts to understand its origin and exploit it for therapeutic purposes. A credible hypothesis, supported by several lines of evidence, suggests that at the root of this phenotype there is intense replicative stress. Here, we review the current understanding of the role of replicative stress in eliciting genomic instability in MM and how MM cells rely on a single protein, Ataxia Telangiectasia-mutated and Rad3-related protein, ATR, to control and survive the ensuing, potentially fatal DNA damage. From this perspective, replicative stress per se represents not only an opportunity for MM cells to increase their evolutionary pool by increasing their genomic heterogeneity, but also a vulnerability that could be leveraged for therapeutic purposes to selectively target MM tumor cells.

Targeting DNA repair pathway in cancer: Mechanisms and clinical application

Over the last decades, the growing understanding on DNA damage response (DDR) pathways has broadened the therapeutic landscape in oncology. It is becoming increasingly clear that the genomic instability of cells resulted from deficient DNA damage response contributes to the occurrence of cancer. One the other hand, these defects could also be exploited as a therapeutic opportunity, which is preferentially more deleterious in tumor cells than in normal cells. An expanding repertoire of DDR-targeting agents has rapidly expanded to inhibitors of multiple members involved in DDR pathways, including PARP, ATM, ATR, CHK1, WEE1, and DNA-PK. In this review, we sought to summarize the complex network of DNA repair machinery in cancer cells and discuss the underlying mechanism for the application of DDR inhibitors in cancer. With the past preclinical evidence and ongoing clinical trials, we also provide an overview of the history and current landscape of DDR inhibitors in cancer treatment, with special focus on the combination of DDR-targeted therapies with other cancer treatment strategies.

Molecular photoswitches in aqueous environments

Molecular photoswitches enable dynamic control of processes with high spatiotemporal precision, using light as external stimulus, and hence are ideal tools for different research areas spanning from chemical biology to smart materials. Photoswitches are typically organic molecules that feature extended aromatic systems to make them responsive to (visible) light. However, this renders them inherently lipophilic, while water-solubility is of crucial importance to apply photoswitchable organic molecules in biological systems, like in the rapidly emerging field of photopharmacology. Several strategies for solubilizing organic molecules in water are known, but there are not yet clear rules for applying them to photoswitchable molecules. Importantly, rendering photoswitches water-soluble has a serious impact on both their photophysical and biological properties, which must be taken into consideration when designing new systems. Altogether, these aspects pose considerable challenges for successfully applying molecular photoswitches in aqueous systems, and in particular in biologically relevant media. In this review, we focus on fully water-soluble photoswitches, such as those used in biological environments, in both in vitro and in vivo studies. We discuss the design principles and prospects for water-soluble photoswitches to inspire and enable their future applications.

CCNE1 copy number is a biomarker for response to combination WEE1-ATR inhibition in ovarian and endometrial cancer models

CCNE1-amplified ovarian cancers (OVCAs) and endometrial cancers (EMCAs) are associated with platinum resistance and poor survival, representing a clinically unmet need. We hypothesized that dysregulated cell-cycle progression promoted by CCNE1 overexpression would lead to increased sensitivity to low-dose WEE1 inhibition and ataxia telangiectasia and Rad3-related (ATR) inhibition (WEE1i-ATRi), thereby optimizing efficacy and tolerability. The addition of ATRi to WEE1i is required to block feedback activation of ATR signaling mediated by WEE1i. Low-dose WEE1i-ATRi synergistically decreases viability and colony formation and increases replication fork collapse and double-strand breaks (DSBs) in a CCNE1 copy number (CN)-dependent manner. Only upon CCNE1 induction does WEE1i perturb DNA synthesis at S-phase entry, and addition of ATRi increases DSBs during DNA synthesis. Inherent resistance to WEE1i is overcome with WEE1i-ATRi, with notable durable tumor regressions and improved survival in patient-derived xenograft (PDX) models in a CCNE1-level-dependent manner. These studies demonstrate that CCNE1 CN is a clinically tractable biomarker predicting responsiveness to low-dose WEE1i-ATRi for aggressive subsets of OVCAs/EMCAs.

Copper-Mediated Cross-Coupling of Diazo Compounds with Sulfinates

A copper-mediated cross-coupling reaction between a diazo compound and a sodium alkane(arene)sulfinate gives a sulfone as the product. This reaction proceeds under mild conditions and features excellent functional group compatibility. A wide range of sodium alkane(arene)sulfinates were successfully applied in this chemistry. Mechanistic studies revealed that the overall reaction efficiency of the sulfinates was in line with their nucleophilicity in this reaction.

Indole Alkaloids, Synthetic Dimers and Hybrids with Potential In Vivo Anticancer Activity

Indole, a heterocyclic organic compound, is one of the most promising heterocycles found in natural and synthetic sources since its derivatives possess fascinating structural diversity and various therapeutic properties. Indole alkaloids, synthetic dimers and hybrids could act on diverse targets in cancer cells, and consequently, possess potential antiproliferative effects on various cancers both in vitro and in vivo. Vinblastine, midostaurin, and anlotinib as the representative of indole alkaloids, synthetic dimers and hybrids respectively, have already been clinically applied to treat many types of cancers, demonstrating indole alkaloids, synthetic dimers and hybrids are useful scaffolds for the development of novel anticancer agents. Covering articles published between 2010 and 2020, this review emphasizes the recent development of indole alkaloids, synthetic dimers and hybrids with potential in vivo therapeutic application for cancers.

Proposing novel MDM2 inhibitors: Combined physics-driven high-throughput virtual screening and in vitro studies

The mouse double minute 2 (MDM2) protein acts as a negative regulator of the p53 tumor suppressor. It directly binds to the N terminus of p53 and promotes p53 ubiquitination and degradation. Since the most common p53-suppressing mechanisms involve the MDM2, proposing novel inhibitors has been the focus of many in silico and also experimental studies. Thus, here we screened around 500,000 small organic molecules from Enamine database at the binding pocket of this oncogenic target. The screening was achieved systematically with starting from the high-throughput virtual screening method followed by more sophisticated docking approaches. The initial high number of screened molecules was reduced to 100 hits which then were studied extensively for their therapeutic activity and pharmacokinetic properties using binary QSAR models. The structural and dynamical profiles of the selected molecules at the binding pocket of the target were studied thoroughly by all-atom molecular dynamics simulations. The free energy of the binding of the hit molecules was estimated by the MM/GBSA method. Based on docking simulations, binary QSAR model results, and free energy calculations, 11 compounds (E1-E11) were selected for in vitro studies. HUVEC vascular endothelium, colon cancer, and breast cancer cell lines were used for testing the binding affinities of the identified hits and for further cellular effects on human cancer cell. Based on in vitro studies, six compounds (E1, E2, E5, E6, E9, and E11) in breast cancer cell lines and six compounds (E1, E2, E5, E6, E8, and E10) in colon cancer cell lines were found as active. Our results showed that these compounds inhibit proliferation and lead to apoptosis.

Recent Advances in Therapeutic Application of DNA Damage Response Inhibitors against Cancer

DNA integrity is continuously challenged by intrinsic cellular processes and environmental agents. To overcome this genomic damage, cells have developed multiple signaling pathways collectively named as DNA damage response (DDR) and composed of three components: (i) sensor proteins, which detect DNA damage, (ii) mediators that relay the signal downstream and recruit the repair machinery, and (iii) the repair proteins, which restore the damaged DNA. A flawed DDR and failure to repair the damage lead to the accumulation of genetic lesions and increased genomic instability, which is recognized as a hallmark of cancer. Cancer cells tend to harbor increased mutations in DDR genes and often have fewer DDR pathways than normal cells. This makes cancer cells more dependent on particular DDR pathways and thus become more susceptible to compounds inhibiting those pathways compared to normal cells, which have all the DDR pathways intact. Understanding the roles of different DDR proteins in the DNA damage response and repair pathways and identification of their structures have paved the way for the development of their inhibitors as targeted cancer therapy. In this review, we describe the major participants of various DDR pathways, their significance in carcinogenesis, and focus on the inhibitors developed against several key DDR proteins.

The Role of PARP Inhibitors in the Treatment of Prostate Cancer: Recent Advances in Clinical Trials

Poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPis) belong to a class of targeted drugs developed for the treatment of homologous recombination repair (HRR)-defective tumors. Preclinical and limited clinical data suggest that PARP inhibition is effective against prostate cancer (PC) in patients with HRR-deficient tumors and that PARPis can improve the mortality rate of PC in patients with BRCA1/2 mutations through a synthetic lethality. Olaparib has been approved by the FDA for advanced ovarian and breast cancer with BRCA mutations, and as a maintenance therapy for ovarian cancer after platinum chemotherapy. PARPis are also a new and emerging clinical treatment for metastatic castration-resistant prostate cancer (mCRPC). Although PARPis have shown great efficacy, their widespread use is restricted by various factors, including drug resistance and the limited population who benefit from treatment. It is necessary to study the combination of PARPis and other therapeutic agents such as anti-hormone drugs, USP7 inhibitors, BET inhibitors, and immunotherapy. This article reviews the mechanism of PARP inhibition in the treatment of PC, the progress of clinical research, the mechanisms of drug resistance, and the strategies of combination treatments.

Small Molecule Inhibitors Targeting Key Proteins in the DNA Damage Response for Cancer Therapy

DNA damage response (DDR) is a complicated interactional pathway. Defects that occur in subordinate pathways of the DDR pathway can lead to genomic instability and cancer susceptibility. Abnormal expression of some proteins in DDR, especially in the DNA repair pathway, are associated with the subsistence and resistance of cancer cells. Therefore, the development of small molecule inhibitors targeting the chief proteins in the DDR pathway is an effective strategy for cancer therapy. In this review, we summarize the development of small molecule inhibitors targeting chief proteins in the DDR pathway, particularly focusing on their implications for cancer therapy. We present the action mode of DDR molecule inhibitors in preclinical studies and clinical cancer therapy, including monotherapy and combination therapy with chemotherapeutic drugs or checkpoint suppression therapy.

Design and synthesis of new indole containing biaryl derivatives as potent antiproliferative agents

A new series of indole containing biaryl derivatives were designed and synthesized, and further biological evaluations of their antiproliferative activity against cancer cell lines (MGC-803 and TE-1 cells) were also conducted. Of these synthesized biaryls, compound 4-methyl-2-((5-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)methyl)quinazoline (23) performed as the most potent antiproliferative agent that inhibited cell viability of MGC-803 cells with an IC₅₀ value of 8.28 µM. In addition, investigation of mechanism exhibited that the compound 4-methyl-2-((5-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)methyl)quinazoline (23) could inhibit the expression of c-Myc and glycolysis related proteins, decrease the ATP and lactate production, and further induce apoptosis by activating the AMP-activated protein kinase (AMPK) and p53 signaling pathways.

DNA Repair Pathways in Cancer Therapy and Resistance

DNA repair pathways are triggered to maintain genetic stability and integrity when mammalian cells are exposed to endogenous or exogenous DNA-damaging agents. The deregulation of DNA repair pathways is associated with the initiation and progression of cancer. As the primary anti-cancer therapies, ionizing radiation and chemotherapeutic agents induce cell death by directly or indirectly causing DNA damage, dysregulation of the DNA damage response may contribute to hypersensitivity or resistance of cancer cells to genotoxic agents and targeting DNA repair pathway can increase the tumor sensitivity to cancer therapies. Therefore, targeting DNA repair pathways may be a potential therapeutic approach for cancer treatment. A better understanding of the biology and the regulatory mechanisms of DNA repair pathways has the potential to facilitate the development of inhibitors of nuclear and mitochondria DNA repair pathways for enhancing anticancer effect of DNA damage-based therapy.

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.

Phosphoproteomics reveals novel modes of function and inter-relationships among PIKKs in response to genotoxic stress

The DNA damage response (DDR) is a complex signaling network that relies on cascades of protein phosphorylation, which are initiated by three protein kinases of the family of PI3-kinase-related protein kinases (PIKKs): ATM, ATR, and DNA-PK. ATM is missing or inactivated in the genome instability syndrome, ataxia-telangiectasia (A-T). The relative shares of these PIKKs in the response to genotoxic stress and the functional relationships among them are central questions in the genome stability field. We conducted a comprehensive phosphoproteomic analysis in human wild-type and A-T cells treated with the double-strand break-inducing chemical, neocarzinostatin, and validated the results with the targeted proteomic technique, selected reaction monitoring. We also matched our results with 34 published screens for DDR factors, creating a valuable resource for identifying strong candidates for novel DDR players. We uncovered fine-tuned dynamics between the PIKKs following genotoxic stress, such as DNA-PK-dependent attenuation of ATM. In A-T cells, partial compensation for ATM absence was provided by ATR and DNA-PK, with distinct roles and kinetics. The results highlight intricate relationships between these PIKKs in the DDR.